ACOUSTIC WAVE DEVICE, MULTIPLEXER, RADIO-FREQUENCY FRONT END CIRCUIT, AND COMMUNICATION DEVICE

Abstract

An acoustic wave device includes a support substrate, a silicon nitride film stacked on the support substrate, a silicon oxide film stacked on the silicon nitride film, a piezoelectric body stacked on the silicon oxide film and made of lithium tantalite, and an IDT electrode provided on one main surface of the piezoelectric body. For a wavelength normalized film thickness of the piezoelectric body, an Euler angle of the piezoelectric body, a wavelength normalized film thickness of the silicon nitride film, a wavelength normalized film thickness of the silicon oxide film, and a wavelength normalized film thickness of the IDT electrode, values are set so that at least one of a response intensity of a first higher order mode, corresponding to the response intensity of a second higher order mode, and of a response intensity of a third higher mode is greater than about −2.4.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an acoustic wave device having a structure in which a piezoelectric body made of lithium tantalate is stacked on a support substrate made of silicon and to a multiplexer, a radio-frequency front end circuit, and a communication device.

2. Description of the Related Art

Heretofore, multiplexers have been widely used in radio-frequency front end circuits of mobile phones and smartphones. For example, a multiplexer serving as a splitter disclosed in Japanese Unexamined Patent Application Publication No. 2014-068123 includes two or more band pass filters having different frequencies from each other. Each band pass filter is formed of a surface acoustic wave filter chip. Each surface acoustic wave filter chip includes a plurality of surface acoustic wave resonators.

Furthermore, Japanese Unexamined Patent Application Publication No. 2010-187373 discloses an acoustic wave device in which an insulating film made of silicon dioxide and a piezoelectric substrate made of lithium tantalate are stacked on a silicon support substrate. The acoustic wave device has improved heat resistance due to the support substrate and the insulating film being bonded to each other at the (111) plane of silicon.

In the multiplexer disclosed in Japanese Unexamined Patent Application Publication No. 2014-68123, a plurality of acoustic wave filters having different frequencies from each other are connected via a common connection on the antenna terminal side.

The inventors of preferred embodiments of the present application discovered that, in a structure where a piezoelectric body made of lithium tantalate is directly or indirectly stacked on a support substrate made of silicon, a plurality of higher order modes appear on the high-frequency side of the utilized main mode. In the case where such an acoustic wave resonator is used in an acoustic wave filter having a lower pass band in a multiplexer, there is a risk that a ripple due to a higher order mode of that acoustic wave filter will appear in the pass band of another acoustic wave filter having a higher pass band in the multiplexer. In other words, in the multiplexer, if a higher order mode of the acoustic wave filter having the lower pass band is located inside the pass band of the acoustic wave filter having the higher pass band, a ripple will be generated in the pass band of the acoustic wave filter having the higher pass band. Therefore, there is a risk of the filter characteristic of the other acoustic wave filter being degraded.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide acoustic wave devices in each of which a ripple due to a higher order mode is unlikely to be generated in another acoustic wave filter, and multiplexers, radio-frequency front end circuits including the multiplexers, and communication devices.

As will be described later, the inventors of preferred embodiments of the present application discovered that in an acoustic wave device in which a piezoelectric body made of lithium tantalate is directly or indirectly stacked on a support substrate made of silicon, first to third higher-order modes, which are described later, appear on the high-frequency side of the main mode of the acoustic wave device.

An acoustic wave device according to a preferred embodiment of the present invention reduces or prevents at least one higher order mode of the first, second, and third higher order modes.

That is, an acoustic wave device according to a preferred embodiment of the present invention preferably includes a support substrate, which is a silicon substrate, a silicon nitride film stacked on the support substrate, a silicon oxide film stacked on the silicon nitride film, a piezoelectric body stacked on the silicon oxide film and made of lithium tantalate, and an InterDigital Transducer (IDT) electrode provided on one main surface of the piezoelectric body. When λ is a wavelength determined by an electrode finger pitch of the IDT electrode, T_LT is a wavelength normalized film thickness of the piezoelectric body, θ_LT is a Euler angle θ of the piezoelectric body, T_N is a wavelength normalized film thickness of the silicon nitride film, T_S is a wavelength normalized film thickness of the silicon oxide film, T_E is a wavelength normalized film thickness of the IDT electrode expressed as an aluminum thickness obtained from a product of the wavelength normalized film thickness of the IDT electrode and a ratio of a density of the IDT electrode to a density of aluminum, ψ_Si is a propagation direction inside the support substrate, and T_Si is a wavelength normalized film thickness of the support substrate. T_LT, θ_LT, T_N, T_S, T_E, and ψ_Si are set so that at least one of I_h corresponding to a response intensity of a first higher order mode, I_h corresponding to a response intensity of a second higher order mode, and I_h corresponding to a response intensity of a third higher order mode is greater than about −2.4, and T_Si>about 20.

$\mathrm{Formula}\left(1\right)$ $I_h=a_{T_{\mathrm{LT}}}^{\left(2\right)}\left({\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)}^2-b_{T_{\mathrm{LT}}}^{\left(2\right)}\right)+a_{T_{\mathrm{LT}}}^{\left(1\right)}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)+a_{T_S}^{\left(2\right)}\left({\left(T_S-c_{T_S}\right)}^2-b_{T_S}^{\left(2\right)}\right)+a_{T_S}^{\left(1\right)}\left(T_S-c_{T_S}\right)+a_{T_N}^{\left(3\right)}\left({\left(T_N-c_{T_N}\right)}^3-b_{T_N}^{\left(3\right)}\right)+a_{T_N}^{\left(2\right)}\left({\left(T_N-c_{T_N}\right)}^2-b_{T_N}^{\left(2\right)}\right)+a_{T_N}^{\left(1\right)}\left(T_N-c_{T_N}\right)+a_{T_E}^{\left(2\right)}\left({\left(T_E-c_{T_E}\right)}^2-b_{T_E}^{\left(2\right)}\right)+a_{T_E}^{\left(1\right)}\left(T_E-c_{T_E}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(4\right)}\left({\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)}^4-b_{{\psi }_{\mathrm{Si}}}^{\left(4\right)}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(3\right)}\left({\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)}^3-b_{{\psi }_{\mathrm{Si}}}^{\left(3\right)}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(2\right)}\left({\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)}^2-b_{{\psi }_{\mathrm{Si}}}^{\left(2\right)}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(1\right)}\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+a_{{\theta }_{\mathrm{LT}}}^{\left(2\right)}\left({\left({\theta }_{\mathrm{LT}}-c_{{\theta }_{\mathrm{LT}}}\right)}^2-b_{{\theta }_{\mathrm{LT}}}^{\left(2\right)}\right)+a_{{\theta }_{\mathrm{LT}}}^{\left(1\right)}\left({\theta }_{\mathrm{LT}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_{\mathrm{LT}}T_S}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left(T_S-c_{T_S}\right)+d_{T_{\mathrm{LT}}T_N}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left(T_N-c_{T_N}\right)+d_{T_{\mathrm{LT}}T_E}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left(T_E-c_{T_E}\right)+d_{T_{\mathrm{LT}}{\psi }_{\mathrm{Si}}}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_{\mathrm{LT}}{\theta }_{\mathrm{LT}}}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left({\theta }_{\mathrm{LT}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_ST_N}\left(T_S-c_{T_S}\right)\left(T_N-c_{T_N}\right)+d_{T_ST_E}\left(T_S-c_{T_E}\right)\left(T_E-c_{T_E}\right)+d_{T_S{\psi }_{\mathrm{Si}}}\left(T_S-c_{T_S}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_S{\theta }_{\mathrm{LT}}}\left(T_S-c_{T_S}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_NT_E}\left(T_N-c_{T_N}\right)\left(T_E-c_{T_E}\right)+d_{T_N{\psi }_{\mathrm{Si}}}\left(T_N-c_{T_N}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_N{\theta }_{\mathrm{LT}}}\left(T_N-c_{T_N}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_E{\psi }_{\mathrm{Si}}}\left(T_E-c_{T_E}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_E{\theta }_{\mathrm{LT}}}\left(T_E-c_{T_E}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{{\psi }_{\mathrm{Si}}{\theta }_{\mathrm{LT}}}\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+e$

Here, coefficients a, b, c, d, and e in the above Formula (1) are values listed in below Tables 1 to 11 determined in accordance with the crystal orientation of the support substrate, a type of higher order mode indicating either the first higher order mode, the second higher order mode, or the third higher order mode, and respective ranges of the wavelength normalized film thickness T_S of the silicon oxide film, the wavelength normalized film thickness T_LT of the piezoelectric body, and the propagation direction ψ_Si inside the support substrate.

	TABLE 1
	Si(100)
	FIRST HIGHER ORDER MODE
	0 < TLT < 0.25	0.25 ≤ TLT ≤ 3.5
	aTLT(2)	0	0
	aTLT(1)	−14.83429368	3.069902124
	bTLT(2)	0	0
	cTLT	0.221296296	0.274301676
	aTS(2)	0	0
	aTS(1)	−5.435055656	−11.51705287
	bTS(2)	0	0
	cTS	0.244907407	0.246648045
	aTN(3)	0	0
	aTN(2)	0	0
	aTN(1)	0.954625056	2.416190553
	bTN(3)	0	0
	bTN(2)	0	0
	cTN	0.32037037	0.345810056
	aTE(2)	163.7465036	194.8374496
	aTE(1)	8.852421424	2.920900643
	bTE(2)	0.001465714	0.001392903
	cTE	0.153587963	0.15377095
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0.004515779
	aψSi(1)	0.078396962	0.109748177
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	64.80134827
	cψSi	7.083333333	10.05586592
	aθLT(2)	0	0
	aθLT(1)	−0.024815031	0.020111202
	bθLT(2)	0	0
	cθLT	−52.03703704	−51.79888268
	dTLTTS	0	0
	dTLTTN	0	0
	dTLTTE	0	−307.8174848
	dTLTψSi	0	0
	dTLTθLT	1.483479323	0
	dTSTN	0	0
	dTSTE	0	0
	dTSψSi	−1.673812731	−1.384976956
	dTSθLT	0	0.672079071
	dTNTE	0	0
	dTNψSi	0	0
	dTNθLT	0	−0.108878788
	dTEψSi	0	0
	dTEθLT	0	0
	dψSiθLT	0.002868735	0
	e	−2.09327176	−2.154987875

	TABLE 2
	Si(110)
	FIRST HIGHER ORDER MODE
	0 ≤ ψ Si < 30	30 ≤ ψSi ≤ 90
	aTLT(2)	0	0
	aTLT(1)	−12.83201212	−9.646567168
	bTLT(2)	0	0
	cTLT	0.256470588	0.250903614
	aTS(2)	156.859599	0
	aTS(1)	−21.52776656	−15.1877177
	bTS(2)	0.001522145	0
	cTS	0.261176471	0.243825301
	aTN(3)	0	0
	aTN(2)	0	0
	aTN(1)	18.19696789	8.364202341
	bTN(3)	0	0
	bTN(2)	0	0
	cTN	0.152941176	0.272891566
	aTE(2)	0	0
	aTE(1)	−6.461494684	−4.137739161
	bTE(2)	0	0
	cTE	0.152941176	0.153463855
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	−0.007084639	−0.003013228
	aψSi(1)	−0.301466226	−0.031376567
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	49.58131488	795.684243
	cψSi	25.35294118	60.63253012
	aθLT(2)	0	0
	aθLT(1)	0	0.009367138
	bθLT(2)	0	0
	cθLT	0	−52
	dTLTTS	140.9204814	0
	dTLTTN	0	24.32908352
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	51.74259913	53.37502263
	dTSTE	0	0
	dTSψSi	0	0
	dTSθLT	0	0
	dTNTE	0	0
	dTNψSi	0	−0.241253979
	dTNθLT	0	0
	dTEψSi	0	0
	dTEθLT	0	0.503490956
	dψSiθLT	0	0
	e	−1.714086264	−1.062610881

TABLE 3
Si(111)
FIRST HIGHER ORDER MODE
aTLT(2) 0
aTLT(1) −11.07513554
bTLT(2) 0
cTLT    0.253819444
aTS(2)  0
aTS(1)  −14.53606605
bTS(2)  0
cTS     0.255555556
aTN(3)  0
aTN(2)  −27.47980058
aTN(1)  11.21718185
bTN(3)  0
bTN(2)  0.012775849
cTN     0.198611111
aTE(2)  0
aTE(1)  0
bTE(2)  0
cTE     0
aψSi(4) 0
aψSi(3) 0
aψSi(2) 0
aψSi(1) 0.199446167
bψSi(4) 0
bψSi(3) 0
bψSi(2) 0
cψSi    31.80555556
aθLT(2) 0
aθLT(1) 0.020411672
bθLT(2) 0
cθLT    −49.55555556
dTLTTS  0
dTLTTN  59.65672759
dTLTTE  0
dTLTψSi 0
dTLTθLT 0
dTSTN   118.0753788
dTSTE   0
dTSψSi  0
dTSθLT  0
dTNTE   0
dTNψSi  0
dTNθLT  0
dTEψSi  0
dTEθLT  0
dψSiθLT 0
e       −1.633231485

TABLE 4
Si(100)
SECOND HIGHER ORDER MODE
aTLT(2) 0
aTLT(1) −11.81358789
bTLT(2) 0
cTLT    0.238372093
aTS(2)  0
aTS(1)  12.8161063
bTS(2)  0
cTS     0.256511628
aTN(3)  51.69588497
aTN(2)  −32.3186317
aTN(1)  −4.371415613
bTN(3)  0.001717063
bTN(2)  0.027148945
cTN     0.29627907
aTE(2)  0
aTE(1)  1.615825178
bTE(2)  0
cTE     0.151744186
aψSi(4) 0
aψSi(3) 0.000212057
aψSi(2) −0.001603831
aψSi(1) −0.204451256
bψSi(4) 0
bψSi(3) −751.8827776
bψSi(2) 48.11032991
cψSi    27.48837209
aθLT(2) 0
aθLT(1) 0.02976445
bθLT(2) 0
cθLT    −49.6744186
dTLTTS  0
dTLTTN  0
dTLTTE  107.5358299
dTLTψSi 0
dTLTθLT 0
dTSTN   0
dTSTE   0
dTSψSi  1.157163274
dTSθLT  0
dTNTE   0
dTNψSi  −0.328790695
dTNψLT  −0.146613553
dTEψSi  0
dTEθLT  0
dψSiθLT 0
e       −3.188900929

	TABLE 5
	Si(110)
	SECOND HIGHER ORDER MODE
	0 ≤ ψSi< 30	30 ≤ ψSi ≤ 90
	aTLT(2)	114.8844473	193.3812097
	aTLT(1)	−8.088688831	0.512582429
	bTLT(2)	0.0016209	0.001754662
	cTLT	0.254008909	0.251239669
	aTS(2)	0	0
	aTS(1)	−7.32209573	−6.329562725
	bTS(2)	0	0
	cTS	0.252672606	0.271900826
	aTN(3)	0	−81.37971878
	aTN(2)	−8.528039509	39.7113193
	aTN(1)	−1.120271161	0.826800765
	bTN(3)	0	0.006887919
	bTN(2)	0.053619178	0.025205929
	cTN	0.423830735	0.200826446
	aTE(2)	0	0
	aTE(1)	9.909256206	0
	bTE(2)	0	0
	cTE	0.160523385	0
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0.003197968
	aψSi(1)	0.018063648	−0.015576788
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	108.7630626
	cψSi	8.797327394	38.92561983
	aθLT(2)	0	0
	aθLT(1)	−0.003063309	0.049075185
	bθLT(2)	0	0
	cθLT	−49.54120267	−48.89256198
	dTLTTS	0	−167.1962018
	dTLTTN	−32.41085998	0
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	33.06314431	0
	dTSTE	124.8374401	0
	dTSψSi	0	0.486860801
	dTSθLT	0	0
	dTNTE	−38.52108083	0
	dTNψSi	0	0
	dTNψLT	0	0
	dTEψSi	0	0
	dTEθLT	0.494639958	0
	dψSiθLT	−0.001623976	0.014724275
	e	−2.271454108	−2.472699496

	TABLE 6
	Si(111)
	SECOND HIGHER ORDER MODE
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 60
	aTLT(2)	0	0
	aTLT(1)	−19.73613055	−14.94881654
	bTLT(2)	0	0
	cTLT	0.239145299	0.24607438
	aTS(2)	0	0
	aTS(1)	−6.009225958	0.384596926
	bTS(2)	0	0
	cTS	0.246837607	0.24862259
	aTN(3)	0	0
	aTN(2)	−20.54217049	−13.90920983
	aTN(1)	−0.500198805	−1.907891682
	bTN(3)	0	0
	bTN(2)	0.036939908	0.04540127
	cTN	0.399487179	0.382644628
	aTE(2)	0	0
	aTE(1)	5.085265993	1.386937823
	bTE(2)	0	0
	cTE	0.158376068	0.157438017
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0.001491321	0
	aψSi(1)	0.042768727	−0.007722013
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	159.6686391	0
	cψSi	14.15384615	47.63085399
	aθLT(2)	0	0
	aθLT(1)	0.012313864	0
	bθLT(2)	0	0
	cθLT	−48.4034188	0
	dTLTTS	0	0
	dTLTTN	−34.27397947	−21.45483754
	dTLTTE	0	0
	dTLTψSi	0.278464842	0
	dTLTθLT	−0.425894828	0
	dTSTN	46.58606596	0
	dTSTE	92.95289822	102.0248205
	dTSψSi	0	0.493711224
	dTSθLT	0	0
	dTNTE	−26.83666562	0
	dTNψSi	−0.133932768	−0.129081681
	dTNψLT	−0.107712568	0
	dTEψSi	0	0
	dTEθLT	0	0
	dψSiθLT	0	0
	e	−2.444079693	−1.863631594

TABLE 7
Si(100)
THIRD HIGHER ORDER MODE
aTLT(2) 0
aTLT(1) −13.69744796
bTLT(2) 0
cTLT    0.242117117
aTS(2)  0
aTS(1)  21.67672451
bTS(2)  0
cTS     0.24740991
aTN(3)  0
aTN(2)  0
aTN(1)  0
bTN(3)  0
bTN(2)  0
cTN     0
aTE(2)  0
aTE(1)  0
bTE(2)  0
cTE     0
aψSi(4) 0
aψSi(3) 0
aψSi(2) 0
aψSi(1) −0.012294125
bψSi(4) 0
bψSi(3) 0
bψSi(2) 0
cψSi    23.5472973
aθLT(2) 0
aθLT(1) −0.043141927
bθLT(2) 0
cθLT    −50.74774775
dTLTTS  0
dTLTTN  0
dTLTTE  0
dTLTψSi 0
dTLTθLT 1.006243214
dTSTN   0
dTSTE   0
dTSψSi  0
dTSθLT  0
dTNTE   0
dTNψSi  0
dTNψLT  0
dTEψSi  0
dTEθLT  0
dψSiθLT −0.002432123
e       −2.624644502

	TABLE 8
	Si(110)
	THIRD HIGHER ORDER MODE
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 90
	aTLT(2)	0	0
	aTLT(1)	−11.03265079	0
	bTLT(2)	0	0
	cTLT	0.256828704	0
	aTS(2)	0	0
	aTS(1)	−4.308771413	0.663966622
	bTS(2)	0	0
	cTS	0.254976852	0.252631579
	aTN(3)	0	−41.616937
	aTN(2)	0	15.26191272
	aTN(1)	0.749735997	1.074574236
	bTN(3)	0	0.006033304
	bTN(2)	0	0.043147922
	cTN	0.380092593	0.303157895
	aTE(2)	0	0
	aTE(1)	−0.678702233	11.03955295
	bTE(2)	0	0
	cTE	0.155960648	0.160921053
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0
	aψSi(1)	0.020332938	0.010235202
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	0
	cψSi	5.99537037	66.78947368
	aθLT(2)	−0.003658214	0
	aθLT(1)	0.048112599	0.016635787
	bθLT(2)	71.1933299	0
	cθLT	−50.89814815	−49.93684211
	dTLTTS	0	0
	dTLTTN	0	0
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	0	0
	dTSTE	0	0
	dTSψSi	0	−0.323118596
	dTSθLT	0	0.713957036
	dTNTE	0	0
	dTNψSi	−0.144459086	0
	dTNψLT	0	0
	dTEψSi	0.79407423	0.334206608
	dTEθLT	0	0
	dψSiθLT	−0.002496666	0.001289273
	e	−2.360031711	−3.077359987

TABLE 9
Si(111)
THIRD HIGHER ORDER MODE
0 < TLT < 0.25
0 ≤ ψSi < 30
aTLT(2) 0
aTLT(1) −23.116307
bTLT(2) 0
cTLT    0.2289801
aTS(2)  0
aTS(1)  −14.28753349
bTS(2)  0
cTS     0.260572139
aTN(3)  0
aTN(2)  0
aTN(1)  −0.440595972
bTN(3)  0
bTN(2)  0
cTN     0.411940299
aTE(2)  0
aTE(1)  0
bTE(2)  0
cTE     0
aψSi(4) 0
aψSi(3) 0
aψSi(2) 0
aψSi(1) 0.029126872
bψSi(4) 0
bψSi(3) 0
bψSi(2) 0
cψSi    11.96517413
aθLT(2) 0
aθLT(1) 0
bθLT(2) 0
cθLT    0
dTLTTS  0
dTLTTN  0
dTLTTE  0
dTLTψSi 0
dTLTθLT 0
dTSTN   0
dTSTE   0
dTSψSi  0.930830627
dTSθLT  0
dTNTE   0
dTNψSi  −0.129081681
dTNψLT  0
dTEψSi  0
dTEθLT  0
dψSiθLT 0
e       −2.122238265

	TABLE 10
	Si(111)
	THIRD HIGHER ORDER MODE
	0 < TLT < 0.25
	30 ≤ ψSi ≤ 60
	0 < TN < 0.3	0.3 ≤ TN < 0.5	0.5 ≤ TN ≤ 2.0
aTLT(2)	0	0	0
aTLT(1)	−8.85598025	−13.00016665	−14.59159182
bTLT(2)	0	0	0
cTLT	0.228097345	0.22804878	0.228054299
aTS(2)	103.6914504	0	0
aTS(1)	−1.916300209	−1.043153875	−2.152482595
bTS(2)	0.001674808	0	0
cTS	0.25420354	0.254634146	0.251809955
aTN(3)	0	0	0
aTN(2)	0	0	0
aTN(1)	−2.052521715	1.895724222	−3.806230027
bTN(3)	0	0	0
bTN(2)	0	0	0
cTN	0.187610619	0.403414634	0.604072398
aTE(2)	0	0	0
aTE(1)	6.773288364	5.622244745	4.676153327
bTE(2)	0	0	0
cTE	0.163274336	0.167317073	0.16561086
aψSi(4)	0	0	0
aψSi(3)	0	0	0
aψSi(2)	0	0	0
aψSi(1)	−0.035810857	0	0.001284581
bψSi(4)	0	0	0
bψSi(3)	0	0	0
bψSi(2)	0	0	0
cψSi	50.7079646	0	47.46606335
aθLT(2)	−0.004232627	−0.004038546	0
aθLT(1)	0.047188385	0.050497193	0.025858407
bθLT(2)	70.63732477	71.2056157	0
cθLT	−50.2300885	−50.47804878	−50.00904977
dTLTTS	0	144.8256764	175.1562687
dTLTTN	0	−71.99871186	62.29352459
dTLTTE	0	0	0
dTLTψSi	0	0	0.579045093
dTLTθLT	0	0	0
dTSTN	0	0	0
dTSTE	0	0	0
dTSψSi	0	0.421981204	0
dTSθLT	0.662353425	0.864834339	0.455548641
dTNTE	0	0	0
dTNψSi	0	0	0.218878849
dTNψLT	0	0	−0.178003295
dTEψSi	0	0	0
dTEθLT	0	0	0
dψSiθLT	0.002492698	0.002050178	0
e	−1.992833526	−1.990755952	−2.158637111

	TABLE 11
	Si(111)
	THIRD HIGHER ORDER MODE
	0.25 ≤ TLT ≤ 3.5
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 60
	aTLT(2)	0	0
	aTLT(1)	−4.28090475	0
	bTLT(2)	0	0
	cTLT	0.275829876	0
	aTS(2)	0	0
	aTS(1)	−10.77092012	−1.545108081
	bTS(2)	0	0
	cTS	0.254356846	0.254105263
	aTN(3)	0	0
	aTN(2)	0	0
	aTN(1)	−0.547621988	−0.893667583
	bTN(3)	0	0
	bTN(2)	0	0
	cTN	0.396680498	0.392631579
	aTE(2)	0	0
	aTE(1)	0	0.708331426
	bTE(2)	0	0
	cTE	0	0.159684211
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0
	aψSi(1)	0.033675166	−0.011260677
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	0
	cψSi	11.70124481	48.21052632
	aθLT(2)	0	−0.003806532
	aθLT(1)	−0.012544759	0.039951436
	bθLT(2)	0	67.93672687
	cθLT	−49.37759336	−49.42315789
	dTLTTS	122.2019913	0
	dTLTTN	0	0
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	0	0
	dTSTE	0	0
	dTSψSi	0.657009296	−0.317058863
	dTSθLT	0	0.702776192
	dTNTE	0	−16.38117608
	dTNψSi	−0.139004432	0.128605996
	dTNψLT	0	0
	dTEψSi	0	0
	dTEθLT	0	0
	dψSiθLT	0.001351095	0.001928116
	e	−2.653122338	−2.237232738

In a preferred embodiment of the acoustic wave device according to the present invention, I_h for the first higher order mode and I_h for the second higher order mode are greater than about −2.4.

In a preferred embodiment of the acoustic wave device according to the present invention, I_h for the first higher order mode and I_h for the third higher order mode are greater than about −2.4.

In a preferred embodiment of the acoustic wave device according to the present invention, I_h for the second higher order mode and I_h for the third higher order mode are greater than about −2.4.

In a preferred embodiment of the acoustic wave device according to the present invention, it is preferable that I_h for the first higher order mode, I_h for the second higher order mode, and I_h for the third higher order mode are all greater than about −2.4. In this case, the responses for all of the first higher order mode, the second higher order mode, and the third higher order mode can be effectively reduced or prevented.

In a preferred embodiment of the acoustic wave device according to the present invention, a thickness of the piezoelectric body is less than or equal to about 3.5λ.

In a preferred embodiment of the acoustic wave device according to the present invention, a thickness of the piezoelectric body is less than or equal to about 2.5λ.

In a preferred embodiment of the acoustic wave device according to the present invention, a thickness of the piezoelectric body is less than or equal to about 1.5λ.

In a referred embodiment of the acoustic wave device according to the present invention, a thickness of the piezoelectric body is less than or equal to about 0.5λ.

In a preferred embodiment of the acoustic wave device according the present invention, an acoustic wave resonator is provided as the acoustic wave device.

An acoustic wave filter according to a preferred embodiment of the present invention includes a plurality of resonators. At least one resonator of the plurality of resonators is defined by an acoustic wave device according to a preferred embodiment of the present invention. Therefore, an acoustic wave filter is obtained in which at least one response out of the first, second, and third higher order modes is reduced or prevented.

A multiplexer according to a preferred embodiment of the present invention includes N (N is greater than or equal to 2) acoustic wave filters having different pass bands from each other. First terminals of the N acoustic wave filters are connected to each other via a common connection on an antenna terminal side. At least one acoustic wave filter of the N acoustic wave filters except for the acoustic wave filter having the highest pass band includes one or more acoustic wave resonators. At least one acoustic wave resonator of the one or more acoustic wave resonators is an acoustic wave device according to a preferred embodiment of the present invention.

The multiplexers according to preferred embodiments of the present invention are preferably used as a carrier aggregation composite filter device.

In addition, a radio-frequency front end circuit according to a preferred embodiment of the present invention includes an acoustic wave filter including an acoustic wave device according to a preferred embodiment of the present invention and a power amplifier connected to the acoustic wave filter.

A communication device according to a preferred embodiment of the present invention includes a radio-frequency front end circuit including an acoustic wave filter including an acoustic wave device according to a preferred embodiment of the present invention, and a power amplifier connected to the acoustic wave filter, and an RF signal processing circuit.

With acoustic wave devices, radio-frequency front end circuits, and communication devices according to preferred embodiments of the present invention, at least one of the response of the first higher order mode, the response of the second higher order mode, and the response of the third higher order mode, which are located on the high-frequency side of the main mode, can be effectively reduced or prevented. Therefore, it is unlikely that a ripple due to a higher order mode will be generated in another band pass filter having a pass band at a higher frequency than that of the acoustic wave devices in the radio-frequency front end circuits and the communication devices including the acoustic wave devices of preferred embodiments of the present invention.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic front sectional view of an acoustic wave device according to a first preferred embodiment of the present invention and FIG. 1B is a schematic plan view illustrating the electrode structure of the acoustic wave device.

FIG. 2 is a diagram illustrating an admittance characteristic of an acoustic wave resonator.

FIG. 3 is a diagram illustrating the relationship between a propagation direction ψ_Si inside a support substrate and a response intensity S11 of a first higher order mode.

FIG. 4 is a diagram illustrating the relationship between a wavelength normalized film thickness T_LT of a piezoelectric body made of lithium tantalate and the response intensity S11 of the first higher order mode.

FIG. 5 is a diagram illustrating the relationship between a cut angle (90°+θ_LT) of the piezoelectric body made of lithium tantalate and the response intensity S11 of the first higher order mode.

FIG. 6 is a diagram illustrating the relationship between a wavelength normalized film thickness T_S of a silicon oxide film and the response intensity S11 of the first higher order mode.

FIG. 7 is a diagram illustrating the relationship between a wavelength normalized film thickness T_E of an IDT electrode and the response intensity S11 of the first higher order mode.

FIG. 8 is a diagram illustrating the relationship between a wavelength normalized film thickness T_N of a silicon nitride film and the response intensity S11 of the first higher order mode.

FIG. 9 is a circuit diagram of a multiplexer including the acoustic wave device of the first preferred embodiment of the present invention.

FIG. 10 is a circuit diagram illustrating an acoustic wave filter that is used in a multiplexer and includes the acoustic wave device of the first preferred embodiment of the present invention.

FIG. 11A is a diagram illustrating a filter characteristic of a multiplexer including an acoustic wave device of a comparative example and FIG. 11B is a diagram illustrating a filter characteristic of a multiplexer of the first preferred embodiment of the present invention.

FIG. 12 is a diagram illustrating the relationships between a wavelength normalized film thickness T_Si of a support substrate and the responses of first, second, and third higher order modes.

FIG. 13 is a diagram illustrating the relationship between a propagation direction ψ_Si inside a support substrate and a response intensity S11 of a second higher order mode.

FIG. 14 is a diagram illustrating the relationship between a wavelength normalized film thickness T_LT of a piezoelectric body made of lithium tantalate and the response intensity S11 of the second higher order mode.

FIG. 15 is a diagram illustrating the relationship between a cut angle (90°+θ_LT) of the piezoelectric body made of lithium tantalate and the response intensity S11 of the second higher order mode.

FIG. 16 is a diagram illustrating the relationship between a wavelength normalized film thickness T_S of a silicon oxide film and the response intensity S11 of the second higher order mode.

FIG. 17 is a diagram illustrating the relationship between a wavelength normalized film thickness T_E of an IDT electrode and the response intensity S11 of the second higher order mode.

FIG. 18 is a diagram illustrating the relationship between a wavelength normalized film thickness T_N of a silicon nitride film and the response intensity S11 of the second higher order mode.

FIG. 19 is a diagram illustrating the relationship between a propagation direction ψ_Si inside a support substrate and a response intensity S11 of a third higher order mode.

FIG. 20 is a diagram illustrating the relationship between a wavelength normalized film thickness T_LT of a piezoelectric body made of lithium tantalate and the response intensity S11 of the third higher order mode.

FIG. 21 is a diagram illustrating the relationship between a cut angle (90°+θ_LT) of the piezoelectric body made of lithium tantalate and the response intensity S11 of the third higher order mode.

FIG. 22 is a diagram illustrating the relationship between a wavelength normalized film thickness T_S of a silicon oxide film and the response intensity S11 of the third higher order mode.

FIG. 23 is a diagram illustrating the relationship between a wavelength normalized film thickness T_E of an IDT electrode and the response intensity S11 of the third higher order mode.

FIG. 24 is a diagram illustrating the relationship between a wavelength normalized film thickness T_N of a silicon nitride film and the response intensity S11 of the third higher order mode.

FIG. 25 is a diagram illustrating the relationship between the film thickness of a LiTaO₃ film and a Q value in an acoustic wave device.

FIG. 26 is a diagram illustrating the relationship between the film thickness of a LiTaO₃ film and a temperature coefficient of frequency TCF in an acoustic wave device.

FIG. 27 is a diagram illustrating the relationship between the film thickness of a LiTaO₃ film and acoustic velocity in an acoustic wave device.

FIG. 28 is a diagram illustrating the relationship between LiTaO₃ film thickness and relative bandwidth.

FIG. 29 is a diagram illustrating the relationships between the film thickness of a silicon oxide film, the material of a high-acoustic-velocity film, and acoustic velocity.

FIG. 30 is a diagram illustrating the relationship between the film thickness of a silicon oxide film, an electromechanical coupling coefficient, and the material of a high-acoustic-velocity film.

FIG. 31 is a configuration diagram of a communication device according to a preferred embodiment of the present invention that includes a radio-frequency front end circuit.

FIG. 32 is a schematic diagram explaining a crystal orientation.

FIG. 33 is a schematic diagram explaining a crystal orientation.

FIG. 34 is a schematic diagram explaining a crystal orientation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the present invention will be described in accordance with specific preferred embodiments of the present invention with reference to the drawings.

The preferred embodiments described in the present specification are merely illustrative examples and it should be noted that elements and portions of the configurations illustrated in different preferred embodiments can be substituted for one another or combined with one another if so desired.

FIG. 1A is a schematic front sectional view of an acoustic wave device of a first preferred embodiment of the present invention and FIG. 1B is a schematic plan view illustrating the electrode structure of the acoustic wave device.

An acoustic wave device 1 is a one-port acoustic wave resonator. The acoustic wave device 1 preferably includes a support substrate 2, a silicon nitride film 3 stacked on the support substrate 2, a silicon oxide film 4 stacked on the silicon nitride film 3, a piezoelectric body 5 stacked on the silicon oxide film 4, and an InterDigital Transducer (IDT) electrode 6 provided on the piezoelectric body 5.

The support substrate 2 is preferably a single crystal silicon substrate, for example. The single crystal silicon may be doped with impurities. The silicon nitride film 3 is preferably a SiN film, and the silicon oxide film 4 is preferably a SiO₂ film, for example. The piezoelectric body 5 is made of lithium tantalate (LiTaO₃). The lithium tantalate may be doped with Fe or the like. The piezoelectric body 5 includes first and second main surfaces 5a and 5b, which oppose each other. The IDT electrode 6 is provided on the first main surface 5a. Reflectors 7 and 8 are provided on both sides of the IDT electrode 6 in an acoustic wave propagation direction.

The silicon nitride film 3 is not limited to being a SiN film and SiN may be doped with another element. In addition, the silicon oxide film 4 may include not only SiO, and, for example, may include silicon oxide obtained by doping SiO₂ with fluorine or the like.

Furthermore, the silicon oxide film 4 may have a multilayer structure including a plurality of layers and an intermediate layer made of titanium, nickel or the like, for example, between the plurality of layers. In other words, the silicon oxide film 4 may have a multilayer structure in which a first silicon oxide film, an intermediate layer, and a second silicon oxide film are sequentially stacked from the support substrate 2 side. The wavelength normalized thickness of the silicon oxide film 4 in this case represents the thickness of the entire multilayer structure. Furthermore, the silicon nitride film 3 may have a multilayer structure including a plurality of layers and an intermediate layer made of titanium, nickel or the like, for example, between the plurality of layers. In other words, the silicon nitride film 3 may have a multilayer structure in which a first silicon nitride film, an intermediate layer, and a second silicon nitride film are sequentially stacked from the support substrate 2 side. The wavelength normalized thickness of the silicon nitride film 3 in this case refers to the thickness of the entire multilayer structure.

In the acoustic wave resonator having a structure in which the piezoelectric body 5 made of lithium tantalate is directly or indirectly stacked on the support substrate 2, the inventors of preferred embodiments of the present application discovered that responses are generated due to the below-described first, second, and third higher order modes.

FIG. 2 is a diagram illustrating an admittance characteristic of an acoustic wave resonator explaining the first to third higher order modes. The admittance characteristic illustrated in FIG. 2 is not the admittance characteristic of an acoustic wave resonator of a preferred embodiment of the present invention but rather the admittance characteristic of an acoustic wave resonator having the following parameters:

Euler angles (ϕ_Si, θ_Si, ψ_Si) of support substrate 2=(about 0°, about 0°, about 45′). Film thickness of silicon oxide film 4=about 0.30λ, film thickness of piezoelectric body 5=about 0.30λ, Euler angles (ϕ_LT, θ_LT, ψ_LT) of piezoelectric body=(0°, −40°, 0°). λ is a wavelength determined by the electrode finger pitch of the IDT electrode 6 and λ=about 1 μm. The IDT electrode 6 is made of a multilayer metal film in which an Al film and a Ti film are stacked and a thickness thereof expressed as an aluminum thickness from the thicknesses and densities of the individual electrode layers is about 0.05λ.

As is clear from FIG. 2, in the above-described acoustic wave resonator, responses of a first higher order mode, a second higher order mode, and a third higher order mode appear on the high-frequency side of the response of the main mode. Here, “main mode” refers to the resonant mode used to obtain the desired frequency characteristic. The frequency positions are as follows: first higher order mode response<second higher order mode response<third higher order mode response. The response of the first higher order mode is closest to the response of the main mode. However, FIG. 2 is merely an example, and the positional relationships between the frequencies of the respective modes may be interchanged depending on conditions, such as electrode thickness.

A feature of the acoustic wave device 1 of the present preferred embodiment is that at least one response among the response of the first higher order mode, the response of the second higher order mode, and the response of the third higher order mode is reduced or prevented.

λ is a wavelength determined by the electrode finger pitch of the IDT electrode 6. T_LT is the wavelength normalized film thickness of the piezoelectric body 5 made of lithium tantalate, θ_LT is the Euler angle θ of the piezoelectric body made of lithium tantalate, T_N is the wavelength normalized film thickness of the silicon nitride film 3, T_S is the wavelength normalized film thickness of the silicon oxide film 4, T_E is the wavelength normalized film thickness of the IDT electrode 6 expressed as an aluminum thickness from the thicknesses and densities of the individual electrode layers, ψ_Si is the propagation direction inside the support substrate 2, and T_Si is the wavelength normalized film thickness of the support substrate 2.

T_LT, θ_LT, T_N, T_S, T_E, and ψ_Si are set so that at least one I_h of I_h corresponding to the response intensity of the first higher order mode, I_h corresponding to the response intensity of the second higher order mode, and I_h corresponding to the response intensity of the third higher order mode as expressed by below Formula (1) is greater than about −2.4, and T_Si>about 20. As a result, at least one out of the responses of the first, second, and third higher order modes is effectively reduced or prevented. This will be described in detail below.

In this specification, a “wavelength normalized film thickness” is a value obtained by normalizing the thickness of a film using the wavelength λ determined by the electrode finger pitch of an IDT electrode. Therefore, a wavelength normalized film thickness is value obtained by dividing the actual thickness by λ. The wavelength λ determined by the electrode finger pitch of the IDT electrode may be determined using the average value of the electrode finger pitch.

The wavelength normalized film thickness T_E of the IDT electrode 6, which is expressed as an aluminum thickness, is obtained by calculating the product of the wavelength normalized film thickness of the IDT electrode and the ratio of the density of the IDT electrode 6 to the density of aluminum. In this case, when there are a plurality of electrode layers as in the IDT electrode 6, the wavelength normalized film thickness T_E of the IDT electrode 6 expressed as an aluminum thickness is calculated by obtaining the density of the IDT electrode 6 from the thicknesses and densities of the individual electrode layers.

$\mathrm{Formula}\left(1\right)$ $I_h=a_{T_{\mathrm{LT}}}^{\left(2\right)}\left({\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)}^2-b_{T_{\mathrm{LT}}}^{\left(2\right)}\right)+a_{T_{\mathrm{LT}}}^{\left(1\right)}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)+a_{T_S}^{\left(2\right)}\left({\left(T_S-c_{T_S}\right)}^2-b_{T_S}^{\left(2\right)}\right)+a_{T_S}^{\left(1\right)}\left(T_S-c_{T_S}\right)+a_{T_N}^{\left(3\right)}\left({\left(T_N-c_{T_N}\right)}^3-b_{T_N}^{\left(3\right)}\right)+a_{T_N}^{\left(2\right)}\left({\left(T_N-c_{T_N}\right)}^2-b_{T_N}^{\left(2\right)}\right)+a_{T_N}^{\left(1\right)}\left(T_N-c_{T_N}\right)+a_{T_E}^{\left(2\right)}\left({\left(T_E-c_{T_E}\right)}^2-b_{T_E}^{\left(2\right)}\right)+a_{T_E}^{\left(1\right)}\left(T_E-c_{T_E}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(4\right)}\left({\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)}^4-b_{{\psi }_{\mathrm{Si}}}^{\left(4\right)}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(3\right)}\left({\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)}^3-b_{{\psi }_{\mathrm{Si}}}^{\left(3\right)}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(2\right)}\left({\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)}^2-b_{{\psi }_{\mathrm{Si}}}^{\left(2\right)}\right)+a_{{\psi }_{\mathrm{Si}}}^{\left(1\right)}\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+a_{{\theta }_{\mathrm{LT}}}^{\left(2\right)}\left({\left({\theta }_{\mathrm{LT}}-c_{{\theta }_{\mathrm{LT}}}\right)}^2-b_{{\theta }_{\mathrm{LT}}}^{\left(2\right)}\right)+a_{{\theta }_{\mathrm{LT}}}^{\left(1\right)}\left({\theta }_{\mathrm{LT}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_{\mathrm{LT}}T_S}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left(T_S-c_{T_S}\right)+d_{T_{\mathrm{LT}}T_N}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left(T_N-c_{T_N}\right)+d_{T_{\mathrm{LT}}T_E}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left(T_E-c_{T_E}\right)+d_{T_{\mathrm{LT}}{\psi }_{\mathrm{Si}}}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_{\mathrm{LT}}{\theta }_{\mathrm{LT}}}\left(T_{\mathrm{LT}}-c_{T_{\mathrm{LT}}}\right)\left({\theta }_{\mathrm{LT}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_ST_N}\left(T_S-c_{T_S}\right)\left(T_N-c_{T_N}\right)+d_{T_ST_E}\left(T_S-c_{T_E}\right)\left(T_E-c_{T_E}\right)+d_{T_S{\psi }_{\mathrm{Si}}}\left(T_S-c_{T_S}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_S{\theta }_{\mathrm{LT}}}\left(T_S-c_{T_S}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_NT_E}\left(T_N-c_{T_N}\right)\left(T_E-c_{T_E}\right)+d_{T_N{\psi }_{\mathrm{Si}}}\left(T_N-c_{T_N}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_N{\theta }_{\mathrm{LT}}}\left(T_N-c_{T_N}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{T_E{\psi }_{\mathrm{Si}}}\left(T_E-c_{T_E}\right)\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)+d_{T_E{\theta }_{\mathrm{LT}}}\left(T_E-c_{T_E}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+d_{{\psi }_{\mathrm{Si}}{\theta }_{\mathrm{LT}}}\left({\psi }_{\mathrm{Si}}-c_{{\psi }_{\mathrm{Si}}}\right)\left({\theta }_{\mathrm{TL}}-c_{{\theta }_{\mathrm{LT}}}\right)+e$

Here, coefficients a, b, c, d, and e in the Formula (1) have values listed in below Tables 12 to 22 determined in accordance the crystal orientation of the support substrate 2, the type of higher order mode indicating either the first higher order mode, the second higher order mode, or the third higher order mode, and the respective ranges of the wavelength normalized film thickness T_S of the silicon oxide film 4, the wavelength normalized film thickness T_LT of the piezoelectric body made of lithium tantalate, the propagation direction ψ_Si inside the support substrate 2, and so forth. In Tables 12 to 22, Si(100), Si(110), or Si(111) represents the crystal orientation of the single crystal Si constituting the support substrate 2. These crystal orientations will be described in detail later.

	TABLE 12
	Si(100)
	FIRST HIGHER ORDER MODE
	0 < TLT < 0.25	0.25 ≤ TLT ≤ 3.5
	aTLT(2)	0	0
	aTLT(1)	−14.83429368	3.069902124
	bTLT(2)	0	0
	cTLT	0.221296296	0.274301676
	aTS(2)	0	0
	aTS(1)	−5.435055656	−11.51705287
	bTS(2)	0	0
	cTS	0.244907407	0.246648045
	aTN(3)	0	0
	aTN(2)	0	0
	aTN(1)	0.954625056	2.416190553
	bTN(3)	0	0
	bTN(2)	0	0
	cTN	0.32037037	0.345810056
	aTE(2)	163.7465036	194.8374496
	aTE(1)	8.852421424	2.920900643
	bTE(2)	0.001465714	0.001392903
	cTE	0.153567963	0.15377095
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0.004515779
	aψSi(1)	0.078396962	0.109748177
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	64.80134827
	cψSi	7.083333333	10.05586592
	aθLT(2)	0	0
	aθLT(1)	−0.024815031	0.020111202
	bθLT(2)	0	0
	cθLT	−52.03703704	−51.79888268
	dTLTTS	0	0
	dTLTTN	0	0
	dTLTTE	0	−307.8174848
	dTLTψSi	0	0
	dTLTθLT	1.483479323	0
	dTSTN	0	0
	dTSTE	0	0
	dTSψSi	−1.673812731	−1.384976956
	dTSθLT	0	0.672079071
	dTNTE	0	0
	dTNψSi	0	0
	dTNψLT	0	−0.108878788
	dTEψSi	0	0
	dTEθLT	0	0
	dψSiθLT	0.002868735	0
	e	−2.09327176	−2.154987875

	TABLE 13
	Si(110)
	FIRST HIGHER ORDER MODE
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 90
	aTLT(2)	0	0
	aTLT(1)	−12.83201212	−9.646567168
	bTLT(2)	0	0
	cTLT	0.256470588	0.250903614
	aTS(2)	156.858589	0
	aTS(1)	−21.52776656	−15.1877177
	bTS(2)	0.001522145	0
	cTS	0.261176471	0.243825301
	aTN(3)	0	0
	aTN(2)	0	0
	aTN(1)	18.19696789	8.364202341
	bTN(3)	0	0
	bTN(2)	0	0
	cTN	0.152941176	0.272891566
	aTE(2)	0	0
	aTE(1)	−6.461494684	−4.137739161
	bTE(2)	0	0
	cTE	0.152941176	0.153463855
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	−0.007084639	−0.003013228
	aψSi(1)	−0.301466226	−0.031376567
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	49.58131488	795.684243
	cψSi	25.35294118	60.63253012
	aθLT(2)	0	0
	aθLT(1)	0	0.009367138
	bθLT(2)	0	0
	cθLT	0	−52
	dTLTTS	140.9204814	0
	dTLTTN	0	24.32908352
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	51.74259913	53.37502263
	dTSTE	0	0
	dTSψSi	0	0
	dTSθLT	0	0
	dTNTE	0	0
	dTNψSi	0	−0.241253979
	dTNψLT	0	0
	dTEψSi	0	0
	dTEθLT	0	0.503490956
	dψSiθLT	0	0
	e	−1.714086264	−1.062610881

TABLE 14
Si(111)
FIRST HIGHER ORDER MODE
aTLT(2) 0
aTLT(1) −11.07513554
bTLT(2) 0
cTLT    0.253819444
aTS(2)  0
aTS(1)  −14.53606605
bTS(2)  0
cTS     0.255555556
aTN(3)  0
aTN(2)  −27.47980058
aTN(1)  11.21718185
bTN(3)  0
bTN(2)  0.012775849
cTN     0.198611111
aTE(2)  0
aTE(1)  0
bTE(2)  0
cTE     0
aψSi(4) 0
aψSi(3) 0
aψSi(2) 0
aψSi(1) 0.199446167
bψSi(4) 0
bψSi(3) 0
bψSi(2) 0
cψSi    31.80555556
aθLT(2) 0
aθLT(1) 0.020411672
bθLT(2) 0
cθLT    −49.55555556
dTLTTS  0
dTLTTN  59.65672759
dTLTTE  0
dTLTψSi 0
dTLTθLT 0
dTSTN   118.0753788
dTSTE   0
dTSψSi  0
dTSθLT  0
dTNTE   0
dTNψSi  0
dTNψLT  0
dTEψSi  0
dTEθLT  0
dψSiθLT 0
e       −1.633231485

TABLE 15
Si(100)
SECOND HIGHER ORDER MODE
aTLT(2) 0
aTLT(1) −11.81358789
bTLT(2) 0
cTLT    0.238372093
aTS(2)  0
aTS(1)  12.8161063
bTS(2)  0
cTS     0.256511628
aTN(3)  51.69588497
aTN(2)  −32.3186317
aTN(1)  −4.371415613
bTN(3)  0.001717063
bTN(2)  0.027148945
cTN     0.29627907
aTE(2)  0
aTE(1)  1.615825178
bTE(2)  0
cTE     0.151744186
aψSi(4) 0
aψSi(3) 0.000212057
aψSi(2) −0.001603831
aψSi(1) −0.204451256
bψSi(4) 0
bψSi(3) −751.8827776
bψSi(2) 48.11032991
cψSi    27.48837209
aθLT(2) 0
aθLT(1) 0.02976445
bθLT(2) 0
cθLT    −49.6744186
dTLTTS  0
dTLTTN  0
dTLTTE  107.5358299
dTLTψSi 0
dTLTθLT 0
dTSTN   0
dTSTE   0
dTSψSi  1.157163274
dTSθLT  0
dTNTE   0
dTNψSi  −0.328790695
dTNψLT  −0.146613553
dTEψSi  0
dTEθLT  0
dψSiθLT 0
e       −3.188900929

	TABLE 16
	Si(110)
	SECOND HIGHER ORDER MODE
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 90
	aTLT(2)	114.8844473	193.3812097
	aTLT(1)	−8.088688831	0.512582429
	bTLT(2)	0.0016209	0.001754662
	cTLT	0.254008909	0.251239669
	aTS(2)	0	0
	aTS(1)	−7.32209573	−6.329562725
	bTS(2)	0	0
	cTS	0.252672606	0.271900826
	aTN(3)	0	−81.37971878
	aTN(2)	−8.528039509	39.7113193
	aTN(1)	−1.120271161	0.826800765
	bTN(3)	0	0.006887919
	bTN(2)	0.053619178	0.025205929
	cTN	0.423830735	0.200826446
	aTE(2)	0	0
	aTE(1)	9.909256206	0
	bTE(2)	0	0
	cTE	0.160523385	0
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0.003197968
	aψSi(1)	0.018063648	−0.015576788
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	108.7630626
	cψSi	8.797327394	38.92561983
	aθLT(2)	0	0
	aθLT(1)	−0.003063309	0.049075185
	bθLT(2)	0	0
	cθLT	−49.54120267	−48.89256198
	dTLTTS	0	−167.1962018
	dTLTTN	−32.41085998	0
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	33.06314431	0
	dTSTE	124.8374401	0
	dTSψSi	0	0.486860801
	dTSθLT	0	0
	dTNTE	−38.52108083	0
	dTNψSi	0	0
	dTNψLT	0	0
	dTEψSi	0	0
	dTEθLT	0.494639958	0
	dψSiθLT	−0.001623976	0.014724275
	e	−2.271454108	−2.472699496

	TABLE 17
	Si(111)
	SECOND HIGHER ORDER MODE
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 60
	aTLT(2)	0	0
	aTLT(1)	−19.73613055	−14.94881654
	bTLT(2)	0	0
	cTLT	0.239145299	0.24607438
	aTS(2)	0	0
	aTS(1)	−6.009225958	0.384596926
	bTS(2)	0	0
	cTS	0.246837607	0.24862259
	aTN(3)	0	0
	aTN(2)	−20.54217049	−13.90920983
	aTN(1)	−0.500198805	−1.907891682
	bTN(3)	0	0
	bTN(2)	0.036939908	0.04540127
	cTN	0.399487179	0.382644628
	aTE(2)	0	0
	aTE(1)	5.085265993	1.386937823
	bTE(2)	0	0
	cTE	0.158376068	0.157438017
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0.001491321	0
	aψSi(1)	0.042768727	−0.007722013
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	159.6686391	0
	cψSi	14.15384615	47.63085399
	aθLT(2)	0	0
	aθLT(1)	0.012313864	0
	bθLT(2)	0	0
	cθLT	−48.4034188	0
	dTLTTS	0	0
	dTLTTN	−34.27397947	−21.45483754
	dTLTTE	0	0
	dTLTψSi	0.278464842	0
	dTLTθLT	−0.425894828	0
	dTSTN	46.58606596	0
	dTSTE	92.95289822	102.0248205
	dTSψSi	0	0.493711224
	dTSθLT	0	0
	dTNTE	−26.83666562	0
	dTNψSi	−0.133932768	−0.129081681
	dTNψLT	−0.107712568	0
	dTEψSi	0	0
	dTEθLT	0	0
	dψSiθLT	0	0
	e	−2.444079693	−1.863631594

TABLE 18
Si(100)
THIRD HIGHER ORDER MODE
aTLT(2) 0
aTLT(1) −13.69744796
bTLT(2) 0
cTLT    0.242117117
aTS(2)  0
aTS(1)  −21.67672451
bTS(2)  0
cTS     0.24740991
aTN(3)  0
aTN(2)  0
aTN(1)  0
bTN(3)  0
bTN(2)  0
cTN     0
aTE(2)  0
aTE(1)  0
bTE(2)  0
cTE     0
aψSi(4) 0
aψSi(3) 0
aψSi(2) 0
aψSi(1) −0.012294125
bψSi(4) 0
bψSi(3) 0
bψSi(2) 0
cψSi    23.5472973
aθLT(2) 0
aθLT(1) −0.043141927
bθLT(2) 0
cθLT    −50.74774775
DTLTTS  0
DTLTTN  0
DTLTTE  0
DTLTψSi 0
DTLTθLT 1.006243214
DTSTN   0
DTSTE   0
DTSψSi  0
DTSθLT  0
DTNTE   0
DTNψSi  0
DTNψLT  0
DTEψSi  0
DTEθLT  0
DψSiθLT −0.002432123
e       −2.624644502

	TABLE 19
	Si(110)
	THIRD HIGHER ORDER MODE
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 90
	aTLT(2)	0	0
	aTLT(1)	−11.03265079	0
	bTLT(2)	0	0
	cTLT	0.256828704	0
	aTS(2)	0	0
	aTS(1)	−4.308771413	0.663966622
	bTS(2)	0	0
	cTS	0.254976852	0.252631579
	aTN(3)	0	−41.616937
	aTN(2)	0	15.26191272
	aTN(1)	0.749735997	1.074574236
	bTN(3)	0	0.006033304
	bTN(2)	0	0.043147922
	cTN	0.380092593	0.303157895
	aTE(2)	0	0
	aTE(1)	−0.678702233	11.03955295
	bTE(2)	0	0
	cTE	0.155960648	0.160921053
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0
	aψSi(1)	0.020332938	0.010235202
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	0
	cψSi	5.99537037	66.78947368
	aθLT(2)	−0.003658214	0
	aθLT(1)	0.048112599	0.016635787
	bθLT(2)	71.1933299	0
	cθLT	−50.89814815	−49.93684211
	dTLTTS	0	0
	dTLTTN	0	0
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	0	0
	dTSTE	0	0
	dTSψSi	0	−0.323118596
	dTSθLT	0	0.713957036
	dTNTE	0	0
	dTNψSi	−0.144459086	0
	dTNψLT	0	0
	dTEψSi	0.79407423	0.334206608
	dTEθLT	0	0
	dψSiθLT	−0.002496666	0.001289273
	e	−2.360031711	−3.077359987

TABLE 20
Si(111)
THIRD HIGHER ORDER MODE
0 < TLT < 0.25
0 ≤ ψSi < 30
aTLT(2) 0
aTLT(1) −23.116307
bTLT(2) 0
cTLT    0.2289801
aTS(2)  0
aTS(1)  −14.28753349
bTS(2)  0
cTS     0.260572139
aTN(3)  0
aTN(2)  0
aTN(1)  −0.440595972
bTN(3)  0
bTN(2)  0
cTN     0.411940299
aTE(2)  0
aTE(1)  0
bTE(2)  0
cTE     0
aψSi(4) 0
aψSi(3) 0
aψSi(2) 0
aψSi(1) 0.029126872
bψSi(4) 0
bψSi(3) 0
bψSi(2) 0
cψSi    11.96517413
aθLT(2) 0
aθLT(1) 0
bθLT(2) 0
cθLT    0
dTLTTS  0
dTLTTN  0
dTLTTE  0
dTLTψSi 0
dTLTθLT 0
dTSTN   0
dTSTE   0
dTSψSi  0.930830627
dTSθLT  0
dTNTE   0
dTNψSi  −0.129081681
dTNψLT  0
dTEψSi  0
dTEθLT  0
dψSiθLT 0
e       −2.122238265

	TABLE 21
	Si(111)
	THIRD HIGHER ORDER MODE
	0 < TLT < 0.25
	30 ≤ ψSi ≤ 60
	0 < TN < 0.3	0.3 ≤ TN < 0.5	0.5 ≤ TN ≤ 2.0
aTLT(2)	0	0	0
aTLT(1)	−8.85598025	−13.00016665	−14.59159182
bTLT(2)	0	0	0
cTLT	0.228097345	0.22804878	0.228054299
aTS(2)	103.6914504	0	0
aTS(1)	−1.916300209	−1.043153875	−2.152482595
bTS(2)	0.001674808	0	0
cTS	0.25420354	0.254634146	0.251809955
aTN(3)	0	0	0
aTN(2)	0	0	0
aTN(1)	−2.052521715	1.895724222	−3.806230027
bTN(3)	0	0	0
bTN(2)	0	0	0
cTN	0.187810619	0.403414634	0.604072398
aTE(2)	0	0	0
aTE(1)	6.773288364	5.622244745	4.676153327
bTE(2)	0	0	0
cTE	0.163274336	0.167317073	0.16561086
aψSi(4)	0	0	0
aψSi(3)	0	0	0
aψSi(2)	0	0	0
aψSi(1)	−0.035810857	0	0.001284581
bψSi(4)	0	0	0
bψSi(3)	0	0	0
bψSi(2)	0	0	0
cψSi	50.7079646	0	47.46606335
aθLT(2)	−0.004232627	−0.004038546	0
aθLT(1)	0.047188385	0.050497193	0.025858407
bθLT(2)	70.63732477	71.2056157	0
cθLT	−50.2300885	−50.47804878	−50.00904977
dTLTTS	0	144.8256764	175.1562687
dTLTTN	0	−71.99871186	62.29352459
dTLTTE	0	0	0
dTLTψSi	0	0	0.579045093
dTLTθLT	0	0	0
dTSTN	0	0	0
dTSTE	0	0	0
dTSψSi	0	0.421981204	0
dTSθLT	0.662353425	0.864834339	0.455548641
dTNTE	0	0	0
dTNψSi	0	0	0.218878849
dTNψLT	0	0	−0.178003295
dTEψSi	0	0	0
dTEθLT	0	0	0
dψSiθLT	0.002492698	0.002050178	0
e	−1.992833526	−1.990755952	−2.158637111

	TABLE 22
	Si(111)
	THIRD HIGHER ORDER MODE
	0.25 ≤ TLT ≤ 3.5
	0 ≤ ψSi < 30	30 ≤ ψSi ≤ 60
	aTLT(2)	0	0
	aTLT(1)	−4.28090475	0
	bTLT(2)	0	0
	cTLT	0.275829876	0
	aTS(2)	0	0
	aTS(1)	−10.77092012	−1.545108081
	bTS(2)	0	0
	cTS	0.254356846	0.254105263
	aTN(3)	0	0
	aTN(2)	0	0
	aTN(1)	−0.547621988	−0.893667583
	bTN(3)	0	0
	bTN(2)	0	0
	cTN	0.396680498	0.392631679
	aTE(2)	0	0
	aTE(1)	0	0.708331428
	bTE(2)	0	0
	cTE	0	0.159684211
	aψSi(4)	0	0
	aψSi(3)	0	0
	aψSi(2)	0	0
	aψSi(1)	0.033675166	−0.011260677
	bψSi(4)	0	0
	bψSi(3)	0	0
	bψSi(2)	0	0
	cψSi	11.70124481	48.21052632
	aθLT(2)	0	−0.003806532
	aθLT(1)	−0.012544759	0.039951436
	bθLT(2)	0	67.93672687
	cθLT	−49.37759336	−49.42315789
	dTLTTS	122.2019913	0
	dTLTTN	0	0
	dTLTTE	0	0
	dTLTψSi	0	0
	dTLTθLT	0	0
	dTSTN	0	0
	dTSTE	0	0
	dTSψSi	0.657009296	−0.317058863
	dTSθLT	0	0.702776192
	dTNTE	0	−16.38117608
	dTNψSi	−0.139004432	0.128605996
	dTNψLT	0	0
	dTEψSi	0	0
	dTEθLT	0	0
	dψSiθLT	0.001351095	0.001928116
	e	−2.653122338	−2.237232738

The inventors of preferred embodiments of the present application performed experiments to discover how the response intensities of the first higher order mode, the second higher order mode, and the third higher order mode changed when the above parameters T_LT, θ_LT, T_N, T_S, T_E, ψ_Si, and T_Si were changed in various ways.

The absolute values of S11 were obtained as the response intensities of the higher order modes when the above parameters were changed. The smaller the decibel display value of the absolute value of S11, the higher the response intensity of the higher order mode. When calculating S11, the electrode finger crossing width was 20λ, the number of pairs of electrode fingers was ninety-four pairs, and S11 was obtained using an electrode finger pair model employing a two-dimensional finite element method.

The IDT electrode has a structure in which Ti/Pt/Ti/Al metal films are stacked in this order from the piezoelectric body side. Furthermore, the thickness of the IDT electrode was changed by changing the thickness of the Pt film. In addition, as the wavelength normalized film thickness T_E of the IDT electrode, a wavelength normalized film thickness expressed as an aluminum thickness using the thicknesses and densities of the individual electrode layers was obtained using the mass of the entire IDT electrode estimated from the densities of the individual metal films.

First Higher Order Mode

An acoustic wave resonator having the admittance characteristic illustrated in FIG. 2 was used as a reference structure.

That is, an acoustic wave resonator in which the Euler angles of the support substrate 2=(about 0°, about 0°, about 45°), the film thickness of the silicon oxide film 4=about 0.30λ, the Euler angles of the piezoelectric body 5=(about 0°, about −40°, about 0°), and the wavelength λ determined by the electrode finger pitch of the IDT electrode 6=about 1λ μm was used as a reference structure. In the reference structure, the IDT electrode 6 is made of a multilayer metal film in which an Al film and a Ti film are stacked. The thickness of the multilayer metal film expressed as an aluminum thickness using the thicknesses and densities of the individual electrode layers was about 0.05λ. FIGS. 3 to 8 are diagrams illustrating changes in the response intensity S11 of the first higher order mode when parameters are changed relative to the reference structure. As illustrated in FIG. 3, when the propagation direction ψ_Si inside the support substrate is changed in a range from about 0° to about 45°, it is clear that the response intensity S11 of the first higher order mode changes relative to the reference structure.

Similarly, as illustrated in FIG. 4, it is clear that the response intensity S11 of the first higher order mode also changes in the case where the wavelength normalized film thickness I_LT of the piezoelectric body made of lithium tantalate is changed.

Furthermore, as illustrated in FIG. 5, the response intensity S11 of the first higher order mode also changes in the case where the cut angle (about 90°+θ_LT) of the piezoelectric body made of lithium tantalate changes.

As illustrated in FIG. 6, the response intensity S11 of the first higher order mode also changes in the case where the wavelength normalized film thickness T_S of the silicon oxide film is changed.

As illustrated in FIG. 7, the response intensity S11 of the first higher order mode also changes in the case where the wavelength normalized film thickness T_E, which is expressed as an Al thickness, of the IDT electrode changes.

As illustrated in FIG. 8, it is clear that the intensity S11 of the first higher order mode changes when the wavelength normalized film thickness T_N of the silicon nitride film is changed.

It is clear from FIGS. 3 to 8 that the response intensity of the first higher order mode can be adjusted by changing these parameters. In other words, the response intensity of the first higher order mode can be reduced by selecting the values of these parameters.

From the calculation results of FIGS. 3 to 8 and so forth, the inventors of preferred embodiments of the present application deduced that I_h corresponding to the response intensity of a higher-order mode can be obtained using the above-described Formula (1) and the coefficients a, b, c, d, and e in above Tables 12 to 22.

The values listed in Tables 12 to 14 were found for the coefficients in Formula (1) in accordance with the crystal orientation (100), (110), or (111) of the support substrate and the respective ranges of the wavelength normalized film thickness T_LT of the piezoelectric body made of lithium tantalate, the wavelength normalized film thickness T_N of the silicon nitride film, the wavelength normalized film thickness T_S of the silicon oxide film, the wavelength normalized film thickness T_E of the IDT electrode, and the propagation direction ψ_Si inside the support substrate. In this way, conditions of T_LT, θ_LT, T_N, T_S, T_E, and ψ_Si at which I_h1, which corresponds to the response intensity of the first higher order mode, is greater than about −2.4 are determined.

Incidentally, in a multiplexer in which a plurality of acoustic wave filters are connected to each other at one end, it is required that the response intensity of a higher order mode be greater than about −2.4 dB for S11. This is in order to make the effect on the bandpass characteristics of other acoustic wave filters negligible. Usually, in mobile phone devices and the like, ripples appearing in the passband are required to be about −0.8 dB or more from the viewpoint of ensuring reception sensitivity. However, when a higher order mode exists in the passband of another acoustic wave filter, a ripple of about ⅓ the response intensity of the higher order mode is generated in the passband of the other filter. Therefore, it is preferable to make the response intensity S11 of such a higher order mode greater than about −2.4 dB in order to make the ripple inside the pass band greater than or equal to about −0.8 dB.

In addition, T_Si>about 20 in the acoustic wave device 1 of the first preferred embodiment of the present invention.

Since I_h>about −2.4 and T_Si>about 20 for the first higher order mode, the effect of the response of the first higher order mode on the passband of the other acoustic wave filter can be effectively reduced or prevented. This will be explained while referring to FIGS. 9 to 12.

FIG. 9 is a circuit diagram of a multiplexer. In a multiplexer 10, first to fourth acoustic wave filters 11 to 14 are connected to each other via a common connection on an antenna terminal 15 side. FIG. 10 is a circuit diagram of the first acoustic wave filter 11. The first acoustic wave filter 11 includes a plurality of series arm resonators S1 to S3 and a plurality of parallel arm resonators P1 and P2. In other words, the first acoustic wave filter 11 is a ladder filter. The series arm resonators S1 to S3 and the parallel arm resonators P1 and P2 are preferably defined using the acoustic wave device 1 of the above-described preferred embodiment. The multiplexer 10 can be used as a carrier aggregation composite filter device, for example.

In a preferred embodiment of the present invention, the circuit configuration of an acoustic wave filter including the acoustic wave device according to the present preferred embodiment is not limited to this example. For example, an acoustic wave filter including a longitudinally coupled resonator filter may be used. In this case, the longitudinally coupled resonator acoustic wave filter may be an acoustic wave device of a preferred embodiment of the present invention. Alternatively, an acoustic wave resonator connected to a longitudinally coupled resonator acoustic wave filter may be defined by using an acoustic wave device according to a preferred embodiment of the present invention.

The pass bands of the first to fourth acoustic wave filters 11 to 14 are respectively referred to as first to fourth pass bands. The frequency positions of the pass bands are as follows: first pass band<second pass band<third pass band<fourth pass band.

For comparison, a multiplexer of a comparative example according to the present invention was prepared in which a first acoustic wave filter was configured in the same manner as in the above-described preferred embodiment except for use of the acoustic wave resonator having the reference structure.

FIG. 11A illustrates the filter characteristics of a first acoustic wave filter and a second acoustic wave filter of the multiplexer of the comparative example. The pass band of the first acoustic wave filter is a first pass band A. The pass band of the second acoustic wave filter is a second pass band B. A large ripple appears in the second pass band B. This is because a large response appears due to the first higher order mode of an acoustic wave resonator used in the first acoustic wave filter.

FIG. 11B is a diagram illustrating the filter characteristic of a multiplexer as a preferred embodiment of the present invention. Here, the first acoustic wave filter is provided using the acoustic wave device of the above-described preferred embodiment. Therefore, a large ripple does not appear in the second pass band B. In other words, a large ripple does not appear in the pass band B of the second acoustic wave filter, which is another filter. Therefore, degradation of the filter characteristic of the second acoustic wave filter is unlikely to occur.

Thus, in the multiplexer according to a preferred embodiment of the present invention, the response of the first higher order mode is reduced or prevented in the acoustic wave filters including the acoustic wave device configured in accordance with a preferred embodiment of the present invention, and therefore degradation of the filter characteristic of the other acoustic wave filter having a higher pass band can be effectively reduced or prevented.

FIG. 12 is a diagram illustrating the relationship between the wavelength normalized film thickness T_Si of the support substrate 2 and the response intensities S11 of the first higher order mode, the second higher order mode, and the third higher order mode. As is clear from FIG. 12, it is clear that the response intensities of the first higher order mode, the second higher order mode, and the third higher order mode can be more effectively reduced or prevented when T_Si>about 20.

Second Higher Order Mode

FIG. 13 is a diagram illustrating the relationship between the propagation direction ψ_Si inside the support substrate and a response intensity S11 of a second higher order mode. As is clear from FIG. 13, the response intensity S11 of the second higher order mode changes when ψ_Si changes. Similarly, as illustrated in FIG. 14, the response intensity S11 of the second higher order mode also changes in the case where the wavelength normalized film thickness T_LT of the piezoelectric body made of lithium tantalate changes. As illustrated in FIG. 15, the response intensity S11 of the second higher order mode also changes in the case where the cut angle (90°+θ_LT) of the piezoelectric body made of lithium tantalate changes.

As illustrated in FIG. 16, the response intensity S11 of the second higher order mode also changes in the case where the wavelength normalized film thickness T_S of the silicon oxide film changes. Furthermore, as illustrated in FIG. 17, the response intensity S11 of the second higher order mode also changes in the case where the Al-converted wavelength normalized film thickness T_E of the IDT electrode changes. In addition, as illustrated in FIG. 18, the response intensity S11 of the second higher order mode also changes in the case where the wavelength normalized film thickness T_N of the silicon nitride film changes.

From the calculation results in FIGS. 13 to 18 and so forth, values of the coefficients in Formula (1) for achieving a I_h2 corresponding to the response intensity of the second higher order mode were obtained, similarly to as in the case of the first higher order mode. I_h2 corresponding to the response intensity of the second higher order mode can be expressed when the coefficients of Formula (1) are set as in above Tables 15 to 17 in accordance with the crystal orientation (100), (110), or (111) of the support substrate and the respective ranges of the wavelength normalized film thickness T_LT of the piezoelectric body made of lithium tantalate, the wavelength normalized film thickness T_N of the silicon nitride film, the wavelength normalized film thickness T_S of the silicon oxide film, the wavelength normalized film thickness T_E of the IDT electrode, and the propagation direction ψ_Si, and the second higher order mode response can also be made sufficiently small by determining T_LT, θ_LT, T_N, T_S, T_E, and ψ_Si conditions for which I_h2 is greater than or equal to about −2.4 among these values of I_h2 and by making T_Si>about 20.

Third Higher Order Mode

FIG. 19 is a diagram illustrating the relationship between the propagation direction ψ_Si inside the support substrate and a response intensity S11 of a third higher order mode. As is clear from FIG. 19, the response intensity S11 of the third higher order mode changes when ψ_Si changes. Similarly, as illustrated in FIG. 20, the response intensity S11 of the third higher order mode also changes in the case where the wavelength normalized film thickness T_LT of the piezoelectric body made of lithium tantalate changes. As illustrated in FIG. 21, the response intensity S11 of the third higher order mode also changes in the case where the cut angle (90°+θ_LT) of the piezoelectric body made of lithium tantalate changes. As illustrated in FIG. 22, the response intensity S11 of the third higher order mode also changes in the case where the wavelength normalized film thickness T_S of the silicon oxide film changes.

Furthermore, as illustrated in FIG. 23, the response intensity S11 of the third higher order mode also changes in the case where the Al-converted wavelength normalized film thickness T_E of the IDT electrode changes. In addition, as illustrated in FIG. 24, the response intensity S11 of the third higher order mode also changes in the case where the wavelength normalized film thickness T_N of the silicon nitride film changes.

From FIGS. 19 to 24 and so forth, the values of the coefficients in Formula (1) expressing I_h3 corresponding to the response intensity of the third higher order mode expressed by Formula (1) were obtained. In other words, I_h3 corresponding to the response intensity of the third higher order mode can be expressed when the coefficients of Formula (1) are set as in above Tables 18 to 22 in accordance with the crystal orientation (100), (110), or (111) of the support substrate and the respective ranges of the wavelength normalized film thickness T_LT of the piezoelectric body made of lithium tantalate, the wavelength normalized film thickness T_N of the silicon nitride film, the wavelength normalized film thickness T_S of the silicon oxide film, the wavelength normalized film thickness T_E of the IDT electrode, and the propagation direction ψ_Si, and the third higher order mode response can be made sufficiently small by determining T_LT, θ_LT, T_N, T_S, T_E, and ψ_Si conditions for which I_h3 is greater than or equal to about −2.4 among these values of I_h3 and by making T_Si>about 20.

Structures of Preferred Embodiments

It is preferable that I_h>about −2.4 for all of the first higher order mode, the second higher order mode, and the third higher order mode. In this case, the effect of the first to third higher order modes on another acoustic wave filter can be effectively reduced or prevented. Furthermore, I_h>about −2.4 may be achieved for I_h for the first higher order mode and the second higher order mode, I_h for the first higher order mode and the third higher order mode, or I_h for the second higher order mode and the third higher order mode. In this case, the effect of two higher order modes from among the first to third higher order modes can be reduced or prevented.

When the structure according to preferred embodiments of the present invention is adopted, as described above, there is a tendency for a higher order mode to be trapped in a portion of the structure where the silicon oxide film 4 and the piezoelectric body 5 are stacked, but by making the portion where the silicon oxide film 4 and the piezoelectric body 5 are stacked thin by making the thickness of the piezoelectric body 5 less than or equal to about 3.5λ, for example, it becomes less likely that a higher-order mode will be trapped.

More preferably, the film thickness of the piezoelectric body 5 made of lithium tantalate is less than or equal to about 2.5λ, for example, and in this case, the absolute value of the temperature coefficient of frequency TCF can be reduced. Still more preferably, the film thickness of the piezoelectric body 5 made of lithium tantalate is less than or equal to about 1.5λ, for example. In this case, the electromechanical coupling coefficient can be easily adjusted. Still more preferably, the film thickness of the piezoelectric body 5 made of lithium tantalate is less than or equal to about 0.5λ, for example. In this case, the electromechanical coupling coefficient can be easily adjusted over a wide range.

In the present invention, crystallographically equivalent orientations are treated as being identical in each substrate material.

Silicon crystal orientations expressed as Si(100), Si(110), and Si(111) as mentioned above will be described in more detail below.

As illustrated in FIG. 32, Si(100) represents a substrate that has been cut along the (100) plane perpendicular to the crystal axis represented by the Miller index [100] in a silicon crystal structure having a diamond structure. Crystallographically equivalent planes such as Si(010) are also included.

As illustrated in FIG. 33, Si(110) represents a substrate that has been cut along the (110) plane perpendicular to the crystal axis represented by the Miller index [110] in a silicon crystal structure having a diamond structure. Other crystallographically equivalent planes are also included.

As illustrated in FIG. 34, Si(111) represents a substrate that has been cut along the (111) plane perpendicular to the crystal axis represented by the Miller index [111] in a silicon crystal structure having a diamond structure. Other crystallographically equivalent planes are also included.

In above Formula (1), a) in the case where Si(100) (Euler angles (ϕ_Si=about 0±5°, θ_Si=about 0±5°, ψ_Si)) is used, the range of ψ_Si is about 0°≤ψ_Si≤about 45°. However, due to the symmetry of the crystal structure of Si(100), ψ_Si and ψ_Si±(n×90°) are synonymous (n=1, 2, 3 . . . ). Similarly, ψ_Si and −ψ_Si are synonymous.

(b) In the case where Si(110) (Euler angles (ϕ_Si=about −45±5°, θ_Si=about −90±5°, ψ_Si)) is used, the range of ψ_Si is about 0°≤ψ_Si≤about 90°. Due to the symmetry of the crystal structure of Si(110), ψ_Si and ψ_Si±(n×180°) are synonymous (n=1, 2, 3 . . . ). Similarly, ψ_Si and −ψ_Si are synonymous.

(c) In the case where Si(111) (Euler angles ϕ_Si=about −45±5°, θ_Si=about −54.73561±5°, ψ_Si)) is used, the range of ψ_Si is about 0°≤ψ_Si≤about 60°. However, due to the symmetry of the crystal structure of Si(111), ψ_Si and ψ_Si±(n×120°) are synonymous (n=1, 2, 3 . . . ). Similarly, ψ_Si and −ψ_Si are synonymous.

In addition, although the range of θ_LT is about −180°<θ_LT≤about 0°, θ_LT and θ_LT 180° may be treated as being synonymous.

In this specification, for example, in Euler angles (about 0°±5°, θ, about 0°±15°), “about 0°±5°” means within a range greater than or equal to about −5° and less than or equal to about +5° and “about 0°±15°” means within a range greater than or equal to about −15° and less than or equal to about +15°.

FIG. 25 is a diagram illustrating the relationship between the film thickness of a LiTaO₃ film and the Q value in an acoustic wave device in which a low-acoustic-velocity film made of a silicon oxide film having a thickness of about 0.35λ and a piezoelectric film made of lithium tantalate having Euler angles (about 0°, about −40°, about 0°) are stacked on a high-acoustic-velocity support substrate made of silicon. The vertical axis in FIG. 25 represents the product of a Q characteristic and a relative bandwidth (Δf) of a resonator. In addition, FIG. 26 is a diagram illustrating the relationship between the film thickness of a LiTaO₃ film and the temperature coefficient of frequency TCF. FIG. 27 is a diagram illustrating the relationship between the film thickness of a LiTaO₃ film and acoustic velocity. From FIG. 25, the film thickness of the LiTaO₃ film is preferably less than or equal to about 3.5λ. In this case, the Q value is higher than in the case where the film thickness is greater than about 3.5λ. More preferably, the film thickness of the LiTaO₃ film is less than or equal to about 2.5λ in order to further increase the Q value.

Furthermore, from FIG. 26, in the case where the film thickness of the LiTaO₃ film is less than or equal to about 2.5λ, the absolute value of the temperature coefficient of frequency TCF can be reduced compared with the case where the film thickness is greater than 2.5λ. More preferably, it is desirable that the film thickness of the LiTaO₃ film be less than or equal to about 2λ, and in this case, the absolute value of the temperature coefficient of frequency TCF can be made to be less than or equal to about 10 ppm/° C. It is further preferable that the film thickness of the LiTaO₃ film be less than or equal to about 1.5λ in order to reduce the absolute value of the temperature coefficient of frequency TCF.

From FIG. 27, if the film thickness of the LiTaO₃ film is greater than about 1.5λ, the change in acoustic velocity is very small.

As illustrated in FIG. 28, the relative bandwidth varies by a large amount in a film thickness range from about 0.05λ to about 0.5λ for the LiTaO₃ film. Therefore, the electromechanical coupling coefficient can be adjusted over a wider range. Therefore, it is desirable that the film thickness of the LiTaO₃ film lie in a range from about 0.05λ to about 0.5λ in order to widen the range over which the electromechanical coupling coefficient and the relative bandwidth can be adjusted.

FIGS. 29 and 30 are diagrams respectively illustrating the relationships between the silicon oxide film thickness (λ) and the acoustic velocity and the electromechanical coupling coefficient. Here, a silicon nitride film, an aluminum oxide film, and diamond were used as the high-acoustic-velocity film underneath the low-acoustic-velocity film made of SiO₂. The film thickness of the high-acoustic-velocity film was about 1.5λ. The acoustic velocity of a bulk wave in silicon nitride is about 6000 m/s, the acoustic velocity of a bulk wave in aluminum oxide is about 6000 m/s, and the acoustic velocity of a bulk wave in diamond is about 12800 m/s. As illustrated in FIGS. 29 and 30, the electromechanical coupling coefficient and the acoustic velocity substantially do not change even when the material of the high-acoustic-velocity film and the film thickness of the silicon oxide film are changed. In particular, from FIG. 30, it is clear that the electromechanical coupling coefficient substantially does not change regardless of the material of the high-acoustic-velocity film when the film thickness of the silicon oxide film lies in the range from about 0.1λ to about 0.5λ. Furthermore, it is clear from FIG. 29 that the acoustic velocity does not change regardless of the material of the high-acoustic-velocity film when the film thickness of the silicon oxide film lies in a range from about 0.3λ to about 2λ. Therefore, the film thickness of the low-acoustic-velocity film made of silicon oxide is preferably less than or equal to about 2λ and more preferably less than or equal to about 0.5λ.

The acoustic wave devices of the above-described preferred embodiments can be used as a component such as a multiplexer of a radio-frequency front end circuit, for example. An example of such a radio-frequency front end circuit will be described below.

FIG. 31 is a schematic configuration diagram of a communication device according to a preferred embodiment of the present invention that includes a radio-frequency front end circuit. A communication device 240 includes an antenna 202, a radio-frequency front end circuit 230, and an RF signal processing circuit 203. The radio-frequency front end circuit 230 is a circuit section that is connected to the antenna 202. The radio-frequency front end circuit 230 includes a multiplexer 210 and amplifiers 221 to 224. The multiplexer 210 includes first to fourth filters 211 to 214. The above-described preferred embodiment of the multiplexer of the present invention can be used as the multiplexer 210. The multiplexer 210 preferably includes an antenna common terminal 225 that is connected to the antenna 202. First terminals of the first to third filters 211 to 213, which are reception filters, and a first terminal of the fourth filter 214, which is a transmission filter, are connected to the antenna common terminal 225 via a common connection. Output terminals of the first to third filters 211 to 213 are respectively connected to the amplifiers 221 to 223. In addition, the amplifier 224 is connected to an input terminal of the fourth filter 214.

The output terminals of the amplifiers 221 to 223 are connected to the RF signal processing circuit 203. The input terminal of the amplifier 224 is connected to the RF signal processing circuit 203.

A multiplexer according to a preferred embodiment of the present invention can be suitably used as the multiplexer 210 in the communication device 240.

A multiplexer according to a preferred embodiment of the present invention may include only a plurality of transmission filters or may include a plurality of reception filters.

The multiplexer includes n band pass filters, where n is greater than or equal to 2. Therefore, the multiplexer according to a preferred embodiment of the present invention may be implemented as a duplexer.

Preferred embodiments of the present invention are widely applicable to communication devices such as mobile phones in the form of filters, multiplexers applicable to multi-band systems, front end circuits, and communication devices.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Claims

1. An acoustic wave device comprising: a support substrate made of silicon;a silicon nitride film on the support substrate;a silicon oxide film on the silicon nitride film;a piezoelectric body on the silicon oxide film and made of lithium tantalate; and

2. The acoustic wave device according to claim 1, wherein Ih for the first higher order mode and Ih for the second higher order mode are greater than about −2.4.

3. The acoustic wave device according to claim 1, wherein Ih for the first higher order mode and Ih for the third higher order mode are greater than about −2.4.

4. The acoustic wave device according to claim 1, wherein Ih for the second higher order mode and Ih for the third higher order mode are greater than about −2.4.

5. The acoustic wave device according to claim 1, wherein Ih for the first higher order mode, Ih for the second higher order mode, and Ih for the third higher order mode are all greater than about −2.4.

6. The acoustic wave device according to claim 1, wherein the thickness of the piezoelectric body is less than or equal to about 3.5λ.

7. The acoustic wave device according to claim 6, wherein the thickness of the piezoelectric body is less than or equal to about 2.5λ.

8. The acoustic wave device according to claim 6, wherein the thickness of the piezoelectric body is less than or equal to about 1.5λ.

9. The acoustic wave device according to claim 6, wherein the thickness of the piezoelectric body is less than or equal to about 0.5λ.

10. The acoustic wave device according to claim 1, wherein the acoustic wave device is an acoustic wave resonator.

11. An acoustic wave filter comprising: a plurality of resonators; whereinat least one resonator of the plurality of resonators is the acoustic wave device according to claim 1.

12. A multiplexer comprising: N acoustic wave filters having different pass bands, where N is greater than or equal to 2; whereinfirst terminals of the N acoustic wave filters are connected to each other via a common connection on an antenna terminal side;at least one acoustic wave filter of the N acoustic wave filters except for the acoustic wave filter having the highest pass band includes one or more acoustic wave resonators; andat least one acoustic wave resonator of the one or more acoustic wave resonators is the acoustic wave device according to claim 1.

13. The multiplexer according to claim 12, wherein the multiplexer is a carrier aggregation composite filter device.

14. A radio-frequency front end circuit comprising: an acoustic wave filter including the acoustic wave device according to claim 1; anda power amplifier connected to the acoustic wave filter.

15. A communication device comprising: a radio-frequency front end circuit including an acoustic wave filter including the acoustic wave device according to claim 1, and a power amplifier connected to the acoustic wave filter; andan RF signal processing circuit.

16. The acoustic wave device according to claim 1, wherein the support substrate is a single crystal silicon substrate doped with impurities; andthe piezoelectric body is made of lithium tantalate doped with iron.

17. The acoustic wave device according to claim 1, wherein the silicon oxide film or the silicon nitride film includes a multilayer structure including a plurality of layers; andthe plurality of layers include an intermediate layer made of titanium or nickel.

18. The multiplexer according to claim 12, wherein the at least one acoustic wave filter includes a plurality of series arm resonators and a plurality of parallel arm resonators defining a ladder filter.

19. The multiplexer according to claim 12, further comprising: an antenna connected to the antenna common terminal.