This application is based on application Nos. 2003-190636 filed in Japan, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a surface acoustic wave device and a communication apparatus, such as a cellular phone, employing the same.
2. Description of the Related Art
Surface acoustic wave devices incorporating SAW (Surface Acoustic Wave) filters have been used in a variety of communication apparatuses.
As the modern communication apparatuses have become more compact, adapted for higher-frequency operations, and more functional, there arises an increasing demand for widening the pass bandwidth of the SAW filter. For instance, a high-performance wide-band filter having an effective pass bandwidth of not less than 80 MHz (a fractional bandwidth of about 4% or more) is desired as a filter for use in a cellular phone operating in a transmission band of 1.9 GHz. It is noted here that the “fractional bandwidth” means a value given by dividing the effective pass bandwidth by the center frequency of the passband.
For achieving such a wide-band transmission, there has been proposed a double-mode SAW resonator filter which includes three IDT (Inter Digital Transducer) electrodes formed on a piezoelectric substrate and utilizes a first-order and third-order longitudinal modes.
Likewise to
The surface acoustic wave is excited by inputting a signal to the input terminal 111 connected to the IDT electrode 102. The surface acoustic wave is propagated to the IDT electrodes 103, 104 on the opposite sides of the IDT electrode 102, so that the signal is outputted from the output terminal 113 connected to the IDT electrodes 103, 104. The surface acoustic wave is reflected by the reflectors 107 on the opposite ends of the filter, thereby forming a standing wave.
The mode of the standing wave includes a first-order mode and a higher-order mode (third-order mode) because of the presence of the three IDT electrodes 102, 103, 104. The pass characteristics of the filter depend upon resonances generated in these modes. Hence, the filter may be broadened in the passband by controlling a distance between the resonant frequencies occurring in these modes.
Conventionally, the distance between the resonant frequencies is controlled as follows. While all the IDT electrodes 102, 103, 104 are so configured as to have the same center-to-center distance (pitch L) between respective pairs of adjoining electrode fingers, the distance between the resonant frequencies is controlled by controlling a distance ‘d’ between adjoining IDT electrodes.
According to the aforementioned control method, the conventional double-mode SAW resonator filter employing a LiTaO3 substrate as the piezoelectric substrate thereof can achieve a fractional bandwidth of about 0.40% (see, Japanese Unexamined Patent Publication No. 1-231417) or, at most, of about 2% (see, Japanese Unexamined Patent Publication No. 4-40705). Although the conventional filter has achieved the maximum fractional bandwidth of 3.7% (see, Japanese Unexamined Patent Publication No. 7-58581), temperature variations must be taken into consideration when the filter is in actual operations. Furthermore, the filter is prone to frequency variations due to the variations in the configuration of the formed electrodes. Accordingly, it is impracticable to apply the conventional double-mode SAW filter to the communication apparatuses, such as the cellular phones, which require a broad pass bandwidth.
In addition, the following attempt has been made to broaden the passband and to reduce the insertion loss. A narrow electrode-finger pitch portion (the inter-electrode portion 105, 106 between the adjoining IDT electrodes shown in
However, the piezoelectric substrate encounters a pyroelectric effect caused by temperature fluctuations during the fabrication process, so that the electric charges concentrate on the narrow pitch portion between the IDT electrodes. The narrow pitch portion may encounter electric discharge caused by potential difference between the electrode fingers and hence, the IDT electrode may be damaged.
It is an object of the invention to provide a surface acoustic wave device having excellent filter characteristics featured by a low insertion loss and a broad passband, as well as to provide a communication apparatus using the same.
A surface acoustic wave device according to the invention includes a plurality of IDT electrodes arranged on a piezoelectric substrate along a propagation direction of a surface acoustic wave propagated on the piezoelectric substrate, the IDT electrode including a plurality of strip-line electrode fingers (hereinafter, referred to simply as “electrode fingers”) extended perpendicularly to the propagation direction. The device may comprise one or more electrode stages laid in parallel, the stage comprising an array of the IDT electrodes. In addition, a reflector is interposed between a pair of IDT electrodes closely spaced from each other along the propagation direction, the reflector including four or more electrode fingers extended perpendicularly to the propagation direction. The device is characterized in that a center-to-center distance (pitch ‘a’ shown in
A surface acoustic wave device according to the invention comprises a plurality of IDT electrodes arranged on a piezoelectric substrate along a propagation direction of a surface acoustic wave propagated on the piezoelectric substrate, the IDT electrode including a plurality of electrode fingers extended perpendicularly to the propagation direction. The device may comprise one or more electrode stages laid in parallel, the stage comprising an array of the IDT electrodes. A reflector is interposed between a pair of IDT electrodes closely spaced from each other along the propagation direction, the reflector including electrode fingers extended perpendicularly to the propagation direction. The device is characterized in that the electrode-finger pitch of the IDT electrode is progressively decreased from a region away from the reflector toward a region close to the reflector.
A surface acoustic wave device according to the invention comprises: five or more IDT electrodes each including electrode fingers extended perpendicularly to a propagation direction of a surface acoustic wave; and a reflector interposed between a pair of IDT electrodes closely spaced from each other along the propagation direction of the surface acoustic wave and including four or more electrode fingers extended perpendicularly to the propagation direction, wherein out of the five or more IDT electrodes, a central IDT electrode and outermost IDT electrodes have an equal electrode-finger pitch, and wherein an IDT electrode (referred to simply as “second IDT electrode”) between the central IDT electrode and the outermost IDT electrode has an electrode-finger pitch which is smaller than the electrode-finger pitch of the central IDT electrode and of the outermost IDT electrodes and is progressively decreased from the opposite ends of the second IDT electrode toward the center thereof.
According to the aforementioned surface acoustic wave devices of the invention, a standing wave mode of the surface acoustic wave excited by the IDT electrodes or the frequencies thereof allowed to pass through a passband may be controlled by varying the electrode-finger pitch of the IDT electrodes or the reflector interposed between the IDT electrodes. That is, the configurations of the invention provide fine adjustment of the first-order mode frequencies, the third-order mode frequencies and the frequencies between these modes. Thus are provided the surface acoustic wave devices featuring a wide-band transmission performance.
Furthermore, the invention also offers the following effects.
For reference purpose,
According to the invention, the configuration is made such that the electrode-finger pitch is varied in a region within the reflector or the IDT electrode, so as to eliminate an abruptly narrowed space between the electrode fingers in the region. This configuration is less prone to the electric discharge caused by an increased magnitude of the electric field between the electrode fingers. Hence, the IDT electrode is less susceptible to pyroelectrical breaking.
In one aspect of the invention, a surface acoustic wave device featuring a more favorable transmission performance may be provided if a configuration is made such that as to the reflector and IDT electrode in adjoining relation with respect to the propagation direction, the maximum value of the electrode-finger pitch of the reflector is smaller than an average value of the electrode-finger pitch of the IDT electrode. Thus is offered a surface acoustic wave filter of high quality, which achieves a broadened pass bandwidth as filter characteristics.
In a case where plural stages of resonator-type electrode similar patterns are provided in parallel, there may be provided a surface acoustic wave device which is excellent in the insertion loss, amplitude balance and phase balance and is increased in the pass bandwidth.
In a case where the reflector and the IDT electrode adjoining each other along the propagation direction are electrically interconnected, the electric charges are excited symmetrically about the center of the standing wave mode of multiple reflection so that an even more preferred transmission performance may be achieved.
In a case where a different resonator-type electrode pattern including one or more IDT electrodes for mode resonance generation and reflectors sandwiching the IDT electrode between there is connected in series or in parallel to the above resonator-type electrode pattern, the pass bandwidth as the filter characteristics may be broadened so that a surface acoustic wave filter featuring a high quality and a low insertion loss may be provided. A ladder-type circuit, in particular, may be formed so as to accomplish impedance matching between input and output, whereas an attenuation pole may be formed. Thus is provided an excellent surface acoustic wave device featuring a great amount of out-of-band attenuation.
An alternative configuration may be made such that one of a comb electrode pair constituting the IDT electrode and including plural electrode fingers in opposing relation is divided and the divided comb-electrode portions each define an electrode connected to a balanced signal for input or output. Thus is provided a surface acoustic wave device having a function as an unbalanced-balanced signal converter.
A communication apparatus according to the invention comprises a receiver circuit and/or a transmitter circuit incorporating the aforementioned surface acoustic wave device, thereby achieving a dramatically enhanced level of signal separation.
A surface acoustic wave device according to the invention will be described hereinbelow by way of examples of a resonator-type SAW filter. In the figures illustrated as below, like components are represented by the same reference numerals, respectively.
As shown in
The IDT electrodes are arranged in plural stages (two stages are shown in the figure). Each of the stages includes IDT electrodes 2, 3, 4 and IDT electrodes 12, 13, 14.
A reflector is interposed between a respective pair of IDT electrodes closely spaced from each other with respect to the aforesaid propagation direction (between the IDT electrodes 2 and 3, the IDT electrodes 3 and 4, the IDT electrodes 12 and 13, and the IDT electrodes 13 and 14). The reflector comprises an electrode including four or more electrode fingers extended perpendicularly to the aforesaid propagation direction. Specifically, a reflector 5 is interposed between the IDT electrodes 2 and 3; a reflector 6 is interposed between the IDT electrodes 3 and 4; a reflector 15 is interposed between the IDT electrodes 12 and 13; and a reflector 16 is interposed between the IDT electrodes 13 and the 14.
In addition, the IDT electrodes 2, 4 in the first stage are connected to the IDT electrodes 12, 14 in the second stage, respectively. A reference numeral 9 represents an input terminal; a reference numeral 10 represents a ground terminal; and a reference numeral 11 represents an output terminal.
As shown in the figure, at least one of the reflectors 5, 6, 15, 16 has an electrode-finger pitch ‘a’ progressively decreased from the electrode fingers at the opposite ends thereof toward a central electrode finger thereof.
On the other hand, reflectors 7, 8, 17, 18 configured to have a constant electrode-finger pitch are disposed at the opposite ends of these resonator-type electrode patterns.
As to the reflector and the IDT electrode in adjoining relation with respect to the aforesaid propagation direction, the maximum value of the electrode-finger pitch ‘a’ of the reflector is smaller than an electrode-finger pitch ‘b’ of IDT electrode.
As described above, the configuration of the invention accomplishes multiple reflection by inserting the reflector between the IDT electrodes.
In at least one of the reflectors interposed between the IDT electrodes, the electrode-finger pitch ‘a’ is progressively decreased from the electrode fingers at the opposite ends of the reflector toward the central electrode finger thereof. Thus is reduced a radiation loss into a bulk wave. As a result, the SAW filter may have an increased pass bandwidth as filter characteristics. Furthermore, the filter may achieve improvement in insertion loss. Accordingly, the SAW filter of high quality may be provided.
This result is effected even more remarkably in a case where as to the reflector and the IDT electrode in adjoining relation with respect to the propagation direction of the surface acoustic wave, the maximum electrode-finger pitch ‘a’ of the reflector is smaller than the electrode-finger pitch ‘b’ of the IDT electrode adjacent thereto.
On the other hand, an attenuation pole may be formed by interconnecting the resonator-type electrode patterns in two-stage configuration, wherein the electrode-finger pitch may be adjusted so as to provide control of the filter characteristics in a desired manner to satisfy specification requirements. The plural resonator-type electrode patterns may be designed to vary the electrode-finger pitch between the patterns, thereby forming plural attenuation poles or providing control of the formation of the attenuation poles. This provides for a design satisfying a higher level of specification requirements.
Incidentally, the IDT electrodes 2, 3, 4, 12, 13, 14; the reflectors 7, 8, 17, 18; and the reflectors 5, 6, 15, 16 interposed between the IDT electrodes each include the electrode fingers in the range of several to several hundreds. For simplicity purpose, therefore, the figure depicts the configurations of these components schematically. The following figures resemblant to
In contrast to the SAW filter of
Specifically, the first stage of resonator-type electrode pattern on the piezoelectric substrate 1 includes the IDT electrodes 2, 3, 4, whereas the second stage of resonator-type electrode pattern on the piezoelectric substrate 1 includes the IDT electrodes 12, 13, 14. The reflectors 5, 6 are interposed between the IDT electrodes 2 and 3, and the IDT electrodes 3 and 4, respectively, the reflectors each including electrode fingers extended perpendicularly to the propagation direction of the surface acoustic wave. On the other hand, the reflectors 15, 16 are interposed between the IDT electrodes 12 and 13, and the IDT electrodes 13 and 14, respectively, the reflectors each including electrode fingers elongated perpendicularly to the propagation direction of the surface acoustic wave.
Similarly to
In the first stage of resonator-type electrode pattern, the reflectors 5, 6 have their electrode fingers connected with a ground-side bus bar of the central IDT electrode 3 adjoining these reflectors, the bus bar connected with the individual electrode fingers constituting the IDT electrode 3. In the second stage of resonator-type electrode pattern, the reflectors 15, 16 have their electrode fingers connected with an output-side bus bar of the central IDT electrode 13 adjoining these reflectors.
In a resonator-type electrode pattern of the second stage, the reflector 15 interposed between the IDT electrodes 12 and 13 is electrically connected with the IDT electrode 12 rather than with the IDT electrode 13, unlike the reflector shown in
The connection between each of the reflectors 5, 6, 15, 16 and the bus bar of the IDT electrode may be implemented in either configurations which connects the reflector with one of the bus bars of the IDT electrode and which connects the reflector with both of the bus bars of the IDT electrode, unless the ground terminal shorts with the input/output terminal. The first stage and the second stage may adopt the same interconnection mode or different interconnection modes.
A SAW filter shown in
The filter differs from the SAW filter of
A SAW filter shown in
The central IDT electrode 3 in one of the two stages of resonator-type electrode patterns defines an unbalanced input or output portion, and is connected with an unbalanced input/output terminal 9 and with the ground terminal 10. On the other hand, the central IDT electrode 13 in the other resonator-type electrode pattern defines a balanced input or output portion, and is connected with a first balanced input/output terminal 11 and a second balanced input/output terminal 19.
Since the SAW filter shown in
It is noted that the method of adding the ladder-type SAW resonators is not limited to the combination of the series connection and parallel connection, as shown in
Specifically, the SAW filter of
In the above resonator-type electrode pattern, the reflectors having the variable finger pitch and interposed between the IDT electrodes provide the multiple reflection of the surface acoustic wave, thereby reducing the radiation loss into the bulk wave as well increasing the pass bandwidth as the filter characteristics. What is more, the above configuration is adapted to reduce the insertion loss, thus offering the SAW filter of high quality.
The ladder-type SAW resonators 20, 21 may be added in series and in parallel, thereby accomplishing impedance matching between an input and an output. Furthermore, the attenuation pole may be formed by connecting the SAW resonators 20, 21 and hence, the characteristics of the filter may be so controlled as to satisfy the specifications required of a great amount of out-of-band attenuation.
A SAW filter shown in
Similarly to the configuration of
A SAW filter of
Specifically, the filter includes one or more stages of plural IDT electrodes (IDT electrodes 2, 3, 4) arranged on the piezoelectric substrate 1 along the propagation direction of the surface acoustic wave propagated on the piezoelectric substrate 1, the IDT electrode including plural electrode fingers extended perpendicularly to the propagation direction. In addition, the reflectors 5, 6 are interposed between the IDT electrodes 2 and 3 and between the IDT electrodes 3 and 4, the reflector including the plural electrode fingers extended perpendicularly to the propagation direction of the surface acoustic wave. Reference numerals 7, 8 in the figure represent reflectors disposed on the individual outer sides of the IDT electrodes. A reference numeral 9 represents an input signal terminal; a reference numeral 10 represents a ground terminal; and reference numerals 11, 19 represent output signal terminals.
In a region of the IDT electrode 2 between the opposite ends thereof, the electrode-finger pitch is progressively decreased from the end thereof farther away from the reflector 5 toward the end thereof close to the reflector 5. In a region of the IDT electrode 4 between the opposite ends thereof, the electrode-finger pitch is progressively decreased from the end thereof farther away from the reflector 6 toward the end thereof close to the reflector 6. In respective regions between the center and the individual opposite ends of the IDT electrode 3 sandwiched between the reflectors 5, 6, the electrode-finger pitch is progressively decreased from the center thereof toward the ends thereof individually adjoining the reflectors 5, 6.
Furthermore, the filter is characterized in that the maximum value of the electrode-finger pitch of the aforesaid reflector is smaller than an average value of the electrode-finger pitch of the adjacent IDT electrode.
Such a configuration is adapted for more effective reduction of the radiation loss into the bulk wave, thereby achieving a broadened pass bandwidth. Thus, the filter may be improved in the insertion loss.
A SAW filter shown in
A SAW filter shown in
A SAW filter shown in
Similarly to the SAW filter shown in
Similarly to the SAW filter shown in
This filter is characterized in that in individual regions R2, R3 of the reflector 5 and individual regions R5, R6 of the reflector 6, the maximum value ‘a’ of the electrode-finger pitch is smaller than the average electrode-finger pitch of the IDT electrodes 2, 3, 4. This contributes to the further reduction of the insertion loss and hence, the filter can achieve an even broader pass bandwidth.
Similarly to the SAW filter of
The configuration differs from that of
First, the resonator-type electrode pattern of
Out of the five IDT electrodes 301 to 305, the centrally located IDT electrode 302 and the outermost IDT electrodes 301, 303 have an equal electrode-finger pitch, which is expressed as P1.
An electrode-finger pitch of the IDT electrodes 304, 305 interposed in respective spaces between the IDT electrodes 301, 302, 303 is expressed as P2. The electrode-finger pitch P2 is defined to be smaller than the electrode-finger pitch P1. That is, P2<P1.
According to the configuration of
Such a relation between the electrode-pitches P1, P2 is graphically represented in
By defining the relation of the electrode-finger pitches of the IDT electrodes in this manner, the resonator-type electrode pattern is adapted for fine adjustment of frequencies between the first-order mode and a higher harmonic mode thereof, and between the third-order mode and a higher harmonic mode thereof. Furthermore, there may be provided a filter featuring broader bandwidth, lower loss and high transmission performance.
The electrode-finger pitch of the above reflectors 306, 307, 308, 309 is expressed as P3. According to the configuration, the electrode-finger pitch P3 is smaller than the electrode-finger pitch P1 of the central IDT electrode 302 and the outermost IDT electrodes 301, 303, but is greater than the electrode-finger pitch P2 of the IDT electrodes 304, 305 interposed between the above IDT electrodes. That is, the configuration is designed to satisfy the relation P2<P3<P1.
Furthermore, the electrode-finger pitch P3 of the reflectors 306, 307 is progressively decreased from place away from the IDT electrode 304 toward the IDT electrode 304. The electrode-finger pitch P3 of the reflectors 308, 309 is progressively decreased from place away from the IDT electrode 305 toward the IDT electrode 305.
A filter having a good transmission performance featured by an even broader bandwidth and an even lower loss than the filter of
According to the resonator-type electrode pattern, the electrode-finger pitch P1 of the IDT electrodes 301, 303 is progressively decreased toward the reflectors 306, 309. On the other hand, the electrode-finger pitch P1 of the IDT electrode 302 is progressively decreased from the center thereof toward the reflectors 307, 308.
A filter having a good transmission performance featured by an even broader bandwidth and an even lower insertion loss than the filters of
It is to be noted that the electrode configurations of the SAW filters of
Next, a brief description is made on a fabrication method for the foregoing SAW filters of
The piezoelectric substrate 1 for the SAW filter may comprise, for example, 36°±3° Y-cut, X-propagation lithium tantalate monocrystal, 42°±3° Y-cut, X-propagation lithium tantalate monocrystal, 64°±3° Y-cut, X-propagation lithium niobate monocrystal, 41°±3° Y-cut, X-propagation lithium monocrystal, or 45°±3° X-cut, Z-propagation lithium tetraborate monocrystal. These substances are preferred as the material for the piezoelectric substrate because they have high electromechanical coupling coefficients but low frequency-temperature coefficients. Out of substrates of these pyroelectrical piezoelectric monocrystals, a substrate subjected to oxygen reduction process and a substrate significantly reduced in pyroelectricity by forming solid solution with Fe or the like are preferred from the standpoint of the reliability of the device. The piezoelectric substrate may preferably have a thickness of 0.1 mm to 0.5 mm. A substrate having a thickness of less than 0.1 mm is fragile. A substrate having a thickness of more than 0.5 mm is not feasible because of an excessively high material cost and an excessively large part size.
The IDT electrodes 2, 3, 4, 12, 13, 14 and the reflectors 5, 6, 7, 8, 15, 16, 17, 18 are formed from Al or an Al alloy (Al—Cu base, Al—Ti base) by a film forming process such as vapor deposition, sputtering and CVD process. An electrode thickness may preferably be in the range of 0.1 μm to 0.5 μm from the standpoint of attaining the characteristics as the SAW filter.
In addition, Si, SiO2, SiNx or Al2O3 may be deposited as a protective film over the electrodes and surface-acoustic-wave propagation portions on the piezoelectric substrate of the SAW filter of the invention for the purposes of preventing conduction by conductive foreign substances or improving power resistance.
The SAW filter of the invention is applicable to communication apparatuses. Specifically, in a communication apparatus including at least one of a receiver circuit and a transmitter circuit or including both the receiver circuit and the transmitter circuit, the SAW filter of the invention may be used as a bandpass filter included in such a circuit.
The aforesaid communication apparatus includes, for example: (1) a communication apparatus including a transmitter circuit wherein a transmission signal is mixed with a carrier frequency by a mixer, passed through a bandpass filter for attenuation of an unwanted signal and then, amplified by a power amplifier and passed through a duplexer so as to be transmitted from an antenna; and (2) a communication apparatus including a receiver circuit wherein a signal received by an antenna and passed through a duplexer is amplified by a low-noise amplifier, passed through a bandpass filter for attenuation of an unwanted signal, and then is extracted by a mixer separating the received signal from a carrier frequency. It is possible to provide excellent communication apparatuses featuring enhanced sensitivities by applying the surface acoustic wave device of the invention to the above communication apparatuses.
The SAW filter shown in
The IDT electrodes 2, 12 each included 17 electrode pairs whereas the IDT electrodes 3, 4, 13, 14 each included 13 electrode pairs. All the IDT electrodes 2, 3, 4, 12, 13, 14 had an electrode-finger pitch of 2.25 μm.
The reflectors 5, 6 each included 6 electrode fingers. Similarly, the reflectors 15, 16 each included 5 electrode fingers. The reflectors 5, 6 each had electrode-finger pitches (hereinafter, referred to as “finger pitch”) of 2.14 μm, 2.0 μm, 1.97 μm, 2.0 μm and 2.14 μm. That is, the finger pitch was progressively decreased toward the center of the reflector 15, 16. An average of these finger pitches was 2.05 μm.
The reflectors 7, 8, 17, 18 disposed on the individual outer sides of the IDT electrodes 2, 4, 12, 14 had a finger pitch of 2.29 μm.
The pattern was formed by a photolithographic process using a sputtering apparatus, reduction projection apparatus (stepper) and RIE (Reactive Ion Etching) apparatus.
First, a substrate material was subjected to an ultrasonic cleaning process using acetone-IPA or the like, so as to be removed of organic substances. Next, the substrate was sufficiently dried by a clean oven and then, subjected to electrode film formation. The electrode film was formed by the sputtering apparatus using an Al(99 wt %)–Cu(1 wt %) alloy. The resultant electrode film had a thickness of about 0.3 μm.
Next, a photoresist was spin coated over the substrate in a thickness of about 0.5 μm and was patterned into a desired shape by means of the reduction projection apparatus (stepper). The photoresist pattern was subjected to a developing apparatus wherein an unwanted photoresist portion was dissolved away by an alkaline developing solution thereby to obtain a desired photoresist pattern. Subsequently, the RIE apparatus was operated to etch the electrode film to complete the patterning process. Thus was obtained the electrode pattern of the SAW resonator constituting the SAW filter.
Subsequently, a protective film was overlaid on a predetermined region of the aforesaid electrode. Specifically, a SiO2 film having a thickness of about 0.02 μm was overlaid on the electrode pattern and the piezoelectric substrate by means of a CVD (Chemical Vapor Deposition) apparatus. Then, the photoresist was patterned by photolithography and a window opening for electrode pad was formed by means of the RIE apparatus or the like. Thereafter, the sputtering apparatus was operated to form an electrode film based on Al. The resultant electrode film had a thickness of about 1.0 μm. Subsequently, the photoresist and an unwanted Al portion were removed at a time by a lift off process. Thus was formed an electrode pad for forming flip-chip bump.
Next, a flip-chip bump of Au was formed on the aforesaid electrode pad by means of a bump bonding apparatus. The resultant bump had a diameter of about 80 μm and a height of about 30 μm.
Next, the substrate was diced along a dicing line so as to be divided into individual chips. Then, each chip with the electrode forming face down was mounted in a package by means of a flip-chip mounting apparatus. Subsequently, the chip was baked in an N2 atmosphere whereby the SAW filter was completed. The used package comprised a square laminate structure having a size of 2.5×2.0 mm.
In Comparative Example 1, the same procedure as the above was taken to fabricate the microscopic electrode pattern as shown in
In Comparative Example 2, there was also fabricated the electrode pattern as shown in
In Comparative Example 3, there was also fabricated the electrode pattern as shown in
In Comparative Example 4, there was also fabricated the electrode pattern as shown in
Next, the SAW filters according to the example of the invention and the foresaid four comparative examples were tested. Measurement was taken at 800 measurement points while inputting a signal of 0 dBm at frequencies of 782 MHz to 982 MHz to the input terminal. There were prepared 30 samples for each filter. As measurement instruments, Multi-port Network Analyzer E5071A commercially available from Agilent Technologies was used.
The frequency dependence of the insertion loss of the filter according to the example of the invention is shown in
The filter characteristics of the invention are represented by the solid lines in
In contrast, the SAW filter of the conventional configuration including no reflector, which was fabricated as the sample of Comparative Example 1, has a narrower pass bandwidth, as indicated by the broken line in
On the other hand, the SAW filter of Comparative Example 2 wherein the reflector having the constant finger pitch is interposed between the IDT electrodes has an even narrower pass bandwidth, as indicated by the broken line in
The SAW filter of Comparative Example 3 has a pass bandwidth as narrow as that of the filter of Comparative Example 2, as indicated by the broken line in
The SAW filter of Comparative Example 4 has a pass bandwidth further reduced from that of the filter of Comparative Example 3, as indicated by the broken line in
Thus, Example 1 of the invention has achieved the broadened pass bandwidth and the reduced insertion loss, as the filter characteristics.
Next, description is made on an example of the SAW filter shown in
The IDT electrode 2 included 16 electrode pairs whereas the IDT electrodes 3, 4 each included 12 electrode pairs. All the IDT electrodes 2, 3, 4 had a finger pitch of 1.0 μm. The reflectors 5, 6 each included 6 electrode fingers which were arranged with finger pitches progressively decreased from the opposite ends of the reflector toward the center thereof. That is, the reflectors 5, 6 each had the finger pitches of 0.97 μm, 0.90 μm, 0.87 μm, 0.90 μm and 0.97 μm. An average of these finger pitches was 0.922 μm. On the other hand, the reflectors 7, 8 disposed on the lateral sides of the IDT electrodes had a finger pitch of 1.02 μm.
A fabrication method of the SAW filter was substantially the same as in Example 1. A difference consists in that an electrode film had a thickness of about 0.15 μm instead of 0.3 μm.
As a sample for comparison, the microscopic electrode pattern shown in
Next, measurement was taken on the SAW filter of the example for determination of the characteristics thereof.
The filter of the invention features a broad passband as indicated by the solid line in
In contrast, the SAW filter of the conventional configuration, which was fabricated as the sample of comparative example, has a somewhat narrower pass bandwidth as indicated by the broken line in
The fractional bandwidths of the example of the invention and the comparative example were determined the same way as in the foregoing example using the network analyzer. The example of the invention has a fractional bandwidth of 4.2% whereas the comparative example has a fractional bandwidth of 3.8%. Thus, Example 2 has also achieved the increased bandwidth and the reduced insertion loss.
Next, description is made on an example of the SAW filter shown in
A fabrication method of the SAW filter was the same as in Example 2 and therefore, the description thereof is dispensed with.
As a comparative sample, the filter used in Example 2 was used as it was.
Next, measurement was taken on the SAW filter of the example for determination of the characteristics thereof. The measurement was taken at 800 measurement points while inputting a signal of 0 dBm at frequencies of 782 MHz to 982 MHz to the input terminal. There were prepared 30 samples for the filter.
As indicated by the solid line in
In contrast, the SAW filter of the conventional configuration, which was fabricated as the comparative sample, has an insertion loss of about 3.6 dB in the pass bandwidth of 1930 MHz to 1990 MHz, as indicated by the broken line in
The fractional bandwidths of the example of the invention and the comparative example were determined the same way as in the foregoing examples using the network analyzer. The example of the invention has a fractional bandwidth of 4.2% whereas the comparative example has a fractional bandwidth of 3.8%. Thus, Example 3 has also achieved the increased bandwidth and the reduced insertion loss.
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