Patent Application
20130279042
The present invention relates to a piezoelectric element, and more particularly, to a thin film piezoelectric element and manufacturing method thereof, a micro-actuator, a head gimbal assembly (HGA), and a disk drive unit with the same.
Piezoelectric material is processed into various piezoelectric elements in accordance with different purposes, particularly, it has been widely used for functional electronic components such as an actuator for generating deformation by applying voltage or a sensor for generating voltage from the deformation of elements in a reverse way, etc.
As the piezoelectric material used for an actuator in the disk drive unit for actuating the fine movements of the slider thereof, a lead (Pb)-based dielectric material having large piezoelectric characteristics, especially, Lead Zirconate Titanate Pb(Zr1-xTix)O3-based perovskite-type ferroelectric called as “PZT”, has been widely used, and the piezoelectric material is generally formed by sintering oxide which is formed of individual elements.
Crystal structure of this piezoelectric material formed of PZT varies with the ratio of PbTiO3/PbZrO3.
However, it's quite hard to control the composition exactly located at the MPB. Thus a conventional thin film piezoelectric element often applies the composition near the MPB, such as Pb(Zr0.52Ti0.48)O3 or Pb(Zr0.58Ti0.42)O3. As shown in
However, the piezoelectric constants of this single-phase piezoelectric element 100 is still inadequate as the product requirement for stroke becomes higher and higher. Moreover, the applied field strength is limited due to the single phase structure wherein the depolarization will occur at field strength larger than the coercive field strength (Ec). Conventionally, one way to enable larger applied field strength is to increase the coercive field strength by coercive imprinting which relates to apply a large stress on the piezoelectric element. However, it will bring high risk of delamination and reliability failure for the piezoelectric element. Another way to enable larger applied field strength is to increase the PZT thickness, which will cause a rise in the cost however. Based on the limitation on the piezoelectric constants and coercive field strength, the stroke of the piezoelectric element applied in the actuator or sensor is insufficient, which does not satisfy the requirement of the product manufacturer.
Thus, there is a need for an improved thin film piezoelectric element to overcome the drawbacks mentioned above.
One aspect of the present invention is to provide a thin film piezoelectric element thereby obtaining high piezoelectric constants, enhanced coercive field strength and good thermal stability, and in turns enabling larger applied field strength without depolarization and achieving a large stroke for its applied device.
Another aspect of the present invention is to provide a manufacturing method of a thin film piezoelectric element thereby obtaining high piezoelectric constants, enhanced coercive field strength and good thermal stability, and in turns enabling larger applied field strength without depolarization and achieving a large stroke for its applied device.
Yet an aspect of the present invention is to provide a micro-actuator with a thin film piezoelectric element, thereby obtaining high piezoelectric constants, enhanced coercive field strength and good thermal stability, and in turns enabling larger applied field strength without depolarization and achieving a large stroke for its applied device.
Still an aspect of the present invention is to provide a head gimbal assembly with a thin film piezoelectric element and good thermal stability, thereby obtaining high piezoelectric constants, enhanced coercive field strength, and in turns enabling larger applied field strength and achieving a large stroke for its applied device.
One more aspect of the present invention is to provide a disk drive unit with a thin film piezoelectric element, thereby obtaining high piezoelectric constants, enhanced applied field strength, good thermal stability and a large stroke for its applied device.
One more aspect of the present invention is to provide a micro-electro-mechanical system with a thin film piezoelectric element, thereby obtaining high piezoelectric constants, enhanced applied field strength, good thermal stability and a large stroke.
To achieve above objectives, a thin film piezoelectric element of the present invention includes a substrate and a piezoelectric thin film stack formed on the substrate. The piezoelectric thin film stack includes a top electrode layer, a bottom electrode layer and a piezoelectric layer sandwiched between the top electrode layer and the bottom electrode layer, wherein the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer whose compositions are different and preferably to have different phase structures.
As a preferred embodiment, one of the first piezoelectric layer and the second piezoelectric layer has a rhombohedra phase structure, the other has a tetragonal phase structure.
As another preferred embodiment, one of the first piezoelectric layer and the second piezoelectric layer has composition at a morphotropic phase boundary, the other has a rhombohedra phase structure or a tetragonal phase structure.
Preferably, the piezoelectric layer is made of Pb(ZrxTi1-x)O3.
Preferably, the first piezoelectric layer and the second piezoelectric layer have different Ti concentrations.
Preferably, the first piezoelectric layer and the second piezoelectric layer have a thickness in the range of 0.1 μm˜1.5 μm.
As an optional embodiment, the piezoelectric layer comprises KNaNbO3, LiNbO3, LiTaO3, BaTiO3, PbTiO3 or BaSrTiO3.
As an optional embodiment, the piezoelectric layer may include more than two layers with different Ti compositions respectively.
As an optional embodiment, the piezoelectric layer can have either a step difference in Ti composition by two-layer or multilayer deposition or a smooth gradient in Ti composition by special deposition arrangement or post annealing treatment.
A manufacturing method of a thin film piezoelectric element of the present invention includes: providing a substrate; depositing a bottom electrode layer on the substrate; and depositing a piezoelectric layer including a first piezoelectric layer and a second piezoelectric layer on the bottom electrode layer, and a top electrode layer on the piezoelectric layer; wherein the first piezoelectric layer and the second piezoelectric layer have different phase structures.
As a preferred embodiment, one of the first piezoelectric layer and the second piezoelectric layer has a rhombohedra phase structure, the other has a tetragonal phase structure.
As another preferred embodiment, one of the first piezoelectric layer and the second piezoelectric layer has composition at a morphotropic phase boundary, the other has a rhombohedra phase structure or a tetragonal phase structure.
Preferably, the piezoelectric layer is made of Pb(ZrxTi1-x)O3.
Preferably, the first piezoelectric layer and the second piezoelectric layer have different Ti compositions.
Preferably, the first piezoelectric layer and the second piezoelectric layer have a thickness in the range of 0.1 μm˜1.5 μm.
As an optional embodiment, the piezoelectric layer comprises KNaNbO3, LiNbO3, LiTaO3, BaTiO3, PbTiO3 or BaSrTiO3.
As an optional embodiment, the piezoelectric layer may include more than two layers with different Ti compositions respectively. As an optional embodiment, the piezoelectric layer can have either a step difference in Ti composition by two-layer or multilayer deposition or a smooth gradient in Ti composition by special deposition arrangement or post annealing treatment.
Accordingly, a micro-actuator of the present invention has a thin film piezoelectric element which includes a substrate; and a piezoelectric thin film stack formed on the substrate. The piezoelectric thin film stack includes a top electrode layer, a bottom electrode layer and a piezoelectric layer sandwiched between the top electrode layer and the bottom electrode layer, wherein the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer whose compositions have different phase structures.
A head gimbal assembly of the present invention includes a suspension, a slider supported by the suspension, and a thin film piezoelectric element formed on the suspension for actuating the slider. And the thin film piezoelectric element includes a substrate and a piezoelectric thin film stack formed on the substrate. The piezoelectric thin film stack includes a top electrode layer, a bottom electrode layer and a piezoelectric layer sandwiched between the top electrode layer and the bottom electrode layer, wherein the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer whose compositions have different phase structures.
A disk drive unit of the present invention includes a head gimbal assembly; a drive arm to connect with the head gimbal assembly, disks and a spindle motor to spin the disks. Therein the head gimbal assembly includes a suspension, a slider supported by the suspension, and a thin film piezoelectric element formed on the suspension for actuating the slider. And the thin film piezoelectric element includes a substrate and a piezoelectric thin film stack formed on the substrate. The piezoelectric thin film stack includes a top electrode layer, a bottom electrode layer and a piezoelectric layer sandwiched between the top electrode layer and the bottom electrode layer, wherein the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer whose compositions have different phase structures.
A micro-electro-mechanical system of the present invention includes a thin film piezoelectric element which includes a substrate and a piezoelectric thin film stack formed on the substrate. The piezoelectric thin film stack includes a top electrode layer, a bottom electrode layer and a piezoelectric layer sandwiched between the top electrode layer and the bottom electrode layer, and the piezoelectric layer includes a first piezoelectric layer and a second piezoelectric layer whose compositions are different and preferably to have different phase structures.
In comparison with the prior art, the present invention provides a thin film piezoelectric element having different phase structures on the compositions of the first and second piezoelectric layers, charge will build up on the two piezoelectric layers when an AC voltage is applied to the thin film piezoelectric element, thereby enhancing coercive field strength of the thin film piezoelectric element, and in turns enabling larger applied field strength without depolarization and enhancing the piezoelectric constants d31 and d33 accordingly. Moreover, the depolarization voltage of the thin film piezoelectric element of the present invention is significantly larger than the conventional thin film piezoelectric element, thereby obtaining a larger stroke, which can be applicable to the larger device that needs large stroke. Furthermore, depoling voltage of the present invention is much stable than that of the conventional thin film piezoelectric element under high temperature or low temperature conditions, and no significant drop appears in the depoling voltage curve, thus larger operation voltage of the thin film piezoelectric element is allowed thereby achieving a larger stroke. Meanwhile, the present invention can achieve good thermal stability under a high temperature condition.
Other aspects, features, and advantages of this invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of this invention.
The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings:
a is a phase diagram of a conventional PZT material;
b is a cross-section view of a conventional thin film piezoelectric element;
a is a contrast diagram of polarization offset between the thin film piezoelectric element of the present invention and the conventional thin film piezoelectric element under an AC voltage is applied;
b is a contrast diagram of stroke between the thin film piezoelectric element of the present invention and the conventional thin film piezoelectric element under an AC voltage is applied;
c is a contrast diagram of depoling voltage change between the thin film piezoelectric element of the present invention and the conventional thin film piezoelectric element under a specific temperature range;
d is a contrast diagram of polarization change between the thin film piezoelectric element of the present invention and the conventional thin film piezoelectric element under a specific temperature range;
Various preferred embodiments of the invention will now be described with reference to the figures, wherein like reference numerals designate similar parts throughout the various views. As indicated above, the invention is directed to a thin film piezoelectric element thereby obtaining high piezoelectric constants, enhanced coercive field strength and good thermal stability, and in turns enabling larger applied field strength without depolarization and achieving a large stroke for its applied device.
Referring to
In this embodiment, the first piezoelectric layer 212 and the second piezoelectric layer 213 are made by Pb(ZrxTi1-x)O3. As an improvement, the first piezoelectric layer 212 and the second piezoelectric layer 213 have different phase structures. As a preferred embodiment, the first piezoelectric layer 212 has a rhombohedra phase structure, for example its composition is Pb(Zr0.61Ti0.39)O3, wherein the ratio of PbTiO3/PbZrO3 is 0.423 (equivalent to the content of the PbTiO3 is 42.3 mol %); and the second piezoelectric layer 213 has a tetragonal phase structure, for example its composition is Pb(Zr0.58Ti0.42)O3, wherein the ratio of PbTiO3/PbZrO3 is 0.469. In this embodiment, the composition gradient of the ratio is 0.046. Preferably, the composition gradient between two piezoelectric layers 212, 213 is in the range of 0.01˜0.90. As shown in
Alternatively, the composition of the first piezoelectric layer 212 has a phase structure in the MPB, and the composition of the second piezoelectric layer 213 has a rhombohedra phase structure or a tetragonal phase structure. In the present invention, the compositions of the first and second piezoelectric layers 212, 213 are not limited, if only their phase structures are different, so as to ensure the thin film piezoelectric element 200 possesses an anisotropic two-phase structure.
As the thin film piezoelectric element 200 has two different phase structures on the compositions of the two piezoelectric layers 212, 213, thus when an AC voltage is applied to the thin film piezoelectric element 200, charge will build up on the two piezoelectric layers 212, 213. Such a charge build up will help to strengthen the domain polarization and enhance the piezoelectric constants d31 and d33. If the composition gradient between the two piezoelectric layers 212, 213 is increased during manufacturing, the charge build up effect becomes much more significant.
As optional embodiment, the piezoelectric thin film stack 210 may further includes a third piezoelectric layer or more, if only the different piezoelectric layers have different compositions, such as different Ti compositions for Pb(ZrxTi1-x)O3 material.
a shows a contrast diagram of polarization offset between the thin film piezoelectric element 200 of the present invention and the conventional thin film piezoelectric element 100 under an AC voltage. As the AC voltage increases, the polarization offset of the thin film piezoelectric element 200 of the present invention is increased, which is significantly larger than that of the conventional thin film piezoelectric element 100. Accordingly, the piezoelectric constants d31 and d33 of the thin film piezoelectric element 200 is increased.
b shows a contrast diagram of stroke between the thin film piezoelectric element 200 of the present invention and the conventional thin film piezoelectric element 100 under an applied AC voltage. As the AC voltage increases, depolarization voltage points A and B of the two thin film piezoelectric elements 100, 200 generate. It can be seen that, the depolarization voltage of the thin film piezoelectric element 200 of the present invention is significantly larger than that of the conventional thin film piezoelectric element 100. As a result, larger operating voltage or larger applied field strength can be applied on the thin film piezoelectric element 200 of the present invention to obtain a larger stroke. As the stroke of the thin film piezoelectric element 200 is increased, thus the thin film piezoelectric element 200 can be applicable to the larger device that needs large stroke.
c shows a contrast diagram of depoling voltage change between the thin film piezoelectric element 200 of the present invention and the conventional thin film piezoelectric element 100 under a temperature ranging from −40˜125° C. about. As the temperature is increased, a significant drop in depoling voltage appears in the conventional curve, which means that higher risk of depoling voltage of the thin film piezoelectric element 100 generates at high temperature. Due to the higher risk, operation voltage of the conventional thin film piezoelectric element 100 must be much lower than the depoling voltage so as to keep safe margin for high temperature operations, which causes the maximum stroke be limited and reduced in turn. In the present invention contrarily, no significant drop appears in the depoling voltage curve under the temperature ranging from −40˜125° C., therefore, larger operation voltage of the thin film piezoelectric element 200 is allowed thereby achieving a larger stroke compared with the conventional one.
d shows a contrast diagram of polarization change between the thin film piezoelectric element 200 of the present invention and the conventional thin film piezoelectric element 100 under a temperature ranging from −40˜125° C. It can be seen that, the polarization change in the conventional thin film piezoelectric element 100 is significant, particularly, the polarization of the conventional thin film piezoelectric element 100 drops sharply at both ends of low and high temperatures. In contrast, the polarization is more stable under the variable temperature condition, which possesses good thermal ability and reduces thermal noise.
As other embodiments of the present invention, the first piezoelectric layer 212 and the second piezoelectric layer 213 can be made by KNaNbO3, LiNbO3, LiTaO3, BaTiO3, PbTiO3 or BaSrTiO3 materials, which are not limited, if only the compositions of the two piezoelectric layers 212, 213 have different phase structures.
As shown, the manufacturing method includes following steps:
(501), providing a substrate;
(502), depositing a bottom electrode layer on the substrate; and
(503), depositing a piezoelectric layer including a first piezoelectric layer and a second piezoelectric layer on the bottom electrode layer, and a top electrode layer on the piezoelectric layer; and the first piezoelectric layer and the second piezoelectric layer have different phase structures.
Concretely, in the step (503), the first piezoelectric layer and the second piezoelectric layer are deposited by two different sputtering targets. As an embodiment, one target has composition of Pb(Zr0.61Ti0.39)O3, another target has composition of Pb(Zr0.58Ti0.42)O3, as a result, the two piezoelectric layers have different phase structures. Concretely, the first piezoelectric layer and the second piezoelectric layer can be made by special deposition arrangement or post annealing treatment.
The thin film piezoelectric element 200 of the present invention explained above can be used in micro-actuator, sensor etc., or other device. Several applications will be described hereinafter.
As an embodiment, a micro-actuator with the thin film piezoelectric element 200 the present invention can be used in field of the disk drive unit, in order to actuating the slider thereon.
According to actual practice, the micro-actuator with the thin film piezoelectric element 200 (not shown in this figure) are attached on two sides of the slider 303, or mounted on the flexure 305 near the slider 303, so as to actuate the slider 303 with fine movement to achieve a good reading and writing. The thin film piezoelectric element 200 includes the same structures as explained above which are omitted here.
As mentioned above, because the thin film piezoelectric element 200 has two different phase structures on the compositions of the two piezoelectric layers 212, 213, charge will build up on the two piezoelectric layers 212, 213 when an AC voltage is applied to the thin film piezoelectric element 200, thereby enhancing coercive field strength of the thin film piezoelectric element 200, and in turns enabling larger applied field strength without depolarization and enhancing the piezoelectric constants d31 and d33 accordingly; moreover, the depolarization voltage of the thin film piezoelectric element 200 of the present invention is significantly larger, thereby obtaining a larger stroke and being beneficial to control the movement of the slider 303. As a result, the performance of the disk drive unit 400 is improved accordingly.
The thin film piezoelectric element 200 of the invention present invention also can be used in a micro-electro-mechanical system (MEMS) (not shown), such as actuators, sensors, gyroscopes, accelerators, radio frequency (RF) resonators, or other MEMS devices, due to the larger maximum stroke and good thermal ability. In the MEMS device with such thin film piezoelectric element 200, the larger maximum stroke helps to obtain bigger signal output and lower power consumption, and the good thermal ability can reduce the thermal noise, bias offset or other drifts.
While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201210116510.6 | Apr 2012 | CN | national |
