JP2009100367A - Piezoelectric vibration device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric vibration device that can achieve limitation of hysteresis phenomenon of impedance characteristics while keeping its temperature property and electrostatic capacitance. <P>SOLUTION: A piezoelectric thin film portion having a piezoelectric film 16 whose main surfaces are provided with first and second electrodes 15, 17 includes its support portion 22 that is supported by a substrate 12, while a piezoelectric vibration portion 20 where the first and second electrodes 15, 17 are overlaid with each other via the piezoelectric film 16 when perspectively viewed in a thickness direction of the piezoelectric film 16 is away from the substrate 12. A piezoelectric vibration device 10 is a type using outline vibration of the piezoelectric vibration portion 20. At least the piezoelectric vibration portion 20 includes a temperature compensation film 19 and a reinforcement film 18. The reinforcement film 18 consists of the same material as the piezoelectric film 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezoelectric vibration device, and more particularly to a piezoelectric vibration device using a contour vibration mode of a bulk wave.

  Piezoelectric vibration devices that use bulk waves use types that use thickness vibration modes in bulk waves, and contour vibration modes such as spreading vibration mode, length vibration mode, and width vibration mode in bulk waves. There are types.

For the piezoelectric vibration device of the type using the latter contour vibration mode, for example, as shown in the cross-sectional view of FIG. 4, the piezoelectric film 6 is sandwiched between the electrodes 5 and 7 and floats from the substrate 2 through the gap 3. A configuration in which temperature compensation films 4 and 8 are provided above and below the piezoelectric vibration unit 9 is disclosed. As the temperature compensation films 4 and 8, for example, SiO ₂ films are formed one by one (see, for example, Patent Document 1).
WO2007 / 086696

In the piezoelectric vibration device of the type shown in FIG. 4, for example, a hysteresis phenomenon occurs in the impedance characteristics as shown in the graph of FIG. FIG. 5 shows a case where a temperature compensation film 8 of 3.3 μm thick SiO ₂ film is formed on a piezoelectric vibration part 9 including a piezoelectric film 6 of AlN film having a thickness of 1.6 μm. 5 is a graph showing the relationship between the frequency and impedance of a piezoelectric vibration device having a temperature compensation film 5 of SiO ₂ film having a thickness of 1.7 μm. The solid line shows the impedance characteristic when sweeping from the higher frequency to the lower frequency. A broken line shows an impedance characteristic when sweeping from a lower frequency to a higher frequency. It can be seen that there is a portion where the broken line and the solid line do not overlap, and a hysteresis phenomenon occurs in which the impedance waveform varies depending on the frequency sweep direction at the time of measurement.

  Hysteresis is presumed to occur when the piezoelectric film vibrates strongly and the vibration displacement increases, and the relationship between displacement and stress is not proportional and enters the nonlinear region, where the impedance waveform changes depending on the sweep direction. . In order to suppress the hysteresis phenomenon, it is desirable to reduce the vibration displacement. The greater the thickness of the temperature compensation film added to the piezoelectric vibrating portion, the smaller the vibration displacement. Therefore, the hysteresis phenomenon can be suppressed by increasing the thickness of the temperature compensating film added to the piezoelectric vibrating portion.

In order to suppress the hysteresis phenomenon, it is desirable to increase the total thickness while maintaining the ratio between the AlN film that is a piezoelectric film and the SiO ₂ film that is a temperature compensation film in order to maintain temperature characteristics. However, when the thickness of the AlN film, which is a piezoelectric film, is increased, the capacitance between the electrodes decreases due to an increase in the distance between the electrodes. If only the SiO ₂ film, which is a temperature compensation film, is thickened to avoid this, the temperature characteristics will deteriorate.

  In view of such circumstances, the present invention is intended to provide a piezoelectric vibration device capable of suppressing the hysteresis phenomenon of impedance characteristics while maintaining temperature characteristics and capacitance.

  In order to solve the above problems, the present invention provides a piezoelectric vibration device configured as follows.

  The piezoelectric vibration device includes (a) a substrate, and (b) a piezoelectric film and first and second electrodes respectively disposed on both main surfaces of the piezoelectric film, and is seen through from the film thickness direction of the piezoelectric film. A piezoelectric thin film portion in which a support portion other than the piezoelectric vibration portion is supported by the substrate in a state in which the piezoelectric vibration portion in which the first and second electrodes overlap with each other through the piezoelectric film is separated from the substrate; Is provided. The piezoelectric device is of a type that uses the contour vibration of the piezoelectric vibration part. The piezoelectric vibration device further includes (c) a temperature compensation film and a reinforcing film at least on the piezoelectric vibration part. The reinforcing film is made of the same material as the piezoelectric film.

  According to the above configuration, by providing the temperature compensation film and the reinforcing film in the piezoelectric vibration part, the total thickness can be increased, the vibration displacement can be reduced, and the hysteresis phenomenon of the impedance characteristic can be suppressed. If the reinforcing film is made of the same material as that of the piezoelectric film, the thickness of the piezoelectric film can be suppressed, and a decrease in capacitance due to an increase in the distance between the electrodes can be prevented. Further, since the ratio between the piezoelectric film and the temperature compensation film can be maintained, the temperature characteristics are not deteriorated. In addition, since the piezoelectric film and the reinforcing film can be formed by the same film forming apparatus, the manufacturing cost can be reduced.

  Preferably, the reinforcing film is formed on the side opposite to the substrate with respect to the piezoelectric vibrating portion.

  In this case, since the reinforcing film can be used as a passivation film that protects the surface of the piezoelectric vibration part, the reliability of the piezoelectric vibration device can be improved.

  Preferably, the reinforcing film is a non-oriented film.

  In this case, since the reinforcing film is not C-axis oriented, an unnecessary vibration mode that occurs due to bending vibration or the like can be suppressed.

  According to the present invention, it is possible to suppress the hysteresis phenomenon of impedance characteristics while maintaining temperature characteristics and capacitance.

  Embodiments of the present invention will be described below with reference to FIGS.

  First Embodiment A piezoelectric vibration device 10 according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of the piezoelectric vibration device 10.

  As shown in FIG. 1, the piezoelectric vibration device 10 includes a piezoelectric resonator, and a support film 14, a lower electrode 15, a piezoelectric film 16, an upper electrode 17, a reinforcing film 18, and a temperature compensation film 19 are laminated on a substrate 12. ing. A reinforcing film 18 and a temperature compensation film 19 are disposed on the piezoelectric vibrating portion 20 in which the piezoelectric film 16 is sandwiched between the electrodes 15 and 17. A support film 14 is disposed under the piezoelectric vibrating portion 20.

  The piezoelectric vibrating portion 20 is a portion where the electrodes 15 and 17 overlap through the piezoelectric film 16 when seen through from the film thickness direction (vertical direction in the drawing) of the piezoelectric film 16. The piezoelectric vibrating portion 20 is, for example, a rectangle when seen through from the film thickness direction of the piezoelectric film 16. The piezoelectric vibration unit 20 vibrates in a contour vibration mode integrally with the support film 14, the reinforcing film 18, and the temperature compensation film 19 disposed above and below the piezoelectric vibration unit 20.

  In the lower electrode 15 and the upper electrode 17, pads 15 s and 17 s are formed at the end portion of the extraction electrode from the piezoelectric vibrating portion 20. The surfaces of the pads 15s and 17s are exposed and can be electrically connected to the outside.

  The piezoelectric thin film portion in which the electrodes 15 and 17 are disposed on both main surfaces of the piezoelectric film 16 includes a piezoelectric vibrating portion 20, a support portion 22, and a connection portion 24. The piezoelectric vibration unit 20 is in a state of floating from the substrate 12 through the gap 13. The piezoelectric vibration part 20 is connected to the support part 22 supported by the substrate 12 via a connection part 24.

For the piezoelectric film 16, a piezoelectric material such as zinc oxide (ZnO) or aluminum nitride (AlN) can be used. In the embodiment, the film is formed under the film forming conditions in which C-axis orientation is performed using AlN using the reactive RF magnetron sputtering method. In this film forming method, a target material mainly composed of Al or AlN is used, and AlN is formed using Ar and N ₂ as gases. By reducing the gas pressure at the time of film formation and improving the perpendicular incidence property of the sputtered particles to the substrate, it is possible to form an AlN film in which the C axis grows well in the direction perpendicular to the substrate.

  The electrodes 15 and 17 have a role of applying a voltage to the piezoelectric film 16 and use a conductive material such as Al, Cu, Au, Pt, Mo, W, Ni, Erin bar, Invar, or a laminate thereof. . In order to improve the adhesion between the lower electrode 15 and the support film 14 or between the electrodes 15 and 17 and the piezoelectric film 16, an adhesion layer may be formed using a material such as Ti or Cr. For the electrodes 15 and 17, a thick wiring for lowering the wiring resistance may be separately formed on the lead electrode from the piezoelectric vibrating portion 20.

  A reinforcing film 18, which is a non-oriented film made of the same material as the piezoelectric film 16, is formed on the upper electrode 17 of the piezoelectric vibration unit 20.

  The reinforcing film 18 is preferably formed under a film forming condition different from that for forming the piezoelectric film 16 to form a non-oriented film. In the AlN film using the reactive RF magnetron sputtering method used in the examples, when the gas pressure during film formation increases to some extent, the number of collisions between the sputtered particles and the gas molecules increases, and the normal incidence to the substrate increases. Be inhibited. Thereby, sputtered particles are incident on the substrate from various angles, the orientation in one direction is lost, and an unoriented AlN film can be formed.

  If the surface roughness of the surface on which the upper electrode 17 is formed is rough, the piezoelectric film is difficult to be C-axis oriented due to the effect of the surface roughness. Good.

With respect to the piezoelectric vibration part 20 reinforced by the reinforcing film 18 which is a non-oriented film made of the same material as the piezoelectric film 16, the films 14 and 19 added to the top and bottom serve for temperature compensation of the resonance frequency, passivation, adjustment of the resonance frequency, and the like. have. As temperature compensation, a film having a sign of the temperature coefficient of longitudinal wave sound velocity opposite to that of the piezoelectric film 16 is formed, but SiO ₂ is often used. In order to fulfill the function as passivation, the electrodes 15 and 17 and the piezoelectric film 16 are formed so as to cover the surfaces and side walls as much as possible. As a material, a dielectric such as SiO ₂ , SiN, Ta ₂ O ₅ can be mainly used. In the embodiment, the films 14 and 19 are SiO ₂ films formed by a sputtering film forming method.

  Patterning of the films 14 to 19 is performed by dry etching, wet etching, or a lift-off method. Among them, the lift-off method is preferable because the patterning accuracy is high and the dimensional variation of the vibrator can be reduced. In forming the upper and lower films 14, 18, 19 of the piezoelectric vibrating portion 20, it is desirable to form them collectively using the same mask pattern in order to eliminate positional deviation between the constituent films.

  The gap 13 is formed by disposing a sacrificial layer on the substrate 12, laminating the support film 14 and the like thereon, and then removing the sacrificial layer.

  As the substrate 12, a semiconductor substrate such as Si or an insulator substrate such as glass is used. Alternatively, a substrate having an oxide film or nitride film formed on the surface may be used.

  Next, a manufacturing example will be described.

The film configuration of the manufacturing example of Example 1 shown in FIG. 1 is as follows: substrate: Si, support film: SiO ₂ (film thickness: 3.0 μm), lower electrode and upper electrode: Pt (each film thickness: 1.0 μm), piezoelectric The film is AlN (film thickness 1.6 μm), the reinforcing film is AlN (film thickness 0.8 μm), and the temperature compensation film is SiO ₂ (film thickness 3.7 μm).

The film structure of the comparative example of the conventional structure shown in FIG. 4 is as follows: substrate: Si, support film: SiO ₂ (film thickness 1.7 μm), lower electrode and upper electrode: Pt (each film thickness 0.1 μm), piezoelectric film : AlN (film thickness 1.6 μm), temperature compensation film: SiO ₂ (film thickness 3.3 μm).

In Example 1, the supporting film (SiO ₂ ) is changed from 1.7 μm to 3.0 μm and 1.3 μm thick as compared with the comparative example. Further, the temperature compensation film (SiO ₂ ) is changed from 3.3 μm to 3.7 μm and is 0.4 μm thick.

  In Example 1, in addition to the thickness of the reinforcing film (AlN), the total thickness is 2.5 μm thicker than that of the comparative example, so that the hysteresis phenomenon of impedance characteristics can be suppressed.

Moreover, in Example 1 and the comparative example, since the ratio of AlN (piezoelectric film, reinforcing film) and SiO ₂ (temperature compensation film, support film) is almost the same at around 0.35, the temperature characteristics do not deteriorate. .

The SiO ₂ film of the temperature compensation film also has a function as a passivation film and a frequency adjustment film. However, a film such as a passivation film or a frequency adjustment film such as SiN or Ta ₂ O ₅ is separately used for the piezoelectric vibration portion. It is also possible to provide it up and down.

  In the piezoelectric vibration device 10 according to the first embodiment, the thickness of the piezoelectric film 16 can be suppressed by forming the reinforcing film 18 which is the same non-oriented film as the piezoelectric film 16 on the upper electrode 17 in the vibrator. Further, it is possible to prevent a decrease in capacitance due to the increase in the distance between the electrodes 15 and 17. Further, by using the reinforcing film 18 which is a non-oriented film made of the same material as the piezoelectric film 16, the ratio of the piezoelectric films 16 and 18 and the temperature compensation film 19 can be maintained, so that the temperature characteristics are not deteriorated. Further, since the reinforcing film 18 formed on the upper electrode 17 in the vibrator is a non-oriented film made of the same material as that of the piezoelectric film 16, the reinforcing film 18 is not C-axis oriented. The generation of unnecessary vibration modes can be suppressed. In addition, since the piezoelectric film 16 and the reinforcing film 18 can be formed using the same film forming apparatus, the manufacturing cost can be reduced.

  Example 2 A piezoelectric vibration device 10a of Example 2 will be described with reference to a cross-sectional view of FIG.

  As shown in FIG. 2, the piezoelectric vibration device 10a is configured in substantially the same manner as the piezoelectric vibration device 10 of the first embodiment. In the piezoelectric vibration device 10a, a support film 14a, a lower electrode 15a, a piezoelectric film 16a, an upper electrode 17a, a reinforcing film 18a, and a temperature compensation film 19a are laminated on a substrate 12a. When seen through from the film thickness direction of the piezoelectric film 16a, the piezoelectric vibrating portion 20a in which the electrodes 15a and 17a overlap through the piezoelectric film 16a vibrates in the contour vibration mode.

  Unlike the piezoelectric vibration device 10 of the first embodiment, the piezoelectric vibration device 10a is in a state in which the piezoelectric vibration portion 20a is separated from the substrate 12a by the recess 13a formed on the upper surface side of the substrate 12a.

  The piezoelectric vibration device 10a suppresses the hysteresis phenomenon of the impedance characteristic while maintaining the temperature characteristic and the capacitance by forming the reinforcing film 18a with the same material as the piezoelectric film 16a, as in the first embodiment. Can do.

  Example 3 A piezoelectric vibration device 10b of Example 3 will be described with reference to a cross-sectional view of FIG.

  As shown in FIG. 3, the piezoelectric vibration device 10b is configured in substantially the same manner as the piezoelectric vibration device 10 of the first embodiment. In the piezoelectric vibration device 10b, a support film 14b, a lower electrode 15b, a piezoelectric film 16b, an upper electrode 17b, a reinforcing film 18b, and a temperature compensation film 19b are laminated on a substrate 12b. When seen through from the film thickness direction of the piezoelectric film 16b, the piezoelectric vibrating portion 20b in which the electrodes 15b and 17b overlap through the piezoelectric film 16b vibrates in the contour vibration mode.

  Unlike the piezoelectric vibration device 10 according to the first embodiment, the piezoelectric vibration device 10b is in a state in which the piezoelectric vibration portion 20b is separated from the substrate 12a by the through hole 13b formed in the substrate 12b.

  As in the first embodiment, the piezoelectric vibration device 10b suppresses the hysteresis phenomenon of the impedance characteristic while maintaining the temperature characteristic and the capacitance by forming the reinforcing film 18b with the same material as the piezoelectric film 16b. Can do.

  <Summary> The piezoelectric vibrators 10, 10a, 10b described above maintain the temperature characteristics and capacitance by forming the reinforcing films 18, 18a, 18b from the same material as the piezoelectric films 16, 16a, 16b. However, the hysteresis phenomenon of impedance characteristics can be suppressed.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications.

It is sectional drawing of a piezoelectric vibration apparatus. Example 1 It is sectional drawing of a piezoelectric vibration apparatus. (Example 2) It is sectional drawing of a piezoelectric vibration apparatus. (Example 3) It is sectional drawing of a piezoelectric vibration apparatus. (Conventional example) It is a graph which shows an impedance characteristic. (Conventional example)

Explanation of symbols

10, 10a, 10b Piezoelectric vibration device 12, 12a, 12b Substrate 13 Gap 13a Recess 13b Through hole 14, 14a, 14b Support film 15, 15a, 15b Lower electrode (piezoelectric thin film portion)
16, 16a, 16b Piezoelectric film (piezoelectric thin film part)
17, 17a, 17b Upper electrode (piezoelectric thin film part)
18, 18a, 18b Reinforcement film 19, 19a, 19b Temperature compensation film 20, 20a, 20b Piezoelectric vibration part

Claims (3)

A substrate,
A piezoelectric film and first and second electrodes respectively disposed on both principal surfaces of the piezoelectric film, wherein the first and second electrodes are seen through the piezoelectric film in a film thickness direction. A piezoelectric thin film portion in which a supporting portion other than the piezoelectric vibrating portion is supported by the substrate in a state where the piezoelectric vibrating portion overlapping with the substrate is separated from the substrate,
With
A piezoelectric vibration device that utilizes contour vibration of the piezoelectric vibration unit,
At least the piezoelectric vibration part further includes a temperature compensation film and a reinforcing film,
The piezoelectric vibration device, wherein the reinforcing film is made of the same material as the piezoelectric film.   The piezoelectric vibration device according to claim 1, wherein the reinforcing film is formed on a side opposite to the substrate with respect to the piezoelectric vibration portion.   The piezoelectric vibration device according to claim 1, wherein the reinforcing film is a non-oriented film.

Images