JP2022012349A - Piezoelectric element and method for manufacturing the same - Google Patents

Abstract

To provide a piezoelectric element and a method for manufacturing the same, which can suppress the effect of residual stress in a piezoelectric film and also suppress the characteristic degradation.SOLUTION: A piezoelectric element comprises a diaphragm 2 consisting of piezoelectric films 5a and 5b, one end of which is fixedly supported by a support substrate 3 and the other end of which is the free end, and electrodes 6a, 6b, and 6c arranged across the piezoelectric films. A part of the surface on the free end side of the diaphragm 2 is a stress relaxation region 9. This stress relaxation region 9 is a region where ions are implanted to disrupt the crystallinity of the piezoelectric film and relieve the stress on the diaphragm 2.SELECTED DRAWING: Figure 2

Description

The present invention relates to a piezoelectric element and a method for manufacturing the same, and particularly to a piezoelectric element and a method for manufacturing the same, which can be used for a piezoelectric type MEMS microphone or the like having high sensitivity and low noise.

In recent years, smartphones, whose demand is rapidly expanding, are often used for microphones using MEMS (Micro Electro Mechanical Systems) technology, which are small and thin and have high temperature processing resistance in the assembly solder reflow process. Furthermore, not only MEMS microphones but also other MEMS devices are rapidly becoming widespread in various fields.

Most of this type of MEMS element is a capacitive element that captures the displacement of the diaphragm due to acoustic pressure or the like as a capacitance change with the facing fixed plate, converts it into an electric signal, and outputs it. However, in the capacitive element, the improvement of the signal-to-noise ratio is becoming a limit due to the acoustic resistance caused by the flow of air in the gap between the diaphragm and the fixed plate. Therefore, attention has been paid to a piezoelectric element capable of extracting acoustic pressure or the like as a voltage change due to distortion of a single diaphragm made of a thin film (piezoelectric film) made of a piezoelectric material.

In the conventional piezoelectric element, a slit 1 having a desired shape as shown in FIG. 3 is formed in the piezoelectric film to form a diaphragm 2 having a cantilever structure. In FIG. 3A, two quadrangular diaphragms 2 are formed, and in FIG. 3B, four triangular diaphragms 2 are formed. This type of piezoelectric element is disclosed in, for example, Patent Document 1.

FIG. 4 is a cross-sectional view of the piezoelectric element. As shown in FIG. 4, a multilayer structure piezoelectric film 5a and 5b are supported and fixed on a support substrate 3 made of a silicon substrate via an insulating film 4, the piezoelectric film 5a is supported and fixed by electrodes 6a and 6b, and the piezoelectric film 5b is an electrode. The structure is sandwiched between the 6b and the electrode 6c, respectively. A cavity 7 is formed in the support substrate 3, and the piezoelectric film and electrodes partitioned by the slit 1 constitute a diaphragm 2 in which one end is fixed to the support substrate 3 and the other end is a free end.

In such a piezoelectric element, when the vibrating plate 2 receives acoustic pressure or the like, the piezoelectric film 5a is distorted and polarization occurs inside the piezoelectric film 5a, and a voltage is generated from the wiring metal 8a connected to the electrode 6a and the wiring metal 8b connected to the electrode 6b. It becomes possible to take out a signal. Similarly, when the piezoelectric film 5b is distorted, polarization occurs inside the piezoelectric film 5b, and it becomes possible to take out a voltage signal from the wiring metal 8a connected to the electrode 6c and the wiring metal 8b connected to the electrode 6b.

Japanese Patent No. 5936154

By the way, in the piezoelectric films 5a and 5b having such a cantilever structure, residual stress is released by forming the slit 1, warpage occurs, and the opening width of the slit 1 is widened. If a piezoelectric element having an opening width of the slit 1 equal to or larger than the design value is used as a microphone, the acoustic resistance is lowered and the characteristics such as the sensitivity in the low frequency region are deteriorated. An object of the present invention is to solve such a problem and to provide a piezoelectric element capable of suppressing the influence of residual stress of a piezoelectric film and suppressing deterioration of characteristics, and a method for manufacturing the same.

In order to achieve the above object, the invention according to claim 1 of the present application comprises a vibrating plate made of a piezoelectric film having one end fixed and the other end free, and a pair of electrodes arranged so as to sandwich the piezoelectric film. In the provided piezoelectric element, the vibrating plate is characterized in that a part of the surface of the piezoelectric film is a stress relaxation region.

The invention according to claim 2 of the present application is the piezoelectric element according to claim 1, wherein the diaphragm is a piezoelectric film supported by a support substrate having a cavity, and is partitioned by a slit penetrating the piezoelectric film. The stress relaxation region is characterized in that it is arranged on the free end side of the diaphragm.

The invention according to claim 3 of the present application is characterized in that, in the piezoelectric element according to any one of claims 1 or 2, the stress relaxation region is an ion implantation region.

The invention according to claim 4 of the present application is a method for manufacturing a piezoelectric element including a vibration plate made of a piezoelectric film having one end fixed and the other end free end, and a pair of electrodes arranged with the piezoelectric film interposed therebetween. In the step of laminating and forming the piezoelectric film on the support substrate, the step of forming the pair of electrodes arranged so as to sandwich the piezoelectric film, and the step of fixing at least one end to the support substrate and the other end as a free end. A stress relaxation region having a stress different from the stress of the piezoelectric film is formed in a part of the piezoelectric film of the vibration plate in which the warp is generated and the step of partitioning the piezoelectric film so as to form the vibration plate. It is characterized by including the process of performing.

The invention according to claim 5 of the present application is characterized in that, in the method for manufacturing a piezoelectric element according to claim 4, the step of forming the stress relaxation region is a step of injecting ions into the piezoelectric film.

The piezoelectric element of the present invention can be made into a diaphragm without warp by providing a stress relaxation region in a part of the piezoelectric film, and acoustic pressure or the like can be efficiently transmitted to the diaphragm 2 to obtain a large output signal. It will be possible.

In particular, in the case of a diaphragm having a structure in which the piezoelectric film is partitioned by slits, by using a diaphragm without warpage, the opening width of the slits becomes as designed, and it becomes possible to obtain a piezoelectric element having desired characteristics. When such a piezoelectric element is used as an acoustic transducer, the acoustic resistance can be maintained high, so that it is possible to suppress a decrease in sensitivity in a low frequency region and a decrease in a signal noise ratio.

The method for manufacturing a piezoelectric element of the present invention is a simple and well-controllable method in which a stress relaxation region can be formed by injecting ions into a piezoelectric film. In particular, by changing the injection conditions, the stress relaxation region can be set to a desired stress, so that the warping of the diaphragm can be easily relaxed according to the degree of warping.

It is explanatory drawing of the manufacturing method of the piezoelectric element of the Example of this invention. It is explanatory drawing of the manufacturing method of the piezoelectric element of the Example of this invention. It is explanatory drawing of the conventional piezoelectric element. It is explanatory drawing of the conventional piezoelectric element.

The piezoelectric element according to the present invention has a part of the diaphragm as a stress relaxation region and is a piezoelectric element provided with a diaphragm without warping. Hereinafter, examples of the present invention will be described in detail according to the manufacturing process.

The piezoelectric element of the present invention is a piezoelectric element provided with a diaphragm having a cantilever structure in which a slit 1 having a desired shape as shown in FIG. 3 is formed.

First, a metal film to be an electrode is formed on a support substrate 3 made of a silicon substrate via an insulating film 4, an electrode 6a is formed by a normal photolithography method, and a piezoelectric film 5a is formed on the electrode 6a and the insulating film 4. Form. Next, a metal film to be an electrode is formed on the piezoelectric film 5a, the electrode 6b is formed by a normal photolithographic method, and the piezoelectric film 5b is formed on the electrode 6b and the piezoelectric film 5a. Next, a metal film to be an electrode is formed on the piezoelectric film 5b, and the electrode 6c is formed by a normal photolithography method. After that, the wiring metal 8a connected to the electrode 6a and the electrode 6c and the wiring metal 8b connected to the electrode 6b are formed.

A part of the piezoelectric films 5b and 5a is removed by etching to form a slit 1. Further, the cavity 7 is formed by removing a part of the support substrate 3 and the insulating film 4. In this state, the piezoelectric films 5a and 5b become a diaphragm 2 having one end supported on the support substrate 3 and the insulating film 4. The above forming method is the same as the conventional method for manufacturing a piezoelectric element.

Since the piezoelectric film generally has residual stress, warpage may occur in the diaphragm 2 having a free end as shown in FIG. When the diaphragm 2 is warped on the opposite side to the cavity 7 as shown in FIG. 1, the piezoelectric film 5b has a larger compressive stress than the piezoelectric film 5a. Therefore, in order to alleviate the warp of the diaphragm 2, specifically, in order to reduce the compressive stress of the piezoelectric film 5b, ions are injected into the surface of the diaphragm 2 from the direction of the arrow shown in FIG. 2 to form a stress relaxation region 9. do. On the surface of the diaphragm 2 (piezoelectric film 5b) on which the stress relaxation region 9 is formed, the crystallinity of the piezoelectric film is disturbed by the injection of ions, and the compressive stress is relaxed. Since it is not desirable to recover the disorder of crystallinity, it is preferable not to perform heat treatment after injecting the ions. By forming the stress relaxation region 9 in this way, the warp of the diaphragm 2 is eliminated.

The stress relaxation region 9 is formed by using, for example, a focused ion beam device and using gallium (Ga) as an ion species under the conditions of an acceleration energy of 30 keV and a current of 30 nA. It was confirmed that the warp was alleviated by injecting ions into the surface of the piezoelectric film on the free end side of the diaphragm 2 in which the warp of about 30 μm was generated under the above conditions. At this time, it was confirmed that the free end side of the diaphragm 2 has a small contribution to the signal output from the piezoelectric element, and there is no problem in the output signal of the piezoelectric element even if the stress relaxation region 9 is formed in this region. ..

As a matter of course, the degree of warpage of the diaphragm 2 changes depending on the magnitude of the residual stress of the piezoelectric film. Therefore, ion injection conditions such as acceleration energy, current, injection time, injection region, and scanning direction may be appropriately set according to the degree of warpage of the diaphragm 2. It is also effective to repeat the injection of ions a plurality of times depending on the degree of warpage of the diaphragm 2.

The stress relaxation region 9 is not limited to the case where it is formed on a part of the surface of the piezoelectric film 5b as shown in FIG. 1, and is formed on the entire piezoelectric film 5b or on both the piezoelectric film 5b and the piezoelectric film 5a. Is also possible.

Further, in the example shown in FIG. 1, the case where the stress relaxation region 9 is formed from the surface side of the piezoelectric film 5b has been described, but it is also possible to form the stress relaxation region 9 on the piezoelectric film 5a from the cavity 7 side.

When the stress relaxation region 9 is provided in this way, the warp of the diaphragm 2 is alleviated, the slit width can be set as designed, and the effect of suppressing deterioration of the characteristics of the piezoelectric element is enhanced.

Although the examples of the present invention have been described above, it goes without saying that the present invention is not limited to the above examples. For example, the ions to be injected are not limited to gallium. Moreover, it is not limited to the piezoelectric film having a multilayer structure.

1: Slit, 2: Diaphragm, 3: Support substrate, 4: Insulating film, 5a, 5b: Hydraulic film, 6a, 6b, 6c: Electrode, 7: Cavity, 8a, 8b: Wiring metal, 9: Stress relaxation area

Claims (5)

In a piezoelectric element provided with a diaphragm made of a piezoelectric film having one end fixed and the other end free, and a pair of electrodes arranged with the piezoelectric film interposed therebetween.
The diaphragm is a piezoelectric element characterized in that a part of the surface of the piezoelectric film is a stress relaxation region. In the piezoelectric element according to claim 1,
In the diaphragm, a piezoelectric film supported by a support substrate having a cavity is partitioned by a slit penetrating the piezoelectric film.
A piezoelectric element characterized in that the stress relaxation region is arranged on the free end side of the diaphragm. In the piezoelectric element according to any one of claims 1 or 2.
The piezoelectric element is characterized in that the stress relaxation region is an ion implantation region. In a method for manufacturing a piezoelectric element including a diaphragm made of a piezoelectric film having one end fixed and the other end free, and a pair of electrodes arranged with the piezoelectric film interposed therebetween.
The process of laminating and forming the piezoelectric film on the support substrate,
The step of forming the pair of electrodes arranged so as to sandwich the piezoelectric film, and
A step of partitioning the piezoelectric film so that at least one end is fixed to the support substrate and the other end is a free end to form the diaphragm.
A method for manufacturing a piezoelectric element, which comprises a step of forming a stress relaxation region having a stress different from the stress of the piezoelectric film in a part of the piezoelectric film of the diaphragm in which warpage occurs. In the method for manufacturing a piezoelectric element according to claim 4,
A method for manufacturing a piezoelectric element, wherein the step of forming the stress relaxation region is a step of injecting ions into the piezoelectric film.

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