JP2010135595A - Piezoelectric element and method of manufacturing the same, and angular velocity sensor using the piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an angular velocity sensor using a piezoelectric sensor that prevents short circuit between a first electrode and a second electrode without reducing Q value of the piezoelectric element. <P>SOLUTION: The piezoelectric element 30 has such a structure that a piezoelectric material 14 whose cross section in the direction of thickness is formed trapezoidal is pinched with a first electrode 13a and a second electrode 15a. The first electrode 13a is provided on a first face F1 on the side of a substrate 10 in the piezoelectric material 14, and the second electrode 15a is provided on a second face F2. An inclined section 14a inclined to the substrate 10 is formed on the side face of the piezoelectric material 14. In addition, a flat section 14b parallel to the substrate 10 is formed in the remaining section excluding the inclined section 14a, on the side face of the piezoelectric material 14. In the piezoelectric material 30, a distance between the first electrode 13a and the second electrode 15a is large, so that shortcircuiting is hard to occur, and a section not contributing to resonance in the piezoelectric material 14 is removed, thereby increasing Q value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric element that changes a contraction movement of a piezoelectric body into a mechanical movement by applying a voltage, a manufacturing method thereof, and an angular velocity sensor using the piezoelectric element.

  A thin film piezoelectric element that changes a contraction movement of a piezoelectric body into a mechanical movement by applying a voltage is widely used as a thin film microresonator for an angular velocity sensor (for example, Patent Documents 1 and 2). ).

FIG. 12 is a schematic view of a conventional angular velocity sensor, and FIG. 13 is a cross-sectional view taken along line AA of FIG.
The conventional angular velocity sensor 100 includes a rectangular substrate 110 on which four driving piezoelectric elements 120 and four detection piezoelectric elements 130 are mounted.
The substrate 110 is made of SOI (Silicon On Insulator) or the like. A thin flexible portion 110 a is formed on the upper surface of the central portion of the substrate 110. A thick fixing portion 110b is formed around the flexible portion 110a. In the center of the lower surface of the flexible part 110a, a weight part 140 provided with a weight body is formed.
The four driving piezoelectric elements 120 and the four detecting piezoelectric elements 130 are mounted on the upper surface of the flexible portion 110a.
Each of the detection piezoelectric elements 130 is formed in the same fan shape. The detection piezoelectric element 130 is disposed in the central portion of the flexible portion 110a so as to face each other with a gap therebetween. Each of the driving piezoelectric elements 120 is formed in the same arc shape. The driving piezoelectric elements 120 are arranged concentrically on the outside of the four detecting piezoelectric elements 130 so as to correspond to each other.
The four driving piezoelectric elements 120 vibrate the flexible portion 110a in the thickness direction, and the four detecting piezoelectric elements 130 detect deformation of the flexible portion 110a in the thickness direction.

  Reference numeral 120 in FIG. 13 denotes a driving piezoelectric element. The driving piezoelectric element 120 is a laminated film in which the first electrode 121, the piezoelectric body 122, and the second electrode 123 are laminated in this order on the flexible portion 110a, and the first electrode 121 and the first electrode facing each other. The thin film piezoelectric element includes a piezoelectric body 122 sandwiched between two electrodes 123. Reference numeral 130 denotes a detection piezoelectric element. The detection piezoelectric element 130 is a laminated film in which a first electrode 131, a piezoelectric body 132, and a second electrode 133 are laminated in this order on the flexible portion 110a, and the first electrode 131 and the first electrode 131 that face each other. The thin film piezoelectric element includes a piezoelectric body 132 sandwiched between two electrodes 133. Lead wires (not shown) are connected to the first electrode 121 and the second electrode 123 of the driving piezoelectric element 120 and the first electrode 131 and the second electrode 133 of the detecting piezoelectric element 130, respectively. Yes.

  The operation of the conventional angular velocity sensor 100 configured as described above will be described. When an AC voltage having a predetermined frequency f is applied to the first electrode 121 and the second electrode 123 of the four driving piezoelectric elements 120, the piezoelectric body 122 expands and contracts along the electrode surface according to the frequency f. Along with the expansion / contraction variation, the flexible portion 110a on which the driving piezoelectric element 120 is mounted vibrates. Due to this vibration, the weight body 140 formed at the center of the substrate 110 vibrates at the frequency f in the axis z direction perpendicular to the surface of the flexible portion 110a. On the other hand, in each detection piezoelectric element 130, a piezoelectric power based on the vibration of the weight body 140 is generated between the first electrode 132 and the second electrode 133. Thus, when an angular velocity is applied around the axis x orthogonal to the axis z direction when the weight body 140 is vibrating in the axis z direction, the weight body 140 has an axis orthogonal to the axis z and the axis x. The Coriolis force in the y direction works, and the component force is transmitted as distortion to the flexible portion 110a around the weight body 140. An output corresponding to the distortion appears on each detection piezoelectric element 130. This output correlates with the magnitude of the Coriolis force. Therefore, the magnitude of the Coriolis force, that is, the angular velocity can be detected by detecting the difference between the voltages output from the first electrode 132 and the second electrode 133 of each detection piezoelectric element 130.

JP 2003-227719 A JP 2006-194911 A

In such a thin film piezoelectric element, in order to increase the Q value, which is one of the indicators of the quality of vibration characteristics, the planar shapes of the first electrode, the piezoelectric body, and the second electrode are the same. It is desirable to be. This is because, in the piezoelectric body, the expansion and contraction motion occurs when a voltage is applied only in the portion sandwiched between the first electrode and the second electrode.
However, when a thin film piezoelectric element that is a microresonator is formed on a substrate by a process such as etching, making the first electrode, the piezoelectric body, and the second electrode in the same shape has a big problem for the following reason. .
That is, since the piezoelectric element has a small area and the electrode and the piezoelectric film are thin films of about several μm, it is difficult to accurately form the second electrode on the upper surface of the piezoelectric element. When the second electrode is formed, the second electrode protrudes from the piezoelectric body due to the displacement of the electrode pattern. As a result, the second electrode and the first electrode are easily short-circuited by conductive impurities adhering to the side surface of the piezoelectric body.
Further, even if the positions of the electrode pattern and the piezoelectric pattern having the same shape are accurately aligned, the piezoelectric body is a thin film, so the distance between the first electrode and the second electrode is close, and a short circuit due to creeping discharge is likely to occur.

As a countermeasure, in Patent Document 1, the piezoelectric body is formed to be sufficiently larger than the second electrode to ensure insulation and prevent a short circuit between the first electrode and the second electrode.
However, as described above, in the piezoelectric body, the expansion / contraction movement occurs only when the voltage is applied, that is, the portion sandwiched between the two electrodes, so that the extra portion protruding from the second electrode in the piezoelectric body to which no voltage is applied. Such a piezoelectric portion does not contribute to the expansion and contraction motion of the piezoelectric material, but rather hinders the resonance motion of the flexible portion of the substrate, resulting in a low Q value.

  In order to solve such a problem, the present inventor conducted etching processing on “a part of the protruding portion of the piezoelectric body that hinders resonance” as a result of intensive research, thereby maintaining a short-circuit preventing effect and a high Q value. I came up with it.

In general, in an etching process of a piezoelectric body, wet etching using a solution that dissolves only the piezoelectric body is frequently used as an etching method for removing unnecessary portions of the piezoelectric body. In this etching process, the electrode is masked with a resist to avoid etching other than necessary portions. Since this wet etching is isotropic etching, it is etched not only in the thickness direction of the piezoelectric body but also in a direction parallel to the surface.
That is, so-called side etching that is excessively etched in the horizontal direction, and wet etching with side etching makes it difficult to control the size of the piezoelectric body in the horizontal direction, and is not preferable for application to the present invention.

  On the other hand, in dry etching (particularly reactive ion etching, RIE) that is anisotropic etching, unnecessary portions of the piezoelectric body can be removed without causing side etching. However, since dry etching by ion milling generally used has low selectivity, there is a problem that not only the piezoelectric portion but also the first electrode necessary as the piezoelectric element is excessively etched.

  The present invention provides a piezoelectric element capable of effectively preventing a short circuit between electrodes without degrading the resonance performance of the piezoelectric element, and also provides an effective use of this piezoelectric element using an etching method. An object of the present invention is to provide a simple manufacturing method.

  According to a first aspect of the present invention for solving the above-mentioned problems, a piezoelectric body having a first surface and a second surface parallel to each other, wherein the first electrode is formed on the first surface and the second electrode is formed on the second surface. In the element, the first surface has a shape having a contour outside the contour projected from the second surface on the first surface, and the first electrode has a shape that is the same as or larger than the contour of the first surface. The second electrode relates to a piezoelectric element having a shape that is the same as or smaller than the contour of the second surface.

As described above, the first surface of the piezoelectric body provided with the first electrode is shaped to have a contour outside the contour projected from the second surface of the piezoelectric body provided with the second electrode on the first surface. As a result, the portion that does not contribute to resonance is reduced, so that the Q value can be increased.
Further, in the electrode formed on the piezoelectric body having the above shape, the first electrode has a shape that is the same as or larger than the contour of the first surface, and the second electrode has a shape that is the same or smaller than the contour of the second surface. Therefore, the distance between the edges of both electrodes becomes long, and a short circuit between the electrodes can be effectively prevented.

According to a second invention, in the first invention, the cross section in the thickness direction of the piezoelectric body is defined as a trapezoid. The “trapezoidal shape” means a shape in which the cross section perpendicular to the thickness direction of the piezoelectric body becomes smaller from the first electrode side to the second electrode side, and the side portion of the piezoelectric body is linear, Including arcs, steps, or a combination of these.
By adopting such a configuration, the portion that does not particularly contribute to resonance is reduced, so that the Q value can be further increased.

In the third invention, in the second invention, a structure having a flat portion on the first surface side of the piezoelectric body is provided.
Here, the “flat portion” means a portion parallel to the first surface of the side surface of the piezoelectric body. With such a configuration, it is possible to further avoid a short circuit between the second electrode and the first electrode while maintaining the Q value at the time of resonance.

According to the first method of manufacturing a piezoelectric element of the present invention, the first electrode is provided on the first surface of the piezoelectric body having the first surface and the second surface parallel to each other, and the second electrode is provided on the second surface. In each of the formed piezoelectric elements, the first surface has a shape having a contour outside the contour projected from the second surface on the first surface, and the first electrode has the same contour as the first surface. A method of manufacturing a piezoelectric element having a large shape, wherein the second electrode has a shape that is the same as or smaller than the contour of the second surface, the first electrode film on the main surface of the substrate, a piezoelectric film, The step of forming the second electrode film in sequence, the step of forming the second electrode from the second electrode film, and the piezoelectric film from the second surface on the second electrode side to the first surface on the first electrode side The etching is performed so that the portion to reach the shape of the piezoelectric body, and whether the first electrode film is the same as the first surface of the piezoelectric body Those of the manufacturing method of the piezoelectric element and a step of forming such a hearing shape.
That is, the first manufacturing method of the present invention is characterized in that a piezoelectric body having the shape of the first invention is formed by using an etching method after forming a piezoelectric film.

Furthermore, in the second manufacturing method of the present invention, in the step of etching the piezoelectric film in the first manufacturing method, the piezoelectric body is formed into a trapezoidal cross section in the thickness direction by dry etching. It is a manufacturing method.
That is, the piezoelectric film having the shape of the second invention is formed by using dry etching after forming the piezoelectric film.

  As a dry etching method, there are ion milling or reactive ion etching (RIE) using a gas that selectively etches only a piezoelectric body. In the former case, it is necessary to use a reactive gas that is more toxic than RIE. There is also an advantage that it is cheaper.

  Furthermore, in another manufacturing method of the present invention, in the second manufacturing method, after the piezoelectric body is formed in a trapezoidal shape, a flat portion is formed on the first surface side of the side surface of the piezoelectric body by wet etching. Is included. Compared to the case where the etching is completed only by dry etching without forming a flat portion, the end face dimensions of the piezoelectric body are stabilized, so that the insulating characteristics are stabilized.

  The piezoelectric element of the present invention can be suitably used for an angular velocity sensor mounted as a driving piezoelectric element and a detecting piezoelectric element on a flexible substrate. The provided angular velocity sensor has a high detection sensitivity for the angular velocity.

  The piezoelectric element of the present invention is less likely to cause a short circuit between the first electrode and the second electrode at the time of manufacture, and further, a portion that does not contribute to resonance in the piezoelectric body is removed. The Q value can be increased.

Hereinafter, a piezoelectric element according to an embodiment of the present invention and a thin film microresonator including the piezoelectric element will be described with reference to the drawings. FIG. 1 shows a cross-sectional view of a microresonator including a piezoelectric element according to an embodiment of the present invention.
A thin film microresonator 40 according to an embodiment of the present invention is obtained by providing a piezoelectric element 30 on one surface of a substrate 10.
The substrate 10 includes a flexible portion 11a that is bent according to an external force, and a fixed portion 11b that is not changed by being fixed.
The piezoelectric element 30 is mounted on the insulating film 12 formed on the entire substrate 10. The piezoelectric element 30 has a structure in which the piezoelectric body 14 is sandwiched between the first electrode 13a and the second electrode 15a.

The piezoelectric body 14 has a first surface F1 that is one main surface parallel to each other and a second surface F2 that is opposite to the one main surface. A first electrode 13a is provided on the first surface F1 on the substrate 10 side, and a second electrode is provided on the second surface F2.
The piezoelectric body 14 has a shape having a contour outside the contour projected from the second surface F2 on the first surface F1 because the cross section in the thickness direction is formed in a trapezoidal shape. An inclined portion 14 a that is inclined with respect to the substrate 10 is formed on the side surface of the piezoelectric body 14. In addition, a flat portion 14b that is parallel to the substrate 10 is formed on the side surface of the piezoelectric body 14 except for the inclined portion 14a. Furthermore, the flat part 14b has a step S between itself and the first electrode 13a because its end face is located inside the end face of the first electrode 13a.
The first electrode 13a can have a shape that is the same as or larger than the contour of the first surface F1, and the second electrode 15a can have a shape that is the same or smaller than the contour of the second surface F2. . In the present embodiment, the first electrode 13a is formed larger than the contour of the first surface F1, and the second electrode 15a is formed smaller than the contour of the second surface F2.
In addition, the side surface of the piezoelectric body 14 should just be an inclined surface which falls as it goes to the 1st surface F1 side from the 2nd surface F2 side. Therefore, the cross-sectional shape of the side surface of the piezoelectric body 14 can be a linear shape, an arc shape, or a staircase shape. When the side surface of the piezoelectric body 14 has an arc shape, it is desirable that the piezoelectric body 14 be concave with respect to the outside. Further, the side surface of the piezoelectric body 14 may be provided with only the inclined portion 14a without providing the flat flat portion 14b as shown in FIG. Moreover, the shape of the level | step difference S may be arbitrary shapes.

  In the piezoelectric element 30, a wiring (not shown) made of, for example, aluminum is connected to the first electrode 13a and the second electrode 15a in order to apply a voltage between both electrodes.

In the present embodiment, Si plates are used as the flexible portion 11a and the fixed portion 11b. However, any material having appropriate elasticity may be used, and metal, metal oxide, glass, or the like can also be used. Further, although SiO ₂ formed by oxidizing a Si plate is used as the insulating film 12 as the insulating film, any insulating material may be used, and a non-conductive resin film or the like may be used. The insulating film 12 needs to have a thickness of about 0.1 to 5 μm in order to maintain the insulation between the flexible portion 11 a and the piezoelectric element 30. Further, in the present embodiment, an example is shown in which the fixing portion 11b is formed only at one end of the substrate 10, but it may be formed at both ends of the substrate 10, and in order to control the expansion and contraction motion of the piezoelectric element 30, You may provide a weight in the flexible part 11a.

  As the material of the first electrode 13a and the second electrode 15a, Pt is used in this embodiment, but is not limited to this, and noble metals represented by Pt, Ir, Pd, Ru, Au, or noble metals are used. Including alloys can be used. Further, the method for producing the electrode is not particularly limited, and a method such as sputtering or plating can be used.

  As the piezoelectric body 14, lead zirconate titanate (PZT) is used in the present embodiment, but is not limited thereto, and can be appropriately selected from piezoelectric bodies such as barium titanate. The thickness of the piezoelectric body 14 is not particularly limited, but the piezoelectric element according to the present embodiment is used in an optimum range of the driving voltage for an angular velocity sensor which is a preferred application example thereof, that is, while ensuring the withstand voltage. In order to realize the use of a high voltage, the thickness of the thickest portion sandwiched between the first electrode 13a and the second electrode 15a (hereinafter referred to as “the thickness T of the central portion of the piezoelectric body”) is set to 0. A thickness of 1 to 10 μm (preferably 1 to 5 μm) is suitable.

Here, in the piezoelectric body 14, the thickness t of the flat portion 14b is 0.5 times or less, preferably 0.3 times or less of the thickness T (see FIG. 8) of the central portion of the piezoelectric body, and the inclined portion 14a The width W is desirably 1 to 6 times, preferably 2 to 5 times the thickness T of the central portion of the piezoelectric body 14.
If the width W is less than 1 times the thickness T of the central portion of the piezoelectric body, when the piezoelectric body 14 is expanded and contracted in the usage state of the piezoelectric element 30, stress concentrates on the lower end side of the inclined portion 14a and breaks. This is not preferable. Further, if the width W of the inclined portion 14a exceeds 6 times, there are many portions of the piezoelectric body 14 that do not expand and contract, and this is not preferable because the Q value becomes small. In addition, the thickness t of the flat part 14b is 0.01-1 micrometer (preferably 1-5 micrometers) in the above-mentioned specific example.

  Hereinafter, a specific example of a preferred method for manufacturing a piezoelectric element according to the present invention will be described with reference to the drawings.

(1) Production of Substrate FIG. 3 shows a substrate used for forming the piezoelectric element of the present embodiment. As the substrate 10 in this embodiment, a substrate in which an insulating film 12 made of silicon oxide (SiO ₂ ) is formed on one surface of a base 11 made of a silicon (Si) plate is used.

(2) Production of Film Formation Substrate Next, as shown in FIG. 4, the first electrode film 13, the piezoelectric film 14 c, and the second electrode film 15 are sequentially formed on the substrate 10. First, a 0.1 to 1 μm first electrode film 13 made of an electrode metal material, for example, Pt, is formed on the substrate 10 by a method such as sputtering or vapor deposition. A film of about 0.02 μm made of Ti may be formed as an adhesion layer between the SiO ₂ insulating film 12 of the substrate 10 and the first electrode film 13.

  Next, a piezoelectric film 14c made of PZT is formed on the first electrode film 13 by a method such as sputtering. The thickness T of the piezoelectric film 14c is 0.1 to 10 μm. Furthermore, a film formation substrate 20 is manufactured by forming a 0.1 to 1 μm second electrode film 15 made of Pt on the piezoelectric film 14c by a method such as sputtering or vapor deposition.

(3) Etching of Second Electrode Film As shown in FIG. 5A, after patterning the resist 16a on the film formation substrate 20, the second electrode is formed by a Pt etching method such as ion milling or reactive ion etching (RIE). The film 15 is etched. Thereafter, as shown in FIG. 5B, the resist 16a is removed to form the second electrode 15a. The resist 16a can be removed without moving to the next etching process of the piezoelectric film 14c.

(4) Etching of Piezoelectric Film In the present embodiment, etching of the piezoelectric film is performed in the following two steps.
(4-1) Dry etching of piezoelectric film (first etching step)
6A and 6B are explanatory views of the dry etching of the piezoelectric film, which is the first etching step. First, after patterning the resist 16b so as to cover the second electrode 15a obtained above, the piezoelectric film 14c is etched by dry etching such as Ar plasma ion milling except for the portion masked by the resist 16b. I do. Here, since the dry etching is hindered by the resist 16b formed so as to cover the second electrode 15a, the etching rate decreases in the vicinity of the side edge of the resist 16b. As a result, an inclined portion 14a that widens from the second electrode 15a side toward the first electrode film 13 side is formed on the side surface of the piezoelectric film 14 in front view.
Further, since the effect of decreasing the etching rate by the resist 16b becomes smaller as the distance from the resist 16b increases, the piezoelectric film 14 is uniformly etched in a region far from the resist 16b, and the piezoelectric film skin layer 14d having a uniform thickness is formed. It is formed.

Here, the shape and the width W of the inclined portion 14a can be changed by changing the dry etching conditions (radiation direction and intensity of ions and etching gas). FIG. 6A shows an example in which the dry etching irradiation angle is set to 90 ° (perpendicular to the substrate). However, since dry etching has high straightness, an inclined portion 14a having a steep inclination and a small width W is formed. The
On the other hand, when dry etching is performed with the dry etching inclined with respect to the substrate as shown in FIG. 6B, the shadowed portion of the resist is not etched, so that an inclined portion 14a having a gentle inclination and a large width W is formed. can do. Here, when the irradiation angle of the dry etching is 30 ° to 60 °, the shape of the inclined portion 14a can be easily and suitably controlled, and the heat generation during the etching is minimized, so that the resist 16a is less altered, There is also an advantage that the removal of the resist 16a in the subsequent process is easy.

  The preferred width W is 1 to 6 times (particularly preferably 2 to 5 times) the thickness of the central portion of the piezoelectric film (T in FIGS. 6A and 6B). If the width W is less than 1 times the thickness of the central portion of the piezoelectric film, stress is applied to the boundary portion between the inclined portion 14a and the flat portion 14b when the piezoelectric body 14 is expanded and contracted after the piezoelectric element is formed. This is not preferable because the boundary portion may be broken and the boundary portion may be damaged. If the width W exceeds six times, the portion that does not expand and contract in the piezoelectric body increases, and the Q value becomes small.

  After performing dry etching in this way, the resist 16b is removed. In this step, resist patterning and resist removal are not essential, and the process can be omitted and proceed to the next step. Further, the side surface of the piezoelectric body only needs to have a shape that expands from the second electrode side to the first electrode side. By appropriately forming and removing the resist 16b, a linear shape, an arc shape, It can also be stepped.

(4-2) Wet etching of piezoelectric film (second etching step)
FIG. 7 is an explanatory diagram of the wet etching of the piezoelectric film, which is the second etching step.
After dry etching, a resist 16c is formed so as to cover the second electrode portion and the side surface portion of the piezoelectric body, and post-baking treatment at 150 ° C. is performed.
Next, wet etching is performed with a wet etching solution composed of a mixed solution of hydrofluoric acid and nitric acid, and a part of the skin layer 14d of the piezoelectric film that remains flat on the substrate is left to be bonded to the inclined portion 14a. Remove other parts. Thereby, the flat portion 14b of the piezoelectric film is formed. According to this method, since the remaining film of the remaining piezoelectric film is small (0.01 to 1 μm), the wet etching time is short, and most of the side surface of the piezoelectric body is protected by the resist. As shown in FIG. 4, there is an advantage that side etching is minimized. Note that the resist removal step is not essential, and may be omitted in some cases and proceed to the next step. Note that the length L of the flat portion 14b after the wet etching can be controlled by the size of the resist 16c, the composition of the wet etching solution, the temperature, and the wetting time. Further, the thickness t of the flat portion 14b is 0.5 times or less of the thickness T of the central portion of the piezoelectric body 14 or 0.01 μm from the viewpoint of the piezoelectric element characteristics such as the characteristics of the piezoelectric element and the manufacturing method of the piezoelectric element. To 1 μm is desirable. When the thickness t of the flat portion 14b exceeds 0.5 times the thickness T of the central portion of the piezoelectric body 14, the Q value is drastically lowered and the characteristics as a piezoelectric element are hindered. Further, from the viewpoint of the piezoelectric element manufacturing method such as etching, if it is less than 0.01 μm, there is a problem that the first electrode film 13 is dry-etched, which is not preferable. On the other hand, when the thickness exceeds 1 μm, side etching at the time of wet etching is likely to occur and dimensional control is difficult. In this embodiment, the size of the resist 16c is determined so that the flat portion remains in the piezoelectric body after the wet etching. However, the flat portion does not remain in the piezoelectric body after the wet etching, and the step S on the first electrode side. The size of the resist 16c may be determined so that only the sloped portion having the above remains.

(5) Etching of First Electrode Film As shown in FIG. 8, after removing the resist 16c, the resist film 16d is patterned on the second electrode, the piezoelectric film and the first electrode film, and then ion milling is performed. Alternatively, the piezoelectric element 30 is manufactured on the substrate 10 by etching the first electrode film 13 by a Pt etching method such as RIE and forming the first electrode 13a by removing the resist.

  The piezoelectric element 30 obtained by the steps (1) to (5) can be used as a thin film microresonator. For this purpose, it is further subjected to the next silicon etching step.

(6) Silicon Etching Step As shown in FIG. 9, in the substrate 10, the end of the surface opposite to the surface on which the piezoelectric element 30 is provided is masked with a resist 16 e, and then the opposite surface is etched. This step may be dry etching or wet etching. By this step, portions other than the portion masked by the resist 16e are etched.
Thereafter, the thin film microresonator 40 shown in FIG. 1 can be obtained by removing the resist 16e. Note that an SOI (Silicon on Insulator) may be used as the substrate 10 in order to improve the accuracy of the thickness of the beam portion.

  In the manufacturing process of the present embodiment, dry etching is employed for the first etching process and wet etching is employed for the second etching process. However, both processes may be performed only by dry etching or only by wet etching. However, the shape of the piezoelectric film 14c is preferably controlled, and the dry etching described above may cause a problem that the first electrode film is excessively etched after the piezoelectric film 14c is thinned. Therefore, the manufacturing method of this embodiment that employs dry etching for the first etching step and wet etching for the second etching step is particularly suitable.

The operation of the thin film microresonator 40 using the piezoelectric element 30 according to this embodiment manufactured as described above will be described. In the thin film microresonator 40, when an AC voltage having a predetermined frequency is applied between the first electrode 13a and the second electrode 15a, the piezoelectric body 14 expands and contracts along the electrode surface according to the predetermined frequency. The first electrode 13a bends in response to the expansion / contraction movement, and this bending is transmitted to the flexible portion 11a, whereby an amplitude movement in the vertical direction (thickness direction of the piezoelectric body 14) occurs in the flexible portion 11a.
In the piezoelectric element 30 according to the present embodiment, the piezoelectric body 14 is formed in a trapezoidal cross section in the thickness direction, and the first electrode 13a having a contour larger than the contour of the first surface F1 is formed on the first surface F1 of the piezoelectric body 14. The second electrode 15a having a smaller contour than the contour of the second surface F2 is formed on the second surface F2, so that the expansion and contraction movement due to the application of voltage is compared with the first electrode 13a and the first electrode 13a. Even if it occurs only in a part of the piezoelectric body 14 located between the second electrode 15a having a small area, the side portion that does not contribute to the resonance of the piezoelectric body 14 is removed, and therefore a high Q value is obtained. Can be secured. Accordingly, the piezoelectric element 30 has a cross section in the thickness direction of the driving piezoelectric element 120, which is a piezoelectric element having a rectangular cross section in the thickness direction of the piezoelectric body shown in FIG. Compared with the rectangular piezoelectric bodies 122 and 123, a high short-circuit prevention effect and high vibration characteristics can be obtained.

Next, as a suitable application example of the piezoelectric element according to the embodiment of the present invention, an angular velocity sensor including the piezoelectric element will be described with reference to the drawings.
FIG. 10 is a schematic view of the angular velocity sensor according to the present embodiment, and FIG. 11 is a cross-sectional view taken along the line BB of FIG. The operation method of this angular velocity sensor is the same as that of the conventional angular velocity sensor shown in FIG.

The angular velocity sensor 200 includes a substrate 210, a driving piezoelectric element 220, and a detecting piezoelectric element 230.
The substrate 210 is a rectangular silicon plate on which a thin plate-like flexible portion 210a, a thick fixing portion 210b, and a thick weight portion 240 are formed. The fixing portion 210b is provided in a rectangular shape along the peripheral edge on the back surface opposite to the mounting surface side on which the driving piezoelectric element 220 and the detection piezoelectric element 230 are provided. The weight portion 240 is provided at the center of the back surface of the substrate 210. And the remaining part except the fixing | fixed part 210b and the weight part 240 of the board | substrate 210 is the flexible part 210a.
The four driving piezoelectric elements 220 and the four detecting piezoelectric elements 230 are mounted on the upper surface of the flexible portion 210a.
Each of the detection piezoelectric elements 230 is formed in the same fan shape. The detection piezoelectric element 230 is disposed in the central portion of the flexible portion 210a so as to face each other with a gap therebetween. The driving piezoelectric elements 220 are each formed in the same arc shape. The driving piezoelectric elements 220 are arranged concentrically on the outside of the four detecting piezoelectric elements 230 so as to correspond to each other.

The driving piezoelectric element 220 and the detecting piezoelectric element 230 are the same in basic configuration except for the shape of the piezoelectric element 30.
The four driving piezoelectric elements 220 are for vibrating the flexible portion 210a in the thickness direction. The four driving piezoelectric elements 220 are for detecting deformation of the flexible portion 110a in the thickness direction.
The driving piezoelectric element 220 is a laminated film in which a first electrode 221, a piezoelectric body 222, and a second electrode 223 are sequentially laminated on the flexible portion 210 a, and the first electrode 221 and the second electrode facing each other. A piezoelectric body 222 is sandwiched between the electrodes 223. Reference numeral 230 denotes a detection piezoelectric element. The detection piezoelectric element 230 is a laminated film in which a first electrode 231, a piezoelectric body 232, and a second electrode 233 are laminated in this order on a flexible portion 210a. The piezoelectric body 232 is sandwiched between the first electrode 231 and the second electrode 233 that face each other.

Similarly to the piezoelectric element 30, each of the driving piezoelectric element 220 and the detecting piezoelectric element 230 has a piezoelectric body 222, 232 having a trapezoidal cross section in the thickness direction. Among the first surfaces F1a and F1b and the second surfaces F2a and F2b, the first surfaces F1a and F1b have a shape having a contour outside the contour projected from the second surfaces F2a and F2b on the first surfaces F1a and F1b. Have.
The piezoelectric bodies 222 and 232 are formed in a trapezoidal shape such that the skirt of the mountain spreads from the second surface side F2a and F2b toward the first surface F1a and F1b side. Steps S <b> 1 and S <b> 2 that expose the end portions of the first electrodes 221 and 231 are formed at the end portions. In addition, flat portions parallel to the substrate 210 are formed in the remaining portions excluding the inclined portions of the piezoelectric bodies 222 and 232.
The first electrodes 221 and 231 are formed on the first surfaces F1a and F1b in the same or larger shape as the contours of the first surfaces F1a and F1b. The second electrodes 223 and 233 are formed on the second surfaces F2a and F2b in the same or smaller shape as the contours of the second surfaces F2a and F2b.

The operation and use state of the angular velocity sensor 200 configured as described above will be described.
A predetermined AC voltage is applied to the four driving piezoelectric elements 220. The application of the predetermined alternating voltage is performed via lead wires (not shown) connected to the first electrodes 221 and the second electrodes 223. When an AC voltage having a predetermined frequency f is applied to each of the first electrode 221 and the second electrode 223, the piezoelectric body 222 expands and contracts along the electrode surface according to the frequency f.
As the piezoelectric body 222 expands and contracts, the first electrode 221 bends as the piezoelectric body 222 expands and contracts. The bending of the first electrode 221 causes the flexible portion 210a to vibrate in the thickness direction. Due to this vibration, the weight body 240 formed at the center of the substrate 210 vibrates at the frequency f in the axis z direction perpendicular to the surface of the flexible portion 210a.
Vibration is transmitted to each detection piezoelectric element 230 via the flexible portion 210a. When the vibration is transmitted to the detecting piezoelectric element 230, the first electrode 231 is bent, and this bending becomes a stress to the piezoelectric body 232. As a result, piezoelectric power based on stress is generated between the first electrode 221 and the second electrode 231 in the piezoelectric body 232.
When an angular velocity around the Y axis is applied as an external force, a Coriolis force is generated in the X axis direction, and the weight body 240 vibrates in the X axis direction. The piezoelectric element 230 for detection detects the bending produced by this vibration as a potential difference. Thereby, the angular velocity is determined.

  The angular velocity sensor 200 according to this embodiment includes a driving piezoelectric element 220 and a detecting piezoelectric element 230 in which the piezoelectric bodies 222 and 232 are formed in a trapezoidal cross section in the thickness direction. Accordingly, since the side portions that do not contribute to the resonance of the piezoelectric bodies 222 and 232 are removed, the driving piezoelectric element 220 and the detecting piezoelectric element 230 can ensure a high Q value. Therefore, the angular velocity sensor 200 can be a highly sensitive angle sensor having high short-circuit prevention.

  Since the piezoelectric element of the present invention can be suitably applied for various uses such as an angular velocity sensor, it is extremely promising industrially.

It is a figure which shows sectional drawing of the microresonator provided with the piezoelectric element which concerns on embodiment of this invention. It is a figure which shows the thin film microresonator using the piezoelectric material element of other embodiment from which the side surface shape of a piezoelectric material differs. It is a figure which shows the structure of the board | substrate of the piezoelectric element which concerns on embodiment of this invention. It is a figure which shows the structure of the film-forming board | substrate of the piezoelectric element which concerns on embodiment of this invention. It is explanatory drawing of the etching of the 2nd electrode film of the piezoelectric element which concerns on embodiment of this invention, (a) is the figure which produced the resist pattern in the 2nd electrode part, (b) shows after resist removal FIG. 4A and 4B are explanatory views of dry etching of a piezoelectric film, which is a first etching process of a piezoelectric element according to an embodiment of the present invention, where FIG. 5A is an example in which an incident angle of dry etching is 90 °, and FIG. This is an example in which the incident angle of etching is 45 °. It is explanatory drawing of the wet etching of a piezoelectric film which is the 2nd etching process of the piezoelectric element which concerns on embodiment of this invention. It is explanatory drawing of the etching of the 1st electrode film of the piezoelectric element which concerns on embodiment of this invention. It is explanatory drawing of the etching of Si substrate in the manufacturing process of the thin film microresonator using the piezoelectric element which concerns on embodiment of this invention. It is a schematic diagram of the angular velocity sensor provided with the thin film microresonator provided with the piezoelectric element of the present invention. It is BB sectional drawing of FIG. It is a schematic diagram of an angular velocity sensor provided with a thin film microresonator provided with a conventional piezoelectric element. It is AA sectional drawing of FIG.

Explanation of symbols

  10: substrate, 11: base, 11a: flexible part, 11b: fixed part, 12: insulating film, 13: first electrode film, 13a: first electrode, 14: piezoelectric body, 14a: inclined part, 14b: flat Part, 14c: piezoelectric film, 14d: skin layer of piezoelectric film, 15: second electrode film, 15a: second electrode, 16a, 16b, 16c, 16d, 16e: resist, 17: direction of dry etching irradiation, 20 : Film formation substrate, 30: Piezoelectric element, 40: Thin film microresonator, 200: Angular velocity sensor 210: Substrate, 210a: Flexible part, 210b: Fixed part, 220: Piezoelectric element for driving, 221, 231: First 1 electrode, 222, 232: piezoelectric body, 223, 233: second electrode, 230: piezoelectric element for detection, 240: weight portion, F1, F1a, F1b: first surface, F2, F2a, F2b: second surface , L: length of the flat part, T: Conductor of the central portion of the thickness, t: thickness of the flat portions, W: inclined portion of the width, S: step.

Claims (7)

In the piezoelectric element in which the first electrode is formed on the first surface and the second electrode is formed on the second surface of the piezoelectric body having a first surface and a second surface parallel to each other,
The first surface is shaped to have a contour outside the contour projected from the second surface on the first surface,
The first electrode has the same or larger shape as the contour of the first surface,
The piezoelectric element, wherein the second electrode has a shape that is the same as or smaller than an outline of the second surface.   The piezoelectric element according to claim 1, wherein a cross section in the thickness direction of the piezoelectric body is trapezoidal.   The piezoelectric element according to claim 1, wherein the piezoelectric body has a flat portion on the first surface side.   4. An angular velocity sensor, wherein the piezoelectric element according to claim 1 is mounted on a flexible substrate as a driving piezoelectric element and a detecting piezoelectric element. In the piezoelectric element in which a first electrode is formed on the first surface and a second electrode is formed on the second surface of the piezoelectric body having a first surface and a second surface that are parallel to each other, the first surface is the first surface. The first surface has a shape having a contour outside the contour projected on the first surface, the first electrode has a shape that is the same as or larger than the contour of the first surface, and the second electrode has a shape that is larger than the contour of the second surface. A method of manufacturing a piezoelectric element having a shape that is the same as or smaller than a contour,
Forming a first electrode film, a piezoelectric film, and a second electrode film in order on the main surface of the substrate;
Forming the second electrode from a second electrode film;
Etching the piezoelectric film so that a portion from the second surface on the second electrode side to the first surface on the first electrode side has the shape of the piezoelectric body;
A method of manufacturing a piezoelectric element comprising: forming the first electrode film so as to have a shape that is the same as or larger than the first surface of the piezoelectric body.   6. The method of manufacturing a piezoelectric element according to claim 5, wherein in the step of etching the piezoelectric film, the piezoelectric body is formed in a trapezoidal shape in the thickness direction by dry etching.   The method of manufacturing a piezoelectric element according to claim 6, further comprising forming a flat portion on the first surface side of the side surface of the piezoelectric body by wet etching after forming the piezoelectric body in a trapezoidal shape.

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