JP2000298138A - Bimorph type piezoelectric element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bimorph type piezoelectric element compact and high in sensitivity with little dispersion in sensitivity by providing a support body on one side of a free vibrating part with a pair of piezoelectric plates jointed face to face and providing the free vibrating part and the support part with an electrode separated by a groove. SOLUTION: A pair of lithium niobate plates are directly jointed to form a rectangular free vibrating part 1, and one main face thereof is integrally provided with a support body 3 with a groove 2 provided at a face opposed to the free vibrating part 1. The support body 3 and the main face of the free vibrating part 1 are provided with an electrode 4 separated by the groove 2. When manufacturing, LN monocrystal rectangular plates are directly jointed in the opposed state of positive polarization faces to form a free vibrating sheet. One face thereof is totally ground to a thickness of about 0.05 mm. With the grounded face as a reference, an ungrounded face is grounded to make the thickness of the free vibrating part sheet about 0.1 mm to simultaneously form the free vibrating part 1 and support body 3. Electrodes 4 are then formed by vapor deposition, sputtering or plating on both faces of the free vibrating part sheet grounded on both sides, and cut in specified size to form the groove 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element used for an acceleration sensor used for detecting vibrations of various devices such as a hard disk drive and a CD-ROM, and more particularly to a bimorph type piezoelectric element and a method of manufacturing the same. is there.

[0002]

2. Description of the Related Art In recent years, with the rapid miniaturization and high performance of personal computers, moving images as well as still images can be easily handled. Therefore, miniaturization and large capacity of a hard disk storage device called an HDD for recording / reproducing a large amount of image data have greatly contributed, and recently, a device exceeding 30 Mbit / cm ² has appeared. As the recording density increases, even if the impact is small, the head may be displaced from the recording track, causing data reading or writing problems. In the worst case, the magnetic head may be moved to the surface of the recording disk. The collision will lead to the destruction of the HDD. In addition, in portable applications, impact may be easily applied, and it is necessary to control the position of the head with respect to the impact. The acceleration sensor for controlling the position of the magnetic head can detect the acceleration with high accuracy. Strictly speaking, the arm on which the magnetic head is mounted is fixed at one end to the voice coil for control. In the position control, the detection of angular acceleration is also required. Until now, a piezoelectric element made of piezoelectric ceramic that detects impact has been developed.However, it is a high-precision piezoelectric element sensor that can only detect the impact of the head and detect the acceleration of the impact and control the position of the head. Has not been realized. This is because hysteresis easily occurs in the history of acceleration due to the structure of the sensor, and sensor characteristics tend to change with time due to the material.

In a conventional piezoelectric element using a piezoelectric ceramic, as shown in the following equation, a distortion is generated in the piezoelectric ceramic by a force F proportional to an acceleration (shock) α, and the distortion is taken out as a charge (voltage). Things. “F = k1 ×
α ”and“ Q (V) = k2 × F ”, where k1
And k2 are proportional constants.

[0004]

In a conventional piezoelectric element, when an acceleration α is applied, a charge (voltage) Q (V) generated in a bimorph type piezoelectric element having a free vibration portion having a length L is
“Q (V) = k3 × L2 × α (where k3 is a proportionality constant)”, and the generated charge is the sensitivity of the sensor. Therefore, the sensor sensitivity is the square of the length L of the free vibration portion. Since it is proportional, the length of the free vibration portion varies, and it is difficult to detect angular acceleration simultaneously.

An object of the present invention is to provide a bimorph type piezoelectric element capable of simultaneously detecting the angular acceleration with a small variation in the length of the free vibration portion and a method of manufacturing the same. Things.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a free vibration portion provided by joining a pair of piezoelectric plates face to face, and the free vibration portion provided integrally with one of the free vibration portions. A support having a groove on a surface opposite to a surface in contact with the vibrating portion, and an electrode separated by the groove on the support and the free vibrating portion.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, there is provided a free vibration portion provided by joining a pair of piezoelectric plates face to face, and the free vibration portion provided integrally with one of the free vibration portions. A support having a groove on a surface opposite to a surface in contact with the portion, and an electrode separated by the groove on the support and the free vibrating portion. This has the function of providing a bimorph type piezoelectric element capable of detecting both acceleration and angular acceleration.

According to a second aspect of the present invention, the electrodes on the main surface without the support according to the first aspect are continuous and common, and a low-cost electrode that does not require a photolithography step in forming the electrodes. This has the function of providing a bimorph type piezoelectric element for an acceleration sensor.

[0009] The invention described in claim 3 is the first invention.
The free vibrating portion described is made of a lithium niobate single crystal, and a main surface facing the same has a rotation Y of 120 ° or more and 150 ° or less.
This is a plate cut surface, and has an effect of providing a bimorph type piezoelectric element which is small, has high sensitivity, has small sensitivity variation, and can detect both translational acceleration and angular acceleration.

[0010] The invention described in claim 4 is the first invention.
The free vibrating portion described has an opposing main surface that is a positively polarized surface, and has an effect of reducing the processing time by utilizing the processing anisotropy of the negatively polarized surface and the positively polarized surface.

The invention described in claim 5 is the first invention.
The electrodes described are Cr / Au, Ti / Au, or Ni.
/ Au, which has an effect of providing a low-cost bimorph-type piezoelectric element that can be easily formed by plating, vapor deposition, or the like.

The invention according to claim 6 is the first invention.
The free vibration portion described is t2 / t, where one thickness of a pair of face-to-face bonded piezoelectric plates is t1 and the other thickness is t2.
1 is 0.7 or more and 1.4 or less, and has an effect of reducing the influence of the pyroelectric effect on the temperature characteristics.

The invention according to claim 7 is the first invention.
The support described above is one in which the corners of the main surface and at least one side surface are curved or chamfered, and has an action of facilitating electrode extraction from the free vibration portion main surface to the support main surface. is there.

The invention described in claim 8 is the same as the invention described in claim 7.
The curved or chamfered support described above has a radius of curvature and an amount of chamfer of not more than 1/4 of the thickness of the support, and facilitates electrode extraction from the free vibration portion main surface to the support main surface. It has.

The invention according to claim 9 is the first invention.
The radius of curvature of a corner between one side surface of the support and the free vibration portion formed by grinding is 0.1 mm or less,
The present invention has a function of providing a bimorph type piezoelectric element which is small, has high sensitivity, has small sensitivity variation, and can detect both translational acceleration and angular acceleration.

According to a tenth aspect of the present invention, in the free vibrating portion according to the first aspect, the surface roughness of the main surface is 0.1 μm or less, and the function of improving the linearity of the output characteristics is achieved. It has.

Further, according to the present invention, a pair of piezoelectric single crystal plates are directly joined by face-to-face joining to form a free vibrating section sheet, and at least one of the free vibrating section sheets is ground to a predetermined thickness. Then, one of the ground free vibration portion sheets is ground to a predetermined interval and depth to simultaneously and simultaneously form a support including a free vibration portion and a non-ground portion,
An electrode is formed on a main surface of a free vibration section sheet formed with a free vibration section and a support, and the free vibration section sheet has the support while cutting the free vibration section and the support section at predetermined intervals. It separates the electrodes on the main surface and has the effect of inexpensively producing a bimorph-type piezoelectric element that is highly sensitive, has small sensitivity variations, and can detect both translational acceleration and angular acceleration.

According to a twelfth aspect of the present invention, one of the ground free vibration portion sheets according to the eleventh aspect is ground to a predetermined interval and a predetermined depth to support a free vibration portion and a non-ground portion. The step of forming the body integrally at the same time is to simultaneously perform the curved surface processing or the chamfering processing of the corners of the main surface of the support and at least one side thereof by grinding. This has the function of inexpensively manufacturing a bimorph type piezoelectric element capable of detecting both accelerations.

According to a thirteenth aspect of the present invention, the curvature radius and the amount of chamfer of the curved surface formed at the corner between the main surface of the support and at least one side surface thereof are determined by the thickness of the support. It is less than 1/4, and has the effect of inexpensively producing a bimorph type piezoelectric element in which electrodes can be easily taken out from the free vibrating section.

According to a fourteenth aspect of the present invention, there is provided a support comprising a free vibrating part and a non-grinding part by grinding one of the ground free vibrating part sheets according to the eleventh aspect to a predetermined interval and depth. The step of simultaneously forming the body integrally has an effect of improving the adhesiveness of an electrode formed on the main surface of the support for simultaneously grinding the main surface of the support.

According to a fifteenth aspect of the present invention, one of the ground free vibration portion sheets according to the eleventh aspect is ground to a predetermined interval and depth to support a free vibration portion and a non-ground portion. Between the step of simultaneously forming the body integrally and the step of forming electrodes on the main surface of the free vibration section sheet formed with the free vibration section and the support, the step of etching the ground surface of the free vibration section It has the function of improving the mechanical strength of the bimorph type piezoelectric element.

According to a sixteenth aspect of the present invention, the amount removed in the etching step of the eleventh aspect is not less than の of the average abrasive grain size of the grinding wheel. It has.

According to a seventeenth aspect of the present invention, one of the ground free vibration portion sheets according to the eleventh aspect is ground to a predetermined interval and depth to support a free vibration portion and a non-ground portion. The step of simultaneously forming the body integrally comprises a group of grinding wheels in which at least one or more grinding wheels are coaxially fixed at a predetermined interval, thereby shortening the processing time and providing an inexpensive bimorph type piezoelectric element. It has an action.

In the invention according to claim 18, the step of cutting the free vibrating section sheet according to claim 11 at a predetermined interval between the free vibrating section and the supporting section is performed by a cutting blade rotating at high speed. Thus, a bimorph-type piezoelectric element having high sensitivity, small sensitivity variation, and capable of detecting both translational acceleration and angular acceleration can be manufactured at low cost.

According to a nineteenth aspect of the present invention, the cutting blade according to the eighteenth aspect comprises a group of cutting blades coaxially fixed at least one or more at a predetermined interval, and has high sensitivity and high sensitivity. The bimorph type piezoelectric element having a small variation and capable of detecting both the translational acceleration and the angular acceleration can be manufactured at low cost.

According to a twentieth aspect of the present invention, in the thirteenth aspect, the step of cutting the free oscillating portion sheet at a predetermined interval between the free oscillating portion and the supporting portion includes separating the electrode on the main surface having the supporting member. This step is performed by etching, and has an effect of inexpensively producing a bimorph type piezoelectric element which has high sensitivity, small sensitivity variation and can detect both translational acceleration and angular acceleration.

According to a twenty-first aspect of the present invention, the step of separating the electrode on the main surface having the support according to the eleventh aspect is performed by sandblasting. The bimorph type piezoelectric element capable of detecting both the angular acceleration can be manufactured at low cost.

According to a twenty-second aspect of the present invention, in the eleventh aspect, the step of forming electrodes on the main surface of the free vibrating part sheet comprising the free vibrating part and the support is performed by plating or vapor deposition. Therefore, the bimorph type piezoelectric element having high sensitivity and small sensitivity variation and capable of detecting both translational acceleration and angular acceleration can be manufactured at low cost.

(Embodiment 1) Hereinafter, a bimorph piezoelectric element according to Embodiment 1 of the present invention will be described with reference to the drawings.

FIG. 1A is a sectional view of a bimorph type piezoelectric element according to Embodiment 1 of the present invention, and FIG. 1B is a perspective view of the same.

In the figure, reference numeral 1 denotes a free vibration portion formed of a rectangular plate provided by directly joining two lithium niobate (hereinafter referred to as “LN”) positively polarized surfaces without interposing an adhesive. is there. Here, the direct bonding is a bonding method via at least one of the oxygen group or the hydroxyl group which is a constituent atom of the LN single crystal plate. By bonding and heating the LN surface while keeping the surface thereof smooth and clean, It is joined and integrated. Although the two LN single crystal plates are completely integrated by this direct bonding, the bonding surface where the polarization direction is reversed is indicated by a dotted line in the figure. The surface roughness of the free vibrating portion 1 is set so that it can withstand an impact acceleration of 1000 G or more.
a is set to 0.1 μm or less.

On one main surface of the free vibrating portion 1, a support 3 having a groove 2 on a surface facing a surface in contact with the free vibrating portion 1 is integrally provided. Electrodes 4 are provided on the main surfaces of the support 3 and the free vibrating section 1 separated by the grooves 2 of the support 3.

The electrode 4 is for taking out the electric charge generated at the time of detecting the acceleration, and when the acceleration is applied,
By fixing the support 3, distortion occurs in the free vibration section 1, and electric charges proportional to the distortion are taken out through the electrode 4 to detect acceleration. The electrode 4 is selected depending on the adhesion to the underlying LN single crystal and the electrode forming method. When sputtering or vapor deposition is used, Cr /
Au, Ti / Au or the like is desirable, and when a plating method such as electroless plating is used, Ni / Au or the like is desirable.

The electrodes 4 formed on the support 3 are separated by the grooves 2, so that the output of the free vibrating section 1 can be separated and detected. Therefore, the support 3
Is fixed, when a translational acceleration is applied to the bimorph type piezoelectric element, an output of the same sign is obtained from the free vibration section 1, and when an angular acceleration is applied, an output of the opposite sign is obtained, and the translation is performed by one bimorph type piezoelectric element. Acceleration and angular acceleration can be detected separately.

In this embodiment, the thickness of the free vibrating section 1 is 0.1 mm, the lengths L1 and L2 are 2.0 mm, the width is 0.5 mm, and the thickness h1 of the support 3 is 0.4 mm. Further, the thickness of the two LN single crystals directly joined to each other with the polarization inversion interface of the free vibrating portion 1 being 0.05
It is provided by grinding to be equal in mm.

The sensor sensitivity S, which is the output voltage of the bimorph type piezoelectric element configured as described above, is represented by a piezoelectric constant “d”, a dielectric constant “ε”, a mass density “ρ”, and a free vibration portion length. Assuming that “L1” and the constant are “α”, “S∝d /
ε * ρ * L1 * α ”. The piezoelectric constant “d” and the dielectric constant “ε” according to this equation have anisotropy in an LN single crystal,
Depends on the cut surface. According to the simulation, the maximum value of the piezoelectric constant “d” has a minimum value near 130 °, and the dielectric constant “ε” has a minimum value near 150 °. Therefore, in order to design the sensitivity “S” to the maximum, the cutting angle of the LN single crystal must be changed. A rotating Y plate having a rotation angle of 120 ° or more and 150 ° or less was used. Furthermore, the free vibration part 1 accompanying the temperature rise is obtained by joining with the polarization direction reversed.
This eliminates the generation of electric charges in the sensor and realizes good temperature characteristics of sensor sensitivity.

As described above, according to the present invention, the free vibrating portion 1 is bimorph-formed by direct bonding without using an adhesive or the like, and the step for forming the support 3 is formed integrally with the LN rectangular plate. Further, by selecting the cut surface of the LN single crystal plate so as to maximize the piezoelectric constant “d” and the electromechanical coupling coefficient “k”, the sensitivity of the bimorph type piezoelectric element using piezoelectric ceramic is two to three times. High sensitivity of 6 mV / G can be obtained.

A method of manufacturing the bimorph type piezoelectric element configured as described above will be described below with reference to the drawings.

FIG. 2 is a diagram for explaining a method of manufacturing a bimorph type piezoelectric element according to the first embodiment of the present invention.

First, as shown in FIG. 2A, a rectangular plate of LN single crystal having a very smooth and clean surface is directly joined with its positively polarized surfaces facing each other to form a free vibration portion sheet 11. I do. At this time, the cutting angle of the rectangular plate of the LN single crystal is set to 120 to 150 ° so that the piezoelectric constant “d” and the electromechanical coupling coefficient “k” are maximized. Is 3 inches or more and has a thickness of 0.2 mm or more, which is relatively easy to handle.

Next, as shown in FIG. 2B, one of the free vibrating section sheets 11 is ground to a thickness of about 0.05 mm.

Next, as shown in FIG. 2 (c), the non-grinding free vibrating portion sheet 11 not polished in the previous step is ground using the grinding wheel 12 having a width w1 with respect to the entire ground surface. Groove grinding is performed so that the thickness of the free vibration portion sheet 11 is 0.1 mm, and the free vibration portion 1 (not shown in this drawing) and the support 3 (not shown in this drawing) are integrated. At the same time. At this time, assuming that the thickness of one free vibration portion sheet 11 after grinding is “t1” and the other thickness is “t2”, the sensor sensitivity “S” is that the length of the free vibration portion is “L1” and the applied acceleration is “g”. , "S∝d / ε * ρ * L1 *
From the equation of α, “S∝ (t1 × t2) × L12 × g / 2
(T1 + t2) ", and the balance between the thicknesses" t1 "and" t2 "of the free vibration portion sheet 11 after the grinding process greatly affects the variation in the sensor sensitivity. Ideally, t1 = t2 is desirable, but from the above expression, “t2 / t
When the value of “1” is in the range of 0.7 to 1.4, the sensor sensitivity variation within the wafer is suppressed to within ± 5%. In the case where only one grinding wheel 12 is used in this step, the feed amount during processing of the grinding wheel 12 is determined so that the support 3 which is a non-grinding portion has a predetermined length “w4”. When the width “w1” of the grinding wheel 12 is set to twice the length “L1” of the free vibrating portion, the number of cuts in the final cutting step can be reduced, and the material can be used without waste and low cost. Enables element formation. Also, the support 3
Assuming that the length of the grinding wheel 12 is “w4”, the grinding wheel 12 has a width w4 ≧
By fixing a plurality of coaxially using the spacers 13 of w2, it is possible to simultaneously grind the plurality of free vibrating portions 1 and the support 3 and to reduce the cost by shortening the machining time. In addition, the surface of the free vibrating portion 1 needs to improve the mechanical strength of the free vibrating portion by removing the processing damage and reducing the surface roughness by etching depending on the element dimensions and the range of the detected acceleration. As an LN etching solution, hydrofluoric acid or a mixed solution of hydrofluoric acid and nitric acid is used, and the higher the etching temperature, the higher the removal rate.
The shape of the surface of the free vibrating portion 1 is a transcript of the surface state of the grindstone 12 for groove grinding, and the amount of abrasive particles protruding from the bond material is about 30 to 50% of the average abrasive particle diameter. As a guide, the average abrasive particle size used for the groove grinding wheel 12 is set to 以上 or more, and the surface roughness is set to 0.1 μm or less in Ra. By introducing the etching process, the free vibration portion can have an impact resistance of 1000 G or more.

Next, as shown in FIG. 2D, electrodes 4 for taking out voltage output are formed on the entire surface of both surfaces of the joined free vibration portion sheet 11 having both surfaces ground. This electrode 4
Is formed by using a vapor deposition method, a sputtering method, a plating method, or the like, and the electrode material is selected in consideration of the adhesion to the underlying LN and the electrode forming method. When a vapor deposition or sputtering method is applied, Ti / Au and Cr / Au are formed, and when a plating method such as electroless plating is applied, Ni / Au is formed relatively easily and is desirable.

Finally, as shown in FIG. 2 (e), the free vibration portion sheet 11 which has been double-side ground is cut into a predetermined size using a cutting blade 14, and the groove 2 is formed. A bimorph type piezoelectric vibrator shown in FIG. 2 (f) is formed. At this time, if a plurality of cutting blades 14 are used, it is possible to simultaneously process a plurality of rows for cutting the element and separating the support 3 and the electrode 4, resulting in low cost. In this case, a plurality of blades 14 having different diameters “r1” and “r2” are used, and if r1> r2, the blade having the diameter “r1” is used for element cutting and the blade having the diameter “r2” is supported. Used to separate electrode 4 on body 3. A plurality of cutting blades 14 are coaxially fixed by spacers 13 (not shown in this drawing) adjusted to match the cutting size of the element or the pitch of electrode separation of the support 3. In this step, as a method of separating the electrodes of the support 3, a method of patterning by photolithography or the like and separating by etching or sandblasting may be used other than the method using the cutting blade. If this manufacturing method is performed on a 3-inch wafer, it is possible to collectively form about 1500 bimorph type piezoelectric elements for an acceleration sensor per wafer, thereby reducing the cost.

(Embodiment 2) Hereinafter, a bimorph type piezoelectric element according to Embodiment 2 of the present invention will be described with reference to the drawings.

FIG. 3A is a sectional view of a bimorph type piezoelectric element according to Embodiment 2 of the present invention, and FIG. 3B is a perspective view of the same. Here, FIG. 3 of the present embodiment and the first embodiment
1 is that the support portion is chamfered, and the same components are denoted by the same reference numerals and description thereof is omitted.

In the figure, reference numeral 21 denotes a chamfered portion, which is provided in the groove 2 of the support portion 3 provided on one main surface of the free vibration portion 1. The chamfered portion 21 has a thickness “h1” of the support portion 3 of 1
By setting / 4 or less, the electrode 4 can be formed without separating the main surface of the support 3 and the main surface of the free vibrating section 1.

A method for manufacturing the bimorph type piezoelectric element configured as described above will be described with reference to the drawings.

FIG. 4 is a view for explaining a method of manufacturing a bimorph type piezoelectric element according to the second embodiment of the present invention. Here, the difference between FIG. 2 of the present embodiment and the first embodiment is that the step of forming the support portion is chamfered at the same time, and the same components are denoted by the same reference numerals and description thereof is omitted. I do.

That is, the free vibrating portion sheet 11 on the non-grinding side which has not been polished in the previous step is formed by using a grinding wheel 12 having a width w1 so that the free vibrating portion sheet 11 has a thickness of 0.1 mm with respect to the entire ground surface. Groove grinding so that free vibration part 1
The support 3 (not shown in this drawing) and the support 3 (not shown in this drawing) are integrally formed simultaneously. At this time, as shown in FIG. 4, the shape of the grinding wheel 12 to be used is formed by using a wheel provided with a grinding wheel chamfered portion 22 for forming the chamfered portion 21.

In the present embodiment, the chamfered portion 21 is provided in a tapered shape. However, as shown in FIG.
The magnet chamfer 22 may have a round shape as shown in FIG.

(Embodiment 3) Hereinafter, a bimorph type piezoelectric element according to Embodiment 3 of the present invention will be described with reference to the drawings.

FIG. 7A is a sectional view of a bimorph type piezoelectric element according to Embodiment 3 of the present invention, and FIG. 7B is a perspective view of the same. Here, FIG. 7 of this embodiment and Embodiment 2
6 is different from FIG. 6 in that the support portion is chamfered, and the same components are denoted by the same reference numerals and description thereof is omitted.

In the drawing, reference numeral 21 denotes a chamfer, which is provided in the groove 2 of the support 3 provided on one main surface of the free vibrating section 1. The chamfered portion 21 has a thickness “h1” of the support portion 3 of 1
By setting / 4 or less, the electrode 4 can be formed without separating the main surface of the support 3 and the main surface of the free vibrating section 1. Further, a contact chamfer 31 is provided on the contact surface between the free vibrating portion 1 and the support portion 3.

A method for manufacturing the bimorph type piezoelectric element configured as described above will be described with reference to the drawings.

FIG. 8 is a view for explaining a method of manufacturing a bimorph type piezoelectric element according to the third embodiment of the present invention. Here, the difference between FIG. 8 of the present embodiment and FIG. 2 of the second embodiment is that, in the process of forming the support portion, chamfering is performed simultaneously and the contact surface between the free vibration portion and the support portion is also chamfered. This is a point that has been processed, and the same components are denoted by the same reference numerals and description thereof is omitted.

That is, the free vibrating portion sheet 11 on the non-grinding side, which has not been polished in the previous step, has a thickness of 0.1 mm with respect to the entire ground surface using the grinding wheel 12 having a width w1. The free vibration portion 1 (not shown in this drawing) and the support 3 (not shown in this drawing) are simultaneously formed integrally by performing groove grinding so that At this time, as shown in FIG. 8, the shape of the grinding wheel 12 to be used is formed by using a wheel provided with a grinding wheel chamfer 22 and a contact surface chamfer 32 for forming the chamfer 21. Things.

(Embodiment 4) Hereinafter, a method for manufacturing a bimorph type piezoelectric element according to Embodiment 4 of the present invention will be described with reference to the drawings.

FIG. 9 is a view for explaining a method of manufacturing a bimorph type piezoelectric element according to the third embodiment of the present invention.

First, as shown in FIG. 9A, a free vibration portion sheet 11 is formed by directly bonding LN single crystal rectangular plates whose surfaces are very smooth and clean with their positively polarized surfaces facing each other. I do. At this time, the cut angle of the rectangular plate of the LN single crystal is a rotating Y plate of 120 ° or more and 150 ° or less so that the piezoelectric constant “d” and the electromechanical coupling coefficient “k” are maximized. Was 3 inches or more in thickness and 0.2 mm or more in thickness, which was relatively easy to handle.

Next, as shown in FIG. 9B, one side of the free vibration portion sheet 11 is entirely ground to a thickness of about 0.05 mm.

Next, as shown in FIG. 9C, the free vibrating section sheet 11 on the non-grinding side is ground by using a grinding wheel 41 so that the free vibrating section sheet 11 has a thickness of 0.
The groove is ground to 1 mm, and the free vibrating section 1 and the support 3 are formed simultaneously and integrally. At this time, the grinding wheel 41
When the free vibration portion sheet 11 and the support 3 are simultaneously formed, the main surface of the support is ground by making the groove depth “D6” processed at the tip of the substrate smaller by several to several tens μm than the thickness “h1” of the support. be able to. Since the main surface of the support 3 is mirror-finished, the adhesion of the electrode film is low. Therefore, the reliability of the electrode film can be improved by increasing the surface roughness by grinding. Further, the thickness of one free vibration portion sheet 11 after grinding is “t1”, the thickness of the other free vibration portion sheet 11 is “t2”, and the free vibration portion length is “L1”.
Assuming that the applied acceleration is “g”, the sensor sensitivity S is “sensor sensitivity S∝ (t1 × t2) × L12 × g / 2 (t1 + t)
2)], the balance between the thicknesses “t1” and “t2” of the free vibration portion sheet 11 after the grinding process greatly affects the variation in sensor sensitivity. Ideally, t1 = t2 is desirable. In this case, when the value of “t2 / t1” is in the range of 0.7 or more and 1.4 or less, the sensor sensitivity variation in the wafer is suppressed to within ± 5%. Grinding wheel 41
By setting the width “w” to twice the length “L1” of the free vibrating part, it is possible to reduce the number of cuts in the final cutting step, and it is possible to form a low-cost element that can use materials without waste. And The surface of the free vibrating portion formed by the grinding process has processing damage, and the surface roughness increases. For this reason, when the applied acceleration increases, the free vibrating portion is easily cracked and chipped. It is necessary to improve the mechanical strength of the free vibrating portion by removing the processing damage and reducing the surface roughness by etching depending on the range of the element dimensions and the detected acceleration. As an LN etching solution, hydrofluoric acid or a mixed solution of hydrofluoric acid and nitric acid is used, and the higher the etching temperature, the higher the removal rate. The shape of the surface of the free vibrating portion is a transfer of the surface state of the grindstone 41, and the amount of the abrasive particles protruding from the bonding material is about 30 to 50% of the average abrasive particle diameter. The average grain size used for the groove grinding grindstone 41 was 以上 or more, and the surface roughness was “Ra” of 0.1 μm or less. By introducing the etching step, the free vibration portion was able to obtain an impact resistance of 1000 G or more.

Next, as shown in FIG. 9D, electrodes 4 for taking out voltage output are formed on both surfaces of the joined free vibration portion sheet 11 having both surfaces ground. As an electrode forming method, a vapor deposition method, a sputtering method, a plating method, or the like is used, and an electrode material is selected in consideration of the adhesion to the underlying LN and the electrode forming method. When a vapor deposition or sputtering method is applied, Ti / Au and Cr / Au are preferably formed, and when a plating method such as electroless plating is applied, Ni / Au is relatively easily formed.

Finally, as shown in FIG. 9 (e), the free vibration portion sheet 11, which has been subjected to double-side grinding, is cut into a predetermined size using a cutting blade 14, and a groove 2 is formed. A bimorph type piezoelectric vibrator shown in FIG. 9F is formed. At this time, if a plurality of cutting blades 14 are used, it is possible to simultaneously process a plurality of rows for cutting the element and separating the support 3 and the electrode 4, resulting in low cost. In this case, a plurality of blades 14 having different diameters “r1” and “r2” are used, and if r1> r2, the blade having the diameter “r1” is used for element cutting and the blade having the diameter “r2” is supported. Used to separate electrode 4 on body 3. A plurality of cutting blades 14 are coaxially fixed by spacers 13 (not shown in this drawing) adjusted to match the cutting size of the element or the pitch of electrode separation of the support 3. In this step, as a method of separating the electrodes of the support 3, a method of patterning by photolithography or the like and separating by etching or sandblasting may be used other than the method using the cutting blade. If this manufacturing method is performed on a 3-inch wafer, it is possible to collectively form about 1500 bimorph type piezoelectric elements for an acceleration sensor per wafer, thereby reducing the cost.

[0065]

As described above, the present invention can provide a bimorph type piezoelectric element which is small, has high sensitivity, has small sensitivity variation, and can simultaneously detect translational acceleration and angular acceleration, and a method of manufacturing the same.

[Brief description of the drawings]

FIG. 1A is a sectional view of a bimorph piezoelectric element according to a first embodiment of the present invention. FIG.

FIG. 2 is a diagram illustrating the manufacturing method.

3A is a sectional view of a bimorph type piezoelectric element according to a second embodiment of the present invention. FIG.

FIG. 4 is a diagram illustrating a method for manufacturing a bimorph piezoelectric element according to Embodiment 2 of the present invention.

FIG. 5 is a diagram illustrating a method of manufacturing a bimorph piezoelectric element according to another embodiment 2 of the present invention.

FIG. 6 is a diagram illustrating a method for manufacturing a bimorph type piezoelectric element according to another embodiment 2 of the present invention.

7A is a sectional view of a bimorph type piezoelectric element according to Embodiment 3 of the present invention. FIG. 7B is a perspective view of the same.

FIG. 8 is a diagram illustrating a method of manufacturing a bimorph piezoelectric element according to Embodiment 3 of the present invention.

FIG. 9 is a diagram illustrating a method for manufacturing a bimorph piezoelectric element according to Embodiment 3 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Free vibration part 2 Groove 3 Support 4 Electrode 11 Free vibration part sheet

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Koji Nomura 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term in the company (reference) 2G064 AA12 AB01 AB02 AB08 BA02 BA03 BD18 BD27 BD42 BD56 DD32

Claims (22)

[Claims] A support having a free vibration portion provided by joining a pair of piezoelectric plates face to face, and a groove provided on a surface opposite to a surface provided integrally with the one free vibration portion and in contact with the free vibration portion. A bimorph type piezoelectric element comprising a body, an electrode separated by the groove in the support and the free vibrating portion. 2. The bimorph type piezoelectric element according to claim 1, wherein the electrode on the main surface having no support is continuous and common. 3. The bimorph-type piezoelectric element according to claim 1, wherein the free vibrating portion is made of a single crystal of lithium niobate, and a main surface facing the cut surface is a cutout surface of a rotating Y plate of 120 ° or more and 150 ° or less. 4. The bimorph type piezoelectric element according to claim 1, wherein the free vibration portion has a main surface facing the positive polarization surface. 5. The bimorph type piezoelectric element according to claim 1, wherein the electrode is one of Cr / Au, Ti / Au, and Ni / Au. 6. The free vibrating portion, wherein one thickness of a pair of face-to-face joined piezoelectric plates is t1 and the other thickness is t2.
2. The bimorph type piezoelectric element according to claim 1, wherein t2 / t1 is 0.7 or more and 1.4 or less. 7. The bimorph type piezoelectric element according to claim 1, wherein a corner of the main surface and at least one side surface of the support is curved or chamfered. 8. The bimorph-type piezoelectric element according to claim 7, wherein the curved or chamfered support has a radius of curvature and a chamfer of not more than ４ of the thickness of the support. 9. The bimorph type piezoelectric element according to claim 1, wherein a radius of curvature of a corner between one side surface of the support and the free vibration portion formed by grinding is 0.1 mm or less. 10. The free vibration portion has a main surface having a surface roughness of 0.5.
The bimorph type piezoelectric element according to claim 1, wherein the thickness is 1 µm or less. 11. A free vibration portion sheet is formed by directly bonding a pair of piezoelectric single crystal plates by face-to-face bonding, and at least one of the free vibration portion sheets is ground to a predetermined thickness, and the ground free vibration is processed. One of the sheets of the free vibration section is formed by grinding one of the sheets at predetermined intervals and depths to simultaneously and simultaneously form a support comprising a free vibration section and a non-grinding section. A method for manufacturing a bimorph type piezoelectric element, wherein an electrode is formed on a surface, the free vibration section sheet is cut at a predetermined interval between the free vibration section and the support section, and an electrode on a main surface having the support is separated. 12. A step of grinding one of the ground free vibration portion sheets to a predetermined interval and depth to simultaneously and simultaneously form a support consisting of a free vibration portion and a non-grinding portion, the step comprising: 2. A curved surface processing or a chamfering process of a corner portion between the substrate and at least one side surface thereof is simultaneously performed by grinding.
2. The method for producing a bimorph type piezoelectric element according to 1. 13. The bimorph-type piezoelectric element according to claim 11, wherein the radius of curvature and the amount of chamfer of the curved surface formed at the corner between the main surface of the support and at least one side thereof are not more than １ ／ of the thickness of the support. Device manufacturing method. 14. The step of grinding one of the ground free vibration portion sheets to a predetermined interval and depth to simultaneously and simultaneously form a support made of a free vibration portion and a non-ground portion, The method for manufacturing a bimorph type piezoelectric element according to claim 11, wherein the main surfaces are simultaneously ground. 15. A step of grinding one of the ground free vibrating section sheets to a predetermined interval and depth to simultaneously and simultaneously form a support comprising a free vibrating section and a non-grinding section; 12. The method for manufacturing a bimorph type piezoelectric element according to claim 11, further comprising an etching step of a ground surface of the free vibration section between the step of forming an electrode on the main surface of the free vibration section sheet on which the support is formed. 16. The method for producing a bimorph type piezoelectric element according to claim 11, wherein the amount removed in the etching step is at least の of the average abrasive grain size of the grinding wheel. 17. A step of grinding one of the ground free-vibration section sheets to a predetermined interval and depth to simultaneously simultaneously form a support including a free-vibration section and a non-grinding section includes the steps of: 12. The method for manufacturing a bimorph type piezoelectric element according to claim 11, comprising at least one or more grindstones coaxially fixed at predetermined intervals. 18. The method for manufacturing a bimorph type piezoelectric element according to claim 11, wherein the step of cutting the free vibrating section sheet at a predetermined interval between the free vibrating section and the supporting section is performed by a cutting blade rotating at a high speed. 19. The cutting blade comprises a group of cutting blades coaxially fixed at least one or more at predetermined intervals.
A method for producing the bimorph piezoelectric element according to the above. 20. The bimorph according to claim 13, wherein the step of cutting the free vibrating section sheet at a predetermined interval between the free vibrating section and the supporting section is performed by etching the electrode on the main surface having the supporting body. Of manufacturing a piezoelectric element. 21. The method according to claim 11, wherein the step of separating the electrode on the main surface having the support is performed by sandblasting. 22. A step of forming an electrode on a main surface of a free vibration section sheet having a free vibration section and a support formed thereon,
The method for manufacturing a bimorph type piezoelectric element according to claim 11, wherein the method is formed by plating or vapor deposition.