JP3183158B2 - Acceleration sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor used for detecting an impact of a hard disk drive and a method of manufacturing the same, and more particularly, to a structure of a bimorph-type detecting element constituting the acceleration sensor and its fabrication. About the procedure.

[0002]

2. Description of the Related Art Conventionally, as an acceleration sensor for detecting an impact, there has been known a sensor using a well-known bimorph type detecting element (hereinafter referred to as a detecting element). Among such acceleration sensors, there is an acceleration sensor as disclosed in JP-A-6-273439.
That is, as shown in a simplified form in FIG. 3, the acceleration sensor is a pair of piezoelectric ceramics having a rectangular flat plate shape and a thin film signal extraction electrode 1 and an intermediate electrode 2 formed on each main surface. Plates 3 and 4, and both end edges along the longitudinal direction of the detection element 5 integrated by face-to-face bonding of the intermediate electrodes 2 formed on the inner main surfaces of the piezoelectric ceramic plates 3 and 4. Only side view "Ko"
It is fixedly supported by a letter-shaped case body 6.

At this time, the longitudinal regions of the piezoelectric ceramic plates 3 and 4 respectively have central portions 3a and 4a and end portions 3b separated by a pair of boundary lines L0 where the stress generated by the action of acceleration changes. , 4b, and the central portions 3a, 4a and the end portions 3b, 4b of the piezoelectric ceramic plates 3, 4 correspond to the polarization directions A, B and C, D which are reversed along the plate thickness direction. After being polarized along the center portions 3a, 4a and the end portions 3b, 4
b, and the polarization directions A and C and B and D are opposite to each other.

In other words, for example, the polarization direction A between the central portions 3a and 4a of the piezoelectric ceramic plates 3 and 4 here.
And C are inwardly approaching each other, while the polarization directions B and D of their end portions 3b and 4b are outwardly facing away from each other. Each of the signal extraction electrodes 1 formed in the above-described manner is electrically connected to each of the external extraction electrodes 7 and 8 formed for different end faces of the case body 6. Although not shown, in the polarization processing of the piezoelectric ceramic plates 3 and 4, a polarization electrode having a size corresponding to each of the central portions 3a and 4a and the end portions 3b and 4b is formed in advance. A polarization process is performed, and it is general that the signal extraction electrode 1 is formed on these polarization electrodes in a later process by lamination.

Further, the use of the detecting element 5 having the above-described configuration is based on the following reasons. That is, when acceleration acts on the acceleration sensor, the central portions 3a, 4a and the end portions 3b, 4b of the piezoelectric ceramic plates 3, 4 constituting the detecting element 5 are deformed by the action of inertial force. Become these parts 3
Each of a, 4a, 3b, and 4b generates a tensile stress or a compressive stress due to deformation. Therefore, each of these parts 3
a, 4a, 3b, 4b, the respective polarization directions A to
This is because the amount of generated charges increases due to the synergistic effect of D and the tensile stress or the compressive stress, and the amount of generated charges of the entire detection element 5 increases. As a result, the detection sensitivity of the acceleration sensor is improved. .

[0006]

By the way, the longitudinal regions of the piezoelectric ceramic plates 3 and 4 constituting the detecting element 5 provided in the conventional acceleration sensor are divided into central portions 3a and 4 respectively.
a and the end portions 3b and 4b are separated from each other by the stress generated in the central portions 3a and 4a and the end portions 3b and 4b of the piezoelectric ceramic plates 3 and 4 due to the action of acceleration. Or, the purpose is to set the detection sensitivity of the acceleration sensor to the required design value as a result of compression. Specifically, calculation using the finite element method, which is one of the numerical analysis methods, is performed. It is to be set based on the result.

However, even when the boundary line L0 is set based on such a method, the material of the piezoelectric ceramic plates 3 and 4 is slightly different from one product lot to another or within a lot, or a processing error occurs. Therefore, it is difficult to provide detection sensitivity that satisfies the design value for all acceleration sensors, and the detection sensitivity of the acceleration sensor varies. That is, if the position of the boundary line L0 in the detection element 5 is simply set so as to obtain the detection sensitivity matching the design value, it is not possible to exceed the allowable error range of the design value having a certain width. It is inevitable that a non-defective product will be manufactured, resulting in a great loss.

The present invention has been made in order to solve such inconveniences. An acceleration sensor whose detection sensitivity falls within an allowable error range of a predetermined design value, It is intended to provide a method of manufacturing an acceleration sensor capable of reliably keeping the detection sensitivity of the acceleration sensor within an allowable error range of a design value.

[0009]

According to the acceleration sensor of the present invention, the longitudinal region is divided into a central portion and an end portion, and the directions of polarization at the central portion and the end portion are mutually reversed. and be comprised comprises a bimorph type detection element, the total length of the central portion within that put longitudinally region of the bimorph type detection element (Y), the free length
Is the length ratio (Y / X) to (X) 44% or more?
First, the stress generated by the action of acceleration changes.
It does not include the length divided by the pair boundary line L0
It is characterized by being shorter . In this case, the bimorph-type detection element has a rectangular flat plate shape, and a longitudinal region is divided into a central portion and an end portion where the polarization direction is reversed, and a signal extraction electrode is formed on the outer main surface. And a pair of piezoelectric ceramic plates having an intermediate electrode formed on the inner main surface thereof, and these piezoelectric ceramic plates faced each other with their polarization directions opposite to each other. Then, they are integrally joined via an intermediate electrode.

On the other hand, according to the method of manufacturing an acceleration sensor according to the present invention, a bimorph-type detecting element is manufactured after a position of a boundary line for dividing a central portion and an end portion of a longitudinal direction region is set in advance. A step of measuring the detection sensitivity after manufacturing the acceleration sensor as a sample product in which the mold detection element is incorporated into the case body, and taking the measurement result of the detection sensitivity into consideration to shift the boundary line toward the center or It is characterized by comprising a step of manufacturing a bimorph-type detection element after resetting to a position near the end portion, and a step of manufacturing an acceleration sensor in which the bimorph-type detection element is incorporated in the case body. .

[0011]

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

FIG. 1 is a cutaway perspective view showing the configuration of an acceleration sensor according to the present embodiment, and FIG. 2 is an explanatory view showing a state in which the acceleration sensor is being manufactured. Each of 12 indicates a piezoelectric ceramic plate. Since the overall configuration of the acceleration sensor at this time is not fundamentally different from that of the conventional example, parts and portions in FIGS. 1 and 2 that are the same as those in FIG. 3 are denoted by the same reference numerals.

As shown in FIG. 1, the acceleration sensor according to the present invention has a pair of piezoelectric ceramic plates 11 and 12 each having a rectangular flat plate shape and a signal extraction electrode 1 and an intermediate electrode 2 formed on a main surface. And an intermediate electrode 2 formed on the inner main surfaces of these piezoelectric ceramic plates 11 and 12.
Only the both edges along the longitudinal direction of the detection element 10 formed by joining the two face to face are fixed and supported by a case body 6 having a U-shape in a side view. Then, the respective longitudinal region piezoceramic plates 11 and 12 constituting the detection element 10 is divided only by comprising a central portion 11a by a pair of boundary line L1 is set in terms of the positioning according to the procedure described below, and 12a end portion 11b, which is only divided into a 12b, a central portion 11a in this case,
The total length Y of 12a is a free length in the longitudinal direction area of the detection element 10, that is, a free length X which is a length area where the detection element 10 can flex freely except for both end edges fixed and supported by the case body 6. Length ratio Y / X from 44% to 7
3% in the range between Do Ri and become accompanied to the action of acceleration originating
Classified by a pair of boundary lines L0 where the generated stress changes
The length is set to be shorter than the specified length .

That is, for example, each of the piezoelectric ceramic plates 11 and 12 constituting the detecting element 10 has a total length of 6.4 mm and a thickness of 0.12 mm, and the free length X of the detecting element 10 in the longitudinal direction is set. Is 5.4mm
, The total length Y of the central portions 11a and 12a is from 2.4 mm (Y / X ≒ 44.4%) to 3.9 mm (Y / X ≒ 44.4%).
/X≒72.2%). When the inventors investigated these acceleration sensors, the detection sensitivity of each acceleration sensor was 1.95, which is a predetermined allowable range of design value.
It has been confirmed that it falls within 2.25 mV / G.

The center portions 11a and 12a of the piezoelectric ceramic plates 11 and 12 constituting the detecting element 10, respectively.
a and the end portions 11b, 12b are polarized along respective polarization directions A, B and C, D, which are opposite to each other along the plate thickness direction, and then the center portions 11a, 12a and the end portions 11b, 12b. The polarization directions A, C, B, and D in the above directions are reversed, and are integrally joined. That is, the central portions 11a, 11a, of the piezoelectric ceramic plates 11, 12 constituting the detection element 10 here.
The polarization directions A and C of the piezoelectric ceramic plates 12a are inwardly approaching each other, while the polarization directions B and D of the end portions 11b and 12b are outwardly away from each other. Each of the signal extraction electrodes 1 formed on the outer main surface of each of the external lead electrodes 7 and 8 formed on different end faces of the case body 6 is electrically connected to each other. Note that the polarization directions of the portions 11a, 12a, 11b, 12b of the piezoelectric ceramic plates 11, 12 may be opposite to those described above, and it goes without saying that such a configuration may be employed.

The acceleration sensor having the structure shown in FIG. 1 is manufactured by employing the manufacturing method according to the present invention, that is, manufactured according to the following procedure. And in this case, first of all,
Manufacturing of an acceleration sensor as a sample product is performed.

That is, at the time of manufacturing a sample product, a pair of piezoelectric ceramic plates that have not been subjected to polarization processing, ie, the piezoelectric ceramic plates 3 and 4 in the conventional example, are selected from each lot of the product or within the lot. After selecting the piezoceramic plate to be used, the piezoceramic plate 3, 3,
4. Position and set a boundary line L0 for dividing each longitudinal region into three parts. Then, as shown in FIG. 2, a mask pattern having a size corresponding to each of the central portions 3a, 4a and the end portions 3b, 4b of each of the piezoelectric ceramic plates 3, 4 divided by the pair of boundary lines L0 is prepared. Then, the polarization electrodes 13 are formed on the outer main surfaces of the piezoelectric ceramic plates 3 and 4 using these mask patterns. Subsequently, an intermediate electrode 2 is formed on the inner main surface of each of the piezoelectric ceramic plates 3 and 4,
In addition, by using these electrodes and applying a high voltage, the polarization directions of the central portions 3a, 4a and the end portions 3b, 4b of the longitudinal direction regions of the piezoelectric ceramic plates 3, 4 are inverted from each other. Is performed. FIG. 2 shows only the piezoelectric ceramic plate 3.

Further, after the signal extraction electrode 1 is formed by laminating on the polarization electrode 13 formed on the outer main surface of the piezoelectric ceramic plates 3 and 4 which have been subjected to the polarization processing, these piezoelectric ceramic plates are formed. The integrated detection element 5 is produced by joining the intermediate electrodes 2 formed on the inner main surfaces of the substrates 3 and 4 face-to-face. Subsequently, only the both edges along the longitudinal direction of the detection element 5 are fixedly supported by the case body 6, and each of the signal extraction electrodes 1 formed on the outer main surfaces of the piezoelectric ceramic plates 3 and 4 is connected to the case body. 6. External extraction electrodes 7, 8 formed for different end faces 6
When this is conducted, the acceleration sensor in which the detecting element 5 is incorporated in the case body 6, that is, the acceleration sensor having the same configuration as the conventional example shown in FIG. 3 is manufactured as a sample product. .

When the detection sensitivities of a plurality of acceleration sensors manufactured as sample products are measured, the variation of the detection sensitivities in these sample products becomes clear, and the piezoelectricity in each product lot or in each lot is clarified. It is possible to grasp the material state of the ceramic plate and the state of the processing error. Therefore, taking into account the measurement results of the detection sensitivities obtained by these sample products, the center portions 11a, 11a, of the longitudinal direction regions of the piezoelectric ceramic plates 11, 12 constituting each of the detection elements 10 to be newly manufactured are started. 12a and end portions 11b, 12
The position of the boundary line L1 set for dividing b is shifted toward the center portions 11a, 12a or the end portions 11b, 12b.
Perform setting again to the closer position.

That is, at this time, if the detection sensitivity of the sample product appears to be increasing, the boundary line L1
Is adjusted so as to lower the detection sensitivity of the acceleration sensor by resetting the position of the acceleration sensor to a position closer to the center portions 11a and 12a. On the other hand, if the detection sensitivity of the sample product appears to be lower, the boundary line L1 Is adjusted so as to increase the detection sensitivity of the acceleration sensor by resetting the position toward the end portions 11b and 12b.

Subsequently, as shown in FIG. 2, the central portions 11a, 12a and the ends of the piezoelectric ceramic plates 11, 12 which are taken out of each lot of the product or from within the lot and for which a pair of boundary lines L1 are newly set. A mask pattern having a size corresponding to each of the portions 11b and 12b is prepared, and after using these mask patterns, the polarization electrodes 13 are formed on the outer main surfaces of the piezoelectric ceramic plates 11 and 12, respectively. Form. And each piezoelectric ceramic plate 1
After the intermediate electrode 2 is formed on the inner main surfaces of the piezoelectric ceramic plates 11 and 12, a high voltage is applied to the piezoelectric ceramic plates 11 and
A polarization process is performed in which the polarization directions of the central portions 11a and 12a and the end portions 11b and 12b of the longitudinal region in FIG. In FIG. 2, only one side of the piezoelectric ceramic plate 11 is shown.

Thereafter, the piezoelectric ceramic plates 11, 1
The signal extraction electrode 1 is laminated on the polarization electrode 13 formed on the outer main surface of the second electrode 2. Here, the polarization electrode 13 is formed on the outer main surfaces of the piezoelectric ceramic plates 11 and 12, however,
For example, an integrated signal extraction electrode 1 is formed on the outer main surface of each of the piezoelectric ceramic plates 11 and 12, and the intermediate electrode 2 on the inner main surface is connected to each of the portions 11a, 12a, 11b, 11b.
It is also possible to divide and form them in a state corresponding to each 12b, which is the same when manufacturing a sample product.

Further, after the intermediary electrodes 2 formed on the inner main surfaces of the piezoelectric ceramic plates 11 and 12 are face-to-face joined to each other, an integrated detection element 10 is manufactured.
Only the both edges along the longitudinal direction of the detecting element 10 are fixedly supported by the case body 6 and each piezoelectric ceramic plate 1
When each of the signal extraction electrodes 1 formed on the outer main surfaces of the first and second outer surfaces 1 and 12 is electrically connected to each of the external extraction electrodes 7 and 8 formed on different end faces of the case body 6, the detection element 10 is turned on. Thus, an acceleration sensor having the configuration shown in FIG. Note that, even when acceleration acts on the acceleration sensor according to the present embodiment, similarly to the conventional example, the central portions 11a and 12a and the end portions 11b and 12b of the piezoelectric ceramic plates 11 and 12 that constitute the detection element 10 respectively. Are deformed by the action of inertia force, and these portions 11a, 12a, 1
As a result of the occurrence of tensile stress or compressive stress in each of 1b and 12b, the amount of charge generation increases due to the synergistic effect of the respective polarization directions A to D and the tensile or compressive stress.

[0024]

As described above, the detection sensitivity of the acceleration sensor according to the present invention is such that even if there is a difference in the piezoelectric ceramic plate material or a processing error among the lots of the product or within the lot, these adverse effects are affected. Without receiving
It is within the allowable error range of the predetermined design value. Therefore, there is obtained an effect that a defective product exceeding the allowable error range of the design value is not manufactured, and loss can be prevented. Further, according to the manufacturing method of the present invention, the detection sensitivity of the acceleration sensor can be reliably set within the allowable error range of the design value.

[Brief description of the drawings]

FIG. 1 is a cutaway perspective view showing a configuration of an acceleration sensor according to an embodiment.

FIG. 2 is an explanatory view showing a state during the production.

FIG. 3 is a cutaway perspective view showing a configuration of an acceleration sensor according to a conventional embodiment.

[Explanation of symbols]

 Reference Signs List 10 detecting element (bimorph type detecting element) 11 piezoelectric ceramic plate 11a central part 11b end part 12 piezoelectric ceramic plate 12a central part 12b end part X free length in the longitudinal direction area of detecting element Y total length of central part Y / X length ratio

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01P 15/09 H01L 41/08

Claims (3)

(57) [Claims] 1. An acceleration sensor comprising a bimorph-type detecting element in which a longitudinal region is divided into a central portion and an end portion, and polarization directions of the central portion and the end portion are mutually reversed. a is the total length of the central portion within that put longitudinally region of the bimorph type detection element (Y), the length ratio of the free length (X) (Y /
X) is 44% or more and occurs due to the action of acceleration
Is divided by a pair of boundary lines L0 at which the changing stress changes.
An acceleration sensor characterized in that the acceleration sensor does not include the length and is shorter than the length . 2. The acceleration sensor according to claim 1, wherein the bimorph-type detecting element has a rectangular flat plate shape and a longitudinal direction region is divided into a central portion and an end portion in which a polarization direction is reversed. And a pair of piezoelectric ceramic plates having a signal extraction electrode formed on the outer main surface thereof and an intermediate electrode formed on the inner main surface thereof. An acceleration sensor characterized in that they are faced to each other with their polarization directions opposite to each other and are integrally joined via an intermediate electrode. 3. A method of manufacturing an acceleration sensor comprising a bimorph-type detecting element in which a longitudinal region is divided into a center portion and an end portion in which a polarization direction is reversed, wherein a center portion and an end of the longitudinal region are provided. After setting the position of the boundary line that separates the part and the bimorph-type detection element, the detection is performed after the bimorph-type detection element is manufactured after manufacturing an acceleration sensor as a sample product incorporated in the case body. A step of measuring the sensitivity, a step of resetting the position of the boundary line to a position closer to the center part or an end part in consideration of the measurement result of the detection sensitivity, and manufacturing a bimorph-type detection element; Manufacturing the acceleration sensor in which the mold detecting element is incorporated inside the case body.