JP2007081570A - Piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate inconvenience due to a temperature special dip phenomenon in a piezoelectric device mounted with a tuning fork type piezoelectric vibrating piece while further miniaturizing, to suppress a CI value low and to secure a stable temperature characteristic.
A tuning fork type crystal vibrating piece having a base 8, a plurality of vibrating arms 9 and 10 extending in parallel from the base, and fixing arms 13 and 14 extending in parallel with the vibrating arm from the base. In the piezoelectric vibrator 1 that is fixedly supported by fixing the fixing arm to the base at the mount portion, the in-phase vibration that occurs in the thickness direction of the vibrating piece and the natural frequency of the bending vibration of the vibrating arm when the vibrating piece is excited. The position, length, or hardness of the mount portion was set such that the natural frequency of the mount portion differs in a predetermined operating temperature range.
[Selection] Figure 1

Description

  The present invention relates to a piezoelectric device such as a piezoelectric vibrator in which a tuning fork type piezoelectric vibrating piece is mounted on a package.

  In recent years, in addition to further miniaturization corresponding to miniaturization of electronic equipment on which the piezoelectric device is mounted, the piezoelectric device reduces vibration loss and suppresses the CI (crystal impedance) value, and exhibits good temperature characteristics. High quality and high stability are required. In order to keep the CI value low in the tuning fork type piezoelectric vibrating piece, a structure in which grooves are provided on the front and back main surfaces of the vibrating arm has been developed (see, for example, Patent Documents 1 and 2). In this grooved vibrating arm structure, an electric field parallel to the main surface of the vibrating arm is generated between the electrode formed on the side surface and the bottom surface of the groove and the electrode formed on each side surface of the vibrating arm. Since it greatly improves, the CI value can be kept low even if the resonator element is downsized.

  Even in such a tuning-fork type crystal vibrating piece having a vibrating arm with a grooved structure, if the length of the base portion from which the vibrating arm protrudes is shortened in order to further reduce the size, variations in CI values occur. There is a problem that it is easy to do. Further, when the width of the vibrating arm is reduced, there is a problem that vibration in the thickness direction component occurs in addition to the normal horizontal bending vibration, and vibration energy leaks from the base. In order to solve such a problem, a tuning fork type piezoelectric vibrating piece is known in which a notch portion is formed in a base portion, vibration leakage is reduced while miniaturization is performed, and variation in CI value between elements is stabilized ( For example, see Patent Document 3).

  In addition, in order to prevent mechanical vibration from leaking from the vibrating arm to the base, the tuning fork type piezoelectric vibrating piece includes a plurality of fixing arms extending in parallel with the vibrating arm from the base, and each fixing arm is in the vicinity of the center of gravity. There has been proposed a piezoelectric device configured to be bonded to a substrate at the position (for example, see Patent Document 4). Similarly, a tuning fork type piezoelectric vibration is provided with a support arm portion extending in parallel with the vibrating arm from the base, and the piezoelectric piece is supported on the mounting substrate in a balanced manner by the tip of the support arm portion extending to the vicinity of the center of the vibrating arm portion. A child is known (see, for example, Patent Document 5). These tuning fork type piezoelectric vibrators can suppress the deviation and change of the oscillation frequency even against an external impact.

  Furthermore, the frame has a vibrating arm having a grooved structure and a frame extending in parallel with the vibrating arm from the base portion, and 2 due to the influence of impact or vibration depending on the relationship between the amplification factor of the amplifier circuit and the feedback factor of the feedback circuit. There is known a tuning fork type crystal resonator that suppresses second harmonic mode vibration and oscillates with fundamental wave mode vibration (see, for example, Patent Document 6). In addition, a tuning fork type crystal resonator in which bending vibration and torsional vibration are combined to improve frequency temperature characteristics is known (see, for example, Patent Document 7).

JP-A-56-65517 No. 00-44092 JP 2002-261575 A JP 2004-297198 A JP 2004-357178 A JP 2005-39767 A Japanese Examined Patent Publication No. 62-58175

  In general, a tuning fork type piezoelectric vibrator has good temperature characteristics when the CI value changes linearly in the operating temperature range and the curve fit error shows a value close to 0, as illustrated in FIG. Understood. However, in practice, as illustrated in FIG. 10, there is a case where the CI value abnormally increases at a certain temperature or temperature range, and accordingly, a phenomenon in which the frequency temporarily changes greatly may occur. This is also called a temperature spurious or temperature special dip. If such a phenomenon exists in the operating temperature range, the frequency and CI value of the piezoelectric vibrator become unstable, causing a problem that drive level characteristics are deteriorated and reliability is lowered.

  On the other hand, when the tuning fork type quartz resonator is reduced in size and the width of the vibrating arm is reduced, the rigidity of the vibrating arm is lowered, the vibration becomes unstable, and the CI value tends to increase. Particularly, the reduction in rigidity of the vibrating arm may cause a problem that the vibrating arm collides with the inner wall of the package due to an impact such as dropping. On the other hand, when the thickness of the vibrating arm is increased to increase the rigidity, vibration in the thickness direction occurs in addition to bending vibration, which causes a problem that the vibration characteristics deteriorate.

  However, none of the above-described prior art patent documents mentions the above-mentioned temperature-specific dip phenomenon and its solution. In addition, when the width of the vibrating arm is reduced by downsizing the tuning fork type crystal resonator, the increase in CI value is eliminated without increasing the thickness, and stable frequency characteristics are maintained against impacts such as dropping. It does not disclose an effective way to ensure. As described in Patent Document 6, a method of adding a correction circuit is also conceivable. However, there is a possibility that the entire apparatus becomes complicated and large in size, resulting in an increase in cost.

  Therefore, the present invention has been made in view of the above-described conventional problems, and the object thereof is to achieve further miniaturization in a piezoelectric device such as a piezoelectric vibrator in which a tuning fork type piezoelectric vibrating piece is mounted. The inconvenience due to the temperature-specific dip phenomenon can be eliminated, thereby suppressing the CI value low and ensuring stable temperature characteristics.

  The inventor of the present application conducted and examined various tests on the above-mentioned temperature-specific dip phenomenon. As a result, when the tuning fork type crystal resonator is heated, in the CI value temperature characteristics as shown in FIGS. 9 and 10, the temperature dip phenomenon shifts to the high temperature side, and on the contrary, an impact such as cooling or dropping is applied. Found that it shifted to the low temperature side. As will be described later, this is considered to be related to the hardness, that is, the Young's modulus of the conductive adhesive that fixes and supports the resonator element to the package.

  Further, the inventor of the present application has a tuning fork crystal having a base and a plurality of vibrating arms extending in parallel from the base and fixedly supported on the base by a fixing arm extending in parallel with the vibrating arm from the base. With respect to the vibrator, the vibration state of the resonator element by the mounting structure of the fixing arm was tested and examined. As a result, when each fixing arm is fixed at one point, a temperature characteristic dip phenomenon always occurs in the normal operating temperature range, and each fixing arm is fixed at two points in the extending direction. In some cases, it was found that the fixed position and the length in the extending direction between the two points are related to the occurrence of the temperature characteristic dip phenomenon. Further, it has been found that when the thickness of the resonator element is increased, the temperature characteristic dip phenomenon hardly occurs, and when the thickness is decreased, it is likely to occur.

  Furthermore, the inventor of the present application has conducted various tests and examined the factors that cause these temperature-specific dip phenomena. As a result, it has been found that the two vibration modes of the tuning fork type quartz vibrating piece and the in-phase vibration generated in the thickness direction are related to the occurrence of the temperature special dip phenomenon. That is, the temperature characteristic dip phenomenon does not occur when the natural frequency of the bending vibration is different from the natural frequency of the in-phase vibration in the thickness direction, but occurs when they match. The present invention has been devised based on such knowledge of the present inventor.

  According to the present invention, in order to achieve the above object, a tuning fork type piezoelectric vibrating piece having a base and a plurality of vibrating arms extending in parallel from the base is fixedly supported on the base, and when the piezoelectric vibrating piece is excited, There is provided a piezoelectric device configured such that the natural frequency of the bending vibration of the vibrating arm and the natural frequency of the in-phase vibration generated in the thickness direction of the piezoelectric vibrating piece are different in a predetermined operating temperature range.

  The inventor further includes a tuning fork type piezoelectric vibrating piece that further includes a fixing arm extending in parallel with the vibrating arm from the base portion and is fixedly supported by a mounting portion that fixes the fixing arm to the base. It was found that the natural frequency of the in-phase vibration in the thickness direction can be configured not to match the fixed frequency of the bending vibration depending on the position of the portion, the length of the mount portion in the extending direction of the fixing arm, and the hardness of the mount portion. .

  Therefore, in one embodiment, the piezoelectric vibrating piece has a fixing arm extending in parallel with the vibrating arm from the base, and is fixedly supported by a mounting portion that fixes the fixing arm to the base. There is provided a piezoelectric device in which the position, length, or hardness thereof is set so that the natural frequency of the bending vibration and the natural frequency of the in-phase vibration in the thickness direction are different within a predetermined operating temperature range.

  In one embodiment, the piezoelectric vibrating piece has a pair of vibrating arms and a pair of fixing arms extending on both sides of the vibrating arms, and the mounting portions of the fixing arms are respectively fixed. By having two joint portions separated along the extension direction of the arm, the piezoelectric vibrating piece can be fixedly supported in a balanced manner.

  In another embodiment, the mounting portion is fixed to the fixing arm with a conductive adhesive, and the Young's modulus of the conductive adhesive is appropriately selected, so that the natural frequency of the flexural vibration and the in-phase vibration in the thickness direction are obtained. The hardness of the mount portion can be set so that the natural frequency differs from the natural frequency in a predetermined operating temperature range.

  In another embodiment, the natural frequency of the bending vibration and the natural frequency of the in-phase vibration in the thickness direction are set to be different within a predetermined operating temperature range in consideration of the frequency shift amount due to an external impact. As a result, it is possible to ensure a stable frequency characteristic against an impact.

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 schematically shows the configuration of a tuning fork type crystal resonator to which the present invention is applied. This crystal unit 1 includes a package 2 and a tuning fork type crystal vibrating piece 3 hermetically sealed inside. The package 2 is generally formed in a rectangular box shape from a base 4 in which a plurality of ceramic thin plates 4 a and 4 b are laminated and a rectangular thin plate lid 5. The lid 5 made of an insulating material such as glass or ceramics is airtightly joined to the upper end surface of the base 4 with, for example, a low melting glass 6. Further, an external terminal 7 for connecting to an external circuit is provided on the bottom surface of the base 4.

  The tuning-fork type crystal vibrating piece 3 has a pair of vibrating arms 9 and 10 extending in parallel from the base portion 8, and the front and back main surfaces are respectively directed to the base side end portion, that is, from the crotch portion of the tuning fork to the tip portion. Thus, linear grooves 11 and 12 extending in the longitudinal direction are formed. Further, the quartz crystal vibrating piece 3 has a pair of fixing arms 13 and 14 that extend in parallel with the vibrating arms 9 and 10 from the base 8 on both sides thereof. On both sides of the base 8, notches 15 and 15 for reducing vibration leakage from the vibrating arm to the base are formed on the tip side from the joints with the fixing arms 13 and 14, respectively.

  As shown in FIG. 1C, the grooves 11 and 12 of the vibrating arms 9 and 10 are respectively formed with first electrodes 16 and 17 made of electrode films formed on the side and bottom surfaces thereof, and the vibrations. Second electrodes 18 and 19 are formed on the side surfaces of the arms. The first electrode 16 (17) of one vibrating arm is electrically connected to the second electrode 19 (18) of the other vibrating arm to constitute a drive electrode for vibrating the crystal vibrating piece 3. As will be described later, connection electrodes 20 and 21 are drawn from the drive electrodes to the base 8 and further to the surfaces of the corresponding fixing arms 13 and 14, respectively.

  The crystal vibrating piece 3 is fixed and supported substantially horizontally on the bottom of the space inside the base 4 by the fixing arms 13 and 14. Each fixing arm 13, 14 is connected to a corresponding connection terminal 26, 27, 28 on the bottom surface of the base 4 by joint portions 22, 23, 24, 25 made of a conductive adhesive at two points separated in the extension direction. , 29 and are electrically connected.

  FIG. 2 shows a tuning fork type crystal resonator according to a modification of the present invention. In this modification, each of the fixing arms 13 and 14 is fixed to the corresponding connection terminal 31 on the bottom surface of the base 4 by a joint portion 30 made of a conductive adhesive continuous between two positions separated in the extension direction. 1 is different from the embodiment of FIG.

  In the embodiment of FIG. 1, when a predetermined AC voltage is applied to the drive electrode from the connection terminals 20 and 21, an electric field is alternately generated in the opposite direction between the adjacent first electrodes 16 and 17 and the second electrodes 18 and 19. Then, the vibrating arms 9 and 10 repeatedly perform bending vibration in the horizontal direction (X direction in the drawing) in opposite directions. At the same time, the vibrating arms 9 and 10 generate in-phase vibrations in the thickness direction (Z direction in the figure) using the mount portion formed of the joint portion as a fulcrum.

  FIG. 3 shows a change in frequency related to the hardness of the conductive adhesive, that is, the Young's modulus. As shown in the figure, the frequency of flexural vibration is substantially constant regardless of the value of Young's modulus. On the other hand, the in-phase vibration in the thickness direction (Z direction) varies depending on the value of Young's modulus. In addition, the frequencies of these vibration modes may coincide at a certain Young's modulus. In such a case, a temperature characteristic dip phenomenon occurs in the crystal unit 1.

  As described above, when the tuning fork type crystal resonator is heated, the temperature dip phenomenon shifts to the high temperature side in the CI value temperature characteristics, and conversely, when an impact such as cooling or dropping is applied, the low temperature side Shift to. Therefore, in this embodiment, by setting the Young's modulus of the conductive adhesive so that the natural frequency of the bending vibration and the fixed frequency of the in-phase vibration in the thickness direction are different in the desired operating temperature range, the temperature characteristic dip phenomenon Can be avoided. In addition, the Young's modulus of the conductive adhesive can be set in consideration of not only the temperature change but also the shift amount due to the impact such as dropping, and the frequency characteristics stable against the impact can be ensured.

  Further, in this embodiment, the distance L1 from the base side end edge of the fixing arms 13 and 14, that is, the end edge 8a of the base part 8 to the base side joint parts 22 and 23, is used as the position of the mount part. By selecting, the natural frequency of the bending vibration and the fixed frequency of the in-phase vibration in the thickness direction can be similarly set differently. Furthermore, in this embodiment, the difference between the distance L2 from the edge 8a of the base 8 to the joints 24 and 25 on the distal end side and the distance L1 is set as the length of the mount portion, and the bending portion is appropriately selected. The natural frequency of the vibration and the fixed frequency of the in-phase vibration in the thickness direction can be set differently.

The tuning fork type crystal resonator of FIG. 1 in which the tuning fork type crystal vibrating piece was mounted with a silicone adhesive under the following conditions was tested for changes in natural frequency and CI value temperature characteristics when the thickness was changed.
Vibration piece dimensions: Vibration piece total length = 1450 μm, vibration arm length = 1250 μm, vibration arm width = 60 μm, groove width = 40 μm
Mount position: L1 = 250 μm
Mount length: LM = 500μm
The result is shown in FIG.

  As shown in FIG. 4A, at a thickness of 100 μm, bending vibration and in-phase vibration in the thickness direction are coupled. It can be seen that when the thickness is 100 μm shown in FIG. 4B, the temperature characteristic dip phenomenon occurs, and when the thickness is 120 μm shown in FIG. 4C, the temperature characteristic dip phenomenon does not occur.

Further, with respect to the tuning fork type crystal resonator of FIG. 1 in which the tuning fork type crystal vibrating piece is mounted with a silicone adhesive under the following conditions, the change in natural frequency and the CI value temperature characteristic when the mounting position L1 is changed. Was tested.
Vibration piece dimensions: Vibration piece total length = 1450 μm, vibration arm length = 1250 μm, vibration arm width = 60 μm, groove width = 40 μm, thickness = 100 μm
Mount length: LM = 500μm
The result is shown in FIG.

  As shown in FIG. 5A, the bending vibration and the in-phase vibration in the thickness direction are coupled at the mount position L1 = 250 μm. When the mount position L1 = 250 μm shown in FIG. 5B, a temperature special dip phenomenon occurs. At the mount position L1 = 0 μm shown in FIG. 5C, no temperature special dip phenomenon occurs. I understand that.

Further, with respect to the tuning fork type crystal resonator of FIG. 1 in which the tuning fork type crystal vibrating piece is mounted with a silicone adhesive under the following conditions, the change in natural frequency and the CI value temperature when the mount length LM is changed. The properties were tested.
Vibration piece dimensions: Vibration piece total length = 1450 μm, vibration arm length = 1250 μm, vibration arm width = 60 μm, groove width = 40 μm, thickness = 120 μm
Mount position: L1 = 250 μm
The results are shown in FIGS.

  As shown in FIGS. 6A and 7A, the bending vibration and the in-phase vibration in the thickness direction are coupled at the mount lengths LM = 100 μm and 250 μm. In these cases, the temperature characteristic dip phenomenon occurs as shown in FIGS. On the other hand, at the mount length LM = 500 μm shown in FIG. 8A, the bending vibration and the in-phase vibration in the thickness direction are not coupled, and the temperature characteristic dip phenomenon occurs as shown in FIG. 8B. I understand that it is not. This tendency was the same result even when the mount position was changed.

  The preferred embodiments of the present invention have been described in detail above. However, as will be apparent to those skilled in the art, the present invention can be implemented by adding various changes and modifications to the above embodiments within the technical scope thereof. For example, the tuning fork type piezoelectric vibrating piece can use various piezoelectric single crystal materials such as lithium niobate in addition to quartz.

(A) is a plan view showing a tuning fork type crystal resonator according to the present invention, (B) is a longitudinal sectional view thereof, and (C) is an enlarged sectional view of a vibrating arm taken along line II in FIG. The fragmentary longitudinal cross-sectional view of the tuning fork type crystal resonator by the modification of this invention. The diagram which shows the change of the frequency regarding the Young's modulus of the conductive adhesive which fixes a quartz crystal vibrating piece to a base in the crystal oscillator of FIG. (A) is a diagram showing changes in the natural frequency with respect to changes in the thickness of the quartz crystal resonator element, and (B) and (C) are diagrams showing temperature characteristics at thicknesses of 100 μm and 120 μm, respectively. (A) is a diagram showing changes in the natural frequency with respect to changes in the mounting position of the tuning-fork type quartz vibrating piece, and (B) and (C) show temperature characteristics at the mounting positions L1 = 250 μm and 0 μm, respectively. Diagram. (A) is a diagram showing a change in natural frequency related to the Young's modulus of an adhesive for fixing a quartz crystal resonator element to a base at a mount length LM = 100 μm, and (B) a diagram showing its temperature characteristics. (A) is a diagram showing a change in natural frequency with respect to Young's modulus of an adhesive for fixing a quartz crystal resonator element to a base at a mount length LM = 250 μm, and (B) is a diagram showing its temperature characteristics. (A) is a diagram showing changes in the natural frequency related to the Young's modulus of the adhesive that fixes the quartz crystal resonator element to the base at a mount length LM = 500 μm, and (B) is a diagram showing its temperature characteristics. The diagram which shows the favorable temperature characteristic of a tuning fork type crystal unit. The diagram which shows the temperature characteristic which has the temperature spurious of a tuning fork type crystal resonator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Quartz crystal resonator, 2 ... Package, 3 ... Crystal oscillation piece, 4 ... Base, 4a, 4b ... Ceramic thin plate, 5 ... Cover, 6 ... Low melting glass, 7 ... External terminal, 8 ... Base part, 9, 10 ... Resonating arm 11, 12, ... groove, 13, 14 ... fixing arm, 15 ... notch, 16, 17 ... first electrode, 18, 19 ... second electrode, 20, 21 ... connection electrode, 22-25, 30 ... Junction part, 26-29,31 ... Connection terminal.

Claims (5)

A piezoelectric device in which a tuning fork type piezoelectric vibrating piece having a base and a plurality of vibrating arms extending in parallel from the base is fixedly supported on a base,
When the piezoelectric vibrating piece is excited, the natural frequency of the bending vibration of the vibrating arm and the natural frequency of the in-phase vibration generated in the thickness direction of the piezoelectric vibrating piece are configured to be different within a predetermined operating temperature range. A piezoelectric device characterized by the above.   The piezoelectric vibrating piece has a fixing arm extending in parallel with the vibrating arm from the base portion, and is fixedly supported by a mount portion that fixes the fixing arm to the base. The natural frequency of the bending vibration 2. The piezoelectric device according to claim 1, wherein the position, the length, or the hardness of the mount portion is set so that the natural frequency of the in-phase vibration in the thickness direction is different in a predetermined operating temperature range. .   The piezoelectric vibrating piece includes a pair of the vibrating arms and a pair of fixing arms extending on both sides of the vibrating arms, and the mount portions of the fixing arms are respectively connected to the fixing arms. The piezoelectric device according to claim 2, wherein the piezoelectric device has two joint portions separated along an extension direction.   The mount portion fixes the fixing arm to the base with a conductive adhesive, and the Young's modulus of the conductive adhesive is determined by the natural frequency of the bending vibration and the natural frequency of the in-phase vibration in the thickness direction. The piezoelectric device according to claim 2, wherein the piezoelectric device is set so as to be different in the operating temperature range.   The natural frequency of the flexural vibration and the natural frequency of the in-phase vibration in the thickness direction are set so as to be different within a predetermined operating temperature range in consideration of a frequency shift amount due to an external impact. Item 5. The piezoelectric device according to any one of Items 1 to 4.

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