JP5151823B2 - Piezoelectric vibrating piece, piezoelectric vibrator and oscillator - Google Patents

Description

The present invention particularly relates to a piezoelectric vibrating piece, a piezoelectric vibrator, and an oscillator in which a thickness of a vibrating part is larger than that of a peripheral part.

  2. Description of the Related Art In recent piezoelectric vibrating pieces that are becoming smaller and thinner, a mesa structure is known for the purpose of confining vibration energy and reducing a CI (crystal impedance) value.

  Here, the mesa structure has effects such as confinement of vibration energy and reduction of the CI value as described above when its characteristics act appropriately, and it is possible to reduce superposition of unnecessary modes. However, if the amount of digging of the substrate for obtaining the mesa structure exceeds the appropriate range, the superposition (coupling) of unnecessary modes again increases, and the substrate surface is etched due to etching (progress of crystal defects) or the like. In addition, the outer shape may vary due to over-etching or the like, which adversely affects the vibration characteristics. Accordingly, it has been proposed to provide a piezoelectric vibrating piece in which an optimum value of the amount of substrate digging for obtaining a mesa structure is determined. For example, the techniques disclosed in Patent Documents 1 and 2 are examples thereof.

  Patent Document 1 describes that the length of a quartz substrate is 20 times or more of the thickness of the substrate, and the amount of excavation of the substrate for obtaining a mesa structure is about 10% to 30% of the thickness. ing. When the mesa digging amount and the side ratio (long side dimension / thickness dimension of the quartz substrate) are determined as in Patent Document 1, it is possible to surely reduce the CI value and suppress the unwanted mode coupling. However, the effects of reducing the CI value and suppressing the coupling of unnecessary modes cannot be achieved uniformly if the above requirements are met, and it is known that variations occur due to the relationship between the side ratio and the amount of mesa digging. It has been.

Therefore, as disclosed in Patent Document 2, the inventors of the present application determine the optimum value of the substrate depth y for obtaining the mesa structure based on the dimension x of the long side of the piezoelectric substrate and the thickness dimension t of the piezoelectric substrate in the vibration part. Proposed mesa type piezoelectric vibrating piece.
JP 2006-340023 A Japanese Patent Application No. 2007-104281

  In Patent Document 2, the optimum value of the mesa digging amount y is defined by the long side dimension x of the piezoelectric substrate, and the bending vibration can be suppressed among the unnecessary modes. However, it is difficult to suppress the temperature characteristic of the CI and flatten it only by specifying the long side dimension x of the piezoelectric substrate. Further, as an example of unnecessary modes, it is considered difficult to suppress contour vibration.

Accordingly, an object of the present invention is to provide a piezoelectric vibrating piece, a piezoelectric vibrator, and an oscillator having a configuration in which a CI value is reduced and an unnecessary mode is suppressed to achieve a particularly advantageous effect.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
In order to solve the above-described problem, a piezoelectric vibrating piece according to the first embodiment of the present invention includes a vibrating portion that is thicker than a peripheral portion and excited by thickness-shear vibration on a piezoelectric substrate, and has a long side of the piezoelectric substrate. Is along the X-axis direction of the quartz substrate, the short side of the piezoelectric substrate is along the direction orthogonal to the X-axis direction, the length of the short side of the piezoelectric substrate is Z, the thickness of the vibrating part is t, When the length of the short side of the vibration part is Mz, 15.68 ≦ Z / t ≦ 15.84 and 0.77 ≦ Mz / Z ≦ 0.82 are satisfied.
The piezoelectric vibrating piece according to the second aspect of the present invention, when the piezoelectric substrate is mounted on the mounting substrate by applying a conductive adhesive, extends from the center of the vibrating portion to the outer periphery of the conductive adhesive. When the shortest distance is L, 7 <L / t <21 is satisfied.
The piezoelectric vibrating piece according to the third aspect of the present invention is characterized in that the piezoelectric substrate is an AT-cut quartz substrate.
A piezoelectric vibrator according to a fourth aspect of the present invention is characterized in that the piezoelectric vibrating piece according to any one of the first to third aspects is mounted on a package.
An oscillator according to a fifth aspect of the present invention is characterized in that the piezoelectric vibrating piece according to any one of the first to third aspects and an integrated circuit element are mounted on a package.
An oscillator according to a sixth aspect of the present invention includes the piezoelectric vibrator according to the fourth aspect and an integrated circuit element.
Application Example 1 An AT-cut quartz crystal resonator element according to the present invention has a vibration portion having a thickness dimension larger than that of a peripheral portion formed on a plate surface of a piezoelectric substrate having thickness shear vibration as a main vibration. A mesa-type piezoelectric vibrating piece in which a long side of a portion is an X-axis direction of a crystal crystal and a short side of the piezoelectric substrate and the vibrating portion is perpendicular to the X-axis direction, When the dimension of the short side is Z, the thickness dimension of the piezoelectric substrate in the vibration part is t, and the dimension of the short side in the vibration part is Mz, 15.68 ≦ Z / t ≦ 15.84, An AT-cut quartz crystal vibrating piece characterized by satisfying the relationship of 0.77 ≦ Mz / Z ≦ 0.82.

Thus, by setting it as the structure which specifies the short side dimension Z of a piezoelectric substrate, CI value can be reduced and a temperature characteristic can be made flat. In addition, it is possible to effectively suppress contour vibration among unnecessary modes at a specific temperature.
Application Example 2 When L is the shortest distance from the center of the vibrating portion to the outer periphery of the conductive adhesive applied when mounting the resonator element on the mounting substrate, a relationship of 7 <L / t <21 And the conductive adhesive is not in contact with the vibrating part. The AT-cut quartz crystal vibrating piece according to application example 1, wherein

By setting it as such a structure, CI value can be reduced entirely and the unnecessary mode in a specific temperature range can be suppressed.
Application Example 3 An AT-cut quartz crystal resonator element according to the present invention is characterized in that the AT-cut crystal resonator element described in Application Example 1 or Application Example 2 is mounted and sealed inside a package. .

With such a configuration, it is possible to provide an AT-cut quartz crystal resonator that exhibits the above effects.
Application Example 4 An oscillator according to the present invention is characterized in that an oscillation circuit is formed by the AT-cut quartz crystal resonator described in Application Example 3 and an integrated circuit element.
With such a configuration, an oscillator having the above effects can be provided.

Hereinafter, embodiments of the piezoelectric vibrating piece, the piezoelectric vibrator, and the oscillator of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below are only some of the embodiments of the present invention.

  FIG. 1 is a diagram showing the shape of an AT-cut quartz crystal vibrating piece (hereinafter simply referred to as a piezoelectric vibrating piece) 10 of the present invention. 1A is a diagram illustrating a planar shape of the piezoelectric vibrating piece, and FIG. 1B is a diagram illustrating a cross section taken along the line AA in FIG.

  The piezoelectric vibrating piece 10 of the present embodiment is a mesa type in which a vibrating portion 14 having a thicker thickness than the peripheral portion 16 is formed on the plate surface of the piezoelectric substrate 12 whose main vibration is thickness shear vibration. Specifically, the piezoelectric substrate 12 constituting the piezoelectric vibrating piece 10 according to the present embodiment is a crystal piece cut out at a cut angle called AT cut, and the outer shape thereof and the shape of the vibrating portion 14 are rectangular. Is formed. Further, each side portion of the vibrating portion 14 is formed in parallel with each side portion of the piezoelectric substrate 12 forming the outer shape. In the piezoelectric vibrating piece 10, the long sides of the piezoelectric substrate 12 and the vibrating portion 14 are set in the X-axis direction of the crystal crystal, and the short sides of the piezoelectric substrate 12 and the vibrating portion 14 are along a direction orthogonal to the X-axis direction. Forming.

  Here, the vibration part 14 may be formed so that a stepped part that forms a boundary with the peripheral part 16 is located at an antinode of an amplitude of an unnecessary mode (for example, a bending mode) propagating to the peripheral part 16. This is because the unnecessary mode can be suppressed and the vibration characteristics can be kept good by adopting such a configuration.

  An excitation electrode 18 is formed on the vibration portion 14 of the piezoelectric substrate 12 having such a shape, and a support portion 20 is formed at one end of the peripheral portion 16. A connection electrode 19 is routed between the excitation electrode 18 and the support portion 20.

  Next, a method for forming a piezoelectric vibrating piece as shown in FIG. 1 will be described. First, a protective film such as a resist film is formed on the main surface of a wafer (not shown), and a mask in which a plurality of individual regions are formed is formed by exposure and development. By etching the wafer using this mask, the outer shape of a plurality of piezoelectric substrates is formed on the wafer. Note that the mesa portion (vibrating portion) can be formed by performing a mask formation process and an etching process step by step. After forming the outer shape of the piezoelectric substrate in units, a metal film (for example, gold with chromium as a base) is formed on the main surface of the wafer by using a technique such as vapor deposition or sputtering. Thereafter, a protective film is formed on the metal film, an electrode shape is formed, and etching is performed in the same manner as the outer shape to obtain a desired electrode pattern. The batch-processed piezoelectric substrate is separated into pieces by being separated from the wafer.

  With respect to the piezoelectric vibrating piece 10 having such a configuration, the inventors of the present application change the short side dimension Z of the piezoelectric substrate 12 and the short side dimension Mz of the vibrating portion 14 to show the relationship between the CI value and the temperature in FIG. The following knowledge was obtained.

  FIG. 2 is a graph showing the relationship between the CI value and the temperature when the short side dimension Z of the piezoelectric substrate and the short side dimension Mz of the vibrating portion are changed. Note that the piezoelectric substrate 12 of the present embodiment uses a piezoelectric substrate in which the plate thickness dimension t of the vibrating portion 14 is t = 61.85 μm.

  Here, the ratio (Z / t) of the short side dimension Z to the plate thickness dimension t of the vibrating portion 14 is fixed at the plate thickness dimension t = 61.85 μm, and the short side dimension Z is changed to Z / t = 15.60. , 15.68, 15.76, 15.84. Further, the ratio (Mz / Z) of the short side dimension Mz of the vibration part 14 to the short side dimension Z of the piezoelectric substrate 12 is fixed by fixing the short side dimension Z of the piezoelectric substrate 12 and changing the short side dimension Mz of the vibration part 14. Mz / Z = 0.71, 0.77, 0.82, 0.87. FIG. 2 is a graph showing the relationship between the temperature of each sample and the CI value by preparing samples A1 to D4 in which each of the four types of side ratios of Z / t and Mz / Z is combined. .

  For convenience of explanation, when Mz / Z = 0.71, the graph of Z / t = 1.60 to 15.84 is A1 to A4, and when Mz / Z = 0.77, Z / t = 1. The graph of 60-15.84 is B1-B4, and when Mz / Z = 0.82, the graph of Z / t = 15.60-15.84 is C1-C4, and Mz / Z = 0.87. Then, the graph of Z / t = 15.60-15.84 is set to D1-D4. The vertical axis of each graph indicates the CI value (Ω), and the horizontal axis indicates the temperature (° C.).

  Here, the good temperature characteristic of the CI value of the present embodiment is, for example, that the CI value at a temperature of −40 ° C. to + 120 ° C. is 65Ω or less and the maximum and minimum values of the CI value at −40 ° C. to + 120 ° C. Is set to a range of 20Ω or less. This is because the smaller the CI value, the more stable the vibrating piece. In addition, if the difference between the maximum and minimum CI values is in a range of 20Ω or less, there is little variation and a certain characteristic can be obtained.

  First, when Mz / Z = 0.71, as shown in graphs A1 to A4, when Z / t is changed, the CI value tends to be higher than 60Ω at room temperature, and the main vibration mode The coupling of the unwanted mode to the thickness shear vibration causes a local increase in CI value at a certain temperature. For example, in graph A3, a significant increase in CI value is observed at 50 ° C. or higher, particularly 90 ° C. or higher, which is due to the coupling of unnecessary modes to the main vibration mode.

  Further, when Mz / Z = 0.87, as shown in D1 to D4, the CI value tends to be high as a whole, or significant coupling of unnecessary modes occurs. For example, in the graph D2, the CI value is 100Ω or more at −10 ° C. to + 20 ° C. This is due to the coupling of the unnecessary mode to the main vibration mode. The increase in CI value near 80 ° C. seen in the graphs D3 and D4 is also due to the coupling of unnecessary modes.

  Next, when Mz / Z = 0.77, in the case of B1 (Z / t = 15.60) where the short side dimension Z is small, the CI value increases in a low temperature region of 0 ° C. or lower, but at 0 ° C. or higher, the CI value increases. The value is reduced to 60Ω or less, and the characteristic change is substantially flat, that is, the difference between the maximum value and the minimum value of the CI value is 20Ω or less. In the case of B2 to B4 (Z / t = 15.68 to 15.84), the CI values are all 65Ω or less, and a slight coupling of unnecessary mode occurs in the high temperature range, but the characteristic change is substantially flat. It becomes.

  In addition, when Mz / Z = 0.82, when C1 (Z / t = 15.60) where the short side dimension Z is small, the CI value tends to be high as a whole, and unnecessary mode coupling occurs near 0 ° C. Has occurred. On the other hand, in the case of C2 to C4 (Z / t = 15.68 to 15.84), even if the short side dimension Z is changed, the CI value is about 40Ω at room temperature and 60Ω or less at −40 ° C. to + 120 ° C. Thus, overall reduction and characteristic change is substantially flat from the low temperature region to the high temperature region.

Inferring from the above-described tendency, the range of the short side dimension Z of the piezoelectric substrate and the short side dimension Mz of the vibration part that can reduce the CI value to make the temperature characteristic flat and suppress the unnecessary mode is shown in the graphs B2 to B2. Range of B4 and C2-C4,
That is, 15.68 ≦ Z / t ≦ 15.84, and
It is preferable to set 0.77 ≦ Mz / Z ≦ 0.82.

  Further, the ranges of graphs B2 to B4 and C2 to C4 are all in the range of temperature characteristics with good CI value, the CI value at −40 ° C. to + 120 ° C. is 65Ω or less, and at −40 ° C. to + 120 ° C. The difference between the maximum and minimum CI values satisfies the range of 20Ω or less.

  By setting such a range, it is possible to select a range in which the CI value is reduced and the characteristic change is flat. Further, unwanted mode coupling can be suppressed, and a piezoelectric vibrating piece having good vibration characteristics can be obtained.

  Next, with respect to the piezoelectric vibrating piece of the present invention, the case where the CI value is reduced and the unnecessary mode is suppressed from other aspects will be described. The inventors of the present application have found that the effects of reducing the CI value and suppressing the unnecessary mode for the mesa-type piezoelectric vibrating piece also change depending on the form when the piezoelectric vibrating piece 10 is mounted on a mounting substrate or the like. That is, when the piezoelectric vibrating piece 10 is fixed to the mounting substrate or the like, the CI value is good, but the unnecessary mode tends to be easily used. In such a tendency, when the fixed state is set within a predetermined range, the inventors of the present application can obtain the effect of suppressing the unnecessary mode while obtaining the effect of lowering the CI value in the use range (room temperature). I found the range that can do.

  Therefore, in this embodiment, as shown in FIG. 3, the shortest distance from the center C of the vibrating portion 14 in plan view of the piezoelectric substrate to the outer periphery of the conductive adhesive 22 is defined as L. An appropriate range of the ratio L / t of the shortest distance L from the center C of the vibration part 14 to the outer periphery of the conductive adhesive 22 is determined with respect to the plate thickness dimension t of the vibration part 14.

  FIG. 4 is a graph showing the relationship between the CI value and temperature when the ratio L / t of the shortest distance L from the center C of the vibrating part to the thickness t of the vibrating part is changed. .

  FIG. 4A is a graph showing the relationship between the CI value and the temperature when L / t is set smaller than 7. FIG. According to this, although the coupling of unnecessary modes is considerably suppressed, the CI value is conspicuously increased in the low temperature region due to being strongly influenced by the fixed state of the piezoelectric vibrating piece with respect to the mounting substrate or the like.

  On the other hand, FIG. 4B is a graph showing the relationship between the CI value and the temperature when L / t is set larger than 21. As can be seen from FIG. 4B, the CI value can be suppressed to a very low value of 40Ω or less, but coupling of unnecessary modes is conspicuous in the temperature range of the use range.

  Here, it is desirable that the conductive adhesive 22 is not in contact with the vibrating portion 14. This is because when the conductive adhesive 22 comes into contact with the vibration part 14, the main mode (thickness shear vibration) in the vibration part 14 is suppressed.

As described above, when the L / t value is set to an extreme range such as smaller than 7 or larger than 21, undesirable characteristics such as coupling of unnecessary modes and an increase in CI value may occur. On the other hand, L / t is 7 <L / t <21
In the case of the range, it was confirmed that the increase of the CI value accompanying the change of the temperature region and the coupling of the unnecessary mode were suppressed.

  Therefore, the ratio L / t of the plate thickness dimension t of the vibration part and the shortest distance L from the center C of the vibration part to the outer periphery of the conductive adhesive is in the range of 7 <L / t <21, and the conductive adhesion It is desirable that the agent is not in contact with the vibrating part. By determining within such a range, it is possible to promote a decrease in CI value while suppressing coupling of unnecessary modes.

  Since Z / t, Mz / Z, and L / t interact with the CI value and the unnecessary mode, respectively, by defining them together, it is possible to reduce the CI value and suppress the unnecessary mode. A high effect can be obtained.

  The AT-cut quartz crystal vibrating piece 10 formed as described above can be used as an AT-cut crystal resonator by mounting and sealing inside the package. Specifically, as shown in FIG. 3, the package 30 can be formed of a ceramic material or the like, and a mounting electrode 34 is formed on the bottom surface of the cavity 32. Then, the conductive adhesive 22 is applied on the mounting electrode 34, and the connection electrode 19 of the piezoelectric vibrating piece 10 is disposed and fixed. A lid 36 is attached to the upper part of the package 30 to keep the inside of the package 30 in a nitrogen atmosphere or the like.

  Further, the AT-cut crystal resonator formed as described above can be used as an oscillator by combining with an integrated circuit element. As an example, an oscillator can be formed by mounting an AT-cut quartz crystal resonator and an integrated circuit element (not shown) shown in FIG. 3 on a substrate on which a wiring pattern is formed. In addition, an oscillator package can be formed by enclosing the integrated circuit element together with the piezoelectric vibrating piece 10 in the package shown in FIG.

It is a figure which shows the shape of the AT cut quartz crystal vibrating piece of this invention. It is a graph which shows the relationship between CI value and temperature at the time of changing the short side dimension of a piezoelectric substrate, and the short side dimension of a vibration part. It is explanatory drawing of the AT cut crystal oscillator of this invention. It is a graph which shows the relationship between CI value and temperature at the time of changing ratio L / t of the shortest distance L from the center C of a vibration part with respect to the plate | board thickness dimension t of a vibration part to the outer periphery of a conductive adhesive.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ......... Piezoelectric vibration piece, 12 ......... Piezoelectric substrate, 14 ......... Vibration part, 16 ......... Peripheral part, 18 ......... Excitation electrode, 19 ......... Connection electrode, 20 ...... Support part, 22 ......... Conductive adhesive, 30 ......... Package, 32 ......... Cavity, 34 ......... Mounting electrode, 36 ......... Cover body.

Claims (6)

The piezoelectric substrate is arranged with a vibrating part that is thicker than the peripheral part and excited by thickness-shear vibration,
The long side of the piezoelectric substrate is along the X-axis direction of the quartz substrate,
The short side of the piezoelectric substrate is along a direction orthogonal to the X-axis direction,
The length of the short side of the piezoelectric substrate is Z,
The thickness of the vibrating part is t,
The length of the short side of the vibration part is Mz,
When
15.68 ≦ Z / t ≦ 15.84 ,
0.77 ≦ Mz / Z ≦ 0.82
A piezoelectric vibrating piece characterized by satisfying When mounting the piezoelectric substrate on the mounting substrate by applying a conductive adhesive, when the shortest distance from the center of the vibration portion to the outer periphery of the conductive adhesive is L,
7 <L / t <21
The piezoelectric vibrating piece according to claim 1, characterized by satisfying the. The piezoelectric vibrating piece according to claim 1, wherein the piezoelectric substrate is an AT-cut quartz substrate . A piezoelectric vibrator comprising the piezoelectric vibrating piece according to claim 1 mounted on a package . The piezoelectric vibrating piece according to any one of claims 1 to 3,
An integrated circuit element;
An oscillator characterized by being mounted in a package . A piezoelectric vibrator according to claim 4,
An integrated circuit element;
An oscillator comprising: