JP2014022802A - Tuning-fork type crystal vibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tuning-fork type crystal vibrator in which reduction in electric field efficiency accompanying miniaturization or thinning is prevented and which is capable of having a peak temperature in the vicinity of a desired temperature.SOLUTION: A tuning-fork type crystal vibrator 11 comprises: a pair of vibrating arms 13, 14 extending from a base; grooves 15, 16 recessed in a length direction of the vibrating arms 13, 14; walls 17, 18 forming the grooves 15, 16; and exciting electrodes 19, 20 provided on surfaces of the walls 17, 18. When a linear function is used for approximating a first-order term temperature coefficient of a Young's modulus of the exciting electrodes 19, 20, a first-order term coefficient is denoted by A, a zero-order term coefficient is denoted by B, a room temperature is denoted by T and a Taylor expansion temperature is denoted by T, the temperature characteristics of the exciting electrodes 19, 20 are represented by E(T)=A(T-T)+B. When the minimum thickness of the walls 17, 18 is 6 μm or less and under the condition of A>-20 MPa/°C, a thickness of the exciting electrodes 19, 20 opposed to at least one of the walls 17, 18 is 1/50 or less as thick as the minimum thickness of the walls 17, 18.

Description

  The present invention relates to a small tuning fork type crystal resonator.

  The tuning fork type crystal resonator includes a base portion on which a mounting electrode portion is provided and a pair of vibrating arm portions extending from the base portion, and an excitation electrode is formed on the surface of the pair of vibrating arm portions to be excited. The vibration frequency is obtained. Further, by forming a concave groove along the longitudinal direction of the pair of vibrating arms and forming an excitation electrode along the inner surface of the groove, the electric field efficiency is improved and the equivalent series resistance (R1) is improved. There is also known a tuning-fork type crystal resonator having a structure for achieving the above (see Patent Document 1).

  The frequency temperature characteristic of such a tuning fork type crystal resonator is expressed by a quadratic function or a cubic function, and is designed so that the peak temperature at which the frequency is highest in the normal temperature range is around 25 ° C.

JP 2007-60729 A

  However, as the quartz crystal resonator becomes smaller and thinner, the vertex temperature tends to be lower than 25 ° C. In order to improve this, it is possible to set the apex temperature to around 25 ° C by increasing the X-axis rotation cut angle from the Z-plate of the crystal body, but if the cut angle exceeds 6 ° Conversely, it is known that the peak temperature decreases. In recent miniaturization and thinning of quartz resonators, there is a limit to the adjustment with the cut angle, and it is difficult to maintain the vertex temperature at around 25 ° C.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a tuning fork crystal resonator that can prevent a reduction in electric field efficiency associated with downsizing and thinning, and can have a vertex temperature near a desired temperature.

In order to solve the above problems, a tuning fork type crystal resonator according to the present invention includes a base, a pair of vibrating arms extending from the base, a groove recessed in the longitudinal direction of the vibrating arm, and the groove. And an excitation electrode provided on the surface of the wall. The excitation electrode has a first-order temperature coefficient A and a zero-order term B when the temperature characteristic of Young's modulus is approximated to a linear function. A tuning fork type crystal resonator represented by a temperature characteristic E (T) = A (T−T ₀ ) + B, assuming a room temperature T and a Taylor development temperature T _0, and the minimum thickness of the wall portion is 6 μm or less. In addition, when A> −20 MPa / ° C., the thickness of the excitation electrode facing at least one wall portion is set to 1/50 or less of the minimum thickness of the wall portion.

  According to the tuning fork type crystal resonator of the present invention, even when the wall portion formed by providing the groove portion on the vibrating arm portion has a thickness of 6 μm or less, the thickness of the excitation electrode is set to the thickness of the wall portion. By setting it to 1/50 or less, it is possible to reduce the equivalent resistance value without lowering the peak temperature in the frequency temperature characteristic. As a result, it has become possible to obtain a small crystal resonator having good frequency-temperature characteristics.

It is a perspective view of the tuning fork type crystal resonator of the present invention. FIG. 3 is a plan view of the tuning fork type crystal resonator. It is AA sectional drawing of the said tuning fork type crystal resonator. It is an expanded sectional view of the wall part of the said tuning fork type crystal resonator. It is a graph which shows the relationship between wall thickness and vertex temperature. It is a graph which shows the change of the vertex temperature with respect to ratio of wall thickness and electrode film thickness. It is an experimental data which shows vertex temperature when changing wall thickness, electrode film thickness, and Young's modulus of an excitation electrode. It is a graph which shows the relationship between wall thickness and vertex temperature when the Young's modulus of an excitation electrode is considered.

  As shown in FIGS. 1 and 2, a tuning fork crystal resonator (hereinafter referred to as a crystal resonator) 11 according to the present invention is a quartz crystal having an electric axis as an X axis, a mechanical axis as a Y axis, and an optical axis as a Z axis. The crystal plate cut in the rectangular coordinate system is processed into a tuning fork shape. Further, in the crystal resonator, a crystal plate of an XY′Z ′ coordinate system obtained by rotating an XY plane (Z plate) of a three-dimensional orthogonal coordinate system made of XYZ by −7 to +7 degrees by X axis rotation. Used, the center vibration frequency is set to 32.768 KHz. 3 shows an AA cross section of the crystal unit 11, and FIG. 4 shows an enlarged cross section of the wall portion.

  The crystal unit 11 includes a rectangular base portion 12 that is conductively supported by a mount portion of a package (not shown), and a pair of vibrating arm portions 13 and 14 that extend in parallel from the base portion 12. Further, excitation electrodes 19 and 20 having different polarities extending from the base portion 12 are formed on the vibrating arm portions 13 and 14.

  The vibrating arm portions 13 and 14 are a pair of elongated rectangular pillars extending from one end of the base portion 12 in the Y-axis direction and parallel to the X-axis direction, on the front surface side (+ Z surface) and the back surface side (−Z surface). Grooves 15 and 16 are provided along the respective Y-axis directions. The groove portions 15 and 16 are provided along the + Z plane of the vibrating arm portions 13 and 14 along the longitudinal (Y-axis) direction and the −Z plane along the longitudinal (Y-axis) direction. By providing the groove portions 15 and 16, the vibrating arm portions 13 and 14 are formed with a pair of wall portions 17 and 18 facing the front surface side and the back surface side. Further, continuous excitation electrodes 19 and 20 are formed on the inner side surfaces of the respective wall portions 17 and 18 and the bottom surfaces of the groove portions 15 and 16.

  The groove portions 15 and 16 are recessed from the front surface side and the back surface side of the vibrating arm portions 13 and 14 so that the wall portions 17 and 18 have a thickness of about several μm. The recessed depth d2 is set to be less than ½ of the thickness d1 of the vibrating arm portions 13 and 14 so that the front surface side and the back surface side do not penetrate. The excitation electrodes 19 and 20 cover the entire region where the groove portions 15 and 16 are provided, and are formed along the concave surfaces of the groove portions 15 and 16.

  As shown in FIG. 3, the present invention is intended for a small crystal resonator 11 in which the width W <b> 1 of the vibrating arm portions 13 and 14 is 60 μm or less, and thus each wall portion 17 that can be provided by providing the groove portions 15 and 16. , 18 (wall thickness) t1 is defined to be 6 μm or less.

  By providing the groove portions 15 and 16, the exposed area of the crystal surface of the vibrating arm portions 13 and 14 is widened, and in the wall portions 17 and 18, the excitation electrodes 19 and 18 having different polarities at a short distance of 6 μm or less. Since 20 faces each other, the maximum electric field efficiency can be obtained.

FIG. 5 shows an FEM analysis of the relationship between the wall thickness t1 and the vertex temperature Tp. According to this, the wall thickness t1 and the vertex temperature Tp draw a curve, and when the wall thickness t1 is relatively thick, the change in the vertex temperature Tp is small. On the contrary, when the wall thickness t1 is reduced due to the miniaturization of the crystal unit, the vertex temperature Tp tends to decrease. Note that the Young's modulus of gold was E (T) = A (T−T ₀ ) + 78.67702e3, and the Young's modulus of quartz was calculated from the elastic stiffness constant. The analysis type is based on modal analysis.

  As shown in FIG. 6, in terms of the ratio between the wall thickness t1 and the thickness (electrode film thickness) t2 of the excitation electrodes 19 and 20, the apex temperature is reached when the value of wall thickness t1 / electrode film thickness t2 is 50 or more. Those having a Tp of 25 ° C. or higher are distributed. For this reason, the problem that the apex temperature Tp becomes low can be solved by designing the electrode film thickness t2 to be 1/50 or less of the wall thickness t1. In the range where Tp is 25 ° C. or more, the vertex temperature can be adjusted by reducing the X-axis rotation cut angle of the crystal. Since the wall thickness t1 is reduced, the distance between the excitation electrodes 19 and 20 facing each other with the wall portions 17 and 18 therebetween is reduced, so that the electric field efficiency is increased accordingly. As a result, the equivalent resistance value (R1) decreases, but the apex temperature Tp decreases. However, by changing the electrode film thickness t2, the apex temperature Tp is suppressed from decreasing, and at the same time, R1 also increases. Can be small. This makes it possible to obtain good vibration characteristics even when the crystal resonator is downsized.

The frequency temperature characteristic of the crystal unit 11 is expressed by the following approximate expression, assuming that the third-order temperature coefficient γ, the second-order temperature coefficient β, the first-order temperature coefficient α, the room temperature T, the Taylor development temperature T ₀ , and the frequency F (f). Represented by
Approximate expression Δf (T) / F = γ (T−T ₀ ) ³ + β (T−T ₀ ) ² + α (T−T ₀ )
Further, the vertex temperature (Tp) at this time is expressed by the following equation.
Apex temperature Tp = ((− 2β ± (4β ² −12γα) ^0.5 ) / (6γ)) + T ₀

From the above approximate expression, the relationship with the Young's modulus of the excitation electrodes 19 and 20 is shown below.
Here, when the temperature characteristics of the Young's modulus of the excitation electrodes 19 and 20 are approximated to a linear function, the primary temperature coefficient (Young's modulus temperature coefficient) A, zero-order term B, room temperature T, and Taylor expansion temperature are T ₀ . Then, the relational expression with the ambient temperature is expressed by the following expression. Note that the Taylor development temperature T ₀ = 25 ° C.
E (T) = A (T−T ₀ ) + B

  FIG. 7 shows measurement results in Experiments 1 to 5 in which the values of the electrode film thickness t2 and A are changed with respect to the wall thickness t1, based on the above relational expression. FIG. 8 is a graph showing the measurement results. It is represented by. In Experiments 1 to 5, when the wall thickness t1 is set to 6 μm, 4 μm, and 3 μm, the electrode film thickness t2 is changed in the range of 0.2 to 0.06 μm, and the temperature coefficient A of Young's modulus is − FEM analysis was performed on the apex temperature Tp when the pressure was 20 MPa / ° C., −10 MPa / ° C., and −1 MPa / ° C.

In Experiments 1 to 5, cases where the vertex temperature (Tp) is 25 ° C. or higher are as follows (shaded portion in FIG. 7).
Experiment 1: When wall thickness t1 is 6 μm and A = −20 MPa / ° C., electrode film thickness t2 is 0.12 μm or less Experiment 2: When wall thickness t1 is 6 μm and A = −10 MPa / ° C., electrode film thickness t2 is 0.20 μm or less Experiment 3: When the wall thickness t1 is 6 μm and A = −1 MPa / ° C., the electrode film thickness t2 is 0.20 μm or less. Experiment 4: When the wall thickness t1 is 4 μm and A = −20 MPa / ° C. Film thickness t2 is 0.08 μm or less Experiment 5: When wall thickness t1 is 3 μm and A = −20 MPa / ° C., electrode film thickness t2 is 0.06 μm or less

  From the above experimental results, it can be seen that in the case of A = −20 MPa / ° C., the apex temperature Tp satisfies 25 ° C. or more when the electrode film thickness t2 is 1/50 or less of the wall thickness t1. Further, when the wall thickness t1 is in the range of 6 to 3 μm and A = −10 MPa / ° C. or more, the electrode film thicknesses 19 and 20 are 0.2 μm or less (the electrode film thickness t2 is 1/30 of the wall thickness t1). It was confirmed that the apex temperature Tp satisfies 25 ° C. or higher as the following thickness).

  In addition to gold, silver, copper, nickel, platinum, palladium, or the like can be used as the material for the excitation electrodes 19 and 20 that satisfy the condition of A> −20 MPa / ° C. Examples of the material of the excitation electrodes 19 and 20 that satisfy the condition of A> −10 MPa / ° C. include gold alloy, silver alloy, copper alloy, nickel alloy, platinum alloy, and palladium alloy.

  From the above experimental results, it can be seen that as the wall thickness t1 is thinner, the electrode film thickness t2 has a greater influence on the vertex temperature Tp. That is, the vertex temperature Tp can be shifted to the optimum range by changing the electrode film thickness t2 with respect to the wall thickness t1. In addition, the excitation electrodes 19 and 20 formed on the wall portion 17 located outside the vibrating arm portions 13 and 14 and the wall portion 18 located inside are substantially the same in electrode film thickness t2. However, there is some variation in the actual formation. Similarly, a difference in electrode film thickness may occur between the groove inner wall surface and the vibrating arm side wall surface. In such a case, the excitation electrode having the largest thickness is the reference. Note that Tp is designed in the range of 15 ° C. to 35 ° C. in consideration of usage environment and manufacturing variations.

  The wall portions 17 and 18 are formed by providing the groove portions 15 and 16 in the vibrating arm portions 13 and 14, but since the groove portions 15 and 16 are formed by etching, the opening side is wide and the bottom side is narrow. The cross section is substantially V-shaped or substantially U-shaped. Thus, since the wall thickness t1 is actually not uniform, when setting the electrode film thickness t2, the wall portions 17 and 18 are set with reference to a portion near the opening side of the groove portions 15 and 16 as a reference. preferable.

  In this embodiment, the groove portions 15 and 16 are provided on the front surface side and the back surface side of the vibrating arm portions 13 and 14, respectively, but two or more groove portions are parallel to the same surface of the vibrating arm portions 13 and 14. It can also be provided. Even when there are two or more grooves on the same surface, Tp can be set to around 25 ° C. by establishing the above relationship between the arm wall surface and the opposite groove wall surface.

DESCRIPTION OF SYMBOLS 11 Crystal oscillator 12 Base 13, 14 Vibrating arm part 15, 16 Groove part 17, 18 Wall part 19, 20 Excitation electrode

Claims (5)

A base and a pair of vibrating arms extending from the base; a groove recessed in the longitudinal direction of the vibrating arm; a wall forming the groove; and an excitation electrode provided on a surface of the wall. ,
When the temperature characteristic of Young's modulus is approximated to a linear function, the excitation electrode has a primary temperature coefficient of A, a zero-order term of B, room temperature T, and Taylor expansion temperature T ₀ .
A tuning fork type crystal resonator represented by a temperature characteristic E (T) = A (T−T ₀ ) + B,
When the minimum thickness of the wall portion is 6 μm or less and A> −20 MPa / ° C., the thickness of the excitation electrode facing at least one wall portion is 1/50 or less of the minimum thickness of the wall portion. A tuning fork type crystal resonator. A base and a pair of vibrating arms extending from the base; a groove recessed in the longitudinal direction of the vibrating arm; a wall forming the groove; and an excitation electrode provided on a surface of the wall. ,
When the temperature characteristic of Young's modulus is approximated to a linear function, the excitation electrode has a primary temperature coefficient of A, a zero-order term of B, room temperature T, and Taylor expansion temperature T ₀ .
A tuning fork type crystal resonator represented by a temperature characteristic E (T) = A (T−T ₀ ) + B,
When the minimum thickness of the wall portion is 6 μm or less and A> −10 MPa / ° C., the thickness of the excitation electrode facing at least one wall portion is 1/30 or less of the minimum thickness of the wall portion. A tuning fork type crystal resonator.   The tuning-fork type crystal according to claim 1 or 2, wherein a plurality of groove portions recessed in the longitudinal direction of the vibrating arm portion are provided in each vibrating arm portion, and excitation electrodes are provided on the surfaces of the wall portions forming the respective groove portions. Vibrator.   The excitation electrode is selected from gold, silver, copper, nickel, platinum, palladium, chromium, titanium, molybdenum, and tungsten, or has a laminated structure of these metals. Tuning fork type quartz crystal.   The excitation electrode is selected from gold alloy, silver alloy, copper alloy, nickel alloy, platinum alloy, palladium alloy, or these metals and gold, silver, copper, nickel, platinum, palladium, chromium, titanium, 4. The tuning fork type crystal resonator according to claim 1, wherein the tuning fork crystal resonator has a laminated structure of molybdenum and tungsten.

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