JP2012049631A - Surface acoustic wave resonator, surface acoustic wave oscillator, electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave resonator, a surface acoustic wave oscillator, and an electronic apparatus.SOLUTION: A SAW resonator 70 comprises: a crystal substrate 30 where Euler's angle is set as (-1.5°≤φ≤1.5°, 117°≤θ≤142°, 41.9°≤|ψ|≤49.57°); and an IDT 72 which includes a plurality of electrode fingers 78 arranged in a line in a stripe shape in a propagation direction of a surface acoustic wave generated on the crystal substrate 30, and generates the surface acoustic wave of a stop band upper end mode. On the crystal substrate 30, a plurality of grooves 84 arranged in a line in a stripe shape in the propagation direction of the surface acoustic wave are formed, and the electrode fingers 78 are formed in the inner bottom surfaces of the grooves 84.

Description

  The present invention relates to a surface acoustic wave resonator, a surface acoustic wave oscillator mounted with the surface acoustic wave resonator, and an electronic apparatus, and more particularly, to a surface acoustic wave resonator of a type in which a groove is provided on a substrate surface, and a surface acoustic wave oscillator mounted with the surface acoustic wave resonator. And electronic devices.

  In a surface acoustic wave (SAW) device (for example, a SAW resonator), changes in frequency temperature characteristics are affected by the stop band of the SAW, the cut angle of the quartz substrate, the formation form of the IDT (interdigital transducer), and the like. A large impact.

  For example, Patent Document 1 discloses a configuration that excites each of the upper end mode and the lower end mode of the SAW stop band, and the distribution of each standing wave in the upper end mode and the lower end mode of the stop band.

  Patent Documents 2 to 5 describe that the upper end mode of the stop band in SAW has better frequency temperature characteristics than the lower end mode of the stop band. In Patent Documents 2 and 3, in order to obtain good frequency temperature characteristics in a SAW device using Rayleigh waves, the cut angle of the quartz substrate is adjusted and the normalized film thickness (H / λ) of the electrode is set. It is described that the thickness is increased to about 0.1.

  Patent Document 4 describes that in a SAW device using Rayleigh waves, the cut angle of the quartz substrate is adjusted and the standardized film thickness (H / λ) of the electrode is increased by about 0.045 or more. Yes.

  In addition, Patent Literature 5 uses a rotation Y-cut X-propagation quartz crystal substrate and uses the resonance at the upper end of the stop band to improve the frequency-temperature characteristics as compared with the case of using the resonance at the lower end of the stop band. Are listed.

  In Patent Document 6 and Non-Patent Document 1, in a SAW device using an ST cut quartz substrate, a groove is provided between electrode fingers constituting the IDT and between conductor strips constituting the reflector. Are listed. Non-Patent Document 1 describes that the frequency temperature characteristic changes depending on the depth of the groove.

  Patent Document 7 describes a configuration for making a curve indicating frequency temperature characteristics into a three-dimensional curve in a SAW device using an LST cut quartz substrate, and in a SAW device using a Rayleigh wave. Describes that a substrate having a cut angle having a temperature characteristic as indicated by a three-dimensional curve could not be found.

Japanese Patent Laid-Open No. 11-214958 JP 2006-148622 A JP 2007-208771 A JP 2007-267033 A JP 2002-100959 A Japanese Patent Laid-Open No. 57-5418 Japanese Patent No. 3851336

Manufacturing conditions and characteristics of groove-type SAW resonators (Electrotechnical Society Technical Report MW82-59 (1982))

  As described above, there are a variety of factors for improving the frequency temperature characteristics. In particular, in a SAW device using Rayleigh waves, increasing the film thickness of the electrode constituting the IDT is a factor contributing to the frequency temperature characteristics. It is considered one. However, the applicant of the present application has experimentally found that environmental resistance characteristics such as aging characteristics and temperature shock resistance characteristics deteriorate when the electrode thickness is increased. In addition, when the main purpose is to improve the frequency temperature characteristics, the electrode film thickness must be increased as described above, and this has inevitably deteriorates the aging characteristics and the temperature shock resistance characteristics. It was. This is also true for the Q value, and it has been difficult to achieve a high Q without increasing the electrode film thickness.

  Accordingly, the problems in providing a surface acoustic wave resonator, a surface acoustic wave oscillator, and an electronic device according to the present invention are firstly to achieve good frequency temperature characteristics, secondly to improve environmental resistance characteristics, and thirdly to high Q To get a value.

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.
Application Example 1 A quartz substrate having Euler angles (−1.5 ° ≦ φ ≦ 1.5 °, 117 ° ≦ θ ≦ 142 °, 41.9 ° ≦ | ψ | ≦ 49.57 °); An IDT having a plurality of electrode fingers arranged in stripes in a propagation direction of the surface acoustic wave generated on the quartz substrate and generating the surface acoustic wave in a stop band upper end mode. A plurality of grooves arranged in stripes in the propagation direction of the surface acoustic wave are formed on the quartz substrate, and the electrode fingers are formed on the inner bottom surface of the grooves. Wave resonator.
With the above configuration, a surface acoustic wave resonator having good frequency temperature characteristics and low loss is obtained.

Application Example 2 The surface acoustic wave resonator according to Application Example 1, wherein the IDT is formed of Al or an Al alloy.
When Al or Al alloy is used as the IDT material, the dependence of the surface acoustic wave propagation speed on the thickness of the IDT is reduced, so that variations in the center frequency can be suppressed, yield can be increased, and cost can be suppressed. .

Application Example 3 A surface acoustic wave oscillator comprising the surface acoustic wave resonator according to Application Example 1 or 2 mounted as an oscillation source.
With the above configuration, a surface acoustic wave oscillator with low loss and low cost is obtained.

Application Example 4 An electronic apparatus having the surface acoustic wave resonator according to Application Example 1 or 2 mounted thereon.
With the above configuration, an electronic device with low loss and low cost is obtained.

It is a figure which shows the structure of the SAW device which concerns on embodiment. It is a figure which shows the relationship between stopband upper end mode and lower end mode. It is a graph which shows the relationship between the depth of an electrode finger groove | channel, and the amount of frequency fluctuations in an operating temperature range. It is a graph which shows the difference of the change of the secondary temperature coefficient accompanying the change of the line occupation rate (eta) in the resonance point of a stop band upper end mode, and the resonance point of a stop band lower end mode. It is a graph which shows the relationship between the line occupation rate (eta) and secondary temperature coefficient (beta) at the time of changing the depth of a groove | channel between electrode fingers by making electrode film thickness 0. It is a graph which shows the relationship between the depth of the electrode finger groove | channel where a secondary temperature coefficient becomes 0 when an electrode film thickness is set to 0, and line occupation rate (eta). It is a graph which shows the relationship between line occupation rate (eta) and frequency variation | change_quantity (DELTA) F when an electrode film thickness is set to 0 and the depth of a groove | channel between electrode fingers is changed. It is a graph which shows the relationship of the frequency difference which arises between the depth of the specific electrode finger groove when the depth of the electrode finger groove is shifted by ± 0.001λ, and the SAW resonator caused by the shift. It is a graph which shows the relationship between the depth of the electrode finger groove | channel where a secondary temperature coefficient becomes 0 in the case of changing an electrode film thickness, and line occupation rate (eta). It is the figure which put together the relationship between (eta) 1 in which the secondary temperature coefficient in each electrode film thickness becomes 0, and a groove | channel between electrode fingers in one graph. It is the figure which showed the relationship between the electrode interdigital groove | channel from electrode film thickness H ≒ 0 to H = 0.035 (lambda), and the line occupation rate (eta) with the approximate line. It is a graph which shows the relationship between the line occupation rate (eta) and secondary temperature coefficient (beta) at the time of changing the depth of a groove | channel between electrode fingers by making an electrode film thickness into 0.01 (lambda). It is a graph which shows the relationship between the line occupation rate (eta) and secondary temperature coefficient (beta) in the case where the electrode film thickness is 0.015λ and the depth of the inter-electrode finger groove is changed. It is a graph which shows the relationship between the line occupation rate (eta) and secondary temperature coefficient (beta) in the case where the electrode film thickness is 0.02λ and the depth of the inter-electrode finger groove is changed. It is a graph which shows the relationship between the line occupation rate (eta) and secondary temperature coefficient (beta) in the case where the electrode film thickness is 0.025λ and the depth of the inter-electrode finger groove is changed. It is a graph which shows the relationship between the line occupation rate (eta) and secondary temperature coefficient (beta) in the case where the electrode film thickness is 0.03λ and the depth of the inter-electrode finger groove is changed. It is a graph which shows the relationship between the line occupation rate (eta) and secondary temperature coefficient (beta) at the time of changing the depth of a groove | channel between electrode fingers by making electrode film thickness 0.035 (lambda). It is a graph which shows the relationship between the line occupation rate (eta) and frequency variation (DELTA) F when changing the depth of a groove | channel between electrode fingers by making an electrode film thickness into 0.01 (lambda). It is a graph which shows the relationship between the line occupation rate (eta) and frequency variation (DELTA) F when changing the depth of an electrode finger groove | channel by making electrode film thickness 0.015 (lambda). It is a graph which shows the relationship between line occupation rate (eta) and frequency variation | change_quantity (DELTA) F when the electrode film thickness is 0.02 (lambda) and the depth of a groove | channel between electrode fingers is changed. It is a graph which shows the relationship between the line occupation rate (eta) and frequency variation | change_quantity (DELTA) F in the case where the electrode film thickness is 0.025 (lambda) and the depth of an electrode finger groove is changed. It is a graph which shows the relationship between the line occupation rate (eta) and the amount of frequency fluctuations (DELTA) F when the electrode film thickness is 0.03 (lambda) and the depth of an electrode finger groove | channel is changed. It is a graph which shows the relationship between line occupation rate (eta) and frequency variation | change_quantity (DELTA) F when the electrode film thickness is 0.035 (lambda) and the depth of a groove | channel between electrode fingers is changed. It is a graph which shows the relationship between the electrode finger groove | channel at the time of determining an electrode film thickness and line occupation rate (eta), and Euler angle (psi). It is the figure which put together the graph of the relationship between the electrode finger groove | channel which changed the electrode film thickness, and Euler angle (psi) into one graph. The secondary temperature coefficient β is a graph showing the relationship between -0.01ppm / ℃ ² become the inter-electrode-finger groove and the Euler angle [psi. The secondary temperature coefficient β is a graph showing the relationship between + 0.01 ppm / ° C. ² become the inter-electrode-finger groove and the Euler angle [psi. It is a graph which shows the relationship between Euler angle (theta) and secondary temperature coefficient (beta) in electrode film thickness 0.02 (lambda) and depth of electrode finger groove | channel 0.04 (lambda). It is a graph which shows the relationship between Euler angle (phi) and secondary temperature coefficient (beta). It is a graph which shows the relationship between Euler angle (theta) and Euler angle (psi) from which a frequency temperature characteristic becomes favorable. It is a figure which shows the example of the frequency temperature characteristic data in four test pieces on the conditions where the frequency temperature characteristic became the best. It is a graph which shows the relationship between the level | step difference which is the sum of a groove | channel between electrode fingers, and an electrode film thickness, and CI value. It is a table | surface which shows the example of the equivalent circuit constant and static characteristic in the SAW resonator which concerns on this embodiment. It is impedance curve data in the SAW resonator according to the present embodiment. It is a graph for comparing the relationship between the step and the Q value in the conventional SAW resonator and the relationship between the SAW resonator step and the Q value according to the present embodiment. It is a figure which shows SAW reflection characteristic of IDT and a reflector. It is a graph which shows the relationship between the electrode film thickness in a heat cycle test, and a frequency fluctuation. It is a figure which shows the structure of the SAW oscillator which concerns on embodiment. FIG. 39A shows a surface acoustic wave (SAW) resonator according to a second embodiment, FIG. 39A is a plan view, FIG. 39B is a partially enlarged sectional view of FIG. 39A, and FIG. It is the elements on larger scale of (B). FIG. 40A shows the path of the electric field between the electrode fingers, FIG. 40A shows the path of the electric field between the electrode fingers of the SAW resonator of the first embodiment, and FIG. 40B shows the electrode finger of the SAW resonator of the second embodiment. The electric field path between them is shown.

Hereinafter, embodiments of a surface acoustic wave resonator and a surface acoustic wave oscillator according to the present invention will be described in detail with reference to the drawings.
First, a first embodiment according to a surface acoustic wave (SAW) resonator of the present invention will be described with reference to FIG. 1A is a plan view of a SAW resonator, FIG. 1B is a partially enlarged sectional view, and FIG. 1C is an enlarged view for explaining details in FIG. 1B. FIG.

  The SAW resonator 10 according to the present embodiment is configured based on a quartz substrate 30, an IDT 12, and a reflector 20. As the crystal substrate 30, a crystal substrate whose crystal axes are indicated by an X axis (electrical axis), a Y axis (mechanical axis), and a Z axis (optical axis) is used.

  In this embodiment, the quartz substrate 30 is represented by Euler angles (−1.5 ° ≦ φ ≦ 1.5 °, 117 ° ≦ θ ≦ 142 °, 41.9 ° ≦ | ψ | ≦ 49.57 °). An in-plane rotating ST-cut quartz substrate was adopted. Here, the Euler angle will be described. A substrate represented by Euler angles (0 °, 0 °, 0 °) is a Z-cut substrate having a main surface perpendicular to the Z-axis. Here, φ of Euler angles (φ, θ, ψ) relates to the first rotation of the Z-cut substrate, and the positive rotation angle is the direction rotating from the + X axis to the + Y axis side with the Z axis as the rotation axis. The first rotation angle. Euler's angle θ is related to the second rotation performed after the first rotation of the Z-cut substrate. The X-axis after the first rotation is the rotation axis, and the rotation from the + Y axis after the first rotation to the + Z-axis is performed. This is a second rotation angle in which the direction to perform is a positive rotation angle. The cut surface of the piezoelectric substrate is determined by the first rotation angle φ and the second rotation angle θ. The Euler angle ψ relates to the third rotation performed after the second rotation of the Z-cut substrate. The Z axis after the second rotation is used as the rotation axis, and the second rotation from the + X axis after the second rotation. This is a third rotation angle in which the direction of rotation toward the + Y-axis side after rotation is a positive rotation angle. The propagation direction of SAW is represented by a third rotation angle ψ with respect to the X axis after the second rotation.

  The IDT 12 has a pair of comb-like electrodes 14a and 14b in which base ends of a plurality of electrode fingers 18 are connected by a bus bar 16, and the electrode finger 18 constituting one comb-like electrode 14a (or 14b) and the other The electrode fingers 18 constituting the comb-like electrodes 14b (or 14a) are alternately arranged at a predetermined interval. Here, the electrode finger 18 is disposed in a direction orthogonal to the X ′ axis, which is the propagation direction of the surface acoustic wave. The SAW excited by the SAW resonator 10 configured as described above is a Rayleigh type SAW and vibrates in both the Z axis after the third rotation and the X axis after the third rotation. It has a displacement component. Thus, by shifting the SAW propagation direction from the X axis, which is the crystal axis of the quartz crystal, it is possible to excite the SAW in the stop band upper end mode.

  Here, the relationship between the stop band upper end mode SAW and the lower end mode SAW will be described. In the stop band lower end mode and the upper end mode SAW formed by the regular IDT 12 as shown in FIG. 2 (the electrode finger 18 constituting the IDT 12 is shown in FIG. 2), each standing wave is an antinode (or The positions of the nodes are shifted by π / 2. FIG. 2 is a diagram showing the distribution of standing waves in the stopband upper end mode and lower end mode in the normal type IDT 12.

  According to FIG. 2, as described above, the standing wave in the stop band lower end mode indicated by the solid line has an antinode at the center position of the electrode finger 18, that is, the reflection center position, and the stop band upper end mode indicated by the alternate long and short dash line. The standing wave has a node at the reflection center position.

  A pair of reflectors 20 are provided so as to sandwich the IDT 12 in the SAW propagation direction. As a specific configuration, both ends of a plurality of conductor strips 22 provided in parallel with the electrode fingers 18 constituting the IDT 12 are connected.

  It should be noted that end face reflection type SAW resonators that actively use the reflected wave from the end face of the quartz substrate in the SAW propagation direction, and that the IDT itself excites SAW standing waves by increasing the number of electrode finger pairs of the IDT. In the anti-IDT type SAW resonator, the reflector is not always necessary.

  As the material of the electrode film constituting the IDT 12 and the reflector 20 thus configured, aluminum (Al) or an alloy mainly composed of Al can be used. When an alloy is used as the electrode film material, the metal other than Al as the main component may be 10% or less by weight. When Al or Al alloy is used as the IDT12 material, the dependence of the surface acoustic wave propagation speed on the film thickness of IDT12 is reduced, so that variations in center frequency can be suppressed, yield is increased, and costs are reduced. it can.

  The quartz crystal substrate 30 in the SAW resonator 10 having the above basic configuration is provided with grooves (interelectrode finger grooves) 32 between the electrode fingers of the IDT 12 and between the conductor strips of the reflector 20.

とすると良い。なお溝深さＧについて上限値を定める場合には、図３を参照することで読み取れるように、

の範囲とすると良い。溝深さＧをこのような範囲で定めることにより、動作温度範囲内（−４０℃〜＋８５℃）における周波数変動量を、詳細を後述する目標値としての２５ｐｐｍ以下とすることができるからである。また、溝深さＧについて望ましくは、

の範囲とすると良い。溝深さＧをこのような範囲で定めることにより、溝深さＧに製造上のばらつきが生じた場合であっても、ＳＡＷ共振子１０個体間における共振周波数のシフト量を補正範囲内に抑えることができる。 The groove 32 provided in the quartz substrate 30 has the SAW wavelength in the stop band upper end mode as λ and the groove depth as G.

And good. When the upper limit value is determined for the groove depth G, as can be read by referring to FIG.

The range is good. This is because by defining the groove depth G in such a range, the amount of frequency fluctuation within the operating temperature range (−40 ° C. to + 85 ° C.) can be set to 25 ppm or less as a target value to be described in detail later. . Desirably, the groove depth G is:

The range is good. By determining the groove depth G in such a range, even if manufacturing variations occur in the groove depth G, the shift amount of the resonance frequency among the 10 SAW resonators is suppressed within the correction range. be able to.

Further, as shown in FIG. 1C, the line occupancy η is the line width of the electrode fingers 18 (in the case of only the crystal projections, the width of the projections) L is the pitch λ / between the electrode fingers 18. It is a value divided by 2 (= L + S). Therefore, the line occupancy η can be expressed by Equation 4.

Here, in the SAW resonator 10 according to the present embodiment, the line occupancy η may be determined in a range such as Equation 5. As can be seen from Equation 5, η can be derived by determining the depth G of the groove 32.

の範囲とすることが望ましい。 Further, the film thickness of the electrode film material (IDT 12, reflector 20, etc.) in the SAW resonator 10 according to the present embodiment is as follows:

It is desirable to be in the range.

Further, when the thickness of the electrode film shown in Expression 6 is considered with respect to the line occupation ratio η, η can be obtained by Expression 7.

With respect to the line occupation ratio η, as the electrode film thickness increases, the manufacturing variation in electrical characteristics (particularly the resonance frequency) increases, and when the electrode film thickness H is within the range of Equation 6, the manufacturing variation is within ± 0.04, and H> At 0.035λ, there is a high possibility of manufacturing variations greater than ± 0.04. However, if the electrode film thickness H is within the range of Equation 6 and the variation in the line occupancy η is within ± 0.04, a SAW device with a small secondary temperature coefficient β can be realized. That is, the line occupancy η can be allowed to fall within the range of Formula 8, which is obtained by adding a tolerance of ± 0.04 to Formula 7.

In the SAW resonator 10 according to the present embodiment having the above-described configuration, the secondary temperature coefficient β is within ± 0.01 ppm / ° C. ² , and preferably the SAW operating temperature range is −40 ° C. to + 85 ° C. In addition, it is an object to improve the frequency temperature characteristics to such an extent that the frequency fluctuation amount ΔF within the operating temperature range can be 25 ppm or less. Since the secondary temperature coefficient β is a secondary coefficient in polynomial approximation of a curve indicating the SAW frequency temperature characteristic, a small absolute value of the secondary temperature coefficient means that the amount of frequency fluctuation is small. It can be said that the temperature characteristics are good. The following is a proof using a simulation that the SAW device having the above-described configuration includes an element capable of achieving the object of the present invention.

Note that a SAW resonator using a quartz substrate called ST cut and having the propagation direction as the crystal X-axis direction has a frequency fluctuation amount ΔF within the operating temperature range of about 117 ppm when the operating temperature range is the same. The temperature coefficient β is about −0.030 ppm / ° C. ² . Also, in the case of a SAW resonator using an in-plane rotating ST-cut quartz substrate in which the cut angle and SAW propagation direction of the quartz substrate are set to Euler angles (0, 123 °, 45 °) and the operating temperature range is the same, The frequency fluctuation amount ΔF is about 63 ppm, and the secondary temperature coefficient β is about −0.016 ppm / ° C. ² .

  As described above, the change in the frequency temperature characteristic of the SAW resonator 10 is related to the line occupation ratio η, the electrode film thickness H, the groove depth G, and the like of the electrode fingers 18 in the IDT 12. The SAW resonator 10 according to the present embodiment uses stopband upper end mode excitation.

  FIG. 4 is a graph showing changes in the secondary temperature coefficient β when SAW is propagated through the quartz crystal substrate 30 by changing the line occupancy η. 4A shows the secondary temperature coefficient β in resonance in the stop band upper end mode when the groove depth G is 0.02λ, and FIG. 4B shows the groove depth G of 0.02λ. The secondary temperature coefficient β in the resonance of the stop band lower end mode is shown. 4 (C) shows the secondary temperature coefficient β in the resonance in the stop band upper end mode when the groove depth G is 0.04λ, and FIG. 4 (D) shows the groove depth G being 0. The secondary temperature coefficient β in the resonance of the stop band lower end mode when .04λ is set is shown. The simulation shown in FIG. 4 shows an example in the case where SAW is propagated in some form to the quartz crystal substrate 30 not provided with the electrode film in order to reduce the factor that fluctuates the frequency temperature characteristic. The cut angle of the quartz substrate 30 was Euler angles (0 °, 123 °, ψ). For ψ, a value that minimizes the absolute value of the secondary temperature coefficient β is appropriately selected.

  From FIG. 4, it can be read that the secondary temperature coefficient β greatly changes when the line occupancy η is 0.6 to 0.7 in both the stop band upper end mode and the lower end mode. it can. When the change in the secondary temperature coefficient β in the stop band upper end mode is compared with the change in the secondary temperature coefficient β in the stop band lower end mode, the following can be read. That is, the characteristic of the change in the secondary temperature coefficient β in the stop band lower end mode is deteriorated by changing from the minus side to the minus side (the absolute value of the secondary temperature coefficient β is increased). On the other hand, the change in the secondary temperature coefficient β in the stop band upper end mode is improved by changing from the minus side to the plus side (the absolute value of the secondary temperature coefficient β is reduced). That is.

  From this, it can be said that it is desirable to use the vibration in the stop band upper end mode in order to obtain good frequency temperature characteristics in the SAW device.

  Next, the inventor examined the relationship between the line occupancy η and the secondary temperature coefficient β when the stop band upper end mode SAW was propagated in the quartz substrate with various groove depths G.

  FIG. 5 is a simulation graph showing the relationship between the line occupancy η and the secondary temperature coefficient β when the groove depth G is changed from 0.01λ (1% λ) to 0.08λ (8% λ). It is. From FIG. 5, the point where β = 0 is reached when the groove depth G is 0.0125λ (1.25% λ), that is, the point where the approximate curve indicating the frequency-temperature characteristic shows a cubic curve starts to appear. Can be read. From FIG. 5, there are two η at which β = 0 (point (η1) where β = 0 when η is larger, and point (η2) where β = 0 when η is smaller)). is there. From FIG. 5, it can be read that η2 has a larger fluctuation amount of the line occupation ratio η with respect to the change of the groove depth G than η1.

  About this point, the understanding can be deepened by referring to FIG. FIG. 6 is a graph plotting η1 and η2 at which the secondary temperature coefficient β becomes 0 when the groove depth G is changed. FIG. 6 shows that η1 and η2 become smaller as the groove depth G increases, but η2 is in the range of 0.5λ to 0.9λ when the groove depth G = 0.04λ. It can be read that the amount of variation increases as the graph shown is scaled out. That is, it can be said that η2 has a large fluctuation amount with respect to the change of the groove depth G.

  FIG. 7 is a graph in which the vertical axis in FIG. 5 is replaced with the secondary temperature coefficient β as a frequency variation ΔF. Naturally, it can be seen from FIG. 7 that the frequency variation ΔF decreases at two points (η1, η2) where β = 0. Further, from FIG. 7, it can be read that at two points where β = 0, the frequency fluctuation amount ΔF is suppressed smaller at the point corresponding to η1 in any graph in which the groove depth G is changed. be able to.

  According to the above tendency, for mass-produced products that are prone to errors during manufacturing, it is considered desirable to adopt η1 that has a smaller fluctuation amount at the point where β = 0 with respect to fluctuations in the groove depth G. FIG. 3 shows a graph of the relationship between the frequency variation ΔF and the groove depth G at the point (η1) at which the secondary temperature coefficient β is minimum at each groove depth G. According to FIG. 3, the lower limit value of the groove depth G at which the frequency fluctuation amount ΔF is 25 ppm or less, which is the target value, is 0.01λ, and the range of the groove depth G is more than that, that is, 0. 01 ≦ G.

  In FIG. 3, an example in which the groove depth G is 0.08 or more is also added by simulation. According to this simulation, when the groove depth G is 0.01λ or more, the frequency variation ΔF is 25 ppm or less, and thereafter, as the groove depth G increases, the frequency variation ΔF decreases. However, when the groove depth G is about 0.9λ or more, the frequency variation ΔF increases again, and when it exceeds 0.094λ, the frequency variation ΔF exceeds 25 ppm.

と示すことができる。 The graph shown in FIG. 3 is a simulation in a state where the electrode film such as the IDT 12 and the reflector 20 is not formed on the quartz substrate 30. As will be understood with reference to FIGS. The SAW resonator 10 is considered to be able to reduce the frequency fluctuation amount ΔF when the electrode film is provided. Accordingly, if the upper limit value of the groove depth G is determined, the maximum value in a state where the electrode film is not formed, that is, G ≦ 0.94λ may be set, and the groove depth G suitable for achieving the target is set. As a range,

Can be shown.

  In the mass production process, the groove depth G has a maximum variation of about ± 0.001λ. Therefore, FIG. 8 shows individual frequency fluctuation amounts Δf of the SAW resonator 10 when the groove depth G is shifted by ± 0.001λ when the line occupation ratio η is constant. According to FIG. 8, when G = 0.04λ, when the groove depth G is shifted by ± 0.001λ, that is, when the groove depth is 0.039λ ≦ G ≦ 0.041λ, It can be read that Δf is about ± 500 ppm.

  Here, if the frequency variation Δf is less than ± 1000 ppm, it is considered that the frequency can be adjusted by various frequency fine adjustment means. However, when the frequency fluctuation amount Δf becomes ± 1000 ppm or more, the frequency adjustment affects static characteristics such as Q value and CI (crystal impedance) value and long-term reliability. This leads to a decrease in the yield rate.

When an approximate expression indicating the relationship between the frequency fluctuation amount Δf [ppm] and the groove depth G is derived for the straight line connecting the plots illustrated in FIG. 8, Expression 10 can be obtained.

とすることが望ましいということができる。 Here, when a value of G satisfying Δf <1000 ppm is obtained, G ≦ 0.0695λ. Therefore, preferably as the range of the groove depth G according to the present embodiment,

It can be said that it is desirable.

  Next, FIG. 9 is a graph showing the relationship between η at which the secondary temperature coefficient β = 0, that is, the line occupancy η indicating the tertiary temperature characteristic and the groove depth G. The quartz substrate 30 has Euler angles (0 °, 123 °, ψ). Here, for ψ, an angle at which the frequency temperature characteristic shows a tendency of a cubic curve, that is, an angle at which the secondary temperature coefficient β = 0 is appropriately selected. FIG. 24 shows the relationship between Euler angle ψ and groove depth G when η where β = 0 is obtained under the same conditions as in FIG. In the graph of the electrode film thickness H = 0.02λ in FIG. 24, the plot of ψ <42 ° is not displayed, but the plot of η2 in this graph is ψ = 41.9 ° at G = 0.03λ. ing. With respect to the relationship between the groove depth G and the line occupancy η for each electrode film thickness, plots are obtained based on FIGS.

  From FIG. 9, it can be read that at any film thickness, as described above, η1 has less fluctuation due to the change in the groove depth G than η2. For this reason, η1 was extracted for each film thickness graph in FIG. 9 and summarized in FIG. From FIG. 10, it can be read that η1 is concentrated in the line indicated by the broken line. Further, according to FIG. 10, the plot showing the upper limit of the line occupation ratio η is a SAW resonator having the electrode film thickness H = 0.01λ, and the plot showing the lower limit of the line occupation ratio η is the electrode film thickness H = The SAW resonator is 0.035λ. That is, it can be said that as the electrode film thickness H is increased, the line occupancy η at which the secondary temperature coefficient β = 0 can be reduced.

Based on these, when the approximate expression is obtained for each of the plot indicating the upper limit and the plot indicating the lower limit of the line occupancy η, Expression 10 and Expression 11 can be derived.

From Equations 12 and 13, it can be said that η can be determined within the range of Equation 14 in the range surrounded by the broken line in FIG.

Here, when the secondary temperature coefficient β is allowed to be within ± 0.01 ppm / ° C. ² , the secondary temperature coefficient β is within ± 0.01 ppm / ° C. ^{2 by} satisfying both Equation 11 and Equation 14. It was confirmed.

  In addition, for the SAW resonator 10 in which the electrode film thicknesses H≈0, 0.01λ, 0.02λ, 0.03λ, and 0.035λ based on Expressions 12 to 14, the groove depth G and β = 0, respectively. FIG. 11 shows the relationship with the line occupancy η as an approximate straight line. The relationship between the groove depth G and the line occupancy η in the quartz crystal substrate 30 without the electrode film is as shown in FIG.

A relational expression between the groove depth G and the line occupancy η where the frequency temperature characteristic is good based on an approximate expression showing an approximate straight line based on the electrode film thickness H is as shown in Expression 15.

With respect to the line occupation ratio η, as the electrode film thickness increases, the manufacturing variation in electrical characteristics (particularly the resonance frequency) increases, and when the electrode film thickness H is within the range of Equation 6, the manufacturing variation is within ± 0.04, and H> At 0.035λ, there is a high possibility of manufacturing variations greater than ± 0.04. However, if the electrode film thickness H is within the range of Equation 6 and the variation in the line occupancy η is within ± 0.04, a SAW device with a small secondary temperature coefficient β can be realized. That is, when the secondary temperature coefficient β is set within ± 0.01 ppm / ° C. 2 in consideration of manufacturing variation of the line occupancy, the line occupancy η is an equation obtained by adding a tolerance of ± 0.04 to Equation 15. A range of up to 16 is acceptable.

  12 to 17, the electrode film thicknesses are 0.01λ (1% λ), 0.015λ (1.5% λ), 0.02λ (2% λ), and 0.025λ (2.5% λ, respectively). ), 0.03λ (3% λ), 0.035λ (3.5% λ), and the relationship between the line occupancy η and the secondary temperature coefficient β when the groove depth G is changed. A graph is shown.

  18 to 23 are graphs showing the relationship between the line occupancy η and the frequency variation ΔF in the SAW resonator 10 corresponding to FIGS. 12 to 17. Note that all quartz substrates have Euler angles (0 °, 123 °, ψ), and an angle that minimizes ΔF is appropriately selected for ψ.

  Here, FIG. 12 is a diagram showing the relationship between the line occupancy η and the secondary temperature coefficient β when the electrode film thickness H is 0.01λ, and FIG. 18 shows the electrode film thickness H is 0.01λ. It is a figure which shows the relationship between the line occupation rate (eta) in the case of having performed, and frequency variation amount (DELTA) F.

  FIG. 13 is a diagram showing the relationship between the line occupancy η and the secondary temperature coefficient β when the electrode film thickness H is 0.015λ, and FIG. 19 shows the electrode film thickness H is 0.015λ. It is a figure which shows the relationship between the line occupation rate (eta) in case, and frequency variation amount (DELTA) F.

  FIG. 14 is a diagram showing the relationship between the line occupancy η and the secondary temperature coefficient β when the electrode film thickness H is 0.02λ, and FIG. 20 shows the electrode film thickness H is 0.02λ. It is a figure which shows the relationship between the line occupation rate (eta) in case, and frequency variation amount (DELTA) F.

  FIG. 15 is a diagram showing the relationship between the line occupancy η and the secondary temperature coefficient β when the electrode film thickness H is 0.025λ, and FIG. 21 shows the electrode film thickness H is 0.025λ. It is a figure which shows the relationship between the line occupation rate (eta) in case, and frequency variation amount (DELTA) F.

  FIG. 16 is a diagram showing the relationship between the line occupancy η and the secondary temperature coefficient β when the electrode film thickness H is 0.03λ, and FIG. 22 shows the electrode film thickness H is 0.03λ. It is a figure which shows the relationship between the line occupation rate (eta) in case, and frequency variation amount (DELTA) F.

  FIG. 17 is a diagram showing the relationship between the line occupancy η and the secondary temperature coefficient β when the electrode film thickness H is 0.035λ, and FIG. 23 shows the electrode film thickness H is 0.035λ. It is a figure which shows the relationship between the line occupation rate (eta) in case, and frequency variation amount (DELTA) F.

In these figures (FIGS. 12 to 23), although there is a slight difference in any of the graphs, the line occupancy η, the secondary temperature coefficient β, and the line occupancy of only the quartz substrate 30 are ascertained. It can be seen that the graph is similar to FIGS. 5 and 7, which are graphs showing the relationship between the rate η and the frequency variation ΔF.
That is, it can be said that the effect according to the present embodiment can also be achieved in the propagation of the surface acoustic wave in the crystal substrate 30 alone excluding the electrode film.

  FIG. 25 summarizes the relationship between ψ obtained by η1 and the groove depth G in the graph shown in FIG. The reason for selecting η1 is as described above. As shown in FIG. 25, even when the film thickness of the electrode film changes, there is almost no difference in the angle of ψ, and the optimum angle of ψ may change according to the variation of the groove depth G. I understand. This can also be said to support that the ratio of the change in the secondary temperature coefficient β is high due to the form of the crystal substrate 30.

In the same manner as described above, we obtain the relationship between the secondary temperature coefficient β = -0.01ppm / ℃ ² become ψ and β = + 0.01ppm / ℃ ² become grooves for ψ depth G, 26, 27 Summarized in When the angle of ψ that can satisfy −0.01 ≦ β ≦ + 0.01 is obtained from these graphs (FIGS. 25 to 27), the preferable angle range of ψ under the above conditions is 43 ° <ψ <45. It can be defined as °, more preferably 43.2 ° ≦ ψ ≦ 44.2.

  Next, FIG. 28 shows a change in the secondary temperature coefficient β when the angle θ is changed, that is, the relationship between θ and the secondary temperature coefficient β. Here, the SAW device used for the simulation is a quartz substrate in which the cut angle and the SAW propagation direction are represented by Euler angles (0, θ, ψ) and the groove depth G is 0.04λ, and the electrode thickness H Is 0.02λ. As for ψ, a value that minimizes the absolute value of the secondary temperature coefficient β was appropriately selected within the above-described angle range based on the set angle of θ. Further, η was set to 0.6383 according to the above formula 15.

Under such conditions, FIG. 28 showing the relationship between θ and the secondary temperature coefficient β shows that the absolute value of the secondary temperature coefficient β is 0. As long as θ is in the range of 117 ° to 142 °. It can be read that it is within the range of 01 ppm / ° C. ² . Therefore, it can be said that the SAW resonator 10 having good frequency temperature characteristics can be configured by setting θ within the range of 117 ° ≦ θ ≦ 142 ° in the above set values.

  FIG. 29 shows a crystal substrate 30 with Euler angle display (φ, 123 °, 43.77 °), a groove depth G of 0.04λ, an electrode film thickness H of 0.02λ, and a line occupancy η. It is a graph which shows the relationship between the angle of (phi), and secondary temperature coefficient (beta), when it is set to 0.65.

  From FIG. 29, when φ is −2 ° and + 2 °, the secondary temperature coefficient β is lower than −0.01, but φ is −1.5 ° to + 1.5 °. If it is within the range, it can be reliably read that the absolute value of the secondary temperature coefficient β is within the range of 0.01. Therefore, by setting φ within the range of −1.5 ° ≦ φ ≦ + 1.5 °, preferably −1 ° ≦ φ ≦ + 1 ° at the set values as described above, good frequency temperature characteristics can be obtained. The SAW resonator 10 can be configured.

In the above description, φ, θ, and ψ each derive an optimum value range in relation to the groove depth G under certain conditions. On the other hand, FIG. 30 shows a very desirable relationship between θ and ψ that minimizes the amount of frequency fluctuation between −40 ° C. and + 85 ° C., and an approximate expression is obtained. According to FIG. 30, the angle of ψ changes as the angle of θ increases, and rises to draw a cubic curve. In the example of FIG. 30, ψ when θ = 117 ° is 42.79 °, and ψ when θ = 142 ° is 49.57 °. When these plots are shown as approximate curves, they become curves shown by broken lines in FIG.

  From this, ψ can be determined by defining θ, and the range of ψ when the range of θ is 117 ° ≦ θ ≦ 142 ° is 42.79 ° ≦ ψ ≦ 49.57 °. it can. In the simulation, the groove depth G and the electrode film thickness H were G = 0.04λ and H = 0.02λ, respectively.

  For the reasons described above, by configuring the SAW resonator 10 under various conditions in the present embodiment, a SAW resonator capable of realizing a good frequency temperature characteristic satisfying the target value can be obtained.

  Further, in the SAW resonator 10 according to the present embodiment, as shown in Equation 6 and FIGS. 12 to 23, the frequency temperature characteristic is obtained after setting the thickness H of the electrode film in the range of 0 <H ≦ 0.035λ. We are trying to improve. This is to improve the frequency temperature characteristics while maintaining the environmental resistance characteristics, unlike the conventional technique in which the film thickness H is extremely increased to improve the frequency temperature characteristics. FIG. 37 shows the relationship between the electrode film thickness (Al electrode film thickness) and the frequency fluctuation in the heat cycle test. The result of the heat cycle test shown in FIG. 37 is that the SAW resonator was exposed to a −55 ° C. atmosphere for 30 minutes, then the temperature was raised to + 125 ° C. and exposed for 30 minutes, and the cycle was continued 8 times. Is. From FIG. 37, compared with the case where the electrode film thickness H is set to 0.06λ and no inter-electrode finger groove is provided, in the range of the electrode film thickness H of the SAW resonator 10 according to this embodiment, the frequency variation (F variation). ) Can be read as 1/3 or less. In FIG. 37, all the plots are H + G = 0.06λ.

  In addition, a high-temperature storage test in which the SAW resonator manufactured under the same conditions as in FIG. 37 was left in an atmosphere at 125 ° C. for 1000 hours was compared with a conventional SAW resonator (H = 0.06λ and G = 0). The SAW resonator according to this embodiment (H = 0.03λ and G = 0.03λ, H = 0.02λ and G = 0.04λ, H = 0.015λ, G = 0.045λ, H = 0. It was confirmed that the amount of frequency fluctuation before and after the test (4 conditions of 01λ and G = 0.05λ) was 1/3 or less.

  Under the above conditions, H + G = 0.067λ (aluminum film thickness 2000 mm, groove depth 4700 mm), IDT line occupancy ηi = 0.6, reflector line occupancy ηr = 0.8, Euler angle (0 °, 123 °, 43.5 °), 120 pairs of IDTs, intersection width 40λ (λ = 10 μm), 72 reflectors (per side) (36 pairs), no inclination angle of electrode fingers (electrodes The SAW resonator 10 manufactured under the condition that the finger arrangement direction and the SAW phase velocity direction match) exhibits frequency-temperature characteristics as shown in FIG.

  FIG. 31 is a plot of frequency temperature characteristics with the number of test pieces n = 4. According to FIG. 31, it can be read that the frequency fluctuation amount ΔF in the operating temperature range by these test pieces is suppressed to about 20 ppm or less.

  In the present embodiment, the influence of the groove depth G and the electrode film thickness H on the frequency temperature characteristics has been described. However, the depth (step) obtained by combining the groove depth G and the electrode film thickness H also affects the static characteristics such as equivalent circuit constants and CI values, and the Q value. For example, FIG. 32 is a graph showing the relationship between the step and the CI value when the step is changed from 0.062λ to 0.071λ. According to FIG. 32, it can be read that the CI value converges when the step is set to 0.067λ, and does not improve (is not lowered) even when the step is further increased.

  FIG. 33 summarizes the frequencies, equivalent circuit constants, and static characteristics of the SAW resonator 10 exhibiting frequency temperature characteristics as shown in FIG. Here, F is a frequency, Q is a Q value, γ is a capacitance ratio, CI is a CI (Crystal Impedance) value, and M is a figure of merit (Figure of Merit).

  FIG. 35 shows a graph for comparing the relationship between the step and the Q value in the conventional SAW resonator and the SAW resonator 10 according to the present embodiment. In FIG. 35, the graph indicated by the bold line shows the characteristics of the SAW resonator 10 according to the present embodiment, and a groove is provided between the electrode fingers and the resonance in the stop band upper end mode is used. . A graph indicated by a thin line shows the characteristics of a conventional SAW resonator, and uses a stop band upper end mode resonance without providing a groove between electrode fingers. As is apparent from FIG. 35, when a groove is provided between the electrode fingers and the resonance in the stop band upper end mode is used, the gap between the electrode fingers is in a region where the step (G + H) is 0.0407λ (4.07% λ) or more. Thus, a higher Q value can be obtained than in the case of using the stop-band lower-end mode resonance without providing a groove.

The basic data of the SAW resonator according to the simulation is as follows.
Basic data H of the SAW resonator 10 according to the present embodiment: 0.02λ
G: Change IDT line occupancy ηi: 0.6
Reflector line occupancy ηr: 0.8
Euler angles (0 °, 123 °, 43.5 °)
Logarithm: 120
Crossing width: 40λ (λ = 10μm)
Number of reflectors (per one side): 60
No inclination angle of electrode fingers Basic data of conventional SAW resonator H: Change G: Zero IDT line occupancy ηi: 0.4
Reflector line occupancy ηr: 0.3
Euler angles (0 °, 123 °, 43.5 °)
Logarithm: 120
Crossing width: 40λ (λ = 10μm)
Number of reflectors (per one side): 60
No electrode finger tilt angle

  Referring to FIGS. 33 and 35 for comparing the characteristics of these SAW resonators, it can be understood how the SAW resonator 10 according to the present embodiment has a high Q. Such a high Q is considered to be due to an improvement in the energy confinement effect, for the following reason.

の関係を満たすように設定すれば良い。これにより、ＩＤＴ１２のストップバンド上端の周波数ｆｔ２において、反射器２０の反射係数Γが大きくなり、ＩＤＴ１２から励振されたストップバンド上端モードのＳＡＷが、反射器２０にて高い反射係数でＩＤＴ１２側に反射されるようになる。そしてストップバンド上端モードのＳＡＷのエネルギー閉じ込めが強くなり、低損失な共振子を実現することができる。 In order to efficiently confine the surface acoustic wave excited in the upper end mode of the stop band, the frequency ft2 at the upper end of the stop band of the IDT 12 and the frequency fr1 at the lower end of the stop band of the reflector 20 and the reflector as shown in FIG. What is necessary is just to set between the frequency fr2 of 20 stopband upper ends. That is,

It may be set so as to satisfy the relationship. As a result, the reflection coefficient Γ of the reflector 20 becomes large at the frequency ft2 at the upper end of the stop band of the IDT 12, and the SAW in the stop band upper end mode excited from the IDT 12 is reflected by the reflector 20 toward the IDT 12 with a high reflection coefficient. Will come to be. And the energy confinement of the SAW in the stop band upper end mode becomes stronger, and a low-loss resonator can be realized.

  On the other hand, the relationship between the frequency ft2 at the upper end of the stop band of the IDT 12, the frequency fr1 at the lower end of the stop band of the reflector 20, and the frequency fr2 at the upper end of the stop band of the reflector 20 is set to a state of ft2 <fr1 or fr2 <ft2. If set, the reflection coefficient Γ of the reflector 20 becomes small at the stop band upper end frequency ft2 of the IDT 12, and it becomes difficult to realize a strong energy confinement state.

  Here, in order to realize the state of Expression 18, it is necessary to shift the frequency of the stop band of the reflector 20 to a higher frequency side than the stop band of the IDT 12. Specifically, this can be realized by making the arrangement period of the conductor strips 22 of the reflector 20 smaller than the arrangement period of the electrode fingers 18 of the IDT 12. As another method, the film thickness of the electrode film formed as the conductor strip 22 of the reflector 20 is made thinner than the film thickness of the electrode film formed as the electrode finger 18 of the IDT 12, or between the electrode fingers of the IDT 12 This can be realized by making the depth of the groove between the conductor strips of the reflector 20 shallower than the depth of the groove. Also, a combination of these methods may be applied.

  In addition, according to FIG. 33, it can be said that high figure of merit M can be obtained in addition to high Q. FIG. 34 is a graph showing the relationship between impedance Z and frequency in the SAW resonator obtained in FIG. From FIG. 34, it can be read that there is no useless spurious near the resonance point.

  In the above embodiment, the IDT 12 constituting the SAW resonator 10 is shown such that all the electrode fingers cross each other alternately. However, the SAW resonator 10 according to the present invention can have a considerable effect only by the quartz substrate. For this reason, even if it is a case where the electrode finger 18 in IDT12 is thinned, the same effect can be produced.

  Further, the grooves 32 may be partially provided between the electrode fingers 18 or between the conductor strips 22 of the reflector 20. In particular, since the central portion of the IDT 12 having a high vibration displacement has a dominant influence on the frequency temperature characteristics, the groove 32 may be provided only in that portion. Even with such a structure, the SAW resonator 10 having good frequency-temperature characteristics can be obtained.

  Moreover, in the said embodiment, it described that the alloy which has Al or Al as a main component was used as an electrode film. However, the electrode film may be configured using other metal materials as long as the metal can achieve the same effect as the above embodiment.

  The above embodiment is a one-terminal-pair SAW resonator provided with only one IDT, but the present invention can also be applied to a two-terminal-pair SAW resonator provided with a plurality of IDTs. The present invention is also applicable to other types of dual mode SAW filters and multimode SAW filters.

  Next, a SAW oscillator according to the present invention will be described with reference to FIG. As shown in FIG. 38, the SAW oscillator according to the present invention accommodates the above-described SAW resonator 10, an IC (integrated circuit) 50 that controls driving by applying a voltage to the IDT 12 of the SAW resonator 10, and the like. Package. In FIG. 38, FIG. 38 (A) is a plan view excluding the lid, and FIG. 38 (B) is a view showing an AA cross section in FIG. 38 (A).

  In the SAW oscillator 100 according to the embodiment, the SAW resonator 10 and the IC 50 are accommodated in the same package 56, the electrode patterns 54 a to 54 g formed on the bottom plate 56 a of the package 56, and the comb-like electrode 14 a of the SAW resonator 10. 14b and the pads 52a to 52f of the IC 50 are connected by a metal wire 60. The cavity of the package 56 that houses the SAW resonator 10 and the IC 50 is hermetically sealed by the lid 58. With such a configuration, the IDT 12 (see FIG. 1), the IC 50, and an external mounting electrode (not shown) formed on the bottom surface of the package 56 can be electrically connected. In addition, the SAW resonator 10 of the present embodiment can be mounted on electronic devices such as a mobile phone, a hard disk, a server, a computer, a wired / wireless base station, and an in-vehicle communication device.

  FIG. 39 shows a surface acoustic wave (SAW) resonator according to the second embodiment. 39A is a plan view, FIG. 39B is a partially enlarged cross-sectional view of FIG. 39A, and FIG. 39C is a partially enlarged view of FIG. 39B. The surface acoustic wave (SAW) resonator 70 of the second embodiment uses the same quartz crystal substrate 30 as that of the first embodiment, and IDTs 72 (electrode fingers 78, bus bars 76, combs) that excite the surface acoustic wave of the stop band upper end mode. The tooth-like electrodes 74a and 74b) and the reflector 80 (conductor strip 82) are formed in common with the first embodiment. However, the difference is that the electrode finger 78 is formed on the inner bottom surface of the groove 84 formed in a stripe shape in the propagation direction of the Rayleigh wave. Therefore, the surface acoustic wave excitation position of the SAW resonator 70 of the second embodiment is the inner bottom surface of the groove 84.

  Similarly, a groove (not shown) is formed at a position where the bus bar 76 and the reflector 80 (conductor strip 82) are formed, and the bus bar 76 and the reflector 80 (conductor strip 82) are formed on the inner bottom surface of the groove (not shown). Is formed. The shapes and orientations of the IDT 72 and the reflector 80 are the same as those of the IDT 12 and the reflector 20 of the first embodiment, respectively. In the SAW resonator 70 of this embodiment, a step (D = G−H) is formed by the difference between the depth (G) of the groove 84 and the film thickness (H) of the electrode finger 78. Further, the line occupation ratio η (η = L / (L + S)) is defined by the width L of the electrode fingers 78 and the width S between the electrode fingers 78, and the value is optimized for the frequency temperature characteristics as in the first embodiment. Adjusted for. Note that this embodiment can also be applied to the above-described SAW resonator 100 and electronic devices.

  In the manufacturing process of the SAW resonator 70 of the second embodiment, a resist film (not shown) is applied on the quartz substrate 30 and a photomask (not shown) corresponding to the shape of the groove 84, IDT 72, and reflector 80 is used. The resist film (not shown) is exposed to light, and the exposed resist film (not shown) is removed. Then, the portion where the quartz substrate 30 is exposed is etched to the depth of the groove 84, and an electrode material (not shown) such as Al is deposited by sputtering or the like. At this time, an electrode material (not shown) is deposited on the resist film (not shown) remaining without being removed. Finally, the resist film (not shown) remaining on the quartz substrate 30 is dissolved, and the resist film (not shown) is removed together with the electrode material (not shown) deposited on the resist film (not shown). 70 is formed.

  Here, although the surface acoustic wave propagates on the surface of the quartz substrate 30, the surface shape of the quartz substrate 30 excluding the IDT 72 and the reflector 80 is qualitative between the first embodiment and the second embodiment. There is no particular difference, and only the formation positions of the IDTs 12 and 72 are different from each other. Therefore, there is no difference in the propagation path of the surface acoustic wave. Therefore, when the same AC voltage is applied to the IDTs 12 and 72 of the first embodiment and the second embodiment, the surface acoustic waves generated in the SAW resonators have a phase difference of λ / 4. It is considered that there is no difference in the characteristics. Therefore, the secondary temperature coefficient of the SAW resonator 70 can be adjusted by adjusting the film thickness of the IDT 72, the depth of the groove 84, and the line occupancy η as in the first embodiment. And a low-loss SAW resonator 70 can be constructed.

  FIG. 40 shows the path of the electric field between the electrode fingers. FIG. 40A shows an electric field path between electrode fingers of the SAW resonator of the first embodiment, and FIG. 40B shows an electric field path between electrode fingers of the SAW resonator of the second embodiment.

となる。 Consider a case in which the AC voltage V ₀ is applied to one IDT 12, 72 and the other IDT 12, 72 is grounded in the first embodiment and the second embodiment. In the case of the first embodiment, the electric field E ₁ applied between the electrode fingers 18 is the strongest in the path 86 from one electrode finger 18 to the other electrode finger 18 along the inner wall of the groove 32.

It becomes.

となる。よって数式１９と数式２０によりＥ_２＞Ｅ_１となることがわかる。従って第２実施形態のＳＡＷ共振子７０は、第１実施形態のＳＡＷ共振子１０よりも高い電界を水晶基板３０に印加することができるので弾性表面波の励振が容易になる。したがって、第２実施形態のＳＡＷ共振子７０の電気機械結合係数は、第１実施形態のＳＡＷ共振子１０の電気機械結合係数よりも高くなると考えられる。 On the other hand, in the second embodiment, the electric field E ₂ applied between the electrode fingers 78 is the strongest in the straight path 88 connecting the one electrode finger 78 and the other electrode fingers 78,

It becomes. Therefore, it can be seen from Equations 19 and 20 that E ₂ > E ₁ . Therefore, since the SAW resonator 70 of the second embodiment can apply a higher electric field to the quartz substrate 30 than the SAW resonator 10 of the first embodiment, the surface acoustic wave can be easily excited. Therefore, it is considered that the electromechanical coupling coefficient of the SAW resonator 70 of the second embodiment is higher than the electromechanical coupling coefficient of the SAW resonator 10 of the first embodiment.

  DESCRIPTION OF SYMBOLS 10 ......... Surface acoustic wave resonator (SAW resonator), 12 ......... IDT, 14a, 14b ......... Comb-like electrode, 16 ......... Bus bar, 18 ......... Electrode finger, 20 ......... Reflection 22 ......... Conductor strip, 30 ......... Quartz substrate, 32 ......... Groove, 50 ......... IC, 52a-52f ......... Pad, 56 ......... Package, 54a-54g ......... Electrode pattern 56a ......... bottom plate, 58 ......... lid, 60 ......... metal wire, 70 ......... surface acoustic wave resonator (SAW resonator), 72 ......... IDT, 74a ......... comb-like electrode, 74b ......... Combine electrode, 76 ......... Bus bar, 78 ......... Electrode finger, 80 ......... Reflector, 82 ......... Conductor strip, 84 ......... Groove, 86 ......... Route, 88 ... ... route.

Claims (4)

A quartz substrate having Euler angles (−1.5 ° ≦ φ ≦ 1.5 °, 117 ° ≦ θ ≦ 142 °, 41.9 ° ≦ | ψ | ≦ 49.57 °), A surface acoustic wave resonator having a plurality of electrode fingers arranged in stripes in a propagation direction of the surface acoustic wave to be generated and generating the surface acoustic wave in a stop band upper end mode,
On the quartz substrate, a plurality of grooves arranged in a stripe shape in the propagation direction of the surface acoustic wave is formed,
The electrode fingers are
A surface acoustic wave resonator formed on the inner bottom surface of the groove.   The surface acoustic wave resonator according to claim 1, wherein the IDT is made of Al or an Al alloy.   A surface acoustic wave oscillator comprising the surface acoustic wave resonator according to claim 1 as an oscillation source.   An electronic apparatus comprising the surface acoustic wave resonator according to claim 1.

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