A SAW resonator which, using a quartz crystal substrate with euler angles (−1.5°≦φ≦1.5°, 117°≦θ≦142°, and 42.79°≦|105|≦49.57°, includes an idt which excites a stop band upper end mode SAW, and grooves hollowed out of the substrate positioned between electrode fingers configuring the idt, wherein, when the wavelength of the SAW is λ and the depth of the inter-electrode finger grooves is G, λ and G satisfy the relationship of 0.01λ≦G and wherein, when the line occupation rate of the idt is η, the groove depth G and line occupation rate η satisfy the relationships of −2.0000×G/λ+0.7200≦η≦−2.5000×G/λ+0.7775 provided that 0.0100λ≦G≦0.0500λ, −3.5898×G/λ+0.7995≦η≦−2.5000+G/λ+0.7775 provided that 0.0500λ<G≦0.0695λ.
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1. A surface acoustic wave resonator provided on a quartz crystal substrate with euler angles (−1.5°≦φ≦1.5°, 117°≦θ≦142°, and 42.79°≦|ψ|≦49.57°), comprising:
an idt which excites a stop band upper end mode surface acoustic wave; and
inter-electrode finger grooves hollowed out of the substrate positioned between electrode fingers configuring the idt, wherein
when the wavelength of the surface acoustic wave is λ and the depth of the inter-electrode finger grooves is G, λ and G satisfy the relationship of
0.01λ≦G and wherein,
when the line occupation rate of the idt is η, the inter-electrode finger groove depth G and line occupation rate η satisfy the relationships of
−2.0000×G/λ+0.7200≦η≦−2.5000×G/λ+0.7775 provided that 0.0100.1λ≦G≦0.0500λ −3.5898×G/λ+0.7995≦η≦−2.5000×G/λ+0.7775 provided that 0.0500λ<G≦0.0695λ. 2. The surface acoustic wave resonator according to
the inter-electrode finger groove depth G satisfies the relationship of
0.01λ≦G≦0.0695λ. 3. The surface acoustic wave resonator according to
when the electrode film thickness of the idt is H, H satisfies the relationship of
0<H≦0.035λ. 4. The surface acoustic wave resonator according to
the line occupation rate η satisfies the relationship of
η=−1963.05×(G/λ)3+196.28×(G/λ)2−6.53×(G/λ) −135.99×(H/λ)2+5.817×(H/λ)+0.732 −99.99×(G/λ)×(H/λ). 5. The surface acoustic wave resonator according to
the sum of the inter-electrode finger groove depth G and electrode film thickness H satisfies the relationship of
0.0407λ≦G+H. 6. The surface acoustic wave resonator according to
ψ and θ satisfy the relationship of
Ψ=1.191×10−3×03−4.490×10−1×02+5.646×101×0−2.324×103±1.0. 7. The surface acoustic wave resonator according to
when a stop band upper end mode frequency in the idt is ft2, a stop band lower end mode frequency in reflectors disposed in such a way as to sandwich the idt in the propagation direction of the surface acoustic wave is fr1, and a stop band upper end mode frequency of the reflectors is fr2, ft2, fr1, and fr2 satisfy the relationship of
fr1<ft2<fr22. 8. The surface acoustic wave resonator according to
inter-conductor strip grooves are provided between conductor strips configuring the reflectors, and
the depth of the inter-conductor strip grooves is less than that of the inter-electrode finger grooves.
9. A surface acoustic wave oscillator comprising:
the surface acoustic wave resonator according to
an IC for driving the idt.
18. The surface acoustic wave resonator according to
when the electrode film thickness of the idt is H, H satisfies the relationship of
0<H≦0.035λ. 19. The surface acoustic wave resonator according to
the sum of the inter-electrode finger groove depth G and electrode film thickness H satisfies the relationship of
0.0407λ≦G+H. |
The present invention relates to a surface acoustic wave resonator, and to a surface acoustic wave oscillator in which the resonator is mounted, and in particular, relates to a type of surface acoustic wave resonator wherein grooves are provided in a substrate surface, and to a surface acoustic wave oscillator in which the resonator is mounted.
In a surface acoustic wave (SAW) device (for example, a SAW resonator), the effect of a SAW stop band, piezoelectric substrate (for example, quartz crystal substrate) cut angle, IDT (interdigital transducer) formation shape, and the like, on changes in frequency-temperature characteristics is considerable.
For example, a configuration exciting each of a SAW stop band upper end mode and lower end mode, the distribution of standing waves in each of the stop band upper end mode and lower end mode, and the like, are disclosed in JP-A-11-214958.
Also, points for which the SAW stop band upper end mode has better frequency-temperature characteristics than the stop band lower end mode are described in JP-A-2006-148622, JP-A-2007-208871, JP-A-2007-267033 and JP-A-2002-100959. Then, it is described in JP-A-2006-148622 and JP-A-2007-208871 that, in order to obtain good frequency-temperature characteristics in a SAW device utilizing a Rayleigh wave, as well as adjusting the cut angle of the quartz crystal substrate, the electrode standardizing film thickness (H/λ) is increased to around 0.1.
Also, it is described in JP-A-2007-267033 that, as well as adjusting the cut angle of the quartz crystal substrate in a SAW device utilizing a Rayleigh wave, the electrode standardizing film thickness (H/λ) is increased by around 0.045 or more.
Also, it is described in JP-A-2002-100959 that, by using a rotated Y-cut, X-propagating quartz crystal substrate, and utilizing the stop band upper end resonance, the frequency-temperature characteristics improve more than in the case of using the stop band lower end resonance.
Also, it is described in JP-A-57-5418 and “Manufacturing Conditions and Characteristics of Grooved SAW Resonators” (Institute of Electronics and Communication Engineers of Japan technical research report MW82-59 (1982)), that grooves (grooves) are provided between the electrode fingers configuring the IDT, and between the conductor strips configuring the reflectors, in a SAW device using an ST cut quartz crystal substrate. Also, it is described in “Manufacturing Conditions and Characteristics of Grooved SAW Resonators” that the frequency-temperature characteristics change depending on the depth of the grooves.
Also, in Japanese Patent No. 3,851,336, as well as describing a configuration for making a curve indicating the frequency-temperature characteristics a tertiary curve in a SAW device using an LST cut quartz crystal substrate, it is described that, in a SAW device using a Rayleigh wave, it has not been possible to find a cut angle substrate having the kind of temperature characteristics indicated by a tertiary curve.
As heretofore described, there is a wide range of elements for improving frequency-temperature characteristics, and it is thought that, particularly with a SAW device using a Rayleigh wave, increasing the film thickness of the electrodes configuring the IDT is one factor contributing to the frequency-temperature characteristics. However, the applicant has found experimentally that on increasing the film thickness of the electrodes, environmental resistance characteristics, such as temporal change characteristics and temperature and shock resistance characteristics, deteriorate. Also, when having the improvement of frequency-temperature characteristics as a principal object, it is necessary to increase the electrode film thickness, as previously described, and an accompanying deterioration of temporal change characteristics, temperature and shock resistance characteristics, and the like, is unavoidable. This also applying to the Q value, it is difficult to realize a higher Q without increasing the electrode film thickness.
Consequently, problems when providing the surface acoustic wave resonator and surface acoustic wave oscillator of the invention are, firstly, to realize good frequency-temperature characteristics, secondly, to improve the environmental resistance characteristics, and thirdly, to obtain a high Q value.
The invention, having been contrived in order to solve at least one portion of the heretofore described problems, can be realized as the following embodiment or application examples.
A surface acoustic wave resonator provided on a quartz crystal substrate with Euler angles (−1.5°≦φ≦1.5°, 117°≦θ≦142°, and 42.79°≦|Ψ|≦49.57°) includes an IDT which excites a stop band upper end mode surface acoustic wave, and inter-electrode finger grooves hollowed out of the substrate positioned between electrode fingers configuring the IDT, wherein, when the wavelength of the surface acoustic wave is λ and the depth of the inter-electrode finger grooves is G, λ and G satisfy the relationship of
[Expression 1]
0.01λ≦G (1)
and wherein, when the line occupation rate of the IDT is η, the inter-electrode finger groove depth G and line occupation rate η satisfy the relationships of
[Expression 2]
−2.0000×G/λ+0.7200≦η≦−2.5000×G/λ+0.7775
provided that
0.0100λ≦G≦0.05002 (5)
[Expression 3]
−3.5898×G/λ+0.7995≦η≦−2.5000×G/λ+0.7775
provided that
0.0500λ<G≦0.06952
According to the surface acoustic wave resonator with these kinds of characteristic, it is possible to achieve an improvement in frequency-temperature characteristics.
With the surface acoustic wave resonator according to application example 1, the inter-electrode finger groove depth G satisfies the relationship of
[Expression 4]
0.01λ≦G≦0.0695λ (3)
According to the surface acoustic wave resonator with these kinds of characteristic, even in the event that the depth G of the inter-electrode finger grooves deviates due to manufacturing error, it is possible to keep the shift of resonance frequency between individual resonators within a correctable range.
With the surface acoustic wave resonator according to application example 1 or 2, when the electrode film thickness of the IDT is H, H satisfies the relationship of
[Expression 5]
0<H≦0.035λ (7)
According to the surface acoustic wave resonator with these kinds of characteristic, it is possible to realize an exhibition of good frequency-temperature characteristics in an operating temperature range. Also, by having these kinds of characteristic, it is possible to suppress the deterioration of environmental resistance characteristics accompanying an increase in the electrode film thickness.
With the surface acoustic wave resonator according to application example 3, the line occupation rate η satisfies the relationship of
[Expression 6]
η=−1963.05×(G/λ)3+196.28×(G/λ)2−6.53×(G/λ)
−135.99×(H/λ)2+5.817×(H/λ)+0.732
−99.99×(G/λ)×(H/λ) (8)
By fixing η in such a way as to satisfy Equation (8) in the range of the electrode film thickness in Application Example 3, it is possible to keep a secondary temperature coefficient substantially within ±0.01 ppm/° C.2.
With the surface acoustic wave resonator according to application example 3 or 4, the sum of the inter-electrode finger groove depth G and electrode film thickness H satisfies the relationship of
[Expression 7]
0.0407λ≦G+H
By fixing the sum of the inter-electrode finger groove depth G and electrode film thickness H as in the above equation, it is possible to obtain a higher Q value than with the heretofore known surface acoustic wave resonator.
With the surface acoustic wave resonator according to any one of application examples 1 to 5, Ψ and θ satisfy the relationship of
[Expression 8]
Ψ=1.191×10−3×θ3−4.490×10−1×θ2+5.646×101×θ−2.324×103±1.0 (31)
By manufacturing the surface acoustic wave resonator using a quartz crystal substrate cut out at cut angles with these kinds of characteristic, it is possible to obtain a surface acoustic wave resonator exhibiting good frequency-temperature characteristics in a wide range.
With the surface acoustic wave resonator according to any one of application examples 1 to 6, when a stop band upper end mode frequency in the IDT is ft2, a stop band lower end mode frequency in reflectors disposed in such a way as to sandwich the IDT in the propagation direction of the surface acoustic wave is fr1, and a stop band upper end mode frequency of the reflectors is fr2, ft2, fr1, and fr2 satisfy the relationship of
[Expression 9]
fr1<ft2<fr2 (32)
By having these kinds of characteristic, a reflection coefficient |Γ| of the reflectors at the stop band upper end mode frequency ft2 of the IDT increases, and a stop band upper end mode surface acoustic wave excited with the IDT is reflected by the reflectors to the IDT side with a high reflection coefficient. Then, the stop band upper end mode surface acoustic wave energy confinement becomes stronger, and it is possible to realize a low-loss surface acoustic wave resonator.
With the surface acoustic wave resonator according to any one of application examples 1 to 7, inter-conductor strip grooves are provided between conductor strips configuring the reflectors, and the depth of the inter-conductor strip grooves is less than that of the inter-electrode finger grooves.
By having these kinds of characteristic, it is possible to make a frequency shift of the stop band of the reflectors to an area higher than the stop band of the IDT. For this reason, it is possible to realize the relationship of Equation (32).
A surface acoustic wave oscillator includes the surface acoustic wave resonator according to any one of application examples 1 to 8, and an IC for driving the IDT.
An electronic instrument includes the surface acoustic wave resonator according to application example 1 or 2.
An electronic instrument includes the surface acoustic wave resonator according to application example 3.
An electronic instrument includes the surface acoustic wave resonator according to application example 4.
An electronic instrument includes the surface acoustic wave resonator according to application example 5.
An electronic instrument includes the surface acoustic wave resonator according to application example 6.
An electronic instrument includes the surface acoustic wave resonator according to application example 7.
An electronic instrument includes the surface acoustic wave resonator according to application example 8.
An electronic instrument includes the surface acoustic wave resonator according to application example 9.
Hereafter, a detailed description will be given, while referring to the drawings, of an embodiment according to a surface acoustic wave resonator and surface acoustic wave oscillator of the invention.
Firstly, referring to
The SAW resonator 10 according to the embodiment is basically configured of a quartz crystal substrate 30, IDT 12, and reflectors 20.
In the embodiment, an in-plane rotation ST cut quartz crystal substrate expressed by Euler angles. (−1°≦φ≦1°, 117°≦θ≦142°, and 42.79≦|Ψ|≦49.57° is employed as the quartz crystal substrate 30. Herein, a description will be given of the Euler angles. A substrate expressed by Euler angles (0°, 0°, and 0°) is a Z cut substrate which has a main surface perpendicular to the Z axis. Herein, φ of Euler angles (φ, θ, and Ψ), relating to a first rotation of the Z cut substrate, is a first rotation angle, with the Z axis as a rotation axis, and with a direction rotating from the +X axis to a +Y axis side as a positive rotation angle. The Euler angle θ, relating to a second rotation carried out after the first rotation of the Z cut substrate, is a second rotation angle, with the X axis after the first rotation as a rotation axis, and with a direction rotating from the +Y axis after the first rotation to the +Z axis as a positive rotation angle. The cut surface of a piezoelectric substrate is determined by the first rotation angle φ and second rotation angle θ. The Euler angle Ψ, relating to a third rotation carried out after the second rotation of the Z cut substrate, is a third rotation angle, with the Z axis after the second rotation as a rotation axis, and with a direction rotating, from the +X axis after the second rotation to the +Y axis side after the second rotation as a positive rotation angle. A propagation direction of the SAW is expressed by the third rotation angle Ψ with respect to the X axis after the second rotation.
The IDT 12 including a pair of pectinate electrodes 14a and 14b wherein the base end portions of a plurality of electrode fingers 18a and 18b are connected by bus bars 16a and 16b respectively, the electrode finger 18a configuring one of the pectinate electrodes 14a, and the electrode finger 18b configuring the other pectinate electrode 14b, are alternately disposed with a predetermined space between them. Furthermore, the electrode fingers 18a and 18b are disposed in such a way that the extension direction of the electrode fingers 18a and 18b is perpendicular to the X′ axis, which is the propagation direction of the surface acoustic wave, as shown in
Also, furthermore, it is possible to give the SAW resonator 10 according to the invention the kinds of shape shown in
Whichever kind of tilted type IDT is used, by disposing the electrode fingers in such a way that a direction perpendicular to the X′ axis is the extension direction of the electrode fingers, as in the working examples, it is possible to realize a low-loss SAW resonator, while maintaining good temperature characteristics in the invention.
Herein, a description will be given of the relationship between a stop band upper end mode SAW and a lower end mode SAW. In the stop band lower end mode and upper end mode SAWs formed by the kind of normal IDT 12 shown in
According to
Also, one pair of the reflectors 20 are provided in such a way as to sandwich the IDT 12 in the SAW propagation direction. As a specific configuration example, both ends of each of a plurality of conductor strips 22, provided parallel to the electrode fingers 18 configuring the IDT 12, are connected.
With an edge reflection type SAW resonator which actively utilizes a reflected wave from the SAW propagation direction end face of the quartz crystal substrate, or a long IDT type SAW resonator which excites the SAW standing wave with the IDT itself by increasing the number of pairs of IDT electrode fingers, the reflectors are not absolutely necessary.
As the material of the electrode film configuring the IDT 12 and reflectors 20 configured in this way, it is possible to use aluminum (Al), or a metal alloy with Al as its base.
By making the electrode thickness of the electrode film configuring the IDT 12 and reflectors 20 extremely small, the effect of the temperature characteristics possessed by the electrodes is kept to a minimum. Furthermore, making the depth of the quartz crystal substrate portion grooves large, good frequency-temperature characteristics are derived from the performance of the quartz crystal substrate portion grooves, that is, by utilizing the good temperature characteristics of the quartz crystal. Because of this, it is possible to reduce the effect of the electrode temperature characteristics on the temperature characteristics of the SAW resonator and, provided that the fluctuation of the electrode mass is within 10%, it is possible to maintain good temperature characteristics.
For the above-mentioned reasons, in the event of using an alloy as the electrode film material, the ratio by weight of metals other than the main element aluminum should be 10% or less, and preferably 3% or less. In the event of using electrodes with a metal other than Al as a base, the electrode film thickness should be adjusted so that the mass of the electrodes is within ±10% of that when using Al. By so doing, good temperature characteristics equivalent to those when using Al can be obtained.
The quartz crystal substrate 30 in the SAW resonator 10 with the heretofore described kind of basic configuration is such that the grooves (inter-electrode finger grooves) 32 are provided between the electrode fingers of the IDT 12 and between the conductor strips of the reflectors 20.
When the SAW wavelength in the stop band upper end mode is λ, and the groove depth is G, the groves 32 provided in the quartz crystal substrate 30 should be such that
[Expression 10]
0.01λ≦G (1)
When fixing an upper limit for the groove depth G, it should be within the range of
[Expression 11]
0.01λ≦G≦0.094λ (2)
as can be seen by referring to
[Expression 12]
0.01λ≦G≦0.0695λ (3)
By fixing the groove depth G within this kind of range, even in the event that manufacturing variation occurs in the groove depth G, it is possible to keep the shift amount of resonance frequency between individual SAW resonators 10 within a correctable range.
Also, the line occupation rate η is a value wherein the line width L of the electrode finger 18 (in the case of the quartz crystal protrusion only, the width of the protrusion) is divided by the pitch λ/2 (=L+S) between the electrode fingers 18, as shown in
Herein, with the SAW resonator 10 according to the embodiment, the line occupation rate η should be fixed within the kind of range which satisfies Equations (5) and (6). As can also be understood from Expressions (5) and (6), η can be derived by fixing the depth G of the grooves 32.
[Expression 14]
−2.0000×G/λ+0.7200≦η≦−2.5000×G/λ+0.7775
provided that
0.01002λ≦G≦0.05002 (5)
[Expression 15]
−3.5898×G/λ+0.7995≦η≦−2.5000×G/λ+0.7775
provided that
0.0500λ<G≦0.0695λ (6)
Also, it is preferable that the film thickness of the electrode film material (IDT 12, reflectors 20, and the like) in the SAW resonator 10 according to the embodiment is within the range of
[Expression 16]
0<H≦0.035λ (7)
Furthermore, when taking into consideration the thickness of the electrode film shown in Equation (7) with regard to the line occupation rate η, η can be obtained from Equation (8).
[Expression 17]
η=−1963.05×(G/λ)3+196.28×(G/λ)2−6.53×(G/λ)
−135.99×(H/λ)2+5.817×(H/λ)+0.732
−99.99×(G/λ)×(H/λ) (8)
The manufacturing variation of the electrical characteristics (particularly the resonance frequency) being greater the greater the electrode film thickness, it is highly likely that the manufacturing variation of the line occupation rate η is ±0.04 or less when the electrode film thickness H is within the range of Equations (5) and (6), and that a manufacturing variation greater than ±0.04 occurs when H>0.03λ. However, provided that the electrode film thickness H is within the range of Equations (5) and (6), and the variation of the line occupation rate η is ±0.04 or less, it is possible to realize a SAW device with a low secondary temperature coefficient β. That is, a line occupation rate η up to the range of Equation (9), wherein a tolerance of ±0.04 is added to Equation (8), is allowable.
[Expression 18]
η=−1963.05×(G/λ)3+196.28×(G/λ)2−6.53×(G/λ)
−135.99×(H/λ)2+5.817×(H/λ)+0.732
−99.99×(G/λ)×(H/λ)±0.04 (9)
With the SAW resonator 10 according to the embodiment with the heretofore described kind of configuration, in the event that 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., the object is to improve the frequency-temperature characteristics to a degree whereby it is possible to keep a frequency fluctuation amount ΔF in the Operating temperature range at or under 25 ppm.
Generally, however, the temperature characteristics of a surface acoustic wave resonator are expressed by the following equation.
Δf=α×(T−T0)+β×(T−T0)2
Herein, Δf represents the frequency change amount (ppm) between the temperature T and the peak temperature T0, α the primary temperature coefficient (ppm/° C.), β the secondary temperature coefficient (ppm/° C.2), T the temperature, and T0 the temperature at which the frequency is highest (the peak temperature).
For example, in the event that the piezoelectric substrate is formed of a so-called ST cut (Euler angles (φ, θ, and Ψ)=(0°, 120° to 130°, and 0°) quartz crystal substrate, the primary constant α=0.0, and the secondary constant β=−0.034, which when expressed in a graph is as in
With the kind of SAW resonator shown in
Consequently, one object of the invention is to solve the heretofore described kind of problem, making the frequency-temperature characteristics of the surface acoustic wave device extremely good ones, and realizing a surface acoustic wave device which operates with a stable frequency, even though the temperature changes.
How a solution to the heretofore described kind of problem may be realized with a SAW device to be configured including the heretofore described kind of technical thought (technical components), that is, how the inventor arrived at the knowledge according to the invention by repeatedly carrying out simulations and experiments, will be described in detail and proved hereafter.
With a SAW resonator using the previously described quartz crystal substrate called an ST cut, with the propagation direction the crystal X axis direction, in the event that the operating temperature range is the same, the frequency fluctuation amount ΔF in the operating temperature range is approximately 133 (ppm), and the secondary temperature coefficient β is about −0.034 (ppm/° C.2). Also, in the event of utilizing a stop band lower end mode excitation in a SAW resonator using an in-plane rotation ST cut quartz crystal substrate with the same operating temperature range, with the quartz crystal substrate cut angles and SAW propagation direction (0, 123°, and 45°) in Euler angle representation, the frequency fluctuation amount ΔF is approximately 63 ppm, and the secondary temperature coefficient β is about −0.016 (ppm/° C.2).
The SAW resonators using the ST cut quartz crystal substrate and in-plane rotation ST cut quartz crystal substrate both utilizing surface acoustic waves called Rayleigh waves, the variation of frequency and frequency-temperature characteristics with respect to the machining accuracy of the quartz crystal substrate and electrodes is extremely small in comparison with the surface acoustic wave, called a Leaky wave, of an LST cut quartz crystal substrate, meaning that they are most suitable for mass production, and are used in various kinds of SAW device. However, with the SAW resonators using the ST cut quartz crystal substrate, in-plane rotation ST cut quartz crystal substrate, or the like utilized to date, as previously described, the secondary temperature characteristics being such that the curve indicating the frequency-temperature characteristics is a quadratic curve, and furthermore, the absolute value of the secondary temperature coefficient of the secondary temperature characteristics being large, the frequency fluctuation amount in the operating temperature range is large, and they cannot be utilized in a SAW device such as a resonator or oscillator used in a wired communication device or wireless communication device which requires a stability of frequency. For example, in the event that it is possible to obtain frequency-temperature characteristics which have secondary temperature characteristics wherein the secondary temperature coefficient β is ±0.01 (ppm/° C.2) or less, corresponding to an improvement in the ST cut quartz crystal substrate secondary temperature coefficient β of ⅓ or less, and in the in-plane rotation ST cut quartz crystal substrate secondary temperature coefficient β of 37% or more, it is possible to realize a device which requires that kind of frequency stability. Furthermore, in the event that it is possible to obtain tertiary temperature characteristics, wherein the secondary temperature coefficient β is substantially zero, and the curve indicating the frequency-temperature characteristics is a tertiary curve, it is more preferable, as the frequency stability in the operating temperature range further increases. With tertiary temperature characteristics such as these, it is possible to obtain an extremely high frequency stability of ±25 ppm or less, which has not been realizable with the heretofore known kind of SAW device, even in the broad operating temperature range of −40° C. to +85° C.
The fact that the electrode finger 18 line occupation rate η in the IDT 12, electrode film thickness H, groove depth G, and the like, are related to the change in the frequency-temperature characteristics of the SAW resonator 10, as heretofore described, has been made clear by knowledge based on the simulations and experiments carried out by the inventor. Then, the SAW resonator 10 according to the embodiment utilizes the excitation of the stop band upper end mode.
From
From this, it is clear that in order to obtain good frequency-temperature characteristics in a SAW device, it is preferable to use the oscillation of the stop band upper end mode.
Next, the inventor investigated the relationship between the line occupation rate η and secondary temperature coefficient β when propagating a stop band upper end mode SAW in quartz crystal substrates with variously changed groove depths G.
Regarding this point, it is possible to increase an understanding thereof by referring to
According to the heretofore described tendency, it can be supposed that it is preferable to employ the β=0 point at which the frequency fluctuation amount with respect to the fluctuation in the groove depth G is smaller, that is, η1, for a mass production article in which discrepancies are liable to occur when manufacturing.
In
The graph shown in
[Expression 19]
0.01λ≦G≦0.094λ (2)
The groove depth G has a maximum variation of around ±0.0012 in the mass production process. Therefore, the individual frequency fluctuation amounts Δf of the SAW resonator 10 in a case in which the groove depth G deviates by ±0.001λ, when the line occupation rate η is taken to be a constant, are shown in
Herein, in the event that the frequency fluctuation amount Δf is less than ±1000 ppm, frequency adjustment is possible using various frequency fine adjustment methods. However, in the event that the frequency fluctuation amount Δf is ±1000 ppm or more, adjusting the frequency has an effect on static characteristics such as the Q value and CI (crystal impedance) value, and on long-term reliability, leading to a reduction in the yield rate as the SAW resonator 10.
By deriving an approximate equation indicating the relationship between the frequency fluctuation amount Δf (ppm) and groove depth G for the straight line linking the plots shown in
[Expression 20]
Δf=16334(G/λ)−137 (10)
Herein, on calculating the values of G at which Δf<1000 ppm, it is found that G≦0.0695λ. Consequently, it can be said that it is preferable that the range of the groove depth G according to the embodiment is optimally
[Expression 21]
0.01λ≦G≦0.0695λ (3)
Next,
From the evaluation results shown in
The coordinates of points a to h in
TABLE 1
Point
G/λ
η
a
0.01
0.70
b
0.03
0.66
c
0.05
0.62
d
0.07
0.55
e
0.07
0.60
f
0.05
0.65
g
0.03
0.70
h
0.01
0.75
[Expression 22]
η≦−2.5000×G/λ+0.7775
provided that
0.0100λ≦G≦0.0695λ (11)
[Expression 23]
η≧2.0000×G/λ+0.7200
provided that
0.0100λ≦G≦0.0500λ (12)
[Expression 24]
η≧−3.5898×G/λ+0.7995
provided that
0.0500λ<G≦0.0695λ (13)
From Equations (11), (12), and (13), it can be said that it is possible to specify the line occupation rates η in the range surrounded by the solid line in
[Expression 25]
−2.0000×G/λ+0.7200≦η≦−2.5000×Gλ+0.7775
provided that
0.0100λ≦G≦0.0500λ (5)
[Expression 26]
−3.5898×G/λ+0.7995≦η≦−2.5000×G/λ+0.7775
provided that
0.0500λ<G≦0.06952
Herein, in the case of allowing the secondary temperature coefficient β to within ±0.01 (ppm/° C.2), it is confirmed that by configuring in such a way as to satisfy both Equation (3) and Equation (5) when 0.0100λ≦G≦0.0500λ, and satisfy both Equation (3) and Equation (6) when 0.0500λ≦G≦0.0695λ, the secondary temperature coefficient β comes within ±0.01 (ppm/° C.2).
The values of the secondary temperature coefficient β for each electrode film thickness H at the points a to h are shown in Table 2 below. From Table 2, it can be confirmed that |β|≦0.01 at all of the points.
TABLE 2
Electrode Film Thickness H
Point
1% λ
1.5% λ
2% λ
2.5% λ
3% λ
3.5% λ
a
−0.0099
−0.0070
−0.0030
0.0030
−0.0050
−0.0060
b
0.0040
0.0030
0.0000
0.0000
−0.0020
−0.0040
c
0.0070
−0.0040
0.0010
−0.0036
−0.0040
−0.0057
d
0.0067
−0.0022
−0.0070
−0.0080
−0.0090
−0.0099
e
−0.0039
−0.0060
−0.0090
−0.0080
−0.0090
−0.0094
f
−0.0023
−0.0070
−0.0050
−0.0062
−0.0060
−0.0070
g
−0.0070
−0.0060
−0.0090
−0.0070
−0.0070
−0.0070
h
−0.0099
−0.0030
−0.0091
−0.0080
−0.0080
−0.0080
Also, when the relationship between the groove depth G and line occupation rate η at each point at which β=0 for SAW resonators 10 in which the electrode film thickness H≈0, 0.1λ, 0.02λ, 0.03λ, or 0.035λ, based on Equations (11) to (13) and Equations (5) and (6) derived therefrom, is indicated by an approximate line, the result is as in
When changing the electrode film thickness H at 3.0% λ (0.030λ) or less, the frequency-temperature characteristics of β=0, that is, the tertiary curve, can be obtained. At this time, a relational equation for G and η when the frequency-temperature characteristics are good can be expressed by Equation (8).
[Expression 27]
η=−1963.05×(G/λ)3+196.28×(G/λ)2−6.53×(G/λ)
−135.99×(H/λ)2+5.817×(H/λ)+0.732
−99.99×(G/λ)+(H/λ) (8)
Herein, the units of G and H are λ.
It should be noted that Equation (8) is established when the electrode film thickness H is in the range of 0<H≦0.030λ.
The manufacturing variation of the electrical characteristics (particularly the resonance frequency) being greater the greater the electrode film thickness, it is highly likely that the manufacturing variation of the line occupation rate η is ±0.04 or less when the electrode film thickness H is within the range of Equations (5) and (6), and that a manufacturing variation greater than ±0.04 occurs when H>0.035λ. However, provided that the electrode film thickness H is within the range of Equations (5) and (6), and the variation of the line occupation rate η is ±0.04 or less, it is possible to realize a SAW device with a low secondary temperature coefficient β. That is, when taking into consideration the manufacturing variation of the line occupation rate, and keeping the secondary temperature coefficient β within ±0.01 ppm/° C.2, a line occupation rate η up to the range of Equation (9), wherein a tolerance of ±0.04 is added to Equation (8), is allowable.
[Expression 28]
η=−1963.05×(G/λ)3+196.28×(G/λ)2−6.53×(G/λ)
−135.99×(H/λ)2+5.817×(H/λ)+0.732
−99.99×(G/λ)×(H/λ)±0.04 (9)
Also,
Herein,
Also,
Also,
Also,
Also,
Also,
Although there are slight differences in all of the graphs in these diagrams (
That is, it can be said that an advantage according to the invention is that it can be accomplished even when propagating a surface acoustic wave on an individual quartz crystal substrate 30 from which the electrode film is omitted.
For each of the two points η1 and η2 at which the secondary temperature coefficient β becomes zero, a simulation is performed for each of the range of η1 and η2 when the range of β is expanded to |β|≦0.01, and the case in which the range of the electrode film thickness H is fixed, and the groove depth G is changed. Of η1 and η2, the larger η at which |β|≦0.01 is taken to be η1, and the smaller η at which |β|≦0.01 is η2. The quartz crystal substrates used are all ones with Euler angles (0°, 123°, and Ψ), and with regard to Ψ, an angle at which ΔF is smallest is appropriately selected.
TABLE 3
Point
G/λ
η
β
a
0.0100
0.7100
−0.0098
b
0.0200
0.7100
−0.0099
c
0.0300
0.7100
−0.0095
d
0.0400
0.7100
−0.0100
e
0.0500
0.7100
−0.0100
f
0.0600
0.7100
−0.0098
g
0.0700
0.7100
−0.0099
h
0.0800
0.7100
−0.0097
i
0.0900
0.7100
−0.0100
j
0.0900
0.4200
0.0073
k
0.0800
0.5700
0.0086
l
0.0700
0.5900
0.0093
m
0.0600
0.6150
0.0077
n
0.0500
0.6300
0.0054
o
0.0400
0.6350
0.0097
p
0.0300
0.6500
0.0097
q
0.0200
0.6700
0.0074
r
0.0100
0.7100
0.0091
From
TABLE 4
Point
G/λ
η
β
a
0.0300
0.5900
0.0097
b
0.0400
0.5800
0.0097
c
0.0500
0.5500
0.0054
d
0.0600
0.5200
0.0077
e
0.0700
0.4800
0.0093
f
0.0800
0.4500
0.0086
g
0.0900
0.4000
0.0073
h
0.0900
0.1800
0.0056
i
0.0800
0.3400
0.0093
j
0.0700
0.4100
0.0078
k
0.0600
0.4600
0.0094
l
0.0500
0.4900
0.0085
m
0.0400
0.5200
0.0099
n
0.0300
0.5500
0.0098
From
TABLE 5
Point
G/λ
η
β
a
0.0100
0.7700
−0.0099
b
0.0200
0.7400
−0.0100
c
0.0300
0.7150
−0.0100
d
0.0400
0.7300
−0.0098
e
0.0500
0.7400
−0.0100
f
0.0600
0.7300
−0.0098
g
0.0700
0.7300
−0.0100
h
0.0800
0.7300
−0.0100
i
0.0800
0.5000
0.0086
j
0.0700
0.5700
0.0100
k
0.0600
0.6100
0.0095
l
0.0500
0.6300
0.0100
m
0.0400
0.6350
0.0097
n
0.0300
0.6550
0.0070
o
0.0200
0.6800
0.0100
p
0.0100
0.7600
0.0016
From
TABLE 6
Point
G/λ
η
β
a
0.0200
0.6500
0.0090
b
0.0300
0.6100
0.0098
c
0.0400
0.5700
0.0097
d
0.0500
0.5500
0.0040
e
0.0600
0.5200
0.0066
f
0.0700
0.4700
0.0070
g
0.0700
0.3700
−0.0094
h
0.0600
0.4400
−0.0096
i
0.0500
0.4800
−0.0096
j
0.0400
0.5200
−0.0095
k
0.0300
0.5500
−0.0099
l
0.0200
0.5900
−0.0100
From
TABLE 7
Point
G/λ
η
β
a
0.0100
0.770
−0.0099
b
0.0200
0.760
−0.0099
c
0.0300
0.760
−0.0099
d
0.0400
0.750
−0.0099
e
0.0500
0.750
−0.0099
f
0.0600
0.750
−0.0099
g
0.0700
0.740
−0.0099
h
0.0800
0.740
−0.0098
i
0.0800
0.340
0.0088
j
0.0700
0.545
0.0088
k
0.0600
0.590
0.0099
l
0.0500
0.620
0.0090
m
0.0400
0.645
0.0060
n
0.0300
0.670
0.0030
o
0.0200
0.705
0.0076
p
0.0100
0.760
0.0010
From
TABLE 8
Point
G/λ
η
β
a
0.0100
0.740
0.0099
b
0.0200
0.650
0.0090
c
0.0300
0.610
0.0090
d
0.0400
0.570
0.0080
e
0.0500
0.540
0.0060
f
0.0600
0.480
0.0060
g
0.0700
0.430
0.0099
h
0.0700
0.3500
−0.0099
i
0.0600
0.4200
−0.0090
j
0.0500
0.4700
−0.0090
k
0.0400
0.5100
−0.0090
l
0.0300
0.5500
−0.0090
m
0.0200
0.6100
−0.0099
n
0.0100
0.7000
−0.0099
From
TABLE 9
Point
G/λ
η
β
a
0.010
0.770
−0.0100
b
0.020
0.770
−0.0100
c
0.030
0.760
−0.0100
d
0.040
0.760
−0.0100
e
0.050
0.760
−0.0100
f
0.060
0.750
−0.0100
g
0.070
0.750
−0.0100
h
0.070
0.510
0.0100
i
0.060
0.570
0.0099
j
0.050
0.620
0.0097
k
0.040
0.640
0.0096
l
0.030
0.660
0.0080
m
0.020
0.675
0.0076
n
0.010
0.700
0.0010
From
TABLE 10
Point
G/λ
η
β
a
0.010
0.690
0.0010
b
0.020
0.640
0.0090
c
0.030
0.590
0.0090
d
0.040
0.550
0.0080
e
0.050
0.510
0.0080
f
0.060
0.470
0.0090
g
0.070
0.415
0.0100
h
0.070
0.280
−0.0100
i
0.060
0.380
−0.0090
j
0.050
0.470
−0.0090
k
0.040
0.510
−0.0090
l
0.030
0.550
−0.0090
m
0.020
0.610
−0.0100
n
0.010
0.680
−0.0100
From
TABLE 11
Point
G/λ
η
β
a
0.010
0.770
−0.0100
b
0.020
0.770
−0.0100
c
0.030
0.760
−0.0100
d
0.040
0.760
−0.0100
e
0.050
0.760
−0.0096
f
0.060
0.760
−0.0100
g
0.070
0.760
−0.0100
h
0.070
0.550
0.0100
i
0.060
0.545
0.0090
j
0.050
0.590
0.0097
k
0.040
0.620
0.0100
l
0.030
0.645
0.0100
m
0.020
0.680
0.0070
n
0.010
0.700
0.0030
From
TABLE 12
Point
G/λ
η
β
a
0.010
0.690
0.0030
b
0.020
0.640
0.0090
c
0.030
0.590
0.0090
d
0.040
0.550
0.0090
e
0.050
0.510
0.0080
f
0.060
0.420
0.0090
g
0.070
0.415
0.0080
h
0.070
0.340
−0.0098
i
0.060
0.340
−0.0100
j
0.050
0.420
−0.0100
k
0.040
0.470
−0.0100
l
0.030
0.520
−0.0093
m
0.020
0.580
−0.0100
n
0.010
0.650
−0.0090
From
TABLE 13
Point
G/λ
η
β
a
0.010
0.770
−0.0098
b
0.020
0.770
−0.0100
c
0.030
0.770
−0.0100
d
0.040
0.760
−0.0100
e
0.050
0.760
−0.0099
f
0.060
0.760
−0.0100
g
0.070
0.760
−0.0100
h
0.070
0.550
0.0080
i
0.060
0.505
0.0087
j
0.050
0.590
0.0090
k
0.040
0.620
0.0100
l
0.030
0.645
0.0100
m
0.020
0.680
0.0083
n
0.010
0.700
0.0052
From
TABLE 14
Point
G/λ
η
β
a
0.010
0.670
0.0052
b
0.020
0.605
0.0081
c
0.030
0.560
0.0092
d
0.040
0.520
0.0099
e
0.050
0.470
0.0086
f
0.060
0.395
0.0070
g
0.070
0.500
0.0080
h
0.070
0.490
−0.0100
i
0.060
0.270
−0.0100
j
0.050
0.410
−0.0100
k
0.040
0.470
−0.0100
l
0.030
0.520
−0.0093
m
0.020
0.580
−0.0099
n
0.010
0.620
−0.0090
From
TABLE 15
Point
G/λ
η
β
a
0.010
0.770
−0.0100
b
0.020
0.770
−0.0098
c
0.030
0.770
−0.0100
d
0.040
0.760
−0.0100
e
0.050
0.760
−0.0100
f
0.060
0.760
−0.0100
g
0.070
0.760
−0.0100
h
0.070
0.550
0.0090
i
0.060
0.500
0.0087
j
0.050
0.545
0.0090
k
0.040
0.590
0.0091
l
0.030
0.625
0.0080
m
0.020
0.650
0.0083
n
0.010
0.680
0.0093
From
TABLE 16
Point
G/λ
η
β
a
0.010
0.655
0.0080
b
0.020
0.590
0.0081
c
0.030
0.540
0.0092
d
0.040
0.495
0.0099
e
0.050
0.435
0.0090
f
0.060
0.395
0.0061
g
0.070
0.500
0.0090
h
0.070
0.550
−0.0100
i
0.060
0.380
−0.0090
j
0.050
0.330
−0.0100
k
0.040
0.410
−0.0095
l
0.030
0.470
−0.0099
m
0.020
0.520
−0.0100
n
0.010
0.590
−0.0100
From
The relationship between Ψ and the groove depth G obtained from η1 in the graphs shown in
In the same way as heretofore described, the relationships between the groove depth G and Ψ when the secondary temperature coefficient β=−0.01 (ppm/° C.2), and Ψ when β=+0.01 (ppm/° C.2), are obtained, and summarized in
A simulation is carried out for the range of Ψ which satisfies the requirement |β|≦0.01 when changing the groove depth G, in the case of changing the electrode film thickness H. The results of the simulation are shown in
With the groove depth G in the range of 0.01λ≦G≦0.0695λ, when approximating the range of the solid line and broken line shown in
[Expression 29]
Ψ≦3.0×G/λ+43.92
provided that
0.0100λ≦G≦0.0695λ (14)
[Expression 30]
Ψ≧−48.0×G/λ44.35
provided that
0.0100λ≦G≦0.0695λ (15)
With the groove depth G in the range of 0.01λ≦G≦0.0695λ, when approximating the range of the solid line and broken line in
[Expression 31]
Ψ≦8.0×G/λ+43.60
provided that
0.0100λ≦G≦0.0695λ (16)
[Expression 32]
Ψ≧−48.0×G/λ+44.00
provided that
0.0100λ≦G≦0.0695λ (17)
With the groove depth G in the range of 0.01λ≦G≦0.0695λ, when approximating the range of the solid line and broken line in
[Expression 33]
Ψ≦10.0×G/λ+43.40
provided that
0.0100λ≦G≦0.0695λ (18)
[Expression 34]
Ψ≧−44.0×G/λ+43.80
provided that
0.0100λ≦G≦0.0695λ(19)
With the groove depth G in the range of 0.01λ≦G≦0.0695λ, when approximating the range of the solid line and broken line in
[Expression 35]
Ψ≦12.0×G/λ+43.31
provided that
0.0100λ≦G≦0.0695λ (20)
[Expression 36]
Ψ≧−30.0×G/λ+44.40
provided that
0.0100λ≦G≦0.0695λ (21)
With the groove depth G in the range of 0.01λ≦G≦0.0695λ, when approximating the range of the solid line and broken line in
[Expression 37]
Ψ≦14.0×G/λ+43.16
provided that
0.0100λ≦G≦0.0695λ (22)
[Expression 38]
Ψ≧−45.0×G/λ+43.35
provided that
0.0100λ≦G≦0.0600λ (23)
[Expression 39]
Ψ≧367.368×G/λ+18.608
provided that
0.0600λ≦G≦0.0695λ (24)
With the groove depth G in the range of 0.01λ≦G≦0.0695λ, when approximating the range of the solid line and broken line in
[Expression 40]
Ψ≧12.0×G/λ+43.25
provided that
0.0100λ≦G≦0.0695λ (25)
[Expression 41]
Ψ≧−50.0×G/λ+43.32
provided that
0.0100λ≦G≦0.0500λ (26)
[Expression 42]
Ψ≧167.692×G/λ+32.435
provided that
0.0500λ≦G≦0.0695λ (27)
With the groove depth Gin the range of 0.01λ≦G≦0.0695λ, when approximating the range of the solid line and broken line in
[Expression 43]
Ψ≧12.0×G/λ+43.35
provided that
0.0100λ≦G≦0.0695λ(28)
[Expression 44]
Ψ≧−45.0×G/λ+42.80
provided that
0.0100λ≦G≦0.0500λ (29)
[Expression 45]
Ψ≧186.667×G/λ+31.217
provided that
0.0500λ≦G≦0.0695λ (30)
Next, the change in the secondary temperature coefficient β when the angle θ is altered, that is, the relationship between θ and the secondary temperature coefficient β, is shown in
Under these kinds of condition, from
Tables 17 to 19 are shown as simulation data proving the relationship between θ and the secondary temperature coefficient β.
TABLE 17
H/λ
G/λ
θ
β
%
%
°
ppm/° C.2
0.01
4.00
117
−0.009
0.01
4.00
142
0.005
3.50
4.00
117
−0.009
3.50
4.00
142
−0.008
Table 17 being a table showing the relationship between θ and the secondary temperature coefficient β when the electrode film thickness H is changed, it shows the values of the secondary temperature coefficient β at the critical values (117° and 142°) of θ when the electrode film thickness H is 0.01% λ, and when the electrode film thickness H is 3.50% λ. The groove depths G in the simulation are all 4% λ. From Table 17, it can be seen that, in the range of 117°≦θ≦142°, even though the thickness of the electrode film thickness H is changed (0≈0.01% λ and 3.5% λ stipulated as critical values of the electrode film thickness), |β|≦0.01 is satisfied regardless of the thickness.
TABLE 18
H/λ
G/λ
θ
β
%
%
°
ppm/° C.2
2.00
1.00
117
−0.009
2.00
1.00
142
−0.008
2.00
6.95
117
−0.009
2.00
6.95
142
−0.009
Table 18 being a table showing the relationship between θ and the secondary temperature coefficient β when the groove depth G is changed, it shows the values of the secondary temperature coefficient β at the critical values (117° and 142°) of θ when the groove depth G is 1.00% λ and 6.95% λ. The electrode film thicknesses H in the simulation are all 2.00% λ. From Table 18, it can be seen that, in the range of 117°≦θ≦142°, even though the groove depth G is changed (1.00% λ, and 6.95% λ stipulated as critical values of the groove depth G), |β|≦0.01 is satisfied regardless of the depth.
TABLE 19
H/λ
G/λ
θ
β
%
%
η
°
ppm/° C.2
2.00
4.00
0.62
117
−0.010
2.00
4.00
0.62
142
−0.003
2.00
4.00
0.76
117
−0.009
2.00
4.00
0.76
142
−0.009
Table 19 being a table showing the relationship between θ and the secondary temperature coefficient β when the line occupation rate η is changed, it shows the values of the secondary temperature coefficient β at the critical values (117° and 142°) of θ when the line occupation rate η is 0.62 and 0.76. The electrode film thicknesses H in the simulation are all 2.00% λ, and the groove depths G are all 4.00% λ. From Table 19, it can be seen that, in the range of 117°≦θ≦142°, even though the line occupation rate η is changed (η=0.62 and 0.76 are the minimum value and maximum value of η when the groove depth is 40% λ in
From
In the above description, the range of optimum values of each of φ, θ, and Ψ r is derived for the relationship with the groove depth G under constant conditions. In contrast to this, an extremely preferable relationship between θ and Ψ, wherein the frequency fluctuation amount at −40° C. to +85° C. is smallest, is shown in
[Expression 46]
Ψ=1.19024×103×θ3−4.48775×10−1×θ2+5.64362×101×θ−2.32327×103±1.0 (31)
Because of this, it is possible to fix Ψ by θ being fixed, and it is possible to make the range of Ψ 42.79°≦Ψ≦49.57° when the range of θ is 117°≦θ≦142°. The groove depth G and electrode film thickness H in the simulation are G=0.04λ, and H=0.02λ.
Due to the heretofore described kinds of reason, by configuring the SAW resonator 10 in accordance with the various conditions fixed in the embodiment, it is possible to obtain a SAW resonator which can realize good frequency-temperature characteristics fulfilling the target values.
Also, with the SAW resonator 10 according to the embodiment, the improvement in the frequency-temperature characteristics is sought by having the film thickness H of the electrode film in the range of 0<H≦0.035λ, as shown in Equation (7) and
Also, on carrying out a high temperature storage test on a SAW resonator manufactured under the same conditions as those in
With the SAW resonator 10 manufactured under the heretofore described kinds of condition, conditions wherein H+G=0.067λ (aluminum film thickness 2,000 Å, groove depth 4,700 Å), the IDT line occupation rate ηi=0.6, the reflector line occupation rate ηr=0.8, the Euler angles are (0°, 123°, and 43.5°), the IDT pair number is 120, the intersection width is 40λ (λ=10 μm), the number of reflectors (per side) is 72 (36 pairs), and the electrode fingers have no angle of tilt (the electrode finger array direction and SAW phase velocity direction correspond), frequency-temperature characteristics like those shown in
In
In the embodiment, a description has been given of the effect on the frequency-temperature characteristics of the groove depth G, electrode film thickness H, and the like. However, the combined depth of the groove depth G and electrode film thickness H (the level difference) also has an effect on static characteristics such as the equivalent circuit constant and CI value, and on the Q value. For example,
The frequency, equivalent circuit constant, and static characteristics of the SAW resonator 10 exhibiting frequency-temperature characteristics like those shown in
Also,
The basic data of the SAW resonators according to the simulation are as follows.
Basic Data of SAW Resonator 10 according to the Embodiment
H: 0.02λ
G: changes
IDT line occupation rate ηi: 0.6
Reflector line occupation rate ηr: 0.8
Euler angles (0°, 123°, and 43.5°)
Pair number: 120
Intersection width: 40λ (λ=10 μm)
Reflector number (per side): 60
No electrode finger tilt angle
Basic Data of Heretofore known SAW Resonator
H: changes
G: zero
IDT line occupation rate ηi: 0.4
Reflector line occupation rate ηr: 0.3
Euler angles (0°, 123°, and 43.5°)
Pair number: 120
Intersection width: 40λ (λ=10 μm)
Reflector number (per side): 60
No electrode finger tilt angle
When referring to
In order to efficiently confine the energy of a surface acoustic wave excited in the stop band upper end mode, a stop band upper end frequency ft2 of the IDT 12 should be set between a stop band lower end frequency fr1 of the reflectors 20 and a stop band upper end frequency fr2 of the reflectors 20, as in
[Expression 47]
fr1<ft2<fr2 (32)
Because of this, a reflection coefficient Γ of the reflectors 20 at the stop band upper end frequency ft2 of the IDT 12 increases, and the stop band upper end mode SAW excited with the IDT 12 is reflected by the reflectors 20 to the IDT 12 side with a high reflection coefficient. Then, the stop band upper end mode SAW energy confinement becomes stronger, and it is possible to realize a low-loss resonator.
As opposed to this, in the event that the relationship between the stop band upper end frequency ft2 of the IDT 12 and the stop band lower end frequency fr1 of the reflectors 20 and stop band upper end frequency fr2 of the reflectors 20 is set to the condition of ft2<fr1, or the condition of fr2<ft2, the reflection coefficient Γ of the reflectors 20 at the stop band upper end frequency ft2 of the IDT 12 decreases, and it becomes difficult to realize a strong energy confinement condition.
Herein, in order to realize the condition of Equation (32), it is necessary to make a frequency shift of the stop band of the reflectors 20 to an area higher than the stop band of the IDT 12. Specifically, this can be realized by making the array cycle of the conductor strips 22 of the reflectors 20 shorter than that of the array cycle of the electrode fingers 18 of the IDT 12. Also, as other methods, it can be realized by making the thickness of the electrode film formed as the conductor strips 22 of the reflectors 20 less than the thickness of the electrode film formed as the electrode fingers 18 of the IDT 12, or by making the depth of the inter-conductor strip grooves of the reflectors 20 less than the depth of the inter-electrode finger grooves of the IDT 12. Also, a plurality of these methods may be employed in combination.
According to
In the heretofore described embodiment, the IDT 12 configuring the SAW resonator 10 is shown in such a way that all the electrode fingers intersect alternately. However, the SAW resonator 10 according to the invention can also achieve a considerable advantage with only the quartz crystal substrate thereof. For this reason, even in the event that the electrode fingers 18 in the IDT 12 are thinned out, it is possible to achieve the same kind of advantage.
Also, regarding the grooves 32 too, they may be partially provided between the electrode fingers 18 and between the conductor strips 22 of the reflectors 20. In particular, as the central portion of the IDT 12, which has a high oscillatory displacement, has a dominant effect on the frequency-temperature characteristics, a structure may be adopted wherein the grooves 32 are provided only in that portion. With this kind of structure too, it is possible to achieve a SAW resonator 10 with good frequency-temperature characteristics.
Also, in the heretofore described embodiment, it is noted that Al or an Al-based alloy is used as the electrode film. However, the electrode film may be configured using another metal material, provided that it is a metal which can achieve the same advantage as the embodiment.
Also, although the heretofore described embodiment is a one-terminal pair SAW resonator in which only one IDT is provided, the invention is also applicable to a two-terminal pair SAW resonator in which a plurality of IDTs are provided, and is also applicable to a longitudinally coupled or transversally coupled double mode SAW filter or multiple mode SAW filter.
Next, a description will be given, referring to
In the SAW oscillator 100 according to the embodiment, the SAW resonator 10 and IC 50 are housed in the same package 56, and electrode patterns 54a to 54g formed on a bottom plate 56a of the package 56, and the pectinate electrodes 14a and 14b of the SAW resonator 10 and pads 52a to 52f of the IC 50, are connected by metal wires 60. Then, a cavity of the package 56 housing the SAW resonator 10 and IC 50 is hermetically sealed with a lid 58. By adopting this kind of configuration, it is possible to electrically connect the IDT 12 (refer to
Therefore, in response to a demand for an expansion of operating temperature range and higher accuracy of internally mounted electronic devices, with the effect of internal heat generation increasing along with the miniaturization of blade servers and other packages, in addition to a higher reference clock frequency due to the speeding-up of information communication in recent years, and furthermore, in response to a market which needs long-term, stable operating in environments from low temperature to high temperature, such as wireless base stations installed outdoors, the SAW oscillator according to the invention is preferred, as it has extremely good frequency-temperature characteristics of a frequency fluctuation amount of approximately 20 (ppm) or less in its operating temperature range (service temperature range: −40° C. to +85° C.).
Furthermore, as the SAW resonator according to the invention, or SAW oscillator including the SAW resonator, realizes a significant improvement in frequency-temperature characteristics, it contributes largely to realizing a product with, as well as extremely good frequency-temperature characteristics, excellent jitter characteristics and phase noise characteristics, for example, a mobile telephone, a hard disc, a personal computer, a tuner receiving a BS and CS broadcast, an instrument processing a high frequency signal transmitted through a coaxial cable or an optical signal transmitted through an optical cable, or an electronic instrument such as a server network instrument or wireless communication instrument which needs a high frequency, high accuracy clock (low jitter, low phase noise) in a wide temperature range, and it goes without saying that it contributes greatly to further system reliability and quality improvement.
As heretofore described, as the SAW resonator according to the invention has inflection points within the operating temperature range (service temperature range: −40° C. to +85° C.), as shown in
As opposed to this, the SAW resonator according to the invention, with the frequency fluctuation amount describing a tertiary curve, or an approximate tertiary curve, within the operating temperature range, realizes a dramatic reduction of the frequency fluctuation amount. Changes in the frequency fluctuation amount within the operating range for a SAW resonator whose IDT and reflectors are covered in a protective film are shown in
The example shown in
Basic Data of SAW Resonator according to Example shown in
H: (material: aluminum): 2,000 (Å)
G: 4,700 (Å)
(H+G=0.067)
IDT line occupation rate ηi: 0.6
Reflector line occupation rate ηr: 0.8
In-plane rotation ST cut substrate with Euler angles (0°, 123°, and 43.5°)
Pair number: 120
Intersection width: 40λ (λ=10 (μm))
Reflector number (per side): 36
No electrode finger tilt angle
Protective film (alumina) thickness 400 (Å)
Secondary temperature coefficient 62 =+0.0007 (ppm/° C.2)
The example shown in
Basic Data of SAW Resonator According to Example Shown in
H: (material: aluminum): 2,000 (Å)
G: 4,700 (Å)
(H+G=0.067)
IDT line occupation rate ηi: 0.6
Reflector line occupation rate ηr: 0.8
In-plane rotation ST cut substrate with Euler angles (0°, 123°, and 43.5°)
Pair number: 120
Intersection width: 40λ (λ=10(μm))
Reflector number (per side): 36
No electrode finger tilt angle
Protective film (SiO2) thickness 400 (Å)
Secondary temperature coefficient β=+0.0039 (ppm/° C.2)
The entire disclosure of Japanese Patent Application No. 2009-045359, filed Feb. 27, 2009 and Japanese Patent Application No. 2009-050112, filed Mar. 4, 2009 are expressly incorporated by reference herein.
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