CN100539411C - surface acoustic wave device - Google Patents

Abstract

The invention provides surface acoustic wave device.Adopt the surface acoustic wave device of quartz base plate to have the device size littler, and show high Q and excellent frequency-temperature characterisitic than conventional structure.On piezoelectric substrate (1), be equipped with by a plurality of interdigitation electrodes and refer to the interdigitation electrode (2) that constitutes, and the both sides of interdigitation electrode (2) be provided with grating reflector (3a, 3b).Piezoelectric substrate (1) is following quartzy flat board: wherein, the cutting angle θ that rotary Y cutting cuts quartz base plate is set in the scope of in the counterclockwise direction-64.0 ° of Z crystallographic axis＜θ＜-49.3 °, the direction of propagation of surface acoustic wave is set to become 90 ° ± 5 ° with respect to the X crystallographic axis, and the sound wave of being excited is the SH ripple.Interdigitation electrode (2) and reflector (3a, 3b) by Al or the alloy that mainly comprises Al constitute, be under the situation of wavelength of surface acoustic wave at λ, be set in the scope of 0.04＜H/ λ＜0.12 by the electrode film thickness H/ λ of standard of wavelengthization.

Description

surface acoustic wave device

technical field

The present invention relates to a surface acoustic wave device using a quartz substrate in which the device size is reduced, the Q value is increased, and the frequency-temperature characteristics are improved.

Background technique

In recent years, surface acoustic wave (hereinafter referred to as SAW) devices have been widely used as components of mobile communication terminals, in-vehicle equipment, etc., and are highly required to be miniaturized, have a high Q value, and have excellent frequency stability.

As a SAW device that realizes these needs, there is a SAW device using an ST-cut quartz substrate. The ST-cut quartz substrate is the cut name of a quartz plate having a face (XZ' face) obtained by rotating the XZ plane from the Z crystal axis at an angle of 42.75° in the counterclockwise direction using the X crystal axis as the axis of rotation, and the ST-cut quartz The substrate uses a SAW (hereinafter referred to as ST-cut quartz SAW) which is a (P+SV) wave (referred to as “Rayleigh wave”) propagating in the X crystal axis direction. ST-cut quartz SAW devices are widely used in SAW resonators used as oscillators, filters for IF installed between the RF section of mobile communication terminals and ICs, etc.

The reason why ST-cut quartz SAW devices can realize small devices with high Q value includes the fact that the reflection of SAW can be effectively used. An ST-cut quartz SAW resonator shown in FIG. 13 will be explained as an example. The ST-cut quartz SAW resonator has the following structure: On the ST-cut quartz substrate 101, an interdigitated electrode (hereinafter referred to as IDT) 102 having a plurality of electrode fingers inserted into each other is provided, and on both sides of the IDT 102, electrodes for Grid reflectors 103a and 103b reflecting SAW. Since the ST-cut quartz SAW is a wave propagating along the surface of the piezoelectric substrate, it is effectively reflected by the grating reflectors 103a and 103b, and the SAW energy can be sufficiently confined in the IDT 102, so that a high Q value can be obtained. small devices.

An important factor for using SAW devices is frequency-temperature characteristics. In ST-cut quartz SAW, it is well known that the primary temperature coefficient of the frequency-temperature characteristic of SAW is zero, and its characteristics are expressed by a quadratic curve, and because the inflection point temperature (turnover temperature) is located at the center of the operating temperature range by performing Adjustment significantly reduces the amount of frequency fluctuation, so SAW has excellent frequency stability.

However, in ST-cut quartz SAW devices, although the primary temperature coefficient is zero, the secondary temperature coefficient is relatively large, eg -0.034 (ppm/°C ² ). Therefore, when the operating temperature range is expanded, the amount of frequency fluctuation becomes extremely large.

As a method for solving this problem, a SAW device is disclosed in "Surface Skimming Bulk Wave" by Meirion Lewis, IEEE Ultrasonics Symp.Proc., pp.744 to 752 (1977) and Japanese Patent Publication No. Sho 62-016050. As shown in FIG. 14, this SAW device is characterized in that the cut angle θ of the rotating Y-cut quartz substrate is set in the vicinity of a position rotated by an angle of −50° in the counterclockwise direction from the Z crystal axis, and the propagation direction of the SAW is set at The direction perpendicular to the X crystal axis (Z' axis direction). Furthermore, when the cut angle is represented by Euler angles, (0°, θ+90°, 90°)=(0°, 40°, 90°) is obtained. This SAW device is characterized in that the SH wave propagating just below the surface of the piezoelectric substrate is excited by the IDT, confining the oscillation energy just below the electrode. The frequency-temperature characteristics of this SAW device form a cubic curve, and excellent frequency-temperature characteristics are obtained because the amount of frequency fluctuation in the operating temperature range is significantly reduced.

However, since the SH wave is a wave traveling substantially submerged inside the substrate, the reflection efficiency for the SAW obtained by the grating reflector is lower than that of the ST-cut quartz SAW propagating along the surface of the piezoelectric substrate. Therefore, there is a problem that it is difficult to realize a small SAW device with high Q. Since the previous publication includes a disclosure about use as a delay line not utilizing SAW reflection, but it does not propose any means utilizing SAW reflection, it is considered difficult to put a SAW device into practical use.

In order to solve the above-mentioned problems, Japanese Patent Publication No. 01-034411 discloses a so-called multi-pair IDT type SAW resonator, wherein, as shown in FIG. And a plurality of pairs (for example, 800±200 pairs) of IDTs 112 are formed on the piezoelectric substrate 111 in which the propagation direction of the SAW is set to a direction perpendicular to the X crystal axis (Z' axis direction), thereby eliminating the need to use grid-shaped reflector and only through the reflection of the IDT 112 itself to confine the SAW energy, thereby achieving high Q.

However, the multi-pair IDT type SAW resonator cannot obtain a highly efficient energy confinement effect compared to a SAW resonator including a grating reflector. Since the number of IDT pairs required to obtain a high Q value is greatly increased to 800±200 pairs, there is a problem that the device size becomes larger than that of an ST-cut quartz SAW resonator, thereby failing to meet the demand for size reduction in recent years.

In the SAW resonator disclosed in Japanese Patent Application Publication No. 01-034411, when the wavelength of the SAW excited by the IDT is expressed as λ, it can be achieved by setting the electrode film thickness to 2% λ or more, preferably 4% λ or smaller to increase the Q value. However, when the resonance frequency is 200MHz, the Q value reaches saturation close to 4% λ, but the Q value obtained at this time becomes only about 20000, compared with ST-cut quartz SAW resonators, which can only be obtained with ST-cut quartz SAW The Q value in the resonator is approximately equal to the Q value. For this reason, it is considered that reflection cannot be effectively utilized since SAW cannot sufficiently concentrate on the piezoelectric substrate surface when the film thickness is in the range of 2% λ or more and 4% λ or less.

[Patent Document 1] Japanese Patent Publication No. 62-016050

[Patent Document 2] Japanese Patent Publication No. 01-034411

[Non-Patent Document 1] Meirion Lewis, "Surface Skimming Bulk Wave, SSBW", IEEE Ultrasonics Symp.Proc., pp.744 to 752 (1977)

Contents of the invention

The problem to be solved by the present invention

The problem to be solved is as follows: When an ST-cut quartz substrate is used as the piezoelectric substrate, the quadratic temperature coefficient of the frequency-temperature characteristic is as large as -0.034 (ppm/°C ² ), so that the amount of frequency fluctuation actually becomes considerably large. The structure of the SAW device disclosed in Japanese Patent Application Publication No. 01-034411 involves the problem that the device size increases because the logarithm of IDT has to be set considerably large.

The device that solves the above-mentioned problems

In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention provides a SAW device including a piezoelectric substrate and an alloy formed on the piezoelectric substrate and consisting of or including Al as a main component The IDT made, the stimulated wave is SH wave, and the SAW device is characterized in that the piezoelectric substrate is a rotating Y-cut substrate made of a quartz plate, wherein the cutting angle θ of the piezoelectric substrate is when the The rotation angle of the Z crystal axis when the piezoelectric substrate rotates around the X crystal axis, the direction in which the piezoelectric substrate rotates from the positive Z side to the positive Y axis side is the direction in which the cutting angle θ is negative, and the cutting angle θ is set within the range of -64.0°<θ<-49.3°, and the propagation direction of the SAW is set to be 90°±5° with respect to the X crystal axis, and, when the wavelength of the SAW to be excited is expressed as λ , the electrode film thickness H/λ normalized by the wavelength of the IDT is set to satisfy 0.04<H/λ<0.12.

The present invention according to claim 2 provides the SAW device, characterized in that the relationship between the cutting angle θ and the electrode film thickness H/λ satisfies: -1.34082×10 ^-4 ×θ ³ -2.34969×10 ^-2 × ^θ2-1.37506 ×θ-26.7895<H/λ<-1.02586× ^10-4 × ^θ3-1.73238 × ^10-2 × ^θ2-0.977607 ×θ-18.3420.

The present invention according to claim 3 provides the SAW device, wherein when the electrode finger width/(electrode finger width+interval between electrode fingers) of the electrode fingers constituting the IDT is defined as the line metallization ratio mr When , the relationship between the cutting angle θ and the product H/λ×mr of the electrode film thickness and wire metallization rate satisfies: -8.04489×10 ^-5 ×θ ³ -1.40981×10 ^-2 ×θ ² -0.825038×θ- 16.0737<H/λ×mr<-6.15517×10 ^-5 ×θ ³ -1.03943×10 ^-2 ×θ ² -0.586564×θ-11.0052.

The present invention according to claim 4 provides a SAW device including a piezoelectric substrate and an IDT formed on the piezoelectric substrate and made of Al or an alloy including Al as a main component, utilizing excited The wave is an SH wave, and the SAW device is characterized in that the piezoelectric substrate is a rotating Y-cut substrate made of a quartz plate, wherein the cutting angle θ of the piezoelectric substrate is when the piezoelectric substrate surrounds the X-crystal The rotation angle of the Z crystal axis when the axis rotates, the direction in which the piezoelectric substrate rotates from the positive Z side to the positive Y axis side is the direction in which the cutting angle θ is negative, and the cutting angle θ is set at -61.4° <θ<-51.1°, and the propagation direction of the SAW is set to be 90°±5° relative to the X crystal axis, and, when the wavelength of the stimulated SAW is expressed as λ, the wavelength normalized by the IDT The electrode film thickness H/λ is set to satisfy 0.05<H/λ<0.10.

The present invention according to claim 5 provides the SAW device, characterized in that the relationship between the cutting angle θ and the electrode film thickness H/λ satisfies: -1.44605×10 ^-4 ×θ ³ -2.50690×10 ^-2 × ^θ2-1.45086 ×θ-27.9464<H/λ<-9.87591× ^10-5 × ^θ3-1.70304 × ^10-2 × ^θ2-0.981173 ×θ-18.7946.

The present invention according to claim 6 provides the SAW device, wherein when the electrode finger width/(electrode finger width+interval between electrode fingers) of the electrode fingers constituting the IDT is defined as the line metallization ratio mr When , the relationship between the cutting angle θ and the product H/λ×mr of the electrode film thickness and wire metallization ratio satisfies: -8.67632×10 ^-5 ×θ ³ -1.50414×10 ^-2 ×θ ² -0.870514×θ- 16.7678<H/λ×mr<-5.92554×10 ^-5 ×θ ³ -1.02183×10 ^-2 ×θ ² -0.588704×θ-11.2768.

The present invention according to claims 7 to 14 provides the SAW device, wherein the SAW device is any one of the following devices: a one-port SAW resonator, a two-port SAW resonator, a transversely coupled multimode filter filter, a longitudinal coupling type multimode filter, a ladder SAW filter, a transverse SAW filter in which an IDT propagating SAW in both directions or in one direction is provided, or a SAW sensor.

The invention according to claim 15 provides the SAW device, characterized in that the SAW device has grid-like reflectors on both sides of the IDT.

The present invention according to claim 16 provides a module device or an oscillation circuit using the SAW device according to any one of claims 1 to 15 .

Invention effect

The SAW device according to claim 1 or 4 of the present invention has the structure of using a rotation Y with a cut angle θ in the range of -64.0°<θ<-49.3°, preferably -61.4°<θ<-51.1° Cut the quartz substrate, use the SH wave excited so that the propagation direction of the SAW is (90°±5°) relative to the X crystal axis, the electrode material for the IDT and grid reflector is Al or an alloy mainly containing Al, The electrode film thickness H/λ normalized by wavelength is set to satisfy 0.04<H/λ<0.12, preferably 0.05<H/λ<0.10. Since the present invention is configured to concentrate waves traveling originally submerged inside the substrate on the surface of the substrate so that a grating reflector or the like can effectively utilize the reflection of the SAW, it is possible to provide a reduced size compared to an ST-cut quartz SAW device. , A SAW device with high Q value and excellent frequency stability.

By satisfying the conditions of electrode film thickness H/λ and cutting angle θ described in claim 2 or 5, the inflection point temperature Tp (° C.) can be set within the actual temperature range.

By satisfying the condition of the product H/λ×mr of the electrode film thickness and wire metallization rate and the cutting angle θ described in claim 3 or 6, the inflection point temperature Tp (° C.) can be set within the actual temperature range.

By using the various system SAW devices described in any one of claims 7 to 14, it is possible to provide a SAW device that is reduced in size, has a high Q value, and is excellent in frequency stability.

Since the SAW device described in claim 15 sufficiently confines the energy of the SAW in the IDT by providing grid-like reflectors on both sides of the IDT, a small SAW device having a high Q value can be provided.

Since the module device or oscillation circuit described in claim 16 uses the SAW device according to the present invention, a small and high-performance module device or oscillation circuit can be provided.

Description of drawings

1 is a diagram for explaining a SAW resonator according to the present invention, wherein FIG. 1( a ) is a plan view of an IDT, and FIG. 1( b ) is a cross-sectional view of the IDT.

2 shows a comparison between a SAW resonator according to the present invention and a conventional product, wherein FIG. 2(a) is a graph showing a comparison with respect to a Q value, a quality factor, and a secondary temperature coefficient, and FIG. 2(b) is A graph showing a comparison about frequency-temperature characteristics.

3 is a graph showing the relationship between the electrode film thickness H/λ and the Q value in the SAW resonator according to the present invention.

4 is a graph showing the relationship between the electrode film thickness H/λ and the secondary temperature coefficient in the SAW resonator according to the present invention.

5(a) is a graph showing the relationship between the electrode film thickness H/λ and the inflection point temperature Tp in the SAW resonator according to the present invention, and 5(b) is a graph showing the relationship between the cut angle θ and the inflection point temperature Tp therein. A graph of the relationship between the bending point temperature Tp.

6 is a graph showing the cut angle θ and the electrode film thickness H/λ obtained when the inflection point temperature Tp (° C.) in the SAW resonator according to the present invention satisfies Tp=-50, 0, +70, and +125 A diagram of the relationship between.

7 is a graph showing the relationship between the product H/λ×mr of the electrode film thickness and the wire metallization rate and the inflection point temperature Tp in the SAW resonator according to the present invention.

8 is a graph showing the relationship between cut angle θ and electrode film thickness and wire metallization when the inflection point temperature Tp (° C.) in the SAW resonator according to the present invention satisfies Tp=-50, 0, +70, and +125 A graph of the relationship between the product H/λ×mr of the rate.

FIG. 9 is a diagram for explaining a two-port SAW resonator according to the present invention.

Fig. 10 is a diagram for explaining a DMS filter according to the present invention, wherein Fig. 10(a) is a diagram showing a transverse coupling type DMS filter, and Fig. 10(b) is a diagram showing a longitudinal coupling type DMS filter .

FIG. 11 is a diagram for explaining a ladder-shaped SAW filter according to the present invention.

Fig. 12 is a diagram for explaining a transversal SAW filter according to the present invention, wherein Fig. 12(a) is a diagram showing a transversal SAW filter provided with an IDT that excites SAW in two directions, and Fig. 12(b) is A diagram showing a transversal SAW filter provided with an IDT that excites the SAW in one direction.

FIG. 13 is a diagram for explaining a conventional ST-cut quartz SAW resonator.

14(a) and 14(b) are diagrams for explaining a -50° rotation Y-cut 90° X propagation quartz substrate.

FIG. 15 is a diagram for explaining a conventional multi-pair IDT type SAW resonator.

Explanation of reference signs

1 piezoelectric substrate

2 IDT

3a, 3b Grid reflector

4a, 4b Input/Output Pads

5a, 5b Metal wire

6 packages

31 Piezoelectric substrate

32, 33 IDT

34a, 34b Grid reflector

41 Piezoelectric substrate

42 SAW resonators

51 piezoelectric substrate

52 IDT

61 piezoelectric substrate

62 One-port SAW resonator

71 piezoelectric substrate

72 Enter IDT

73 Output IDT

74 shield electrode

75 sound-absorbing material

82, 83 single-phase unidirectional transducer

Detailed ways

The present invention will be described in detail below based on the embodiments shown in the drawings. Fig. 1 (a) is the plan view according to the SAW resonator of the present invention, wherein on the piezoelectric substrate 1 is provided with the IDT 2 that has the positive electrode finger that interposes and negative electrode finger, and is positioned at IDT 2 two sides for pairing Grid reflectors 3a and 3b for SAW reflection. The input pad 4a/output pad 4b of the IDT 2 and the input/output terminal of the package 6 are electrically connected to each other through metal wires 5a and 5b, and the opening part of the package 6 is hermetically sealed by the cover. As shown in FIG. 14 , the piezoelectric substrate 1 is a quartz flat plate in which the cut angle θ of the rotary Y-cut quartz substrate is set near a position rotated by an angle of −50° in the counterclockwise direction from the Z crystal axis, and the propagation of the SAW The direction is set to a direction approximately perpendicular to the X crystal axis (90°±5°), and the excited SAW is a SH wave. The electrode material used for the IDT 2 and the grid reflectors 3a and 3b is Al or an alloy containing Al as a main component. Fig. 1(b) shows the cross section of IDT 2, when the wavelength of the SAW excited on IDT 2 is represented as λ in this embodiment, the electrode film thickness is represented as the value H/λ normalized by wavelength, and when When the electrode finger width L/(electrode finger width L+interval S between electrode fingers) of the electrode fingers constituting the IDT 2 is defined as the line metallization rate mr, mr=0.60 is satisfied.

In the present invention, considering the defects in the conventional technology, the SAW is concentrated on the surface of the piezoelectric substrate by setting the electrode film thickness H/λ larger than the conventional electrode film thickness, so that the grating reflector can be effectively used for The reflection of SAW, and even if the number of IDT logarithms or grid reflectors is reduced, the SAW energy can be confined in the IDT, thereby reducing the size of the device.

In general, in optimal design of a SAW resonator, it is very important to have excellent frequency-temperature characteristics, a high Q value, and a small capacitance ratio γ (that is, a large quality factor (Q/γ)). Various characteristics of the SAW resonator according to the present invention are examined here. Figure 2 depicts various properties of the resonator obtained when, in the SAW resonator shown in Figure 1, a -51° rotation is used to Y-cut a 90° X-propagating quartz substrate (expressed in Euler angles as (0 °, 39°, 90°)) as the piezoelectric substrate 1; the resonance frequency is set to 315MHz; the electrode film thickness H/λ is set to 0.06; the logarithm of IDT 2 is 100; and the grid reflectors 3a and 3b The quantities are 100 each. Figure 2(a) shows the Q value, quality factor, and secondary temperature coefficient based on actual trial production results, and Figure 2(b) shows the frequency-temperature characteristics based on them. For comparison, various characteristics of an ST-cut quartz SAW resonator having a piezoelectric substrate having the same size as that of the SAW resonator according to the present invention are also shown as various characteristics in conventional products.

Referring to FIG. 2, when the SAW resonator according to the present invention and a conventional ST-cut quartz SAW resonator are compared with each other, large values are obtained that the Q value of the former is 1.8 times or more that of the latter, and the quality of the former The factor is about twice that of the latter. Regarding frequency-temperature characteristics, very excellent effects can be confirmed in the SAW resonator according to the present invention: an inflection point temperature Tp of about +25°C can be obtained, and the amount of frequency fluctuation due to temperature is reduced to about 0.6 times that of the conventional technology .

The SAW resonator according to the present invention can reduce the size of the piezoelectric substrate while maintaining a Q value better than that of an ST-cut quartz SAW resonator. This is because the amount of SAW reflection at the IDT or grating reflector according to the present invention increases much more than in the case of an ST-cut quartz SAW resonator with respect to an increase in the electrode film thickness H/λ of the SAW resonator. That is, the SAW resonator according to the present invention can use a smaller number of IDT pairs or grid reflectors than that of an ST-cut quartz SAW resonator by making the electrode film thickness H/λ large. number of registers to achieve a high Q value.

Fig. 3 shows the relationship between the electrode film thickness H/λ and the Q value in a SAW resonator according to the present invention in which the resonator design conditions are the same as those described above. It can be seen from FIG. 3 that a value exceeding the Q value (=15000) of the ST-cut quartz SAW resonator can be obtained in the range of 0.04<H/λ<0.12. In addition, high Q values over 20000 can be obtained by setting the range at 0.05<H/λ<0.10.

Comparing the Q values of the pairs of IDT type SAW resonators shown in Japanese Patent Publication No. 01-034411 with the Q values of the SAW resonators according to the present invention, the Q values obtained in said patent application are obtained when the resonance frequency is the value at 207.561 (MHz), and when the resonance frequency changes to the resonance frequency 315 (MHz) applied in this embodiment, the Q value is about 15000, where the Q value is approximately equal to that of the ST-cut quartz SAW resonator Q value. In a comparison of the dimensions of the resonators, the multi-pair IDT type SAW resonator described in said patent application requires 800 ± 200 IDT pairs, but the present invention only needs to accommodate 200 for both IDTs and grating reflectors space for IDT pairs, so the present invention can significantly reduce the size. Therefore, by setting the electrode film thickness within the range of 0.04<H/λ<0.12 and providing a grating reflector to effectively reflect the SAW, it is possible to achieve resonance with the multi-pair IDT type SAW disclosed in Japanese Patent Publication No. 01-034411 Compared with SAW devices with smaller size and higher Q value.

Next, FIG. 4 shows the relationship between the electrode film thickness H/λ and the secondary temperature coefficient in the SAW resonator according to the present invention, in which the design conditions of the resonator are the same as those described above. It can be seen from Fig. 4 that in the range of 0.04<H/λ<0.12 where a high Q value can be obtained, a value better than the secondary temperature coefficient -0.034 (ppm/°C ² ) of the ST-cut quartz SAW resonator can be obtained.

Based on the above, by setting the electrode film thickness H/λ within the range of 0.04<H/λ<0.12, it is possible to provide a size comparable to the ST-cut quartz SAW device and the SAW device disclosed in Japanese Patent Publication No. 01-034411 Smaller SAW devices with higher Q values and excellent frequency stability.

Although only the case of setting the cut angle θ to -51° has been described above, even if the cut angle θ is changed in the SAW resonator according to the present invention, the film thickness dependence does not change greatly, and thus, By setting the electrode film thickness within the range of 0.04<H/λ<0.12, excellent Q value and excellent quadratic temperature coefficient can be obtained even if the cutting angle is shifted by several degrees from -51°.

The SAW resonator according to the present invention exhibits tertiary temperature characteristics in a very wide temperature range, but the temperature characteristics can be regarded as quadratic characteristics in a specific narrow temperature range, and the inflection point temperature Tp in this temperature range depends on the electrode Varies in film thickness and cut angle. Therefore, no matter how excellent the frequency-temperature characteristic is, when the inflection point temperature Tp fluctuates outside the use temperature range, the frequency stability is significantly deteriorated. In order to realize excellent frequency stability in the practical use temperature range (-50°C to +125°C), not only the quadratic temperature coefficient but also the inflection point temperature Tp must be considered in detail.

Fig. 5(a) shows the relationship between the electrode film thickness H/λ and the inflection point temperature Tp obtained when the cut angle θ is set to -50.5° in the SAW resonator according to the present invention. It is obvious from Fig. 5(a) that when the electrode film thickness H/λ becomes larger, the inflection point temperature Tp becomes lower, and the relationship between the electrode film thickness H/λ and the inflection point temperature Tp can be obtained by the following approximate formula express.

Tp(H/λ)＝-41825×(H/λ) ² +2855.4×(H/λ)-26.42 …(1)

Apart from its intercept point, this approximation (1) can be applied to cut angles around -50°.

FIG. 5( b ) shows the relationship between the cut angle θ and the inflection point temperature Tp obtained when the film thickness H/λ is set to 0.06 in the SAW resonator according to the present invention. It is apparent from FIG. 5(b) that when the absolute value of the cut angle θ decreases, the inflection point temperature Tp decreases, and the relationship between the cut angle θ and the inflection point temperature Tp can be expressed by the following approximate formula.

Tp(θ)＝-43.5372×θ-2197.14 ...(2)

Subsequently, it can be seen from formula (1) and formula (2) that when the electrode film thickness H/λ is set to satisfy 0.04<H/λ<0.12, in order to set the inflection point temperature Tp within the actual use temperature range ( -50°C to +125°C), it is sufficient to set the cutting angle θ in the range of -59.9°≤θ≤-48.9°.

The inflection point temperature Tp is expressed by the following approximate formula using formula (1) and formula (2) when both the electrode film thickness H/λ and the cut angle θ are considered.

Tp(H/λ, θ)=Tp(H/λ)+Tp(θ)=-41825×(H/λ) ² +2855.4×(H/λ)-43.5372×θ-2223.56 …(3)

In order to set the inflection point temperature Tp within the operating temperature range (-50°C to +125°C), the electrode film thickness H/λ and cut angle θ can be set at the following equation obtained from approximate equation (3): In the range.

0.9613≤-18.498×(H/λ) ² +1.2629×(H/λ)-0.019255×θ≤1.0387 …(4)

Therefore, in the present invention, using a rotating Y-cut quartz substrate with a cut angle θ in the range of -59.9° ≤ θ ≤ -48.9°, using a SH excited so that the propagation direction of the SAW is a direction approximately perpendicular to the X-axis wave, the electrode material used for the IDT and grid reflector is Al or an alloy containing Al as a main component, and the electrode film thickness H/λ is set to satisfy 0.04<H/λ<0.12. With this structure, it is possible to realize a SAW device that is smaller in size than ST-cut quartz SAW devices, has a higher Q value, and is excellent in frequency stability.

Optimal conditions will be examined here. As shown in FIG. 3 , preferably, the electrode film thickness H/λ is set within the range of 0.05<H/λ<0.10 where a Q value of 20000 or higher can be obtained. Furthermore, preferably, the cutting angle θ is set within the range of -55.7°≤θ≤-50.2° to set the inflection point temperature Tp within a more practical application temperature range (0°C to +70°C). Further, it is preferable to set the cutting angle θ and the electrode film thickness H/λ within the range defined by the following formula obtained from approximate formula (3).

0.9845≤-18.518×(H/λ) ² +1.2643×(H/λ)-0.019277×θ≤1.0155 …(5)

In the above description, it has been based on the relationship between the electrode film thickness H/λ and the inflection point temperature Tp obtained when the cutting angle θ shown in Fig. 5(a) is set to -50.5°, and when the The relationship between the cutting angle θ and the inflection point temperature Tp obtained when the electrode film thickness H/λ is set to 0.06 shown in 5(b), deduces the case where the inflection point temperature Tp falls within the actual use temperature range The relationship between the lower electrode film thickness H/λ and the cutting angle θ. More specific conditions were found out by experiments carried out in an extended range of the cutting angle θ, and they will be described below.

6 shows the relationship between the cut angle θ of the quartz substrate and the electrode film thickness H/λ obtained when the inflection point temperature Tp (°C) in the SAW resonator satisfies Tp=-50, 0, +70 and +125 Relationship, where the approximate formula of each Tp characteristic is as follows:

It can be seen from Fig. 6 that in order to set the inflection point temperature Tp (° C.) to satisfy -50≤Tp≤+125 as the actual range, the cut angle θ and the electrode film thickness H/λ can be set to satisfy the requirement of Tp=-50 The area enclosed by the curve of ℃ and Tp=+125℃, namely -1.34082×10 ^-4 ×θ ³ -2.34969×10 ^-2 ×θ ² -1.37506×θ-26.7895<H/λ<-1.02586×10 ^-4 × θ ³ -1.73238×10 ^-2 ×θ ² -0.977607×θ-18.3420. At this time, the range of the electrode film thickness H/λ must be set to satisfy 0.04<H/λ<0.12 which makes the characteristics better than those of conventional ST-cut quartz devices, and the range of the cutting angle θ must be set to meet the same value as shown in FIG. 6 The range shown from point A to point B corresponds to -64.0<θ<-49.3.

Furthermore, in consideration of more optimal conditions, preferably, the inflection point temperature Tp (° C.) is set to satisfy 0≦Tp≦+70 corresponding to a more practical use temperature range. In order to set Tp(°C) within the above range, the cutting angle θ and electrode film thickness H/λ can be set to satisfy the area surrounded by the curves Tp=0°C and Tp=+70°C shown in Figure 6, ie -1.44605 ×10 ^-4 ×θ ³ -2.50690×10 ^-2 ×θ ² -1.45086×θ-27.9464<H/λ<-9.87591×10 ^-5 ×θ ₃ -1.70304×10 ^-2 ×θ ² -0.981173×θ- 18.7946. Further, preferably, the electrode film thickness H/λ is set to satisfy a range of 0.05<H/λ<0.10 where a Q value of 20000 or higher can be obtained. In addition, in order to set the electrode film thickness within the above range and set the inflection point temperature Tp(°C) within the range of 0≤Tp≤+70, it is necessary to set the cutting angle θ to satisfy the same as that obtained from Fig. 6(a). The range shown from point C to point D corresponds to -61.4<θ<-51.1.

According to the above detailed investigation, it has been found that by using the rotation Y-cut quartz substrate with the cutting angle θ satisfying -64.0°<θ<-49.3°, preferably -61.4°<θ<-51.1°, the use of the excited to make the SAW SH wave whose propagation direction is a direction approximately perpendicular to the X-axis, an electrode material for an IDT or a grating reflector is formed of Al or an alloy mainly containing Al, and the electrode film thickness H/λ is set to satisfy 0.04<H/ λ<0.12, preferably 0.05<H/λ<0.10, excellent temperature characteristics with a Q value greater than that of ST-cut quartz SAW devices can be obtained, and the inflection point temperature Tp can be set within the actual operating temperature range.

While an example in which the wire metallization ratio mr of the IDT is fixed at 0.60 has been described above, an example of Tp characteristics obtained when the wire metallization ratio is included in the variable will be considered below.

FIG. 7 shows the relationship between the product H/λ×mr of the electrode film thickness and the wire metallization rate and the inflection point temperature Tp. The vertical axis represents the inflection point temperature Tp (° C.), while the horizontal axis represents the product H/λ×mr of the electrode film thickness and the wire metallization rate. At this time, the cut angle θ of the quartz substrate was set to -51.5°. As shown in FIG. 7 , it can be seen that the inflection point temperature Tp decreases as the value of the product H/λ×mr of the electrode film thickness and the wire metallization rate increases.

Next, FIG. 8 shows the product H/λ× The relationship between mr. The approximate formula of each Tp characteristic is as follows:

It can be seen from Fig. 8 that in order to set the inflection point temperature Tp (°C) to satisfy -50≤Tp≤+125 as a practical range, the product H/λ× mr is set to satisfy the area surrounded by the curves Tp=-50°C and Tp=+125°C, i.e. -8.04489× ^10-5 × ^θ3-1.40981 × ^10-2 × ^θ2-0.825038 ×θ-16.0737<H/λ ×mr<-6.15517×10 ^-5 ×θ ³ -1.03943×10 ^-2 ×θ ² -0.586564×θ-11.0052. At this time, it is necessary to set the range of electrode film thickness H/λ to 0.04<H/λ<0.12, which can obtain better characteristics than those in conventional ST-cut quartz devices, and to set the range of cut angle θ to -64.0<θ<-49.3.

In order to set the inflection point temperature Tp (°C) to satisfy the more practical operating temperature range of 0≤Tp≤+70, the cutting angle θ and the product H/λ×mr of the electrode film thickness and wire metallization ratio can be set To satisfy the area surrounded by the curves Tp=0°C and Tp=+70°C shown in Figure 8, that is, -8.67632×10 ^-5 ×θ ³ -1.50414×10 ^-2 ×θ ² -0.870514×θ-16.7678<H /λ×mr<-5.92554×10 ^-5 ×θ ³ -1.02183×10 ^-2 ×θ ² -0.588704×θ-11.2768. At this time, it is preferable to set the electrode film thickness H/λ to satisfy 0.05<H/λ<0.10 that can obtain a Q value of 20000 or higher, and, in order to set the electrode film thickness to the above-mentioned range and to set the inflection point temperature Tp (°C) is set within the range of 0≤Tp≤+70, and the cutting angle θ is preferably set to satisfy -61.4<θ<-51.1.

Although only the one-port SAW resonator as shown in FIG. 1 has been described so far, the present invention can be applied to other SAW devices other than the one-port SAW resonator. The structures of various SAW devices will be described below.

9 shows a two-port SAW resonator in which IDTs 32 and 33 are provided on a piezoelectric substrate 31 along the propagation direction of the SAW, and grid-shaped reflectors 34a are provided on both sides of the IDTs 32 and 33. and 34b, in this two-port SAW resonator also a high Q value can be achieved like the one-port SAW resonator.

FIG. 10 shows a system using a dual-mode SAW (DMS) filter acoustically coupled with SAW resonators as a resonator filter, where FIG. Adjacent to the transversely coupled DMS filter provided with the SAW resonator 42, Fig. 10 (b) shows where the two-port longitudinal coupling of the SAW resonator comprising the IDT 52 is provided on the piezoelectric substrate 51 along the propagation direction of the SAW type DMS filter. The transversely coupled DMS filter utilizes acoustic coupling perpendicular to the direction of propagation, while the two-port longitudinally coupled DMS filter utilizes acoustic coupling horizontal to the direction of propagation. These DMS filters feature a flat passband and excellent out-of-band rejection. A two-port longitudinally coupled DMS filter can be connected with a SAW resonator to highly attenuate frequency bands near the passband. The present invention can be applied to a multimode SAW filter utilizing high-order modes, or to a multimode SAW filter performing acoustic coupling both in the direction perpendicular to the propagation direction and in the horizontal direction.

11 shows a ladder-type SAW filter constituted by arranging a plurality of one-port SAW resonators 62 in a trapezoidal shape (composed of series, parallel, and series) on a piezoelectric substrate 61, as another system of resonator filters. . The ladder-type SAW filter can obtain filter characteristics in which the attenuation slope near the passband is steeper than the attenuation slope near the passband in the DMS filter.

12 shows a transversal SAW filter, wherein FIG. 12(a) shows a transversal SAW filter in which an input IDT 72 and an output IDT 73 are arranged at predetermined intervals along the propagation direction of the SAW on a piezoelectric substrate 71. IDTs 72 and 73 propagate the SAW in both directions. Shield electrodes 74 may be provided to prevent the influence of direct waves between the input and output terminals, or sound absorbing materials 75 may be applied on both ends of the piezoelectric substrate 71 to suppress unnecessary reflected waves from the end faces of the substrate. Since the amplitude characteristics and phase characteristics of the transversal SAW filter can be designed independently of each other and its out-of-band rejection is high, the transversal SAW filter is often used as an IF filter.

The transverse SAW filter has a problem that the insertion loss of the filter becomes large since the SAW propagates equally to the right and to the left along the propagation direction. As a method for solving the above-mentioned problem, as shown in FIG. The excitation and reflection of the SAW are weighted by changing the arrangement of the electrode fingers or the width of the electrode fingers, so as to excite the SAW in one direction. Since excitation of the SAW is performed unidirectionally, low-loss filter characteristics can be obtained. As other structures, there is a so-called reflection bank type transverse SAW filter in which grid-shaped reflectors are provided between active electrodes of the IDT, and the like.

In the above-mentioned various SAW devices, it is obvious that by using a quartz flat plate as the piezoelectric substrate in which the cut angle θ of the Y-cut quartz substrate is set to satisfy -64.0°<θ from the Z crystal axis in the counterclockwise direction <-49.3° range, preferably -61.4°<θ<-51.1° range, and the propagation direction of the surface acoustic wave is set to be 90°±5° relative to the X crystal axis, and the electrode film thickness H/λ Setting to satisfy the range of 0.04<H/λ<0.12, preferably 0.05<H/λ<0.10, can obtain advantages similar to those obtained in the present invention.

In the above-mentioned SAW device, it is obvious that even if a protective film (for example, a protective film made of _SiO2 , etc., a protective film obtained by anodizing Al, etc.) is formed on the IDT or grid reflector, Alternatively, a tight adhesion layer or other metal thin film for improving electrical resistance is formed on the upper or lower portion of the Al electrode, and similar advantages to those obtained in the present invention can also be obtained. It goes without saying that the SAW device according to the present invention can be applied to sensor devices or module devices, oscillation circuits, and the like. Since the capacity ratio γ can be reduced by using the SAW device according to the present invention in a voltage controlled SAW oscillator (VCSO) or the like, a wider frequency variation range can be employed.

In addition to the structure in which the SAW chip and the package are wire-bonded to each other as shown in FIG. Connected flip-chip bonding (FCB) structure, a CSP (Chip Scale Package) structure in which a SAW chip is flip-chip bonded on a wiring substrate and resin-sealed around the SAW chip, in which the SAW chip is formed by forming metal layer or resin layer without using a package or a WLCSP (Wafer Level Scale Package) structure of a wiring substrate or the like. An AQP (All Quartz Package) structure may be employed in which lamination and sealing are performed in a state where quartz devices are sandwiched between quartz substrates or glass substrates. Since the AQP structure is simply sandwiched using a quartz substrate or a glass substrate, no encapsulation is required, thinning can be performed, and outgassing by adhesives can be reduced by sealing with low-melting glass or direct bonding ( out gas), so that advantages such as excellent aging characteristics can be realized.

Claims (16)

1. A surface acoustic wave device comprising a piezoelectric substrate and an interdigitated electrode formed on the piezoelectric substrate and formed of Al or an alloy containing Al as a main component, the stimulated wave being an SH wave, in, The piezoelectric substrate is a rotating Y-cut substrate made of a quartz plate, Wherein the cut angle θ of the piezoelectric substrate is the rotation angle of the Z crystal axis when the piezoelectric substrate rotates around the X crystal axis, The direction in which the piezoelectric substrate is rotated from the positive Z side to the positive Y axis side is a direction in which the cutting angle θ is negative, and The cut angle θ is set within the range of -64.0°<θ<-49.3°, and the propagation direction of the surface acoustic wave is set to be 90°±5° relative to the X crystal axis, and, When the wavelength of the excited surface acoustic wave is expressed as λ, the electrode film thickness H/λ normalized to the wavelength of the interdigitated electrode is set to satisfy 0.04<H/λ<0.12. 2. The surface acoustic wave device according to claim 1, wherein the relationship between the cutting angle θ and the electrode film thickness H/λ satisfies -1.34082×10 ^-4 ×θ ³ -2.34969×10 ^-2 ×θ ² -1.37506 ×θ-26.7895<H/λ<-1.02586×10 ^-4 ×θ ³ -1.73238×10 ^-2 ×θ ² -0.977607×θ-18.3420. 3. The surface acoustic wave device according to claim 1, wherein when defining the line metallization rate When , the relationship between the cutting angle θ and the product H/λ×mr of the electrode film thickness and wire metallization ratio satisfies -8.04489×10 ^-5 ×θ ³ -1.40981×10 ^-2 ×θ ² -0.825038×θ-16.0737 <H/λ×mr<-6.15517×10 ^-5 ×θ ³ -1.03943×10 ^-2 ×θ ² -0.586564×θ-11.0052. 4. A surface acoustic wave device comprising a piezoelectric substrate and an interdigitated electrode formed on the piezoelectric substrate and made of Al or an alloy containing Al as a main component, utilizing a stimulated wave as SH waves, of which The piezoelectric substrate is a rotating Y-cut substrate made of a quartz plate, Wherein the cut angle θ of the piezoelectric substrate is the rotation angle of the Z crystal axis when the piezoelectric substrate rotates around the X crystal axis, The direction in which the piezoelectric substrate is rotated from the positive Z side to the positive Y axis side is a direction in which the cutting angle θ is negative, and The cutting angle θ is set within the range of -61.4°<θ<-51.1°, and the propagation direction of the surface acoustic wave is set to be 90°±5° relative to the X crystal axis, and, When the wavelength of the excited surface acoustic wave is expressed as λ, the electrode film thickness H/λ normalized to the wavelength of the interdigitated electrode is set to satisfy 0.05<H/λ<0.10. 5. The surface acoustic wave device according to claim 4, wherein the relationship between the cutting angle θ and the electrode film thickness H/λ satisfies -1.44605×10 ^-4 ×θ ³ -2.50690×10 ^-2 ×θ ² -1.45086 ×θ-27.9464<H/λ<-9.87591×10 ^-5 ×θ ³ -1.70304×10 ^-2 ×θ ² -0.981173×θ-18.7946. 6. The surface acoustic wave device according to claim 4, wherein, When defining the wire metallization rate

When , the relationship between the cutting angle θ and the product H/λ×mr of the electrode film thickness and wire metallization rate satisfies -8.67632×10 ^-5 ×θ ³ -1.50414×10 ^-2 ×θ ² -0.870514×θ-16.7678 <H/λ×mr<-5.92554×10 ^-5 ×θ ³ -1.02183×10 ^-2 ×θ ² -0.588704×θ-11.2768. 7. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a one-port surface acoustic wave resonator provided with at least one interdigitated electrode on the piezoelectric substrate. 8. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a two-port surface acoustic wave resonator in which at least two interdigitated electrodes are arranged on the piezoelectric substrate along the propagating direction of the surface acoustic wave. 9. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a transversely coupled multimode filter in which a plurality of surface acoustic wave resonators are arranged on the piezoelectric substrate parallel to the propagation direction of the surface acoustic wave and close to each other. 10. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a longitudinally coupled multimode filter in which a two-port surface acoustic wave resonator including a plurality of interdigitated electrodes is arranged on the piezoelectric substrate along the propagation direction of the surface acoustic wave. 11. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a ladder-type surface acoustic wave filter in which a plurality of surface acoustic wave resonators are connected in a trapezoidal shape on the piezoelectric substrate. 12. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a transverse surface acoustic wave filter in which a plurality of interdigital electrodes bidirectionally propagating surface acoustic waves are provided on the piezoelectric substrate at predetermined intervals. 13. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a transverse surface acoustic wave filter provided with at least one interdigital electrode for propagating surface acoustic waves in one direction on the piezoelectric substrate. 14. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device is a surface acoustic wave sensor. 15. The surface acoustic wave device according to any one of claims 1 to 6, wherein, The surface acoustic wave device has grid-like reflectors on both sides of the interdigitated electrodes. 16. A modular device or an oscillating circuit using the surface acoustic wave device according to any one of claims 1 to 6.

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