JPH09162679A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress increase of the chip and mounting areas by forming a comb-line electrode strip in an operating frequency band by through an area where a comb-line electrode excites a surface acoustic wave and an area where the excitation of the surface acoustic wave is suppressed. SOLUTION: In an operating frequency band of a surface acoustic wave device, the strip of a comb-line electrode 2 includes a 1st area where a surface acoustic wave is excited and a 2nd area where the excitation of the surface acoustic wave is suppressed. The 2nd area is included in the strip of the electrode 2 where the 1st area is formed in the direction vertical to the propagating direction of the surface acoustic wave and at a position adjacent to the 1st area. In the operating frequency band of the surface acoustic wave device, the surface acoustic wave is excited primarily in the 1st area. Thus the influence of the surface acoustic wave excited in the 2nd area can be neglected in regard to the characteristic that is required to the surface acoustic wave device. As a result, the pass band width can be controlled while the increase is suppressed for the chip and mounting areas.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is mainly applied to VHF band to UHF band.
The present invention relates to a surface acoustic wave device used as a filter or a one-terminal pair resonator depending on a band frequency.

[0002]

2. Description of the Related Art A surface acoustic wave one-terminal pair resonator is expected to be a resonator compatible with a frequency band of 100 MHz or more because of its excellent characteristics such as small size, light weight and high frequency compatibility. FIG.
(a) is a schematic diagram of a surface acoustic wave multi-pair comb-type electrode-type one-terminal pair resonator, and is presented in the Proceedings of the Acoustical Society of Japan, April 1977, pp. 33-34.
It is reported on page etc. This is composed of a comb-shaped electrode 2 composed of a pair of electrodes in which a large number of pairs of strips are interdigitated on a piezoelectric substrate 1. FIG. 8B shows an equivalent circuit of a general surface acoustic wave one-terminal pair resonator. Figure 8 (b)
The equivalent circuit of is the same as the equivalent circuit of the conventional crystal resonator by the thickness vibration, and is equivalent to the equivalent inductance L, the equivalent capacitance C, the equivalent resistance R, and the inter-comb capacitance C _T due to the excitation of the surface acoustic wave. expressed. The resonance characteristics of the circuit of FIG. 8 (a) have already been analyzed, and the relationship between the resonance frequency fr and the antiresonance frequency fa is fa = fr (1 + C / C _T ) ^1/2 (1) Is. From equation (1), it can be seen that fa and fr are separated by increasing the capacitance ratio C / C _T , and are closer by decreasing C / C _T. By changing the capacitance ratio C / C _T in this way, the resonance characteristics of the one-terminal pair resonator can be adjusted. For this reason, methods of adjusting various capacitance ratios C / C _T are being studied.

Further, a filter using a surface acoustic wave device is
Because of its small size, light weight, and high performance, it is widely used in communication equipment such as mobile communication, broadcasting equipment, and measurement equipment. Conventionally, an intermediate frequency filter used in an analog communication system is required to have a narrow band characteristic. For such applications, ST
3dB ratio bandwidth formed on the cut quartz substrate is 0.03 to 0.1%
A surface acoustic wave filter or the like is used. In addition, the intermediate frequency filter used in the digital communication system which has become widespread in recent years is required to have a specific bandwidth of about 0.2 to 0.5%, and a surface acoustic wave filter formed on a lithium tetraborate substrate or the like is used. As such, the demands on the filter are diversified, and an effective method for adjusting the bandwidth of the filter is required.

By the way, the bandwidth of the surface acoustic wave filter can be adjusted by connecting a capacitor in parallel to the comb electrodes forming the surface acoustic wave filter. For example,
5-22074 and Japanese Unexamined Patent Publication (Kokai) No. 5-167384, there is a method of connecting a capacitor in parallel to a comb-shaped electrode composed of a pair of electrodes in which a plurality of strips are interdigitated, and a comb-shaped electrode composed of a pair of electrodes in which strips are interdigitated. A method of forming and connecting a capacitive element on a piezoelectric substrate by making the pitch of the strip arrangement different from the pitch of the comb-shaped electrodes that excite surface acoustic waves is disclosed.

[0005]

A surface acoustic wave one-terminal pair resonator formed on a piezoelectric substrate is connected in parallel with a capacitive element 7 and a comb-shaped capacitive electrode 2 formed on the same piezoelectric substrate. An example is shown in FIG. In this configuration, the wiring is extended from the common electrodes of the comb-shaped electrode 2 forming the surface acoustic wave one-terminal-pair resonator facing each other, and the wiring is connected to the capacitive element 7 formed of the comb-shaped electrode arranged outside the comb-shaped electrode 2. doing. However, in such a configuration, a wiring for arranging the capacitance element and a common electrode for connecting the strip of the capacitance element must be arranged outside the comb-shaped electrode forming the resonator, and the chip size There is a problem in that Further, the method of providing a capacitive element outside the package and connecting the capacitive element to the comb-shaped electrode also causes a problem of increasing the mounting area.

The present invention has solved the above-mentioned problems.
The purpose is to provide a surface acoustic wave device capable of adjusting the frequency interval between the resonance frequency and the antiresonance frequency when the surface acoustic wave device is a resonator while suppressing an increase in chip area and mounting area.
Another object of the present invention is to provide a surface acoustic wave device capable of adjusting the pass band width when the surface acoustic wave device is a filter.

[0007]

The present invention provides a surface acoustic wave device having a comb-shaped electrode composed of a pair of electrodes in which at least one strip is interdigitated with each other, on a piezoelectric substrate. The strip is formed so as to suppress the excitation of the surface acoustic wave and the first region formed so that the comb electrode can efficiently excite the surface acoustic wave in the frequency band in which the surface acoustic wave device is operated. A surface acoustic wave device comprising: a second region.

In this surface acoustic wave device, the strips in the second region are arranged so as to be inclined from a direction perpendicular to the propagation direction of the surface acoustic wave excited in the first region. And a pitch of strips in the second region,
The surface acoustic wave device is characterized by being arranged so as to have a pitch different from that of the strip in the region.

Further, the surface acoustic wave device is characterized in that the piezoelectric substrate is lithium tetraborate or quartz.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A first region in which surface acoustic waves are excited in a frequency band in which a surface acoustic wave device operates and a surface acoustic wave excitation in a frequency band in which a surface acoustic wave device operates are formed on a strip of comb electrodes. The second that tried to suppress
Is formed. As shown in FIGS. 1 and 2, the second region is adjacent to the strip of the comb-shaped electrode forming the first region, in a direction perpendicular to the propagation direction of the surface acoustic wave, and adjacent to the first region. To arrange. In the frequency band in which the surface acoustic wave device operates, the surface acoustic wave is excited mainly in the first region, and the influence of the surface acoustic wave excited in the second region is due to the characteristics required for the surface acoustic wave device. Make it so that it can be ignored. Therefore, the inter-comb-electrode capacitance when the comb-shaped electrodes are formed only in the first region and the inter-comb-type electrode capacitance generated in the second region are added to increase the overall inter-comb-type electrode capacitance. Therefore, the interval between the resonance frequency and the anti-resonance frequency can be narrowed, and the band can be narrowed.

As an example of the structure of the comb-shaped electrode, as shown in FIG. 1A, the strip in the second region is inclined from the direction perpendicular to the propagation direction of the surface acoustic wave excited in the first region. 1), or by arranging the strips in the second area so that the cycle of the strips in the second area is different from the cycle of the strips in the first area, as shown in FIG. 1 (b). At, a second region for suppressing the excitation of the surface acoustic wave is formed. The capacitance generated in the second region is, for example, the second
Can be controlled by expanding or contracting the length of the strip in the area (2) or adjusting the ratio of the width of the strip in the second area to the pitch of the strip.

Further, as shown in FIG. 2, the strips in the second area may be arranged so that their widths are different from the widths of the strips in the first area (FIG. 2 (a)). By arranging the thickness so that it is different from the thickness of the strip in the first region (FIG. 2 (b)), or by forming the dielectric 8 on the strip in the second region (FIG. 2 (c)). A second suppression of surface acoustic wave excitation in a frequency band in which the surface acoustic wave device operates
Is formed.

As described above, since the second region is incorporated in the comb-shaped electrode, the common electrode for drawing the wiring to form the comb-shaped capacitive element and connecting the strip of the comb-shaped capacitive element to each other. Is not necessary, which is advantageous for downsizing the chip.

[0014]

【Example】

(Embodiment 1) FIG. 3A shows a multi-pair comb electrode type composed of a comb-shaped electrode 2 consisting of a pair of electrodes in which a large number of strips of aluminum conductive metal are interdigitated on a piezoelectric substrate 1 of ST-cut quartz. It is a one-terminal pair resonator. The strip of the comb-shaped electrode 2 includes a first region extending in a direction perpendicular to the propagation direction of the excited surface acoustic wave and a second region arranged at both ends thereof with a 45 ° inclination from the strip of the first region. It is composed of The crossing length of the strips in the second region of the comb-shaped electrode 2 is 50 μm, the number of strip pairs in the comb-shaped electrode 2 is 600.5 when the opposing strips are counted as one pair, and the period of the strip pairs is 20 μm. The crossing length of the strips is 400 μm (FIG. 3 (b)).

FIG. 4 shows the impedance characteristic of this surface acoustic wave resonator (line A in FIG. 4). For comparison, when the crossing length of the strips in the second area is set to 0 μm
The impedance characteristic (that is, line B in FIG. 4) of the surface acoustic wave resonator (that is, when the second region is not formed) is also shown. It can be seen from FIG. 4 that the interval between the resonance frequency and the anti-resonance frequency is narrowed by forming the second region, and the interval between the resonance frequency and the anti-resonance frequency can be adjusted.

(Embodiment 2) In FIG. 5, two surface acoustic wave propagation tracks are formed on a piezoelectric substrate 1 made of lithium tetraborate, and an input comb electrode 3 is formed on the first surface acoustic wave propagation track. , A comb-shaped electrode 4 for connection along the surface acoustic wave propagation direction,
A reflector 5 having a period slightly wider than the period of the comb-shaped electrode is arranged on both outer sides thereof, and similarly, the output comb-shaped electrode 6 is connected to the second surface acoustic wave propagation track along the surface acoustic wave propagation direction. Energy combing-type elasticity in which the comb-shaped electrodes 4 for connection and the reflectors 5 having a period slightly wider than the period of the comb-shaped electrodes are arranged on both outer sides thereof and the comb-shaped electrodes 4 for connection of each surface acoustic wave propagation track are electrically connected in cascade. It is a surface wave filter. The strip of the comb-shaped electrode 4 for connection has a first region extending in a direction perpendicular to the propagation direction of the excited surface acoustic wave and a second region arranged at both ends thereof with a 45 ° inclination from the strip of the first region. It is composed of areas. Comb-shaped electrode 2
The crossing length of the strips in the second region is 100 μm, the number of pairs of strips forming the input comb electrode 3 and the output comb electrode 6 is 40.5, and the number of strips forming the connection comb electrode 4 is 25.5. , The number of reflectors 5 is 120, the period of the strip pair of comb-shaped electrodes is 22 μm, and the distance between the comb-shaped electrodes for input and output and the comb-shaped electrode for connection is the distance between the centers of the closest strips. 11 μm, the distance between the centers of the closest strips between the comb electrodes and the outer reflectors is 10.5 μm, the intersecting length of the strips of the input and output comb electrodes and the number of the connecting comb electrode 4 The crossing length of the strips in area 1 is 154 μm. The material of each comb-shaped electrode and reflector is aluminum.

6A and 6B, the pass characteristic of this surface acoustic wave filter is shown by a dotted line A. Note that FIG. 6 (b) is shown in FIG. 6 (a).
It is an expansion of. For comparison, the solid line B also shows the pass characteristic in the case where the crossing length of the strips of the second region of the connecting comb-shaped electrode is set to 0 μm (that is, when the second region is not formed). By forming it in the second region, it is possible to narrow the pass band width of the surface acoustic wave filter without substantially impairing the minimum insertion loss and the attenuation amount.

In the above embodiment, the second region is formed by using the strip inclined by 45 ° with respect to the strip in the first region. However, the angle of inclination need not be 45 °, and the surface acoustic wave may be formed. Any inclination angle can be selected as long as the specifications required for the device are satisfied. Further, as shown in FIG. 7, the structure may be such that the surface acoustic wave is not excited in the frequency band in which the surface acoustic wave device is operated, for example, the strip in the second region is formed into a dogleg shape.

Further, the present invention is not limited to the above-mentioned embodiment but can be applied to various surface acoustic wave devices. For example, it may be used in the energy confinement type one-terminal-pair surface acoustic wave resonator in which the reflection electrodes are arranged on the left and right sides of the comb-shaped electrodes of the multi-pair comb-shaped one-terminal pair resonator of the first embodiment. In addition, the second embodiment
The surface acoustic wave propagation track of the surface acoustic wave filter may be used in a surface acoustic wave filter having only one stage instead of two stages or a surface acoustic wave filter having three or more stages connected in cascade.

The second region provided on the strip may be formed not on the connecting comb-shaped electrode but on the input comb-shaped electrode and the output comb-shaped electrode.

Further, the second regions provided in the strip do not necessarily have to be provided on both sides of the strip in the first region, but may be provided only on one side of the strip in the first region.

As the material for the comb-shaped electrodes, aluminum, copper, silicon, titanium, HfB ₂ or the like may be added, or another conductive material may be used, and the number of reflectors is required. It may be adjusted in consideration of insertion loss, chip size and the like.

[0023]

As described above, the present invention provides a surface acoustic wave device having, on a piezoelectric substrate, at least one comb-shaped electrode composed of a pair of electrodes in which strips are interdigitated with each other. The comb electrode strips are
In the frequency band in which the surface acoustic wave device is operated, a first region formed so that the comb-shaped electrode can efficiently excite surface acoustic waves, and a second region formed so as to suppress excitation of surface acoustic waves. And a surface acoustic wave device.

By forming the strips of the comb-shaped electrodes in this manner, the capacitance generated in the second region has a function equivalent to that of the capacitance element connected in parallel to the comb-shaped electrodes of the prior art. Since the second region can be formed by extending the strip of the comb-shaped electrode by about several tenths, it is necessary to connect the wiring to form a capacitive element or to connect the strip of the capacitive element to another place of the chip. It is not necessary to dispose the common electrode of, which is advantageous for miniaturization of the chip.

Therefore, for example, when the surface acoustic wave device is a resonator, it is possible to provide a means for designing the resonance characteristics such as the interval between the resonance frequency and the anti-resonance frequency while suppressing the expansion of the chip area. Also, when the surface acoustic wave device is a filter,
It is possible to provide a means for adjusting the pass band width while suppressing the expansion of the chip area. As described above, the degree of freedom in designing the surface acoustic wave device can be improved, and the small-sized and high-performance surface acoustic wave device required for mobile communication can be provided.

[Brief description of the drawings]

1A and 1B are schematic views showing an example of a surface acoustic wave device of the present invention.

2A, 2B, and 2C are schematic views showing an example of the surface acoustic wave device of the present invention.

FIG. 3A is a diagram showing a surface acoustic wave one-terminal pair resonator according to a first embodiment. (b) is a diagram showing details, particularly the second region.

FIG. 4 is a diagram showing impedance characteristics of the surface acoustic wave one-terminal pair resonator of the first embodiment. Line A is when the second region is provided on the strip of comb electrodes, and line B is when the second region is not provided on the strip of comb electrodes.

FIG. 5 is a diagram showing a surface acoustic wave filter according to a second embodiment.

6A and 6B are diagrams showing pass characteristics of the surface acoustic wave filter according to the second embodiment. The dotted line A is when the second area is provided on the comb electrode strip, and the solid line B is when the second area is not provided on the comb electrode strip.

FIG. 7 is a schematic diagram showing an example of the surface acoustic wave device of the present invention.

8A is a diagram showing a conventional multi-pair comb electrode type one-terminal pair type surface acoustic wave resonator, and FIG. 8B is an equivalent circuit of the surface acoustic wave resonator shown in FIG. 8A. It is the figure which showed.

FIG. 9 is a diagram showing an example of a conventional surface acoustic wave device in which a capacitive element is connected in parallel to a comb-shaped electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Comb-shaped electrode 3 Comb-shaped electrode for input 4 Comb-shaped electrode for connection 5 Reflector 6 Comb-shaped electrode for output 7 Capacitive element 8 Dielectric

Claims (4)

[Claims] 1. A surface acoustic wave device having a comb-shaped electrode composed of a pair of electrodes, in which at least one strip is interdigitated with each other, on a piezoelectric substrate. In the frequency band in which the device is operated, the comb-shaped electrode comprises a first region formed so as to efficiently excite surface acoustic waves and a second region formed so as to suppress the excitation of surface acoustic waves. A surface acoustic wave device. 2. In the surface acoustic wave device, the strips in the second region are arranged so as to be inclined from a direction perpendicular to a propagation direction of the surface acoustic wave excited in the first region. The surface acoustic wave device according to claim 1, wherein: 3. The surface acoustic wave device according to claim 1, wherein the pitch of the strips in the second area is different from the pitch of the strips in the first area. The surface acoustic wave device according to the paragraph. 4. The piezoelectric substrate according to claim 1, wherein the piezoelectric substrate is lithium tetraborate or quartz.
A surface acoustic wave device according to any one of the preceding claims.