JP2008283725A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure of a surface acoustic wave device having sharp attenuation characteristics without changing a piezoelectric substrate, cut azimuth and electrode film thickness. <P>SOLUTION: In the surface acoustic wave device, wherein an input terminal electrode 5, an output terminal electrode 6 and an excitation electrode generating a surface acoustic wave are formed on a piezoelectric substrate, the excitation electrode is disposed to engage electrode fingers of an input comb-shaped electrode 1 connected to the input terminal electrode 1 and electrode fingers of an output comb-shaped electrode 2 connected to the output terminal electrode 5 respectively with electrode fingers of a comb-shaped floating electrode 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode structure of a surface acoustic wave device that is frequently used as a high-frequency element in mobile communication devices such as mobile phones and cellular phones in the telecommunications field.

In recent years, many surface acoustic wave devices have been used as constituent elements such as filters, delay lines, and transmitters of electronic devices that use radio waves.
In particular, surface acoustic wave devices that are small, lightweight, and have high steep cut-off performance as filters have come to be frequently used as RF stage and IF stage filters for mobile terminal devices in the field of mobile communication, and have low loss and There is a demand for a surface acoustic wave device having excellent attenuation characteristics outside the passband, high attenuation characteristics, and a wide bandwidth.

FIG. 15 is a schematic plan view of an electrode pattern of a conventional general surface acoustic wave resonator J1.
As shown in this figure, the conventional surface acoustic wave resonator includes an electrode finger 1 a of the input comb-like electrode 1 connected to the input terminal electrode 5 and an output comb-like electrode 2 connected to the output terminal electrode 6. The electrode fingers 2a are arranged so as to cross each other, an alternating electric field is applied between these input / output terminal electrodes, and a surface acoustic wave is generated on the piezoelectric substrate to be excited.

  Also, the energy of the surface acoustic wave excited by the electrode pattern of the spatial periodic structure is confined at both ends of the pair of comb-like electrodes (hereinafter referred to as IDT electrodes). It is common to arrange a ladder-like reflector 4 having

  Up to now, in the surface acoustic wave device, from the viewpoint of electrode configuration, a plurality of IDT electrodes are connected in cascade to a ladder type (ladder type) circuit, and a plurality of IDT electrodes are provided to change an electric signal into a surface acoustic wave and propagate it. In addition, a longitudinal mode coupled resonator type that has an IDT electrode in the propagation direction and propagates a signal by its resonance has been put to practical use. Among them, a ladder type surface acoustic wave device has a low loss. In addition, it has a good cutoff characteristic in the vicinity of the passband, and has high reliability in terms of power resistance accompanying the miniaturization of electrodes due to higher frequencies, which is very promising.

FIG. 16 is a plan view schematically showing an electrode structure of a general ladder-type surface acoustic wave device J2.
Thus, the surface acoustic wave resonator J1 shown in FIG. 15 is connected in series and in parallel between the input / output terminal electrodes 5 and 6 on the piezoelectric substrate 14.
In the case of this surface acoustic wave device (filter), the specific bandwidth BW / fo (BW: passband width, fo: center frequency) is the difference between the resonance frequency and the antiresonance frequency of the surface acoustic wave resonator constituting the filter. A certain Δf (= fa−fr; where fa: anti-resonance frequency, fr: resonance frequency) is normalized by the resonance frequency and is almost determined, and this Δf is one of the material constants of the piezoelectric substrate. Since it greatly depends on the coefficient, in order to obtain a desired specific bandwidth, it is necessary to select a piezoelectric substrate having an appropriate electromechanical coupling coefficient and an electrode film thickness to produce a filter.
Microfilm of Japanese Utility Model No. 52-149663 (Japanese Utility Model Publication No. 54-75629)

  In recent years, with the rapid change of mobile phone systems, the required specifications on the system side have become stricter, and a surface acoustic wave device having a steepness of a shoulder closer to a rectangle in a wide band is desired. Since the steepness of the shoulder of such a surface acoustic wave device is also determined by Δf, a filter is designed by selecting a piezoelectric substrate having an appropriate electromechanical coupling coefficient, substrate cut orientation, and electrode film thickness. However, there is usually no optimal combination, and it is unavoidable that a general piezoelectric substrate is used.

  Accordingly, an object of the present invention is to provide an electrode structure of a surface acoustic wave device having a steep attenuation characteristic without changing the piezoelectric substrate, the cut orientation, and the electrode film thickness.

  In order to solve the above problems, a surface acoustic wave device according to the present invention is a surface acoustic wave device in which an input terminal electrode, an output terminal electrode, and an excitation electrode for generating surface acoustic waves are formed on a piezoelectric substrate. The excitation electrode includes an electrode finger of the comb-like floating electrode, an electrode finger of the input comb-like electrode connected to the input terminal electrode, and an output comb-like electrode connected to the output terminal electrode. Each of the electrode fingers is disposed so as to mesh with each other, and among the electrode fingers of the input comb-like electrode, an electrode finger located at an end of the output comb-like electrode side and the output comb-like electrode A boundary electrode finger, which is an electrode finger of the comb-shaped floating electrode, is disposed between the electrode fingers positioned at the end portion on the input comb-shaped electrode side of the electrode fingers, and the boundary electrode One end of the finger contacts the bus bar electrode that connects the electrode fingers of the comb-shaped floating electrode. The other end is a state of not being connected to the other electrode, at both ends of the excitation electrode is characterized in that the reflector is arranged with being.

  The surface acoustic wave device of the present invention is a surface acoustic wave device in which an input terminal electrode, an output terminal electrode, and an excitation electrode for generating a surface acoustic wave are formed on a piezoelectric substrate, the excitation electrode comprising: The electrode fingers of the comb-like floating electrode are connected to the electrode fingers of the input comb-like electrode connected to the input terminal electrode and the electrode fingers of the output comb-like electrode connected to the output terminal electrode. Of the electrode fingers of the input comb-shaped electrode and the electrode fingers of the output comb-shaped electrode and the electrode fingers of the output comb-shaped electrode Between the electrode fingers positioned at the end on the input comb-like electrode side, a plurality of electrode fingers of the comb-like floating electrode are arranged so as to mesh with each other, and a plurality of comb-like floating electrodes are arranged. Among the electrode fingers, adjacent electrode fingers are not electrically connected. To.

  The excitation electrodes constituting the surface acoustic wave device of the present invention are connected to the electrode fingers of the comb-shaped floating electrode, the electrode fingers of the comb-shaped electrode for input connected to the input terminal electrode, and the output connected to the output terminal electrode The electrode structure of the ladder type surface acoustic wave device (filter) having a steep attenuation characteristic without changing the piezoelectric substrate, the cut orientation and the electrode film thickness. Can be provided.

  In addition, since the excitation electrode is divided into a plurality of parts, the applied voltage is divided, resulting in excellent power resistance characteristics. Furthermore, electrode breakdown due to static electricity generated by the pyroelectric effect during electrode patterning is also possible. A highly reliable surface acoustic wave device that can be prevented as much as possible can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view schematically showing an electrode structure of excitation electrodes (hereinafter referred to as IDT electrodes) constituting a surface acoustic wave resonator (surface acoustic wave device) according to the present invention.
As described above, at least the input terminal electrode 5, the output terminal electrode 6, and the IDT electrode for generating the surface acoustic wave are formed on the piezoelectric substrate. The IDT electrode is connected to the input terminal electrode 5. The electrode fingers 1 a of the input comb-like electrode 1 and the electrode fingers 2 a of the output comb-like electrode 2 connected to the output terminal electrode 6 mesh with the electrode fingers 3 a of the comb-like floating electrode 3, respectively. It is configured to be arranged as described above.

  Further, the interval 14 between the center of the electrode finger 1b located at the end of the input comb-like electrode 1 and the center of the electrode finger 3b of the comb-like floating electrode 3 at the position adjacent to this electrode finger is: The length is preferably ¼λ (where λ is the period length of the IDT electrode and is approximately equal to the wavelength of the surface acoustic wave). In addition, it is preferable that the reflectors 4 formed of an electrode pattern having a periodic structure are disposed on both ends of the IDT electrode because there is no leakage of energy. Of the electrode fingers of the input comb-like electrode 1, the electrode finger positioned at the end of the output comb-like electrode 2 and the end of the output comb-like electrode on the input comb-like electrode 1 side For the sake of convenience, the electrode finger 3b of the comb-shaped floating electrode 3 disposed between the electrode fingers located in the section is also referred to as a boundary electrode finger. Moreover, the part which connects the electrode fingers of the tooth-like floating electrode 3 is also called a bus-bar electrode for convenience.

  FIG. 2 shows the frequency characteristics of impedance in the surface acoustic wave resonator. Here, the horizontal axis represents frequency and the vertical axis represents impedance absolute value. As shown in this figure, the impedance characteristic 10 of the surface acoustic wave resonator S1 having the configuration of the present invention has an anti-resonance frequency lower than the impedance characteristic 11 of the surface acoustic wave resonator J1 having the conventional structure, and the resonance frequency. Δf which is the difference between the anti-resonance frequency and the frequency characteristic of steep impedance is realized.

FIG. 3 shows a structure in which one of the short electrodes is cut so that the IDT electrode of the conventional surface acoustic wave resonator is divided into two at the center in the propagation direction of the surface acoustic wave.
By adopting this structure, the input / output terminal electrodes 5 and 6 that are power supply ports can be arranged as shown in the figure.

  4 shows an example in which the IDT electrode is similarly divided into three in the propagation direction, FIG. 5 shows an example in which the IDT electrode is similarly divided into four in the propagation direction, and FIG. 6 similarly shows the IDT electrode in the propagation direction. This is an example of dividing into five. By dividing in this way, Δf changes, and a steeper impedance can be obtained. It should be noted that the illustration is merely schematic and does not represent the number of electrode fingers correctly. Even when the number of electrode fingers shown in the figure is one, each of the divided comb-like electrodes must be a plurality of electrode fingers. It shall be configured.

  FIG. 7 shows the number of combinations of comb-shaped floating electrode electrode fingers and input / output comb-shaped electrode finger fingers (hereinafter referred to as IDT logarithm) in the number of IDT electrode divisions of the surface acoustic wave resonator according to the present invention. And Δf. In the figure, the horizontal axis indicates the IDT logarithm, and the vertical axis indicates Δf. The curve in the figure shows the case of the conventional IDT electrode and the case of the IDT electrode according to the present invention divided into two and three parts. Thus, it has been found that Δf is 1/2 and 1/3 compared to the conventional case.

  As described above, Δf decreases by dividing the IDT electrode. The reason will be described below. The IDT electrode normally behaves as a capacitance in a frequency region other than the resonance / antiresonance point. This is because the comb-like electrode of the IDT electrode is equivalent to a capacitor having two opposing electrodes. Here, considering a case where one short cut is made on one side of the short electrode and the IDT electrode is divided into two, the capacitance increases in series with respect to the capacitance before the division, and is seen between the terminals. In this case, the capacitance decreases conversely, and the antiresonance frequency depending on the capacitance moves to the low frequency side, so that Δf becomes small.

  FIG. 8 shows the case where the surface acoustic wave resonator S1 of the present invention is used as a series resonator and the conventional configuration is used as a parallel resonator and is connected to the input / output terminal electrodes 5 and 6 and the ground terminal electrode 7, respectively. The electrode structure of ladder type surface acoustic wave filter S2 is shown typically. The frequency characteristics of this filter S2 are shown in FIG. In the cutoff characteristic on the high frequency side of the pass band, a characteristic 12 that is very steep compared to the conventional characteristic 13 is realized.

  In FIG. 9, the surface acoustic wave resonator S1 of the present invention is used as a parallel resonator, and a conventional surface acoustic wave resonator is used as a series resonator. It is a top view of the structure of ladder type surface acoustic wave filter S3 at the time of making it connect to. The frequency characteristics of this filter are shown in FIG. In the cut-off characteristic on the low band side of the pass band, a characteristic 12 that is very steep compared to the conventional characteristic 13 can be realized. FIG. 8 shows the configuration of a ladder-type surface acoustic wave filter S4 when the surface acoustic wave resonator S1 of the present invention is used as a series-parallel resonator and connected to the input / output terminal electrodes 5, 6 and the ground terminal electrode 7, respectively. FIG. The frequency characteristics of this filter are shown in FIG. Compared to the conventional characteristic 13, a characteristic 12 that is very steep can be realized in both the high band side and low band side cutoff characteristics of the passband. By using these inventions, a filter with a large attenuation near the band can be realized.

Further, according to the present invention, the IDT electrode is divided into a plurality of parts, whereby the applied voltage is divided, and as a result, a surface acoustic wave device having excellent power durability can be manufactured.
Similarly, electrode breakdown due to static electricity generated by the pyroelectric effect during electrode patterning is less likely to occur because the voltage is divided.

  Next, FIG. 14 shows the impedance characteristics of the resonator when the interval 14 (see FIG. 1) in the resonator S1 according to the present invention is changed. The appropriate range of the interval 14 in the surface acoustic wave resonator of the present invention shown in FIG. 1 is as follows when the interval 14 is 3 / 4λ in FIG. 14A and when the interval 14 is 5 / 8λ in FIG. 14 (c) shows the case where the interval 14 is 1 / 2λ, and FIG. 14 (d) shows the case where the interval 14 is 3 / 8λ. In particular, the interval 14 is preferably 7 / 16λ to 9 / 16λ. It was found that the ripple decreased. Further, it was found that when the interval 14 is 1 / 2λ, there is no ripple at all and it is optimal. When the surface acoustic wave resonator is manufactured with the interval 14 outside the range of 7 / 16λ to 9 / 16λ, as shown in FIGS. 14A, 14B, and 14D, the resonance point and the antiresonance point are separated. It was found that ripples occurred in the meantime and adversely affected the filter characteristics of the surface acoustic wave device.

  In the above embodiment, the case where the electrode finger of the input comb-like electrode is the end is shown, but the same applies to the case where the electrode finger of the output comb-like electrode is the end, which is the same as FIG. The result is obtained and the preferred range and the optimum value are equal.

  Hereinafter, more specific examples of the present invention will be described.

  In the surface acoustic wave resonator constituting the ladder type surface acoustic wave device, the number of pairs of IDT electrodes (1/2 of the number of electrode fingers) is 40 to 120 pairs, and the intersection width between the electrode fingers and the electrode fingers is 10 to 30λ (λ: (Corresponding to the wavelength of the surface acoustic wave), λ is different in series and parallel, but is approximately 2 μm. Here, the number of reflective electrodes is 20 for both the series resonator and the parallel resonator. Examples of the filter configuration are as shown in FIGS. FIG. 8 shows an example in which the surface acoustic wave resonator according to the present invention is used as a series resonator, which is a 2.5-stage π type composed of two series resonators and three parallel resonators. FIG. 9 shows an example in which the surface acoustic wave resonator according to the present invention is used as a parallel resonator, and FIG. 10 shows an example in which the surface acoustic wave resonator according to the present invention is used in a series-parallel resonator.

  Next, an example in which a ladder-type surface acoustic wave device according to the present invention is prototyped will be described.

  A fine electrode pattern made of an Al (98 wt%)-Cu (2 wt%) alloy was formed on a 42 ° Y-cut LiTaO 3 single crystal substrate. For pattern production, photolithography was performed using a reduction projection exposure machine (stepper) and an RIE (Reactive Ion Etching) apparatus.

First, the substrate material was subjected to ultrasonic cleaning with acetone / IPA or the like to remove organic components.
Next, the substrate was sufficiently dried by a clean oven, and then an electrode was formed.
For electrode film formation, a sputtering apparatus was used to form an Al—Cu alloy film. The electrode film thickness was about 2000 mm. Next, a resist was spin-coated to a thickness of about 0.5 μm, and desired patterning was performed by a reduction projection exposure apparatus (stepper). The stepper requires a reticle as a patterning original, but this may be 5 times the size of the actual pattern because the image is reduced to 1/5 by the optical system of the stepper itself. For this reason, on the contrary, 5 times the resolution can be obtained as compared with the conventional contact aligner.

  Next, an unnecessary portion of the resist was dissolved with an alkaline developer by a developing device to reveal a desired pattern, and then an electrode made of an Al—Cu alloy was etched by the RIE device to complete the patterning.

Thereafter, a protective film is produced. SiO ₂ was deposited by a sputtering apparatus, and then resist was patterned by photolithography, and a wire bonding window opening portion was etched by an RIE apparatus or the like to complete a protective film pattern.

  Next, the substrate was diced along dicing lines and divided into chips. Then, each chip was picked up by a die bonding apparatus, and adhered to the SMD package with a resin mainly composed of Si resin. Thereafter, it was dried and cured at a temperature of about 160 ° C. The SMD package used was a 3 mm square laminate structure. Next, a 30 μφ Au wire was ball-bonded on the pad portion of the SMD package and the Al pad on the chip, and then the lid was placed on the package and completed by welding and sealing with a sealing machine. The ground electrode patterns on the chip were separated and wired, and bonded to the ground pads on the package by Au ball bonding.

  11, 12, and 13 are examples of frequency electrical characteristics when a filter is manufactured using the present invention. FIG. 11 shows the electrical characteristics of the surface acoustic wave device in which the surface acoustic wave resonator of the present invention is used for the series resonator of FIG. 8, and FIG. 12 shows the surface acoustic wave resonance of the present invention for the parallel resonator of FIG. FIG. 13 shows the electrical characteristics of the surface acoustic wave device having the configuration using the surface acoustic wave device of the present invention in the series-parallel resonator of FIG. is there. In the actual measurement, a network analyzer was used to conduct electrical measurement of the power transmission characteristics.

As shown in these figures, for example, when a large attenuation is taken near the high band side of the pass band, good electrical characteristics are obtained as shown by characteristic 12 in FIG. 11 when the configuration is as shown in FIG. .
Further, when the amount of attenuation is large in the vicinity of the low band side of the pass band, good electrical characteristics can be obtained as shown by the characteristic 12 in FIG. Furthermore, in the case where the amount of attenuation is large in the vicinity of the high and low frequencies of the pass band, the configuration as shown in FIG. 10 provides optimum electrical characteristics as shown by the characteristic 12 in FIG.

It is a top view which illustrates typically the electrode structure of the surface acoustic wave resonator which concerns on this invention. It is a characteristic view which shows the electrical property of a surface acoustic wave resonator. It is a top view which illustrates typically the electrode structure of the surface acoustic wave resonator which concerns on this invention. It is a top view which illustrates typically the electrode structure of the other surface acoustic wave resonator which concerns on this invention. It is a top view which illustrates typically the electrode structure of the other surface acoustic wave resonator which concerns on this invention. It is a top view which illustrates typically the electrode structure of the other surface acoustic wave resonator which concerns on this invention. It is a graph which shows the change of (DELTA) f in the surface acoustic wave resonator of this invention. 1 is a schematic plan view of a surface acoustic wave device using a surface acoustic wave resonator of the present invention as a series resonator. 1 is a schematic plan view of a surface acoustic wave device using a surface acoustic wave resonator according to the present invention as a parallel resonator. 1 is a schematic plan view of a surface acoustic wave device using a surface acoustic wave resonator according to the present invention for both a series resonator and a parallel resonator. It is a diagram explaining the characteristic of the surface acoustic wave apparatus which used the surface acoustic wave resonator of this invention for the series resonator. It is a diagram explaining the characteristic of the surface acoustic wave apparatus which used the surface acoustic wave resonator of this invention for the parallel resonator. It is a diagram explaining the characteristic of the surface acoustic wave apparatus which used the surface acoustic wave resonator of this invention for both a series resonator and a parallel resonator. It is a diagram which shows an impedance characteristic at the time of changing the center space | interval of the electrode finger end part of the comb-tooth-shaped electrode for input / output, and the electrode finger end part of a comb-tooth-shaped floating electrode. It is a top view which illustrates the conventional surface acoustic wave resonator typically. It is a top view which shows typically the electrode structure of a general ladder type surface acoustic wave apparatus.

Explanation of symbols

1: Input comb-like electrode 1a: Input comb-like electrode finger 1b: Input finger electrode end 2: Output comb-like electrode 2a: Output comb-like electrode Electrode finger 3: Comb-like floating electrode 3a: Comb-like floating electrode electrode finger 3b: Comb-like floating electrode end 4: Reflector 5: Input terminal electrode 6: Output terminal electrode 7: Ground terminal Electrode 8: Series surface acoustic wave resonator 9: Parallel surface acoustic wave resonator 10: Impedance characteristic example of surface acoustic wave resonator of the present invention 11: Impedance characteristic example of conventional surface acoustic wave resonator 12: Elasticity of the present invention Example 13 of electrical characteristics of surface acoustic wave device: Example 14 of electrical characteristics of conventional surface acoustic wave device: Piezoelectric substrate S1: Surface acoustic wave resonator according to the present invention (surface acoustic wave device)
S2 to S4: Surface acoustic wave device according to the present invention

Claims (2)

A surface acoustic wave device in which an input terminal electrode, an output terminal electrode, and an excitation electrode for generating a surface acoustic wave are formed on a piezoelectric substrate,
The excitation electrode includes an electrode finger of a comb-like floating electrode, an electrode finger of an input comb-like electrode connected to the input terminal electrode, and an electrode of an output comb-like electrode connected to the output terminal electrode Each of the fingers is arranged to engage,
Of the electrode fingers of the input comb-like electrode, the electrode fingers located at the end on the output comb-like electrode side and of the electrode fingers of the output comb-like electrode on the input comb-like electrode side Between the electrode fingers located at the end, one boundary electrode finger that is an electrode finger of the comb-shaped floating electrode is arranged,
The boundary electrode finger is in a state where one end is connected to the bus bar electrode connecting the electrode fingers of the comb-shaped floating electrode and the other end is not connected to the other electrode,
A surface acoustic wave device in which reflectors are arranged on both ends of the excitation electrode. A surface acoustic wave device in which an input terminal electrode, an output terminal electrode, and an excitation electrode for generating a surface acoustic wave are formed on a piezoelectric substrate,
The excitation electrode includes an electrode finger of a comb-like floating electrode, an electrode finger of an input comb-like electrode connected to the input terminal electrode, and an electrode of an output comb-like electrode connected to the output terminal electrode Each of the fingers is arranged to engage,
Of the electrode fingers of the input comb-like electrode, the electrode fingers located at the end on the output comb-like electrode side and of the electrode fingers of the output comb-like electrode on the input comb-like electrode side Between the electrode fingers located at the ends, the plurality of electrode fingers of the comb-shaped floating electrode are arranged so as to mesh with each other,
Of the plurality of electrode fingers of the comb-shaped floating electrode, adjacent electrode fingers are not electrically connected to each other, and the surface acoustic wave device is characterized in that:

Images