JP2000295070A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure attenuation quantity suppressing a harmonic signal that is twice or three times as high as a passing frequency in a high frequency side of a passband. SOLUTION: In this surface acoustic wave device 81 arranges a surface acoustic wave element E composed by connecting parallelly plural resonators R to an input-output signal line L on a substrate K, the substrate K has at least 1st and 2nd dielectric layers 11 and 12, ground electrodes 6 connected to at least one of the resonators R are formed plurally on the layer 11, and also, a common electrode 8 connected to all of the plural electrodes 6 is formed on the layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device for a resonator and a frequency band filter incorporated in a mobile radio device such as a mobile phone and a mobile phone.

[0002]

2. Description of the Related Art In recent years, many surface acoustic waves have been used as electronic components such as frequency filters (hereinafter, referred to as filters), delay lines, and transmitters for electronic devices that communicate using radio waves. (Surface Acoustic Wave
(Hereinafter abbreviated as SAW)). A resonator and a SAW filter are used.

In particular, in the mobile communication field, an RF (Radio Frequency: radio frequency or high frequency) block and an IF (Intermediate F) of a portable terminal device such as a cellular phone are used.
requency (intermediate frequency) block is often used as a filter. For example, in a communication system using mobile wireless devices such as a mobile phone and a mobile phone, the occupied frequency is set to a high frequency band of about 2 GHz, and harmonics are amplified by distortion of an amplifier in the device. A filter that can greatly attenuate twice or three times the frequency band of about 4 GHz or about 6 GHz is desired.

FIGS. 9A to 9C show the configuration of a conventional filter. The resonator R of the SAW element E constituting the SAW filter J is formed by a pair of interdigital electrodes (InterDigital Transduce).
r, hereinafter abbreviated as IDT electrode) is connected to, for example, a ladder-type circuit. The SAW excited from the IDT electrode
In order to efficiently resonate the SAW on the propagation path of
Reflectors may be placed on both sides of the electrode. In the figure, 1 is a package lid, K is a plate-shaped base constituting the package, 2 is a side input electrode, 3 is a side ground electrode, 4 is an input electrode pad, 5 is an output electrode pad, and 6 is a ground electrode pad. ,
7 is a ground connection electrode, 8 is a ground common electrode, and 9 is a bonding wire.

Here, the resonator R is formed by depositing a conductive material such as Al or an Al—Cu alloy on a piezoelectric substrate made of, for example, a 42 ° Y-cut X-propagating lithium tantalate single crystal or the like by vapor deposition or sputtering. Then, patterning is performed by photolithography so as to be fine electrodes, and the SAW element E is manufactured.

Further, a substrate K on which the SAW element E is mounted
Is composed of a plurality of upper layers 91 and lower layers 92 mainly made of alumina and having electrodes disposed thereon. Then, the input / output electrodes or the ground electrodes are connected to the respective lead electrodes by wires 9 or connected by flip-chip using Au bumps, or the protective film at the electrical connection portion is removed by etching or lift-off. The connection is made by applying a conductive resin to the electrode connection portion.

FIGS. 9 (b) and 9 (c) are perspective views of a substrate K composed of a ceramic layer. Between the ground electrode 6 wired on the upper layer 91 and the ground connection pad electrode of the SAW element E;
The input / output electrode pads 4 and 5 are connected to the ground connection pad electrodes of the SAW element E by wire bonding. The lower layer 92 is connected from the upper layer 91 to the ground common electrode 8 through the side ground electrode 3.

FIG. 10A is a top view of a conventional SAW filter J, and FIG.
10A is a cross-sectional view, and FIG. 10C is BB ′ of FIG.
It is sectional drawing. FIG. 11 shows a schematic equivalent circuit of electric components of a conventional SAW filter at a high frequency, and reference numerals indicate equivalent elements corresponding to the respective portions.

As described above, in the conventional SAW filter J, the ground electrodes connected to the SAW elements E (resonators connected in parallel to the input / output signal lines L) of the base K have the same potential. The attenuation is increased by connecting the ground electrode to all the base layers. Also, at most 3
It suffices to secure the amount of attenuation in a frequency band of about GHz, and the configuration of the SAW filter J is also applicable.

However, as the operating frequency band of the SAW filter becomes closer to the quasi-millimeter wave band, the length of the ground electrode approaches the frequency wavelength region. Twice of
There is a problem that it is not possible to secure an attenuation amount for suppressing the triple harmonic signal.

Therefore, the present invention has been proposed to solve the above-mentioned problem, and an object of the present invention is to provide a SAW filter having an excellent characteristic capable of preventing and attenuating a pass band, particularly in a high band side. .

[0012]

According to the present invention, there is provided a surface acoustic wave device comprising a substrate and a surface acoustic wave element comprising a plurality of resonators connected in parallel to input / output signal lines. A wave device, wherein the substrate has at least a first dielectric layer and a second dielectric layer, and at least one of the resonators is provided on the first dielectric layer.
A plurality of ground electrodes connected to the plurality of ground electrodes, and a common electrode connected to all of the plurality of ground electrodes is formed on the second dielectric layer. Then, an inductor component is provided between the first dielectric layer and the second dielectric. In particular, the value obtained by dividing the inductance between the common electrode and the ground potential by the inductance between the parallel resonator and the common electrode was 10 to 20.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a surface acoustic wave device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a SA which is a surface acoustic wave device according to the present invention.
FIG. 2 shows a partially cutaway perspective view of a W filter S1. FIG. 4 shows an equivalent circuit thereof. Note that the same reference numerals are given to members similar to those in the already described drawings, and a part of the description is omitted.

As described above, the SAW filter S1 is formed by connecting a plurality of resonators R in parallel to the input / output signal line L of the ladder circuit, and the SAW element E is mounted on the base K. .

Here, the base K is composed of an upper base 11, which is a first dielectric layer having a plurality of ground electrodes 6 connected to at least one of the parallel resonators R, and a common electrode 8 connected to all the ground electrodes 6. And at least a lower substrate 13 as a second dielectric layer.
Have an inductor component between them.

FIGS. 2A to 2C are exploded perspective views of the substrate K of the SAW filter of the present invention, and FIG. 3A is a top view of the substrate of the SAW filter of the present invention, and FIG. Figure 3
FIG. 3A is a sectional view taken along line AA ′, and FIG. 3C is a sectional view taken along line BB ′ in FIG. FIG. 4 shows the SAW of the present invention.
1 shows a schematic equivalent circuit of an electric component at a high frequency of a filter, and reference numerals indicate equivalent elements corresponding to respective portions.

The ground electrode pads 6 respectively connected to the parallel resonators R of the SAW element E are independent of each other on the upper substrate 11. The ground electrode 6 is shown in FIG.
It is connected to the ground common electrode 8 of FIG. 2C via the ground electrode connection part 7 of FIG. 2B, and is connected to the external substrate by the side ground electrode 3 of FIG. The input / output signals of the SAW element E are connected to input / output electrode pads 4 and 5, and are connected to input / output signals of an external substrate via the side electrodes 2.

The resonator R disposed in the SAW element E has a high frequency capacitive property, and is formed by a parallel LC circuit by the inductor R of the equivalent circuit, the bonding wire 9, and the inductor components of the ground electrodes 3, 6, and 7 of the base. An attenuation pole occurs. There are two attenuation poles depending on the circuit configuration. The attenuation pole on the low frequency side is generated by the inductor component from the parallel resonator R to the ground common electrode 8 and the capacitance of the parallel resonator R, and the attenuation pole on the high frequency side. The pole is generated by the inductor component from the ground common electrode 8 to the ground potential and the capacitance of the parallel resonator R. From this,
By increasing the inductor component from the parallel resonator R to the common ground electrode 8, the attenuation pole generated in the frequency band equal to or more than three times the pass band by the LC circuit can be shifted to a low frequency. By reducing the inductor component from 8 to the ground potential, the attenuation pole generated in the pass band by the LC circuit can be moved to a high frequency.

By making the ground electrodes 6 independent like the upper base 11, the parallel resonators R and the ground common electrode 8
By arranging the common electrode near the ground potential of the external substrate, the inductor component from the ground common electrode 8 to the ground potential can be reduced. With such a structure, good electrical characteristics of attenuation on the high frequency side of the pass band can be obtained.

In particular, the range in which the amount of attenuation can be increased in the frequency bands twice and three times the pass band is the ground common electrode 8.
A value obtained by dividing an inductor component between the parallel resonator R and the common electrode 8 by an inductor component between the parallel resonator R and the common electrode 8 may be 10 to 20.

In the above description of the embodiment, the connection method with the SAW resonator is made by wire bonding. However, the connection is made by flip chip using Au bumps, or the protective film at the electric connection part is removed by etching or lift-off. In the case where a conductive resin is applied to the electrode connection portion in the state where the connection is made, the inductor of the bonding wire is formed by the meandering electrode 10 in FIG. Is also good.

The piezoelectric substrate constituting the SAW element is composed of a single crystal of lithium tantalate, a single crystal of lithium niobate, a crystal, a single crystal of lithium tetraborate, a single crystal having a langasite-type crystal structure, a single crystal of potassium niobate, and a single crystal of gallium. Arsenic is mainly applicable. Further, as the IDT electrode material, aluminum, aluminum / copper alloy, aluminum / titanium alloy, aluminum / silicon alloy, gold, silver, silver / palladium alloy can be mainly applied. The lead electrode material is mainly aluminum, aluminum / copper alloy, aluminum / titanium alloy, aluminum / silicon alloy, gold, silver, silver /
Palladium alloy is mainly applicable, and if a base material is required to improve the adhesion of the electrodes and reduce the electrical resistance, chrome,
Titanium and copper are mainly applicable. Further, as the insulating member, SiO ₂ , SiN, Si, DLC (Diamond
(Like Carbon), ZnO, polyimide, fluorine-based resin, olefin-based resin, and a photosensitive cured resin such as a positive resist used in a wafer process. Their specific resistance is 10 ⁻⁸ cmΩ or more, but when other insulating members are used, the specific resistance is 10 ⁻⁵ cmΩ.
Any material of cmΩ or more can be applied. In addition, if the electrode material is insulated by using an anodic oxidation method, the same effect as that of the protective film appears.

It should be noted that the present invention is not limited to the above-described embodiment. The present invention can be applied not only to a SAW filter but also to a SAW duplexer, and various changes may be made without departing from the scope of the present invention. No problem.

[0025]

[Embodiment 1] As shown in FIG. 1, a SAW element E is composed of a 42 ° Y-cut X-propagating lithium tantalate single crystal piezoelectric substrate, a period length of IDT electrodes of 1.99 μm, and a logarithm of 110 pairs. Ladder-type series arm resonators R having an intersection width of 39.8 μm, a period length of 2.1 μm, a logarithm of 75 pairs, and an intersection width of 4
Three ladder type parallel arm resonators R of 2.0 μm were designed, and all the resonators were designed with 20 reflectors.
An l-Cu alloy was formed to a film thickness of 2000 ° by a sputtering method, and was patterned by a photolithography process usually performed in a wafer process. The protective film was formed by sputtering a material SiO ₂ to a film thickness of 500 ° over the entire surface of the device. Thereafter, the part to be connected to the wire is inserted into the CDE (Che
(Micro Dry Etching), and the wafer was diced and cut into individual devices. This element is mounted on the substrate K shown in FIG.
AW element connection pad and upper substrate 11 electrode pad 4,
It was connected between 5 and 6. Thereafter, the lid 1 was hermetically sealed with a lid 1 by a seam welding method.

FIG. 6 shows the evaluation of the electrical characteristics of the SAW filter of the present invention. The evaluation method was such that a 3.5 mm diameter connector was connected to the input / output terminals of the external circuit board assembled as described above, and measurement was performed using a network analyzer. The solid line in FIG. 6 is the result of the present embodiment, and the broken line is the result of the conventional structure. From this measurement result, it is found that the attenuation is 14 d in the SAW filter having the conventional structure at a frequency twice the pass band.
B, the attenuation was 41 dB in the present embodiment, and the attenuation was 11 dB in the conventional SAW filter and 28 dB in the present embodiment at a frequency three times the passband.

[Embodiment 2] Next, as shown in FIG.
On a piezoelectric substrate of 2 ° Y-cut X-propagating lithium tantalate single crystal, the period length of the IDT electrode is 1.99 μm and the logarithm is 110
A ladder-type series arm resonator R having an intersection width of 39.8 μm
Pieces, cycle length 2.1 μm, logarithm 75 pairs, intersection width 42.0 μm
m, three ladder-type parallel arm resonators R were designed, and the number of reflectors of all the resonators was designed to be 20; The patterning was performed by a photolithography process usually performed in the process. The protective film is made of the material SiO
₂ was formed in a thickness of 500 ° by a sputtering method. After this,
The portion to be connected to the Au bump was removed by CDE, the wafer was diced, and cut into individual devices.

This element is mounted on a substrate K as shown in FIG. 5 and connected by Au bumps. Thereafter, the lid 1 was hermetically sealed with a lid 1 by a seam welding method. The meandering electrode in the first dielectric layer has a width of 0.1 mm and a length of 2 mm.
mm electrode structure and the electrode material is W material for the underlayer and Au for the upper layer.
Material.

FIG. 7 shows the evaluation of the electrical characteristics of the SAW filter. In the evaluation method, a 3.5 mm diameter connector was connected to the input / output terminals of the external circuit board assembled as described above, and measurement was performed with a network analyzer. The solid line in FIG. 7 is the present embodiment, and the broken line is the result of the conventional SAW filter. From the measurement results, it is found that the attenuation is 21 dB in the conventional flip-chip type SAW filter and 38 dB in the present embodiment at a frequency twice as high as the pass band at a frequency twice as high as the pass band.
At twice the frequency, the conventional SAW filter has 26 dB,
In this embodiment, the attenuation is 35 dB. From this result,
It has been found that the structure according to the invention obtains good values.

The inductor from the common electrode section 8 to the ground potential in FIG.
The suitable range of the inductor was experimentally determined by changing the length of the meandering electrode of (b) by a width of 0.1 mm and using a substrate with various inductors.

FIG. 8 shows the result. In the figure, the mark ● indicates the attenuation at twice the frequency of the pass band, and the mark ○ indicates the attenuation of the pass band 3
This is the attenuation at twice the frequency. Desired attenuation is at least 20
Since it is sufficient that the inductance is not less than dB, it has been found that it is sufficient that the meandering electrode or the spiral electrode wiring has an inductor of 0.5 nH or more and 1.0 nH or less. That is, the value obtained by dividing the inductor component (inductance) between the common electrode and the ground potential by the inductor component between the parallel resonator and the common electrode is 1
It was found that the best characteristics were exhibited when the value was 0 to 20.

[0032]

According to the surface acoustic wave device of the present invention, the SA
It is possible to greatly improve the stop band attenuation on the high band side of the pass band of the W filter. In particular, when used in the RF stage of a mobile phone or the like, it is possible to sufficiently suppress the harmonic signal at twice or three times the local oscillation frequency generated by the mixer.

Further, when the SAW element and the substrate are directly joined, the amount of attenuation can be greatly improved, and an inexpensive and small SAW filter can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a surface acoustic wave device according to the present invention.

FIGS. 2A to 2C are perspective views of a substrate of the surface acoustic wave device according to the present invention.

3A and 3B are diagrams illustrating a surface acoustic wave device according to the present invention, wherein FIG. 3A is a partially cutaway top view, FIG. 3B is a cross-sectional view taken along line AA ′ of FIG. FIG. 3A is a cross-sectional view taken along line BB ′ of FIG.

FIG. 4 is an equivalent circuit diagram of the surface acoustic wave filter according to the present invention.

5A and 5B are diagrams illustrating another surface acoustic wave device according to the present invention, wherein FIG. 5A is a partially cutaway sectional view, FIG. 5B is a perspective view of an upper substrate, and FIG. It is a perspective view.

FIG. 6 shows electrical characteristics of a conventional surface acoustic wave filter according to the first embodiment and a surface acoustic wave filter according to the present invention.

FIG. 7 shows electrical characteristics of a conventional surface acoustic wave filter according to a second embodiment and a surface acoustic wave filter according to the present invention.

FIG. 8 is a diagram showing a relationship between an inductor component of a connection electrode and attenuation at twice and three times the pass band.

FIG. 9 is a diagram illustrating a conventional surface acoustic wave device;
(A) is a partially cutaway sectional view, (b) is a perspective view of an upper base, and (c) is a perspective view of a lower base.

FIG. 10 is a view for explaining a conventional surface acoustic wave device;
(A) is a partially broken top view, and (b) is A- of (a).
FIG. 3A is a cross-sectional view taken along line A ′, and FIG. 3C is a cross-sectional view taken along line BB ′ in FIG.

FIG. 11 is an equivalent circuit diagram of a conventional surface acoustic wave filter.

[Explanation of symbols]

 1: lid 2: side input electrode 3: side ground electrode 4: input electrode pad 5: output electrode pad 6: ground electrode pad 7: ground connection electrode 8: ground common electrode 9: wire 10: meandering electrode S1, S2 : SAW filter E: SAW element R: resonator K: base

Claims (1)

[Claims] 1. A surface acoustic wave device having a surface acoustic wave device comprising a plurality of resonators connected in parallel to input / output signal lines on a substrate, wherein the substrate is at least a first dielectric material. A body layer and a second dielectric layer, a plurality of ground electrodes connected to at least one of the resonators are formed on the first dielectric layer, and the plurality of ground electrodes are formed on the second dielectric layer. Wherein a common electrode connected to all of the ground electrodes is formed.