JPH10270974A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a chip dimension without deteriorating the frequency characteristic by etching/working the surface of a substrate between IDT electrodes in a surface acoustic wave element, providing a groove and reducing apparent propagation speed. SOLUTION: At the time of etching a piezoelectric substrate material, a part where normal IDT electrode, an apodization IDT electrode and a shielding electrode are not formed, a part between the normal IDT electrodes 2a and a part between the apodiation IDT electrodes are etched and the groove A6 is formed. The apparent transmission speed of the surface acoustic wave(SAW) shown by a code A7 becomes small for the piezoelectric substrate on which the groove is worked, and the electrode pitches of the respective IDT electrodes can be reduced. Thus, the whole dimension of the chip can be reduced. Thus, the chip dimension can be made small without deteriorating the frequency characteristic without changing the basic design of an SAW filter. The IDT electrodes are formed by materials whose specific gravity is larger than aluminum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device capable of reducing the size of a chip.

[0002]

2. Description of the Related Art A conventional surface acoustic wave (SAW) filter has, for example, a center frequency of several tens of MHz and a band of 4 MHz.
z, in-band ripple within 1 dB, out-of-band attenuation 35 dB
In the following, a transversal type SAW filter having a large chip size is used.

A conventional transversal type SAW filter has a device structure as shown in FIGS. 4 and 5, and a regular type IDT electrode B2, a shield electrode B4 and an apodized type IDT electrode B3 are formed on a piezoelectric substrate B1 by photolithography. It is formed of an aluminum thin film using technology. In addition,
In the figure, B5 indicates a damper agent.

In this case, the electrode pitch p between the regular IDT electrode B2 and the apodized IDT electrode B3 is regulated by the target center frequency f0 and the propagation speed v of the piezoelectric substrate B1 in the SAW propagation direction. That is, the electrode pitch p is p = １ ／ ·
v / f0. That is, since the propagation speed v of the piezoelectric substrate B1 in the SAW propagation direction is a characteristic value of the material, the electrode pitch p cannot be changed.

[0005] Next, since the chip size is naturally determined by the specifications of the desired frequency characteristics, it is impossible to reduce the size of the chip itself unless the specifications of the desired frequency characteristics are reduced. Cannot be realized without deteriorating the current frequency characteristics.

[0006]

In order to reduce the size of a circuit incorporating a SAW filter, for example, an RF circuit, or to increase the number of chips to be taken from a SAW wafer, the chip size can be reduced. Is desirable.

However, as described above, the conventional SAW filter needs to satisfy a certain filter specification.
Since the chip size is defined by the propagation speed and the electromechanical coupling coefficient inherent to the piezoelectric material, the only way to reduce the chip size is to sacrifice the filter specifications to some extent (spec down). The design burden of the RF circuit to be incorporated increases,
There is a disadvantage that the performance of the F circuit itself must be deteriorated. Further, unless the filter performance is reduced, the SAW filter itself cannot be reduced in size, thus limiting the miniaturization as a set.

An object of the present invention is to provide a surface acoustic wave device that can reduce the chip size without changing the basic design of the SAW filter and without deteriorating the frequency characteristics.

[0009]

According to the first aspect of the present invention, there is provided a surface acoustic wave device in which a groove is provided by etching a substrate surface between IDT electrodes in a surface acoustic wave device. The chip size is reduced by apparently reducing the propagation speed.

The propagation speed v of the SAW of the piezoelectric substrate is constant with respect to the propagation direction of the cut surface. However, by adopting the above structure, the propagation speed can be apparently reduced, and as a result, the SAW filter Chip size can be reduced without deteriorating the characteristics of the chip.

According to the second aspect, the first aspect is provided.
In the surface acoustic wave device described above, the IDT electrode is formed of a material having a higher specific gravity than aluminum.

As a result, the propagation speed v apparently decreases, and the chip size can be reduced.

[0013]

FIG. 1 is a plan view showing an embodiment of a surface acoustic wave device according to the present invention, FIG. 2 is a sectional view of the same, and FIG. 3 is an enlarged view of a portion a in FIG. It is. For example, in the case of a transversal-type SAW filter, a regular-type IDT electrode A2 and an apodized IDT electrode A with a desired weight opposed thereto are provided on a piezoelectric substrate A1.
3. Regular type IDT electrode A2 and apodized IDT electrode A3
In between, the shield electrode A4 is formed of a pure metal or alloy having a specific gravity higher than that of aluminum. In the figure, A5
Is a damper material.

Thereafter, the piezoelectric substrate material is etched with an etchant having a selectivity between the piezoelectric substrate material and the pure metal or alloy material. At this time, the regular type IDT electrode A2, the apodized IDT electrode A3, and the shield electrode A4
Is not formed, between the electrodes 2a, 2a of the normal type IDT electrode A2, and the electrode 3 of the apodized IDT electrode A3.
The groove A6 is formed by etching between the portions a and 3a. This etching can also be performed by reactive ion etching using an etching gas having selectivity.

The piezoelectric substrate A1 thus grooved is provided.
In the above, apparently, the propagation speed v of the SAW indicated by reference numeral 7A is reduced, and the electrode pitch of each of the IDT electrodes A2 and A3 can be reduced, so that the size of the entire chip can be reduced. In addition, each IDT electrode A is made of a pure gold metal or alloy having a higher specific gravity than aluminum.
Since the electrodes A2 and A3 and the shield electrode A4 are formed, the electrode pitch of the IDT electrodes can be further reduced, and the overall size of the chip can be reduced.

[0016]

According to the present invention, the chip size can be reduced without changing the basic design of the SAW filter and without deteriorating the frequency characteristics.

In addition, the design cost can be greatly reduced, and the burden of designing a circuit using a SAW filter can be reduced. Further, according to the present invention, SA
An increase in the number of chips taken from the W wafer leads to a reduction in material cost, and a reduction in the size of the SAW filter also enables a reduction in the size of the RF circuit and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a surface acoustic wave device according to the present invention.

FIG. 2 is a sectional view of a surface acoustic wave device according to the present invention.

FIG. 3 is an enlarged view of a part “a” in FIG. 2;

FIG. 4 is a schematic diagram of a conventional SAW filter.

FIG. 5 is a cross-sectional view of a conventional SAW filter.

[Explanation of symbols]

 A1 Piezoelectric substrate A2 Regular type IDT electrode 2a electrode A3 Apodized type IDT electrode 3a electrode A4 Shield electrode A5 Damper agent A6 Groove A7 SAW

Claims (2)

[Claims] A surface elasticity characterized in that a chip size is reduced by providing a groove by etching a surface of a substrate between IDT electrodes in a surface acoustic wave element to reduce an apparent propagation speed. Wave element. 2. The surface acoustic wave device according to claim 1, wherein the IDT electrode is formed of a material having a higher specific gravity than aluminum.