Wave transmission lines and networks – Coupling networks – Delay lines including elastic bulk wave propagation means
Patent
1999-01-08
2000-04-04
Lee, Benny
Wave transmission lines and networks
Coupling networks
Delay lines including elastic bulk wave propagation means
333193, 310311, 310313R, 29 2535, H03H 946, H03H 915
Patent
active
060466561
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a boundary wave device for use with a filter device and an oscillator in, for example, a TV set, a portable telephone unit, a PHS unit, and so forth and to a fabrication method thereof.
BACKGROUND ART
As an example of a device using an elastic wave, a SAW (Surface Acoustic Wave) device is well known. The SAW device is used for various circuits (such as a transmission band-pass filter, a reception band-pass filter, a local oscillation filter, an antenna duplexer, an IF filter, and an FM modulator) that process radio signals in a frequency band of, for example, 45 MHz to 2 GHz.
FIG. 8 shows a basic structure of such an SAW device. Referring FIG. 8, the SAW device is composed of a piezoelectorc substrate 100 and IDTs (Interdigital Transducers) 101 and 102. The piezoelectric substrate 100 is composed of, for example, LiNbO.sub.3. The IDTs 101 and 102 are composed of a metal material such gas Al thin films. The IDTs 101 and 102 are formed on the piezelectric substrate 100 by etching or the like. When a racic frecuency electric signal is applied the IDT 101, a SAW 103 excited on the surface of the piezoelectric substrate 100. The excited SAW 103 is propagated to the IDT 102 through the surface of the piezoelectric substrate 100. The IDT 102 converts the SAW 103 into an electric signal.
Since the SAW device uses a boundary surface between the solid surface and vacuum or gas (namely, uses an elastic wave that is propagated through the solid surface), the surface of the piezoelectric substrate that is a propagation medium should be a free surface. Thus, chips on the SAW device cannot be packaged with plastic mold that is used for semiconductors. Thus, the SAW device should have a hollow portion that assures such a free surface.
However, when such a hollow portion is formed in the package, the cost of the device rises and the size thereof becomes larger.
SUMMARY OF THE INVENTION
Accordingly, the inventor of the present invention has proposed a boundary wave device that has functions similar to the SAW device and whose size and cost are easily reduced. In the boundary wave device, a piezoelectric substrate and a Si substrate are layered with IDTs disposed therebetween. The present invention is a modification of such a boundary wave device.
In other words, a first object of the resent invention is to provide boundary wave device and a fabrication method thereof that allow the conversion efficiency of an elastic wave excited by an electrode to be improved.
In addition, a second object of the cresent invention is to provide a boundary wave device from and a fabrication method thereof that prevent the device from being affected by parasitic resistance between electrodes.
To solve such problems, as one feature of the present invention is a boundary wave device, including a piezoelectric first substrate, a plurality of electrodes, formed on a main surface of the piezoelectric first substrate, for exciting a boundary wave, a dielectric film formed on the piezoelectric first substrate so that the dielectric film covers the plurality of electrodes and has a smooth surface thereon, and a Si second substrate lavered on the surface of the dielectric film.
The present invention is also directed to a fabrication method for a boundary wave device, including the steps of (a) forming a plurality of electrodes for exciting a boundary wave on a main surface of a piezoelectric first substrate, (b) forming a dielectric film on the main surface of the first substrate with the plurality of electrodes formed, (c) smoothing the surface of the dielectric film formed on the main surface of the piezoelectric first substrate, and (d) layering a Si second substrate on the surface of the smoothed dielectric film.
The present invention is also directed to a fabrication method, wherein the stcw (b) is performed by forming the dielectric film so that the thickness of the dielectric film is larger than the thickness of the plurality of electrodes, and wherein the step (c) is performed of smoothin
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Kabushiki Kaisha Toshiba
Lee Benny
Summons Barbara
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