Surface acoustic wave device

Abstract

The surface acoustic wave device includes a plurality of output gate electrodes provided between two signal input transducers on a piezoelectric layer on a semiconductor substrate, so that each output gate electrode receives a bias voltage unique to it and supplies an output signal based on the unique bias voltage.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed or defined as follows: 1. A surface acoustic wave device comprising: a semiconductor substrate; a piezoelectric film provided on one surface of said substrate; two signal input transducers which are provided at spaced locations on said piezoelectric film and can each enter a signal thereinto; a plurality of electrically separate output gate electrodes provided on said piezoelectric film between said input transducers, said substrate having a plurality of interaction regions which are each associated with a respective said gate electrode; bias voltage applying means connected directly to each said output gate electrode for applying to each of said output gate electrodes a respective bias voltage independently selected to optimize a capacity-to-voltage characteristic in the associated interaction region of said substrate, said bias voltage applying means including a plurality of independently variable bias voltage sources which are each connected to a respective said output gate electrode; and output signal extracting means for extracting a respective output signal from each of said output gate electrodes, said output signal extracting means including a plurality of DC blocking capacitors which each have one end connected to a respective one of said output gate electrodes, each said output signal being extracted through a respective said blocking capacitor. 2. A surface acoustic wave device of claim 1 wherein said output signal extracting means includes a dielectric film provided on said output gate electrodes and said blocking capacitors include a plurality of signal extracting electrodes provided on said dielectric film at locations aligned with respective said gate electrodes. 3. A surface acoustic wave device of claim 2, including a matching circuit having an input, each of said signal extracting electrodes being connected to said input of said matching circuit. 4. A surface acoustic wave device of claim 1, wherein said output signal extracting means is directly electrically connected to each said output gate electrode. 5. A surface acoustic wave device of claim 4, wherein said output signal extracting means includes a matching circuit having an input, each said capacitor having a further end which is remote from said one end and is connected to said input of said matching circuit. 6. A surface acoustic wave device of claim 4, including a plurality of matching circuits which each have an input, each said capacitor having a further end which is remote from said one end and which is connected to the input of a respective said matching circuit. 7. A surface acoustic wave device, comprising: a semiconductor substrate having first and second surfaces on opposite sides thereof; an insulation film provided on said first surface of said substrate; a piezoelectric film provided on said insulation film; two signal input transducers provided at spaced positions on said piezoelectric film; a ground electrode provided on said second surface of said semiconductor substrate and connected to ground; a plurality of signal output gate electrodes provided on said piezoelectric film between said two signal input transducers; optimum bias applying means connected to said output gate electrodes for supplying each said output gate electrode with an optimum d.c. bias voltage which optimizes the capacitance-voltage characteristic of a respective region under such output gate electrode where an interaction occurs between surface acoustic waves and a depletion layer provided along said first surface of said substrate; and output signal extracting means for extracting a respective output signal from each said output gate electrode, said output signal extracting means including a plurality of d.c. blocking capacitors which each have a terminal connected to a respective said output gate electrode so that each said output signal is extracted through a respective said d.c. blocking capacitor. 8. A surface acoustic wave device of claim 7, wherein said optimum bias applying means includes a plurality of variable d.c. bias sources which are each connected to a respective said output gate electrode and which are adjustable independently. 9. A surface acoustic wave device of claim 7, wherein said optimum bias applying means includes a resistance layer and d.c. bias source means connected to said resistance layer, said resistance layer having a plurality of bias voltage extracting taps which are each connected to a respective said gate electrode.
This application is a continuation of U.S. Ser. No. 774 423, filed Sept. 10, 1985. FIELD OF THE INVENTION This invention relates to a monolithic surface acoustic wave device comprising a semiconductor substrate and a piezoelectric film provided thereon, and more particularly to a surface acoustic wave convolver or correlator based on said structure. BACKGROUND OF THE INVENTION Surface acoustic wave convolvers or correlators are known as a small-scaled device which utilizes a surface acoustic wave for signal processing. They are generally classified into one type having monolithic structures and the other type having non-monolithic structures. Monolithic structures are more advantageous in manufacturing and effectiveness of these devices. In a monolithic surface accoustic wave convolver or correlator comprising a semiconductor substrate and a piezoelectric film, its signal processing function is caused by a non-linear interaction between a surface acoustic wave and a space charge region along a surface of the semiconductor. A structure which has been conventionally proposed to use the phenomenon is shown in FIGS. 9 and 10 wherein an insulating film 3 is provided on one surface of a semiconductor substrate 1, and a piezoelectric film 2 is provided on the insulating film 3. On the piezoelectric film 2 and near both ends thereof are provided input transducers 4a-4b for entering a signal thereinto and a gate electrode 5 for outputting a processed signal. FIG. 9 also shows a ground or bottom electrode 6 provided along the other surface of the semiconductor substrate 1. FIG. 10 further shows a variable d.c. bias source 7, a d.c. blocking capacitor 8, matching circuits 9a-9b-9c, signal sources 10a-10b, and an external load resistance 11 from which an output signal is extracted. With this arrangement, non-linear interaction takes place just below the gate electrode 5 (this region is referred to as "interaction region" in this text), and an output is picked up from a point between the gate electrode 5 and bottom electrode 6. The magnitude of the interaction depends on the capacity-to-voltage (C-V) characteristic in the interaction region along the surface of the semiconductor substrate 1, and greatly varies with d.c. bias voltage applied between the gate electrode 5 and the bottom electrode 6 connected to ground. Therefore, it has been most usual in the prior art to uniformly apply to the entire interaction region a single bias voltage maximixing the total output from the gate electrode. However, since the C-V characteristic of the interaction region is not uniform but varies with location, a uniform bias cannot be the best voltage value for some locations with different C-V characteristics, and cannot cause the optimum function of the device. This is particularly serious in a device having an elongated interaction region for an improved signal processing capacity. Montress U.S. Pat. No. 4,328,473 and Minagawa U.S. Pat. No. 4,473,767 disclose technologies corresponding to the aforegoing prior art. In particular, Montress U.S. Pat. No. 4,328,473 discloses multiple bias applying gate electrodes and a single output gate electrode. However, since the output gate electrode is unitary or integral on the substrate, the bias applying gate electrodes and the output gate electrode are separate members. Therefore, although multiple bias sources are shown, they do not contribute to solution of the aforementioned problem. Minagawa U.S. Pat. No. 4,473,767 teaches the use of a SAW device having a bias gate electrode. However, the bias gate electrode is used for adding alternating components of both transducers to a d.c. bias component. Therefore, although a bias is applied, no non-linear interaction occurs just under the bias gate electrode (this occurs in a separate semiconductor), and the output electrode of the device is a member separate from the gate electrode. This means that the device is far from a solution of the aforementioned problem. OBJECT OF THE INVENTION It is therefore an object of the invention to provide a monolithic surface acoustic wave device which can apply different, unique and optimum d.c. bias voltages to individual locations with different C-V characteristics in the interaction region so as to optimize the resulting total effectiveness of the device. SUMMARY OF THE INVENTION In accordance with the invention, there is provided a surface acoustic wave device comprising: a semicondutor substrate; a piezoelectric film provided on one surface of said substrate; two signal input transducers provided at both ends of of said piezoelectric film to enter a signal; a plurality of output gate electrodes provided on said piezoelectric film and between said input transducers; bias voltage applying means for applying unique bias voltages to respective said output gate electrodes; and output signal extracting means for extracting output signals from said respective output gate electrodes. The invention will be understood better from the description given below, referring to some preferred embodiments illustrated in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic plan view of a surface acoustic wave device embodying the invention and some related circuit elements; FIG. 2 is a diagrammatic plan view illustrating a second embodiment of the invention; FIG. 3 is a diagrammatic plan view showing a third embodiment of the invention; FIG. 4 is a cross-sectional view of the device of FIG. 3; FIG. 5 is a diagrammatic plan view of a forth embodiment of the invention; FIG. 6 is a fragmental diagrammatic plan view illustrating an alternative form of the resistance layer in the embodiment of FIG. 5; FIG. 7 is a fragmental diagrammatic plan view illustrating a further embodiment of the invention; FIG. 8 is a cross-sectional view of the device of FIG. 7; FIG. 9 is a cross-sectional view of a prior art surface acoustic wave device; and FIG. 10 is a diagrammatic plan view of the device of FIG. 9 and some related circuit elements. DETAILED DESCRIPTION FIG. 1 is a diagrammatic plan view of a surface acoustic wave device embodying the invention. The same members or elements as in the prior art of FIG. 10 are identified by the same reference numerals as in FIG. 10. The gate electrode 5, d.c. bias source 7 and d.c. voltage blocking capacitor 8 in the prior art (FIG. 10) are divided or branched into some segments or lines shown at 5'--5', 7'--7' and 8'--8', respectively. These gate electrodes 5'--5' are aligned in a direction connecting the input transducers 4a and 4b provided near both ends of the device. Each gate electrode 5' is connected to one d.c. bias source 7' which is independently controlled or adjusted to give the gate electrode 5' the optimum bias voltage most suitable for the C-V characteristic of the location of the interaction region just under the associated gate electrode 5'. Individual locations under the respective gate electrodes 5'--5' process a signal and produce their own results which are passed through the capacitors 8' and gathered together into an output. The monolithic surface according to the invention is based on a multi-layer structure including the semiconductor substrate 1 and piezoelectric film 3. For improved operation and temperature characteristic or for facilitating incorporation into an integrated circuit, preferred structures are some combinations of aluminum oxide Al 2 O 3 (sapphire single crystal), silicon single crystal Si, silicon dioxide SiO 2 and a piezoelectric film of zinc oxide ZnO or aluminum nitride AlN, i.e. ZnO/SiO 2 /Si, ZnO/SiO 2 /Si/Al 2 O 3 , AlN/Si or AlN/Si/Nl 2 O 3 . FIG. 2 is a plan view of a surface acoustic wave device which is a second embodiment of the invention wherein the matching circuit 9c and external load resistance 11 in the embodiment of FIG. 1 are divided or branched into some segments or lines shown at 9'--9'c and 11'--11', corresponding to the individual gate electrodes 5'--5', d.c. bias sources 7'--7' and d.c. blocking capacitors 8'--8'. Therefore, a result of signal processing by one group associated with one gate electrode 5' can be extracted or detected as an output independently and separately from other results from other groups. FIG. 3 is a plan view of a third embodiment of the invention, and FIG. 4 is a cross-sectional view of the device of FIG. 3. In both Figures, the same reference numerals as those in the first embodiment of FIG. 1 denote identical elements or members. The third embodiment employs a specific form of d.c. voltage blocking capacitors. More specifically, a dielectric film 12 of a predetermined thickness is provided on the gate electrodes 5'--5', and a plurality of signal extracting electrodes 13'--13' are provided on the dielectric film 12 at opposite locations with respect to the gate electrodes 5'--5'. The gate electrode 5' and signal extracting electrode 13' are insulated so as block the flow of direct current and therefore form a d.c. voltage blocking capacitor. Obviously, application of different bias voltages to locations of the interaction region under the gate electrodes 5'--5', separate signal processings in said respective locations and extraction of a resultant output in the third embodiment are effected in the substantially same fashion as in the first embodiment. FIG. 5 is a plan view showing a fourth embodiment of the invention wherein the same reference numerals used in FIGS. 9, 10 denote identical elements or parts. On the same plane as the gate electrodes 5'--5' are provided a constant voltage terminal 14 and an earth or ground terminal 15 which are connected by a resistance layer 16 having an appropriate sheet resistivity. The resistance layer 16 is preferably a nichrom or cermet (Cr-SiO) vacuum vapour deposition layer, tentalum nitride (Ta 2 N) sputtering layer or the like which are readily manufactured and have an appropriate sheet resistivity. Across the resistance layer 16 are provided bias voltage take-up taps 17 at an appropriate interval. The bias voltage to each gate electrode 5' is properly selected by connecting the gate electrode 5' to one of the taps 17 which gives it a desired voltage upon application of a constant voltage to the constant voltage terminal 12, and may be further adjusted by trimming the resistance layer 16 by a laser or electrode beam. Thus each gate electrode 5' receives a bias voltage which is most preferable to the C-V characteristic of the location in the interaction region just under it. Each result of each signal processing in each location is outputted through the associated d.c. voltage blocking capacitor 8'. FIG. 6 shows a resistance layer 18 made of an antimony, bismuth, tantalum or other metal film which replaces the resitance layer 16 of FIG. 2. FIG. 7 is a plan view of a further embodiment using a resistance layer 19 formed in the semiconductor substrate 1, and FIG. 8 is a cross-sectional view along IV-IV line of FIG. 7. Before the insulating film 3 is provided on the semiconductor substrate 1, impurities are entered in a region of the substrate 1 encircled by a broken line in FIG. 7 up to a predetermined impurity concentration, and form a high impurity concentration region 19 which serves as the resistance layer. After the insulating film 3 is provided on the substrate 1 and the region 18, the insulating film 3 is selectively removed by etching to form windows which expose selective portions of the high impurity concentration region 19, and electrodes are provided in the windows. One of the end electrodes serves as the constant voltage terminal 14, and the other of the end electrodes is used as the earth terminal 15. The other electrodes between both terminal electrodes 14 and 15 are used as bias voltage take-up taps 17. As described above, since the monolithic surface acoustic wave convolver or correlator according to the present invention employs divisional output gate electrodes, the bias voltage to the gate electrodes can be adjusted location by location so as to give each gate electrode 5' a unique value of the bias voltage which is most suitable for the C-V characteristic of the interaction region just under the gate electrode 5'. Therefore, the resulting effectiveness of the entire device is significantly improved.

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Patent Citations (2)

    Publication numberPublication dateAssigneeTitle
    US-4328473-AMay 04, 1982United Technologies CorporationIsolated gate, programmable internal mixing saw signal processor
    US-4473767-ASeptember 25, 1984Clarion Co., Ltd.Surface acoustic wave convolver with depletion layer control

NO-Patent Citations (0)

    Title

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    US-5870670-AFebruary 09, 1999Motorola, Inc.Integrated image reject mixer
    US-6198197-B1March 06, 2001Asahi Kasei Kogyo Kabushiki Kaisha, Kazuhiko YamanouchiSurface acoustic wave element and electronic circuit using the same
    US-5757847-AMay 26, 1998Omnipoint CorporationMethod and apparatus for decoding a phase encoded signal
    US-5881100-AMarch 09, 1999Omnipoint CorporationMethod and apparatus for coherent correlation of a spread spectrum signal
    US-5850600-ADecember 15, 1998Omnipoint CorporationThree cell wireless communication system
    US-5784403-AJuly 21, 1998Omnipoint CorporationSpread spectrum correlation using saw device
    US-5291516-AMarch 01, 1994Omnipoint Data Company, Inc.Dual mode transmitter and receiver
    US-5832028-ANovember 03, 1998Omnipoint CorporationMethod and apparatus for coherent serial correlation of a spread spectrum signal
    US-6317452-B1November 13, 2001Xircom, Inc.Method and apparatus for wireless spread spectrum communication with preamble sounding gap
    US-2003219063-A1November 27, 2003Vanderpool Jeffrey S.Spread spectrum wireless communication system
    US-5038363-AAugust 06, 1991Clarion Co., Ltd.Correlation processing device using a surface acoustic wave convolver
    US-5016255-AMay 14, 1991Omnipoint Data Company, IncorporatedAsymmetric spread spectrum correlator
    US-5265267-ANovember 23, 1993Motorola, Inc.Integrated circuit including a surface acoustic wave transformer and a balanced mixer
    US-6621852-B2September 16, 2003Intel CorporationSpread spectrum wireless communication system
    US-5953370-ASeptember 14, 1999Omnipoint CorporationApparatus for receiving and correlating a spread spectrum signal
    US-5754584-AMay 19, 1998Omnipoint CorporationNon-coherent spread-spectrum continuous-phase modulation communication system
    US-5963586-AOctober 05, 1999Omnipoint CorporationMethod and apparatus for parallel noncoherent correlation of a spread spectrum signal
    US-5742638-AApril 21, 1998Omnipoint CorporationSpread-spectrum data publishing system
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    US-5497424-AMarch 05, 1996Omnipoint Data CompanySpread spectrum wireless telephone system
    US-5276704-AJanuary 04, 1994Omnipoint Data Company, Inc.SAWC phase detection method and apparatus
    US-7603909-B2October 20, 2009Oes, Inc.Piezoelectric polymer sensor device
    US-4900969-AFebruary 13, 1990Clarion Co., Ltd.Surface acoustic wave convolver
    US-5355389-AOctober 11, 1994Omnipoint CorporationReciprocal mode saw correlator method and apparatus
    US-5332983-AJuly 26, 1994Com Dev Ltd.Filterbank using surface acoustic wave technology
    US-5365207-ANovember 15, 1994Motorola, Inc.Multi-bandwidth saw filter
    US-5648982-AJuly 15, 1997Omnipoint CorporationSpread spectrum transmitter
    US-5285469-AFebruary 08, 1994Omnipoint Data CorporationSpread spectrum wireless telephone system
    US-5243250-ASeptember 07, 1993Clarion Co., Ltd.Surface acoustic wave convolver device
    US-5754585-AMay 19, 1998Omnipoint CorporationMethod and apparatus for serial noncoherent correlation of a spread spectrum signal
    US-7120187-B2October 10, 2006Intel CorporationSpread spectrum wireless communication system
    US-6046524-AApril 04, 2000Asahi Kasei Kogyo Kabushiki KaishaElastic surface wave functional device and electronic circuit using the element
    US-4882715-ANovember 21, 1989Canon Kabushiki KaishaSurface acoustic wave convolver with dielectric film of high non-linear effect
    US-5402413-AMarch 28, 1995Omnipoint CorporationThree-cell wireless communication system
    US-5081642-AJanuary 14, 1992Omnipoint Data Company, IncorporatedReciprocal saw correlator method and apparatus
    US-5214338-AMay 25, 1993United Technologies CorporationEnergy coupler for a surface acoustic wave (SAW) resonator
    US-5856998-AJanuary 05, 1999Omnipoint CorporationMethod and apparatus for correlating a continuous phase modulated spread spectrum signal
    US-2008078255-A1April 03, 2008Kiet Ngo, Paul Hogendoorn, Michael ReevePiezoelectric polymer sensor device
    US-5022047-AJune 04, 1991Omnipoint Data CorporationSpread spectrum correlator
    US-5640674-AJune 17, 1997Omnipoint CorporationThree-cell wireless communication system
    US-5153476-AOctober 06, 1992The United States Of America As Represented By The Secretary Of The ArmyAcoustic vibrator with variable sensitivity to external acceleration
    US-5629956-AMay 13, 1997Omnipoint CorporationMethod and apparatus for reception and noncoherent serial correlation of a continuous phase modulated signal
    US-5455822-AOctober 03, 1995Omnipoint CorporationMethod and apparatus for establishing spread spectrum communication
    US-2003125030-A1July 03, 2003Robert C. DixonWireless cellular communication system
    US-6115412-ASeptember 05, 2000Omnipoint CorporationSpread spectrum wireless telephone system
    US-6118824-ASeptember 12, 2000Omnipoint CorporationSpread-spectrum data publishing system
    US-6421368-B1July 16, 2002Xircom Wireless, Inc.Spread spectrum wireless communication system
    US-5499265-AMarch 12, 1996Omnipoint Data Company, IncorporatedSpread spectrum correlator
    US-5627856-AMay 06, 1997Omnipoint CorporationMethod and apparatus for receiving and despreading a continuous phase-modulated spread spectrum signal using self-synchronizing correlators
    US-5610940-AMarch 11, 1997Omnipoint CorporationMethod and apparatus for noncoherent reception and correlation of a continous phase modulated signal
    US-6983150-B2January 03, 2006Intel CorporationWireless cellular communication system
    US-4841470-AJune 20, 1989Clarion, Co., Ltd.Surface acoustic wave device for differential phase shift keying convolving
    US-7411936-B2August 12, 2008Intel CorporationWireless communication method and apparatus
    US-5692007-ANovember 25, 1997Omnipoint CorporationMethod and apparatus for differential phase encoding and decoding in spread-spectrum communication systems with continuous-phase modulation
    US-2001000136-A1April 05, 2001Dixon Robert C., Vanderpool Jeffrey S.Wireless communication method and apparatus
    US-5680414-AOctober 21, 1997Omnipoint CorporationSynchronization apparatus and method for spread spectrum receiver