Wide band surface acoustic wave filter having constant thickness piezoelectric layer and divergent transducers
First Claim
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1. A wide band surface acoustic wave filter comprising:
- a semiconductor substrate having a given outer surface;
a piezoelectric layer of given thickness formed on said outer surface of said semiconductor substrate; and
an input and an output transducer disposed on an outer surface of said piezoelectric layer and being characterized by coupling coefficients thereto, said input transducer when excited generating surface acoustical waves propagating in a direction of propagation along a path, said output transducer being disposed to be in said path, each said transducer having associated therewith at least three interdigitated electrodes configured as a spatially periodic array having periodic inter-electrode spacings and oriented generally perpendicular to said direction of propagation, the inter-electrode spacing between each adjacent pair of said interdigitated electrodes increasing from a minimum to a maximum spacing value along a direction perpendicular to said propagation direction, the thickness of said piezoelectric layer being of substantially constant value under said interdigitated electrodes, the thickness of said piezoelectric layer and said minimum spacing value being such that the coupling coefficient of said transducers decreases from an upper frequency corresponding to said minimum spacing value to a lower frequency corresponding to said maximum spacing value.
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Abstract
In a wide band surface acoustic wave filter having a multilayered structure, in which an elastic substrate and a piezoelectric thin film are combined, transducers are so constructed that the period of electrodes thereof varies in the direction perpendicular to the propagation direction of the surface acoustic wave.
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Citations
11 Claims
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1. A wide band surface acoustic wave filter comprising:
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a semiconductor substrate having a given outer surface; a piezoelectric layer of given thickness formed on said outer surface of said semiconductor substrate; and an input and an output transducer disposed on an outer surface of said piezoelectric layer and being characterized by coupling coefficients thereto, said input transducer when excited generating surface acoustical waves propagating in a direction of propagation along a path, said output transducer being disposed to be in said path, each said transducer having associated therewith at least three interdigitated electrodes configured as a spatially periodic array having periodic inter-electrode spacings and oriented generally perpendicular to said direction of propagation, the inter-electrode spacing between each adjacent pair of said interdigitated electrodes increasing from a minimum to a maximum spacing value along a direction perpendicular to said propagation direction, the thickness of said piezoelectric layer being of substantially constant value under said interdigitated electrodes, the thickness of said piezoelectric layer and said minimum spacing value being such that the coupling coefficient of said transducers decreases from an upper frequency corresponding to said minimum spacing value to a lower frequency corresponding to said maximum spacing value. - View Dependent Claims (3, 4, 5, 6)
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2. A wide band surface acoustic wave filter comprising:
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a semiconductor substrate having a given outer surface; an insulating layer formed on said outer surface; a piezoelectric layer of given thickness formed on said insulating layer; and an input and an output transducer disposed on an outer surface of said piezoelectric layer and being characterized by coupling coefficients thereto, said input transducer when excited generating surface acoustical waves propagating in a direction of propagation along a path, said output transducer being disposed to be in said path, each said transducer having associated therewith at least three interdigitated electrodes configured as a spatially periodic array having periodic inter-electrode spacings and oriented generally perpendicular to said direction of propagation, the inter-electrode spacing between each adjacent pair of said interdigitated electrodes increasing from a minimum to a maximum spacing value along a direction perpendicular to said propagation direction, the thickness of said piezoelectric layer being of substantially constant value under said interdigitated electrodes, the thickness of said piezoelectric layer and said minimum spacing value being such that the coupling coefficient of said transducers decreases from an upper frequency corresponding to said minimum spacing value to a lower frequency corresponding to said maximum spacing value. - View Dependent Claims (7)
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8. A wide band surface acoustic wave filter comprising:
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a wave propagation medium formed as a piezoelectric layer of given thickness affixed to a given surface of a substrate, and an input transducer and an output transducer for producing and receiving surface acoustical waves respectively, both of said transducers being disposed on said piezoelectric layer to be coupled thereto, each having a plurality of stripe-shaped interdigitated electrodes with spaces therebetween and connected to associated first and second terminal electrodes and disposed so that the spacing between adjacent stripes varies progressively from a given minimum spacing in regions proximate to said first terminal electrode to a given maximum spacing in regions proximate to said second terminal electrode, said minimum and maximum spacings establishing given passband upper and lower frequencies respectively, said propagation medium having the property that the coupling between said transducers and said wave propagation medium varies with frequency so as to have a maximum coupling value at a given frequency, said given frequency varying according to said given thickness of said piezoelectric layer, the thickness of said piezoelectric layer being of substantially constant value under said interdigitated electrodes, said minimum spacing and said given thickness of said piezoelectric layer having respective values placing said passband upper frequency generally no higher than said given frequency. - View Dependent Claims (9, 10, 11)
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Specification