Shallow bulk acoustic wave devices

Abstract

Acoustic wave devices employing shallow bulk acoustic waves rather than surface acoustic waves, to provide higher frequencies of operation and other significant advantages, such as less susceptibility to aging and less sensitivity to surface contamination. In each embodiment of the invention, a transmitting transducer and a receiving transducer are oriented on the surface of an anisotropic piezoelectric crystal to achieve substantial coupling of shallow bulk acoustic waves and essentially zero coupling of surface acoustic waves. In one embodiment of the invention, various types of grating filters utilize shallow bulk acoustic waves, and a set of parallel mechanical or electrical discontinuities at or near the surface of the crystal provide reflection of acoustic energy at a frequency determined by the spacing of the discontinuities. Uniformly spaced gratings provide bandpass filter operation, and gratings with graduated spacings provide for frequency compression or expansion. In another embodiment of the invention, variations in device characteristics due to temperature changes are compensated for by directing the shallow bulk waves through materials having favorable or opposite temperature characteristics compared with those of the material into which the waves are originally launched. In other embodiments of the invention, a shallow bulk acoustic wave includes a multistrip coupler, for transferring electroacoustic energy from one propagation path to another, for use in bandpass filters, delay lines or unidirectional transducers.