Shallow bulk acoustic wave devices

A shallow bulk acoustic wave device comprising:

• a block of anisotropic piezoelectric material having physical properties that may be defined by reference to a set of crystallographic axes and having a surface into which both surface acoustic waves and shallow bulk acoustic waves may be propagated;
• a sending interdigital transducer and a receiving interdigital transducer disposed on said surface and so oriented with respect to said crystallographic axes that coupling of surface acoustic waves is minimized and coupling of shallow bulk acoustic waves is substantial;
• and
• a multistrip coupler disposed on said surface and having a portion of its width aligned with a first propagation path from said sending transducer and another portion of its width aligned with a second propagation path to said receiving transducer, whereby energy is coupled from said first propagation path to said second propagation path.

A temperature-compensated shallow bulk acoustic wave device comprising:

• a block of anisotropic piezoelectric material having physical properties which may be defined by reference to a set of crystallographic axes and having a surface into which both surface acoustic waves and shallow bulk acoustic waves may be propagated;
• a pair of electroacoustic transducers disposed on said surface and so oriented with respect to said crystallographic axes that coupling of surface acoustic waves is minimized and coupling of shallow bulk waves is substantial;
• and
• temperature compensation means situated between said transducers, wherein said temperature compensation means includes a portion of a second piezoelectric material interposed in the path of the shallow bulk acoustic waves and having a temperature coefficient of velocity change less than or opposite to that of said block of piezoelectric material, whereby the overall temperature coefficient of velocity change is substantially reduced.

A shallow bulk acoustic wave device comprising:

• a pair of electroacoustic transducers;
• and
• means defining a path between said transducers for the transmission of shallow bulk acoustic waves, said means including a block of anisotropic piezoelectric crystalline material having a surface into which both surface acoustic waves and shallow bulk waves can be propagated, and said transducers being so oriented on said surface that the electromechanical coupling coefficient is practically zero for surface waves but is substantial for shallow bulk waves;
• and wherein said means defining a path between said transducers further includes at least one set of reflective elements located on said surface and so oriented with respect to the direction of propagation of the wave that the direction of propagation of selected frequency components is changed between said transducers.

A shallow bulk acoustic wave device comprising:

• a pair of electroacoustic transducers;
• and
• means defining a path between said transducers for the transmission of shallow bulk acoustic waves, said means including a block of anisotropic piezoelectric crystalline material having a surface into which both surface acoustic waves and shallow bulk waves can be propagated, and said transducers being so oriented on said surface that the electromechanical coupling coefficient is practically zero for surface waves but is substantial for shallow bulk waves;
• and wherein said means defining a path between said transducers further includes means for compensating for the effects of temperature on said device.

A shallow bulk acoustic wave device comprising:

• a block of anisotropic piezoelectric material having crystallographic axes and having a surface into which surface acoustic waves and shallow bulk acoustic waves may be propagated;
• a sending electroacoustic transducer and a receiving electroacoustic transducer disposed on said surface and so oriented with respect to the crystallographic axes that the electromechanical coupling coefficient is essentially zero for surface acoustic waves and is relatively large for shallow bulk acoustic waves, whereby shallow bulk acoustic waves can be launched into said piezoelectric material in a first propagation direction from said sending transducer;
• a first set of reflective elements located at the surface of said piezoelectric material and inclined at an angle to said first propagation direction, said reflective elements being operative to change the direction of propagation of predetermined frequency components of the shallow bulk acoustic waves;
• and
• a second set of reflective elements, operative to reflect predetermined frequency components of the reflected shallow bulk acoustic wave into a direction parallel with said first propagation direction, to be received by said receiving transducer;
• and
• wherein said reflective elements are spaced nonuniformly to reflect different selected frequency components at different portions of said sets of reflective elements, whereby components at some frequencies traverse a longer path than components at other frequencies, and the times of occurrence of the various frequency components are compressed or expanded with respect to time.