10+ GHz piezoelectric BAW resonators based on semiconductor multilayer heterostructures

A novel type of ultrasonic (f/spl gsim/10 GHz) piezoelectric bulk acoustic wave (BAW) resonators on the base of multilayer semiconductor heterostructures is proposed. Their design is developed and frequency characteristics are studied. A single-crystal heterostructure can be grown with the molecular-beam epitaxial (MBE) technique. The BAW resonators can have better quality factor Q than surface acoustic wave (SAW) devices. The semiconductor resonators are the suitable means of creating miniature high Q filters and frequency control elements compatible with monolithic microwave integrated circuits. Besides, the fabrication cost of the BAW semiconductor devices should be lower. Resonators with one piezoelectric layer, multilayer reflector, and substrate are studied in this report. The reflector is a periodical conductive heterostructure from alternating layers of different composition with thicknesses equal to a quarter of the acoustic wave length in them. The number of the reflector layers is determined by the required Q. The relation between them is derived in analytical form. The thickness of the piezoelectric layer (for a structure based on GaAlAs) is slightly less than a quarter of the acoustic wave length in it. The impedance of the structure at resonance frequency is obtained in analytical form. As an example, frequency characteristics of the resonator on the base of GaAlAs grown on n+-GaAs substrate oriented in [111] direction are computed.