MULTILAYER ZNO ACOUSTIC TRANSDUCERS AT MILLIMETER-WAVE FREQUENCIES.

Thin-film ZnO acoustic transducers were developed for bulk acoustic wave generation at millimeter-wave frequencies (30-300 GHz). A multilayer design for the transducers was used to obtain high conversion efficiency. The transducers were fabricated by vacuum-sputtering layers of ZnO with alternating crystal structure. The transducers were designed for operation in the Ka-band (26. 5-40 GHz) and W-band (75-110 GHz). Conversion loss of these transducers was measured at cryogenic temperatures to reduce the acoustic attenuation in the sapphire substrates. The best untuned two-way conversion loss values were less than 30 and 50 dB near 29 and 96 GHz, respectively, measured at 77 K. The effect of the transducer size and the bonding technique on the conversion loss of the transducers are described.