Metal-insulator-semiconductor convolver

A surface-acoustic-wave (SAW) convolver structure with a zinc oxide film on a silicon substrate is studied. The zinc oxide films are deposited by cathode sputtering in a dc diode system. The substrates are n-type silicon wafers with a resistivity of 4.5 ohm-cm (100) coated with a silicon dioxide layer 1000 A thick. The zinc oxide is doped with copper during the film growth; this reduces the disorientation of the hexagonal axis of the crystal grains to 1.5 deg and increases the resistivity of the films to 10 to the 7th ohm-cm. The structures are then used to fabricate delay lines that operate in the band 140-160 MHz with an insertion loss of 26 dB without matching. Applying a static transverse field to the transducer region acts to modulate the SAW excitation efficiency. As the voltage varies from -1.5 to -10 V the SAW amplitude changes by 6 dB. It is found experimentally that this change derives from a change in the conditions at the semiconductor-insulator interface.