ZINC OXIDE ON SILICON SURFACE ACOUSTIC WAVE DEVICES

MICHAEL RAYMOND MELLOCH, Purdue University

Abstract

Results will be presented describing the operational behavior of a metal-ZnO-SiO(,2)-Si (MZOS) surface acoustic wave (SAW) device with a new transducer configuration. In the new configuration the transducer is positioned at the ZnO-SiO(,2) interface; there is a metal overlay above the transducer at the outer ZnO surface. The transduction in a SAW delay line is observed to vary by 30 dB when a dc voltage is applied to the interface transducer. Also the lowest measured insertion loss is 20 dB, a value comparable to that obtained from conventional MZOS devices. A new transducer configuration, the separate comb transducer, will also be introduced, which enables one to double the possible operating frequency for a given photolithographic capability. The increase is due to the metal widths and spacings being one-half of the wavelength for the separate comb transducer while the metal widths and spacings for the conventional interdigital transducer are a quarter of the wavelength. The separate comb transducer structure also has yield advantages compared to the interdigital transducer structure. The separate comb transducer has been utilized in the fabrication of higher frequency MZOS convolvers than previously reported (285 MHz synchronous frequency Rayleigh and 355 MHz synchronous frequency Sezawa devices). The occurrence of conversion from the Sezawa mode to the Rayleigh mode due to periodic gratings in the MZOS device structure is demonstrated. In order to avoid unwanted stopbands, the occurrence of such a conversion must be considered in the design of grating structures, such as the multistrip coupler, in layered monolithic configurations. Recently the elimination of the bias instability in the MZOS structure has been achieved by use of a low temperature nitrogen anneal. This technique has been utilized in the fabrication of a bias stable MZOS Rayleigh mode convolver.

Degree

Ph.D.

Subject Area

Acoustics

COinS