Highly Sensitive UV Sensors Based on SMR Oscillators

The interest in ultraviolet (UV) light sensors have been stimulated in the fields of ozone layer and ultraviolet radiation monitoring, satellite communications and UV astronomy. Zinc oxide (ZnO) thin film is an attractive candidate for acoustic wave devices and ultraviolet optoelectronics, due to its high coupling coefficient and the direct energy band gap of approximately 3.2 eV at room temperature. In general, thin film bulk acoustic wave (TFBAW) devices, which are solidly mounted resonator (SMR) devices in this study, possess a higher operating frequency and better frequency response than those of surface acoustic wave (SAW) devices. Therefore, ZnO thin films in the SMR devices acting as both the piezoelectric layer and UV sensing layer were adopted to investigate the acoustic and UV properties in this study. The SMR-based oscillator is composed of a high frequency amplifier, the matching networks, and an SMR device. The resonance frequency of the SAW oscillator is 619.31 MHz with output power of -18.75 dBm, and the phase noise is -60.63 dBc at 100 kHz. The frequency shifts of SMR oscillators show a trend as a function of the illumination intensities of UV light. Finally, the maximum frequency shift of 552 kHz could be obtained when the illumination intensity of UV light was 212 mu W/cm(2). (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of MRS-Taiwan