ZnO Films and Tungsten Oxide Film

Tungsten trioxide is used for many purposes in everyday life. It is frequently used in industry to manufacture tungstates for x-ray screen phosphors, for fireproofing fabrics and in gas sensors. Due to its rich yellow color, WO3 is also used as a pigment in ceramics and paints.In recent years, tungsten trioxide has been employed in the production of electrochromic windows, or smart windows. These windows are electrically switchable glass that change light transmission properties with an applied voltage.This allows the user to tint their windows, changing the amount of heat or light passing through.

The deposition process of ZnO/ultra-nanocrystal diamond (UNCD) film is simplified using the high target ultilisation sputtering technology and hot-filament chemical vapor deposition technique, which allow the growth of the high-quality multi-layer films with strong (0002) texture and fine grains. The ZnO/UNCD films have been successfully applied to fabricate SAW devices and the transmission signal obtained for the Rayleigh mode SAW is better than those using the conventional magnetron sputtering technique. The phase velocities show a significant thickness effect. The temperature coefficients of the frequency (TCF) for the SAW devices have been measured and a value of less than -30ppm/oC for the TCF could be obtained when the thickness of the UNCD layer ranges from 1.14 to 1.79 μm. For the SAW device with ZnO thickness of 7.68 μm and UNCD thickness of 1.06 mm, SAW achieves a coupling coefficient of 5.2%.The low TCF of -23.4 ppm/oC was obtained for the SAW devices with the 2.72μm-thick ZnO and 1.1 μm-thick UNCD film.

Love mode surface acoustic wave ultraviolet sensors have been fabricated using sputtered ZnO films on 36 Y-cut LiTaO3 substrate. Results from the UV sensing measurements show that the amplitude response of the Love mode SAW UV sensor operated at 41.5 MHz changed up to  6.4 dB and the fre-quency shift approached 150kHz under a 254 nm illumination at the power density of 350 μW/cm2. Whereas under a 365 nm illumination at a power density of 570 μW/cm2 the amplitude of thetransmission signal decreased only 2.5dB with no significant frequency shift. The frequency hopping effect during the downshift and recovery periods was identified due to the simultaneous interplays between the variations of the acoustic velocity andattenuation during the acoustic-electric interaction.

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