Love Wave Ultraviolet Photodetector Fabricated on a TiO2/ST-Cut Quartz Structure

Walter Water,Yi-Shun Lin,Chi-Wei Wen

doi:10.1155/2014/270186

Walter Water, Yi-Shun Lin + Show 1 more

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https://doi.org/10.1155/2014/270186

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Abstract

A TiO2thin film deposited on a 90° rotated 42°45′ ST-cut quartz substrate was applied to fabricate a Love wave ultraviolet photodetector. TiO2thin films were grown by radio frequency magnetron sputtering. The crystalline structure and surface morphology of TiO2thin films were examined using X-ray diffraction, scanning electron microscope, and atomic force microscope. The effect of TiO2thin film thickness on the phase velocity, electromechanical coupling coefficient, temperature coefficient of frequency, and sensitivity of ultraviolet of devices was investigated. TiO2thin film increases the electromechanical coupling coefficient but decreases the temperature coefficient of frequency for Love wave propagation on the 90° rotated 42°45′ ST-cut quartz. For Love wave ultraviolet photodetector application, the maximum insertion loss shift and phase shift are 2.81 dB and 3.55 degree at the 1.35-μm-thick TiO2film.

Highlights

Titanium dioxide (TiO2) is a wide gap semiconductor and has three kinds of crystallography structures named anatase, brookite, and rutile
Leaky waves of LiTaO3 and LiNbO3 and surface skimming bulk waves (SSBW) of ST-cut quartz have been used as substrates for Love wave devices applications [20,21,22]; typically ZnO, fused silica (SiO2), and polymethylmethacrylate (PMMA) thin films have been used to construct the layered structure for the Love wave sensor [18, 23, 24]
After the contact electrode of interdigital transducers (IDTs) with a protection, the TiO2 films were deposited by RF magnetron sputtering using a TiO2 target (99.9%)

Summary

Introduction

Titanium dioxide (TiO2) is a wide gap semiconductor and has three kinds of crystallography structures named anatase, brookite, and rutile. Leaky waves of LiTaO3 and LiNbO3 and surface skimming bulk waves (SSBW) of ST-cut quartz have been used as substrates for Love wave devices applications [20,21,22]; typically ZnO, fused silica (SiO2), and polymethylmethacrylate (PMMA) thin films have been used to construct the layered structure for the Love wave sensor [18, 23, 24]. ZnO thin film is an excellent guiding layer for Love wave devices applications because it is a piezoelectric material and can be deposited as various surface. TiO2 is not a piezoelectric material, its strong mechanical and chemical stability, excellent photoelectric activity, and ease of synthesizing the various surface morphologies with nanostructures provide the potential as the guiding and sensing layer for Love wave sensors applications

Experimental

Results and Discussion

Conclusions