Flexible ZnO thin film-based surface acoustic wave devices for environmental and biomedical sensing applications

Abstract

Flexible ZnO thin film on aluminium foil-based SAW devices have been investigated for the first time as sensors for temperature, UV light, and humidity as well as breath and apnoea detection, and these devices were performing sensing while they were placed in flat and bending (curved) positions. Flexible SAW devices offer a promising technology of low cost, highly sensitive and bendable sensors. They also exhibit high potential for wearable, point of care and microfluidics and lab-on-chips applications. The ZnO thin film was deposited on the aluminium foil and ZnO nanorods were grown on the surface of selected samples. The SAW sensors were fabricated by patterning Au/Cr IDTs with various wavelengths. Film and nanorods possessed the preferred structure and piezoelectric properties. Lamb modes were identified, and they were in a good agreement with the FEA results. The maximum value of TCF was -773 ppm/K which is among the highest values mentioned in the literature. The sensors showed excellent linearity and repeatability during temperature cycling test. The maximum value of sensitivity to UV light was 63 ppm (mW/cm2)-1. ZnO nanorods enhanced the sensitivity by 1.76 times. The sensors showed excellent repeatability and reliability during UV light cycling in flat, bent-up and bent-down positions. The maximum values of sensitivity to humidity were 47.7 kHz at 90%RH for nanorodenhanced device and the maximum frequency shift was -57 kHz. The sensors exhibited good repeatability in response to humidity cycling. Besides, the devices exhibited an excellent response, sensitivity, and reliability for various breath patterns (e.g., healthy breathing, apnoea, slow and fast breathing).

Date of Award	30 Sept 2019
Original language	English
Awarding Institution	Northumbria University
Supervisor	John Dean (Supervisor), Glen McHale (Supervisor) & Yongqing (Richard) Fu (Supervisor)