Development of flexible ZnO thin film surface acoustic wave strain sensors on ultrathin glass substrates

Flexible surface acoustic wave (SAW) strain sensors made on ZnO/ultrathin glass (100 mu m) substrates have been developed. The sensitivity of the SAW strain sensors under different strain angles and annealing temperatures, as well as the mechanical stability, are investigated. It was shown that the thickness of ZnO has a strong effect on the sensitivity of the strain sensors, and thicker ZnO makes sensors with better performance. Thermal annealing at a temperature up to 200 degrees C also improves the sensitivity of the strain sensor significantly. The temperature coefficient of frequency remains unchanged under different strains, showing good thermal stability. A cyclic bending test with the strain varied between zero and 2000 mu epsilon exhibits good mechanical stability and reliability of SAW strain sensors. All the results demonstrate the great potential of flexible SAW strain sensors for flexible electronic applications.