High-Sensitivity Strain Sensing Over an Ultrawide Range Achieved on Temperature-Compensated Multimodal Flexible SAW Device

In this work, flexible surface acoustic wave (SAW) devices are prepared based on ZnO in thickness of $3~\mu $ m deposited on a polyimide (PI) film. The ZnO piezoelectric film possesses superior piezoelectric properties (piezoelectric coefficient ${d}_{{33}}$ of 22 pm/V at 1 MHz) and an ideal orientation (002). The devices with the wavelength of $20~\mu $ m exhibit two wave modes, including the Rayleigh and Lamb waves with resonant frequencies of 68.4 and 212.3 MHz and electromechanical coupling coefficient ( ${K}^{{2}}$ ) of 9.71% and 4.82%, respectively. These characteristics bring the potential for developing a high-performance strain sensor with our device, which significantly improves the strain sensitivity to 1330 Hz/ $\mu \varepsilon $ in Lamb wave mode with an ultrawide testing range of $3000~\mu \varepsilon $ . Moreover, based on the device’s dual-mode response, an on-chip temperature compensation scheme was therefore proposed. All these results indicate that this developed sensor is an excellent candidate for strain measurement and can be proposed for noninvasive conformal monitoring.