Leveraging Innate Piezoelectricity of Ultra-Smooth Silk Thin Films for Flexible and Wearable Sensor Applications

In this paper, the innate peizoelectricity of silk is utilized to demonstrate an optimized silk thin film-based pressure sensor. Furthermore, a novel approach to pattern silk films is proposed, which could potentially lead to the development of a variety of miniaturized, flexible, and wearable sensors. The key in this endeavor is to achieve a uniform thin film of silk. The preparation methodology was optimized to achieve an ultra-smooth, reproducible thin film. The surface quality of the optimized thin film was analyzed using atomic force microscopy and the RMS roughness was found to be 2.43 nm. The piezo-response of the silk film was measured using Piezo force microscopy and the average d33 value of the silk piezoelectric thin film was estimated at 56.7 pm/V. A pressure sensor using silk piezoelectric thin film was developed with a simple process flow. This process is devoid of any silk patterning steps. Keeping in view the potentiality of piezoelectric silk films in MEMS, a novel lithography-based technique was developed to pattern the silk films. This patterning technique can easily be integrated with any standard MEMS/Post CMOS process flow, thus opening up a new avenue in developing a variety of sensors.