Piezoelectric Micromachined Ultrasonic Transducer Using Silk Piezoelectric Thin Film

In this letter, we present for the first time, a successful fabrication and characterization of silk piezoelectric thin film-based piezoelectric micromachined ultrasonic transducer (PMUT). One of the exacting problems in the PMUT research is to find a suitable piezoelectric material to be used as the sensing and actuating element. Utilizing its innate piezoelectricity, we have used ultra-smooth silk thin film (RMS roughness = 2.84 nm, d(33) = 56.2 pm/V) as the piezoelectric element of the PMUT. The silicon membrane of the PMUT is realized by bulk micromachining. The challenging task of integrating the silk thin film above the micromachined membrane is successfully accomplished and the device functionality is demonstrated. The silk PMUT exhibited center frequency at 76.59 kHz with a fractional bandwidth of 3.18 %, when characterized in air.