Piezotransistive transduction of femtoscale displacement for photoacoustic spectroscopy

Measurement of femtoscale displacements in the ultrasonic frequency range is attractive for advanced material characterization and sensing, yet major challenges remain in their reliable transduction using non-optical modalities, which can dramatically reduce the size and complexity of the transducer assembly. Here we demonstrate femtoscale displacement transduction using an AlGaN/GaN heterojunction field effect transistor-integrated GaN microcantilever that utilizes piezoelectric polarization-induced changes in two-dimensional electron gas to transduce displacement with very high sensitivity. The piezotransistor demonstrated an ultra-high gauge factor of 8,700 while consuming an extremely low power of 1.36 nW, and transduced external excitation with a superior noise-limited resolution of 12.43 fm Hz −1/2 and an outstanding responsivity of 170 nV fm −1 , which is comparable to the optical transduction limits. These extraordinary characteristics, which enabled unique detection of nanogram quantity of analytes using photoacoustic spectroscopy, can be readily exploited in realizing a multitude of novel sensing paradigms. Microelectromechanical systems—micrometre-sized devices with movable parts—make highly sensitive transducers. Here, the authors fabricate an integrated gallium nitride microcantilever and heterojunction field effect transistor that uses piezoelectric effects to measure displacement at the femtoscale level.