Towards Ultra-High Spatial Resolution Sensing of GHz Ultrasound Using Strain Modulation of Field Effect Transistors

This work demonstrates the detection of GHz ultrasonic (U/S) pulses using a 130nm technology-based PFET transistor, monolithically integrated with a GHz Fresnel focusing ultrasonic transducer. The focusing transducer enables the concentration of the ultrasonic strain at the PFET location resulting in observable modulation of the transistor current due to piezoresistivity in the transistor conduction channel. 50ns wide U/S pulses with 1-2 GHz frequencies were successfully detected using the PFET transistor. The outcome of measuring strain with nm-scale transistors indicates the potential application of 3D arrays of CMOS transistors for sub-μm spatial resolution and high bandwidth active sensing of high-frequency ultrasonic pulses and waves.