CMOS event-driven tactile sensor circuit

In this paper, we present a device for low-latency compressive pressure sensing based on the use of a piezoelectric material coupled to mixed-mode neuromorphic CMOS circuits. The sensing element is based on the POSFET (Piezoelectric Oxide-Semiconductor-Field-Effect-Transistor) device, whereby the polarization induced by pressure in the piezoelectric material biases a CMOS transistor. The resulting output current feeds a subthreshold Leaky Integrate and Fire neuron that encodes the sensed force into trains of digital pulses. The proposed device produces output pulses whose instantaneous frequency is proportional to the applied force, only when the input force changes, drastically compressing the signal. The output features also low latency with respect to the change, as it is not limited by the sampling frequency of clocked digital to analog converters. We present the simulation as well as the full electrical and electromechanical characterization of the latest device prototype produced in AMS 180-nm process – coupled with the piezoelectric material – highlighting improvements over older versions, comprising smaller silicon estate, higher sensitivity, lower power consumption and bandwidth.