Electrical Tunability of Partially Depleted Silicon on Insulator (PD-SOI) Neuron

The hardware realization of spiking neural network (SNN) requires a compact and energy efficient electronic analog to the biological neuron. A knob to tune the response of the as-fabricated neuron allows the network to perform various functioning without altering the hardware. Earlier, our group has experimentally demonstrated an LIF (leaky integrate & fire) neuron on a highly matured 32 nm SOI CMOS technology. In this work, we have experimentally demonstrated electrical tunability of the same through its intrinsic charge dynamics based on impact ionization (II) enabled floating body effect. First, a tunable input threshold (V<inf>th</inf>) is achieved by changing the drain bias. Second, above threshold, a firing frequency (f) to input (V) sensitivity (df/dV) tuning is successfully demonstrated by controlling the SOI-MOSFET's current threshold. We show that both the independent control of sensitivity and threshold is fundamentally enabled by the non-linearity of the impact ionization based carrier dynamics. The SOI neuron provides equivalent electrical tunability to Resistor-Capacitor (RC) based LIF neurons without degrading its original area and power advantages for clock-less, asynchronous SNNs. Further, we show that the neuronal behavior (threshold and sensitivity) is a key determinant of network performance, specifically the learning accuracy. Such flexibility based on post-fabrication electrical tuning will be an attractive enabler for the SNN hardware.