Fig. 2: Quasi-stationary I–V characteristics of a floating-bulk n-channel 180-nm MOSFET showing neuro-synaptic capabilities.
From: Synaptic and neural behaviours in a standard silicon transistor
a, Simplified equivalent circuit of an n-channel MOSFET with parasitic substrate components. IB is the impact-ionization current component. RB and RD are the bulk and drain spreading resistances, respectively. VS is the source voltage. b, ID–VD characteristics of an n-channel MOSFET. The normal conditions (grounded bulk, red curves) are compared with the floating-bulk condition (blue curves). c, Sketch of the current components in an n-channel MOSFET with a grounded-bulk connection and in the saturation condition (high VD), where h+ represents holes and e− electrons in the p-type silicon bulk. d, Same as c but under the floating-bulk condition, where the bulk is floated through an external control device that regulates the bulk current (IB) under punch-through avalanche conditions. e,f, ID–VD characteristics of the MOSFET device depicted in d under different VG2 (bulk bias control voltage) for a neuron (e) and a synapse (f). Different hysteretic behaviours are visible, from a typical thresholding neuron to the synaptic plasticity regime. In all cases, VG was varied between 0.25 and 0.45 V in 0.05 V steps. g, Robust and reproducible resistance change during thresholding of the floating-bulk device under fast ramp cycling for 10 million cycles (see Methods for measurement conditions). pSi, p-type silicon bulk, n+Si, highly doped n-type silicon; VBS, bulk-to-source voltage.
