  Many real-world mission-critical applications require continual online
learning from noisy data and real-time decision making with a defined
confidence level. Probabilistic models and stochastic neural networks can
explicitly handle uncertainty in data and allow adaptive learning-on-the-fly,
but their implementation in a low-power substrate remains a challenge. Here, we
introduce a novel hardware fabric that implements a new class of stochastic NN
called Neural-Sampling-Machine that exploits stochasticity in synaptic
connections for approximate Bayesian inference. Harnessing the inherent
non-linearities and stochasticity occurring at the atomic level in emerging
materials and devices allows us to capture the synaptic stochasticity occurring
at the molecular level in biological synapses. We experimentally demonstrate
in-silico hybrid stochastic synapse by pairing a ferroelectric field-effect
transistor -based analog weight cell with a two-terminal stochastic selector
element. Such a stochastic synapse can be integrated within the
well-established crossbar array architecture for compute-in-memory. We
experimentally show that the inherent stochastic switching of the selector
element between the insulator and metallic state introduces a multiplicative
stochastic noise within the synapses of NSM that samples the conductance states
of the FeFET, both during learning and inference. We perform network-level
simulations to highlight the salient automatic weight normalization feature
introduced by the stochastic synapses of the NSM that paves the way for
continual online learning without any offline Batch Normalization. We also
showcase the Bayesian inferencing capability introduced by the stochastic
synapse during inference mode, thus accounting for uncertainty in data. We
report 98.25%accuracy on standard image classification task as well as
estimation of data uncertainty in rotated samples.
