4 research outputs found
Neural Sampling Machine with Stochastic Synapse allows Brain-like Learning and Inference
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
Plasmonics-based detection of H2 and CO: discrimination between reducing gases facilitated by material control
Monitoring emissions in high-temperature-combustion applications is very important for regulating the discharge of gases such as NO2 and CO as well as unburnt fuel into the environment. This work reports the detection of H2 and CO gases by employing a metal–metal oxide nanocomposite (gold–yttria stabilized zirconia (Au–YSZ)) film fabricated through layer-by-layer physical vapor deposition (PVD). The change in the peak position of the localized surface plasmon resonance (LSPR) was monitored as a function of time and gas concentration. The responses of the films were preferential towards H2, as observed from the results of exposing the films to the gases at temperatures of 500 °C in a background of dry air. Characterization of the samples by XRD and SEM enabled the correlation of material properties with the differences in the CO- and H2-induced LSPR peak shifts, including the relative desensitization towards NO2. Sensing characteristics of films with varying support thicknesses and metal-particle diameters have been studied, and the results are presented. A comparison has been made to films fabricated through co-sputtered PVD, and the calibration curves of the sensing response show a preferential response towards H2. The distinction between H2 and CO responses is also seen through the use of principal-component analysis (PCA). Such material arrangements, which can be tuned for their selectivity by changing certain parameters such as particle size, support thickness, etc., have direct applications within optical chemical sensors for turbine engines, solid-oxide fuel cells, and other high-temperature applications