Fig. 4
Prototypical fully integrated capacitive neural network. a The scanning electron micrographs of the network consisting of a 4 × 4 crossbar array of synapses (blue box) linked with four neurons (red box). b Each neuron was interfaced to four synapses. c, d The DPM neurons and the NPM synapses were both built utilizing Ag-based memristors (magenta and cyan boxes, respectively) in series with integrated capacitors (red and blue boxes). e Structural analysis of the neuro-transistor. The cross-sectional transmission electron micrograph shows the diffusive memristor sitting on the gate of a convention n-MOSFET. f The high-resolution transmission electron micrograph of the diffusive memristor showing the amorphous SiOx dielectric matrix with nano-crystalline thin Ag layers. g Structural analysis of the integrated synapse. The transmission electron micrograph shows the electrochemical metallization cell on top of a HfO2 capacitor. h The zoomed high-resolution transmission electron micrograph of the electrochemical metallization cell shows the thick Ag electrode responsible for the longer retention time of the high conductance state of the memristor. i, j Schematic illustration and experimental observation of the synapse programming using the Hebbian-like mechanism. Simultaneous pre-synaptic signals (blue and green lines in j) were applied to both the low capacitance state (LCS) synapse and the high capacitance state (HCS) synapse. The post-synaptic neuron fired (red lines in j) and the LCS synapse was subsequently potentiated, which made the neuron fire within a shorter integration time from 280 to 400 μs (red curve of j)
