Band to Band Tunneling-Based Low Power and Low Area Tunable Spike Delay Element

Bio-inspired axonal and dendritic delay-based spiking neural network algorithms perform spatiotemporal pattern recognition efficiently within feed-forward networks, making complex and suboptimal recurrent neural network structures unnecessary. Including trainable dendritic or axonal delays in feed-forward neural networks reduces neural network complexity and improves classification performance significantly. However, generating tunable low-power hardware spike delays of the biological timescale (few μs to ms ) without adding an extra penalty on the area has been challenging over the years. We present a novel band-to-band tunneling-based tunable delay element for spiking neural network hardware. The proposed low-power core delay element capable of providing spike delays of up to 0.4 ms (without explicit capacitance) consumes an area of 50 μm² in GF45RFSOI technology with a peak power of 320 nW, which is the lowest among state-of-the-art spike delay generation circuits. Moreover, the order of the spike delay can be extended to 25 ms by adding an explicit on-chip capacitance of 500 fF.