Total Ionizing Dose Response of 128 Analog States in Computational Charge-Trap Memory

The total ionizing dose response of 128 distinct conductance states in 40 nm SONOS charge-trap memory was experimentally characterized, which reveals in fine detail the analog state dependence of the ionizing radiation effect. The 128 states were programmed onto an array of 128K SONOS cells that were irradiated by Co-60 gamma rays up to 1.5 Mrad(Si) total dose. The observed response after radiation and subsequent annealing suggests that radiation deposits a net positive charge in traps that have both shallow and deep energy levels within the nitride bandgap. We use the measured data to simulate a SONOS-based analog in-memory computing accelerator operating under radiation, and evaluate its accuracy on large image recognition neural networks. The impact of ionizing radiation on the algorithm depends on the regime of operation of the irradiated SONOS devices, with states in the weak inversion regime having a larger effect on accuracy. Periodic refreshes of the SONOS states are expected to enable reliable, efficient, and long-term operation in space.