Study and Optimization of Two-State Transient Currents at Millisecond Time Scales in MIS Tunnel Diodes

In this article, the behavior of two-state transient currents in metal-insulator-semiconductor tunnel diodes (MISTDs) is described in detail using experiments and simulations. Transient currents at a timescale of 50 ms, which is close to the refresh time of the dynamic memory, are revealed to saturate after voltage pulses with both polarities when the write voltage and write time are sufficiently large. For the negative write pulses, the read current is determined by the number of minority carriers that need to be generated, which remains similar regardless of whether switching from the depletion or accumulation condition. For positive pulses with a larger write voltage, more inversion charges are initially stored in the semiconductor. However, this stored charge causes band bending to become very small (or even negative). As a result, a number of majority carriers flow for recombination, forcing band bending to fulfill the minimum requirement at hundreds of nanoseconds, resulting in read current saturation. The read current is also revealed to be strongly dependent on the oxide thickness. Optimal parameters are also suggested based on numerous experiment results for different design considerations.