Substrate-bias assisted hot electron injection method for high-speed, low-voltage, and multi-bit flash memories

The authors present a highly efficient program method for high-speed, low-voltage, and multi-bit/cell operation in the conventional silicon/oxide/nitride/oxide/silicon structure. This method uses a forward bias for collecting the electrons into the substrate whilst both substrate and drain biases are used for injecting the electrons into the nitride layer. With an aid of the substrate bias for electron injection, we obtained a program time as short as 600 ns and an ultralow-voltage operation with a drain voltage of 2 V and a substrate voltage of -3 V. In addition, a localized chargeinjection near the junction edge was confirmed with a threshold voltage difference of 1 V between the forward and reverse read.