Multi-level flash/EPROM memories: new self-convergent programming methods for low-voltage applications

This paper proposes new low voltage programming methods for storing multi-levels of threshold voltage (V_T) in flash memory cells. These methods are based on hot electron injection under low voltage (<5v) bias at drain or gate. Abundant hot electrons can be generated from the high field near drain together with various “seed” currents for avalanche mechanism, such as punch-through and parasitic bipolar currents in cell. The programmed cell V_T has excellent linear relation to the gate bias used for programming, therefore this technique is also useful for storing analog signals in cells. Many array architectures, such as NVG or ETOX, can be implemented with capability of programming one or more entire columns of cells into multi-levels or analog signals simultaneously. The methods demonstrated in this paper are promising for next generation high density and low power flash memory with applications in both digital and analog systems