Multi-level memory cell device and method for self-converged programming

Abstract

A multi-level memory cell device and method for self-converged programming which includes a memory cell switchably coupled to a non-programmable reference cell (or dummy cell), the cells arranged in respective arrays. A current source voltage between the source node and ground of the cells is relational to the threshold voltage, so as the threshold voltage is increased, the current source voltage decreases. The threshold voltage of the dummy cell is set by a stable voltage source. The memory cell is programmed and the current source voltage of the memory cell is compared to the current source voltage of the reference cell and therefore the difference in the voltages can be used to sense convergence of the programmed cell with a target threshold level set on the reference cell. A controller is also included between the reference cell and memory cell for adjusting the threshold voltage of the dummy cell according to the gate coupling ratio of the floating gate memory cell. The controller is also used to adjust voltages for both programming and read operations. The voltage difference resulting from the sources of the memory cell and reference cell is used to provide program control signals and thereby cease programming of the memory cell when convergence has been reached.