Method and device for improved programming threshold voltage distribution in electrically programmable read only memory array

A method and device to compensate for the series resistance effect along, for example, the source region in an electrically programmable read only memory array is described. One or more resistors are provided between the ground contact and ground. When a cell is programmed, the source is coupled to ground through one or more of the resistors, such that the resistance between source and ground for all cells is approximately equal. Therefore, the potential of the source of each cell is approximately equal for all cells during programming. In this way, the potential difference between the control gate and source is approximately equal for every cell, thereby resulting in more uniform programming levels and therefore more uniform threshold voltages. The method and device of the present invention is particularly applicable to multi-level cells, which employ several different threshold voltages to represent several different logic states. In addition to providing for uniform threshold voltages, the resistors of the present invention can be used to provide for programming to different levels using a single programming voltage on the control gate. For each level, the source of a cell is coupled to ground through one or more resistors, such that the potential difference between the control gate and the source has the appropriate value for that level.