Non-volatile ram device

Abstract

Juxtaposing, on a common p-type substrate, an array of field effect transistor memory cells each including a random access memory dynamic RAM device comprising a floating gate portion and a storage node, and each including also a non-volatile unit comprising a double electron injector structure (DEIS) adjacent the floating gate portion, but remote from the storage node, provides a simple, low current dynamic random access memory array with non-volatile restart capability in case of power interruption. The non-volatile unit in each memory cell shares the control gate and substrate in common with the dynamic RAM device and thus shares access to the floating gate but is remote from the storage node. Situated between the floating gate and the substrate is a silicon-rich DEIS stack. During normal operation, the device functions as a dynamic RAM device. When non-volatile storage is required, electrons are written into the floating gate by raising the voltage on the control gate. This injects electrons into an insulating layer in the DEIS; the electrons flow to the floating gate where they are stored indefinitely. Subsequent write and erase operations are carried out by applying an appropriately polarized voltage pulse to the control gate electrode, moving electrons with respect to the floating gate portion of the RAM device.