Nonvolatile dynamic random access memory device

Abstract

A nonvolatile memory cell for a random access memory device is provided. The invented memory cells are similar in configuration to the memory cells of known DRAM devices, so that DRAM devices embodying the invented cells may replace existing DRAM devices. The invented nonvolatile cell also affords a memory device that has low cost of manufacture, high data storage capacity, and low power consumption. Each memory cell includes a floating layer of polysilicon that is interposed between a reference voltage source and a node polysilicon. The floating polysilicon provides nonvolatile storage of data previously stored on the node polysilicon. An electron charge stored on the node polysilicon is transferred to the floating polysilicon, using known electron tunneling methods, before power to the device is removed, so that the data is not lost. When power is reapplied to the device, the data is transferred back to the node polysilicon from the floating polysilicon, so that the data can be accessed as if the data were stored in a conventional DRAM device. With the invented memory cells, data is accessed and manipulated substantially faster than known nonvolatile memory devices. Additionally, an insulating oxide layer is interposed between the floating polysilicon and the reference voltage source, for reducing leakage current from the floating polysilicon to the reference voltage source. This enhances the ability of the floating polysilicon to retain data thereon.