Gatefield Corporation

Zycad Corporation

Robert U Broze

Jack Zezhong Peng

Kyung Joon Han

Volker Hecht

Robert M Salter, Iii

Victor Levchenko

John M Caywood

Robert J Lipp

Joseph G Nolan, Iii

Richard D Freeman

Disclosed is a FPGA cell and array structure which use FN tunneling for program and erase. Each cell comprises a switch floating gate field effect transistor and a sense floating gate field effect transistor with the floating gates being common and the control gates being common. Programming of a cell is effected by voltage biasing the common control gate line and the source/drains of the sense transistor. The source/drains of the sense field effect transistor are formed from buried doped layers (e.g. N+ in a P-doped substrate) which are formed prior to formation of the polysilicon floating gate and control gate. Lateral diffusion of dopant from the buried source/drains into the channel beneath the floating gate facilitates electron tunneling during erase and program operations, and the graded junctions of the buried source/drains lower band-to-band tunneling leakage.

Nonvolatile reprogrammable interconnect cell with programmable buried

Disclosed is a FPGA cell and array structure which use FN tunneling for program and erase. Each cell comprises a switch floating gate field effect transistor and a sense floating gate field effect transistor with the floating gates being common and the control gates being common. Programming of a cell is effected through a buried bitline in juxtaposition with the switch transistor and the sense transistor over which are the floating gate and the control gate. The sense transistor can be fabricated simultaneously with fabrication of the switch transistor whereby the two transistors are identical in dopant concentrations.

The present invention provides for an improved EPROM transistor cell which forms the programming portion of the programmable interconnect interconnect of an FPGA integrated circuit, and a method of manufacturing the EPROM cell. The EPROM cell has a floating gate disposed over a P region of the substrate. Aligned with one edge of the floating gate and at the surface of the substrate is a lightly doped P- region; on the opposite edge of the floating gate is a heavily doped N+ region. A control gate lies over the P-, P substrate and over the N+ region. N+ regions are formed at the opposite edges of the control gate. One N+ region is contiguous to the P- region and forms the source of the EPROM cell and the other N+ region is connected to the N+ region under the control gate and forms the drain of the EPROM cell. This structure allows for easy process control of the V.sub.T of the access transistor formed by the control gate and the P- surface, and of the space charge region formed by the P substrate and the N+ drain of the EPROM cell.

Floating gate FPGA cell with counter-doped select device

A programmable interconnect which closely integrates an independent switching transistor with separate NVM programming and erasing elements. The programming element is an EPROM transistor and the erasing element is a Fowler-Nordheim tunneling device. A unitary floating gate is shared by the switching transistor and the NVM programming and elements which charge and discharge the floating gate. The shared floating gate structure is the memory structure of the integrated programmable interconnect and controls the impedance of the switching transistor.

General purpose, non-volatile reprogrammable switch

An array of programmable interconnect cells, each cell having a floating gate as the gate of an MOS switch transistor which programmably connect or disconnects nodes, is used in an FPGA. The floating gate of each cell, which is capacitively coupled to a control gate, is programmed by Fowler-Nordheim tunneling through an tunneling oxide above a programming/erase line in the integrated circuit substrate. Contiguous and parallel to the programming/erase line is at least one tunneling control line which forms a PN junction in close proximity to the programming/erase line region under the tunneling oxide. Under a reverse bias, a deep charge depletion region is formed in the programming/erase line region to block tunneling. In this manner, a selected cell can be programmed/erased, while the non-selected cells are not.

Growing community of inventors

Santa Cruz, CA, United States of America

Robert U Broze