Advanced Micro Devices Corporation

Michael K Han

Narbeh Derhacobian

Darlene G Hamilton

Hao Fang

Yider Wu

Tim Thurgate

Janet S Y Wang

A system and methodology is provided for programming first and second bits of a memory array of dual bit memory cells at a substantially high delta VT. The substantially higher VT assures that the memory array will maintain programmed data and erase data consistently after higher temperature stresses and/or customer operation over substantial periods of time. At a substantially higher delta VT, programming of the first bit of the memory cell causes the second bit to program harder and faster due to the shorter channel length. Therefore, the present invention employs selected gate and drain voltages and programming pulse widths during programming of the first and second bit that assures a controlled first bit VT and slows down programming of the second bit. Furthermore, the selected programming parameters keep the programming times short without degrading charge loss.

Charge injection

An efficient NAND array structure includes memory cells coupled in series between a bit-line and a select source transistor, without a select drain transistor. The memory cells each include a floating gate transistor, having a control gate connected to a word-line, which selects the memory cell during its programming. In one embodiment, the NAND array structure includes a buried layer at a junction between the substrate and a well in which the memory cells are formed. Programming is achieved using hot electron injection. In one embodiment, multiple memory cells are programmed simultaneously.

NAND array structure and method with buried layer

Dummy wordlines are provided between gaps of blocks of memory cells to compensate for higher charge loss at higher stress temperatures exhibited at edge wordlines of blocks of memory cells having large gaps. The dummy wordlines minimize the gap between the blocks. The dummy wordlines can be positioned between the blocks. Alternatively, the wordline width for the last block or sector wordline can be changed or different nitride used with less conductance in high temperatures. The dummy wordlines are typically ignored in normal operations on the memory.

Data retention characteristics as a result of high temperature bake

A method and circuit for sensing multi states of a NAND memory cell by varying source bias, at a constant gate voltage, preferably zero volts, generating a memory cell current in response to the source bias, and sensing the memory cell state.

Multi state sensing of NAND memory cells by varying source bias

A method and circuit for sensing multi states of a NAND memory cell by applying reverse bias voltage at a constant gate voltage, preferably zero volts, generating a memory cell current in response to the applied reverse P well bias, and sensing the memory cell state.

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San Jose, CA, United States of America

Michael K Han