A new cell structure for sub-quarter micron high density flash memory

A new cell structure named ACT (Asymmetrical Contactless Transistor) is proposed for high density data storage applications which require low voltage, low power consumption and fast program/erase. The ACT cell with a lightly doped source and heavily doped drain realizes a simple virtual ground array using the Fowler-Nordheim (FN) tunneling mechanism for both program and erase. A self-aligned floating-gate wing technology is introduced to increase gate coupling ratio in word-line direction without sacrificing cell area. A cell area as small as 0.39 μm² with a coupling ratio of 0.55 is obtained using 0.3 μm process technology. The low programming current of the ACT cell enables multiple programming to be used and thus it is possible to achieve fast programming (<1 μs/byte) with a low single supply voltage (<3 V). A good disturb immunity in program, erase and read modes is also obtained