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

Abstract

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 prograderase.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 selfaligned floating-gate wing technology is introduced to increase gate coupling ratio in wordline direction without sacrificing cell area. A cell area as small as 0 . 3 9~" with a coupling ratio of 0.55 is obtained using 0.3pm 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 (< lyshyte) with a low single supply voltage (< 3V). A good disturb immunity in program, erase and read modes is also obtained.

Flash memory cells-an overview

“…37) introduced in 1995 [79]. It has been proposed for high-density data storage, which requires low-voltage low-power consumption and fast program/erase.…”

Scalable Virtual-Ground Multilevel-Cell Floating-Gate Flash Memory

“…A virtual-ground cell structure is simplified by avoiding the need for shallow trench isolation (STI) and replacing the drain contact and source rail across STI [10], [11] with buried BL diffusion. A virtual-ground flash memory cell, however, suffers from a low GCR [13], [17], because it uses the short-side edge of the FG along its channel width (W g ) direction as the surface area of an interpoly capacitor, while a conventional NOR cell uses the long-side edge of FG along its channel length (L g ) direction. A high GCR is required for reduction of FG-to-FG coupling interference and for low-voltage operation, as will be described later.…”