12/17/2003 - Hitachi, Ltd. (TSE:6501, NYSE:HIT) and Renesas Technology Corp. announced the development of a basic flash memory cell technology that achieves the world's smallest cell area of 0.016 mm2 (on a 1-bit basis) and fastest programming speed of 10 Mbyte/s. This basic memory cell technology improves the source-drain structure of an AG-AND (Assist Gate-AND)*1 flash memory cell featuring multi level cell technology*2 and high speed, enabling the memory cell area to be reduced by approximately 30% when using a 90 nm process.
Renesas Technology plans commercial production of 4-Gbit AG-AND flash memory based on this technology in the third quarter of 2004, and will offer compact, high-density, high-speed recording media for the "ubiquitous computing society."
High-density flash memory is beginning to permeate our lives as a bridge medium (information delivery device), especially in mobile applications, including use as image storage memory for digital cameras and mobile phones, and USB storage as replacements for floppy disk drives. Next-generation flash memory cards offering portability of large-volume, high-quality moving picture data such as movies will require significantly high density and higher programming speeds to handle fast data downloads.
In response to these needs, in 2001 Hitachi and Renesas Technology jointly developed a first-generation AG-AND flash memory offering a high programming speed of 10 Mbyte/s through the use of assist gates (AGs) to prevent inter-cell interference together with multi level cell technology, and Renesas Technology currently mass-produces 130 nm process 1-Gbit AG-AND flash memory. However, to meet the need for high density while maintaining high speed operation, it became necessary to make advances in memory cell structure to restrict lateral expansion by altering the source-drain structure*3, and minimise the memory cell area as far as physical limitations allow.
Against this backdrop, Hitachi's Central Research Laboratory and Renesas Technology collaborated in the development of a basic technology for second-generation AG-AND flash memory that offers both high-speed writing and a fine process. The features of this newly developed technology are summarised below.
This new technology makes possible fast downloading and portability of large volume content data such as moving pictures and music. As a result, usage scenarios previously restricted to digital cameras and PCs can now be extended to mobile terminals and digital home appliances, expanding the range of system solutions that employ flash memory as a storage medium.
These results were announced at the 2003 IEEE International Electron Devices Meeting (IEDM) being held in Washington, D.C. from 7 December, 2003.
(1) AG-AND (Assist Gate-AND) is a flash memory cell jointly developed by Hitachi and Renesas Technology. The cell structure employs original Hitachi and Renesas Technology field isolation technology comprising a combination of alternating assist gates that prevent inter-cell interference, enabling a smaller cell area and high-speed programming.
(2) Multi level cell technology: A technology suitable for high-density flash memory, effective in reducing chip size, whereby four or more values, such as 00, 01, 10, and 11, can be held as opposed to the usual two values, 0 and 1, of ordinary memory. When four values are used, one cell does the work of two ordinary cells.
(3) lateral expansion by altering the source-drain structure : In the first generation, a source and drain are formed by means of a diffusion layer* using the ion implantation method in the same way as ordinary MOS (Metal-Oxide-Semiconductor) transistors, but as this diffusion layer extends laterally, it is an obstacle to achieving finer memory cells.
*Diffusion layer: Ions are implanted into a silicon substrate, and high-density electrons are generated by applying a voltage to this region. This is the usual method for forming the source and drain of an MOS transistor.
(4) Inversion layer: A high-density electron region generated in the extremely shallow region of a silicon substrate when a voltage is applied to the gate. Used as an MOS transistor channel.
(5) Hot electron injection method: A programming method whereby high-energy "hot" electrons accelerated by a channel field are injected into a floating gate. The cell programming time is 10 ms or less, an order of magnitude faster than with the conventional tunnel programming method.
About Renesas Technology Corp.
Renesas Technology Corp. designs and manufactures highly integrated semiconductor system solutions for mobile, automotive and PC and Audio Visual markets. Established on April 1, 2003 as a joint venture between Hitachi, Ltd. (TSE:6501, NYSE:HIT) and Mitsubishi Electric Corporation (TSE:6503) and headquartered in Tokyo, Japan, Renesas Technology is one of the largest semiconductor companies in the world and the number one microcontroller supplier globally. Besides microcontrollers, Renesas Technology offers system-on-chip devices, Smart Card ICs, mixed-signal products, flash memories, SRAMs and more.
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