Sandia National LaboratoriesAlbuquerque, N. Mex.

Proton-based nonvolatile semi-conductor memory

Doug Bartholomew, Samuel Greengard, Glenn Hasek, John Jesitus, Scott Leibs, Kristin Ohlson, Robert Patton, Barb Schmitz, Tim Stevens, and John Teresko contributed to this article. Anyone who has ever lost work on a computer because of a temporary power failure knows the value of nonvolatile memory. Memory devices such as hard-disk drives, optical disks, floppy disks, and Zip drives are, of course, nonvolatile but are also slow. So far flash memory is the only commercially available nonvolatile rewritable semiconductor memory and is already widely used in notebook computers, cellular phones, and digital cameras. But flash has disadvantages. For one thing, flash memory is relatively expensive. For another, most flash requires a voltage of 12 to 15 volts making demands on batteries of the portable devices that are the principal applications for flash memory. Now researchers at Sandia National Laboratories -- which also led investigators at France Telecom, the U.S. Air Force Phillips Laboratory, and AMMPEC Inc. -- have found a way to convert an ordinary field-effect transistor (FET) into a nonvolatile device in a way that can be accomplished using much the same methods as are used to produce other semiconductor devices. Not only does this result in a nonvolatile semiconductor memory device that costs less and requires less power than flash, it appears the device can be hardened against radiation. For this new class of devices, Bill Warren, senior technical staff member at Sandia and lead researcher on the project, likes the term NVFET (nonvolatile field effect transistor), but it is also referred to as protonic memory. Warren describes the NVFET as consisting of a "gate oxide, which contains mobile protons capped with a polysilicon layer. When a positive write voltage is applied to the polysilicon gate of the NVFET, the protons will collect at the silicon-substrate/oxide interface and activate the transistor. Similarly, a negative write voltage collects the protons at the gate and shuts the transistor off." Sandia researchers see these protonic memory devices not just replacing flash memory in applications such as memory cards for portable devices, but replacing other technologies as well. In portable computers, eliminating the need to use power to maintain data in memory can extend battery life. Not only that, but the biggest power hog of all, the display, can be put on a diet. By replacing the thin-film transistors that are now used to switch display pixels on and off with NVFETs, the power demands of the display can be significantly reduced. Sandia's protonic memory development has generated a great deal of interest around the world. Texas Instruments Inc., Dallas, is now studying the technology. The discovery was originally made in the course of work done jointly with France Telecom and the University of New Mexico. In the U.S., private industry and government laboratories are examining the technology. Now under development are memory structures that are expected to meet or exceed the performance specifications of flash memory. But don't expect the flash-memory industry to call a halt to development just yet. Sandia's work, while extremely promising, is at a very early stage.

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