Ultraviolet & EPROM's

This memory element was developed by Frohman-Bentchkowsky at Intel Corporation and was known as the Floating-Gate-Avalanche-Injection MOS (FAMOS) transistor. It was essentially a silicon gate MOS field effect transistor in which no connection was made to the gate. The gate was in fact electrically "floating" in an insulating layer of silicon dioxide. The devices have been fabricated in two structures: P-channel and N-channel. The P-channel devices were the first EPROMs available commercially, but many devices are now using n-channel technology. N-channel MOS devices have the advantage of being able to function with a single power supply.      By application of sufficiently large potential difference between the source and drain, charge can be injected into the "floating" gate which induces a charge in the substrate. The source-to-drain impedance changes and a "P-channel" or "N-channel" is created, depending upon the type of substrate. The presence or absence of conduction is the principle of data storage. Application of short wave (254 nm) ultraviolet radiation causes the gate charge to leak away and restores the device to its original unprogrammed state. EPROM manufacturers provide "nominal erasing energies" to their devices; the amount of UV energy required to erase a chip's memory. Erasing time can be calculated using following formula: Time(seconds)=(nominal erasing energy (W-sec/cm²)*1,000,000)/UV Irradiance(uW/cm²))      Most EPROMs have a nominal erasing energy of 15W-sec/cm². Some chips, however, require as little as 6 or 10W-sec/cm², or as much as 25W-sec/cm², for complete erasure.

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Last Update: 10:17 AM 3/2/02