A micron bit-size charge-storage device

The use of a scanning electron microscope to produce selective, stable, and reversible charge storage in the oxide layer of an MOS transistor is discussed. Electron beam switching of MOST structures from a conducting state to a nonconducting state is described. Electron bombardment of small areas of the gate electrode, typically 5 micrometers × 5 micrometers, allows storage of many bits of information on a single three-terminal MOST. The information can be read out in a nondestructive manner. By extension of the memory operation, it is possible to perform computer logic functions with a single MOST and a small diameter electron beam. Time constants associated with electron-beam charge storage are of the order of 30ms., while discharge time constants are typically 5ms. The relationship of the charge storage phenomena to the gate voltage during electron bombardment, the electron beam voltage and current, and the geometry of the MOST are discussed. A simple roodel for the charging phenomena is presented. The use of electron beam bombardment of MOST´s after fabrication to adjust the threshold voltage of different devices on a single wafer is described.