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In the field of semiconductor manufacturing and storage devices, increasing circuit densities and faster switching speeds have been achieved with the use of a variety of improved materials and components. This has resulted in the development of smaller and faster memory cells that use charge storage devices. One such type of charge storage device is a thin film memory cell, which typically includes a thin film of silicon dioxide (SiO2) or other insulating materials sandwiched between a pair of conductive materials.
Thin film memory cells have been developed and are described in U.S. Pat. No. 4,554,444 to Karnezos; U.S. Pat. No. 5,051,566 to DiCarlo; U.S. Pat. No. 5,130,812 to Ferro; and U.S. Pat. No. 5,150,142 to Dennison et al., which are hereby incorporated herein by reference. In order to use the charge storage properties of these thin film memory cells, it is necessary to provide a charge with respect to the silicon substrate. This may be accomplished by injecting or removing charges to or from the charge storage devices.
For example, Fowler-Nordheim tunneling involves creating a high potential across a thin insulating film (such as SiO2) to induce a current to pass through the film. If the tunneling conditions are suitably chosen, a conducting filament or channel is formed through the SiO2. Alternatively, electrons can be ejected from the SiO2 using a sufficiently high voltage to create an electric field of sufficient strength. A current then flows and the ejected electrons flow in the opposite direction. Because these tunneling currents are very small, they are often difficult to detect.
Another type of charge injection uses the electron-hole pairs created by a charge particle striking a crystalline material. As is well known in semiconductor physics, the impact of a charge particle creates a number of electron-hole pairs. For example, in silicon, a 1 MeV electron creates about 1.3×1016 hole-electron pairs. The number of electron-hole pairs created per impact is dependent on the energy of the charge particle (which determines the energy of the resulting electron-hole pairs). Most of the electrons and holes in the pairs created by a charge particle of high energy are spatially separated. In semiconduct ac619d1d87
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