Enhanced conduction and minimized charge trapping in electrically alterable read-only memories using off-stoichiometric silicon dioxide films

Abstract

An electrically alterable read-only memory using silicon dioxide and silicon-rich silicon dioxide layers capable of being cycled ≳107 times by minimizing electron charge trapping in the SiO2 layers of the device by incorporation of small amounts of silicon is discussed in detail. Charge transfer to and from a floating polycrystalline silicon layer from a control gate electrode is accomplished by means of a modified dual-electron-injector-structure stack. This modified stack has the intervening silicon dioxide layer, which is sandwiched between silicon-rich silicon dioxide injectors, replaced by a slightly off-stoichiometric oxide containing between 1 and 6% excess atomic silicon above the normal 33% found in silicon dioxide. The operation of the electrically alterable device structures in terms of write/erase voltages, cyclability, breakdown, and retention is related to current-voltage characteristics obtained from capacitors. A physical model based on direct tunneling between Si islands in the off-stoichiometric oxide layer is proposed to account for the observed increase in the moderate electric field conductance and decrease in charge trapping in these oxide layers incorporated into devices and capacitors. This model and the observed current-voltage characteristics are used to predict device operation for a variety of conditions.