Non-volatile semiconductor memory elements and methods of making

Abstract

The invention is embodied in a non-volatile metal-insulator-semiconductor having a novel combination of insulating layers including a titanium dioxide layer covered by a silicon dioxide layer. In one embodiment of the invention the insulator combination also includes a second layer of silicon dioxide located between the titanium dioxide and the semiconductor. In another embodiment the insulator combination also includes a layer of silicon nitride located between the titanium dioxide layer and the semiconductor. The memory elements are fabricated using a novel sequence of steps for forming multiple dielectric layers. The titanium dioxide of a type known as rutile is formed by evaporation of titanium metal upon the silicon dioxide and oxidation of the titanium in an oxygen ambient at high temperatures. Writing is accomplished by injection of charge into the titanium dioxide layer thus shifting the threshold voltage of the structure. Erasure is accomplished by forcing the injected charge back into the semiconductor to recombine with majority carriers. The charge can be electrons or holes depending on the semiconductor type. The memory element of the invention has lower write/erase voltages, shorter write/erase times and longer memory retentivity.