Device and circuit modeling and development of a nonvolatile random access memory cell, utilizing an amorphous silicon thin film floating-gate transistor based technology

High density storage mechanisms are generally created using either magnetic or optical implementation techniques. Both of these techniques require mechanical transport of the medium and, therefore, have low reliability factors. These devices also generate unwanted low level ambient noise, which is of particular concern when considering modern quiet office standards. Additionally, optical techniques tend to be read-only in nature. Both mechanisms exhibit random access times that are measured in milli-seconds, rather than in micro-seconds. Therefore, the creation of a non-volatile random access memory as a replacement for the above mentioned storage techniques would be of great advantage in terms of access time, reliability, and ambient noise level. Described within are the device and circuit modeling and fabrication techniques used to develop a non-volatile random access memory cell from an amorphous silicon thin-film transistor based technology. Amorphous silicon thin-film transistors are fabricated by depositing the metal, the insulator and the semiconductor materials with a sputtering mechanism in a vacuum at 220 degrees centigrade, rather than by diffusion at 2000 degrees centigrade, as is done with crystalline silicon. By depositing a metal in the insulator, which is located between the gate and the channel, and by using an insulator material with extremely high resistivity, one can store charge in the gate region for a long period of time without external power. For example, this period of time can be as little as one week or as long as over one year. With a periodic refresh, one can extend the memory time of this storage mechanism indefinitely. Thin-film transistors can be deposited on a variety of materials such as glass, quartz or plastic by means of a stationary or continuous motion fabrication system. This material can be either rigid or flexible, and can be comparatively large in size. This allows for much greater circuit density than a standard crystalline silicon chip that contains devices of a comparable channel length. Ten-thousand mega bytes, or more, of virtual storage could become common place. In summary, this approach represents a large scale, high density, high speed "non-volatile" storage device, with read-write random access capability, without moving parts.