A Floating Gate and Its Application to Memory Devices

Abstract

A structure has been proposed and fabricated in which semipermanent charge storage is possible. A floating gate is placed a small distance from an electron source. When an appropriately high field is applied through an outer gate, the floating gate charges up. The charges are stored even after the removal of the charging field due to much lower back transport probability. Stored-charge density of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has been achieved and detected by a structure similar to an metal-insulator-semiconductor (MIS) field effect transistor. Such a device functions as a bistable memory with nondestructive read-out features. The memory holding time observed was longer than one hour. These preliminary results are in fair agreement with a simple analysis.