Single electron memory utilizing nano-crystalline Si over short-channel silicon-on-insulator transistors

Abstract

A promising approach for high density/low power consumption memory devices is to store a single charge in a nano-scale memory node, which affects electron transport in a nearby channel. Advantages of this design are room temperature operation and self limiting charge storage by Coulomb repulsion. Two notable approaches to this concept are nanocrystalline-Si (nc-Si) acting as a floating gate in a large area MOSFET (Tiwari et al., 1996) and a single polysilicon dot defined by e-beam lithography over a narrow SOI channel (Guo et al., 1997). A device which is sensitive to a single charge while using a method of nc-Si dot fabrication that is scalable to VLSI is required. Single electron memory devices based on two approaches of forming nc-Si with large area deposition processes are reported here. To make the active region of the device sensitive to a single charged dot, narrow channels (40 nm length by 30 nm width) are defined by e-beam lithography of thin (20 nm) SOI. The first approach for nc-Si synthesis is gas phase nucleation and growth by pulsed-source remote PECVD, which form 8/spl plusmn/1 nm diameter nc-Si dots (Ifuku et al., 1997). The second approach for scalable nc-Si formation is to deposit a thin film of SiO/sub x/ (x<2). Annealing of this film results in high density 3-8 nm nc-Si dots isolated from each other by a SiO/sub 2/ tunnel barrier (Hamasaki et al., 1978).