US Patent 7732853 - Multibit nanocrystal FET

http://www.freepatentsonline.com/7732853.html

Non-volatile memory such as floating gate transistors (Flash memory) have relied on scaling of transistor dimensions to increase storage density. An alternative to scaling is the use of multibit memory in which two or more bits of data are stored using a single memory cell transistor. This patent from Samsung teaches one variation of multibit memory using nanocrystals. Claim 1 reads:

1. A multi-bit nonvolatile memory cell comprising:

a substrate;

spaced apart source and drain regions in the substrate;

a trench in the substrate between the spaced apart source and drain regions;

a plurality of charge trapping nano-crystals on the substrate between the spaced apart source and drain regions;

a gate on the substrate that includes a protrusion portion that extends into the trench, wherein the protrusion portion is closer to the source region than to the drain region; and

a layer between the nano-crystals and the substrate, that is thicker on the substrate outside the trench than in the trench.