Sunday, October 17, 2010

US Patent 7811883 - Fabrication of nanocrystal floating gate memory using nanowires

Over the past several years nanocrystals have been found to improve the operation of floating gate memory transistors since (1) They are less susceptible to defects in the program oxide since the charge is stored on isolated nanocrystal sites, (2) They can store two bits per cell by reversing the role of the source and drain since the charge is localized at the injection point, and (3) They have potentially lower voltage operation and higher retention. This patent from IBM teaches a manufacturing method n which the size and spacing of the nanocrystals may be more easily controlled by using nanowire growth. Claim 1 reads:

1. A method of forming a semiconductor structure comprising:

epitaxially growing a crystalline program oxide over a surface of a semiconductor substrate;

placing a plurality of catalyst particles over said program oxide;

growing nanowires perpendicular to the substrate surface from said catalyst particles;

forming a control oxide over said nanowires and said program oxide;

forming a gate conductor over said control oxide; and patterning said gate conductor.