US Patent 7443711 - Nanoscale memristor

http://www.freepatentsonline.com/7443711.html

Just a few months ago researchers at Hewlett Packard announced the practical implementation of a fourth fundamental circuit element called a memristor (i.e. memory resistor). One of the interesting properties of the memristor is that it has the potential to combine both data storage and data processing capabilities in a single element and can thus offer a new building block for artificial intelligence. This patent from HP seems pretty fundamental to the memristor switch possessing a continuum of possible programmed resistance states. Claim 1 reads:

1. A programmable impedance device, comprising:

a first electrode;

a second electrode disposed to form a junction wherein the second electrode at least partially overlaps the first electrode; and

a programmable material of nanometer-scale thickness disposed between the first electrode and the second electrode at least at the junction, the programmable material operably coupling the first electrode and the second electrode such that the programmable impedance device exhibits a non-volatile programmable impedance that is tunable through a continuum of impedance values between and including a low impedance state and a high impedance state using a first bias direction to decrease the impedance and a second bias direction to increase the impedance.

However, some prior art overlooked during the examination includes a presentation by University of Houston researchers discussing a programmable impedance material tunable to a plurality of states (link).