Fundamental Issues and Problems in the Realization of Memristors

It appears that some in the scientific community are beginning to catch on to the problems of HP's "memristor" models. A recent preprint was posted in arXiv by Paul Meuffels and Rohit Soni criticizing Leon Chua and HP's memristor framework on the grounds that it does not obey the "no energy discharge property" and is not consistent with principles of thermodynamics (link). Dr. Meuffels co-authored an earlier paper in Applied Physics A pointing out an incorrect assumption about ionic conductivity by the HP Labs group in one of their early memristor papers (link).

Back in 2010 I was invited to speak at the IEEE International Symposium on Circuits and Systems during a special session on memristors. At the time I noted some of the inconsistencies with HP's and Chua's arguments including that it is not properly considered a fourth fundamental circuit element and it was never missing as claimed by Chua (link). Last year I also posted a paper on arXiv pointing to more realistic dynamic systems models for thin film resistance switching devices (link). Hopefully the efforts of Dr. Meuffels and others will be constructive to move beyond the hype of HP and Chua and open the doors for more realistic models applicable to ReRAM and other resistance switching technologies.

US Patent 8233017 - Electrostatic printing with nanocarbon image generator

http://www.freepatentsonline.com/8233017.html

Xerox continues its efforts in using nanostructured materials to improve the operability of electrophotographic printers. This latest patent teaches using graphene or carbon nanotubes in forming an electrostatic image for smaller, more energy efficient printers. Claim 1 reads:

1. An electrostatic latent image generator comprising:

a substrate;

an array of pixels disposed over the substrate, wherein each pixel of the array of pixels comprises a layer of one or more nano-carbon materials, and wherein each pixel of the array of pixels is electrically isolated and is individually addressable; and

a charge transport layer disposed over the array of pixels, wherein the charge transport layer comprises a surface disposed opposite to the array of pixels, and wherein the charge transport layer is configured to transport holes provided by the one or more pixels to the surface.

US Patent 8232722 - Nanocrystal LED with reduced radiative loss

http://www.freepatentsonline.com/8232722.html

This patent from MIT teaches using nanocrystals to form an LED structure including a lightly doped layer to improve the efficiency of photon generation. Claim 1 reads:

1. A light emitting device comprising:

a first charge transporting layer including a first inorganic material in contact with a first electrode arranged to introduce charge in the first charge transporting layer;

a second electrode;

a plurality of colloidally-grown semiconductor nanocrystals disposed between the first electrode and the second electrode; and

a lightly doped layer proximal to the nanocrystals, wherein the lightly doped layer is doped in an amount effective to minimize non-radiative losses due to exciton quenching by unbound charge carriers in the transporting layer.

Memristors and Claim Construction

It is no surprise to regular readers of this blog that I oppose the hype surrounding HP's memristor. A recent online article in Wired covers some of my concerns (link).

However, even for those who support the memristor hype I would recommend caution when using the term "memristor" in the claims of patent applications. The original definition of the memristor from Chua required a non-linear relationship between magnetic flux linkage and electric charge. HP's definition from their 2008 article in Nature suggested that thin films of metal oxides may be considered memristors if there was a linear relationship between the drift of oxygen vacancies in the thin film and an applied current (or voltage). The problem is that this linearity is not true for most resistance switching materials. If an inventor or corporation uses the term "memristor" to limit their claims they face two potential problems if they try to enforce their patent.

1) The claims may be held invalid under 35 USC 112 for lack of enablement if the materials taught in the specification do not support linearity between oxygen vacancy (or ion) drift and the applied current (or voltage).

2) During a Markman hearing the claims may be limited to only a specific type of material (such as TiO2 as described by HP) even though many other resistance switching materials may be used in the invention.

So for those who choose to use the "memristor" term in their patent claims it is a much better strategy to reserve the term for a dependent claim while using more generic terminology for independent claims (e.g. memory resistor, programmable resistor, etc.) Also, it would be advisable to include alternatives in the specification based on the known types of materials exhibiting memory resistance effects (chalcogenides, perovskites, etc.) rather than limiting to the specific memristor term.

US Patent 8232074 - Nanotips for measuring electrical properties of cells

http://www.freepatentsonline.com/8232074.html

This patent from Cellectricon teaches nanoelectrode arrays performing high-throughput electrophysiological recordings for drug discovery. Claim 1 reads:

1. A microfluidic system comprising:

a) at least one measurement chamber wherein the measurement chamber comprises walls and a base;

b) at least one hollow nanotip protruding from the walls or base of the measurement chamber and having an aperture at an end of the nanotip; and

c) at least one microchannel connected to the measurement chamber, the microchannel having at least one inlet positioned to receive an aqueous solution and at least one outlet positioned to deliver the aqueous solution into the measurement chamber.

US Patent 8231770 - Nanoporous carbon actuator

http://www.freepatentsonline.com/8231770.html

Carbon nanotubes have been proposed to produce actuators with a greater energy density per mass but such actuators are difficult to produce since the nanotubes are expensive and are not available in 3D shapes which limits applicability. This patent from Lawrence Livermore National Security instead teaches using a nanoporous carbon material which may be used for molding 3D actuator structures at lower cost than carbon nanotube materials. Claim 1 reads:

1. An electrochemically driveable actuator, comprising:

a nanoporous carbon aerogel composition capable of exhibiting charge-induced reversible strain when wetted by an electrolyte and a voltage is applied thereto.                             

US Patent 8231013 - Fluid separation membrane with nanoparticle filler

http://www.freepatentsonline.com/8231013.html

Growth in industrialization has led to a increased demands on freshwater supplies and an increased interest in wastewater recycling. This patent from the Research Foundation of the State University of New York teaches a way to use nanomaterials to form a water filtration system having a high permeation rate and a reduced fouling rate compared to filtration systems currently available. Claim 1 reads:

1. An article comprising:

a fibrous support comprising nanofibers, the fibrous support having a thickness from 5 μm to about 50 μm; and

an interfacially polymerized polymer layer disposed on a surface of the fibrous support,

wherein the interfacially polymerized polymer layer further comprises at least one hydrophilic or hydrophobic nanoparticulate filler.