Memristor Identity Crisis
June 11, 2012
First, a mild disclaimer. None of this article is criticism of someone's research. The problem discussed is one of nomenclature, not scientific misconduct. It's also good to realize that the greatest discoveries get the most criticism, since lesser "discoveries" are just ignored. If Alexander Graham Bell had invented a better post hole digger, I'm sure he would not have needed to defend his patents in the courts for so many years.
The controversy is about a supposed electrical circuit element called a memristor. As its name implies, it's a resistor with a memory; specifically, a memory of how much current has passed through it. In this information age, such a device would be useful. If someone asked me to make such a device, there would be various ways I could do it. If you wanted it in a day and weren't worried about its size or performance, I could combine a microcontroller and a field effect transistor to produce such a device.
To produce a more elegant device, I would likely look back into the decades old technology of tungsten oxide electrochromic devices that work by reversibly plating one material onto another in an electrochemical cell. If such a device were really important, a little research would yield far better material systems, and a better device.
The problem, however, is that the memristor is supposedly a fundamental device, not a device that depends on any material system. Its properties are predicted by looking at the symmetry of the fundamental electrical devices, resistors, capacitors and inductors, and filling in the gap.
Resistor: ∂v = R⋅∂i
In these equations, v is the voltage, i is the current, φ is the magnetic flux; and R, C, L and M are the resistance, capacitance, inductance and memristance. The fundamental symmetry can be seen easily in the following figure, which shows these four electrical elements much like the ancients represented their four elements.
Leon Chua, famous for his eponymous chaotic oscillator circuit, started people thinking about the possibility of the memrister in a 1971 paper. The operation of this element is simply that its resistance will increase when current flows through it in one direction; and, it will decrease when current flows through it in the other direction.
As the equations dictate, magnetism should be involved because of the flux term, ∂φ, as Chua realized; viz.,
Capacitor: ∂q = C⋅∂v
Inductor: ∂φ = L⋅∂i
Memristor: ∂φ = M⋅∂q
"The physical mechanism characterizing a memristor device must come from the instantaneous (memoryless) interaction between the first-order electric field and the first-order magnetic field."
That was in 1971, and it wasn't until 2008 that the first memristors devices were described. I wrote about these in an earlier article (Memristor, May 14, 2008). Unlike my microcontroller version mentioned earlier, these were true, passive devices that didn't need electrical power. Chua was happy to acknowledge these devices as memristors.
Although these devices do have the resistance properties required of a memristor, the problem is that they don't involve magnetism in any way. Hewlett Packard's memristor device behaves mathematically as a memristor, but its action is via a chemical effect and not the faster, and more useful, electromagnetic effect of Chua's original proposal.
The original Hewlett Packard device functioned through ionic migration in a 5 nanometer film of titanium dioxide sandwiched between electrodes. As electrical charge is accumulated in this film, it becomes charged with oxygen vacancies that increase its conductance. The conductance effect of vacancies in bulk titanium dioxide was known for years prior to its use in memristors. It's used in some types of oxygen gas sensors.
An analysis of the true nature of the memristor has been published on the arXiv Preprint Server by Sascha Vongehr of the Department of Philosophy, Nanjing University, China. Vongehr is skilled to comment in this area, since he also has an appointment at the National Laboratory of Solid-State Microstructures (Nanjing, China), and he has a physics Ph.D. from the University of Southern California.
Vongehr writes that true memristor devices may not exist at all, since there are reasons that they might be unstable. Says Vongehr, "The memristor is either impossible or still to be discovered." And it's not just he who has doubts. Devices that perform as memristors were produced earlier than 2008, but the discoverers of these devices did not claim them to be memristors, nor did they claim prior discovery after publication of the 2008 work.
Vongehr writes that "memristor" was a catchy label, so there was a flood of memristors papers without any critical thought as to what a memristor really is. I can relate to that, since I once worked in the area of magnetic bubbles, which seemed to persist long after its utility, perhaps because it, too, had a catchy label. Vongehr's hope is that the mis-definition of memristors doesn't stop its actual discovery; or, proof that memristors, indeed, don't exist.
|Atomic force microscope (AFM) image of seventeen memristors. The wires are 50 nm wide, which is only 150 atoms.|
Photo by J. J. Yang, HP Labs, via Wikimedia Commons).
- Leon O. Chua, "Memristor" The Missing Circuit Element", IEEE Transactions on Circuit Theory, vol. CT-18, no. 5 (September 1971), pp. 507-519.
- R. Colin Johnson, "'Missing link' memristor created: Rewrite the textbooks?" (EETimes, April 30, 2008).
- Dmitri B. Strukov, Gregory S. Snider, Duncan R. Stewart, and R. Stanley Williams, "The missing memristor found," Nature, vol. 453 (1 May 2008), pp. 80-83.
- HP Labs Proves Existence of New Basic Element for Electronic Circuits (HP Press Release, April 30, 2008).
- Jamie Beckett, "Demystifying the memristor: Proof of fourth basic circuit element could transform computing," (HP Press Release, April, 2008).
- Sascha Vongehr, "The Missing Memristor: Novel Nanotechnology or rather new Case Study for the Philosophy and Sociology of Science?" arXiv Preprint Server, March 1, 2012.
- H. M. Upadhyaya and Suresh Chandra, "Polarity dependent memory switching behavior in Ti/Cd Pb S/Ag system." Semiconductor Science and Technology vol. 10, no. 3 (March, 1995), pp. 332-338.
Permanent Link to this article
Linked Keywords: Disclaimer; nomenclature; scientific misconduct; N-rays; Alexander Graham Bell; post hole digger; patent; electrical circuit element; memristor; resisto; non-volatile memory; memory; electric current; information age; microcontroller; field effect transistor; technology; tungsten oxide; electrochromic; electroplating; plating; electrochemical cell; symmetry; resistor; capacitor; inductor; voltage; electric current; current; magnetic flux; resistance; capacitance; inductance; memristance; Ancient Greece; four elements; Wikimedia Commons; Leon Chua; Chua's circuit; chaotic oscillator circuit; magnetism; passive device; electrical power; Hewlett Packard; chemical; electromagnetic; HP Labs; ionic; nanometer; titanium dioxide; electrode; electric charge; oxygen; vacancy defect; vacancy; conductance; oxygen gas sensor; arXiv Preprint Server; Sascha Vongehr; Department of Philosophy; >Nanjing University; China; National Laboratory of Solid-State Microstructures; physics; Ph.D.; University of Southern California; magnetic bubble.
Latest Books by Dev Gualtieri
Thanks to Cory Doctorow of BoingBoing for his favorable review of Secret Codes!
Blog Article Directory on a Single Page
- Soybean Graphene - March 23, 2017
- Income Inequality and Geometrical Frustration - March 20, 2017
- Wireless Power - March 16, 2017
- Trilobite Sex - March 13, 2017
- Freezing, Outside-In - March 9, 2017
- Ammonia Synthesis - March 6, 2017
- High Altitude Radiation - March 2, 2017
- C.N. Yang - February 27, 2017
- VOC Detection with Nanocrystals - February 23, 2017
- Molecular Fountains - February 20, 2017
- Jet Lag - February 16, 2017
- Highly Flexible Conductors - February 13, 2017
- Graphene Friction - February 9, 2017
- Dynamic Range - February 6, 2017
- Robert Boyle's To-Do List for Science - February 2, 2017
- Nanowire Ink - January 30, 2017
- Random Triangles - January 26, 2017
- Torricelli's law - January 23, 2017
- Magnetic Memory - January 19, 2017
- Graphene Putty - January 16, 2017
- Seahorse Genome - January 12, 2017
- Infinite c - January 9, 2017
- 150 Years of Transatlantic Telegraphy - January 5, 2017
- Cold Work on the Nanoscale - January 2, 2017
- Holidays 2016 - December 22, 2016
- Ballistics - December 19, 2016
- Salted Frogs - December 15, 2016
- Negative Thermal Expansion - December 12, 2016
- Verbal Cues and Stereotypes - December 8, 2016
- Capacitance Sensing - December 5, 2016
- Gallium Nitride Tribology - December 1, 2016
- Lunar Origin - November 27, 2016
- Pumpkin Propagation - November 24, 2016
- Math Anxiety - November 21, 2016
- Borophene - November 17, 2016
- Forced Innovation - November 14, 2016
- Combating Glare - November 10, 2016
- Solar Tilt and Planet Nine - November 7, 2016
- The Proton Size Problem - November 3, 2016
- Coffee Acoustics and Espresso Foam - October 31, 2016
- SnIP - An Inorganic Double Helix - October 27, 2016
- Seymour Papert (1928-2016) - October 24, 2016
- Mapping the Milky Way - October 20, 2016
- Electromagnetic Shielding - October 17, 2016
- The Lunacy of the Cows - October 13, 2016
- Random Coprimes and Pi - October 10, 2016
- James Cronin (1931-2016) - October 6, 2016
- The Ubiquitous Helix - October 3, 2016
- The Five-Second Rule - September 29, 2016
- Resistor Networks - September 26, 2016
- Brown Dwarfs - September 22, 2016
- Intrusion Rheology - September 19, 2016
- Falsifiability - September 15, 2016
- Fifth Force - September 12, 2016
- Renal Crystal Growth - September 8, 2016
- The Normality of Pi - September 5, 2016
- Metering Electrical Power - September 1, 2016
Deep Archive 2006-2008