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Missing link' memristor created: Rewrite the textbooks?
EE Times ^ | 04/30/2008 1:00 PM EDT | R. Colin Johnson

Posted on 04/30/2008 5:01:51 PM PDT by ThePythonicCow


PORTLAND, Ore. — The long-sought after memristor--the "missing link" in electronic circuit theory--has been invented by Hewlett Packard Senior Fellow R. Stanley Williams at HP Labs (Palo Alto, Calif.) Memristors--the fourth passive component type after resistors, capacitors and inductors--were postulated in a seminal 1971 paper in the IEEE Transactions on Circuit Theory by professor Leon Chua at the University of California (Berkeley), but their first realization was just announced today by HP. According to Williams and Chua, now virtually every electronics textbook will have to be revised to include the memristor and the new paradigm it represents for electronic circuit theory.

"My situation was similar to that of the Russian chemist Dmitri Mendeleev who invented the periodic table in 1869," said Chua. "Mendeleev postulated that there were elements missing from the table, and now all those elements have been found. Likewise, Stanley Williams at HP Labs has now found the first example of the missing memristor circuit element."

When Chua wrote his seminal paper, he used mathematics to deduce the existence of a fourth circuit element type after resistors, capacitors and inductors, which he called a memristor, because it "remembers" changes in the current passing through it by changing its resistance. Now HP claims to have discovered the first instance of a memristor, which it created with a bi-level titanium dioxide thin-film that changes its resistance when current passes through it.

"This new circuit element solves many problems with circuitry today--since it improves in performance as you scale it down to smaller and smaller sizes," said Chua. "Memristors will enable very small nanoscale devices to be made without generating all the excess heat that scaling down transistors is causing today."

HP has already tested the material in its ultra-high-density crossbar switches, which use nanowires to pack a record 100 Gbits onto a single die--compared with 16 Gbits for the highest density flash memory chips extant.

"We have been looking for years for the best material to use in our ultra-dense nanowire crossbar switches, which can fit 100 billion crossbars into a square centimeter. What we have finally realized is that the ideal material is a memristor," said Williams, primary inventor of the memristor's titanium-dioxide-based material and founding director of HP's 12-year-old Information and Quantum Systems Lab, where his team perfected its formulation.

The hold-up over the last 37 years, according to professor Chua, has been a misconception that has pervaded electronic circuit theory. That misconception is that the fundamental relationship in passive circuitry is between voltage and charge. What the researchers contend is that the fundamental relationship is actually between changes-in-voltage, or flux, and charge. Such is the insight that enabled HP to invent the memristor, according to Chua and Williams.

"Electronic theorists have been using the wrong pair of variables all these years--voltage and charge. The missing part of electronic theory was that the fundamental pair of variables is flux and charge," said Chua. "The situation is analogous to what is called "Aristotle's Law of Motion, which was wrong, because he said that force must be proportional to velocity. That misled people for 2000 years until Newton came along and pointed out that Aristotle was using the wrong variables. Newton said that force is proportional to acceleration--the change in velocity. This is exactly the situation with electronic circuit theory today. All electronic textbooks have been teaching using the wrong variables--voltage and charge--explaining away inaccuracies as anomalies. What they should have been teaching is the relationship between changes in voltage, or flux, and charge."

The virtues of hysteresis

HP invited Chua to speak about his theory a few years ago, but at that time the lab did not tell Chua that they were actively seeking the memristor. Only two weeks ago did Williams tell Chua that he had used the proper variables--flux and charge--to invent the world's first working memristor.

A memristor works by virtue of hysteresis, whereby its rate of change accelerates as it moves from one state to the other--"on" to "off," or vice versa. Hysteresis has been explained away by current circuit theory as an anomaly, according to Chua and Williams, whereas its existence is, in fact, a fundamental property of passive circuitry.

"Hysteresis is a tell-tale manifestation of the fourth circuit element--the memristor," said Chua. "And Stan Williams is very smart to have realized that if you cannot explain something properly, then there must be a better explanation."

For instance, electrical engineers have known that titanium dioxide changes its resistance in the presence of oxygen--this is the principle behind titanium dioxide oxygen sensors--but they could not explain why.

"They traced its curve, and knew it contained hysteresis, but because they could not explain it, they could only design the simplest of devices using it--sensors," said Chua. "But now that it has been explained, they will be able to design all types of new circuitry using it. This is a wonderful development."

Chua predicts that electrical engineers will soon begin discovering all types of new materials that manifest the hysteresis relationship between flux and charge. He predicts that this new era of electronics will be able to solve the problems with scaling--such as using too much power and generating too much heat--that are currently plaguing progress in circuit design.

"The memristor is our salvation, because it works better and better as you make it smaller and smaller," said Chua. "The era of nanoscale electronics will be enabled by the memristor. This is not just an invention, it is a basic scientific discovery. It has always been there--we just had to face these nanoscale problems to realize its importance."

The memristor behaves like a non-linear resistor with memory--a small, compact and highly energy-efficient means of creating a memory device. But Chua and Williams claim it is also a new type of circuit element that should enable the creation of new devices never before imagined.

The world's first memristor invented at HP Labs by Williams and his research team is based on a two-layer sandwich of titanium dioxide films. As a memory element, it works by changing the atomic structure of the films--by coupling the motion of atoms in the material with the movement of electrons through the material. The bottom layer of HP's material uses a symmetrical lattice of titanium atoms and oxygen atoms, which makes it a good insulator. But the top layer has had oxygen vacancies introduced as a dopant, which makes it into a good conductor--the more vacancies, the more conductive. HP's secret sauce for creating these oxygen vacancies in titanium dioxide involves using sputter deposition that begins with an excess of oxygen, then cuts back on the oxygen flow to create the layer with vacancies.

By placing the crossbar of nanowires above and below the sandwiched layers, charge can be passed through the material. "The way I discovered the material for our memristor was by studying how titanium dioxide oxygen sensors work--that got me thinking about moving oxygen vacancies around in the material to create a memristor," said Williams. "By running current through the device, we can push oxygen vacancies from the layer that has them into the layer that does not, thereby changing its resistance by a factor of 1000 or even more, thus switching the memristor 'on,' then by reversing the current we can move the vacancies back into the first layer, thereby switching the memristor 'off'."

New era of devices

As Chua predicted, Williams is already thinking about creating new types of devices with HP's crossbar architecture beyond a simple memory device. "If we push current through it hard and fast, it acts like a digital device, but if we run current through it gently and slowly it acts as an analog device," said Williams. "We are already designing new types of circuits in both the digital and analog domains using our crossbar architecture. In the analog domain, we want to build memristor-based devices that operate in a manner similar to how the synapse works in the brain--neuron-like analog computational elements that could perform control functions where decisions must be made involving comparisons as to whether something is larger or smaller than something else. We are not building a neural network yet, but we think that using the memristor in its analog mode with our crossbar is a pretty good representation of a neural net."

Later in 2008, HP promises to begin releasing details of how its memristor material works with its already perfected nanoscale crossbar switch architecture in these various types of circuits.

"The memristor is not just a replacement technology for existing memory devices, but will be used to make a whole range of new types of devices that no one has ever thought of before," said Williams.



TOPICS: Technical
KEYWORDS: alientech; computer; electronics; fluxcapacitor; memory; memresistor; nanoo; reverseengineering; tio2; titaniumdioxide; ufotechnology
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This looks big to me ... in the long run. One more reason to stay healthy and live long; this fun we've been having inventing computers isn't over yet.

The one thing I haven't figured out -- how do they read out? How do they tell whether it's the upper layer or lower layer of titanium oxide that has the holes, and so is low resistance?

1 posted on 04/30/2008 5:01:52 PM PDT by ThePythonicCow
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To: ThePythonicCow
They coulda just asked me.

I knew that all along.

: )

2 posted on 04/30/2008 5:10:48 PM PDT by Publius6961 (MSM: Israelis are killed by rockets; Lebanese are killed by Israelis.)
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To: ThePythonicCow
A memristor ...changes its resistance when current passes through it.

So does a coil.

I got to read this again and let it sink in.

3 posted on 04/30/2008 5:11:02 PM PDT by Rudder (Klinton-Kool-Aid FReepers prefer spectacle over victory.)
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To: ThePythonicCow
Perhaps we have a fundamental mistake in the economic law of supply and demand, analogous to the above mentioned mistakes in choice of variables for the laws of motion and circuits.

Perhaps the same shifts in view point:

  1. first from Aristotle's force versus velocity, to Newton's force versus acceleration (the rate of change in velocity), then
  2. second (in the above article) from charge versus voltage, to charge versus flux (the rate of change in voltage), also applies to
  3. economics, price and supply.
Perhaps price is not proportional to supply, but to the rate of change in supply.
4 posted on 04/30/2008 5:11:43 PM PDT by ThePythonicCow (By their false faith in Man as God, the left would destroy us. They call this faith change.)
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To: ThePythonicCow
The hold-up over the last 37 years, according to professor Chua, has been a misconception that has pervaded electronic circuit theory. That misconception is that the fundamental relationship in passive circuitry is between voltage and charge. What the researchers contend is that the fundamental relationship is actually between changes-in-voltage, or flux, and charge. Flux-capacitor invented!?!
5 posted on 04/30/2008 5:15:49 PM PDT by DrGunsforHands
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To: Rudder
A coil changes its resistance only -while- the current is passing (actually, while the current flux, the rate of change in the current, is non-zero.)

A memresistor changes its resistance -permanently-.

Pass a current through the top conductor just briefly, and the bottom titanium layer becomes, and stays, conductive. Days or years (or nanoseconds) later, pass a current through the bottom conductive layer, and the two titanium layers reverse their state, with the top layer becoming conductive.

Even after removing all source of electrical power, these memresistor devices remember their state; which of the two titanium layers is more conductive doesn't change or decay.

6 posted on 04/30/2008 5:16:13 PM PDT by ThePythonicCow (By their false faith in Man as God, the left would destroy us. They call this faith change.)
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To: DrGunsforHands
Yeah - once again, reality mimics art ;).
7 posted on 04/30/2008 5:17:06 PM PDT by ThePythonicCow (By their false faith in Man as God, the left would destroy us. They call this faith change.)
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To: ThePythonicCow

Now, where’s that interociter?


8 posted on 04/30/2008 5:20:59 PM PDT by tacticalogic ("Oh bother!" said Pooh, as he chambered his last round.)
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To: ThePythonicCow
This is BIG!
9 posted on 04/30/2008 5:24:28 PM PDT by urabus
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To: ThePythonicCow
Here's another version of this same story, with pictures, from Crave (cnet.com):
Apr 30 2008

HP makes memory from a once-theoretical circuit

Author: Michael Kanellos

It's the tale of the lost circuit.

Thirty-seven years ago, Leon Chua, a professor at the University of California at Berkeley, mathematically theorized that scientific symmetry demands that there should be a fourth fundamental circuit element. Engineers were already familiar with resistors (which resist the flow of electricity), capacitors (which store electricity), and inductors (which resist changes to the flow of electrical current), which can be combined to build more complex devices. The fourth circuit, which Chua called a "memristor" for memory resistor, would register how much current had passed.

"He looked at fundamental circuit equations and noticed there was a hole," said Stan Williams, who heads up the Information and Quantum Systems lab at HP Labs, "There should be a device that remembers how much current flowed through a device."

An atomic force microscope image of a circuit with 17 memristors in a row. The memristor consists of two titanium dioxide layers connected to wires. When a current is applied to one, the resistance of the other changes. That change can be registered as data. (Credit: J.J. Yang, HP Labs)

Williams and other scientists at Hewlett-Packard are publishing a paper in Nature on Wednesday demonstrating that that these things actually exist. HP has a few discrete memristors as well as a silicon chip embedded with memristors. It's a first, according to HP.

If memristors can be commercialized, it could lead to very dense, energy-efficient memory chips. Scientists have made devices that function like memristors, but it took a good number of transistors and several capacitors, Williams said. Memristor chips would function like flash memory and retain data even after a computer is turned off, but require less silicon, consume less energy, and require fewer transistors.

A memristor effectively stores information because the level of its electrical resistance changes when current is applied. A typical resistor provides a stable level of resistance. By contrast, a memristor can have a high level of resistance, which can be interpreted as a computer as a "1" in data terms, and a low level can be interpreted as a "0." Thus, data can be recorded and rewritten by controlling current. In a sense, a memristor is a variable resistor that, through its resistance, reflects its own history, Williams said.

Varying resistance is the same principle at work with phase change memory. The difference in phase change memory, which will come to market later this year, is that changes in resistance are accomplished through a substantial amount of heating. A bit on a CD-like substrate is heated rapidly a few hundred degrees and then cooled. Depending on how rapidly the bit cools, the material becomes crystalline or amorphous. The different states--crystalline and amorphous--exhibit different states of resistance.

"We can get it (resistance changes) with less energy," Williams said. "It is a large amount of resistance change with a small amount of memory."

The secret sauce in HP's memristors is two layers of titanium oxide, a crystalline material consisting of one titanium atom and two oxygens, sandwiched between two metal wires. The bottom layer consists of standard, consistent titanium dioxide. The upper layer is missing a few oxygens--less than 1 percent--which creates voids. When a current is applied (via the wire) to the upper layer, the vacancies are pushed into the lower level of titanium dioxide. That changes the resistance of the lower level. Subsequent bursts of current can then reverse it.

"All we have to do is push around a very small number of vacancies in a crystalline material," Williams said. "We can switch it very fast, faster than we can measure."

Pushing the voids into the consistent layer of titanium dioxide does not change its characteristics otherwise. He likens it to bubbles in beer. "You can have bubbles in it, but it's still beer," he said.

Memristors in green. The wires in this image are 50 nanometers wide, which comes to about 150 atoms.(Credit: J.J. Yang, HP Labs)

Memory and storage are the new frontier for chip designers. The explosion of data will require new ways to retrieve and store it. Cloud computing? It's a big hard drive, if you think about it. Numonyx, the Intel and STMicroelectronics joint venture, is leading the effort to commercialize phase change memory. IBM is working on ways to store data through magnetic charges on a wire. Seagate Technology, Hitachi, Zettacore, Grandis, and others are working on different memory and storage concepts.

HP has largely exited the chip business, but it has increased efforts to license the intellectual property inside its labs. The company, for instance, will likely try to commercialize the crossbar latch technology, which allows molecular grids to perform calculations. (Williams also works on that.)

While memristors can be made on silicon chips, memristor devices will require engineers to learn a new circuit design discipline.

"The technology is in good shape. The big barrier is not whether you can make it," Williams said. "It is the effort to design new circuits."

10 posted on 04/30/2008 5:27:31 PM PDT by ThePythonicCow (By their false faith in Man as God, the left would destroy us. They call this faith change.)
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To: ThePythonicCow

That’s a very interesting postulation.


11 posted on 04/30/2008 5:31:09 PM PDT by visualops (artlife.us . nature photography desktop wallpapers)
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To: ThePythonicCow

So, will this enable Moore’s Law to remain valid for the foreseeable future? Or does it completely usurp Moore’s Law? Or is not related at all?


12 posted on 04/30/2008 5:34:05 PM PDT by DrGunsforHands
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To: ThePythonicCow
Bookmark for later read.


13 posted on 04/30/2008 5:34:39 PM PDT by 50mm
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To: Rudder
A memristor ...changes its resistance when current passes through it.

So does a coil.

I got to read this again and let it sink in.

Perhaps you're thinking of a coil's impedance, which varies with the frequency of the signal being passed through it. At DC, there isn't any inductive effect, just the DC resistance of the coil's wire. These devices seem to take on permanent changes to their resistance after a current has been passed through and then removed.

14 posted on 04/30/2008 5:38:01 PM PDT by Bob
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To: ThePythonicCow
A memresistor changes its resistance -permanently-.

Oh. I didn't catch that. Thanks!

15 posted on 04/30/2008 5:38:18 PM PDT by Rudder (Klinton-Kool-Aid FReepers prefer spectacle over victory.)
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To: Bob
Perhaps you're thinking of a coil's impedance, which varies with the frequency of the signal

Yes, but I left out the frequency and the dc part just to keep it simple. Thanks.

16 posted on 04/30/2008 5:41:53 PM PDT by Rudder (Klinton-Kool-Aid FReepers prefer spectacle over victory.)
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To: visualops
Yes - interesting - likely to be lost as off topic here however.

It was my actual motivation for posting this thread however. I was reading about this memresistor while listening to Mark Levin explain the economics of oil prices, and a couple of my synapses short circuited (a familiar occurrence for me.)

17 posted on 04/30/2008 5:42:01 PM PDT by ThePythonicCow (By their false faith in Man as God, the left would destroy us. They call this faith change.)
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To: ThePythonicCow

One day you have tubes. The next day, transistors.

What were you doing when they announced the invention of the Memrister?

It might be one of those events worth remembering.

I wonder if most of the electronic circuits in the world we now be redesigned.


18 posted on 04/30/2008 5:42:41 PM PDT by yefragetuwrabrumuy
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To: Admin Moderator
How in heck do I add "computers" to the "topics" for this post?

I've clicked on the Click to Add Topic link at the bottom of the original post, and entered a dozen different variations of "computers", always to generate an error screen, complaining, of whatever word or misspelling I tried, "unknown: computers".

19 posted on 04/30/2008 5:45:16 PM PDT by ThePythonicCow (By their false faith in Man as God, the left would destroy us. They call this faith change.)
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To: ThePythonicCow
Wow. It does look like a big deal!

The one thing I haven't figured out -- how do they read out? How do they tell whether it's the upper layer or lower layer of titanium oxide that has the holes, and so is low resistance?

They send things to the upper or lower layer by switching the current direction. If you've got a current direction corresponding to the high resistance side, you're going to get an "off". I think your "read" circuit would only go through one of the layers, and the write would go through both. But I don't know crap about electronics...

20 posted on 04/30/2008 5:46:30 PM PDT by r9etb
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