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'[EE:] memristor'
2008\04\30@191552 by Shawn Tan

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Thought this might be of interest.

http://www.popsci.com/scitech/article/2008-04/hp-discovers-potential-god-particle-electronics

--
with metta,
Shawn Tan

Aeste Works (M) Sdn Bhd - Engineering Elegance
http://www.aeste.net


'[EE:] memristor'
2008\05\01@110525 by Alex Harford
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On Wed, Apr 30, 2008 at 4:15 PM, Shawn Tan <spam_OUTshawn.tanTakeThisOuTspamaeste.net> wrote:
> Thought this might be of interest.
>
>  http://www.popsci.com/scitech/article/2008-04/hp-discovers-potential-god-particle-electronics

Very interesting!

A post on Slashdot sums it up nicely:
<http://hardware.slashdot.org/comments.pl?sid=539458&cid=23258198>

--------------------------------------
There are four fundamental circuit variables; current, voltage,
charge, and flux.

We can define the relationships between charge and current and between
flux and voltage. (charge as an integral of current, flux as an
integral of voltage over time)

A resistor provides a function to relate voltage and current.
A capacitor provides a function to relate charge and voltage.
An inductor provides a function to relate flux and current.

Until now we did not know how to construct a passive device which
would provide a function relating charge and flux. The only remaining
combination of these fundamental variables.
--------------------------------------

2008\05\01@132037 by Dr Skip

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I like the comment suggesting they call it a 'flux capacitor'... ;)

Alex Harford wrote:
{Quote hidden}

2008\05\01@141614 by Sean Breheny

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Hmm, I'm not familiar with flux being defined as "the integral of
voltage over time". Normally flux refers to either electric or
magnetic flux, and is the integral of the perpendicular component of
the E or B field over a surface.

I just took the definition of inductance (V=Ldi/dt) and was able to
maneuver it into integral(V)=k*phi where phi is magnetic flux. This is
a bit odd, though, because if this is what they mean, then their
choice of "four fundamental circuit variables" is a bit arbitrary. Why
did they not consider electric flux? Why no magnetic polarization
(equivalent of "charge" in the magnetic side of things)?

Also, one of the articles I read on this (can't remember the one),
gave an explanation of a memristor which didn't involve magnetism at
all. It described it as a semiconductor made of titanium dioxide where
current flow would gradually make the resistance drop over time due to
migration of holes from one region into the other. Doesn't seem to
involve magnetism at all AND their voltage current relationship for
the device was something like: V=M*I*integral(Idt), so that the
effective resistance is the "memristance" times the integral of
current over time.

Sean


On Thu, May 1, 2008 at 11:05 AM, Alex Harford <harfordspamKILLspamgmail.com> wrote:
{Quote hidden}

> --

2008\05\01@182551 by Dr Skip

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more memristor:

http://www.spectrum.ieee.org/may08/6207

2008\05\01@200641 by William \Chops\ Westfield

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On May 1, 2008, at 3:25 PM, Dr Skip wrote:
> more memristor: http://www.spectrum.ieee.org/may08/6207

>> The reason that the memristor is radically different from the  
>> other fundamental circuit elements is that, unlike them, it  
>> carries a memory of its past. When you turn off the voltage to the  
>> circuit, the memristor still remembers how much was applied before  
>> and for how long. That's an effect that can't be duplicated by any  
>> circuit combination of resistors, capacitors, and inductors, which  
>> is why the memristor qualifies as a fundamental circuit element.

So how come none of the articles compare it to a capacitor?  A  
capacitor in a sense "remembers" the current that has flowed through  
it because it collects charges on the plates.  Remove the current and  
the voltage stays the same.  A good number of memory technologies are  
based on this effect.  For the memristor, it sounds like the current  
through the device is remembered based on the voltage that has been  
across it ?  Turn off the voltage, and the current remains the same  
(when you next measure it?)?  But I'm not seeing the physical basis  
for such an effect??  It seems like the HP device manages to simulate  
the mathematical behavior through nanoscale complexity (similar to  
the way you can create circuits that act like capacitors using op-
amps?), but I'm not feeling very warm and fuzzy :-(  (Perhaps the  
"simple" device requires monopoles or other "magnetic charge carrier"  
to make it work?  A direct magnetic equivalent of the capacitor?)

BillW

2008\05\01@202808 by Jake Anderson

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sounds a bunch like an eeprom cell to me.

William Chops Westfield wrote:
{Quote hidden}

2008\05\01@210047 by Dr Skip

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I think you're right on target. In fact, the orig. author produced a circuit to
mimic that behavior too early on. It doesn't seem to be a basic physical
property, but that's good, since this is an engineering list and not a physics
one I hear... ;)  (I couldn't resist)

For me, scalability is one defining factor. Change the size and your device can
handle Mega-Amps rather than uA or MV vs nV - like caps, resistors and
inductors - it's a property whose existence is not related to size. Not so for
this one, but the quantum mechanical folks live in their own reality... ;) It
seems pretty easy to manufacture though, and it has really useful properties,
so it will certainly change things. It should have a multiplicative effect on
semi technology rather than just an add-on new device.

The sad part is that unlike inductors, caps and resistors, you can't make one
at home...



William "Chops" Westfield wrote:
{Quote hidden}

2008\05\01@212641 by Jinx

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> sounds a bunch like an eeprom cell to me.

AIUI EEPROM stores a digital voltage. Devices like ISD
sound recorder chips store an analogue voltage

The name "memresistor" seems to fit if I understand this
description correctly

"a layer of titanium dioxide sandwiched between two metal
electrodes. The researchers discovered that the amount of
resistance it exerts depends on how much electric charge had
previously passed through it"

"the amount of resistance it exerts" (not well put, I think, but
perhaps they mean the resistance it "exerts" on the read voltage
to make a current when the device is next powered) implies to
me that the element could be compared to a digital pot. IOW
a resistor that has its resistance changed by a voltage and is left
with that resistance after the voltage has gone. Or, on a larger
scale, like the domains left on magnetic audio tape after recording


2008\05\01@222035 by Apptech

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>> sounds a bunch like an eeprom cell to me.
>
> AIUI EEPROM stores a digital voltage. Devices like ISD
> sound recorder chips store an analogue voltage

Both the same in basic function - how the cell is used
differs. Usually you want a cell full or empty to give
logical high low (or the inverse).  BUT ISD cleverly (and
retrospectively wholly obviously) fill the cell variably to
give 256 discrete levels.


       Russell

2008\05\02@045110 by Alan B. Pearce

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>more memristor:
>
> http://www.spectrum.ieee.org/may08/6207

The original article in PDF form, is at
http://www.nature.com/nature/journal/v453/n7191/pdf/nature06932.pdf


2008\05\02@071805 by Dario Greggio

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Dr Skip wrote:

> I like the comment suggesting they call it a 'flux capacitor'... ;)

yep, definitely, McFly :)))

2008\05\03@104046 by sergio masci

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On Fri, 2 May 2008, Alan B. Pearce wrote:

> >more memristor:
> >
> > http://www.spectrum.ieee.org/may08/6207
>
> The original article in PDF form, is at
> http://www.nature.com/nature/journal/v453/n7191/pdf/nature06932.pdf

Does anyone know of a source that does not require payment?

Anyway, as I understand it, you apply a DC voltage to set the resistance,
then an AC voltage to read it.

This reminds me of a timer device I heard of maaaaany years ago. It
consisted of a gold and silver electrode in a solution of silver nitrate.
To set the timer you applied a voltage across the electrodes such that
silver was deposited on the gold electrode. The amount of silver
deposited was dependent on the time for which the current flowed. To read
it you applied the voltage in the opposite direction. Current would flow
while there was silver available on the gold electrode and when it was all
gone the current flow changed significantly.

Now it occurs to me that if you vary the amount of silver deposited on a
gold electrode you might be able to use an AC voltage to give a reading
proportional to the amount of silver deposited - kind of like a big
memister.

Any thoughts?

Regards
Sergio

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