
The case for rejecting the memristor as a fundamental circuit element (2018) - gbrown_
https://www.nature.com/articles/s41598-018-29394-7
======
jameshart
I'm not, I apologize, an electronic engineer, so I mainly only get to view the
whole memristor discussion as one of competing narratives - and certainly the
'whatever HP are pitching, it's not what was originally envisaged, and there's
no certainty that's even a thing' narrative is certainly compelling. But there
is a slight feel in this paper of an attempt to reconcile an unclear new
concept with an orthodoxy, and that rubs me the wrong way. It reads a little
like an alchemist dismissing the concept of phlogiston. Maybe you're both
wrong?

"The basic question of the “missing element” is whether we can we have a new
passive element that cannot be made from the combination of existing passive
elements. Water (W), Fire (F), Earth (E) and Air (A) are the four fundamental
passive elements that a contemporary alchemical engineer is familiar with....
"

~~~
sgt101
I think that the exposition of the manipulation and deployment of the fab
three differentiates this discussion from the descriptive and mystical
narrative of alchemy.

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krackers
See also:
[https://news.ycombinator.com/item?id=17807926](https://news.ycombinator.com/item?id=17807926)

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60654
Oh what a thoroughly impressive academic hatchet job, and I mean that in the
kindest possible sense. It's intended to kill the idea of memristors as
fundamental passive circuit elements, and it's very good at doing just that.

TLDR: by re-deriving the periodic table of passive elements from first
principles, it shows that memristors don't fit. The "missing fourth element"
from Strukov's table is not really a missing type of a passive element.
Rather, it shows that Strukov's table itself is _wrong,_ that it's just a view
of the standard C/R/I relationships that conflates two different ways of
looking at resistance specifically (see especially
[https://www.nature.com/articles/s41598-018-29394-7/figures/3](https://www.nature.com/articles/s41598-018-29394-7/figures/3)
)

FWIW this _does not_ diminish memristors as potentially industry-changing
inventions, like transistors. But it denies them the status of fundamental,
irreducible passive circuit elements, specifically, partly by showing that
while fundamental elements are all connected by charge-voltage relationships
(specifically, changes over time, like position/velocity/acceleration are in
classical physics), memristors don't have a unique spot there; and also
because fundamental elements can't be composed from each other, while the
memristors demonstrated so far are "nonlinear composition of resistors with
active hysteresis".

~~~
tiglionabbit
Is it not possible to create the other "fundamental" components using
combinations of other components? I know with logic gates one might think of
AND/OR/NOT as fundamental but yet one can make anything out of NANDs or NORs,
so they could be considered fundamental instead. It's a thing in mathematics
as well that you can often define essentially the same system using different
sets of prepositions.

I saw a comment later on in here that explained that memristors, resistors,
capacitors, and inductors round out all four combinations of relating charge
or the derivative of charge over time with flux or the derivative of flux over
time.

~~~
60654
I'm not sure the logic gate metaphor works here, because the domain is so
different, the questions relate to the charge-voltage relationship and its
first and second derivatives.

Maybe a different metaphor would be better: a bank statement involves stored
money (like a capacitor), and a profit/loss sheet involves effects of money
moving over time (like a resistor), and you can see how they're related
through integration/differentiation, but they're fundamental because you can't
create a bank account by nailing a bunch of P&Ls together.

Ok, so maybe that's not a great metaphor either? ;)

The paper does discuss equivalence categories (along the lines of nth
derivatives of charge and voltage) so it's probably best to refer directly to
that!

------
ChuckMcM
I enjoyed this look at the memristor. Coming at the question from first
principles is one that works for me. I've saved it in my notebook for forward
to folks who go on and on about how revolutionary they are.

~~~
acqq
However this work doesn't say anything about how revolutionary for our
ordinary use cases some device based on something commonly called memristors
could be.

Like iPhone: it is not "fundamental" in any sense, but one can really see the
difference "before and after."

The mobile phones existed before, but the way people use them hugely changed.

Another problem is that we read for years how memristors will be
revolutionary, but then just some time passes and we read it again... I
haven't researched the background to that, maybe somebody here has some
insider info?

~~~
ndesaulniers
Memristors are fundamental in that they relate charge w/ flux.

Capacitors relate charge to voltage. q = Cv

Resistors relate voltage to current. v = Ri

Inductors relate current to flux. theta = Li

Before memristors, nothing related charge to flux. theta = Mq

(also, voltage is the derivative of flux over time, and current is the
derivative of charge over time, which makes a nice symmetry that memristors
complete)

(skimmed the article briefly, seems like they're arguing that memristors are
not fundamental because hysteresis is a non-linear relationship? Can I get a
TL;DR HN?)

~~~
neltnerb
More that it requires active and time dependent history to know the state of
the device, making it not fundamental in the sense that the resistance doesn't
depend on history.

It's a fair point I'd say, and they're clear that this isn't something that
diminishes utility of any practical device. Just that it isn't fundamental.
This seems clear if you define fundamental things as not requiring history or
energy to be defined. If you don't define it that way I'm sure you can come to
a different conclusion.

------
aj7
You kind of lost me with your emphasis on the differential forms of the v-i
relations. As I’ve advanced, the integral relations are more fundamental. The
accumulation of charge on a pair of conductors increases the voltage. The
volt-time integral across an inductor gives rise to the flux therein. Etc.

~~~
bollu
Aren't they equivalent? what makes one "more fundamental" than the other?

~~~
aj7
It’s kind of a cause and effect thing that designers use. Of course, from
calculus, you are right. But for instance in practice, you charge a capacitor
with voltage as the outcome. You don’t look at the voltage, and then
differentiate it to infer the current. Indeed, you get into trouble if you
think you can put an independent voltage source across a capacitor. With an
inductor, you build up the flux by applying a voltage. In both cases, the
fundamental idea is the electric or magnetic field stored energy in the
component, which the component acquires by accumulation, i.e. integration.

------
basicplus2
The credit for the first functional memristor goes to the Hewlett-Packard
Company—in particular, researchers R. Stanley Williams, Dmitri B. Strukov,
Gregory S. Snider, and Duncan R. Stewart—for building a bi-level titanium
dioxide thin film containing dopants (impurities) on one side that migrate to
the other side when a current is applied and back when the opposite current is
applied, changing the resistance in each case. Hewlett-Packard is working on
incorporating memristors into traditional integrated circuits.

[https://www.britannica.com/technology/memristor](https://www.britannica.com/technology/memristor)

------
dfox
In my opinion whatever thing you want to call fundamental circuit element
should have a relationship to the physical reality strong enough that
theoretical model consisting of some idealized conductive solids of trivial-
ish geometry works for most of the practical problems. L, C and R satisfies
this test with various levels of "-ish" (with R being the hard one) and
handwaving, while nobody even knows how to model an memristor in that view.

~~~
ndesaulniers
> while nobody even knows how to model an memristor in that view.

Isn't hysteresis the model? Pretty sure that model was in the original paper
introducing the concept of memristors by Chua, IIRC.

~~~
dfox
My point is that you can take length of insulated wire, do something
relatively trivial to it and end up with single port device that is decidedly
mostly L, C or R. You can not construct practical memristor that way.

~~~
TheOtherHobbes
Indeed you can't. You also can't construct a diode or a transistor.

There are two parallel arguments here. One is yours. The other is whether or
not it's possible to construct a resistor with memory _at all._

It clearly isn't if you all you have is copper wire. But copper wire is only
fundamental in the 19th century pre-semiconductor sense.

None of the practical memristor models assume that. They all rely on junction
effects, spin effects, and other exotica.

~~~
fhars
You are arguing that the memristor is an interesting active device like a
transistor (which it may be, and which isn't addressed by the article). What
the article argues against is the claim that is a the long missing last
fundamental passive device.

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madengr
Someone asked me once if the resistor was really needed as a circuit element.
I postulated that it was not desired, nor needed for any circuit that didn’t
intend to waste energy.

~~~
gmueckl
I will bite and counter that resistors are needed to prevent wasting energy.
Current limiting resistors are used in many different places like low power
electronics (these are always very high resistance) and drivers for electric
motors (a powered electric motor blocked at rest is the same as a short
circuit).

~~~
madengr
Though you can do the same current limiting with a pulse width modulated
switch (similar to a switching power supply).

My point being you can take a resistive element and replace it with a switched
transistor. All ideally of course, since it’s not practical many times.

~~~
magicalhippo
How would you make a constant-current power supply without resistors?

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VonGuard
If Memristors aren't a thing yet, they're never gonna be. This is HP CEO #3 to
be pushing the cursed things when they're still not even market viable.

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Isinlor
Could someone provide a context to this article? Why is it important?

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leowoo91
But how does those results compare to capacitor?

