Comment by mindslight | Hacker News Reader

Comment by mindslight | Hacker News Reader

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> it must somehow follow that parasitic mem-resistance must have been with us all along

I'm not so sure about that. It's impossible to make things without unwanted series/parallel resistances because conductors/insulators aren't perfect. It's impossible to make things without parasitic capacitance because without a perfect insulator, any two points have some capacitance between them - just like how there's also a parasitic gas discharge tube if the electric field between terminals reaches the dielectric breakdown voltage of air (this is another two terminal device, it's just not linear). These are all well-known physical phenomena that we deliberately assume away when we draw simple schematic symbols on paper, and then have to add back in when they end up applying.

Constraining the domain to two-terminal AND passive AND linear devices, one will have a very small number of possibilities for equations that describe them. Good old R/C/L that we know and love, and purportedly "M". But what is THE physical process that M describes and therefore gets made interesting by?

One could create a battery-powered opamp circuit that had two external terminals and fulfilled whatever equation you dreamed up (once again up to the limit of your abstraction, in this case constrained to lower frequencies). But the existence of that equation/device doesn't imply that there has to be a low-level physical phenomenon that will let you directly implement it.

Every time I try to read about memristors, I grok the bits in isolation, but mostly come away confused. C and L have state as well, and would also make great computer memory but for those nasty parasitic effects. From the wikipedia page: researchers everywhere are working on memristors, yet memristance was documented 200 years ago, yet the creator is arguing that the definition applies to phase change ram? I almost feel it's the "Cloud" of device physics research.

The big problem is that your two terminal battery powered op-amp circuit would (1) sooner or later run out of battery power and (2) would have to exhibit it's memory function through some 'ordinary' memory device.

If we're going to use 'ordinary' memory devices anyway then the whole exercise is moot.

What exactly drives 'M' is the billion dollar (and probably many billions of dollars) question...

It's more like the cold fusion of semiconductors, but apparently they have something. I'll hold off any judgment until they do their unveiling, but this had better be good and not yet another promise.

Yes, either linear memory devices like C/L, or creating digital memory cells out of positive feed back hysteresis. Running out of battery is just one of the limits of the abstraction. I mean it as a mental exercise in demonstrating that one can easily build a circuit that fulfills the equation of a memristor - does its mere emulated existence make it interesting? Why aren't these "emulated memristors" (obviously with a third terminal for a power supply, a different abstraction limit) a standard building block of modern circuits, even in just hobbyist discrete form?

I'm sure there are specific devices being worked on that have exciting applications to memory, and I'm certainly not putting down the researchers involved with them or their work. But it seems like the "memristor" narrative is a bit of a hype train that has taken on a life of it's own. Let's say one team of researchers were to develop a miniature device with a similar but decidedly non-linear effect. Would this make it any less important?

(And if my judgment is wrong and we end up with an entirely new family of passives based on the same fundamental physics with usual differentiation based on power handling/size/etc, I'll be happy to eat my words).

> And if my judgment is wrong and we end up with an entirely new family of passives based on the same fundamental physics with usual differentiation based on power handling/size/etc, I'll be happy to eat my words

That will be the best case ever of being happy to be wrong. If true the implications are on par with some pretty advanced SF in terms of computing power and storage. Content addressable memory anybody?

Every effect is linear if you constraint your domain enough.

But you are right - the real news is more that we've got a new way to manufacture some type of memory storage element (that's also conveniently fundamentally tiny).

It is definitely not the only way though: IBMs been working on magnetic racetrack memory for some time which would have many of the same advantages.

Magnetic racetrack sounds like bubble memory warmed over with associated feelings. The good news is that 'bubbles' are real, they just never broke through commercially.

http://en.wikipedia.org/wiki/Bubble_memory

vs

http://en.wikipedia.org/wiki/Racetrack_memory

So many common elements.

memristors, like core memory, are destructively read. You measure the current to set them to 1 capturing the ones where you needed more current (they were zero initially) and the ones that needed less current (they were one initially). You capture the state in a register, and in the second half of the cycle you write the zeros back where the register shows the were originally zero.

As core memory before it showed, you can do this with sufficient accuracy if the hysteresis difference is large enough. The only requirement is that it take a different amount of current to set it to a known state if it was already in that state, than it does to set it to the same known state when it was in the opposite state.

memristors, like core memory, are destructively read but are they really, with HP implementation - which is not a "real" memristor? In the video presentation [1] they show that they change the state of the memristor using very short "high" voltage impulses, and then measure its resistance using lower voltages that do not make the oxygen vacancies migrate - and thus do not change the state, if I understood that correctly.

If they can use these low voltages (and low currents) to effectively read the state without altering it, they get incredibly simplified management of the memory, and incredibly low power read operations, which would justify their assertion that their memristors can be packed in 3d without thermal problems.

[1] https://www.youtube.com/watch?v=bKGhvKyjgLY

>It's impossible to make things without parasitic capacitance because without a perfect insulator...

Maybe a nit, but I don't believe that is technically correct. Parasitic capacitance (and inductance) exist between any two objects because the electric (and magnetic) field extend from a charge (or current) to infinity. These fields store energy, even in perfect vacuum. The lumped circuit model of stored electric energy is capacitance, the model of stored magnetic energy is inductance so anything physical which carries charge or current will have capacitance or inductance (will store finite energy). An insulating material (dielectric) in a capacitor can increase the energy storage (by the sqrt of the dielectric constant of the material) but non-ideal materials are not necessary for the "parasitic" effect to occur.

Any signal that has some non-zero propagation time also needs proportionally high capacitances/inductances because of the energy storage requirement you mentioned (resistors are memoryless so can't model that).

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