With the amount of NVRAM that’s used these days the amount of innovation in the sector has been comparatively little. For the most part the advances have come from the traditional avenues, die shrinks and new gate technologies, with the biggest advance in 3D construction only happening last week. There’s been musings about other kinds of technology for a long time like memristors which had their first patent granted back in 2007 and were supposed to making their way into our hands late last year, but that never eventuated. However news comes today of a new memory startup that’s promising a lot of things and whilst they don’t say it directly it looks like they might be one of the first to market with memristor based products.
Crossbar is a new company that’s been working in stealth for some time on a new type of memory product which, surprisingly, isn’t anything particularly revolutionary. It’s called Resistive RAM (RRAM) and a little research shows that there’s been companies working on this idea as far back as 2009. It’s based around a fairly interesting phenomena whereby a dielectric, an electric insulator, can be made to conduct through the application of high voltage. This forms a filament of low resistance which can then be reset, breaking the connection, and then set again using another high voltage jolt. This idea lends itself well to applications in memory as the two states translate perfectly to binary and if the specifications are anything to go by the performance that will come out of them should be quite spectacular.
If this is sounding familiar then you’re probably already familiar with the idea of memristors. These are the 4th fundamental component of electronic circuits that were postulated back in 1971 by Leon Chua and were made real by HP in 2007. In a basic sense their resistance is a function of the current following through them and when the current is removed that resistance is remembered, hence their name. As you can see this describes the function of RRAM pretty well and there is a solid argument to be made that all RRAM technologies are in fact memristors. Thus whilst it’s pretty spectacular that a start up has managed to perfect this technology to the point of producing it on a production fab it’s actually technology that’s been brewing for quite some time and one that everyone in the tech world is excited about.
Crossbar’s secret sauce could likely come from their fabrication process as they claim that the way they create their substrate means that they should be able to stack them, much in the same way that Samsung can now do with their VNAND. Now this is exciting because previously HP alluded to the fact that memristor based storage could be made much more dense than NAND, several orders of magnitude more dense to be precise, and considering the density gains Samsung got with their 3D chips a layered memristor device’s storage capacity could be astronomical. Indeed Crossbar claims this much with up to 1TB for a standard chip that could be stacked multiple times, enabling terabytes on a single chip. That puts good old fashioned spinning rust disks on notice as they just couldn’t compete, even when it comes to archival storage. Of course the end price will be a big factor in this but that kind of storage potential could drive the cost per GB through the floor.
So the next couple months are going to be quite interesting as we have Samsung, the undisputed king of NAND, already in the throws of producing some of the most dense storage available with Crossbar (and multiple other companies) readying memristor technology for the masses. In the short term I give the advantage to Samsung as they’ve got the capital and global reach to get their products out to anyone that wants them. However if memristor based products can do even half of what they’re claimed to be capable of they could quickly start eating Samsung’s lunch and I can’t imagine it’d be too long before they either bought the biggest players in the field or developed the technology themselves. Regardless of how this all plays out the storage market is heading for a shake up, one that can’t come quick enough in my opinion.
The computer (or whatever Internet capable device you happen to be viewing this on) is made up of various electronic components. For the most part these are semiconductors, devices which allow the flow of electricity but don’t do it readily, but there’s also a lot of supporting electronics that are what we call fundamental components of electronics. As almost any electrical enthusiast will tell you there are 3 such components: the resistor, capacitor and inductor each of them with their own set of properties that makes them useful in electronic circuits. There’s been speculation of a 4th fundamental component for about 40 years but before I talk about that I’ll need to give you a quick run down on what the current fundamentals properties are.
The resistor is the simplest of the lot, all it does is impede the flow of electricity. They’re quite simple devices, usually a small brown package banded by 4 or more colours which denotes just how resistive it actually is. Resistors are often used as current limiters as the amount of current that can pass through them is directly related to the voltage and level of resistance of said resistor. In essence you can think of them as narrow pathways in which electric current has to squeeze through.
Capacitors are intriguing little devices and can be best thought of as batteries. You’ve seen them if you’ve taken apart any modern device as they’re those little canister looking things attached to the main board of said device. They work by storing charge in an electrostatic field between two metal plates that’s separated by an insulating material called a dielectric. Modern day capacitors are essentially two metal plates and the dielectric rolled up into a cylinder, something which you could see if you cut one open. I’d only recommend doing this with a “solid” capacitor as the dielectrics used in other capacitors are liquids and tend to be rather toxic and/or corrosive.
Inductors are very similar to capacitors in the respect that they also store charge but instead of an electrostatic field they store it in a magnetic field. Again you’ve probably seen them if you’ve cracked open any modern device (or say looked inside your computer) as they look like little circles of metal with wire coiled around them. They’re often referred to as “chokes” as they tend to oppose the current that induces the magnetic field within them and at high frequencies they’ll appear as a break in the circuit, useful if you’re trying to keep alternating current out of your circuit.
For quite a long time these 3 components formed the basis of all electrical theory and nearly any component could be expressed in terms of them. However back in 1971 Leon Chua explored the symmetry between these fundamental components and inferred that there should be a 4th fundamental component, the Memristor. The name is a combination of memory and resistor and Chua stated that this component would not only have the ability to remember its resistance, but also have it changed by passing current through it. Passing current in one direction would increase the resistance and reversing it would decrease it. The implications of such a component would be huge but it wasn’t until 37 years later that the first memristor was created by researchers in HP’s lab division.
What’s really exciting about the memristor is its potential to replace other solid state storage technologies like Flash and DRAM. Due to memristor’s simplicity they are innately fast and, best of all, they can be integrated directly onto the chip of processors. If you look at the breakdown of a current generation processor you’ll notice that a good portion of the silicone used is dedicated to cache, or onboard memory. Memristors have the potential to boost the amount of onboard memory to extraordinary levels, and HP believes they’ll be doing that in just 18 months:
Williams compared HP’s resistive RAM technology against flash and claimed to meet or exceed the performance of flash memory in all categories. Read times are less than 10 nanoseconds and write/erase times are about 0.1-ns. HP is still accumulating endurance cycle data at 10^12 cycles and the retention times are measured in years, he said.
This creates the prospect of adding dense non-volatile memory as an extra layer on top of logic circuitry. “We could offer 2-Gbytes of memory per core on the processor chip. Putting non-volatile memory on top of the logic chip will buy us twenty years of Moore’s Law, said Williams.
To put this in perspective Intel’s current flagship CPU ships with a total of 8MB of cache on the CPU and that’s shared between 4 cores. A similar memristor based CPU would have a whopping 8GB of on board cache, effectively negating the need for external DRAM. Couple this with a memristor based external drive for storage and you’d have a computer that’s literally decades ahead of the curve in terms of what we thought was possible, and Moore’s Law can rest easy for a while.
This kind of technology isn’t you’re usual pie in the sky “it’ll be available in the next 10 years” malarkey, this is the real deal. HP isn’t the only one looking into this either, Samsung (one of the world’s largest flash manufacturers) has also been aggressively pursuing this technology and will likely début products around the same time. For someone like me it’s immensely exciting as it shows that there are still many great technological advances ahead of us, just waiting to be uncovered and put into practice. I can’t wait to see how the first memristor devices perform as it will truly be a generational leap ahead in technology.