The recent announcement that Rice University grad student Jun Yao has demonstrated a new memory device has created a stir. As well it should.
The new device is non-volatile, offers fast sub-100 ns switching times, can be written 10,000 times and is fully compatible with current CMOS manufacturing processes. A 1,000 bit proof-of-concept chip has been built by a private company.
Those specs are better than or equal to current MLC NAND flash, but there are 3 other important advantages:
- Size: devices are only 5 nm wide - 1/5th the feature size of the latest flash devices - which means much higher storage capacity.
- Capacity: the architecture lends itself to stacking multiple dies - so-called 3D chips - to create even higher capacity devices.
- Simplicity: it is a 2 terminal memory, not 3 as in most memories. This reduces device size and complexity.
The device
The device uses silicon oxide (SiOx), a universal component of semiconductor devices for decades, in a novel way. The SiOx is used to create a conductor - not an insulator.
From the Rice press release:
Applying a charge to the electrodes created a conductive pathway by stripping oxygen atoms from the silicon oxide and forming a chain of nano-sized silicon crystals. Once formed, the chain can be repeatedly broken and reconnected by applying a pulse of varying voltage.
I did not find a mention of the voltage needed to form the chain, but given the feature size and mechanism I’d expect it to be much less than the 20 volts required to pump NAND flash. If correct that should also reduce the chance of catastrophic die failure when the insulation shorts out.
Here’s a graphic that starts at the chip level and goes down to the nanocrystal level:
Why the limited write/erase lifespan? Presumably the local region runs out of nearby oxygen atoms, stopping the process, accounting for the ≈10,000 write limit. Clever materials or manufacturing process engineering might increase that limit.
The Storage Bits take
It’s great to see something novel found in such a common material as SiOx. Professor James Tour, in whose lab Jun Yao works, says SiOx is one of the most studied materials on earth.
Flash designers have been sounding alarms because they aren’t sure they can go below 20nm feature sizes - a fast approaching limit. Of course, storage and semiconductor engineers have been sounding alarms for decades: that’s how you keep the suits funding research.
But this development has great promise not only for its theoretical capabilities, but because it creates technological competition. We’ll all benefit from that.
Comments welcome, of course.
