A way of making highly manufacturable memristors which switch a hundred times faster than flash and use a hundred times less energy to switch, has been accidentally discovered at University College, London (UCL).
UCL’s Anthony Kenyon and a team of researchers were working on LEDs when they accidentally discovered that a the silicon oxide on their devices behaved in the same way as a memristor.
This means memristors don’t need exotic materials and don’t need low temperatures to work.
Kenyon’s team reports: ‘A study of resistive switching in a silicon-based memristor/resistive RAM (RRAM) device in which the active layer is silicon-rich silica. The resistive switching phenomenon is an intrinsic property of the silicon-rich oxide layer and does not depend on the diffusion of metallic ions to form conductive paths. In contrast to other work in the literature, switching occurs in ambient conditions, and is not limited to the surface of the active material.’
The researchers propose: ‘A switching mechanism driven by competing field-driven formation and current-driven destruction of filamentary conductive pathways.’
The team demonstrates: ‘That conduction is dominated by trap assisted tunneling through noncontinuous conduction paths consisting of silicon nanoinclusions in a highly nonstoichiometric suboxide phase. We hypothesize that such nanoinclusions nucleate preferentially at internal grain boundaries in nanostructured films. Switching exhibits the pinched hysteresis I/V loop characteristic of memristive systems, and on/off resistance ratios of 104:1 or higher can be easily achieved.’
The UCL memristor’s programming currents can be as low as 2 μA, and transition times are on the nanosecond scale.
The energy to switch is a hundredth the energy needed in flash and the switching speed is much higher. Kenyon points out that flash switches at 10 microseconds while their memristor switches at least as fast as 90 nanoseconds.
He says his equipment can only measure speeds as fast as 90ns and his memristors are at least as fast as that.
Last October, in Seville, HP senior fellow Stan Williams told IEF2011 that HP intended to have a memristor alternative technology to flash on the market in eighteen months, an alternative to DRAM in three to four years and, following DRAM, a replacement for SRAM.
“We’re planning to put a replacement chip on the market to go up against flash within a year and a half,” said Williams, “and we also intend to have an SSD replacement available in a year and a half.”
“In 2014 possibly, or certainly by 2015, we will have a competitor for DRAM and then we’ll replace SRAM,” said Williams.
“Flash is a done deal,” said Williams, “now we’re going after DRAM, and we think we can do two orders of magnitude improvement in terms of switching energy per bit.”
HP’s technology allows the memory layers to be put directly on top of the processor layer making for very fast systems on chip.
“We put the non-volatile memory right on top of the processor chip, and, because you’re not shipping data off-chip, that means we get the equivalent of 20 years of Moore’s Law performance improvement,” said Williams.
“We’re running hundreds of wafers through the fab,” said Williams, we’re way ahead of where we thought we would be at this moment in time.”
HP’s approach is memristor thin film technology which it allows it to stack an “arbitrary number of layers,” said Williams, with 500bn memristors per layer at 5nm.
However HP had no plans to make memristors, said Williams, it was looking to license it.