Crossbar gets around a nasty obstacle to dense 3D memory chips

Creating 3D memory chips isn’t too hard. But packing the memory cells so they contain a lot of dense storage is a problem that has bedeviled chip makers for a while. Memory chip startup Crossbar said it has figured out a way to create 3D structures with a lot of densely packed circuitry.

The result could be memory chips that can store a ton of data in a very small space. Santa Clara, Calif.-based Crossbar disclosed what it called a breakthrough innovation at the 2014 International Electron Devices Meeting in San Francisco today. It will enable high-density storage with faster response times and lower power consumption. As such, it could be useful in everything from data centers to smartphones.

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Crossbar has developed custom Resistive RAM (random access memory) chips that are aimed at disrupting the $60 billion flash memory chip market. Crossbar can fit a terabyte of data on a chip the size of a postage stamp, and it can access that data 20 times faster than today’s best flash memory, the company says.

The company’s patented invention is the Field Assisted Superlinear Threshold Selector, which is designed to overcome a problem dubbed the sneak path current problem. That unintended current interferes with reliable reading of data from individual memory cells — one of the most challenging hurdles in the industry. Crossbar’s engineers have figured out a way to suppress this sneak path current.

Crossbar said the invention means that its 3D RRAM terabyte-on-a-chip product will soon be ready for commercialization.

“When we unveiled Crossbar RRAM eighteen months ago, we laid out aggressive plans to deliver a new generation of memory capable of scaling to 1 terabyte (TB) on a chip the size of a postage stamp,” said George Minassian, CEO of Crossbar, in a statement. “Crossbar continues to overcome the major technical hurdles that have, in the past, kept others from bringing RRAM to market. With this latest achievement, we are one step closer to commercialization, enabling the implementation of RRAM technology in commercial products; a groundbreaking achievement that will redefine what is possible with enterprise storage and high-capacity non-volatile SoC memories.”

The solution is dubbed 1TnR (1 Transistor driving n Resistive memory cells). It makes it possible for a single transistor to manage a very large number of interconnected memory cells, which enables very high capacity solid-state storage. While 1TnR enables a single transistor to drive over 2,000 memory cells with very low power, it also experiences leakage of a sneak path current that interferes with the performance and reliability of a typical RRAM array. Crossbar’s device solves that leakage problem by utilizing a super linear threshold layer.

In that layer, a volatile conduction path is formed at the threshold voltage. This device is the industry’s first selector capable of suppressing the leakage current at very small dimensions, and it has been successfully demonstrated in a four-megabit test memory chip.

“Without an effective way to suppress the sneak path current, high-density 3D RRAM has been technically unachievable,” said Alan Niebel, founder and CEO of market researcher WebFeet Research. “Crossbar’s selector is the first solution to overcome this design challenge, paving the way for terabyte storage-on-a-chip to become a reality and positioning RRAM as the leading next-generation NAND memory replacement.”

Founded in 2010, Crossbar has funding from Kleiner Perkins Caufield & Byers, Artiman Ventures, Northern Light Venture Capital, the University of Michigan, SAIF Partners, Korea Investment Partners, CBC Capital, and Tao Invest.

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