Ultra-Low Switching Current Phase-Change Memory On A Flexible Substrate

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Researchers from Stanford University have overcome a key obstacle that has limited widespread adoption of phase-change memory.

As cloud-based applications and big data platforms have increased, the need for data storage infrastructure increases linearly, and as a result, power consumption increases significantly.  In past decades, researchers and scientists have searched for faster, more energy-efficient data storage technologies for everything from large data centers to mobile sensors and other flexible electronics. Among the most promising data storage technologies, phase-change memory  is thousands of times faster than conventional hard drives but uses a lot of electricity.

Phase-change memory is a type of non-volatile random-access memory which takes advantage of rapid heat-controlled changes in the material’s physical property between amorphous and crystalline states. A typical phase-change memory consists of a compound of three chemical elements—germanium, antimony and tellurium (GST)—sandwiched between two metal electrodes.

In phase-change memories, the 1s and 0s represent measurements of electrical resistance in the GST material. A high-resistance state 0, and a low-resistance state 1. The resistance states can switch from 1 to 0 and back again in nanoseconds using heat from electrical pulses generated by the electrodes.

Heating to about 300 degrees Fahrenheit turns the GST compound into a crystalline state with low electrical resistance. At about 1,100 F, the crystalline atoms become disordered, turning a portion of the compound to an amorphous state with much higher resistance.

But switching between states typically requires a lot of power, which could reduce battery life in mobile electronics. To address this issue, researchers from Stanford University have designed a phase-change memory cell that operates with low power and can be embedded on flexible plastic substrates commonly used in bendable smartphones, wearable body sensors and other battery-operated mobile electronics.

However, many flexible substrates lose their shape or even melt at around 390 F. Researchers discovered that a plastic substrate with low thermal conductivity can help reduce current flow in the memory cell, allowing it to operate efficiently. 

“Our new device lowered the programming current density by a factor of 10 on a flexible substrate and by a factor of 100 on rigid silicon,” said Eric Pop, a professor of electrical engineering and senior author of the study. “Three ingredients went into our secret sauce: A superlattice consisting of nanosized layers of the memory material, a pore cell—a nanosized hole into which we stuffed the superlattice layers—and a thermally insulating flexible substrate. Together, they significantly improved energy efficiency.”

The research has been published in the journal Science.


 

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