Phase-change memory is a form of non-volatile computer random-access memory (RAM) that stores data by altering the state of the matter from which the device is fabricated. While it offers several advantages - such as speed - as an alternative to current memory technologies, it is not the most energy-efficient among emerging memory types.
“People have long expected phase-change memory to replace much of the memory in our phones and laptops,” says Eric Pop, a professor of electrical engineering and senior author of the study. “One reason it hasn’t been adopted is that it requires more power to operate than competing memory technologies. In our study, we’ve shown that phase-change memory can be both fast and energy efficient.”
Unlike conventional memory chips built with transistors and other hardware, a typical phase-change memory device consists of a compound of three chemical elements – germanium, antimony, and tellurium (GST) – sandwiched between two metal electrodes. Conventional devices, like flash drives, store data by switching the flow of electrons on and off - a process symbolized by 1s and 0s.
In phase-change memory, the 1s and 0s represent measurements of electrical resistance in the GST material – how much it resists the flow of electricity.
“A typical phase-change memory device," says doctoral candidate Asir Intisar Khan, co-lead author of the study, "can store two states of resistance: a high-resistance state 0, and a low-resistance state 1. We can switch from 1 to 0 and back again in nanoseconds using heat from electrical pulses generated by the electrodes.”
Heating to about 300°F (150°C) turns the GST compound into a crystalline state with low electrical resistance. At about 1,100°F (600°C), the crystalline atoms become disordered, turning a portion of the compound to an amorphous state with much higher resistance. The large difference in resistance between the amorphous and crystalline states is used to program memory and store data.
The large resistance change is reversible and