Phase-change random access memory, or PRAM, is a nonvolatile technology that works by the rapid heating of a chalcogenide material, which shifts it between its crystalline and amorphous states. These two states have different electrical resistances, which are used to represent the bits 0 and 1. Manipulation of these bits is the basis of computer programming.
Researchers from Japan’s LEAP project will discuss fundamental work they conducted with a new type of PRAM they call “topological-switching random-access memory,” or TRAM. It stores data according to the movement of germanium (Ge) atoms in the material’s GeTe/Sb2Te3 crystal superlattice (its atomic structure). It requires much less programming energy than the traditional chalcogenide-based PRAM to change states (as little as 1/20th).
The researchers built TRAM devices that operated with a set/reset current as low as 55 µA, the lowest for any ultra-dense memory. Electron microscope observations revealed Ge-Te and Sb-Te sequences in the superlattice, which the researchers used to understand the retention and endurance characteristics of the TRAM. They also fabricated superlattices with 6-nm-thick Sb2Te3 layers and others with composite bottom layers to understand TRAM electrical characteristics.
(Paper #29.2, “55-µA GexTe1-x/Sb2Te3 Superlattice Topological-Switching Random-Access Memory (TRAM) and Study of Atomic Arrangement in Ge-Te and Sb-Te Structures,” N. Takaura et al, Low-Power Electronics Association and Project (LEAP))