Self-shocks turn crystal to glass at ultralow power density

Researchers have shown that utilizing shallow power, a crystalline material called indium selenide can “shock” itself to a glassy phase. This transformation lies at the heart of memory storage in devices like CDs and computer RAMs. It uses a billion times less electricity than the traditional melt-quench process for converting crystal to glass, and the discovery might revolutionise data storage in gadgets ranging from cell phones to computers. 

Glasses function similarly to solids but lack the regular periodic arrangement of atoms. To avoid the glass from getting too organized, a crystal is liquefied (melted) and then rapidly chilled (quenched) during the manufacturing process. This melt-quench technique is also employed in CDs, DVDs, and Blu-ray discs, where laser pulses are used to rapidly heat and quench a crystalline material to the glassy phase in order to write data; reversing the process erases data. Computers use similar materials known as phase-change RAMs, in which information is stored depending on the high versus low resistance provided by the glassy and crystalline phases.

The difficulty is that these devices consume more power, particularly during the writing process. The crystals must be heated to temperatures exceeding 800^oC and then rapidly cooled. If it is possible to convert the crystal directly to glass without using the intermediate liquid phase, the amount of power required for memory storage can be greatly reduced. 

 A team of researchers from the Indian Institute of Science (IISc), Bangalore, University of Pennsylvania School of Engineering and Applied Science (Penn Engineering), Pennsylvania and Massachusetts Institute of Technology (MIT), Harvard, USA discovered that when electric current was passed through wires made of indium selenide, a 2D ferroelectric material, long stretches of the material transformed into glass. These breakthrough findings were published in the journal Nature. The research was supported by ANRF (erstwhile SERB) established through an Act of Parliament: ANRF, Act 2023.

The scientists unearthed that when a continuous current is passed parallel to the material’s 2D layers, they slide against each other in various directions. This results in the formation of many domains – tiny pockets with a specific dipole moment enclosed by defective regions that separate the domains. When multiple defects intersect in a small nanoscopic region, like too many holes punched in a wall, the structural integrity of the crystal collapses to form glass locally. 

These domain boundaries are like tectonic plates. They move with the electric field, and when they collide against each other, mechanical (and electrical) shocks are generated akin to an earthquake. This earthquake triggers an avalanche effect, causing disturbances far away from the epicentre, creating more domain boundaries and resulting glassy regions, which in turn spawns more earthquakes. The avalanche stops when the entire material turns into glass (long-range amorphisation). 

Prof. Nukala points out that multiple unique properties of indium selenide – its 2D structure, ferro electricity and piezoelectricity – all come together to allow this ultralow energy pathway for amorphisation through shocks. He further emphasized that the current findings will unlock a wider range of phase-change memory (PCM) applications.