Electronically Tuned Phase Transition in Germanium Telluride (GeTe) Cells for Memory and RF switch Applications

Dushyant Tomer1 , and Ronald A. Coutu, Jr.*

1 Department of Electrical and Computer Engineering, Marquette University, USA 

Abstract: Germanium telluride (GeTe) is a phase change material that undergoes an amorphous to crystalline transition upon heating to ~ 200°C. This transition is reversible in nature and results in ~ six orders of magnitude difference in GeTe resistivity which makes it a suitable candidate for data storage and other functional devices. In this work, micro-size phase change test cells were fabricated by RF sputtering GeTe thin films onto silicon (Si) wafers and Si wafers coated with silicon dioxide (SiO2), silicon nitride (Si3N4), and alumina (Al2O3) films. Two different heating methods, conductive and electrical (i.e., Joule heating), were applied to induce the phase transition mechanism in the GeTe cells. The phase change, obtained from two different heating methods, was investigated using spectroscopic ellipsometry, thermal, electrical and radio-frequency methods. It was observed in ellipsometry that the extinction coefficient, hence the absorption coefficients of GeTe cells increases with amorphous to crystalline phase change. Furthermore, an optical contrast of ∆n + i∆k = -0.858 + i1.056 was also recorded suggesting a sharp transition between phases. In addition, a growth dominated crystallization and fracturing of conductive crystallites when deposited on Al2O3 was noticed in the thermal experiments. A current-voltage (I-V) characteristic, similar to a memory-type device, was observed during the electronic experiments. Finally, radio frequency (RF) measurements were performed on GeTe cells to investigate the capability of being utilized as improved RF switches. 

Key words: phase change materials, electronic memory, germanium telluride, RF switching