In-situ crystallization of GeTe\GaSb phase change memory stacked films

Abstract

Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 C and 198 C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 C. Furthermore, at 210 C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples. V

Thermal Stress Effect on the Structure and Properties of Single and Double Stacked Films of GeTe and SnSe

“…Fcc Ge (ICDD PDF# 00‐004‐0545) might also be present but its crystalline peaks closely overlap Te peaks. Ge and Te phase segregation is common in annealed GeTe films and it was observed previously …”

“…Migration of Sn from the top to the bottom layer was observed in GeTe\SnTe and GeTe\SnSe at high temperatures and the formation of a Ge x Sn 1− x Te solid solution. Since GeTe is known to have a crystalline structure with many vacancies, foreign atoms can easily diffuse in its structure, as it was also observed with Ga atoms in GeTe\GaSb double stacked film …”

Chalcogenide Science in Romania

“…A new material with the required thermal stability was predicted. In another study, [ 30 ] the possibility to record multiple states in a single memory cell by stacking several films of phase‐change materials was investigated. Two binary materials were used: a chalcogenide GeTe [ 31 ] and a pnitcogenide GaSb, each of them with its advantages.…”

Overview of Probe-based Storage Technologies

“…Therefore, three data values “0”, “1”, and “2” can be assigned to these three resistance states, respectively, allowing for multi-level operations in phase-change probe memory. In addition to the use of conductive AFM, scanning thermal microscopy (SThM) was recently reported to have the capability of measuring the thermal conductivities and thermal boundary resistances of GeTe (GT) and GST thin films [ 112 , 113 ]. During the measurement, the SThM probe is repeatedly brought into and out of contact with material surface and the thermal properties of the probed materials can be determined by measuring the comparison of the heat flow from the SThM probe before and after the contact.…”