| AVS 64th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Thursday Sessions |
| Session EM-ThP |
| Session: | Electronic Materials and Photonics Poster Session |
| Presenter: | Kayla Cooley, The Pennsylvania State University |
| Authors: | K. Cooley, The Pennsylvania State University H. Simchi, The Pennsylvania State University H. Aldosari, The Pennsylvania State University J. O'Neil, The Pennsylvania State University S-Y. Yu, The Pennsylvania State University A. Molina, The Pennsylvania State University S.E. Mohney, The Pennsylvania State University |
| Correspondent: | Click to Email |
Germanium telluride is an emerging phase change material (PCM) that has shown exceptional promise for radio frequency (RF) switch technology. When an appropriate heating schedule is applied, this material quickly transitions between crystalline (conductive ON state) and amorphous (highly resistive OFF state). Currently, the contact resistance (Rc) contributes 20-50% of the ON-state resistance of the switch and significantly degrades RF circuit performance. Low-resistance Ohmic contacts that are able to withstand the thermal cycling necessary for changing the phase of GeTe are therefore necessary for successful implementation of GeTe-based RF switches .
We investigated selected contact metals (Ti, Sn, Cr, Mo, Ni, Au, and Pt), resulting in Rc from 0.004 to 0.036 Ω-mm (specific contact resistances of 5 x 10-9 to 4 x 10-7 Ω-cm2) . We also characterized surfaces and interfaces using X-ray photoelectron spectroscopy and transmission electron microscopy with energy dispersive spectroscopy. The lowest Rc values (0.004 ± 0.001 Ω-mm) were achieved using Sn and Mo-based contacts, with Rc ranked according to the first metal deposited as follows: Mo or Sn < Cr < Ti < Au < Ni < Pt. This trend is surprising, as high work function metals, like Au and Pt, would be expected to provide lower Rc values to p+ GeTe.
In the case of Sn-based contacts, low Rc can be attributed to a beneficial interfacial reaction that formed SnTe upon deposition at the contact interface; however, for Mo-based contacts, no such interfacial reaction was observed. Chemical reactions at the interface were not always favorable. In the case of Pt and Ni, the formation of metal tellurides resulted in very high Rc. Thermal stability of all contact metals was also investigated up to 200 oC for 30 min. While Sn and Mo-based contacts performed just as well after annealing, Rc of most other contacts increased. Te sublimation was a common source of thermal instability, with Te crystallites forming on the sides of contacts and within the gap.