Plan view scanning transmission electron microscopy was used to investigate the microstructural connections to device resistance in inline phase change switch devices. It was revealed that massive structural changes occur in GeTe during switching, most notably the formation of an assembly of voids along the device centerline and large GeTe grains on either side of an "active region." Restructuring of this variety was tied to changes in ON-state resistance with increasing pulse number, where initially porous and fine-grained (10-20 nm) GeTe was converted to large crystalline domains comprising the majority of the RF gap (400-700 nm). A phenomenological model for this microstructure is presented in which the OFF pulse melts a given width of GeTe, and upon cooling crystalline material outside the melt region acts as a template for an inward-propagating crystalline growth front. The voids observed along the device centerline were correlated to increasing OFF state resistance and a relatively stable ON state with increasing pulse number via a series resistance model. As a result of this analysis, OFF state resistance was suggested as an early indicator of device reliability. An improved GeTe deposition process was implemented to limit void formation, which is shown to have a more stable OFF-state resistance with increasing pulse number.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)