PE-ALD of GeS amorphous chalcogenide alloys for OTS applications

Three-dimensional (3D) cross-point (X-point) technology, including amorphous chalcogenide-based ovonic threshold switching (OTS) selectors, is bringing new changes to the memory hierarchy for high-performance computing systems. To prepare for future 3D X-point memory scaling, we studied the plasma-enhanced atomic layer deposition (PE-ALD) of Ge 1− x S x amorphous chalcogenide alloy thin films, the selection of which was motivated by their high optical bandgap and wide amorphous forming regions. The PE-ALD Ge 1− x S x thin films were synthesized using a GeCl 4 precursor and H 2 S plasma reactant, and their self-limited growth characteristics were studied in detail as a function of the exposure time of the ALD steps, temperature, and plasma power. The PE-ALD GeS 2 thin film showed an RMS roughness of 0.29 nm and good conformality in the vertical 3D structure. Moreover, the OTS behavior of GeS 2 and Ge 2 S 3 mushroom-type devices with a 50 nm bottom electrode contact (BEC) were investigated as well as the trade-off relationship between the threshold voltage (1.9-6.2 V) and the normalized off current (20-250 nA) based on scaling the film thickness down from 30 nm to 5 nm. In particular, the GeS 2 device showed a higher threshold field (∼3.1 MV cm −1 ) and lower normalized off current characteristics than the Ge 2 S 3 device due to the higher trap density (2.1 × 10 21 cm −3 ), according to the modified Poole-Frenkel (PF) model. The results achieved by this PE-ALD research on this novel binary GeS 2 amorphous chalcogenide for OTS applications will contribute to the development of future 3D cross-point memory scaling. Three-dimensional (3D) cross-point (X-point) technology, including amorphous chalcogenide-based ovonic threshold switching (OTS) selectors, is bringing new changes to the memory hierarchy for high-performance computing systems.