Atomic layer deposition of germanium-selenium-tellurium compounds for low-leakage, tunable ovonic threshold switches

Abstract

Chalcogenide compounds are leading a revolution in the electronic memories space. Phase-change-memory (PCM) elements and ovonic threshold switches (OTSs) combined in the cross-point (X-point) architecture produce memory arrays with access and write times orders of magnitude faster than state-of-the-art flash nands and also provide nonvolatile storage, a larger scale of integration compared to traditional memory arrays, and the opportunity to develop beyond von Neumann architectures to support computationally demanding applications such as artificial intelligence. The commercial success of chalcogenide X-point arrays will depend on the ability to integrate chalcogenide films into sophisticated three-dimensional architectures such as vertical structures for economical manufacturing. To do so, highly conformal deposition techniques are required such as atomic layer deposition (ALD). State-of-the-art chalcogenide cross-point devices are currently fabricated using PVD, which fails to provide any film conformality. ALD PCMs with performance comparable to their PVD counterparts have been demonstrated; however, fabricating OTS selectors using ALD remains a challenge. Here, we present an approach to deposit ALD ternary germanium-selenium-tellurium (Ge-Se-Te) spanning a wide range of compositions. The ALD Ge-Se-Te films show excellent conformality, low surface roughness, and good compositional homogeneity. We fabricated OTS devices and demonstrated the ability to produce low leakage selectors with threshold voltage tuning achieved by control over the film composition.