Composition Controlled Atomic Layer Deposition of Phase Change Memories and Ovonic Threshold Switches with High Performance.

Chalcogenide compounds are the main characters in a revolution in electronic memories. These materials are used to produce ultra-fast ovonic threshold switches (OTSs) with good selectivity and moderate leakage current and phase change memories (PCMs) with excellent endurance and short read/write times when compared with state-of-the-art FLASH-NANDs. The combination of these two electrical elements is used to fabricate non-volatile memory arrays with a write/access time orders of magnitude shorter than state of the art flash-NANDs. These devices have a pivotal role for the advancement of fields such as artificial intelligence (AI), machine learning (ML), and big-data. Chalcogenide films, at the moment, are deposited by using physical vapor deposition (PVD) techniques that allow for fine control over the stoichiometry of solid solutions but fail in providing the conformality required for developing large-memory-capacity integrated 3D structures. Here we present conformal ALD chalcogenide films with control over the composition of germanium, antimony, and tellurium (GST). By developing a technique to grow elemental Te we demonstrate the ability to deposit conformal, smooth, composition-controlled GST films. We present a thorough physical and chemical characterization of the solids and an in-depth electrical test. We demonstrate the ability to produce both OTS and PCM materials. GeTe4 OTSs exhibit fast switching times ~ 13 ns. Ge2Sb2Te5 ALD PCM exhibit a wide memory window exceeding two-orders-of-magnitude, short write times (~ 100 ns), and a reset current density as low as ~ 107 A/cm2 - performance matching or improving over state of the art PVD PCM devices.