Effect of Electrode Material on the Crystallization of GeTe Grown by Atomic Layer Deposition for Phase Change Random Access Memory.

Seung Ik Oh,Seok Choi,Taeyong Eom,Byung Joon Choi,Chanyoung Yoo,Cheol Seong Hwang,In Hyuk Im,Sung Yeon Ryu,Yong Kim

doi:10.3390/mi10050281

Abstract

The electrical switching behavior of the GeTe phase-changing material grown by atomic layer deposition is characterized for the phase change random access memory (PCRAM) application. Planar-type PCRAM devices are fabricated with a TiN or W bottom electrode (BE). The crystallization behavior is characterized by applying an electrical pulse train and analyzed by applying the Johnson–Mehl–Avrami kinetics model. The device with TiN BE shows a high Avrami coefficient (>4), meaning that continuous and multiple nucleations occur during crystallization (set switching). Meanwhile, the device with W BE shows a smaller Avrami coefficient (~3), representing retarded nucleation during the crystallization. In addition, larger voltage and power are necessary for crystallization in case of the device with W BE. It is believed that the thermal conductivity of the BE material affects the temperature distribution in the device, resulting in different crystallization kinetics and set switching behavior.

Highlights

Given the recent ever-increasing growth of the memory market, research on low-power, high-speed, and high-density nonvolatile memory for the generation is being actively conducted
Phase change random access memory (PCRAM)—one of the next-generation memory candidates—utilizes a reversible phase change between amorphous and crystalline phases through Joule heating generated by the current passing through a nanoscale device [1,2,3]
PCRAM has been seriously considered as a new storage-class memory and can be used for 3D Xpoint memory owing to its high read/write speed, high density, and nonvolatile characteristics [4,5]

Summary

Introduction

Given the recent ever-increasing growth of the memory market, research on low-power, high-speed, and high-density nonvolatile memory for the generation is being actively conducted. Between the two memory operations, i.e., switching from the amorphous to crystalline state (set) and that from the crystalline to amorphous state (reset), reset takes higher current consumption because it involves the (local) melt-quenching process of the phase change material. The different BE materials can have different interface energies, which influences the heterogeneous nucleation of the crystalline seed They can have different thermal conductivities, which can influence the thermal efficiency and local temperature, which critically increases the overall nucleation and growth of the crystalline phase. It is necessary to study the effect of electrode material on the device characteristics to understand the crystallization process in PCRAM operation. An atomic-layer-deposited GeTe-based PCRAM device was fabricated on TiN and W as BE, and the effect of electrode material on the crystallization of the GeTe phase-changing material was investigated. An electro-thermal simulation was conducted to understand the thermal effect of BE material in determining the crystallization process

Materials and Methods

Results

Discussion