Periodic cycle number modulating effect on crystallization temperature in superlattice-like [Ge/Ge8Sb92]n phase-change films and exploration of mechanism

Xinyi Liu,Tianshu Lai,Yifeng Hu

doi:10.1063/1.4986879

Abstract

Superlattice-like (SLL) phase-change films provide more controllable parameters for the optimization of the performance of phase-change films, including the thickness of each constituent layer, the thickness ratio of two constituent layers and cycle number of periodicity. The effects of the first two parameters on the performance of SLL films have been studied widely. However, the influence of last parameter, cycle number of periodicity, was studied sparsely. In this study, we have studied the period number effect on crystallization temperature of SLL [Ge/Ge8Sb92]n films, and designed and fabricated a series of superlattice-like (SLL) [Ge/Ge8Sb92]n phase-change films. Their crystallization behaviors are studied by the measurement of temperature-dependent sheet resistance. We find that crystallization temperature decreases with increasing cycle number of periodicity, revealing period-cycle-number modulation effect. However, such the effect cannot be explained by current interface effect model. We test the existence of periodic structures of the crystallized SLL films by coherent acoustic phonon (CAP) spectroscopy. Apparent folded CAP modes related to SLL nanostructures are observed, implying the existence of excellent periodic structures or no alloying within one period in crystallized SLL films. Therefore, such period number manipulation effect cannot be explained by the cooperative effects of interface and alloying effects either, implying new mechanisms to be unveiled. We tentatively propose two kinds of possible long-range effects, built-in electric field and strain effects. Based on strain effect, our results can be explained phenomenologically.

Highlights

INTRODUCTIONCrystallization rate and not raise the resistance of crystallized Ge20Sb80 films. Obviously, it is difficult for alone doping simultaneously to optimize multiple parameters, thermal stability, crystallization speed and power consumption etc
Phase change random access memory (PCRAM) is recognized as most promising one of generation of non-volatile data memories[1] due to its potential excellent performances, such as high density, high speed, long thermal stability, low power consumption and large cycle number of reversible transitions etc
We further study the existence of nano-periodic structures in SLL films using coherent acoustic phonon spectroscopy which is non-contact and non-destructive

Summary

INTRODUCTION

Crystallization rate and not raise the resistance of crystallized Ge20Sb80 films. Obviously, it is difficult for alone doping simultaneously to optimize multiple parameters, thermal stability, crystallization speed and power consumption etc. The opinion of alloying within one period was not supported by experimental facts reported.[6,11,12] Wang et al[6] observed cross-section of SLL [Si (5 nm)/Sb80Te20 (5 nm)]10 films by TEM, and achieved clear layer-structured images either before or after crystallization of SLL [Si (5 nm)/Sb80Te20 (5 nm)]10 films. It was found that Al doping raised crystallization temperature, while sandwich structure reduced that of GeSb film Those experimental facts mentioned above did not support the opinion of alloying within a single period in SLL films. We still find that crystallization temperature reduces with increasing n, similar to the phenomena reported by Zhu et al.[10] We further study the existence of nano-periodic structures in SLL films using coherent acoustic phonon spectroscopy which is non-contact and non-destructive. We tentatively propose a strain effect, and explain the period number manipulation effect phenomenologically based on the strain effect

SAMPLES AND EXPERIMENTAL METHODS

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CONCLUSIONS