相变存储材料Ge_1Sb_2Te_4和Ge_2Sb_2Te_5薄膜的结构和电学特性研究

Study of structural and electrical properties of phase-change materials Ge_1Sb_2Te_4 and Ge_2Sb_2Te_5 thin films

采用射频磁控溅射方法制备了两种用于相变存储器的Ge1Sb2Te4和Ge2Sb2Te5相变薄膜材料,对其结构、电学输运性质和恒温下电阻随时间的变化关系进行了比较和分析.X射线衍射(XRD)和原子力显微镜(AFM)的结果表明:随着退火温度的升高,Ge1Sb2Te4薄膜逐步晶化,由非晶态转变为多晶态,表面出现均匀的、高度起伏小于10nm的突起;而对于Ge2Sb2Te5薄膜样品,其结构也从非晶态向多晶态转变,但表面形貌的变化不太明显.霍尔效应测量结果表明,无论是原始淀积的还是退火的样品,Ge1Sb2Te4薄膜的载流子浓度均比Ge2Sb2Te5高三个数量级以上,由此推论:Ge1Sb2Te4较高的电导主要来自其较大的载流子浓度.利用变温探针台测量了Ge1Sb2Te4和Ge2Sb2Te5在相变前恒温条件下电阻随时间变化关系,结果表明在相同的恒温条件下Ge2Sb2Te5电阻保持时间更长,更加有利于数据的存储.

The Ge1Sb2Te4 and Ge2Sb2Te5 thin films were deposited on quartz and silicon substrates by radio frequency magnetron sputtering from Ge1Sb2Te4 and Ge2Sb2Te5 alloy targets. Structure properties and electrical transport characteristics of Ge1Sb2Te4 and Ge2Sb2Te5 thin films were studied and compared. X-ray diffraction spectra and atomic force microscopic images were used to characterize the structure of Ge1Sb2Te4 and Ge2Sb2Te5 before and after thermal annealing. With increasing annealing temperature,Ge1Sb2Te4 crystallized gradually and transformed to polycrystalline state from the amorphous state. Surface of Ge1Sb2Te4 thin films was uniform nanoparticles with roughness less than 10 nm. After thermal annealing,Ge2Sb2Te5 also transformed to polycrystalline state from amorphous state,but its surface morphology did not change significantly compared with the as-deposited film. Results of Hall effect measurement indicated the carrier concentrations of both the as-deposited and annealed films of Ge1Sb2Te4 were three orders of magnitude larger than those of Ge2Sb2Te5. From the above results,we conclude that Ge1Sb2Te4 tends to be more conductive than Ge2Sb2Te5 owing to the larger carrier concentration. Results of resistance versus time measurements under isothermal condition suggested Ge2Sb2Te5is more thermally stable and better fit for data storage than Ge1Sb2Te4.