应用于相变存储器的硅掺杂锗锑碲相变材料制备及光电性质

发布时间：2018-02-26 17:05

  本文关键词： 相变随机存储器 锗锑碲相变材料 硅掺杂 数据保持时间 结晶激活能 光学带隙 擦除写入过程 开关特性　出处：《南京大学》2012年硕士论文　论文类型：学位论文

【摘要】：相变随机存储器(Phase-change Random Accessed Memory,PCRAM)是利用相变材料的可逆转的相变来存储信息的一种新型存储器,被认为是未来替代随机存储器(DRAM)的最优选择之一。本文以si掺杂锗锑碲(GST)相变材料为中心。对电子束蒸发制备Si掺杂GST相变材料的热致相变过程以及其光电特性进行了研究,并利用PCRAM原型器件对相变材料的开关特性进行了初步研究。 我们利用电子束蒸发系统和Si掺杂Ge2Sb2Te5靶材制备了Si-GST相变材料薄膜。利用实验方法研究了不同掺杂浓度的Si-GST相变材料的热致相变过程。Si-GST薄膜方块电阻在原位热退火的过程中发生两次明显的下降,对应两次相变过程。通过与纯GST薄膜的热致相变的过程的对比,可以看出：Si掺杂在增大了薄膜晶态方块电阻的同时维持了晶态非晶态之间必需的“开关比”。计算了不同掺杂浓度Si-GST薄膜的结晶激活能,Si原子摩尔比分别为4.76at.%、13.0at.%和16.7at.%的Si-GST薄膜估算其结晶激活能分别为：3.51eV、4.05eV和4.23eV。利用原位恒温退火方法对不同掺杂浓度Si-GST薄膜进行研究,通过外推法,推算出在80℃时不同Si-GST薄膜的数据保持时间均能达到十年(3×108s)以上。 利用分光光度计对不同掺杂浓度的Si-GST薄膜的光学性质进行了研究,确定了它们的吸收系数,结合公式拟合得出了不同掺杂比例Si-GST薄膜在晶态和非晶态时的光学带隙。结果表明,Si掺杂增大了GST225薄膜的光学带隙,分别为非晶态下的约0.85eV和晶态下的最低0.51eV。Si-GST薄膜的晶态光学带隙随着掺杂浓度的增大而线性增大；而非晶态的Si-GST薄膜的光学带隙在不同的掺杂浓度下基本保持在0.85eV附近,在误差范围内基本相同。 制作了PCRAM存储单元原型器件,对相变材料开关特性进行了初步研究。发现,相变存储单元均能完成写入和擦除的过程。纯GST有源层器件的平均阈值电压为1.6V,Si掺杂GST有源层(9.09at.%)平均阈值电压为2.6V。Si掺杂使器件的平均阈值电压有所提高,增大了有源层晶态电阻,降低了擦写电流,有效降低了工作功率。对不同有源层厚度的器件研究表明,发现平均阈值电压与样品厚度成正比,对于同一组分的相变材料,不同有源层厚度的器件平均阈值场强基本保持一致。
[Abstract]:Phase-change Random Accessed memory (PCRAM) is a new type of memory that uses the reversible phase transition of phase change materials to store information. It is considered as one of the best alternatives to random access memory (RAM) in the future. In this paper, the thermal phase transition process and its photoelectric properties of Si-doped GST phase change materials prepared by electron beam evaporation have been studied, focusing on si doped antimony germanium tellurium phase change materials. The switching characteristics of phase change materials are studied by using PCRAM prototype device. We have prepared Si-GST phase change material thin films by electron beam evaporation system and Si doped Ge2Sb2Te5 target. The thermal induced phase transition process of Si-GST phase change materials with different doping concentration. Si-GST thin film sheet resistance in situ thermal degradation has been studied by experimental method. There have been two distinct drops in the course of the fire, By comparing with the thermo-induced phase transition of pure GST thin films, It can be seen that the ratio of Si atoms to Si atoms in Si-GST films with different doping concentration is 4.76at.130at.% and 16.7 at.%, respectively, while increasing the square resistance of crystalline state while maintaining the "switching ratio" between crystalline and amorphous states. The activation energies of Si atoms are 4.76at.% and 16.7at.%, respectively. The crystallization activation energies of Si-GST thin films were estimated to be 4.05 EV and 4.23 EV, respectively. In situ constant temperature annealing method was used to study Si-GST films with different doping concentrations. By extrapolation, the data retention time of different Si-GST films at 80 鈩，

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