零密度变化的Ge-Sb基新型相变存储材料研究

Phase-change memory (PCM) has the potential to become the next-generation memory devices. It takes advantage of the fast reversible transition between the crystalline and amorphous phases and their large resistivity contrast. Despite of its great applications, the density change during the phase transition will lead to large stress, significantly limiting the life of devices. The project will focus on a zero-density-change PCM, which is based on the Te-free Ge-Sb material. Compared with the widely used chalcogenides Ge-Sb-Te (GST), the chalcogen-free Ge-Sb compounds have many advantages such as fast phase transition and long archival life time. The mass density difference between crystal and glass of Ge-Sb is also better than GST (Ge-Sb 5% versus GST 6~7%). To further reduce the density difference, we plan to dope elements such as C, O, N, Ga into the Ge-Sb material. Strong covalent bonds are expected to form between those dopants and Ge/Sb so that vacancies/voids are largely eliminated, and hence the volume change during the phase transition could be reduced. We anticipate to discover 2~3 useful PCMs with density change less than 3% (or even achieve the zero-density change). The development of such zero-density-change PCM will significantly increase the stability of devices, improve the capacity of large-scale integration, and meet the national strategy to develop high-density memory devices.

相变存储是下一代高密度存储器的候选技术之一。它利用相变材料晶体和非晶体的可逆相变以及较大的电阻差来实现信息的存储。然而，由于其在相变前后的密度差，导致存储单元在工作时会产生较大的应力，严重影响了器件的使用寿命。本项目将集中研发一种几乎没有密度变化的相变存储材料。我们的研究基于一种不含Te的Ge-Sb材料，它相比起以往常用的由Ge-Sb-Te (GST)组成的硫系化合物有着相变速度快、数据保存时间长的优点。同时，Ge-Sb相变密度差较GST也有较大的改善(Ge-Sb: 5%，GST: 6~8%)。为进一步减小其密度差，我们对其进行C、O、N、Ga等共价元素的掺杂。这些杂质元素能够与Ge和Sb形成较强的共价化学键，减少晶体转变到非晶过程中微空洞的产生，从而降低了相变过程中的体积变化。研发出这种零密度变化的相变存储介质将大大提高器件的稳定性和集成度，迎合我国发展自主研发的高密度存储器的战略目标。

相变存储器是下一代非易失存储器的重要候选技术之一，但是由于其晶体与非晶体之间快速切换的工作机理，导致其存在稳定性和工作寿命等缺陷，尤其是大部分相变材料的晶体和非晶体存在较大的密度差（>7%），使得在多次循环擦写过程中出现空洞最后导致器件失效。本项目通过高通量计算筛选了若干低密度变化的相变存储材料，并通过实验手段验证了低密度变化特性，同时也保证这些材料能够进行擦写操作。研究发现了多种低密度变化的相变材料，例如GeSbC、CrGeTe等。研究结果为国产相变存储器的材料研发提供了有力的支持，成果在Advanced Functional Materials、Advanced Electronic Materials、Journal of Materials Chemistry C等高水平期刊报道，发表相关论文11篇，申请专利6项，其中4项已经授权并实现转化。培养博士后3名，博士研究生4名，硕士研究生4名，大部分已毕业学生仍在关键岗位从事相变存储相关研发。