非揮發記憶體用銻基相變化材料開發

Novel Antimony-based Phase Change Materials

洪敬懿(Ching-Yi Hung)

指導教授 ： 金重勳

國立清華大學/工學院/材料科學工程學系/碩士(2008年)

https://doi.org/10.6843/NTHU.2008.00470

摘要

相變化記憶體(phase change memory)為近年來受高度重視之非揮發性記憶體，利用電流脈衝在高阻態與低阻態間作可逆之相變化而達成儲存之目的。Ge2Sb2Te5為一習用於相變化記錄之相變材料，以材料的觀點切入，仍存在許多缺點與值得增進之處：碲為低熔點與高蒸氣壓之有毒元素易導致材料內部之相分離；此外，Ge2Sb2Te5之低結晶溫度(~160 ℃)使資料高溫穩定性略顯不足而其高熔點(613 ℃)會造成操作時過多的能量消耗。本實驗以開發二元與三元銻基合金為目標。銻為非硫屬元素且銻基材料具有成長控制型結晶機制，可於非晶態與結晶態間作快速之相轉換。
在MgxSb100-x (x= 24 ~ 57 at.%)系統開發中，Mg含量越高使得晶格排列更為散亂而達到提升初鍍態與結晶態電阻率之效果，且均具有相轉換之特性。隨Mg含量增高從兩階之相轉換合而為一。此外，運用非恆溫與恆溫結晶動力學可推導其結晶活化能與反應係數，並利用外插的方式估算其資料穩定性。Mg57Sb43雖已脫離原本實驗設計以銻基為主軸之開發初衷，但其電阻率差值可達三個數量級，在電性表現與資料穩定性方面皆比Ge2Sb2Te5優異。
在Al-Sb之二元合金系統中，受限於AlSb結晶相在室溫大氣中易於潮解而形成原生氧化物，有鑒於氧含量之控制不易，本實驗僅針對成份Al16Sb84深入研究。Al16Sb84初鍍薄膜為非晶態，且可穩定保存於大氣中，從室溫升至400℃具有三階段之阻值變化，相較於Ge2Sb2Te5，Al16Sb84在結晶溫度(197 ℃)與結晶活化能(3.74 eV)之表現較為優異，具有良好之熱穩定性，但其主要缺點為結晶態電阻率過低，僅6.72E-04 (W•cm)。
第三部份為三元合金之開發，In3Sb7為ㄧ已用於光碟系統之相變化材料，Mg添加之In3Sb7在相變化材料開發各項研究指標中均能有效改善，涵蓋提升初鍍態與結晶態之電阻率，增進感測區域範圍，提高結晶溫度並些微降低熔點，僅在結晶活化能的部份下降，但其外插後在車用電子操作溫度120 ℃下之使用年限已相當足夠。

關鍵字

相變化記憶體 ； 銻基相變化材料 ； 電阻率 ； 結晶溫度 ； 結晶活化能 ； 結晶動力學

並列摘要

Research on phase change random access memory (PCRAM) has grown significantly in the past 10 years. PCRAM is based on the resistance switching, which is caused by the phase change triggered by electric pulses. Te-based Ge2Sb2Te5 has received intensive attention for their application to PCRAM due to large sensing margin, rapid phase changes for writing and erasing of data. However, some problems still remain. It is well known that Te is with low melting temperature, high vapor pressure and toxic, which may lead to phase separation within the materials. It has also been noticed that its low crystallization temperature and high melting temperature affects the stability of amorphous state and leads to high reset current during operation. In this study, novel non-chalcogenide Sb-based binary and ternary phase change materials have been investigated, aiming at a chance to replace the commercial Ge2Sb2Te5.
We have proposed novel amorphous MgxSb100-x films with new functionality for use in PCRAM due to appropriate characteristics. Both resistivity at crystalline state and crystallization temperature increase with increasing Mg content. These films all show switching phenomena between high and low resistance states. Crystallization kinetics of these films was studied by measuring the temperature dependent electrical resistance during non-isothermal heating. The activation energy (Ea), rate factor (K0) were deduced from Kissinger’s plot. Furthermore, data retention was calculated from the extrapolation of the Arrhenius plot. Mg57Sb43 films exhibited a three-order of magnitude decrease in resistivity, better electrical performance and data retention than Ge2Sb2Te5 does.
In the binary Al-Sb system, serious oxidation was encountered during experimental processes, specifically when the aluminum content is high. The crystalline AlSb is instable in air and high reactivity with oxygen and moisture. These drawbacks limit the development of Al-Sb binary alloys. In this study, we focused on the Al16Sb84 film, which remains stable at the amorphous state even after exposuring to air for a month. Al16Sb84 possesses high crystallization temperature(197 ℃) and activation energy(3.74 eV) which is helpful for amorphous stability.
In the ternary alloys, metal added Sb-rich InSb is a promising phase change material for 16x rewritable DVD media. In3Sb7 has been selected in this study due to its high crystallization speed and a high thermal stability. According to the experience in the binary Mg-Sb system, we elevated its crystallization temperature and the resistivity of crystalline state successfully by doping magnesium.

並列關鍵字

phase change memory ； antimony-based phase change materials ； resistivity ； crystallization temperature ； activation energy ； crystallization kinetics

參考文獻

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