氮氧化矽薄膜之電阻式記憶體轉態特性探討與研究

Study on resistance switching characteristics in SiON thin film for resistive random access memory

林育仕(Yu-Shih Lin)

指導教授 ： 葉鳳生

國立清華大學/電機資訊學院/電子工程研究所/碩士(2010年)

摘要

近幾年來，由於非揮發性記憶體的應用與發展備受矚目，加上快閃記憶體在微縮上遇到難以突破的瓶頸，所以新穎式非揮發性記憶體的研究與開發正蓬勃地展開。其中，電阻式非揮發性記憶體元件具有結構簡單、耗損能量低、操作電壓低、密度高、操作速度快、耐久度高、儲存時間長和非破壞性存取等優點，使其成為新穎式非揮發性記憶體元件的最熱門人選。
在本篇論文中，電阻式記憶體的轉態特性探討與研究著重於探討氮化鈦/氮氧化矽/銅/白金結構的電流傳導物理機制。其內容主要可以分為四大部分，包含不同上電極結構上的差異，亦或超薄氮氧化矽結構的特性與尺寸效應及上下電極都含有銅層的結構上的不同，來進一步檢視記憶體轉態的物理機制的研究。在利用不同上電極結構的部分，上電極利用不含銅層結構和擁有銅層結構來探討元件轉態的物理機制。其結果發現銅原子於元件操作時會擴散進氮氧化矽薄膜內並產生尖端電場效應，使得元件有較好的基本特性。經過電流-電壓曲線機制的探討並計算出有效的轉態區只有薄薄的一小層並位於氮化鈦和氮氧化矽的界面處。接著利用超薄氮氧化矽去驗證上述實驗的正確性，發現元件可以操作只是穩定度不佳，主要原因是缺乏銅擴散後的尖端電場效應。利用尺寸效應實驗發現，高電阻態的阻態會隨著元件的微縮而變大，而低電阻態並不會有變化。最後，利用上下電極都含有銅層的結構的實驗，再次證實銅擴散入氮氧化矽理論的正確性。

關鍵字

電阻式記憶體

並列摘要

Recently, the conventional nonvolatile floating memory is expected to reach certain technical and physical limits in the future. In order to overcome this problem, alternative memory technologies have been extensively investigated, including ferroelectric random access memory (FeRAM), magneto resistive RAM (MRAM), phase-change RAM (PCRAM) and resistive RAM (RRAM).In all next generation nonvolatile memory, the resistive random access memories (RRAM) owing to the advantages of simple structure, lower consumption of energy, lower operating voltage, higher density, higher operating speed, higher endurance, higher storage time and non-destructive access which make it be the most popular candidate. In this thesis, we investigate and discuss the resistance switching current conduction mechanism for resistive random access memory of TiN/SiON/Cu/Pt structure RRAM device. The research can be split into four parts, the characteristic of RRAM devices with different top electrodes, the characteristics of ultra thin SiON film device, size effect and the device structure with copper layer at top and bottom electrode.
At the part of the characteristic of RRAM devices with different top electrodes, we employed the Pt top electrode or Pt/Cu top electrode to figure out the physical resistance switching mechanism. The results showed that the copper atom will be introduced to SiON film when the device operate applied with bias voltage and formed Cu filament that can be served as a stretched electrode stretched electrode. Thus, a large electrical field can be generated at the tip of the electrode when applying bias on the device, resulting in better resistance switching characteristics. By fitting the current-voltage curve, we can extract the effective thickness of resistance switching layer which is very thin and at the interface between SiON and TiN electrode.
Then, in order to verify the mechanism that we present, we fabricated a device with the ultra thin SiON film and Pt top electrode. The ultra thin SiON device present bipolar resistance switching characteristic, but the characteristic was more unstable than 38 nm SiON device with Pt/Cu top electrode. Because the ultra thin device was short of the tip electric field effect caused by Cu filament tip, the oxygen vacancies conduction path can be formed in anywhere of the SiON film and every circle of resistance switching may take place on different oxygen vacancies conduction path. At the part of size effect experiment, the resistance of high resistance state is dependent the area and the resistance of low resistance state is independent the area, this result conform to filament theory. Finial, we use the structure with copper layer as top and bottom electrode to confirm the correctness of mechanism of copper atom introduce to SiON.

參考文獻

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