氧化鋁/二氧化矽/碳化矽堆疊元件中兩態缺陷輔助穿隧電流現象

Two-State Trap-Assisted Tunneling Current Phenomenon in Al2O3/SiO2/4H-SiC Stacked Device

江榮進(Jung-Chin Chiang)

指導教授 ： 胡振國

國立臺灣大學/電機資訊學院/電子工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.02586

摘要

本篇論文中，我們討論了在氧化鋁/二氧化矽/碳化矽堆疊元件中，存在兩種缺陷輔助穿隧電流導通狀態的現象。在高介電常數/二氧化矽疊層金氧半電容元件中，我們相信在高介電常數介電層製備中產生的氧空缺缺陷，對於缺陷輔助穿隧電流有著很大的影響。我們的研究中使用寬能隙材料做為基板，利用其為數甚多的介面缺陷以增強缺陷輔助穿隧電流兩態現象，使這個現象能清楚的被觀察和研究。接著我們調變不同的介電層製程條件，研究對這個電流兩態現象有何影響。我們量測電流–電壓特性時發現所有的元件皆有這種電流兩態現象。對於缺陷輔助穿隧電流而言，利用硝酸氧化所得氧化鋁製成的元件，其電壓閾值較利用陽極氧化所得氧化鋁的元件來的小。此外，前者可施加正電壓使其重設回原來的狀態而後者則否，且前者的復位電流很小。同時，二氧化矽製備中缺少紫外光照射的元件有著比有被紫外光照射的元件還要快的復位速度。這些結果顯示製程條件影響我們的氧化鋁/二氧化矽/碳化矽堆疊元件的電流特性甚鉅。在進一步的研究重設過程的實驗中，我們證實缺陷輔助穿隧電流的兩態現象與氧化鋁中的氧空缺有關。是一個中性的氧空缺接收以及釋出電子的過程。我們監控狀態‘1’的電流時發現它會隨著時間而上升接近狀態‘0’的電流型態，接著飽和。但其飽和時的電流大小仍然與狀態‘0’的電流有所區別。這表示於狀態‘1’時，電子穿隧於介電層中的缺陷的機率與狀態‘0’仍然有差。此外，元件展示出來重複操作的耐久性顯示其利用在記憶體元件的潛力。

關鍵字

高介電常數材料 ； 氧空缺 ； 電阻式隨機存取記憶體 ； 電阻值切換 ； 缺陷輔助穿隧 ； 寬能隙

並列摘要

In this thesis, we explain the two-state trap-assisted tunneling current phenomenon in Al2O3/SiO2/4H-SiC stacked device. In the high-k/SiO2 stacked dielectric MOS capacitor, it is believed that the defects associated with the oxygen vacancies were formed during high-k dielectric preparation, which may affect the trap-assisted tunneling current of the device. Wide bandgap material was utilized as substrate in our work for its considerable amount of interface states which are important to enhance the effect of trapped charges on the tunneling current. Two-state current behavior was clearly observed. After that, the two-state current conduction phenomenon was also explored by varying the process conditions of dielectric preparation. All the devices exhibited obvious two-state current conduction behavior under I–V measurements. The threshold voltage of trap-assisted tunneling current conduction in the devices with Al2O3 layer prepared by HNO3 oxidation occurred at a smaller voltage than that by anodization; additionally, the former could be reset after positive bias stress with very small reset current but the latter could not. Meanwhile, the sample in SiO2 formation without UV light illumination exhibited faster electrical reset speed than that with UV light illumination. The results show that different dielectric layer preparations strongly affect the characteristics of two-state current conduction in our Al2O3/SiO2/4H-SiC stacked device. With further investigation of reset process, the two-state phenomenon induced by trap-assisted tunneling current was demonstrated to be related to the oxygen vacancy. The energy level of the dominant trap extracted from the time variations of gate currents is mainly caused by the oxygen vacancy in the Al2O3 layer, which involves capture and emission of the electron by neutral oxygen vacancy (V0, V0 + e− → V− → V0 + e− ). The state ‘1’ gate current changes and saturates with time, but even the saturation value can still be distinguished from the state ‘0’ current. Reliable endurance of this device was shown for possible memory application.

並列關鍵字

high-k material ； oxygen vacancy ； RRAM ； resistive switching ； trap assisted tunneling ； wide bandgap

參考文獻

[1] J. H. Zhao, P. Alexandrov, and X. Li, “Demonstration of the First 10-kV 4H-SiC Schottky Barrier Diodes,” IEEE Electron Device Lett. 24, 402 (2003).

[2] G. Gudjonsson, H. O. Olafsson, F. Allerstam, P.-A. Nilsson, E. O. Sveinbjornsson, H. Zirath, T. Rodle, and R. Jos, “High Field-effect Mobility in n-channel Si Face 4H-SiC MOSFETs with Gate Oxide Grown on Aluminum ion-implanted Material,” IEEE Electron Device Lett. 26, 96 (2005).

[3] S. W. Huang and J. G. Hwu, “Ultra-Thin Aluminum Oxide Gate Dielectric on N-Type 4H-SiC Prepared by Low Thermal Budget Nitric Acid Oxidation,” IEEE Trans. Electron Devices 51, 1877 (2004).

[4] V. V. Afanas’ev, A. Stesmans, F. Chen, S. A. Campbell, and R. Smith, “HfO2-based Insulating Stacks on 4H–SiC(0001),” Appl. Phys. Lett. 82, 922 (2003).

[5] S. Hazra, S. Chakraborty, and P. T. Lai, “Density Profiles and Electrical Properties of Thermally Grown Oxide Nanofilms on p-type 6H–SiC(0001),” Appl. Phys. Lett. 85, 5580 (2004).