濺鍍鈦酸鍶鋇介電薄膜與氧化鋅變阻器的製備與基本性質之研究

Abstract

本文中 ,我們利用磁控濺散法成長鈦酸鍶鋇薄膜並研究其在不同的基板上 的缺陷 ,電學與光學性質 .利用深能階暫態能量測量得知 ,當薄膜長在鉑 金屬層 ,我們可以發現一個載子缺陷 ,對於製程溫度450與550C的沉積薄 膜其活化能分別為0.45eV及0.53eV .另外 ,成長溫度在550C時 ,則有二個 缺陷 ,其活化能為0.2及0.4eV .藉由蕭特基及蒲爾-法蘭克電流電壓模型 ,我門發現其能障高度為0.45eV與缺限活化能相當接近 .此外 ,我們利用 交流的電導與電容圖 ,來探討薄膜的介電鬆弛現象 ,並提出其等效電路 .我們發現一組串聯缺陷電組及電容並聯連接本體阻抗及高頻電容的模型 ,可以解釋介電鬆弛現象 .當薄膜長在矽基板上時 ,不同的氧分壓會影響 其導電機構 .氧分壓為零時 ,薄膜電流呈現歐姆現象 ;而氧分壓為67% ,低電場時為蕭特基機制 ;而高電場時則為蒲爾-法蘭克模型 .由高頻之電 容-電壓分析得知 ,高氧分壓的濺鍍薄膜成長 ,容易導制二氧化矽層的形 成 ,並且造成平帶電壓的漂移與更多的界面缺陷 .此外 ,我門也探討薄膜 在玻璃基板上的光學與結構性質 .我們發現其薄膜的折射係數遵守單能階 振動模式 .當薄膜長在石英與氧化鋁基板時 ,其能隙為3.5eV .由反射率 的資料分析得知 ,製程溫度介於450與550C時 ,可以使薄膜得到較佳的光 學均勻性 .另一方面 ,我們也使用深能階暫態能量測來探討氧化鋅積層變 阻器的劣化現象 .我門發現經突波電流劣化後 ,其中活化能為0.94eV的缺 陷濃度減少最大 ,而此缺陷與氧空缺有關 .氧化鋅積層變阻器的劣化現象 是由氧離子與氧空缺起中和反應 ,而導致其邊界能障減少 . In this thesis, we explored the growth , defect states , electrical and optical properties of rf-sputtered (Ba,Sr)TiO3 (BST) on various substrates. By empolying the deep level transient spectroscopy (DLTS), we detected a single trap at 0.45 eV in the BST films deposited at the 450C on Pt layers and 0.53 ev in the ones deposited at 500C. Whereas, two traps located at 0.2 and 0.4 eV appear in the BST films deposited at 550C. By Schottky-emission or Poole-Frenkel models, the barrier height and trapped level are , respectively, estimatd to be 0.46 and 0,51 eV , corresponding to the trap activation energy 0.4 ~ 0.53 eV obtained from ous DLTS measurement. We investigated the trapping dielectric relaxation of rf-sputtered BST films on Pt layers and proposed an equivalent circuit on the basis of the admittance and capacitance spectra. The equivalent circuit, consisting of a series trapping resistance and capacitance combination in parallel with leakage resistance and high- frequency limit capacitance. is adpoted to explain satisfactorily the ac response and to identify the contribution of the shalllow trap on the electrical properties of BST thin film. When BST films were prepared on Si substrates at 450C with various O2/Ar mixing ratiosd (OMRs) , the leakage current of the films at OMR=0 % exhibited an ohmic conduction behavior and that of the films at OMR=50% displays a SCLC behavior. For the films deposited at OMR=67%, the dominant conduction is due to the Schottky emissiom (SE) at low electric field (E<1.2 MV/cm)and Poole-Frenkel (PF) at high electric field (E>1.2 MV/cm). Analysis of Capacitance-voltage characteristics reveals that high OMR deposition would lead to large flat0band voltage shift and more interface traps owing to the formation of an interfacial layer. We also studied the structural and optical properties of BST films deposited on the transparent substrates at various temperatures of 350 ~ 650 C. The refractive index dispersion data related to the short-range-oeder structure of BST films obeyed the single oscillation energy model. The indirect energy gap of the films deposited on Al2O3 and quartz substrates was found to be about 3.5 eV. According to the analysis of refletance data, the optical inhomogeneity of films can be reduced by depositing the films at the intermediate temperatures 450 ~ 550 C. The degradation of non-ohmic electric characteristics of ZnO-glass chip varistors due to high- intensity impulse currents was correlated with the deep levels investigated by means of deep level transient spectroscopy.The concentration of the traps at 0.94 eV was decreased and ascribed to oxygen vacancies existing at the grain boundaries of the varistors. The electrical degradatiuon phenomena of the chip varistor is closele related with the reaction between trap at 0.94 eV and adsorbed oxygen ions at the grain boundaries.