低溫製備之鍶鈦酸鉛鐵電電容器應用於1T-FeRAM之研究

Abstract

本研究以低溫製程的脈衝雷射濺鍍方式鍍製鍶鈦酸鉛薄膜，並且探討其物理性質與電特性。其後，並將此以低溫脈衝雷射濺鍍方式鍍製之鍶鈦酸鉛薄膜應用於”金屬/鐵電/矽”電容器之製作上。 我們藉由量測”金屬/鐵電/金屬”電容器的方法來觀察脈衝雷射濺鍍過程中，不同的雷射能量密度、氧分壓、以及基板溫度對沈積鍶鈦酸鉛薄膜的影響。在進行分析的過程中，我們利用了許多不同的分析方式例如X光繞射分析、原子力顯微鏡、掃瞄式電子顯微鏡、及歐傑電子能譜分析儀來分析鍶鈦酸鉛薄膜的基本物理性質。同時，我們也做了許多電性的分析，例如電流密度對電場、電容對電壓、極化值對電場、以及鐵電疲勞特性。接著，我們藉由分析後的結果決定脈衝雷射鍍製鍶鈦酸鉛薄膜的最佳雷射能量密度、氧分壓、及基板溫度條件，分別為1.55J/cm2、80mtorr、400℃。於是，我們便將最佳條件所鍍製出來的鍶鈦酸鉛薄膜應用於”金屬/鐵電/矽”電容器上，並且得到1.56V的記憶範圍值(Memory Window)。然而，我們意外的發現，原本不是最佳基板溫度條件的450℃下所製作的”金屬/鐵電/矽”電容器有更高的記憶範圍值為1.76V，原因是鍶鈦酸鉛薄膜與矽之間沒有擴散的情形發生，這個結果可以從歐傑電子能譜分析儀的結果得知。於是我們便將此電容器進一步做電性及疲勞特性分析，結果得到在3V的操作電壓下，漏電流低於10-7A/cm2 ，而在經過1010 的操作次數後記憶範圍值僅僅下降了10％的幅度而已。此一良好的特性使之成為應用於單一電晶體鐵電記憶元件上的最佳選擇。

In this study, we investigated the physical and electrical properties of Pb0.6Sr0.4TiO3 (PST) ferroelectric thin films prepared by pulsed laser deposition (PLD). And the metal- ferroelectric -silicon (MFS) capacitors using the PST ferroelectric thin films were fabricated by low temperature process of PLD method. Effects of laser energy density, oxygen pressure and substrate temperature on properties of PST thin films were investigated by measuring the metal-ferroelectric-metal (MFM) capacitors with structure of Pt/PST/Pt/Ti/SiO2/Si. Various physical analysis techniques such as X-ray diffraction analysis (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and auger electron spectroscopy (AES) have been used to observed the basic characteristics of PST thin films. Also, various electrical analysis techniques such as current density-electric field (J-E), capacitance-voltage (C-V), polarization-electric field (P-E) and fatigue measurements have been used to observe the electrical and ferroelectric behavior of the PST thin films. Then, optimized conditions of each PLD parameters were obtained by comparing the J-E, P-E, fatigue properties of PST thin films, which are 1.55J/cm2 for laser energy density, 80mtorr for oxygen pressure and 400℃ for the substrate temperature respectively. The optimized PST thin films were then used to fabricate the MFS capacitors for 1T-FeRAM applications. The MFS capacitor with optimized PST thin film possesses the memory windows of 1.56V, and surprisingly, the MFS capacitor with deposition temperature of 450℃ exhibit even larger memory window of 1.76V since no diffusion was observed by AES inspection. Therefore, the MFS capacitor with deposition temperature of 450℃ was further investigated by measuring the leakage current and fatigue characteristics. The leakage current density is below 10-7A/cm2 at operating voltage of 3V for and the memory window only reduced 10% after 1010 switching cycles of fatigue testing. The superior properties of large memory window, low leakage current and low fatigue problem of MFS capacitor using PST thin film prepared by low temperature PLD process make it the most promising candidate for 1T-FeRAM applications.