鉭鈮酸鍶鉍薄膜的鐵電性質

Abstract

近年來，鐵電材料因著它具備高介電值和高極化值，許多的研究試圖找出特性良好的鐵電薄膜以應用在強介電記憶體（FeRAM）。由於鐵電材料的晶化溫度相當高，而且成分不易控制，所以現今一般多以化學液態沈積法來成長。本實驗使用物理氣相沈積法中的濺鍍法 (sputtering) 來成長薄膜，並利用固態反應法的特性來製備標靶。首先將薄膜沈積在以鉑為底電極的矽晶片上，探討基板溫度、氧偏壓對鐵電特性的影響。結果顯示，在570OC的基板溫度及25%的氧偏壓下，可以得到鐵電特性良好 (2Pr = 36 mC/cm2, 2Ec = 52 kV/cm, 漏電流密度 = 1.5x10-8A/cm2) 的鉭鈮酸鍶鉍薄膜。 現今鐵電材料多以鉑等貴重金屬作為電極，我們再根據上述實驗所找出的最佳化條件，將鉭鈮酸鍶鉍薄膜成長在其他不同的底電極上，分析底電極與薄膜物性、鐵電特性及可靠度的關連，進而找出在強介電記憶體中最適合使用的電極金屬。

In recently years, ferroelectric materials have widely studied for the application of ferroelectric random access memory (FeRAM) because of their properties of high dielectric constant and high remanent polarization value. Due to their high crystallization temperature and hard to control the composition. Most researchers employed the chemical solution methods to deposit the ferroelectric thin film. In our investigation, we use sputtering, one of the physical vapor deposition (PVD) method, to grow our ferroelectric thin film. We prepared the Sr0.8Bi2.75Ta1.2Nb0.8O9+x (SBTN) targets by using the solid-state reaction process. We deposited the films on Pt/SiO2/Si substrate and measured their properties at substrate temperature of 575OC and 25 % OMR to find out the best parameters for the sputtering process, such as substrate temperature, OMR (oxygen mixing ratio). We can obtain the rf sputtered films with good ferroelectric properties (2Pr = 36 mC/cm2, 2Ec = 52 kV/cm, leakage current density = 1.5x10-8A/cm2). We also deposited the SBTN thin film on other bottom electrode material, such as Ir, IrO2, and Ru. We analyzed the relationship between the physical, electrical properties of SBTN thin film and bottom electrode to find the suitable electrode material for FeRAM. ABSTRACT (in Chinese) i ABSTRACT (in English) ii ACKNOWLEDGEMENT iv CONTENTS v TABLE CAPTIONS viii FIGURE CAPTIONS ix Chapter 1 Introduction 1 1-1 General Background 1 1-2 Motivation 3 1-3 Thesis Organization 3 Chapter 2 Literature review 5 2-1 Ferroelectricity 5 2-1.1 Phase transformation 6 2-1.2 Hysteresis loop 7 2-1.3 Dielectric behavior 8 2-2 Reliability 10 2-2.1 Fatigue 10 2-2.2 Retention 13 2-2.3 Imprint 15 2-2.4 Leakage current 16 2-3 Ferroelectric memory 17 2-3.1 Basic operation 17 2-3.2 Ferroelectric memory types 17 Chapter 3 Experimental details 19 3-1 Sputtering system 19 3-2 Target preparation 19 3-3 Films fabrication 20 3-3.1 Preparation of SBTN films 20 3-3.2 Preparation of bottom electrodes 21 3-4 Physical and electrical measurement 21 3-4.1 Physical characterization techniques 21 3-4.2 Electrical characterization techniques 22 Chapter 4 Results and discussion 23 4-1 Basic ferroelectric properties of SBTN thin films 23 4-1.1 Effect of substrate temperature on properties of SBTN films 23 4-1.2 Effect of OMR on properties of SBTN films 26 4-2 Effect of bottom electrode on properties of SBTN films 31 Chapter 5 Conclusion 35 Reference 36 Tables 44 Figures 47