以低Ba離子濃度在水熱-化學電池法生成BaTiO3薄膜機制之探討

Abstract

This research is to synthesize BaTiO3 films on TiN/Si substrate by the hydrothermal-galvanic couple method. Investigated BaTiO3 films with different [Ba2+] concentration compared with those synthesized by hydrothermal-galvanic couple method. BaTiO3 films were fabricated by using various concentrations of Ba(CH3COO)2 mixed with 2 M NaOH reaction solutions at 80°C for 60 minutes. According to different Ba(CH3COO)2 concentrations, characteristics of voltage and current , the relative intensity, the average grain size were discussed. The influence of [Sr2+] in SrTiO3 were also be compared. While Ba(CH3COO)2 concentration is higher than 0.04 M, spontaneous voltage and current between TiN and platinum electrodes were observed apparently which confirmed the existence of galvanic couple in this system. XRD identify the cubic phase crystalline BaTiO3 films. The BaTiO3 relative intensity at different concentration [Ba2+] from hydrothermal-galvanic couple is higher than a single hydrothermal method. FE-SEM observed morphology and cross-sectional structure of as-deposited TiN /Si. The continuous dense BaTiO3 covered over TiN / Si at [Ba2+] concentration above 0.04 M by hydrothermal-galvanic couple method. Grain size and thickness of the BaTiO3 film was decreased with [Ba2+]concentrations decreased significantly. When the concentration of Ba(CH3COO)2 increased from 0.04 M to 0.5 M, the die-lectric constant of BaTiO3 films decreased. The dielectric constant of BaTiO3 films at 10 kHz obtained at 0.04 M Ba(CH3COO)2 was 179 and dielectric loss was 3.18. Another part of this study, the experimental results and SrTiO3 with different strontium ions concentration were compared. BaTiO3, and SrTiO3 have the same structure. However, the maximum current, the quantity of electric charge, energy den-sity, and relative intensity and the data analysis of different concentrations of [Ba2+] is much lower than [Sr2+] under the same basic conditions. SrTO3 film can be prepared at low [Sr2+] concentration of 0.0001 M, but [Ba2+] is at least 0.04 M.

本研究利用水熱-化學電池法於TiN/Si基材上製備鈦酸鋇膜，探討溶液中鋇離子[Ba2+]濃度對BaTiO3膜成長之影響，並以水熱法為對照組作比較，此為文獻中從未為探討過的主題。以不同濃度之Ba(CH3COO)2與2M NaOH混合液作為反應溶液，於80°C，反應60分鐘製備鈦酸鋇薄膜。針對不同Ba(CH3COO)2濃度條件，BaTiO3膜成長過程中之電流、電壓及電量，以及XRD相對強度、平均晶粒尺寸及膜的變化趨勢進行探討及並將結果與鍶離子對鈦酸鍶之影響之趨勢比較。 以LabView程式監控反應過程中電壓及電流變化，當Ba(CH3COO)2濃度高於0.04 M以上，水熱-化學電池法在反應過程中可監測到明顯且不同的自發電位差及電流變化，顯示此反應系統具有伽凡尼即化學電池之機制。利用XRD鑑定不同醋酸鋇濃度濃度生成鈦酸鋇薄膜之結晶相，在不同鋇離子濃度條件下，水熱-化學電池法所得之BaTiO3 XRD繞射峰相對強度明顯較單一水熱法要高。FE-SEM下觀測反應前後TiN/ Si表面及橫截面微結構形貌，水熱-化學電池法在[Ba2+]濃度0.04 M以上之條件下，生成之鈦酸鋇已覆蓋滿TiN/Si上，而形成一連續緻密的BaTiO3膜。BaTiO3膜的晶粒大小及膜厚均隨[Ba2+]濃度有明顯降低趨勢。介電常數方面，醋酸鋇濃度從0.04 M增加到0.5 M，BaTiO3膜介電常數增加，在0.04 M 醋酸鋇所生成之BaTiO3薄膜在10 kHz下之介電常數為179、介電損失為3.18。 本研究另一部分是將實驗結果與不同濃度鍶離子對鈦酸鍶膜製備的結果進行比較。鈦酸鋇與鈦酸鍶兩者結構相近，但經比較後發現在最大電流、總電量、能量密度、及相對強度，數據分析中，不同濃度[Ba2+]之結果均比[Sr2+]的結果要來得低，在相同鹼性條件下，[Sr2+]可在0.0001 M的低濃度下製備出鈦酸鍶膜，但[Ba2+]則至少需要0.04 M。