還原氣氛退火對PZT與SBT鐵電薄膜的劣化研究

Abstract

本研究是利用化學溶液法將SBT與PZT鐵電薄膜，分別沉積在Pt/Ti/SiO2/Si(MFM)與Al2O3/Si(MFIS)二種基板上，藉此探討試片經過2000C〜5000C還原氣氛退火後，在結構與電性上的差異。實驗發現還原氣氛退火對MFM結構的SBT與PZT鐵電薄膜試片會造成殘留極化值的降低，且降低的程度隨退火溫度而提昇。對MFM結構的PZT鐵電薄膜試片而言，本身抵抗還原氣氛退火的劣化作用可達5000C；但沉積Pt上電極後，其殘留極化值在2000C時就會嚴重劣化，這應該是與Pt的觸媒效應有關。另外對於SBT鐵電薄膜而言，經過還原氣氛退火後會造成MFM結構試片的殘留極化值降低；及MFIS結構試片的電容值嚴重降低，根據SIMS結果可發現造成電性劣化的來源，來自於鐵電成分的變動。當SBT試片沉積上電極後，電性受還原氣氛退火的劣化程度會降低，此現象則出自於上電極抑制SBT鐵電成分的變動所致。在漏電流方面，實驗顯示MFIS結構的SBT試片經過還原氣氛退火後，會大幅降低漏電流密度，此應該是由於退火過程中，基板形成鋁-矽-氧非晶質所致。

The SBT and PZT thin films were fabricated on Pt/Ti/SiO2/Si and Al2O3/Si substrates by using MOD process. The effects of forming gas annealing on structure and electrical properties of ferroelectric thin films annealed at 200oC~ 500oC will be investigated in this work. The results show that the forming gas annealing will cause the degradation of remanent polarization of both SBT and PZT films on Pt/Ti/SiO2/Si (MFM structure). However, the degradation is more serious for the PZT films with Pt coating prior to forming gas annealing that could be related to the catalyst effect of Pt. On the other hand, For the PZT and SBT films on Al2O3/Si, since the PZT films is difficult to crystallize the peorvskite phase on the Al2O3/Si, the effect of forming gas annealing is focused on the SBT /Al2O3/Si. It was found that after forming gas annealing treatment, the capacitance was reduced. According to SIMS analysis, it shows that the degradation is probably related to the composition variation of SBT film. However, it was observed that the leakage current of SBT films on Al2O3/Si substrates was reduced about one and half orders magnitude as compared to that without forming gas annealing.