以選擇性磊晶成長法製備釔系高溫超導量子干涉元件之研究

Abstract

選擇性磊晶成長法(Selective Epitaxial Growth, SEG)製作超導元件是在基板上加鍍一層圖案化之遮罩薄膜，利用遮罩上之超導失去導電性，達成超導薄膜圖案化之選擇性成長目的。本文嘗試找出穩定的選擇性磊晶成長條件，並以此製程條件製備釔系高溫超導量子干涉元件。遮罩薄膜層是以直流濺鍍法將鈦金屬靶在氬氣氧氣之混合氣體環境中濺鍍於鈦酸鍶基板上，得到的產物為在鈦酸鍶基板上附著性良好之透明氧化鈦薄膜。實驗結果證實以此作為選擇性磊晶成長之遮罩材料，其上成長之釔鋇銅氧薄膜，超導與非超導區域選擇性良好。由上述製程初步製作出之超導量子干涉元件( SQUID )，經實驗顯示，電流對電壓曲線符合RSJ模型所描述特性，並於77K及其他溫度量得電壓隨磁通調制變化。本研究顯示以選擇性磊晶成長法直接製作不同結構的電子元件應極具可行性。

A process of “Selective epitaxial growth (SEG)” was used to fabricate high-Tc “Superconducting Quantum Interference Device (SQUID)” in-situ, avoiding degradation of superconducting thin films caused by after-deposition lithography. It was demonstrated that the SQUIDs made by the present process exhibit noticeable V-Φ modulations. The SEG process was realized by using a dc-sputtered TiO2 layer as the masking template on a 36.8∘SrTiO3 bicrystal substrate. To avoid the over-oxidation of the patterned photo resist (which retard the subsequent lift-off process significantly) the sputtering gas was optimized to have a mixture of Ar:O2=29:1. The resultant TiO2 layer showed excellent selectivity for subsequent YBCO deposition. The performance of the SQUID is expected to be significantly improved by further reduction of junction self-inductance.