釔鋇銅氧高溫超導薄膜之場效特性研究

Abstract

以直流賤射鍍膜系統,在氧化鎂基板上成長釔鋇銅氧的薄膜,我 們製備了一個包含高溫超導薄膜,具低損耗性的介電質絕緣層以及一金接 觸面結構之超導場效電晶體,同時並量測探討這超導層的場效特性.討論的 重點在於當超導薄膜之厚度約等於或甚至小於電磁波之穿透深度時,包含 基板的材料選擇,基板的溫度,基板的熱傳導與退火時間長短都是我們討論 的重點.我們製備了一臨界溫度超過85K的平坦C軸薄膜,利用此高品質的超 導薄膜緊接著製備金/二氧化矽絕緣層/超導的通道層/氧化鎂的絕緣基板 結構供研究量測分析討論.除了以湯姆斯-費米的模型來探討絕緣層之外, 並將通道層變成為兩不同性質層的結果都納入考慮.我們更謹慎地探討了 超導膜厚度,量測溫度,通道電流電壓的變化知效應.結果得到在低於臨界 溫度的電阻變化率超過百分之二十的較高電場效應;而且很明顯的在超導 層的電場效應被觀測到了! Thin films of YBa2Cu3O7-x have been made by dc magnetron sputtering deposition on various substrates. We have investigated the effects of substrates materials, substrate temperature, substrate heat contact, and annealing time on the properties of high temperature superconducting YBa2Cu3O7-x thin films by means of a structure composed of a superconducting thin film, a lower lossy dielectric substrate and a gold ground layer. Theemphasis is placed on the case of superconducting film with a thickness comparable or even less than the field penetration depth. The experimentalresults shows that the films, with flatness oriented in the c-axis and a zero- resistance temperature of 85 K were fabricated by an in-situ growth technique. Following the results, we prepared the structure of Au/CeO2/YBa2Cu3O7-x/MgO field effect transistors and measured their materials andelectrical characteristics. While the Thomas-Fermi model is used for explaining the behavior of the CeO2 insulating layer, the influenced and unaffected regions of the YBa2Cu3O7-x channel are inclued in the discussion.In the field-effect of YBa2Cu3O7-x channel by such a structure, we observedthat the changes of resistance and channel current can occur in applying various gate voltages and the structure would act as a semiconductor field-effect-transistor under certain conditions, resulting in a sudden change inthe magnitude of carrier concentration introduced into the affected channel.The effects of superconducting film thickness, operating temperature, applying gate voltages and channel currents were carefully measured. Consequently, the stronger effects were investigated by the change of resistance of more than 20 % below the critical temperature. The electricalcharacteristics of the field effect were obviously observed in the superconducting channel.