磁控濺鍍高溫超導釔鋇銅氧薄膜臨界電流密度及表面電阻特性之研究

Abstract

本實驗研究利用磁控濺鍍系統於鈦酸鍶(SrTiO3)(001)基板上成長釔鋇銅氧(YBa2Cu3Oy,YBCO)薄膜，以功率90 W、720°C、時間3.5小時與壓力400 mtorr條件下製程，經由X-ray繞射儀量測確認YBCO晶體結構及生長方向後，利用四點量測電阻對溫度( R–T diagram )測得臨界溫度(critical temperature , Tc)，可得為沿c軸方向生長、厚度為278 nm、Tc為86.92 K的釔鋇銅氧超導薄膜，後續對薄膜進行光學微影酸蝕刻，利用電性方法測得臨界電流(critical current, Ic)，換算得臨界電流密度(critical current density , Jc)，在80 K時電流密度為1.4×104 A/cm2，利用定溫下外磁化強度(M)與外加磁場(H)之關係，獲得上下臨界磁場(Hc1、Hc2 )，計算出穿透深度(penetration depth,λ)、相干長度(coherence length,ξ)，結果與參考文獻接近。透過SQUID系統量測磁滯曲線，藉由Bean model公式推算出臨界電流密度(critical current density , Jc)，80 K時可達3x105 A/cm2，將電流密度(Jc)換算成表面電阻(Rs)，電阻值與參考文獻接近，同時也運用High Frequency Structure Simulator(HFSS)模擬軟體，模擬蝕刻後不同微帶線長與寬情況下表面電阻，模擬最佳化電阻值與磁性量測時77-80 K之電阻值數量級一致。經由上述實驗結果顯示可獲得高品質之釔鋇銅氧薄膜。In this experiment, yttrium barium copper oxide (YBCO) thin film was grown on strontium titanate (SrTiO3) (001) substrate by magnetron sputtering. The process condition is under 90 W, 720°C, 3.5 hours, and 400 mtorr. The YBCO crystal structure and growth direction were determined by X-ray diffractometer measurement. The R-T diagram is obtained by four-point probe measurement and then the critical temperature is measured. It can be obtained that the YBCO are grown along the c-axis, thickness of 278 nm and T_c at 86.92 K. Subsequent photolithographic acid etching of the film. The critical current is measured by the electrical method and the critical current density is obtained. The critical current density is 1.4×104(A/cm2) at 80 K. The critical magnetic field is obtained by the intensity of magnetization and external magnetic fieldat constant temperature. Penetration depth and coherence length were calculated, and the results were close to those of reference literature. The critical current density is estimated by Bean model formula and achieves 3x105(A/cm2) at 80 K. The current density (J_c) is converted to surface resistance (R_s) by literature formula. The resistance value is close to that of reference literature. At the same time, the simulation software is used to simulate the surface resistance of different microstrip lengths and widths after etching. The optimized resistance value in simulation is the same order of magnitude as the resistance value at 77-80 K during magnetic measurement. The results of the above experiments showed that high quality yttrium barium copper oxide thin film was obtained.