應用於生物磁場的高靈敏超導量子干涉元件之製作與特性研究

Abstract

應用於生物磁場的高靈敏度超導量子干涉元件之製作與特性探討. 為了追求高重複性和高品質的元件,我們建立了一新的製作階梯方法. 利用兩步驟改善階梯品質.成功的將階梯製作達到最佳化.將階梯應用於串聯式超導量子干涉元件,我們發現雜訊隨著串連各數增加而降低.另外利用1公分的雙晶體我們製作出了高靈敏度的超導量子干涉元件.且利用我們創新的串聯式磁通水壩,成功的抑制了低頻雜訊.而使得雜訊値在77K時達到30–80 fT/Hz1/2.最後利用原子力顯微鏡和掃瞄穿隧電子顯微鏡,我們亦發現超導薄膜品質亦對SQUID 雜訊有很大的影響.

The fabrication and characterization of high-Tc sensitivity SQUID magnetometers for biomagnetism at 77 K were investigated. To pursue the high reproducibility and quality step edge for high-Tc SQUIDs, we have developed two-step procedures of fabricating very good step-edge substrates. We have characterized high-Tc step-edge SQUIDs connected in series. The flux-to-voltage transfer function increase with the number of SQUIDs. The flux noise, SΦ of the serial SQUID arrays scale as 1/N1/2. Second, we fabricated a serial low-noise direct-current superconducting quantum interference device (SQUID) magnetometer on a 10 mm × 10 mm SrTiO3 (100) bicrystal substrate. This field sensitivity around 30–80 fT/Hz1/2 has been obtained at 77 K in the white noise region. The latter noise has been avoided by optimizing the geometry of the pickup coil as well as by using the so-called flux dam. As a result, the 1/f noise of SQUIDs has been much improved. Finally, using atomic Force microscope (AFM) and scanning electric microscopy (SEM), we observe an inhomogeneous distribution and microstructural defects on YBCO grain-boundary Josephson junctions. SEM images show that these defects cause the grain boundary of YBCO thin film grown on the bicrystal to a few submicron depth of the groove in film. The existence of these defects is expected to affect the superconducting current and the motion of the magnetic flux in the films and hence generate noise in the devices.