Development of High T_C SQUID Magnetometer Systm

在本项目中，我们研制了一种高温超导量子干涉仪（SQUID）。首先，我们阐明了高性能SQUID磁强计的发展要求。我们指出，在T= 77 K时，约瑟夫森结的临界电流密度I_O和电阻R应分别为I_O= 20 μ A和R=10 Ω，超导量子干涉仪的电感L=50-I50 pH。当满足这些要求时，我们可望研制出磁场分辨率为B_n=20 fT/Hz^的高精度磁强计</2>。双晶衬底的最佳取向差角为30度。用30 °衬底，我们首次成功地实现了I_o=20 μ A，R=10 Ω的约瑟夫森结。我们还表明，在这种情况下，工作在T= 77 K的SQUID的性能得到了显著的改善。与传统的SQUID相比，30 °双晶结的性能非常好.我们还研制了直接耦合SQUID磁强计，其中拾波线圈和100-pH SQUID集成在1cm × 1cm SrTiO_3衬底上.测得磁力仪的磁场rcsolution为B_nn=30 fT/Hz^</2n>fT/Hz^&lt;1/2&gt;，与dcsign值接近。该值是直接耦合SQUID磁强计迄今为止测得的最低值，可用于心磁图的测量。

In this project, we have developed superconducting quantum interference device (SQUID) using high T_C supercnductors. First, we clarify requirements for the development of high performance SQUID magnctometer. We show that the critical ctqrrentI_O and the resistance R of the Josephsonjunction should be I_O=20muA and R=10 OMEGAat T=77K,and the SQUID inductance shouldbe L=50-I50pH.When these requiremts are satisfied, we can expect high prformance magnetometer with magnetic fild resolution of B_n=20 fT/Hz^</2>.In order to satisfy these requirements, we have developedd Josephson junctions fabricated on SrTiO_3 bicrystal substrates. Optimum value of the misorientation angle of the bicrystal substrate has been found be 30 dbgrees. Using the 30 degree substrate, we have succeeded, for the first time, in rcalizing the Josephson jucticn with I_o=20 muA and R=10 OMEGA. We have also shovm tnt the pcrformance of the SQUID operating at T=77K is significantly improved in this case. The performance obtained from the 30 degree bicrystal junction is cxtremely good when compared to the conventional SQUIDs.The so- called directly-couled SQUID magnetometer has been also developed, where pickup coil snd 100-pH SQUID are integrated on 1cmx1cm SrTiO_3 substrate. The magutic field rcsolution of the magnetometer was measured to be B_nn=30 fT/Hz^</2n>fT/Hz^<1/2>, which is close to the dcsign value. This value is the lowestvalue rcprted so far in the directly-coupled SQUID magnetometer, and is enough for the meauresment of magnetocardiogram.