Development of High T_C SQUID Magnetometer Systm

在本项目中，我们利用高温超导材料研制了超导量子干涉器件(SQUID)。首先，明确了研制高性能鱿鱼磁强计的要求。在T=77K时，约瑟夫森结的临界电流密度I_O和电阻R应为I_O=20µA和R=10欧米伽，SQUID电感应为L=50-I50pH。当这些要求得到满足时，我们有望获得磁场分辨率为B_n=20FT/Hz^/2&gt；的高性能磁强计。为了满足这些要求，我们在SrTiO_3双晶衬底上制备了约瑟夫森结。双晶衬底的择优取向角的最佳值为30 dgrees。使用30度衬底，我们首次成功地将I_o=20MUA，R=10欧米伽的约瑟夫森Jucticn规格化。在这种情况下，在T=77K下工作的鱿鱼的性能有了显著的改善。与传统的SQUID相比，30度双晶结的性能非常好。还开发了所谓的直接耦合SQUID磁强计，将拾取线圈和100-pH SQUID集成在1 cm×1 cm的SrTiO_3衬底上。测得该磁强计的磁场解为B_nn=30 fT/hz^&lt；/2n&gt；fT/hz^&lt；1/2&gt；接近dcsign值。该值是迄今为止直接耦合SQUID磁强计测得的最低值，足以测量心磁图。

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.