Development Of High Temperature SQUID Chip Test Platfor

Superconducting Quantum Interference Devices（SQUID）is one of the most sensitive magnetic sensors,capable of transforming extremely small magnetic field changes into measurable voltage signals with low noise,high sensitivity and stable structure.On the basis of SQUID,we can have many kinds of measuring instruments,which are widely used in the fields of biomedicine,geological exploration and deep-sea exploration.Based on the critical transition temperature,SQUID can be divided into low-temperature SQUID and high-temperature SQUID,low-temperature SQUID generally operate in a liquid helium environment（4.2 K）,the application of low-temperature SQUID is greatly limited by the complexity and cost of the technology used to maintain the low temperature environment.The high-temperature SQUID can work in a higher temperature liquid nitrogen environment（77K）,which greatly reduces the cost of use,improves portability,and can be used in more fields.Based on the basic working principle of SQUID,this paper conducts research on the high-temperature SQUID chip test bench,and the innovations are as follows:Firstly,The DC SQUID is simulated and modeled by the Pspice circuit simulation software,and the effects of bias current,junction resistance and asymmetry on the characteristics of the DC SQUID are explored.The simulation results show that in order to obtain the maximum output voltage swing and thus improve the slope of the working point,an appropriate bias current and junction resistance should be selected.The asymmetry will significantly reduce the maximum flux transfer coefficient of the DC SQUID,so it should be avoided in the fabricating process.Then,The hardware of the high-temperature SQUID chip test bench has been comprehensively designed by Auto CAD,Solidworks,Altium Designer and other design software,The hardware of the test bench mainly includes mechanical control module,liquid nitrogen cryogenic module,low-pass filter module and data acquisition module.In order to obtain a clean electromagnetic environment and avoid external electromagnetic interference,the magnetic shielding device in the liquid nitrogen low temperature module is specially annealed and heat treated,which greatly improves its magnetic shielding ability.Finally,The software of the high temperature SQUID chip test bench is designed by the LabVIEW program development environment.The measurement procedures include:critical transition temperature measurement,critical current measurement,comprehensive measurement of SQUID electrical properties,and magnetic flux voltage modulation curve measurement.After the development of the test bench,the performance parameters of the high-temperature SQUID were measured.The measurement results showed that the critical transition temperature of the superconducting thin film constituting the high-temperature SQUID was about 90 K,the critical current density is 2.5 MA/cm²,the maximum flux transfer coefficientα_max=6.42×10^-4Φ₀/mV.