| Cryogenic technology plays an important role in the development of aerospace,life science and superconductivity.The wide application of cryogenic technology in various fields also puts forward higher requirements for cryogenic measurement.The temperature measuring element should not only realize the wide temperature range measurement under low temperature,but also have a good R-T linear relationship to ensure the sensitivity and reproducibility accuracy of the thermometer.The difficulties in thermometer manufacturing include: constant concentration of impurity diffusion on silicon wafers,cutting and sealing of semiconductor chips,and precise assembly of thermometer components.In addition,the accuracy of thermometer calibration also determines the measurement level Through the comparison of a variety of thermometers,this paper selected silicon semiconductor cryogenic thermometer as the research and development target of this topic.Firstly,on the basis of PN junction carrier theory and energy band theory,this paper selects a special phosphorus source thermal diffusion method to complete the doping of monolayer silicon wafers.Secondly,the theoretical calculation of voltage drop value of single-layer PN junction was completed according to doping concentration and junction depth,and the working feasibility of single-layer chip at normal temperature was verified by forward voltage detection.Finally,after the analysis and selection of the various structural materials of the thermometer,the metal coating on the base of the thermometer and the internal circuit were welded by using the magnetron sputtering target and ultrasonic bonding machine.During the design and manufacture of thermometers,the following methods are used to optimize the test performance of thermometers:(1)The thermal response time of the thermometer is shortened through the selection of specific component materials and structural design;(2)Through special impurity source and diffusion process,the chip has good R-T linear relationship;(3)A good and stable low temperature environment for calibration and testing through advanced refrigeration technology is provided;(4)Through the cooperation of PLC and configuration monitoring software,the calibration and test data are more accurate.In order to complete the calibration of self-made thermometer,this research group has set up a complete calibration system including refrigeration system,data acquisition system and PLC program.Using this system,the temperature of standard thermometer and the resistance value of homemade thermometer are obtained.Through linear fitting and function calculation,the R-T data graph of homemade thermometer with good linear relationship and small error is obtained.In order to verify the feasibility and effectiveness of the thermometer design,the research group built a set of experimental system including vacuum system,refrigeration system and measurement system on the basis of the calibration system.The system is used to test the performance of the thermometer.The temperature range test results show that the thermometer can complete the temperature range of 4.4～300K;The reproducibility results show that the temperature error of the thermometer is within 0.05 K when the temperature drops from 6 liters to the lowest point,which shows a very high reproducibility accuracy in the same type of thermometer.The design of the low temperature thermometer in the working temperature area and reproducibility and other measured indicators have reached the design standards,can be used for new materials,small samples,film materials of ultra-low temperature detection.Good R-T linear relationship also makes it has a very high measurement accuracy.The successful research and development of the thermometer aims to promote the comprehensive technology level in the field of low temperature in China and the development of related fields of low temperature technology. |
