Research On Self-Heating Of High Temperature Superconducting THz Sources

The electromagnetic waves in the terahertz?THz?band is defined as from 10¹¹ Hz to 10¹³Hz,which occupies a particular location covering the transition area from electronics to photonics in the whole electromagnetic spectrum.However,due to lack of effective generation and detection means,THz wave has not been fully researched and applied.It is considered to be the last frequency band needing further study,known as "Terahertz Gap".High temperature superconductor Bi₂Sr₂CaCu₂O₈?BSCCO?IJJs?intrinsic Josephson junction?can emit continuous tunable terahertz radiation when biased appropriately.This new type of solid-state terahertz source provided one of the useful solutions for THz technology application.In terms of solid-state terahertz sources,the intrinsic Josephson junction?IJJ?stacks show good performance at sub-THz frequencies,typically between 0.4 and 0.8 THz.In order to bridge the THz gap,the superconducting IJJs emitters need to move upwards with increasing their operation frequencies.However,the main challenge is to overcome the self-heating caused by the applied dc power.Self-heating is a double-edged sword for the THz emission.A heat-induced hot-spot,which formed at"high-bias" regime can be helpful to narrow the emission line and to tune the frequency.But it raises the stack temperature in both the "hot" and the "cold" parts of the stack,reduces the maximum voltage across the stack,and consequently limits the highest emission frequency.On the basis of previous research work on GBG?gold-BSCCO-gold?structured devices,this dissertation aims to make further study on the characteristics of HTS BSCCO IJJ terahertz source and the radiation mechanism.It focuses on the analysis of the mechanism and causes of the self-heating problem.It is hoped that the IJJs THz source will make a better actual performance and broaden its application by making better use of the self-heating characteristics.A novel sandwich?SWS?structure was proposed to improve the thermal conductivity of the GBG sample.It is worth emphasizing that,the radiation signal with frequency higher than 1 THz was observed from the SWS sample-a first international case.The research work of this paper mainly covers the aspects of device design,sample fabrication,performance test,simulation and analysis of results,practical application and so on,specifically as follows:1)The brief introduction of THz technology,superconductivity of HTS,IJJs and other background knowledge;the development and application of BSCCO THz sources,the explanations of their emission mechanism,and the effect of self-heating;2)The introduction of GBG-structured THz source,including device design and fabrication,characteristics testing and analysis;3)A novel sandwich?SWS?structure was proposed,the realization of remarkable increase of the maximum voltage across the sample,the maximum operation temperature and the highest operation frequency;4)Simulation on the thermal mechanism of GBG and SWS samples using 3D finite element software COMSOL.Suggestions are given for future improvement of IJJs THz sources.