Research On The Characteristics Of Terahertz Superconducting Electronic Mixers And Phase Change Edge Detectors

Terahertz(THz)frequencies play a vital role in the study of primordial gravitational wave,cosmic microwave background,formation and evolution of galaxies,star and planets,physics and chemistry of exoplanet atmosphere.Until now,a number of telescope working at THz frequencies have been built,(such as ALMA,SOFIA,JCMT,APEX,etc.),where high sensitive coherent and incoherent detectors(or arrays)were applied.Though superconducting hot electron bolometer(HEB)mixers become the detector of choice at frequencies beyond 1.5THz,still there is much room to improve,with regard to the sensitivity,intermediate frequency(IF)bandwidth and operation temperature.Superconducting transition edge sensors(TES)with background noise limited sensitivity and multiplexing read-out capability are very suitable for detection of broad band continuum spectrum in array imaging systems.This thesis focused on the development of superconducting hot electron bolometers and superconducting transition edge sensors for ultra-sensitive THz astronomical observation.We have achieved the following main results:1.We have thoroughly studied the effect of NbN-Au contact pads on the performance of a NbN superconducting hot electron bolometer mixer.It has been found that when the contact pads were at resistive state,the receiver noise temperature deteriorated dramatically due to the increase of the conversion loss with bath temperature.Meanwhile,the effective microbridge became shorter due to the proximity effect,which made the IF bandwidth increased as a result of the enhanced the electron diffusion cooling.2.We have explored the electrical features of FeSeTe superconducting hot electron bolometer based on the 100 nm thick FeSeTe film.Based on the characterization of the resistivity FeSeTe film at different temperature,we designed and fabricated hot electron bolometer.The critical temperature of the hot electron bolometer is reduced to 6K from 15 K due to the over-etching,and the required local oscillator power of the device is about 500 nW,comparable to normal NbN superconducting HEB mixers.This work provides the basis for further optimization of a FeSeTe superconducting HEB mixer.3.We have studied the electrical characteristics of free-standing membrane supported Ti TES in detail.By doing KOH we etching,the critical temperature of the Ti microbridge is reduced to 350 mK and its normal state resistance is increased to 30 ?.The measured thermal conductance is 800 pW/K,effective response time is 5?s,and noise equivalent power is 5x10-17 W/Hz0.5,which meet the requirements for the background noise limitation of ground-based applications.In conclusion,this study provides further understanding of superconducting HEB mixers and TES detectors,and also lays a foundation for applications on terahertz telescopes in the future.