Research On The Key Technology Of Terahertz High Sensitivity Detector Based On Noise Thermometry

Terahertz band occupies nearly half of the photon energy of the universe after microwave background radiation(CMB),which is especially suitable for observing and studying the most important frontier scientific problems in astronomy,such as the formation and evolution of the first generation stars,galaxies,star and planetary systems,the physical and chemical properties of the atmosphere of extraterrestrial planetary systems,and the origin of cosmic life.High sensitivity terahertz incoherent detector is needed for terahertz continuous spectrum detection of cosmic dust thermal radiation and low resolution detection of ultra wideband terahertz molecular/atomic spectral lines(combined with spectrometer).At present,terahertz high-sensitivity incoherent detector technology mainly includes superconducting transition-edge sensors and superconducting kinetic inductance detectors,both of which can achieve background limit detection sensitivity,and have been applied in several terahertz astronomical telescopes(such as JCMT telescope in the United States,IRAM telescope in Europe,etc.).In recent years,another emerging terahertz band high-sensitivity incoherent detector technology,namely terahertz hot electron detection technology based on noise thermometry,has received extensive attention all over the world.Terahertz hot electron detector based on noise thermometry has the advantages of no DC bias,wide operating temperature range,large dynamic range,and relatively mature development of low noise amplifier.At present,terahertz hot electron bolometer based on noise thermometry is still in its infancy.For future terahertz astronomical applications,it is necessary to further understand the physical mechanism and material characteristics of terahertz hot electron bolometer based on noise thermometry.Based on the above background,this paper will study the detection mechanism and characteristics of terahertz hot electron bolometer based on three different materials.The main research contents and innovations include:Based on the noise thermometry technique,the direct detection characteristics of titanium hot electron bolometer are characterized.The high energy gap superconducting niobium electrode is used to suppress the thermal conductance due to electron diffusion of the microbridge.The results show that the thermal conductance due to electron diffusion in the hot electron bolometer is effectively reduced.The thermal conductance due to the noise equivalent power increases with temperature as NEP(?)T2.5.At 3.0 K,the thermal conductance is found to be G=3.79 × 10-8 W/K and the electrical NEP is as low as NEP=2.3×10-11W/(?).In addition,the HEB works efficiently up to 15 ?W input power.The development of a graphene-based hot electron bolometer is characterized by Johnson noise readout.The bolometer is a graphene microbridge connected to a log spiral antenna by Au contact pads.The Fourier transform spectrometer measurement shows the bolometer has high coupling efficiency in the frequency range from 0.3 to 1.6 THz.The result shows that the optical noise equivalent power is 5.6×10-12 W/(?)at 3.0 K.In addition,the experiment results shows that the thermal conductance due to electron diffusion decreases with the increase of the length of the microbridge.The investigation of direct detection behavior of a superconducting niobium nitride hot electron bolometer is characterized by noise thermometry.The measured noise equivalent power of the superconducting niobium nitride hot electron bolometer at different bias voltages shows that the superconducting niobium nitride hot electron bolometer has a noise equivalent power of 1.24×10-12W/(?)at its optimal bias point.The noise equivalent power measured by noise thermometry at two different readout bandwidths is also been studied.The results show that the noise equivalent power is better under wider readout bandwidth.It is found that the noise equivalent power represented by noise thermometry is smaller that of current readout due to the current readout is limited by readout circuit.The demonstration of an ultra-high-sensitivity superconducting hot electron bolometer heterodyne receiver at 2.5 THz with a quantum cascade laser based on a bound to continuum active region design and a semi-insulating surface-plasmon waveguide as its local oscillator has been reported.The most integrated hot electron bolometer and quantum cascade laser heterodyne mixer receiver has been successfully developed(integrated hot electron bolometer and quantum cascade laser in a same block at 4K).Measured with a vacuum setup,the heterodyne receiver exhibits a double sideband receiver noise temperature of 800 K at 2.5 THz with the IR filter contribution corrected,which is approximately 7hv/kB.The stability of the superconducting hot electron bolometer mixer is improved by PID controller.The research work of this paper has deepened the understanding of the performance of the hot electron bolometer.The noise thermometry method is used to characterize the performance of the hot electron bolometer as a direct detector.It lays an important foundation for the hot electron bolometer as a high sensitivity direct detection detector.It provides a higher possibility for subsequent large-scale integrated hot electron bolometers.