Research On The Key Technology Of The Terahertz Radiometer Front End

Terahertz wave lies between microwave and light wave,it has the advantages of them both and it has great application prospects.Many countries in Europe and North America have all listed terahertz technology as a key development orientation.At present,the frequency for solid state application is high up to 5THz.The terahertz radiometer is one kind of receivers to measure the electromagnetic energy radiating from an object.It has the advantages of high security,resolution and sensitivity.Therefore,the terahertz radiometer is one of the important applications of terahertz technology.The methodology to build the Schottky diode model is thoroughly analyzed in this dissertation.The Schottky diodes are developed and applied in the 330 GHz and 420 GHz subharmonic mixers.Monolithic integration technology is researched to achieve system miniaturization.A 330 GHz GaAs monolithically integrated subharmonic mixer and a 420 GHz heterogeneously integrated subharmonic mixer based on quartz substrate are successfully developed,assembled and measured.This dissertation proposes an analysis method to optimize the Schottky diode according to the mixer performance.The nonlinear characteristics and physical mechanisms of the Schottky diode are theoretically analyzed;the geometric structure and the main parameters of the Schottky diode are studied;the frequency conversion mechanism of the Schottky diode is deeply analyzed and finally an accurate three-dimensional model of the Schottky diode is established.According to the system requirements,the Schottky diode is designed and optimized.The vertical channel structure is proposed to decrease the diode parasitic parameters.Finally a planar Schottky diode is realized.The in-depth study from diode to circuit can maximize the conversion efficiency of the subharmonic mixer circuit.The measured I-V curve agrees well with the simulated one.330GHz and 420 GHz hybrid integrated subharmonic mixers are designed and optimized based on the designed Schottky diodes in this dissertation.Simulation method to optimize the subharmonic mixer is described and the tolerance analysis is carried out.The main factors affecting the performance of the mixer are discussed in detail.The simulation and measured results are in good agreement,which verifies the theoretical analysis and provides a realizing approach for the terahertz subharmonic mixer design.In order to improve the system integration,the GaAs monolithic integration technology and heterogeneous integration technology are researched in this dissertation.The 330 GHz monolithically integrated subharmonic mixer is realized on a 12?m gallium arsenide substrate and its minimum conversion loss is 12 dB.In order to reduce the loss introduced by the substrate,a new 420 GHz heterogeneously integrated subharmonic mixer is realized on a 50?m quartz substrate with a lower dielectric constant.The 420 GHz heterogeneously integrated subharmonic mixer achieves best conversion loss of 10 dB.On the basis of key component realization,the experiment on the equivalent noise temperature and temperature sensitivity is carried out.The equivalent noise temperature measurement platform and the temperature sensitivity measurement platform of the superheterodyne radiometer system are set up based on the 330 GHz subharmonic mixer.The Y-factor method is used to measure the noise temperature of the receiver,which is about 3112 K.Under the testing condition of 20 ms integration time and 150 MHz bandwidth before detection,the radiometer temperature sensitivity is 1.96 K.