Modeling and measured performance of integrated terahertz HEB receivers and focal plane arrays
This dissertation presents a detailed study of the intermediate frequency (IF) properties of NbN hot electron bolometric (HEB) terahertz mixers, performed over the widest reported IF frequency range. A broadband technique to obtain the IF small signal impedance of HEB devices using network analyzer measurements is presented. The superconducting mixer impedance is measured for local oscillator (LO) frequencies ranging from 694 GHz to 1.9 THz and for a 1-10 GHz IF range. The results obtained are in agreement with the so-called Standard and NSGR models. Further, the variation of receiver noise, mixer gain, and output noise with IF frequency is experimentally estimated for several devices and for a wide range of dynamic conditions using LO frequencies of up to about 2 THz (fLO < 2 THz). Empirical results demonstrate near-quantum limited noise performance with wide receiver bandwidth. A record IF noise bandwidth of 8 GHz (measured for f LO = 694 GHz) and a record effective IF bandwidth of 5 GHz (measured for fLO = 1:6 THz) are demonstrated without using ferrite isolators. The stability of HEB mixers is measured for different IF bandwidths for the first time using the so-called Allan variance. Further evidence of intrinsic device stability limitations is presented.
An algorithm to design integrated receivers based on HEB mixer elements is proposed and implemented. The measured impedance of the mixer is used to obtain consistent model parameters. The Standard model formalism for the mixer is used in combination with computer models for the IF amplifier to find theoretical estimates of the receiver performance. Good agreement between theoretical and empirical results is found.
The direct and close integration of HEB mixers with InP microwave monolithic integrated circuit (MMIC) IF amplifiers is accomplished for the first time. Several compact down-converter prototypes for terahertz frequencies are demonstrated using two- and three-dimensional integration methods. Using the integration techniques described here, it has been possible to decrease the volume of our receivers by a factor of 20 (with a corresponding mass reduction of 15:1) while maintaining good electrical performance.
Finally, a compact 3-element focal plane array (FPA) based on 2D integrated receivers is designed, constructed, and experimentally verified. This is the first heterodyne FPA to be reported for any frequency greater than 1 THz. It is hoped that the results presented here will serve as the basis for the development of large-format arrays with potentially hundreds of elements.