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Modeling and measured performance of integrated terahertz HEB receivers and focal plane arrays

Fernando Rodríguez‐Morales

Published Jan 1, 2007• 1 citation
OpenAlex

Abstract

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.

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Impedance and Bandwidth Characterization of NbN Hot Electron Bolometric Mixers

Fernando Rodríguez‐Morales, Sigfrid Yngvesson

We are presenting here our recent results of noise temperature and impedance measurements for NbN Hot Electron Bolometer (HEB) mixers. The noise temperature measurements were performed over a 1-8 GHz IF band using an LO frequency of about 1.6 THz using quasi-optical coupling and a single low noise HEMT MMIC amplifier. On the other hand, the impedance measurements were completed with a network analyzer in the presence of LO power and DC bias, over a 2-10 GHz frequency range. The experimental results of both sets of measurements are used to predict noise and gain bandwidth of our devices and for comparison with those obtained from the standard model.

•Apr 1, 2003•9 citations

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In this paper we discuss the stability of heterodyne terahertz receivers based on small volume NbN phonon cooled hot electron bolometers (HEBs). The stability of these receivers can be broken down in two parts: the intrinsic stability of the HEB mixer and the stability of the local oscillator (LO) signal injection scheme. Measurements show that the HEB mixer stability is limited by gain fluctuations with a 1∕f spectral distribution. In a 60MHz noise bandwidth this results in an Allan variance stability time of ∼0.3s. Measurement of the spectroscopic Allan variance between two intermediate frequency (IF) channels results in a much longer Allan variance stability time, i.e., 3s between a 2.5 and a 4.7GHz channel, and even longer for more closely spaced channels. This implies that the HEB mixer 1∕f noise is strongly correlated across the IF band and that the correlation gets stronger the closer the IF channels are spaced. In the second part of the paper we discuss atmospheric and mechanical system stability requirements on the LO-mixer cavity path length. We calculate the mixer output noise fluctuations as a result of small perturbations of the LO-mixer standing wave, and find very stringent mechanical and atmospheric tolerance requirements for receivers operating at terahertz frequencies.

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New advances in hot electron bolometer (HEB) mixers have recently resulted in record-low receiver noise temperatures at terahertz frequencies. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 2.24 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and local-oscillator power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers that will further increase the detection speed of terahertz systems.

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Experimental work on the development of a quasi-optical heterodyne receiver for the THz frequency range is reported. The mixing device is a superconducting hot electron bolometer (HEB) made from ultrathin, d = 3 - 5 nm, niobium nitride (NbN) films. Work described in this thesis comprises: The design of a prototype receiver using quasi-optical coupling. Device fabrication involving reactive magnetron sputtering of NbN films and lithographic definition of the antenna integrated mixer. An investigation of the receiver performance at frequencies between 0.6 THz and 2.5 THz. The best performance is obtained with HEB mixers made from NbN films with a thickness d = 3-3.5 nm and a critical temperature T c = 9 - 9.5 K. Double-side band receiver noise temperatures are 530 K at 0.6 THz, 650 K at 1.6 THz and 1100 K at 2.5 THz. Corrected for losses in the receiver input optics, these values amount to only 10 times the theoretical quantum limit. MgO as the substrate material has been shown to provide improved acoustic coupling between NbN film and the substrate compared to other materials such as Si or sapphire. A maximum IF gain bandwidth of 4.5 GHz has been measured under the same operating conditions which yield lowest noise temperature. The local oscilltor power requirement is ~250 nW absorbed in the bolometer. Quasi-optically coupled HEB mixers have become the device-of-choice for radio astronomical applications in the frequency regime at and above 1 THz.

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Heterodyne measurements of a NbN superconducting hot electron mixer at terahertz frequencies

Pavel A. Yagoubov, M. Kroug, H. Merkel +6 more

The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. The device is made from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are 0.2/spl times/2 /spl mu/m. The best results of the DSB noise temperature at 1.5 GHz IF frequency obtained with one device are: 1300 K at 650 GHz, 4700 K at 2.5 THz and 10000 K at 3.12 THz. The measurements were performed at 4.5 K ambient temperature. The amount of local oscillator (LO) power absorbed in the bolometer is about 100 nW. The mixer is linear to within 1 dB compression up to the signal level 10 dB below that of the LO. The intrinsic single sideband conversion gain measured at 650 GHz is -9 dB, the total conversion gain is -14 dB.

IEEE Transactions on Applied Superconductivity•Jun 1, 1999•6 citations
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.
We are presenting here our recent results of noise temperature and impedance measurements for NbN Hot Electron Bolometer (HEB) mixers. The noise temperature measurements were performed over a 1-8 GHz IF band using an LO frequency of about 1.6 THz using quasi-optical coupling and a single low noise HEMT MMIC amplifier. On the other hand, the impedance measurements were completed with a network analyzer in the presence of LO power and DC bias, over a 2-10 GHz frequency range. The experimental results of both sets of measurements are used to predict noise and gain bandwidth of our devices and for comparison with those obtained from the standard model.
In this paper we discuss the stability of heterodyne terahertz receivers based on small volume NbN phonon cooled hot electron bolometers (HEBs). The stability of these receivers can be broken down in two parts: the intrinsic stability of the HEB mixer and the stability of the local oscillator (LO) signal injection scheme. Measurements show that the HEB mixer stability is limited by gain fluctuations with a 1∕f spectral distribution. In a 60MHz noise bandwidth this results in an Allan variance stability time of ∼0.3s. Measurement of the spectroscopic Allan variance between two intermediate frequency (IF) channels results in a much longer Allan variance stability time, i.e., 3s between a 2.5 and a 4.7GHz channel, and even longer for more closely spaced channels. This implies that the HEB mixer 1∕f noise is strongly correlated across the IF band and that the correlation gets stronger the closer the IF channels are spaced. In the second part of the paper we discuss atmospheric and mechanical system stability requirements on the LO-mixer cavity path length. We calculate the mixer output noise fluctuations as a result of small perturbations of the LO-mixer standing wave, and find very stringent mechanical and atmospheric tolerance requirements for receivers operating at terahertz frequencies.
New advances in hot electron bolometer (HEB) mixers have recently resulted in record-low receiver noise temperatures at terahertz frequencies. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 2.24 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and local-oscillator power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers that will further increase the detection speed of terahertz systems.
Experimental work on the development of a quasi-optical heterodyne receiver for the THz frequency range is reported. The mixing device is a superconducting hot electron bolometer (HEB) made from ultrathin, d = 3 - 5 nm, niobium nitride (NbN) films. Work described in this thesis comprises: The design of a prototype receiver using quasi-optical coupling. Device fabrication involving reactive magnetron sputtering of NbN films and lithographic definition of the antenna integrated mixer. An investigation of the receiver performance at frequencies between 0.6 THz and 2.5 THz. The best performance is obtained with HEB mixers made from NbN films with a thickness d = 3-3.5 nm and a critical temperature T c = 9 - 9.5 K. Double-side band receiver noise temperatures are 530 K at 0.6 THz, 650 K at 1.6 THz and 1100 K at 2.5 THz. Corrected for losses in the receiver input optics, these values amount to only 10 times the theoretical quantum limit. MgO as the substrate material has been shown to provide improved acoustic coupling between NbN film and the substrate compared to other materials such as Si or sapphire. A maximum IF gain bandwidth of 4.5 GHz has been measured under the same operating conditions which yield lowest noise temperature. The local oscilltor power requirement is ~250 nW absorbed in the bolometer. Quasi-optically coupled HEB mixers have become the device-of-choice for radio astronomical applications in the frequency regime at and above 1 THz.
New advances in Hot Electron Bolometer (HEB) mixers have resulted in record low receiver noise temperatures at THz frequencies recently. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 1.56 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and LO power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers which will further increase the detection speed of THz systems.
The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. The device is made from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are 0.2/spl times/2 /spl mu/m. The best results of the DSB noise temperature at 1.5 GHz IF frequency obtained with one device are: 1300 K at 650 GHz, 4700 K at 2.5 THz and 10000 K at 3.12 THz. The measurements were performed at 4.5 K ambient temperature. The amount of local oscillator (LO) power absorbed in the bolometer is about 100 nW. The mixer is linear to within 1 dB compression up to the signal level 10 dB below that of the LO. The intrinsic single sideband conversion gain measured at 650 GHz is -9 dB, the total conversion gain is -14 dB.