Vladimir Drakinskiy

Hot-electron bolometer terahertz mixers for the Herschel Space Observatory.

We report on low noise terahertz mixers (1.4-1.9 THz) developed for the heterodyne spectrometer onboard the Herschel Space Observatory. The mixers employ double slot antenna integrated superconducting hot-electron bolometers (HEBs) made of thin NbN films. The mixer performance was characterized in terms of detection sensitivity across the entire rf band by using a Fourier transform spectrometer (from 0.5 to 2.5 THz, with 30 GHz resolution) and also by measuring the mixer noise temperature at a limited number of discrete frequencies. The lowest mixer noise temperature recorded was 750 K [double sideband (DSB)] at 1.6 THz and 950 K DSB at 1.9 THz local oscillator (LO) frequencies. Averaged across the intermediate frequency band of 2.4-4.8 GHz, the mixer noise temperature was 1100 K DSB at 1.6 THz and 1450 K DSB at 1.9 THz LO frequencies. The HEB heterodyne receiver stability has been analyzed and compared to the HEB stability in the direct detection mode. The optimal local oscillator power was determined and found to be in a 200-500 nW range.

Integrated 200–240-GHz FMCW Radar Transceiver Module

We present a 220-GHz homodyne transceiver module intended for frequency modulated continuous wave radar applications. The RF transceiver circuits are fabricated on 3-μm-thick GaAs membranes, and consist of a Schottky diode based transmitter frequency doubler that simultaneously operates as a sub-harmonic down-converting mixer. Two circuits are used in a balanced configuration to improve the noise performance. The output power is > 3 dBm over a 40-GHz bandwidth (BW) centered at 220 GHz, and the receiver function is characterized by a typical mixer conversion loss of 16 dB. We present radar images at 4-m target distance with up to 60-dB dynamic range using a 30-μs chirp time, and near-BW-limited range resolution. The module is intended for applications in high-resolution real-time 3-D radar imaging, and the unit is therefore designed so that it can be assembled into 1-D or 2-D arrays.

A Room Temperature Bolometer for Terahertz Coherent and Incoherent Detection

We present a novel room temperature bolometer with nanosecond response that can be used both for coherent and incoherent detection through the entire terahertz frequency range. A responsivity of up to 15 V/W, and a noise equivalent power (NEP) ~ 450 pW/Hz0.5 were measured at modulation frequencies from 0.5 kHz to 100 kHz. A conversion gain of -28 dB was demonstrated at an intermediate frequency of 20 MHz with a Local Oscillator power of 0.74 mW. Possible improvements of the bolometer characteristics are discussed.

Terahertz mixing in MgB2 microbolometers

Authors report on a terahertz (600 GHz) mixing experiment with MgB2 microbolometers in the resistive state. We observed that for a 20 nm film a mixer gain bandwidth of 2.3 GHz can be achieved, corresponding to an energy relaxation time of 70 ps. The experimental results were analyzed using a two-temperature model. As a result, the phonon escape time  20 ps was deduced. At 1.6THz the MgB2 mixer uncorrected noise temperature was 11000K. The obtained results show that MgB2 bolometers are good prospects for the terahertz range as both broadband mixers and fast direct detectors.

Low noise MgB2 terahertz hot-electron bolometer mixers

We report on low noise terahertz bolometric mixers made of MgB2 superconducting thin films. For a 10-nm-thick MgB2 film, the lowest mixer noise temperature was 600 K at 600 GHz. For 30 to 10-nm-thick films, the mixer gain bandwidth is an inverse function of the film thickness, reaching 3.4 GHz for the 10-nm film. As the critical temperature of the film decreases, the gain bandwidth also decreases, indicating the importance of high quality thin films for large gain bandwidth mixers. The results indicate the prospect of achieving a mixer gain bandwidth as large as 10-8 GHz for 3 to 5-nm-thick MgB2 films.

Millimetre-Wave Phase Shifter Based on Dielectric Rod Waveguide

In this work we propose a novel millimetre-wave phase shifter targeted on thin ferroelectric film technology. Architecture of the phase shifter is proposed to use a dielectric rod waveguide with a periodic printed array of electrically small dipoles loaded with a ferroelectric varactor (pin diode, Schottky diode, etc.) with the function of control the phase of the propagating wave. The proposed architecture of the phase shifter is verified by measuring two prototypes, where the tuneable elements (ferroelectric varactor) are replaced by non-tuneable capacitors with 10 fF and 15 fF respectively. The measurements revealed a considerable phase shift and small insertion losses. It is demonstrated that the proposed periodic structure using the dielectric rod waveguide allows to fully realize a potential of known tuneable elements at millimetre-wavelengths.

Development of a 557 GHz GaAs monolithic membrane-diode mixer

We present the development of a monolithically integrated 557 GHz membrane Schottky diode mixer. RF test shows state-of-the-art performance with an optimum receiver noise temperature below 1300 K DSB and an estimated mixer DSB conversion loss of 9 dB and a mixer DSB noise temperature of 1100 K including all losses.

Gain bandwidth of NbN hot-electron bolometer terahertz mixers on 1.5 um Si3N4 /SiO2 membranes

The gain bandwidth of NbN hot-electron bolometer terahertz mixers on electrically thin Si3N4 /SiO2 membranes was experimentally investigated and compared with that of HEB mixers on bulk substrates. A gain bandwidth of 3.5 GHz is achieved on bulk silicon, whereas the gain bandwidth is reduced down to 0.6–0.9 GHz for mixers on 1.5 um Si3 N4 /SiO2 membranes. We show that application of a MgO buffer layer on the membrane extends the gain bandwidth to 3 GHz. The experimental data were analyzed using the film-substrate acoustic mismatch approach.

Study of IF Bandwidth of

A noise bandwidth (NBW) of 6-7 GHz was obtained for hot-electron bolometer (HEB) mixers made of 10 nm MgB₂ films. A systematic investigation of the (IF) gain bandwidth as a function of the MgB₂ film thickness (30, 15, and 10 nm) is also presented. The gain bandwidth (GBW) of 3.4 GHz was measured for a 10 nm film, corresponding to a mixer time constant of 47 ps. For 10 nm films a reduction of the GBW was observed with the reduction of the critical temperature (<i>Tc</i>). Experimental data were analyzed using the two-temperature model. From the theoretical analysis, the electron-phonon time (τ_{e - ph}), the phonon escape time (τ_esc) and the electron and phonon specific heats (c_e, c_ph) were extrapolated giving the first model for HEB mixers of MgB₂ films.

{\hbox{MgB}}_{2}

A high sensitivity broadband terahertz direct detector based on YBa₂Cu₃O₇ high-Tc superconductor microbolometers is presented. At 77 K, the responsivity of the spiral antenna-integrated microbolometers (1.5 μm ×1.5 μm) is 190 V/W, referenced to the input of the silicon substrate lens, across the frequency range of 330 GHz-1.63 THz in a single device. The response time is approximately 300 ps. Using a room temperature readout, we measure an optical noise equivalent power (NEP) of 20 pW/Hz^0.5 (readout noise limited) for modulation frequencies ranging from 500 Hz to 100 kHz.