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Softwaretechnik-Trends

NbTiN Based Tuning Structures for Broadband Nb-Al 2 O >3 -Nb SIS Mixers from 640 GHz-800 GHz

S. Glenz, Sybille Haas, Cornelia E. Honingh, Karl Jacobs

Published Dec 1, 2001• 0 citations
OpenAlex

Abstract

We present measurements with a prototype waveguide SIS mixer for band 2 (640 GHz – 800 GHz) of HIFI (Heterodyne Instrument for FIRST). The Nb/Al2O3/Nb junctions have an RnA product from 12–18 Ωμm. These junctions are embedded in microstrip circuits tuning out the device capacitance using a NbTiN ground layer and various top conductor materials such as NbTiN, Nb and Al. The NbTiN films are fabricated by DC magnetron sputtering which is optimized for a minimum value of the DC resistivity and for a high critical temperature by varying the sputter pressure, sputter power and Ar:N2 flow. Typical NbTiN film parameters for device fabrication are ρ = 120 μΩcm and Tc = 14.5 K. The best uncorrected noise temperatures we measured so far are for devices with NbTiN/SiO2/Nb tuning. At 4.2 K bath temperature, a standard Yfactor measurement yields uncorrected receiver noise temperatures of 350 K at 642 GHz and 500 K at 810 GHz for 1.5 GHz intermediate frequency. We discuss the effect of the various tuning circuit materials on the mixer performance. In addition, measurements at IF’s between 4 GHz and 8 GHz will be presented.

Related papers

Broadband Array SIS Mixers for 780-880 GHz with Aluminum Tuning Circuits

Sybille Haas, Stefanie Wulff, D. Hottgenroth +2 more

Abstract—As a building block for an 8-pixel 800 GHz array receiver at KOSMA we developed a low noise SIS mixer. The mixerblock is tunerless and similar to the "stamped waveguide cavity " mixers we have used from 345 GHz to 800 GHz before [1]. We embedded the SIS junction into a standard broadband tuning circuit, commonly used at lower frequencies. The circuit consists of a short end-loaded stub in series with two impedance transforming sections. For the 780-880 GHz band, we fabricated the electrodes of the tuning circuit as a combination of niobium and aluminum layers in different sequences. First heterodyne tests were performed on devices with a tuning microstrip circuit ground plane consisting of 40nm Nb with 200nm of Al on top and a top conductor consisting of a 70 nm thick Nb layer with a 280 nm thick Al layer on top. The Nb-Al2O3-Nb junction has an area of about 0.5 µm 2 and is fabricated with optical lithography. For anisotropic Nb etching, we use a RIE gas mixture of CCl2F2 and NF3. The Al2O3 barrier is removed with Ar sputter etching. Fabrication yield improved considerably when we introduced a light CMP-step after self-aligned SiO dielectric liftoff. For a SIS junction with RnA equal to 14 Ωµm 2, the RSubgap/Rn value of 15.4 is remarkably good. We measured uncorrected receiver noise temperatures around 400 K over the whole band from 780 to 880 GHz, with a best noise temperature of 370 K at 804 GHz. 1

•May 1, 2000•3 citations

MIXER DEVELOPMENT FOR HIFI BAND 2 (640 — 800 GHz)

Cornelia E. Honingh, M. Justen, R. Teipen +2 more

We present a fixed tuned SIS waveguide mixer for 640-800 GHz. The waveguide and filter design has been done using 3D EM-Simulation to improve the accuracy of the design for the required large fractional bandwidth. In this frequency range we use standard Nb—Al20 3—Nb SIS junctions with an R NA product of approximately 15 ohm!Am 2 , and areas between 1 gm 2 and 0.4 firll 2 . The choice of tuning structure material is not directly obvious because the frequency range includes the niobium gap frequency at 700 Gliz. Therefore devices with a NbTiN ground plane and as a choice with a niobium or an aluminum top electrode are used Current best noise temperatures are 300 K at the lower frequency end of the band and 450 K at the high end of the band, measured with the prototype HIFI mixer at 4-8 GHz IF frequency, for a device with a niobium top electrode., Measurements and analysis of devices with different designs, and both integrated tuning structure top electrode materials will be presented. The accuracy of the RF mixer design will be evaluated.

•Mar 1, 2002•0 citations

Mixing Properties of NbN-Based SIS Mixers With NbTiN Wirings

Mahoto Takeda, Wenlei Shan, Takafumi Kojima +5 more

We report on the mixing properties of waveguide SIS mixers with epitaxial NbN/AlN/NbN junctions and NbN/SiO2/NbTiN microstrips on MgO substrates. The superconducting transition temperature and 20-K resistivity of NbTiN film on the SiO2dielectric were 14.7 K and 175 muOmega cm, respectively. The junction tuning circuit was composed of an NbN/SiO2/NbTiN microstrip and two parallel-connected NbN/AlN/NbN junctions 0.9 mum in diameter. The critical current density and normal-state resistance of the fabricated NbN junction were 13 kA/cm2and 22 Omega, respectively. The heterodyne response was measured using 295- and 77-K blackbody sources, a local oscillator (LO) source, and a 25-mum-thick Kapton film as a beam splitter. An intermediate frequency (IF) amplifier with a bandwidth of 4-12 GHz was used in the measurements. The receiver noise temperature corrected for losses in the beam splitter and in the vacuum window of the cryocooler was 370 K at 860 GHz and was comparable to that of all-NbN mixes with NbN/MgO/NbN microstrips.

IEEE Transactions on Applied Superconductivity•May 27, 2009•10 citations

NbTiN/SiO 2 /NbTin and NbTiN/SiO 2 /Al Tuning Circuits for 1 THz Waveguide SIS Mixers

Brian D. Jackson, Gert J. de Lange, W. M. Laauwen +3 more

Waveguide SIS mixers are presented in which Nb/Al-AlOx/Nb tunnel junctions are integrated with both NbTiN/SiO2/NbTiN and NbTiN/SiO2/Al tuning circuits. The mixers with a NbTiN/SiO2/NbTiN tuning circuit yield relatively low receiver noise temperatures between 700 and 830 GHz, but their sensitivity drops significantly above ~ 850 GHz. In contrast, low-noise heterodyne mixing near 1 THz is observed in mixers incorporating a NbTiN/SiO2/Al tuning circuit. In particular, an uncorrected receiver noise temperature of 585 K is measured at 970 GHz. From an analysis of the receiver sensitivity and gain, it is determined that the loss in the NbTiN ground plane is low (≤ 0.6 dB) below 970 GHz. A decrease in receiver sensitivity above 1 THz is attributed to an onset of rf loss in the NbTiN.

•May 1, 2000•1 citation

Fabrication and Noise Measurement of NbTiN Hot Electron Bolometer Heterodyne Mixers at THz Frequencies

P. Khosropanah, S. Bedorf, Serguei Cherednichenko +4 more

The paper reports the latest development and the measured results of NbTiN hot electron bolometer mixers at THz frequencies. The devices are based on 4-7 nm thin NbTiN films, which were deposited by reactive magnetron sputtering of NbTi target in an Ar/N2 atmosphere, on heated high-resistivity Si substrates over a 20 nm thick AlN buffer layer. The quality parameters of the film are transition temperature and normal-state resistivity, which were optimized by varying the sputtering parameters. The resistivity and the critical temperature of the films are about 400 μΩcm and 9 K, respectively. Bolometers (4 μm wide and 0.7 μm long), integrated with logarithmic spiral antennas are fabricated. Mixer noise performance is tested in a quasi-optical receiver in 1.5-4 GHz IF band. The DSB receiver noise temperature of 700 K, 1100 K and 3000 K is obtained at 0.7, 1.6 and 2.6 THz LO frequencies, respectively.

•Apr 1, 2003•5 citations

Low-noise waveguide SIS mixer with NbN/AlN/NbN tunnel junctions tuned by an NbN/MgO/NbTiN microstrip circuit

Masanori Takeda, Wenlei Shan, Takafumi Kojima +4 more

The low-noise performance of a waveguide SIS mixer with NbN/AlN/NbN tunnel junctions and an NbN/MgO/NbTiN tuning circuit on an MgO substrate was demonstrated at frequencies above the gap frequency of Nb. To design the mixer, the complex refractive index of the MgO substrate was measured by using a THz time-domain spectrometer. The superconductive properties of NbTiN films on MgO were examined in detail. An uncorrected receiver noise temperature of 262 K (DSB) at 820 GHz was achieved in an IF bandwidth of 4-12 GHz at a bath temperature of 4.2 K. By comparing the measured and calculated conversion gains, the loss in the NbN/MgO/NbTiN tuning circuit was estimated to be 0.98 dB at 810 GHz.

Superconductor Science and Technology•Jun 10, 2009•10 citations
We present measurements with a prototype waveguide SIS mixer for band 2 (640 GHz – 800 GHz) of HIFI (Heterodyne Instrument for FIRST). The Nb/Al2O3/Nb junctions have an RnA product from 12–18 Ωμm. These junctions are embedded in microstrip circuits tuning out the device capacitance using a NbTiN ground layer and various top conductor materials such as NbTiN, Nb and Al. The NbTiN films are fabricated by DC magnetron sputtering which is optimized for a minimum value of the DC resistivity and for a high critical temperature by varying the sputter pressure, sputter power and Ar:N2 flow. Typical NbTiN film parameters for device fabrication are ρ = 120 μΩcm and Tc = 14.5 K. The best uncorrected noise temperatures we measured so far are for devices with NbTiN/SiO2/Nb tuning. At 4.2 K bath temperature, a standard Yfactor measurement yields uncorrected receiver noise temperatures of 350 K at 642 GHz and 500 K at 810 GHz for 1.5 GHz intermediate frequency. We discuss the effect of the various tuning circuit materials on the mixer performance. In addition, measurements at IF’s between 4 GHz and 8 GHz will be presented.
Abstract—As a building block for an 8-pixel 800 GHz array receiver at KOSMA we developed a low noise SIS mixer. The mixerblock is tunerless and similar to the "stamped waveguide cavity " mixers we have used from 345 GHz to 800 GHz before [1]. We embedded the SIS junction into a standard broadband tuning circuit, commonly used at lower frequencies. The circuit consists of a short end-loaded stub in series with two impedance transforming sections. For the 780-880 GHz band, we fabricated the electrodes of the tuning circuit as a combination of niobium and aluminum layers in different sequences. First heterodyne tests were performed on devices with a tuning microstrip circuit ground plane consisting of 40nm Nb with 200nm of Al on top and a top conductor consisting of a 70 nm thick Nb layer with a 280 nm thick Al layer on top. The Nb-Al2O3-Nb junction has an area of about 0.5 µm 2 and is fabricated with optical lithography. For anisotropic Nb etching, we use a RIE gas mixture of CCl2F2 and NF3. The Al2O3 barrier is removed with Ar sputter etching. Fabrication yield improved considerably when we introduced a light CMP-step after self-aligned SiO dielectric liftoff. For a SIS junction with RnA equal to 14 Ωµm 2, the RSubgap/Rn value of 15.4 is remarkably good. We measured uncorrected receiver noise temperatures around 400 K over the whole band from 780 to 880 GHz, with a best noise temperature of 370 K at 804 GHz. 1
We present a fixed tuned SIS waveguide mixer for 640-800 GHz. The waveguide and filter design has been done using 3D EM-Simulation to improve the accuracy of the design for the required large fractional bandwidth. In this frequency range we use standard Nb—Al20 3—Nb SIS junctions with an R NA product of approximately 15 ohm!Am 2 , and areas between 1 gm 2 and 0.4 firll 2 . The choice of tuning structure material is not directly obvious because the frequency range includes the niobium gap frequency at 700 Gliz. Therefore devices with a NbTiN ground plane and as a choice with a niobium or an aluminum top electrode are used Current best noise temperatures are 300 K at the lower frequency end of the band and 450 K at the high end of the band, measured with the prototype HIFI mixer at 4-8 GHz IF frequency, for a device with a niobium top electrode., Measurements and analysis of devices with different designs, and both integrated tuning structure top electrode materials will be presented. The accuracy of the RF mixer design will be evaluated.
We report on the mixing properties of waveguide SIS mixers with epitaxial NbN/AlN/NbN junctions and NbN/SiO2/NbTiN microstrips on MgO substrates. The superconducting transition temperature and 20-K resistivity of NbTiN film on the SiO2dielectric were 14.7 K and 175 muOmega cm, respectively. The junction tuning circuit was composed of an NbN/SiO2/NbTiN microstrip and two parallel-connected NbN/AlN/NbN junctions 0.9 mum in diameter. The critical current density and normal-state resistance of the fabricated NbN junction were 13 kA/cm2and 22 Omega, respectively. The heterodyne response was measured using 295- and 77-K blackbody sources, a local oscillator (LO) source, and a 25-mum-thick Kapton film as a beam splitter. An intermediate frequency (IF) amplifier with a bandwidth of 4-12 GHz was used in the measurements. The receiver noise temperature corrected for losses in the beam splitter and in the vacuum window of the cryocooler was 370 K at 860 GHz and was comparable to that of all-NbN mixes with NbN/MgO/NbN microstrips.
Waveguide SIS mixers are presented in which Nb/Al-AlOx/Nb tunnel junctions are integrated with both NbTiN/SiO2/NbTiN and NbTiN/SiO2/Al tuning circuits. The mixers with a NbTiN/SiO2/NbTiN tuning circuit yield relatively low receiver noise temperatures between 700 and 830 GHz, but their sensitivity drops significantly above ~ 850 GHz. In contrast, low-noise heterodyne mixing near 1 THz is observed in mixers incorporating a NbTiN/SiO2/Al tuning circuit. In particular, an uncorrected receiver noise temperature of 585 K is measured at 970 GHz. From an analysis of the receiver sensitivity and gain, it is determined that the loss in the NbTiN ground plane is low (≤ 0.6 dB) below 970 GHz. A decrease in receiver sensitivity above 1 THz is attributed to an onset of rf loss in the NbTiN.
The paper reports the latest development and the measured results of NbTiN hot electron bolometer mixers at THz frequencies. The devices are based on 4-7 nm thin NbTiN films, which were deposited by reactive magnetron sputtering of NbTi target in an Ar/N2 atmosphere, on heated high-resistivity Si substrates over a 20 nm thick AlN buffer layer. The quality parameters of the film are transition temperature and normal-state resistivity, which were optimized by varying the sputtering parameters. The resistivity and the critical temperature of the films are about 400 μΩcm and 9 K, respectively. Bolometers (4 μm wide and 0.7 μm long), integrated with logarithmic spiral antennas are fabricated. Mixer noise performance is tested in a quasi-optical receiver in 1.5-4 GHz IF band. The DSB receiver noise temperature of 700 K, 1100 K and 3000 K is obtained at 0.7, 1.6 and 2.6 THz LO frequencies, respectively.
The low-noise performance of a waveguide SIS mixer with NbN/AlN/NbN tunnel junctions and an NbN/MgO/NbTiN tuning circuit on an MgO substrate was demonstrated at frequencies above the gap frequency of Nb. To design the mixer, the complex refractive index of the MgO substrate was measured by using a THz time-domain spectrometer. The superconductive properties of NbTiN films on MgO were examined in detail. An uncorrected receiver noise temperature of 262 K (DSB) at 820 GHz was achieved in an IF bandwidth of 4-12 GHz at a bath temperature of 4.2 K. By comparing the measured and calculated conversion gains, the loss in the NbN/MgO/NbTiN tuning circuit was estimated to be 0.98 dB at 810 GHz.