Terahertz Integrated Circuits for Radio Astronomy Applications

Sina Fathi EUC Berlin, 2014

07.05.2014 Sina Fathi, CST European User Conference 1

Agenda

Introduction − Radio Astronomy − Radio telescope and atmospheric window

KOSMA Laboratory − Superconducting based detectors (SIS, HEB,…)

CST Suite Software − 3D design of waveguides, antennas,… − Modeling of superconducting materials − Some examples of designed circuits − Comparison between simulation result and FTS

measurement of HEB mixer at 4.7THz Conclusion

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Introduction

Radio Astronomy: Mixing sky signals (RF) to lower frequencies (IF) Observations begin from hundred GHz to a few THz

(~5THz)

27.05.2014 3 0.1 – 10 GHz IF

0.3 – 5 THz RF

Introduction

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Pillars of Creation

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far-infrared: ESA/Herschel/PACS/SPIRE/Hill, Motte, HOBYS Key Programme Consortium; ESA/XMM-Newton/EPIC/XMM-Newton-SOC/Boulanger; optical: MPG/ESO; near-infrared/VLT/ISAAC/McCaughrean & Andersen/AIP/ESO

Radio Telescope

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Filter Spectrometer Single Ended Receiver

Applying heterodyne receiver because of no sufficient low noise amplifier for electronic processing of weak signals from 300 GHz to several THz

Receivers with HEMT amplifier at 100 GHz

K H Gundlach and M Schicke, IRAM, Supercond.

Sci. Technol. 13 (2000)

SMART Receiver on Nanten 2

Great Receiver on SOFIA, 2010

Atmospheric Window

Atmospheric frequency windows determine ground based observations

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Observations especially at lower THz frequencies should be done at high altitude

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Herschel Satellite (May 2009) 3.5 meter mirror 480 GHz to 1910 GHz (SIS and

HEB mixers) Band 2 (640-800 GHz) by KOSMA

ALMA observatory (2013 Inauguration)

SOFIA Observatory (First light on May 2010) NANTEN 2 Observatory (May 2006)

1.3 - 1.4 THz / 1.9 THz / 2.5 THz / 4.7 THz (May 2014) (HEB Mixers, KOSMA)

Atacama Desert, Chile, 4800 meter altitude 110 GHz to 880 GHz (SIS mixers, KOSMA)

Atacama desert Chile, 5,058 meter altitude 66 telescopes (12 meter and 7 meter) 31-950 GHz frequency range (HEMT for two

lowest bands and SIS mixers for above 84GHz)

KOSMA Laboratory

Development of superconducting based detectors working at millimeter and sub-millimeter frequency ranges: Development:

Design Micro/nano-fabrication Cryogenic THz measurements Waveguide machining

Detectors: Nonlinear mixing devices like SIS or HEB, Balanced and side band separating mixers, Waveguides, antennas,…

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SIS and HEB Mixers Superconductor-Insulator-Superconductor (SIS):

The most sensitive heterodyne receivers from 100 GHz to 1.1 THz Two superconductors are separated by a really thin layer insulator Two common frequency mixers are Nb/AlOx/Nb or high current density

Nb/AlN/Nb (Tc of Nb≈9 K) Current passes through the junction via tunneling process Strong nonlinear current-voltage (I-V) characteristic Modelling as a parallel resistor and large junction capacitance

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𝒉𝝂 𝒆� 𝒎𝒎

30𝜇𝜇

𝒅 = 𝟎.𝟗𝟗𝒎

SIS and HEB Mixers Hot Electron Bolometer (HEB):

Not limited by energy gap of the superconductor (up to several THz) Required very low LO power (20-1000 nW) and unlike SIS does not

increase with frequency HEB is a square law mixer Model as a resistor (proximity effect-NbN is simulated as a normal

conductor)

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Au

Microbridge of NbN, NbTiN,…

Au NbN NbN

Tc = 9.3 K Ic= 400 µA

At 4.2 K in He(l)

Balanced Mixer

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Advantages of balanced mixer configuration over the single ended mixer:

Reduces a side band noise of LO Separates the RF and LO inputs from each other that eases integration of

several pixels in focal plane arrays configuration

CST 3D models Using mainly CST microwave suite to design our THz integrated circuits Integrated superconducting balanced mixer working at 350-500 GHz

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Port 3

Port 2

Port 4

Port 1

Nb based circuitry SiO2 bridges (No airbridge) 9𝜇𝜇Silicon membrane

12 micron

−𝟗𝟎.𝟐𝟐𝟐 −𝟐𝟏𝟏.𝟓𝟓

S3,1

S2,1

E-Field Monitor of IBAMI Absolute E-Field monitor of IBAMI mixer (Two antennas and a 90° branch line coupler)

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Fabricated IBAMI

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1 cm

Receiver Noise Temperature of prototype LF band of CHAI Receiver

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The measured receiver noise temperature over an IF bandwidth from1 to 6 GHz for a LO frequency of 462 GHz

25 meter CCAT observatory, 5600 meter altitude, Cerro Chajnantor, Chile

𝑵𝑵 = 𝟐𝟎 𝑳𝑳𝑳𝟐𝟎 (𝑻𝑻𝒆𝑻 𝑻𝑳⁄ + 𝟐) = 𝟐.𝟐𝟐𝟐𝟐

Modeling of Superconducting Materials in CST

I. Analytically calculate the surface impedance using Mattis-Bardeen theory II. Putting in CST via surface calculating impedance table III. Fitting process

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Tabulated Surface Impedance

Error Limit: 0.06 Error: 0.035

180° RF Hybrid at 0.8-1.1 THz Applying NbTiN superconducting material in the design of a Rat-race180°RF

hybrid Towards designing a balanced SIS mixer from 800 GHz to 1.1 THz

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− 9µ𝜇 Silicon − SiO2 micro bridges − NbTiN superconductor

8 um

𝑀𝑀𝑀 1𝐷 = arg 𝑆𝑆,1 − arg (𝑆𝑆,1)

−180°

E-field Monitor of Rat-Race at 0.8-1.1 THz

Absolute E-Field monitor:

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8 um

Fitting of Gold material • CST model of 200 nm Gold using anomalous limit for designing HEB mixer

at 4.7 THz

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Tabulated Surface Impedance Error Limit: 0.1 Error: 0.038

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Feedhorn / mixer-block

Mixer block without Feedhorn Mixer block with Feedhorn

zoom

671 µm

Device

SMA connector

Silicon IF board

Wire bonds

1000 µm

HEB for upGreat Receiver in SOFIA

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2 µm Silicon membrane 200 nm Gold for circuitry 3 µm Beamleads

E-Field Monitor of 4.7 THz

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Fabricated 4.7 THz HEB

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Comparison of Simulation and Measurement of a 4.7 THz HEB

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Good agreament between CST simulation and FTS measurement results

Conclusion

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Development of state-of-the-art SIS and HEB mixers in KOSMA laboratory at Universität zu Köln

Using CST suite as a main 3D software to design our THz circuits

First integrated balanced SIS mixer working at 350-500 GHz

Very good agreement between simulation and FTS measurement of 4.7 THz HEB is reported

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Thank You!