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Submillimeter-Wave Waveguide Frontends by Silicon-on-Insulator Micromachining
KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Micro and Nanosystems.ORCID iD: 0000-0002-8894-7930
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents novel radiofrequency (RF) frontend components in the submillimeter-wave (sub-mmW) range implemented by silicon micromachining, or deep reactive ion etching (DRIE). DRIE is rapidly becoming a driving technology for the fabrication of waveguide components and systems when approaching the terahertz (THz) frequency range. The conventional method to manufacture microwave waveguide components, CNC-milling, shows important limitations when used at sub-mmW frequencies or above, due to the reduced size of the waveguides. At the same time, the classic electromagnetic designs, oriented to CNC-milling, are often not suitable for their fabrication using alternative technologies. The work in this thesis aims to develop fabrication-oriented electromagnetic structures, making use of the full flexibility of silicon on insulator (SOI) micromachining, and enabling the implementation of complex RF frontends at a low fabrication complexity.

The first part of the thesis reports on a turnstile orthomode transducer (OMT) in the WM-864 band (220 – 330 GHz). OMTs are key components in the feed-chain for radio astronomy, communications, or radiometry applications. However, their complex geometry has often limited their use when approaching the THz range, where polarization diversity is commonly avoided, or optical systems are preferred.

The second part reports on a high-gain and broadband waveguide corporatefed array antenna in the WM-570 band (330 – 500 GHz). High gain and broadband antennas are required for the future generation of THz wireless communications. Reflector and lens antennas can meet these specifications, but their fabrication for the THz range requires precision machining, resultingin a high cost, low yield, and small scale production. The use of silicon micromachined antenna arrays overcomes these issues while providing a more compact frontend.

In the third part of the thesis, a parallel plate waveguide (PPW) leaky wave antenna (LWA) fed by a quasi-optical beamforming network (BFN) in the WM-864 band is presented. The antenna frontend generates a pencil shaped beam scanning in elevation. The compact design, large bandwidth, and beam steering capabilities make this antenna a suitable frontend for THz radar applications.

The final part of this thesis reports on a novel waveguide single pole double throw (SPDT) switch in the WM-570 band. The switch is demonstrated in a two-port network configuration with two switching states (ON/LOAD), used for receiver calibration, or for avoiding backward waves in transmitter switching. A more complex 1×4 switching matrix is also designed for the implementation of an active radar antenna operating at 340 GHz.

Abstract [sv]

Denna avhandling presenterar nya radio frekvens (RF) frontend komponenter inom submillimeter våg (sub-mmW) bandet som kan implementeras med mikrofabrikationsteknik i kisel samt djup reaktiv jonetsning (DRIE). DRIE är en snabbt växande teknik som har blivit drivande för fabrikation av vågledarkomponenter och system som angränsar terrahertz (THz) frekvensbandet. Den konventionella tillverkningsmetoden för vågledarkomponenter, CNC-fräsning, påvisar stora begränsningar vid användning för sub-mmW bandet eller högre, på grund av de små dimentionerna av vågledarkomponenterna. Samtidigt är de klassiska elektomagnetiska konstruktionerna, som ofta är orienterade mot CNC-fräsning, inte lämpade för alternativa tillverkningsmetoder. Syftet med denna avhandling är att utveckla tillverknings orienterade strukturer genom att använda flexibiliteten av silicon on insulator (SOI) mikrofabrikationsteknik och att möjliggöra implementeringen av komplexa RF frontend med en låg tillverkningskomplexitet.

Den första delen av avhandlingen redogör för turnstile orthomode omvandlare (OMT) i WM-864 bandet (220 - 330 GHz). OMT är nyckelkomponenter i feedchain till radioastronomi, kommunikation och radiometritillämpningar. Likväl, har deras komplexa geometri ofta begränsat deras användning när THz bandet angränsas, där polariserings diversitet typiskt undviks, eller optiska systems är att föredra.

Den andra delen redogör för högvinst-, och bredbands,- parallellmatad arrayantenn i WM-570 vågledarteknologi (330 - 500 GHz). Högvinst- och bredbandsantenner behövs för den kommande generationens trådlösa THz kommunikation. Reflektor- och linsantenner kan uppfylla dessa specifikationer men deras tillverkning i THz bandet kräver mycket precis skärande bearbetning, vilket resulterar i höga kostnader, låg avkastning, och småskalig tillverkning. Genom användning av kisel mikrofabrikationstillverkade arrayantenner är det möjligt att övekomma sådana problem och samtidigt tillhandahålla en mer kompakt frontend.

I den tredje delen av denna avhandling presenteras en parallelplats-vågledar- (PPW) läckande-våg-antenn (LWA) matad av kvasi-optiska strålformande nätverk (BFN) i WM-864 bandet. Denna antenn-frontend genererar en pennformad strålskanning i elevations riktningen. Den kompakta utformningen, stora bandbredden, och strålstyrningsmöjligheterna gör denna antenn väl anpassad för THz radar tillämpningar.

Den sista delen i avhandlingen beskriver en ny vågledar-, single pole double throw (SPDT)-, omkopplare i WM-570 bandet. Omkopplaren påvisas i en tvåports- nätverkskonfiguration med två växlar (ON/LOAD) som används för mottagarkalibrering, eller för att undvika bakåtgående vågor i sändarväxlingen. En mer komplex 1 x 4 växlingsmatris utformas även för implementeringen av en aktiv antenn för en radar som opererar i 340 GHz.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2020. , p. 131
Series
TRITA-EECS-AVL ; 2020:28
Keywords [en]
antenna, orthomode transducer, switch, waveguide, radiofrequency, beamforming network, submillimeter-wave, terahertz, silicon micromachining, deep reactive ion etching, silicon on insulator
National Category
Telecommunications
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-273332ISBN: 978-91-7873-528-0 (print)OAI: oai:DiVA.org:kth-273332DiVA, id: diva2:1430173
Public defence
2020-06-12, Seminar Room, Floor 5, Malvinas väg 10, Stockholm, 16:00 (English)
Opponent
Supervisors
Note

QC 20200515

Available from: 2020-05-15 Created: 2020-05-13 Last updated: 2020-05-15Bibliographically approved
List of papers
1. Compact silicon-micromachined wideband 220 – 330 GHz turnstile orthomode transducer
Open this publication in new window or tab >>Compact silicon-micromachined wideband 220 – 330 GHz turnstile orthomode transducer
2018 (English)In: IEEE Transactions on Terahertz Science and Technology, ISSN 2156-342X, E-ISSN 2156-3446, Vol. 9, no 1, p. 38-46, article id 8542680Article in journal (Refereed) Published
Abstract [en]

This paper reports on a turnstile-junction orthomode transducer (OMT) implemented by silicon micromachiningin the 220 – 330 - GHz band. Turnstile OMTs are very widebandand allow for co-planar ports, but require accurate and complex geometries which makes their fabrication challenging at higher frequencies. The compact 10 mm x 10 mm x 0.9 mm OMT-chip presented in this paper is the first micromachined full-band OMT in any frequency range, and only the second turnstile OMT implemented above 110 GHz. The measured insertion loss(0.3 dB average, 0.6 dB worst-case) and the cross-polarization (60 dB average, 30 dB worst-case) over the whole waveguide band represent the best performance of any wideband OMT, regardless of design or fabrication technology, in the 220 –330 - GHz band. The return loss with 22 dB average (16 dB worst case) is comparable or better than previous work. The paper discusses design considerations and compromises of this complex 9 layer silicon micromachined device, including the influence of sidewall slopes, underetching, and post-bonding misalignment between the chips. It is shown that for a device which is very sensitive to geometrical variations, such as a turnstile OMT, it is necessary to anticipate and compensate for any fabrication imperfections in the design to achieve high RF performance.

Place, publisher, year, edition, pages
IEEE, 2018
Keywords
OMT, orthomode transducer, turnstile, silicon micromachining, DRIE, MEMS, millimeter wave, mmW, terahertz, THz
National Category
Telecommunications
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-239727 (URN)10.1109/TTHZ.2018.2882745 (DOI)000455919800004 ()2-s2.0-85057820646 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , SE13-007EU, Horizon 2020, 616846
Note

QC 20181217

Available from: 2018-11-30 Created: 2018-11-30 Last updated: 2020-05-13Bibliographically approved
2. Micromachined Waveguide Interposer for the Characterization of Multi-port Sub-THz Devices
Open this publication in new window or tab >>Micromachined Waveguide Interposer for the Characterization of Multi-port Sub-THz Devices
2020 (English)In: Journal of Infrared, Millimeter and Terahertz Waves, ISSN 1866-6892, E-ISSN 1866-6906Article in journal (Refereed) Published
Abstract [en]

This paper reports for the first time on a micromachined interposer platform for characterizing highly miniaturized multi-port sub-THz waveguide components. The reduced size of such devices does often not allow to connect them to conventional waveguide flanges. We demonstrate the micromachined interposer concept by characterizing a miniaturized, three-port, 220–330-GHz turnstile orthomode transducer. The interposer contains low-loss micromachined waveguides for routing the ports of the device under test to standard waveguide flanges and integrated micromachined matched loads for terminating the unused ports. In addition to the interposer, the measurement setup consists of a micromachined square-to-rectangular waveguide transition. These two devices enable the characterization of such a complex microwave component in four different configurations with a standard two-port measurement setup. In addition, the design of the interposer allows for independent characterization of its sub-components and, thus, for accurate de-embedding from the measured data, as demonstrated in this paper. The measurement setup can be custom-designed for each silicon micromachined device under test and co-fabricated in the same wafer due to the batch nature of this process. The solution presented here avoids the need of CNC-milled test-fixtures or waveguide pieces that deteriorate the performance of the device under test and reduce the measurement accuracy.

Keywords
Waveguide, Silicon micromachining, Terahertz, Multi-port, Measurement, Interposer, Test-fixture, DRIE, Orthomode transducer
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-266451 (URN)10.1007/s10762-019-00663-4 (DOI)000513450100002 ()2-s2.0-85078630059 (Scopus ID)
Note

QC 20200113

Available from: 2020-01-10 Created: 2020-01-10 Last updated: 2020-05-13Bibliographically approved
3. A 38 dBi Gain, Low-Loss, Flat Array Antenna for 320 GHz to 400 GHz Enabled by Silicon-On-Insulator Micromachining
Open this publication in new window or tab >>A 38 dBi Gain, Low-Loss, Flat Array Antenna for 320 GHz to 400 GHz Enabled by Silicon-On-Insulator Micromachining
Show others...
2020 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 68Article in journal (Refereed) Published
Abstract [en]

Two high-gain flat array antenna designs operatingin the 320 – 400 GHz frequency range are reported in this paper. The two antennas show measured gains of 32.8 dBi and 38 dBi and consist of a 16x16 (256) element array and a 32x32 (1024) element array, respectively, which are fed by a corporate H-tree beamforming network. The measured operation bandwidth for both antennas is 80 GHz (22% fractional bandwidth), and the total measured efficiency is above −2.5 dB and above −3.5 dB forthe two designs in the whole bandwidth. The low measured loss and large bandwidth are enabled by optimizing the designs to the process requirements of the SOI micromachining technology used in this work. The total height of the antennas is 1.1mm (1.2 at the center frequency), with sizes of 15mm x 18mm and 27mm x 30mm for both arrays. The antennas are designed to be directly mounted onto a standard WM-570 waveguide flange.The design, fabrication, and measurements of eight prototypes are discussed in this paper and the performance of the antennas compared to the simulated data, as well as manufacturability and fabrication repeatability are reported in detail.

National Category
Telecommunications
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-273331 (URN)10.1109/TAP.2020.2969753 (DOI)
Funder
EU, Horizon 2020, 616846Swedish Foundation for Strategic Research , SE13-007
Note

QC 20200523

Available from: 2020-05-13 Created: 2020-05-13 Last updated: 2020-05-23Bibliographically approved
4. A Low-Profile and High-Gain Frequency Beam Steering Subterahertz Antenna Enabled by Silicon Micromachining
Open this publication in new window or tab >>A Low-Profile and High-Gain Frequency Beam Steering Subterahertz Antenna Enabled by Silicon Micromachining
Show others...
2020 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 68, no 2, p. 672-682Article in journal (Refereed) Published
Abstract [en]

A very low-profile sub-THz high-gain frequencybeam steering antenna, enabled by silicon micromachining, is reported for the first time in this paper. The operation bandwidth of the antenna spans from 220 GHz to 300 GHz providing a simulated field of view of 56°. The design is based on a dielectric filled parallel-plate waveguide (PPW) leaky-wave antenna fed by a pillbox. The pillbox, a two-level PPW structure, has an integrated parabolic reflector to generate a planar wave front. The device is enabled by two extreme aspect ratio, 16 mm x16 mm large perforated membranes, which are only 30 μm thick, that provide the coupling between the two PPWs and form the LWA. The micromachined low-loss PPW structure results in a measured average radiation efficiency of −1 dB and a maximum gain of 28.5 dBi with an input reflection coefficient below −10 dB. The overall frequency beam steering frontend is extremely compact (24mm x 24mm x 0.9 mm) and can be directly mounted on a standard WM-864 waveguide flange. The design and fabrication challenges of such high performance antenna in the sub-THz frequency range are described and the measurement results of two fabricated prototypes are reported and discussed.

Place, publisher, year, edition, pages
IEEE Press, 2020
Keywords
beam steering, leaky-wave antennas, silicon micromachining, terahertz radiation, quasi-optics, submillimeter-wave antennas, silicon on insulator
National Category
Telecommunications
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-261201 (URN)10.1109/TAP.2019.2943328 (DOI)000511198600006 ()2-s2.0-85079266916 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , SE13-007EU, Horizon 2020, 616846
Note

QC 20200224

Available from: 2019-10-03 Created: 2019-10-03 Last updated: 2020-05-13Bibliographically approved

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