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Novel RF MEMS Devices for W-Band Beam-Steering Front-Ends
KTH, School of Electrical Engineering (EES), Microsystem Technology. (RF MEMS)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents novel millimeter-wave microelectromechanical-systems (MEMS) components for W-band reconfigurable beam-steering front-ends. The proposed MEMS components are novel monocrystalline-silicon dielectric-block phase shifters, and substrate-integrated three-dimensional (3D) micromachined helical antennas designed for the nominal frequency of 75 GHz.

The novel monocrystalline-silicon dielectric-block phase shifters are comprised of multi-stages of a tailor-made monocrystalline-silicon block suspended on top of a 3D micromachined coplanar-waveguide transmission line. The relative phase-shift is obtained by vertically pulling the suspended monocrystalline-silicon block down with an electrostatic actuator, resulting in a phase difference between the up and downstate of the silicon block. The phase-shifter prototypes were successfully implemented on a high-resistivity silicon substrate using standard cleanroom fabrication processes. The RF and non-linearity measurements indicate that this novel phase-shifter design has an excellent figure of merit that offers the best RF performance reported to date in terms of loss/bit at the nominal frequency, and maximum return and insertion loss over the whole W-band, as compared to other state-of-the-art MEMS phase shifters. Moreover, this novel design offers high power handling capability and superior mechanical stability compared to the conventional MEMS phase-shifter designs, since no thin moving metallic membranes are employed in the MEMS structures. This feature allows MEMS phase-shifter technology to be utilized in high-power applications. Furthermore, the return loss of the dielectric-block phase shifter can be minimized by appropriately varying the individual distance between each phase-shifting stage.

This thesis also investigates 3D micromachined substrate-integrated W-band helical antennas. In contrast to conventional on-chip antenna designs that only utilize the surface of the wafer, the novel helical radiator is fully embedded into the substrate, thereby utilizing the whole volume of the wafer and resulting in a compact high-gain antenna design. The performance of the antenna is substantially enhanced by properly etching the substrate, tailor making the antenna core, and by modifying size and geometry of the substrate-integrated ground plane. A linear line antenna array is composed of eight radiating elements and is demonstrated by simulations. Each antenna is connected to the input port through a multi-stage 3-dB power divider. The input and output of the single-stage 3-dB power divider is well matched to the 50-Ω impedance by four-section Chebyshev transformers. The simulation results indicate that the novel helical antenna arrays offer a narrow radiation beam with an excellent radiation gain that result in high-resolution scan angles on the azimuth plane. The proposed helical antenna structures can be fabricated by employing standard cleanroom micromachining processes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xii, 84 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:011
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-93507ISBN: 978-91-7501-296-4 (print)OAI: oai:DiVA.org:kth-93507DiVA: diva2:516789
Public defence
2012-05-25, Q1, Osquldas väg 4, entréplan, KTH, Stockholm, 09:30 (English)
Opponent
Supervisors
Note
QC 20120427Available from: 2012-04-27 Created: 2012-04-19 Last updated: 2012-04-27Bibliographically approved
List of papers
1. Binary-Coded 4.25-bit W-Band Monocrystalline-Silicon MEMS Multistage Dielectric-Block Phase Shifters
Open this publication in new window or tab >>Binary-Coded 4.25-bit W-Band Monocrystalline-Silicon MEMS Multistage Dielectric-Block Phase Shifters
2009 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 57, no 11, 2834-2840 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a novel concept of a microwave microelectromechanical systems (MEMS) reconfigurable dielectric-block phase shifter with best loss/bit at the nominal frequency and best maximum return and insertion loss ever reported over the whole W-band. A seven-stage phase shifter is constructed by lambda/2-long high-resistivity silicon dielectric blocks, which can be moved vertically by MEMS electrostatic actuators based on highly reliable monocrystalline silicon flexures on-top of a 3-D micro-machined coplanar transmission line. The dielectric constant of each block is artificially tailor made by etching a periodic pattern into the structure. Stages of 15 degrees, 30 degrees, and 45 degrees are optimized for 75 GHz and put into a binary-coded 15 degrees + 30 degrees + 5 x 45 degrees configuration with a total phase shift of 270 degrees in 19 x 15 degrees steps (4.25 bits). Return and insertion losses are better than -17 and -3.5 dB at 75 GHz, corresponding to a loss of -0.82 dB bit, and a phase shift efficiency of 71.1 degrees/dB and 490.02 degrees/cm. Return and insertion losses are better than 12 and 4 dB for any phase combination up to 110 GHz (98.3 degrees/dB; 715.6 degrees/cm). The intercept point of third order, determined by nonlinearity measurements and intermodulation analysis, is 49.15 dBm for input power modulation from 10 to 40 dBm. The power handling is only limited by the transmission line itself since no current-limiting thin air-suspended metallic bridges as in conventional MEMS phase shifters are utilized. This is confirmed by temperature measurements at 40 dBm at 3 GHz with skin effect adjusted extrapolation to 75 GHz by electrothermal finite-element method simulations.

Keyword
Microelectromechanical systems (MEMS), microwave, millimeter wave, phase shifter, RF MEMS, x-band, intermodulation, capacitors, switches
Identifiers
urn:nbn:se:kth:diva-18953 (URN)10.1109/tmtt.2009.2032350 (DOI)000271678400024 ()2-s2.0-70450280774 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Deep-Reactive-Ion-Etched Wafer-Scale-Transferred All-Silicon Dielectric-Block Millimeter-Wave MEMS Phase Shifters
Open this publication in new window or tab >>Deep-Reactive-Ion-Etched Wafer-Scale-Transferred All-Silicon Dielectric-Block Millimeter-Wave MEMS Phase Shifters
2010 (English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 19, no 1, 120-128 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on design, fabrication, and characterization of a novel multistage all-silicon microwave MEMS phase-shifter concept, based on multiple-step deep-reactive-ion-etched monocrystalline-silicon dielectric blocks which are transfer bonded to an RF substrate containing a 3-D micromachined coplanar waveguide. The relative phase shift of 45 degrees of a single stage is achieved by vertically moving the lambda/2-long blocks by MEMS electrostatic actuation. The measurement results of the first prototypes show that the return and insertion loss of a 7 x 45 degrees multistage phase shifter over the whole frequency spectrum from 1 to 110 GHz are better than -12 and -5.1 dB, respectively. The monocrystalline high-resistivity silicon blocks are acting as a dielectric material from an RF point of view, and at the same time as actuation electrodes for dc electrostatic actuation. The mechanical reliability was investigated by measuring life-time cycles. All tested phase shifters with three-meander 36.67-N/m mechanical spring and a pull-in voltage of 29.9 V survived 1 billion cycles after which the tests were discontinued, no indication of dielectric charging could be found, neither caused by the dielectric block nor by the Si3N4 distance keepers to the bottom electrodes. Finally, it is investigated that, by varying the fill factor of the etch hole pattern, the effective dielectric constant of the block can be tailor made, resulting in 45 degrees, 30 degrees, and 15 degrees phase-shifter stages fabricated out of the same dielectric material by the same fabrication process flow. [2009-0201]

Keyword
Microelectromechanical systems (MEMS), microwave, millimeter wave, phase shifter, radio frequency microelectromechanical system (RF MEMS), x-band, resistivity, line
Identifiers
urn:nbn:se:kth:diva-19171 (URN)10.1109/jmems.2009.2036943 (DOI)000274213700012 ()2-s2.0-76349112476 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Power Handling Analysis of High-Power W-Band All-Silicon MEMS Phase Shifters
Open this publication in new window or tab >>Power Handling Analysis of High-Power W-Band All-Silicon MEMS Phase Shifters
2011 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 58, no 5, 1548-1555 p.Article in journal (Refereed) Published
Abstract [en]

This paper analyzes the power handling capability and the thermal characteristics of an all-silicon dielectric-block microelectromechanical-system (MEMS) phase-shifter concept, which is the first MEMS phase-shifter type whose power handling is not limited by the MEMS structures but only by the transmission line itself and by the heat-sink capabilities of the substrate, which enables MEMS phase-shifter technology for future high-power high-reliability applications. The power handling measurements of this concept are performed up to 43 dBm (20W) at 3 GHz with an automatic gain-controlled setup, assisted by a large-signal network analyzer, and the temperature rises of the devices were measured with an infrared microscope camera. The measurement results are extended to 40 dBm at 75 GHz by calibrating electrothermal simulations with the measurements. A comparative study to conventional state-of-the-art MEMS phase-shifter concepts based on thin metallic bridges is carried out. The simulated results show that the all-silicon phase-shifter designs have the maximum temperature rise of only 30 degrees C for 40 dBm at 75 GHz, which is 10-20 times less than conventional MEMS phase shifters of the comparable RF performance.

Keyword
microwave, millimeter wave, phase shifter, radio-frequency microelectromechanical systems (RF MEMSs)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-33726 (URN)10.1109/TED.2011.2117429 (DOI)000289952800037 ()2-s2.0-79955544661 (Scopus ID)
Note
QC 20110517Available from: 2011-05-17 Created: 2011-05-16 Last updated: 2017-12-11Bibliographically approved
4. Microwave MEMS Devices Designed for Process Robustness and Operational Reliability
Open this publication in new window or tab >>Microwave MEMS Devices Designed for Process Robustness and Operational Reliability
Show others...
2011 (English)In: International Journal of Microwave and Wireless Technology, ISSN 1759-0787, Vol. 3, no 5, 547-563 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an overview on novel microwave micro-electromechanical systems (MEMS) device concepts developed in our research group during the last 5 years, which are specifically designed for addressing some fundamental problems for reliable device operation and robustness to process parameter variation. In contrast to conventional solutions, the presented device concepts are targeted at eliminating their respective failure modes rather than reducing or controlling them. Novel concepts of MEMS phase shifters, tunable microwave surfaces, reconfigurable leaky-wave antennas, multi-stable switches, and tunable capacitors are presented, featuring the following innovative design elements: dielectric-less actuators to overcome dielectric charging; reversing active/passive functions in MEMS switch actuators to improve recovery from contact stiction; symmetrical anti-parallel metallization for full stress-control and temperature compensation of composite dielectric/metal layers for free-standing structures; monocrystalline silicon as structural material for superior mechanical performance; and eliminating thin metallic bridges for high–power handling. This paper summarizes the design, fabrication, and measurement of devices featuring these concepts, enhanced by new characterization data, and discusses them in the context of the conventional MEMS device design.

Place, publisher, year, edition, pages
Cambridge University Press and the European Microwave Association, 2011
Keyword
RF MEMS, Reliability, MEMS design, Phase shifter, Tuneable capacitor, MEMS switch
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-48388 (URN)10.1017/S1759078711000845 (DOI)000208613500007 ()2-s2.0-80455144997 (Scopus ID)
Note

Invited.

QC 20111124

Available from: 2011-11-24 Created: 2011-11-17 Last updated: 2014-03-28Bibliographically approved
5. Design Approach for Return-Loss Optimisation of Multi-Stage Millimetre-Wave MEMS Dielectric-Block Phase Shifters
Open this publication in new window or tab >>Design Approach for Return-Loss Optimisation of Multi-Stage Millimetre-Wave MEMS Dielectric-Block Phase Shifters
2012 (English)In: IET Microwaves, Antennas & Propagation, ISSN 1751-8725, E-ISSN 1751-8733, Vol. 6, 1429-1436 p.Article in journal (Refereed) Published
Abstract [en]

This study reports on the radiofrequency (RF) performance optimisation of a novel multi-stage microelectromechanical system (MEMS) dielectric-block phase-shifter concept. The objective is to minimise the average return loss for all possible operation states of a multi-stage phase shifter, without substantially compromising the overall insertion loss or in phase-shift performance. The optimisation method presented in this study is generally applicable to any type of multi-stage RF MEMS devices that are operated in all possible state combinations of the different stages. The return loss is optimized for a seven-stage MEMS dielectric-block phase shifter by adjusting the individual distances between the phase shifter stages, for the nominal frequency of 75 GHz as well as for 500 MHz and 1 GHz bandwidth. A total of seven different designs following different optimisation approaches are investigated by simulations and measurements of fabricated devices. The best concept was found for exponentially increasing distances between the stages that takes into account the proper actuation sequence for all possible phase-shift combinations. As compared with a non-optimised device previously published by the authors, the design offering the best compromise between return loss and insertion loss, achieved by this optimisation method, results in a significant return loss improvement of 11.8 dB (simulated) and 6.98 dB (measured), whereas compromising the insertion loss by only 0.75 dB (simulated) and 0.92 dB (measured). In contrast to that all other investigated concepts, including intuitive optimisation methods such as λ/4 distances or optimisation of equidistant concepts result in a much smaller or no return-loss improvement and some even in a drastic worsening of the insertion loss.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-79407 (URN)10.1049/iet-map.2012.0299 (DOI)000318230200005 ()2-s2.0-84880032164 (Scopus ID)
Note

QC 20160504

Available from: 2012-02-08 Created: 2012-02-08 Last updated: 2017-12-07Bibliographically approved
6. Three-dimensional micromachined silicon-substrate integrated millimetre-wave helical antennas
Open this publication in new window or tab >>Three-dimensional micromachined silicon-substrate integrated millimetre-wave helical antennas
2013 (English)In: IET Microwaves, Antennas & Propagation, ISSN 1751-8725, E-ISSN 1751-8733, Vol. 7, no 4, 291-298 p.Article in journal (Refereed) Published
Abstract [en]

This study presents a design study of a novel concept of a three-dimensional (3D) micromachined square helical antenna designed for 75 GHz, which is completely integrated into a semiconductor silicon substrate. In contrast to conventional on-chip integrated antennas which typically are built on top of the substrate surface, the proposed antenna concept utilises, for the first time to the knowledge of the authors, the whole volume of the wafer by building the helical structure inside the substrate, which results in a very area-efficient high-gain radiating element for a substrate-integrated millimeter-wave system. The effective permittivity of the antenna core and the surrounding substrate can be tailor-made by 3D micromachining, for optimising the maximum antenna performance with this design study it was found, that such an antenna concept can achieve a maximum gain of 13.2 dBi, a radiation efficiency of 95.3% at the axial ratio of 0.94 and a half-power beamwidth (HPBW) of smaller than 40 degrees, and a return loss S11 of -22.3 dB at the nominal frequency of 74.5 GHz, with a 15-GHz bandwidth with a reflection coefficient better than -10 dB. A 16-element substrate-integrated helical line array is demonstrated and achieves a maximum gain of 24.2 dBi with a HPBW of 6.3 degrees in the y-z-plane. This study also studies intensively the influences of the surrounding silicon substrate and dielectric-core etching, the matching transition between the helical structure and a coplanar-waveguide feeding, as well as size and geometry of the ground structure.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-91537 (URN)10.1049/iet-map.2012.0345 (DOI)000321706200010 ()2-s2.0-84891641764 (Scopus ID)
Funder
Vinnova
Note

QC 20130814. Updated from accepted to published

Available from: 2012-03-17 Created: 2012-03-17 Last updated: 2017-12-07Bibliographically approved

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