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Monocrystalline-Silicon Based RF MEMS Devices
KTH, School of Electrical Engineering (EES), Microsystem Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents novel radio-frequency microelectromechanical (RF MEMS) devices, for microwave and millimeter wave applications, designed for process robustness and operational reliability using monocrystalline silicon as structural material. Two families of RF MEMS devices are proposed. The first comprises reconfigurable microwave components integrated with coplanar-waveguide transmission lines in the device layer of silicon-on-insulator wafers. The second consists of analog tuneable millimeter wave high-impedance surface arrays.

The first group of reconfigurable microwave components presented in this thesis is based on a novel concept of integrating MEMS functionality into the sidewalls of three-dimensional micromachined transmission lines. A laterally actuated metal-contact switch was implemented, with the switching mechanism completely embedded inside the signal line of a coplanar-waveguide transmission line. The switch features zero power-consumption in both the on and the off state since it is mechanically bistable, enabled by interlocking hooks. Both two-port and three-port configurations are presented. Furthermore, tuneable capacitors based on laterally moving the ground planes in a micromachined coplanar-waveguide transmission line are demonstrated.

The second group of reconfigurable microwave components comprises millimeter-wave high-impedance surfaces. Devices are shown for reflective beam steering, reflective stub-line phase shifters and proximity based dielectric rod waveguide phase shifters, as well as a steerable leaky-wave antenna device based on the same geometry. Full wafer transfer bonding of symmetrically metallized monocrystalline silicon membranes, for near-ideal stress compensation, is used to create large arrays of distributed MEMS tuning elements. Furthermore, this thesis investigates the integration of reflective MEMS millimeter wave devices in rectangular waveguides using a conductive adhesive tape, and the integration of substrates with mismatched coefficients of thermal expansion.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , x, 67 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:050
Keyword [en]
RF MEMS, radio frequency, microelectromechanical system, microsystem technology, monocrystalline silicon, switch, tuneable capacitor, high-impedace surface, phase shifter, rectangular waveguide, transmission line
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-104314ISBN: 978-91-7501-532-3 (print)OAI: oai:DiVA.org:kth-104314DiVA: diva2:563820
Public defence
2012-11-23, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121101

Available from: 2012-11-01 Created: 2012-10-31 Last updated: 2012-11-01Bibliographically approved
List of papers
1. Static Zero-Power-Consumption Coplanar Waveguide Embedded DC-to-RF Metal-Contact MEMS Switches in Two-Port and Three-Port Configuration
Open this publication in new window or tab >>Static Zero-Power-Consumption Coplanar Waveguide Embedded DC-to-RF Metal-Contact MEMS Switches in Two-Port and Three-Port Configuration
2010 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 57, no 7, 1659-1669 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on novel electrostatically actuated dc-to-RF metal-contact microelectromechanical systems (MEMS) switches, featuring a minimum transmission line discontinuity since the whole switch mechanism is completely embedded inside the signal line of a low-loss 3-D micromachined coplanar waveguide. Furthermore, the switches are based on a multistable interlocking mechanism resulting in static zero-power consumption, i.e., both the onstate and the offstate are maintained without applying external actuation energy. Additionally, the switches provide with active opening capability, potentially improving the switch reliability, and enabling the usage of soft low-resistivity contact materials. Both two-port single-pole-single-throw (SPST) switches featuring mechanical bistability and three-port single-pole-double-throw (SPDT) T-junction switches with four mechanically stable states are presented. The switches, together with the transmission lines, are fabricated in a single photolithography process. The loss created by the discontinuity of the switch mechanism alone is 0.08 dB at 20 GHz. Including a 500 mu m long transmission line with less than 0.4 dB/mm loss up to 20 GHz, the total insertion loss of the two-port devices is 0.15 and 0.3 dB at 2 and 20 GHz, and the isolation is 45 and 25 dB at 2 and 20 GHz. The three-port switches, including their T-junction transmission line, have an insertion loss of 0.31 and 0.68 dB, and an isolation of 43 and 22 dB, at 1 and 10 GHz, respectively. Actuation voltages are 23-39 V for the two-port switches and 39-89 V for the three-port switches. The microwave propagation in the micromachined transmission line and the influence of the different switch designs were analyzed by finite-element method (FEM) simulations of electromagnetic energy and volume current distributions, proving the design advantages of the proposed concept.

Place, publisher, year, edition, pages
IEEE, 2010
Keyword
Electrostatic actuator, RF microelectromechanical systems (MEMS), switch
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-27274 (URN)10.1109/TED.2010.2048239 (DOI)000278995900022 ()2-s2.0-77954028661 (Scopus ID)
Note
© 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20101214Available from: 2011-12-08 Created: 2010-12-09 Last updated: 2017-12-11Bibliographically approved
2. Electrochemically Assisted Maskless Selective Removal of Metal Layers for Three-Dimensional Micromachined SOI RF MEMS Transmission Lines and Devices
Open this publication in new window or tab >>Electrochemically Assisted Maskless Selective Removal of Metal Layers for Three-Dimensional Micromachined SOI RF MEMS Transmission Lines and Devices
2011 (English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 20, no 4, 899-908 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a novel electrochemically assisted wet-etching method for maskless selective removal of metal layers. This method has been developed as the key process step for enabling the fabrication of low-loss 3-D micromachined silicon-on-insulator-based radio-frequency microelectromechanical systems transmission line components, consisting of a silicon core in the device layer covered by a gold metallization layer. For this application, the full-wafer sputtered metallization layer must be locally removed on the handle layer to guarantee for a well-defined and low-loss coplanar-waveguide propagation mode in the slots of the transmission line. It is not possible to use conventional photolithography or shadow masking. Gold areas to be etched are biased by a 1.2-V potential difference to a saturated calomel reference electrode in a NaCl(aq) solution. The measured etch rate of the proposed local electrochemically biased etching process is 520 nm/min, and no detectable etching was observed on unbiased areas even after a 1-h etch. The suitability of different adhesion layers has been investigated, and Ti-based adhesion layers were found to result in the highest yield. The new etching method has been successfully applied for the fabrication of transmission lines with integrated microswitches, lowering the insertion loss of the waveguide at 10 GHz from 1.3 to 0.3 dB/mm. The issue of unwanted thin metallic connections caused by secondary deposition during sputtering is discussed but found not to significantly affect the process yield. Finally, local removal of gold on isolated features even within the device layer is presented for locally removing the metallization on stoppers of laterally moving electrostatic actuators, to drastically reduce the mechanical wear on stopper tips.

Place, publisher, year, edition, pages
IEEE Press, 2011
Keyword
Coplanar waveguide (CPW), radio-frequency (RF) microelectromechanical systems (MEMS), transmission lines
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-38985 (URN)10.1109/JMEMS.2011.2159100 (DOI)000293751100016 ()2-s2.0-79961208102 (Scopus ID)
Note
© 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111207Available from: 2011-12-07 Created: 2011-09-05 Last updated: 2017-12-08Bibliographically approved
3. 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
4. Analog-type millimeter-wave phase shifters based on MEMS tunable high-impedance surface and dielectric rod waveguide
Open this publication in new window or tab >>Analog-type millimeter-wave phase shifters based on MEMS tunable high-impedance surface and dielectric rod waveguide
Show others...
2011 (English)In: International Journal of Microwave and Wireless Technologies, ISSN 1759-0787, Vol. 3, no 5, 533-538 p.Article in journal (Refereed) Published
Abstract [en]

Millimeter-wave phase shifters are important components for a wide scope of applications. An analog-type phase shifter for W-band has been designed, analyzed, fabricated, and measured. The phase shifter consists of a reconfigurable high-impedance surface (HIS) controlled by micro-electromechanical system (MEMS) varactors and placed adjacent to a silicon dielectric rod waveguide. The analog-type phase shift in the range of 0–32° is observed at 75 GHz whereas applying bias voltage from 0 to 40 V to the MEMS varactors. The insertion loss of the MEMS tunable HIS is between 1.7 and 5 dB, depending on the frequency.

Place, publisher, year, edition, pages
Cambridge University Press and the European Microwave Association, 2011
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-61049 (URN)10.1017/S1759078711000821 (DOI)000208613500005 ()2-s2.0-80455156017 (Scopus ID)
Note

QC 20120119

Available from: 2012-01-19 Created: 2012-01-16 Last updated: 2013-12-02Bibliographically approved
5. Symmetrical Anti-Directional Metallization for Stress-Compensation of Transfer-Bonded Monocrystalline Silicon Membranes
Open this publication in new window or tab >>Symmetrical Anti-Directional Metallization for Stress-Compensation of Transfer-Bonded Monocrystalline Silicon Membranes
2013 (English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 22, no 1, 195-205 p.Article in journal (Refereed) Published
Abstract [en]

This paper demonstrates a very robust and fabrication-parameter insensitive concept of full stress compensation in metallized monocrystalline silicon membranes by symmetrical antidirectional metal deposition on both sides of a transfer-bonded silicon membrane. This concept results in previously unmatched near-perfectly flat, temperature-compensated, and high-reliability metal-coated membranes, independent on the thickness, residual stress, and material of the metal layers. Application examples are high-performance optical mirror devices and quasi-optical tunable microwave surfaces, the latter being presented in this paper. The influence of the thickness ratio of the metal films on the membrane curvature is investigated, demonstrating a controllable curvature range from -0.3 to 0.1 mm(-1) for the investigated devices by varying the top-to-bottom metal thickness ratio from 0.38 to 3.5 using metal thicknesses from 200 to 800 nm. Near-zero curvature down to 0.004 mm(-1) is also demonstrated. Theoretical analysis of the stress-compensated multilayer structures and characterization results of fabricated test devices are included in this paper, as well as the influence of unsymmetrically etched structures in the two metallization layers on the stress-induced curvature. Reliability tests up to 100 million cycles showed no detectable change in curvature or plastic deformation, proving the robustness and repeatability of this new design concept of zero-curvature temperature-compensated monocrystalline silicon-core membranes with thick metal coating. [2012-0230]

Keyword
Microelectromechanical systems (MEMS), micromachining, stress compensation, transfer bonding
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-104306 (URN)10.1109/JMEMS.2012.2224642 (DOI)000314726900027 ()2-s2.0-84873288661 (Scopus ID)
Note

QC 20130308

Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2017-12-07Bibliographically approved
6. Multi-Position RF MEMS Tunable Capacitors Using Laterally Moving Sidewalls of 3-D Micromachined Transmission Lines
Open this publication in new window or tab >>Multi-Position RF MEMS Tunable Capacitors Using Laterally Moving Sidewalls of 3-D Micromachined Transmission Lines
2013 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 61, no 6, 2340-2352 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a novel concept of RF microelectromechanical systems (MEMS) tunable capacitors based on the lateral displacement of the sidewalls of a 3-D micromachined coplanar transmission line. The tuning of a single device is achieved in multiple discrete and well-defined tuning steps by integrated multi-stage MEMS electrostatic actuators that are embedded inside the ground layer of the transmission line. Three different design concepts, including devices with up to seven discrete tuning steps up to a tuning range of 58.6 to 144.5 fF, (C-max/C-min = 2.46) have been fabricated and characterized. The highest Q factor, measured by a weakly coupled transmission-line resonator, was determined as 88 at 40 GHz and was achieved for a device concept where the mechanical suspension elements were completely de-coupled from the RF signal path. These devices have demonstrated high self-actuation robustness with self-actuation pull-in occurring at 41.5 and 47.8 dBm for mechanical spring constants of 5.8 and 27.7 N/m, respectively. Nonlinearity measurements revealed that the third-order intermodulation intercept point (IIP3) for all discrete device states is above the measurement-setup limit of 68.5 dBm for our 2.5-GHz IIP3 setup, with a dual-tone separation of 12 MHz. Based on capacitance/gap/spring measurements, the IIP3 was calculated for all states to be between 71-91 dBm. For a mechanical spring design of 5.8 N/m, the actuation and release voltages were characterized as 30.7 and 21.15 V, respectively, and the pull-in time for the actuator bouncing to drop below 8% of the gap was measured to be 140 mu s. The mechanical resonance frequencies were measured to be 5.3 and 17.2 kHz for spring constant designs of 5.8 and 27.7 N/m, respectively. Reliability characterization exceeded 1 billion cycles, even in an uncontrolled atmospheric environment, with no degradation in the pull-in/pull-out hysteresis behavior being observed over these cycling tests.

Place, publisher, year, edition, pages
IEEE Press, 2013
Keyword
RF MEMS, switched capacitor, tunable capacitor, micromachined transmission line, micromachining
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-104307 (URN)10.1109/TMTT.2013.2259499 (DOI)000319979300009 ()2-s2.0-84878800249 (Scopus ID)
Note

QC 20130710

Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2017-12-07Bibliographically approved
7. MEMS tuneable high-impedance surfaces and their microwave applications
Open this publication in new window or tab >>MEMS tuneable high-impedance surfaces and their microwave applications
(English)Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-104310 (URN)
Note

QS 2012

Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2012-11-01Bibliographically approved
8. Integration of microwave MEMS devices into rectangular waveguide with conductive polymer interposers
Open this publication in new window or tab >>Integration of microwave MEMS devices into rectangular waveguide with conductive polymer interposers
2013 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 23, no 12, 125020- p.Article in journal (Refereed) Published
Abstract [en]

This paper investigates a novel method of integrating microwave microelectromechanical systems (MEMS) chips into millimeter-wave rectangular waveguides. The fundamental difficulties of merging micromachined with macromachined microwave components, in particular, surface topography, roughness, mechanical stress points and air gaps interrupting the surface currents, are overcome by a double-side adhesive conductive polymer interposer. This interposer provides a uniform electrical contact, stable mechanical connection and a compliant stress distribution interlayer between the MEMS chip and a waveguide frame. The integration method is successfully implemented both for prototype devices of MEMS-tuneable reflective metamaterial surfaces and for MEMS reconfigurable transmissive surfaces. The measured insertion loss of the novel conductive polymer interface is less than 0.4 dB in the E-band (60-90 GHz), as compared to a conventional assembly with an air gap of 2.5 dB loss. Moreover, both dc biasing lines and mechanical feedthroughs to actuators outside the waveguide are demonstrated in this paper, which is achieved by structuring the polymer sheet xurographically. Finite element method simulations were carried out for analyzing the influence of different parameters on the radio frequency performance.

Keyword
waveguide integration, conductive polymer interposer, microwave MEMS, RF MEMS
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-104311 (URN)10.1088/0960-1317/23/12/125020 (DOI)000327437000020 ()2-s2.0-84889026540 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 224197
Note

QC 20140113.  Updated from accepted to published.

Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2017-12-07Bibliographically approved
9. Integration of CTE-Mismatched Substrates by Wafer Counter-Bonding
Open this publication in new window or tab >>Integration of CTE-Mismatched Substrates by Wafer Counter-Bonding
(English)Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-104313 (URN)
Note

QS 2012

Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2012-11-01Bibliographically approved

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