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Multi-Position RF MEMS Tunable Capacitors Using Laterally Moving Sidewalls of 3-D Micromachined Transmission Lines
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.ORCID iD: 0000-0002-8264-3231
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
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. Vol. 61, no 6, 2340-2352 p.
Keyword [en]
RF MEMS, switched capacitor, tunable capacitor, micromachined transmission line, micromachining
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-104307DOI: 10.1109/TMTT.2013.2259499ISI: 000319979300009Scopus ID: 2-s2.0-84878800249OAI: oai:DiVA.org:kth-104307DiVA: diva2:563788
Note

QC 20130710

Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Monocrystalline-Silicon Based RF MEMS Devices
Open this publication in new window or tab >>Monocrystalline-Silicon Based RF MEMS Devices
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
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:nbn:se:kth:diva-104314 (URN)978-91-7501-532-3 (ISBN)
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
2. Novel RF MEMS Devices Enabled by Three-Dimensional Micromachining
Open this publication in new window or tab >>Novel RF MEMS Devices Enabled by Three-Dimensional Micromachining
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents novel radio frequency microelectromechanical (RF MEMS) circuits based on the three-dimensional (3-D) micromachined coplanar transmission lines whose geometry is re-configured by integrated microelectromechanical actuators. Two types of novel RF MEMS devices are proposed. The first is a concept of MEMS capacitors tuneable in multiple discrete and well-defined steps, implemented by in-plane moving of the ground side-walls of a 3-D micromachined coplanar waveguide transmission line. The MEMS actuators are completely embedded in the ground layer of the transmission line, and fabricated using a single-mask silicon-on-insulator (SOI) RF MEMS fabrication process. The resulting device achieves low insertion loss, a very high quality factor, high reliability, high linearity and high self actuation robustness. The second type introduces two novel concepts of area efficient, ultra-wideband, MEMS-reconfigurable coupled line directional couplers, whose coupling is tuned by mechanically changing the geometry of 3-D micromachined coupled transmission lines, utilizing integrated MEMS electrostatic actuators. The coupling is achieved by tuning both the ground and the signal line coupling, obtaining a large tuneable coupling ratio while maintaining an excellent impedance match, along with high isolation and a very high directivity over a very large bandwidth. This thesis also presents for the first time on RF nonlinearity analysis of complex multi-device RF MEMS circuits. Closed-form analytical formulas for the IIP3 of MEMS multi-device circuit concepts are derived. A nonlinearity analysis, based on these formulas and on  measured device parameters, is performed for different circuit concepts and compared to the simulation results of multi-device  conlinear electromechanical circuit models. The degradation of the overall circuit nonlinearity with increasing number of device stages is investigated. Design rules are presented so that the mechanical parameters and thus the IIP3 of the individual device stages can be optimized to achieve a highest overall IIP3 for the whole circuit.The thesis further investigates un-patterned ferromagnetic NiFe/AlN multilayer composites used as advanced magnetic core materials for on-chip inductances. The approach used is to increase the thickness of the ferromagnetic material without increasing its conductivity, by using multilayer NiFe and AlN sandwich structure. This suppresses the induced currents very effectively and at the same time increases the ferromagnetic resonance, which is by a factor of 7.1 higher than for homogeneous NiFe layers of same thickness. The so far highest permeability values above 1 GHz for on-chip integrated un-patterned NiFe layers were achieved.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xiii, 79 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2014:014
Keyword
Microelectromechanical systems, MEMS, Radio frequency microelectromechanical systems, RF MEMS, Micromachined transmission line, Micromachining, Tuneable capacitor, Switched capacitor, Coupled-line coupler, Tuneable directional coupler, Intermodulation distortion, MEMS varactor, Two-tone IIP3 measurement, Passive components and circuits, Reliability, Magnetic materials, NiFe multilayer composite, Permeability, Permittivity, Micromachined inductors
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-143757 (URN)978-91-7595-075-4 (ISBN)
Public defence
2014-04-24, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140328

Available from: 2014-03-28 Created: 2014-03-27 Last updated: 2016-08-11Bibliographically approved

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