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Electrochemically Assisted Maskless Selective Removal of Metal Layers for Three-Dimensional Micromachined SOI RF MEMS Transmission Lines and Devices
KTH, School of Electrical Engineering (EES), Microsystem Technology.
KTH, School of Electrical Engineering (EES), Microsystem Technology.
KTH, School of Electrical Engineering (EES), Microsystem Technology.ORCID iD: 0000-0001-9552-4234
KTH, School of Electrical Engineering (EES), Microsystem Technology.
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. Vol. 20, no 4, 899-908 p.
Keyword [en]
Coplanar waveguide (CPW), radio-frequency (RF) microelectromechanical systems (MEMS), transmission lines
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-38985DOI: 10.1109/JMEMS.2011.2159100ISI: 000293751100016ScopusID: 2-s2.0-79961208102OAI: diva2:438783
© 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: 2012-11-01Bibliographically 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.
Trita-EE, ISSN 1653-5146 ; 2012:050
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
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)

QC 20121101

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

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