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Robust actuation of silicon MEMS using SMA wires integrated at wafer-level by nickel electroplating
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
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2013 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 189, 108-116 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on both the wafer-level fixation and electrical connection of pre-strained SMA wires to silicon MEMS using electroplating, and on the fabrication of the first Joule-heated Shape memory alloy (SMA) wire actuators on silicon. The integration method provides both high bond strength and electrical connections in one processing step, and it allows mass production of microactuators having high work density. SEM observation showed an intimate interconnection between the SMA wires and the silicon substrate. The variation of the actuators' performance across the wafer was evaluated on three 4.5 mm × 1.8 mm footprint devices, proving repeatable results. The actuators showed a mean hot state deflection of 536 μm and a mean stroke of 354 μm at a low power consumption (less than 70 mW). One actuator was tested for m150 × 103 cycles, and it demonstrated a highly reliable long-term performance, showing neither material degradation, nor failure of the nickel anchors.

Place, publisher, year, edition, pages
2013. Vol. 189, 108-116 p.
Keyword [en]
Actuator, Electroplating, MEMS, Shape memory alloy, SMA, Wafer level integration
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-47630DOI: 10.1016/j.sna.2012.08.036ISI: 000314622600015Scopus ID: 2-s2.0-84870571842OAI: oai:DiVA.org:kth-47630DiVA: diva2:455839
Funder
EU, European Research Council, 267528
Note

QC 20130205. Updated from submitted to published.

Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Heterogeneous Integration of Shape Memory Alloysfor High-Performance Microvalves
Open this publication in new window or tab >>Heterogeneous Integration of Shape Memory Alloysfor High-Performance Microvalves
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents methods for fabricating MicroElectroMechanical System (MEMS) actuators and high-flow gas microvalves using wafer-level integration of Shape Memory Alloys (SMAs) in the form of wires and sheets.

The work output per volume of SMA actuators exceeds that of other microactuation mechanisms, such as electrostatic, magnetic and piezoelectric actuation, by more than an order of magnitude, making SMA actuators highly promising for applications requiring high forces and large displacements. The use of SMAs in MEMS has so far been limited, partially due to a lack of cost efficient and reliable wafer-level integration approaches. This thesis presents new methods for wafer-level integration of nickel-titanium SMA sheets and wires. For SMA sheets, a technique for the integration of patterned SMA sheets to silicon wafers using gold-silicon eutectic bonding is demonstrated. A method for selective release of gold-silicon eutectically bonded microstructures by localized electrochemical etching, is also presented. For SMA wires, alignment and placement of NiTi wires is demonstrated forboth a manual approach, using specially built wire frame tools, and a semiautomatic approach, using a commercially available wire bonder. Methods for fixing wires to wafers using either polymers, nickel electroplating or mechanical silicon clamps are also shown. Nickel electroplating offers the most promising permanent fixing technique, since both a strong mechanical and good electrical connection to the wire is achieved during the same process step. Resistively heated microactuators are also fabricated by integrating prestrained SMA wires onto silicon cantilevers. These microactuators exhibit displacements that are among the highest yet reported. The actuators also feature a relatively low power consumption and high reliability during longterm cycling.

New designs for gas microvalves are presented and valves using both SMA sheets and SMA wires for actuation are fabricated. The SMA-sheet microvalve exhibits a pneumatic performance per footprint area, three times higher than that of previous microvalves. The SMA-wire-actuated microvalve also allows control of high gas flows and in addition, offers benefits of lowvoltage actuation and low overall power consumption.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 79 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:014
Keyword
Microelectromechanical systems, MEMS, silicon, wafer-level, integration, heterogeneous integration, wafer bonding, Au-Si, eutectic bonding, release etching, electrochemical etching, microvalves, microactuators, shape memory alloy, SMA, NiTinol, TiNi, NiTi, cold-state reset, bias spring, gate valves, wire bonding
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-94088 (URN)978-91-7501-304-6 (ISBN)
Public defence
2012-06-01, sal E3, Osquarsbacke 14, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120514Available from: 2012-05-14 Created: 2012-05-07 Last updated: 2012-05-14Bibliographically approved

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Stemme, Göranvan der Wijngaart, Wouter

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