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Design and wafer-level fabrication of SMA wire microactuators on silicon
KU Leuven, Division of Production Engineering, Machine Design and Automation (PMA) . (Micro and Precision Engineering Research Group)
KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
KU Leuven, Division of Production Engineering, Machine Design and Automation (PMA) . (Micro and Precision Engineering Research Group)
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2010 (English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 19, no 4, 982-991 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on the fabrication of microactuators through wafer-level integration of prestrained shape memory alloy wires to silicon structures. In contrast to previous work, the wires are strained under pure tension, and the cold-state reset is provided by single-crystalline silicon cantilevers. The fabrication is based on standard microelectromechanical systems manufacturing technologies, and it enables an actuation scheme featuring high work densities. A mathematical model is discussed, which provides a useful approximation for practical designs and allows analyzing the actuators performance. Prototypes have been tested, and the influence of constructive variations on the actuator behavior is theoretically and experimentally evaluated. The test results are in close agreement with the calculated values, and they show that the actuators feature displacements that are among the highest reported.

Place, publisher, year, edition, pages
IEEE Press, 2010. Vol. 19, no 4, 982-991 p.
Keyword [en]
Actuator, adhesive bonding, bias spring, cantilever, microelectromechanical systems (MEMS), NiTi, reset mechanism, shape memory alloy (SMA), silicon structure, SU-8, TiNi, wafer-level integration
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-11829DOI: 10.1109/JMEMS.2010.2049474ISI: 000283543400029Scopus ID: 2-s2.0-77955414734OAI: oai:DiVA.org:kth-11829DiVA: diva2:284098
Note

QC 20100729 Uppdaterad från accepted till published (20110217)

Available from: 2010-01-04 Created: 2010-01-04 Last updated: 2015-06-18Bibliographically approved
In thesis
1. Wafer-level heterogeneous integration of MEMS actuators
Open this publication in new window or tab >>Wafer-level heterogeneous integration of MEMS actuators
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents methods for the wafer-level integration of shape memory alloy (SMA) and electrostatic actuators to functionalize MEMS devices. The integration methods are based on heterogeneous integration, which is the integration of different materials and technologies. Background information about the actuators and the integration method is provided.

SMA microactuators offer the highest work density of all MEMS actuators, however, they are not yet a standard MEMS material, partially due to the lack of proper wafer-level integration methods. This thesis presents methods for the wafer-level heterogeneous integration of bulk SMA sheets and wires with silicon microstructures. First concepts and experiments are presented for integrating SMA actuators with knife gate microvalves, which are introduced in this thesis. These microvalves feature a gate moving out-of-plane to regulate a gas flow and first measurements indicate outstanding pneumatic performance in relation to the consumed silicon footprint area. This part of the work also includes a novel technique for the footprint and thickness independent selective release of Au-Si eutectically bonded microstructures based on localized electrochemical etching.

Electrostatic actuators are presented to functionalize MEMS crossbar switches, which are intended for the automated reconfiguration of copper-wire telecommunication networks and must allow to interconnect a number of input lines to a number of output lines in any combination desired. Following the concepts of heterogeneous integration, the device is divided into two parts which are fabricated separately and then assembled. One part contains an array of double-pole single-throw S-shaped actuator MEMS switches. The other part contains a signal line routing network which is interconnected by the switches after assembly of the two parts. The assembly is based on patterned adhesive wafer bonding and results in wafer-level encapsulation of the switch array. During operation, the switches in these arrays must be individually addressable. Instead of controlling each element with individual control lines, this thesis investigates a row/column addressing scheme to individually pull in or pull out single electrostatic actuators in the array with maximum operational reliability, determined by the statistical parameters of the pull-in and pull-out characteristics of the actuators.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii, 78 p.
Series
Trita-EE, ISSN 1653-5146 ; 2010:002
Keyword
Microelectromechanical systems, MEMS, silicon, wafer-level, integration, heterogeneous integration, transfer integration, packaging, assembly, wafer bonding, adhesive bonding, eutectic bonding, release etching, electrochemical etching, microvalves, microactuator, Shape Memory Alloy, SMA, NITINOL, TiNi, NiTi, cold-state reset, bias spring, stress layers, crossbar switch, routing, switch, switch array, electrostatic actuator, S-shaped actuator, zipper actuator, addressing, transfer stamping, blue tape
National Category
Computer Engineering
Identifiers
urn:nbn:se:kth:diva-11833 (URN)978-91-7415-493-1 (ISBN)
Public defence
2010-02-05, Lecture Hall F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100729Available from: 2010-01-12 Created: 2010-01-04 Last updated: 2010-07-29Bibliographically approved
2. 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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