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Heterogeneous Integration of Shape Memory Alloysfor High-Performance Microvalves
KTH, School of Electrical Engineering (EES), Microsystem Technology.
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 [en]
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: urn:nbn:se:kth:diva-94088ISBN: 978-91-7501-304-6 (print)OAI: oai:DiVA.org:kth-94088DiVA: diva2:525287
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
List of papers
1. Localized removal of the Au-Si eutectic bonding layer for the selective release of microstructures
Open this publication in new window or tab >>Localized removal of the Au-Si eutectic bonding layer for the selective release of microstructures
2009 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 19, no 10, 105014-105023 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents and investigates a novel technique for the footprint and thickness-independent selective release of Au–Si eutectically bonded microstructures through the localized removal of their eutectic bond interface. The technique is based on the electrochemical removal of the gold in the eutectic layer and the selectivity is provided by patterning the eutectic layer and by proper electrical connection or isolation of the areas to be etched or removed, respectively. The gold removal results in a porous silicon layer, acting similar to standard etch holes in a subsequent sacrificial release etching. The paper presents the principle and the design requirements of the technique. First test devices were fabricated and the method successfully demonstrated. Furthermore, the paper investigates the release mechanism and the effects of different gold layouts on both the eutectic bonding and the release procedure.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2009
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-11830 (URN)10.1088/0960-1317/19/10/105014 (DOI)000270133900014 ()2-s2.0-70350630503 (Scopus ID)
Note

QC20100729

Available from: 2010-01-04 Created: 2010-01-04 Last updated: 2015-06-18Bibliographically approved
2. Wafer-level integration of NiTi shape memory alloy on silicon using Au-Si eutectic bonding
Open this publication in new window or tab >>Wafer-level integration of NiTi shape memory alloy on silicon using Au-Si eutectic bonding
Show others...
2013 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 23, no 1, 1-14 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on the wafer level integration of NiTi shape memory alloy (SMA) sheets with silicon substrates through Au-Si eutectic bonding. Different bond parameters, such as Au layer thicknesses and substrate surface treatments were evaluated. The amount of gold in the bond interface is the most important parameter to achieve a high bond yield; the amount can be determined by the barrier layers between the Au and Si or by the amount of Au deposition. Deposition of a gold layer of more than 1 mu m thickness before bonding gives the most promising results. Through patterning of the SMA sheet and by limiting bonding to small areas, stresses created by the thermal mismatch between Si and NiTi are reduced. With a gold layer of 1 mu m thickness and bond areas between 200 x 200 and 800 x 800 mu m(2) a high bond strength and a yield above 90% is demonstrated.

Keyword
Microactuators, Gold, Temperature, Fabrication, Film
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-93492 (URN)10.1088/0960-1317/23/1/015008 (DOI)000312248200008 ()2-s2.0-84877969669 (Scopus ID)
Funder
EU, European Research Council, 267528
Note

QC 20130110. Updated from accepted to published.

Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2017-12-07Bibliographically approved
3. Design and wafer-level fabrication of SMA wire microactuators on silicon
Open this publication in new window or tab >>Design and wafer-level fabrication of SMA wire microactuators on silicon
Show others...
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
Keyword
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:nbn:se:kth:diva-11829 (URN)10.1109/JMEMS.2010.2049474 (DOI)000283543400029 ()2-s2.0-77955414734 (Scopus ID)
Note

QC 20100729 Uppdaterad från accepted till published (20110217)

Available from: 2010-01-04 Created: 2010-01-04 Last updated: 2015-06-18Bibliographically approved
4. Robust actuation of silicon MEMS using SMA wires integrated at wafer-level by nickel electroplating
Open this publication in new window or tab >>Robust actuation of silicon MEMS using SMA wires integrated at wafer-level by nickel electroplating
Show others...
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.

Keyword
Actuator, Electroplating, MEMS, Shape memory alloy, SMA, Wafer level integration
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-47630 (URN)10.1016/j.sna.2012.08.036 (DOI)000314622600015 ()2-s2.0-84870571842 (Scopus ID)
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
5. Wire-bonder-assisted integration of non-bondable SMA wires into MEMS substrates
Open this publication in new window or tab >>Wire-bonder-assisted integration of non-bondable SMA wires into MEMS substrates
Show others...
2012 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 22, no 5, 055025- p.Article in journal (Refereed) Published
Abstract [en]

This paper reports on a novel technique for the integration of NiTi shape memory alloy wires and other non-bondable wire materials into silicon-based microelectromechanical system structures using a standard wire-bonding tool. The efficient placement and alignment functions of the wire-bonding tool are used to mechanically attach the wire to deep-etched silicon anchoring and clamping structures. This approach enables a reliable and accurate integration of wire materials that cannot be wire bonded by traditional means.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2012
Keyword
Bonding, Electromechanical devices, Integration, MEMS
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-90858 (URN)10.1088/0960-1317/22/5/055025 (DOI)000303197000025 ()2-s2.0-84860433128 (Scopus ID)
Funder
EU, European Research Council, 267528 277879
Note
QC 20120528Available from: 2012-04-20 Created: 2012-03-01 Last updated: 2017-12-07Bibliographically approved
6. SMA Microvalves for Very Large Gas Flow Control Manufactured Using Wafer-Level Eutectic Bonding
Open this publication in new window or tab >>SMA Microvalves for Very Large Gas Flow Control Manufactured Using Wafer-Level Eutectic Bonding
2012 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 59, no 12, 4895-4906 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a novel gas microvalve design concept, in which a flow control gate is opened by a pneumatic pressure and closed by a shape memory alloy actuator, allowing large flow control. Two different design variations were fabricated using a novel wafer-level Au-Si eutectic bonding process for TiNi to silicon integration. The resulting microvalves demonstrate a record pneumatic performance per footprint area; a microvalve with a footprint of only 1 x 3.3 mm(2) successfully controls a flow difference of 3100 sccm at a pressure drop of 70 kPa using a power of 0.35 W.

Keyword
Eutectic bonding, Microvalve, Shape Memory Alloy, Wafer-scale integration
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-47632 (URN)10.1109/TIE.2011.2173892 (DOI)000306142000040 ()2-s2.0-84863768457 (Scopus ID)
Funder
EU, European Research Council, 267528
Note
QC 20120806Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-12-08Bibliographically approved
7. A low-power high-flow shape memory alloy wire gas microvalve
Open this publication in new window or tab >>A low-power high-flow shape memory alloy wire gas microvalve
Show others...
2012 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 22, no 7, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

In this paper the use of shape memory alloy (SMA) wire actuators for high gas flow control is investigated. A theoretical model for effective gas flow control is presented and gate microvalve prototypes are fabricated. The SMA wire actuator demonstrates the robust flow control of more than 1600 sccm at a pressure drop of 200 kPa. The valve can be successfully switched at over 10 Hz and at an actuation power of 90 mW. Compared to the current state-of-the-art high-flow microvalves, the proposed solution benefits from a low-voltage actuator with low overall power consumption. This paper demonstrate that SMA wire actuators are well suited for high-pressurehigh-flow applications.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2012
Keyword
MICROACTUATORS, PRESSURE, SILICON
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-90852 (URN)10.1088/0960-1317/22/7/075002 (DOI)000305890600016 ()2-s2.0-84863831072 (Scopus ID)
Note

QC 20150618

Available from: 2012-03-01 Created: 2012-03-01 Last updated: 2017-12-07Bibliographically approved

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