This paper reports on the wafer-scale integration of pre-strained SMA wires to microstructured silicon devices and the performance of the microactuator prototypes. The overall goal is to obtain low cost microactuators having high work densities and a mass production compatible manufacturing, without having to deal with the inherently high costs of a pick-and-place approach or with the complex composition control and annealing process of sputtered NiTi films. Testing above the SMA transformation temperature shows repeatability in actuation of the fabricated structures, with net strokes of 170 mum for the double cantilever actuators.
This paper reports on the first integration of SMA wires into silicon based MEMS structures using a standard wire bonder. This approach allows fast and efficient placement, alignment and mechanical attachment of NiTi-based SMA wires to silicon-based MEMS. The wires are mechanically anchored and clamped into deep-etched silicon structures on a wafer. The placement precision is high with an average deviation of 4 μm and the mechanical clamping is strong, allowing successful actuation of the SMA wires.
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 $1 \times 3.3\ \hbox{mm}^{2}$ successfully controls a flow difference of 3100 sccm at a pressure drop of 70 kPa using a power of 0.35 W.
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.
This paper reports on the successful demonstration of a novel microfabrication method in which eutectic gold bonded microstructures are selectively electrochemically release etched. This method offers several advantages: both a strong permanent bond and a temporary bond is achieved on the same die, the footprint of the temporary bonded structures is allowed to be larger than the footprint of the permanently bonded structures and the used etchants provide a larger process compatibility than the etchants of other release etch methods. Eutectically bonded 350 mum wide silicon structures were fully released after 1 hour of electrochemical etching followed by 1.5 hours wet etching of the TiW adhesion layer.
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.
a b s t r a c t 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 m and a mean stroke of 354 m at a low power consumption (less than 70 mW). One actuator was tested for m150 × 10 3 cycles, and it demonstrated a highly reliable long-term performance, showing neither material degradation, nor failure of the nickel anchors.
Thispaper reports onthewafer-scale integration of pre-strained SMA wires tomicrostructured silicon devices andtheperformance ofthemicroactuator prototypes. Theoverall goalistoobtain lowcost microactuators havinghighworkdensities anda massproduction compatible manufacturing, without having todealwith theinherently highcosts ofapick-and-place approach or withthecomplex composition control andannealing process ofsputtered NiTifilms. Testing abovetheSMA transformation temperature showsrepeatability in actuation of thefabricated structures, withnetstrokes of170ptmforthedouble cantilever actuators. INTRODUCTION Microelectromechanical systems (MEMS)
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 μm 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 μm thickness and bond areas between 200 × 200 and 800 × 800 μm2 a high bond strength and a yield above 90% is demonstrated.
This paper reports on the performance of Joule-heated shape memory alloy (SMA) microactuators on silicon MEMS.The actuators consist of pre-strained SMA wires connected to micromachined silicon structures by electroplatedfixtures. Response of the actuators upon long term cycling by electrical heating is evaluated. Measurements on a 4.5x 1.6 mm2 footprint device demonstrated excellent stability of the actuator, without any loss of performance over150·103 cycles. These actuators are potentially suited for industrial applications with stringent demands on actuationperformance, reliability, and cost.
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