Henrik Gradin

SMA Microvalves for Very Large Gas Flow Control Manufactured Using Wafer-Level Eutectic Bonding

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 3.3 mm2 successfully controls a flow difference of 3100 sccm at a pressure drop of 70 kPa using a power of 0.35 W.

Design and Wafer-Level Fabrication of SMA Wire Microactuators on Silicon

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.

Wafer-level integration of NiTi shape memory alloy wires for the fabrication of microactuators using standard wire bonding technology

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.

Wafer-level mechanical and electrical integration of SMA wires to silicon MEMS using electroplating

This paper reports on the wafer-level fixation and electrical connection of pre-strained SMA wires on silicon MEMS using electroplating, providing high bond strength and electrical connections in one processing step.

Wire-bonder-assisted integration of non-bondable SMA wires into MEMS substrates

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 ...

Microactuation Utilizing Wafer-Level Integrated SMA Wires

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 ¿m for the double cantilever actuators.

Localized removal of the Au?Si eutectic bonding layer for the selective release of microstructures

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 th ...

Selective electrochemical release etching of eutectically bonded microstructures

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 µm wide silicon structures were fully released after 1 hour of electrochemical etching followed by 1.5 hours wet etching of the TiW adhesion layer.

Wafer-level integration of NiTi shape memory alloy on silicon using Au-Si eutectic bonding

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 thickne ...

Awafer-level, heterogeneously integrated, high flow SMA-silicon gas microvalve

This paper presents a novel gas microvalve design in which a flow control gate is opened by the pneumatic pressure and closed by a SMA actuator, allowing large flow control. The microvalves 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 of only 1×3.3 mm2 footprint successfully controls 3000 sccm at a pressure drop of 130 kPa.