Manfred Kohl

Thin film shape memory microvalves with adjustable operation temperature

Abstract Gas microvalves of about 3×3×5 mm 3 size are presented, which are actuated by a microdevice of shape memory alloy (SMA) thin film with stress-optimized shape. By variation of the chemical composition of the material system Ti–Ni–Pd, the phase transformation temperatures have been adjusted in a range below 405 K in order to design the operation temperature of the valves. The main fabrication technologies were magnetron sputtering and electrolytic photoetching of the thin films and hybrid integration of the valve components. The SMA microvalves work in a normally open mode and allow control of pressure differences below 2500 hPa at gas flows below 360 standard ccm (sccm).

SMA microgripper with integrated antagonism

Abstract A microgripper of 2×3.9×0.1 mm3 size is presented consisting of a single device microfabricated from a shape memory alloy (SMA) thin sheet. The device consists of two integrated actuation units of a stress-optimized shape, which actuate in opposite directions and thus form an antagonistic pair. The fabrication procedure is reduced to one micromachining step of a rolled SMA sheet and subsequent bonding onto a substrate. The maximum displacement of the gripping jaws is 180 μm, the maximum gripping force 17 mN. For an electrical power of 22 mW, a response time of 32 ms is observed.

Sputter deposition of TiNi, TiNiPd and TiPd films displaying the two-way shape-memory effect

Abstract TiNi, TiNiPd and TiPd films exhibiting the one-way and two-way shape-memory effect have been prepared by d.c. magnetron sputtering onto unheated substrates followed by annealing and training processes. In the case of TiNi, films could be prepared showing the R-phase transition, the important feature of which is its small hysteresis of about 1 K. By the Ni-Pd substitution the transition temperatures (austenite/martensite finish temperatures) could be increased from 32 °C/–38 °C for the binary NiTi alloy to a maximum of 570 °C/498 °C for TiPd films. The films have been subject to further microstructuring for developing micro-actuators displaying the two-way shape-memory effect.

SMA microgripper system

A microgripper system is presented, which consists of a monolithic shape memory alloy (SMA) device of 2 mm x 5.8 mm x 0.23 mm size and an integrated optical position sensor. Gripper closing and opening is performed by two integrated actuators, which form an antagonistic pair. Investigations of temperature profiles by coupled finite-element simulations and infrared microscopy demonstrate a sufficient thermal insulation of the actuators for their selective control. The motion of gripping jaws is transmitted by an integrated gearing mechanism into a linear motion of an integrated optical slit, which is detected by change of optical transmission. The maximum stroke and force of the gripping jaws are 300 μm and 35 mN, respectively. In the range between 10 and 90% of the maximum stroke, positioning is achieved within 140 ms with an accuracy of about 2 μm.

Shape memory microvalves based on thin films or rolled sheets

Abstract This paper reports on recent developments of gas microvalves, which are actuated by microfabricated shape memory alloy (SMA) thin films or sheets with stress-optimised shapes. TiNi, TiNiCu and TiNiPd thin films of 10 μm thickness have been fabricated by sputter deposition. TiNi sheets of 30–100 μm thickness have been made by hot-forging and cold-rolling. The main fabrication technologies of the valves have been laser cutting or electrolytic photoetching and subsequent hybrid integration. By variation of the chemical composition of the thin films, the valve operation temperature was adjusted between 30 and 120°C. The thin film devices have been operated in tension mode allowing the control of maximum pressure differences of 3000 hPa (3 bar). The corresponding maximum gas flow is about 360 Standard ccm. The maximum control power for TiNiCu and TiNi microvalves is 110 mW, for TiNiPd microvalves 220 mW. SMA sheet microdevices have been operated in bending mode, which allows large strokes and thus large gas flows.

Development of stress-optimised shape memory microvalves

A shape memory microdevice consisting of stress-optimised beams of 100 μm thickness has been developed to actuate a membrane microvalve for high pressure applications. The lateral widths of the microbeams are designed for homogeneous stress distributions along the beam surfaces allowing an optimised use of the shape memory effect and a minimisation of fatigue effects. Infrared microscopy investigations of the beams reveal maximum temperature variations of 14 K. For valve actuation, a rhombohedral phase transformation is used. This allows operation below pressure differences of 1200 hPa in designs with one valve chamber and below 4500 hPa in pressure-compensated designs with a second valve chamber above the membrane. Maximum gas flows of 1600 sccm and work outputs of 35 μN m are achieved for a driving power of 210 mW. The response times for closing the valves vary between 0.5 and 1.2 s and for opening between 1 and 2 s depending on the applied pressure difference.

From Highly Monodisperse Indium and Indium Tin Colloidal Nanocrystals to Self-Assembled Indium Tin Oxide Nanoelectrodes

Indium tin oxide (ITO) nanopatterned electrodes are prepared from colloidal solutions as a material saving alternative to the industrial vapor phase deposition and top down processing. For that purpose highly monodisperse In(1-x)Sn(x) (x < 0.1) colloidal nanocrystals (NCs) are synthesized with accurate size and composition control. The outstanding monodispersity of the NCs is evidenced by their self-assembly properties into highly ordered superlattices. Deposition on structured substrates and subsequent treatment in oxygen plasma converts the NC assemblies into transparent electrode patterns with feature sizes down to the diameter of single NCs. The conductivity in these ITO electrodes competes with the best values reported for electrodes from ITO nanoparticle inks.

Recent Progress in FSMA Microactuator Developments

The giant magneto-strain effect is particularly attractive for actuator applications in micro- and nanometer dimensions as it enables contact-less control of large deformations, which can hardly be achieved by other actuation principles in small space. Two different approaches are being pursued to develop ferromagnetic shape memory (FSMA) microactuators based on the magnetically induced reorientation of martensite variants: (1) the fabrication of free-standing epitaxial Ni-Mn-Ga thin film actuators in a bottom-up manner by magnetron sputtering, substrate release and integration technologies and (2) the top-down approach of thickness reduction of bulk Ni-Mn-Ga single crystals to foil specimens of decreasing thicknesses (200 – 40 μm) and subsequent integration. This review describes the fabrication technologies, procedures for thermo-mechanical training adapted to the quasi-two-dimensional geometries of film and foil specimens as well as the performance characteristics of state-of-the art actuators after processing and training.

Silicon-Organic Hybrid (SOH) and Plasmonic-Organic Hybrid (POH) Integration

Silicon photonics offers tremendous potential for inexpensive high-yield photonic-electronic integration. Besides conventional dielectric waveguides, plasmonic structures can also be efficiently realized on the silicon photonic platform, reducing device footprint by more than an order of magnitude. However, neither silicon nor metals exhibit appreciable second-order optical nonlinearities, thereby making efficient electro-optic modulators challenging to realize. These deficiencies can be overcome by the concepts of silicon-organic hybrid (SOH) and plasmonic-organic hybrid integration, which combine SOI waveguides and plasmonic nanostructures with organic electro-optic cladding materials.

Plasmonic communications : light on a wire

By coupling light to the charges at metal interfaces, plasmonics enables scientists to manipulate photons in a way they never have before: at the subwavelength level. With its potential to produce ultra-compact devices that relay information almost instantaneously, plasmonics may be the next big-and small-thing in optical communications.