588 Y.Bellouand Materials Science and Engineering A 481-482 (2008)582-589 20 case for melt-spinning (where molten metal is rapidly solidi 1.6 fied on a high speed spinning wheel)and thin-film fabricated by Laser annealed actuator yers of Ni and ctrs bending effect.As for the bimorph-like construction,it offers 04 limited design options. Raw material (Cold rolled in-plane micro-actuators design. -12 Heating 7.Future directions 40 60 Tempentergm 80 120 are deve at a fast emerging as powerful platform for multifunctional integration n a varety of packages and substrates This and electronics can bem on a sins (smart bandage for instance).Ni-Tialloys being bio-compatible materials are quite that Although early e actuator 3 ere mad As stated before.the main design objective in SMA micro- Observing SME effect at the nanoscale has been of grea interest recently both from an application and theoretica with a work output point-o 4 h ale L Fig.15 summarizes the various principles available toinduce 145]have also shown that the type of microstructure found in a reversible macroscopic shape change.The most commonly nanograins is size dependant and has a unique crystallographic pombrdmentmeas SMA actuato ks may trigger new developments toward nano- or inhomogeneities which combined with unaffectedz ones tenc Inconclusion,carefully designed,SMA micro-actuatorsoffer a very attractive solution for low-bandwidth microsystems in Reversible shape change References Intrinsic biasing mechanism N MaedAreen touse bo Extrinsic biasing 15-216. McmEne 28 d.Bia projection/ mplantaion.inmtem 16A.D.Joson.V.V.Martynov.Int.Conf.Shape Memory Supere in Special pr CA.Micro-Actuator.US M dt,B.Winzek.S.Miyazaki.D.M.Allen Fig.15.Overview of methods that induc sible shape change in SMA 588 Y. Bellouard / Materials Science and Engineering A 481–482 (2008) 582–589 Fig. 14. Differential scanning calorimetry (DSC) of the micro-gripper main parts, namely, the pull-back spring and the actuator element (laser annealed). The signal for the raw material – as received – is shown for comparison. For each of the three DSC the mass specimen are similar. 6. Summary of design principles to achieve a reversible effect As stated before, the main design objective in SMA micro￾actuators is to achieve a macroscopic reversible shape change in which the actuator switches back and forth between two shapes with a work output. Fig. 15 summarizes the various principles available to induce a reversible macroscopic shape change. The most commonly found techniques were briefly outlined in the previous para￾graphs. In addition to these techniques, one should add ion bombardment as a means to produce localized amorphization or inhomogeneities which combined with unaffected zones tend to induce an intrinsic two-way effect [41]. Special fabrication processes can also lead to intrinsic two-way effects: this is the Fig. 15. Overview of methods that induce reversible shape change in SMA. case for melt-spinning (where molten metal is rapidly solidi- fied on a high speed spinning wheel) and thin-film fabricated by stacking sequence of thin layers of Ni and Ti [42]. These two￾way effects essentially result from the particular microstructures found across the material thickness that induce an out-of-plane bending effect. As for the bimorph-like construction, it offers limited design options. Local annealing technique offers a way to bypass process compatibilities issues resulting from the need for high￾temperature processing as well as a convenient method for in-plane micro-actuators design. 7. Future directions Electronics on flexible substrate are developing at a fast pace. So-called polymer electronics or “plastic” MEMS are rapidly emerging as powerful platform for multifunctional integration in a variety of packages and substrates. This is particularly attractive for biomedical applications where fluidic, optics and electronics can be merged on a single, flexible substrate (smart bandage for instance). Ni–Ti alloys being bio-compatible materials are quite attractive in that context. Although early demonstrations of Ni–Ti/polyimide actuator [34] were made, more work is needed to expand the process capabilities. Observing SME effect at the nanoscale has been of great interest recently both from an application and theoretical point-of-view. Nano-indentations experiments [43,44] have demonstrated nano-scale shape memory effect. Waitz et al. [45] have also shown that the type of microstructure found in nanograins is size dependant and has a unique crystallographic structure [46]. These works may trigger new developments toward nano￾SMA actuators. In conclusion, carefully designed, SMA micro-actuators offer a very attractive solution for low-bandwidth microsystems in general and in particular for applications where force, compact￾ness as well as smooth and continuous actuation is needed. References [1] N. Maluf, An Introduction to Micro Electro Mechanical Systems Engineer￾ing, 1st ed., Artech House Publishers, 1999, ISBN 0-89006-581-0. [2] K. Ikuta, Proc. IEEE Int. Conf. Robotics Autom., Cincinatti, 1990, pp. 215–216. [3] P. Krulevitch, A.P. Lee, P.B. Ramsey, J.C. Trevino, J. Hamilton, M.A. Northup, J. MEMS 5 (1996) 270–282. [4] J. Hesselbach, R. Pittschellis, E. Hornbogen, M. Mertmann, Proc. Shape Memory and Superelastic Technol., Pacific Grove, CA, 1997, pp. 251– 256. [5] Y. Bellouard, R. Clavel, J.-E. Bidaux, R. Gotthardt, T. Sidler, Proc. Shape Memory Superelastic Technol., Pacific Grove, CA, 1997, pp. 245– 250. [6] A.D. Johnson, V.V. Martynov, Proc. 2nd Int. Conf. Shape Memory Supere￾lastic Technol., Pacific Grove, CA, 1997, pp. 149–154. [7] J.D. Busch, A.D. Johnson, Shape-Memory Alloys Micro-Actuator, US Patent 5,061,914, June 27 (1989). [8] M. Kohl, D. Dittmann, E. Quandt, B. Winzek, S. Miyazaki, D.M. Allen, Mater. Sci. Eng. A 273–275 (1999) 784–788. [9] W.L. Benard, H. Kahn, A.H. Heuer, M.A. Huff, J. MEMS 7 (1998) 245–251