Recent Progress in FSMA Microactuator Developments

Abstract

Abstract. 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.

Magnetic Shape Memory Microactuators

“…Sputtering is the most favorable deposition method to obtain thick films on a large scale as required for MEMS technology [2,14]. The resulting film structure depends on various parameters including substrate, deposition temperature, sputtering power, and annealing conditions.…”

“…As illustrated in Figure 1, generally any change of one of the physical properties induced by an external stimulus causes characteristic changes of the other physical properties. Owing to their multiferroic coupling properties, FSMAs (Ferromagnetic shape memory alloys) exhibit various modes of combined sensing and actuation capabilities [2]. As a consequence, MSMA actuators may only consist of a single piece of material, but still may perform several functions.…”

“…Recent efforts in miniaturization of MSM actuators follow a top-down approach by thinning bulk single crystals to foil specimens [2,9,10]. An alternative is MSMA films that are fabricated in a bottom-up manner by film deposition [11][12][13][14].…”

Insight into variant selection of seven-layer modulated martensite in Ni–Mn–Ga thin films grown on MgO(0 0 1) substrate

“…Epitaxial thin films of Ni-Mn-Ga ferromagnetic shape memory alloys have attracted considerable attention during the past decade [1][2][3][4][5][6][7][8], due to their potential application as new materials for micro-actuators and sensors in microelectro-mechanical systems [9][10][11][12][13]. To obtain qualified thin films, the choice of an appropriate substrate is important.…”

Growth, microstructure and thermal transformation behaviour of epitaxial Ni-Ti films

“…One open research question is if epitaxial NiTi films can be used to contribute to a more fundamental understanding of the basic behaviour of NiTi SMA, as sketched above for magnetic SMA. Moreover, epitaxial NiTi films might even improve the functionality compared to polycrystalline NiTi films, which have already been developed towards microactuators [12], stents for brain surgery [13], elastocaloric refrigeration [14], or used for the combinatorial search for low hysteresis materials [15,16].…”