Giant-Amplitude, High-Work Density Microactuators with Phase Transition Activated Nanolayer Bimorphs

Abstract

Various mechanisms are currently exploited to transduce a wide range of stimulating sources into mechanical motion. At the microscale, simultaneously high amplitude, high work output, and high speed in actuation are hindered by limitations of these actuation mechanisms. Here we demonstrate a set of microactuators fabricated by a simple microfabrication process, showing simultaneously high performance by these metrics, operated on the structural phase transition in vanadium dioxide responding to diverse stimuli of heat, electric current, and light. In both ambient and aqueous conditions, the actuators bend with exceedingly high displacement-to-length ratios up to 1 in the sub-100 μm length scale, work densities over 0.63 J/cm(3), and at frequencies up to 6 kHz. The functionalities of actuation can be further enriched with integrated designs of planar as well as three-dimensional geometries. Combining the superior performance, high durability, diversity in responsive stimuli, versatile working environments, and microscale manufacturability, these actuators offer potential applications in microelectromechanical systems, microfluidics, robotics, drug delivery, and artificial muscles.

Molecular actuators driven by cooperative spin-state switching

“…For compound 1, we obtained W/V ¼ 0.6 J cm À 3 . This value is comparable to (or even higher than) the volumetric work that could be performed using piezoelectric ceramics and magnetostrictors 11 and is certainly a few orders higher than the work via a simple thermal expansion. For example, for the same complex 1, a volumetric work density for a purely thermal actuation in a 5-K wide region (far from the spin transition) is B0.0001 J cm À 3 .…”

“…The deliberate construction of a bimetallic strip analogue (BSA) designed to amplify motion produced by a phase transition has recently been demonstrated for VO 2 , which undergoes a thermally induced metal-insulator transition above room temperature, concomitant with a 0.3% volume change in the material 9,10 . Very recently, micro-actuators were also created from this same material, and actuation was observed as a direct result of the phase transition 11 . However, this system is restricted by the very narrow operating temperature range and relatively small volume change, severely limiting the potential applications of the actuating device.…”

Switchable molecule-based materials for micro- and nanoscale actuating applications: Achievements and prospects

“…Obviously the relative importance of these requirements will depend on the targeted application. Nevertheless, following the proposition of Liu et al [14], a very useful classification is possible if one plots the Young's modulus of the material versus the maximum achievable linear strain (Fig. 2a).…”

“…For many applications in the MEMS/NEMS context it is desirable to achieve high work densities due to the space (and mass) limitations. This requirement is currently fulfilled only by shape memory alloys, but their further development is hampered by the degradation of their properties at sub-micrometric sizes [14,15]. Beside stifness and strain, the speed of response (or frequency bandwidth) is also an important attribute in the MEMS/NEMS technology.…”

VO2: A Phase Change Material for Micromechanics

“…VO2 is an optimum candidate as active material in micro-/nano-actuators because of its sharp solid state phase transitions (SSPT) at 68 °C that in single crystals can produce strain up to 1% and large applied forces, being at the same time intrinsically fast (ps) [1,2]. Efficient actuation in VO2 micro-beams or prototypical thin film structures has been already demonstrated [3,4], but the potentialities of this material are still to be further explored, in particular for what concerns its integration in thin film nano-devices. Here, we achieve high-frequency mechanical actuation of micro-and nano-electro-mechanical devices enabling the direct transduction of a DC voltage bias into a mechanical excitation in the MHz range [5].…”