Colossal thermal-mechanical actuation via phase transition in single-crystal VO2 microcantilevers

Abstract

The spontaneous strain associated with the structural change in the metal-insulator transition in VO 2 is orders of magnitude higher than thermal expansion mismatch used in bimetallic strips. Here we show that this strain can be leveraged to thermally activate bending of crystalline VO 2-based bilayer microcantilevers at extremely large curvatures, making them suitable for thermal sensors, energy transducers and actuators with unprecedented sensitivities. The single-crystallinity, deposition conditions, and postdeposition treatments were utilized to control the metal-insulator domain structure along the cantilever, by which we achieved bending curvatures a few hundred times higher than conventional bilayer cantilevers with the same geometry.

Performance of Electro-Thermally Driven ${\rm VO}_{2}$-Based MEMS Actuators

“…Subsequent relevant work was mainly focused on the use of VO 2 's SPT for micro-actuation purposes, which included the use of single crystal VO 2 nanobeams [3], the photothermal induction of the SPT in air and aqueous media [25] and the effects of Cr doping concentrations and different monoclinic phases of VO 2 [26]. In order to transform the SPT of VO 2 into a viable MEMS technology, it is necessary to comprehensively characterize the dynamics of a completely monolithic VO 2 MEMS device.…”

“…When highly oriented VO 2 thin film coatings are deposited on suspended micromechanical structures, the SPT of the VO 2 induces strains up to −0.32% in the bimorph microactuator, which have been used to tune the resonant frequency of simple VO 2 -coated SiO 2 micro-bridges up to −23% [2], and to generate curvatures in VO 2 -coated single crystal silicon (SCS) cantilevers over 2,000 m −1 [1]. Larger curvatures changes were obtained on initially curved single crystal VO 2 microcantilevers (20,000 m −1 ) [3] and 50 nm thick Cr cantilevers coated with polycrystalline VO 2 (14,000 m −1 ) [4]; which were straightened during the phase change. This paper presents the first monolithically integrated VO 2 -based device (a micro-actuator) driven by electric signals (i.e.…”

Molecular actuators driven by cooperative spin-state switching

“…The differential thermal expansion of the two layers causes the strip to bend when heated or cooled. 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 .…”

Tailoring of the thermomechanical performance of VO2 nanowire bimorph actuators by ion implantation

“…the preferential growth direction of VO 2 nanowires) and is thus ideally suited to build nanowire bimorphs where a single crystalline VO 2 nanowire is mechanically coupled along its length either to a metal [13][14][15] or to VO 2 material in which the MIT is deactivated as described in this work for the first time. The length change of VO 2 from the M1 to the R phase is À1% and takes place over a very narrow temperature interval across the MIT resulting in an abrupt and large bending of a VO 2 nanowire based bimorph.…”