Flexible, All-Inorganic Actuators Based on Vanadium Dioxide and Carbon Nanotube Bimorphs

Abstract

Flexible actuators responsive to multiple stimuli are much desired in wearable electronics. However, general designs containing organic materials are usually subject to slow response and limited lifetime, or high triggering threshold. In this study, we develop flexible, all-inorganic actuators based on bimorph structures composed of vanadium dioxide (VO) and carbon nanotube (CNT) thin films. The drastic, reversible phase transition of VO drives the actuators to deliver giant amplitude, fast response up to ∼100 Hz, and long lifetime more than 1 000 000 actuation cycles. The excellent electrical conductivity and light absorption of CNT thin films enable the actuators to be highly responsive to multiple stimuli including light, electric, and heat. The power consumption of the actuators can be much reduced by doping VO to lower its phase transition temperature. These flexible bimorph actuators find applications in biomimetic inspect wings, millimeter-scale fingers, and physiological-temperature driven switches.

A 0.2 V Micro‐Electromechanical Switch Enabled by a Phase Transition

“…Moreover, such a phase‐transition MEM switch is able to function as an ultralow‐power temperature switch to control circuits in temperature‐sensitive systems. We also note that doping VO 2 with other metals (such as tungsten and chromium) can effectively and continuously reduce or increase its T c , hence covering a wide range of operation temperatures.…”

“…Third, unlike SMA, VO 2 has little or no ductility, and is able to work with a relatively narrow hysteretic loop at nanoscale thicknesses, thus having the potential to be integrated into MEM switches for optimized switching time and power consumption. Indeed, using conventional microfabrication processes/facilities, VO 2 ‐based bimorph microactuators have been demonstrated with ≳10 6 operating cycles or ≳kHz switching frequencies . Consequently, the phase‐transition material of VO 2 is potentially an effective solution to solve the two major problems of operating voltage and lifetime in MEM switches…”

“…Third, the phase‐transition temperature of VO 2 can be engineered by doping, defects, stoichiometry, and microstructures, creating abundant design space. For example, the performance of the VO 2 ‐based MEM switch can be further improved by W‐doping for lower T c, and Cr‐doping may increase T c to allow the phase‐transition MEM switch to operate at temperatures as high as +85 °C . Downscaling the device size with NEM technology can significantly reduce power consumption as well as switch‐on time (see the Supporting Information), and better electrode–electrode contact can be attained by optimizing the fabrication process and device configuration for higher contact force and lower contact resistance.…”

Optically Induced Phase Change for Magnetoresistance Modulation

“…The magnetic sensitivity (Figure 2a) accompanied with the photosensitivity (Figure 2c) in this heterostructure result in a highly controllable feature of its resistance, which can be adopted for different electronic applications . Figure 5a demonstrates an example of six different resistance states achieved via the synergistic control of the light illumination and magnetic field in the PCAMR device.…”

Vanadium Dioxide: The Multistimuli Responsive Material and Its Applications

“…Manipulating the MIT of VO 2 by external stimuli is an active research area, making VO 2 a material of great interest for novel electronic and optical devices. For example, the thermally induced MIT has been extensively studied for electro/thermal‐chromic, actuators, and thermoelectricity applications, while electrical field manipulation can be used for memory devices and Mott field effect transistor (FET) to circumvent the fundamental limits encountered in Si‐based electronics . It has been shown that VO 2 based photodetectors can respond to optical stimulation over a broad spectral range from terahertz to ultraviolet (UV), and the time‐resolved optical pump‐probe techniques provide an effective means to study the phase transition dynamics in VO 2 .…”