This dissertation presents the programmability of emissivity states in a monolithically in-tegrated micro window based on vanadium dioxide (VO2) thin films. The 400μm windowfeatures a VO2thin film with integrated electrodes for actuation and sensing. The phasetransition was induced by resistive heating, while the electrical resistivity and optical trans-mittance (for near IR wavelength of 1550 nm) of the VO2thin film were monitored simul-taneously. Abrupt drops in electrical resistance and optical transmittance confirmed thequality of the VO2thin films. Electronic pulses were used to program emissivity states inthe VO2window. The emissivity programmed state was shown for a specific DC current overimposed with the programming pulse; but any emissivity state that belongs to the minorhysteretic curves can be obtained by choosing different electronic inputs. The fully mono-lithically integrated device presented here can be used for IR cloaking applications, wheredifferent emissivity values can be programmed with electronic pulses.Micrometer-sized VO2-based devices with integrated resistive heaters of different configu-rations were fabricated. Quality of the VO2films was confirmed by measuring the character-istic drop in transmittance and negative differential emissivity for these films. A two-interfacemodel for optical transmittance, reflectance, and absorbance is presented. This method andanalytic model presents an advantage over most typically used approaches in that it doesnot require direct measurements of the material’s optical constants to estimate transmit-tance. By combining the substrate and the VO2film into one layer with a reduced opticaladmittance, the two-interface model was reduced to a single-layer model. Moreover, thepresent work demonstrates the implementation of the developed VO2-based devices in adap-tive camouflage and shape-converting applications. Electrical pulses are used to programdifferent emissivity states to convert geometric shapes inside a fully integrated VO2-basedelectro-optical window. This resulted in the reconfiguring of thermal images to either createnew shapes, or shift from one to another.A transient heat deflection model is developed which can be applied for any bimorphstructure actuated electro-thermally and for which the dimensions and material propertiesare known. Micrometer size VO2based cantilevers with integrated resistive heaters arefabricated and deflections due to an input of current are recorded using a high-speed camera.From the high frame rate videos, deflection measurements and dynamic response is extractedand compared to numerical data obtained from the model. The transient heat as caused bythe current input is studied, and a model is developed.VO2-based MEMS tunable optical attenuators are demonstrated. The design consists ofa VO2-based cantilever attached to a VO2-based optical window with integrated resistiveheaters for individual mechanical actuation of the cantilever structure, tuning of the opticalproperties of the window, or both. Optical transmittance measurements as a function ofcurrent for both heaters demonstrates that the developed devices can be used as analogoptical attenuators, where the intensity of a light beam can be tuned to any value within therange of VO2phase transition. A transmittance drop off 30% is shown for the optical window,with tuning capabilities greater than 30% upon actuation of the cantilever. Unlike typicalmechanical attenuators, these devices are not restricted to binary optical states. Opticalmodulation of the optical window is demonstrated with an oscillating electrical input. Thisproduces a transmittance signal that oscillates around an average value within the rangeoff VO2’s phase transition. For an input current signal with fixed amplitude (fel= 0.28Hz), tuned to be at the onset of the phase transition, a transmittance modulation of 14% isshown. Similarly, by modulating the DC-offset, a transmittance modulation of VO2alongthe hysteresis is obtained.
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