High Frequency Dielectric Characteristics of Electrochromic, WO3 and NiO Films with LiNbO3 Electrolyte

Abstract

A great deal of attention has been recently focused on Electrochromic (EC) materials and EC based devices, promoting mainly applications related to display technology. In this case, EC based displays are usually actuated by the application of low dc bias voltages, changing their appearance from transparent to opaque. A variety of studies related to the optical characteristics of EC materials have been reported, however, no serious studies so far have been reported on the possible high frequency tunability of the dielectric characteristics of these materials, with the exception of the work by Rose, which presented the operation of a microwave shutter based on conductive polymers operating in the X-band. Here we report tuneable high frequency dielectric characteristics of an Electrochromic (EC) cell with a complimentary structure of Conductor/WO3/LiNbO3/NiO/Conductor in the frequency range from 1 GHz to 20 GHz. The EC cell was prepared using standard semiconductor processing technology, such as lithography, etch and deposition techniques. Our measured results indicate that tunability of high frequency dielectric characteristics as a function of dc bias voltage is achieved, and that a possibility exists for this tunability to be tailored.

Variable Temperature Broadband Microwave and Millimeter-Wave Characterization of Electrochromic (WO3/LiNbO3/NiO) Thin Films

“…1 (b). In order to extract the dielectric characteristics of the unknown dielectric material accurately, the effect of this transition needs to be taken into account [9]. Due to the symmetry and reciprocity properties of the microstrip line the following holds,…”

“…To ensure that the thicknesses of these two layers are the same, specific dimension measurements were performed during fabrication of the test cells [9]. As such, all of the individual layers in the test cells were characterized using Stylus profilometry on a KLA Tencore P-11 profilometer to determine the thickness.…”

“…The work was inspired by observations in the optical frequency [10], [11] where a change in colour occurs upon EC films actuation by application of a low DC bias voltage. Although the optical properties of EC have been widely reported in the literature, only two works [9], [12] have elaborated on the behaviour of these films in the microwave band, and, to the best of our knowledge, no study has ever been conducted to establish the electrical behaviour of EC at different operating temperatures and in the millimetre wave band.…”

“…The results are shown to compare favourability with LC mixtures, which give a satisfactory tunability and loss, but only over a limited temperature range where the material exists in the nematic phase state [6], [7]. Test cells previously developed and successfully employed for the work reported in [9], are also used in the present measurements in a temperaturecontrolled experimental set-up, suitable for wafer probing. Each test cell consists of two wideband coplanar waveguide (CPW) to microstrip line transitions to facilitate on-wafer RF measurements as well as to provide the required bias voltage excitation [13].…”

“…In 2016, two of the authors reported, for the first time, a new class of dielectric material, namely Electro-Chromic (EC) films, which were shown to exhibit electronic tunability in the frequency range from 1 GHz to 20 GHz [9]. The work was inspired by observations in the optical frequency [10], [11] where a change in colour occurs upon EC films actuation by application of a low DC bias voltage.…”