Color depth modulation and resolution in Phase-Change Material nano-displays

Color modulation has been a topic of longstanding interest in science and engineering given its multiple applications in display technology, smart glass, security marks and active optical components.[1,2] Passive elements such as optical coatings employing a wide range of materials, multilayer configurations or structured films have been extensively used in optical systems to obtain a full range of colors and spectral windows in both reflective and transmissive devices.[1–6] Moreover, active materials with unique physical or chemical properties such as electrochromism,[7–9] piezochromism,[10] plasmonic effect,[11] photoluminescence[12,13] and volatile phase-change materials[14] have been exploited for color modulation purposes. The dynamic modulation of optical properties by such materials has given rise to remarkable resolution, low dimensionality and low energy operation of displays.[15] However, a combination of both, i.e. a device with high resolution featuring offline color retention while still allowing full-gamut modulation, had been elusive or had required external chemical agents[16] until recently, when an optoelectronic framework using nonvolatile nucleation dominated phase-change materials (PCMs) was proposed to fill this gap by employing Ge2Sb2Te5 (GST) as the active bistable component.[17]