The use of thin film functional materials in optoelectronic framework applications

Phase change materials (PCMs) are bi-stable, exhibiting two different states at room temperature. By applying electrical or optical pulses the materials can be switched between a stable crystalline phase and a metastable amorphous phase. We have recently demonstrated that growth dominated phase change materials can also be used in nanodisplay applications via colour modulation in optical cavities. This results in the change in the optical resonance of the thin film cavity. By designing the thin film layers appropriately, any change in colour can be effected resulting in vivid thin film reflective displays. Our work has shown that both greyscale modulation as well as a colour gamut exceeding those of current OLEDs is possible. In particular, we have used the alloy AgInSbTe which presents a very similar behavior when compared with GeSbTe in terms of switching threshold and colour gamut (under the same ITO/PCM/ITO/Mirror structure). However, given the nucleation dominated nature of GST, the resolution in AIST can be worse, as bigger nuclei are created during the crystallization process. This difference is noticeable at 50 nm scale pixels.

More interestingly, we have demonstrated multilayer stacks containing an ultra-thin film of AIST to prove colour depth modulation. By tuning the switching voltage applied by an AFM tip to the phase change material different crystallization levels can be achieved and, therefore, images with continuous greyscale modulation could be successfully transferred onto the sample, featuring resolutions down to 300nm in scanning mode and ~50nm in pixel-by-pixel mode. Such displays are entirely Solid State Reflective Displays (SRD).

In this project, key areas of knowledge gap will be probed. Firstly, this doctoral project will explore the use of such techniques to develop holographic displays. Then, leveraging off the WAFT project funded by EPSRC, and by using advanced nanomanufacturing techniques, this project will seek to create flexible displays based on pixelated PCM stacks, looking towards wearable electronics applications.
Feasibility studies of using PCMs in the field of advanced retinas will also be carried out. The skills that will be gained by the doctoral student will include a range of techniques from electron beam lithography and other advanced micro- and nanofabrication techniques (etching, including dry etching and wet etching), process development, process troubleshooting and device imaging using electron microscopes.
Furthermore, skills in modeling and research skills such as understanding design software and their modification, as required, including finding the appropriate software for the goals of the project will be gained.

EPSRC Themes - Manufacturing the Future; Engineering; ICT; Physical Sciences.