Phase change materials for next generation adaptive displays

Phase change materials (PCMs) can vary their electrical and optical properties between different phases, which makes them ideal for inclusion in devices such as adaptive reflective displays and “smart windows”. However, challenges to ensure that PCMs can be switched between phases in a uniform and complete manner.

Researchers at the University of Oxford have developed a new PCM switching device to address these challenges. By providing a capacitor structure, together with an alternating current, a distributed varying current can be made to flow through a PCM to heat it and induce a uniform phase change.

Phase change materials (PCMs) have been the subject of intense research and development over the last decade in the contexts of electronic memories and next-generation displays. For example, PCMs are able to exhibit vastly different electrical and optical properties between different phases, making them ideal candidates for next-generation reflective displays or “smart windows”.

Such devices can be designed with ultra-thin film structures such that white light is reflected back as red, green or blue. Having PCMs in these thin film structures means that the light reflected back in the displays can be adapted and tuned on demand.

PCMs can also be switched on a sub-nanosecond timescale with high reproducibility. New and improved PCM materials, such as the so-called phase-change super-lattice materials, are expected to deliver even better performance in the future.

The PCMs can switch phase in response to appropriate heat stimuli, which can be delivered through applying an electrical current, heating the PCM in the appropriate region (Joule heating). However, there is a common problem in that the current will tend to be restricted to a small region or filament of PCM, which means that a uniform and complete switching action of the material will not take place, possibly affecting the performance of a display.

Researchers at the University of Oxford have developed a new PCM switching device to address this problem. By providing a capacitor structure, together with an alternating current, a distributed varying current can be made to flow through a PCM without being restricted to a small region of the material. This arrangement enables heating across the PCM and, therefore, a uniform and complete switching action.

The device can be integrated into existing display technology to address the problems of achieving reliable, rapid and uniform switching of PCM layers and thin films. Further applications of this technology relate to photonic waveguides and electronic memories.
This novel technology is the subject of a patent application. Oxford University Innovation is now seeking commercial partners to adopt the new technology and support its future development.

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