A new material is poised to provide us with faster, higher-resolution displays. Researchers from Hokkaido University explain what makes this material so special and open the door to application and further development.
All displays consist of a grid of small points of light, called pixels, whose brightness can be individually controlled. The total number of pixels – and therefore the resolution and display size – is limited by the number of these pixels that can be addressed within a certain fraction of a second. Therefore, display manufacturers in the pixel controllers are trying to use materials that exhibit very high “electron mobility”, which is a measure of how fast current will flow through a controller in response to applied voltage – and thus how fast the pixel is.
A new material called ITZO (due to its constituent elements indium, tin, zinc and oxygen) promises to be up to seven times faster than the current state-of-the-art material. However, it is not clear where this improvement is coming from, which hinders its adoption for industrial applications.
Materials scientist Hiromichi Ohta of Hokkaido University and his team used their unique measurement technique to clarify this point. In their recent article published in the magazine ACS Applied Electronic Materialsthey showed that the higher electron mobility results from the unusual fact that in ITZO films of sufficient thickness, free charges accumulate at the interface with the support material and thus allow passing electrons to travel unimpeded through most of the material.
The unique power comes down to a very simple formula: the electron mobility is proportional to the free travel time of the charge carriers – in this case electrons – divided by their effective mass. And while measuring electron mobility itself is a relatively standard technique, effective mass and free travel time cannot be measured so easily, so it is difficult to say which factor is responsible for the electron mobility.
But by measuring how the electric field in the material changes in response to an applied magnetic field and to a temperature gradient, Ohta’s team was able to deduce the effective mass of the electrons — and then calculate the free travel time. It turns out that both the effective mass is significantly smaller than in the current state-of-the-art materials and the free travel time is much higher and therefore both factors contribute to the higher electron mobility. Moreover, by observing how their results depend on the thickness of the ITZO material, they were able to infer how the interface and the bulk of the material contribute to these effects.
Ohta explains the importance of this analysis: “Using the knowledge gained from this study, we can in the future design other transparent oxide semiconductor thin film transistors with different chemical compositions that exhibit even better electron mobility properties.” This research is therefore an important step towards the next generation of ultra-high-resolution displays.
A highway for electrons in oxide heterostructures
Hui Yang et al, Thermopower modulation analyzes of high mobility transparent amorphous oxide semiconductor transistors, ACS Applied Electronic Materials (2022). DOI: 10.1021/acsaelm.2c01210
Quote: Analysis of a new material promising faster, higher-resolution displays (2022, October 14), retrieved October 14, 2022 from https://phys.org/news/2022-10-material-faster-higher-resolution.html
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