The Retina displays featured on Apple's iPhone 4 and 5 models pack a pixel density of 326 ppi, with individual pixels measuring 78 micrometers. That might seem plenty good enough given the average human eye is unable to differentiate between the individual pixels, but scientists in the UK have now developed technology that could lead to extremely high-resolution displays that put such pixel densities to shame.
Led by Oxford University scientists, a research team has created a prototype device that features pixels just 30 x 30 nanometers in size. The high resolution potential of the technology was discovered while the team was exploring the link between the electrical and optical properties of phase change materials (PCMs) that can switch from an amorphous to a crystalline state.
By sandwiching a seven-nanometer thick layer of the PCM Germanium-Antimony-Tellurium (Ge2Sb2Te5 or GST) between two layers of transparent electrodes made of indium tin oxide (ITO), the scientists discovered they could "draw" still images within the sandwich "stack" using an atomic force microscope. They then found that the "nano-pixels" could be switched on and off electronically, creating colored dots that could be used as the basis for an extremely high-resolution display.
"We didn't set out to invent a new kind of display," said Professor Harish Bhaskaran of Oxford University's Department of Materials, who led the research. "We were exploring the relationship between the electrical and optical properties of phase change materials and then had the idea of creating this GST 'sandwich' made up of layers just a few nanometers thick. We found that not only were we able to create images in the stack but, to our surprise, thinner layers of GST actually gave us better contrast. We also discovered that altering the size of the bottom electrode layer enabled us to change the color of the image."
But extremely high-resolution isn't the only impressive quality of the technology. The layers that make up the GST sandwich are created using a sputtering technique, which would allow them to be deposited as thin films on extremely thin and flexible substrates.
"We have already demonstrated that the technique works on flexible Mylar sheets around 200 nanometres thick," said Professor Bhaskaran. "This makes them potentially useful for 'smart' glasses, foldable screens, windshield displays, and even synthetic retinas that mimic the abilities of photoreceptor cells in the human eye."