Fraunhofer Examines Bi-Directional Data

By Raverstead

Fraunhofer had a large stand divided into several different sections, each of which was dedicated to a different branch of the institute.

LiFi technology was being shown by Fraunhofer IPMS. Two units, roughly 2m apart, were sending data to each other (bi-directionally) at 1Gbps, using IR light. A 10m distance is possible, though. The module combines an optical transceiver and protocol controller with a Giagbit ethernet interface, so can be integrated into common industrial systems. It was shown connected to a Surface Pro tablet using the ethernet jack, although we were told that the system could potentially replace any cable.

Frank Deicke, of IPMS, told us that he expects LiFi technology to be mainstream, for both industrial and consumer use, within five years.

At Fraunhofer FEP we saw an energy harvesting concept and OLED microdisplays. The microdisplays (800 x 600) were bi-directional; as well as coloured RGBW sub-pixels, each pixel contained a photodiode (image sensor); this meant that the displays could both produce and detect light. We saw it being used to show a monochrome image of a paperclip on a monitor. The latency was very good, which we commented on; a spokesperson said that the image sensor is able to operate at the same speed as the microdisplay – in this case, 60Hz.

Flexible monochrome OLED displays were also shown, although these were older.

Getting power from vibrations was an item of interest. A piece of silicon wafer, covered in piezoelectric aluminium nitride (AIN) layers, was connected to a generator. AIN possesses more favourable mechanical properties than the commonly-used lead-zirconium-titanium composites (PZT). The generator produced vibrations at a specific frequency to create a charge – more energy was being put in than was coming out (although this did apparently reach several hundred Watts), but it was just a demonstration! Vibrations at different frequencies will generate less of a charge. The concept could see use in planes or cars, where space is at a premium, to power sensors.

Piezoelectric deposition has been an issue, up to now; a certain volume is required to produce sufficient energy. Producing the coatings was economically unfeasible, as deposition rates, homogeneity and coatings were too small. The FEP researchers said that a new process that they had developed could precipitate homogeneous layers on diameters of up to 200mm, with high deposition rates.

Reactive magnetron sputtering of aluminium targets in an argon-nitrogen atmosphere, onto a silicon wafer, was used to deposit the coatings. From Fraunhofer’s press material: ‘With this physical procedure, atoms from solid bodies are discharged into the gas phase by bombarding the targets with highly energetic noble gas ions. They then deposit on the wafer as a layer’. A double-ring magnetron sputter source was used, with two ring-shaped targets. As the discharges of both targets overlap, the AIN layers can be deposited uniformly onto a large surface.

Scientists are now working with layers made using aluminum-scandium-nitride, deposited through reactive co-sputtering. Compared to pure AIN, these layers demonstrate higher piezo-coefficients and can generate three-to-four times the power.

Energy harvesting was also the focus at Fraunhofer IIS – this time, with more of a wearable focus. Several different devices were on show, including units that generated a charge through a thermal difference (being warmer on one side than the other); vibrations; or voltage change (converting from AC to DC). These latter two were shown to generate enough energy to power a display.