Cutting edge Active μLED
BAMBAM will make use of μLED based on a unique architecture of gallium nitride (GaN) nanowires on silicon. As compared to LCDs and OLED, the technology developed by Aledia (WireLED™) shows:
Increased energy efficiency
Higher brightness
Better color quality
Higher dynamic range
Faster display switching speed
To yield the active pixel at the heart of the BAMBAM concept.
Aledia’s μLED will be connected to a micro integrated circuit from XDC that will drive the μLED in place of the TFT panel found in other displays. The consortium will also explore the use of the SmartPixel technology from Aledia, that correspond to a μLED pixel with an embedded driving microelectronics.
Ultra Precise Deposition or µprinting for printing of silver-based conductive wire.
The cost of a μLED display is strongly influenced by the μLED pixel size, for which the size of contact pads and wires are an important contributing factor. Keeping the μLED pixel size low, thus implies to have access to a high-precision contact technology capable of creating a conductive bridge between :
- structures of several tens of micrometres inside the pixel
- a contact pad of a few micrometres on the pixel and a larger pad on the substrate.
Such a high-resolution printing process for conductors with widths in the two micrometres range has recently been developed by XTPL and implemented in a commercially available lab printing system installed in the laboratories of the University Of Stuttgart.
This high-resolution printing process consists in an extrusion-based high-resolution additive manufacturing method. It has been named UPD for Ultra Precise Deposition or µprinting. It will be used to wire pixel elements together and with contact pads on the substrate.
Printed Quantum Dot for Color Conversion.
A key component of the envisioned µLED display is the color conversion layer added on top of ALEDIA’s blue µLEDs. Over the last 25 years, Quantum Dots (QDs) have emerged as unique optoelectronic materials that combine high absorption coefficients with narrow and size-tunable emission properties. More recently, InP-based QDs have evolved as an excellent color-conversion material for wide-gamut displays with small pixel sizes. They are compliant with the European Directive RoHS (Restriction of hazardous substances in electrical and electronic equipment) and show several attractive properties: a narrow emission spectra (FWHM < 45 nm); a high quantum yield (close to unity) throughout the visible spectrum, a very small size (typically 5-10 nm) and solution processability.
BAMBAM will use XTPL’s UDP technology to print on top of its active µLED a color conversion layer based on InP-based QDs (QustomDot). To achieve this, a significant challenge will be the development of QD materials with a sufficient thermal budget to withstand the manufacturing process and their integration into a high-resolution ink formulation that can be printed with the UDP technology.
Mass transfer of µLED and µICs.
In OLEDs displays, all active elements are manufactured together by successive coatings and structuring by photolithography to build an active matrix of thin film transistors (TFT) on the glass substrates. In contrast, µLEDs and their driving components must be manufactured on a separate substrate and cut into single elements which are then transferred onto the display substrate.
Mass transfer is already effectively used to transfer simple two-terminal planar µLEDs onto rigid or flexible substrates. BAMBAM will take up the challenge of pushing the current limits of mass transfer to transfer Aledia’s µLEDs and associated µICs from either a wafer or a film frame onto the display substrate. This will expand the list of microdevice types that may be mass-transferred to devices that include many-terminal integrated optoelectronics with three-dimensional topography.
Fine pitch and low power demonstrators.
The processes and associated materials developed in BAMBAM will be integrated into two fine pitch and low power display demonstrators. Specifications for these demonstrators will be designed early in the project together with the visualization solution provider BARCO and will guide the project’s work. These specifications will not only include electro- and opto-mechanical criteria but will also cover eco-friendliness and life-cycle aspects. Deviations in performance of the display demonstrators vis-à-vis these specifications can be caused by various phenomena including local variabilities in the different processes. The performance of the demonstrators will be measured and compared to the electrical and optical performance targets defined in the specifications. This will allow the consortium to propose hardware and software calibration solutions to improve the display performance and make them meet the defined specifications. This approach will make sure that the technologies developed in BAMBAM meet the end-users’ requirements and successfully reach the market in the years following the project.
Picture of an existing high-resolution LED-product from Barco that could be replaced by the BAMBAM technology.