Periodic Reporting for period 3 - HiLICo (High Luminescence In Cockpit)
Berichtszeitraum: 2020-06-01 bis 2021-12-31
In many application fields, there is a growing market demand for high quality information displays. This is true in commercial avionics where high luminance displays able to provide readable information in a very bright environment are expected. Nowadays, the existing technologies do not allow the manufacturing of displays emitting the desired brightness (>50,000 cd/m2 white light) at low power consumption and in a compact volume. This is why the HiLiCO project implemented in the framework of the Clean Sky 2 programme aims at developing a new generation of very bright monochrome and full-colour GaN micro-displays with high pixel resolution (WUXGA), and good form factor capabilities. It should enable the design of ground breaking compact see-through systems for next generation avionics applications.
To achieve this goal, the HiLICO project addresses numerous technical topics: (i) development of high-quality GaN based LED epilayers, (ii) design and fabrication of a dedicated CMOS matrix (ASIC) to control each individual pixel, (iii) coupling of the LED structure to the CMOS matrix followed by high precision LED pixelisation (9.5 µm pixel pitch), (iv) transfer on blue emitting devices of dedicated light conversion layers to manufacture bi- or full-colour display demonstrators and (v) manufacturing and testing of LED microdisplay demonstrators.
Among these objectives, four of them have been achieved with very significant progress. The technical results have demonstrated performances that match and sometimes exceed the existing state of the art. This is the case for the GaN epilayer EQE, the HILICO ASIC capabilities, the microLED display technology and the red conversion efficiency. For the last objective (demonstrators), the results obtained so far constitute a solid working basis for further development of colour LED microdisplays.
In terms of impact, compared to existing LCD technologies, the LED technology offers not only higher luminance and contrast but also potential higher energy efficiency. We estimate that at long term, its energy efficiency could reach 6%, twice the efficiency of LCD microdisplays. Beyond the reduced environmental impact, another benefit is clearly the enhanced aircraft safety with more readable information. Finally, the HILICO developments will contribute to the building of a new LED microdisplay industry since, beyond avionics, new application fields have recently emerged as optical wireless communications or health applications.
To achieve this goal, the HiLICO project addresses numerous technical topics: (i) development of high-quality GaN based LED epilayers, (ii) design and fabrication of a dedicated CMOS matrix (ASIC) to control each individual pixel, (iii) coupling of the LED structure to the CMOS matrix followed by high precision LED pixelisation (9.5 µm pixel pitch), (iv) transfer on blue emitting devices of dedicated light conversion layers to manufacture bi- or full-colour display demonstrators and (v) manufacturing and testing of LED microdisplay demonstrators.
Among these objectives, four of them have been achieved with very significant progress. The technical results have demonstrated performances that match and sometimes exceed the existing state of the art. This is the case for the GaN epilayer EQE, the HILICO ASIC capabilities, the microLED display technology and the red conversion efficiency. For the last objective (demonstrators), the results obtained so far constitute a solid working basis for further development of colour LED microdisplays.
In terms of impact, compared to existing LCD technologies, the LED technology offers not only higher luminance and contrast but also potential higher energy efficiency. We estimate that at long term, its energy efficiency could reach 6%, twice the efficiency of LCD microdisplays. Beyond the reduced environmental impact, another benefit is clearly the enhanced aircraft safety with more readable information. Finally, the HILICO developments will contribute to the building of a new LED microdisplay industry since, beyond avionics, new application fields have recently emerged as optical wireless communications or health applications.
(i) Fully optimized GaN LED epilayers were grown at NOVAGAN, that provide 80 µm2-micro-LEDs with external quantum efficiency (EQE) of~12% at 440 nm. Similarly, another new growth technology was implemented showing 6% EQE at 520 nm. At the end, improvements by 250 and 300% is demonstrated for blue and green microLEDs, respectively.
(ii) A dedicated ASIC has been designed and manufactured to drive the LED microdisplays (1640 x 1033 resolution, 9.5 µm-pixel pitch). It is among the largest and most powerful (3W) ASIC for LED microdisplays. An electronics has been developed to drive this ASIC and electrical tests show it meets most expected specifications.
(iii)A dedicated microLED technology has been developed. It enables the coupling at wafer level of a GaN LED structure to an integrated circuit (IC) followed by high precision LED pixelisation. To qualify the manufacturing workflow, static green displays with a size representative of future microdisplays have been first processed on passive ICs. Very high luminance (1.4 M cd/m2) was measured in electrical conditions compatible with ASIC capabilities. Several static displays have been delivered to THALES avionics for evaluation on a optical bench representative of the optical combiner used in the Augmented Reality headset.
(iv) Two light conversion technologies, 2D-conversion epilayers or Nano-platelets (NPL)-based photoresists, have been investigated. The theoretical study done at CEA showed that the conversion technology must meet External Power Conversion Efficiency (EPCE) of at least 25% to comply with a white luminance >50.000 cd/m2.
For blue-to-red conversion, the AlInGaP epilayer offers very efficient blue light absorption, effective blue-to-red conversion but very difficult light extraction. In return, the NPL-based red photoresist developed by NEXDOT provides outstanding EPCE (31%) exceeding the current state of the art.
For blue-to-green conversion, while the InGaN QW/GaN epilayers are poor absorbers, the novel 2D-green conversion epilayers developed in HiLiCO exhibit a blue light absorption two times higher but still below specification. The NPL-based green photoresist shows however much better absorption and EPCE up to 12%. These results are promising but require further improvements.
Despite this, the NPL-photoresist technology is today the best solution. Moreover, it complies with an integration on small pixels although colour cross-talk still needs to be addressed.
(v) Several wafers of blue and green LED microdisplays on ASIC have been successfully processed. The full electrical testing of green microdisplays on ASIC with the electronic display module developed for that purpose is still on going with hopefully first image displayed very soon. As for the colour displays, the manufacturing of red and blue microdisplays could be attempted in the coming months beyond the HILICO project timeframe.
Most of these results have been disseminated towards scientific and industrial audiences (10 conferences & workshops, 6 peer-reviewed articles and 7 website publications).Our work has been recognized by the society for information display with the "best of Eurodisplay 2019" award and also the JSID's Best Paper Award of 2021.It provides many technological building blocks that can be exploited for the future high luminance microdisplay applications.
(ii) A dedicated ASIC has been designed and manufactured to drive the LED microdisplays (1640 x 1033 resolution, 9.5 µm-pixel pitch). It is among the largest and most powerful (3W) ASIC for LED microdisplays. An electronics has been developed to drive this ASIC and electrical tests show it meets most expected specifications.
(iii)A dedicated microLED technology has been developed. It enables the coupling at wafer level of a GaN LED structure to an integrated circuit (IC) followed by high precision LED pixelisation. To qualify the manufacturing workflow, static green displays with a size representative of future microdisplays have been first processed on passive ICs. Very high luminance (1.4 M cd/m2) was measured in electrical conditions compatible with ASIC capabilities. Several static displays have been delivered to THALES avionics for evaluation on a optical bench representative of the optical combiner used in the Augmented Reality headset.
(iv) Two light conversion technologies, 2D-conversion epilayers or Nano-platelets (NPL)-based photoresists, have been investigated. The theoretical study done at CEA showed that the conversion technology must meet External Power Conversion Efficiency (EPCE) of at least 25% to comply with a white luminance >50.000 cd/m2.
For blue-to-red conversion, the AlInGaP epilayer offers very efficient blue light absorption, effective blue-to-red conversion but very difficult light extraction. In return, the NPL-based red photoresist developed by NEXDOT provides outstanding EPCE (31%) exceeding the current state of the art.
For blue-to-green conversion, while the InGaN QW/GaN epilayers are poor absorbers, the novel 2D-green conversion epilayers developed in HiLiCO exhibit a blue light absorption two times higher but still below specification. The NPL-based green photoresist shows however much better absorption and EPCE up to 12%. These results are promising but require further improvements.
Despite this, the NPL-photoresist technology is today the best solution. Moreover, it complies with an integration on small pixels although colour cross-talk still needs to be addressed.
(v) Several wafers of blue and green LED microdisplays on ASIC have been successfully processed. The full electrical testing of green microdisplays on ASIC with the electronic display module developed for that purpose is still on going with hopefully first image displayed very soon. As for the colour displays, the manufacturing of red and blue microdisplays could be attempted in the coming months beyond the HILICO project timeframe.
Most of these results have been disseminated towards scientific and industrial audiences (10 conferences & workshops, 6 peer-reviewed articles and 7 website publications).Our work has been recognized by the society for information display with the "best of Eurodisplay 2019" award and also the JSID's Best Paper Award of 2021.It provides many technological building blocks that can be exploited for the future high luminance microdisplay applications.
Among the five objectives of HILICO, four of them have been achieved.The obtained technical results have demonstrated technical performances that match and sometimes exceed the existing state of the art. This is the case for the GaN epilayer EQE, the HILICO ASIC capabilities, the microLED display technology and the red conversion efficiency. For the last objective (LED microdisplay), the results obtained so far constitute a solid working basis for a further development of colour LED microdisplays.
In terms of technical and environmental impact, compared to existing technologies, the LED technology developed within HILICO offers not only much higher luminance and contrast but also potential higher energy efficiency. Based on the HILICO technical data, the wall plug efficiency of LED microdisplays is estimated to be ~3%, value comparable to the LCD performance. At full maturity, it should reach 6%. A recent publication reports indeed doubled microLED efficiency (24%) with appropriate light extraction structures. At long-term, the replacement of LCD by LED microdisplays in avionics can hence contribute to a slight reduction of environmental impact. The net environmental benefit is real but limited. However, the benefit for aircraft safety is very significant. In terms of socio-economic impact, the HILICO developments will contribute to the building of a new LED microdisplay industry since, beyond avionics, new application fields have recently emerged as intra- or inter-chip optical wireless communications or health applications (head-mounted displays to aid high-precision manual tasks in surgery).
In terms of technical and environmental impact, compared to existing technologies, the LED technology developed within HILICO offers not only much higher luminance and contrast but also potential higher energy efficiency. Based on the HILICO technical data, the wall plug efficiency of LED microdisplays is estimated to be ~3%, value comparable to the LCD performance. At full maturity, it should reach 6%. A recent publication reports indeed doubled microLED efficiency (24%) with appropriate light extraction structures. At long-term, the replacement of LCD by LED microdisplays in avionics can hence contribute to a slight reduction of environmental impact. The net environmental benefit is real but limited. However, the benefit for aircraft safety is very significant. In terms of socio-economic impact, the HILICO developments will contribute to the building of a new LED microdisplay industry since, beyond avionics, new application fields have recently emerged as intra- or inter-chip optical wireless communications or health applications (head-mounted displays to aid high-precision manual tasks in surgery).