... MicroLEDs, QDs & the Energy Gap |QD-LED & Cd-Free QDs
Welcome to this week's edition of our newsletter. First a couple of housekeeping notes:
We have begun to cover select display and QD technologies in this newsletter. There are two reasons (1) additive electronics is used in this areas since, for example, QDs are areasolutions processed or microLEDs can be transfer printed, and (2) we are hosting a unique world-class event on microLEDs and QDs on 30 NOV-2 Dec - see schedules here www.TechBlick.com/microLEDs
please note that there is strong demand for our onsite event in Eindhoven - the Future of Electronics RESHAPED. The masterclass and tours are almost sold out. Please reserve your spot now if you wish to join us https://www.techblick.com/electronicsreshaped
Topics for this edition: Copper Nanoparticle Scale-up | Warp Knitting of E-Textiles | Functional Crystals in Structural Electronics | MicroLEDs and the Energy Gap | Advances in QD-LED and Cd-Free QDs | Stable QDs for microLEDs
Will copper nanoparticle inks finally come of age to disrupt the dominance of silver in the conductive paste business?
Cost of production has been a major barrier despite the fact that Cu raw material prices are far lower than Ag. This is because this large raw material cost difference does not often get translated into equally large nanoparticle dispersion or ink cost differences.
To overcome this issue, Zachary James Davis et al at Teknologisk Institut have scaled up copper nanoparticle production with particle sizes between 30-300nm. As can be seen below, they have already achieved the following:
10+ Kg per day - here the main bottleneck is the heating and mixing of the green ingredients
300 Euros per Kg cost of production which is comparable to the cost of production of Ag nanoparticles. This level of production cost- coupled with much lower raw material cost @36.7 Euro/Kg - can translate into a much lower product cost
Inkjet printable inks with DGME-based solvents are able to lay down 0.5-1um thick layers in a single pass achieving 60mOhm per sqr
screen printable versions (in development) targeting 50 mOhm/sqr
The scale-up of Cu nanoparticle production with automated workflows is an important step towards making Cu ink and paste technology a commercially viable alternative to the dominant Ag inks and pastes.
What are the latest status of QD-LED technology and Cd-free QD materials?
Fraunhofer-Institut für Angewandte Polymerforschung IAP is a leading research group in the field, always pushing forward the performance boundries of QD technology. As shown below, Armin Wedel shares some updates in his May 2021 TechBlick presentation. Here are some key points:
1) Cd-free QD materials: slide one shows optimized results for QY, FWHM, and PL of blue, green, and red QDs based on Cd-free chemistries.
The B, G, and R QDs consist of ZnTeSe/ZnSe/ZnS, InZnP, GaP/ZnSe/ZnS, and InZnP/ZnSe/ZnS core-shell structures, enabling one to approach BT.2020 standards in a non-emissive display.
These are very innovative chemistries and core-shell structures: The Te doping in ZnSe core enables very saturated blue colours with high QY (92%); the GaP shell and controlled heating enables the narrowing of the usually wide FWHM of InP-based QDs to 41nm, and the application sodium oleate during core synthesis of R QDs enables even narrower FWHM
2) QDs as colour conversation in microLEDs: Slide two shows that CdSe and InP QDs can be used as colour converters in microLEDs, whilst slide three shows QDs can be stable in a matrix system for uLEDs. QD colour conversion is very promising for
3) Emissive QD-LEDs: OLED max luminance and EQE still beat that of emissive QD-LEDs which are far less mature. CdSe have improved over the years, offering excellent performance, but Cd toxicity is a concern. The performance of InP QD-LEDs lags far behind in terms of Cd/m2, EQE, and lifetime.
This is an exciting development area. Indeed, there is already a roadmap from RGB OLED or WOLED to full inkjet printed (IJP) emissive QD-LED via the development and scale up of Blue OLED + IJP (R,G) QD Conversation technology.
To learn more join the world's firfirst-everst ever microLED and QD event online https://lnkd.in/eDRi5kp2
Integrate electronic circuits into standard textiles using a mass production techniques?
Warp knitting is an excellent candidate. It combines weaving and weft knitting, allowing the warp knitted fabrics to have the stability of woven fabrics and the elasticity of knitted ones. This well established technology can enable the integration of complex circuit patterns using functional / conductive fabrics with standard textiles using a mass production technique able to handle many different fibers in the same process.
textile as remote control for commanding a mini robot
working mobile phone charger pad based on textiles
smart shirt for measuring heart rate, temperature and humidity
What are micro-, mini-, and traditional LEDs?
Traditional LEDs come in SMD or through-hole packages and the dies are typically 1mm or larger. This well-established application finds use in general lighting, automotive lighting, and LCD backlights.
Min-LEDs are typically smaller than 200um in die size but larger than 50um, and come in SMD or CoB (chip-on-board) packages. They are currently commercial and find applications in LCD and keyboard backlights, narrow-pixel pitch LED direct view LEDs, and other sectors. In the LCD sector, they are suited to provide local dimining to imrpove contrast, making LCDs more like OLEDs on this feature.
and micro-LEDs are very small, typically smaller than 50um. The size of the microLEDs is expected to shrink further as the technology progresses to reduce LED cost (more LEDs per wafer) and transfer cost/time (e.g., more LEDs transfered within the same stamp).
Evidently each class of LEDs is very different in every sense from growth techniques to performance to application.
Join TechBlick's microLED event to hear Eric and 30 other top-class speakers covering every aspects of microLED industry https://lnkd.in/eDRi5kp2
Stable RoHS-compliant Cd-free QDs for microLEDs?
This technology is required to simplify the manufacturing of microLEDs- this way one need not transfer R G B uLEDs but can only transfer the already efficient blue uLEDs and achieve RGB color via red and green QD color conversation.
There are of course multiple material challenges including achieving Cd-free RoHS-compliant green and red QDs with (1) high enough thermal and light stability for direct integration into microLED chips/dies, (2) high blue absorbance even at low thicknesses to prevent blue color leakage, (3) narrow FWHM and high QY, (4) low self excitation, etc
QustomDot -spin off from Zeger Hens group at Ghent University- is making excellent progress in this field. They have a novel high-controlled synthesis process for InP based QDs. Last year, at TechBlick they shared some interesting stability data for QD integration in macro and thin film LEDs. These results are shown in the slides below. They show a clear pathway towards development of QDs for direct on-uLED integration
The 500um thick QD level integrated on a macro LED shows >>300hours stability even under 1W/cm2, and a 100-150um QD thin film under 130mW/cm2 also shows >>1500 hours photostability in insert conditions
These are results from last year. To hear the latest developments from QustomDot on QD-on-microLED please join TechBlick's microLED and QD event. Check the world-class agenda at www.TechBlick.com/microLEDs
Why can microLED technology can help narrow the energy gap in electronic devices?
@Khaled Ahmed from Intel Corporation offered a data-rich unique assessment at TechBlick's display event in 2021.
The first slide shows the battery gap- Ahmed has collected data by year showing that power demand of phones far exceeds the power supply level of batteries, creating a "battery gap" which widens each year as more power-hungry features are added whilst battery technologies imporves only incrementally. Some 70% of power consumption of a mobile phone or tablet is by the display, showing its outsize importance in shrinking this gap.
The second slide shows the improvements in the efficiency (lm/W) of 'released' OLED devices per year. The OLED efficiency has clearly plateaued in produced or released products. The backdot represents the projected potential of microLEDs, showing how the microLED technology can be a game changer.
The third slide shows that there is a gap between EQE of laboratory OLEDs and that of released products. The origins are not clear but likely involve trade-offs neccessary in production and trade-offs between lifetime stability and EQE.
The four side compares the efficiency of GaNw LEDs at various wavelenghts vs organic LEDs (from previous slides). It shows that GaN LEDs offer dramatically higher EQE levels compared to OLEDs at all wavelenghts except red. Indeed, there is a red efficiency gap in GaN microLED technology, the filling of which is the subject of intense global R&D
This charts clearly demonstrate that while OLED technology seems to have plateaued and thus will not likely ever overcome the Battery Gap, the emerging microLED technology offers high promise to do us. Of course development and manufacturing of microLEDs involves other challenges such as rapid transfer as well as high-yield production which we will disucss elsewhere.
To learn more about microLED technologies, join the world's first ever specialist technology on the topic. Check out the world-class agenda at https://lnkd.in/eDRi5kp2
Functional crystals meet printed electronics meet structural/embedded electronics meet automotive interiors?
Rafael Michalczuk howcases fantastic and beautiful demonstrators combining all these technologies. Here, in collaboration with PolyIC and Kurz, they showcase beautiful interactive smart surfaces with integrated functional crystals for automotive.
The embedded (hidden) electronics technology is from Kurz (based on PolyIC technology) based on its R2R metal mesh technology (10um linewidth and 100um spacing with ultrathin (100 nm) layers of printed Ag nanoparticles) together with their so-called Functional Foil Bonding, which enables these metal mesh films to be integrated on the back of shaped plastic parts together with decoration layers. This creates part with electronics seamlessly integrated within the curved or 3D shaped part
SWAROVSKI I provides the beautiful functional crystals which enhance the aesthetics but also allow for continued touch and optical interaction with the underlying electronics.