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EETE APRIL 2013

LED-on-microwire startup raises 10 million euros By Peter Clarke Aledia SA (Grenoble, France), a startup developer of lightemitting diodes (LEDs) on microwires of gallium-nitride-on-silicon has made its first LEDs on 200-mm diameter wafers and raised 10 million euros in a first round of venture capital finance. The 3-D GaN-on-Silicon microwire technology was developed over a six-year period at the LETI research institute in Grenoble and the claim is that Aledia’s LEDs will have a production cost of one quarter that of conventional planar LEDs. Aledia’s technology uses millions of sub-micron diameter lightemitting GaN pillars standing up from the silicon surface to obtain an improved area efficiency of light generation. This produces three times more light per square millimeter of planar area, the company claims. In addition little material is used to form the microwires, approximately two-thirds of the material cost in planar LEDs and this added to 200-mm wafer processing should produce the 25 percent cost base, the company said. A secondary advantage claimed for the technology is that multiple colours can be created on single wafer or even on single die, which should produce advantages for tuning the output for general lighting applications. A further claimed advantage is that the so-called WireLED devices for general lighting could be fabricated without the use of phosphors. This is because WireLEDs can be tailored to produce green and red as well as the industrystandard blue Microwire pillars include vertical stacked compound semiconductor layers to provide increased light emission compared with horizontal layers in planar LEDs. Source: Aledia. GaN LEDs. The company has been spun out of LETI by the technical developers with Georgio Anania as co-founder, CEO and chairman. Anania was previously CEO of Bookham Ltd., a supplier of optical components which Anania helped take public. Anania’s co-founders are Xavier Hugon, COO, and Philippe Gilet, CTO. Aledia raised 10 million euro in a Series A that closed in 2012 with Braemar Energy Ventures, Sofinnova Partners, Demeter Partners and CEA Investissement participating. “Since our financing last year, we have scaled up our microwire manufacturing process and transferred it to 8-inch silicon wafers. We can now push forward to optimize the performance of these products and bring them to market,” said Anania, in a statement. As part of the company’s spin-out from LETI it has received exclusive worldwide rights to all present and future CEA patents on microwire technology as applied to the area of lighting. Several additional patents have already been filed directly by Aledia. ZnO-based n-channel TFTs on flexible foil could drive future AMOLED displays By Julien Happich Holst Cent re and imec have demonstrated a new technology for fabricating state-of-the-art ZnO-based n-channel thinfilm transistors (n-TFTs). The n-TFTs have been processed directly on top of flexible polyethylene naphthalate (PEN) foil by using spin-coating and post-anneal temperatures as low as 160°C. The threshold voltage of 3V makes the technology favorable for hybrid complementary line-drive circuitry at the borders of future flexible active-matrix organic light-emitting diode (AMOLED) displays 30x30mm PEN foil after processing and after being delaminated of the rigid carrier. on PEN foil. By integrating the display drive circuitry directly onto the flexible substrate, the line drivers no longer restrict the flexibility of the display, and fabrication costs can be further reduced. Key building block of this technology is the solution-processed ZnO-based metal oxide n-type TFT. The n-TFTs have been processed directly on top of a 25μm thick PEN foil by spin-coating and post-annealing at temperatures as low as 160°C. PEN foils are preferred over other flexible plastic substrates because they are colorless, cheaper and less water absorbing. So far, however, the high annealing temperature (200 – 400°C) needed to process ZnO-based films was incompatible with using PEN foils. The new n-TFTs show excellent transistor performances with saturation mobilities μsat of 0.60 up to 1.10cm2/Vs and Ion/Ioff ratios exceeding 107. 24 n-TFTs randomly spread over a 9cm2 area on PEN foil show good electrical uniformity and have promising bias-stress properties. A threshold voltage of 3V makes the technology favorable for hybrid complementary line-drive circuitry. Such a complementary thin-film technology at the edges of the rollable display is preferred because of its high robustness and reliability. The ZnO-based n-TFTs have therefore been integrated with imec’s baseline organic pentacene p-TFT backplane technology. Both complementary inverters and ring-oscillators have been fabricated. 18 Electronic Engineering Times Europe April 2013 www.electronics-eetimes.com


EETE APRIL 2013
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