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Allos GaN-on-Si epiwafer achieves over 1400V breakdown voltage


Latest measurements from IEMN show more than 1400V breakdown voltage for vertical and 1600V for lateral (grounded) products for 1200V devices

A team from the IEMN research institute in France has made devices and conducted measurements on two different GaN-on-Si epiwafer products supplied by Allos Semiconductors of Germany.

One is a prototype of Allos' upcoming product specifically designed for 1200V device applications. With this epiwafer IEMN achieved over 1400V for vertical and 1600V for lateral (grounded) breakdown.

The other epiwafer is Allos' established product for 600V applications which equally showed very high breakdown voltages of 1200V and more for both lateral and vertical measurements.

The new epiwafer product for 1200V device applications is from an ongoing internal development program at Allos. Its strong performance results from an innovative structure combining Allos' unique strain-engineering and high crystal quality approach with additional measures to suppress leakage and enhance breakdown voltage further.

This was achieved without compromising on other essential parameters like crystal quality or wafer bow and without introducing carbon-doping. Epi growth was conducted on a standard Aixtron G5 MOCVD reactor.

Already at the International Forum on Wide Bandgap Semiconductors (IFWS) in Beijing in November 2017 Allos showed device results from an industry partner using Allos' 600V epiwafer. With a mature device design and measurement setup for up to 1000V leakage values of 0.003 µA/mm² at 600V and of 0.033 µA/mm² at 1000V were achieved.

"This feedback by our partner was great news for us as it was another confirmation for the capability of our technology for 600V applications" explains Atsushi Nishikawa, CTO of Allos. "Now the big question was at which voltage above 1000V the physical breakdown occurs and whether we are on track with our development in the 1200V domain too."

The answer is now available with the results shown by IEMN. It used simplified device design and processes allowing a much faster feedback than from an industrial process.

On a prototype of Allos' new epiwafer product for 1200V devices IEMN achieved more than 1400V for vertical and 1600V for lateral (grounded) breakdown voltage (Figure 1 (a) and 2 (b) respectively). Supplementing characterisation with a floating measurement setup resulted in a lateral breakdown of more than 2000V with 12 µm contact distance (Figure 1 (c)). Saturation of lateral floating breakdown occurred at 12 µm contact distance for the 7 µm thick epi-stack with breakdown already more than 1100V for 4 µm contact distance (Figure 1 (d)).

Putting these results into perspective Farid Medjdoub, who led the IEMN team, explains: "With over 1400V for vertical and 1600V for lateral breakdown with substrate grounded Allos' epiwafer favorably compares to all the samples we have measured so far from various industry and research partners. Furthermore, the results we have seen indicate that the device performance is very uniform over the wafer, which is a very important characteristic to qualify for actual device production."

On Allos' 600V epiwafer product IEMN achieved 1200V for vertical and 1500V for lateral (grounded) breakdown voltage. Both epiwafer products are not doped with carbon, which is often used by GaN-on-Si makers to enhance isolation but has negative impacts on crystal quality and dynamic switching behavior. Both products are available with 675 µm thickness for 150 mm wafer diameter and 725 µm thickness for 200 mm. Bow for all Allos epiwafer products is tightly controlled at below 30 µm.

"The results now available show that we are already at 1.7 MV/cm laterally and 2 MV/cm vertically "“ and we have a program to realize further improvements on epiwafer-level. Now is the time to establish a strong partnership with an industrial partner also in the 1200V product range." says Burkhard Slischka, CEO of Allos.

"As we are a pure epiwafer technology provider without own device making we are seeking a close cooperation with an experienced power electronics player to exploit the opportunities for their 1200V GaN-on-Si based applications. With our technology GaN-on-Si has the potential to effectively compete with SiC performance at a fraction of the wafer cost."

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