Allos Semiconductors moving away from power electronics and transferring its patents & know-how to a new entrant in GaN-on-Si technology

SOPHIA ANTIPOLIS, France – July 22, 2020 | On July 8th, 2020, Allos Semiconductors disclosed a deal with Azur Space, a company specializing in the development and production of multi-junction solar cells, to sell its GaN RF and power electronics business, in a view to focus on its GaN-on-Si micro LED epiwafer technology for up to 300 mm. Azur Space is a new entrant in the power electronics business; in fact it has no preexisting intellectual property (IP) assets related to GaN-on-Si epitaxy and power GaN device technology, but it does have the ability to leverage its manufacturing expertise and facilities for high-volume production with a relatively limited initial investment (10 million euros).
Since the very beginning and its foundation in 2014, Allos Semiconductors has made its epiwafer technology – inherited from Azzurro Semiconductors – available through licensing and technology transfer to “high-power electronics companies that would like to enter the GaN-on-Si sector and avoid the cost, risk and uncertainty of starting their own epi development from scratch”. In other words, Allos Semiconductors would enable new players to safely enter the GaN-on-Si business, relying on Allos’ patented and proprietary growth techniques and epi-structures.
In 2017, the licensing & technology engineering firm further strengthened its value proposition by disclosing a carbon-doping-free GaN-on-Si technology, offering good dynamic resistance, good crystal quality and extremely low leakage current all at once, thereby enabling customers to overcome the usual trade-off between these parameters when using carbon doping in epi-structures. Moreover, it would provide an effective way for customers to avoid conflicts with well-established IP competitors relying on carbon doping to achieve the power electronics industry’s requirements. As of 2017, Allos Semiconductors’ approach was based on the insertion of multiple interlayers in an unintentionally doped thick GaN buffer layer (Fig. 1). To our knowledge, neither Allos nor Azzurro has filed patents describing such a structure, or how to design and grow the interlayers in order to effectively reduce the leakage current in high-voltage applications.

Figure 1: Typical GaN-HEMT epi-structures grown by MOCVD without intentional carbon doping or other doping. Electrical performance is optimized by position and number of interlayers. Source: ‘Low vertical leakage current of 0.07µm/mm2 at 600V without intentional doping for 7µm-thick GaN-on-Si’ presented at ICNS-12 in Strasbourg, France (July 2017).

At the time of Azzurro Semiconductors’ bankruptcy, the GaN-on-Si epi-foundry had filed 29 patent families (i.e. single inventions patented in multiple countries). Most of them were reviewed by Knowmade in the GaN-on-Silicon Patent Landscape 2020. However, since Allos Semiconductors was created in 2014 and acquired Azzurro’s technology, know-how and patents, the engineering and consulting company has not relied on patents to protect new inventions. As a result, Allos Semiconductors’ IP portfolio shrunk to 8 alive patent families (21 of Azzurro’s inventions were abandoned and no patent application has been filed by Allos), grouping less than 50 patents and patent applications filed in the main area of interest for Azzurro Semiconductors’ business: Europe (12), USA (9), China (8), Korea (5), Japan (2) and Taiwan (2). Furthermore, as of 2020, all Allos’ alive patent families have already been the subject of a transfer of rights to Azur Space.
Indeed, the first patent transfers between the two companies occurred in 2015 and concerned the most relevant inventions for power applications, filed by Azzurro Semiconductors in 2013:
• P-doping of group-III-nitride buffer layer structure on a hetero-substrate, to provide good stress management and the high resistivity required for RF & power applications (Fig. 2, Patent US 9,496,349).
• Layer structure for a group-III nitride normally-off transistor, with a recess-free design (Fig. 3 Patent US 9,773,896).

Figure 2: (Patent US 9,496,349) The buffer-layer structure comprises at least one stress-management layer sequence S including an interlayer structure arranged between and adjacent to a first and a second III-N layer, wherein the interlayer structure comprises a III-N interlayer material having a larger band gap than the materials of the first and second III-N layers, and wherein a p-type-dopant-concentration profile drops.

Both patent families were granted thereafter with a protection in main market areas such as Europe, USA, China and Korea, with the notable exception of Japan. Moreover, four domestic granted patents (filed only in Germany) dealing with electronics as well as optoelectronics were transferred to Azur Space in 2016:
• III-nitride p-channel transistor structures to produce logic components comprises growing an aluminum indium nitride barrier layer on a group-III nitride buffer layer (patent DE10200403434)
• Field-effect transistors, comprises an aluminum-gallium-indium-nitrogen layer, aluminum-gallium-nitrogen intermediate layer, and another aluminum-gallium-indium-nitrogen layer (patent DE102006030305)
• Group-III nitride transistor component on a Si substrate for high temperature and microwaves, with a buffer layer formed by gas phase epitaxy, iron-doping of GaN-based buffer layers (patent DE10256911)
• Production of a planar tear-free light emitter structure comprises applying an aluminum-containing group III-V seed layer, aluminum-containing group III-V intermediate layers, and silicon nitride intermediate layers on a Si substrate (patent DE10151092).

Scheme extracted of a patent.

Figure 3: (Patent US 9,773,896) An III-N electron-supply layer (910), a III-N back-barrier layer (906), a III-N channel layer (908) between the electron-supply layer (910) and the back-barrier layer (906) having a bandgap energy that is lower than the bandgap energies of the other layers. The back-barrier layer (906) is of p-type conductivity, while the material of the electron-supply layer (910) and the material of the channel layer (908) are not of p-type conductivity, the bandgap energy of the electron-supply layer (910) is smaller than the bandgap energy of the back-barrier layer (906); in absence of an external voltage a lower conduction-band-edge of the third III-N material in the channel layer (908) is higher in energy than a Fermi level of the material in the channel layer (908).

Eventually, Allos Semiconductors completed the IP transfer in the second quarter of 2020 with two additional patent families related to improvements in terms of stress management when using a masking layer (e.g. SiN) for the growth of high-quality GaN epilayers on Si substrates, especially for LED applications (patent EP 2,112,699 and patent US 9,406,505).
Interestingly, in 2019, Azur Space also acquired IP rights on two patent families filed by the Ulm University spin-off, MicroGaN, related to a diode circuit combining a GaN-HEMT and a GaN Schottky barrier diode (patent EP 2,633,555) including a GaN-on-Si embodiment, and a method of contacting a number of GaN devices together in a more compact way (patent US 8,748,944).
In conclusion, the present deal provides Azur Space with very relevant patents to develop GaN-on-Si technology and stand out from competitors. Besides patents, it can rely on Allos’ renowned know-how in the field, although not all aspects of Allos’ technology are visible in patents. Indeed, the company seems to have put the emphasis on know-how and technology transfer rather than IP licensing in the development of its business. As a matter of fact, Allos Semiconductors is actively developing its GaN-on-Si technology for micro-LEDs and, according to the latest announcement, will focus its activities on micro-LEDs in the next years. However, this has not translated into patenting activity yet, so it is likely to follow the same strategy as for power & RF electronics, focusing on trade secrets and technology transfer.
The power GaN patent landscape and GaN-on-Si patent landscape have been evolving fast in recent years, with numerous innovative startups and major power electronics’ players aiming to strengthen their position, to prepare for the promising power GaN markets. For any of them, GaN-on-Si IP is crucial and has fostered multiple acquisitions and partnerships with well-established players in the field. In this very dynamic environment, Knowmade has set up a GaN Power & RF Patent Monitor service in order to track and analyze, month by month, the latest patenting activity of IP competitors engaged in the development of these technologies.

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Rémi Comyn, PhD, Rémi works for Knowmade in the field of Compound Semiconductors and Electronics. He holds a PhD in Physics from the University of Nice Sophia-Antipolis (France) in partnership with CRHEA-CNRS (Sophia-Antipolis, France) and the University of Sherbrooke (Québec, Canada). Rémi previously worked in compound semiconductors research laboratory as Research Engineer.

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