Unlike the common use of GaN power ICs in the 650V range, the project targeted sub-100V DC/DC conversion—low-power PoL converters for server applications, automotive, and aerospace industries. Eleven industry leaders and research institutes from Austria, Belgium, Germany, Netherlands, and Ireland participated. The RECOM group contributed to developing these technologies, supporting innovative, integrated (3DPP®) and reliable power conversion solutions.
GaNonCMOS – Next steps in POL integration
2021. 10. 29
Smaller and more efficient power converters have been trending for decades and will continue evolving. This is achieved using new topologies, new materials, and new integration processes. Materials innovation was the focus of the European Union’s Horizon 2020 Project, funding the GaNonCMOS project. The project focused on the monolithic integration of GaN-on-SOI and Si at different levels (PCB, stack, and chip), developing new soft magnetic materials suitable for high switching frequencies and PCB embedding.
Table of contents
Embedding
One of the focus areas of the project was embedding components into the PCB. This technique allows one or more components to be placed within the PCB core. The main limitation involves component thickness and its behavior under various environmental conditions. The embeddable component could be an IC, switch, or passive, depending on design requirements. Using thick copper planes connected to embedded component leads creates a well-defined thermal path. The IC and MOSFET bodies are placed close together, reducing parasitic inductance and enabling higher switching speeds.
Small passives such as resistors and capacitors can be embedded in the same cavity, while larger components such as magnetics and capacitors remain external. Capacitors experience reduced thermal stress due to FR4 material insulation. While the layout becomes more complex, embedding offers advantages like shorter switching and control loops, a smaller solution area, and protection against reverse engineering.
Another approach reduces PCB height. In a buck converter design, the inductor is typically the tallest component. If a low-profile solution is needed, finding a suitable inductor can be challenging. This project demonstrated the feasibility of embedding magnetics. However, standard chip-sized inductors were too large for embedding.
To address this, the project used magnetic sheet materials—thin (100–200 μm) materials with specific magnetic properties, cut into different shapes and placed on the PCB. The PCB routing formed a winding structure, creating an inductor with a larger surface area but reduced height compared to standard chip inductors. Several demonstrators validated this technology. The optimal space-saving solution is an inductor sized similarly to other PCB components (see Figure 1). A toroidal inductor design with internal windings is shown in Figure 2.
Fig. 2: Side view of the buck converter design with embedded toroidal inductor showing the magnetic sheet inside the PCB.
Small passives such as resistors and capacitors can be embedded in the same cavity, while larger components such as magnetics and capacitors remain external. Capacitors experience reduced thermal stress due to FR4 material insulation. While the layout becomes more complex, embedding offers advantages like shorter switching and control loops, a smaller solution area, and protection against reverse engineering.
Another approach reduces PCB height. In a buck converter design, the inductor is typically the tallest component. If a low-profile solution is needed, finding a suitable inductor can be challenging. This project demonstrated the feasibility of embedding magnetics. However, standard chip-sized inductors were too large for embedding.
To address this, the project used magnetic sheet materials—thin (100–200 μm) materials with specific magnetic properties, cut into different shapes and placed on the PCB. The PCB routing formed a winding structure, creating an inductor with a larger surface area but reduced height compared to standard chip inductors. Several demonstrators validated this technology. The optimal space-saving solution is an inductor sized similarly to other PCB components (see Figure 1). A toroidal inductor design with internal windings is shown in Figure 2.
Fig. 2: Side view of the buck converter design with embedded toroidal inductor showing the magnetic sheet inside the PCB.
Other configurations depend on available space, required coupling, and current capacity. Figure 3 illustrates a 1:1 transformer using the same ring core. Embedding transformers reduces pollution degree and minimizes creepage and clearance constraints. As inductance and current requirements increase, so does the necessary area. Although magnetic sheet embedding is feasible for larger areas (10×10 cm), its primary application is lower-current designs—up to 2A. Increasing the number of windings raises DCR, affecting efficiency.
Materials and reliability
Within the project, 10+ sheet materials were tested for embedding suitability. Like chip inductor materials, sheet materials vary significantly. Sheets are embedded under high pressure and encapsulated within the PCB. Long-term AEC-Q200-based reliability tests assessed electrical and mechanical stability. Tests included:
Only a few materials maintained parameters without delamination, highlighting the need for precise material selection.
Fig. 4: Cross-section of the embedded magnetic sheets with delamination (left) and without delamination (right).
Most tested materials supported 1MHz to 5MHz switching frequencies, but the project also developed new materials supporting 20MHz operation. Several trials led to a successfully embedded compound.
- Temperature cycling (2000 cycles)
- Temperature humidity bias (1000 hours at 85°C, 85% RH)
- High-temperature storage (1000 hours at 125°C)
- Low-temperature storage (1000 hours at -55°C)
- Highly accelerated stress testing (96 hours at 130°C, 85% RH)
Only a few materials maintained parameters without delamination, highlighting the need for precise material selection.
Fig. 4: Cross-section of the embedded magnetic sheets with delamination (left) and without delamination (right).
Most tested materials supported 1MHz to 5MHz switching frequencies, but the project also developed new materials supporting 20MHz operation. Several trials led to a successfully embedded compound.
Chip-level integration
As the project name suggests, one goal was integrating GaN HEMTs with CMOS drivers. Both GaN and Si devices were developed and manufactured within the project, undergoing several iterations to meet integration requirements. The newly developed direct wafer bonding (IBM) process allows bonding two wafers before dicing.
This complex process remains in the trial phase, but once optimized, it will mark a milestone in semiconductor integration. Combining two materials in one device eliminates parasitic inductance between the driver and switch, enabling ultra-high switching frequencies in the hundreds of MHz. This advancement significantly reduces passive component size requirements, leading to extreme miniaturization in power conversion.
This complex process remains in the trial phase, but once optimized, it will mark a milestone in semiconductor integration. Combining two materials in one device eliminates parasitic inductance between the driver and switch, enabling ultra-high switching frequencies in the hundreds of MHz. This advancement significantly reduces passive component size requirements, leading to extreme miniaturization in power conversion.
GaNonCMOS members: Katholieke Univeriteit Leuven, University College Cork – National University of Ireland (Tyndall – UCC), Fraunhofer Gesellschaft zur Förderung der Angewandten Forschung E.V, IHP GmbH – Innovations for High Performance Microelectronics/Leibniz-Institut für Innovative Mikroelektronik GmbH, EpiGan NV, IBM Research GmbH, AT&S Austria Technologie & Systemtechnik Aktiengesellschaft AG, RECOM Engineering GmbH & CO KG, NXP Semiconductors Netherlands BV, X-FAB Semiconductor Foundries AG, PNO Innovation NV
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