Power supply chains in many electronic applications consist of multiple stages of AC-DC and DC-DC voltage converter modules and power interconnects, from the main AC supply to the C4 connectors on the electronic boards for the data centers and automotive examples. A point of load (PoL) VRM provides a point of load with the appropriate supply voltage, like converting 12 V to a much lower voltage (e.g. 1V), as required by a CPU, close to the final load. In the context of IT applications, VRM differs in specifications, topology and design depending upon the specific computing application considered: mainframe servers, cloud computing systems, mobile applications etc. Most significantly, the voltage and current rating for each application determines the structure and design of the VRM.
The loss of efficiency in a power supply chain in all applications arises mainly from the following two sources:
- Loss in the VRM during the voltage down-conversion
- IR losses in the power interconnects across the PCB
Losses in the VRM can be reduced by minimizing the number of stages of voltage conversion along the power supply chain. This requires efficient large voltage-ratio converters. While VRM efficiency is a complex function of its design, subcomponent characteristics and operating conditions, its efficiency drops with increasing voltage conversion ratios- a challenge that must be overcome with innovation in materials, improved design and by increasing operating frequencies. IR losses are minimized either by reducing electrical resistance along the power supply chain via increasing the number of power interconnects to the CPU or by bringing the PoL conversion as close as possible to the CPU, thereby reducing the currents in the long power interconnects across the PCB.
In addition, energy-efficient operation of a typical multi-core CPU entails the dynamic voltage and frequency scaling (DVFS) of the various cores and other logic components of the CPU. Fast voltage scaling in MHz frequencies can result in energy savings up to 40-60%. Hence, a highly granular multiple voltage domains power supply whose output voltages can be dynamically varied is needed for improving the overall energy efficiency of the entire computing system.
Therefore, the ideal power converter for these applications consists of an efficient, compact, granular, large voltage ratio power converter situated as close as possible to the PoL and has a wide dynamic operating range. This will be realized by integrating GaN power switches with CMOS drivers densely together using different integration schemes from the package level up to the chip level including wafer bonding between GaN on Si(111) and CMOS on Si (100) wafers.
Integrate – Develop – Optimize – Improve
The overall objective of the project is to develop novel low cost and reliable GaN-based process, components, modules and integration schemes, and demonstrate their performance and economic potential on system level for significant energy reduction in a wide range of energy intensive applications.
The GaNonCMOS project aims to bring GaN power electronic systems to the next level of maturity by providing the most densely integrated systems to date. The key innovations steps are:
- Integrate GaN power switches with CMOS drivers densely together using 3 different integration schemes (see Fig.1) from the package level up to the chip level using wafer-bonding between GaN on Si(111) and CMOS on Si (100) wafers.
- Optimize the GaN materials stack and device layout to enable fabrication of normally-off devices for such low temperature integration processes (max 400oC).
- Develop new soft magnetic core materials reaching switching frequencies up to 300 MHz with ultralow power losses to be integrated at different levels.
- New materials and methods for miniaturized packages to allow GaN devices, modules and systems to operate under maximum speed and energy efficiency.
- Long term reliability improvements over the full value chain of materials, devices, modules and systems with consortium partners that cover the entire value chain.
The development of beyond the state-of-the-art materials in devices, modules and systems in GaNonCMOS will drive a new generation of densely integrated power electronics and pave the way toward low cost, highly reliable systems for energy intensive applications.