GaN and SiC power devices deliver big benefits to mil/aero systems

By Maurizio Di Paolo Emilio, editor-in-chief, Power Electronics News

The increasing need for higher power density and improved cooling on military and aerospace platforms is pushing silicon-based power electronics systems to their operational limits. Wide-bandgap (WBG) semiconductor materials — silicon carbide (SiC) and gallium nitride (GaN) — offer a new generation of broadband power devices that deliver big advantages over silicon-based counterparts in these applications.

WBG power modules offer features and capabilities that are orders of magnitude greater than their silicon counterparts, including 10× voltage blocking capability, 10× to 100× switching speed capability, and one-tenth the energy losses. They are also intrinsically radiation-hardened (rad-hard) and offer a theoretical junction temperature operation of up to 600°C. This technology could provide power systems with power densities up to 10× higher than current silicon-based devices in addition to lower cooling requirements.

SiC promises lighter-weight components for lower fuel consumption and lower emissions for the aerospace industry. This material facilitates higher switching and higher power density for a given voltage and current rating in a smaller, lighter device.

GaN, like silicon, can be used to create semiconductor devices such as diodes and transistors. A power supply designer could choose a GaN transistor instead of silicon for its small form factor and high efficiency. GaN transistors also dissipate less power and offer higher thermal conductivity, compared to silicon devices with higher thermal management requirements.

In such a context, 65-V GaN technology is triggering a new generation of radar systems that are also opening up opportunities in a range of commercial applications. The RF GaN market is set to exceed $1 billion by 2022, according to Strategy Analytics, with the military radar segment expected to be the largest user of GaN devices in the defense sector.

The use of GaN components is growing rapidly in radar system designs as an alternative or replacement for lateral diffusion MOSFET (LDMOS) components. LDMOS transistors have a higher C_GS /C_DS capacitance, which will limit bandwidth, compared to GaN transistors with a much lower parasitic capacitance, which makes it easier for wideband matching at the same power level.

Fig. 1: Military radar demand is driving opportunities for 65-V GaN in the electronic warfare market. (Image: Shutterstock)

SiC for aerospace
The aviation industry has experienced rapid growth recently compared to the last few decades. The new aerospace world has found new power management solutions in SiC devices for power supply and motor control applications. SiC promises low-weight components to reduce fuel consumption and emissions in the aeronautics industry, while the stable operation of SiC MOSFETs at higher operating temperatures has drawn researchers’ interest for high-power-density power converters.

However, one of the critical design problems for power electronics and motor drive circuits using SiC devices is the management of the gate drive conditioning circuit. Managing gate timing is a serious challenge. New 1,200-V SiC MOSFETs have reached an outstanding quality level in terms of high channel mobility, oxide lifetime, and threshold voltage stability to respond to this challenge.

Solid State Devices introduced the SFC35N120 1,200-V SiC power MOSFETs for high-reliability aerospace and defense power electronics applications like high-voltage DC/DC converters and PFC boost converters.

These N-channel MOSFETs provide a maximum continuous drain current of 26 A to 30 A and a low R_DS(ON) of 96 µΩ max at 20 A and 25°C. With an ignition resistance of 190 mΩ max at 150°C, this device also exhibits high-temperature performance, which allows for smaller devices, facilitates parallel configurations, and reduces thermal management hardware such as fans and heat sinks.

Another solution is the 1,200-V CAS325M12HM2 SiC power supply module, configured in a SiC half-bridge topology, from Wolfspeed, a Cree company. It represents a new generation of all SiC power modules housed in a high-performance 62-mm package. This module uses 1,200-V C2M SiC MOSFETs and 1,200-V Schottky diodes (Fig. 2 ).

Fig. 2: The CAS325M12HM2 SiC power supply module (Image: Wolfspeed)

GaN at 65 V
Radar systems have been primarily developed for military and defense purposes and are also widely used in the automotive sector. The most common military radar markets are ultra-high-frequency (UHF) radar, active electronically scanned array (AESA) radar, identification friend or foe (IFF), and distance measurement equipment (DME). These markets require power amplification of between hundreds and thousands of watts.

Technological advances, such as power amplification, are leading to the development of lightweight solutions. The main technology used in these applications is HEMT GaN due to its superior properties.

Thanks to its high gain and high power levels in the L-band and beyond, and more recently in UHF, GaN has rapidly gained favor in many applications. GaN HEMT transistors on SiC substrates offer excellent heat dissipation for long-term reliability. GaN-on-SiC is well suited for high-power pulsed applications, and its power density allows excellent cooling management. Today’s radars increasingly use GaN-on-SiC RF transistor technology for a variety of reasons. These include increased power, high efficiency, higher robustness, lower power consumption, smaller size, frequency availability, higher channel temperature, and longer life.

In space applications, the feasibility of GaN-on-SiC has recently increased, especially in applications in which GaN efficiency is complementary to operating at higher frequencies. The power density of GaN millimeter waves (mmWave) brings a new set of design techniques that can be used to achieve higher levels of thermal compensation.

Qorvo Inc. offers transistors in a wide range of power ratings, achieving high-power kilowatt amplification in a smaller, more reliable form factor. As an example, the 65-V GaN-on-SiC achieves a small form factor, lower operating costs, and reduced RF front-end complexity.

The Qorvo QPD1013 is a 150-W (P3dB) discrete GaN-on-SiC HEMT that operates from DC to 2.7 GHz. This is a single-stage, unmatched power amplifier transistor in an over-molded plastic package. The high power and wide bandwidth of the QPD1013 makes it suitable for many different applications (Fig. 3 ).

Fig. 3: Block diagram of the Qorvo QPD1013 (Image: Qorvo)

GaN technology can offer great improvements in the latest generation of AESA radars, developed to significantly increase the reliability, accuracy, performance, and configuration flexibility of the detection system, compared to more traditional solutions. Among the latter, for example, passive electronically scanned array (PESA) radars, or even less complex systems with servo-motor–driven antennas, are subject to wear and tear, and the risk of failure rises with increasing duty cycles.

WBG semiconductors are strategically important in the development of next-generation spaceborne systems. GaN, in its enhanced-mode version (eGaN), is widely used in the development of FETs and HEMTs for space applications.

eGaN FETs provide radiation tolerance, fast switching speed, and improved efficiency, which leads to smaller and lighter power supplies (smaller magnets and reduced heat sink size or even elimination of heat sinks in many cases). Power supply designers can choose whether to increase the frequency to allow for smaller magnets or increase efficiency or even design a satisfactory balance for both.

eGaN FETs are smaller than the equivalent MOSFETs. They provide a faster transient response, which can also reduce capacitor size.

Power devices used in critical applications such as space missions, high-altitude flights, or strategic military applications must be resistant to failures and malfunctions caused by ionizing radiation. Commercial GaN power devices offer significantly higher performance when compared to traditional rad-hard devices based on silicon technology.