Rounding-up GaN-based Transistors for High-power and Frequency Applications

As silicon is approaching its theoretical limits, manufacturers are now looking into employing wide bandgap (WBG) materials to manufacture efficient high-power and high-frequency field-effect transistors (FETs). 

With outstanding electrical characteristics, WBG materials, like GaN and silicon-carbide (SiC), have overcome the limitations experienced in silicon- (Si) based high-frequency electronic devices. What’s more, WBG semiconductors could be employed in scalable automotive electrical systems and electric vehicles (EVs).

 

An example schematic of a WBG on-board charger for EVs. Image used courtesy of onsemi [PDF]

 

Furthermore, transistors manufactured from the two wide bandgap compound semiconductors, like GaN and SiC, are said to have high breakdown voltages and can operate in high temperatures.

With this in mind, this article intends to look at the differences between GaN and SiC transistors and then round up three recent GaN devices to hit the market. 

 

GaN vs. SiC for Transistors

GaN and SiC have often been considered top materials for high-power and frequency electronics applications thanks to their high voltage capabilities, fast switching speed, and tolerance for high temperatures. However, there are still remarkable differences between them in their performances when put to use, specifically when it comes to transistors.

 

A comparison of GaN, SiC, and Si for power devices. Image used courtesy of Alex Avron

 

First off, SiC demands a high gate drive voltage that ranges from 18 V to 20 V to turn on devices with a low on-resistance. This attribute is in contrast to transistors made from GaN. Furthermore, SiC transistors require a negative voltage ranging from -3 V to -5 V to switch to the off state.

Secondly, GaN, thanks to a higher switching speed than SiC, is majorly adopted as a power amplifier in wireless RF electronics with frequencies up to 100 gigahertz.

Notwithstanding, the two WBG transistors are generally adopted by manufacturers and could sometimes be used instead of Si in: 

• Lateral double-diffused metal oxide semiconductor (LDMOS)
• Metal–oxide–semiconductor field-effect transistors (MOSFETs)
• Super junction MOSFETs
• Insulated-gate bipolar transistors (IGBTs)

With a few of those benefits setting GaN apart, the next sections discuss the latest GaN transistors that are fabricated to achieve more efficiencies in high-power and frequency electronics applications.

 

ST’s VIPERGAN50 High Voltage Converter

The first announcement we'll dive into is from STMicroelectronics. Recently it has introduced VIPERGAN50, a GaN transistor-based power converter to provide high-efficiency power designs in consumer and industrial applications such as power adapters, USB-PD chargers, and power supplies for home appliances.

It is said that the new device accelerates designs in medium power quasi-resonant zero voltage switching (ZVS) flyback converters up to 50 W.

This device, aiming to maximize efficiency at all line and load conditions, leverages multi-mode operations such as:

• Quasi-resonant mode
• Valley-skipping mode
• Frequency foldback mode
• Burst mode

Thanks to its robust features, including current-sensing and protection circuitries like output over-voltage protection, brown-in and brown-out protection, and input over-voltage protection, the device is manufactured to ensure safety and reliability during operation.

 

Close-up view of the VIPERGAN50 product. Image [modified[ used courtesy of ST Microelectronics

 

Packaged in a 5 mm x 6 mm QFN package, the converter promises to meet eco-design codes that target global energy savings and net-zero carbon emissions.

 

EPC’s Rad-hard Power Transistor

The second recent product we'll look at is from EPC (Efficient Power Conversion Corporation). Targeting critical applications while ensuring high reliability in avionics and deep space, EPC has announced its new EPC7019 eGaN rad-hard power transistor device. 

 

 The eGaN transistor comes in passivated die form. Image used courtesy of EPC

 

The new product leverages GaN WBG material to achieve high electron mobility and a low-temperature coefficient. The device boasts an ultra-high frequency, and thanks to the lateral structure of the die, the EPC7019 rad-hard power transistor device features an ultra-low gate charge.

Commenting on the product, Alex Lidow, CEO and co-founder of EPC noted that the GaN-based transistor offers designers a solution with a figure of merit that is 20 times better than best-in-class silicon rad-hard devices while still maintaining a significantly smaller and lower cost.

 

Cambridge GaN Devices Ltd Debuts Enhanced New Gallium Nitride-based Technology

The final product in this round-up came from the APEC 2022 event. At this event, Cambridge GaN Devices announced its Integrated Circuit Enhancement Gallium Nitride (ICeGaN) technology to modify GaN-based power transistors' gate behavior. 

The new technology is based on an enhancement GaN high electron mobility transistor and features an ultra-low specific on-state resistance and very low capacitances.

The ICeGaN products boast a high threshold voltage of about 2.5 V, enabling the inhibition of dV/dt related spurious turn-on events, making it safe for operation.

 

Close-up view of the ICeGaN technology transistor. Image used courtesy of Cambridge GaN Devices

 

In addition, engineers can employ the ICeGaN technology in half-bridge LLC designs because it enables designers to push up switching frequency and increase density, cutting the cost of a complicated and lengthy development cycle.

An example of the ICeGaN device is the CGD65A130S2. As an ICeGaN device, it exploits the unique material properties of GaN to deliver high current, high breakdown voltage, and high switching frequency for a wide range of electronics applications. 

It also features an integrated current sense function that enables designers to eliminate external current sense resistors in their designs to accelerate and improve thermal performance.

All in all, after seeing each of these new devices hopes to keep the ball rolling for more GaN power devices. It will be interesting to see what other technologies will start to pop up.