GaN-on-Diamond HEMT: The Future of High-Power Devices

Gallium nitride (GaN)-based power devices have proven their remarkable performance in high-frequency and high-power applications owing to their high breakdown field, elevated electron mobility, and exceptional electron saturation rates. From 5G communication base stations to satellite communication systems, GaN-based HEMTs are popular in multiple applications. 

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Under high-temperature, high-power, and high-frequency operating conditions, GaN devices are affected by major obstacles, thereby making the implementation of alternative heat dissipation technologies a critical imperative. Numerous methods have been employed to address the thermal management challenges and among them GaN-on-Diamond has proven to be highly valuable. 

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Among the various heat dissipation strategies being explored, GaN-on-Diamond has emerged as the most promising. CVD-grown diamond offers thermal conductivity up to 2,200 W/m·K which is roughly 12 times that of silicon and 5 to 6 times better than silicon carbide (SiC). In this blog, we provide a detailed overview about GaN-on-Diamond HEMT, its benefits and the future of this market. 

What are GaN HEMTs? 

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GaN HEMTs are transistors that use gallium nitride as its semiconductor material.  Let us break down GaN HEMTs to understand what it actually means: 

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• Gallium Nitride (GaN) is a mechanically stable semiconductor made of gallium and nitrogen. It is a wide bandgap semiconductor which can withstand higher electric fields effectively. 
• ‍HEMT (High Electron Mobility Transistor) is a transistor that uses semiconductor materials having high electron mobility and results in high-speed switching.

Limitations of GaN HEMTs

GaN HEMTs possess several advantages, however there are many technical barriers that limit its widespread adoption. In this section, let us understand the limitations on GaN HEMTs: 

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a. Manufacturing Issues

GaN HEMT devices involve significantly higher cost compared to silicon-based alternatives. The production of GaN wafer has many complex epitaxial growth processes on non-native substrates including silicon carbide or sapphire. This results in defect densities that impact the reliability of devices. When compared to Si and SiC, GaN it is difficult to crystallize GaN from melted material, which can cause significant hurdles in bulk crystal growth development. Wafer bowing and cracking can also be observed during the epitaxial growth of GaN. The buffer layer addition prior to the growth of GaN increases the production cost as well.

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b. Reliability Concerns 

When it comes to power electronic applications, GaN represents significant obstacles. Issues such as collapse phenomena, gate leakage, and dynamic on-resistance degradation under high voltage switching conditions affect GaN HEMTs. These reliability issues are caused due to charges that get trapped in material interfaces and passivation layers. This requires advanced designs and manufacturing techniques to improve device performance.

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c. Integration Hurdles 

Existing silicon-based systems pose significant integration challenges. When compared to silicon, GaN HEMTs deliver superior performance at higher frequencies. To utilize their maximum potential and leverage their benefits,  they require redesigned gate drivers, protection circuits and layout considerations. This need for specialized peripheral components not only adds layers of system complexity but also drives up development costs considerably.

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d. Thermal and Degradation Challenges 

GaN devices represent significant challenges when it comes to thermal management owing to high-power and high frequency operation. The thermal conductivity limitation causes hotspots which can lead to further device degradation. 

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e. Other Challenges 

In applications like space, aerospace, and nuclear systems, GaN HEMTs are exposed to harsh radiation. Heavy-ion irradiation is another challenge, as it creates lattice defects within the material. These defects result in device degradation and reduce the overall breakdown performance. 

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Furthermore, selective doping through ion implantation is more difficult in GaN than in Si and SiC devices. Crystal structure distortion upon implantation and high processing temperatures (>1200 °C) are serious concerns with GaN technology. GaN requires special equipment that can operate efficiently under extremely high temperature and pressure.

What is GaN-on-Diamond HEMT?

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GaN-on-Diamond is made by growing GaN on diamond substrate which combines the electronic advantage of GaN with the heat management capability of diamond. Together this synergy leads to improved device performance, longevity and reduced thermal stress.

Key Advantages of GaN-on-Diamond HEMTs

Diamonds have excellent thermal conductivity and thermal stability which makes them a suitable option for heat dissipation compared to Si and SiC (lower thermal conductivity). By using CVD diamonds as a substrate, it is possible to enhance the thermal performance of devices under high-frequency and high-power conditions.

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Thorough investigations have shown that utilizing a diamond substrate with exceptional thermal conductivity can significantly reduce the internal thermal resistance of the device to effectively mitigate the junction temperature rise induced by self-heating.

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Therefore, introducing diamond as a substrate is the optimal solution for enhancing heat dissipation in GaN devices and a key solution for producing GaN devices with high power and reliability. 

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By using diamond as a substrate with GaN it offers the following significant advantages listed below: 

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1. Enhances Heat Dissipation Performance 

As it is well-known that the thermal conductivity of diamonds is remarkable at 2200 Wm/K. This is about 10 times more compared to that of Si and about 4 times compared to SiC. This property is crucial for addressing the heat dissipation challenges in existing devices. What diamond does, is it enables rapid heat transfer from the GaN channel region to the external packaging. 

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This improved thermal management can help mitigate the issue of current collapse. Current collapse is a situation where GaN devices result in significant drop in current under high-power operation due to charge trapping at the gate surface and surface states of the material. 

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GaN-on-Diamond can help mitigate the junction temperature due to its high thermal management capabilities. This leads to alleviating the charge trapping effects and decreases the probability of current collapse. That being said, this further enhances the power density of GaN-on-Diamond devices to 40 W/mm or even higher. 

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2. Excellent Mechanical Properties 

Diamonds possess excellent mechanical properties and thermal stability which results in maintaining stability under harsh conditions including high temperatures and electric fields. This results in excellent reliability and improves the long-term stability of devices. 

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3. Performance Improvement 

GaN-on-Diamond delivers an exceptional leap in performance. Through heat dissipation and reduction in current collapse effects, GaN-on-diamond devices operate at much higher power densities. The reduced operating temperature and enhanced thermal stability result in reduced thermal stress and material degradation. 

Why CVD Diamonds Outperform Other Substrates? 

The table below depicts the comparison of the three substrates used for Gan HEMTs. The three substrates compared include: Si (Silicon), SiC (Silicon Carbide) and CVD Diamond. 

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With Aga9’s tailored CVD diamond substrates it is now possible to push past the current thermal limits. Let us develop the future of high-power electronics, together.

The Bottom Line 

The electronics industry is growing fast. As electronic devices are powering high-frequency and high-power applications, the need for devices that can effectively handle the increased output power is in demand. Gallium Nitride (GaN) is emerging as a reliable solution for use in next-generation electronic power devices. These are now being deployed in radar systems, cellular base stations and 5G communication networks. 

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GaN-on-Diamond HEMT represents one of the most promising solutions. By combining gallium nitride with CVD diamond, the unmatched thermal conductivity of diamond can be leveraged on to effectively help break the heat barrier. 

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Frequently Asked Questions 

Here are some interesting FAQs on GaN-on-Diamond HEMTs: