Center for Device Thermography and Reliability
The Center for Device Thermography and Reliability (CDTR), led by Professor Martin Kuball is a world-leading research center focusing on improving the thermal management, electrical performance and reliability of novel devices, circuits and packaging.
Probing RF properties of GaN-based devices
Bundling unique European expertise for spaceborne devices
Ferdinand-Braun-Institut, SweGaN AB, and the University of Bristol are partnering in the European Space Agency funded Kassiopeia project. The teams join forces to develop high-performance Ka-band GaN MMICs (monolithic microwave integrated circuits). Applications for these devices include beam steering antennas for satellite communications and radar applications.
In March, the Kassiopeia project was launched to provide a value-added chain using internationally leading technology only available in Europe. The consortium project, led by Ferdinand-Braun-Institut (FBH) in Berlin, aims to demonstrate a fully independent European supply chain, from silicon carbide (SiC) substrates, gallium nitride (GaN) epitaxy, GaN device processing up to power amplifiers. For this purpose, Ka-band MMICs using novel epitaxy, processing, and circuit concepts towards highly efficient GaN and aluminium nitride (AlN) devices will be developed and demonstrated. The Ka-band frequency band is used, for example, in satellite communications.
The CDTR at the University of Bristol’s research within this program focuses on direct thermal measurements on active GaN transistors by using micro-Raman thermography and advanced device characterizations and modeling. This will provide a continuous feed-back to all device and epitaxial developments planned in Kassiopeia.
FBH contributes its industry-compatible Ka-band MMIC technology on 100 mm GaN-on-SiC wafers. “The unique selling point of our GaN MMIC technology is its highly reproducible and reliable iridium sputter-gate technology”, emphasizes Dr. Joachim Würfl, head of FBH’s Power Electronics Department. “This technique reduces dynamic losses (gate lagging) to values up to two times less than competing institutional and industrial technologies.” The technology is also known to significantly improve device reliability. Together with new approaches in terms of process technology and circuit concepts both targeting for parasitic loss reduction highly efficient Ka-band MMICs will be developed. The groundbreaking technology will thus provide advantages in performance and reliability, which are particularly important for spaceborne devices.
SweGaN participates with its unique buffer-free solution for GaN-on-SiC epiwafers, QuanFINE®, bringing its expertise in epitaxial layer design and optimization to the project. SweGaN will also supply in-house developed semi-insulating SiC substrates for evaluation. "We are excited to participate in this ESA-aligned project together with FBH and University of Bristol, shares Jr-Tai Chen, CTO, SweGaN. Conventional GaN-on-SiC materials for Ka band applications still lack maturity, leaving significant room for innovation and improvement. SweGaN will introduce its revolutionary epitaxial manufacturing process to address the challenge.”
The Kassiopeia project is funded under the ESA ARTES Advanced Technology Programme: “European Ka-band high power solid-state technology for active antennas”.
SEM image of gallium nitride MMICs
A sustainable energy grid for the future
A U.S. Department of Energy (DOE) award is empowering the Centre for Device Thermography and Reliability (CDTR) at the University of Bristol to create a resilient and sustainable electricity grid with the use of next-generation ultra-wide bandgap materials and devices.
The four-year, $12.4 million award from the DOE’s Office of Basic Energy Sciences, establishes a Research Center led by the University of Arizona, with the CDTR here in Bristol, the only non-US partner involved. Professor Martin Kuball, Director of the CDTR and Royal Academy of Engineering Chair in Emerging Technologies, says “we are excited to be part of this large US funded activity to enable the technology needed for so-called smart grids and helping our society to achieve zero carbon emission”. The Center will employ creative, multi-disciplinary scientific teams to tackle the toughest scientific challenges preventing advances in energy technologies, as well as investigating fundamental questions about ultra-wide bandgap semiconductors.
Picture credit: Karsten Wurth on Unsplash
Ultra-wide bandgap semiconductors are for example aluminium nitride, boron nitride or diamond, which possess extraordinary physical and electrical properties. Devices constructed from them can operate at higher temperatures, voltages and frequencies than Silicon (Si), making them significantly more powerful and energy efficient than conventionally used Si-based power electronics. Through the use of ultra-wide bandgap materials, power substations could potentially shrink a hundredfold — to virtually the size of a suitcase — saving space and increasing the reliability of the grid. Wide band gap materials can also enable better integration of renewable energy sources into any electricity grid. While electricity grids traditionally only delivered power in one direction — from power plants to consumers — today’s grids must be flexible, giving and taking power as required. Renewable energy sources such as wind and solar power supply energy under the right conditions, but their cells and batteries require recharging when there is not enough wind or sun. A “smart grid” to meet these multidirectional demands is within reach, thanks to the research that the CDTR is doing.
We are hiring!
We have a PhD Studentship available, (UK, European and international students are eligible; start date 2021) in thermal management research of ultra-wide band gap semiconductors, associated with the DOE ULTRA centre we are involved with- if you are (or know someone who is) interested please get in touch: Martin.Kuball@bristol.ac.uk.
Professor Martin Kuball named as Royal Academy of Engineering Chair in Emerging Technologies
Professor Kuball is one of eight engineering academics across the UK to receive support from the Royal Academy of Engineering’s largest research funding scheme—the Chairs in Emerging Technologies – which has allocated a total of £22 million to support these innovative researchers and global leaders in their fields whose projects made it through the rigorous selection process in the face of stiff competition.
For his project as Chair, ‘Ultra-wide bandgap emerging power electronics for a low-carbon economy’, Professor Kuball aims to develop a new class of semiconductor power electronic devices using ultra-wide bandgap materials such as gallium oxide, boron nitride and aluminium nitride. Thanks to the outstanding properties of these materials, the new devices will be compact, highly versatile and energy efficient. This new generation of power electronics is the key to transforming a wide range of real-life applications, from data centres and motor drives to electric vehicle chargers to smart grids, all contributing to the realisation of a greener society.
Why do we exist?
In today's fast-moving technological world, semiconductor devices need more ‘muscle power’, but devices must not overheat. It is projected that the next generation of wireless architecture (5G) will increase data communciation speeds to multiple times that of existing 4G. Semiconductors enable this wireless architecture. Today's devices run too hot, wasting energy and giving them a short operating life time.
If we use today’s technology, by 2035 the planet’s datacentres will cover 6 x the land area of the M25 and use over 40% of global energy production. Artificial Intelligence (AI) will become the biggest single contributor to climate change. Better semiconductors can help mitigate this. The world needs new devices which are more energy efficient, that can also run at high powers. This is what we aim to achieve in the CDTR.
To achieve this goal, since 2001 we have been developing and applying new techniques for temperature, thermal conductivity, electrical conductivity and traps analysis, especially for microwave and power electronic semiconductor devices, made of wide bandgap materials, such as GaN, SiC, Gallium Oxide and diamond. Our team of about 20 international researchers and PhD students works with industry and academia from across the globe to develop the next generation of technology for communications, microwave and power electronics to enable the low carbon economy.
- Mapping of temperature fields in GaAs MMIC HPA modules
- Electrical device characterization
- Reliability and failure analysis of AF & power electronic devices
- Device electrical and thermal modelling
- Measurements of junction temperature in AlGaN/GaN HFETs during operation for accelerated life time tests
- Thermal resistance in heteroepitaxial device structures. Examples include: GaN on SiC, Si and diamond