Ultra-high voltage (>30KV) power devices through superior materials for HVDC transmission
Lead Research Organisation:
University of Warwick
Department Name: Sch of Engineering
Abstract
In October 2014 the UK energy surplus during winter months dropped to below 5% overcapacity. In the future, this emergency overcapacity may be further diminished and actually become devastatingly insufficient, necessitating the national grid to divert large power demands to areas at opposite ends of the country or face serious and harmful disruption to energy supply. A viable solution to this supply problem is to build new national high voltage DC (HVDC) energy network connections in addition to more international connections to the super grid. To implement HVDC effectively, companies are considering two options: 1) to implement mature Si 300 MW HVDC technologies (circa 2009) requiring large overhead, land requirements, maintenance costs and cooling systems by scaling with the number of converters per line. Or 2) to invest in technologies which upscale the blocking voltage and the current capacity of individual power devices in a converter where fewer line converters and greater efficiency can be achieved for 2 GW MMC HVDC. Even by reducing the series chain effect in power transmission across the UK and conversion a 3% saving can equate to three 500 MW coal power stations from the current UK power usage of approximately 37 GW.
This fellowship seeks to develop revolutionary Silicon Carbide (SiC) material for ultra-high voltage (UHV) >30 kV power devices with large current ratings, up to 150A, with the intention of pushing the current rating as far as possible. The current rating of UHV vertical devices depends on availability of large surface areas (> 1 cm2) and is presently limited due to defects from excess material deposits forming on the wafer during the material growth. This is a problem which I believe will be a critical roadblock to such technology and receives little attention as the proposed power ratings are currently off the 5-10 year power electronics roadmap. Problematically, many in the field trust it will be solved at that point, however, no major research drive is currently underway to solve this essential problem.
Chemical vapour deposition (CVD) is the industry gold-standard technique for creating the semiconductor materials used in these UHV devices due to its excellent uniformity, scalability and reproducibility and so must be developed for quick uptake of any power device technology. For UHV devices the material choice and quality is key, where a defect free, thick (~100 um) layer with a large surface area is needed. Chlorinated chemistry is a recent development in SiC CVD and helps push growth rates up to 100 um/hr for thick layers and can be used to better achieve low background doping densities which are both required for high power technology. Here, thick high quality material will be achieved by state of the art epitaxial growth in the UK's only industrial SiC CVD at Warwick. In tandem to improving the material, its superiority will be shown by fabrication of vertical UHV devices: Schottky Diodes, PiN Diodes and MOSFETS, whilst developing IGBT processing, to show their potential for future modular multi-level converter (MMC) HVDC networks.
Bipolar devices such as Si thyristors and Si PiN diodes will be used in rail traction and grid level HVDC applications due to the high quality of Si material which allows large current ratings. In 2014, Yole predicted that these sectors would boost the >3.3 kV SiC market and in 2015 Mitsubishi showed an all SiC 3.3 kV traction inverter system. I further predict that SiC devices will only completely replace Si IGBTs in the > 10 kV range when the current-limiting surface defects are minimised and device reliability due to minor material defects is better understood. Only then will large current ratings be achieved, which will allow the technology to surpass current HVDC technology. This fellowship directly studies these limiting mechanisms and will develop the material and associated technology to underpin this step change in power technology
This fellowship seeks to develop revolutionary Silicon Carbide (SiC) material for ultra-high voltage (UHV) >30 kV power devices with large current ratings, up to 150A, with the intention of pushing the current rating as far as possible. The current rating of UHV vertical devices depends on availability of large surface areas (> 1 cm2) and is presently limited due to defects from excess material deposits forming on the wafer during the material growth. This is a problem which I believe will be a critical roadblock to such technology and receives little attention as the proposed power ratings are currently off the 5-10 year power electronics roadmap. Problematically, many in the field trust it will be solved at that point, however, no major research drive is currently underway to solve this essential problem.
Chemical vapour deposition (CVD) is the industry gold-standard technique for creating the semiconductor materials used in these UHV devices due to its excellent uniformity, scalability and reproducibility and so must be developed for quick uptake of any power device technology. For UHV devices the material choice and quality is key, where a defect free, thick (~100 um) layer with a large surface area is needed. Chlorinated chemistry is a recent development in SiC CVD and helps push growth rates up to 100 um/hr for thick layers and can be used to better achieve low background doping densities which are both required for high power technology. Here, thick high quality material will be achieved by state of the art epitaxial growth in the UK's only industrial SiC CVD at Warwick. In tandem to improving the material, its superiority will be shown by fabrication of vertical UHV devices: Schottky Diodes, PiN Diodes and MOSFETS, whilst developing IGBT processing, to show their potential for future modular multi-level converter (MMC) HVDC networks.
Bipolar devices such as Si thyristors and Si PiN diodes will be used in rail traction and grid level HVDC applications due to the high quality of Si material which allows large current ratings. In 2014, Yole predicted that these sectors would boost the >3.3 kV SiC market and in 2015 Mitsubishi showed an all SiC 3.3 kV traction inverter system. I further predict that SiC devices will only completely replace Si IGBTs in the > 10 kV range when the current-limiting surface defects are minimised and device reliability due to minor material defects is better understood. Only then will large current ratings be achieved, which will allow the technology to surpass current HVDC technology. This fellowship directly studies these limiting mechanisms and will develop the material and associated technology to underpin this step change in power technology
Planned Impact
The Silicon Carbide market is currently of the order of $200 million p.a. and is rising exponentially, set to reach $1 billion p.a. by 2022, predicting that Silicon Carbide will start to replace Silicon in 2022 and be a much sought after future technology. The UK can gain a foothold in this research area from developing this material ahead of the expected roadmap power ratings, the support statements accompanying this proposal echoing this intention. This would allow both intellectual property and manufacturing to be developed and in turn permit new industry to flourish in the UK. Society more generally will benefit from the continued prosperity of indigenous businesses and will also enjoy sustainability benefits arising from the increased, and more efficient, use of renewable energy sources. It is expected that some of these benefits will start to feed into the industrial base after 10 years of the programme start, with increasing levels of uptake beyond that date.
This fellowship seeks to deal with the critical trilemma of power transmission: rising costs of technology, reduction of CO2 emissions and energy security. The electricity generation and distribution sector will be the major benefactor from efficient and secure energy transmission across the UK - in turn allowing energy providers to supply cheap, reliable power across the UK. An intention to interweave sustainable energy into the network underlies this requirement and is implicitly thought to possible though renewable energy. The uptake for weather dependent renewable energy sources, such as wind or solar, is slow due in part to unreliable generation all year and imparts a major constraint on nationwide implementation: energy resilience versus power generation uptake from green sources. For serious uptake of renewable energy, energy transmission cross-country needs be improved to mitigate this unreliability and reduce energy security risk, currently this is not possible and inevitably increases consumption from risk-free non-renewable sources. However, if the requirement for extra energy availability is lower due to efficient nationwide transmission, this constraint is relaxed and allows a greater percentage of green energy sources to be incorporated into the national grid. Not only will this will enable the UK to meet the CO2 emissions targets set by the G8 summit and the climate change act 2008, it will allow surplus energy to be sold on a common market to the rest of the EU, possibly worldwide, and leave a legacy of sustainable energy where the UK will take leadership by foresight into the technology. Directly, the partners from the Energy Systems Catapult (ESC) and the Energy Research Accelerator (ERA), centrally located in the Midlands, (e.g. Highview and JLR) would both benefit from the extended foresight into power technology which this fellowship will deliver - allowing informed decisions for the UK's future.
With projected population growth and the necessary housing expansion the property sector would also indirectly benefit from the devices proposed in this project. They will allow significant reduction of the area needed for the supporting power transmission and conversion infrastructure, preserving greenland and areas of natural beauty and hence increase the density of housing closer to major cities and towns. Other sectors such as Aeronautics and Defence (Rolls-Royce, BAE, Halliburton, TT electronics, etc.) would benefit from high purity Silicon Carbide material through its use in harsh-environments where its temperature resilience and radiation hardness would lead to robust devices. Such applications of these robust devices could be in downhole drilling for oil extraction, high-frequency data transmission, low-temperature high radiation space applications and would lead to reduced volume of devices to reduce the load taken by power electronics on aeroplanes.
This fellowship seeks to deal with the critical trilemma of power transmission: rising costs of technology, reduction of CO2 emissions and energy security. The electricity generation and distribution sector will be the major benefactor from efficient and secure energy transmission across the UK - in turn allowing energy providers to supply cheap, reliable power across the UK. An intention to interweave sustainable energy into the network underlies this requirement and is implicitly thought to possible though renewable energy. The uptake for weather dependent renewable energy sources, such as wind or solar, is slow due in part to unreliable generation all year and imparts a major constraint on nationwide implementation: energy resilience versus power generation uptake from green sources. For serious uptake of renewable energy, energy transmission cross-country needs be improved to mitigate this unreliability and reduce energy security risk, currently this is not possible and inevitably increases consumption from risk-free non-renewable sources. However, if the requirement for extra energy availability is lower due to efficient nationwide transmission, this constraint is relaxed and allows a greater percentage of green energy sources to be incorporated into the national grid. Not only will this will enable the UK to meet the CO2 emissions targets set by the G8 summit and the climate change act 2008, it will allow surplus energy to be sold on a common market to the rest of the EU, possibly worldwide, and leave a legacy of sustainable energy where the UK will take leadership by foresight into the technology. Directly, the partners from the Energy Systems Catapult (ESC) and the Energy Research Accelerator (ERA), centrally located in the Midlands, (e.g. Highview and JLR) would both benefit from the extended foresight into power technology which this fellowship will deliver - allowing informed decisions for the UK's future.
With projected population growth and the necessary housing expansion the property sector would also indirectly benefit from the devices proposed in this project. They will allow significant reduction of the area needed for the supporting power transmission and conversion infrastructure, preserving greenland and areas of natural beauty and hence increase the density of housing closer to major cities and towns. Other sectors such as Aeronautics and Defence (Rolls-Royce, BAE, Halliburton, TT electronics, etc.) would benefit from high purity Silicon Carbide material through its use in harsh-environments where its temperature resilience and radiation hardness would lead to robust devices. Such applications of these robust devices could be in downhole drilling for oil extraction, high-frequency data transmission, low-temperature high radiation space applications and would lead to reduced volume of devices to reduce the load taken by power electronics on aeroplanes.
Publications
Baker G
(2019)
Study of 4H-SiC Superjunction Schottky Rectifiers with Implanted P-Pillars
in Materials Science Forum
Lioliou G
(2022)
Mo/4H-SiC Schottky diodes for room temperature X-ray and ? -ray spectroscopy
in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Mitrovic I
(2022)
(Invited) Rare Earth Oxides on Wide Band Gap Semiconductors
in ECS Meeting Abstracts
Renz A
(2021)
Initial investigations into the MOS interface of freestanding 3C-SiC layers for device applications
in Semiconductor Science and Technology
Renz A
(2020)
Development of High-Quality Gate Oxide on 4H-SiC Using Atomic Layer Deposition
in Materials Science Forum
Renz A
(2022)
The Improved Reliability Performance of Post-Deposition Annealed ALD-SiO<sub>2</sub>
in Materials Science Forum
Renz A
(2019)
Surface Effects of Passivation within Mo/4H-SiC Schottky Diodes through MOS Analysis
in Materials Science Forum
Renz A
(2020)
The improvement of Mo/4H-SiC Schottky diodes via a P2O5 surface passivation treatment
in Journal of Applied Physics
Description | Silicon Carbide technology for power electronics has ramped in industry in the last year. Billion-dollar agreements have have been made between suppliers such as Wolfspeed(Cree) Infineon, STMicroelectronics, Rohm, Toyota etc, to secure their production lines for a competitive market. We have been investigating the role of defects and material quality for routes to enhance reliability and efficiency for end applications such as High Voltage Cirect Current (HVDC) transmission, electric vehicles (EVs), aviation and traction in trains. This project develops SiC semiconductor material using the UK's only SiC epitaxy tool - this performs the crystal growth for device active material. Here the aim was to develop very thick high quality layers and utilise them in power electronics devices. In the material defects can affect the performance and reliability of said devices so methodology of detection and improvement were base research that required research. We have worked with UK companies on the 1. Evaluation techniques of defects and 2. A categorisation of supplier material. Other work from this grant includes 3. Improvements of epitaxy material by in situ and post-growth treatments, 4. using other existing device fabrication techniques, e.g. ALD, to improve the metal-oxide-semiconductor interface 5. Improving the carrier lifetime by setting up new chemistries in the SiC epitaxy tool and evaluation of measurement techniques. The material from this grant has gone to various projects in the process of fabricating devices, but work is on-going in the post-award COVID research stage to secure results. |
Exploitation Route | The outcomes from the project will enhance UK research in SiC technology and device development, e.g. the £16m ESCAPE (from APC-12), £30m @Future BEV (from APC-15), SiCER (£300k, Innovate UK), HubNet (€6.5m, EP/I013636/1), and VESI (€4.2, EP/I038543/1) which are all concerned with SiC MOSFET and PiN diode development with breakdown voltage ranges from 3.3 kV to 10 kV and beyond. Within these projects, Dr Shah is developing growth and characterisation methodology for material suitable for >10 kV power devices. In particular, the knowledge will be used within the UK's flagship project ESCAPE (End-to-end Supply Chain development for Automotive Power Electronics) to setup a SiC pilot line within the UK to go from materials to a drivetrain to be used in Maclaren EVs. |
Sectors | Electronics Energy |
URL | https://aip.scitation.org/doi/pdf/10.1063/1.5133739 |
Description | We have been able to contribute to open discussions about challenges in inspecting materials in bulk for production: https://semiengineering.com/inspection-metrology-challenges-grow-for-sic/ |
First Year Of Impact | 2018 |
Sector | Electronics,Energy |
Description | Electric Fields by 4D scanning transmission electron microscopy |
Amount | £975,473 (GBP) |
Funding ID | EP/V028596/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 05/2021 |
End | 12/2024 |
Description | Eliminating defects in wide bandgap materials for power electronics reliability [STU0447] |
Amount | £91,422 (GBP) |
Funding ID | STU0447 |
Organisation | Diamond Light Source |
Sector | Private |
Country | United Kingdom |
Start | 09/2022 |
End | 04/2026 |
Description | Silicon Carbide Power Conversion for Telecommunications Satellite Applications |
Amount | £746,426 (GBP) |
Funding ID | EP/V000543/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 03/2021 |
End | 03/2024 |
Description | TESiC-SuperJ - Trench Epitaxy for SiC Superjunctions: technology enabling low loss HVDC power electronics. |
Amount | £398,801 (GBP) |
Funding ID | EP/W004291/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 09/2021 |
End | 09/2024 |
Description | A Plasma Polish Dry Etch process to prepare 4H-SiC substrates for device fabrication. |
Organisation | Oxford Instruments Plasma Technology |
Country | United Kingdom |
Sector | Private |
PI Contribution | Oxford Instruments developed the PPDE process, Warwick provided epitaxy and materials anlaysis. |
Collaborator Contribution | Silicon Carbide (4H-SiC) is an ideal material for high-voltage (>1.2kV), harsh environment and temperature operation devices because of its high critical electric field, excellent thermal conductivity, and material maturity [1-2]. However, its substrate price is still a large component of the overall device production and hinders technological implementation, where the process includes boule growth, sawing, grinding and polishing [3]. A flat (< 10µm bow), low roughness (< 1nm) and damage-free substrate surface is crucial for subsequent epitaxy and device fabrication - normally achieved by Chemical and Mechanical Polishing (CMP). Prior to CMP, subsurface damage can be created by the lapping and grinding processes and if this subsurface damage is not removed then defects can propagate through the following epilayer and reduce device yield [4]. A disadvantage of using CMP is that some subsurface damage effects can remain afterwards and can impact the subsequent SiC epi-deposition by mean of propagation of defects from the substrate and new formation of defects that are detrimental for some devices such as diodes and MOSFETs. [5] In this study, a new method to replace CMP involving a Plasma Polish Dry Etch (PPDE) process is reported. PPDE can offer many advantages over CMP, including lower production costs, reduction of wafer breakage, reduction of wet chemical usage, cross wafer uniformity, reproducibility and even application post-epitaxy. [6-7] The PPDE process has been carried out by ICP/RIE in an Oxford Instruments PlasmaPro100 etcher on the Si face of 150 mm 4H-SiC 325 µm 4° offcut substrates without CMP |
Impact | Talk at conference ICSCRM 2022: A Plasma Polish Dry Etch process to prepare 4H-SiC substrates for device fabrication. |
Start Year | 2021 |
Description | Becoming a satellite facility for the National Epitaxy Facility |
Organisation | University of Sheffield |
Department | National Epitaxy Facility |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | We can provide SiC growth nationally through the NEF. |
Collaborator Contribution | We can provide SiC growth nationally through the NEF. |
Impact | N/A |
Start Year | 2021 |
Description | Identifying defects in SiC |
Organisation | Bruker Corporation |
Department | Bruker (United Kingdom) |
Country | United Kingdom |
Sector | Private |
PI Contribution | We are able to cross-correlate defect etching of defects in SiC to X-ray topography. |
Collaborator Contribution | They have provided their expertise to characterising samples and to time at the diamond light source. |
Impact | Funding of PhD Studentship between DLS, Bruker and Warwick. Poster at conference: P3: Correlation study between molten KOH etching and laboratory X-ray diffraction imaging (X-ray topography) in n+ 4H-SiC wafers David Jacques1, Vishal Ajit Shah2, Richard Bytheway1, Tamzin Lafford1, Benjamin Renz2, Peter Gammon2, Paul Ryan1, and Hrishikesh Das3 1Bruker UK Ltd, Durham, United Kingdom & 2School of Engineering, Power Electronics, University of Warwick, Coventry, United Kingdom & 3ON Semiconductor, South Portland, Maine, USA. |
Start Year | 2018 |