TESiC-SuperJ - Trench Epitaxy for SiC Superjunctions: technology enabling low loss HVDC power electronics.

2019年，英国每日平均32吉瓦能源需求中有48.5%是无碳能源，主要来自风力发电场、太阳能和核能，以及海底互连器和生物质能进口的能源。这一趋势支持了政府在2019年签署的“净零”承诺。然而，仍然需要开发重要的技术来实现这一目标。其中一个关键技术是高压直流（HVDC）电网级传输，它将使“超级电网”成为可能。这是一个跨越国家和上述能源生产设施之间的长距离输电线路网络，特别是在海上风力发电场等偏远地区。提高每个电网互连的效率和功率等级（以及减少它们的体积和重量），这将意味着更广泛的实施，从而更好的能源安全，更低的碳足迹和更好的能源经济。在大多数互连器中，50%的体积是电力电子设备，传统上由硅技术制成。与目前的硅技术相比，碳化硅（SiC）具有明显的优势，例如高温和更高频率的操作，并且最终的系统重量和体积更小。最近，商用SiC功率器件已经进入市场，预计到2024年价值将达到20亿美元，汽车行业的一些早期采用者（如特斯拉）正在积极推动这项技术的快速增长。然而，对于高压（>1.7 kV）电力传输，双极硅器件（igbt, gto）效率更高，因此目前必须根据应用选择技术。为了消除这一限制，所有类型的SiC功率器件都可以通过SuperJunction （SJ）技术额外增强，从而提高材料的效率，并完全准备好挑战Si技术。本提案旨在开发新的6.5 kV SiC SJ材料和器件技术，以增加电力传输。目前对SiC SJ器件的研究仅包括少数关于单个器件的报告，虽然令人鼓舞，但该技术仍处于起步阶段。英国有机会从头开始发展这项技术，并成为一个名副其实的国际品牌。主要的挑战是，SiC加工方法无法大规模生产超结材料，一种方法昂贵且复杂，另一种方法需要非常严格的参数精度，最后需要在电流额定值上妥协。具体来说，我们建议发展沟槽外延（TE），在非常高纵横比的微沟槽中沉积晶体材料。沉积方法是化学气相沉积（CVD），被公认为是快速生产、高质量材料的行业黄金标准，因此在开发该技术时必须选择这种方法。开发TE的挑战在于将气体输送到沟槽底部，以便a)蚀刻材料，b)为沉积做好准备，c)用改性材料完全重新填充沟槽，d)确保表面恢复到以前的状态。更复杂的挑战在于这项工作的非互斥化学性质，其中一个参数的改变可能会改变更多参数。华威目前拥有英国唯一的工业SiC CVD，拥有专用的SiC器件制造洁净室和许多分析工具，因此是英国进入这一领域的理想场所，以便在入口点为技术做出贡献。华威大学是EPSRC电力电子中心的重要成员，也是价值1700万英镑的APC-12 ESCAPE（汽车电力电子端到端供应链开发）项目的一部分，该项目正在开发由迈凯轮领导的以英国为中心的SiC生产线，因此在开发后存在全面实施TE SiC SJ技术的途径。

In 2019 48.5% of the 32 GW daily average energy demand in the UK was carbon-free - contributed by wind farms, solar and nuclear energy, alongside energy imported by subsea interconnectors and biomass. This trend supports the "net zero" commitment signed by the government in 2019. However, significant technologies still need to be developed to enable this goal. One key such technology is high voltage direct current (HVDC) grid level transmission which will enable the "supergrid". This is a network of long distance power transmission lines across and between countries and those aforementioned energy production facilities, particularly in remote locations such as offshore wind farms. Increasing the efficiency and power rating of each grid interconnection (as well as reducing their volume and weight) it would mean more widespread implementation and hence better energy security, lower carbon footprint and better energy economy for the UK. Within most interconnectors, 50% of the volume is the power electronics devices, traditionally made from Silicon technology. Silicon Carbide (SiC) has clear advantages over current Silicon technology such as high temperature and higher frequency operation, with lower resultant system weight and volume. Recently, commercially available SiC power devices have recently entered the market with force, predicted to be worth $2bn by 2024, with rapid growth in this technology is being actively driven by a number of early adopters in the automotive sector, e.g. Tesla. However for high voltage (>1.7 kV) power transmission, bipolar Silicon devices (IGBTs, GTOs) are more efficient - so the technology must presently be chosen relative to application. To remove this restriction, SiC power devices of all types can be additionally bolstered by SuperJunction (SJ) technology, improving the efficiencies of the material and fully ready to challenge Si technology. This proposal intends on developing new 6.5 kV SiC SJ materials and devices technology for the goal of increased power transmission. Current research in SiC SJ devices consists only of a handful of reports on single devices, whilst encouraging, the technology is still in its infancy. The UK has an opportunity to develop the technology from the ground up and become a serious international name. The major challenge being that SiC processing methods fall short of being able to mass-produce the superjunction material, with one method being expensive and complicated, another requiring very tight precision of parameters and the last compromising on current rating.Specifically here we propose to develop Trench Epitaxy (TE), which deposits crystalline materials in very high aspect ratio micro trenches. The deposition method is chemical vapour deposition (CVD), which is accepted as the industry gold standard of fast throughput, high quality materials production and so must be the method of choice when developing this technology. The challenges in developing TE lie in the transport of the gases to the bottom of the trenches to a) etch the material, b) condition it ready for deposition and c) fully refilling the trenches with modified material and d) ensuring the surface is returned to its previous state. The more complex challenges lie in the non-mutually exclusive chemical nature of the work, where a change in one parameter may change many more.Warwick currently houses the only industrial SiC CVD in the UK, has a dedicated SiC device fabrication cleanroom and many analytical tools so is the ideal place for the UK to enter this field with the view to contributing to the technology at the point of entry. The University of Warwick is a key member of EPSRC Centre for Power Electronics and is part of the £17M APC-12 ESCAPE (End-to-end Supply Chain development for Automotive Power Electronics) project which is developing a UK centred SiC production line, led by McLaren, so pathways exist of fully implementing TE SiC SJ technology after development.