High Permittivity, Quasi Linear Dielectrics for High Field/Temperature Capacitors in Power Electronics

Power electronics will play a central role in the impending energy transition from fossil fuels to electrification, which will profoundly change transport and energy distribution infrastructure. New wide-bandgap semiconductor technologies provide active components that can operate at 200ºC or above, allowing reductions in heatsink size and equipment weight. However, the high switching speeds of these wide-bandgap devices requires that passive and active components must be in close proximity (i.e. co-packaged), demanding high temperature operation of the passive components. A key component in power electronics are multilayer ceramic capacitors (MLCCs). MLCCs are found everywhere in modern technology, with over 3 trillion produced every year. A smartphone may have up to 500, and a notebook computer or tablet device up to 800, while an electric vehicle may require up to 15,000. However, no MLCCs exist with the high temperature, voltage and volumetric efficiency required. The development of next generation Class-II dielectrics with a wide operating temperature range, from -55 to 200-300ºC is thus of global importance. In addition, they must work at higher operating fields (> 150 MV/m), be Pb-free and not prohibitively expensive to manufacture, i.e. compatible with base metal electrodes such as Ni. BaTiO3 is ubiquitous in MLCCs for consumer electronics, but BaTiO3 based capacitors perform poorly at high fields since the capacitance is heavily modified. Moreover, X7R core-shell MLCCs break down at the high fields required in power electronics and cannot operate above 125 °C. High permittivity Class II dielectrics such as Bi based relaxors and various anti-ferroelectric compositions have been proposed but they are either incompatible with low-cost electrodes and/or exhibit large strains and sudden changes in permittivity. As a result, the current default in power electronics is a Class I dielectric based on CaZrO3 whose volumetric efficiency is low due to its low permittivity. In this project, we will develop new, low-loss Class-II, quasi-linear dielectrics based on the Q phase of NaNbO3 to achieve higher operating temperature (200-300ºC), higher field (>250 MV/m) and higher energy density (>40 J/cm3) base metal electrode MLCCs for power electronics. A successful outcome to our project will benefit UK companies who manufacture MLCCs, battery manufacturers who will gain superior system performance, the wider solid state chemistry community who will gain greater understanding of the crystal chemistry of perovskites and dielectrics, early career academics who will obtain experience of being involved in a consortium grant, and PDRAs and PhDs who will advance their careers by working on critical net-zero technologies with leading UK academics.