Research

Underpinning a low carbon future

A low carbon future is linked with achieving an increased penetration of green energy in the grid, efficient conversion, transmission and control of electrical power, from milliwatts to gigawatts. My research focuses on technologies that underpin efficient and stable power systems, smart grids and low carbon projects worldwide. I also have a particular interest in adapting those technologies for use in automotive applications, e.g. for vehicles with more electric power train. It includes semiconductor devices, power electronics and (more recently) batteries.

Semiconductor devices and power electronics

Power electronics is the discipline of controlling, converting and conditioning electrical power using power solid state electronic devices (also known as power semiconductors or power semiconductor devices). Advancements in many sectors, such as the automotive, aerospace, traction and consumer electronics are indeed coupled to the advancements in power electronics; specifically, to the target of achieving increased power handling capability, increased efficiency of electric power conversion and of reducing size, weight and cost of the power converters. These are underpinned by the technological advancements achieved through Semiconductor Engineering in power semiconductor device design and semiconductor materials.

Silicon is currently the semiconductor material of choice for power electronics. Emerging wide bandgap semiconductor materials such as the Silicon Carbide (SiC) and the Gallium Nitride (GaN) have superior electrical characteristics compared to Silicon (Si). As a result, when used in power electronic converters, a real step-improvement in performance, efficiency and the ability to operate at elevated temperatures can be achieved. In hybrid and electric vehicles, the electric powertrain requires less cooling and it becomes more efficient if wide band gap semiconductor devices are used in the power electronics system. Further, the range and “fuel” economy of the vehicle increases and more cabin area becomes available. Similar benefits arise when wide bandgap power devices are used in other applications, for example in power transmission systems, in conditioning power from wind and solar farms, consumer electronics, smart grids and so on.

My research includes addressing issues associated with the functionality, efficient performance and reliability of semiconductor devices. To achieve that, I combine modelling, simulation, design, fabrication and testing.

Advanced semiconductor device models with Technology Computer Aided Design (TCAD) tools

Advanced modelling of power devices allows the accurate simulation of failure phenomena and the explanation of the failure mechanisms in devices.

  • N. Lophitis, M. Antoniou, F. Udrea, I. Nistor, M. Arnold, T. Wikstrom, J. Vobecky, and T. Wikström, “Experimentally validated three dimensional GCT wafer level simulations,” in IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2012.
  • N. Lophitis, M. Antoniou, F. Udrea, T. Wikstroem, and I. Nistor, “Turn-off failure mechanism in large area IGCTs,” in IEEE International Semiconductor Conference (CAS), 2011, vol. 2, pp. 361–364.
Performance and efficiency: Novel structures and optimisation
  • N. Lophitis, M. Antoniou, U. Vemulapati, M. Arnold, I. Nistor, J. Vobecky, M. Rahimo, and F. Udrea, “New Bi-Mode Gate-Commutated Thyristor Design Concept for High-Current Controllability and Low ON-State Voltage Drop,” IEEE Electron Device Letters, vol. 37, no. 4, pp. 467–470, Apr. 2016.
  • M. Antoniou, N. Lophitis, F. Bauer, I. Nistor, M. Bellini, M. Rahimo, G. Amaratunga, and F. Udrea, “Novel Approach Toward Plasma Enhancement in Trench-Insulated Gate Bipolar Transistors,” IEEE Electron Device Letters, vol. 36, no. 8, pp. 823–825, Aug. 2015.
  • N. Lophitis, M. Antoniou, F. Udrea, U. Vemulapati, M. Arnold, I. Nistor, J. Vobecky, and M. Rahimo, “Improving Current Controllability in Bi-Mode Gate Commutated Thyristors,” IEEE Transactions on Electron Devices, vol. 62, no. 7, pp. 2263–2269, Jul. 2015.
  • J. Vobecky, N. Lophitis, M. Arnold, T. Wikström, I. Nistor, M. Antoniou, and F. Udrea, “Parameters influencing the maximum controllable current in gate commutated thyristors,” IET Circuits, Devices & Systems, vol. 8, no. 3, pp. 221–226, May 2014.
  • N. Lophitis, M. Antoniou, F. Udrea, I. Nistor, M. T. Rahimo, M. Arnold, T. Wikstroem, and J. Vobecky, “Gate Commutated Thyristor With Voltage Independent Maximum Controllable Current,” IEEE Electron Device Letters, vol. 34, no. 8, pp. 954–956, Aug. 2013.
  • N. Lophitis, M. Antoniou, F. Udrea, F. D. Bauer, I. Nistor, M. Arnold, T. Wikstrom, and J. Vobecky, “The Destruction Mechanism in GCTs,” IEEE Transactions on Electron Devices, vol. 60, no. 2, pp. 819–826, Feb. 2013.
  • N. Lophitis, M. Antoniou, F. Udrea, U. Vemulapati, M. Arnold, M. Rahimo, and J. Vobecky, “4.5kV Bi-mode Gate Commutated Thyristor design with High Power Technology and shallow diode-anode,” in IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2016, pp. 371–374.
  • U. Vemulapati, M. Arnold, M. Rahimo, J. Vobecky, T. Stiasny, N. Lophitis, and F. Udrea, “An Experimental Demonstration of a 4.5 kV Bi-mode Gate Commutated Thyristor (BGCT),” in IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2015, pp. 109 – 112.
  • M. Antoniou, N. Lophitis, F. Udrea, F. Bauer, I. Nistor, M. Bellini, and M. Rahimo, “Experimental demonstration of the p-ring Trench IGBT concept: A new design for minimizing the conduction losses,” in IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2015, vol. 2015-June, pp. 21–24.
  • N. Lophitis, M. Antoniou, F. Udrea, M. Rahimo, I. Nistor, M. Arnold, T. Wikstrom, J. Vobecky, and M. Rahimo, “The Stripe Fortified GCT : A new GCT design for maximizing the controllable current,” in IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2014, pp. 123–126.
  • N. Lophitis, M. Antoniou, F. Udrea, I. Nistor, M. Arnold, T. Wikström, and J. Vobecky, “Optimization of Parameters influencing the Maximum Controllable Current in Gate Commutated Thyristors,” in IET International Seminar on Power Semiconductors (ISPS), 2012.

Other research interests

My research interests also include the condition monitoring of power electronic converters but also the degradation and state of health of batteries for automotive applications.