1. Microelectronics Research Unit Faculty of Information Technology and Electrical Engineering University of Oulu P.O. Box 4500 Oulu FIN‐90014 Finland
2. Research Unit of Medical Imaging Physics and Technology Faculty of Medicine University of Oulu Oulu FIN‐90014 Finland
3. Department of Electronics and Nanoengineering Aalto University Aalto FIN‐00076 Finland
4. Department of Applied Physics Aalto University Aalto FIN‐00076 Finland