1. Freiburg Materials Research Center, FMF, University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg, Germany
2. Laboratory for Sensors, Department of Microsystems Engineering, IMTEK, University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany
3. Department of Electrical and Electronic Engineering, Faculty of Engineering, University Putra Malaysia, UPM, Serdang, Selangor 43400, Malaysia