[1] Tech Univ Sofia, Dept Microelect, BG-1000 Sofia, Bulgaria
[2] Univ Skopje, IT Ss Cyril & Methodius, Fac Elect Engn, MK-1000 Skopje, Macedonia
[3] Univ Appl Sci Western Switzerland, HEIG VD, Inst Micro & Nanotech, Lab Appl NanoSci, CH-1401 Yverdon, Switzerland