1. STMicroelectronics, 850 rue Jean Monnet, 38926 Crolles Cedex, France
2. Univ. Grenoble Alpes, CNRS, LTM, F-38000 Grenoble, France
3. IBM, 850 rue Jean Monnet, 38926 Crolles Cedex, France
4. IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598, USA