1. IBM T. J. Watson Research Center, 1101 Kitchawan Road, P. O. Box 218, Yorktown Height, New York 10598, USA
2. IBM Microelectronics, 2070 Route 52, Hopewell Junction, New York 12533, USA
3. IBM Microelectronics, 1000 River Street, Essex Junction, Vermont 05452, USA
4. School of Electrical Engineering, Korea University, Seoul, Korea 136-701, Korea