Hi Stefan,
One of the reasons for having the polysilicon blanket underneath your
resonator is to control the electric field that you resonator senses.
Without the polysilicon blanket, the resonator will see a floating
substrate, which may lead to unpredictable behavior.
Good Luck,
Behraad
--
Behraad Bahreyni
Room 456D, Department of Electrical and Computer Engineering
The University of Manitoba
15 Gillson St., Winnipeg, MB, Canada R3T 5V6
Email: Behraad@ieee.org Fax: +1-(204)-261 4639