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