Message-Id:   <9610211233.AA06349@speedy.cip.physik.tu-muenchen.de>

Dear MEMS,

I have the following problem:
With a test-actuator fabricated via Surface Micromachining it seems that
there are "some" charges on or in the SiO2 which resides on the Si-Wafer.
I have 1.5 um SiO2 produced via wet oxidation on p-doped (B) <100> Wafer
(10-20 Ohm cm).
What happens is that after pull-in of the structures at 50 - 200 V there
is a strange behavior like this (the structure is about 5 um distant
from the SiO2):


0 V                  |    30 V    |    20 V    |   10 V    |   0 V




                                                ------------
                                   -------------
---------------------                                       ------------
                      -------------


##########################SiO2###########################################
++++++++++++++++++++++++++p-doped Si+++++++++++++++++++++++++++++++++++++

The ordinate means the deflection.

The diagramm should show that at +30 V there is a deflection towards the
substrate. At +20 V there is a deflection away from the substrate.
The same at +10 V. The 0-V-level is at the position between +30V
and +20V. 0V means active-low (shortcut).
It seems that there are so much charges on or in the SiO2 or in the
interface SiO2/Si that the 0-V-level is "moved to 25V".

If I calculate how many elemantar-charges are necessary for this I get
about 1E+15. (That is about the number of the SiO2 molecules on the
surface!?)

Has anybody an idea?


Thank You very much

Guenter Wippich  (gwippich@physik.tu-muenchen.de)