Yu,

I would recommend two options to cover your metal electrodes: 1)SiO2
deposited by PECVD. Nitride is also OK, but there are a lot of pin holes
from PECVD (definitely you can not use LPCVD) which decreases the break
through of the film. I used 0.8um SiO2 which survived 160V. 2). Parylene.
1um Parylene C can survive 220V. You can also use parylene N. which suppose
to have a bit higher break down voltage, but the deposition process is a bit
more tricky. We have a paper in JMEMS recently for your reference,

H.Zeng, A. Feinerman, Z.Wan, and P. Patel: Piston-Motion Micromirror Based
on Electrowetting of Liquid Metals, JMEMS, VOL. 14, NO. 2, pp285-294, APRIL
2005

Please let me know if you have a problem to access it and I can send you an
electronic reprint. Also, let me know if you have an adhesion problem during
the parylene coating.

Good luck,

Hongjun Zeng, PhD

MEMS/Nano Scientist
Nanotechnology core facility
University of Illinois at Chicago

-----Original Message-----
From: Yu Chan
Sent: Friday, September 23, 2005 10:08 AM
To: General MEMS discussion
Subject: [mems-talk] insulating Au electrodes

Hello All:

I want to evaporate SiO2 by e-beam evaporator on Au electrodes to
insulate them as I need to operate the sample in buffer solution.

two questions:
1. what is the minimum thickness should be to protect Au electrodes
which is 150nm thick? operation voltage is small than 100mV.

2. SiO2 does not stick very well on the Au, is there a way to improve
the adherence of SiO2 on Au?

or you have any other better way to insulate the Au electrodes?