One possible trick is to use (and possible fabricate in situ) very resistive
leads.  For example,

Outside world -----resistor--cap--resistor--- outside world

Measuring the current flow as a function of time and applied voltage would
give you a measurement of the capacitor.  Only the capacitance after the
resistors would matter significantly, so putting the resistors right up
against the capacitor would remove much of the parasitics.

You might want to simulate something like this first to make sure it works,
as I've never actually done it myself.

David Nemeth
Senior Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA
Ph: (703) 961-9573 x206
Fax:(703) 961-9576

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org]On Behalf Of jaeyoung kim
Sent: Sunday, December 12, 2004 9:28 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] as for the very small capacitance measurement


To mems guys

these days I've been measuring the capacitance change of the micromachined
parallel plate and shunt switch. The analytical values and simulated one are
very closed, and turned out to be around a few picofarad. However, the
experimental values via HP 4284A are very unstable and inconsistent ones due
to parasitic capacitance from many sources like probe tip/station or
something.

Would you please give me your know-how to reduce the parasitic capacitance
in order to get accurate capacitance?

I apprecaite your help in advance.

jay

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