Degradation of RF MEMS capacitive switches


Herfst, Roelof Willem (2008) Degradation of RF MEMS capacitive switches. thesis.

Abstract:In this study, degradation mechanisms in Radio Frequency Micro-Electromechanical
systems (RF MEMS) capacitive switches have been investigated. We presented a
methodology to characterize device degradation in a way that minimizes the in°u-
ence of the measurement on the device itself, even if relatively slow equipment is used. An automated fast RF-CV measurement setup was developed, which enabled
us to measure a whole C-V curve with minimal in°uence on the device.
With the setup a wide array of systematic, fast and accurate degradation ex-
periments were done. With these experiments we gained more insight in the time
dependence of laterally homogeneous dielectric charging. Also, it enabled us to
develop a framework to distinguish mechanical degradation from laterally inhomo-
geneous dielectric charging, two totally di®erent degradation mechanisms which,
despite their di®erences, have similar e®ects on the device. The framework also
allowed us to choose stress patterns that speci¯cally target mechanical degrada-
tion. This was used to investigate the in°uence of various operating conditions on
mechanical degradation.
The phenomenon of laterally inhomogeneous dielectric charging was also stud-
ied more directly with Scanning Kelvin Probe Microscopy. The SKPM measure-
ments also showed that trapped charge di®use in the lateral direction. This con-
tributes to the recovery e®ects we observed with electrical measurements.
Finally, due to the level of automation of the developed measurement setup,
and the availability of enough measurement material, it was possible to do a large
number of measurements. This allowed us to study how spread in device degrada-
tion impacts the way characterization of those degrading devices should be done.
We saw that measuring whole distributions of degrading devices is important when
studying the various mechanisms that contribute to degradation of RF MEMS ca-
pacitive switches, as di®erences in device degradation due to for instance a change
in stress intensity can easily be masked by the spread in degradation rates.
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