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High Q resonator measurement difficulties

Question asked by steveor on Oct 11, 2010
My group produces and measures high Q FBAR resonators.  A typical Process Control Monitor is a single resonator shunted to ground.  This device has S11 magnitude near 1 and makes a nice circle around the outer edge of a Smith Chart.  Some of the figures of merit include Rs and Rp--the real impedance where the circle crosses the real axis of the Smith Chart (please see the attached figure).  The resonant frequency varies by design and ranges from a few hundred Megahertz to a few Gigahertz

As our technology has improved, we're able to get Rp higher (into several kiloOhms) while holding Rs close to zero Ohms.  As you might imagine, the measurements of Rp are difficult to reproduce as they get higher.   That is, it's much more difficult to reproduce readings of 6000 Ohms compared to 3000 Ohms.

What have other users done to get repeatable (and / or accurate) measurements for devices like these?  Any ideas on controlling the measurement here?

Thanks,
Steve Ortiz  

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