Agilent Capacitance Measurement Fundamentals 8-Capacitance Measurement c20130117 [1] free download

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Excerpt Edition This PDF is an excerpt from Chapter 8 of the Parametric Measurement Handbook. The Parametric Measurement Handbook Third Edition March 2012 Chapter 8: Capacitance Measurement Fundamentals "Furious activity is no substitute for understanding." -- H. H. Williams Introduction Capacitance measurement is one area of parametric test where many easily preventable measurement mistakes are often made. The reason for this is not lack of intelligence on the part of the user, but rather a lack of fundamental training on capacitance measurement theory and how to make good capacitance measurements. Unfortunately, this type of information is typically not taught in universities and can usually only be learned either through (rather painful) experience or by reading about it in a publication such as this. Why do engineers make so many mistakes when measuring capacitance (especially on-wafer)? The most common reasons are: 1. Capacitance measurement requires compensation to remove parasitic inductance and capacitance from the measurement cables and fixturing, and many times this is done improperly (or not at all). 2. An induced current flows through the outer shield of the BNC connectors (if used) on a capacitance meter, and this current is necessary to balance the measurement current of the capacitance meter. If the outer shield is grounded, then the induced current flow is shorted to ground and the bridge may not be able to balance. Many users are unaware of this issue. 3. Measuring capacitance on a semiconductor wafer on a wafer chuck is very different from measuring a discrete device. The effects of the wafer prober chuck on the measurement cannot be ignored. 4. For higher measurement frequencies (> 5 MHz), structure (layout) design has a major impact on the success or failure of the measurements. As we progress through this (rather lengthy) chapter we will cover all of these issues in detail 145 MOSFET capacitance measurement Review of MOSFET capacitance behavior Before delving into capacitance measurement theory, it is useful to first review MOSFET device op