Measurement Science

In the book by the author Markys G Cain, (M. G. Cain, Characterisation of Ferroelectric Thin Films: Solutions for Metrology. Springer, 2014, ISBN 140209311X, 9781402093111), we set out reminding ourselves the nature of polarisation in bulk materials and how this property is practically measured. We highlight some of the measurement pitfalls and common sources of error when you carry out the ubiquitous PE-loop measurement! Next we turn our attention to one of the standard measurement methods (available as an international standard in fact) for the evaluation of low field properties of piezoelectric ceramics, based on resonance analysis. A practical worked example takes the reader through the precise details of this test method and assists in the calculation of the materials properties.Another ‘standard’ test method, based on the original ideas set out by Don Berlincourt back in the 1950’s is presented in our next chapter and measurement good practice has been developed alongside one of the manufacturers of the test equipment. The results of an inter laboratory round robin are included in this chapter to show how the test method has been improved with regards accuracy of result.The pyroelectric properties of crystals (where a temperature change induces a polarisation in the material) are incredibly important for low light level thermal imaging cameras, motion detectors, people detectors and so on, and one of the leading experts in this field describes the details of how the tensor is measured accurately on a number of materials types.

The use of interferometry to traceably measure the actuation displacement or strain of piezoelectric materials is next described using the double beam interferometric method. There are many additional details associated with the assessment of the materials properties of thin films which are not dealt with in this chapter, but are the subject of current intense research effort worldwide.

The thermal properties of piezoelectrics often dominate high power use – such as in high power sonar or ultrasonic welding, for example. The particular issues with regards assessing the evaluation of the materials polarisation or strain characteristics at high temperatures is a complicated measurement problem which is explored in some detail in this chapter. An extension to the problems associated with self-heating (when a piezo transducer is electrically `over-driven’) in such high power applications is the subject of the next chapter and here we propose various ways in which the thermal properties of the transducer may be modelled using fairly simple methods.

One of the more recent additions to the family of measurement methods for piezoelectrics (especially piezo thin films) is Piezoresponse Force Microscopy (PFM). Now, there are many excellent reviews published on this technique and indeed, the method is constantly evolving and new operational modes are being discovered every year. So, in this chapter we force ourselves to focus on the measurement apparatus and the principle mode of operation. Issues such as contact electro-mechanics and surface quality of the piezo film are evaluated and methods for quantifying the (to date) qualitative method are proposed.

The mechanical properties of piezo thin films are of great importance in piezo-MEMS technology for example, and we devote a chapter to describe the operational principles behind an industry-standard mechanical indentation method for evaluating the elastic properties of piezo ceramics. The technique, on its own, is not sufficient to quantify all the elastic properties but, used with complementary methods such as SAW/ultrasonic propagation methods, it is a very useful tool that also allows for in situ electrical excitation of the piezo material.

Finally, we spend some time discussing the measurement of dielectric breakdown in bulk piezoelectric ceramics based on the standards already developed for bulk electronic substrate dielectric materials.

A final chapter on current standards (with links online) completes this volume.[Copyright: Springer]