107
Chapter 5 Piezoelectric Materials
Characterisations
5.1 Introduction
Five series of samples as described were characterised; A, B, C, D and IDa. Samples A, B, C and D are multilayer cantilever structures with plated electrodes, while sample IDa
is a cantilever with interdigitated IDT electrodes. Each series of samples was fabricated in the same way, but with slight differences in the printing process as
summarised in Table 4-.
Firstly, the thickness of the samples was measured with a Solder Paste Inspection Data Analyst SPIDA system. SPIDA is a non-contact, optical inspection and measurement
system designed for measuring wet or dry solder paste deposits, which is suitable to measure the thickness of thick-films deposited on rigid substrates.
In order to investigate the structural and electrical properties of the piezoceramic samples, the free-standing part of the samples were detached from the base. In this
condition, the samples are flexible and easier to handle. The surface and structural properties of the free-standing piezoceramic samples were inspected using a Scanning
Electron Microscope SEM at magnifications of 300, 800 and 4000. Two series of samples similar to sample D but co-fired at different profiles with peak temperatures of
850 °C and 950 °C were also inspected. These samples were also measured for their piezoelectric charge constant,
d
33
using the Berlincourt method. A dynamic measurement method, however, requires an external excitation voltage to produce the
108 measurement; therefore the samples have to be connected to the electrode pads adhered
on the substrate. The measured electrical properties of the unclamped free-standing piezoceramic will be compared with clamped samples to verify the theory developed by
Torah
et al
[82] and Steinhausen
et al
[84].
5.2 Thick-Film Dimensions Measurement
The thickness of the films was measured using a Solder Paste Inspection Data Analyst SPIDA system, Z-Check 700 S
www.timco-worldwide.com , as shown in Figure 5-1
a is a non contact inspection and measurement system designed for measuring solder paste deposits, adhesive glue, component placement and a wide range of related
electronic assembly applications.
The SPIDA system consists of a glade table where samples are positioned and inspected under a video camera with a magnification of up to 160. With the assistance of a laser
pointer, the thickness of the thick-film sample can be calculated by measuring the different between the “high point” and “low point” of the light as shown in Figure 5-1
b. The calculation is performed on the captured video image by image processing software provided by the manufacturer.
Film thickness is dependent on the viscosity of the thick-film paste, the coarseness of the screen mesh, the screen emulsion thickness and the adjustable printing gap between
substrate and screen. Two 12 inch 12 inch screens with different mesh coarseness
defined by the density and thickness of the mesh filaments and different emulsion thicknesses were used for printing the PZT ceramics and the electrodes. A screen with a
wider mesh opening of 250 meshes number of wires per inch and emulsion thickness of 25
m was used for printing the PZT ceramics, whilst a smaller opening mesh 325 wires per inch and 20
m thick emulsion was used for finer printing of the electrodes.
Since gold is more expensive then AgPd, it is not used as the electrode material. However, the electrode pad that provides electrical connection to the device requires a
high temperature solderable material; therefore a thin layer of gold is used for this component of the design. Besides playing a role as an electrode, the AgPd layer also
acts as the physical support platform for the free-standing structure. Two printed-dried
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