PhD Thesis Arne Lüker final version V4 - Cranfield University

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144 PST as a buffer layer for PZT on SiO2 sequentially may introduce damage to the device layers and degrade the properties of the functional materials. However there is a possibility in the modified process design that PZT may suffer from post-annealing issues such as PZT bubbling and microcracks during PZT crystallisation on non-uniform patterned Pt/Ti/SiO2/Si substrates. A crack-free PST layer as a diffusion buffer could prevent PZT bubbling during PZT crystallisation on a patterned Si substrate and is expected to be beneficial to wafer-scale integration of the PZT microdevices. In addition, high quality PST films can be deposited cheaper with easy composition control using sol-gel technique, similar to PZT films deposition, thus reducing the process complexity, undesired damage to PZT device layers and overall process time. 8.1 XRD-Studies In order to study the growth and quality of PZT thin films on top of a buffer PST layer, XRD analysis was carried out on a batch of samples prepared with various types of device layers. These comprised PZT films deposited directly on a PST/SiO2/Si template and PZT on platinised Si substrates suitable for transducer design, for example PZT/Pt/Ti/PST/SiO2/Si composites with PST barrier deposited at different annealing temperatures. As shown in Fig. 8.3, it was observed in all the various device structures Intensity [arb. Unit] PZT/Pt/Ti/PST/SiO2/Si (d) 700 °C (c) 650 °C (b) 600 °C (a) 550 °C 110 111 Pt (111) 20 25 30 35 40 45 50 55 60 2-Theta [°] Fig. 8.3: X-ray diffractograms of PZT deposited on Pt/Ti/PST/SiO2/Si. The PST layer was annealed at (a) 550°C, (b) 600°C, (c) 650°C, and (d) 700°C.
Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications with bottom Pt/Ti electrode investigated here that the PZT film was preferentially (111) oriented with a less pronounced (110) orientation. The peak intensity of PZT (110) phase was lowest from the device structure with underneath PST layer crystallised at 550°C and gradually became stronger and sharper with higher annealing temperature of PST films as depicted in Fig. 8.3(a-d). However the PZT (111) peak has still higher intensity than (110) peak in all the samples revealing the fact that the piezoelectric properties in these device structures will be dominated by the preferred perovskite (111) grains as expected with PZT film of 30/70 compositions [3]. It was further noticed that the PZT device layer with buffer PST crystallised at lower temperature of 550°C, as shown in Fig. 8.3(a), exhibited maximum intensity for preferred PZT (111) phase along with lowest intensity and broadest (110) peak compared to other samples with PST deposited at higher annealing temperatures. The phase behaviour of the PZT film was studied further on by estimating the relative intensity profile of dominant PZT (111) grains against the annealing temperature of the underlying PST layer that is expected to give an insight to the optimum crystallisation conditions for the PST diffusion barrier to promote the preferred grain orientation of the top PZT film. In one approach the relative intensity of the PZT (111) peak was calculated by setting the intensity for the PZT stacks with buffer PST deposited at 550°C as unity and normalising all other intensity profiles of PZT/Pt/Ti/PST stacks with PST deposited at higher annealing temperatures to this setting (approach 1) [9]. The relative intensity of the PZT (111) peak was also estimated by considering the impact of the Pt (111) peak on the nucleation and growth of the PZT film, e.g., Irel = IPZT/(IPt + IPZT) where IPZT and IPt were intensities of the PZT (111) and Pt (111) peak respectively (approach 2). The relative intensity profile of PZT as illustrated in Figure 8.4 exhibited similar nature of the plots for both types of evaluation techniques. These indicate strongest orientation of the PZT preferred (111) phase with buffer PST layer annealed at 550°C and a sharp decline in PZT (111) peak intensity at and beyond PST crystallisation temperature of 650°C. It was observed from initial XRD analysis that the crystallisation conditions of the underlying PST layer can be monitored and optimised to obtain high quality PZT films on its top. In this case annealing of PST diffusion barrier in the temperature range of 550-600°C could promote the PZT preferred (111) phase with a stronger and sharper peak and is, therefore, 145
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Sol-Gel derived Ferroelectric Thin
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Abstract Ferroelectric perovskite t
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Table of Content Introduction and M
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Page 95 and 96: Sol-Gel derived Ferroelectric Thin
Page 99 and 100: Intensity [arb. Units] (g) (f) (e)
Page 103 and 104: Relative diel. diel. constant Const
Page 113 and 114: Intensity [arb. Units] Intensity [a
Page 121 and 122: Tunability [%] 100 90 80 70 60 50 4
Page 131 and 132: (g) (f) (e) (d) (c) (b) (a) Sol-Gel
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Page 149 and 150: Intensity [arb. Units] Sol-Gel deri
Page 175 and 176: Internships: Sol-Gel derived Ferroe
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PhD Thesis Arne Lüker final version V4 - Cranfield University

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