PhD Thesis Arne Lüker final version V4 - Cranfield University

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A.3 Technology 168 Appendix A: PZT actuated Diamond Cantilever Technology The starting material for the cantilever actuator structure was a 2.0 µm thick NCD film with a grain size of approx 50 nm deposited onto a (100)-oriented Si substrate. The film was grown by MWPECVD with high re-nucleation rate to obtain a stress balanced film (3D NCD; [5]). Usually the following step is the deposition of a metallic bottom electrode. This layer serves also as oxygen diffusion barrier during PZT deposition and the following post annealing step and as adhesion layer to accommodate the high bending moments required by the high diamond stiffness. PZT can be deposited by MOCVD [6], pulsed laser deposition [7], sputter deposition [8], ECR-PECVD [9], or sol-gel spin-on [10]. Most of these methods need a post-annealing step for dipole orientation in the PZT Pt NCD Si Fig. A5: Cross section SEM view of a sol-gel derived PZT film on NCD including Pt adhesion layer. perovskite structure in the range of 550 – 650 °C. In this work a sol-gel process was used for PZT deposition. The adhesion layer and bottom electrode was PVD platinum. The sol- gel PZT was deposited using a spin- coater and post-annealed at 570°C in ambient atmosphere [2]. This method and material combination benefits from homogenous and large area deposition at low thermal budget. A cross sectional view of this material system is illustrated with Fig. A5. After realisation of the Si/NCD/Pt/PZT material stack the Al top electrode is deposited by evaporation and patterned by lithography to define the cantilever geometry. This pattern serves then as a hard mask for the anisotropic dry etching of the PZT/Pt/NCD stack in different atmospheres of Ar and Ar/O2, respectively, and the undercut isotropic plasma etching in CF4/O2 of the Si-substrate to release the cantilever beam. It is therefore self-aligned and the top electrode covers the entire cantilever surface to obtain a uniform electrical field across the piezoceramic. In a last step the bottom Pt electrode is contacted
Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications through a wet chemically etched window. Fig. A6 shows SEM micrographs of a processed 50 micron cantilever. A.4 Results top electrode bottom electrode Fig.A6: Fabricated cantilever actuator with 50 µm length. Fig. A7 shows the PE hysteresis loops obtained after deposition of PZT. It can be observed that PZT indeed shows piezoelectric behaviour and is well suited for actuator fabrication. Fig. A7: Measured hysteresis curve of sol-gel PZT on NCD 169
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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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Intensity [arb. Units] (g) (f) (e)
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Relative diel. diel. constant Const
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PhD Thesis Arne Lüker final version V4 - Cranfield University

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