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Issues in the Flexible Integration of Sputter-Deposited PZT Thin Films with Polysilicon and Ti/Pt Electrode Layers for Use as Sensors and Actuators in Microelectromechanical Systems (MEMS)

Published online by Cambridge University Press:  17 March 2011

C.F. Knollenberg ,
T.D. Sands ,
A.S. Nickles  and
R.M. White
C.F. Knollenberg
Affiliation:
Department of Materials Science and Engineering, University of California, Berkeley, CA 94720.
T.D. Sands
Affiliation:
Department of Materials Science and Engineering, University of California, Berkeley, CA 94720.
A.S. Nickles
Affiliation:
Capacitor Division, Applied Materials, San Jose, CA.
R.M. White
Affiliation:
Department of Electrical Engineering & Computer Sciences, University of California, Berkeley, CA 94720.
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Abstract

Sputter-deposited piezoelectric lead zirconate titanate (PZT) thin films with Ti/Pt and polysilicon electrode layers are being investigated for use in Microelectromechanical Systems (MEMS). Existing research shows the nucleation of the perovskite phase of the PZT is linked to the lattice spacing of the underlying Pt electrode and/or seed layers, and is key in obtaining PZT layers with good piezoelectric/ferroelectric properties. Our research with piezoelectric PZT films on Ti/Pt electrode layers aims at employing these films to generate and receive acoustic waves in flexural plate wave devices (FPWs). Our experiments indicate the formation of a random polycrystalline perovskite phase is linked to the emergence of oriented <100> Pt grains within the dominant <111>-oriented crystal structure during rapid thermal annealing in an oxygen environment. Pt films annealed in nitrogen, in contrast, retained their <111> preferential orientation without the formation of Pt <100> grains. PZT films deposited on these electrodes and annealed in nitrogen were strongly oriented in the <111> direction, but exhibited lossy ferroelectric behavior and were prone to delamination. We are also investigating the feasibility of using doped polysilicon electrode layers with PZT thin films. The multiple layers used with the Pt electrode (Pt, Ti, and SiO2 adhesion layer) have significant interactions with one another, and replacing these layers with a single electrode layer should alleviate these complications. A low-temperature PZT deposition process (300°C) and short annealing cycles (30 sec.), coupled with a TiO2 barrier/seed layer should prevent interdiffusion and reactions between the polysilicon and PZT layers. Our experiments show that PZT films deposited and annealed on doped polysilicon layers develop a random polycrystalline perovskite phase, but are subject to tensile cracking. The use of polysilicon as an electrode layer should also facilitate the integration of piezoelectric PZT layers with polysilicon surface micromachined structures using SiGe sacrificial layers.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 657: Symposia EE – Materials Science of Microelectromechanical Systems (MEMS) Devices III , 2000 , EE5.35
Copyright
Copyright © Materials Research Society 2001

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References

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