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Investigation of composition irregularities and inter-diffusion in strontium-doped lead zirconate titanate thin films on gold-coated silicon substrates

Sharath Sriram 1Madhu Bhaskaran 1David R. Mitchell 2Ken T. Short 2Anthony S. Holland 1Arnan Mitchell 1

1. RMIT University, Sch. of Elec. and Comp. Engg., Microelectronics and Materials Technology Centre (RMIT), GPO Box 2476V, Melbourne, Victoria, Melbourne 3001, Australia
2. Australian Nuclear Science and Technology Organisation, Institute of Material Science and Engg. (ANSTO), PMB 1, Menai, New South Wales, Sydney 2234, Australia


This paper discusses the results of extensive transmission electron microscopy (TEM) based characterisation of strontium-doped lead zirconate titanate thin films. The thin films were deposited by RF magnetron sputtering at 300 ºC on gold-coated silicon substrates, which used a 15 nm titanium adhesion layer between the 150 nm thick gold film and (100) silicon. The films analyzed include cross-sectional samples of films deposited for durations of 2 and 4 hours, which were about 600 nm and 1400 nm thick respectively. The TEM analysis was carried out using a combination of high resolution imaging, energy filtered imaging, energy dispersive X-ray analysis (EDX), selected-area electron diffraction (SAED), and hollow cone illumination (HCI).

At the interface of the films and gold, an amorphous zirconium-rich layer (about 4 nm thick) was observed, while the composition of the films appeared to be uniform elsewhere (verified by EDX). The films were found to be polycrystalline with a preferential columnar orientation perpendicular to the substrate; this was observed using a combination of SAED and HCI. The highly crystalline nature of the films was also evident from the accentuated roughness of the film surface, which was highlighted by the presence of faceted peaks. The films deposited for four hours exhibited a higher density of these peaks. These crystalline peaks on the film surfaces were also verified using atomic force microscopy.

Inter-diffusion between the bottom metal layers and silicon was observed; which could be due to the temperature of deposition being close to the eutectic point of gold and silicon (363 ºC). The diffused regions in silicon were composed primarily of gold (analyzed by EDX), and appeared to stop at (111) silicon planes, highlighted by the triangular diffused regions observed in the 2-D TEM image. The influence of introducing 200 nm of silicon dioxide to isolate the metal layers from silicon is also discussed in this paper.


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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium J, by Sharath Sriram
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-04-28 23:53
Revised:   2009-06-07 00:44