The production and properties of TCO coatings prepared by pulsed magnetron sputtering from powder targets

Zhou, Y

Abstract

Mith their unique transparent and conductive properties, TCO (transparent
conductive oxide) coatings are becoming increasingly studied These commercially
important coatings have a promising future due to their various applications as
components in optoelectronic devices, photovoltaic solar cells, flat panel displays,
electroluminescent devices, etc. Their high transmittance and low resistivity are
generally achieved through the use of specific dopant materials, whilst adjustments
are made to the deposition processes to improve the structure of the coatings.
TCO coatings are commonly deposited by the magnetron sputtering process.
Sputtering normally takes place from a solid plate, known as the target, of the
material to be deposited. Clearly, each solid target can only be of a single
composition. Thus, to change the compositions ofthe coatings, the whole target has to
be replaced Furthermore, alloy, or doped targets can be very expensive and the
choice ofavailable compositions is likely to be limited.
In this project, instead of using solid targets, metal or ceramic powder blends were
used as the targets. The powder blends were spread across the surface of a magnetron
and lightly tamped down to produce a smooth surface. The benefits of this approach
are that any material that is available in powderform can be considered as a target
material and alloy or multi-component compositions can be readily blended
The basic aim of this project, therefore, was to produce novel TCO coatings by
magnetron sputteringfrom powder targets. The coatings were deposited in a specially
designed rig with a number of important features, including a pulsed DC power
supply and a closed magnetic field. The project concentrated on the production of commercially useful zinc oxide-based TCO coatings. Coatings were produced with
different dopant materials and concentrations, and their optical and electrical
properties were measured. After the coatings were annealed at 500 *Cfor 2 hours in
vacuo, aluminum and gallium doped zinc oxide coatings showed their low resistivity,
which were no larger than 5.19xI0-3S2cm, and the lowest resistivity was obtained
from 3at% A 1-doped ZnO coating; 1.95 xI 00cm. The average transmittance in the
visible range of the ZnO coatings was 90%. From this, optimal compositions were
identified For comparison purposes, coatings were also produced of the TCO
material most commonly used at present; namely ITO (Indium tin oxide). The results
showed that ITO coatings generally had lower resistivity and visible transmittance,
(4-6xlO-492cm and 80-8216), than doped ZnO coatings. Also, the electrical and
optical properties of ITO coatings were very sensitive to the content of oxygen in the
deposition atmosphere. Finally, theflexibility offered by this approach was exploited
through the use of multi-component target compositions to produce TCO coatings
with tailored optical and electrical properties.

Citation

Zhou, Y. The production and properties of TCO coatings prepared by pulsed magnetron sputtering from powder targets. (Thesis). University of Salford, UK

• Thesis Type: Thesis
• Deposit Date: Jul 1, 2009
• Publicly Available Date: Jul 1, 2009
• Additional Information: Additional Information : PhD supervisor: Dr Peter James Kelly
• Award Date: Jan 1, 2005