English

technology report 02
Going to the
movies – at home
Production of high-definition flat-panel
screens starts with sputtering targets
Technology from Heraeus plays an important role in ensuring
that movies are broadcast into our living rooms in
high-definition, or HDTV quality. Special sputtering targets
are used right from the start for manufacturing the glass
substrates used in displays. They apply functional layers
a mere 20 to 300 nanometers thick, which later generate
the image on the glass screen.
Watching TV with premium theater-quality resolution
is one reason why flat screens with liquid
crystal displays (LCDs) are growing in popularity.
Flat screens were already outselling conventional
cathode tube TVs by 2002.
Modern display technology is constantly improving on picture
quality while increasing the size of the screen at the
same time. Faster refresh rates ensure that rapid movements
on screen are also displayed with sharp, precise
resolution. The keys to this high performance are special
low-resistance metal electrodes integrated into the display
and the thin film transistors they trigger. The electrodes in
these thin film transistors (known as TFT electrodes) have
INDUSTRY
to be highly conductive, adhere well to the glass substrate
and respond well to wet chemical etching.
A few base metals such as aluminum and copper are very
well suited for this application. However, aluminum cannot
be used as an electrode material on its own because
of insufficient thermal resistance, so it needs to be coated
with a layer of molybdenum.
These are called
Mo/Al/Mo electrodes. The
molybdenum serves as
a passivation layer and
establishes firm contact
to the substrate. Copper
layers, which are equally
conductive, also require
additional adhesive and
barrier layers on the substrate
to function well. In
other words, to produce
high-performance TFT
electrodes, manufacturers must apply increasing numbers
of nanometer-thick metal functional layers onto the
display substrate. In the case of Mo/Al/Mo electrodes, first
comes a layer of molybdenum, then a layer of aluminum,
and finally another layer of molybdenum. Then additional
complex lithography and etching steps are used to craft
the proper electrodes.
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