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SPUTTERING

Introduction

Physical Vapor Deposition ( PVD ) is a method to deposit thin layers of a desired material onto a substrate.. The process consists of a magnetron to dissociate atoms, from a source or “target” onto a substrate, such as silicon wafers or glass.
 
This can be used in thin anti-reflection coatings on glass for optical applications, the production of thin film transistors, or nitriding of tools. Sputtering is most useful when (a) there is a large area of deposition (b) when the thin film is from a high temperature material that cannot be deposited through evaporation or (c) when it is necessary to keep the substrate at low temperatures or (d) when a thin atomic layer is required.

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Thin film transistor liquid crystal display (TFT LC)

Thin film transistors (TFT) are used to control the color of light (red, blue, or green) in each pixel of flat panel displays. Image quality on television sets, computer monitors, mobile phones, handheld video game systems, navigation systems and any other devices utilizing screens is greatly improved.
 
Often TFT technology requires Molybdenum or Molybdenum alloys to be a barrier between the transistors and glass substrates. It provides a stable layer, which has a good adhesion to glass, onto which to deposit the conductive layer, while protecting the circuitry from subsequent etching processes. The purity of the Molybdenum will tell how effective the bond to the glass substrate is and the evenness of the coating. Any impurities within will cause splashing and an uneven coating.
 
A magnetron sputtering process deposits the Molybdenum coating which induces plasma ions of a gas to bombard a Molybdenum target. Then the surface atoms of the target material are deposited onto the surface of the substrate. The most common form of target is the planar disc or rectangle (although rotary tubes are also used) bonded to a Copper backing plate.
 
Although the size of the plate depends on the size of the substrate to be coated, there is a push towards larger plates in order to improve the cost/area for TFT LCD production.

Organic LED Technologies

OLEDs are used in the same consumer electronic applications as TFT LCD FPD but they do not require backlighting panels. Therefore they offer improved energy usage and are thinner and lighter. For higher resolution and larger displays, many OLEDs use a thin film transistor backplane to switch each individual pixel on or off, similar to TFT LCD technology.
 
OLEDs contain a very thin (250 nm) layer of Molybdenum Aluminum, which is on a glass substrate and is used as a buffer layer to the Indium Tin Oxide electrode material. This layer improves reflectivity and is much thinner than that used in TFT LCD technologies. Although it is expected that the growth and commercialization of OLED displays will use more of Molybdenum, this may not increase the tonnage because of the reduced sputtering thickness.

Solar

Photovoltaic technologies used in capturing energy from sunlight in solar panels have focused on the cost per kw energy produced as well as the increasing efficiency gained from the production of energy from daylight rather than direct sunlight. As Silicon prices rise to the demand of the solar industry, two type of thin film technologies have become commercially available; both of which utilize Molybdenum.

Copper Indium Gallium Selenide (CIGS) PV Technology

CIGS is a semiconductor material can be used for the manufacturing of solar cells because the material is strongly absorbent to sunlight. This results in less material than silicon based technologies, which reduces the cost while maintaining efficiency. In a CIGS solar cell, the CIGS absorber material is deposited onto a thin film of Molybdenum which is attached via sputtering to a glass substrate. The Molybdenum serves as both the back electrical contact and is used to reflect any unabsorbed light back to the absorbing layer.

Cadmium Telluride (CdTe) PV Technology

CdTe technology was developed as a lower cost alternative to Crystalline Silicon. It uses Cadmium Telluride semiconductor material to absorb light. CdTe enables high-volume, low-cost production of solar modules in a continuous, automated process that uses less semiconductor materials. Molybdenum is used as the metal buffer layer because it is chemically compatible with the CdTe material and is extremely stable. It is deposited as a thin film via sputtering.