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Case Study
 Solar photovoltaics are arrays of cells containing a material that converts solar radiation into direct current electricity. Materials presently used for photovoltaics include amorphous silicon, polycrystalline silicon, microcrystalline silicon, cadmium telluride, and copper indium selenide/sulfide. Due to the growing demand for renewable energy sources, the manufacture of solar cells and photovoltaic arrays has advanced dramatically in recent years.Physical vapor deposition (PVD) or sputtering is commonly used for creating films of material on a substrate in the solar energy and semiconductor industry. In the PVD process, a negatively charged electrode is slowly disintegrated by molecular bombardment. The PVD medium is typically argon because this gas generates sufficient momentum to free atoms from the target. In a vacuum environ¬ment, these free target atoms deposit themselves on the surface of the material and form the desired coating or plating. Maintaining a specified gas mass flow rate to the vacuum chamber is critical during the PVD process. Typically, vacuum pumping stations require a throttle valve or orifice-limiting device to control the pump’s output when the PVD gas is introduced. This method is extremely pressure sensitive and can result in inefficient gas delivery and poor product quality. PVD presents two critical challenges in the manufacturing of films used in solar photovoltaics. The first is the use of high vacuum. Since there is so little pressure drop to work with, PVD processes require flow control devices that are relatively insensitive to the absolute pressure in the chamber. This rules out devices like orifice plates that require a large pressure difference to operate efficiently. The second issue is maintaining very precise flow rates. Since the layers deposited by PVD processes can, in many cases, be only molecules thick, very precise delivery methods of the doping gases are required. The Smart Trak® 50 Series provides solutions for both of these challenges. Sierra's 50 Series with CompodTM automatically compensates for changes in system pressure (vacuum pump fluctuations) or loss of pressure from the gas source (cylinder depletion). By utilizing the best laminar flow element in the industry and a proprietary frictionless-hovering control valve, The SmartTrak 50 Series 2 with Compod delivers a precisely controlled gas mass flow rate to the vacuum chamber to maintain high quality end-product.   |
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