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Design And Construction Of Bipolar Pulsed-DC Power Supply For Magnetron Sputtering System

Tosawat Seetawan, Weerasak Somkhunthot, Thanusit Burinprakhon, Ian Thomas, Vittaya Amornkitbamrung

A bipolar pulsed-dc power supply has been designed and constructed for used in a magnetron sputtering system and for thin film synthesis. The power supply consists of three major parts: (1) Two high voltage direct current (dc) power supplies utilizing a phase control circuit for power delivery, (2) Pulse generator and two power switching circuits, and (3) Feedback circuits for current and voltage controls, displays, and safety measures. For a high level of safety operation, optical connections were employed in the circuit design to isolate between the low and high voltage parts. The constructed power supply was tested using a test load consisting of ten 100 W 250V light bulbs with tungsten filaments connected in series. It was found that the power supply was capable of supplying either symmetric or asymmetric pulsed-dc power of maximum peak-to-peak voltage of 1250 V. The negative and positive pulse widths were selectable between 10-100 s, with maximum pulse frequency of 25 kHz. This frequency limit is due to the limited speed of the power transistors used in the power switching circuit operating under high voltage. It is anticipated that the constructed power supply can be used as a plasma generator in a magnetron sputtering system for the deposition of oxide thin films such as Al2O3, NaxCo2O4, ITO and ZnO. This will be further investigated.