We present the circuit design of a unit for medium-frequency modulated direct-current (dc) reactive sputter deposition of electrical insulators. The unit is connected in series between a commercial dc sputtering power supply and a sputtering cathode (target). It modulates the voltage applied to the sputtering cathode in a pulsed, asymmetric bipolar fashion. The pulsing effectively eliminates the problem of arcing at the target surface. The simple circuit is a low-cost, flexible alternative to commercially available units. To demonstrate its utility, we deposited a film of 5 SiO2/TiO2 bilayers, forming a highly reflective dielectric optical mirror with a stop band centered near a wavelength in air of 600 nm.
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