A power supply device for plasma processing, wherein electric arcs may occur, comprises a power supply circuit for generating a voltage across output terminals, and a first switch connected between the power supply circuit and one of the output terminals. The system includes a switching system comprising at least one power transistor for each of a plurality of phases of a disk-drive spindle motor. The copper precursor is in the form of a CuCl or CuBr composition in a nonaromatic, nonplanar and heteroatom-free liquid organic solvent which exhibits at least two nonconjugated unsaturations. This description is not intended to be a complete description of, or limit the scope of, the invention. The bias circuit which supplies a bias voltage to the last amplifying stage includes a circuit which produces a bias voltage which has a nonlinear response to the control signal for high-power mode. A dielectric layer of a stepwise laminate structure is formed on the AlGaN layer so that the electric field distribution between the gate Schottky electrode and the drain ohmic electrode is substantially uniformed.