Designing a 40.68 MHz power-combining resonant inverter with eGaN FETs for plasma generation

This paper presents the design of a 40.68 MHz, 1.2 kW power-combining resonant inverter using eGaN FETs for plasma generation. Operating at very high frequency (VHF) allows the use of smaller passive components and has the potential to improve the power density of an RF power amplifier for plasma applications. To provide high power at 40.68 MHz switching frequency, a class Φ2 inverter topology with wide band gap (WBG) devices such as eGaN FETs was selected. Using WBG devices in resonant inverters helps us increase switching frequencies while providing relatively higher efficiency compared to silicon devices. In contrast to using RF MOSFETS with large on-resistance and input capacitance, using eGaN FETs with lower on-resistance and input capacitance results in relatively higher efficiency of resonant inverters. However, these FETs in high-power operation cannot effectively dissipate heat at VHF. To reduce the losses in each eGaN FET, we designed and implemented the power-combining inverter based on a class Φ2 inverter to provide 1.2 kW output power at 40.68 MHz. The tuning method of a single class Φ2 inverter enables us to easily connect four inverters in parallel, creating a power-combining inverter that increases the output power. Also, the proposed inverter topology reduces the power loss in each switching device, which can decrease the size of the heat sink. This study demonstrates that power-combining resonant inverters using eGaN FETs can increase efficiency and power density while operating at 40.68 MHz.