915 MHz rectangular shape microwave reactor for large-size diamond growth based on microwave engineering design

The utilization of 915 MHz microwave reactors is crucial for large-sized single crystal and polycrystalline diamonds growth. Optimizing the performance of the 915 MHz cavity can further improve diamond deposition size and quality. In this study, we propose a 915 MHz rectangular cavity based on the expansion of 2.45 GHz and optimize cavity performance, power and frequency stability, and electric field distribution using a three-dimensional numerical model. Our electromagnetic and plasma simulations, compared to cylindrical cavities, demonstrate that the rectangular cavity effectively couples with TM021, TM031, and TM011 modes, enabling precise control of microwave energy distribution, electric field intensity, and uniformity in the deposition region by adjusting the cavity’s side length. In contrast to the 2.45 GHz rectangular cavity, the 915 MHz cavity exhibits an enlargement of ∼8 times in the plasma region area while maintaining the same level of electric field intensity. In addition, this cavity design avoids high-field regions outside the deposition area, enabling stable deposition at high power to extend the deposition area. With the increase in input power from 20 to 75 kW, the area range of the equivalent plasma density expands by ∼4 times. The implementation of the rectangular cavity enhances the deposition flexibility of the microwave reactor, making it applicable to diverse diamond required for different applications.