Development of a flat cutoff probe covered with a dielectric layer for non-invasive plasma diagnostics

Abstract Herein, we investigated the effect of a dielectric film on the transmission spectrum of a bar-type flat cutoff probe (BCP). By conducting electromagnetic wave simulations, we found that placing a dielectric film with a thickness of 1 mm or less on the sensor did not affect the measurement of the BCP under thin sheath condition. However, a film thickness of 1 mm or more results in a low-frequency shift in the cutoff frequency. The shift in the cutoff frequency was related not only to the film thickness, but also to the dielectric constant of the film and sheath width, which could be understood through a circuit model of the BCP. The calculated results were experimentally validated using alumina plates of various thicknesses. Consequently, our findings demonstrate that measuring the electron density on a BCP is feasible even when a dielectric film is deposited, thereby improving the accuracy of the measurement.