Investigation of TiN film on an RF ceramic window by atomic layer deposition

To reduce the secondary emission yield of an RF window ceramic so as to suppress the occurrence of a multipactor, we propose coating the window with a titanium nitride (TiN) film by atomic layer deposition. We investigate two groups of samples with film thicknesses of 56 and 8 nm, respectively, to analyze the composition and optimize the coating thickness of the TiN film on the ceramic. For the first group of samples (56 nm films), x-ray photoelectron spectroscopy (XPS) results show that the film can be divided into three mixed layers: a top layer composed of TiOxNy and TiO2; a middle layer consisting of TiN, TiOxNy, TiO2, and TiC; and a bottom layer called a diffusion layer, formed by decreasing TiN, TiOxNy, TiO2, TiC, and increasing Al2O3 as the ceramic is approached. The depth of this bottom layer is ∼8 nm. Two more films (8 nm films) in the second group of samples were grown on a 96 ceramic and silicon to determine the sheet resistance, those on silicon is ∼1 kΩ/□ as measured by spectroscopic ellipsometry. According to the XPS results of the two 8 nm films, the content of TiOxNy and TiO2 increased while TiN content decreased in the film on 96 ceramic, compared to the film on silicon. Therefore, the 8 nm film is suitable for use as a coating for the RF window to weaken the multipactor effect and lower conductivity. To test the film performance, an RF ceramic window is coated with an 8 nm TiN film. Low-power measurements show that, within a frequency of 100 MHz, the 8 nm film on the RF ceramic window has a negligible effect on its transmission characteristics. 8 kW RF power tests indicate that the film coating can significantly improve the power transmission, anti-multipaction, and stability of the RF window.