The new application of boron-doped diamond film: Attenuator for high frequency and high power vacuum electronic devices

Abstract

Boron-doped diamond film which was used as microwave attenuation material was prepared by DC arc jet chemical vapor deposition (CVD) and the boron-doped diamond attenuator for W-band traveling wave tube (TWT) was fabricated. The effects of boron concentration on microstructure, mechanical property and dielectric property were analyzed. Meanwhile, the performance of boron-doped diamond attenuators was evaluated. The results showed that the fracture strength of boron doped diamond was higher than 400 MPa, although it was slight decreased with the increasing of boron content in the diamond films. Very interestingly, the fracture strength of growth side was larger than that of nucleation side, the twinning band within the grains in the growth side play a critical role for this phenomenon. With the boron concentration increasing from 6.1 × 1018 cm−3 to 23.5 × 1018 cm−3, the average loss tangent of diamond films was increased from 0.05 to 0.32 in the range of 75–110 GHz, which indicated that the complex permittivity of diamond film could be controlled by tailoring boron content. Furthermore, the return loss and insertion loss of the boron-doped diamond attenuator was below −20 dB and −40 dB, respectively. These findings indicated that the boron-doped diamond displayed low reflection and good microwave attenuation. The boron-doped diamond attenuator was promising for using in vacuum electronic device with high performance.