Dielectric properties of CVD diamond for radiofrequency window applications

Free-standing discs of CVD diamond were produced with a new technique by which windows with a diameter up to 6 inches can be formed. Specimen sets grown with this technique were studied for their dielectric parameters in a wide frequency range from 10(exp 3) Hz up to 10(exp 11) Hz by different methods (LCR meter, Hybrid cavity, Fabry-Perot resonator) at room temperature. In addition the temperature dependence of loss tangent (tan delta) was investigated in the cryogenic (70 K to 300 K) and high temperature (300 K to 700 K) regime. In the best grades, values of tan delta lower than 5x10(exp -5) at 145 GHz (300 K) were obtained.