Dielectric Properties of Plasma-Polymerized Hexamethldisiloxane Films: 1 Complex Permittivity

Prompted by our extensive earlier studies of structure and properties of plasma-polymerized hexamethyldisiloxane (PPHMDSO) films prepared under different fabrication conditions, we have investigated their dielectric properties. The complex per-mittivity ε*=ε'-𝒾ε" has been measured over a wide frequency range (10-2 to 104 Hz), as a function of temperature ( 25°C to > 300°C) and ambient relative humidity. The principal fabrication variable, substrate temperature Ts, was varied from 25°C to 400°C. Films prepared at Ts=25°C show the same instability towards atmospheric oxygen and humidity, and concomitant high dielectric losses, reported in t-he literature by other workers. On the other hand, films prepared at Ts=400°C show low losses (tanδ≈7x10-4), little susceptibility to aging, and low moisture absorption. Films deposited at intermediate values of Ts display behavior lying between these two extremes. We correlate the observed dielectric properties with film structure and morphology, and describe a hitherto unreported low-frequency dielectric relaxation due to absorbed humidity.