Electric-field profile and thermal properties in substrate-supported dielectric films

The transient pyroelectric response of a dielectric film on a substrate is used to determine both the electric-field profile across the film and its thermal properties. The response is a convolution of the field and temperature profile. A closed-form expression for the transient temperature profile is obtained for a generic model in terms of thermal parameters. This expression allows analysis of the pyroelectric response using an iterative procedure consisting of deconvolution and variation of thermal parameters. Tikhonov regularization is used in the deconvolution with a Honerkamp-Weese self-consistent regularization parameter. Simulations show that, at least in the cases tested, the electric-field profile, the thermal diffusivity and conductivity (and thus the heat capacity, which is their ratio), and the thermal resistance of the dielectric/substrate interface can be determined. Experiments on polyimide films adhered to substrates unambiguously reveal bound negative charge within a small depth of the free surface of virgin samples and also weaker, broader charge distributions injected from the substrate in samples under an applied voltage. The analysis resolves both sharp and broad features and gives thermal properties characteristic of the near-surface region, suggesting that the heat capacity may be significantly higher in this region than in the bulk.