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A simple technique for measuring the thermal diffusivity of dielectric films on thermally sinking substrates is proposed and demonstrated. It is an outgrowth of the thermal pulse technique for measuring charge and polarization profiles. The thermal diffusivity is derived from the transient electrical response induced by a thermal pulse applied to a dc voltage-biased sample. Because the response is proportional to the bias voltage, the signal-to-noise ratio is adjustable independently of the thermal pulse energy and may be made as large as required for determining the diffusivity with high precision. Measuring times of around 1 ms or shorter are sufficient for polymers with thicknesses up to 10 μm. Experimental results for two different polyimide films spin coated on crystalline silicon substrates are presented and discussed.

The transient pyroelectric response of a dielectric film on a substrate is used to determine both the electricfield 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 ratio͒, 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.

This paper is the first of a series with the common theme of comparing thermal and acoustic pulse methods of measuring charge or polarization profiles across the thickness of slabshaped samples that are representative of different types of materials. In this paper, thermal and pressure pulse measurements are reported of the polarization distribution in poled, ferroelectric ceramic samples. The results obtained from both methods are complementary so that there is a benefit to using both. The results also demonstrate that large deviations from uniform polarization can be induced by processing differences. 854

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