Investigation of Space Charge Detection in Micron Polyimide Films Based on Waveform Symmetry of Thermal Response Current

The electrical performance including conduction, aging and breakdown of polymer films is strongly related to the space charge behaviors. However, due to the limitation of spatial resolution, acoustic-based methods including Pressure Wave Propagation (PWP) method and Pulsed Electro-Acoustic (PEA) method are difficult to meet the measurement requirements for the micrometer-thick films. Although Thermal pulse method (TPM) can offer spatial resolutions better than sub-micrometer levels, complex signal processing involving amplitude-frequency conversion and deconvolution algorithms are required. Therefore, it is necessary to develop a simpler method of space charge detection for polymer films. This study proposes a semiquantitative estimation method for space charge distribution based on the waveform symmetry of thermal response current. The comparison of positive and negative thermal response current indicates that when the field is below <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20 ~\mathrm{V} / \mu \mathrm{m}$</tex>, the positive and negative thermal response current waveforms showed consistent symmetry. However, as the field intensity further increased, discernible discrepancies emerged in amplitude between positive and negative waveforms, indicating localized electric field distortion caused by space charge accumulation. Therefore, this asymmetric disparity between positive and negative thermal response current enables semi-qualitative determination of both the existence and polarity of accumulated space charges through comparative waveform analysis, which correlates with the injection mechanism of space charges. The method based on the waveform symmetry of thermal response current avoids complex signal processing algorithms and demonstrates superior simplicity in space charge detection.