Thermal Pulse Method for Space Charge Measurement in Micrometer-Thin Polyimide Films Under Ultrahigh Temperature

Thermal Pulse Method (TPM) technique, which can reach the spatial resolution of sub-micron level, exhibits significant advantages in elevated temperature for space charge measurement in micrometer-thin polymer films. With enhancements to the heating and measurement setup, the TPM—which inherently operates without the need for sensing elements—enables accurate determination of space charge and internal electric fields in 8 μm-thick polyimide (PI) films across a wide temperature range from 25 °C to 250 °C. The experimental results indicate that elevated temperatures can significantly influence charge accumulation and evolution in polyimide (PI). While charge injection is nearly symmetric between positive and negative carriers at room temperature, a dominant accumulation of negative charges is observed above 100 °C. This tendency intensifies with temperature, and at 250 °C, the resulting electric field distortion approaches 30%.