Effects of Imidization Process on the Electric Breakdown Strength of Polyimide Thin Film

The electric breakdown voltage (Vbd) is a fundamental performance index for insulation thin film in MEMS, and plays a dominant role for the operation reliability of this kind of devices. In this work, positive polyimide (PI) photoresist was used to prepare thin films by spin-coating and thermal imidization. Electric breakdown experiments were carried out under DC voltage mode. The effect of imidization temperature on Vbd was also studied by setting three different imidization temperature profiles. XRD was applied to test the composition and microstructure of the PI thin films. Results show that the imidization degree of the PI thin film will be increased with the raising of the imidization temperature from 280 to 350°C. This means that a more completed imidization process can be achieved in the PI thin film by using higher imidization temperature. The highest Vbd of about 2740V and an average Vbd of 343kV/mm can be achieved on a 8.5μm thick PI thin film imidized at 350°C.