High Temperature Dielectric Behavior of Al/Polyimide/Al Capacitor Structures

An unstable behavior of Al/polyimide/Al capacitor structures has been observed by isothermal dielectric spectroscopy at 275degC with a progressive decrease of the dielectric permittivity and the loss factor. In spite of a close similarity with the typical dielectric behaviors involved by crystallization phenomena for crystallizable polymers, DSC measurements have not exhibited an exothermic crystallization peak up to 500degC which can exclude this assumption. Moreover, residual polar impurities such as moisture, solvent and polyamic acid, seems to have been completely removed of the PI films after a high temperature process curing at 400degC, as shown by FTIR spectroscopy. These elements lead to prove that the dielectric stabilization should not be due to PI bulk chemical changes, but could involve an evolution of the metal/PI interface.