This paper introduces a terahertz (THz) temporal differentiator employing a planar resonator with a metal-polar material bilayer, specifically utilizing calcium magnesium carbonate (CaMg(CO3)(2)). The working mechanism is based on strong interference in the metal and the optical phonon response of the CaMg(CO3)(2) thin film. Simulation results indicate that this lithography-free planar resonator exhibits first-order time derivative characteristics, with an operational bandwidth of approximately 400 GHz. The proposed differentiator exhibits potential applications in the domain of ultrafast analog computing and signal processing devices.