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Complex impedance and non-linear response were measured for high-dielectric composite films at AC voltages using a waveform technique. With decreasing dielectric thickness, these materials operate at higher electric fields, which cause non-linear dielectric effects and lead to a time dependent dielectric-breakdown. The waveforms were Fourier transformed from time domain to frequency domain and analyzed at fundamental and higher order harmonic frequencies. It was found that the conventional epoxy resin laminates exhibit an impedance characteristic that is nearly independent on applied electric field, up to the material dielectric breakdown. When the electric field approaches near dielectric breakdown conditions, the second-order non-linear dielectric susceptibility decreases abruptly while the third harmonic response dominates non-linear dielectric behavior. In comparison, the impedance of dielectric materials made of organic resins and ferroelectric ceramics decreases continuously with increasing voltage. The non-linear dielectric effect is dominated by the third harmonic response that originates from a polarization reversal of the ferroelectric component. When the electric field approaches near dielectric breakdown conditions, again, the second-order non-linear dielectric susceptibility decreases abruptly.