In this study, Zn0.15Nb0.3Ti0.55O2(ZNT)/polyolefin substrates filled with SiO2 ((83 − x) ZNT/xSiO2/polyolefin, x = 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.% and 25 wt.%) have been fabricated to realize a near-zero temperature coefficient of dielectric constant ( \(\tau_{\varepsilon }\) ). Specifically, modified fillers and polyolefin composite substrates were obtained by the doctor-blade method and hot-pressing. The successful modification of ceramics by the coupling agent A171 was confirmed through Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), and contact angle tests. The microstructure, dielectric properties, and thermal performance of the composite substrates were also analyzed. The findings indicate that the thermal properties of the composite substrates remain unaffected by the substitution of ZNT with SiO2 fillers. The agglomeration of ceramic filler particles in the matrix leads to localized regions with significantly higher polarization intensity compared to the uniformly dispersed state. This abnormal local polarization weakens the overall polarization effect, thereby resulting in a decrease in the dielectric constant. Due to the positive \(\tau_{\varepsilon }\) of SiO2, the original system has a negative \(\tau_{\varepsilon }\) , resulting in a composite substrate with a near-zero \(\tau_{\varepsilon }\) according to the principles of the mixing rule. As a result, when x = 25 wt.%, the composite substrates realized medium dielectric constant ( \(\varepsilon_{r}\) = 6.29), low dielectric loss ( \({\text{tan}}\delta\) = 0.0016), and near-zero \(\tau_{\varepsilon }\) (+1.14 ppm/°C). These findings indicate the potential of these composites in advanced electronic applications.
