Fabrication and Electrical Characterization of Radio Frequency Magnetron Sputtered BaSrTiO3/Si3N4 Bilayer Dielectric Thin Films Deposited on Platinized Silicon for Metal–Insulator–Metal Capacitor Applications

Metal–insulator–metal (MIM) capacitors based on engineered dielectric thin films are of interest for integrated electronic applications where controlled capacitance, low dielectric loss, and stable electrical response are required. In this work, the electrical response of single-layer BST and BST/Si 3 N 4 bilayer dielectric structures was comparatively investigated. Approximately 200 nm-thick barium strontium titanate (BST) and approximately 300 nm-thick BST/Si 3 N 4 bilayer dielectric stacks were deposited on platinized silicon substrates by RF magnetron sputtering, followed by fabrication of circular Cr/Au top electrodes to form Pt/BST/Au and Pt/BST/Si 3 N 4 /Au MIM capacitors. Film thicknesses were evaluated using stylus profilometry, while surface morphology was characterized by atomic force microscopy (AFM). The electrical characteristics were investigated from −20 to +20 V at frequencies of 100 kHz, 200 kHz, 500 kHz, 700 kHz, and 1 MHz. The BST capacitor exhibited a capacitance of approximately 4.934 × 10⁻¹¹ F at 100 kHz, which decreased to 4.648 × 10⁻¹¹ F at 1 MHz. After incorporation of the Si 3 N 4 layer, the capacitance decreased to approximately 2.217 × 10⁻¹¹ F at 100 kHz and 2.165 × 10⁻¹¹ F at 1 MHz, consistent with the increased dielectric thickness and series dielectric configuration. The effective dielectric constant of the BST capacitor varied from 5.669 to 5.361, whereas that of the BST/Si 3 N 4 structure varied from 3.827 to 3.737 over the investigated frequency range. The dielectric loss decreased from 0.0657 to 0.0470 for BST and from 0.0349 to 0.0247 for BST/Si 3 N 4 , corresponding to approximately 47% lower loss for the bilayer at 100 kHz and 1 MHz. The bilayer also exhibited lower measured conductance throughout the investigated frequency range. Stored charge, stored energy, and volumetric energy density were calculated from the measured capacitance and applied voltage rather than independently measured. At 100 kHz and ±20 V, the calculated volumetric energy density was approximately 2.5 × 10⁵ J m⁻³ for BST and 0.75 × 10⁵ J m⁻³ for BST/Si 3 N 4 . These results demonstrate that incorporation of Si 3 N 4 substantially modifies the effective electrical response of BST-based MIM capacitors, particularly by reducing the measured conductance and dielectric loss, while the lower effective capacitance results in lower capacitance-derived energy-storage quantities.