RF MIM capacitors using Si3N4 dielectric in standard industrial BiCMOS technology

Metal-insulator-metal (MIM) capacitors are frequently applied in monolithic RF and microwave. Several 0.25 μm-BiCMOS standard Si technology MIM capacitors with different device geometries were realised, measured and modeled in the GHz frequency range. Two different insulators are compared: SiO₂ of permittivity 4.2 and Si₃N₄ of permittivity 7.5. The theoretical SiO₂ and Si₃N₄ capacitance densities are respectively 1.06 fF/μm² and 2.07 fF/μm² for thickness of 35 nm and 32 nm. Experimental devices were characterised using a HP8720ES network analyser and on-wafer measurements with microwaves probes. The parasitic capacitances of the pad frame were accurately subtracted from the measurement data with a SOLT calibration and with an open de-embedding structure. A lumped element equivalent circuit for MIM capacitor is used to represent the different capacitors and other surrounding elements. All capacitor were analysed and experimental S-parameters were compared to the lumped element equivalent circuit, using agilent-advanced design system software. Good agreements between measured data and models were achieved between 45 MHz and 18 GHz for capacitances between 0.5 pF and 20.7 pF.