Voltage-dependent capacitance behavior and underlying mechanisms in metal–insulator–metal capacitors with Al2O3–ZrO2–SiO2 nano-laminates

Abstract

Nano-laminates consisting of high-permittivity dielectrics and SiO2 have been extensively studied for radio frequency metal–insulator–metal (MIM) capacitors because of their superior voltage linearity and low leakage current. However, there are no reports on the capacitance–voltage (C–V) characteristics at a high sweep voltage range. In this work, an interesting variation in the voltage-dependent capacitance that forms a ‘ω’-like shape is demonstrated for the MIM capacitors with Al2O3/ZrO2/SiO2 nano-laminates. As the thickness ratio of the SiO2 film to the total insulator increases to around 0.15, the C–V curve changes from an upward parabolic shape to a ‘ω’ shape. This can be explained based on the competition between the orientation polarization from SiO2 and the electrode polarization from Al2O3 and ZrO2. When the SiO2 film is very thin, the electrode polarization dominates in the MIM capacitor, generating a positive curvature C–V curve. When the thickness of SiO2 is increased, the orientation polarization is enhanced and thus both polarizations are operating in the MIM capacitors. This leads to the appearance of a multiple domain C–V curve containing positive and negative curvatures. Therefore, good consistency between the experimental results and the theoretical simulations is demonstrated. Such voltage-dependent capacitance behavior is not determined by the stack structure of the insulator, measurement frequency and oscillator voltage, but by the thickness ratio of the SiO2 film to the whole insulator. These findings are helpful to engineer MIM capacitors with good voltage linearity.