On the profile of frequency dependent series resistance and surface states in Au/Bi4Ti3O12/SiO2/n-Si(MFIS) structures

The frequency dependent capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the metal-ferroelectric-insulator-semiconductor (Au/Bi₄Ti₃O₁₂/SiO₂/n-Si) structures (MFIS) were investigated by considering series resistance (R_s) and surface state effects in the frequency range of 1 kHz-5 MHz. The experimental C-V-f and G/ω-V-f characteristics of MFIS structures show fairly large frequency dispersion especially at low frequencies due to R_s and N_ss. In addition, the high frequency capacitance (C_m) and conductance (G_m/ω) values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real capacitance of MFIS structures. The R_s-V plots exhibit anomalous peaks between inversion and depletion regions at each frequency and peak positions shift towards positive bias with increasing frequency. The C⁻²-V plot gives a straight line in wide voltage region, indicating that interface states and inversion layer charge cannot follow the ac signal in the depletion region, but especially in the strong inversion and accumulation region. Also, it has been shown that the surface state density decreases exponentially with increasing frequency. The C-V-f and G/w-V-f characteristics confirm that the interface state density (N_ss) and series resistance (R_s) of the MFIS structures are important parameters that strongly influence the electrical properties of MFIS structures.