Effects of Frequency and Bias Voltage on Dielectric Properties and Electric Modulus of Au/Bi4Ti3O12/n-Si (MFS) Capacitors

Abstract

In this work, a metal-ferroelectric-semiconductor (MFS) type capacitor was fabricated and admittance measurements were held in a wide frequency range of 1 kHz-5 MHz at room temperature for the investigation of frequency and voltage dependence of complex dielectric constant, complex electric modulus and electrical conductivity of the MFS capacitor . Bismuth titanate (Bi 4 Ti 3 O 12 ) with high dielectric constant was used as interfacial ferroelectric material and the structure of MFS capacitor was obtained as Au/Bi 4 Ti 3 O 12 /n-Si. Experimental results showed that dielectric, modulus and conductivity parameters are strong functions of frequency and voltage especially in depletion and accumulation regions due to the existence of surface states (N ss ), series resistance (R s ), interfacial polarization and interfacial layer. It was found that R s of the structure and interfacial ferroelectric layer are efective in accumulation region whereas surface states (N ss ) and interfacial polarization are efective in depletion region. Also the changes in dielectric, modulus and conductivity parameters become considerably high particularly at low frequencies due to high values of R s and N ss . The observed anomalous peak in voltage dependent plots of capacitance and dielectric constant was atributed to the particular density distribution of N ss , R s and minority carrier injection. Moreover, the value of conductivity at low and intermediate frequencies is almost independent of frequency thus low frequency data was used to extract d.c. conductivity. This work showed that the use of high-dielectric Bi 4 Ti 3 O 12 as ferroelectric interfacial layer in a MFS capacitor is preferable due to high values of its dielectric constant compared with traditional insulator layer materials such as SiO 2 and SnO 2 . Therefore, a MFS capacitor with Bi 4 Ti 3 O 12 interfacial layer can store more energy thanks to its high dielectric constant.