Energy storage performance of BTCO/BTS bilayer thin film capacitor

Abstract

Ferroelectric (FE) capacitors can be energy storage device with a high power density, but a low energy density (Ud) compared to those of electrochemical energy storage devices is a serious hindrance for the FE energy storage applications. To increase the Ud of ferroelectric capacitors, energy loss during discharging process should be suppressed. Relaxor ferroelectrics (RFE) are a primary choice to reduce the ferroelectric loss of FE capacitor; however, conduction loss exponentially increases at the high electric field eventually leading to device breakdown with low breakdown strength (Eb). In this study, to enhance Ud under high Eb, FE/RFE bilayer capacitors are developed using Co-doped BaTiO3 (BTCO)/ Sn doped BaTiO3(BTS) epitaxial thin films. The FE and RFE epitaxial layers were optimized to achieve an ultrahigh energy density of 117.3 J/cm3 with an Eb of 6.96 MV/cm from BTCO/BTS bilayer capacitor, which outperforms the BTS and BTCO single layer capacitors. The high Eb and Ud of BTCO/BTS bilayer capacitor are attributed to the suppression of conduction loss due to the breaking of leakage path formation at the interface of BTCO and BTS layer. The electric field cycling and thermal stability of the bilayer capacitor were stable up to 10^8 cycles. Bilayer engineering of RFE/FE structure is a promising strategy to enhance the Eb through which a high Ud can be achieved.