Enhanced Performance of Non-stoichiometric BZN-based Thin Film Varactor through Surface Electric Field Effect

s In this work, Bi-Zn-Nb base cubic pyrochlore with A 2 B 2 O 7 structure was purposefully trimmed to make Zn ions in the A site slightly deviate from stoichiometric ratios, and non-stoichiometric (Bi 1.5 Zn 0.5+x )(Zn 0.5 Nb 1.5 )O 7.0+x (BZN, -0.15 ≤ x ≤ 0.05) thin films were fabricated on FTO (fluorine-doped tin oxide) electrodes using the sol-gel process. The structural characterization results confirmed that the phase structure of the BZN films remained cubic pyrochlore after little composition shift. It was found that proper reduction of Zn content can optimize the performance of BZN films, and thin film with a composition corresponding to x = -0.1 demonstrated optimal crystallinity and superior dielectric properties. More specifically, this film exhibited a high tunability of 19.26% (1.17 MV/cm), relatively low loss tangent of 0.0089, and a large figure of merit of 21.6. Furthermore, by introducing the semiconductor FTO as the bottom electrode, the coefficient of the dielectric nonlinearity β for the sol-gel BZN film has been optimized, which is 180% of higher than that of on metal Pt electrode. The excellent properties are attributed to the combination effect of the intrinsic tuning characteristic of non-stoichiometric BZN cubic pyrochlore and the surface electric field effect in Metal Insulator Semiconductor (MIS) structure. This research provides a promising approach to boost the performance of functional thin film electronic devices.