Comprehensive dielectric performance of bismuth acceptor doped BaTiO3 based nanocrystal thin film capacitors

Abstract

We present a novel approach to preparing bismuth acceptor doped barium titanate nanocrystal formulations that can be deposited in conjunction with polymers in order to prepare a thin film nanocomposite dielectric that exhibits desirable capacitor characteristics. Exploring the limits of dielectric function in nanocomposites is an important avenue of materials research, while paying strict attention to the overall device quality, namely permittivity, loss and equivalent series resistance (ESR). Pushing capacitor function to higher frequencies, a desirable goal from an electrical engineering point of view, presents a new set of challenges in terms of minimizing interfacial, space charge and polarization effects within the dielectric. We show the ability to synthesize BaTi_0.96Bi_0.04O₃ or BaTi_0.97Bi_0.03O₃ depending on nominal molar concentrations of bismuth at the onset. The low temperature solvothermal route allows for substitution at the titanium site (strongly supported by Rietveld and Raman analysis). Characterization is performed by XRD with Rietveld refinement, Raman Spectroscopy, SEM and HRTEM. A mechanism is proposed for bismuth acceptor substitution, based on the chemical reaction of the alkoxy-metal precursors involving nucleophilic addition. Dielectric analysis of the nanocrystal thin films is performed by preparing nanocrystal/PVP 2–2 nanocomposites (no annealing) and comparing BaTi_0.96Bi_0.04O₃ and BaTi_0.97Bi_0.03O₃ with undoped BaTiO₃. Improvements of up to 25% in capacitance (permittivity) are observed, with lower loss and dramatically improved ESR, all to very high frequency ranges (>10 MHz).