VCC-α nullification and leakage reduction in Pt/Ba0.5Sr0.5TiO3/Pt thin-film capacitor by MgO barrier and PDA for energy storage application

Abstract

A critical performance parameter of thin-film metal–insulator–metal capacitors when used for energy storage application is leakage current. Introduction of another insulator barrier layer at metal–insulator interface having low electron affinity enhances leakage current performance. The probability of deterioration in capacitance is higher while enhancing leakage performance by barrier layer establishment. The effects of Pt-Ba0.5Sr0.5TiO3 (BST) interface barrier layer and post deposition annealing (PDA) on voltage coefficient of capacitance and leakage current density in Pt/Ba0.5Sr0.5TiO3/Pt thin-film capacitor are reported in this paper. The capacitance measurement is done at low frequency as it meant for energy storage. It is observed that PDA of Pt/MgO/Ba0.5Sr0.5TiO3/MgO/Pt thin-film capacitor at 700 0C in O2 gas environment for 30 min nullifies quadratic voltage coefficient of capacitance (VCC-α). The VCC-α obtained for as-deposited capacitor is −34408 ppm V−2 while that of capacitor annealed at 700 0C is 4.88 ppm V−2 which is the least VCC-α ever reported. A gradual leakage current performance enhancement is observed while increasing annealing temperature and a very low leakage current density of 48 nA cm−2 is observed when annealed at 700 0C. The diffraction peaks in XRD pattern of capacitor annealed at 700 0C indicate good crystallinity achieved in Pt, Ba0.5Sr0.5TiO3 and MgO layers due to high-temperature PDA process. This substantiates the best leakage current characteristics in Pt/MgO/Ba0.5Sr0.5TiO3/MgO/Pt thin-film capacitor annealed at 700 0C than as-deposited capacitor and capacitor annealed at lower temperatures. Further we observed an energy band gap enhancement of 0.055 eV in every 100 0C rise in temperature from the UV–Vis NIR spectroscopy. This continuous energy band gap enhancement while increasing annealing temperature also justifies the reduction in leakage current density at high PDA temperature.