VCC-α nullification and leakage reduction in Pt/Ba_0.5Sr_0.5TiO₃/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-Ba 0.5 Sr 0.5 TiO 3 (BST) interface barrier layer and post deposition annealing (PDA) on voltage coefficient of capacitance and leakage current density in Pt/Ba 0.5 Sr 0.5 TiO 3 /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/Ba 0.5 Sr 0.5 TiO 3 /MgO/Pt thin-film capacitor at 700 0 C in O 2 gas environment for 30 min nullifies quadratic voltage coefficient of capacitance (VCC-α). The VCC-α obtained for asdeposited capacitor is −34408 ppm V −2 while that of capacitor annealed at 700 0 C 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 0 C. The diffraction peaks in XRD pattern of capacitor annealed at 700 0 C indicate good crystallinity achieved in Pt, Ba 0.5 Sr 0.5 TiO 3 and MgO layers due to high-temperature PDA process. This substantiates the best leakage current characteristics in Pt/MgO/Ba 0.5 Sr 0.5 TiO 3 /MgO/Pt thin-film capacitor annealed at 700 0 C 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 0 C 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.