Electrical properties of the amorphous BaTi₄O₉ thin films for metal-insulator-metal capacitors

Amorphous BaTi₄O₉ (BT₄) film was deposited on Pt/Si substrate by RF magnetron sputter and their dielectric properties and electrical properties are investigated. A cross sectional SEM image and AFM image of the surface of the amorphous BT₄ film deposited at room temperature showed the film was grown well on the substrate. The amorphous BT₄ film had a large dielectric constant of 32, which is similar to that of the crystalline BT₄ film. The leakage current density of the BT₄ film was low and a Poole-Frenkel emission was suggested as the leakage current mechanism. A positive quadratic voltage coefficient of capacitance (VCC) was obtained for the BT₄ film with a thickness of <70 nm and it could be due to the free carrier relaxation. However, a negative quadratic VCC was obtained for the films with a thickness ≥96 nm, possibly due to the dipolar relaxation. The 55 nm-tbick BT₄ film had a high capacitance density of 5.1 fF/μm² with a low leakage current density of 11.6 nA/ cm² at 2 V. Its quadratic and linear VCCs were 244 ppm/V² and -52 ppm/ V, respectively, with a low temperature coefficient of capacitance of 961 ppm/°C at 100 kHz. These results confirmed the potential suitability of the amorphous BT₄ film for use as a high performance metal-insulator-metal (MIM) capacitor.