High density Al₂O₃/TaN-based metal--insulator-- metal capacitors in application to radio frequency integrated circuits

Metal--insulator--metal (MIM) capacitors with atomic-layer-deposited Al_2O_3 dielectric and reactively sputtered TaN electrodes in application to radio frequency integrated circuits have been characterized electrically. The capacitors exhibit a high density of about 6.05 fF/\mu m^2, a small leakage current of 4.8\times 10^-8 A/cm^2 at 3 V, a high breakdown electric field of 8.61 MV/cm as well as acceptable voltage coefficients of capacitance (VCCs) of 795 ppm/V^2 and 268 ppm/V at 1 MHz. The observed properties should be attributed to high-quality Al_2O_3 film and chemically stable TaN electrodes. Further, a logarithmically linear relationship between quadratic VCC and frequency is observed due to the change of relaxation time with carrier mobility in the dielectric. The conduction mechanism in the high field ranges is dominated by the Poole--Frenkel emission, and the leakage current in the low field ranges is likely to be associated with trap-assisted tunnelling. Meanwhile, the Al_2O_3 dielectric presents charge trapping under low voltage stresses, and defect generation under high voltage stresses, and it has a hard-breakdown performance.