Electrode modulated capacitance-electric field nonlinearity in metal-insulator-metal capacitors

摘要

Metals with low enthalpy of oxide formation (∆H_(OX)) are used to examine the influence of the metal/dielectric interface, in the absence of a significant interfacial layer oxide (ILO), on the voltage nonlinearity of capacitance for metal-insulator-metal capacitors. For both atomic layer deposited AI_2O_3 and HfO_2 dielectrics, Ag electrode devices show the lowest quadratic electric field coefficient of capacitance (a_(ECc)), followed in increasing order by Au, Pd, and Ni. The difference between the metals is greater for thinner dielectrics, which is consistent with increased influence of the interface. In addition, with decreasing dielectric thickness the quadratic voltage field coefficient of capacitance increases, whereas α_(ECC) decreases. It is proposed that the thickness dependencies are due to an interaction between vertical compression of the dielectric under an applied bias and the concomitant lateral expansion induced stress that is concentrated near the interface. Through this interaction, the metal interface inhibits lateral expansion of the dielectric resulting in a reduced α_(ECC)- Indeed, α_(ECC) is found to increase with the increasing lattice mismatch at the metal/dielectric interface, likely due to edge dislocations. Finally, Al, a high ∆H_(OX) metal, is found to fit the trend for AI_2O_3 but not for HfO_2, due to the formation of a thin reduced-k ILO at the HfO_2/Al interface. These results suggest that minimization of metal/dielectric lattice mismatch may be a route to ultra-low nonlinearity in highly scaled metal-insulator-metal devices.