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

Abstract

Metals with low enthalpy of oxide formation (ΔHox) 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 Al2O3 and HfO2 dielectrics, Ag electrode devices show the lowest quadratic electric field coefficient of capacitance (αECC), 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 αECC 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 αECC. Indeed, αECC is found to increase with the increasing lattice mismatch at the metal/dielectric interface, likely due to edge dislocations. Finally, Al, a high ΔHox metal, is found to fit the trend for Al2O3 but not for HfO2, due to the formation of a thin reduced-k ILO at the HfO2/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.