The origins and characteristics of negative capacitance in metal–insulator–metal devices

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Abstract
Impedance analysis of ZnS metal–insulator–metal structures has revealed strong negative capacitance behaviour. Under low-field conditions, the devices are highly insulating with capacitance consistent with their geometry and dielectric constant. However, at high fields they become conducting and the capacitance falls to zero and then becomes negative. It may exceed the geometrie value by over five orders of magnitude. This frequency-domain behaviour is explained in terms of the unusual time-domain behaviour of the devices. The origins of negative capacitance are shown to He in the modulation of the differential conductance by the a.c. measurement voltage, combined with the interpretation of the response in terms of an electrical equivalent circuit. The application of equivalent-circuit analysis to such systems is discussed. Negative capacitance has been observed in a wide range of other systems which can now also be understood within the theoretical framework presented.