Pulsed measurements of Fowler-Nordheim tunneling current in metal-insulator-metal capacitors
Metal-insulator-metal (MIM) structures where the insulator is a ferroelectric are being developed for use as a resistive random access memory. A fundamental property of these structures is the metal/ferroelectric barrier height which determines the current and depends on the ferroelectric polarization. This project explored whether the Fowler-Nordheim (FN) tunneling characteristics can be observed in MIM diodes, from which the metal-FE barrier can be directly extracted. A set of MIM structures was prepared to examine the insulators HfO2, ZrO2, ferroelectric HfZrO2, and Si3N4. A M-SiO2-Si structure was also examined for which the FN tunneling characteristics are easily measured over 5 orders of magnitude using high resolution current-voltage (I-V) measurements. The theoretical characteristics for each of the measured structures were calculated based on barrier height, tunneling effective mass, and thickness of the insulator to predict where the FN characteristics should be observed. I-V measurements of the MIM structures broke down at voltages below where the FN characteristics should become apparent. Pulsed measured were explored to see whether a pulsed I-V characteristic could be used in the MIM structure without breakdown. No pulse protocol was found at the voltages needed. It appears there are no prior reports of FN tunneling in MIM structures.