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Investigation of Metal-Insulator-Metal (MIM) and Nanolaminate Barrier MIIM Tunnel Devices Fabricated via Atomic Layer Deposition
Metal-insulator-metal (MIM) tunnel devices have been proposed for high speed applications such as hot electron transistors, IR detectors, optical rectennas for IR energy harvesting, and backplanes for LCDs. The majority of these applications require highly asymmetric and non-linear current versus voltage (I-V) behavior at low applied voltages and ultra-high frequencies. The objective of this work is to develop MIM tunnel devices with improved electrical properties including I-V asymmetry and non-linearity. The standard approach to achieving asymmetric operation in MIM devices is through the use of electrodes with different metal work functions. This approach is investigated using a variety of thin film dielectrics deposited by atomic layer deposition (ALD). To assess suitability for high speed operation, the physical mechanisms of electron transport in each dielectric are investigated. Next, as an alternative approach to achieving asymmetric and non-linear operation, pairs of dielectrics with different band-gaps and band-offsets are combined to form asymmetric tunnel barrier metal-insulator-insulator-metal (MIIM) diodes. MIIM diodes are fabricated using ALD to form nanolaminate pairs of Al2O3, HfO2, ZrO2, and Ta2O5 between asymmetric electrodes. It is found that the performance of the MIIM diodes is sensitive to the choice, relative thickness, and arrangement of the individual dielectric layers. It is shown that asymmetric dual-dielectric tunnel barriers can overwhelm the influence of asymmetric electrodes and it is demonstrated that MIIM structures can be designed to provide improved asymmetry at low electric fields. Low field asymmetry improvements are shown to be due to a step tunneling phenomenon. Finally, the formation and influence of interfaces, as a means for providing insight into engineering of nanolaminate barrier tunnel devices is examined by comparing different atomically smooth bottom electrodes.

Major Advisor: John Conley
Committee: John Wager
Committee: Thomas Plant
Committee: Douglas Keszler
GCR: Brady Gibbons

• Electrical Engineering and Computer Science*