UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
2 results
Search Results
Item ULTRA-THIN ON-CHIP ALD LIPON AS SOLID-STATE ELECTROLYTE FOR HIGH ENERGY AND HIGH FREQUENCY CAPACITOR APPLICATIONS(2022) Ahuja, Kunal; McCluskey, F. Patrick; Rubloff, Gary W.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Liquid electrolytes dominate the supercapacitor market due to their high ionic conductivity leading to high energy and power density metrics. However, with the increase in demand for portable and implantable consumer electronics, all solid-state supercapacitor systems with high safety are an attractive option from both application perspectives and their similar charge storage mechanism. For solid state ionic capacitors, there remains significant room for innovation to increase the ionic conductivity and capacitor architecture to enhance the performance of these devices. Nano-structuring along with advanced manufacturing techniques such as atomic layer deposition (ALD) are powerful tools to augment the performance metrics of these all-solid-state capacitors that can compete with state-of-the-art liquid electrolyte-based supercapacitors. This dissertation has two primary objectives; 1) Study the behavior of polymorphs of ALD LiPON as a capacitor material and 2) Enhance the performance metrics using advanced materials and 3D nanostructuring for improved energy storage and high-frequency applications.In this work, ALD LiPON-based solid state capacitors are fabricated with a gold current collector to study the behavior of the solid electrolyte. LiPON shows a dual energy storage behavior, in low frequency (<10 kHz), LiPON shows an ionic behavior with electric double layer type energy storage, beyond this frequency, LiPON shows an electrostatic behavior with a dielectric constant of 14. The capacitor stack's thin film structure and dual frequency behavior allow for extended frequency operation of these capacitors (100 Hz to 2000 MHz). Next, LiPON's energy storage metrics are enhanced by pseudocapacitive energy storage behavior and increased surface area using ALD oxy-TiN. Finally, new fabrication techniques and ALD recipes are developed and optimized for integration into 3D templates. For fabrication of these capacitors, the material's chemistry is analyzed, and ALD techniques are developed for the deposition of electrode/electrolyte materials and current collectors into the 3D nanostructures. The intermixing during the ALD processes are studied to understand the behavior and reliability of these thin films. This work highlights LiPON characteristics as a capacitor material for high-energy and high-frequency applications. Though incomplete, we discuss progress towards the development of all ALD solid-state 3D supercapacitors that can compete against state-of-the-art capacitors available in the market.Item High Frequency Generation from Carbon Nanotube Field Effect Transistors Used as Passive Mixers(2012) Tunnell, Andrew Jacob; Williams, Ellen; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The high mobilities, low capacitances (due to small sizes), and high current densities of carbon nanotube field-effect transistors (CNT FETs) make them valid candidates for high frequency applications. The high cost of high frequency measurement equipment has been the largest hurdle to observing CNT transistor behavior at frequencies above 50 GHz. One economic solution to this barrier is to use an external harmonic mixer to convert high frequency signals to lower frequencies where they can be detected by a standard spectrum analyzer. By using this detection method, a new regime of high frequency CNT FET behavior is available for study. In this dissertation, we describe the design and fabrication of CNT FETs on quartz substrates using aligned arrays of CNTs as the device channel. The nonlinear input voltage to output drain current behavior of the devices is explained and approximated to the first order by using a Taylor expansion. For the high frequency mixing experiments, two input voltages of different frequencies are sourced on the gate of the devices without any device biasing. The input frequencies are limited to 100 kHz to 40 GHz by the signal generators used. The nonlinearities of the fabricated CNT FETs cause the input frequencies to be mixed together, even in the absence of a source-drain bias (passive mixing). The device output is the drain current, which contains sum and difference products of the input frequencies. By using an external harmonic mixer in combination with a spectrum analyzer to measure the drain current, output frequencies from 75 to 110 GHz can be observed. Up to 11th order mixing products are detected, due to the low noise floor of the spectrum analyzer. Control devices are also measured in the same experimental setup to ensure that the measured output signals are generated by the CNTs. The cutoff frequencies from previous passive mixing experiments predict that our devices should stop operating near 13 GHz, however our measurement setup extends and overcomes these cutoffs, and the generation of high frequency output signals is directly observed up to 110 GHz. This is the highest output frequency observed in CNT devices to date.