Browsing by Author "Carl Osburn, Committee Member"

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Applications of Redox Active Molecules in Solid State Electronics Devices and Organic Photovoltaic Cells
(2009-12-08) Chen, Zhong; Veena Misra, Committee Chair; Carl Osburn, Committee Member; Michael Escuti, Committee Member; Orlin Velev, Committee Member
Redox active molecules have been studied for several years due to their interesting charge storage properties for future application in molecular memory devices with multi-bit low-voltage operation and ultimate scalability. Hybrid Si-Molecular devices with liquid electrolyte as gate contact have been demonstrated for future DRAM and FLASH memories. The focus of this dissertation work has been on developing the completely solid state hybrid Si-Molecular devices embedded with redox active molecules to facilitate ease of integration. In addition, redox active molecules have also been explored in potential application in organic photovoltaic cells. This work exploits the charge storage properties of redox molecules in solid state devices and the absorption profile of the redox polymers. The charge transfer and charge screening process in conventional electrochemical cell with liquid electrolyte has been characterized using cyclic voltammetry measurements. The role of the liquid electrolyte and the electrical double layer in electrochemical cell for the redox process has been discussed. The solid state approach to hybrid Si-Molecular devices has been proposed. The solid state dielectric layer has been considered to replace electrical double layer. The requirements of dielectric layer and deposition methods in solid state molecular memory device are investigated for preservation and characterization of the redox molecules. AlN, Al2O3 and HfO2 are deposited and examined on top of redox active polymers or redox monolayer in metal-insulator-molecules-silicon (MIMS) or metal-insulator-molecules-metal (MIMM) capacitors. The CyV measurements indicate that the redox properties are preserved after dielectric layer deposition on molecules. The leakage of MIMM capacitors has been greatly improved after the optimization on HfO2 atomic layer deposition conditions and the W/WN gate stack. The low leakage current of MIMM structure provide a reliable test platform for redox molecules as well as the other molecule with more functionalities. The redox process in the ionic cell has been modeled with equivalent circuits. The capacitance at different frequencies for EMS capacitors is simulated to study the electrical properties of the solid state molecular device. The frequency dispersion of capacitance measurements for MIMM capacitance has been explored for understanding the redox charging or trapping in the molecular layer. Si nano-membranes are fabricated as an alternative contact to molecules. Solid state molecular transistors are demonstrated for the possible application in FLASH memory. Redox polymers are investigated for the application in renewable energy area. The organic nanoparticles-polymer solar cell has been compared with conventional bulk Si solar cell. The integration of redox polymers helps to improve the absorption profile of active layer in organic solar cells. Organic solar cells with P3HT and PCBM are fabricated and characterized for the future incorporation of redox molecules. In summary, this work provides the fundamental insights and realistic approaches for the applications of redox active molecules with unique charge storage properties into solid state electronic devices and organic photovoltaic cells, which may enable the solutions for the low cost multi-bit low-voltage scalable molecular memories as well as the high efficiency organic solar cell embedded with redox molecules.
Electron Transport in Bulk-Si NMOSFETs in Presence of High-k Insulator-charge Trapping and Mobility
(2006-11-29) Maitra, Kingsuk; Mark Johnson, Committee Member; Douglas Barlage, Committee Member; Carl Osburn, Committee Member; Veena Misra, Committee Chair
Recent advancements in gate stack engineering has led to the development of aggressively scaled, high mobility, high-k dielectric based NMOSFETs with metal gates. Most of the current literature on the subject also stressed on the need for a high temperature process step to attain the high mobility under minimal change of effective oxide thickness. However, the physical origin of high mobility is not well understood. In this work, fundamental insight into the necessity of the high temperature process step is provided. Novel experimental strategies are developed to understand the impact of interface states and bulk traps separately and exclusively on channel mobility. It is conjectured that the interface states at the SiO2⁄(100) bulk-Si interface are identical in nature (as far as coupling with the channel electrons is concerned) to those at the high-k⁄SiO2⁄(100) bulk-Si interface. Thus, the response of interface states on channel electrons in high-k insulator based NMOSFETs is properly calibrated by a novel thermal desorption of hydrogen experiment on SiO2⁄(100) bulk-Si NMOSFETs to yield a highly accurate parameterized equation. The value of interface state response parameter determined by the aforementioned experiment is compared with theoretical predictions, and independently determined projections from electrical stress measurements. The impact of transient charging on transport in the channel is investigated. It is conclusively shown that remote charge has minimal impact on mobility in the channel. The role of nitrogen induced fixed oxide charge is studied on a set of Hf-silicate samples. Role of soft optical phonon scattering and the beneficial impact of metal gates on soft optical phonon limited mobility are thoroughly investigated both theoretically and experimentally. Conclusions are drawn on the fundamental limit of mobility attainable in high-k dielectric based NMOSFETs.
High-Rate Diamond Deposition by Microwave Plasma CVD
(2008-08-01) Li, Xianglin; Zlatko Sitar, Committee Chair; Ramon Collazo, Committee Member; Gerd Duscher, Committee Member; Carl Osburn, Committee Member
INTERFACES IN NOVEL ELECTRONIC MATERIALS
(2008-01-10) Liu, Fude; Nadia A. El-Masry, Committee Member; Carl Osburn, Committee Member; Robert Nemanich, Committee Co-Chair; Gerd Duscher, Committee Chair
Metal alloys and Gate Stack Engineering for CMOS Gate Electrode Application
(2006-10-24) Chen, Bei; D. W. Barlage, Committee Member; Mark Johnson, Committee Member; Veena Misra, Committee Chair; Carl Osburn, Committee Member
The purpose of this research has been to search for proper metallic gate electrodes for CMOS devices. This dissertation covers several binary alloy metal gate research topics. First, intermetallic binary alloy RuY was investigated. From C-V analysis we obtained the effective work function of Ru-Y thin films to range from 5.0eV to 3.9eV which is suitable for dual metal gate CMOS. The rich Y film was found to be not stable on SiO2 dielectrics because of the high oxygen affinity of Y. RuxYy thin film may still be a candidate for low temperature process, especially due to its large range of work function. More over, RuY has smaller grain size than Ru which demonstrates one of the advantages of alloy by reducing grain size to achieve more uniform gate film and more uniform effective work function for the nano-size device applications. Chapter 3 presents MoxTay as a potential candidate for dual metal CMOS applications. The electrical characterization results of MoTa alloy indicates that the effective work function can be controlled to around 4.3 eV on SiO2 and is suitable for NMOS gate electrode application. The MoTa alloy forms a solid solution instead of an intermetallic compound. We report that the MoTa solid solution can achieve low work function values and is stable up to 900°C. X-ray diffraction results indicated only a single MoTa alloy phase. Moreover, from Auger electron spectroscopy and Rutherford backscattering spectroscopy analysis, MoTa was found to be stable on SiO2 under high temperature anneals and no metal diffusion into substrate Si channel was detected. This indicates that MoxTay is a good candidate for CMOS metal gate applications. Chapter 4 evaluates Ru and W capping layer for MoTa metal gate electrodes in Metal Oxide Semiconductor capacitor applications. We report that the oxygen diffusion from the capping layer plays an important role in determining the MoTa alloy effective work function value on SiO2. MoTa alloy metal gate with Ru capping exhibit stable effective work function up to 900°C anneal but is not stable with W capping. Auger electron spectroscopy and Rutherford backscattering spectroscopy analysis shows minimal oxygen diffusion into the MoTa gate stacks with Ru capping while severe oxygen diffusion into the gate is observed with W capping metal after 900°C anneal. In chapter 5, We have studied the φm behavior of AlTa alloys with varying compositions ranging from pure Al to pure Ta. The effective work function of AlTa alloy increased up to 4.45 eV as compared to pure Al work function (~4.1eV) or pure Ta work function (~4.2eV) on SiO2 at 400°C FGA. We ascribe the φm increase due to an interface dipole originating from a thin negative charged reaction layer formed between the AlTa alloy and dielectric layer. In order to further increase the stability of the AlTa alloy while still obtaining φm tuning, N was added to make AlTaN. These alloy electrodes resulted in effective work function values of ~5.13 eV after a 1000°C anneal making them suitable candidates for PMOS electrodes. Chapter 6 shows a new method that can tune the effective work function utilizing dipole layers has been demonstrated. Continued work function values can be expected by modifying the dipole strengths. This routine can potentially provide a new method for the metal gate work function research for the future wide gape semiconductor device.
Properties of Zr Silicate and Zr-Si Oxynitride High-k Dielectric Alloys for Advanced Microelectronic Applications; Chemical and Electrical Characterizations
(2005-09-27) Ju, Byongsun; Gerald Lucovsky, Committee Chair; Jon-Paul Maria, Committee Member; Robert Nemanich, Committee Member; Carl Osburn, Committee Member
As the microelectronic devices are aggressively scaled down to the 1999 International Technology Roadmap, the advanced complementary metal oxide semiconductor (CMOS) is required to increase packing density of ultra-large scale integrated circuits (ULSI). However, SiO2 or Si oxynitride (SiOxNy) films which is a traditional gate oxide materials shows its limitations in direct tunneling current density at the below about 3nm thickness, and moreover, the priority of leakage current is ranked high in device performance and reliability as the portable device prevails. High-k alternative dielectrics can provide the required levels of EOT for device scaling at larger physical thickness, thereby providing a materials pathway for reducing the tunneling current. Zr silicates and its end members (SiO2 and ZrO2) and Zr-Si oxynitride films, (ZrO2)x(Si3N4)y(SiO2)z, have been deposited using a remote plasma-enhanced chemical vapor deposition (RPECVD) system. After deposition of Zr silicate, the films were exposed to He/N2 plasma to incorporate nitrogen atoms into the surface of films. The amount of incorporated nitrogen atoms was measured by on-line Auger electron spectrometry (AES) as a function of silicate composition and showed its local minimum around the 30% silicate. Characterization by AES and x-ray photoelectron spectroscopy (XPS) indicated that the nitrogen atoms were substituted for the oxygen atoms' position and made a bond with Si and Zr depending on the silicate composition. The effect of nitrogen atoms on capacitance-voltage (C-V) and leakage-voltage (J-V) were also investigated by fabricating metal-oxide-semiconductor (MOS) capacitors. Results suggested that incorporating nitrogen into silicate decreased the leakage current in SiO2-rich silicate, whereas the leakage increased in the middle range of silicate. The pseudo-ternary alloy composition was determined by Rutherford back scattering (RBS) that was calibrated by on-line Auger electron spectroscopy (AES) and showed the composition's thermodynamically stable boundary composition in ternary phase diagrams. Zr-Si oxynitride was a pseudo-ternary alloy and no phase separation was detected by x-ray photoelectron spectroscopy (XPS) analysis up to 1100°C annealing. The leakage current of Zr-Si oxynitride films showed two different temperature dependent activation energies, 0.02 eV for low temperature and 0.3 eV for high temperature. Poole-Frenkel emission was the dominant leakage mechanism. Zr silicate alloys with no Si3N4 phase were chemically separated into the SiO2 and ZrO2 phase as annealed above 900°C. While chemical phase separation in Zr silicate films with Si3N4 phase (Zr-Si oxynitride) were suppressed as increasing the amount of Si3N4 phase due to the narrow bonding network in Si3N4 phase. (3.4 bonds/atom for Si3N4 network, 2.67 bonds/atom for SiO2 network)