Browsing by Author "Angus Kingon, Committee Member"

Now showing 1 - 7 of 7

Active Body Bias for Low-Power Silicon-On-Insulator Design
(2007-04-18) Damiano, John; W. Rhett Davis, Committee Member; Antonio Montalvo, Committee Member; Brian Hughes, Committee Member; Paul Franzon, Committee Chair; Angus Kingon, Committee Member
SOI device technology offers the circuit designer higher performance and greater flexibility. This work proposes the use of a targeted substrate bias and innovative device and circuit topologies to achieve higher performance and lower power while providing a strategy to compensate for wide temperature and process variations. This project introduces and evaluates a modified H-gate device topology (integrated drain-body transistor, or IDBT) vs. alternative structures using simulation supported by electrical results obtained from test circuits. The IDBT can be used to locally and dynamically reduce MOSFET VTH, increase switching speed, and improve circuit energy-delay product by up to 30%. For all structures investigated, the dynamic body bias provided by IDBTs provides improved logic cell performance vs. conventional source-tied cell designs. This work also examines use of body bias to compensate for temperature or process variations. The temperature range seen by space electronics exceeds standard commercial specs and even military specs. Integrated circuits placed on a satellite or lander vehicle may be expected to operate from below -200°C to over 200°C. In this environment, the stabilization of key circuit parameters across temperature, whether power consumption or performance metrics, can be accomplished through a targeted substrate bias. The amount of stabilization available, i.e. the degree to which key parameters can be shifted in-situ, is explored. Similarly, variations in device parameters due to process variations can also be compensated using this technique. Finally, these efforts exposed marginalities in the models for Honeywell MOI5 MOSFETs. At low temperatures, the simulated device characteristics diverged substantially from the electrical data, while the PMOS device simulation results displayed incorrect body factor. This work interprets these results and develops improved models based on electrical results from a series of test structures.
Frequency agile RF/microwave circuits using BST varactors
(2004-04-08) Jin, Zhang; Angus Kingon, Committee Member; Jon-Paul Maria, Committee Member; Griff Bilbro, Committee Member; Gianluca Lazzi, Committee Member; Amir Mortazawi, Committee Chair
The research has focused on characterizing barium strontium titanate or BST film at RF/microwave frequencies, improving BST capacitor quality factors and designing frequency agile RF/microwave circuits. A simple and fast measurement technique is developed to extract BST loss tangent and dielectric constant in a parallel plate capacitor. An error analysis is performed to indicate the measurement accuracy. In addition, the BST capacitor layout is optimized to achieve the best possible quality factor. BST capacitor based tunable band-pass filters are designed. Two coupled half-wavelength microstrip resonators are used in the filter. BST capacitors are placed at the end of resonators, which change the filter performance. Analysis shows that with the increase in BST capacitance, the filter skirt sharpness increases, the circuit size decreases, and the tunability increases but the insertion loss increases. Different filter specifications are achieved using various BST capacitances. In addition, a new topology is developed to maintain the 3-dB bandwidth of filters at different biases. The bandwidth change decreases from 54% to only 4% using the new topology. A tunable microstrip antenna is designed, fabricated and measured. Multiple varactors are used to load the rectangular microstrip antenna. A figure of merit is defined to find the optimum number of varactors. Good tunability of 25% and maximum gain of 7.8 dB are achieved within the tuning range. Almost uniform radiation patterns at different biases are also obtained. The measurement results prove that tunable microstrip antennas using multiple varactors loading can achieve better performance than those using single varactor loading. A tunable high impedance surface is designed, fabricated and measured. The surface uses lumped elements to form a parallel resonant circuit. Unlike other lumped-element high impedance surfaces, the inductor in this surface is obtained from the grounded substrate, which shows much higher quality factor and requires less substrate height than those using vias to obtain inductance. Measured tunability of 62% is achieved.
Improved Behavioral Modeling Based on the Input Output Buffer Information Specification.
(2007-04-10) Varma, Ambrish Kant; Paul D. Franzon, Committee Chair; Michael B. Steer, Committee Member; Doug Barlage, Committee Member; Angus Kingon, Committee Member
High level behavioral modeling is widely used in lieu of low level transistor models to ascertain the behavior of I⁄O drivers and receivers. IBIS (Input Output Buffer Information Specification) is one of the most widely used methodology to model digital drivers as it satisfies the basic requirements of a behavioral model such as intellectual property protection, simple structure, fast simulation time and good accuracy. As driver technology gets increasingly complicated and rise time of input signal gets increasingly smaller, important phenomenae such as simultaneous switching noise (SSN) becomes a major consideration when simulating multiple I⁄O drivers in the integrated circuit. Misrepresentation of noise might result in overestimation of signal strength and quality resulting in a high bit error rate and poor signal to noise ratio at the receiver end. This might lead to total failure of the system. With the size of the transistor shrinking, more and more I⁄Os can be accommodated on the chip, resulting in a greater probability of more drivers switching simultaneously, hence increasing the problems of SSN furthermore. Experiments show that IBIS models over-represents noise in the quiet line when placed in an environment where multiple drivers were present and switching simultaneously. A thorough analysis is performed to determine the inadequacies in IBIS with regards to SSN. A method is presented for compensating for the missing information by complimenting the IBIS model with a black box that is simulator independent, without compromising with the speed that IBIS enjoys over the transistor models. Model validation and system level tests are done with the IBIS model in conjunction with the black-box by passing a pseudo random bit sequence (PRBS) at the input. Eye diagrams are used to determine the quality of the received signal at the input for the behavior models as well as transistor models. These tests demonstrated a better response of the behavior model than the plain IBIS model when compared to the circuits with the transistor model. The enhancement of the IBIS models resulted in at least a 20% improvement in the simulation accuracy with behavioral models.
Reliability of Gap Capacitors
(2008-12-08) Kupferschmidt, James R.; Jon-Paul Maria, Committee Chair; Angus Kingon, Committee Member; J.C. Poindexter, Committee Member
The requirements for communication devices continue to become more challenging each year leading to rapid developments in varying technologies to meet the demands. Tunable filters, utilizing ferroelectric varactors, are merely one solution to the ever-demanding need for microwave communication systems. Barium Strontium Titanate (BST) can be employed as the dielectric material necessary to make tunable devices. The broad range of BSTâ€™s remarkable properties allow for easy integration into many devices, such as MEMS, oscillators, phase shifters, and tunable filters. BST deposition is done via RF magnetron sputtering for our purposes. Previous work completed here at NCSU has led to a sophisticated process to fabricate tunable filters chips that work over the 6-18 GHz range. Using polycrystalline alumina substrates with varactors made up of a pair of 4 Î¼m silver gap capacitors in series as well as utilizing the BST dielectric creates excellent tunable chips. There are however issues related to the reliability of the gap capacitors composing the varactors. Existing theory (Paschenâ€™s Law) describing capacitor failure reveals gaps with relatively close spacings (below 5 Î¼m) should maintain robust breakdown strengths. However, our research, as well as numerous additional literature, proves this theory to be inaccurate. Mooreâ€™s Law has led to a return to this research area, after almost a four decade hiatus, relatively recently as well as additional modifications to electrical systems that are presently occurring. Townsend discharge and electric field emission can be used to describe the mechanisms of gap capacitor breakdown. The Fowler-Nordheim equation and Weibull statistics, via the Bernard median rank equation for determining cumulative probability, are employed to analyze the breakdown data. Various mechanisms lead to breakdown occurring among these capacitors and further investigation into silver electromigration was undertaken to explore the possibility of migration as a significant factor towards failure. The details involved in fabricating tunable filters is detailed and shown to be relatively similar to the construction of samples with loads of gap capacitors. BST thin-film deposition is completed initially, followed by photolithography processes to define the outline for the filters. Silver metallization is accomplished using DC magnetron sputtering, and patterning is completed by lift-off in an acetone solution, due to the lack of harmful effects to the BST thin-film. Samples with roughly 250 gap capacitors on them were also fabricated on alumina substrates, with gaps ranging between 2 to 5 microns and widths between 100 to 750 microns. Large number of the gap capacitors were placed under ramping DC bias to observe if failure occurred using a suitable probe station. Proper analysis was undertaken using Weibull statistics, and several critical variables were examined, including roughness, patterning processes, adhesion of silver metal to the substrate, as well as varying the type of ground metal. SEM was utilized in examining the capacitor failure, including carrying out experiments looking into silver electromigration. In this thesis, we will show the inadequacies of Paschenâ€™s Law for describing capacitor failure with gap spacings of less than 5 Î¼m. Also, an explanation into the process improvements for utilizing Ag gap capacitors on alumina substrates, for our tunable filters purposes, to eventually using Cr-Au gap capacitors on sapphire substrates is provided. For silver gap capacitors, the existence of the electromigration process is established and verified confirmed through SEM and EDS analysis.
Synthesis and Characterization of Sol-Gel Nanocomposites Demonstrating Enhanced Mechancial Properties
(2007-10-13) Mosher, Brian Patrick; Fuh-Gwo Yuan, Committee Member; Angus Kingon, Committee Member; Taofang Zeng, Committee Chair; William Roberts, Committee Co-Chair
The mild reaction conditions of the sol-gel process allow incorporation of an inorganic component into organic materials, making it very favorable for the synthesis of organicinorganic nanocomposite materials. However, researchers still strive to produce materials with the unique properties of inorganic compounds which also possess the mechanical properties of organic polymers. We have developed several sol-gel derived nanocomposite silicate materials using both inorganic precursors and organic-inorganic precursors, which show superior mechanical properties due to nanoscale structural reinforcement. The materials reported were developed in three separate investigations, although the synthesis techniques are relatively similar. STRUCTURAL EVOLUTION OF PARTICLE REINFORCED ORGANIC-INORGANIC WATER-BASED NANOCOMPOSITE MATERIALS We present for the first time, the use of Al(ClO4)3, an effective catalyst for synthesis of 3-Glycidoxypropyltrimethoxysilane (GPTMS) - based nanocomposite materials via sol-gel chemistry. Aluminum perchlorate (Al(ClO4)3) simultaneously serves as catalyst for epoxy polymerization and methoxysilane hydrolysis at room temperature. Catalytic effects of Al(ClO4)3 were demonstrated through nuclear magnetic resonance (NMR) of precursor sols and structural investigation of resulting films by Fourier transform infrared spectroscopy (FTIR). Our method incorporates nanophase particulate reinforcement; Ludox® TMA colloidal silica, which possesses surface silanols (Si-OH), further activate the epoxy groups and expedite organic polymerization. The silica nanoparticles chemically link with the organic-inorganic network through Si-O-Si and Si-O-C bonds. Nanoparticles reinforcement serves to strengthen the network and enhance mechanical properties such as microhardness and abrasion resistance while maintaining the unique optical properties of these materials. Furthermore, the synthesis is water-based, providing for an environmentally friendly synthetic route to hybrid materials. We present a general strategy for synthesis of particle reinforced nanocomposite organic-inorganic sol-gels that can serve as a building block for synthesis of more advanced hybrid materials. PARTICLE-REINFORCED WATER-BASED ORGANIC-INORGANIC NANCOMPOSITE COATINGS FOR TAILORED APPLCATIONS Based on the concepts in the work described above, we further developed synthetic routes to three organic-inorganic coatings with nanoparticle reinforcement, which serves to enhance mechanical properties. The films are sol-gel derived using non-ionic surfactant, with aluminum perchlorate (Al(ClO4)3) as a catalyst and 3-Glycidoxypropyltrimethoxysilane (GPTMS) as precursor. Through the aid of nanoparticle colloids and a minute amount of catalyst, dense, hard and monolithic materials are obtained. Incorporating metal oxide nanoparticles brings forth unique properties, such as absorbing harmful UV radiation. Silica colloid composites provide greatly enhanced mechanical properties without modifying the unique optical properties of inorganic materials. Water-based synthesis of these coatings is straightforward and produces very few harmful byproducts, making them ideal materials in industry. The materials presented are relatively hard and abrasion resistant with very good adhesion; two of the coatings are UV absorbent. Various colloids can be employed in our methods to tailor properties and resulting materials may serve applications such as optical, protective, catalytic, guest-host, and multifunctional coatings. ENHANCING MECHANICAL PROPRETIES OF SILICA AEROGELS THROUGH NANOENGINEERING Furthermore, we have developed a novel method to prepare modified silica aerogels, in which a small amount of water-soluble inorganic synthetic nanocomposite is added (Laponite® RDS). The molecular-level synergism between silica nanoparticles and molecular cross-linkers inverts the relative host-guest roles in glass-polymer composites, leading to new stronger and more robust low-density materials. After drying with supercritical CO2, the materials were characterized by 3-point bending, transient hotwire techniques, bulk density measurements, transmission electron microscopy (TEM), and Brunauer, Emmett and Teller (BET) method. Transient hotwire methods confirm that the nanocomposite materials retain the ultra low thermal conductivity of pure silica aerogels.
Synthesis and Properties of Barium Titanate Solid Solution Thin Films on Copper Substrates
(2006-09-26) Ihlefeld, Jon F.; Jon-Paul Maria, Committee Chair; Angus Kingon, Committee Member; Robert Nemanich, Committee Member; Zlatko Sitar, Committee Member; William Borland, Committee Member
Barium titanate thin films were deposited via chemical solution deposition using a hybrid-chelate chemistry directly on copper foil substrates. A process was developed to crystallize and densify the ferroelectric films at 900C by using a reductive atmosphere containing nitrogen, hydrogen, water vapor, and oxygen impurities such that film constituents were oxidized to form barium titanate and the foil substrate remained metallic. The crystallized films are polycrystalline with equiaxed morphology and average grain diameters in excess of 100 nm. The dielectric properties exhibit permittivities in excess of 1800 at room temperature and zero bias with tunabilites of greater than 90% and high field loss tangents of less than 1%. A series of samples was prepared with varying grain and crystallite sizes by dividing and processing a single film over a range of temperature from 700 to 900C. This ensures that the chemical composition and film thickness is invariant for each sample. It is shown that the grain size increases with higher process temperatures and results in a concomitant increase in permittivity and tunability. These enhancements, combined with the constant paraelectric⁄ferroelectric phase transition temperature, indicated that a combination of film crystallinity and grain size is responsible for diminished performance. The phase transition temperature and temperature coefficient of capacitance modified by partially substituting zirconium, hafnium, and tin for titanium. The resulting films were single phase and the phase transition shifts were consistent with bulk materials. A reduction in permittivity was observed for increasing substituent level and was attributed to a reduction in grain size for both barium titanate zirconate and barium titanate hafnate. Processing conditions were chosen to stabilize Sn2+ during the firing process in an attempt to flux the system and increase grain size. The barium titanate stannate films had less reduction in grain size per substituent level than either zirconium or hafnium, however a similar reduction in permittivity was observed. The diminished dielectric response was explained by a defect reaction involving divalent tin and oxygen vacancies that quenched the extrinsic domain response to the dielectric constant. Defect equilibria were investigated with respect to processing atmosphere, stoichiometry, and dopant concentration. The solubility of excess barium and titanium was found to be greater in the films than is expected in the bulk, however it is unclear that equilibrium is achieved in the process. It was demonstrated that dopants could successfully eliminate the necessity of a reoxidation anneal to compensate for oxygen point defects resulting from the low pO2 atmospheres. The dopant levels necessary and insulation resistance of pure BaTiO3 were greater than expected from thermodynamic calculations. It was suggested that this is the result of a reduction in the enthalpy of reduction, stemming from an increase in grain boundary volume. Barium borate fluxes were used to improve densification and crystallinity. Barium borate additions between 0 and 3% uniformly increased grain size and density, while levels greater than 3% resulted in anomalous grain growth. Films with exaggerated grains show tetragonal peak splitting in the X-ray diffraction patterns, consistent with bulk barium titanate. In materials without exaggerated grain growth, dielectric measurements revealed permittivities in excess of 3000 at room temperature (for average grain sizes of approximately 160 nm). This value is equivalent to the finest-prepared bulk ceramics and substantially greater than any polycrystalline film ever reported. This has been attributed to in improvement in film crystallinity. These two accomplishments — tetragonal crystal symmetry and permittivities in excess of 3000 — represent dramatic breakthroughs in ferroelectric thin film technology.
Tray Based Millimeter-wave Quasi-Optical Amplifiers and Dual Polarized Phased Arrays
(2005-01-09) Al-Zayed, Ayman S; Amir Mortazawi, Committee Chair; Angus Kingon, Committee Member; Gianluca Lazzi, Committee Member; Griff Bilbro, Committee Member
At millimeter wavelength, spatial power combining techniques offer a viable approach to realize compact, reliable, lightweight, robust, higher-power and economical systems This work focus on the tray based perpendicularly fed array systems, several design issues such as bandwidth improvement, power combining efficiency, dual polarity and beam steering were addressed in this thesis. A broadband tray based spatial power amplifier that employs dielectrically filled miniature horn arrays was investigated. Bandwidth improvement was achieved by replacing the patch arrays of an earlier design with the broadband dielectrically filled miniature horn arrays. This 5x5 spatial power amplifier with miniature horn arrays has a 3dB bandwidth of 1.32 GHz (13%), which is more than 4.5 times the 3 dB bandwidth of the perpendicularly fed patch array spatial power amplifier. This work presents experimental and numerical investigations on a 49-element Ka-band amplifier array. This study is aimed at determining the origin of various losses in the amplifier array. Passive simulation data confirms that the load seen by the active devices is well matched and that most of the power is coupled to the LSE10 mode. This means that coherent power combining should take place if there is no phase and amplitude variation due to the active devices and phase correcting dielectric lenses. This thesis presents a single aperture multibeam spatial power combining system that can support two separate polarizations. A Rotman lens is used as the power dividing network, which also has the ability to scan the beam over discrete angles. 1x9 dual polarized array was designed to demonstrate the beam steering in azimuth plane. The entire system is designed for the Ka band, with a center frequency of 32.6GHz. Through simulations and measurements, a ±30 degree scan range was achieved for the horizontal and vertical polarizations. The cross polarization for both the vertical and horizontal polarization ports was better than –16dB.