Browsing by Author "Jacqueline Krim, Committee Member"

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Analysis and Design Considerations for AC Coupled Interconnection Systems
(2005-03-29) Mick, Stephen; Paul D. Franzon, Committee Chair; John Muth, Committee Member; Rhett Davis, Committee Member; Jacqueline Krim, Committee Member
As the process technologies for microelectronic integrated circuits continue to improve, both the amount of integrated, on-chip functionality and the number of required off-chip interconnections (I/O) will continue to increase. These I/O will not only become more numerous but also will need to be packed densely and be capable of operating both with high bandwidth and low power. Packaging technology research is aimed at increasing I/O density and circuit research is underway to improve the bandwidth and power performance of I/Os. Advances are being made in each of these areas, but industrial roadmaps predict that these advances will not keep pace with the needed improvements. The research in this dissertation addresses this widening technological gap. The central thesis in this work hinges on the recognition that arrays of densely packed, low-power, high-bandwidth I/Os can be created if the physical structure of each I/O is optimized for the type of information it must transmit. For example, the DC component of digital signals carries no information. Instead, digital signals contain information at frequencies well above DC (where the exact frequency spectrum of the information depends upon the edge rate of the data transitions). This can be exploited by recognizing that AC information can be transmitted across a boundary with non-contacting structures such as two plates of a capacitor or two coupled inductors. An I/O array can then be built with non-contacting structures for AC signals and direct contacts such as solder bumps only where DC signal transfers are needed. In this way, AC signal paths are freed from the mechanical constraints of direct, contacting structures and both the compliance and rework problems encountered in other high density interconnect technologies can be alleviated. Capacitive and Inductive AC Coupled Interconnections are extensively analyzed and measured in this work and presented as a means to provide an array of sub-100 micrometer pitched, low-power, multi-gigabit per second per pin interconnections. A packaging structure that enables AC Coupled Interconnections is also presented.
Electrostatic Generation and Control on Textiles.
(2010-08-06) Liu, Lu; Abdel-fattah Seyam, Committee Chair; William Oxenham, Committee Chair; Jacqueline Krim, Committee Member; Pamela Banks-Lee, Committee Member; Thomas Theyson, Committee Member; Jacqueline Hughes-Oliver, Committee Member
Heteroepitaxy and Properties of III-V Materials Grown on Nanoscopically Roughened (001) Si.
(2008-12-02) Liu, Xiang; David E. Aspnes, Committee Chair; John E. Rowe, Committee Member; Robert M. Kolbas, Committee Member; Jacqueline Krim, Committee Member
Polar-on-nonpolar heteroepitaxy of mainly III-V materials on Si by organometallic chemical vapor deposition (OMCVD) has attracted much interest due to its potential technological importance. The objectives of this work are (1) to study OMCVD growth mechanisms, focusing on the lattice-matched but chemically mismatched heteroepitaxy of GaP on Si, and (2) to explore the possibility of improving the quality of the deposited GaP. We examine particularly the possibility of improving GaP quality by using Si substrates that were deliberately roughened on the scale of nm. We also study comparatively on the chemically compatible but lattice-mismatched system of GaP on GaAs, and the polar-on-polar system of GaP on thermally generated amorphous SiO2. Inadvertent but nonetheless important data in establishing growth details were also obtained from the surface of the Mo susceptor surrounding the sample. We use spectroscopic polarimetry (SP) to follow growth chemistry in real time, and then analyze the deposited material with various techniques including atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). To understand the growth process quantitatively, we investigated in detail the gas-phase kinetics inside our vertical-flow, low-pressure OMCVD reactor chamber. We calculated various kinetics parameters and characteristic dimensionless numbers based on simple hard-sphere approximations. According to the results, we now have a significantly better understanding of the processes as taking place inside the reactor chamber, and can design growth conditions to optimize any specific task that we would like to achieve. We have proposed a model for the growth of GaP in OMCVD using the precursors trimethylgallium (TMG) and PH3. This model is primarily based on our observations that different regions of the growth surface are in communication through the gas phase. The model considers the effects of the substrate and the formation of reactants that are directly responsible for GaP growth. Our model, when used together with the thermodynamics and kinetic theories of nucleation and epitaxy, provides a consistent explanation of the various growth behaviors that we have observed. We have found that GaP films grown in our reactor usually have nonuniform thicknesses, which may be thinner or thicker at the edges, but in all cases shows an exponential dependence on radius. The causes all trace back to the differences in chemical properties of the various surfaces investigated here, more specifically, to the different catalytic effects that these surfaces exert on PH3 decomposition and their tendencies to achieve good-quality GaP heteroepitaxy. These data provide unambiguous evidence that deposition occurs via a precursor that involves both Ga and P, and is formed by heterogeneous catalysis. It addition, this precursor is likely to be largely desorbed and to decompose in the gas phase. Starting with the diffusion equation, we derive analytic expressions that describe the variations in terms of the diffusion parameters and evaluate the diffusion length quantitatively. These results coincide with our observations, and show that different parts of the surface â€“ including that of the susceptor â€“ are in constant contact with each other during growth through gas-phase diffusion.
Linearly Tunable RF-MEMS Capacitors Implemented Using An Integrated Removable Self-Masking Technique
(2003-04-08) Wilson, John Michael; Jacqueline Krim, Committee Member; Gianluca Lazzi, Committee Member; Thomas Conte, Committee Member; Paul D. Franzon, Committee Chair
MEMS tunable capacitors exhibit a non-linear capacitance verses voltage tuning characteristic. In addition, electro-statically actuated devices suffer from 'pull-in' after exceeding 33% of their total displacement. This non-linear behavior and limitation on continuous tuning that occurs from 'pull-in', limits the easy-of-use and tuning range of previously reported MEMS tunable capacitors. This dissertation presents a MEMS tunable capacitor that produces a wide tuning range with linear tuning throughout. The basic concept is similar to that of trimming/tuning capacitors used in early radios, where multiple metal plates create a capacitor that is varied by rotating a shaft which changes the overlap area. However, this device is built using modern IC processing methods that enable batch fabrication. The core of the design comes from high yield, mechanically proven gear structures defined in the SUMMiT design library, available from Sandia National Labs. Significant alterations were made to the physical gear structure to realize the final device. A novel masking technique that enables the complex patterning of metal(s), in different amounts, on any layer(s) of a released chip was also conceived. This 'integrated removable self-masking technique' enables the construction of low-loss controlled impedance structures such as coplanar waveguides in a polysilicon only MEMS process. In addition, this technique allows metal to be deposited in a regulated manner on multiple layers of a post release chip so that low-loss metal-insulator-metal capacitors can be built. Numerous device topologies are possible each with advantages and disadvantages. These various topologies and their design are discussed in detail. The metallization techniques for depositing single or dual metal layers are presented, along with a discussion on the construction of the masking layers so that they can be easily removed. Device simulation, modeling, and measurement are then presented.
Nanoscale Investigation of the Piezoelectric Properties of Perovskite Ferroelectrics and III-Nitrides
(2004-02-09) Rodriguez, Brian Joseph; Angus Kingon, Committee Co-Chair; Robert Nemanich, Committee Chair; Salah Bedair, Committee Member; Jacqueline Krim, Committee Member; Alexei Gruverman, Committee Member
Nanoscale characterization of the piezoelectric and polarization related properties of III-Nitrides by piezoresponse force microscopy (PFM), electrostatic force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM) resulted in the measurement of piezoelectric constants, surface charge and surface potential. Photo-electron emission microscopy (PEEM) was used to determine the local electronic band structure of a GaN-based lateral polarity heterostructure (GaN-LPH). Nanoscale characterization of the imprint and switching behavior of ferroelectric thin films by PFM resulted in the observation of domain pinning, while nanoscale characterization of the spatial variations in the imprint and switching behavior of integrated (111)-oriented PZT-based ferroelectric random access memory (FRAM) capacitors by PFM have revealed a significant difference in imprint and switching behavior between the inner and outer parts of capacitors. The inner regions of the capacitors are typically negatively imprinted and consequently tend to switch back after being poled by a positive bias, while regions at the edge of the capacitors tend to exhibit more symmetric hysteresis behavior. Evidence was obtained indicating that mechanical stress conditions in the central regions of the capacitors can lead to incomplete switching. A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM, respectively) has been used to map the out-of-plane and in-plane polarization distribution, respectively, of integrated (111)-oriented PZT-based capacitors, which revealed poled capacitors are in a polydomain state.
Nonvolatile Spin Memory based on Diluted Magnetic Semiconductor and Hybrid Semiconductor Ferromagnetic Nanostructures
(2008-06-27) Enaya, Hani; Salah Bedair, Committee Member; Ki Wook Kim, Committee Chair; Jacqueline Krim, Committee Member; Venna Misra, Committee Member; John Zavada, Committee Member
Stiction Reduction Agents Studies Using QCM
(2003-11-28) Hussain, Yazan Ahed; Jacqueline Krim, Committee Member; Christine Grant, Committee Chair; Saad Khan, Committee Member
The problem of stiction in microelectromechanical systems (MEMS) is highly limiting their fabrication and functionality. The problem occurs during the fabrication, release stiction, as well as during the use of the devices, in-use stiction. Anti-stiction agents are currently an active area of research in the MEMS field to address this issue. These agents are primarily deposited in the form of self-assembled monolayers (SAM's) on the substrate to change its surface properties; to reduce what is known as the stiction problem. One commonly used SAM is the octadecyltrichlorosilane (OTS). On silicon substrates, the most used material in MEMS fabrication, OTS has shown high effectiveness in reducing devices stiction. The use of a quartz crystal microbalance (QCM) as an analytical technique for studying the OTS anti-stiction agent is presented in this work. Using the QCM as the primary analytical tool, we were able to extract comprehensive information about the formed SAM. The dependence of SAM deposition on the bulk phase concentration of the deposit solution is shown. A rough estimation of the adsorption kinetics' rate constants were calculated, and the equilibrium constant was determined from their values. The equilibrium constant shows the high favorability of OTS deposition on silicon substrate compared to the reverse desorption process. The complex nature of the OTS SAM and its formation mechanism were also shown. These conclusions were made based upon comparison between the more robust SAM system of thiols on gold and the OTS on silicon. Finally, the interaction between the OTS and a vapor-phase lubricant (tertiary-butyl phenyl phosphate, TBPP), for friction reduction, was studied. Preliminary QCM results show a change in the adsorption of lubricant on bare silicon compared to OTS coated silicon. In addition, the lubricant film is believed to have higher slippage when OTS was present as an underlayer.