Application of Six Sigma in Semiconductor Manufacturing: A Case Study in Yield Improvement

The purpose of this chapter is to outline systematic implementation of the Six Sigma DMAIC methodology as a case study in solving the problem of poor wafer yields in semiconductor manufacturing. The chapter also describes well-known industry standard business processes to be implemented and benchmarked in a semiconductor wafer fabrication facility to manage defect and yield issues while executing a Six Sigma project. The execution of Six Sigma enabled identification of the key process factors, root cause analysis, desired performance levels, and Cpk improvement opportunities. Implementing multilevel factorial design of experiments (DOE) study revealed critical input parameters on process tools contributing to defect formation. Improvement performed on these process tools resulted in in-line defect reduction and ultimately improving final yields

High-Voltage-Gain DC-DC Power Electronic Converters -- New Topologies and Classification

This dissertation proposes two new high-voltage-gain dc-dc converters for integration of renewable energy sources in 380/400V dc distribution systems. The first high-voltage-gain converter is based on a modified Dickson charge pump voltage multiplier circuit. The second high-voltage-gain converter is based on a non-inverting diode-capacitor voltage multiplier cell. Both the proposed converters offer continuous input current and low voltage stress on switches which make them appealing for applications like integration of renewable energy sources. The proposed converters are capable for drawing power from a single source or two sources while having continuous input current in both cases. Theoretical analysis of the operation of the proposed converters and the component stresses are discussed with supporting simulation and hardware results. This dissertation also proposes a family of high-voltage-gain dc-dc converters that are based on a generalized structure. The two stage general structure consists of a two-phase interleaved (TPI) boost stage and a voltage multiplier (VM) stage. The TPI boost stage results in a classification of the family of converters into non-isolated and isolated converters. A few possible VM stages are discussed. The voltage gain derivations of the TPI boost stages and VM stages are presented in detail. An example converter is discussed with supporting hardware results to verify the general structure. The proposed family of converters can be powered using single source or two sources while having continuous input current in both cases. These high voltage gain dc-dc converters are modular and scalable; making them ideal for harnessing energy from various renewable sources offering power at different levels --Abstract, page iv

Instabilities in the axisymmetric magnetoelastic deformation of a cylindrical membrane

We study the inflation of a weakly magnetizable isotropic incompressible cylindrical membrane and the effects of an external magnetic field generated by a current carrying wire placed along the axis of cylinder. A variational formulation based on magnetization is used and the computational results obtained by using four elastic constitutive models (neo-Hookean, Mooney–Rivlin, Ogden, and Arruda–Boyce) are studied and compared. Cylinders of various aspect ratios are studied in each case. Our study shows that the external magnetic field alters the elastic limit point, does not lead to equilibrium solutions below certain value of internal pressure, and can give rise to multiple equilibrium states for a given value of pressure. Presence of magnetic limit point, a phenomenon recently reported in the literature is reconfirmed. Magnetic limit point is a state where a further strengthening of the applied magnetic field at a given pressure does not yield any static equilibrium state. In this case it is detected when the cylindrical membrane deflates into the volume enclosed by itself. We also observe a quadratic relation between the defined magnetic energy parameter and the internal pressure at the magnetic limit point. Relaxed form of the strain energy density is used to account for wrinkling in this case of inward inflation. A finite difference method coupled with an arc-length technique is used for the computations and the stability of the solution is determined from the second variation

Limit points in the free inflation of a magnetoelastic toroidal membrane

One common phenomenon native to inflation of membranes is the elastic limit-point instability–a bifurcation point at which the membrane begins to deform enormously at the slightest increase of pressure. In the case of magnetoelastic materials, there is another possible phenomenon which we call magnetic limit-point instability, a state referring to the non-existence of an equilibrium state –either stable or unstable. In this work, we are concerned with such instabilities in an incompressible isotropic magnetoelastic toroidal membrane with an initial circular cross-section. A non-uniform magnetic field is generated using a circular current carrying loop placed inside the membrane in addition to inflation by a uniform hydrostatic pressure. An energy formulation based on magnetization is used to model the magneto-mechanical coupling along with a Mooney-Rivlin constitutive model for the elastic strain energy density. Computations show that the magnetic field strongly influences the location of elastic limit points and in some cases can cause them to vanish. Multiple equilibrium states are obtained as solutions of the governing equations and a criterion based on second variation is employed to determine their stability. Existence and dependence of magnetic limit point on the magnetic field is demonstrated. While the quantitative results obtained here are specific to the toroidal geometry, the deformation behaviour can be generalised to any magnetoelastic membrane

Development of novel apparatus for vapour-liquid equilibrium measurements at moderate pressures.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2006.In this work, a novel experimental apparatus has been designed, constructed and commissioned for the measurement of VLE at pressures up to 750 kPa and temperatures up to 600 K. The project undertaken represents a complete re-working of the design of Harris (2004), which was plagued by irregularities in the equipment operation and in the acquisition of experimental data. As in the work of Harris (2004), the design of the apparatus presented here is based upon the highly successful glass VLE still design of Raal (Raal and Muhlbauer, 1998). The novel apparatus is principally constructed from machined 316 stainless steel and features sight glasses in strategic positions to allow for an observation of the fluid flow characteristics in specific sections of the apparatus. The key criteria that encompassed the design of the equipment were expediency, operational efficiency and versatility in the acquisition of reliable VLE data. An initial test of the performance of the equipment was achieved through the measurement of pure-component vapour pressures of selected hydrocarbons (n-alkanes and a cycloalkane) and alkanols. The test system for vapour-liquid equilibrium (P-T-x-y) measurements with the novel apparatus was that of cyclohexane + ethanol at a pressure of 40 kPa. Good agreement between the literature and the experimental data was observed. Isobars for the cyclohexane + ethanol system at 69.8 kPa, 97.7 kPa and ISO kPa were also measured. The latter constitutes new data that have been measured for this system. Novel vapour-liquid equilibrium data were also obtained for the systems of I-propanol + 2-butanol, I-propanol + n-dodecane and 2-butanol + ndodecane at temperatures of 373.15 K, 393.15 K and 423.15 K. For the very high relative volatility alkanol + n-dodecane systems, uncertainties in the measurement of the vapour phase (y) resulted in only P-T-x experimental data being presented here, where the vapour phase composition was computed with the Wilson equation. The theoretical treatment of the experimental VLE data was achieved through a combination of the gamma-phi and the phi-phi approaches in the fitting of the VLE data to various thermodynamic models. In the gamma-phi method, a variety of activity coefficient models (Wilson, T-K Wilson, NRTL, UNIQUAC and modified UNIQUAC) together with the truncated virial equation of state were employed to find the best fit for the data. In the phi-phi method, the isothermal data sets were treated with the Peng-Robinson-Stryjek-Vera equation of state with the original Huron-Vidal (HV) and the modified Huron-Vidal mixing rules (MHVI and MHV2) in the correlative procedure. Thermodynamic consistency testing was also performed with the Direct Test of Van Ness (1995) to assess the quality of the experimental P-T-x-y VLE data sets measured in this study

COMPARISON OF CARTILAGE TYPE IIIA AND IIIB TYMPANOPLASTY IN INDIAN PATIENTS WITH CHRONIC SUPPURATIVE OTITIS MEDIA

Objective: This prospective comparative study determined the efficacy of type III tympanoplasty using homologous septal spur cartilage in patients with chronic otitis medis (COM).Methods: We selected patients by random sampling. Complete otolaryngologica examination including otological examination, tuning fork tests, pure tone audiometry (PTA), and relevant investigations was done. Post-tympanoplasty residual air-bone gap (ABG) was graded. Type III tympanoplasty was done for all and followed up until month 6.Results: Of 50 patients, 70.0% were men. Mean age was 27.72±10.81 years, 24 and 26 patients underwent type IIIA and IIIB tympanoplasty, respectively. Pre-operative mean PTA and ABG was 50.08 dB and 38.27 dB, respectively. Pre-operative ABG of 31–60 dB was seen in 41 patients while nine had an ABG of 0–30 dB. Overall, pre- and post-operative PTA was 50.24 dB and 28.54 dB, respectively. Overall, pre- and post-operative ABG was 38.32 dB and 16.40 dB (III A 36.92 dB and 14.79 dB; III B 39.62 dB and 17.88 dB). Mean overall hearing gain postoperatively in PTA was 21.70 dB (type III A 22.33 dB, III B −21.115 dB). Overall, ABG closure was 23.53 dB (type III A 22.333 dB, III B −21.115 dB). None had failure (>30 dB). Good ABG of 10–20 dB was seen in 72% and 78% of patients at month 3 and 6, respectively.Conclusion: Significant post-operative hearing improvement was seen in both types of tympanoplasty using homologous cartilage graft for ossicular reconstruction. Type III A is better than type IIIB as the stapes superstructure is vital for hearing

DNA Methylation Pattern Of Cpg Site In The Promoter Region Of CALCA-Alpha Gene As A Putative Epigenetic Biomarker In Neonatal Sepsis- A Prospective Observational Study In South India

Background: Recently, several studies have been reported on epigenetic modifications of DNA as a predisposing factor for several diseases among neonates and adults. Here we aimed to study the changes in the DNA methylation pattern in the promoter region of the CALCA gene among the neonates suspected to have sepsis in a tertiary care hospital. Methodology: All the neonates suspected to have sepsis based on the inclusion criteria during the study period were included in the study as cases. Normal healthy neonates were included in the study as controls. Positive cases were isolated from suspected cases based on positive blood culture and sensitivity reports. DNA extraction was done by the non-enzymatic salting-out method and was subjected to bisulfite conversion by manual method. Methylation-specific PCR was performed on a Thermal cycler gradient using a standard protocol. Positive samples were further analyzed for their melting behavior using the EpiTetHRM kit. Results: A total of 115 neonates were included in the study out of which 63 were normal healthy controls and 52 were diagnosed to have sepsis by the neonatologist based on the clinical presentation. Out of the 52 neonates suspected to have sepsis only 7 had positive blood culture. DNA methylation of the CALCA gene was detected in one healthy control and 5 neonates in the sepsis group. Conclusion: DNA methylation status in the promoter region of the CALCA gene were more from the methylation status in the normal healthy controls. Hence, this may serve as a useful biomarker for sepsis in the future