A fundamental feature scale model for low pressure deposition processes

1991 ◽  
Vol 9 (3) ◽  
pp. 524-529 ◽  
Author(s):  
T. S. Cale ◽  
T. H. Gandy ◽  
G. B. Raupp
Keyword(s):  
Low Pressure ◽  
Scale Model ◽  
Fundamental Feature ◽  
Deposition Processes ◽  
Feature Scale

Paper 10: The Influence of Moisture on the Efficiency of a One-Third Scale Model Low Pressure Steam Turbine

1965 ◽  
Vol 180 (15) ◽  
pp. 39-49
Author(s):  
A. Smith
Keyword(s):  
Steam Turbine ◽  
Correction Factor ◽  
Rotational Speed ◽  
Direct Injection ◽  
Maximum Level ◽  
Low Pressure ◽  
Full Scale ◽  
Scale Model ◽  
Supersaturation Ratio ◽  
Multi Stage

The rapid increase in blade-tip diameters and peripheral speeds of low pressure turbines in large 3000 rev/min turbo-generators has presented the designer with many difficult mechanical and aerodynamic problems. To assist in the aerodynamic development of such blading, design studies on an experimental low pressure (l.p.) turbine were started early in 1959. Economic and technical considerations limited the choice to a one-third scale model steam turbine capable of running at three times the normal rotational speed to preserve full-scale working Mach numbers on the blading. Overall output and steam consumption were measured on a hydraulic dynamometer and by volumetric tanking respectively. The inlet steam temperature was controlled by a direct injection desuperheater so that the expansion could be kept dry for traversing or reduced to design inlet temperatures for normal wet running. Three multi-stage sets with last row blade diameters corresponding to 90-in, 120-in, and 136-in full-scale turbines have now been tested in the experimental turbine and the wet performance of the largest forms the subject of this paper. The overall wetness losses on the model 136-in diameter turbine have been assessed from a series of seven tests in which the inlet superheat and rotational speed were varied whilst maintaining fixed inlet and outlet pressure levels. To isolate the stage moisture correction factor (α), however, where a stage-by-stage approach was adopted, in which the dry stage efficiencies were initially established from interstage traverses under dry steam conditions. Two wet steam analyses were made, the first assuming equilibrium and the second supersaturated expansion, but the choice seemed immaterial since the moisture correction factor was almost the same for both. In the case of the supersaturated expansion calculation, it was necessary to establish the point of reversion from supersaturated to near equilibrium expansion (the Wilson point) and supplementary water extraction results were used to establish the maximum supersaturation ratio. These suggest that the maximum level is nearer to 3 in the model turbine than to the value of 4–6 quoted for convergent-divergent nozzles.

A Model of Silicon Nanocrystal Nucleation and Growth on SiO2 by CVD

2004 ◽  
Vol 830 ◽  
Author(s):  
M. W. Stoker ◽  
T. P. Merchant ◽  
R. Rao ◽  
R. Muralidhar ◽  
S. Straub ◽  
...  
Keyword(s):  
Crystallite Size ◽  
Flash Memory ◽  
Silicon Nanocrystals ◽  
Large Scale ◽  
Process Development ◽  
Electron Tunneling ◽  
Nucleation And Growth ◽  
Scale Model ◽  
Size Distributions ◽  
Deposition Processes

ABSTRACTSilicon nanocrystals can be used in non-volatile memory devices to reduce susceptibility to charge loss via tunnel oxide defects, allowing scaling to smaller sizes than possible with conventional Flash memory technology. In order to optimize device performance, it is desirable to maximize the nanocrystal density and surface coverage, while maintaining sufficient inter-crystallite separation to limit electron tunneling between adjacent crystallites. Ideally, crystallite densities in excess of 1012cm-2 with relatively narrow particle size distributions must be obtained, posing a significant challenge for process development and control. In order to facilitate development of such a process, a rate-expression-based model has been developed for the nucleation and growth of silicon nanocrystals on SiO2 in a CVD process. The model addresses the phenomena of nucleation, growth, and coalescence and includes the effects of exclusion zones surrounding the growing nuclei. The model uses a phenomenological expression to describe the nucleation rate and assumes that following nucleation, crystallite growth is dominated by gas-phase deposition processes, analogous to CVD of polycrystalline silicon. The model-predicted time-evolutions of crystallite densities and crystallite size distributions are consistent with experimental distributions as measured by Scanning Electron Microscopy (SEM). By coupling the model to a reactor-scale model of polysilicon CVD, it is possible to predict variations in the crystallite size distributions at various locations across a wafer as a function of reactor settings (temperature, pressure, flow rates, etc…). This in turn can be used for process control and optimization in order to ensure uniform deposition of nanocrystals in a large-scale manufacturing environment.

A feature scale model for chemical mechanical planarization of damascene structures

2004 ◽  
Vol 449 (1-2) ◽  
pp. 192-206 ◽  
Author(s):  
Ravi Saxena ◽  
Dipto G. Thakurta ◽  
Ronald J. Gutmann ◽  
William N. Gill
Keyword(s):  
Chemical Mechanical Planarization ◽  
Scale Model ◽  
Feature Scale
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