LINE
Specify a mesh line location.
SYNOPSIS
- line ( x | y | z ) location = n [spacing = n] [tag = string]
DESCRIPTION
This statement is used to specify the position and spacing of mesh lines. All line statements should come before region and boundary statements, which should in turn be followed by an initialize statement.
Only flat structures can be specified with line / region / boundary statements. To create the grid for a more complicated structure, use the interactive grid generator skel.
- x | y | z
- A mesh line is either horizontal, vertical, or into the screen. The x coordinate increases from left to right. The y coordinate increases into the substrate, that is, from top to bottom. People who learned analytic geometry with the y axis pointing up seem to find this confusing. The z coordinate is supported, somewhat. Rectangular grid generation in three dimensions is the only three dimensional part of the program. It is anticipated that the next release will be fully one, two, and three dimensional.
- location
- The location along the chosen axis, in microns.
- spacing
- The local grid spacing, in microns. SUPREM-IV will add mesh lines to the ones given according to the following recipe. Each user line has a spacing, either specified by the user or inferred from the nearest neighbor. These spacings are then smoothed out so no adjacent intervals will have a ratio greater than 1.5. New grid lines are then introduced so that the line spacing varies geometrically from the user spacing at one end of each interval to that at the other. The example below might alleviate the confusion you must be experiencing.
- tag
- Lines can be tagged with a label for later reference by boundary and region statements. The label is any word you like.
EXAMPLES
-
line x loc=0 spa=1 tag=left
line x loc=1 spa=0.1
line x loc=2 spa=1 tag=right
line y loc=0 spa=0.02 tag=surf
line y loc=3 spa=0.5 tag=back
- There are three user-specified x lines and two user y lines. Taking the x lines for illustration, there is finer spacing in the center than at the edges. After processing, SUPREM-IV produces a mesh with x lines at 0.0, 0.42, 0.69, 0.88, 1.0, 1.12, 1.31, 1.58, and 2.0 microns. Around the center, the spacng is 0.12, approximately what was requested. At the edge, the spacing is 0.42 microns, because that was as coarse as it could get without having an interval ratio greater than 1.5. If the interval ratio was allowed to be 9, say, then we would have got one interval of 0.9 microns and one interval of 0.1 microns on each side. In this example, specifying a spacing of 1 microns at the edges was redundant, because that's what the spacing of the user lines was anyway.
BUGS
It's hard to guess how many lines are going to be generated in each interval.
Coarse spacings are sometimes rounded down by the smoothing algorithm in an undesirable way, creating too many grid points.
Automatic re-grid has been broken since oxidation introduced moving boundaries. Therefore the initial mesh specification is quite important to the success of the simulation. Use "best guess" numbers for the profiles, or coarse-grid simulations, to get a feel for the required spacings in the initial and final profile.