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====== Layout Editor ======

Layout Editor is open source and reasonably powerful. However, it is less intuitive to learn than DesignCAD. The Layout Editor software and instructions are available at http://www.layouteditor.net/. A nice feature of layout editor is "cells". It's important to work with cells so that repeated structure are easy to edit. It takes about 1 hour to learn the basics. 

Suggestions about learning to use the layout editor for designing a mask:

  *Look at someone else’s design and see how it is built out of cells
  *Learn to use layers, make sure you are adding new shapes to the correct layer.
  *Learn to select forms or cells, move them around, copy paste, delete etc.
  *Find the ruler function
  *Learn to create arrays

When creating a mask, here are some general considerations:
  *When naming layers, don't use the name "main". This name is incompatible with the Direct Write Lithography system which we use to write masks.
  *Our tube furnace inner diameter is about 22 mm. This means the overall chip dimension should be about 19~20 mm. When we cut the chips we need 1.5 mm padding of empty space around the electrode design. Therefore, working area for the electrodes is about 16 mm.
  *the contact aligner doesn’t perform consistently if features are less than 4 micron.
  *typical catalyst size is 4 micron
  *when you print multiple layers of a design, assume that alignment between layers could be 2~3 microns off.
  *nanotubes on SiO2 can grow 50~100 microns in unpredictable directions. Make sure that stray nanotubes won’t create unwanted short circuits.
  *contact pads should be > 150 x 150 micron.
  *Electrodes that will contact liquid should be kept to a minimal surface area to minimize Faradaic currents. 10 micron wide electrodes will work well.
  *Putting extra space between objects usually makes the photolithography more straight forward. After metal evaporation, lift-off of the photoresist is never perfect - metal features that are close together have a chance of getting short circuited. Another problem with close spacing can be "ghost exposure": photoresist which gets exposed by light bouncing around in the cracks.

Using the DWL with Layout:

  * If your main cell makes use of other cells you need to flatten those cells before trying to use the DWL. Select all cells in your main cell and use 'cell flat multilevel'. Make sure to save a copy of the original before doing this. 
  * Getting the DWL software to pick your main cell can be difficult. A fool proof way is to just delete all of the other cells after flattening everything on the main cell. Again, save a copy of the original before this.
  * If curved surfaces seem to have problems in the .gds format, try using the .dxf format.
  * Name your layers so you can differentiate between them with the DWL software. CTRL + SHIFT + left click on the layer button renames a layer.