Using Design CAD

Overview

Export your DesignCAD drawing in the .dxf format. All shapes in this file must be closed polygons. For example, a rectangle drawn with the rectangle tool is a closed polygon, however, 4 individual lines that touch at 4 corners do not form a closed polygon. If necessary, you can bind together a selection of lines with the key stroke shortcut “b”, thereby creating a closed polygon.

Important features

  • The zero of the coordinate system can always be reset. Use the button in top left of window used to set the zero of coordinate system
  • DRAW:ARRAY
  • EDIT:SELECTION EDIT:ROTATE
  • EDIT:SELECTION EDIT:DUPLICATE (shortcut is N).
  • EDIT:SELECTION EDIT:MOVE (shortcut is N).
  • You can write text on a mask, you must use “save in vector” and “true type font”

Key stroke shortcuts

  • z = zoom
  • l = layer
  • g = grid (ctrl g = grid settings)
  • . = gravity, puts a handle on the nearest corner (now you can copy paste and use the x-y coordinate command for precision
  • : = allows you to type in an x-y coordinate rather using the mouse
  • b = bind together a selection of lines into polygons.

General considerations

When creating a mask, here are some general considerations:

  • 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.

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