Basics of LCD Operation

  A cross sectional view of a liquid crystal display is shown below in
Figure 1. As can be seen in the diagram, the display is simply two 
pieces of extremely flat glass, over coated with a number of chemical 
layers, and filled with liquid crystal fluid.
  Please notice that this drawing is not made to scale. To give some 
perspective, the bottom and top glass substrates are typically .043" thick
each. The thin film coatings, SiO2, ITO, and PI, are each a few hundred 
angstroms thick. The space in the middle, marked "LC Fluid", is about 5
microns thick and is adjusted slightly to match the characteristics of 
the chosen fluid. If this drawing was made to scale, it would be very 
difficult to see any detail at all between the glass plates.
  A liquid crystal display (LCD) is a parallel plate capacitor with a 
dielectric, in this case the liquid crystal fluid, between the plates. 
First we select glass coated with a transparent metal coating for the 
electrodes of the display. The glass is usually made of soda lime, but
in some instances it can be a more expensive borosilicate, or because
few manufacturers provide borosilicate any more without a fight, 
aluminasilicate type. 
  The transparent metal coating can be any thin layer of conductive material,
such as gold, silver or tin. In order to keep the cost down and have a 
reasonable process window with a highly transparent coating, the industry 
has been using indium-tin oxide (ITO) as the preferred electrode material.

Photoresist is then put on top of the ITO coating and a photolithographic 
process is used to image the pattern. The exposed patterns are then developed
and the glass is sent through an acid bath where the excess ITO is removed,
similar to the way a PC board is made. The remaining photoresist is then 
stripped away and the patterned segment and common plane electrodes remain
on the glass.