7
II. Operation of a liquid crystal display.
The liquid crystal molecules are long and thin as shown in Figure 2 on the right. On the bottom glass substrate, the PI
layer has been rubbed from back to front, and the molecules are aligned
in that direction. Remember, the direction of
this orientation determines the viewing angle of the part.
Because the PI layer of the top glass has been rubbed from right to left, the molecules attached to the top piece of glass
are oriented perpendicular to the ones at the bottom. This 90
o
rotation is the "twist" in a twisted nematic display.
Fig. 2
The liquid crystal molecules between the top and bottom glass form a spiral structure that will twist light as it goes
through the cell. As can been seen in Figure 3 on the left, a beam of light entering from above passes through the top
polarizer along the axis of polarization.
The light beam goes through the cell, and is twisted as it goes in the same direction as the twist of the LC fluid.
The light exits the display, and passes through the polarizer on the bottom glass which is oriented perpendicular to the
polarizer on the top.
Fig. 3
