Written by: Jeremy Van Derslice
Pure electrical insulators are highly transparent, but highly conductive metals are opaque. So what material can be used that is both transparent and conductive? We must find such a material to make our displays and touchscreens work.
Indium tin oxide (ITO) is both transparent and conductive. ITO optical properties vary a lot with deposition conditions and annealing, so monitoring the quality of the ITO and its thickness is important. Ellipsometry is used for monitoring ITO film thickness and transparency at visible wavelengths while also being sensitive to absorptions in the ultraviolet, but it is very important for monitoring absorption in the infrared, which corresponds to the film’s electrical conductivity.
Improvements in display speed are critical for fast action in movies and sports. Imagine a baseball, golf ball, or hockey puck leaving a comet tail behind on the screen because the display cannot refresh fast enough. Display pixel speed has been significantly enhanced using crystallised silicon films on the rear panel of the display. Ellipsometry is used to monitor the thickness and crystallinity of these deposited polysilicon films.
LCD displays used to be small, monochrome in color, and used in calculators, digital watches, etc. Modern displays are full colour, extremely fast, and very large. The coated films must be uniform over the entire panel size, and film uniformity has been a limiting factor in the size of displays for decades. With each new generation of larger displays, the film uniformity must be maintained. An ellipsometer can fly over the large panels as they move on a production line to monitor film quality.
To discuss ellipsometry and your application…
Contact our Technical Director, Dr. Shayz Ikram, by email below or call (01372) 378822.
