According to this old Popular Mechanics article, flat screen televisions have been around since 1958 -- or at least the technology. Designed mainly for military use, it just never caught on due to patents/licensing issues. Click the image for full article.
From the article: "The picture tube, only 2-5/8 inches thick, is made of two rectangular pieces of plate glass with about an inch of space between them. The edges are sealed with powdered-glass solder to hold the vacuum. The surface of the thin tube is the equivalent of a 21-inch conventional screen."
[Modern Mechanix via MAKE - ShoutIt]