TV in a Picture Frame

Almost from the time that the first television picture tube appeared in the 1920s, electronic engineers have been looking for a simpler, less fragile and more economical device for displaying images transmitted over the air waves. Now scientists at the Westinghouse Research Laboratories in Pittsburgh think that they may have found a way. At this month's electro-optics and international laser exhibition in San Francisco, they displayed the prototype of a flat-screen TV system that is less than one-eighth of an inch thick and may some day be hung on a wall like a pane of plate glass in an ordinary picture frame.

In the bulky picture or cathode-ray tubes used in conventional TV sets, a beam of electrons originates in the stem of the tube and sweeps rapidly to and fro across the tube face. Its intensity is controlled by the signal from the TV station. As the beam hits dots of phosphorescent material in the tube face, they glow with a brightness proportional to the strength of the beam. This rapid action produces at least 25 still pictures per second on the screen, creating the illusion of moving images. In the new Westinghouse system, the images are also formed by producing glowing dots on the phosphorescent surface of the screen in the proper sequence. But the electronic stimulus that triggers the dots occurs within the screen itself; because there is no electron beam, there is no need for a deep-throated, bulky cathode-ray tube.

The secret of Westinghouse's magic pane lies in the relatively recent union of chemistry and electronics called thin-film technology. Using a masking technique somewhat like that used by artists in the silk-screen process, scientists can create thousands of tiny electronic components--transistors, capacitors, resistors, etc.--on a single flat surface called a "chip." Linked together in so-called integrated circuits, enough of these microscopic components can be included on a chip no larger than a postage stamp, and perform all the electronic functions of. say, a stereo amplifier, a hearing aid or even a pocket calculator. In the Westinghouse TV system, the chip is relatively large--a 6-in. by 6-in. surface that forms the TV screen. The chip contains some 36,000 electronic components--"probably the world's largest integrated circuit," says Physicist T. Peter Brody, head of the research team.

Control Chip. Laid out in 120 horizontal and 120 vertical lines, these components form a graph-paper-like pattern in which there are 14,400 points of intersection. At each intersection, there are two transistors and one capacitor. If a signal is sent to a particular intersection, the components there will light up the layer of phosphorescent material immediately above them. That creates a dot that can glow with varying intensity. If a number of intersections are triggered simultaneously, an image is formed. In their current prototype, the Westinghouse engineers form images by using an external switching device to feed signals to the appropriate intersections. But they are already working on an integrated switching device that could be imprinted directly onto two edges of the screen. With another chip (containing a "coder" to control the switching device) clamped to the screen, the entire TV could be contained in one thin package.

For all its novelty, the model shown in San Francisco is still relatively crude. It has a resolution only good enough to display letters, numbers and simple images in silhouette. But the system's developers are convinced that the quality of the image can be upgraded to existing television-picture standards within the next few years. In fact, they see no reason why the Westinghouse system--which now operates in a single color against a dark background--could not eventually be converted into full color.

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