1970

LCD Screen

One measure of engineering success is the degree to which a technology becomes ubiquitous. By this measure, LCD screen technology certainly has succeeded. We see LCD screens in watches, calculators, clocks, microwave ovens, smart phones, tablets, laptops, and TVs. It is quite possible that many people today spend more time looking at an LCD than they spend looking at the real world.

If we look back to the birth of the technology, it solved a very real problem. The first digital watch in 1972, the Pulsar 1, was typical. You had to push a button to see the time because the LED display took so much power. But by 1973, engineers had perfected the twisted nematic field effect LCD, first patented by Swiss health care company Hoffmann-LaRoche in 1970. It consumed essentially zero power.

LCDs are also incredibly simple and therefore inexpensive to mass produce. An LCD display for a watch is a six-layer sandwich. At the bottom is a mirror. Next is a piece of plastic that polarizes light in one direction. Next is a piece of glass covered in a transparent conductor, usually indium tin oxide. Next is the twisted nematic liquid crystal layer. Then there’s another piece of glass with the display segments or pixels etched on using a clear conductor. On the top is another piece of plastic that polarizes light, offset 90 degrees from the first.

Because of the 90-degree offset, the two polarizing filters should block all light and turn the display black. But the liquid crystal layer twists the light 90 degrees as it passes through. So the display appears white. Applying a voltage to one of the segments destroys the twisting and the segment turns black. The display uses virtually no power because no current flows—it is a field effect.

Engineers then made a color display by shrinking the pixel size, adding a backlight, and adding RGB color filters over the pixels. The backlight consumes power, but the LCD itself is extremely efficient.

It is possible that the Active Matrix OLED display or something similar will eventually replace LCDs but that does not detract from the massive success engineers had with the LCD for several decades. It made many of the electronic devices we cherish today possible.

SEE ALSO Microwave Oven (1946), AMOLED Screen (2006), Smart Phone (2007), Tablet Computer (2010).

Pictured: Reflective twisted nematic with liquid crystal display.