IBM researchers have discovered a new process for manufacturing computer displays that, they say, can vastly improve screen quality and viewing angles while saving manufacturers millions of dollars. The breakthrough, they add, holds the first real potential to replace a nearly century-old technique that all manufacturers currently use to build display products.
IBM has demonstrated a new non-contact method that uses beams of ions – electrically charged atoms – to align the liquid crystal molecules inside the flat-panel liquid crystal displays used in portable and desktop computers and other electronic devices. The new method is the first to replace a process discovered 95 years ago that proved when a substrate is rubbed, it forms a pattern that the liquid crystals align to. Although scientists cannot fully explain how this rubbing process works, it has been used for building displays with LCDs for about 20 years.
IBM is considering licensing the patented process to other manufacturers in the $20 billion per year flat-panel display industry and expects to have converted the pilot-line it used to develop this new technique into a full-blown production line by the end of the year.
When properly aligned, the molecules inside an LCD turn pixels on and off by twisting and rotating in response to electronic signals sent by the computer processor. Until now, the only method to reliably align the molecules involved rubbing a polymer substrate with a velvet cloth. When placed onto the ‘rubbed’ substrate, the liquid crystal molecules line up along the rubbing direction as if they were in a precision marching band.
Without rubbing, the liquid crystal molecules would orient themselves in many different directions and would not be controlled uniformly, resulting in a useless flat-panel display.
‘Replacing the rubbing process has been a ‘Holy Grail’ of flat-panel display manufacturing,’ said Praveen Chaudhari, lead scientist on the project, IBM Research. ‘Display manufacturers told us that the single most important thing that science could do to improve their business was to invent a non-contact method for aligning liquid crystals. When our new process is successfully integrated in manufacturing, it will enable new generations of displays that are higher quality and lower cost.’
The first step in IBM’s new method is to deposit a thin layer of diamond-like carbon instead of using a polymer substrate. Next, atoms are shot by an ion gun at an angle that push aside many of the surface carbon atoms, forming atomic-scale rows. When the rod-shaped liquid crystal molecules are added, one end of each molecule attaches to an exposed carbon atom, resulting in the alignment of all the liquid crystal molecules in the direction of the rows.
IBM’s new method reduces manufacturing time and produces higher-quality displays, especially at higher resolutions. Since its discovery in 1906, rubbing to align liquid crystals has been developed into a high art. Manufacturers use an object similar to a paint roller with a velvet cloth attached, which is run across the surface of a substrate. It is believed that the threads of the roller make contact with the atoms, hooking them much like the two sides of Velcro hook together. As the roller passes along the substrate, it drags the hooked atoms across the surface, which can cause streaks and scratches which will be most noticeable in higher resolution displays.
While the rubbing technique is a viable one, it has many disadvantages. The rubbing process is still not entirely understood, which makes it difficult to improve or to solve problems that arise. Replacing worn velvet clothes every shift interrupts the manufacturing process. Defects caused by the rubbing process cannot be detected until much later in the manufacturing process, when they are difficult or impossible to correct.
As a result, today countless displays must be discarded, wasting time and money. Rubbed displays must be removed from the clean room manufacturing line to avoid contamination from the velvet cloths used in rubbing. Then they must be washed and baked to eliminate contaminants before returning to the manufacturing line. Since it is built right into the clean manufacturing line, IBM’s new method does not require those extra steps and saves space as well.
The first public demonstration of a prototype display made with IBM’s new ion-beam liquid-crystal-alignment process will be conducted at the annual meeting of the Society of Information Display, which will be held June 3-8, 2001 in San Jose, CA.