Samsung is the latest TV manufacturer to demonstrate a technology that uses a type of backplane—the array of transistors used to switch the pixels on and off—based on metal oxide semiconductors. These materials offer higher performance than the amorphous silicon widely used today, without increasing costs. In April, manufacturer Sharp announced it will begin manufacturing displays based on metal oxide transistor arrays by the end of the year at its plant in Kameyana, Japan.
Metal oxide semiconductors conduct electrons very rapidly, and they can be deposited using relatively inexpensive methods. The hurdle has been figuring out which mixtures of metals to use and how exactly to work with them on today's equipment, says Randy Hoffman, a senior engineer at HP. The leading material is now a mixture of indium, gallium, and zinc called IGZO.
Semenza speculates that Sharp might be planning to take advantage of the high pixel densities enabled by metal oxide backplanes to make crisper mobile displays. Based on the size of the equipment at the company's Kameyana production line, he speculates that the company may be aiming to provide a high-resolution tablet display, perhaps for the next generation of Apple's iPad. "The high-water mark for this," says Semenza, "is the retina display" in the latest iPhone, which uses an expensive backplane based on another form of silicon transistor called low-temperature polysilicon. Metal oxide transistor arrays are less expensive to make and provide the necessary performance. Sharp might be able to offer a very good performance alternative to the retina display at a lower price, says Semenza.
Volume manufacturing of metal oxide backplanes could also be a boon for richly colored, energy-efficient organic light-emitting diode displays (OLEDs). These displays have been incorporated into some mobile devices and small high-end televisions, but they tend to be expensive. Part of the problem is that they can't be made with conventional backplanes: the high currents needed for these devices burn out amorphous-silicon transistors. So, OLED makers have been using the expensive polysilicon backplanes. Replacing those with metal oxide backplanes could make OLEDs more competitive.
Other qualities of metal oxides will be attractive in future display technologies, says HP's Hoffman. Every layer in a display tends to absorb some light and decrease overall efficiency and brightness. But metal oxides are transparent, so displays with these backplanes should get more light out and operate more efficiently. Hoffman expects this to be a particular advantage in reflective displays. HP is working on a flexible display that integrates a metal oxide backplane with a full-color reflective display.
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