Ongoing advances in smartphone functionality are driving increases in screen size and pixel density, even as power consumption continues to be a critical performance issue, according to a report from NPD DisplaySearch.
For these reasons, low temperature polysilicon (LTPS) thin-film transistor (TFT) liquid crystal displays (LCDs) are increasing their share of the mobile phone display market. LTPS-based displays enable high resolution at lower power consumption than other panels, and they can therefore command higher prices.
A higher process temperature is required to manufacture LTPS, compared to traditional a-Si or oxide TFT manufacturing, and the photomask process is more complicated, the report noted.
While the standard a-Si TFT process requires five to six photomask steps, LTPS TFT requires nine to 12, which increases capital investment required and increases the difficulty of achieving high yield rates.
For instance, for five-inch smartphone panels with 1920×1080 resolution, LTPS TFT LCD panel cost is 14 percent higher than a-Si TFT LCD, due mainly to lower yield rate and higher equipment cost.
On the production side, the technology is currently dominated by three players, including Japan Display, Sharp and LG Display, the report noted.
For mobile phone displays with pixel density higher than 300 pixels per inch (PPI), LTPS TFT-LCD is the preferred technology, which is why many panel makers are now gearing up development of LTPS, including a long line of Chinese manufacturers including BOE, Tianma, Infovision and Century.
“Despite the added complexity in producing LTPS TFT-LCDs, requirements for high resolution and longer battery life in smartphones will continue to drive growth in this technology,” David Hsieh, vice president of the greater China market at NPD DisplaySearch, said in a statement. “Meanwhile, after a decade of manufacturing experience, many LTPS TFT-LCD panel makers have reached high yield rates, which enable high production volumes.”
The report said the mobile phone revenue share of LTPS-based displays is expected to reach 44 percent in 2014 and 51 percent in 2020, as unit volume increases from 19 percent of shipments in 2013 to 33 percent in 2020.
Meanwhile, LTPS TFT-LCDs accounted for 37 percent of mobile phone display revenues in 2013, surpassing AMOLED displays, a-Si (amorphous silicon) TFT LCD, and oxide TFT LCD.
While smartphones have been the dominant application for LTPS TFT-LCDs, the technology is being adopted for high-resolution tablet PCs. At the recent Consumer Electronics Show (CES) 2014, Samsung announced the first LTPS-based tablet PC, the Galaxy Tab Pro.
“The benefit of LTPS is higher pixel density, lower consumption and driving circuits that can be integrated on the glass substrate,” Hsieh said.
