- With the kick-off of the UHD TV market, the Cu electrode has become the key in producing LCD panels.
- With higher electric conductivity compared to Al or Mo electrodes, the Cu electrode has advantages in realizing panels in large sizes, with high brightness and high resolution.
- The change to use Cu electrodes requires mass production technology and modification in production lines.
- LG Display is more than five years ahead of its competitors in the Cu electrode technology.
- After Samsung Display started mass production of the Cu electrode in 2010, AUO, Innolux, BOE, and CSOT followed suit beginning 2013.
Why Cu electrodes?
Until the mid-2000s, most of TFT-LCD panel makers, excluding Sharp Corporation, have been using aluminum (Al) for the gate and S/D electrodes. (Molybdenum (Mo) or Mo alloy used for the barrier.) Some devices apply chromium (Cr), but more than 90% of the time, Al was used. But as TV size gets bigger, the industry demanded metal electrodes with low resistance, raising the need for copper (Cu) electrodes.
The Cu electrode has higher electrical conductivity than the Al electrode. So even if the Cu wiring is made relatively thin, it can send stable signals as it almost doesn't cause any distortion in electrical signals. As a result, the response rate and brightness can improve. Also, it does not require additional substance or process, which are usually needed to manufacture large-sized TV panels to make up for the lack of electrical conductivity.
It is not impossible to realize the ultra-high definition (UHD) resolution using the traditional electrode materials. One could make the wiring thicker or increase the number of driver integrated circuits (ICs) used. But such methods would eventually weaken the product’s competitive edge, and particularly for a UHD LCD panel, they would not be favored. As a result, many companies have been investing in the R&D to apply Cu electrodes to the mass production of TFT-LCD panels.
History of Cu electrode application to the mass production of LCD panels
LG Display (LGD) applied Cu electrodes to its mass production lines in 2006 for the first time in the world. LGD sharply raised the application rate of Cu electrodes in 2008-2009 and now they are applied to most of its products. Since LGD introduced Cu electrodes, Samsung Display Co. (SDC), AU Optronics Corp. (AUO), Innolux Corporation, Panasonic LCD, and Sharp have also been seeking to apply Cu electrodes, but none of the companies succeeded until 2010.
In the second half of 2010, SDC (then Samsung Electronics) started applying the Cu electrode to the mass production lines. It was the world’s second company that succeeded in using the metal electrode for mass production. But SDC experienced a lot of difficulties in the initial stage, so it took some time until it expanded the application of the material. Since 2013, SDC has used the Cu electrodes in most of its mass production lines. In the beginning, its application rate of Cu electrodes to S/D was extremely low, but recently, the rate has been rising significantly.
Companies other than LGD also recognized the need for Cu electrodes and proceeded with R&D, but they haven’t been able to apply Cu electrodes for at least five years since LGD began to apply. But with panel resolution swiftly advancing and UHD-level panels being mass produced, the need for Cu electrodes is growing.
In line with this mood, SDC is sharply raising the application rate of Cu electrodes. After a long development effort, Taiwan’s AUO also began to apply Cu electrodes to its mass production lines in 2013 in full scale. In addition, as production of UHD panels kicked into high gear in 2013-2014, Chinese panel makers, which are gearing up for mass production of UHD panels, are also putting efforts to use Cu electrodes. In 2014, Shezhen China Star Optoelectronics Technology Corporation (CSOT) and BOE Technology Group Co. (BOE) already applied or plan to apply Cu electrodes to some of their devices.
Led by AUO and BOE, Taiwanese/Chinese companies also employing Cu electrodes
AUO is almost the only Taiwanese company that is using Cu electrodes, while other Taiwanese companies haven’t joined the trend yet because of expenses needed to convert to Cu; panel prices; and technological difficulties. Since 2013, AUO has applied Cu electrodes to the 8G lines and is gradually expanding the application. But the application rate is still low. It is employing the Cu electrode only for full HD TV panels. Development is currently underway to apply it to UHD panels in the future. UHD panels are currently using Al electrodes, but they are highly likely to change to Cu electrodes within 2014. Cu electrodes haven’t been employed in 6G lines yet, but once its 8G lines stabilizes, the application of Cu can be expected in the lines as well.
Innolux just started applying Cu electrodes to its mass production. It is using the material for part of products produced in the Fab7, and development is underway at Fab6. But the application rate of Cu electrodes seems marginal. Innolux is producing UHD panels using Al electrodes, and is not optimistic about the effects of the conversion to Cu. Yet, demand for the change is increasing from the customer side.
China-based BOE hasn’t applied Cu electrodes to mass production yet. Currently, it is testing the application of Cu electrodes to mass production beginning with its B5 lines located in Hefei. The Cu/Mo(Nb) structure is used for both its gate and S/D electrodes. If the mass production test proceeds as planned, it is likely to apply Cu electrodes to a mass production line beginning the second half of this year. But it is highly likely to apply Cu electrodes to the products from a B5 line within this year, initially for 55-inch panels.
CSOT is likely to apply Cu electrodes to part of the products from the mass production lines beginning 2014. It applied Cu/Mo to both gate and S/D electrodes. So far, it is highly likely to apply Cu electrodes to 49-inch UHD panel production, but once mass production stabilizes, the application is expected to expand to other lines.
With the kick-off of the UHD panel, needs for Cu wiring has increased. No wonder major TFT-LCD panel makers started expanding the application of Cu wirings or plan to do so. Naturally, it is expected that Cu will be the mainstream in the TFT-LCD panel wirings.