LTPO Screen Technology

LTPO's full name is "Low-Temperature Polycrystalline Oxide". It is the current OLED screen mainstream- The combination of LTPS and IGZO.

LTPO Screen Technology

In 2019, Apple Watch 4 and Apple Watch 5 watches will be the first to adopt the LTPO screen, the new screen technology added to the Apple Watch 5 watch lifetime has also improved a lot, the lifetime increased to 18 hours, effectively solving the previous wearable devices do not give the problem of life, it can be said that the addition of LTPO screen for Apple Watch 5 is very significant.

What is LTPO screen technology? 

LTPO and OLED are not opposing perspectives, the two are two different things. LTPO is the driving method, while OLED is the display screen. LTPO is to provide OLED drive circuit, OLED screen needs TFT backplane support, and LTPO is one of the TFT backplane technology solutions.

 

LTPO's full name is "Low-Temperature Polycrystalline Oxide". It is the current OLED screen mainstream- The combination of LTPS and IGZO. Talking about this, we have to introduce the LTPS and IGZO two technologies, in order to ensure that you can read and understand, I try to use easy to understand words.

 

LTPS - low-temperature polycrystalline silicon, is now the technology used in most cell phone screens. The biggest advantage is to have ultra-high electron mobility, but also has a high resolution, high response rate, high brightness, high opening rate, and other advantages, but the disadvantages are also relatively obvious. Not only the high cost of production, and power consumption is also relatively large, due to Electron mobility is relatively large, leakage current is also relatively large, low drive power consumption is also larger, less suitable for low refresh rate.

 

Apple first began to use (low temperature) polysilicon as a transistor material in order to meet the needs of the high-end market, the display industry.

 

Compared to a-Si amorphous silicon, low-temperature polysilicon screens are thinner, more responsive, better color and brightness, and can make higher resolution screens because of the smaller size of the individual transistors.

 

Apple was able to make a "retina" screen, low-temperature polycrystalline silicon has not a small credit.

 

Most of the screens on cell phones, whether LCD route or OLED route, their internal transistors with low-temperature polysilicon material. Low Temperature, polycrystalline, silicon is the abbreviation of LTPS.

 

LTPO material's full name is called -- low temperature, polycrystalline, oxide.

 

The LTPS material is still used for the light-emitting transistors and driver transistors of LTPO screens, but the material for the switching transistors is replaced with Indium Gallium Zinc Oxide (IGZO) from low temperature polycrystalline silicon.

 

According to industry tests, the IGZO transistor has almost no leakage in the off state, which is better than a-Si and LTPS, and requires less current to turn on than LTPS.

 

Moreover, when the storage capacitor (Cst) is not charged for a long time, it does not cause screen flicker due to leakage, which is the hardware basis for the very low refresh rate of 1Hz.

 

In OLED panels, the conventional practice is to increase the TFT electron mobility and make the capacitor smaller in order to increase the panel resolution, while the capacitor size must be smaller due to the multiple transistors per pixel in OLED.

 

Smaller capacitors will inevitably make the channel resistance electrical signal delay, the most effective approach is to enhance the electron mobility through LTPS, in order to achieve the effect of power-saving. But LTPS still has a big problem, it is difficult to apply to large-size substrates, and LTPS for small and medium-sized OLED panels high-performance state is not optimized, that is, we have often mentioned in cell phones, notebooks, high refresh rate screen will be under LTPS, bringing higher power consumption.

 

From LTPO process patent documents, LTPO needs to build an oxide layer on top of LTPS. One of the most significant tackles last year was that manufacturers needed to ensure that the transistor characteristics in the original LTPS interlayer medium were not affected when laying down the oxide layer. With Apple starting mass production of OLED screens with LTPO and putting it on the Apple Watch, which has the number one share of smartwatches, are proving that Apple has made a big step forward in mass production of LTPO.

 

Cell phones equipped with LTPO screen technology also provide more control over the future development of cell phones, which will greatly improve the configuration of cell phones and add more features due to the improvement of the battery life. For example, the previous users have been longing for 2K screen + 120Hz high brush, now a plus 9 is not brought for everyone, and then the future 5G full coverage, always open 5G communication. If the problem of battery life is not solved, 2K high brush screen coupled with 5G communication, the phone's battery life must avalanche.

 

LTPO is also not the only doorway to explore screen power-saving technology, the mainstream believes that the technology can be applied to the OLED substrate in addition to the previously mentioned LTPS, silicon-based, and IGZO from Sharp, and molybdenum disulfide transistors from Yonsei University in South Korea.