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--- screen_manufacturing [2026/05/29 17:52] – [Glass substrate fabrication] sophie
+++ screen_manufacturing [2026/06/01 01:31] (current) – [5. pixel fabrication] sophie
@@ Line 5: / Line 5: @@
 Once the glass substrates are ready, the next step depends on the kind of thin film transistor (TFT) backplane technology that is being employed. The TFT backplane is the electronic controller for the display and controls individual pixels within the display. There are several types of TFT backplanes such as amorphous silicon (a-Si), indium gallium zinc oxide (IGZO), low temperature polysilicon (LTPS), and low temperature polyoxide (LTPO).
 s
-## Transistor technology
-#### Amorphous silicon (a-Si)
-Amorphous silicon (a-Si) is the most mature and widely used backplane technology due to its straightforward manufacturing and scalability to massive substrate sizes. It involves depositing an unorganized silicon film via plasma-enhanced chemical vapor deposition (PECVD), which is highly cost-effective. While it is excellent for general applications, a-Si has low electron mobility (around 0.5 to 1.0 cm²/Vs), limiting its use in ultra-high-resolution or high-refresh-rate displays [( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]]). Additionally, it lacks the bias stability required for current-driven devices like OLEDs. Despite these limitations, a-Si remains the benchmark for mainstream TVs, budget notebooks, and desktop monitors. Recent efforts have focused on reducing mask counts (to 4 or 5) to further lower production costs
-[( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])].
-#### Indium-galium-zinc oxide (IGZO)
+---
+-
-IGZO, being a metal oxide semiconductor, represents a major leap in performance over a-Si. It offers 10 to 20 times higher mobility [(Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])], enabling smaller transistors that increase pixel aperture ratios and allow for higher resolutions. One of IGZO's most unique properties is its extremely low off-state leakage current, which permits low-refresh-rate driving (as low as 1Hz) to save power during static images [([[https://www.tandfonline.com/doi/full/10.1080/15980316.2023.2281224|Recent progress in liquid crystal devices and materials of TFT-LCDs]], Jung, Junho, et al. Journal of Information Display 25.1 (2024): 121-142)]. It is highly compatible with existing a-Si manufacturing lines, making it a scalable solution for large 8K TVs and high-end monitors. While it is more sensitive to moisture and oxygen, leading to the need for advanced passivation layers [([[https://www.tandfonline.com/doi/full/10.1080/15980316.2020.1818641|Recent progress in the development of backplane thin film transistors for information displays]], Ji, Dongseob, et al. Journal of Information Display 22.1 (2021): 1-11)], it is currently a leading backplane for both LCDs and large OLED TVs.
-#### Low-temperature polycrystalline silicon (LTPS)
-Low-temperature polycrystalline silicon (LTPS) is a high-performance backplane technology mainly used in premium smartphones and mobile devices. It is produced by using excimer laser annealing (ELA) to transform amorphous silicon into a highly organized crystalline structure. This results in very high electron mobility (often >100 cm²/Vs), allowing for much smaller transistors and the integration of complex circuits directly on the glass [( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])]. This technology, called system on glass (SOG), helps manufacturers create ultra-thin bezels in modern smartphones. However, the laser process is expensive, complex, and difficult to scale to large TV-sized substrates with uniform quality [( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])].
-#### Low-temperature polycrystalline oxide (LTPO)
-Low-temperature polycrystalline oxide (LTPO) is an advanced hybrid backplane technology that combines LTPS and oxide TFT technologies on the same substrate. LTPS transistors handle fast switching and processing tasks, while oxide transistors are used for pixel driving because they consume very little power. This combination allows displays to adjust refresh rates dynamically, switching from very high refresh rates for gaming to extremely low refresh rates, such as 1 Hz, for power saving [([[https://www.tandfonline.com/doi/full/10.1080/15980316.2020.1818641|Recent progress in the development of backplane thin film transistors for information displays]], Ji, Dongseob, et al. Journal of Information Display 22.1 (2021): 1-11)]. As a result, LTPO displays can significantly improve battery life. The manufacturing process is more complicated and expensive because it requires more photolithography steps and precise temperature control [([[https://www.tandfonline.com/doi/full/10.1080/15980316.2020.1818641|Recent progress in the development of backplane thin film transistors for information displays]], Ji, Dongseob, et al. Journal of Information Display 22.1 (2021): 1-11)]. Currently, LTPO is used in flagship smartphones and smartwatches, where energy efficiency and display performance are especially important.
-### Manufacturers
-- Samsung Display and LG Display are the dominant global producers of LTPS backplanes for high-resolution mobile devices and flexible OLEDs
-- Sharp Corporation is famous for the commercialization of IGZO (Oxide TFTs), applying it to their high-resolution LCDs and specialized handheld panels
-- BOE Technology Group mass-produces large panels using both Oxide TFTs for 8K televisions and LTPS for advanced mobile applications
-- AU Optronics (AUO) has established production lines for both technologies to compete in premium monitor and notebook segments
-- Sony and Panasonic have historically developed Oxide backplanes for large OLED TV prototypes and high-transmittance IPS monitors
-- For LTPO technology, Samsung and LG are currently the primary suppliers for high-end consumer electronics manufacturers
-----
 ## 0. Glass substrate fabrication
@@ Line 64: / Line 38: @@
 \\
+------------
 ## LCD screen manufacturing
@@ Line 219: / Line 196: @@
 Light from the LEDs enters a Light Guide Plate (LGP) designed to distribute it evenly across the screen area. The LGP uses internal reflection and surface patterns to direct light forward[( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])]. Multiple optical films, including diffuser sheets and prism films, are stacked on top of the LGP. Diffusers scatter the light to hide LGP patterns, while prism films collimate the light toward the viewer to enhance brightness. A reflector film is placed underneath the LGP to recycle escaping light. These components are securely held within a plastic module frame.
-#### Frame Assembly
-The completed LCD panel and backlight unit are integrated into a protective frame assembly. A plastic frame maintains the alignment of the optical films and the light guide. A metal bezel is then attached to provide structural strength and house the control electronics. Screws, adhesives, and clips are used to permanently join the module components. This housing protects the sensitive panel and circuits from external moisture and mechanical impacts[( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])]. Once assembled, the display is a complete module ready for final quality assurance.
-#### Final Testing
-The assembled module undergoes electrical and visual inspections before being shipped. Automated Optical Inspection (AOI) identifies dot pixel defects, line faults, and luminance non-uniformity. "Aging" is a common step where modules are operated in a high-temperature environment to ensure early-stage reliability[( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])]. Functional patterns (White, Black, Red, Green, Blue) are displayed to verify chromaticity and switching response. Modules with cosmetic flaws, such as scratches or cracks, are identified and sorted for repair or scrap. Only modules that pass all performance and safety standards are packaged for final shipment.
 ---
@@ Line 272: / Line 243: @@
   - it can work as a white subpixel in WRGB pixel structures. As there is no color filter layer in the white pixels, the empty space is filled with overcoat material, making it a white subpixel, for this reason, the overcoat layer should be thicker than the color layers.
-{{ :capture_d_ecran_2026-04-16_160810.png?direct&400 |}
+{{ :capture_d_ecran_2026-04-16_160810.png?direct&400 |}}
-}
 ### 5. pixel fabrication
 #### anode fabrication
+The anode is formed on the substrate and the pixel control circuit. In the case of bottom-emission, the anode must be transparent to allow light to pass through it. Conversely, if the OLED is configured for top-emission, the anode must be reflective. The light passes through the cathode, and the reflective properties of the anode serve primarily to increase the light output efficiency. {{ref>anodefab}} illustrates the deposition of the anode (coloured in yellow) onto a TFT substrate of a white OLED.
+<figure center|anodefab>
 {{ :capture_d_ecran_2026-04-16_160913.png?direct&400 |}}
+<caption> anode fabrication one the substrate </caption>
+</figure>
 #### bank fabrication
-An organic insulator film is used to set apart different colors with a blank layer, and to prevent short circuit between the electrodes. The organic insulator film should be selected among those materials that would not absorb moisture and that show minimum outgassing [([[https://doi.org/10.1002/j.2168-0159.2012.tb06108.x|Transmissive Low Outgassing Organic Insulator Suitable for Various OLED Displays]], Hiroaki Shindo, Takashi Tsutsumi, Takaaki Sakurai, Masahiro Hanmura, Akira Honma, 2012)].
-{{ :capture_d_ecran_2026-04-16_161258.png?direct&400 |}}
+An organic insulator film is used to set apart different colors with a blank layer, and to prevent short circuit between the electrodes. The organic insulator film should be selected among those materials that would not absorb moisture and that show minimum outgassing [([[https://doi.org/10.1002/j.2168-0159.2012.tb06108.x|Transmissive Low Outgassing Organic Insulator Suitable for Various OLED Displays]], Hiroaki Shindo, Takashi Tsutsumi, Takaaki Sakurai, Masahiro Hanmura, Akira Honma, 2012)]. The figure illustrates the addition of the insulating layer to the anode. {{ref>bakfab}} illustrates the addition of the insulating layer to the anode during the manufacture of a white OLED.
+<figure center|bakfab>
+{{ :capture_d_ecran_2026-04-16_161258.png?direct&400 |}}
+<caption> insultating layer fabrication on the anode and TFT substrate </caption>
+</figure>
 #### cleaning
-several possibilites for cleaning treatment: wet[([[https://pubs.aip.org/aip/apl/article-abstract/70/20/2741/67015/Effects-of-aquaregia-treatment-of-indium-tin-oxide?redirectedFrom=fulltext|Effects of aquaregia treatment of indium–tin–oxide substrates on the behavior of double layered organic light-emitting diodes]], F. Li, H. Tang, J. Shinar, O. Resto, S. Z. Weisz, 1997)], plasma (e.g.O, N and Ar gases in plasma state)[([[https://pubs.aip.org/aip/apl/article-abstract/70/11/1348/67449/Surface-modification-of-indium-tin-oxide-by-plasma?redirectedFrom=fulltext|Surface modification of indium tin oxide by plasma treatment: An effective method to improve the efficiency, brightness, and reliability of organic light emitting devices]], C. C. Wu, C. I. Wu, J. C. Sturm, A. Kahn, 1997)], UV ozone [([[https://sml.hkbu.edu.hk/pdf/ASS_adxps_uvo_ito.pdf|Angle dependent X-ray photoemission study on UV-ozone treatments of indium tin oxide]], Weijie Song, S.K. So, Daoyuan Wang, Yong Qiu, Lili Cao, 2001)]. Plasma treatment show good effectivness [(flat panel handbook, p.149)]
+There are several cleaning treatment: wet[([[https://pubs.aip.org/aip/apl/article-abstract/70/20/2741/67015/Effects-of-aquaregia-treatment-of-indium-tin-oxide?redirectedFrom=fulltext|Effects of aquaregia treatment of indium–tin–oxide substrates on the behavior of double layered organic light-emitting diodes]], F. Li, H. Tang, J. Shinar, O. Resto, S. Z. Weisz, 1997)], plasma (e.g.O, N and Ar gases in plasma state)[([[https://pubs.aip.org/aip/apl/article-abstract/70/11/1348/67449/Surface-modification-of-indium-tin-oxide-by-plasma?redirectedFrom=fulltext|Surface modification of indium tin oxide by plasma treatment: An effective method to improve the efficiency, brightness, and reliability of organic light emitting devices]], C. C. Wu, C. I. Wu, J. C. Sturm, A. Kahn, 1997)], UV ozone [([[https://sml.hkbu.edu.hk/pdf/ASS_adxps_uvo_ito.pdf|Angle dependent X-ray photoemission study on UV-ozone treatments of indium tin oxide]], Weijie Song, S.K. So, Daoyuan Wang, Yong Qiu, Lili Cao, 2001)]. Plasma treatment show good effectivness [(flat panel handbook, p.149)]
 #### organic material depositions
-There are various stacks of material possible, depending on the display size or even on the display performance (brightness, power consumption). A one-stack OLED consists of the superposition of anode, HIL, HTL, EML, ETL, EIL, cathode. A two-stacked OLED consists of two one-stack OLED in series connection. The interconnection layer is called a charge generation layer (CGL) and plays both roles of anode and cathode.
+There are various stacks of material possible, depending on the display size or even on the display performance (brightness, power consumption). A one-stack OLED consists of the superposition of anode, HIL, HTL, EML, ETL, EIL, cathode. A two-stacked OLED consists of two one-stack OLED in series connection. The tables below set out the material layouts for these different options. The interconnection layer is called a charge generation layer (CGL) and plays both roles of anode and cathode.
 ^ one-stack RGB side-by-side OLED ^ material ^
@@ Line 330: / Line 308: @@
 |Synthesis and Characterization of Iridium Complex for Green Organic Light Emitting Devices]], Ritu Srivastava))].
+<figure center|emittermaterialdeposition>
 {{ :capture_d_ecran_2026-04-15_175209.png?direct&400 |}}
+<caption> Sequential deposition of emitter materials (red, green, and blue) via thermal vacuum evaporation combined with an FMM in the case of a side-by-side RGB OLED </caption>
+</figure>
   * **vacuum thermal evaporation with open mask** - _for larger sized display_: the use of an FMM is not appropriate due to a loss of resolution when the substrate size is increased (there has been a concluant FMM deposition for larger sized screen - 55 inches - but it seems it never reached the production scale).
+<figure center|resolutionFMM>
 {{ :capture_d_ecran_2026-04-15_175500.png?direct&400 |}}
+<caption> Difference in resolution during deposition via vacuum thermal deposition combined with an FMM for a small substrate (left) and a large substrate (right) </caption>
+</figure>
+[comment]: <> (
-_to be deleted or moved in an other topic. Some notes about the size of the screen and what is considered "small" or "large".
+to be deleted or moved in an other topic. Some notes about the size of the screen and what is considered "small" or "large".
 In 2009 LG commercialized a 15-inch OLED TV --> this is nowadays more the size of a laptop screen. When reading article that were written at this period of time we have to be carefull with the adjectives "large" and "small" applied to screen._
+)
+All the materials for the organic layers (HIL, HTL, EML, ETL) are therefore deposited using the methods described above.
-##### HIL (hole injection layer) and HTL (hole transport layer) deposition
-TBA
-##### EML (emission layer) deposition
-TBA
-##### ETL (electron transport layer) deposition
-TBA
 #### cathode fabrication
@@ Line 357: / Line 333: @@
 The cathode is mostly made of Al or Ag [(OLED_fundamentals > [[https://ia801606.us.archive.org/35/items/ebooks_201907/Daniel%20J.%20Gaspar%2C%20Evgueni%20Polikarpov%20-%20OLED%20Fundamentals_%20Materials%2C%20Devices%2C%20and%20Processing%20of%20Organic%20Light-Emitting%20Diodes-CRC%20Press%20%282015%29.pdf | Daniel J. Gaspar, Evgueni Polikarpov - OLED Fundamentals_ Materials, Devices, and Processing of Organic Light-Emitting Diodes-CRC Press (2015)]])] for bottom-emission (it needs to be reflective), and and Mg:Ag [(OLED_fundamentals)] for top-emission (semi-transparent).
-The processes used for deposition of the cathode are either **vacuum thermal evaporation combined with an FMM** (Fine Metal Mask)[([[https://advanced.onlinelibrary.wiley.com/doi/epdf/10.1002/aelm.202500555|Vacuum Thermal Evaporation for OLEDs: Fundamentals, Optimization, and Implications for Perovskite LEDs] for small displays, or **vacuum thermal evaporation with open mask** for large displays.
+The processes used for deposition of the cathode are either **vacuum thermal evaporation combined with an FMM** (Fine Metal Mask)[([[https://advanced.onlinelibrary.wiley.com/doi/epdf/10.1002/aelm.202500555|Vacuum Thermal Evaporation for OLEDs: Fundamentals, Optimization, and Implications for Perovskite LEDs]])] for small displays, or **vacuum thermal evaporation with open mask** for large displays.
-\\
+\
+\
 ### 6. Encapsulation
@@ Line 421: / Line 397: @@
 This method can be used for flexible screens.
 Sources : ([https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing]
-)
-### 7. Assembly
+---------------
+## 7. Frame Assembly
+The completed panel unit is integrated into a protective frame assembly. A plastic frame maintains the alignment of the optical films and the light guide. A metal bezel is then attached to provide structural strength and house the control electronics. Screws, adhesives, and clips are used to permanently join the module components. This housing protects the sensitive panel and circuits from external moisture and mechanical impacts[( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])]. Once assembled, the display is a complete module ready for final quality assurance.
 ----
-### 8. Testings
+## 8. Testings
+The assembled module undergoes electrical and visual inspections before being shipped. Automated Optical Inspection (AOI) identifies dot pixel defects, line faults, and luminance non-uniformity. "Aging" is a common step where modules are operated in a high-temperature environment to ensure early-stage reliability[( Flay_Panel_Display_Manufacturing>[[https://www.wiley.com/en-es/Flat+Panel+Display+Manufacturing-p-9781119161363|Flat Panel Display Manufacturing, Jun Souk, Shinji Morozumi, Fang-Chen Luo, Ion Bita, 2018]])]. Functional patterns (White, Black, Red, Green, Blue) are displayed to verify chromaticity and switching response. Modules with cosmetic flaws, such as scratches or cracks, are identified and sorted for repair or scrap. Only modules that pass all performance and safety standards are packaged for final shipment.
 ----
+## References