How is TFT active matrix manufactured?
As a supplier of TFT active matrix, I am often asked about the manufacturing process of this essential component in modern display technology. In this blog, I will take you through the detailed steps of how TFT active matrix is manufactured, shedding light on the intricate processes that bring high - quality displays to life.
1. Substrate Preparation
The first step in manufacturing a TFT active matrix begins with the selection and preparation of the substrate. Usually, glass is the preferred material for the substrate due to its smooth surface, high transparency, and good thermal stability. The glass substrate is cleaned thoroughly to remove any dust, dirt, or organic contaminants. This is typically done using a combination of chemical cleaning agents and de - ionized water in a cleanroom environment. The cleanroom is crucial as even the tiniest particle can cause defects in the final product.
Next, a thin layer of silicon dioxide (SiO₂) is deposited on the glass substrate. This layer serves as an insulating layer between the substrate and the subsequent layers of the TFT structure. Chemical vapor deposition (CVD) is a common method for depositing this silicon dioxide layer. During CVD, precursors in the gas phase react on the surface of the substrate to form the desired thin film.
2. Semiconductor Layer Deposition
After the substrate is prepared, the semiconductor layer is deposited. Amorphous silicon (a - Si) is widely used in TFT active matrix manufacturing because of its relatively simple deposition process and good electrical properties. Plasma - enhanced chemical vapor deposition (PECVD) is the standard technique for depositing amorphous silicon.
In PECVD, a plasma is created from a mixture of silane (SiH₄) gas and hydrogen (H₂) gas. The plasma breaks down the silane molecules, and silicon atoms are deposited on the substrate to form the amorphous silicon layer. The thickness of the amorphous silicon layer is carefully controlled, usually in the range of 100 - 200 nanometers. This semiconductor layer will later form the channel region of the thin - film transistors.
3. Gate Insulator Deposition
Once the semiconductor layer is in place, a gate insulator layer is deposited on top of it. Silicon nitride (Si₃N₄) is commonly used as the gate insulator material because of its high dielectric constant and good insulating properties. Similar to the previous deposition steps, PECVD is also used to deposit the silicon nitride layer.
The gate insulator layer serves to electrically isolate the gate electrode from the semiconductor channel. Its quality is of utmost importance as any defects in this layer can lead to leakage currents and poor transistor performance. The thickness of the gate insulator layer is typically around 300 - 500 nanometers.
4. Gate Electrode Formation
After the gate insulator is deposited, the gate electrode is formed. The most common material for the gate electrode is chromium (Cr) or molybdenum (Mo). A thin layer of the chosen metal is deposited on the gate insulator using physical vapor deposition (PVD) techniques such as sputtering.
In sputtering, a high - energy plasma bombards a target made of the metal. Atoms from the target are ejected and deposited on the substrate to form the gate electrode layer. Photolithography is then used to pattern the gate electrode. A photoresist is applied to the metal layer, exposed to ultraviolet light through a mask, and then developed. The unexposed photoresist is removed, and the underlying metal is etched away, leaving behind the desired gate electrode pattern.
5. Source and Drain Formation
The next step is to form the source and drain regions of the TFT. This involves implanting impurities into the amorphous silicon layer to create n - type or p - type regions. Phosphorus is commonly used for n - type doping. Ion implantation is the technique used to introduce these impurities into the semiconductor layer.
After ion implantation, a heat treatment process called annealing is carried out. Annealing helps to activate the implanted impurities and repair any damage to the crystal structure of the amorphous silicon caused by the ion implantation process. Similar to the gate electrode formation, photolithography and etching are used to pattern the source and drain electrodes. A metal layer, usually aluminum (Al), is deposited and patterned to form the source and drain contacts.
6. Passivation Layer Deposition
Once the source and drain regions are formed, a passivation layer is deposited on top of the entire structure. The passivation layer protects the TFTs from environmental factors such as moisture and oxygen, which can degrade the performance of the transistors over time. Silicon nitride or silicon dioxide can be used as the passivation layer material, and PECVD is used for its deposition.
The passivation layer also helps to planarize the surface of the TFT active matrix, making it suitable for the subsequent deposition of other layers, such as the color filter and the liquid crystal layer in a TFT - LCD display.
7. Pixel Electrode Formation
The final step in the TFT active matrix manufacturing process is the formation of the pixel electrodes. Indium tin oxide (ITO) is the material of choice for pixel electrodes because of its high transparency and good electrical conductivity. ITO is deposited on the passivation layer using sputtering.
Photolithography and etching are again used to pattern the ITO layer into individual pixel electrodes. Each pixel electrode is connected to the source electrode of its corresponding TFT. This allows for the independent control of each pixel in the display, enabling the display to show different colors and intensities.
Application in Displays
The manufactured TFT active matrix is a key component in various types of displays, such as TFT - LCDs. When combined with a color filter, a liquid crystal layer, and polarizers, it forms a complete display panel. The TFTs in the active matrix act as switches, controlling the voltage applied to each pixel. By adjusting the voltage, the orientation of the liquid crystal molecules can be changed, which in turn controls the amount of light passing through the pixel and thus the color and brightness of the pixel.
If you are interested in high - quality TFT active matrix products, we offer a wide range of solutions suitable for different applications. For example, our 15.0 Inch 1024x768 TFT LCD Display showcases the excellent performance of our TFT active matrix technology. It provides clear and sharp images, making it ideal for applications such as industrial control panels, medical devices, and digital signage.
Contact for Purchase
If you are in the market for TFT active matrix products or have any questions about our manufacturing process, we encourage you to reach out to us. We are ready to have in - depth discussions with you about your specific requirements and provide you with the best solutions. Whether you need a small - scale prototype or a large - scale production order, we have the expertise and resources to meet your needs.
References
- Sze, S. M., & Ng, K. K. (2007). Physics of Semiconductor Devices. Wiley.
- Bhattacharya, P. K. (2006). Semiconductor Optoelectronic Devices. Prentice Hall.
- Kuo, C. - C., & Lin, J. - H. (2012). Thin - Film Transistors: Principles, Technologies, and Applications. Wiley.