TFT LCD Basic Knowledge
What is TFT Display?
Brief History of TFT LCDs
1957 – John Wallmark of RCA filed a patent for a thin film MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
1992 – Paul K. Weimer of RCA leveraged Wallmark’s patent and developed thin-film transistor technology (TFT).
1968 – Bernard Lechner of RCA implemented TFT technology in the liquid-crystal display (LCD) for the first time
1971 – Lechner, F. J. Marlowe, E. O. Nester, and J. Tults demonstrated a 2-by-18 matrix display driven by a hybrid circuit using the dynamic scattering mode of LCDs.
1973 – T. Peter Brody, J. A. Asars, and G. D. Dixon at Westinghouse Research Laboratories developed a CdSe (cadmium selenide) TFT,
1974 – Brody and Fang-Chen Luo demonstrated the first flat active-matrix liquid-crystal display (AM LCD) using CdSe TFTs,
1975 – Brody coined the term “active matrix LCDs”,
2020 – TFT LCD display technology dominants the display market now. Within the last 20 years, it has crushed the market of CRT (cathode-ray tube) and plasma technology. The only challenges TFT technology currently faces are OLED (organic light-emitting diode)and micro LED.
How Do TFT Displays Work
TFT LCD Display (Thin-Film-Transistor Liquid-Crystal Display) technology is made of a liquid crystal material sandwiched between two glass plates. Two polarizer filters, color filters (RGB aka red/green/blue), and two alignment layers determine the exact amount of light that is allowed to pass through and what colors the light will be. In summary, the TFT layer controls the amount of light, the color filter determines the color, and the top layer is where the visible screen is housed.
To control the amount of light that passes through the display, an applied electrical charge changes the modifies the molecular structure of the liquid crystal material which allows various wavelengths of backlight to “pass-through” the TFT display. TFT LCDs have capacitors and transistors. The active matrix of the TFT display is in constant flux and refreshes rapidly depending upon the incoming signals from the control device.
The pixels of TFT displays are determined by the underlying density (resolution) of the color matrix and TFT layout. The more pixels the higher detail is available. Available screen size, power consumption, resolution, interface (how to connect) define the TFT displays.
The TFT screen itself can’t emit light like OLEDs can, it has to be used in conjunction with a back-light of white bright light to generate a picture. Newer panels utilize LED backlight (light emitting diodes) to generate their light and therefore utilize less power and require less depth by design.
TFT display modules include the TFT display screen, LED backlight, and driving circuitry.
TFT Benefits and Uses
TFT LCDs offer several advantages over other types of displays (CRT, Plasma). It is light, thin, and energy efficient which is key to enabling modern consumer devices such as mobile phones, laptops, LCD TVs, flat computer LCD monitors, and especially smaller handhold devices possible. TFT LCDs are also relatively inexpensive which makes it the current dominant technology in the display world.
When we say types of LCD technology, there are two kinds: active TFT color display and monochrome passive display. Before TFT display was invented, the world used passive matrix LCD for many years. Passive matrix LCD can only be used for monochrome displays such as calculators, watches (not color smart watches), thermostats (not Nest), utility meters, etc. It is thanks to TFT LCD, that display world is so much more colorful.
New TFT Technologies
TFT technology used to have viewing angle and slow response time issues. However, thanks to the IPS display (in-plane switching), a new TFT LCD screen technology, those industry issues have been resolved. For future development, the TFT LCDs are continually getting bigger (146 inches by Samsung at CES’19), high resolution (8K 7680 × 4320 pixels), faster refresh rates which is good for gaming, wider viewing angles which is good up to 170 degrees, high contrast ratio for most demanding aviation monitors, high image quality fitting most critical medical surgery computer monitors, and combining with PCAP (capacitive touch screen).