TFT LCD 內部到底有什麼？

When you take apart a TFT panel layer by layer, and the stack is way more interesting than most people think. It's less "glass sandwich with water" and more a precision-engineered mille-feuille where every sheet does one very specific job. Here's the full tour, front to back of display.

Front polarizer of TFT LCD with anti-glare/anti-reflection treatment or other special treatment. The outermost film isn't just plastic. Its core is a uniaxially stretched PVA layer that has absorbed iodine, forming polyiodide complexes aligned along the stretch direction. Those complexes give the film dichroic absorption -light vibrating along one axis gets absorbed, light along the other passes. That's what produces linearly polarized output, the prerequisite for the liquid crystal to switch light at all. TAC films sandwich the PVA: the outer one is an optically isotropic support and moisture barrier, while the inner one can also carry retardation compensation to widen viewing angle. An AR/hard-coat treatment on top cuts surface reflections and scratches.

Front glass substrate of LCD. Ultrathin, chemically strengthened, and coated with a transparent conductive film-usually ITO (indium tin oxide). Depending on thickness and process, ITO transmittance at 550 nm can reach about 90% or higher (a 50 nm film lands around 90%; thinner films go higher). This is where the common electrode lives. Color filter layer of TFT LCD. Red, green, and blue subpixel resins, separated by a black matrix (chrome or black resin) that stops colors from bleeding into each other. Each color filter sits over its own ITO patch. This layer is the entire reason you get color instead of a gray blob.

Liquid crystal layer. Twisted nematic, IPS, or VA molecules sitting in a gap just a few microns thick, held in alignment by polyimide layers rubbed in one direction with a cloth. No voltage: molecules stay twisted and let polarized light through. Apply voltage: they straighten and block it. Cell-gap uniformity here is measured in microns-get it wrong and you get mura (blotches) everywhere.

TFT array glass. The backplane: a grid of thin-film transistors-amorphous silicon, IGZO, or LTPS-one per subpixel, each acting as a tiny switch that charges and holds its pixel capacitor. In the common bottom-gate configuration, the stack runs bottom-up: gate electrode, silicon nitride gate insulator, semiconductor layer, source/drain electrodes, then a passivation cap. Amorphous silicon is photosensitive, so the array side is shielded by the passivation layer plus the black matrix-not just by sealing the backlight.

TFT 的後偏光片。 

与前面的角度交叉 90°，因此“关闭”状态会阻挡光线，“开启”状态会通过光线。這對交叉的光閥是整個光閥的心臟。

TFT的背光单元。 

整個面板中最被低估的堆疊。自下而上：向前反射雜散光的反射片、將邊緣 LED 點光源散佈到均勻表面的導光板、使其平滑的擴散片，以及至少兩片棱鏡膜（一片水平，一片垂直）將散佈的光準直至觀察者。 

跳過其中任何一個，螢幕就會變暗或有斑點。這種堆疊也是黑色不是真正的黑色的原因——總是會有一些光洩漏。

LCD 的可選附加功能：防靜電層、防紫外線薄膜，有時還包括直接層壓到堆疊中的內嵌式觸控感應器網格。其天才之處在於，TFT LCD 的每一層都恰好解決了一個問題——偏振、顏色、切換、照明——而且所有這些都必須符合微米公差。