Hardware Reference
In-Depth Information
Active-Matrix Displays
LCD panels use a type of active-matrix technology known as a
thin-film transistor (TFT)
array. TFT is a method for packaging from one (monochrome) to three (RGB color) tran-
sistors per pixel within a flexible material that is the same size and shape as the display.
Thus, the transistors for each pixel lie directly behind the liquid crystal cells they control.
Two TFT manufacturing processes account for most of the active-matrix displays on the
markettoday:hydrogenatedamorphoussilicon(a-Si)andlow-temperaturepolysilicon(p-
Si). These processes differ primarily in their costs. At first, most TFT displays were man-
ufactured using the a-Si process because it required lower temperatures (less than 400°C)
than the p-Si process of the time. Now, lower-temperature p-Si manufacturing processes
are making this method an economically viable alternative to a-Si.
ToimprovehorizontalviewinganglesinthelatestLCDs,somevendorshavemodifiedthe
classic TFT design. For example, Hitachi's in-plane switching (IPS) design—also known
as STFT—aligns the individual cells of the LCD parallel to the glass, running the elec-
tric current through the sides of the cells and spinning the pixels to provide more even
distribution of the image to the entire panel area. Hitachi's Super-IPS technology also re-
arranges the liquid crystal molecules into a zigzag pattern, rather than the typical row-
columnarrangement,toreducecolorshiftandimprovecoloruniformity.Thesimilarmul-
tidomain vertical alignment (MVA) technology developed by Fujitsu divides the screen
into different regions and changes the angle of the regions.
Both Super-IPS and MVA provide a wider viewing angle than traditional TFT displays.
Othercompanieshavedifferentnamesforthesametechnology—forexample,Sharpcalls
it Ultra High Aperture (UHA). Manufacturers often like to think up their own buzzwords
for the same technology because it makes their products seem different, but the results
they generate are largely the same. Because larger LCDs can exhibit shifts in viewing
