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    LED on Silicon: LEDoS - Two Approaches

      Kei May Lau
     Feb 24, 2015

    LUE in LCD system- Light utilized efficiency in an LCD system is typically 5%, UP to 95% of the light consumed by TFT panel, polarized, LC, and colour filters, Very powerful LED BLU is demanded behind the stage, High brightness LED BLU brought opportunities to Pico- Projectors using LCos(Liquid Crystal silicon). Liquid Crystal Silicon- Potable, more brightness desired, Lower than 10% LUE, Only 10-30lm light output with a 450lm LED backlight, 50 minitues operating time with a standard battery, Moving LEDs from back Stage to the front. From LCDs to LEDos- Moving LED direct display with active matrix addressable driving circuits, lED on silicon displays, Advantage: Self emiting, high light output efficency, low power consuption, long life time, wide operating enviroment, simpler optics. Challenges: small wafer size, process compatibility. Stucture of LED micro-array- Pixel size: 300μm x 300μm square, LED pixels in the same row share a common n-electrode, p-electrode of each LED pixel is individually connected to the output of AM driving circuits. Design consideration of AM panel- Pixel circuit area limitation --- LED pixel pitch, Equipment availability in NFF (HKUST) --- 5μm & 1 μm feature size, Allow high driving capability --- output current ≥20mA (for 300μm pixel) and 5mA (for 50μm pixel), Low operation voltage ≤ 5V (USB compatible), High refresh frequency --- single crystal Si MOS, Immunity from photo-current --- metal cover. About LUE- Light output of the LEDoS chips were not fully utilized (LUE = 2.5%)because the trichroic prism was specially designed for LCDs, After removal of filter layers (output trimming filters) on the surface of prism, LUE of the projector was greatly improved from 2.5% to 10%, With a prism less sensitive to polarization, the LUE increased to 26%, LUE will be further increased by a custom-designed trichroic prism.

    Important Tags: LUE in LCD system, LED on Silicon, LEDoS, LED
    Views: 3548
    Domain: Electronics
    Category: Semiconductors

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