We studied a coplanar hydrogenated amorphous silicon thin-film transistor (TFT) to control the backlight brightness in liquid-crystal display (LCD). This was done by designing the inverse-staggered TFT for the switching device and the coplanar TFT to absorb the illumination from backlight. We achieved the field-effect mobility of 0.3 cm(2)/V s, threshold voltage of 3.6 V, and the subthreshold voltage swing of 1.3 V/d for the coplanar TFT. The TFT showed the photocurrent of similar to 10(-8) A and dark current of similar to 10(-11) A in the operation region of backlight for TFT-LCD. The dynamic range was 50 dB which is good enough to control the brightness of the backlight. (c) 2007 Elsevier Ltd. All rights reserved.