UNIT PIXEL OF CMOS IMAGE SENSOR RESTRAINING BAD PIXEL FAIL USING DUMMY TRANSISTOR

摘要

PURPOSE: A unit pixel of a CMOS image sensor is provided to restrain bad pixel fail and to reduce the number of contact by directly connecting a gate of a drive transistor to a floating diffusion node using a dummy transistor. CONSTITUTION: A unit pixel comprises a photodiode(21) and four NMOSFETs. The four NMOSFETs are provided with a transfer transistor(22) for transferring optical charges to a floating diffusion node(23), a reset transistor(24), a drive transistor used as source follower and a select transistor(26). A power voltage node(VDD) is commonly connected to a drain of the drive transistor and a drain of the reset transistor. The unit pixel further includes a dummy transistor(27) between a source of the drive transistor and the floating diffusion node. The threshold voltage of the dummy transistor is higher than the power voltage, so that the dummy transistor maintains always turn-off state.