To obtain a photodiode whose capacity for trapping photo-charge in an initial state is kept unchanged in a linear manner for a longer term, by a method wherein the photodiode enables a pinned layer (N-diffusion region) in a perfect depletion state to trap photo-charge and transfer it without delay.
For instance, a photodiode has a structure where a P-epitaxial layer 302 is formed on a grounded P-substrate 301 though an epitaxial growth method, and an N+-diffusion region 304 connected to a power supply voltage VDD through the intermediary of a switch 305 is provided under the surface of the P-epitaxial layer 302. An N-diffusion region 303 that is turned perfectly depleted at a voltage between a power supply voltage VDD and a ground potential is formed in a certain region inside the P-epitaxial layer 302 under the N+-diffusion region 304. This phototiode is capable of collecting a large quantity of photo-charge keeping its linear properties until the potential of the N+- diffusion region 304 gets equal to a pinning voltage, al photo-charge (electron) generated without lessening depth in a depletion region can be transferred to the N+-diffusion region 304.
PARK KI NAM
LEE DO YOUNG
EOM JAE WON
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