Semiconductor device including image pick up device
The performance of a semiconductor device is improved by preventing 1/f noise from being generated in a peripheral transistor, in the case where the occupation area of photodiodes, which are included in each of a plurality of pixels that form an image pickup device, is expanded. In the semiconductor device, the gate electrode of an amplification transistor is formed by both a gate electrode part over an active region and a large width part that covers the boundary between the active region and an element isolation region and the active region near the boundary and that has a gate length larger than that of the gate electrode part.
1. A semiconductor device comprising:
a photoelectric conversion element that generates a signal electric charge in accordance with a light amount of incident light;
a forwarding transistor that forwards the signal electric charge to a charge detector;
an amplification transistor that outputs an electric signal corresponding to a potential variation in the charge detector;
a resetting transistor that resets a potential of the charge detector to a predetermined value; and
a selection transistor that externally outputs the electric signal the amplification transistor outputs,
wherein a first gate electrode of the amplification transistor and a second gate electrode of the selection transistor, which cross over an active region surrounded by an element isolation region, are formed in the active region, and
wherein in a portion immediately above the active region, a gate length of at least one end portion in a gate width direction of the first gate electrode is larger than that of a central portion in the gate width direction of the first gate electrode.
2. The semiconductor device according to claim 1 ,
wherein the first gate electrode has a structure in which a plurality of third electrodes arrayed in the gate width direction are coupled in parallel with each other.
3. The semiconductor device according to claim 1 ,
wherein in a portion immediately above the active region, a gate length of each of both end portions in the gate width direction of the first gate electrode is larger than that of a central portion in the gate width direction of the first gate electrode.
4. The semiconductor device according to claim 1 ,
wherein in a portion immediately below the first gate electrode, a diffusion layer, having the same conductive type as that of a channel region of the amplification transistor, is formed in the active region adjacent to the element isolation region.
5. The semiconductor device according to claim 4 ,
wherein in a portion immediately below the second gate electrode, a diffusion layer, having the same conductive type as that of a channel region of the selection transistor, is formed in the active region adjacent to the element isolation region.
6. The semiconductor device according to claim 5 ,
wherein the resetting transistor, the forwarding transistor, and the photoelectric conversion element do not include the diffusion layer.
7. The semiconductor device according to claim 1 ,
wherein the amplification transistor is arranged to be sandwiched by a plurality of photodiodes in the gate width direction of the first gate electrode.