Unit pixel in CMOS image sensor with high sensitivity
A unit pixel in a CMOS image sensor with a high sensitivity is employed by modifying a unit pixel circuit and a layout. The unit pixel in the CMOS image sensor including: an active area defined by an FOX; a photodiode formed in a predetermined location of the active area; a transfer transistor including source/drain regions disposed between the photodiode and a floating diffusion node, wherein a transfer control signal is applied to a gate thereof; a reset transistor including source/drain regions disposed between the floating diffusion node and a power supply voltage (VDD) terminal, wherein a reset control signal is applied to a gate and a VDD is applied to a drain; a drive transistor of which a gate is connected to the VDD terminal and a drain is connected to the floating diffusion node; and a selection transistor of which a drain is connected to a source of the drive transistor and a source is connected to an output terminal, wherein a select control signal is applied to a gate thereof.
1. A unit pixel for use in a complementary metal oxide semiconductor (CMOS) image sensor, comprising:
an active area defined by a field oxide (FOX);
a photodiode formed in a predetermined location of the active area;
a transfer transistor disposed between the photodiode and a floating diffusion node, wherein a transfer control signal is applied to a gate thereof;
a reset transistor disposed between the floating diffusion node and a power supply voltage (VDD) terminal, wherein a reset control signal is applied to a gate and a VDD is applied to a drain;
a drive transistor of which a gate is connected to the VDD terminal and a drain is connected to the floating diffusion node; and
a selection transistor of which a drain is connected to a source of the drive transistor and a source is connected to an output terminal, wherein a select control signal is applied to a gate thereof.
2. The unit pixel as recited in claim 1 , wherein the drain of the drive transistor is electrically connected to the floating diffusion node through a metal interconnection.
3. The unit pixel as recited in claim 1 , wherein the active area includes:
a first active area where the photodiode is formed;
a second active area having a first region and a second region where the transfer transistor, the floating diffusion node and the reset transistor are formed, the second active area being connected to a side of the photodiode; and
a third active area where the drive transistor and the selection transistor are formed, wherein the third active area is separated from the first and the second active areas by predetermined distances.
4. The unit pixel as recited in claim 3 , wherein the third active area is electrically isolated from the second active area by an FOX area.
5. The unit pixel as recited in claim 3 , wherein the second active area has a first region for the transfer transistor and the floating diffusion node and a second region for the reset transistor, wherein the first region is extended from a middle portion of the side of the first active area and the second region is in contact with the first region perpendicularly of which one end is connected to a VDD contact.
6. The unit pixel as recited in claim 5 , wherein a gate of the transfer transistor is formed over an interface between the first active area and the first region of the second active area and a gate of the reset transistor is formed over a portion of the second region of the second active area.
7. The unit pixel as recited in claim 5 , wherein a gate of the drive transistor and a gate of the selection transistor are formed over portions of the third active area which are separated from each other by a predetermined distance.
8. The unit pixel as recited in claim 5 , wherein one end of the drive gate is extended to the second region so as to be connected to the VDD contact.
9. The unit pixel as recited in claim 8 , wherein the VDD contact has a butting contact structure.
10. The unit pixel as recited in claim 1 , further comprising another reset transistor disposed between the photodiode and the VDD terminal, wherein a reset control signal is applied to a gate and a VDD is applied to a drain.
11. A unit pixel for use in a CMOS image sensor, comprising:
an active area defined by a field oxide (FOX);
a photodiode formed in a predetermined location of the active area;
a transfer transistor disposed between the photodiode and a floating diffusion node, wherein a transfer control signal is applied to a gate thereof;
a reset transistor disposed between the photodiode and a VDD terminal, wherein a reset control signal is applied to a gate and a VDD is applied to a drain;
a drive transistor of which a gate is connected to the VDD terminal and a drain is connected to the floating diffusion node; and
a selection transistor of which a drain is connected to a source of the drive transistor and a source is connected to an output terminal, wherein a select control signal is applied to a gate thereof.
12. The unit pixel as recited in claim 11 , wherein the active area includes:
a first active area where the photodiode is formed;
a second active area where the transfer transistor, the floating diffusion node, the drive transistor and the selection transistor are formed, the second active area being formed extended from one end of a side of the photodiode; and
a third active area where the reset transistor is formed, wherein a VDD contact is connected to one end of the third active area, the third active area being formed extended from the other end of the side of the photodiode.
13. The unit pixel as recited in claim 12 , wherein a gate of the transfer transistor is formed over an interface between the first active area and the second active area and a gate of the drive transistor and a gate of the selection transistor are formed over portions of the second active area separated from each other by a preset distance.
14. The unit pixel as recited in claim 12 , wherein a gate of the reset transistor is formed over an interface between the first active area and the third active area.
15. The unit pixel as recited in claim 13 , wherein one end of the gate of the drive transistor is extended to the third active area so as to be connected to the VDD terminal through a butting contact.
16. The unit pixel as recited in claim 11 , wherein the floating diffusion node is connected to the drive transistor without a contact by means of an ion-implantation into a predetermined portion of the second active area.
17. The unit pixel as recited in claim 11 , further comprising another reset transistor disposed between the floating diffusion node and the VDD terminal, wherein a reset control signal is applied to a gate and a VDD is applied to a drain.