Abstract The accuracy of an active pixel sensor cell is increased by utilizing a reset diode in lieu of the reset transistor that is conventionally used to reset the voltage on the photodiode of the cell. The reset diode, which is largely unaffected by 1/f noise, consistently resets the photodiode to a substantially constant voltage as opposed to the reset transistor which varies the reset voltage on the photodiode across integration periods due to the effect of 1/f noise. In the present invention, the photodiode is formed by forming a well region of a second conductivity type in a substrate of a first conductivity type. The reset diode is then formed by forming a reset region of the first conductivity type in the well region.
An active pixel sensor cell formed in a semiconductor substrate of a first conductivity type, the cell comprising: a well region of a second conductivity type formed in the substrate; a reset region of the first conductivity type formed in the well region; and a buffer transistor having a gate connected to the well region.
Claim 2
Dependent Claim
55 words
An active pixel sensor cell formed in a semiconductor substrate of a first conductivity type, the cell comprising: a well region of a second conductivity type formed in the substrate; a reset region of the first conductivity type formed in the well region; and a buffer transistor having a gate connected to the well region.
Claim 3
Dependent Claim
17 words
The cell of claim 1 and further comprising a row select transistor connected to the buffer transistor.
Claim 4
Dependent Claim
37 words
The cell of claim 1 and further comprising a contact region of the second conductivity type formed in the well region, wherein the dose of the contact region is greater than the dose of the well region.
Claim 5
Dependent Claim
18 words
The cell of claim 1 wherein the junction between the well region and the substrate forms a photodiode.
Claim 6
Dependent Claim
20 words
The cell of claim 1 wherein the junction between the reset region and the well region forms a reset diode.
Claim 7
Dependent Claim
15 words
The cell of claim 1 wherein the well region is implanted with an n-type material.
Claim 8
Dependent Claim
15 words
The cell of claim 1 wherein the reset region is implanted with a p+ material.