Light sensors with infrared suppression
View Patent ↗Embodiments of the present invention are directed to light sensors, that primarily respond to visible light while suppressing infrared light. Such sensors are especially useful as ambient light sensors because such sensors can be used to provide a spectral response similar to that of a human eye. Embodiments of the present invention are also directed to methods of providing such light sensors, and methods for using such light sensors.
1. A light sensor, comprising:
a layer of a first conductivity type;
a first region of a second conductivity type in the layer of the first conductivity type and forming a first PN junction photodiode with the layer of the first conductivity type, wherein the first PN junction photodiode is generally perpendicular to a surface of the first region that is not in contact with the layer of the first conductivity type;
a second region of the second conductivity type in the layer of the first conductivity type and forming a second PN junction photodiode with the layer of the first conductivity type, wherein the second PN junction photodiode is generally perpendicular to a surface of the second region that is not in contact with the layer of the first conductivity type; and
at least one further layer intrinsic to CMOS technology that covers the second region of the second conductivity type, but not the first region of the second conductivity, the at least one further layer blocking visible light while allowing at least a portion of infrared (IR) light to pass therethrough;
wherein carriers are produced in the layer of the first conductivity type when light, including both visible light and IR light, is incident on the light sensor;
wherein a portion of the carriers produced due to the visible light and the IR light incident on the first region of the second conductivity type are captured by the first region of the second conductivity type and contribute to a first photocurrent that is generally perpendicular to the at least one further layer and is indicative of both the visible light and the IR light; and
wherein a further portion of the carriers, produced due to the IR light that passes through the at least one further layer, are captured by the second region of the second conductivity type and contribute to a second photocurrent that is generally perpendicular to the at least one further layer and is indicative of the IR light; and
wherein a differential photocurrent, produced by determining a difference between the first and second photocurrents, has a spectral response with a significant part of the IR light removed.
2. The light sensor of claim 1 , where the difference used to produce the differential current is a weighted difference that compensates for at least a portion of the IR light not passing through the at least one further layer.
3. The light sensor of claim 2 , wherein the layer of the first conductivity type comprises an epitaxial layer.
4. The light sensor of claim 1 , wherein:
the layer of the first conductivity type comprises a P − layer;
the first region of the second conductivity type comprises a first N + region; and
the second region of the second conductivity type comprises a second N + region.
5. The light sensor of claim 1 , wherein:
the layer of the first conductivity type comprises an N − layer;
the first region of the second conductivity type comprises a first P + region; and
the second region of the second conductivity type comprises a second P + region.
6. The light sensor of claim 1 , wherein the at least one further layer includes a layer of silicide.
7. The light sensor of claim 1 , wherein the at least one further layer includes a layer of Poly-Silicon.
8. The light sensor of claim 1 , wherein the at least one further layer includes a layer of Poly-Silicon covering the second region of the second conductivity type, and a layer of silicide over the Poly-Silicon.
9. The light sensor of claim 1 , wherein the at least one further layer includes a first layer of Poly-Silicon covering the second region of the second conductivity type, and at least one further layer of Poly-Silicon over the first layer of Poly-Silicon.
10. The light sensor of claim 9 , wherein the at least one further layer includes a layer of silicide over the uppermost layer of Poly-Silicon.