PN-structured gate demodulation pixel
View Patent ↗A novel photo-sensitive element for electronic imaging purposes and, in this context, is particularly suited for time-of-flight 3D imaging sensor pixels. The element enables charge-domain photo-detection and processing based on a single gate architecture. Certain regions for n and p-doping implants of the gates are defined. This kind of single gate architecture enables low noise photon detection and high-speed charge transport methods at the same time. A strong benefit compared to known pixel structures is that no special processing steps are required such as overlapping gate structures or very high-ohmic poly-silicon deposition. In this sense, the element relaxes the processing methods so that this device may be integrated by the use of standard CMOS technology for example. Regarding time-of-flight pixel technology, a major challenge is the generation of lateral electric fields. The element allows the generation of fringing fields and large lateral electric fields.
1. A demodulation pixel, comprising:
a substrate for generating photocharges therein, the substrate including a demodulation part having a photogate region and integration regions, the substrate further including sense node regions; and
a gate layer over the substrate, the gate layer comprising a plurality of alternating p-doped and n-doped regions forming a series of p-n junctions in parallel to a surface of the substrate over which the gate layer is disposed and arranged to have different respective potentials applied to the p-doped and n-doped regions so as to generate a potential distribution in the substrate for transferring the photocharges alternately to different ones of the integration regions, and from the integration regions to respective ones of the sense node regions,
wherein the p- and n-doped regions of the gate layer define a photogate, a respective toggle gate having a double p-n arrangement at each side of the photogate, a respective integration gate adjacent each of the toggle gates, and a respective decoupling gate adjacent each of the integration gates.
2. The demodulation pixel of claim 1 wherein respective voltages are applied to the p-doped and n-doped regions such that the p-n junctions are reverse biased.
3. The demodulation pixel of claim 1 wherein respective voltages are applied to the n-doped regions in an increasing manner.
4. The demodulation pixel of claim 1 wherein the p-doped and n-doped regions have substantially the same size as one another.
5. The demodulation pixel of claim 1 wherein the photogate and integration gates are n-doped regions of the gate layer, and the decoupling gates are p-doped regions of the gate layer.
6. The demodulation pixel of claim 5 wherein, during integration periods, the integration gates have an applied potential higher than potentials of the other gates.
7. The demodulation pixel of claim 5 wherein, during integration periods, the decoupling gates have a relatively low applied potential so as to provide a barrier to electron flow between each of the integration regions and its respective sense node region.
8. The demodulation pixel of claim 1 wherein the gate layer is composed of p-doped and n-doped poly-silicon.
9. The demodulation pixel of claim 1 further comprising:
a dump node operable to flush photogenerated charges prior to a demodulation cycle.