Dual VPIN HDR image sensor pixel

• US 10,134,788 B2
• Filed: 09/17/2013
• Issued: 11/20/2018
• Est. Priority Date: 09/17/2013
• Status: Active Grant

• Current Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Original Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Inventors: Lyu, Jeong-Ho, Manabe, Sohei
• Primary Examiner(s): Epps, Georgia Y
• Assistant Examiner(s): Wyatt, Kevin
• Application Number:
  US14/029,515
• Publication Number:
  US 20150076330A1
• Time in Patent Office: 1,890 Days
• Field of Search: 2502081, 2502141, 348294
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/14616 characterised by the channel of the transistor, e.g. channel having a doping gradient
• CPC Class Codes: H01L 27/14641 Electronic components shared by two or more pixel-elements, e.g. one amplifier shared by two pixel elements
• CPC Class Codes: H04N 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/778 comprising amplifiers shared between a plurality of pixels, i.e. at least one part of the amplifier must be on the sensor array itself

Abstract

A CMOS photodiode device for use in a dual-sensitivity imaging pixel contains at least two areas of differential doping. Transistors are provided in electrical contact with these areas to govern operation of signals emanating from the photodiode on two channels, each associated with a different sensitivity to light. A plurality of such photodiodes may be incorporate into a shared arrangement forming a single pixel, in order to enhance the signals.

Claims

1. A photodiode device having multiple sensitivity to light conditions, comprising:

a first doped region and a second doped region formed within a common photoactive area region, the common photoactive area being a single photoconversion region adapted to provide photocurrent to both the first doped region and the second doped region;

the first and second doped region being directly adjacent or overlapping in the common photoactive area;

a first transistor positioned to govern transfer of charge from the first doped region of the photoactive area, the first transistor electrically coupled to a first diffusion (FD1) node;

a second transistor positioned to govern transfer of charge from the second doped region of the photoactive area into a second diffusion (FD2) node; and

an isolation transistor electrically coupled between the FD1 node and the FD2 node for selectively coupling the FD1 node to the FD2 node,

a single source follower transistor adapted to serve for reading charge from the FD2 node or charge from the FD1 and FD2 nodes when the FD1 and FD2 node are coupled together;

whereby due to differences in a first doping of the first doped region of the photoactive area and a second doping of the second doped region of the photoactive area;

the first doped region of the photoactive area as compared to the second doped region of the photoactive area is better suited for imaging conditions under one of a low light condition and a bright light condition,

the first doped region of the photoactive area has an inherent pin voltage material property of V_pin1 associated with the first doping, and

the second doped region of the photoactive area has an inherent pin voltage material property of V_pin2 associated with the second doping,

such that V_pin1 differs from V_pin2.

2. The photodiode device of claim 1, further including circuitry incorporating the photodiode device in a pixel that uses the first transistor to sense a bright light condition and the second transistor to sense a low light condition.

3. The photodiode device of claim 2, wherein the first transistor has an internal threshold voltage V_t1 and the second transistor has an internal threshold voltage V_t2, such that V_t1 is approximately equal to V_t2.

4. The photodiode device of claim 3, further comprising means for resetting a charge accumulation state of the pixel.

5. The photodiode device of claim 3, further comprising means for sensing a charge accumulation state of the pixel.

6. The photodiode device of claim 2 incorporated in a pixel that shares a plurality of such photodiode devices.

7. The photodiode device of claim 1, wherein

the first doping resides in the first transistor and the second doping resides in the second transistor such that the first transistor has an increased internal threshold voltage Vt as compared to the second transistor.

8. The photodiode device of claim 7, further including circuitry incorporating the photodiode device in a pixel that uses the first transistor to sense a bright light condition and the second transistor to sense a low light condition.

9. The photodiode device of claim 7 incorporated in a pixel that shares a plurality of such photodiode devices.

10. The photodiode device of claim 1 incorporated in a pixel that shares a plurality of such photodiode devices.

11. The photodiode device of claim 1, further including circuitry providing the photodiode device with means for using the first region of the photoactive area to sense a bright light condition and means for using the second region of the photoactive area to sense a low light condition.

12. A method of operating the photodiode device of claim 1, including the steps of:

resetting the photodiode device to a predetermined voltage;

turning off the first transistor and the second transistor by application of a gate voltage V_TX1 to the first transistor and a second gate voltage V_TX2 to the second transistor, where V_TX1 equals V_TX2;

impinging light upon the photodiode device to produce an accumulated charge;

switching on at least one of the first transistor and the second transistor to allow charge to flow from the photodiode device.

13. In a CMOS pixel, the improvement comprising

a differentially doped photodiode constructed and arranged through associated circuitry to provide a first channel producing a signal allocated to a first level of sensitivity to light and a second channel producing a signal allocated to a second level of sensitivity to light, the first channel electrically coupled to a first floating diffusion (FD1) node via a first transistor, the second channel electrically coupled to a second floating diffusion (FD2) node via a second transistor, the FD1 node selectively coupled to the FD2 node by an isolation transistor, and a single source follower transistor adapted to serve for reading charge from the FD2 node or charge from the FD1 and FD2 nodes when the FD1 and FD2 node are coupled together;

wherein the photodiode comprises a first doping and the second doping residing in a first and a second region of its common photoactive area respectively such that;

the first region of the photoactive area has an inherent pin voltage material property of Vpin1 associated with the first doping and corresponds to the first channel,

the second region of the photoactive area has an inherent pin voltage material property of Vpin2 associated with the second doping and corresponds to the second channel,

such that Vpin1 has a different magnitude than Vpin2, and

the common photoactive area is a single photoconversion region adapted to provide photocurrent to both the first and second regions of the photoactive area, the first and second doped region being directly adjacent or overlapping in the common photoactive area; and

the first and second doped region being directly adjacent or overlapping in the common photoactive area.

14. In a CMOS pixel, the improvement comprising

a common photoactive area feeding a plurality of channels, the common photoactive area being a single photoconversion region adapted to provide photocurrent to each of the plurality of channels;

a plurality of transistors each governing flow of accumulated charge from the common photoactive area into a corresponding channel of the plurality of channels,

each of the plurality of transistors being differentially doped with respect to the other transistors to produce a different voltage potential on each channel attributable to different internal threshold voltages of the respective transistors,

a first transistor of the plurality of transistors being electrically coupled directly between the photoactive area and a first floating diffusion (FD1) node,

a second transistor of the plurality of transistors being electrically coupled directly between the photoactive area and a second floating diffusion (FD2) node, and

the FD1 node being selectively isolatable from the FD2 node by an isolation transistor;

wherein a first region of the photoactive area has a first doping and a second region of the photoactive area has a second doping such that;

the first region of the photoactive area has an inherent pin voltage material property of Vpin1 associated with the first doping, and

the second region of the photoactive area has an inherent pin voltage material property of Vpin2 associated with the second doping,

such that Vpin1 has a different magnitude than does Vpin2, the first and second region being directly adjacent or overlapping in the common photoactive area.