1. Field of the Invention
The subject matter disclosed, generally relates to structures and methods for sampling color images on solid state image sensors and reconstructing the color images.
2. Background Information
Photographic equipment such as digital cameras and digital camcorders may contain electronic image sensors that capture light for processing into still or video images. Electronic image sensors typically contain millions of light capturing elements generally known as photoelectric conversion units, such as photodiodes. The elements each receives light that passes through a color filter in a two-dimensional color filter array.
Conventional image sensors suffer from stray charges that diffuse laterally in the substrate across pixels, resulting in blurred images and poor color reproduction. There is a need to reduce the lateral propagation of charges in the substrate.
According to a first aspect, the present invention relates to an image sensor supported by a substrate of a first conductivity type, comprising a two-dimensional array of a two-by-two subarray of adjacent pixels where the two-by-two subarray comprises a pair of green pixels along a diagonal and a pair of a red pixel and a blue pixel along the other diagonal, where each of the green pixels has a green color filter and a photoelectric conversion unit that receives light from the green color filter, where the red pixel has a red color filter and a photoelectric conversion unit that receives light from the red color filter, and where the blue pixel comprises (a) a blue color filter, (b) a doped region of a second conductivity type in the substrate arranged to collect charge carriers generated by photons that enter the substrate from the blue color filter; (c) a transfer switch connected to transfer charges from the doped region; (d) a trap region of the second conductivity type buried under the doped region, charge carriers collected by the trap region during a charge integration period of the doped region are drained to a surface of the substrate, no charges collected by the trap region during the charge integration period is used for generating a color image that is generated using a signal that results from charge carriers collected by the doped region during the charge integration period.
In the first aspect, it is preferable that a barrier region of the first conductivity type is disposed laterally adjacent to the trap region to stop a depletion region that extends from the trap region.
In the first aspect, it is preferable that a barrier region of the first conductivity type is disposed above the trap region and under the doped region to stop a depletion region that extends from the trap region.
In the first aspect, it is preferable that a relative lateral position of the trap region with respect to the doped region varies between a center region of the pixel array and a corner region of the pixel array.
According to a second aspect, one of the green pixels of the two-by-two subarray of the first aspect is replaced with a white pixel arranged to receive white light.
According to a third aspect, the green pixels of the two-by-two subarray of the first aspect are replaced with the blue pixels and the blue pixel is replaced with the green pixel.
Disclosed is a color image sensor that includes a two dimensional pixel array supported by a substrate. The pixel array includes a plurality of pixels to detect visible light of different colors. Each of the plurality of pixels includes a photoelectric conversion unit in the substrate. Light that enters the substrate generate charge carriers that are collected by the photoelectric conversion unit. The pixel array includes a blue pixel that includes a charge trap region under the blue pixel's photoelectric conversion unit. The charge trap region and the substrate belong to opposite conductivity types.
Referring to the drawings more particularly by reference numbers,
The doped region 54 preferably reaches a depth of between 0.4 um to 1.2 um.
Adjacent to the blue color filter 114B are color filters of other color(s) 114G for adjacent pixels of the other color(s). Conducting interconnect wires 83 and via 85 are embedded in an insulating layer (not shown) between the light guides of adjacent pixels.
A trap region 70 of the second conductivity type is disposed below the doped region. The trap region 70 preferably begins from a depth of between 1.7 um and 2.5 um. It serves to trap stray charges in the substrate 56. For example, red light that penetrates to more than 2 μm into the substrate 56 can release free charge carriers, which are electrons where the first conductivity type is p-type, that diffuse laterally to adjacent pixels or even farther, causing blurriness of the color image and incorrect color detection and reproduction. The trap region 70 helps to trap such stray electron and improve picture sharpness and better colors. During the charge integration period of the photodiode 100, charges freed by blue light received from the blue color filter 114B are collected by the doped region 54. At the same time, stray charges are collected by the trap region 70. These collected stray charges are removed to a surface of the substrate 56 through a connection region of the second conductivity type in the substrate 56, and subsequently removed to terminal Vsink connected to the uppermost connection region 72a. In
The doped region 54 collects charges generated by blue light transmitted from the blue color filter 14a during a charge integration period of the blue pixel. Charges from the doped region 54 are subsequently transferred across the transfer transistor 117 to the drain diffusion 111 to cause a voltage change on the gate of output transistor 116. As a result of the gate voltage change, a corresponding output signal is transmitted along the aforementioned output signal line within the bus 18 to the light reader circuit 16 to be sampled. The sampled signal is used in generating a color image. On the other hand, no charges collected by the trap region 70 is used to generate a signal to be used in the generating of the color image.
The trap region may have an impurity concentration that peaks between 3e16/cm3 and 5e17/cm3. Where the substrate 56 is p-type, the trap region may be doped with phosphorus.
Barrier regions 64 of the first conductivity type may be disposed laterally adjacent to the trap region 70 and connection regions 72a to 72d to stop depletion regions that extend from the latter from extending further laterally.
Additional barrier regions 66, 68 may be disposed between the trap region 70 and the connection regions 72a to 72d, respectively, and the doped region 54 to stop depletion regions that extend from the trap region 70 and the connection regions 72a to 72d, respectively from merging with a depletion region that extends from the doped region 54. A neutral region in each of the barrier regions 66, 68 is sandwiched between the depletion that extends from the trap region 70 (or connection regions 72a to 72d) and the depletion region that extends from the doped region 54.
Dashed lines 71a, 71b shows boundaries of depletion regions that extend from the trap region 70 and the connection regions 72a-72d.
These barrier regions 64, 66, 68 have may have doping concentration may peak between 1e16/cm3 to 5e17/cm3. Where the substrate is p-type, they may be doped with boron.
The trap region may be biased to a potential during the charge integration period. Charges collected in the trap region may be removed between successive charge integration periods of the blue pixel. Charges collected in the trap region may be removed during the charge integration period.
Although
The demosaicking unit 222 may generate the missing colors. Ultimately, all the generated missing colors are assembled together with the colors in the mosaic image to form a full-color image by color interpolation. The signal generated from charges collected by the doped region 54 during the charge integration period of the blue pixel 14a is used to generate the color image. No signal generated from charges collected by the trap region 70 is used to generate the color image.
Although the reconstructed full-color image is shown to be sent to a color correction unit 224 in
A nonvolatile memory, which may be external to the camera processor 212 or may be part of it, such as the Read-Only Memory (ROM) 228 shown in
The color filter 114B, 114G may each comprise a different color material, or colorant, such as a dye or a organic or inorganic or organometallic pigment. The color filter may comprise a resin in which the dye is dissolved or the organic or inorganic or organometallic color pigment is suspended, where the resin may be organic or comprise a polymer that has at least an organic group such as methyl, ethyl or phenyl (an example being silicone). Alternatively, the color filter may comprise a transmissive inorganic material (e.g. silicon nitride) having particles of a color pigment (e.g. an inorganic color pigment such as iron oxide, a cobalt or manganese or zinc or copper pigment, or an organometallic pigment, or a complex inorganic color pigment) dispersed therein.
Adjacent color filters exhibit different colors in white light. Preferably, each has a highest transmittance and a least transmittance of at least 50% and at most 10%, respectively, between wavelengths (in air) of 400 nm to 700 nm. Alternatively, a ratio between its highest and least transmittances shall be more than 4-to-1.
Alternatively, any of the color filters may be more generally a color filter means for providing different transmittance to visible light of different colors. Preferably, each has a highest transmittance and a least transmittance of at least 50% and at most 10%, respectively, between wavelengths (in air) of 400 nm to 700 nm. Alternatively, a ratio between its highest and least transmittances shall be more than 4-to-1. The color filter means can be a grating.
In an alternative embodiment for the blue pixel, the uppermost connection region 72a does not reach the upper surface of the substrate 56. Instead, it is under a layer of surface region of the first conductivity type in the substrate. A transistor is provided adjacent to the uppermost connection region 72a to conduct away the stray charges from the uppermost connection region 72a. Such as transistor may be a buried-channel transistor.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
This application claims priority to U.S. Provisional Patent Application No. 61/617,655 filed on Mar. 29, 2012.
Number | Date | Country | |
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61617655 | Mar 2012 | US |