Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
  • H10F39/10—Integrated devices
  • H10F39/12—Image sensors
  • H10F39/15—Charge-coupled device [CCD] image sensors
  • H10F39/153—Two-dimensional or three-dimensional array CCD image sensors
  • H10F39/1538—Time-delay and integration
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/50—Control of the SSIS exposure
  • H04N25/57—Control of the dynamic range
  • H04N25/571—Control of the dynamic range involving a non-linear response
  • H04N25/575—Control of the dynamic range involving a non-linear response with a response composed of multiple slopes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
  • H04N25/62—Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels
  • H04N25/621—Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels for the control of blooming
  • H04N25/622—Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels for the control of blooming by controlling anti-blooming drains
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/70—SSIS architectures; Circuits associated therewith
  • H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
  • H04N25/711—Time delay and integration [TDI] registers; TDI shift registers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
  • H10F39/10—Integrated devices
  • H10F39/12—Image sensors
  • H10F39/15—Charge-coupled device [CCD] image sensors
  • H10F39/158—Charge-coupled device [CCD] image sensors having arrangements for blooming suppression

Definitions

• the present invention is related to the field of imaging devices. More specifically, to extending the dynamic range of Time Delay and Integrate (TDI) imagers.
• TDI Time Delay and Integrate
• Typical single line imagers for example, Charge Coupled Device (CCD) imagers, incorporate a single row of photosensitive electrical devices, such as photo-detectors, to collect photonic charge.
• a photo-detector converts the collected photonic charge into an electrical charge that is related to the amount of photonic charge collected.
• a Time Delay & Integration (TDI) method of operating CCD imagers incorporates multiple single row CCD scanners in an imaging array.
• Each row in the array collects image data for a finite period of time as the target image and the imager move relative to each other. Typically, the collected charge moves from one row to the next at the same speed as the target image moves across the imager to prevent blurring.
• TCI-CCD scanners offer an advantage over single line scanners in that TDI-CCD devices provide for longer times to collect and integrate photonic charge from the target image. The longer collection time also increases the sensitivity of the imager.
• Another method to avoid excess charge-accumulation problems is to reduce the amount of time that is used in collecting an image.
• This method has the disadvantage of reducing sensitivity of the imaging device. Thus, dark images remain relatively dark.
• TDI-CCD devices that allows for the collection of sufficient image data to view dark images while not losing data from relatively bright images.
• a method that increases the intra-scene dynamic range of a TDI-CCD device by selectively limiting the amount of charge collected in each stage by selectively setting blooming barrier levels.
• the maximum accumulated charge collected in each cell is incrementally increased as the charge is passed from one cell to a subsequent cell.
• the level of the barrier is set in a step-wise increasing manner that limits the amount of charge collected in each stage while allowing for the accumulation of progressively greater amounts of collected charge in subsequent cells.
• a step-wise increase in the barrier levels changes the reference level at which charge is accumulated in a cell.
• Figure 1 illustrates a schematic diagram of an exemplary TDI-CCD device
• Figure 2 depicts a cross-sectional view of a pixel cell and barrier of a CCD structure
• Figure 3 illustrates typical response characteristic of a TDI-CCD device
• Figure 4 illustrates a schematic diagram of a TDI-CCD device in accordance with the principles of the invention
• Figure 5 illustrates a response characteristic of a TDI-CCD device illustrated in Figure 4 in accordance with the principles of the invention
• Figure 6a illustrates one exemplary embodiment of limiting charge capacity in accordance with the principles of the invention
• Figure 6b illustrates a second exemplary embodiment of limiting charge capacity in accordance with the principles of the invention
• Figure 7a illustrates a third exemplary embodiment of limiting charge capacity in accordance with the principles of the invention
• Figure 7b illustrates a fourth exemplary embodiment of limiting charge capacity in accordance with the principles of the invention
• Figure 8 illustrates an exemplary response characteristic of a TDI-CCD device in accordance with a second embodiment of the invention
• Figure 9 illustrates an exemplary response characteristic of a TDI-CCD device in accordance with another embodiment of the invention
• Figure 10a illustrates a cross-sectional view of an exemplary embodiment of a back-illuminated TDI-CCD device having a response characteristic as illustrated in Figure 8;
• Figure 10b illustrates a cross-sectional view of a second exemplary embodiment of a back-illuminated TDI-CCD device having a response characteristic as illustrated in Figure 8;
• Figure 10c illustrates a cross-sectional view of an exemplary embodiment of a top-illuminated TDI-CCD device having a response characteristic as illustrated in Figure 8.
• FIG. 1 illustrates an exemplary schematic diagram of an 8-stage TDI-CCD device 100. Only four photosensitive devices (pixel cells) 115, among a plurality of cells in each stage are shown to describe the operation of the TDI-CCD device. In operation, the photonic charge from a target image is collected beginning in pixel cells 115 associated with the first stage — i.e., stage 101. As the target image or imager moves, the image moves past the pixel cells in a next stage (102).
• the cells in this stage then collect photonic charge from the target image.
• the charge collected in previous cells is added to the charge collected in the currently-imaging cell.
• the charge collected in pixel cell 115 associated with stage 101 for example, is added or transferred to pixel cell 115 associated with stage 102, as the image moves past stage 102.
• the accumulated charge in pixel cell 115 associated with stage 102 is added to the charge collected in pixel cell 115 associated with stage 103, as the image moves past stage 103.
• This transferring of accumulated photonic charge from a cell in one stage to a cell in a subsequent stage continues, one stage at a time, until an end stage is reached — in this case, stage 108.
• the photonic charge collected for the image is accumulated and integrated over the depth of the TDI-CCD device, « i.e., stages 101-108.
• the accumulated charge is read out from the TDI-CCD device.
• the charge is transferred along a channel of pixel cells 115, known as a transfer channel, illustrated for one channel of pixel cells as 120.
• a transfer channel illustrated for one channel of pixel cells as 120.
• the excess energy would normally overflow the cell and "spread" into an adjacent cell.
• channels are isolated from one another by blooming drains 125 and barriers 130. The level at which accumulated charge is deemed excessive is determined by barrier 130 that exists between, for example, transfer channel 120 and drain 125.
• barrier 130 The greater the level, or potential, of barrier 130, the greater the amount of accumulated charge that may be collected in each cell 115.
• the levels of barrier 130 are set to achieve the maximum accumulation of charge - i.e., saturation level ⁇ in a pixel cell.
• barrier 130 is positioned horizontally adjacent to channel 120 and 121.
• barrier 130 may also be positioned vertically adjacent to channels 120 and 121 to limit the charge capacity of pixel cell 115.
• Figure 2 illustrates the operation of barrier 130 in controlling excessive charge.
• pixel cell 115 fills to a value that is set by barrier 130.
• the excess as represented by charge 140, is directed into drain 125.
• any further charge that may be collected is simply discarded. The maximum level of barrier 130 thus limits the accumulated charge.
• Figure 3 illustrates an exemplary performance characteristic of TDI-CCD device of Figure 1 for three images of different brightness levels.
• the charge collected by the imager is represented by response characteristic 400.
• each pixel cell 115 in a stage adds a substantially similar amount of charge to pixel cell 115 in the next subsequent stage as the imager and target image move past each other.
• the accumulated charge collected increases proportionally to the number of stages in the imager.
• the total amount of charge collected after the eight stages remains below the barrier level 465 set by barrier 130.
• the charge collected is represented by response characteristic 420.
• the charge of an even brighter image is collected.
• the response to this brighter image is represented by response characteristic 440.
• the brightness of the image causes the accumulated charge to exceed the maximum level set by barrier 130 (at level 465) after scanning of the image by only about two of the CCD stages.
• barrier level 465 limits the response characteristic of the imager. Charge above barrier level 465 is simply discarded into drain 125 and the accumulated charge for this third exemplary image thus remains limited at level 465 as represented by response characteristic 460.
• Figure 4 illustrates an 8-stage TDI-CCD in accordance with the principles of the invention.
• barrier 130 is selectively set in accordance with the capacity charge curve 510. Accordingly, the amount of charge accumulated and retained in each stage is incremental increased.
• barrier 130 is set to limit the accumulated charge to twenty-five per cent (0.25) of maximum barrier level 465 in stages 101-105 of the imager, and fifty percent of that level for stages 106 and 107.
• the level of barrier 130 is set to the maximum barrier level 465.
• the maximum barrier level may be set independently of the maximum capacity of pixel cell 115, but is typically set substantially equal to the maximum capacity of the pixel cell.
• barrier 130 is selectively set in an step-wise pattern that limits the amount of data collected in the early stages of collection while allowing for incrementally greater amounts of charge in latter stages.
• stages 101-105 accumulate 25 percent of the charge that could be collected.
• Stages 106 and 107 accumulate 50 percent of the charge that could be collected, and stage 108 allows for the accumulation of a maximum amount of charge.
• the maximum amount of charge may be collected without causing a saturation of pixel cell 115.
• Figure 5 illustrates the response characteristics of a TDI-CCD device having barrier characteristics selectively set in accordance with the exemplary characteristics illustrated in Figure 4 for the three exemplary images discussed in regard to Figure 3.
• the charge collected is represented by response characteristic 600.
• Response characteristic 600 is similar to the response characteristic 400 of Figure 3, as the accumulated charge does not exceed the selectively set barrier levels of stages 101-105, 106-107 or 108. Accordingly, the response characteristic is not altered and the accumulated charge is not limited.
• the accumulated charge is shown to exceed the first barrier level while charge is collected in stage 102. That is, the accumulation of the charge collected in stage 101 and the charge being collected in stage 102 exceeds the barrier level selectively set for stages 101 through 105. Any additional charge collected in stages 103 through
• stage 105 would, accordingly, cause the accumulated charge to exceed the level of barrier 130 and is thus drained off.
• the accumulated charge in stages 103 through 105 remains limited to 25 percent of the charge that may be collected, as represented by response characteristic 620.
• the level of barrier 130 is increased to 50 percent of the maximum barrier level to allow an incremental increase in the charge collected.
• stage 106 moves past the target image, charge is accumulated in pixel cells 115 associated with stage 106.
• the increase in accumulated charge is represented by response characteristic 630.
• the accumulated charge exceeds the level of barrier 130 during the charge collection of stage 107 and the excess charge is drained off.
• the accumulated charge remains limited to the 50 percent level, as represented by response characteristic 640.
• the level of barrier 130 is increased to allow an incremental increase in the charge collected.
• response characteristic 650 As stage 108 moves past the target image, charge is accumulated, as represented by response characteristic 650. The charge level continues to accumulate until the collected charge is read out in stage 110.
• the accumulated charge level is substantially less than the maximum level; hence, the brightest image data is not lost because the image data is compressed.
• an imager incorporating a step-wise increase in the level of barrier 130 causes alterations or shifts in reference points that are used by subsequent cells to accumulate charge. These alterations in the reference points allow for the collection of more data from brighter images.
• a third exemplary image similar to the brightest image discussed in regard to
• the brightness of the image causes the charge collected to exceed the first level of barrier 130 during the collection phase of stage 101. Any charge collected as the target image moves past stages 101 through 105 is thus drained off.
• the level of the accumulated charge remains fixed at the barrier level as represented by response characteristic 620.
• the level of barrier 130 is increased.
• charge is again accumulated in pixel cell 115 associated with stage 106, as represented by response characteristic 670.
• the brightness of the image causes the accumulated charge to quickly exceed the increased barrier level.
• any charge collected after this increased barrier level is exceeded is drained off. Accordingly, the accumulated charge level remains limited during stage 106 and continuing through stage 107, as represented by response characteristic 640.
• the level of barrier 130 is incrementally increased and charge is again accumulated, as represented by the response characteristic 680.
• the brightest portions of the image are collected and the brightest portions of the image are not lost.
• the altered reference points compress the image data to allow pixel cells to accumulate charge that would otherwise be greater than their maximum capability. These alterations in the reference points allow for the collection of image data from brighter images that would otherwise be lost without affecting low light level performance.
• the dynamic range of a TDI- CCD device is extended by selectively setting levels of barriers that limit the charge collection capability.
• the selectively set barrier levels shift the reference point of accumulated charge.
• the altered, or shifted, reference point causes the imager to compress brighter portions of an image while not influencing the lower intensity portions of the same image.
• the scope of the invention is not limited to the step-wise increase in charge capacity in the exemplary 8-stage TDI-CCD device illustrated. Rather the method of setting progressive barrier levels, and thereby progressively accumulating charge in a TDI-CCD device, may also be determined using, for example, exponential, logarithmic, inverse logarithmic, geometric or polynomial functions. Furtherstill, the number of barrier levels also may be increased commensurate with the number of stages in a TDI-CCD device. Thus, the number of different barrier levels may be set substantially equal to the number of stages.
• Figure 6a illustrates one embodiment for fabricating a TDI-CCD imager having a charge capacity illustrated in Figure 4.
• the barrier level 130 is set to limit the amount of charge collected.
• barrier levels are set to limit pixel cell 115 associated with stages 101 through 105 to collect only twenty-five (25) percent of full capacity of pixel cell 115 — i.e., maximum level 465.
• barrier levels are set to limit pixel cell 115 associated with stages 106 and 107 to collect and retain an accumulated charge that corresponds to fifty (50) percent of full capacity.
• the barrier levels are set to the full width of pixel cell 115 to collect and retain an accumulated charge that is substantially equal to full capacity.
• Figure 6b illustrates a second embodiment for fabricating a TDI-CCD imager having a charge capacity illustrated in Figure 4.
• the barrier levels, or potentials are constant but are positioned to adjust the width of pixel cells 115 to limit the charge collected. In this case, the amount of charge collected is limited by the size of the pixel cells. Further, the width of barrier level 130 remains substantially constant.
• Figure 7a illustrates a second embodiment of fabricating a TDI-CCD device to achieve the exemplary step-wise accumulated charge characteristics illustrated in Figure 4.
• the pixel cell charge capacity is set in designated stages to limit the accumulated charge.
• the width of pixel 115 in stages 101 through 104 is set at a maximum level 465 — i.e., full collection capacity.
• the width of pixel 115 is reduced to twenty-five (25) percent of maximum level 465.
• the width of pixel 115 is again increased to maximum level 465, and at stage 107, the width of pixel 115 is reduced to fifty (50) percent of maximum level 465.
• FIG. 108 the width of pixel 115 is again increased to maximum level 465.
• the narrow channel regions at stages 105 and 107 act as charge clippers.
• Figure 7b illustrates another embodiment, similar to that described in regard to Figure 7a, wherein the width of barrier 130 is remains substantially constant. This embodiment is advantageous as the width of drain 125 is correspondingly increased when the size of pixel 115 is decreased. This increase in drain 125 allows for the draining of excessive accumulated charge.
• the depth of the pixel cell 115 may also be used to control pixel charge capacity.
• the depth of pixel cells 115 associated with stages 101-105 may be set to collect twenty-five percent of full charge capacity.
• the depth of pixel cells 115 associated with stages 106-107 may be set to collect fifty percent of full charge capacity and the depth of pixel cell 115 associated with stage 108 may be set to accumulate a full charge.
• Figure 8 illustrates the response characteristics of this embodiment of the invention to the three exemplary images discussed in regard to Figure 3 and Figure 5.
• the response characteristic to the first exemplary image is represented by the response characteristic 800.
• the accumulated charge in stages 101 through 108 remains lower than the associated barrier levels.
• the selectively set levels do not influence the response characteristic of the TDI-CCD device to this first exemplary image.
• the charge accumulated in stages 101 through 104 rises to maximum level 465.
• the charge capacity of pixel cell 115 is set to twenty-five percent of maximum level 465. Accordingly, as the target image passes stage 105, the accumulated charge above this twenty-five percent level is drained off, as represented by response 820. Furthermore, any additional charge collected during stage 105 is also drained off. Thus, the accumulated charge remains limited, as represented by response characteristic 830.
• the charge capacity of pixel cell 115 is again increased to maximum level 465 and charge is again accumulated, as represented by response characteristic 840.
• the charge capacity of the associated pixel cell 115 is reduced to fifty percent. Any charge collected above this fifty-percent level is, accordingly, drained off and the accumulated charge remains at a fixed level, as is represented by response characteristic 850.
• the charge capacity of the associated pixel cell 115 increased to maximum level 465 and charge again is accumulated, as represented by response characteristic 860. Accordingly, the brighter portions of the imager are again captured in the imaging device similar to that illustrated in Figure 5.
• the accumulated charge quickly rises to maximum level 465, as illustrated by response characteristic 865.
• Any additional charge that may be collected in stages 102 - 104 is drained off, as represented by response characteristic 870.
• the charge capacity of the associated pixel cell 115 is set at twenty five percent and any accumulated charge above this level is drained off, as represented by response characteristic 875. Further, any additional charge collected is similarly drained off and the accumulated charge level remains constant, as represented by response characteristic 830.
• the charge capacity of the associated pixel cell 115 is again increased to maximum level 465. The charge is again accumulated, as represented by response characteristic 880.
• the charge capacity of the associated pixel cell 115 is again reduced to fifty percent, and the accumulated charge above this reduced level is again drained off, as represented by response characteristic 885.
• the accumulated charge remains fixed at this level as any additional charge collected is drained off, as represented by response characteristic 850.
• the charge capacity of the associated pixel cell 115 is again increased and the accumulated charge again increases, as represented by response 890.
• the brightest portions of this third exemplary image are thus captured in a manner similar to that illustrated in Figure 5. It should be understood, the representation of the transfer channel having varying size is intended merely to illustrate different methods of achieving the exemplary model of varying barrier levels. Other methods may also be used to achieve similar increases in accumulated charge.
• a further means of increasing dynamic range is achieved by placing a filtering element over at least one stage of a TDI-CCD device.
• Filter elements are used to further extend dynamic range by reducing the intensity of an image as the image moves with respect to the collection stages.
• Figure 4 illustrates the placement of filter 500 over stage 108.
• filter 500 is used to reduce the image intensity as the image passes stage 108.
• Filter 500 may be, for example, a neutral-density filter, or a slotted metal filter. Filtering is well known in the art and need not be discussed in detail herein.
• Figure 9 illustrates the response characteristic of the TDI-CCD imager illustrated in Figure 4 with filter 500 positioned over stage 108.
• the response to the three exemplary images is similar to the responses illustrated in Figure 5, except for the response in the filtered stage. That is, the response of this embodiment to the first exemplary image is similar to response characteristic 600 of Figure 5.
• the imposed filter 500 causes the image intensity to decrease during charge collection at stage 108. The amount of charge collected is thus reduced and this reduction in the accumulated charge is represented by response characteristic 910.
• the responses of the second and third exemplary images, as illustrated in Figure 9 are equivalent to corresponding responses illustrated in Figure 5, except for the response during stage 108.
• dynamic range of TDI-CCD is further extended by selectively using filters over at least one collection stage to collect highly intense images.
• Figure 10a illustrates a cross-sectional view of an exemplary embodiment of an 8- stage back-illuminated TDI-CCD imager incorporating filtering over one stage (stage 108).
• Figure 10b illustrates a cross-sectional view of a second exemplary embodiment of an 8-stage back-illuminated TDI-CCD imager incorporating filtering over one stage (stage 108).
• Figure 10c illustrates a cross-sectional view of an exemplary embodiment of an 8-stage top-illuminated TDI-CCD imager incorporating filtering over one stage (stage 108).
• TDI-CCD imager 1010 is composed of eight (8) stages, - i.e., stages 101-108. Stages 101-108 are formed in wafer 1000, which is typically made of a semi-conductor material, such as silicon or GaAs. Attached to wafer 1000 is block 1020. Block 1020 provides support and protection for wafer 1010. Typically block 1020 is an optically transparent material.
• block 1020 may be constructed of materials such as glass, plastic, acrylic or polymer, that allows light 1040 to pass without significant degradation or loss.
• block 1020 may be constructed of materials such as silicon.
• block 1020 may be materials such as quartz and calcium chloride.
• Filter 1030 is positioned on surface 1070 between block 1020 and wafer 1010.
• Filter 1030 similar to filter 500 discussed previously, is positioned over stage 108 to reduce the charge collected in this stage.
• the placement of filter 1030 is not limited to surface 1070, as illustrated. Rather, filter 1030 may be placed, for example, on surface 1060, or may even be incorporated within block 1020 to achieve a reduction in the intensity of the image.
• a filter may be included within block 1020, by altering the index of reflective of the material of block 1020. The altered index of reflective reduces the intensity of light that traverses block 1020 and is collected in stages 101-108 in wafer 1000. Further still, filter 1030 may be incorporated onto wafer 1010.
• filter 1030 on wafer 1010 has the disadvantage that when a change of filtering is necessary wafer 1010 is affected. Accordingly, incorporating filter 1030 onto block 1020 allows for filter changes without affecting wafer 1010.
• Filters may be used over a plurality of stages and each of these filters need not cause the same reduction in image intensity. For example, filters may be graduated along the depth of a TDI-CCD such that no filtering occurs in the earlier collection stages while significant reductions of intensity occurs in the latter collection stages. graduated filtering, thus, does not affect the low intensity portions of any image but will affect the brighter portions, as illustrated in Figure 9.
• the examples given herein are presented to enable those skilled in the art to more clearly understand and practice the instant invention.

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• 2000
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