JP2739601B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an interline transfer
The present invention relates to an imaging apparatus that performs imaging with a charge-coupled solid-state imaging device of a transfer type, and in particular, improves a resolution and an aperture ratio by applying a vertical charge transfer path in a light receiving area of the solid-state imaging device to a photosensitive unit (pixel). The present invention relates to an imaging device designed to achieve this.

[Conventional technology]

The conventional interline charge-coupled solid-state imaging device
Description will be made based on the drawings. In the figure, 1 is a light receiving area,
Reference numeral 2 denotes a horizontal charge transfer path, reference numeral 3 denotes an output amplifier, and n × m photodiodes arranged in a matrix in a vertical (row direction) and a horizontal (column direction) are formed in the light receiving region 1.
Pixels a _1.1 , a _1.2 ... A having blue spectral sensitivity by stacking blue (B) color filters on the respective light incident surfaces of the photodiodes arranged in odd-numbered rows (first rows)
_1.m , a _3.1 , a _3.2 ... a _3.m , a _n-1.1 , a _n-1.2 ... a
_n-1.m are formed, and a pixel a having a green spectral sensitivity is formed by stacking a green (G) color filter on each light incident surface of the photodiodes arranged in even rows (second rows). _{2.1, a 2.2 ...... a 2.m,} a 4.1, a 4.2 ...... a 4.m, a n.1,
a _n.2 ... a _nm are formed.

Dish, each blue and green pixels in the vertical charge transfer paths l ₁ adjacent groups arranged in columns, l ₂ ...... l _m is formed, the vertical signal charge based on a drive signal of the so-called four-phase drive system Transfer electrodes (not shown) made of polysilicon for transferring in the direction are stacked.

And the end of the vertical charge transfer paths l _1, l ₂ ...... l _m is connected in parallel to the horizontal charge transfer path 2, the output amplifier 3 to the output terminal of the horizontal charge transfer path 2 are formed.

Further, the structure of the light receiving area will be described in detail with reference to FIG.
The structure near the blue (B) pixels a _1.1 , a _1.2 , a _1.3 and the green (G) pixels a _2.1 , a _2.2 , a _2.3 will be described as a representative.
In the figure, each blue and green pixel and vertical charge transfer path
l ₁ , l ₂ , and l ₃ are separated by a channel stopper indicated by oblique lines, and a pair of transfer electrodes is provided for pixels arranged in each row.
G ₁ , G ₂ , G ₃ , G ₄ are stacked on the upper surface of the vertical charge transfer paths l ₁ , l ₂ , l ₃ (however, stacked avoiding the upper surfaces of the blue and green pixels), and these transfer electrodes The driving signal φ ₁ according to the so-called four-phase driving method,
φ _2, φ _3, the vertical charge transfer paths by applying a phi ₄
Potential wells (hereinafter, these potential wells are referred to as packets) for signal charge transfer are generated in l ₁ , l ₂ , and l ₃ .

Further, transfer between one end and the packet adjacent to those pixels and blue gate Tg _1, the transfer gate Tg ₂ is formed between the one end and the packet adjacent to those of the green pixel, a predetermined transfer electrodes G _2, It has a configuration to conduct a transfer gate Tg ₁ and Tg ₂ by applying a drive signal of high voltage G _4.

Further, the sectional structure of the vertical charge transfer path taken along line XX in FIG. 8 will be described with reference to FIG. 9. A silicon oxide film (S) serving as a gate oxide film layer is formed on the surface of a P well layer in a semiconductor substrate. transfer _{electrodes i} O ₂₎ through a polysilicon
G ₁ , G ₂ , G ₃ , G ₄ ... Are formed. For example, the drive signals φ ₁ , φ ₂ of “H” level are applied to the transfer electrodes G ₁ , G ₂ , and “L” is applied to the transfer electrodes G ₃ , G _4.
When the level driving signals φ ₃ and φ ₄ are applied, a deep potential well is generated below the transfer electrodes G ₁ and G ₂ , and a potential barrier is generated below the transfer electrodes G ₃ and G ₄ as shown in FIG. can do.

Then, at the time of imaging, By increasing the potential level of the portion of the packet indicated by, it is used as a red pixel. For example, in FIG. 8, a red (R) color filter is formed on the upper surface of the transfer electrodes G ₁ , G ₂ , G ₃ , and the driving signals φ ₁ to φ ₃ to these transfer electrodes are applied at the time of imaging. By setting the drive signal φ ₄ to the transfer electrode G ₄ to “H” level and the drive signal φ ₄ to “L” level, the transfer electrodes G ₁ , G
_2, the transfer elements by G ₃ and the pixel of red (R), performs pixel separation in the transfer electrode G ₄ under the potential barrier. The drive signal φ is applied to the other transfer electrodes in the same phase relationship.
Constituting the same pixel by applying a ₁ to [phi] _4.

Next, an imaging operation by the solid-state imaging device having such a configuration will be described. First, during an exposure period, a predetermined drive signal (for example, φ _{2 to} φ ₄ ) is set to “H” level, and the remaining drive signals (for example, φ ₁₎ ) Is set to the “L” level, so that a red pixel group is generated in the vertical charge transfer path, and the signal multi-charge is integrated with the blue and green pixels formed by the photodiodes. After the completion of the exposure, the red signal charges are transferred to the horizontal charge transfer path 2 by the transfer using a so-called four-phase driving method, and the signal is read out in the horizontal charge transfer path 2 in synchronization with the transfer operation. Read the pixel signal. Then, the transfer electrode drive signal of a predetermined normal than the high voltage (e.g., FIG. 8 in the G ₂₎ in the conductive transfer gate Tg ₁ corresponding to the blue pixel by applying the blue pixel signal charge Is transferred to the vertical charge transfer path, the transfer gate Tg ₁ is turned off again, and the blue signal charge is transferred to the horizontal charge transfer path 2 by transfer using a so-called four-phase drive method, and is synchronized with the transfer operation. Then, the signal is read out in the horizontal charge transfer path 2 to read out all the blue pixel signals. Next, a transfer signal Tg ₂ corresponding to the green pixel is turned on by applying a drive signal of a voltage higher than normal to a predetermined transfer electrode, and the signal charge of the green pixel is transferred to the vertical charge transfer path. After the transfer gate Tg ₂ is turned off, the green signal charges are transferred to the horizontal charge transfer path 2 by transfer using a so-called four-phase drive method, and the signals are read out on the horizontal charge transfer path 2 in synchronization with the transfer operation. And read out all the green pixel signals.

In this way, the pixel signals for each color are read out by the plane sequential scanning readout, and as is apparent from FIG.
2) xm pixel signals of the same number and the same resolution are obtained.

[Problems to be solved by the invention]

By the way, in such an imaging apparatus, since the sensitivity of blue and green to the sensitivity of red is low, it is desired to improve the aperture ratio of each pixel of blue and green.

That is, when a packet of a vertical charge transfer path using a polysilicon layer as a transfer electrode is a red pixel and blue and green pixels are formed by a photodiode, the red quantum efficiency η _R is about
Since the quantum efficiency of blue η _B and the quantum efficiency of green η _G are both about 0.5 in contrast to 0.7, in order to compensate for such a difference in quantum efficiency, the aperture ratio of the blue and green pixels is particularly large. Need to be increased.

In order to satisfy such requirements, it is conceivable to reduce the width of the vertical charge transfer path and increase the area of the blue and green pixels accordingly, but the signal charge transfer capability of the vertical charge transfer path is considered. There is a limit when considering.

As described above, in addition to a decrease in sensitivity due to a low aperture ratio, when an image is reproduced from pixel signals of each color obtained from a solid-state imaging device having such a variation in sensitivity, a problem that color balance is deteriorated also occurs. I do.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an imaging device having high sensitivity and having less variation in sensitivity of each pixel.

[Means for solving the problem]

In order to achieve such an object, the present invention applies a photoelectric conversion element such as a photodiode to blue and green pixels,
A transfer formed between the blue pixel and the vertical charge transfer path is intended for an image pickup apparatus using an interline transfer type charge-coupled solid-state imaging device that applies a predetermined packet of a vertical charge transfer path to a red pixel. The potential levels of the gate and the transfer gate formed between the green pixel and the vertical charge transfer path are variably controlled, and each pixel signal generated in the blue and green pixels is read out by a plurality of field scan readings. The potential level of the transfer gate in the first field scan reading is made shallow to read a part of each pixel signal, and the potential level of the transfer gate in the second and subsequent field scan readings is gradually increased as the number of times increases. Deeper, and at the last field scan readout, The remaining pixel signals are read out by setting the initial level to the deepest, and the signals read out in such a plurality of times are finally added and calculated for each pixel to form blue and green pixel signals. I decided that.

Further, the aperture areas of the blue and green pixels are set so as to make the sensitivity of each color equal, and the width of the vertical charge transfer path applied to the red pixels is set at the same time. The pixel signal for each color is read out by reading.

[Action]

According to the imaging device having such a configuration, the signal charges integrated in the blue and green pixels are divided into small amounts and read out a plurality of times, so that the width of the vertical charge transfer path can be reduced, and Accordingly, the aperture ratio of the blue and green pixels can be increased.

On the other hand, the width of the vertical charge transfer path is designed to be small in view of the fact that the quantum efficiency of the blue and green pixels by the photoelectric conversion element is lower than the quantum efficiency of the red pixel by the vertical charge transfer path. As a result of increasing the aperture ratio of the green pixel so as to equalize the sensitivity for each color, the charge transfer capacity of the vertical charge transfer path becomes insufficient, and the blue and green pixel signals are reduced by one each.
Even when the reading cannot be performed by the field scanning readouts, the pixel signals of all the pixels can be read out by the field scanning readings a plurality of times.

As described above, it is possible to provide an imaging device in which the aperture ratio is increased and the sensitivity for each color is equalized, and the degree of freedom in design can be improved.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

First, the overall configuration of the imaging apparatus will be described with reference to FIG. In the figure, 1 is a light receiving area of a solid-state imaging device,
Reference numeral 2 denotes a horizontal charge transfer path, reference numeral 3 denotes an output amplifier, and n × m photodiodes arranged in a matrix in a vertical (row direction) and a horizontal (column direction) are formed in the light receiving region 1.
By stacking blue (B) color filters on the respective light incident surfaces of the photodiodes arranged in odd rows (first rows), pixels having blue spectral sensitivity are formed, and even rows (second rows) are formed. Pixels having green spectral sensitivity are formed by laminating green (G) color filters on the respective light incident surfaces of the photodiodes arranged in (row).

Furthermore, the blue and green pixels in the vertical charge transfer paths l ₁ adjacent groups arranged in columns, l ₂ ...... l _m is formed, longitudinally signal charges on the basis of a drive signal of the so-called four-phase drive system A transfer electrode (not shown) made of polysilicon and a red strike type filter for transfer to the substrate are stacked.

And the end of the vertical charge transfer paths l _1, l ₂ ...... l _m is connected in parallel to the horizontal charge transfer path 2, the output amplifier 3 to the output terminal of the horizontal charge transfer path 2 are formed.

Further, the structure of the light receiving region will be described in detail with reference to FIG.
It should be noted that blue (B) pixels a _ij , a arranged in a certain odd-numbered row i
The structure near the green (G) pixels a _{i + 1.j} and a _{i + 1.j + 1} arranged in _{i.j + 1} and the adjacent even-numbered row i + 1 will be described as a representative. In the figure, the blue and green pixels and the vertical charge transfer paths l _j each are separated by the channel stopper hatched portion, the transfer electrodes g _2i of each pair with respect to pixels arranged in each row, g _{2i + 1} , g _{2i + 2} and g _{2i + 3} are the vertical charge transfer paths l _j
(Except for the top surfaces of the blue and green pixels), and drive signals φ ₁ , φ ₂ , φ ₃ , φ ₄ according to a so-called four-phase drive method are applied to these transfer electrodes. potential well (i.e., packets) for signal charges transferred to the vertical charge transfer paths l _j by to generate a further predetermined packet corresponding to blue and green pixels applied to the red pixel.

Further, a transfer gate Tg ₁ is formed between one end of the blue pixel and a packet adjacent thereto, and a transfer gate Tg ₂ is formed between one end of the green pixel and a packet adjacent thereto, and a predetermined transfer electrode g _{2i + 1,} transfer to g _{2i + 3} by applying a driving signal of a predetermined voltage gate Tg ₁ and T
g ₂ is made conductive.

Next, the size of the blue and green pixels and the size of the vertical charge transfer path will be described. In the second view, and g _2i to the pair of transfer electrodes (pixel a _ij for each row of pixels g
_{2i + 1} , the width in the row direction of g _{2i + 2} and g _{2i + 3} ) for the pixel a _{i + 1.j} is v, the pitch interval between the vertical charge transfer paths is h, the width of each vertical charge transfer path is b, Let λ be the width of the part that shields the periphery of the photodiode. Note that the transfer electrodes are slightly displaced in accordance with the so-called layout rule in the semiconductor manufacturing technology, and are ignored for convenience of explanation.

When representing the portion of the pixel a _ij and the vertical charge transfer paths l _j corresponding thereto, firstly, the charge amount Q ₁ of the pixel a _jj can accumulate
Can be expressed by the product of the opening area and the saturated charge amount per unit area (capacitance due to the depletion layer) α, so that Q ₁ = (v−2λ) × (h−2λ−b) × α (1) , The amount of charge Q ₂ that can be stored by the red pixel (packet) in the vertical charge transfer path corresponding to the pixel a _ij is determined by the area of the packet and the saturated charge amount (capacity of the MOS capacitor) β per unit area. Since it can be expressed as a product, Q ₂ = b × v × σ × β (2) The coefficient σ represents the ratio of the number of packets to be applied to the red pixels to transfer phase number, e.g., four-phase drive a pair of blue and green pixel _{(a jj, a i + 1.j} ) red pixels to In the case of two packets below the transfer electrodes g _2i and g _{2i + 1} of the method, σ = 2.

Further, when the red and blue signal charges are respectively read out by τ times of field scan reading, the τ times charge transferable capacity Q ₃ is calculated from the above equation (2) by Q ₃ = τ × Q ₂ = τ × b × v × σ × β (3)

Assuming that the amount of charge transferred by the vertical charge transfer path is equal every time, from the above equations (1) and (3), each size is set so that the relationship of Q ₁ ≦ Q _3. Determine v, h, b.

However, in order to design in consideration of equalizing the sensitivity of each pixel, each size should be set so that the sensitivity of the pixel is equal.
After determining v, h, b, the number of transfers τ by the vertical charge transfer path
To determine.

That is, since the sensitivity of each pixel is proportional to the product of the quantum efficiency and the aperture area, the sensitivity of the blue and green pixels is Γ ₁ , the sensitivity of the red pixel is Γ ₂ , and the aperture area of the blue and green pixels is S ₁ , the light receiving area of the red pixel is S ₂ , the coefficients including the light transmittance of the blue and green color filters are ε ₁ and ε ₂ , and the coefficient including the light transmittance of the red color filter is ε _{3, respectively.} Then Becomes Then, from the above equations (5) and (6), Or The areas of the blue, green, and red pixels are determined based on the relational expression, and these areas are further substituted into the above expressions (1) to (3) to finally satisfy the condition of the above expression (4). Size v, h,
b and the number of transfers τ are determined.

Next, means for dividing and reading out the signal charges of the blue and green pixels by a plurality of field scan readings will be described with reference to FIG. FIG. 3 shows a potential profile between a photodiode and a vertical charge transfer path along a transfer gate, wherein the potential level of the photodiode is higher than the deepest potential level of a packet generated in normal signal charge transfer. The transfer gate is formed so as to be shallow, and furthermore, at the time of normal signal charge transfer, the potential level of the transfer gate becomes so shallow that it becomes a so-called potential barrier separating the photodiode and the packet.

The potential level of the transfer gate is varied by changing the voltage of the drive signal applied to the transfer electrode on the transfer gate, and the signal charge transferred from the blue and green pixels (photodiodes) to the vertical charge transfer path is reduced. Adjust.

For example, when a pixel signal is read out by two field scan readings for each pixel, the drive voltage for completely turning on the transfer gate is V _M , and the signal charge at an arbitrary ratio k (where 0 <k <1). the driving voltage for transferring the k × V _M, is the time of the first field scan reading to the potential level P ₁ shown in FIG. 3 for example by setting the drive voltage to the k × V _M (a) that the the show only a portion signal charges above this potential level P ₁ from the transferred to the vertical charge transfer path side reading, in the next field scan read by setting the drive voltage to the V _M for example FIG. 3 (a) by the potential level P _2, reads from the remaining was transferred signal charge to the vertical charge transfer path side.

Referring back to FIG. 1, reference numeral 4 denotes a four-phase drive type drive signal φ _{1 to} φ applied to the transfer electrode of the vertical charge transfer path.
₄ , a drive signal generation circuit for generating drive signals φ _H1 and φ _{H2 of} a two-phase drive method for driving the horizontal charge transfer path 2 and a control signal for controlling the transfer gate, etc. It is a timing control circuit for controlling.

Further, reference numeral 6 denotes a sample-and-hold circuit for sampling a pixel signal read via the output amplifier 3, 7 an A / D converter for encoding the sampled pixel signal into digital pixel data, and 8 a red ( R) a first memory for storing the pixel data of
9 is a second memory for storing blue (B) pixel data, 10 is a third memory for storing green (G) pixel data, and the second and third memories 9, 10 are plural memories corresponding to the number of times of reading. Memory area. Reference numeral 11 denotes a channel switch, which switches the connection between the A / D converter 7 and the memories 8, 9, and 10 in accordance with the reading for each color.

Reference numeral 12 denotes an arithmetic circuit, which performs an addition operation on pixel data divided and stored in each of the memory regions of the memories 9 and 10 for each pixel to generate a pixel signal generated in blue and green pixels. The corresponding pixel data is reproduced.

Next, the operation of the imaging apparatus having such a configuration will be described with reference to the timing chart of FIG. FIG. 1 shows a case where the present invention is applied to a camera for capturing a still image, such as an electronic still camera.

First, in step 100, the drive signal of the voltage V _M phi ₂
Is added to make the transfer gates for the blue (B) pixels completely conductive, and unnecessary charges remaining in these pixels are transferred to the adjacent vertical charge transfer path.
In step 110, the driving signals φ ₁ to φ 4 of the four-phase driving method
at the same time to perform the charge transfer operation in the vertical charge transfer path according to phi _4, the driving signal phi _H1 of 2-phase drive system, the horizontal charge transfer path 2 according phi _H2 are read at a predetermined timing.

After reading the unnecessary charges from the pixels of all the blue, at the next step 120, it is the transfer gate related group of pixels the green (G) by applying a driving signal phi ₄ of the voltage V _M to the fully conductive Unnecessary charges remaining in the pixel are transferred to the adjacent vertical charge transfer path.
In 130, at the same time to perform the charge transfer operation in the vertical charge transfer path in accordance with driving signals phi ₁ to [phi] ₄ of four-phase drive system, the drive signal of the 2-phase drive method phi _H1, according phi _H2 are horizontal charge transfer path 2 given And unnecessary charges remaining in all the green pixels are discharged to the outside.

The processes in steps 100 to 130, it becomes possible to discharge the unnecessary charges of the pixel and the vertical charge transfer path, immediately after the discharge, in step 140, the voltage level for the drive signals phi ₁ and phi ₂ normal charge transfer By setting “H” and driving signals φ ₃ and φ ₄ to “L” level, a packet that becomes a red pixel is generated in the vertical charge transfer path under the transfer electrode to which the driving signals φ ₁ and φ ₂ are applied. At the same time, a mechanical shutter (not shown) arranged in front of the light receiving area 1 is opened, exposure is performed for a time corresponding to the shutter speed, and the mechanical shutter is closed again.

Next, in step 150, in synchronization with the driving signals phi ₁ to [phi] ₄ of four-phase drive system to perform the charge transfer operation by the vertical charge transfer path, line by line the transferred come signal charges horizontal charge transfer path 2 Is read out through the output amplifier 3, and by repeating this operation, the pixel signal for one frame received by the red pixel is read out. Further, during this reading, each pixel signal is converted into red pixel data by the sample hold circuit 6 and the A / D converter 7, and is stored in the first memory 8 via the channel switch 11 in accordance with the red pixel arrangement. To remember.

Next, in step 160, sets the ratio k ₁ of the maximum voltage V _M applied to the transfer gate, in step 170, specifies the memory area of the second memory 9 in the third memory 10.

Next, in step 180, the transfer gate Tg ₁ for the blue (B) pixel arranged in the first field.
The to conduction by a drive signal phi ₂ of the voltage k ₁ × V _M. At this time, since the transfer gate Tg ₁ is not a most deep potential level, only the signal charges of minute blue higher than the potential level level is transferred to the vertical charge transfer paths, the non-conductive again transfer gate after a predetermined time I do.

Next, in step 190, in synchronization with the driving signals phi ₁ to [phi] ₄ of four-phase drive system to perform the charge transfer operation by the vertical charge transfer path, line by line the transferred come signal charges horizontal charge transfer path 2 Is read out via the output amplifier 3, and by repeating this operation, a part of the pixel signal received by the blue pixel is read out, and the sample / hold circuit 6, the A / D converter 7
And the second memory 9 via the channel switch 11
Is stored in the designated memory area corresponding to the pixel array.

Next, in step 200, the transfer gate Tg ₂ for the green (G) pixel arranged in the second field
The to conduction by the drive signal phi ₄ of the voltage k ₁ × V _M. At this time, since the transfer gate Tg ₂ does not reach the deepest potential level, only the green signal charges of a level higher than the potential level are transferred to the vertical charge transfer path, and after a predetermined time, the transfer gate Tg ₂ is reset again. Make it conductive.

Next, in step 210, in synchronization with the driving signals phi ₁ to [phi] ₄ of four-phase drive system to perform the charge transfer operation by the vertical charge transfer path, line by line the transferred come signal charges horizontal charge transfer path 2 Is read out via the output amplifier 3 and by repeating this operation, a part of the pixel signal received by the green pixel is read out, and the sample-and-hold circuit 6, the A / D converter 7
And a third memory 10 via a channel changeover switch 11
Is stored in the designated memory area corresponding to the pixel array.

Next, in step 220, a preset number of times τ
It is determined whether or not reading has been completed. If not, the process proceeds to step 230. Step 2
At 30, the ratio k of the voltage applied to the transfer gate is changed. However, the ratio is set to be higher than the applied voltage. Further, in step 240, the second
The next memory area in the memory 9 and the third memory 10 is designated.

Then, the next memory by performing in accordance with the voltage k × V _M newly set the processing of step 180 to 220, further divided blue and green pixel data and second memory 9 in the third memory 10 The information is stored in the area according to the pixel arrangement.

As described above, when the reading process is repeated τ times a preset number of times, the process proceeds to step 260.

In step 250, the arithmetic circuit 12 is activated, pixel data stored in each memory area of the second memory 9 is subjected to an addition operation corresponding to each pixel array, and corresponds to a pixel signal generated in each blue pixel. The pixel data is reproduced and stored in a predetermined memory area.

Next, in step 260, the arithmetic circuit 12 is activated,
Pixel data stored in each memory area of the third memory 10 is subjected to an addition operation corresponding to each pixel array, and pixel data corresponding to a pixel signal generated in each green pixel is reproduced. Store.

Then, each of the memories 8, 9, 10 is read by well-known memory reading.
By outputting the pixel data from, it can be used for reproducing a still image on a monitor or the like.

Further, another embodiment will be described with reference to FIGS. 5 and 6. FIG. In this embodiment, the vertical charge transfer path in the light receiving region 1 of the solid-state imaging device shown in FIG. 1 is configured to perform charge transfer based on a two-phase driving method. Drive signals φ _V1 and φ _{V2 of the} phase drive system are output. Then, similarly to the first embodiment, a blue (B) and green (G) pixel group and a vertical charge transfer path group are formed.

Based on FIG. 5, the structure of the light receiving region is changed to a certain odd-numbered row i.
Blue (B) pixels a _ij , a _{i.j + 1} and green (G) pixels a _{i + 1.j} , arranged in the even-numbered row i + 1 adjacent _thereto .
A description will be given on behalf of the neighborhood of a _{i + 1.j + 1} . In the figure, the blue and green pixels and the vertical charge transfer paths l _j each are separated by the channel stopper hatched portion, transfer electronic g _i of one for pixels arranged in each row, g _{i + 1,} ... are stacked on the upper surface of the vertical charge transfer paths l _j (where, to avoid the upper surface of the blue and green pixels stacked) is the two-phase drive, as shown in FIG. 6 (d) to these transfer electrodes driving signals phi _V1 in conformity with scheme, potential well for signal charges transferred to the vertical charge transfer paths l _j by applying the phi _V2 (i.e., a packet) is generated, further, correspond to the blue and green pixels Apply a given packet to the red pixels.

Further, a transfer gate Tg is formed between one end of the blue and green pixels and a packet adjacent thereto, and the transfer gate Tg is made conductive by applying a drive signal of a predetermined voltage to the transfer electrode.

The vertical charge transfer path has a longitudinal sectional structure shown in FIG. 6 (a) or (b).

As one specific example, as shown in FIG. 6A, on the surface of a P-well layer in a semiconductor substrate, each transfer electrode has a silicon oxide film (S _i ) having a different thickness in the signal charge transfer direction.
O ₂ ), and these transfer electrodes are connected to each other as shown in FIG.
By supplying the two-phase drive signals φ _V1 and φ _V2 shown in
By generating a potential profile as shown in FIG. 6C, the signal charges are transferred to the horizontal charge transfer path side.
That is, the time point t ₁ shown in FIG. 6D (that is, φ _V1 is “H”,
phi ₂ is "L" when the level) potential profile indicated by a solid line in FIG. 6 (c) during the time t ₂ shown in FIG. 6 (d)
(That is, when φ _V1 is “L” and φ ₂ is at “H” level), the potential profile shown by the dotted line in FIG. 6C is obtained, and the signal charge is transferred by repeating this.

In other embodiments, as shown in FIG. 6 (b), the surface of the P- well layer in a semiconductor substrate, each transfer electrode through an equal thickness of the silicon oxide film (S _i O ₂₎ Stacked on the P-well layer under each transfer electrode in the direction of signal charge transfer.
A buried layer of a P ⁺ type impurity and a portion without this buried layer are formed. Then, these transfer electrodes are applied to FIG. 6 (d).
By supplying the two-phase drive signals φ _V1 and φ _V2 shown in
By generating a potential profile as shown in FIG. 6C, the signal charges are transferred to the horizontal charge transfer path side.

Since the same function can be obtained in any of the specific examples, it is appropriately selected in this embodiment.

Next, the size of the blue and green pixels and the size of the vertical charge transfer path will be described. In FIG. 5, the width in the row direction corresponding to the pixels in each row is v, the pitch interval between the vertical charge transfer paths is h, the width of each vertical charge transfer path is b, and the width of the portion that shields the periphery of the photodiode from light. Is λ. Note that a slight shift of the transfer electrode in accordance with the so-called layout rule in the semiconductor manufacturing technology is ignored for convenience of explanation.

As a representative of the pixel a _ij and the corresponding portion of the vertical charge transfer path l _j , first, the charge amount Q ₁ that the pixel a _ij can accumulate
Can be expressed by the product of the opening area and the saturated charge amount per unit area (capacitance due to the depletion layer) α, so that Q ₁ = (v−λ) × (h−2λ−b) × α (9) , The amount of charge Q ₂ that can be stored by the red pixel (packet) in the vertical charge transfer path corresponding to the pixel a _ij is determined by the area of the packet and the saturated charge amount (capacity of the MOS capacitor) β per unit area. Since it can be expressed as a product, Q ₂ = b × v × σ × β (10) The coefficient σ indicates the ratio of the number of packets applied to the red pixel to the number of transfer phases, and σ = σ.

Further, when the red and blue signal charges are respectively read out by τ times of field scan reading, τ times of the charge transferable capacity Q ₃ can be calculated from the above equation (9) by Q ₃ = τ × Q ₂ = τ × b × v × σ × β (10)

Assuming that the amount of charge transferred by the vertical charge transfer path is equal every time, from the above equations (1) and (3), each size is set so that the relationship of Q ₁ ≦ Q _3. Determine v, h, b.

In addition, in order to perform the design in consideration of equalizing the sensitivity of each pixel, the sensitivity of the blue and green pixels is _{１ 1} , the sensitivity of the red pixel is Γ ₂ , and the opening area of the blue and green pixels is S ₁ , the light receiving area of the red pixel is S ₂ , the coefficients including the light transmittance of the blue and green color filters are ε ₁ and ε ₂ , and the coefficient including the light transmittance of the red color filter is ε _{3, respectively.} Then Becomes Then, from the above equations (12) and (13), Or The areas of the blue, green, and red pixels are determined based on the relational expression, and these areas are further substituted into the above expressions (9) to (11) to finally satisfy the condition of the above expression (11). Size v, h,
b and the number of transfers τ are determined.

As in the first embodiment, a plurality of read scans are performed, and the potential level of the transfer gate is made variable when signal charges are transferred from the blue and green pixels to the vertical charge transfer path at each read. In addition, all pixel signals can be read out even in a narrow vertical charge transfer path, and the sensitivity of blue and green can be set to be equal to the sensitivity of red.

〔The invention's effect〕

As described above, according to the present invention, conventionally, the sensitivity of red formed in the vertical charge transfer path is higher than the sensitivity of blue and green formed by the photoelectric conversion element, resulting in poor color balance. The width of the vertical charge transfer path and the opening areas of blue and green are designed so that the signal charge transfer capability of the vertical charge transfer path can be reduced by one signal readout multiple times Therefore, it is possible to easily solve the problem of the color balance, and at the same time, obtain an excellent effect that the imaging sensitivity for each color can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a configuration of an embodiment of a solid-state imaging device according to the present invention, FIG. 2 is an explanatory view showing an enlarged structure of a main part of a light receiving area in FIG. 1, and FIG. FIG. 4 is a flow chart for explaining an imaging operation in the embodiment. FIG. 5 is a structure showing an enlarged main part structure of a light receiving region of a solid-state imaging device of another embodiment. FIG. 6 is an explanatory diagram for explaining the structure and operation of the vertical charge transfer path in FIG. 5, FIG. 7 is a structural explanatory diagram showing the configuration of a conventional solid-state imaging device, and FIG. FIG. 9 is an enlarged structural explanatory view showing a main structure of a light receiving region in FIG. 9, and FIG. 9 is a partial sectional view of a vertical charge transfer path in FIG. Reference numerals in the drawing: 1; light receiving area 2; horizontal charge transfer path 3; output amplifier 4; drive signal generation circuit 5; timing control circuit 6; sample and hold circuit 7; A / D converter 8; first memory 9; 2 memory 10; third memory 11; channel switching circuit 12; arithmetic circuit l ₁ , l ₂ , l ₃ ,...; Vertical charge transfer paths a _ij , a _{i.j + 1} , a _{i + 1.j} , a _{i + 1.j + 1} . … ,; blue or red pixel g _i , g _{i + 1} ……, g _2i , g _{2i + 1} ……; transfer electrode

Claims (1)

(57) [Claims] A plurality of photoelectric conversion elements are formed in a matrix in the vertical and horizontal directions, and a group of photoelectric conversion elements arranged in a first row is a pixel group having blue (B) spectral characteristics, a second row. Are formed as a group of pixels having spectral characteristics of green (G), and a vertical charge transfer path is formed adjacent to each pixel group in each column arranged in the column direction. Is applied to the red (R) pixel group, and a transfer gate is formed between the blue pixel and the vertical charge transfer path and between the green pixel and the vertical charge transfer path by an interline transfer method. In an image pickup apparatus for picking up an image by a combined solid-state image pickup device, the potential level of the transfer gate is variably controlled, and respective pixel signals generated in blue and green pixels are read out by a plurality of field scan readings. An image pickup apparatus characterized in that by sequentially increasing the potential level of the transfer gate in accordance with the field scan reading order, a pixel signal is divided and read for each field scan read.