JP2003078819A - Solid-state imaging device and method for sweeping out electric charge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten an operation time by sweeping out a signal electric charge without performing a transfer operation of a transfer register. SOLUTION: First, clock pulses Vϕ1, Vϕ2 and Vϕ3 to be a drive voltage of a vertical transfer register 120 are set to a low level, electric charges are made to be difficult to remain in the vertical transfer register 120, and generation of a dark current is also prevented. Next, a voltage pulse ϕSUB is turned on, and the electric charges of a photosensor 110 and the vertical transfer register 120 are immediately discharged to a substrate side by applying large voltage to the substrate of an element chip 300. A mechanical shutter is subsequently opened to perform exposure for a prescribed time, and signal electric charges accumulated in the photosensor 110 are read to the vertical transfer register 120 by the clock pulse Vϕ2. Then, the clock pulses Vϕ1, Vϕ2 and Vϕ3 are made to operate to perform transfer by the vertical transfer register 120.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device used in various image sensors, and more particularly to a method of sweeping away unnecessary charges before exposure of a photosensor.

[0002]

2. Description of the Related Art Conventionally, this type of solid-state image pickup device has a plurality of photosensors arranged in a two-dimensional matrix on a semiconductor substrate and a plurality of vertical transfer registers provided for each column of the photosensors. And a horizontal transfer register for transferring the signal charge from the vertical transfer register to the output unit, and an output unit for converting the signal charge into a voltage signal, and the signal charge generated by the exposure of the photosensor is transferred to the vertical transfer register. Then, the signal charges are sequentially transferred to the horizontal transfer register, and further, the signal charges are sequentially transferred from the horizontal transfer register to the output section, whereby the signal charges are sequentially converted into a voltage signal and output as an imaging signal. .

[0003]

By the way, in the solid-state image pickup device as described above, a semiconductor is formed by using a so-called electronic shutter function in which unnecessary signal charges accumulated in the photosensor are applied to the semiconductor substrate with a voltage higher than a certain level. It is possible to sweep to the substrate side, but for unnecessary signal charge remaining in the vertical transfer register, there is only a way to perform sweep transfer to the horizontal transfer register. It took only the transfer time.

FIG. 3 is a timing chart showing a conventional charge sweeping operation. First, a voltage pulse φ is applied to the semiconductor substrate in order to sweep away the charge of the photo sensor before exposure.
Set up SUB. After that, high-speed transfer of signal charges is performed by each clock pulse Vφ1, Vφ2, Vφ3 of each vertical transfer register, and the charges of the vertical transfer register are swept away. As described above, when the signal charges are swept away before the exposure of the photosensor, the transfer operation of the vertical rolling register is required, and a certain amount of time is required. For example, when performing continuous shooting with a camera, this sweep-away transfer must be performed before exposure, which slows down the continuous shooting speed.

Therefore, an object of the present invention is to remove the signal charges without performing the transfer operation of the transfer register, and to shorten the operation time, and the solid-state image pickup device and the charge cleaning method. To provide.

[0006]

In order to achieve the above object, the present invention provides a plurality of photosensors on a semiconductor substrate, a transfer register for transferring signal charges of the photosensors to an output section, and a voltage for the signal charges. In a solid-state imaging device having an output unit for converting into a signal, reading the signal charge generated by the exposure of the photosensor to the transfer register and transferring the signal charge to the output unit, before the exposure of the photosensor,
After turning off the drive voltage of the transfer register, a large voltage is applied to the semiconductor substrate to sweep out the signal charges stored in the photosensor and the transfer register to the semiconductor substrate side at once.

According to the present invention, a semiconductor substrate has a plurality of photosensors, a transfer register for transferring the signal charges of the photosensors to an output section, and an output section for converting the signal charges into a voltage signal. A method of sweeping out a charge of a solid-state imaging device, which reads out a signal charge generated by exposure of a photosensor to a transfer register and transfers the signal charge to an output unit, in which a drive voltage of the transfer register is turned off before exposure of the photosensor. 1) and a second operation step in which a large voltage is applied to the semiconductor substrate and the signal charges stored in the photosensor and the transfer register are swept to the semiconductor substrate side at a time.

In the solid-state image pickup device of the present invention, before the exposure of the photosensor, the drive voltage of the transfer register is first turned off so that the electric charge is less likely to be accumulated and the dark current is less likely to occur. After that, a large voltage is applied to the semiconductor substrate, and the signal charges stored in the photosensor and the transfer register are swept away to the semiconductor substrate side at once. After that, the exposure operation of the photo sensor is performed. Thus, the signal charges of the photosensor and the transfer register can be collectively swept away before the exposure of the photosensor without performing the transfer operation of the transfer register, and the operation time can be shortened.

In the charge sweeping method of the present invention, before the photosensor is exposed, first, the drive voltage of the transfer register is turned off in the first operation step so that the charge is less likely to accumulate and the dark current is less likely to occur. State. After that, in the second operation step, a large voltage is applied to the semiconductor substrate, and the signal charges stored in the photo sensor and the transfer register are swept away to the semiconductor substrate side at once. After that, the exposure operation of the photo sensor is performed. As a result, the signal charges of the photosensor and the transfer register can be collectively swept away before the exposure of the photosensor without performing the transfer operation of the transfer register.
It is possible to reduce the operation time.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are given. However, the scope of the present invention is not limited to the present invention in the following description. Unless otherwise stated, the present invention is not limited to these embodiments.

In this embodiment, a large number of photosensors are arranged in a matrix on a semiconductor substrate, and signal charges generated by each photosensor are transferred to an output section by a vertical transfer register and a horizontal transfer register. The present invention is applied to a two-dimensional image sensor that outputs an image pickup signal by performing charge-to-voltage conversion in the above. The sweeping-out of the charge before exposure of the photosensor in this two-dimensional image sensor is performed by the vertical transfer register transfer operation. In order to realize without performing the above, first, all the drive voltages of the vertical transfer registers are turned off, that is, set to the low level, so that it is difficult to store the charges in the transfer path, and then the electronic shutter function of the photo sensor is used. By applying a large voltage to the semiconductor substrate, not only the charge of the photo sensor but also the charge of the vertical transfer register Collectively it is obtained as swept into the semiconductor substrate side.

First, an outline of the two-dimensional image sensor according to the present embodiment will be described prior to the description of the charge sweeping operation which is a feature of the present invention. FIG. 1 is a schematic plan view showing the configuration of the two-dimensional image sensor according to this embodiment. This two-dimensional image sensor is provided with an image pickup section 100 for picking up an image of a subject on an element chip 300 made of a silicon substrate, and an output section 200 for outputting an image pickup signal from the image pickup section 100 to the outside. The image pickup unit 100 includes photosensors 110 that form a large number of unit pixels arranged in a two-dimensional matrix in the vertical (V) direction and the horizontal (H) direction, and are arranged for each photosensor column in the vertical direction. It has a plurality of vertical transfer registers 120 for vertically transferring the signal charges of the photo sensor 110. In addition, a horizontal transfer register 130 that horizontally transfers the signal charges transferred from each vertical transfer register 120 is arranged on the side of the imaging unit 100, and the output unit 200 is provided at the end of the horizontal transfer register 130. It is provided. On the upper surface of the image pickup unit 100, an on-chip lens (OCL), a color filter, etc., which are not shown, are arranged,
The incidence of light on the light receiving portion of each photo sensor 110 is controlled.

In such a two-dimensional image sensor, the signal charge accumulated by the photosensor 110 is read out through a vertical transfer register 120 via a read gate (not shown).
, And the signal charges are sequentially transferred in the vertical direction.
Then, the signal charge transferred from the vertical transfer register 120 is read out through the horizontal transfer register 13 via the read gate.
The data is sequentially read out to 0, sequentially transferred in the horizontal direction, and sent to the output unit 200. The output unit 200 converts the signal charge transferred by the horizontal transfer register 130 into a voltage signal and outputs the voltage signal.

Next, a method of sweeping away unnecessary electric charges before exposure of the photosensor in the above-described two-dimensional image sensor of this example will be described. FIG. 2 is a timing chart showing the charge sweeping operation in the two-dimensional image sensor of this example. In the two-dimensional image sensor of this example, the vertical transfer register 12 is exposed before the photosensor 110 is exposed by opening the mechanical shutter of the digital camera, for example.
The first operation step of turning off the drive voltage of 0 to a low level, and applying a large voltage larger than the electronic shutter function to the silicon substrate of the element chip 300, the signal charges stored in the photo sensor 110 and the vertical transfer register 120 are simultaneously The second operation step of sweeping away to the silicon substrate side is performed to sweep away unnecessary charges.

That is, in FIG. 2, in order to simultaneously sweep away the charges in the photosensor 110 and the vertical transfer register 120 with the mechanical shutter closed, first, clock pulses Vφ1 and Vφ2 serving as the drive voltage of the vertical transfer register 120. , Vφ3 is set to a low level to prevent charges from accumulating in the vertical transfer register 120 and to prevent generation of dark current. That is, in the conventional example shown in FIG. 3, in the state before exposure, the clock pulse V.phi.
Is on (high level), but in the present example, this clock pulse Vφ2 is replaced with other clock pulses Vφ1, Vφ1.
Similar to φ3, it is controlled to off (low level).

Next, by turning on the voltage pulse φSUB and applying a large voltage to the substrate of the element chip 300,
The charges of the photo sensor 110 and the vertical transfer register 120 are discharged to the substrate side. As a result, the charges of the vertical transfer register 120 can be swept to the substrate side of the element chip 300 without being swept and transferred to the horizontal transfer register 130. After that, the mechanical shutter is opened to perform exposure for a predetermined period, the read gate pulse by the clock pulse Vφ1 is turned on, and the signal charge accumulated in the photosensor 110 is read to the vertical transfer register 120. Then, the clock pulse Vφ
1, Vφ2, Vφ3 are activated to activate the vertical transfer register 1
20 transfer is performed. Here, the clock pulse Vφ2
Are of the same polarity with respect to the clock pulses Vφ1 and Vφ3.

When the above two-dimensional image sensor is used in a digital camera, for example, the following merits can be obtained. That is, in the conventional digital camera, when capturing a one-shot image, the dark component of the vertical transfer register was swept to the horizontal transfer register for transfer, and then exposure for capturing the image was performed. In this case, it took a long time to sweep away the charges from the vertical transfer register, which reduced the number of continuous shooting frames, which is an important performance of the camera. On the other hand, when the configuration of this example is used, it is possible to sweep away the charges of the photo sensor and the vertical transfer register at the same time by adopting the method of sweeping out the charges of the vertical transfer register together with the photo sensor. , It is possible to prevent the time of sweep-out transfer from being lost and to prevent the number of continuous shooting frames from decreasing.

The solid-state image pickup device of the present invention can be used in an image pickup device other than the above-mentioned digital camera, and instead of a two-dimensional image sensor, for example, an image pickup signal from a plurality of sensor arrays is used. You may use for the line sensor which outputs individually. Further, the solid-state imaging device according to the present invention is not limited to the one having the configuration shown in FIG. 1, and various modifications can be made without departing from the gist of the present invention.

[0019]

As described above, according to the solid-state image pickup device of the present invention, before the exposure of the photosensor, the drive voltage of the transfer register is first turned off so that the charge is less likely to be accumulated and the dark current is generated. After that, the semiconductor substrate was applied with a large voltage to sweep out the signal charges stored in the photosensor and the transfer register to the semiconductor substrate side at a time. Before the exposure of the sensor, the signal charges of the photo sensor and the transfer register can be collectively swept away, and the operation time can be shortened.

According to the charge sweep-away method of the present invention, before the exposure of the photosensor, the drive voltage of the transfer register is first turned off in the first operation step so that the charge is less likely to be accumulated and the dark current is generated. In the second operation step, a large voltage is applied to the semiconductor substrate so that the signal charges stored in the photosensor and the transfer register are swept away to the semiconductor substrate side at a time. It is possible to collectively sweep out the signal charges of the photosensor and the transfer register before the exposure of the photosensor without performing the above, and to shorten the operation time.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a configuration of a two-dimensional image sensor according to an embodiment of the present invention.

2 is a timing chart showing a charge sweeping operation in the two-dimensional image sensor shown in FIG.

FIG. 3 is a timing chart showing a charge sweeping operation in the conventional two-dimensional image sensor.

[Explanation of symbols]

100 ... Imaging unit, 110 ... Photo sensor, 120 ...
... Vertical transfer register, 130 ... Horizontal transfer register, 2
00 ... Output part, 300 ... Element chip.

Claims (8)

[Claims] 1. A semiconductor substrate having a plurality of photosensors, a transfer register for transferring signal charges of the photosensors to an output unit, and an output unit for converting the signal charges into a voltage signal. In a solid-state imaging device that reads out signal charges generated by exposure to the transfer register and transfers the signal charge to an output unit, a high voltage is applied to the semiconductor substrate after the drive voltage of the transfer register is turned off before the exposure of the photosensor. A solid-state image pickup device characterized in that the signal charges accumulated in the photosensor and the transfer register are swept away to the semiconductor substrate side at a time. 2. The photosensors are arranged in a two-dimensional matrix on a semiconductor substrate, and the transfer registers include a plurality of vertical transfer registers provided for each column of the photosensors and signals from the vertical transfer registers. The solid-state imaging device according to claim 1, further comprising a horizontal transfer register that transfers charges to an output unit. 3. The driving voltage of the transfer register is turned off by
The solid-state image sensor according to claim 1, wherein the operation is an operation of controlling the drive voltage to a low level. 4. The solid-state image sensor according to claim 1, wherein the large voltage applied to the semiconductor substrate is a voltage sufficiently higher than the electronic shutter function of the photo sensor. 5. A semiconductor substrate having a plurality of photosensors, a transfer register for transferring signal charges of the photosensors to an output unit, and an output unit for converting the signal charges into a voltage signal. A method of sweeping out a charge of a solid-state imaging device, which reads out a signal charge generated by exposure to the transfer register and transfers the signal charge to an output unit, the first operation of turning off a drive voltage of the transfer register before exposure of the photosensor. And a second operation step in which a large voltage is applied to the semiconductor substrate and signal charges stored in the photosensor and the transfer register are swept away to the semiconductor substrate side at one time. How to sweep away. 6. The photosensors are arranged in a two-dimensional matrix on a semiconductor substrate, and the transfer registers include a plurality of vertical transfer registers provided for each column of the photosensors and signals from the vertical transfer registers. 6. A method for sweeping away charges from a solid-state image sensor according to claim 5, further comprising a horizontal transfer register for transferring charges to the output section. 7. The driving voltage of the transfer register is turned off by
6. The method for sweeping away charges from a solid-state image sensor according to claim 5, wherein the driving voltage is controlled to a low level. 8. The method for sweeping away charges from a solid-state image pickup device according to claim 5, wherein the large voltage applied to the semiconductor substrate is a voltage sufficiently higher than the electronic shutter function of the photosensor.