JPS5896467A - Driving method for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To obtain a driving method suitable for infrared ray pickup, by providing the process where the potential at a photoelectric conversion section is set with an overflow drain and overflow control electrode, and a signal charge storaging process by means of photoelectric conversion. CONSTITUTION:A transfer gate 102 controls the transfer of signal charges of a photoelectric conversion section 101 and a vertical register 100. An overflow control electrode 104 controls the transfer of signal charges of the photoelectric conversion section 101 and an overflow drain 103. In the said inter-line transfer type charge transfer pickup device, the potential of the section 101 is set by using the overflow drain 103 and the overflow control electrode 104. The section 101 stores signal charges with the photoelectric conversion and transfers a part of signal charges to a vertical register through the use of a transfer gate 102.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a solid-state imaging device, particularly an infrared solid-state imaging device.Among solid-state imaging devices, those using a charge transfer device are indestructible, have low noise, low power consumption, It is rapidly developing based on the advantages of ease of use such as high I reliability and the advantages of characteristics such as low noise, residual image, and no burn-in. There are interline transfer methods and frame transfer methods, and it has mainly developed as a visible light imaging device.More recently, there has been a strong demand for infrared imaging devices.Visible light Il image and infrared light The long distance of imaging is not only due to the wavelength of the light to be imaged and the accompanying difference in the photosensitive material.In imaging using night light, imaging is generally performed using sunlight or reflected light from various light sources, and the imaging should be performed using sunlight or reflected light from various light sources. The contrast of the scene reaches more than 10'-10'. On the other hand, in imaging using infrared light, imaging is generally performed using radiation from an object, and the contrast of the scene is often less than a few degrees. Therefore, imaging using infrared light requires a different device configuration and driving method than when using visible light.

A conventional charge transfer imaging device using an interline transfer method, as shown in FIG. and an electrically separated photoelectric conversion section 10), a transfer gate electrode 102 that controls the transfer of signal charges between the vertical shift register and the charging conversion section, and one side of the photoelectric conversion section (
an overflow drain 103 located opposite to the vertical shift register and electrically isolated; an overflow control electrode 104 for controlling the transfer of signal charges between the photoelectric conversion section and the overflow drain; and an overflow control electrode 104 located at one end of the vertical shift register. Horizontal shift register 10 provided
5 and a device 106 for detecting signal charges provided at one end of such a horizontal shift register.The vertical shift register receives pulses φ8 and φ from terminals 107 and 108.
, the transfer gate is driven by terminal 10
9, the overflow drain is biased by a DC voltage VOFD from a terminal 110, and the overflow control electrode is biased by a DC voltage VOFD from a terminal 112. Biased by the PCB In such an interline transfer type imaging device, signal charges corresponding to the amount of incident light are accumulated in the photoelectric converter 5tot.When the amount of incident light is extremely large, excessive signal charges are accumulated from the photoelectric converter. overflows and the overflow control electrode 19
4 and flows into the overflow drain 103 @ When the photoelectric conversion accumulation period ends, the signal charge remaining in the charge conversion unit 101 is transferred to the corresponding vertical shift register lOO via the transfer gate 102. After transferring the signal charge to the register 101, the transfer gate 102 is closed and the photoelectric conversion @101 accumulates the signal charge to be read out in the next cycle (field or frame). On the other hand, the signal charges transferred vertically to the sister 100 are transferred vertically in parallel and transferred to the horizontal register 105 for each horizontal line of the direct register. The signal charge sent to the horizontal register is transferred in the horizontal direction until the next signal charge is transferred from the vertical register, and is taken out from the charge detection section 106 as a video signal.

Figure 2 (a) is a cross-sectional view of a typical unit cell using such an interline transfer method, and the potential distribution at each part is shown in Figure 2 (b).
).

In the following description, parts designated by the same numbers have the same structures and perform the same functions. In FIG. 2(m), 201 is a PfIi substrate, 202 is a gate oxide film, and 203 is a PfIi substrate.
field oxide film 204 is channel stop diffusion, 2
0s is the charge transfer electrode of the vertical register, 206 is the speed-of-light layer made of Aj, etc., 207 is the interlayer insulating film O, 20B is the N9 layer of the photoelectric conversion region, 209 is one layer of the overflow drain, 210 and 211 are the layers of the overflow drain. These are the N area and P area of the vertical register. General #c! In the storage region of the 1-direction register, the P region 211 in this figure becomes the N region, and in the /Iria region, the structure shown in this figure is shown in Figure 2. 103, Oats-flow control electrode 1
The potential and surface potential of
Electrons statically existing in the N0 layer 208 of the photoelectric conversion region, which becomes a floating potential, are shown by the single diagonal solid line and are generated by charge conversion. The signal charge 212 is accumulated in the N'' region when the transfer gate 102 is turned off and light is applied to the photoelectric conversion region in Fig. 2.0 The amount of incident light is very large. With a large M, the signal charge passes under the overflow control electrode 104 and flows into the overflow drain.Therefore, the potential of the N9 region will not drop below the surface potential under the overflow control vL, no matter how large the amount of incident light is. Even if the signal is -7: there will be no overflow to the direct register.When the photoelectric conversion accumulation period ends, the transfer gate is turned on and the signal charge is transferred to the vertical register.Next, when the transfer gate is turned off, the photoelectric conversion area Then, accumulation of signal charges begins, and the charges transferred to the vertical registers are transferred to the output section in the manner described in FIG.

As can be seen from this explanation, in this driving method, all the charges generated in the photoelectric conversion region are transferred to the vertical register in a portion where no overflow of signal charges occurs. This driving method is an excellent method for visible light photography where the contrast of the scene to be imaged is high, but it is not a desirable method because it is poor for infrared light photography where the contrast of the scene is extremely low. .

The purpose of the present invention is to provide a driving method for a solid-state imaging device suitable for infrared resistant imaging using an interline transfer method that improves the conventional drawbacks. According to the present invention, the same electrode group is used. at least one or more charge transfer vertical registers to be driven; a photoelectric conversion section located on one side of the vertical register and electrically isolated;
A vertical register, a transfer gate that controls the transfer of signal charges in the photoelectric conversion section, and one photoelectric conversion section ([1
The electrically isolated O/C flow drain is located on the opposite side of the direct resistor, and the photoelectric conversion section and the O/L<
- Controls the flow drain signal charge transfer
In an interline transfer type charge transfer imaging device consisting of an e-flow control electrode, a horizontal register provided at one end of each vertical register, and a signal charge detecting device provided at one end of the horizontal register, the potential of the photoelectric conversion section is determined. The method is characterized by including a step of setting using an overflow drain and an overflow control electrode, a step of accumulating signal charges in a photoelectric conversion section by photoelectric conversion, and a step of transferring a part of the signal charges to a vertical register using a transfer gate. The present invention provides a driving method for a solid-state imaging device that allows a high image density to be obtained.

FIG. 3 is a diagram for explaining the driving method according to the present invention (m
) is a cross-sectional view of a unit cell using the interline transfer method, which is the same as that shown in FIG. 2(s), and FIG. and the surface potential are shown by solid lines, and the part to which the pulse voltage is applied (overflow control electrode,
The potentials of the transfer gates and vertical registers and the surface potentials are plotted as dotted lines. Electrons existing in the static structure are shown by solid single diagonal lines, Pacckland charges among the charges generated by photoelectric conversion are shown by dotted single diagonal lines, and charges that contribute to contrast are shown by solid double diagonal lines. The zero operations performed are as follows. First, the transfer gate is kept off, the overflow control gate 104 is turned on, the potential of the N+ region 208 is set to 302, and it is immediately turned off. At this time, the potential of the photoelectric conversion region 208 becomes 302. When light enters the photoelectric conversion region i in this state, signal charges 212 are accumulated there. The signal charge includes a part 300 that forms a contrast with the pack-ground part 301. When the zero-order transfer gate is turned on and its surface potential is set to 303, the signal charge that forms the contrast and a slight pack-ground charge are perpendicular to each other. 0 transferred to the register Next, the transfer gate is turned off, and the overflow control electrode is briefly turned on and immediately turned off. Signal charges begin to accumulate in the photoelectric conversion region, and the charges transferred to the vertical register are the first! Move to the output section using the method explained in I3.0 As you can see from this explanation, with this driving method, most of the charges moving through the vertical register can be made into charges that form a contrast. Time Delay Integration
A case where the present invention is applied to infrared imaging in n) mode will be explained.

Fig. 4 is a conceptual diagram of a device for explaining the 42TDI mode. ◎ In Fig. 4, 301.301303,
..., 304 is a charge transfer vertical register 3
05 is a charge transfer horizontal register electrically connected to these, and 306 is a charge detector provided at one end of the horizontal register.

In TDI mode, the imaged screen is scanned by a mirror from top to bottom in accordance with the charge transfer rate of the vertical register. Therefore, the charge generated by a specific point on the image is transferred while being integrated in the vertical register. become.

The charge that reaches the bottom of the vertical register is read out by the horizontal register 〇 Like this! In order to realize the DI mode with the device shown in Figure 1, the signal charge in the vertical register must be moved from the photoelectric conversion area to the vertical register every time the signal charge is shifted in the vertical direction in accordance with the image scanning speed. good.

Next, as a second embodiment of the present invention, such a TDI mode is applied to the device shown in Fig. 1, and pulse timing for transferring only signal charges contributing to contrast will be explained. Fig. 5 shows this pulse timing. show. Reference numeral 501 is a time axis, and a unit period is the time for the charge in the vertical register to move vertically by one pixel, and ψPi and ψ71 are voltages applied to the overflow control voltage 11 and the transfer gate electrode.

In Fig. 5, let t, ~t6+x be the period in which the signal charge for a specific part of the image is in the nth stage of the vertical register. At the beginning of this period, ψP1 is turned off → on → off. Later on, pyit is turned off → Turning on → off 7. Building - As you can see from the explanation for the figure, only the charges that contribute to contrast among the charges generated in the photoelectric conversion region from when 1□ turns off until Tl turns on are transferred to the vertical register. The amount of time that can be moved depends on the timing of ψPm and φTl, the pulse height, the ratio of contrast-forming charges to the total signal charge during the pulse, the scanning speed of the image, the brightness, the desired vertical resolution, etc. All you have to do is choose an appropriate value. In this explanation, we have explained the case where a specific part of the image is located on a specific part of the device, but with the above operation, the contrast is good in the entire area of the device! DI operation is being performed 0 Although the present invention has been described assuming a silicon device, the driving method of the present invention is not limited to silicon devices (, lag Cd T・ or In8n?@,
It goes without saying that it can also be applied to devices using infrared materials such as G5Am and LM8b. P-N of another material in parallel with
It is clear that the driving method of the present invention can be applied even when an i1 coupling is formed.Although the present invention is applied to an N-channel device, it can also be applied to a P-channel device. Needless to say.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of a conventional interline transfer type solid-state imaging device. 10G is a vertical shift register, 101 is a photoelectric conversion region, ioz is a transfer gate, and 103
104 is an overflow drain, 104 is an overflow control gate, 105 is a horizontal register, 106 is a charge detector, 107 and 108 are vertical register drive terminals, 10
9.110 and 112 are transfer gates, respectively.
0 which is the drive terminal for the overflow drain and overflow control gate. Substrate, 202 is a gate insulating film, 203 is a field oxide film, 204 is a channel stop diffusion, 20
S is a transfer electrode, 206 is an aluminum optical layer, 207 is an interlayer insulating film, 208.209 is an N region, 210.211 is a Pl [mechanical] and N region, and 212 is a signal charge. a) is the same as Fig. 2(a), and Fig. 3(a) is the same as Fig. 2(a).
b) is the first example of the driving method of the present invention. In FIG. 3, 30G is a signal charge that contributes to contrast, 301 is a signal charge that does not contribute to contrast, and 302 and 303 are potentials. FIG. 4 is a diagram for explaining the DI mode, and 301 to 304 are vertical registers, 305 is a horizontal register, and 305 is a charge detector. Further, FIG. 5 shows another embodiment of the present invention, in which 501 is a time axis, NaPI and Naa,
indicates the voltage applied to the overflow control electrode and transfer gate 〇Figure 4tn-2tn-ttn
in+t tn+z tns3
1p13 figure (b)

Claims (1)

[Claims] at least one charge transfer vertical register driven by the same electrode group; located on one side of the vertical register;
and an electrically separated photoelectric conversion section, a transfer gate that controls the transfer of signal charges between the vertical register and the photoelectric conversion/conversion section, and an electrically separated photoelectric conversion section located on one side of the photoelectric conversion section (opposite the vertical register). an overflow control electrode that controls the transfer of signal charges between the photoelectric conversion section and the overflow drain, a horizontal register provided at one end of each vertical register, and a signal charge provided at one end of the horizontal register. In an interline transfer type charge transfer imaging device consisting of a device that detects the A gate is used to transfer a portion of the signal charge to a vertical register! 7. A method for driving a solid-state imaging device, comprising: