JPH0682693B2 - Charge transfer device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge transfer device, and more particularly to a long contact CCD image sensor in which a plurality of chips are arranged.

Configuration of Conventional Example and Its Problems In recent years, a so-called contact-type image sensor in which a plurality of one-dimensional solid-state image pickup elements are arranged to have the same size as a document of a subject has been actively developed, and a level of practical application is partially achieved. Has reached.

FIG. 1 is a sectional view of a transfer main part of a conventional contact type CCD one-dimensional solid-state imaging device, and FIGS. 2 and 3 are potential diagrams and applied pulses for two-phase driving in each section. The timings t ₁ and t ₂ are shown. In FIG. 1, 1
Is a P-type substrate, 2 is an N well region, 3 is a barrier region having the same conductivity type as that of the N well region 2, and its concentration is lower than that of the N well region 2. Reference numeral 4 is a storage gate, 5 is a barrier gate, and 6 is a gate oxide film. P ₁ and P ₂ are electrodes to which the driving pulse signals φ ₁ and φ ₂ are applied. In FIG. 2, the transfer charge 7 is transferred from the left side to the right side by applying the pulse signals φ ₁ and φ ₂ to the electrodes P ₁ and P ₂ , respectively. Since the contact type sensor has a one-to-one correspondence between the subject and the image pickup element without a condensing lens, the pixel pitch becomes larger than that of the condensing sensor, and the dimension of the transfer unit also increases accordingly. 16 pixels / m
In the case of m, the gate length of the storage gate 4 in FIG. 1 is 19 μm
Therefore, the gate length of the barrier gate 5 is 12.25 μm, and therefore CC that gives each pulse signal φ ₁ and φ ₂ in the two-phase drive
One bit of D is twice the gate length of both gates, so 62.5 μm is one pitch in the device. This is a conventional concentrating sensor, for example, the storage gate is 9μ.
Both the pitch and the gate length are more than twice as large as those of a CCD having a barrier gate of 5 μm and a length of 1 μm of 28 μm.

As described above, the contact type CCD sensor requires a gate length that is at least twice as long as that of the condensing type sensor, and considering that the transfer speed is inversely proportional to the square of the gate length, the high-speed operation characteristics are remarkable. Will be inferior.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and provides a charge transfer device capable of higher speed.

To achieve this object, the charge transfer device of the present invention comprises:
At least three opposite conductivity type regions formed on one conductivity type substrate are made to have different concentrations in each adjacent region as a charge transfer unit that sequentially transfers a predetermined charge in a bit unit by a transfer signal. And has at least one region of the opposite conductivity type region that does not have an electrode immediately above and maintains a fixed potential that does not depend on the transfer signal, and the remaining opposite conductivity type region has The transfer signal applied to the insulating gate electrode immediately above is configured to generate a fluctuating potential, thereby enabling high speed operation.

Description of Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a sectional view of a main part of a transfer unit of the contact type CCD image pickup device according to the embodiment of the present invention. In the figure, reference numeral 11 is a P-type substrate, and 12, 13, 14 are N well regions, and the N well region 14 has the highest concentration and the N well region 13 has the highest concentration.
Is the lowest.

Further, 20 is a storage gate and 21 is a barrier gate, and these two gates are commonly connected. P ₁ and P ₂ are electrodes for applying the periodic pulse signals φ ₁ and φ ₂ , respectively. The potential diagram of FIG. 5 is shown for each of the timings t _{1 to} t ₂ of FIG. In FIGS. 4 to 6, when the electrodes P ₁ and P ₂ are both at a low level, that is, at the timing t ₁ , each of the N well regions 12, 13 and 14 becomes a potential due to the concentration difference of the N well. There is a difference. At the timing t ₂ , the pulse φ ₁ becomes high level, the transfer charge 19 is accumulated in the region 12 under the accumulation gate 20 having the lowest potential, and at this time, the barrier gate 21 functions as a barrier for preventing backflow of charges. To do. Next, at the timing t ₃ , the pulse φ ₁ becomes low level and the pulse φ ₂ becomes high level, so that the transfer charge 19 is transferred from the accumulation gate portion under the electrode P ₁ to the electrode P ₂
Are transferred to the bottom of the storage gate 20 at once. As shown in FIG. 5, since there is no gate above the N well region 14, the potential depends only on the impurity concentration of the N well region 14, and the potential is centered on the potential of the N well region 14 and the electrode
Periodic pulse signals φ ₁ and φ for charge transfer applied to P ₁ and P ₂
Gates 12 and 13 depending on the low and high levels of ₂
It can be seen that the potential of each region under and up and down transfers charges. In the embodiment shown in FIG.
μm, barrier gate 10 μm, and N without gate
Set the length of the well region 14 to 8.25 μm and
The pitch is the same as in the example of FIG. Therefore, in the present embodiment, the maximum storage gate length (19 μm in the example of FIG. 1 is maximum) is 13 μm, which is smaller than that of the example of FIG. 1 even if the pitch is the same. Usually, since the transfer speed is inversely proportional to the square of the gate length, the charge transfer device of this embodiment has an advantage that the transfer speed is more than doubled as compared with the conventional transfer device shown in FIG.

EFFECTS OF THE INVENTION As described above, according to the present invention, one bit of the two-phase drive transfer section described in the embodiment is configured as a 4 (or more) gate 6 (or more) area configuration as compared with the conventional 4 gate 4 area configuration. By providing the two regions without the gate electrode, if at least three regions of opposite conductivity type formed on the one conductivity type substrate are made to have different concentrations from each other in adjacent regions, Periodically provided, at least one of the opposite conductivity type regions does not have an electrode directly above, and an insulated gate electrode is provided immediately above the remaining opposite conductivity type region, and a transfer electrode provided to this gate electrode is provided. By performing charge transfer with a signal, a charge transfer device capable of higher-speed charge transfer can be obtained, and the practical effect thereof is great.

[Brief description of drawings]

FIG. 1 is a conventional CCD sectional view, FIG. 2 is a conventional CCD potential diagram, FIG. 3 is a driving pulse diagram thereof, FIG. 4 is a structural sectional view of the present invention, FIG. 5 is a potential diagram thereof, and FIG. FIG. 6 is a drive pulse diagram of FIG. 11 …… P-type substrate, 12,13,14 …… N with different concentrations
Well area, 20, 21 ... Gate.

Claims (1)

[Claims] 1. A charge transfer section for sequentially transferring a predetermined charge in a bit unit in accordance with a transfer signal, wherein at least three regions of opposite conductivity type formed on a substrate of one conductivity type are provided for each adjacent region. Concentrations are made different from each other and periodically provided, and at least one region of the opposite conductivity type regions does not have an electrode immediately above and maintains a fixed potential independent of the transfer signal, and the remaining opposite regions. The charge transfer device according to claim 1, wherein the conductivity type region is configured to generate a fluctuating potential by the transfer signal given to the insulating gate electrode immediately above.