JPH02275645A - Charge coupled device - Google Patents

Abstract

PURPOSE:To utilize the charge storage capacity of a floating-junction maximally, and to widen a dynamic range greatly by making the reset-drain side wider than the floating-junction side regarding channel width under drain-gate. CONSTITUTION:The reset-drain side 105 is made wider than the floating-junction side 4 regarding channel width under drain-gate 6. Consequently, a narrow channel effect is utilized positively, and the floating-junction 4 side is made lower than the reset-drain 105 side regarding channel potential under the drain- gate 6, thus preventing the reverse current of charges under the drain-gate 6 on reset. Accordingly, the charge storage capacity of a floating-junction is displayed maximally, and the dynamic range of an output is widened greatly.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to charge coupled devices.

[Conventional technology]

The output end of a conventional charge-coupled device has a structure as shown in FIG. 4, for example.

In the figure, 1-1.1-2. ... is a -th layer polycrystalline silicon film, 2-1.2-2. . . . are second-layer polycrystalline silicon films, which are arranged alternately to form gate electrodes. 3 is the outer edge of the channel stopper, inside which a channel for charge transfer is created. Further, 4 is a floating junction from which signals are read out. 5 is a reset pin for resetting after reading the signal.
The drain 6 is a train gate which is a switch for operating 5. The horizontal register of the charge-coupled device shown in this example employs two-phase drive. The operating mechanism at the output end will be explained with reference to FIGS. 5(a) to 5(d). FIG. 5(a) shows a potential diagram immediately after the voltage at the final stage of the transfer gate is turned off. The ita charge accumulated under the transfer gate overcomes the potential below 0G (2-1, 1-1) and is accumulated in the floating junction 4. Next, as shown in FIG. 5(b), a voltage is applied to the drain gate 6 to reset the floating junction 4 to VRD, which is at the same potential as the reset drain 5.

Further, the gate to which φ1 is applied is turned on, and the charge accumulated in the gate portion to which φ2 is applied is transferred to the gate portion to which φ1 is applied. Next, Figure 5 (C
), the drain gate 6 is turned off and the reset drain 5 and floating junction 4
are separated, but at that time, at the timing shown in FIG. 5(b), a part of the charge existing under the drain gate 6 causes a reverse flow under the floating junction 4, and the potential of the floating junction 4 increases. is reset/
The potential is lower than the potential of the drain 5 (VRD). Next, as shown in FIG. 5(d), the gate to which φ1 is applied is turned off, and the charges accumulated there flow into the floating junction 4, and the potential at this time and the gate shown in FIG. Floating junction 4 in condition c)
A signal is read out from the potential difference between the two.

[Problem to be solved by the invention]

In the conventional charge-coupled device described above, as shown in FIG. The floating junction causes backflow to the junction, which prevents the floating junction from making full use of its inherent charge storage ability. As a result, the dynamic range of the output signal obtained becomes narrow.

SUMMARY OF THE INVENTION An object of the present invention is to provide a charge-coupled device that can prevent narrowing of the dynamic range due to residual charges in the floating junction portion at the time of reset.

[Means to solve the problem]

The charge-coupled device of the present invention has a channel width under the drain gate that is wider on the reset drain side than on the floating junction side, which prevents residual charge under the floating junction during reset, thereby It is possible to obtain an output voltage with a large dynamic range.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1(a) is a schematic plan view of a semiconductor chip showing a first embodiment of the present invention, and FIG. 1(b) is a sectional view taken along line xx' in FIG. 1(a).

As shown in the figure, the channel width under the drain gate 6 is wider on the reset drain 105 side than on the floating junction 4 side.

Next, the operation of this embodiment will be explained. Figure 2 (a
) to (d) are potential distribution transition diagrams for explaining the operation of the first embodiment.

In FIG. 2(a), since ○G is set to the off voltage, the gate electrode 2-1.1 moves below the floating junction 4.
The charges accumulated under -1 flow into it. Next, Figure 2 (
In b), the drain gate 6 is turned on and the floating junction 4 is reset to VRD, which is at the same potential as the reset drain 5. Also, φl becomes the on-voltage,
The charges accumulated under the gate electrode to which φ2 is applied are transferred to the gate electrode to which φ1 is applied. Next, as shown in FIG. 2(c), the drain and gate 6 are turned off, and the reset drain 5 and floating junction 4 are separated. At this time, the channel width under the train gate 6 is narrower on the reset drain 5 side than on the floating junction 4 side as shown in FIG. becomes higher in terms of potential (the energy of electrons becomes lower), and when the drain gate 6 is turned off, the charge accumulated under the drain gate 6 returns to the reset drain 105 side and becomes a floating junction. Backflow to the 4th side is eliminated. next,
As shown in FIG. 2(d), φ1 becomes an off-voltage, and the charges accumulated under the gate electrode flow into the floating junction 4 and are read out as an output signal.

In the structure of the output section of the conventional charge-coupled device described above, the charge under the reset drain flows back into the floating junction at reset, which partially sacrifices the inherent charge storage ability of the floating junction. In contrast, in the present invention, the channel width under the drain and gate is increased from the floating junction side.
By widening the reset/drain-in side, we actively utilize the narrow channel effect and make the channel potential under the drain/gate lower on the floating junction side than on the reset/drain side. The difference is that it prevents charge backflow, thereby maximizing the charge storage capacity of the floating junction, and providing a wide output dynamic range.

FIGS. 3(a) and 3(b) are a schematic plan view and a sectional view showing the second embodiment. In the first embodiment, the channel width under the drain gate 6 is increased linearly from the floating junction 4 side to the reset drain in 5 side, but in the second embodiment, the channel width under the drain gate 6 is increased linearly as shown in FIG. 3(a). The channel width under the drain gate increases linearly from the floating junction 4 side to the reset drain 5 side, and then remains constant. In this example, the channel width floating junction 4
Since the rate of change from the side to the side of the reset drain 5 is large, the rate of change of the channel potential is also large, which has the advantage that residual charges can be more reliably prevented.

〔Effect of the invention〕

As explained above, the charge-coupled device of the present invention has a floating channel width under the drain and gate at the output.
By making the reset drain side wider than the junction side, the reverse flow of charge to the floating junction during reset is prevented, and by making full use of the floating junction's charge storage ability, the output signal is This has the effect of increasing the dynamic range.

[Brief explanation of drawings]

FIG. 1(a) is a schematic plan view showing the first embodiment of the present invention, FIG. 1(b) is a sectional view taken along the line X-X' of FIG. 1(a), and FIG. 2(a>, (b), (c). (d) is a potential distribution transition diagram for explaining the operation of the first embodiment, FIG. 3(a) is a schematic plan view showing the second embodiment, and FIG. Figure (b) is a sectional view taken along the line xx' in Figure 3 (a),
FIG. 4(a) is a schematic plan view showing the structure of the output part of a conventional charge-coupled device, and FIG. 4(b) is xx' in FIG. 4(a>).
The line sectional views and FIGS. 5(a), 5(b), 5(c), and 5(d) are potential distribution transition diagrams for explaining the operation of the conventional example. 1-1.1-2. ..., ...-th layer polycrystalline silicon film, 2-1.2-2. ..., ... second layer polycrystalline silicon film, 3... outer edge of channel stopper, 4...
・Floating Junction, 5,105°20
5... Reset drain (n+ diffusion layer), 6...
Drain/gate, 7...p-type silicon substrate, 8...
- N well, 9-1.9-2...p type diffusion layer.

Claims (1)

[Claims] A charge-coupled device characterized in that, in an output section of the charge-coupled device, the channel width under the drain and gate is wider on the reset drain side than on the floating junction side.