JPH06101485B2 - Charge transfer device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a charge transfer device.

[Conventional technology]

Conventionally, as a general structure of a charge transfer element, a floating diffusion layer method has been used as a charge detection means. In this floating diffusion layer method, transfer charges are flown into the floating diffusion layer, and a potential change that changes according to the amount of charges is amplified and output.

FIG. 2A is a diagram of an output portion of a conventional example of this type of charge transfer element. This device includes a transfer channel 1 for transferring charges, first-layer gate electrodes 2-1, 2-2, 2-3 and second-layer gate electrodes 3-1, 3-2, 3-3 (gate electrode 2 -1 and 3-2 and 2-2 and
3-3 are respectively connected to form a transfer gate, and electrodes 3-1
Is the output gate of the final stage), the floating diffusion layer 4, and the reset transistor 7 for charging the floating diffusion layer 4.
The output transistor 5 and the output terminal 6 for outputting the potential change of the floating diffusion layer 4 through the output transistor 5. This charge transfer device is a general two-phase clock driven charge transfer device, and the second layer gate electrodes 3-2, 3-
Channel potential level below 3 is the first layer gate electrodes 2-1 to 2-3
It is designed to be shallower than the lower channel potential level.

Appropriately a DC bias is applied to the terminal φ _0, and a clock having a phase difference of 180 ° is applied to the terminals φ ₁ and φ ₂ . Terminal φ ₁ ,
The charges transferred by the clock applied to φ ₂ flow under the second layer output gate electrode 3-1 and flow into the floating diffusion layer 4 whose potential is set in advance by the reset transistor 7. Since the potential of the floating diffusion layer 4 fluctuates due to the inflow charge, the potential fluctuation is amplified by the output transistor 5 and output from the output terminal 6.

[Problems to be solved by the invention]

In the above-described conventional charge transfer device, the channel width is narrowed toward the output side in order to make the floating diffusion layer 4 small and increase the charge detection sensitivity. However, when the channel width is narrowed, due to the narrow channel effect, charges are transferred toward the output side, but a potential barrier is formed.

Figure 2 (b) in FIG. 2 (a), a constant voltage which is the terminal phi _0, a voltage lower than the terminal phi ₁ is applied to the terminal phi _0, the terminal phi ₂ terminal phi ₀ Voltage higher than that applied to the gate electrodes 3-1, 2-1, 2-2, 3- of the floating diffusion layer 4 when the voltage set by the transistor 7 is applied. The potential level below 2 is shown. Numbers 9, 10 and 11 respectively indicate the potentials under the gate electrodes 2-1, 3-2 and 2-2, and it can be seen that the potential becomes shallower along the output direction due to the narrow channel effect. Due to the shallowness, the transfer charge is left behind as indicated by the white circles in the figure. This appears as a deterioration in transfer efficiency. This deterioration of the transfer efficiency not only causes a decrease in the transfer charge amount, but is also swept out later to become a false signal.

[Means for solving problems]

The charge transfer element of the present invention is a charge transfer element having a charge transfer channel and an output floating diffusion layer provided adjacent to a final gate thereof, wherein the output floating diffusion layer has a width narrower than that of the charge transfer channel. And a part of the charge transfer channel is defined by the final gate inside the end of the charge transfer channel.

As described above, in the charge transfer device of the present invention, a small floating diffusion layer can be formed without narrowing the transfer channel, and as a result, the transfer efficiency is improved without impairing the charge detection sensitivity.

〔Example〕

FIG. 1 is a plan view of an embodiment of the charge transfer device of the present invention. Here, the same components as those in FIG. 2A are designated by the same reference numerals.

In this embodiment, the transfer channel 1 is formed with the same width up to the output end 8. Further, the floating diffusion layer 4 (the hatched portion in FIG. 1) has a width narrower than that of the transfer channel 1 and is formed so as to enter the transfer channel 1 side from the terminal end 8 of the transfer channel 1.

〔The invention's effect〕

As described above, the present invention has an effect that the transfer efficiency can be improved without deteriorating the charge detection sensitivity by forming the small floating diffusion layer without narrowing the transfer channel.

[Brief description of drawings]

FIG. 1 is a structural diagram of an embodiment of a charge transfer device of the present invention, FIG. 2 (a) is a structural diagram of a conventional example, and FIG. 2 (b) is a potential level under each gate electrode of the conventional example. It is a figure. 1 ... Transfer channel, 2-1,2-2,2-3 ... first layer gate electrode, 3-1,3-2,3-3 ... second layer gate electrode, 4 ... floating diffusion layer 5 ... Output transistor, 6 ... Output terminal, 7 ... Reset transistor, 8 ... Termination of transfer channel 1, 9, 10, 11 ... Potential under gate.

Claims (1)

[Claims] 1. A charge transfer device having a charge transfer channel having a predetermined width and an output floating diffusion layer provided adjacent to a terminal end portion of the charge transfer channel, wherein the charge transfer channel is constant up to the terminal end portion. Formed with a width of
The width of the output floating diffusion layer is narrower than the width of the charge transfer channel, and a part of the output floating diffusion layer extends inside the end portion of the charge transfer channel and is defined at the end portion of the charge transfer channel. A charge transfer device characterized by: