JPS62113473A - Charge transfer device and drive method thereof - Google Patents

Abstract

PURPOSE:To remove the fluctuation of potential, and to realize a high S/N ratio by constituting the impurity surface density of a floating diffusion layer for an output section to 3X10<12>cm<-2> or less and depleting the floating diffusion layer after reset. CONSTITUTION:Transfer gate electrodes 1, an output gate electrode 2, a floating diffusion layer 3, a reset-gate electrode 4, a reset-drain electrode 5 and an amplifier 6 detecting and outputting the potential of the floating diffusion layer 3 are provided. The impurity surface density of the floating diffusion layer 3 is lowered previously so that the floating diffusion layer 3 is depleted completely at voltage lower than voltage applied to the reset-drain electrode 5. Consequently, impurity surface density must be brought to 3.13X10<12>cm<-2> or less. Accordingly, impurity surface density is made lower than 3X10<12>cm<-2>, and predetermined reset pulse voltage is applied to an output section so that the floating diffusion layer 3 is depleted completely, thus preventing KTC noises, then obtaining a high S/N ratio.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a charge transfer device.

BACKGROUND OF THE INVENTION In recent years, charge transfer glazing devices have been developed and their performance has been improved. In particular, improvements have been made to improve the signal-to-noise ratio (S/N ratio).

A conventional charge transfer device will be described below with reference to the drawings. FIG. 3 shows a schematic diagram of the main parts of a conventional charge transfer device. 11 is a transfer gate electrode, 12 is an output gate electrode, 13 is a floating diffusion rIi layer, 14 is a reset gate electrode, 15 is a reset drain electrode, 16 is an amplifier that detects and outputs the potential of the floating diffusion layer 13, and 17 is its It is an output terminal.

The operation of the conventional charge transfer H device configured as described above will be described below. The signal charge is transferred to the transfer gate electrode 11
From below, beyond the bottom of the output gate electrode 12, the floating diffusion layer 13
is transferred to and converted into voltage.

Problems to be Solved by the Invention In the above configuration, the potential of the floating diffusion layer 13 is reset and
Although set by the potential of the drain electrode 15, the potential after reset in the floating diffusion layer 13 fluctuates, which causes KTC noise, which has become a major problem. For example, J. E. Carnes and W. F. Kosonotsky: [Noise sources in charge coupled devices]
Ei Review Volume 33 Beige 327 (19
72) (J, E, Carnes and W, F
KOsonocky: “No1se 5source
sin Charqe-Coupled-Devic
es"RcA Review Vol, 33P 3
27 (1972)).

The present invention solves the above problems, and eliminates fluctuations in the potential after reset in the floating diffusion layer, resulting in a high S/N ratio.
The object of the present invention is to provide a charge transfer device and a method for driving the same that can realize a high ratio.

Means for Solving the Problems In order to solve the above problems, the charge transfer device of the present invention includes:
The impurity surface density of the floating diffusion layer in the output section is set to 3x10@ca-
2 or less, and is configured to deplete the floating diffusion layer after reset.

Effect With this configuration, the floating diffusion layer to which a predetermined reset pulse is applied is completely depleted, so it is not affected by the reset pulse, and the potential of the floating diffusion layer after reset is always fixed and does not fluctuate. noise can be significantly reduced.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic diagram of a charge transfer device in one embodiment of the present invention. In FIG. 1, 1 is a transfer gate electrode, 2 is an output gate electrode, 3 is a floating diffusion layer, 4 is a reset gate electrode, 5 is a reset drain electrode, 6
is an amplifier that detects and outputs the potential of the floating diffusion layer 3, and 7 is its output terminal. It is lower. In this way, in order to completely deplete the floating diffusion layer 3, the impurity surface density needs to be 3.13×10@α-2 or less. For example, GST Fan on the general relationship between depletion layer and breakdown electric field in Si: "On the Design Off Ion Implanted Valid Channel Charge Coupled Device"
Solid State Electronics, 1977, Volume 20, Heshe 665-669LJ, S, T,
Hu an9: “Qn The [)sign
of , 1on Implanted Bu
ried Channel Qharge Co
Upled Devices (BCCDs)”
3o1id-3tate [:1 electronics
, 1977, Vol.

20 pp. 665-669).

The operation of the charge transfer device configured in this manner will be described below. The signal charge Q that has passed from below the transfer gate electrode 1 to below the output gate electrode 2 is transferred to the floating diffusion layer 3. The potential change in the floating diffusion layer 3 due to this signal charge Q is outputted through the amplifier 6. After being output, a reset pulse voltage is applied to the reset gate electrode 4 to discharge the signal charge Q below the reset drain electrode 5. The voltage of the reset pulse at this time is applied so that the channel potential under the reset drain electrode 5 is deeper than the potential of the floating diffusion layer 3. The potential relationship at this time is shown in FIG. By doing this, the floating diffusion layer 3 is completely depleted by the voltage applied to the reset drain electrode 5, and is not affected by the reset pulse. Therefore, since the potential of the floating diffusion layer 3 after reset is always fixed, KTC noise does not occur, and a high S/N ratio can be achieved.

Effects of the Invention As described above, the present invention reduces the impurity surface density of the floating diffusion layer to 3.
By applying a predetermined reset pulse voltage to the output section so that the floating diffusion layer is completely depleted, KTC noise can be prevented and a high S/N ratio can be achieved. The practical effect is great.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a charge transfer device according to an embodiment of the present invention, FIG. 2 is a potential relationship diagram thereof, and FIG. 3 is a schematic diagram of a conventional charge transfer device. 1... Transfer gate electrode, 2... Output gate electrode, 3
... floating diffusion layer, 4... reset gate electrode, 5.
...Reset drain electrode, 6...Amplifier, 7...
Output terminal, Q...Signal charge agent Yoshihiro Morimoto (Figure 1, 7-Genka) Figure 2

Claims (1)

[Claims] 1. A charge transfer device having a transfer section that transfers signal charges and an output section that reads out the signal charges transferred from the transfer section, wherein the impurity surface density of the floating diffusion layer of the output section is is 3×
A charge transfer device that is less than 10^1^2 cm^-^2. 2. The impurity surface density of the output section of a charge transfer device having a transfer section that transfers signal charges and an output section that reads out the signal charges transferred from the transfer section is 3 x 10^1^2c.
A method for driving a charge transfer device, characterized in that a predetermined reset pulse voltage is applied to the output section so that a floating diffusion layer lower than m^-^2 is completely depleted.