JPS59221177A - Charge transfer device - Google Patents

Abstract

PURPOSE:To decrease the scanning time without cutting photosensitive picture element train or a transfer electrode train into pieces by tansferring a signal charge in two directions opposite to each other from a middle part of a transfer electrode to extract the charge by two output circuits. CONSTITUTION:The transfer electrode train 8 is formed that the transfer direction of the signal charge is reversed at a half of the arrangement length. That is, a barrier 11 is formed to a semiconductor substrate 10 under each transfer electrode and a potential well of downward staircase form is formed in opposite direction to each other toward both ends of the transfer electrode train 8. The signal charge generated in each photosensitive picture element is transferred once to the transfer electrode train 8 and stored in each potential well. Then the signal charge under each transfer electrode is transferred sequentially in opposite directon and read by an output circuit by applying two-phase driving of the transfer electrode train 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a charge transfer device used in a -dimensional or two-dimensional solid-state imaging device.

[Technical background of the invention and its problems]

FIG. 1 shows an example of a conventional charge transfer device. Reference numeral 1 indicates a one-dimensional array of photosensitive pixels, and along this photosensitive pixel column 1, a plurality of transfer electrode columns 2 are formed. An output circuit 3 is provided at one end of the transfer electrode row 2, and signal charges transferred from the photosensitive pixel row 1 are sequentially transferred by the transfer electrode row 2 and read out as electrical signals by the output circuit 3.

A drawback of the charge transfer device having the configuration shown in FIG. 1 is that it takes a long time to transfer read signal charges.

In order to solve this problem, it has been proposed to divide the transfer electrode into two to shorten the transfer time.

An example is shown in FIG. As can be seen from FIG. 2, the transfer electrode 5 is divided into two parts in the middle. An output circuit 6 is formed at one end of each divided transfer electrode array 5. By doing this, the transfer length becomes 1/2 compared to the example shown in FIG. 1, and therefore the scanning time can also be reduced to 1/2. That is, if the scanning time in the case of Fig. 1 is TO, then in the case of Fig. 2 divided into two, Tψ
becomes.

However, in the case of FIG. 2, the transfer electrode array is divided, and it is extremely difficult to arrange the output circuit at an intermediate position of the transfer electrode array without dividing it.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a charge transfer device that can shorten scanning time without dividing a photosensitive pixel array or a transfer electrode array.

[Summary of the invention]

In order to achieve the above object, the charge transfer device according to the present invention is provided with an output circuit at each end of the transfer electrode row, and includes an output circuit in the semiconductor substrate under the transfer electrode row from an intermediate portion in the arrangement direction of the electrode row. A symmetrical stepped potential well is formed for each of the transfer electrodes toward each end, so that signal charges are transferred to each output circuit from the intermediate portion in mutually opposite transfer directions. It is characterized by the following.

[Embodiments of the invention]

Embodiments of a charge transfer device according to the present invention will be described below with reference to the drawings.

As shown in FIG. 3, output circuits 9A and 9B are provided at both ends of the transfer electrode array 80, respectively.

Each of the output circuits 9A and 9B is supplied with signal charges transferred from the transfer electrode array 8 in the opposite transfer direction.

That is, as shown in FIG. 4, the transfer electrode array 8 is arranged such that the direction of signal charge transfer is reversed at a half point in the arrangement direction. More specifically, the configuration is as follows. A barrier 1 is placed on the semiconductor substrate 1 () under each transfer electrode.
1 is formed, and step-like potential wells with downward slopes in opposite directions are formed between the transfer electrodes 8A and 8a corresponding to the 1/2 point of the transfer electrode column 8 toward both ends of the transfer electrode column 80. It is formed. For example, electrode 8A toward the left side in the figure.
, 8B.

8C,...FC@Once, four step-like potential wells were formed, and on the other hand, electrode 8a towards the right side of the figure.

Four stepped potential wells are formed toward sb, sc, . . . .

The signal charge generated in each photosensitive pixel 7 is transferred to the electrode row 8 at once.
and accumulated in each potential well as shown. Next, the transfer electrode array 8 is driven in two phases. That is, each transfer electrode 8A, 8B, 8C, . . . and 8a, 8
b, 8c, . . . have transfer signals φ1.b, 8c, . φ2 is applied, and the signal charges under each transfer electrode are sequentially transferred in reverse directions to the left and right sides of the diagram and read out to output circuits 9A and 9B. in this way,
The signal charges are transferred in opposite directions from the central 1/2 point of the transfer electrode array 8. As a result, if the number of transfer stages is N, it takes N/1 to scan the charges of all pixels.
Two stages are sufficient, and the scanning time becomes 1/2. This means that the transfer electrode array can be divided into two as in the conventional case (Fig. 2).
For example, if we consider a 2000-bit single-channel dimensional image sensor, the minimum scanning time for reading at 1 MHz is 200μ8ee, but According to the present invention, even if read at the same 10 MHz, 1
This results in a scanning time of 00 μgea.

Note that even in the case of dual channel, if four output circuits are similarly provided, the scanning time can be similarly reduced to 1/2. Furthermore, although the above explanation has been made using a one-dimensional image sensor as an example, it goes without saying that the present invention can also be applied to a two-dimensional image sensor. That is, the present invention may be applied to both the horizontal shift register and the vertical shift register.

〔Effect of the invention〕

As described above, according to the present invention, by forming potential wells in the transfer electrode row so as to transfer signal charges in the opposite direction with the intermediate portion as a boundary, the photosensitive pixel row or the transfer 'tlY,
Scanning time can be shortened without separating the pole rows.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first example of a conventional charge transfer device;
FIG. 2 is a block diagram showing a second example of the same as above; FIG. 3 is a block diagram showing an embodiment of a charge transfer device according to the present invention; FIG. 4 is a longitudinal section showing a cross-sectional structure of a charge transfer device according to the present invention. It is a diagram. 7... Photosensitive pixel row, 8... Transfer electrode row, 8A, 8B
. 8C,..., 8a, 8b, 8c... Transfer electrode, 9... Output circuit, 10... Semiconductor substrate, 1
1... Barrier, φ1. φ2... Transfer nolus ξ. Figure 1 Figure 2 Oval Figure 3 So b': 3 φ1

Claims (1)

[Scope of Claims] 1. In a charge transfer device comprising a transfer electrode array that transfers signal charges from a photosensitive pixel array and an output circuit that extracts the transferred signal charges as an electric signal, both ends of the transfer electrode array An output circuit is provided for each of the transfer electrodes, and a symmetric step-like potential well is formed for each transfer electrode in the semiconductor substrate under the transfer electrode row from the middle part toward each end in the arrangement direction of the electrode row. A charge transfer device configured such that signal charges are transferred from the intermediate portion side to each of the output circuits in mutually opposite transfer directions. 2. The charge transfer device according to claim 1, wherein the intermediate portion is a point IA in the arrangement direction of the transfer electrode array. 3. A charge transfer device according to claim 1 or 2, wherein the transfer electrode array is used in a one-dimensional solid-state imaging device. 4. A charge transfer device according to claim 1 or 2, wherein the transfer electrode array is a horizontal shift register or a vertical shift register of a two-dimensional solid-state imaging device.