JPS5849066B2 - charge transfer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge transfer device, and particularly to a charge transfer device that prevents charges generated outside the active portion from entering the active portion and compensates for dark current and pulse spike current. This invention relates to a charge transfer device.

Conventionally, in this type of charge transfer device, methods to prevent charges generated outside the transfer channel from entering the transfer channel include increasing the concentration of the semiconductor substrate other than the transfer channel, and thickening the insulating layer covering the substrate surface. Methods such as this are used.

However, this type of conventional method has the disadvantage that minority charges generated outside the transfer channel by light, heat, avalanche, etc. are mixed into the transfer channel by diffusion.

Such a phenomenon becomes a problem especially when a charge transfer imaging device or a charge transfer device is driven at a low frequency.

An object of the present invention is to provide a charge transfer device that prevents charge carriers generated outside the channel from entering the transfer channel and compensates for dark current and pulse spike current generated in the transfer channel.

According to the present invention, a compensation channel for compensating for dark current and spike current is provided adjacent to and electrically separated from the main channel of a charge transfer device for transferring information charges, and further for surrounding the main channel and the compensation channel. A sub-channel is provided on both sides of the charge transfer device to absorb charges mixed in from the outside by diffusion, and these channels are configured to be driven by the same transfer electrode.According to the present invention, the main channel of the charge transfer device, the compensation Charges generated outside the channels can be prevented from being mixed into these channels, and dark currents generated in the main channel and spike currents mixed into the output can be compensated for by the compensation channel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a conventional charge transfer imaging device and a charge transfer delay line will be described in detail with reference to the drawings, taking a charge transfer delay line as an example.

FIG. 1 schematically shows a plan view of a typical conventional charge transfer one-dimensional photosensitive device.・
It consists of Sn1, charge transfer registers 11 and 12 that transfer the signal charges photoelectrically converted in the photosensitive section, and a signal charge detection section 13 that takes out the output from the register.In particular, as a one-dimensional photosensitive device, as shown in FIG. photosensitive part eyelet S1,
S2...Transfer register 11 above and below Sn
, 12 is a typical example.

The operation of the one-dimensional photosensitive device shown in FIG. 1 will be briefly explained.

Photosensitive parts S1, S2, . . . A charge information pattern is formed by converting the incident pattern into charges at the photosensitive parts biased with the photosensitive electrodes 14 that form potential wells in Sn.

During the period when information charges are accumulated in this photosensitive section, the charge transfer register 11. Since transfer pulses are always supplied to the 12 electrode groups, control electrodes 15 and 16 are provided between the photosensitive array and the transfer register in order to separate the potential well of the photosensitive section and the potential well of the transfer register.

A photosensitive electrode 14 and a control electrode 1 are used to transfer information charges accumulated for an arbitrary period from the photosensitive array to the transfer register.
5.16 Information charges are transferred to the photosensitive parts S1, S2, etc. by applying pulses to each of the electrodes of the transfer register in that order.
...Move to directly below the electrodes of transfer registers 11 and 12 corresponding to Sn.

(Although one transfer register element is shown as one block in the drawing, it actually consists of one to four electrodes in consideration of the driving method.

) Then the pulses of the control electrodes 15 and 16 are removed and the photosensitive electrodes 1
A pulse is applied to 4, and information charges are accumulated again in each photosensitive section.

On the other hand, transfer register 11. The charges sent to the terminal 12 are sent to the signal charge detection section by applying a pulse to the transfer electrode of the transfer register and read out from the terminal 9.

When the information charges transferred to the transfer register are completely read out, the information charges are transferred from the photosensitive section to the transfer register again and read out to the outside by the same means as described above.

In the charge transfer device described above, when the charge accumulation time in the photosensitive section is long and the frequency of the readout transfer pulse of the transfer register becomes low, the potential well is saturated by thermally generated charges, that is, dark current charges, and information charges are read out. I won't be able to do that.

In general, the dark current of a semiconductor device depends on the lifetime of charge generation.
Although it does not depend on the geometrical position of the device, the first
In a charge transfer one-dimensional photosensitive device as shown in the figure, the charge transfer is determined by the dark current in the transfer registers 11 and 12.

The reason for this will be explained using FIG. 2.

FIG. 2 schematically depicts a cross section and surface potential distribution along the line AA' in FIG. 1, and portions corresponding to those in FIG. 1 are indicated by the same symbols.

The channel portion of the transfer register is isolated from the outside by, for example, increasing the thickness of the insulating layer 11 on the semiconductor substrate 10 other than the channel.

The transfer electrodes 18 and 19 extend outside the channel and are connected to the transfer clock pulse line outside the drawing.

Further, although not shown, it is desirable to optically shield areas other than the photosensitive portion.

Now, when a pulse is applied to the photosensitive electrode 14 and the transfer electrode 18, 19, the surface potential distribution is schematically drawn as a curve 20.

Considering the charge due to dark current one-dimensionally, in the photosensitive section Sx, it is approximately proportional to the length of the photosensitive section (Lsx), but in the transfer registers 11 and 12, it is proportional to the channel width W of the transfer register.
Charges generated within 1 and diffusion length L of minority charges from the channel
Absorbs the charge generated up to n.

For this reason, the dark current charge per unit area is larger from the register portion than from the photosensitive portion.

Therefore, the factors determining the charge accumulation time and the transfer pulse low frequency limit of the registers are determined by the dark current charge in the transfer registers 11, 12.

In practice, as a way to compensate for this drawback, there are methods such as cooling the photosensitive device shown in Figure 1 and increasing the readout speed of the information charges transferred to the transfer register compared to the charge accumulation period in the photosensitive section. It compensates for the deficiencies mentioned above.

However, these methods are not a complete solution.

The object of the present invention is to reduce the dark current in the transfer register, which is the drawback mentioned above.

FIG. 3 shows a one-dimensional photosensitive device of the present invention corresponding to the conventional charge transfer one-dimensional photosensitive device shown in FIG. 1, and the same functional parts as in FIG. 1 are indicated by the same symbols.

The difference from FIG. 1 is that there are compensation channels 26 and 27 adjacent to the transfer register IL12 and sub-channels 21 . 22 was established.

The compensation channels 26, 27 and the sub-channels 21, 22 are configured to be driven by the same transfer electrode (not shown) as the transfer register.

FIG. 4 schematically shows the B-B'i cross section of FIG. 3 and the surface potential distribution, in which photosensitive electrodes 14, control electrodes 15, 16, transfer electrodes 18. 19 is formed.

With this structure, transfer registers 11 and 12 and compensation channel 2
6.27 Since the same voltage is applied to the sub-channels 21 and 22, it is necessary to separate each channel.

In general, channel separation can be achieved by increasing the concentration of the substrate or by increasing the thickness of the insulating layer 17.

When a pulse voltage is applied to the photosensitive electrode 14 and the transfer electrodes 18 and 19 in the cross-sectional structure shown in FIG. 4, the surface potential is drawn as a curve 23.

Considering the dark current in each region, which is a problem here, in the photosensitive section, it is defined by the length Lsx of the photosensitive section, as in the conventional case.

Additionally, transfer registers 11.12 and compensation channels 26
．． 27 is also determined to have a length W that is approximately equal to the channel width.

On the other hand, in the electrically separated sub-channels adjacent to both sides of the photosensitive device, charges generated within the diffusion length Ln of charge carriers are also collected.

In this way, the photosensitive sections S1, S2, which are the active sections of the one-dimensional photosensitive device shown in FIG. 3...Sn transfer register 1 1 . All charges entering the photosensitive device by diffusion from sources other than the 1-2 compensation channel 26.27 are collected in the secondary channel 21.22.

The charge collected in the subchannel is transferred in the direction of the arrow shown in FIG. 3 by driving the subchannel, transfer register, and compensation channel by the same transfer electrode, and is partially overlapped directly under the final electrode of the subchannels 21 and 22. It flows into the formed reverse biased PN junctions 24 and 25, and is separated from the signal charge and taken out to the outside.

In this way, charges generated outside the active region can be completely removed.

On the other hand, by guiding the output of the transfer register, which is the main channel, and the output signal 32 of the compensation channel to the differential amplifier 30, the dark current and spy noise of the main channel are removed from the output 31 of the differential amplifier.

Above, we have described a one-dimensional charge transfer photosensitive device with transfer registers on both sides of one row of photosensitive arrays using an example. By providing a sub-channel on the outer side so as to surround the photosensitive array, transfer register, and compensation channel, the dark current of the photosensitive section and transfer register can be reduced and the dark current of the transfer register can be compensated for.

FIG. 6 shows still another embodiment of the present invention, in which a one-dimensional charge transfer delay line is formed with four rows of channels including a main channel for delaying signal charges, and each channel is connected to the same transfer electrode. Drive.

One of the two channels in the center is the main channel 33 for signal delay, and the other is the compensation channel 34 for dark current of the main channel or spike noise in the output section.In this case, the compensation channel is somewhat different from the main channel. It is desirable that the shape be the same as that of the

Furthermore, the two outer channels 35 and 36 are sub-channels for preventing interference between charges generated outside the active region and signal charges as described above.

When four columns of channels are transferred using the same transfer electrode in the delay line shown in FIG. 5, the main channel 33 transfers the signal charge injected from the input section 37 and the dark current charge generated in the main channel, and is read out from the output terminal 38. .

In addition, the sub-channels 35 and 36 collect dark current charges generated in the sub-channels and charges mixed in from the outside by diffusion, and transfer them to the reverse biased P-N junction 39 and 40 at the end of the sub-channels. The compensation channel 34 is read out from the output terminal 41 while collecting the dark current charge generated within the compensation channel.

By directing the signals at the output terminal 38 of the main channel and the output terminal 41 of the compensation channel to the differential amplifier 42, the output 43 of the differential amplifier can simultaneously eliminate the dark current of the main channel and the pulse spike noise.

[Brief explanation of drawings]

Figure 1 is a plan view of a conventional one-dimensional charge transfer photosensitive device, Figures 2a and b are cross-sectional views taken along line A-A' in Figure 1 and a schematic diagram of the surface potential distribution, and Figure 3 is a schematic diagram of the surface potential distribution. A plan view of a one-dimensional charge transfer photosensitive device using the present invention, FIGS. 4a and 4b are a cross-sectional view taken along B-B' in FIG.
FIG. 5 shows yet another embodiment according to the invention. In the figure, 11.12.33 is the signal transfer main channel, 2
1, 22, 35, 36 are secondary channels, 26.27.3
4 is a compensation channel, 9 is a terminal, 10 is a semiconductor substrate, 13
14 is a photosensitive electrode, 15.16 is a control electrode, 17 is an insulating layer, 18.19 is a transfer electrode, 32 is an output signal of a compensation channel, 37 is an input section, 38, 4L43 is an output terminal, 39 ．． 40 is a PN junction, and 42 is a differential amplifier.

Claims (1)

[Claims] 1. Charge transfer, in which an insulator is provided on a semiconductor substrate, and a plurality of electrodes are further provided on the insulator, charge, which is an information source, is transferred to the semiconductor substrate, and a voltage is sequentially applied to the electrode portions so as to read it out. In the apparatus, means for forming a charge transfer compensation channel adjacent to and electrically isolated from the charge transfer main channel for transferring information charges; means for forming an electrically separated sub-channel; means for driving the main channel, compensation channel, and sub-channel with the same transfer electrode; and means for providing a sub-channel charge extraction section at a charge transfer termination portion of the sub-channel. , circuit means for differentially shifting the output signal of the main channel and the output signal of the compensation channel.