JPH0347625B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device that scans pixels without using clock pulses and also enables parallel signal readout.

Conventional solid-state image sensors can be broadly divided into
There are two types: MOS type and CCD type.

In a typical MOS type solid-state image sensor, signal charges collected by a photodiode manufactured by diffusion or ion implantation are transferred to a MOSFET (hereinafter referred to as vertical) connected to the photodiode.
It's called MOST. ) to the vertical signal transmission line (hereinafter referred to as the vertical transmission line), the MOSFET adjacent to the end of the vertical transmission line (hereinafter referred to as the horizontal MOST
It is called. ) to a horizontal signal transmission line (hereinafter referred to as a horizontal transmission line), and simultaneously read out as an electrical signal at a signal output section. Here, the vertical MOST turns on when selected by a pulse from the vertical scanning circuit, and the horizontal MOST turns on when selected by a pulse from the horizontal scanning circuit.

On the other hand, in a typical CCD-type solid-state image sensor (an interline configuration is used here as an example), signal charges collected by a photodiode made in the same way as a MOS-type are transferred adjacent to the photodiode. After being guided to a vertical CCD register (hereinafter referred to as vertical CCD) via a MOS gate, it is transferred to a horizontal CCD register (hereinafter referred to as vertical CCD) by a transfer operation.
It is called horizontal CCD. ), and is further carried to a signal output section by a transfer operation and read out as an electrical signal.

The resolution of such solid-state image sensors is determined by the number of photodiodes that form pixels, but currently, the resolution is 2/2.
Typically, there are approximately 500 vertical and 400 horizontal sensors in a 3-inch light-receiving area. However, in order to achieve the same resolution as color negative film with this solid-state image sensor, a minimum of 2,500 pixels vertically and 2,000 horizontally, or 5 million pixels in a 2/3-inch light-receiving area, is required. (In practice, the r, m, s granularity of the film must be taken into account,
It will be 20 to 30 times more than this value. ) The number of horizontal pixels is
When you say 2000 cells, the cell size including one pixel is approximately 4.8μm in the horizontal direction (in the case of 2/3 inch light receiving area).
becomes. (Since the number of vertical pixels is 2500, the vertical cell size is approximately 2.8 μm.) When trying to realize such a high density pixel number, the MOS type requires only one scanning circuit. The design becomes extremely difficult, and the frequency of the two drive pulses is approximately 35MHg in a horizontal scanning circuit, making the drive itself extremely difficult. Even with the CCD type, it is extremely difficult to design a transfer electrode for one CCD, and the frequency of two drive pulses is 35MHg for a horizontal CCD, so the MOS
Like the mold, the drive itself is extremely difficult.

As described above, it can be seen that the typical conventional scanning method is unsuitable for increasing the resolution (that is, increasing the density) of solid-state image sensors.

Therefore, an object of the present invention is to provide a solid-state imaging device that can implement a scanning method suitable for increasing the resolution (that is, increasing the density) of a solid-state imaging device.

In order to achieve the above object, in the present invention, signal charges of a photodiode formed on one side of a semiconductor substrate are read out to the other side of the substrate via a channel turned on by a plurality of resistive gate electrodes. It is characterized by the fact that it is made as follows.

The basic structure of a resistive gate electrode is shown in FIG. 1a. n ^- region 102 formed on P substrate 101
Resistive gate electrode 1 is placed on top of the insulating film 103.
04 is created and a voltage E is applied across it, a potential distribution of the n ^- region 102 as shown in FIG. 1b is obtained. At this time, n ^- area 10
Assuming that the depletion potential of 2 is ψ=ψ ₀ , the range indicated by A corresponds to the region to be depleted.

To realize the scanning function using such resistive gate electrodes, at least two resistive gate electrodes are required, as shown in FIG.

FIGS. 2a and 2b show a top view and a sectional view, respectively, and FIG. 2c shows a potential distribution.
A resistive gate electrode 20 is formed on an n ^- region 202 formed on a P substrate 201 via an insulating film 203.
4 and 205 are made.

A voltage E ₁ is applied between terminals B and C at both ends of the resistive gate electrode 204 (corresponding potential is ψ ₁ ), and a voltage E 1 is applied between terminals B and C at both ends of the resistive gate electrode 205 .
A voltage _E2 is applied between E. (The corresponding potential is ψ ₂ ) At this time, if the depletion potential of the n ^- region 202 is ψ = ψ ₀ , then the range indicated by F becomes the depletion region for the resistive gate electrode 204.
For the resistive gate electrode 205, the range indicated by G becomes a depletion region. Therefore, in the direction perpendicular to the resistive gate electrodes 204 and 205, the n ^- region 2
Looking at 02, a channel is formed in the range indicated by H.

In order to scan the channel to the right, for example, the sawtooth waves R ₁ and R ₂ may be supplied between the B and C terminals and between the D and E terminals via capacitors, respectively.

The present invention applies the scanning function obtained by such a plurality of resistive gate electrodes to a plurality of resistive gate electrodes embedded in a substrate. I will explain using

FIG. 3 shows one embodiment of the present invention.
Regarding each pixel, a shows a bottom view, b shows a cross-sectional view along the line X-X', c shows a cross-sectional view along the Y-Y' line, and d shows an equivalent circuit diagram.

In Figure 3, n ^- is made of semiconductor such as silicon.
Separated by an insulator 302 on one surface of the substrate 301
The n ⁺ region 303 is covered with a transparent film 304. On the other hand, on the opposite surface of the n ^- substrate 301, an n ⁺ region 305 is formed opposite to the n ⁺ region 303.
It is connected to a signal transmission line 307 through an opening in the insulating film 306 .

The n ⁺ region 303 has the function of a photodiode, and the ^n- region between the n ⁺ region 303 and the n ⁺ region 305 has a P region 308 which acts as a first resistive gate electrode and a second resistive gate electrode. When a voltage that depletes the n ^- region 301 is applied to the P region 309 serving as a gate electrode, the signal of the n ⁺ region 303 is
A readout channel is formed in the n ⁺ region 305. This is clearly expressed in the equivalent circuit shown in FIG. 3d. Here, the photodiode 310 corresponds to the n ⁺ region 303, and the n ⁺ region 3
05 corresponds to the drain terminal 311, the first
A first gate portion 312 corresponds to the P region 308 as a resistive gate electrode, a second gate portion 313 corresponds to the P region 309 serving as a second resistive gate electrode, and the first gate portion The colored portions of 312 and the second gate portion 313 represent the range of the depletion state. Therefore, the first gate 312 intersects with the gate portion 314 of the equivalent circuit of FIG. 3d.
and the second gate 313 are both colored,
A channel is formed under the gate part 314, and the signal terminal of the photodiode 310 is connected to the drain terminal 3.
11 side.

A one-dimensional or two-dimensional imaging device can be constructed by forming an array of unit pixels as described above.

FIG. 4 shows an embodiment of a solid-state imaging device in which the unit pixels shown in FIG. 3 are arranged two-dimensionally. (this is,
The three-dimensional structure is displayed two-dimensionally using the equivalent circuit shown in FIG. 3d. ) A photodiode 401 is placed on one surface of the semiconductor substrate.
are arranged in a two-dimensional array, and for each row, the voltage E ₁
Through a channel opened by a first resistive gate electrode 402 to which a voltage E ₂ is applied and a second resistive gate electrode 403 to which a voltage E 2 is applied, the signal charge of the photodiode 401 is transferred to a signal on the opposite surface of the semiconductor substrate. The signal is read out to the transmission line 404. The horizontal scan in this example consists of sawtooth waves R ₁ and
R ₂ between terminals B and C and between terminals D and E, respectively.
This is done by applying the voltage via a capacitor between them. In addition, vertical scanning is not performed in this embodiment,
Signals are output simultaneously for each row.

As described above, according to the present device, when scanning photodiodes that are discretely arranged in two dimensions,
The conventional clock pulse is no longer necessary. As a result, in order to perform scanning with the increase in pixel density in conventional solid-state imaging devices, (1)
Designing high-speed scanning circuits is difficult. (2) Power consumption is extremely high because it is driven by high-speed clock pulses. As a result, (3) fever occurs. This problem will disappear.

In the embodiment shown in FIG. 4, signals are output simultaneously for each row, but it is also possible to output signals sequentially like a conventional solid-state imaging device.

FIG. 5 shows an embodiment of a solid-state imaging device capable of sequentially outputting signals. (FIG. 5 also shows a three-dimensional structure two-dimensionally using the equivalent circuit shown in FIG. 3d.) A photodiode 501 is placed on one surface of the semiconductor substrate.
are arranged in a two-dimensional array, and in each row, the signal charge of the photodiode 501 is transferred to the opposite surface of the semiconductor substrate through a channel opened by a first resistive gate electrode 502 and a second resistive gate electrode 503. The signal is read out to the signal transmission line 504.

In this embodiment, a resistive gate electrode is also used for vertical scanning. That is, both ends of the first resistive gate electrode 502 in each row are connected to the third resistive gate electrode 505 and the fourth resistive gate electrode 506.
are connected to terminals B and C respectively through channels opened by . Further, both ends of the second resistive gate electrode 503 in each row are connected to terminals D and E, respectively, through channels opened by the third resistive gate electrode 505 and the fourth resistive gate electrode 506. Ru.

The vertical scan in this example is a sawtooth wave R ₃
is applied via a capacitor between both ends FG of the third resistive gate electrode 505 to which a voltage E ₃ is applied, and a sawtooth wave R ₄ is applied to the fourth resistive gate electrode 505 to which a voltage E ₄ is applied. This is done by applying the voltage between both ends H and I of 506 via a capacitor. In FIG. 5, the colored portion of the resistive gate electrode indicates a depleted state, indicating that the rows in the range J are being scanned. (In other words, this is a scanning method commonly called simultaneous two-row readout.) The horizontal scanning in this embodiment is basically the same as that in FIG. 4, in which sawtooth waves R ₁ and R ₂ are connected to voltage E ₁ . This is done by applying the voltage between the terminals B and C to which the voltage E ₂ is applied and between the terminals D and E to which the voltage E 2 is applied via a capacitor. (Of course, this is limited to vertically scanned rows.) In the embodiments described above, two-dimensionally arranged discrete photodiodes are used, so the horizontal scanning signal is output as a discrete signal.

However, the invention is not limited to discrete photodiodes, but is also applicable to continuous photoconductive films.

FIG. 6 shows a bottom view of one basic pixel unit in such an embodiment, b a cross-sectional view taken along line X-X', and FIG.
c shows a YY' sectional view, and d shows an equivalent circuit.

In Figure 6, n ^- is made of semiconductor such as silicon.
On one surface of the substrate 601, photoconductive materials (sulfides such as Pb, Cd, selenide, InSb, GaAs, etc.) can be used, depending on the usage conditions such as single crystal, vapor deposited film, sintered film, etc. )
A photoconductor region 602 is formed and covered with a transparent film 603. On the other hand, n ^-substrate 6
An n ⁺ region 604 is formed on the opposite surface of 01,
It is connected to a signal transmission line 606 through an opening in the insulating film 605 .

In the photoconductor region 602, there are two cases in which conduction charges are mainly holes (P type) and electrons (N type).
When combined with the n ⁺ region 303, the former needs to function as an electron depletion operation, and the latter as an electron accumulation operation.

The n ^- region between the photoconductor region 602 and the n ⁺ region 604 is divided into a P region 607 serving as a first resistive gate electrode and a P region 608 serving as a second resistive gate electrode ^. When a voltage is applied that completely depletes region 601, a channel is formed for reading signal charges in photoconductor region 602 to n ⁺ region 604.

The above is expressed in an easy-to-understand manner in the 6th section.
This is the equivalent circuit of Figure d. In FIG. 6d, photoconductor region 60 corresponds to photoconductor region 602.
9. Corresponding to the n ⁺ area 604 is the n ⁺ area 610,
P region 607 serves as first resistive gate electrode
The first gate portion 611 corresponds to the first gate portion 611, the second gate portion 612 corresponds to the P region 608 serving as the second resistive gate electrode, and the first gate portion 6
11 and the colored portions of the second gate portion 612 represent the range of the depletion state. Therefore, in FIG. 6d, a channel corresponding to the width K is opened from the photoconductor region 609 to the n ⁺ region 610, and the signal charge in the photoconductor region 609 is transferred to the n ⁺ region 6.
It is read out to the 10 side. (The width indicated by K can be set freely, so by narrowing this width, the goal of high resolution can be achieved.) By arranging the basic pixel units as described above on a plane, one-dimensional or two-dimensional An image sensor can be constructed.

FIG. 7 shows an embodiment of a solid-state imaging device in which the basic pixel units shown in FIG. 6 are arranged two-dimensionally. (This is a two-dimensional representation of a three-dimensional structure using the equivalent circuit shown in FIG. ), each row is represented by a vertically separated n ⁺ region 704. The signal of the photoconductor region 701 is passed through a channel opened for each row by a first resistive gate electrode 702 to which a voltage E ₁ is applied and a second resistive gate electrode ₇₀₃ to which a voltage E 2 is applied. Charge is read out to n ⁺ region 704 on the opposite surface of the semiconductor substrate. The horizontal scan in this example is a sawtooth wave.
This is done by applying R ₁ and R ₂ via capacitors between terminals B and C and between terminals DE and E, respectively. Further, vertical scanning is not performed in this embodiment, and signals are output simultaneously for each row, but vertical scanning can also be performed in the same manner as in FIG. 5.

As described above, according to this device, when continuously scanning a two-dimensionally formed photoconductor, the same method as in the case of a conventional image pickup tube can be applied, simplifying the scanning method and reducing consumption. Not only can electrical power be easily realized, but also high resolution can be realized extremely easily.

FIG. 8 shows a modification of the basic pixel unit of FIG. 6, in which a shows a bottom view and b shows a sectional view taken along the line X-X'. The difference from the one in FIG. 6 is that the first resistive gate electrode 607 is buried in FIG. 6b.
The ^second resistive gate electrode 608 is separated by an insulator 801 and is formed in contact with the photoconductor 602, which is similar to the process shown in FIG. It's getting easier.

In the above embodiments, an n ^- type semiconductor substrate was used, but
The principles and structure of the present invention are valid even if the conductivity type is reversed or even if other semiconductors are used.

As described above, according to the present invention, since clock pulses are not used for pixel scanning, the driving method can be simplified and power consumption can be reduced.

Since the entire surface of the semiconductor substrate can be used as a light receiving section, it is advantageous in terms of sensitivity.

Since this is an analog scanning method that does not use clock pulses and is compatible with so-called image pickup tubes, it can be used with either discrete photodiodes or continuous photoconductors as light receiving elements.

When controlled by two resistive gate electrodes, the scanning width can be set by controlling the depletion range, so high-resolution readout can be easily achieved when a photoconductor is used.

By using resistive gate electrodes, parallel output of signals can be easily realized.

This feature makes it possible to apply it to fields such as electronic still cameras, broadcasting solid-state cameras, and holographic information detection cameras, making it possible to realize solid-state imaging devices that fully surpass image pickup tubes.

[Brief explanation of drawings]

Figure 1 a, b is a cross-sectional view and potential distribution diagram of a basic resistive gate electrode, and Figure 2 a, b, c is a top view, cross-sectional view, and diagram of a scanning circuit using two resistive gate electrodes. Potential distribution diagram, Figures 3a, b, c, and d are a bottom view, an X-X' sectional view, a Y-Y' sectional view, and an equivalent circuit diagram showing a unit pixel of a solid-state imaging device in an embodiment of the present invention. , FIG. 4 is a circuit diagram showing the configuration of a solid-state imaging device in which the unit pixels of FIG. Circuit diagram, FIGS. 6a, b, c, and d are a bottom view, an X-X' sectional view, a Y-Y' sectional view, and an equivalent circuit showing basic pixel units of a solid-state imaging device in another embodiment of the present invention. 7 is a circuit diagram showing the configuration of a solid-state imaging device in which the basic pixel unit of the embodiment of FIG. 6 is two-dimensionally formed, and FIGS. 8a and 8b are one of the basic pixel units of the embodiment of FIG. It is a bottom view and XX' sectional view of a modification. 101,201...P substrate, 102,202...
...n ^- region, 103,203...insulating film, 104,
204, 205...Resistive gate film, 301...
n ^- region, 302, 306...insulating film, 303...
...n ⁺ area, 305...n ⁺ area, 307,405,
504... Signal transmission line, 308, 309... P region, 310, 401, 501... Photo diode, 311... Drain terminal, 312, 402,
502...first gate section, 313,403,50
3... Second gate part, 505... Third resistive electrode, 506... Fourth resistive gate electrode, 601
...n ^-substrate , 602 ... photoconductor region, 603
...Transparent film, 604...n ⁺ region, 605...Insulating film, 606...Signal transmission line, 607, 608...
...P area.

Claims (1)

[Scope of Claims] 1. A photoelectric conversion region formed on one surface of the semiconductor substrate and a signal transmission region formed on the opposite surface of the substrate are separated along a channel formed inside the substrate. What is claimed is: 1. A solid-state imaging device comprising a plurality of resistive gate electrodes embedded in the photoelectric conversion region and continuous in the direction of scanning the photoelectric conversion region. 2. The solid-state imaging device according to claim 1, wherein discrete photoelectric conversion elements are arranged in a matrix as the photoelectric conversion region. 3. The solid-state imaging device according to claim 1, wherein a continuous photoconductor is formed in a planar manner as the photoelectric conversion region. 4. As a signal transmission region, the photoelectric conversion region is connected in the scanning direction, separated in a direction perpendicular to the scanning direction, and the signals read from each signal transmission region are output in parallel and at the same time. A solid-state imaging device according to claim 1, characterized in that: 5 A plurality of resistive gate electrodes are made up of a first gate and a second gate, and a voltage is applied so that opposite potential gradients are formed at both ends of the first gate and both ends of the second gate, and 2. The solid-state imaging device according to claim 1, wherein scanning is performed by applying sawtooth waves having opposite increases and decreases in an alternating current manner.