JPS5845828B2 - Hand-made construction work - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a low-noise semiconductor optical image detection device in which a large number of photodetection means and an electrical scanning circuit for scanning these by sample operation are integrated on a single semiconductor substrate. It is related to.

The semiconductor optical image detection device currently under consideration is one in which a photodiode is used as a photosensitive element, and a photodetector is integrated with an MO8 field effect transistor (hereinafter abbreviated as MO8T) connected as a switching element.

In putting such an optical image detection device into practical use, the removal of noise components from the readout output is a very important problem.

There are various types of noise in optical image detection devices, and the following two are the most representative ones.

That is, the first is spike noise caused by the signal readout voltage pulse applied to the gate to switch the MO8T leaking to the video output line through the gate-drain capacitance or gate-source capacitance.
Alternatively, it is spike noise caused by parasitic capacitance between the line to which the clock pulse applied to the shift counter is applied and the video output line.

The second is switching MO due to the diffusion of carriers excited by light incident from the light receiving window or other than the light receiving window.
This is a noise component (hereinafter referred to as a pseudo signal) sensed by the drain section of 8T.

Various studies have been made to eliminate only spike noise among these noise components, but an on-chip differential amplification method is ultimately effective.

Figure 1 shows the above noise, that is, spike noise and MO8.
FIG. 2 is a circuit diagram of a conventional optical image detection device that uses a differential amplifier to eliminate a pseudo signal at the drain portion of T.

In FIG. 1, PD1 to PDn are signal detection photodiodes, which are connected to the sources of signal switching MO8TM1 to Mn.

Noise detection switching MO8T Noise detection photodiode RD1 connected to the source of RM1 to RMn
RDn is used to detect noise components, and is optically shielded so as to always maintain a dark state.

Here, the noise detection photodiodes RD1 to RDn and the noise detection switching MO8T RM1 to RMn are the corresponding signal detection photodiodes PD1 to P, respectively.
Dn and signal detection switching MO8T M, ~M
It has exactly the same shape and structure as o, and is arranged symmetrically.

SP, ~SPn are scanning pulse application lines, and each set of two switching MO8Ts M1-RM, ,...
. . . Commonly drives the gates of 2Mn-RMn, and is connected to the shift counter 5.

Switching MO8T for signal detection A signal load resistor R is connected to the signal output line 1 that commonly connects the drains of M1 to Mn.
1 is connected, switching MO8T R for noise detection
Noise output line 2 that commonly connects the drains of M and ~RMn
A noise load resistor R2 is connected to.

A negative potential is applied to the two resistors from the DC power supply B, and the read outputs from the Okayama power lines 1 and 2 are input to the differential amplifier 3.

Next, the circuit operation of the device shown in FIG. 1 will be explained.

For example, a voltage pulse is applied to the scanning pulse application line SP1, and two switching MO8TM, , RM
l becomes conductive.

At that time, the signal appearing on the signal output line 1 is a charging current when the junction of the signal detection photodiode is charged to almost the same potential as the power supply B through the load resistor R1 and the signal detection switching MO8T Ml.

Therefore, this charging current supplements the amount of charge discharged by the photodiode within one scanning period in proportion to the amount of light incident on the photodiode, and is therefore proportional to the amount of light incident on the photodiode.

Furthermore, this signal output line 1 appears.

In addition to the optical signal proportional to the amount of incident light read out from the photodiode, the signal includes spike noise generated from the switching MO8T for signal detection and the switching 'MO8T.
It also includes the sum of the pseudo signals sensed at the drain of.

On the other hand, on the noise output line 2, the sum of the spike noise and the pseudo signal of the drain section of the switching MO8T appears.

As is clear from FIG. 1, since the shapes and structures of the elements connected to the two output lines 1 and 2 are exactly the same, the noise components appearing in the two output lines 1 and 2, that is, spike noise, The sum of the pseudo signals at the drain of the switching MO8T is almost equal, so the differential amplifier 3 (
Therefore, in principle, the above two noise components should be almost completely eliminated.

However, if such a system is designed on one semiconductor chip, the scanning pulse application lines SP1 to SPn must be wired long to the gates of the signal detection switching MO8T M1 to Mn and the noise detection switching MO8T RM1 to RMn. Both switching MO8T
The overlapping capacitance between the gate and source becomes too large, causing large spike noise.

In addition, the carriers excited by the light incident from the light receiving section are diffused, and the excited carriers are accumulated in the noise detection photodiode. The signal read out from the noise detection photodiode shows a constant value, but the signal read out from the noise detection photodiode increases in proportion to the amount of incident light.

As a result, the output of the differential amplifier should originally show a certain saturation value when the amount of light incident on it exceeds the saturation amount.
This method does not exhibit a constant saturation value, but gradually decreases in proportion to the amount of incident light, causes malfunctions, and is difficult to withstand in normal use.

That is, the conventional low-noise semiconductor optical image detection device has the above-mentioned disadvantages in terms of noise.

In view of the above-mentioned points, the present invention has been made in order to almost completely eliminate various noise components. and corresponding to the photosensitive element, the area of the junction is significantly smaller than that of the photosensitive element, and the junction element is shielded from light (from the switching element for reading out the signal from the junction element). The noise detection circuit section and the noise detection circuit section are arranged symmetrically to each other,
The drive gate electrodes, which are the control electrodes of both of the switching elements, are commonly connected, and a readout scanning pulse is applied thereto, and the optical signal from the photodetection circuit section and the signal generated from the noise detection circuit section are differentiated. It is characterized in that it is configured to lead to a dynamic amplifier and detect the optical signal from the differential amplifier.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

The explanation will be given for pn photodiode-p channel MO8T, but np photodiode n-channel MO8
The essential operation is the same for T.

In FIG. 2, the parts inside the broken line are built into a single semiconductor substrate, and the circles on the broken line are external input/output terminals.

Further, the shift counter 5, which is a scanning pulse generator, is a dynamic one and is a known device.

M1 to Mn are switching MO8T for signal detection,
A photodetection circuit section is constructed by using signal detection photodiodes PD1 to PDn between the source portion of the MO8T and the semiconductor substrate.

The drains of the signal detection switching MO8T M1 to Mn are commonly connected to each other and connected to one input terminal of the differential amplifier 3 via the signal output line 1.

RM1 to RMn are switching MO8Ts for noise detection, and noise detection photodiodes RD1 to RDn are connected between the source portion of the MO8T and the semiconductor substrate, and constitute a noise detection circuit section.

The noise detection photodiodes RD and ~RDn are used to detect noise components and are always kept in a dark state.
The source section (
The noise detection photodiodes RD1 to RDn) are made as small as possible.

The area of the noise detection photodiodes RD1 to RDn is significantly smaller than the area of the signal detection photodiodes RD1 to RDn, usually 1/10 or less, preferably 1/50 to 1/50.
It is better to reduce it to 1/1000.

The drains of the noise detection MO8T RM, ~RMn are commonly connected to each other, and are connected to the differential amplifier 3 via the noise output line 2.
Further, the signal output line 1 and the noise output line 2 are connected to the power supply B via load resistors R1 and R2, respectively.

Both switching MO8T M1-Mn, RMl-RMn
The shapes and structures are exactly the same except that the area of the source portion is different.

Furthermore, both switching MO8T sets M, -RMn, -,
-, Mn-RMn gates as control electrodes are commonly connected, respectively, and scanning pulse application lines SP1 to
Connect S PnG.

Next, the circuit operation of the device shown in FIG. 2 will be explained.

After optical information is incident on the signal detection photodiodes PD1 to PDn and accumulated, the shift counter 5 is operated and a negative voltage pulse is first applied to the first scanning pulse application line SP1. M and the noise detection switching MO8TRM1 become conductive.

At this time, the signal load resistor R1 contains a signal corresponding to the optical information accumulated in the signal detection photodiode PD1, spike noise generated from the signal detection switching MO8T Ml, and further the same switching MO8T M1.
An output signal appears which is the sum of the pseudo signals sensed at the drain of 1.

On the other hand, since the noise detection photodiode RD is in a dark state in the noise load resistor R2, the sum of spike noise and pseudo signal appears.

Here, as is clear from FIG. 2, the elements connected to the two output lines 1゜2 are both photodiodes PD1゜RDl.
are the same in shape, structure, and number except for the difference in area, and furthermore, the two output lines 1 and 2 are placed as close as possible to the short axis direction of the semiconductor chip, and as a result, the above two load resistances R , , the sum of the noise components appearing in R2, that is, the spike noise and the pseudo signal, is almost equal.

Therefore, the noise component is almost completely canceled by the differential amplifier 3, and only the signal corresponding to the optical information from the output terminal 4 of the amplifier 3 is amplified and output.

Next, when the scan pulse is transferred to the scan pulse application line SP2, the switching MO8T M2. RM2 becomes conductive, and the signal detection photodiode P is activated in the same manner as in the previous stage.
Only the amplified output pulses of the information signal stored in D2 appear at the output terminal 4 of the differential amplifier 3.

In this way, the signal detection photodiodes PD1 to PD
The output voltage pulse train corresponding to the optical information incident on n can be sequentially read out with noise components completely eliminated.

From the above explanation, according to the device according to this embodiment, by simply adding a width equivalent to one MO8T in the short axis direction of the chip, which uses a noise detection photodiode with a minimized size as the source part, approximately the same noise can be generated. components appear in the Okayama force lines of the signal and noise, and the noise components in the differential amplifier are almost completely cancelled. As a result, the length of the chip in the short axis direction is shortened, and the length of the photodiode chip for noise detection is reduced. Since the length in the short axis direction is shortened, both switching ``MO''
The scanning pulse application line connecting the gates of the 8T is shortened, and spike noise caused by the overlapping capacitance between the gate and source of the MO8T can be suppressed as much as possible.

FIG. 3 is a partial plan view of a photodetecting section in which the optical image detecting device explained in FIG. 2 is constructed on a silicon substrate.

In FIG. 3, section 45 indicates the corresponding part of the shift counter 5 in FIG.
A photodetector array consisting of O8T is arranged in pairs in two stages, upper and lower.

In the following description, one structural unit of a large number of pairs of photodetecting sections will be explained in detail.

A p10n junction consisting of an n-type semiconductor substrate and a p10 diffusion region 21 is used as a photodiode for optical information, and the same p10 diffusion region 21 is also used as a source, and another p10 diffusion region ( drain) 23, gate part 22
Together, they constitute one switching MO8T for signal detection.

Similarly, the p1 diffusion region (source) 31, which is also used as a noise detection circle photodiode, constitutes a noise detection MO8T together with another p1 diffusion region (drain) 33 having a conductive electrode 34 and the gate part 32. There is.

The gate and drain shapes and structures of both switching MO8Ts are exactly the same, and only the source portions are different.

That is, the area of the source section 31 of the switching MO8T for noise detection is significantly smaller than the area of the source section 21 of the switching MO8T for signal detection.

The conductive path 41 corresponds to the scanning pulse application line, and is connected to the gate 22.3 of the signal and noise switching MO8T.
2 are commonly connected.

Further, the drain 23 of the switching MO8T for signal detection is coupled to the signal output line 25 through the conduction electrode 24, and the drain 33 of the switching MO8T for noise detection is coupled to the noise output line 35 through the conduction electrode 34.

A light-receiving region 60 (usually covered with an oxide film) that allows light to enter is provided above the signal detection photodiode,
It is located approximately at the center of the p10 diffusion region 21.

Further, the top of the chip other than the light receiving area 60 is covered with a film 61 having a light blocking effect unless there is any problem with wiring such as input/output lines.

In addition to the noise detection photodiode 31 that is always kept in a dark state, there is also a signal and noise switching MO8.
The T section also definitely blocks light.

In addition, the area around the chip without the array is also shielded from light as much as possible, and the light that enters from other than the light-receiving window is minimized as much as possible.

What should be noted in the film 61 that uses an aluminum vapor-deposited film as a light-shielding film is that the drain 23 of the switching MO8T
The terminal end 6 of the coating 61 extends from the signal output line 25 in close proximity to the signal output line 25.
2, the output line 25 and the termination 62 of the coating 61
A distance is required to minimize the degree to which the light entering from the aperture area 63 between the drain part 23 and the drain part 23 is directly sensed.
In this example, the thickness is set to 80 μm due to the lifetime of excited carriers and the density of the element structure.

The thickness of the noise generating section is also 80 μm.

On the other hand, the width of the light receiving window 60 is set to 50 μm, which is equal to the pitch width of the photodiodes, depending on the resolution characteristics of the optical image detection device.

Further, the p1 diffusion region 21 of the signal detection photodiode has a large area necessary to operate in the charge accumulation mode.

The optical image detecting device having the pattern shown in FIG. 3 can be manufactured on a single silicon chip by using the MO8 technology necessary for manufacturing the conventional optical image detecting device explained in FIG. It is most convenient to use an aluminum vapor-deposited film as the light blocking film.

Furthermore, in the circuit shown in Fig. 3, it is only necessary to add one MO8T with a large source part and one pMO8T with a small source part in the short axis direction of the chip per unit of photodetection element. The length in the minor axis direction is shorter than that in the example, which is advantageous in terms of manufacturing technology when using multiple bits.

In fact, when we prototyped a 64-bit optical image detection device with the pattern shown in Figure 3, we found that even though the area of the noise detection photodiode was small (the area of the signal detection photodiode was 800 times the area of the noise detection photodiode) Spike noise and pseudo-signals in the drain section are almost completely eliminated, and the optical arrangement is fully considered even for light incidence several times higher than the photodiode saturation. This device operated stably with few malfunctions.

In addition, in the case of low-level optical input close to the dark state, a uniform optical signal pulse waveform containing almost no noise components can be obtained, and the signal-to-noise ratio (S/N ratio) is reliably over 50 dB. was gotten.

Although a photodiode was used as the photosensitive element in the above embodiment, it goes without saying that the same effect can be expected when a phototransistor or the like is used.

As detailed above, the semiconductor optical image detection device of the present invention is characterized in that the junction area of the junction element of the noise detection circuit section is significantly smaller than the junction area of the junction photosensitive element of the photodetection circuit section. , because the junction area of the junction element in the noise detection circuit is small, and as a result the pulse application line is short, optical noise due to the diffusion of carriers excited by the incident light is not stored in the noise detection photodiode. ,
In addition, spike noise caused by overlapping capacitance between the gate and source can be suppressed as much as possible, and the noise component of the signal output from the differential amplifier is almost completely eliminated, making it extremely effective in practical use. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional low-noise semiconductor optical image detection device, FIG. 2 is a circuit diagram of a low-noise semiconductor optical image detection device according to the present invention, and FIG. 3 is a circuit diagram of a low-noise semiconductor optical image detection device according to the present invention. FIG. 2 is a partial plan view of the device. PD1 to PDn...Photodiode for signal detection, M1 to Mn...Switching MO for signal detection
S.T. RM1 to RMn...Switching 1 for noise detection
! viO8T. RD1 to RDn... Photodiode for noise detection, SP1 to SPn... Scanning pulse application line,
R1...Load resistance for signal, R2...Load resistance for noise, B...Power supply, 1...Signal output line, 2...・Noise output line, 3...
Differential amplifier, 4... Output terminal of differential amplifier, 5
... Digit counter, 21 ... Source section for signal detection, 22 ... Gate section for signal detection, 2
3... Drain section for signal detection, 31...
・Source part for noise detection, 32... Gate part for noise detection, 33... Drain part for noise detection, 60
......Light receiving window, 61......Light shielding coating.

Claims (1)

[Claims] 1. A photodetection circuit section formed by arranging a plurality of connected bodies of a junction photosensitive element and a first switching element having one of its main electrodes connected to the junction photosensitive element, and a junction that is significantly smaller in area than the junction area of the junction photosensitive element. a plurality of connected bodies each including a junction element having a certain area and shielded from light and a second switching element to which one of the main electrodes is connected to the junction element, and which is the same as the photodetection circuit section. a noise detection circuit section disposed symmetrically with the photodetection circuit section, a scanning pulse generator section connected to commonly connected control electrodes of the first and second switching elements, and the photodetection circuit section. A semiconductor optical image detection device comprising: a differential amplifier connected to the noise detection circuit section, respectively.