JPS6121891Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a semiconductor optical image detection device with reduced noise.

Conventional configurations and their problems A semiconductor optical image detection device that operates a photodiode or phototransistor array in an accumulation mode to perform solid-state scanning uses a photodiode as a photosensitive element, and a MOS field effect transistor (hereinafter referred to as MOST) as a switching element. It consists of an integrated photodetector connected to a photodetector.

In putting such an optical image detection device into practical use, a major problem is the removal of noise components from the readout output. There are various types of noise in optical image detection devices, but the following three are typical. The first is spike noise caused by a signal readout scanning pulse applied to the gate to switch the MOST, which is a switching element, leaking into the signal line through the gate-drain capacitance. The second is the dark current accumulated in the photodiode in the dark state due to the leakage current of the pn junction, and the third is the noise component (hereinafter referred to as (abbreviated as pseudo signal). Various studies have been made to eliminate only spike noise among these three noise components, and methods such as delayed sampling and differential amplification have been proposed.

FIG. 1 shows a circuit diagram of a conventional optical image detection device that uses a differential amplifier to eliminate spike noise. PD ₁ to PD _o are photodiodes, which are connected to P channel enhancement type optical signal readout switching MOST M ₁ to _Mo. C ₁ -C _o are noise readout MOS capacitors, which have the same structure as the above-mentioned switching MOST M ₁ -M _o except that they do not have a source region. Signal lines 1 and 2 are connected to drains of switching switches MOST M ₁ to _{M o} for optical signal readout and MOS capacitors C ₁ for noise readout, respectively.
~C _o is connected to the drains thereof, and is also connected to the input end of the differential amplifier 3 via one ends of load resistors R ₁ and R ₂ . A negative potential from DC power supply B is connected to the other ends of load resistors R ₁ and R ₂ .

The pulse lines SP ₁ to _{SP o} connected to the readout scanning pulse generator 5 are connected to the commonly connected gates of each of the switching MOST and MOS capacitor sets (M ₁ -C ₁ ) to (M _o -C _o ), This is for applying scanning pulses. Next, the spike noise removal operation of the optical image detection device shown in FIG. 1 will be explained. For example, when reading optical information accumulated in the photodiode PD ₁ , the pulse line SP ₁ is
Apply a negative scanning pulse to the switching
Turn on MOST M ₁ and MOS capacitor C ₁ . Then, the readout output appearing at the load resistor _R1 is a composite output of a signal component corresponding to the optical information stored in the photodiode _PD1 and a spike noise component. On the other hand, MOS capacitor C ₁ is connected to load resistance R ₂ .
Only the spike noise components that pass through appear. Therefore, when the outputs appearing at the load resistors R ₁ and R ₂ are input to the differential amplifier 3, the output terminal 4 of the amplifier 3
A signal component from which spike noise has been removed is output. This is a noise removal operation using a differential amplifier.

However, it is impossible to obtain true optical information only by removing spike noise from the readout output appearing at the load resistor _R1 . Because the signal still has dark current and switching
This is because it includes a pseudo signal generated at the drain section of MOST. In other words, in order to operate a photodiode in storage mode like a photosensitive element, a large area is required;
In p-n junctions, the influence of dark current cannot be ignored. On the other hand, switching directly connected to the signal line
Similar to the source part, which is a component of a photodiode, the drain part of the MOST is connected to the semiconductor substrate.
It forms a p-n junction and is optically sensitive. It is very difficult to prevent the drain portion from sensing light entering from an opening area other than the light-receiving window from the viewpoint of device fabrication, and this appears as a false signal when optical information is read out. Conventional semiconductor optical image detection devices have had various noise problems as described above.

Purpose of the Invention In view of the above-mentioned problems, an object of the present invention is to provide a semiconductor optical image detection device that can completely eliminate various noise components.

Structure of the invention The optical image detection device according to the invention includes an optical signal readout circuit section consisting of a photosensitive element having the same structure and a field effect transistor for reading out a signal from the photosensitive element, and an optical signal readout circuit section having the same structure as the circuit section. The noise readout circuit section with The readout signal is input to the differential amplifier via the first and second output lines, which are mutually connected to the drains of the field effect transistors in the circuit section and arranged symmetrically, and the noise component is completely canceled to produce an optical information signal. It is designed to obtain only the following.

DESCRIPTION OF EMBODIMENTS The optical image detection device of the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment of the optical image detection device according to the present invention, in which the three types of noise components described above are removed using a differential amplifier. Although the embodiment will be described with reference to a p ⁺ n photodiode-p channel MOST system, the essential operation is the same for an n ⁺ p photodiode-n channel MOST system. In FIG. 2, PD ₁ -PD _o are photodiodes for reading out optical signals, and are connected to the sources of switching MOST M _{1 -Mo} for reading out optical signals. This is the optical signal readout circuit section. Noise readout photodiode RD 1 ~ _{RD o} connected to the source of noise readout switching MOST RM _{1 ~} RM _o
is used to detect noise components, and is completely optically shielded to maintain a dark state at all times.
This is the noise readout circuit section. Here, the noise readout photodiodes RD ₁ to _{RD o} have exactly the same structure as the corresponding optical signal readout photodiodes PD ₁ to PD _o and optical signal readout switching MOST M ₁ to M _o and are arranged symmetrically. There is. SP ₁
〜SP _o is n scanning pulse application lines, and a set of switching MOSTs (M ₁ −RM ₁ ), 〜(M _o −
RM _o ), and is connected to the read scanning pulse generator 5. switching
A load resistor R ₁ is connected to the optical signal readout output line ₁ that commonly connects the drains of MOST M 1 to _{M o} , and a noise readout switching circuit MOST RM ₁ to
A load resistor R ₂ is connected to the noise readout output line 2 that commonly connects the drains of RM _o . As is clear from the figure, the optical signal readout output line 1 and the noise readout output line 2 are arranged symmetrically. 2
A negative potential is applied from the DC power source B to the two load resistors R ₁ and R ₂ , and the read outputs from the load resistors R ₁ and R ₂ are input to the differential amplifier 3 .

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

After optical information is incident on the n photodiodes PD ₁ to PD _o and accumulated, the readout scanning pulse generator 5 is operated, and when a negative scanning pulse is applied to the first pulse line SP ₁ , the switching MOST is activated.
M ₁ and RM ₁ are turned on. At this time, the load resistance
R ₁ contains a signal corresponding to the optical information stored in the photodiode PD ₁ , a signal corresponding to the dark current, a spike noise generated from the switching MOST M ₁ , and a pseudo signal sensed at the drain of the switching MOST M ₁ . The output signal of the sum of all appears. On the other hand, since the photodiode RD ₁ is in a dark state in the load resistor R ₂ , an output signal that is the sum of a signal corresponding to a dark current, spike noise, and a pseudo signal appears. Here, as is clear from FIG. 2, the structure of the element connected to the two output lines 1 and 2,
Since the numbers are the same and their positions are symmetrical,
The circuit is completely symmetrical, and the electrical characteristics such as distributed capacitance and optical characteristics such as incident light distribution are the same, and the noise components appearing in the two load resistors R ₁ and R ₂ are the same.
That is, the sum of spike noise, dark current, and pseudo signal is almost equal. Therefore, differential amplifier 3
As a result, the noise component is almost completely removed, and only the signal corresponding to the optical information is amplified and output from the output terminal 4 of the differential amplifier 3.

Next, the readout scanning pulse is applied to the second pulse line.
When moving to SP ₂ , switching MOST M ₂ and RM ₂ are turned on, and in the same way as in the previous stage, only the amplified output pulse of the optical information signal stored in photodiode PD ₂ is sent to the output terminal of differential amplifier 3. Appears in 4. By sequentially applying scanning pulses in this manner, it is possible to sequentially read out the pulse trains of optical signals corresponding to the optical information incident on the photodiodes PD ₁ to PD _o , with noise components completely removed. can.

From the above explanation, the feature of the optical image detection device of the present invention is that the optical signal readout circuit section and the noise readout circuit section, which are two one-dimensional arrays having the same structure and shape, and their output lines are placed in symmetrical positions. In addition to equalizing the electrical characteristics such as distributed capacitance of both the readout and noise output lines, this arrangement also compensates for noise based on the basic structure of the photosensitive element, and reduces the optical It is possible to equalize the influence of the result,
Approximately equal noise components appear on both output lines, and the noise components in the differential amplifier are almost completely cancelled. Furthermore, as an advantage of the present invention, when manufacturing a large number of photosensitive elements arranged long in one dimension on a single silicon chip, it is extremely difficult to make the entire element uniform; It is also possible to compensate for the positional non-uniformity of noise components.

In addition, there are various possible symmetrical structures for the two arrays constituting the two circuit sections described above, but for example, the positions of the photodiode and the switching MOST in the noise readout circuit section may be reversed, and Photodiode and switching
It is clear that those placed in parallel with MOST also exhibit the above effects.

FIG. 3 is a partial plan view of the photosensitive element of the optical image detecting device according to the present invention explained in FIG. 2, constructed on a silicon substrate. Category 45 in Figure 3
shows the scanning pulse generator 5 in FIG. 2,
Next to that is an array for reading out optical signals, and next to that is an array for reading out noise. In the following description, one structural unit among the many pairs of photosensitive elements will be described in detail.

P ⁺ n consisting of an n-type semiconductor substrate and p ⁺ diffusion region 21
Using the junction as a photodiode for optical signal readout,
In addition, the p ⁺ diffusion region (source part) 21 has another conductive ^electrode 24 .
2. Together with the gate section 23, it constitutes one optical signal readout switching MOST. Similarly, the p ⁺ diffusion region (source part) 31 of the photodiode for noise readout is integrated with the p ⁺ diffusion region (drain part) 32 and gate part 33 having another conductive electrode 34 .
This constitutes a switching MOST for noise readout. The conductive path 41 corresponds to a pulse line, and is used for optical signal readout and noise readout switching.
It connects the gate parts 23 and 33 of the MOST in common, and the noise readout switching MOST passes between the photodiodes and reaches the gate part.
Further, the drain part 22 of the switching MOST for reading out optical signals is coupled to the output line 25 for reading out optical signals through the conductive electrode 24, and the switching MOST for reading out noise is connected to the output line 25 for reading out optical signals.
The drain portion 32 of the MOST is coupled to a noise readout output line 35 through a conductive electrode 34. A light-receiving area 60 (usually covered with an oxide film) that allows light to enter is provided only on the photodiode for reading out optical signals and is located in the center of the p ⁺ diffusion area 21, and all photosensitive elements other than the light-receiving window 60 are exposed to light. It is covered with a film 61 that has a cooling effect. In other words, not only the noise readout photodiode 31 which always remains in a dark state, but also the optical signal readout and noise readout switching MOST parts are reliably illuminated, and the optical signal readout output line 25 and the noise readout output line are connected as shown in the figure. Cover the area between 35 and 35 with a light-shielding film. What should be especially noted about this light-shielding film is the drain part 2 of the switching MOST.
2 to the terminal end 62 of the optical shielding film extending close to the optical signal readout output line 25.
A distance is required to minimize the degree to which the light incident from the aperture region between the two is directly sensed by the drain section 22, and in this embodiment, the distance is set to 80μ in view of the lifetime of excited chiral radiation and the density of the element configuration.
This distance is exactly the same for noise readout. 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 photodiode, depending on the resolution characteristics of the photodetector. The p ⁺ diffusion regions 21 and 31 of the photodiode also have a large area necessary to operate in charge storage mode. The optical image detection device having the pattern shown in FIG. 3 can be fabricated on a single silicon chip using the same MOS technology required to make the conventional optical image detection device explained in FIG. It is easiest to use an Al vapor deposited film as the light-shielding film.

The circuit shown in Figure 3 includes two MOSTs and two photodiodes per constituent unit of the photosensitive element, but the number of steps is the same as in the conventional method, and the density is the shift used to scan the array. For one-dimensional arrays, which are highly dependent on the dimensions of the counter, this does not make integration any more difficult.

In fact, when we prototyped a 64-bit optical image detection device with the pattern shown in Figure 3, we were able to obtain a uniform optical signal pulse waveform that contained almost no noise components even when low-level optical input was near a dark state. The signal-to-noise ratio (S/N ratio) was definitely over 45dB.

Effects of the Invention As described above in detail with respect to the embodiments, signals from the optical signal readout circuit section and the noise readout circuit section of the present invention, which have exactly the same configuration, structure, and shape, are transmitted through the respective output lines arranged symmetrically. Semiconductor optical image detection devices that read out optical signals by amplifying them with differential amplifiers can completely eliminate spike noise, dark current, and pseudo-signal noise components, and can be used even when configuring large-scale arrays. It is also possible to compensate to the maximum extent for non-uniformity in device characteristics caused by the manufacturing process.
In the above example, a photodiode is used as the photosensitive element, but it goes without saying that the same effect can be expected when a phototransistor is used.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional optical image detection device, FIG. 2 is a circuit diagram of an optical image detection device according to the present invention, and FIG. 3 is a partial plan view of the optical image detection device manufactured based on the present invention. . PD ₁ ~ PD _o ... photodiode for optical signal readout,
M ₁ ~M _o ...Switching MOST for optical signal readout,
RD ₁ ~ RD _o ... photodiode for noise readout,
RM ₁ ~ RM _o ... Noise reading switching
MOST, R ₁ , R ₂ ... Load resistance, B ... DC power supply.

Claims (1)

[Scope of utility model registration request] A plurality of first photosensitive elements arranged one-dimensionally on a semiconductor substrate and a plurality of first photosensitive elements having the same number and the same structure as the first photosensitive elements,
A first main electrode is connected to each of the first photosensitive elements and a second photosensitive element arranged in a one-dimensional manner so as to face each of the photosensitive elements and further provided with a light shielding means. A first main electrode is connected to each of the first switching element and the second photosensitive element. a second switching element having the same structure as the first switching element; a scanning pulse generation circuit in which two conduction control electrodes of the opposing first and second switching elements are respectively commonly connected; an optical signal readout output line to which the second main electrode of the first switching element is connected; a noise output line to which the second main electrode of the second switching element is connected; and the optical signal readout output line. and a differential amplifier connected to the noise output line, wherein the first switching element and the optical signal readout output line are connected to the second switching element and the noise output line, respectively. Second
A semiconductor optical image detection device characterized in that the photosensitive elements are arranged symmetrically in the same manner as in the symmetrical relationship of the photosensitive elements.