JP3215864B2 - Thermal infrared sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermal infrared sensor in which thermopiles or bolometers are two-dimensionally arranged.

[0002]

2. Description of the Related Art Thermal type infrared sensors include a thermopile type and a bolometer type.

Conventionally, a thermopile type infrared sensor in which light receiving elements are arranged two-dimensionally is a MOS type transistor 2 in which a thermopile 1 (combination of a plurality of thermocouples) is operated in a weak inversion state as shown in FIG. The signal is read out by connecting directly to the gate. Here, one pixel is composed of a thermopile 1, a MOS transistor 2, and a charge storage unit 3, and one end 4 of the thermopile is a MOS transistor.
The other end 5 of the thermopile is connected to a second voltage source 6. The source of the MOS transistor 2 is a third voltage source 7
, And the drain is connected to the transfer gate 9 which is one of the components of the charge storage unit 3 and the charge readout unit 8.

FIG. 4 is an overall configuration diagram of an infrared sensor in which pixels are two-dimensionally arranged and the configuration of a charge reading section 8 is shown. In the figure, one end of a charge storage section 3 is connected to a transfer gate 9 arranged corresponding to each pixel, and a vertical CCD 1 is provided corresponding to the transfer gate 9.
0 is provided. A horizontal CCD 11 is provided at an end of the vertical CCD 10 in the transfer direction.
An output section 12 is formed at the end in the transfer direction. Transfer gate 9, vertical CCD 10, horizontal CCD 1
1, the output section 12 constitutes the charge reading section 8. The thermopile 1, the MOS transistor 2,
Each pixel and the charge readout unit 8 configured by the charge storage unit 3 are formed on the same silicon substrate (semiconductor substrate).

The operation of the infrared sensor will be described with reference to FIGS. In FIG. 3, the temperature of the contact portion of the thermopile 1 increases in accordance with the amount of incident infrared rays, thereby generating an electromotive voltage in the thermopile 1. This electromotive voltage is added to the second voltage source 6 and applied to the gate of the MOS transistor 2 to change the drain current.
This drain current is stored in the charge storage unit 3 for a certain period of time. When the accumulation time ends, the transfer gate 9 is turned on, and the accumulated charges are transferred from the charge accumulation unit 3 to the charge readout unit 8 using a scanning circuit called a CCD type. As shown in FIG. 4, in the charge reading section 8, when the transfer gate 9 is turned on, the signal charge is changed to the vertical CC.
At the same time as the transfer to D10, the potential of the charge storage section 3 is reset to the channel potential of the transfer gate 9. Thereafter, the transfer gate 9 is turned off, and the next accumulation starts. In the accumulation period, the signal charges transferred to the vertical CCD 10 are sequentially transferred to the output unit 12 by the action of the vertical CCD 10 and the horizontal CCD 11, and the signal is taken out. The charge reading section 8 includes a transfer gate 9, a vertical CCD 10, a horizontal CCD 11, and an output section 12.

[0006]

SUMMARY OF THE INVENTION As in the prior art,
When the electromotive voltage of the thermopile is directly connected to the gate of the MOS transistor, the current flowing into the charge storage unit is MO
There is a problem that the portion due to the bias voltage applied to operate the S-type transistor is large, and the ratio of the signal current due to the electromotive voltage of the thermopile is small. Therefore, the output voltage of the signal is low and the shot noise determined by the charge storage capacity is relatively high, and high sensitivity cannot be obtained.
Further, there is a drawback that external induction noise is easily picked up and sensitivity is deteriorated.

Further, in the conventional method, the output voltage of each pixel is apt to be affected by the variation of the threshold voltage of the MOS type transistor with respect to the incidence of infrared rays having the same intensity, and the fixed pattern noise is large. Was. For this reason, when an infrared image is obtained, there is a problem that the image quality is significantly deteriorated.

Although the thermopile type infrared sensor has been described above, the situation is the same for the bolometer type infrared sensor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is intended to increase the output voltage of a signal and reduce the influence of variations in the threshold voltage of a MOS transistor. An object of the present invention is to provide a thermal infrared sensor having high sensitivity and good image quality.

[0010] Other objects and novel features of the present invention will be clarified in embodiments described later.

[0011]

In order to achieve the above object, a first thermal infrared sensor according to the present invention comprises a plurality of thermopiles arranged two-dimensionally on a main surface of a substrate, and a plurality of thermopiles. A bar provided on the substrate corresponding to
Bipolar transistors and their respective bipolar transistors
A MOS transistor provided in the substrate corresponding to the register, and each of the MOS-type transistor charge storage part provided on the substrate in correspondence with, provided on the substrate corresponding to each of the charge storage portion a thermal type infrared sensor comprising a charge readout portions, said bipolar DOO
An emitter of the transistor is connected to one end of the thermopile, a base of the bipolar transistor is connected to a first voltage source, and a collector of the bipolar transistor is connected to a source of the MOS transistor ;
The drain of the MOS transistor is connected to the charge storage section.
Connected to the bipolar transformer by the first voltage source.
The collector junction of the transistor is reverse-biased .

A second thermal type infrared sensor according to the present invention comprises:
A plurality of bolometers two-dimensionally arranged on the main surface of the substrate, connected in series to each bolometer, and a resistor provided on the substrate, connected to a subsequent stage corresponding to each bolometer, and A bar provided on the substrate
Bipolar transistors and their respective bipolar transistors
A MOS transistor provided in the substrate corresponding to the register, and each of the MOS-type transistor charge storage part provided on the substrate in correspondence with, provided on the substrate corresponding to each of the charge storage portion a thermal type infrared sensor comprising a charge readout portions, said bipolar DOO
An emitter of the transistor is connected to one end of the bolometer, a base of the bipolar transistor is connected to a first voltage source, a collector of the bipolar transistor is connected to a source of the MOS transistor ,
The drain of the MOS transistor is in contact with the charge storage section.
Connected to the bipolar transistor by the first voltage source.
It is characterized in that the collector junction of the transistor is reverse-biased .

[0013]

[0014]

[0015]

The effect of the present invention that the output voltage of a signal is increased and that the variation in the output voltage due to the variation in the threshold voltage of the MOS transistor can be reduced will be described in detail with reference to FIG.

In FIG. 5, one pixel includes a thermopile 13, a bipolar transistor 14, a MOS transistor 15, and a charge storage section 16. For explanation purposes, the bipolar transistor 14 used here is a PNP type. The components of the pixel are connected as follows. That is, one end 17 of the thermopile is connected to the emitter region 18 of the bipolar transistor 14, and the other end 19 of the thermopile is connected to the second voltage source 20. Second voltage source 20
Is applied to the emitter junction 21 of the bipolar transistor 14 so as to be forward biased. The base region 22 of the bipolar transistor 14 is connected to a first voltage source 23. The first voltage source 23 is connected to the collector junction 2
4 is applied so as to have a reverse bias. Collector region 25 is connected to the source of MOS transistor 15. The drain of the MOS transistor 15 is connected to the charge storage unit 16 and the charge readout unit 26, and the gate is connected to the third
Is connected to the voltage source 27.

The output voltage of the signal in the infrared sensor is
The higher the portion of the limited accumulated charge amount due to the signal voltage which is the electromotive voltage of the thermopile, the higher the amount. Most of the electric charge accumulated in the electric charge accumulating unit 16 is due to the emitter current _IE , and _IE is the sum of the electric current by the second voltage source 20 and the electric current by the signal voltage. Emitter junction 21 in bipolar transistor 14 used in the present invention
The reverse saturation current I ₀₁ is relatively large at 10 ⁻⁸ amperes or more. By doing so, the differential resistance of the emitter junction 21 during operation decreases, and the signal current for the same signal voltage increases. Note that the current from the second voltage source 20 can be adjusted to an appropriate amount by adjusting the voltage. The base current I _B of the bipolar transistor 14 so flows to the charge storage unit 16 is additive to the emitter current I _E, I _B to increase the amount of stored charge by I _E must be reduced. Therefore, there is a need to reduce the reverse saturation current I ₀₂ of the collector junction 24 which determines the magnitude of the I _B, the practical ^10-9 amperes is appropriate.

According to the present invention, if I ₀₁ -I _B > 0, and therefore approximately I ₀₁ > I ₀₂ , the amount of signal charges stored in the charge storage unit 16 is larger than in the conventional method, and the signal output voltage is higher. Will be higher. Such a condition can be realized by adjusting the amount of impurity doping or the area of the junction in each region of the bipolar transistor 14 and utilizing a hetero junction such as a Ge junction on Si.

Next, a description will be given of how the variation in the output signal due to the variation in the threshold voltage of the MOS transistor 15 can be reduced. In FIG. 5, the second voltage source 23 and the third voltage source 27 are adjusted so that the collector junction 24 of the bipolar transistor 14 is in the reverse saturation current region. In this state, the base current I _B of the bipolar transistor 14, the base - the voltage between the collector hardly changes vary. Variation in the threshold voltage of the MOS transistor 15, the base of the bipolar transistor 14 - affects the voltage applied between the collector, the amount of charges stored in the base current I _B thus charge accumulation portion 16 the reasons aforementioned MOS type It is hardly affected by variations in the threshold voltage of the transistor 15.

Although FIG. 5 shows the case where a PNP type bipolar transistor is used, the situation is the same even when an NPN type bipolar transistor is used.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a thermal infrared sensor according to the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show a first embodiment of the present invention. FIG. 1 shows the components of one pixel in the thermal infrared sensor, and FIG. 2 shows the entire thermal infrared sensor showing two-dimensionally arranged pixels and a charge readout unit for reading out the signal of each pixel. It is a block diagram. In FIG. 1, components denoted by the same symbols as those in FIG. 5 indicate the same components. In addition, there are two types of charge readout units, CC
There is a first charge readout unit using a D-type scanning circuit and a second charge readout unit using a MOS-type scanning circuit. The components of the pixel in the present invention are shown in FIG.
As shown in FIG. 3, a thermopile 13, a bipolar transistor 14, a MOS transistor 15, a charge storage section 16
And are connected as follows. That is, one end 17 of the thermopile is connected to the emitter of the bipolar transistor 14, and the other end 19 of the thermopile is connected to the second voltage source 20. The second voltage source 20 applies a forward bias to the emitter junction of the bipolar transistor 14. Bipolar transistor 14
Are connected to a first voltage source 23. The first voltage source 23 applies a reverse bias to the collector junction. The collector is connected to the source of the MOS transistor 15. The first voltage source 23 or the second voltage source 20 can be grounded. The gate of the MOS transistor 15 is connected to the third voltage source 27, and the drain is connected to the source of the transfer gate 28 which is one of the components of the charge storage unit 16 and the first charge readout unit 29. The first voltage source 23, the second voltage source 20, and the third voltage source 27 are commonly connected to each pixel. In addition, as the charge storage unit 16, a MOS capacitor, a junction capacitor, or a stack capacitor used in a dynamic RAM is used.

FIG. 2 shows a two-dimensional array of pixels and a CCD.
FIG. 2 is a configuration diagram of the entire thermal infrared sensor showing the configuration of a first charge readout unit 29 called a mold. In the figure, one end of the charge storage section 16 is connected to the source of a transfer gate 28 arranged corresponding to each pixel, and an embedded vertical CCD 30 is provided corresponding to the transfer gate 28. The channel of the vertical CCD 30 also serves as the drain of the transfer gate 28. A horizontal CCD is provided at the end of the vertical CCD 30 in the transfer direction.
31 are provided. Further, a floating diffusion layer type output section 32 is formed at an end of the horizontal CCD 31 in the transfer direction. Transfer gate 28, vertical CCD 30, horizontal CCD 31,
The output unit 32 constitutes a first charge readout unit 29.

In this thermal infrared sensor, each pixel constituted by the thermopile 13, the bipolar transistor 14, the MOS transistor 15, and the charge storage section 16 and the first charge readout section 29 have the same silicon substrate (semiconductor substrate). ) Is formed.

FIG. 1 shows the operation of this thermal infrared sensor.
This will be described in detail with reference to FIG. In FIG. 1, the temperature of the contact portion of the thermopile 13 rises in accordance with the amount of incident infrared rays, thereby generating an electromotive voltage in the thermopile 13. This electromotive voltage is added to the second voltage source 20 to change the emitter current of the bipolar transistor 14.
The sum of the emitter current and base current I _B flows to the collector current I _A, and the charge storage portion 16 through the MOS transistor 15 in the ON state of the bipolar transistor 14. This current is accumulated in the charge accumulation section 16 during the accumulation period, and becomes a signal charge. At this time, the MOS transistor 15 is used for turning on and off the current flowing into the charge storage section 16 by adjusting the voltage of the third voltage source 27, but may also be used for adjusting the amount of current in some cases. When the accumulation period ends, the MOS transistor 15 is turned off and the transfer gate 28 is turned on, and the accumulated signal charges are transferred from the charge accumulation unit 16 to the first charge readout unit 29. As shown in FIG. 2, when the transfer gate 28 is turned on, the signal charges are transferred to the vertical CCD 30 and at the same time, the potential of the charge storage section 16 is reset to the channel potential of the transfer gate 28. After that, the transfer gate 28 is turned off, and the next accumulation starts. During the accumulation period,
By the operation of the vertical CCD 30 and the horizontal CCD 31, the signal charges transferred to the vertical CCD 30 are sequentially transferred to the output unit 32, and the signal is extracted to the outside.

FIGS. 6 and 7 are explanatory diagrams of a second embodiment of the present invention. Those indicated by the same symbols as those in FIG. 1 indicate the same components. In this embodiment, as shown in FIG. 6, the pixel is composed of a thermopile 13, a bipolar transistor 14, a MOS transistor 15, and a charge storage section 16, as in the first embodiment shown in FIG. This is a thermal infrared sensor using a second charge readout unit 33 called a MOS type for charge readout. The difference from the thermal infrared sensor shown in the first embodiment lies in the method of reading out the signal charges stored in the charge storage unit 16, which will be described. In FIG. 7, a vertical switch 34 is formed corresponding to the charge storage unit 16. The vertical switch 34 is formed by a MOS transistor. The source is connected to the charge storage unit 16, and the gate is commonly connected to the tap of the vertical shift register 35 that generates a pulse delayed in a horizontal period for each row. The drains of the vertical switches 34 are commonly connected to a vertical signal line 36 for each column. The horizontal switch 37 corresponding to the vertical signal line 36
Are formed. The horizontal switch 37 is a MOS transistor. The source is connected to the vertical signal line 36, and the gate is connected to each tap of the horizontal shift register 38. The drain is commonly connected to the output line 39. In this embodiment, a vertical switch 34, a vertical shift register 35, a vertical signal line 36, a horizontal switch 3
7, the horizontal shift register 38 and the output line 39
Of the charge readout unit 33.

Each pixel comprising a thermopile 13, a bipolar transistor 14, a MOS transistor 15, and a charge storage section 16, and a second charge read section 33
Are formed on the same silicon substrate (semiconductor substrate).

The operation of the pixel in this thermal infrared sensor is the same as that of the first embodiment.
The method for reading out the electric charge accumulated in No. 6 will be described. 7, when a certain tap of the vertical shift register 35 is turned on, the vertical switch 34 in the row connected to this tap is turned on, and the signal charge is stored in the corresponding vertical charge register. The signal is read out to the signal line 36. This signal charge is sequentially read out to the output line 39 via the horizontal switch 37 by each tap output from the horizontal shift register 38. When all the signals of the charge storage section 16 corresponding to a certain tap of the vertical shift register 35 are read out, the vertical shift register 35 advances by one row to turn on the next tap, and at the same time, the row of the row corresponding to that tap is turned on. Charge storage unit 1
6 are read out to the corresponding vertical signal lines 36. Thereafter, by repeating the same operation, the signal charges stored in the charge storage unit 16 can be read for each row. After the signal charge is transferred to the vertical signal line 36 and the potential of the charge storage unit 16 is reset, the next storage period starts after the vertical switch 34 is turned off.

In this thermal infrared sensor, the operation of each pixel is the same as in the first embodiment, and the signal readout section has the same function. Therefore, the magnitude of the output voltage of the signal and the MOS transistor The effect on the effect of the variation in the threshold voltage of No. 15 is the same as that of the first embodiment.

FIG. 8 shows a third embodiment of the present invention. Those indicated by the same symbols as those in FIG. 1 indicate the same components. One pixel of the thermal infrared sensor in this embodiment includes a bipolar transistor 14, a MOS transistor 15, a charge storage unit 16, a bolometer 40, and a resistor 4.
1 and these pixels are two-dimensionally arranged. An infrared sensor using the first charge readout unit 29 described in the first embodiment for reading out signals from each pixel. The difference from the infrared sensor shown in the first embodiment lies in the components of the pixel and the operation thereof. As shown in FIG. 8, each component of the pixel is connected to one end 42 of the bolometer by the bipolar transistor 1.
4 and the other end 43 of the bolometer is connected to a fourth voltage source 44. The fourth voltage source applies a forward bias to the emitter junction of the bipolar transistor 14. A resistor 41 having a resistance substantially equal to that of the bolometer 40 is connected to one end 42 of the bolometer, and the other end of the resistor is connected to a fifth voltage source 45. The base of the bipolar transistor 14 is connected to the first voltage source 23. The first voltage source applies a reverse bias to the collector junction of the bipolar transistor 14. The collector of the bipolar transistor 14 is connected to the source of the MOS transistor 15,
The drain of the OS-type transistor 15 is connected to the charge storage section 16 and the drain of the transfer gate 28, and the gate is connected to the third voltage source 27. First voltage source 23, third voltage source
Voltage source 27, fourth voltage source 44 and fifth voltage source 45
Is commonly connected to each pixel. For charge reading, the first charge reading unit 29 using the CCD-type scanning circuit described in the first embodiment is used.

In this thermal infrared sensor, each pixel including the bipolar transistor 14, the MOS transistor 15, the charge storage section 16, the bolometer 40, and the resistor 41, and the first charge readout section 29 have the same silicon substrate ( Semiconductor substrate).

This thermal infrared sensor operates as follows. The temperature of the bolometer 40 rises according to the amount of incident infrared rays, thereby changing the resistance value of the bolometer 40. This change in resistance changes the current flowing through the bolometer 40 and the resistor 41, and eventually changes the potential of the emitter of the bipolar transistor 14. This potential change acts on the bipolar transistor 14 in the same manner as the electromotive voltage of the thermopile 13 in the first embodiment.
It acts on the S-type transistor 15, the charge storage section 16, and the first charge readout section 29. Therefore, the effect of the magnitude of the output voltage of the signal and the influence of the variation in the threshold voltage of the MOS transistor 15 are the same as those in the first embodiment.

In this thermal infrared sensor, the first voltage source 23 and the fifth voltage source 45 are adjusted so that the base potential of the bipolar transistor 14 becomes slightly lower than the emitter potential. As a result, the dark current component of the emitter current decreases, so that the signal current component increases due to a rise in the emitter potential due to the incidence of infrared rays.
Higher sensitivity.

In this embodiment, the charge is read out using C
Although the first charge readout unit 29 using the CD type scan circuit is used, the same effect can be obtained by using the second charge readout unit 33 using the MOS type scan circuit.

[0035]

Although the present invention has been described with respect to the case where infrared light receiving elements such as thermopiles are two-dimensionally arranged, one-element or one-dimensionally arranged infrared sensors can be two-dimensionally arranged by changing the signal reading section. The effect is similar to that of the array.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the embodiments and that various modifications and changes can be made within the scope of the claims. There will be.

[0038]

According to the thermal infrared sensor of the present invention, by adding a new bipolar transistor to the conventional pixel configuration, the output voltage of the signal can be reduced by 10 compared with the conventional method.
It can be increased by about 0 times. Therefore, there is an advantage that the shot noise determined by the charge storage capacity can be relatively reduced, and the sensitivity is increased. Further, there is an advantage that the influence on external induction noise can be reduced.

Further, in the conventional method, there is a problem of generation of fixed pattern noise due to variation in threshold voltage of the MOS transistor. However, according to the present invention, there is an advantage that this effect can be greatly reduced. It is possible to obtain a high quality image.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a pixel of a thermal infrared sensor according to a first embodiment of the present invention.

FIG. 2 is a schematic plan view of a charge reading unit of the thermal infrared sensor according to the first embodiment of the present invention.

FIG. 3 is a schematic plan view of a pixel of a conventional thermal infrared sensor.

FIG. 4 is a schematic plan view of a charge reading section of a conventional thermal infrared sensor.

FIG. 5 is a schematic plan view of a pixel according to the first embodiment of the present invention.

FIG. 6 is a schematic plan view of a pixel of a thermal infrared sensor according to a second embodiment of the present invention.

FIG. 7 is a schematic plan view of a charge reading section of a thermal infrared sensor according to a second embodiment of the present invention.

FIG. 8 is a schematic plan view of a thermal infrared sensor according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 thermopile 14 bipolar transistor 15 MOS transistor 16 charge accumulation part 17 one end of thermopile 19 the other end of thermopile 20 second voltage source 23 first voltage source 26 charge readout part 29 first charge readout part 33 second charge Readout unit 40 Bolometer 41 Resistance 42 One end of Bolometer 43 The other end of Bolometer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI G01J 5/24 G01J 5/24 5/48 5/48 D

Claims (2)

(57) [Claims] A plurality of thermopiles arranged two-dimensionally on a main surface of a substrate; a bipolar transistor provided on the substrate corresponding to each of the thermopiles ;
It is installed on the substrate corresponding to each bipolar transistor.
Comprising: a MOS type transistor kicked, a charge storage part provided in the substrate in correspondence to each of the MOS transistors, and a charge reading section provided on the substrate corresponding to each of the charge storage portion thermal infrared sensor der
I, the emitter of the bipolar transistor is connected to one end of the thermopile, <br/> base of the bipolar transistor is connected to a first voltage source, the bipolar tiger
The collector of the transistor is connected to the source of the MOS transistor, and the drain of the MOS transistor is
The first voltage source is connected to the charge storage unit,
The collector junction of the bipolar transistor is reverse biased
Thermal infrared sensor, characterized in that it is. 2. A plurality of bolometers two-dimensionally arranged on a main surface of a substrate, a resistor connected to each bolometer in series and provided on the substrate, and a subsequent stage corresponding to each bolometer. And a bipolar transistor connected to the substrate and provided on the substrate.
M provided on the substrate corresponding to the polar transistor
A thermal infrared ray comprising: an OS transistor; a charge storage unit provided on the substrate corresponding to each MOS transistor; and a charge readout unit provided on the substrate corresponding to each charge storage unit. a sensor, the emitter of the bipolar transistor is connected to one end of the bolometer, base <br/> chromatography scan of the bipolar transistor is connected to a first voltage source, the bipolar Trang
The collector of the transistor is connected to the source of the MOS transistor, and the drain of the MOS transistor is connected to the front.
The first voltage source is connected to the charge storage unit.
Bipolar transistor collector junction is reverse biased
Thermal infrared sensor, characterized by being.