JP2734226B2 - Infrared sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermopile infrared sensor.

[0002]

2. Description of the Related Art Thermopile infrared sensors use two types of thermoelectric materials. Conventionally, the Dictionary of Physical and Chemical Sciences (4th edition) 48
According to page 6, combinations of bismuth and antimony, chromel and constantan, and iron and constantan have been used. Also, P.I. M. Sarro and A. W. V. H
erwaarden 「InfraredDetect
or Based on an Integrated
Silicon ThermoPile ”(Proc
According to the teachings of SPIE 807, pp. 113-118), p-type silicon and aluminum are used. C.I. Shibata,
C. Kimura and K.M. Mikami 「Fa
r Infrared Sensor with Th
thermoPile Structure "(Proce
eding of the 1stSensor Sy
According to mPosium 1981, pp. 211-255), tellurium and indium antimony are used.

[0003] Japanese Patent Application No. 1-40769 filed by the present applicant discloses the use of p-type and n-type semiconductors as thermoelectric materials. In particular, when p-type and n-type silicon are used, a silicon IC manufacturing technique can be advantageously used. FIG. 2 is a plan view (FIG. 2A) and a cross-sectional view (FIG. 2B) of a thermopile infrared sensor using p-type and n-type silicon as a thermoelectric material. A silicon nitride film 2 formed by a CVD method or a plasma CVD method is formed on a silicon substrate 1 having a plane orientation of (100), and a silicon substrate below a central portion of the nitride film 2 is etched into a truncated pyramid shape. , A cavity 3 is formed. The film covering the upper surface of the cavity 3 is called a diaphragm 4. An n-type silicon film 5 and a p-type silicon film 6 as thermoelectric materials are formed on nitride film 2. The contact portion 7 has a metal layer such as aluminum, and the n-type silicon film 5 and the contact portion 7 form an ohmic contact with the p-type silicon film 6 and the contact portion 7, respectively. In the thermopile, a hot contact of the contact on the diaphragm 4 and a contact provided on the silicon substrate outside the diaphragm region 4 are called a cold contact. Increasing the number of these contacts increases the sensitivity of the thermopile, so that the pattern has a serpentine pattern as shown in the figure. In order to protect the n-type silicon film 5, the p-type silicon film 6, and the contact portion 7, a protection film 8 of a silicon nitride film or a silicon oxide film is formed. A slit 9 is formed in the protective film 8 and the nitride film 2. The slit 9 is located on a diagonal line of the diaphragm area 4. The cavity 3 is formed from the slit 9 using an anisotropic etching solution. The protective film 8 and the nitride film 2 have the purpose of protecting the n-type silicon film 5, the p-type silicon film 6, and the contact portion 7 from the anisotropic etching solution.

An example in which thermopiles are arranged one-dimensionally or two-dimensionally to constitute an infrared image sensor is disclosed in I.I. H. Ch
oi and K. D. Wise's "A Silicon-Th"
erotic-Based Infrared S
sensing Arrayfor Use in Au
tomated Manufacturing "(IE
EE Transactions on Electr
on Devices ED-33, 1986, 72-
79 pages) with 8 × 1 pixels and 16 × 2 pixels. However, each of them has a disadvantage that the configuration is not suitable when the number of pixels is small and the number of pixels is large.
Therefore, a configuration suitable for a case where the number of pixels is large has been required.

In Japanese Patent Application No. 2-83480 filed by the present applicant, an electromotive voltage of a thermopile is input to the gate of a MOSFET.
The drain current of the MOSFET is modulated by the electromotive voltage. The storage operation is performed by providing a capacitor for storing the drain current. Thermopile and MOSFET
And a unit pixel having a capacitor. The reading of signal charges from each capacitor is performed by using a CCD image sensor or MO
This is performed in the same manner as the S-type image sensor. This method is suitable for a case where the number of pixels is large.

[0006]

However, the thermopile infrared sensor has lower sensitivity than the quantum infrared sensor. Therefore, a configuration that can be applied even when the number of pixels is large and has high sensitivity has been required.

[0007]

SUMMARY OF THE INVENTION There are three infrared sensors of the present invention. One is a plurality of diaphragm regions provided on the main surface of the semiconductor substrate; the diaphragm region has one contact group; the other has a contact group outside the diaphragm region; A MOS type transistor having a source connected to the other end of the thermopile, a gate connected to the second voltage source, and a drain serving as a charge storage unit; And a charge readout unit provided correspondingly to the infrared sensor.

[0008] The second is a plurality of diaphragm regions provided on the main surface of the semiconductor substrate; one contact group in the diaphragm region, the other contact group outside the diaphragm region, one end A thermopile connected to a first voltage source; a CCD provided corresponding to the plurality of diaphragm areas; a source connected to the other end of the thermopile, and a gate connected to the second voltage source; An infrared sensor having a configuration in which a drain has a MOS transistor serving as a channel of the CCD.

Third, a plurality of diaphragm regions arranged two-dimensionally on the main surface of the semiconductor substrate; one contact group in the diaphragm region, and the other contact group outside the diaphragm region. A thermopile connected to a first voltage source; a first vertical CCD provided corresponding to the plurality of diaphragm areas; a source connected to the other end of the thermopile, and a gate connected to the other end. A MOS transistor connected to the second voltage source, the drain of which is the channel of the first vertical CCD; and a second vertical CCD connected in series to the first vertical CCD and having a number of transfer stages equal to or greater than the number of transfer stages of the first vertical CCD. And; the first vertical CC of the second vertical CCD
Horizontal C provided corresponding to the end not connected to D
An infrared sensor having a configuration including a CD and an output unit provided at an end of a horizontal CCD in a transfer direction.

[0010]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic plan view of a first embodiment of the present invention. The first embodiment is an infrared sensor in which a large number of thermopiles as shown in FIG. 2 are two-dimensionally arranged, and a charge storage section and a scanning circuit are integrated on a silicon main surface. In the figure, a large number of thermopiles 10 are two-dimensionally arranged. The thermal contacts of the thermopile 10 are formed on a diaphragm. One end 11 of the thermopile 10 is commonly connected to a first voltage source 12. One MOS transistor 14 is formed corresponding to each thermopile 10. The other end 13 of the thermopile 10 is MOS
It is connected to the source of the type transistor 14. MOS
The gates of the type transistors 14 are commonly connected to a second voltage source 15. The first voltage source 12 can be set to the potential of the silicon substrate, that is, the ground. further,
Each pixel is provided with a charge storage section 16. As the charge storage section 16, a MOS capacitance, a junction capacitance, a stack capacitance or a trench capacitance used in a dynamic RAM is used. The drain of the MOS transistor 14 is connected to the charge storage section 16 and the source of a transistor gate 17 provided in each pixel. An embedded vertical CCD 18 is provided corresponding to the transfer gate 17. The channel of the vertical CCD 18 also serves as the drain of the transfer gate 17. Also, vertical CC
A part of one electrode of D18 may be a surface type channel and also serve as the transfer gate 17. Vertical C
A horizontal CCD 19 is provided at the end of the CD 18 in the transfer direction. Further, a floating diffusion layer type output section 20 is formed at an end of the horizontal CCD 19 in the transfer direction. The transistor gate 17, the vertical CCD 18, the horizontal CCD 19, and the output unit 20 form a read unit.

In this infrared sensor, the temperature of the diaphragm rises in accordance with the amount of incident infrared rays, thereby generating an electromotive voltage in the thermopile 10. The polarity of the electromotive voltage generated at the other end 13 of the thermopile with respect to the one end 11 of the thermopile 10 can be selected by switching the connection. This electromotive voltage is added to the first voltage source 12 and applied to the source of the MOS transistor 14 to change the drain current. When the MOS transistor 14 is of an n-channel type, when the voltage at the other end 13 of the thermopile changes in the negative direction, the drain current increases and changes in the positive direction.

The thermopile 10 is made of two kinds of thermoelectric materials, each having an electric resistance, and the electric resistance has a temperature characteristic. Generally, as the temperature rises, the electrical resistance of a semiconductor decreases, and the opposite is true for a metal. As apparent from FIG. 1, the electric resistance of the thermopile 10 can be regarded as a parasitic resistance added to the source of the MOS transistor 14. As the electric resistance of the thermopile 10 increases, the drain current decreases.

Since the drain current of the MOS transistor 14 changes due to the thermoelectromotive voltage of the thermopile 10 and the temperature change of the electric resistance, it is important to make the actions of the two in the same direction. That is, when the temperature of the diaphragm rises and the electric resistance of the thermopile 10 increases, when the MOS transistor 14 is an n-channel type, the electromotive voltage at the other end 13 of the thermopile is positive and the MOS transistor 14 is a p-channel type. At this time, the thermopile is connected so that the electromotive force at the other end 13 becomes negative. Conversely, when the temperature of the diaphragm rises and the electric resistance of the thermopile 10 decreases, when the MOS transistor 14 is an n-channel, the electromotive voltage at the other end 13 of the thermopile is negative and M
The connection is made so that the electromotive voltage at the other end 13 of the thermopile becomes positive when the OS type transistor 14 is a p-channel type.

This drain current is stored in the charge storage section 1 during the storage period.
6 and becomes signal charges. When the accumulation period ends,
The transfer gate 17 is turned on, the stored signal charges are transferred from the charge storage unit 16 to the vertical CCD 18, and the potential of the charge storage unit 16 is reset to the channel potential of the transfer gate 17. The transfer gate 17 is turned off, and the next accumulation period starts. During the accumulation period, the signal charges transferred to the vertical CCD 31 are sequentially transferred to the output unit 20 by the operation of the vertical CCD 18 and the horizontal CCD 19, and the signal is extracted to the outside.

The MOS transistor 14 is operated in a weak inversion state or a saturation region. Assuming that the maximum value of the drain current is I ₁ ampere and the accumulation period is T seconds, the maximum accumulated charge amount is I ₁ × T clone. It is necessary to set the charge storage unit 16, the vertical CCD 18, and the horizontal CCD 19 so that the charge amount can be stored and transferred.

FIG. 3 is a schematic plan view of a second embodiment of the present invention. In this embodiment, a large number of thermopiles are arranged two-dimensionally as shown in FIG.
This is an infrared sensor in which a scanning circuit called a mold is integrated on a silicon main surface. Those indicated by the same symbols as those in FIG. 1 indicate the same components. The difference from the infrared sensor shown in FIG. 1 lies in the method of reading out the signal charges stored in the charge storage unit 16.
Explain it.

The vertical switch 2 corresponding to the charge storage section 16
1 is formed. The vertical switch 21 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 22 that generates a pulse delayed in a horizontal period for each row. The drains of the vertical switches 21 are commonly connected to a vertical signal line 23 for each column. Vertical signal line 2
3 corresponds to a horizontal switch 24 of a MOS transistor.
Are formed. The source of the horizontal switch 24 is connected to the vertical signal line 23. The gate is connected to each tap of the horizontal shift register 25. The drain is commonly connected to the output line 26. The vertical switch 21, the vertical shift register 22, the vertical signal line 23, the horizontal switch 24, the horizontal shift register 25, and the output line 26 form a reading section.

In this infrared sensor, signal charges are stored in the charge storage section 16 during the storage period, similarly to the infrared sensor of the first embodiment. The accumulated signal charge is
When a certain tap of the vertical shift register 22 is turned on, the vertical switches 21 in the row connected to this tap are turned on, and the signal charges are respectively stored in the corresponding vertical signal lines 23.
Is read out. This signal charge is sequentially read out to the output line 26 via the horizontal switch 24 by each tap output from the horizontal shift register 25. When all the signals of the charge storage unit 16 corresponding to a certain tap of the vertical shift register 22 are read out, the vertical shift register 22 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. The signal charges in the charge storage unit 16 are read out to the corresponding vertical signal lines 23. 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 23 and the potential of the charge storage unit 16 is reset, the next storage period starts after the vertical switch 21 is turned off.

FIG. 4 is a schematic plan view of a third embodiment of the present invention. This embodiment is an infrared sensor in which a large number of thermopiles as shown in FIG. 2 are two-dimensionally arranged, and a vertical CCD for both charge accumulation and transfer is integrated on a silicon main surface. The configuration is close to that of a full frame type image sensor for visible light. Those indicated by the same symbols as those in FIG. 1 indicate the same components. In the figure, a large number of thermopiles 10 are two-dimensionally arranged. One end 11 of the thermopile 10 is commonly connected to a first voltage source 12. A MOS transistor 14 is formed corresponding to the thermopile 10. The other end 13 of the thermopile 10 is MOS
It is connected to the gate of the type transistor 14. MOS
The gates of the type transistors 14 are commonly connected to a second voltage source 15. The second voltage source 15 can be set to the potential of the silicon substrate, that is, the ground. further,
An embedded vertical CCD 27 is provided corresponding to the MOS transistor 14. The channel of the vertical CCD 27 also serves as the drain of the MOS transistor 14. A horizontal CCD 1 is provided at the end of the vertical CCD 27 in the transfer direction.
9 are provided. Further, a floating diffusion layer type output section 20 is formed at an end of the horizontal CCD 19 in the transfer direction.

In the infrared sensor of the first and second embodiments, the function of accumulating the signal charge performed by the charge storage section 16 is replaced by the vertical CCD 27 in the infrared sensor of the third embodiment.
Has done. The temperature of the diaphragm rises in response to the amount of incident infrared radiation, thereby generating an electromotive voltage in the thermopile 10. This electromotive voltage is added to the first voltage source 12 and applied to the source of the MOS transistor 14 to change the drain current. This drain current is accumulated in the vertical CCD 27 corresponding to the accumulation period and becomes a signal charge. When the accumulation period ends, the signal charges are transferred to the vertical CCD 27 and the horizontal CCD.
By the function of 19, the signal is sequentially transferred to the output unit 20, and the signal is taken out to the outside. The first voltage source 12 is pulse-driven, that is, during the accumulation period, the MOS transistor 14
During the period in which signal charges are transferred to a voltage at which the signal charges are operated in a weak inversion state or a saturation region.
The voltage of the first voltage source is set to a voltage at which the OS transistor 14 enters a cutoff state. Then, the signal charges do not mix with the signal charges of other pixels during transfer through the vertical CCD 27.

FIG. 5 is a schematic plan view of a fourth embodiment of the present invention. In this embodiment, a large number of thermopiles as shown in FIG. 2 are two-dimensionally arranged, and a first vertical CCD serving as a charge storage and a transfer and a second vertical CCD serving as a frame memory are provided on a silicon main surface. It is an integrated infrared sensor. The configuration is close to that of a frame transfer type image sensor for visible light. 1 and 4 denote the same components. Vertical CC of the third embodiment
The difference from the third embodiment is that a frame memory is provided between D27 and the horizontal CCD 19. That is, MO
The first vertical CCD 28 serves as a drain of the S-type transistor 14 and stores signal charges, in addition to the first vertical CCD 28.
A second vertical CCD 29 is provided in series in the transfer direction of. The number of transfer stages of the second vertical CCD 29 is the first vertical CC.
The number is set to be equal to or slightly larger than the number of transfer stages of D28.
The horizontal CCD 1 is located at the end of the second vertical CCD 29 in the transfer direction.
9 are provided.

In the infrared sensor of this embodiment, the first vertical CCD 28 stores signal charges. When the accumulation period ends, the signal charges accumulated in the first vertical CCD 28 are transferred to the second vertical CCD 29 by frame. Thereafter, accumulation of the next signal charge is started in the first vertical CCD 28. Further, signal charges are transferred from the second vertical CCD 29 to the vertical CCD 19 line by line, and are sequentially transferred to the output unit 20 by the operation of the horizontal CCD 19, and the signals are taken out to the outside. As in the third embodiment, when the voltage of the first voltage source 12 is set so that the MOS transistor 14 is in the cutoff state during the transfer operation of the first vertical CCD 28, a good output signal without mixing of signals is obtained. Is obtained.

[0024]

The thermopile type infrared sensor according to the present invention has an advantage that a chopper is not required as compared with a pyroelectric type sensor, and operates in a storage mode. The sensitivity is very good because both the temperature characteristics of the electric resistance and the electric resistance are used. Further, the present invention can be applied to a one-dimensional or two-dimensional image sensor having a large number of pixels.

The infrared sensor according to the present invention can be realized with either a p-type channel or an n-type channel.

[Brief description of the drawings]

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

FIGS. 2A and 2B are a plan view and a sectional view of a thermopile, respectively.

FIG. 3 is a schematic plan view of an infrared sensor according to a second embodiment of the present invention.

FIG. 4 is a schematic plan view of an infrared sensor according to a third embodiment of the present invention.

FIG. 5 is a schematic plan view of an infrared sensor according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 4 Diaphragm area 7 Contact 10 Thermopile 11 One end of thermopile 12 First voltage source 13 The other end of thermopile 14 MOS transistor 15 Second voltage source 16 Charge storage unit 17 Transfer gate 18, 27 Vertical CCD 19 Horizontal CCD Reference Signs List 20 output unit 21 vertical switch 22 vertical shift register 23 vertical signal line 24 horizontal switch 25 horizontal shift register 26 output line 28 first vertical CCD 29 second vertical CCD

Claims (3)

(57) [Claims] A plurality of diaphragm regions provided on a main surface of a semiconductor substrate; one contact group in the diaphragm region, and another contact group outside the diaphragm region; A MOS type transistor having a source connected to the other end of the thermopile, a gate connected to the second voltage source, and a drain serving as a charge storage unit; An infrared sensor comprising: a charge readout unit provided in the sensor. 2. A plurality of diaphragm regions provided on a main surface of a semiconductor substrate; one contact group in the diaphragm region, and another contact group outside the diaphragm region; A thermopile connected to a plurality of diaphragm areas; a CCD connected to the other end of the thermopile; a gate connected to a second voltage source; and a drain connected to the CCD.
And a MOS transistor as a channel of the infrared sensor. 3. A plurality of diaphragm regions two-dimensionally arranged on a main surface of a semiconductor substrate; one contact group in the diaphragm region, and another contact group outside the diaphragm region; A thermopile connected to a first voltage source; a first vertical CCD provided corresponding to the plurality of diaphragm areas; a source connected to the other end of the thermopile, and a gate connected to the second voltage source. A MOS transistor connected to the drain of the first vertical CCD and having a drain connected in series with the first vertical CCD;
The second vertical CCD having the number of transfer stages equal to or greater than the number of transfer stages of CD
A horizontal CCD provided corresponding to an end of the second vertical CCD that is not connected to the first vertical CCD;
And an output unit provided at an end in the transfer direction.