JP2001215152A - Infrared solid-state imaging element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared solid-state imaging element in which the temperature rise of a diode due to self-heating at a time when a current is made to flow to a pixel is compensated, and in which the temperature change of the pixel and that of a readout circuit due to a change in a substrate temperature are compensated. SOLUTION: The infrared solid-state imaging element is provided with effective pixels 24 wherein first absorption parts 106 which comprise first hollow structures 102, 103 formed on a semiconductor substrate 1 via a gap 104 and which absorb infrared rays emitted from a subject are formed and first detection parts 110 which are formed in the first hollow structures 102, 103, whose temperature is raised on the basis of heat by the infrared rays absorbed by the first absorption parts 106, and in which first detection parts 110 used to generate a detection signal according to the temperature are installed are formed. The imaging element is provided with reference pixels 25 which comprise second hollow structures 2, 3 formed on the semiconductor substrate 1 via a gap 4, which are formed in the second hollow structures 2, 3, whose temperature is raised when infrared rays by the effective pixels 24 are detected, and in which second detection parts 10 used to generate a reference signal according to the temperature, are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared solid-state imaging device using a thermal detector.

[0002]

2. Description of the Related Art Along with recent advances in silicon (Si) LSI technology, a large number of photodetectors are arranged in an array on a semiconductor substrate, and a signal charge readout circuit and an output amplifier are formed on the same substrate. Many solid-state imaging devices have been developed. Among these, infrared solid-state imaging devices using infrared detectors as photodetectors have been put into practical use as infrared cameras in combination with infrared lenses, drive circuits, signal processing circuits, etc., and are used for security, news, measurement, remote sensing, etc. It is used in various fields. Infrared detectors are roughly classified into quantum detectors and thermal detectors according to their light detection mechanisms. As the quantum detector, a compound semiconductor detector utilizing inter-band transition, a Schottky diode composed of a metal / semiconductor junction, or the like is used. The sensitivity is higher and the response speed is faster than that of a thermal detector. There are advantages.
However, these quantum detectors have an operating temperature of -200 ° C.
Since the temperature is extremely low, it is necessary to cool the element for imaging, and the imaging apparatus becomes large and expensive. On the other hand, thermal detectors do not require element cooling, so they are suitable for miniaturization and cost reduction of devices, and their development has rapidly progressed with the advancement of silicon micromachining technology.

The thermal detector forms a hollow structure thermally separated from a substrate above a semiconductor substrate, and detects a temperature change of the hollow structure when receiving an infrared ray emitted from a subject. . As means for detecting the temperature change, there is a bolometer system for detecting a resistance change by forming a bolometer on the hollow structure, or a PN junction diode is formed on the hollow structure to allow a forward current to flow. A diode method or the like for detecting a voltage change has been proposed.

FIG. 11 is a sectional view of a pixel showing a conventional structure of a diode type thermal detector using an SOI substrate as a semiconductor substrate. In FIG. 11, 101 is bulk Si of the SOI substrate, 102a and 102b are box oxide films of the SOI substrate, and 103 is a silicon thin film on the oxide film of the SOI substrate. The space 104 is formed below the box oxide film 102b by using silicon micromachining technology.
Is formed, and the box oxide film 102b and the silicon thin film 103 have a hollow structure so that the underlying bulk Si 10
1 and thermally separated. Here, 105 is the gap 10
4, and a part of the underlying bulk Si 101 is removed through the etching hole 105. Although not shown here, a PN junction diode is formed on the silicon thin film 103. Reference numeral 106 denotes an absorbing umbrella provided to increase the infrared absorption efficiency, and 107 denotes an umbrella support of the absorbing umbrella 106.

FIG. 12 is a plan view of a pixel of the conventional thermal detector shown in FIG. In FIG.
Is a hollow structure composed of the box oxide film 102b and the silicon thin film 103, 109 is a supporting leg composed of the box oxide film 102a for supporting the hollow structure 108, and 110 is formed in the silicon thin film 103 of the hollow structure 108. A plurality of PN junction diodes connected in series, 111 is a thin film wiring for electrically connecting the PN junction diode 110, and 112 is a thin film wiring 111 for a signal line (not shown).
This is a contact for making an electrical connection with the device. Also, 1
13 is an absorbing umbrella 10 formed above the hollow structure 108
6 denotes an area, and 114 denotes an area of the umbrella support 107 where the absorbing umbrella 106 contacts the hollow structure 108. Reference numeral 115 schematically shows a boundary of one pixel.

Next, an infrared detecting operation in a conventional thermal detector will be described with reference to FIGS. When the infrared rays emitted from the subject enter the pixels, the infrared rays are absorbed by the absorbing umbrella 106, the temperature of the absorbing umbrella 106 rises, and heat is transmitted through the umbrella support 107, and the temperature of the hollow structure 108 is reduced. To rise. At this time, the hollow structure 10
When a constant forward current is applied to the diode 110 formed on the diode 8, the potential difference generated between both ends of the diode 110 depends on the temperature. Therefore, infrared rays can be detected by detecting a change in the voltage. Since a voltage change per diode due to a temperature change is minute, the sensitivity is improved by connecting a plurality of diodes in series in the conventional example of FIG.

In the above infrared detecting operation, the absorbing umbrella 1
Assuming that the infrared energy absorbed at 06 is ΔP, the temperature of the diode 110 is Td, the temperature of the underlying bulk Si 101 is Ts, and the thermal conductance of the support leg 109 is Gt, the infrared energy absorbed and the support Since the amount of heat released from the legs to the bulk Si 101 becomes equal, the following equation is established. ΔP = Gt (Td−Ts) (Equation 1) That is, the diode temperature is determined by the infrared energy incident on the detector and the temperature of the underlying bulk Si 101. However, since the temperature of the bulk Si 101 fluctuates due to the influence of ambient temperature, self-heating during element driving, and the like, in order to perform infrared detection with high sensitivity, the bulk Si 101 needs some method.
It is necessary to compensate for the temperature fluctuation. As a method,
A reference pixel for outputting temperature information of the bulk Si 101 is formed on the same substrate, and a pixel for detecting infrared rays (hereinafter, referred to as a pixel).
A method has been proposed in which a difference between two outputs of a valid pixel and a reference pixel is used as a pixel output.

FIG. 13 is a sectional view showing a conventional reference pixel for performing substrate temperature compensation. In FIG. 13, reference numeral 116 denotes bulk Si of the SOI substrate, 117 denotes S
The box oxide film on the OI substrate, 118 is a silicon thin film on the oxide film on the SOI substrate, and a diode is formed on the silicon thin film 118. Reference numeral 119 denotes an absorbing umbrella, and 120 denotes an umbrella support of the absorbing umbrella 119. Unlike the case of the effective pixel shown in FIG. 11, the reference pixel of FIG. 13 does not have a void under the silicon thin film 118 and does not have a hollow structure. Therefore, the diode temperature is always equal to the temperature of the bulk Si 116 irrespective of the presence / absence of infrared rays.

FIG. 14 is a block diagram showing a configuration of a conventional infrared solid-state imaging device which performs substrate temperature compensation using an effective pixel and a reference pixel. In FIG. 14, 12
1 is an effective pixel arranged in a two-dimensional array, 122 is a reference pixel provided for each column of the effective pixel array, 123a and 123b are power supply lines for applying a voltage to the effective pixel 121 and the reference pixel 122, 124a and 124b are vertical signal lines connected to the effective pixel 121 and the reference pixel 122;
Reference numerals a and 125b denote constant current sources for supplying a constant current to the effective pixel 121 and the reference pixel 122; 126, a differential amplifier circuit; 127, an integration circuit; 128, a vertical scanning circuit; 129, a horizontal scanning circuit; MOS transistors, 131 is a horizontal signal line, and 132 is an output amplifier.

Next, the operation of the conventional infrared solid-state imaging device will be described with reference to FIG. First, one of the power supply lines 123a is selected by the vertical scanning circuit 128, and the voltage V is applied to the diode in the selected row. The current flowing through each diode is controlled to a constant value by a constant current source 125a. At this time, a potential difference Vd is generated between both ends of each diode according to the diode temperature determined by the incidence of infrared rays, and the potential of the vertical signal line 124a becomes V-Vd. On the other hand, the voltage V is also applied to the reference pixel 122 via the power supply line 123b, and the constant current source 125b allows the same constant current as the effective pixel to flow to the diode of the reference pixel. At this time, since the diode temperature of the reference pixel is equal to the substrate temperature, a potential difference Vs occurs between both ends of the diode of the reference pixel according to the substrate temperature, and the potential of the vertical signal line 124b becomes V-Vs. Outputs from the two pixels are output to a differential amplifier circuit 126 provided for each column.
And differentially amplified by the integrating circuit 127. next,
When one horizontal selection MOS transistor 130 is selected by the horizontal scanning circuit 129, the differential output of the corresponding pixel is output to the outside of the element via the horizontal signal line 131 and the output amplifier 132. By scanning the vertical scanning circuit 128 and the horizontal scanning circuit 129, the output from each pixel arranged in an array is read out in time series to obtain a two-dimensional infrared image.

FIG. 15 is a block diagram showing an example of the configuration of a readout circuit provided for each column in the conventional infrared solid-state imaging device shown in FIG. In FIG. 15, 133a and 133b are input MOS transistors, 134 is a constant current MOS transistor,
A portion surrounded by a circle corresponds to the differential amplifier circuit 126 in FIG. 135 is the integral capacity, 136 is the integral capacity 135
Reset transistor, 137 is an integration control MOS transistor, and 138 is a sample and hold circuit (S / H)
The portion surrounded by a dotted line 127 corresponds to the integrating circuit 127 in FIG. 130 is a horizontal selection MOS transistor, 131 is a horizontal signal line, and 132 is an output amplifier. The other reference numerals in FIG. 15 are the same as those shown in FIG.

Next, a reading operation for each column in the conventional infrared solid-state imaging device will be described with reference to FIG. First, the integration control MOS transistor 137 is turned off.
In the state of F, the reset transistor 136 is turned on,
The potential of the integration capacitor 135 is reset to the potential Vr. Next, when the effective pixel 121 is selected by vertical scanning and a constant current flows through the diode, the input MOS transistor 13
The gate potential of 3a becomes V-Vd. On the other hand, when the same constant current flows through the reference pixel 122, the gate potential of the input MOS transistor 133b becomes V-Vs. When the integration control MOS transistor 137 is turned on in this state, the input MOS transistor 133 is output from the integration capacitor 135.
A discharge current flows through a, and the current value I is given by I = α (Vs−Vd) + Ic / 2 (Equation 2). Here, α is an amplification factor determined by a transistor constituting the differential amplifier circuit, and Ic is a constant current flowing through the constant current MOS transistor 134. Next, the integration control transistor 137 is turned off after a certain integration time t has elapsed.
Then, the discharge causes the potential Vc of the integration capacitor 135 to decrease, and Vc = Vr−I × t / C (Equation 3). Next, after sampling the potential of the integration capacitor 135 for each column by the sample and hold circuit 138,
When the horizontal selection MOS transistors 130 are sequentially turned on by horizontal scanning, the output of the sample and hold circuit 138 is read out to the outside via the output amplifier 132. Since the pixel output obtained by the above read operation is a differential output between the effective pixel 121 and the reference pixel 122, the influence of the substrate temperature fluctuation is canceled.

[0013]

However, the conventional infrared solid-state imaging device has the following problems. First, when a constant current Id is passed through a diode, Joule heat of Id ＾ 2 × Rd is generated when the forward resistance of the diode is Rd. Since the effective pixels have a hollow heat insulating structure, the temperature of the diode increases due to the self-heating regardless of the incidence of infrared rays. on the other hand. Since the conventional reference pixel does not have a heat insulating structure, the generated Joule heat escapes to bulk Si, and the diode temperature does not rise. For this reason, in the conventional infrared solid-state imaging device, there is a problem that although the fluctuation of the substrate temperature can be offset, the diode temperature difference due to self-heating is not compensated. In order to increase the sensitivity of the device, it is necessary to reduce the readout noise by increasing the integration time (that is, the current supply time to the diode). However, the longer the current supply time, the higher the temperature of the effective pixel due to self-heating. Become more noticeable, and this problem is further exacerbated. Further, in the conventional infrared solid-state imaging device, the detector is compensated for the substrate temperature fluctuation, but the readout circuit such as the differential amplifier is not compensated. For this reason, when the substrate temperature fluctuates, characteristics such as the threshold voltage of the transistors constituting the circuit change, and a problem such as a temperature drift of the element output occurs. As a countermeasure, there is a method of using a Peltier element or the like to keep the substrate temperature constant. However, problems such as an increase in the size of the apparatus, an increase in power consumption, and an increase in cost arise.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to prevent a diode temperature rise due to self-heating when a current flows through a pixel and a temperature fluctuation of a pixel and a readout circuit due to a substrate temperature fluctuation. It is an object to obtain an infrared solid-state imaging device to be compensated.

[0015]

An infrared solid-state imaging device according to the present invention has a first hollow structure provided on a semiconductor substrate through a gap, and absorbs infrared light emitted from a subject. A first absorption unit provided in the first hollow structure, the temperature rising based on the heat of the infrared light absorbed by the first absorption unit, and generating a detection signal corresponding to the temperature.
And an effective pixel provided with a detection unit, and a second hollow structure provided on the semiconductor substrate via a gap, provided in the second hollow structure, when detecting infrared rays by the effective pixel A reference pixel provided with a second detection unit for raising the temperature and generating a reference signal corresponding to the temperature. Further, the effective pixel includes a first support leg that supports the first hollow structure, and the reference pixel includes:
It has a second support leg for supporting the second hollow structure. In addition, the reference pixel includes a first shielding film that covers the second hollow structure, and a support that supports the first shielding film. The area of the second hollow structure is larger than the area of the first hollow structure. Also, the second
Is shorter than the first support leg. Further, the thermal conductance of the reference pixel is larger than the thermal conductance of the effective pixel. Further, the reference pixel has a second absorption unit connected to the second detection unit for absorbing infrared rays. Further, the reference pixel includes a second shielding film that covers the second hollow structure. Further, at the time of detecting infrared rays, a constant current is supplied to each of the effective pixel and the reference pixel. Also,
At a predetermined time after the start of infrared detection, the temperature of the first detection unit rises by a predetermined temperature rise, and the temperature of the reference pixel also rises by a predetermined temperature rise. Also, the first
And the second detector are diodes. In addition, a read circuit that receives a detection signal from the first detection unit and a reference signal from the second detection unit and generates a differential output of the two signals is provided. The effective pixels are arranged in a matrix, the reference pixels are provided for each column of the effective pixels, and a signal line from the first detection unit to the readout circuit is arranged between the reference pixels. The reference pixels are arranged in a staggered arrangement. Also, a dummy pixel having the same configuration as the reference pixel, and a compensation circuit for detecting a temperature variation of the semiconductor substrate based on the reference signal and a signal from the dummy pixel and compensating for an output offset variation of the readout circuit. It is.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG.
FIG. 2 is a pixel cross-sectional view showing a configuration of a reference pixel of the infrared solid-state imaging device according to Embodiment 1 of the present invention. FIG.
Wherein 1 is the bulk Si of the SOI substrate, 2a and 2
b is a box oxide film of the SOI substrate, and 3 is a silicon thin film on the oxide film of the SOI substrate. A void 4 is formed below the box oxide film 2b by using silicon micromachining technology, and the box oxide film 2b and the silicon thin film 3 have a hollow structure and are thermally separated from the underlying bulk Si1. ing. Reference numeral 5 denotes an etching hole for forming the void 4, and the underlying bulk Si is formed through the etching hole 5.
Part of 1 is removed. Although not shown here, a PN junction diode is formed on the silicon thin film 3. Reference numeral 6 denotes a shielding film made of an infrared absorbing film, and reference numeral 7 denotes a column for holding the infrared shielding film 6. The reference pixel in FIG. 1 has a structure in an infrared solid-state imaging device using a diode-type thermal detector using an SOI substrate. In FIG. 1, unlike the absorption umbrella of the conventional effective pixel, in the reference pixel, the shielding film 6 is not connected to the hollow structure portion, but is thermally connected to the bulk Si1 by the pillar portion 7 in the peripheral portion of the pixel.

FIG. 2 is a pixel plan view showing the plane structure of the reference pixel of FIG. In FIG. 2, reference numeral 8 denotes a hollow structure composed of the box oxide film 2b and the silicon thin film 3, 9
Is a supporting leg made of a box oxide film 2a for supporting the hollow structure 8, 10 is a PN junction diode formed in the silicon thin film 3 of the hollow structure 8 and a plurality of PN junction diodes are connected in series, and 11 is a PN junction diode. Reference numeral 10 denotes a thin film wiring for electrically connecting the thin film wiring, and 12 denotes a contact for electrically connecting the thin film wiring 11 to a signal line (not shown). 13
Indicates a region of the infrared shielding film 6 formed above the hollow structure 8, and a region 14 indicated by oblique lines indicates a column 7.
It is. Numeral 15 schematically shows a boundary of one pixel.

Next, the operation of the reference pixel shown in FIGS. 1 and 2 will be described. FIG. 3 is a diagram showing a time change of the diode temperature when a constant current flows through the PN junction diode. FIG. 3 shows a time change of each diode temperature in the effective pixel, the conventional reference pixel, and the reference pixel of the present invention. FIG. 3 shows the first embodiment as a reference pixel temperature (1).

First, an effective pixel is at a temperature Td before a current flows through the diode. At this time, the difference Td−Ts from the substrate temperature is determined by the infrared energy ΔP absorbed by the pixel per unit time and the thermal conductance Gt of the supporting leg.
And is given by ΔP / Gt. Next, when energization is started, the diode temperature starts to rise due to self-heating. The gradient of the graph immediately after energization is Id ＾ 2 × Rd / H
t (where Ht is the heat capacity of the effective pixel), and the diode temperature increases exponentially with the saturation value T over time.
s + (ΔP + Id ＾ 2 × Rd) / Gt.

Next, in the reference pixel of the conventional infrared solid-state imaging device, the diode temperature does not change before and after the current flows through the diode, and is always the substrate temperature Ts. For this reason, in the conventional infrared solid-state imaging device, the diode temperature difference between the effective pixel and the reference pixel increases as the energization time increases.

On the other hand, in the reference pixel of the infrared solid-state imaging device according to the first embodiment, the diode temperature before current flow is Ts. However, when current starts to flow, the diode temperature rises due to self-heating. In the infrared solid-state imaging device according to the first embodiment, the temperature rise due to self-heating occurs in both the effective pixel and the reference pixel, so that the temperature difference between the two is suppressed from increasing, and the differential output is obtained, so that the current can be reduced during power-on. Can reduce the influence of self-heating. The reference pixel does not cause a temperature rise due to the incidence of infrared rays due to the shielding film 6.

Further, the infrared solid-state imaging device according to the first embodiment uses an infrared absorbing film used as an absorbing umbrella in an effective pixel as a shielding film 6 in a reference pixel. Can be formed.

FIG. 4 is a pixel plan view showing a planar structure of a reference pixel of another infrared solid-state imaging device according to the first embodiment of the present invention. In FIG. 4, the configuration is the same as that shown in FIG. 2 except that it has the shape of the infrared shielding film surrounded by the dotted line 16 and the shape of the column shown by the hatched region 17. In FIG. 4, the region where the infrared shielding film 16 is formed is partially reduced as compared with FIG. 2, and a part of the etching hole 5 is not covered by the infrared shielding film 16 when viewed from above. Therefore, the occurrence of etching failure in the hollow structure forming step is suppressed by the etching gas entering from the uncovered portion, as compared with the configuration in FIG. In the configuration shown in FIG. 4, the shape of the infrared shielding film 16 is arbitrary, and may be any shape as long as it covers at least the hollow structure when viewed from above.

Embodiment 2 FIG. FIG. 5 is a pixel plan view showing a structure of a reference pixel of the infrared solid-state imaging device according to Embodiment 2 of the present invention. Reference pixel is SOI
This is a configuration of an infrared solid-state imaging device using a diode-type thermal detector using a substrate. In FIG. 5, the area of the hollow structure 18 of the reference pixel is larger than the area of the hollow structure of the effective pixel. The area is
The heat capacity of the hollow structure 18 due to the increase in the area is set to be substantially the same as the heat capacity of the absorbing umbrella in the effective pixel. Other reference numerals are the same as those shown in FIG.

The operation of the reference pixel shown in FIG. 5 will be described with reference to FIG. In FIG. 3, it is shown as the reference pixel temperature (2). When energization of the reference pixel is started, the diode temperature starts to rise due to self-heating. The slope of the graph immediately after energization is Id ＾ 2
X Rd / Ht '(where Ht' is the heat capacity of the reference pixel), and the diode temperature exponentially approaches the saturation value over time. On the other hand, also in the effective pixel, when the energization is started, the diode temperature starts to rise due to self-heating, and the slope of the graph immediately after the energization is Id
＾ 2 × Rd / Ht. At this time, if the heat capacity Ht of the effective pixel and the heat capacity Ht ′ of the reference pixel are designed to be substantially the same, the temperature rise due to self-heating after the start of energization is substantially equal between the two, and the differential output of the two pixels is reduced. This cancels out the influence of self-heating, so that the effect of self-heating during energization can be further reduced as compared to the first embodiment.

In this infrared solid-state imaging device, since the area of the hollow structure 18 is increased, it may be necessary to make the reference pixel larger than the effective pixel. However, the reference pixel is not necessarily the same size as the effective pixel. It is not necessary that the characteristics of the diodes and the like formed in both of them be the same.

Embodiment 3 FIG. 6 is a pixel plan view showing a structure of a reference pixel of the infrared solid-state imaging device according to Embodiment 3 of the present invention. Reference pixel is SOI
This is a configuration of an infrared solid-state imaging device using a diode-type thermal detector using a substrate. In FIG. 6, the support leg 19 of the reference pixel is shorter than the support leg of the effective pixel. Reference numeral 20 denotes an area of the umbrella support portion that contacts the hollow structure 8. 39 is an absorbing umbrella. Other reference numerals are the same as those of the configuration shown in FIG. In the third embodiment, an absorbing umbrella 39 and an umbrella support 20 are provided instead of the infrared shielding film.

Next, the operation of the reference pixel shown in FIG. 6 will be described. FIG. 7 is a diagram showing a time change of the diode temperature when a constant current flows through the PN junction diode. FIG. 7 shows a time change of each diode temperature in the effective pixel, the conventional reference pixel, and the reference pixel of the third embodiment.

In the reference pixel shown in FIG. 6, the diode temperature before energization is Td ', and the difference from the substrate temperature is Td'.
d′−Ts is given by ΔP / Gt ′ (Gt ′: thermal conductance of the reference pixel). Due to infrared irradiation, Td 'is higher than Ts. At this time, in the reference pixel shown in FIG. 6, since the support leg 19 is formed short, the thermal conductance Gt ′ of the reference pixel is larger than the thermal conductance Gt of the effective pixel. Therefore, even if infrared rays are incident on the reference pixels, the temperature rise due to the incident infrared rays is small.
Next, when the energization is started, the diode temperature rises due to self-heating, but the slope of the graph immediately after the energization is IdＩ2 ×
It does not depend on Rd / Ht 'and Gt. Since the reference pixel shown in FIG. 6 is the same as the effective pixel except for the length of the support leg 19, the heat capacity Ht ′ of the reference pixel is equal to the heat capacity Ht of the effective pixel. Therefore, the temperature rise due to self-heating in the effective pixel and the reference pixel is almost the same as long as the short period immediately after the start of energization (the period of the thermal time constant: about a fraction of Ht '/ Gt').

In a standard infrared solid-state imaging device of about several hundreds × several hundreds of pixel arrays, the thermal time constant Ht / Gt of the effective pixel is about several tens of msec, while the energization time to the pixel diode is several tens μsec. It is about. Therefore, if the thermal time constant Ht / Gt ′ of the reference pixel is set to about several hundred μsec, the above condition is satisfied, and the effect of self-heating upon energization is obtained by obtaining a differential output between the effective pixel and the reference pixel. Can compensate.

Incidentally, in the embodiment shown in FIG.
Although the thermal conductance Gt ′ of the reference pixel is increased by shortening the length of the reference numeral 9, the same effect is obtained when the thermal conductance is increased by increasing the width of the support leg 19. Further, in the configuration shown in FIG. 6, the absorbing umbrella 39 is formed in the effective pixel and the reference pixel, but the present invention can be applied to a case where the infrared absorbing film is not formed for the purpose of simplifying the element manufacturing process.

Embodiment 4 FIG. FIG. 8 is a pixel plan view showing a structure of a reference pixel of the infrared solid-state imaging device according to Embodiment 4 of the present invention. Reference pixel is SOI
This is a configuration of an infrared solid-state imaging device using a diode-type thermal detector using a substrate. In the reference pixel of the infrared solid-state imaging device shown in FIG. 8, the thermal conductance is increased by forming the shielding film and shortening the support legs. Reference numeral 21 denotes a support leg, an area 22 indicated by a dotted line denotes an infrared shielding film, and an area 23 indicated by a hatched portion denotes a support. Other symbols are the same as those in the configuration of FIG.

When the intensity of the infrared ray incident on the reference pixel is extremely high, a part of the infrared ray may pass through the shielding film and reach the hollow structure. At this time, in the reference pixel, in addition to the temperature rise due to self-heating, the temperature rise due to the incidence of infrared rays also occurs, so that accurate temperature compensation cannot be performed. Since the reference pixel of the infrared solid-state imaging device in FIG. 8 increases the thermal conductance of the support leg 21, even when transmitted infrared rays are incident, a rise in temperature due to the incidence of infrared rays is suppressed, and self-heating is more accurate. Temperature compensation can be performed.

Embodiment 5 FIG. 9 is a layout diagram showing a method of arranging reference pixels of the infrared solid-state imaging device according to Embodiment 5 of the present invention. The infrared solid-state imaging device in this figure performs temperature compensation by a differential output between an effective pixel and a reference pixel. In FIG. 9, reference numeral 24 denotes effective pixels arranged in a two-dimensional array on a semiconductor substrate, reference numeral 25 denotes reference pixels arranged on each column of the array of effective pixels 24 on the same substrate, and reference numerals 26a and 26b denote effective pixels, respectively. A power supply line for applying a voltage to the pixel 24 and the reference pixel 25, 27a is a vertical signal line connected to the effective pixel, and 27b is a vertical signal line connected to the reference pixel.

In the case where reference pixels are provided for each column of the effective pixel array in the infrared solid-state imaging device, if the reference pixels are arranged in a straight line, the horizontal length of the reference pixels is larger than the horizontal length of the effective pixels. I can't. Further, when the two pixel sizes are the same, it is necessary to wire a vertical signal line from the effective pixel through the reference pixel. For this reason, a significant restriction is imposed on the design of the effective pixel and the reference pixel. For example, the detector area in the pixel has to be narrowed.

The infrared solid-state imaging device shown in FIG. 9 is designed to reduce design restrictions. Instead of arranging the reference pixels 25 in a straight line,
For example, an interval is provided between adjacent reference pixels 25 by using a stagger arrangement. Therefore, the pixel size of the reference pixel 25 can be made larger than the pixel size of the effective pixel 24. The vertical signal line 27a from the effective pixel 24 is
Wiring can be performed through an empty area between the reference pixels 25, and the effective pixel 24 and the reference pixel 25 can be connected.
This increases the degree of freedom in design.

Although the reference pixels 25 are arranged in a staggered arrangement in FIG. 9, any arrangement method may be used as long as an interval is provided between adjacent reference pixels 25.

Embodiment 6 FIG. FIG. 10 is a diagram showing a configuration of an infrared solid-state imaging device according to Embodiment 6 of the present invention.
This infrared solid-state imaging device performs temperature compensation by a differential output between an effective pixel and a reference pixel. 10, reference numeral 28 denotes a dummy pixel having the same structure as that of the reference pixel 25; 29a, a constant current source for flowing a constant current to the effective pixel 24 and the dummy pixel 28; 29b, a constant current source for flowing a constant current to the reference pixel 25. Current source, 30 is a differential amplifier circuit, 31 is an integration circuit, 32 is a vertical scanning circuit, 33 is a horizontal scanning circuit, 34 is a horizontal selection MOS
A transistor, 35 is a horizontal signal line, and 36 is an output amplifier. 37 is a control circuit provided outside the element, and 38 is an input signal line for feeding back a control signal from the control circuit 37 to the readout circuit. Effective pixels 24,
The reference pixels 25 and the dummy pixels 28 are arranged in an array. Other reference numerals are the same as those shown in FIG. The dummy pixel 28 is connected to the power supply wiring 26b and the vertical signal line 27a.

Next, the operation of the infrared solid-state imaging device shown in FIG. 10 will be described. When the substrate temperature changes in the infrared solid-state imaging device, not only the characteristics of the detector but also the characteristics such as the threshold voltage of the transistor change, and the output offset of the device changes. In the infrared solid-state imaging device shown in FIG. 10, when 28 rows of dummy pixels are selected by the vertical scanning circuit 32, the output of the device is the dummy pixel 28 and the reference pixel 2.
5, the dummy pixel 28 and the reference pixel 25 have the same structure, so that the obtained element output reflects only the characteristics of the readout circuit. Accordingly, the differential output between the dummy pixel 28 and the reference pixel 25 is appropriately monitored by the control circuit 37 provided outside the element, and the control signal is fed back to the readout circuit so that the output fluctuation becomes zero.
The output offset fluctuation of the read circuit with respect to the substrate temperature fluctuation can be compensated.

As a method of controlling the output offset of the read circuit, for example, if the read circuit shown in FIG. 15 is used, the gate voltage of the constant current MOS transistor 134 in the differential amplifier circuit 126 is controlled to integrate Capacity 1
For example, there is a method of adjusting the discharge current from 35. If the input potential difference to the differential amplifier circuit 126 is 0, the discharge current is の of the value of the current flowing through the constant current MOS transistor 134, but if the current value changes due to substrate temperature fluctuation, And the input signal line 38, it is possible to change the gate voltage of the constant current MOS transistor 134 so as to compensate for this. In addition, temperature control of the element is not required, and the size, power consumption, and cost of the infrared solid-state imaging device can be reduced.

In FIG. 10, the dummy pixels 28 are arranged in each column of the effective pixel 24 array. However, the dummy pixels 28 may be represented by one, and the number and arrangement method are arbitrary. is there.

[0042]

As described above, according to the present invention, a diode temperature rise due to self-heating when a current flows through a pixel can be compensated, and a high-sensitivity infrared solid-state imaging device can be obtained. Further, it is possible to compensate for the temperature fluctuation of the pixel and the readout circuit due to the substrate temperature fluctuation. In addition, the restrictions on the design of the effective pixel and the reference pixel can be eliminated, and a high-sensitivity infrared solid-state imaging device can be obtained.

[Brief description of the drawings]

FIG. 1 is a pixel sectional view showing a configuration of a reference pixel of an infrared solid-state imaging device according to a first embodiment of the present invention;

FIG. 2 is a pixel plan view showing a plane structure of a reference pixel of FIG. 1;

FIG. 3 is a diagram showing a time change of a diode temperature when a constant current flows through a PN junction diode.

FIG. 4 is a pixel plan view showing a planar structure of a reference pixel of another infrared solid-state imaging device according to Embodiment 1 of the present invention;

FIG. 5 is a pixel plan view showing a planar structure of a reference pixel of the infrared solid-state imaging device according to Embodiment 2 of the present invention;

FIG. 6 is a pixel plan view showing a planar structure of a reference pixel of the infrared solid-state imaging device according to Embodiment 3 of the present invention;

FIG. 7 is a diagram illustrating a time change of a diode temperature when a constant current flows through a PN junction diode in the third embodiment.

FIG. 8 is a pixel plan view showing a planar structure of a reference pixel of an infrared solid-state imaging device according to Embodiment 4 of the present invention;

FIG. 9 is a layout diagram showing a method of arranging reference pixels of the infrared solid-state imaging device according to Embodiment 5 of the present invention;

FIG. 10 is a diagram illustrating a configuration of an infrared solid-state imaging device according to Embodiment 6 of the present invention;

FIG. 11 is a pixel sectional view showing a configuration of an effective pixel of a conventional infrared solid-state imaging device.

12 is a pixel plan view showing a plane structure of the conventional effective pixel shown in FIG.

FIG. 13 is a pixel sectional view showing a configuration of a conventional reference pixel.

FIG. 14 is a diagram showing a configuration of a conventional infrared solid-state imaging device.

FIG. 15 is a diagram illustrating a configuration of a read circuit in FIG. 14;

[Explanation of symbols]

1 bulk Si of SOI substrate, 2 box oxide film of SOI substrate, 3 silicon thin film, 4 void, 5
Etching hole, 6 shielding film, 7 support, 8 hollow structure, 9 support leg, 10 PN junction diode,
DESCRIPTION OF SYMBOLS 11 Thin film wiring, 12 contacts, 13 shielding film area, 14 support part, 16 shielding film, 17 support part, 18 hollow structure, 19 support leg, 20
Umbrella support, 21 support leg, 22 shielding film, 23
Support part, 24 effective pixels, 25 reference pixels,
26 power supply wiring, 27 vertical signal line, 28 dummy pixel, 29 constant current source, 30 differential amplifier circuit,
31 integration circuit, 32 vertical scanning circuit, 33 horizontal scanning circuit, 34 horizontal selection MOS transistor, 3
5 horizontal signal line, 36 output amplifier, 37 control circuit, 38 input signal line 39 absorption umbrella.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G065 AA04 AB02 BA34 BA40 BB21 BC05 BC11 BC15 CA21 CA30 DA20 4M118 AA01 AA06 AA10 AB01 BA05 CA03 CA40 FA50 FB09

Claims (15)

[Claims] A first hollow structure provided on a semiconductor substrate via a gap, the first hollow structure absorbing an infrared ray emitted from a subject, and a first hollow structure provided in the first hollow structure. An effective pixel provided with a first detection unit that is provided, and provided with a first detection unit configured to increase a temperature based on heat by the infrared light absorbed by the first absorption unit and generate a detection signal corresponding to the temperature; A second hollow structure provided on the substrate with a gap therebetween, the second hollow structure being provided in the second hollow structure, wherein the temperature rises upon detection of the infrared ray by the effective pixel, and a reference corresponding to the temperature; And a reference pixel provided with a second detection unit for generating a signal. 2. The effective pixel includes a first support leg that supports the first hollow structure. The reference pixel includes a second support leg that supports the second hollow structure. The infrared solid-state imaging device according to claim 1, wherein: 3. The reference pixel according to claim 1, wherein the reference pixel includes a first shielding film that covers the second hollow structure, and a support portion that supports the first shielding film. The infrared solid-state imaging device according to claim 2. 4. The infrared solid-state imaging device according to claim 1, wherein an area of the second hollow structure is larger than an area of the first hollow structure. . 5. The infrared solid-state imaging device according to claim 2, wherein the second support leg is shorter than the first support leg. 6. The solid-state infrared imaging device according to claim 5, wherein a thermal conductance of the reference pixel is larger than a thermal conductance of the effective pixel. 7. The reference pixel according to claim 5, wherein the reference pixel includes a second absorption unit connected to the second detection unit for absorbing the infrared light. Infrared solid-state imaging device. 8. The infrared solid-state imaging device according to claim 5, wherein the reference pixel includes a second shielding film that covers the second hollow structure. 9. The infrared solid-state imaging device according to claim 1, wherein a constant current is supplied to each of the effective pixel and the reference pixel when the infrared light is detected. 10. A predetermined time after the start of the detection of the infrared ray, the temperature of the first detection unit increases by a predetermined temperature increase, and the temperature of the reference pixel also increases by the predetermined temperature increase. The infrared solid-state imaging device according to claim 1, wherein: 11. The infrared solid-state imaging device according to claim 1, wherein each of the first detection unit and the second detection unit is a diode. 12. A read circuit for receiving the detection signal from the first detection unit and the reference signal from the second detection unit, and generating a differential output of the two signals. The infrared solid-state imaging device according to claim 1. 13. The effective pixels are arranged in a matrix, the reference pixels are provided for each column of the effective pixels, and a signal line from the first detector to the readout circuit is provided between the reference pixels. The infrared solid-state imaging device according to claim 12, wherein the infrared solid-state imaging device is disposed. 14. The infrared solid-state imaging device according to claim 13, wherein the reference pixels are arranged in a staggered arrangement. 15. Compensating for an output offset variation of the readout circuit by detecting a temperature variation of the semiconductor substrate based on a dummy pixel having the same configuration as the reference pixel and a signal from the reference signal and the dummy pixel. The infrared solid-state imaging device according to any one of claims 12 to 14, further comprising: a compensating circuit that performs the operation.