JP3495309B2 - Thermal infrared imaging device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal infrared imaging device, and more particularly to a thermal infrared imaging device for performing infrared imaging using a heat sensitive device arranged on a semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, as an infrared detector, a thermal type detector represented by a bolometer has been known.
A bolometer is a kind of resistance element composed of a member having a large temperature coefficient, and is widely used in fields such as temperature measurement and remote sensing. Recently, for the purpose of miniaturization and weight reduction, attention has been paid to a thermal infrared image pickup device in which heat sensitive elements are arranged on a semiconductor substrate.

In this thermal infrared imaging device, a temperature change due to incident (imaging) infrared rays is detected by a plurality of thermosensitive elements arranged on a semiconductor substrate, and a signal corresponding to a resistance change of each thermosensitive element is imaged. It is taken out as a signal. In this case, in order to improve the sensitivity of the thermal infrared detector, the heat-sensitive element is a thin film made of a substance having a large rate of resistance change due to temperature change, and the heat-sensitive element is connected to the semiconductor substrate by a supporting leg having a low heat conductivity. It By applying a bias current to the heat sensitive element, a change in the resistance value of the heat sensitive element is detected as a voltage change, which is amplified and output.

[0004]

An infrared image can be detected by arranging a large number of heat-sensitive elements as described above on a semiconductor substrate and detecting the temperature change of each heat-sensitive element, but the temperature change of the heat-sensitive element can be detected. Therefore, the signal output of the thermosensitive element also changes depending on the temperature change of the semiconductor substrate and the periphery of the semiconductor substrate. In particular, the temperature rise occurs in the semiconductor substrate due to heat generation by the bias current for reading the resistance change of the heat sensitive element, and a temperature difference of about 10 ° C. occurs between the center and the periphery of the semiconductor substrate. When the heat-sensitive elements are arranged at a pitch of 50 μm, the temperature resistance coefficient is several% / K, and the thermal conductance of the supporting leg is about 5 × 10 ⁻⁸ W / K, the bias current and the resistance values of the heat-sensitive elements cause variations. The difference between the output signals of the heat sensitive elements is several V, and the output signal due to the temperature change of each heat sensitive element caused by the incident infrared rays is several mV or less. In addition to this, if the temperature difference between the center and the periphery of the semiconductor substrate is large as described above, there arises a problem that the infrared detector operates stably only in the center of the substrate.

The present invention has been made in view of the above circumstances, and provides a thermal infrared imaging device capable of equalizing the temperature of the semiconductor substrate in the photosensitive portion in the vicinity of the center of the photosensitive portion and the periphery of the photosensitive portion. The purpose is to provide.

[0006]

In order to solve the above-mentioned problems, the present invention provides a thermal type composed of a semiconductor substrate and a photosensitive portion including a plurality of heat-sensitive elements two-dimensionally arranged on the semiconductor substrate. In the infrared imaging device, a second wiring member having a higher thermal conductivity than that of the first wiring member is provided around a plurality of heat-sensitive elements of the photosensitive section connected to the semiconductor substrate via the first wiring member. Connected to the semiconductor substrate via
It is characterized in that a plurality of pseudo heat sensitive elements having a resistance higher than that of the heat sensitive elements are arranged.

In this thermal infrared imaging device, since a plurality of pseudo-thermosensitive elements are arranged around the plurality of thermosensitive elements constituting the photosensitive section, the photosensitive section is self-heated by the current flowing through the pseudo-thermosensitive elements. The ambient temperature can be increased. For this reason, it becomes possible to make the temperature of the semiconductor substrate in the photosensitive portion uniform in the vicinity of the center of the photosensitive portion and in the periphery of the photosensitive portion. In particular, with regard to the pseudo-thermosensitive element, the resistance value is increased to increase the amount of heat generation, and since it is connected to the semiconductor substrate by a member having a higher thermal conductivity (low thermal resistance) than the wiring member of the photosensitive element in the photosensitive section, Heat can be efficiently transferred from the pseudo heat sensitive element to the semiconductor substrate, and the temperature can be made uniform only by providing a relatively small number of pseudo heat sensitive elements in several rows and several columns.

Further, it is preferable that the plurality of pseudo heat-sensitive elements are connected to the same row lines and column lines as the plurality of heat-sensitive elements constituting the photosensitive section. As a result, it is possible to drive the heat-sensitive element and the pseudo-heat sensitive element of the photosensitive section together in units of row lines by a normal row-line drive circuit, so it is necessary to prepare a dedicated circuit for driving the pseudo-heat-sensitive element. Is eliminated, and downsizing can be achieved.

Further, by arranging the plurality of pseudo-thermosensitive elements two-dimensionally around the photosensitive portion so as to surround the four sides thereof, it is possible to further enhance the temperature equalizing effect.

Since it is not necessary to detect a signal for the pseudo thermosensitive elements, the arrangement pitch between the pseudo thermosensitive elements is
It is preferable to set it to be narrower than the arrangement pitch between the heat-sensitive elements of the photosensitive section. As a result, it is possible to minimize the increase in the element size due to the arrangement of the pseudo thermosensitive elements.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the basic structure of a thermal infrared imaging device according to an embodiment of the present invention. This thermal infrared imaging element is for performing infrared imaging using thin film thermosensitive elements arranged on the semiconductor substrate 11, and as shown in the figure, the photosensitive area 12 is arranged on the semiconductor substrate 11. There is. The photosensitive area 12 is for detecting infrared rays and is composed of a large number of thin film thermosensitive elements which are two-dimensionally arranged in a matrix of rows and columns.

Each thin film thermosensitive element in the photosensitive area 12 is connected to a row line (vertical scanning line) and a column line (horizontal scanning line) driven by the vertical scanning circuit 14 and the horizontal scanning circuit 15, respectively.

Further, a dummy thin film thermosensitive element array 13 is provided around the photosensitive area 12 so as to surround the four sides of the photosensitive area 12. The dummy thin film thermosensitive element array 13 is a pseudo thermosensitive element provided for equalizing the temperature of the entire photosensitive area 12, and is composed of a group of dummy thin film thermosensitive elements of several rows and several columns.

These dummy thin film thermosensitive element groups are connected to the same vertical scanning lines and horizontal scanning lines as the plurality of thermosensitive elements constituting the photosensitive area 12, respectively.
Are simultaneously driven row by row with a plurality of heat-sensitive elements constituting the.

While the thin film thermosensitive element in the photosensitive area 12 is connected to the semiconductor substrate 11 by a member having a low thermal conductivity (high thermal resistance), the resistance value of the dummy thin film thermosensitive element is the resistance value of the thin film thermosensitive element in the photosensitive area 12. It is connected to the semiconductor substrate 11 with a member having a high thermal conductivity (low thermal resistance) so as to obtain a sufficient temperature bias effect while increasing the heat generation amount by increasing the temperature. As described above, the dummy thin film thermosensitive element has a smaller heat generation amount (resistance value), and is connected to the semiconductor substrate 11 with a member having a higher thermal conductivity than that of the thin film thermosensitive element in the photosensitive area 12 to reduce the heat generation amount. The dummy thin film thermosensitive element can efficiently conduct heat to the semiconductor substrate 11.

At the time of detecting infrared rays (at the time of image pickup), the thin film thermosensitive elements in the photosensitive area 12 are sequentially selected by the vertical scanning circuit 14 and the horizontal scanning circuit 15, and a signal corresponding to the temperature of each element is output as an image pickup signal. 16 is read. During this imaging, each dummy thin film thermosensitive element of the dummy thin film thermosensitive element array 13 is also driven at the same time, and the heat generated by the current flowing through the dummy thin film thermosensitive element is transferred from the dummy thin film thermosensitive element to the semiconductor substrate 11 immediately thereunder. .

FIG. 2 shows the temperature distribution of the semiconductor substrate 11 below the photosensitive area 12 during steady driving. The horizontal axis in FIG. 2 is the distance L from the center of the photosensitive area 12.
And the vertical axis represents the temperature. The solid line in FIG. 2 shows the temperature distribution when the dummy thin film thermosensitive element array 13 is not provided, and the dotted line shows the temperature distribution when the dummy thin film thermosensitive element array 13 is provided.

As shown by the solid line in FIG. 2, when the dummy thin film thermosensitive element array 13 is not present, the temperature of the semiconductor substrate 11 in the photosensitive area 12 is the same as that in the photosensitive area 12.
It is highest near the center and lower toward the periphery of the photosensitive area 12. On the other hand, when the dummy thin film thermosensitive element array 13 is provided around the photosensitive area 12 as in the present embodiment, as shown by the dotted line in FIG. 2, self-heating due to the current flowing through the dummy thin film thermosensitive element during driving. As a result, the ambient temperature of the photosensitive area 12 can be increased, so that the temperature of the semiconductor substrate 11 in the photosensitive area 12 can be made uniform in the vicinity of the center of the photosensitive area 12 and the periphery of the photosensitive area 12.

Therefore, by only providing the dummy thin film thermosensitive element array 13 of several rows and several columns, it is possible to increase the number of photosensitive elements having a uniform temperature bias with the central portion of the photosensitive area 12 by ΔN in each of the left, right, up, and down 4 directions. Therefore, the ratio of the number of effective elements that can be used for heat detection to the total number of heat-sensitive elements can be significantly increased. Specifically, for example, when a 256 × 256 thermosensitive element is formed, only about 220 × 220 of those elements can be used for actual heat detection, but by providing the dummy thin film thermosensitive element array 13, 2 out of 256 x 256 thermal elements
It is possible to use an element of about 53 × 253 for actual heat detection.

Next, with reference to FIG. 3, a circuit configuration of the thermal type infrared imaging device of FIG. 1 will be described. FIG. 3 exemplifies a case where dummy thin film thermosensitive elements are arranged around the photosensitive area 12 in rows and columns. In FIG. 3, 111 is a vertical scanning line, 112 is a horizontal scanning line, 113 is a vertical MOS transistor for vertical scanning line selection, and 114 is a horizontal MOS transistor for horizontal scanning line selection. Each vertical MOS transistor 113 is connected between the power supply VDD and the corresponding vertical scanning line 111, and each horizontal MOS transistor 114 is connected between the signal output line and the corresponding horizontal scanning line 112. . Further, 115 is a sample hold capacitor, 201 is a dummy thin film thermosensitive element, and 202 is a thin film thermosensitive element constituting the photosensitive area 12.

The thin film heat sensitive element 202 is made of a material such as a metal oxide film or ceramics having a large rate of change in resistance with temperature. Therefore, these thin film thermosensitive elements 202 are sequentially driven row by row by the vertical scanning circuit 14, and the difference in the accumulated voltage of the sample and hold capacitors 115 at this time is selected and read out for each column to read the object (target) to be imaged. An image pickup signal corresponding to the temperature change can be obtained.

The problem here is the temperature change due to the current flowing in each thin film thermosensitive element 202 during image pickup.
FIG. 4 shows how the temperature changes due to this self-heating.

FIG. 4 shows how the temperature changes per thin-film thermosensitive element 202 (one cell). Each vertical scanning line 111 has a period of, for example, 1/60 second, and the vertical scanning circuit 1
4 is selected by a vertical drive pulse periodically generated. The selected vertical scanning line 111 is connected to the power supply VDD via the vertical MOS transistor 113. As a result, the power supply VDD is applied to each thin film thermosensitive element 202 connected to the selected vertical scanning line 111, and a current flows through the thin film thermosensitive element 202. At this time, due to the current flowing through the thin film heat sensitive element 202, the thin film heat sensitive element 20
The temperature of 2 rapidly rises, and gradually decreases after the end of driving. The temperature rise due to this self-heating is several hundred times larger than the amount of temperature change due to the original signal component. The temperature change due to the original signal component appears in a form superimposed on the temperature change due to self-heating.

By repeating such driving, the temperature of the semiconductor substrate 11 under the photosensitive area 12 starts to rise, and when driven for a certain period of time, the temperature distribution converges as shown by the solid line in FIG.

In the present embodiment, when the thin film thermosensitive element 202 is driven, the dummy thin film thermosensitive element 201 is also driven. Therefore, the temperature of the dummy thin film thermosensitive element 201 also rises due to the current flowing therethrough, and the heat is transferred to the semiconductor substrate 11 around the photosensitive area 12. Therefore, the bias temperature of the semiconductor substrate 11 around the photosensitive area 12 can be increased, and the bias temperature of the semiconductor substrate 11 in the photosensitive area 12 can be set to the vicinity of the center of the photosensitive area 12 and the photosensitive area 12.
It becomes possible to make it uniform with the surrounding area.

Since the dummy thin film thermosensitive element 201 is only for the purpose of equalizing the temperature, it is not used for signal reading.

Next, the wiring structure of each cell will be described with reference to FIGS. FIG. 5 shows a wiring pattern around each cell, and FIG. 6 shows its sectional structure.

Both the dummy thin film thermosensitive element 201 and the thin film thermosensitive element 202 have the same wiring layout, and the base portion 300 on which the thin film thermosensitive element is formed has a hollow portion provided between it and the semiconductor substrate 11. , And is supported on the semiconductor substrate 11 by the wiring members 301 and 302 which are the supporting legs.

One end of the thin film thermosensitive element on the base portion 300 is connected to the vertical scanning line 111 formed of the wiring layer formed on the semiconductor substrate 11 via the wiring member 301, and the thin film thermosensitive element on the base portion 300 is connected. The other end of is connected to the horizontal scanning line 112 formed of a wiring layer formed on the semiconductor substrate 11 via the wiring member 302.

In this case, the wiring members 301 and 302 of the base portion 300 on which the thin film thermosensitive element 202 is formed are
A member having a low thermal conductivity (high thermal resistance) is used for each, and a base portion 30 on which the dummy thin film thermosensitive element 201 is formed
For the wiring members 301 and 302 of 0, members having high thermal conductivity (low thermal resistance) are used.

As a result, the thin film thermosensitive element 202 is connected to the semiconductor substrate 11 with high thermal resistance, and the dummy thin film thermosensitive element 2 is connected.
01 has a low thermal resistance and is connected to the semiconductor substrate 11. Therefore, in the thin-film thermosensitive element 202, the temperature increased by the current flowing at the time of selection can be returned to the original state by the next selection, and the dummy thin-film thermosensitive element 2
With respect to 01, the heat generated at the time of driving can be efficiently transferred to the semiconductor substrate 11.

The pitch for arranging the thin film thermosensitive elements 202 is usually about 50 μm, but since it is not necessary to detect a signal in the dummy thin film thermosensitive element 201, the pitch can be narrowed. In addition, in the portion of the dummy thin film thermosensitive element 201, the light incident window is basically unnecessary, so that the miniaturization effect can be obtained. Therefore,
An increase in the size of the entire photosensitive area size caused by the addition of the dummy thin film thermosensitive element 201 can be suppressed to a necessary minimum.

Further, in this embodiment, the dummy thin film thermosensitive element 201 is connected to the same row line as the thin film thermosensitive element 202 so as to be driven together with the thin film thermosensitive element 202. It is also possible to provide a dedicated drive circuit for passing a current.

Further, in the present embodiment, in consideration of the situation that the temperature of the center of the semiconductor substrate becomes high and the periphery thereof becomes low due to the heat generation of the heat sensitive element, the dummy thin film heat sensitive elements 201 arranged in the periphery of the photosensitive area 12 are considered. Although the resistance value is increased to increase the amount of heat generation and the semiconductor substrate 11 is connected with high thermal conductivity, the peripheral circuit elements such as the output amplifier 16 and the vertical MOS transistor 113 also actually generate heat. For the dummy thin film thermosensitive element 201, the thermal conductivity of the support leg connected to the semiconductor substrate 11 and the heat generation amount (resistance value) of the dummy thin film thermosensitive element are adjusted so that the thermal conductivity of the dummy thin film thermosensitive element 201 is lower than that of the other portions. It is preferable to connect to the semiconductor substrate at a rate.

[0035]

As described above, according to the present invention,
By arranging the plurality of pseudo heat-sensitive elements around the plurality of heat-sensitive elements forming the photosensitive section, it is possible to make the bias temperature of the photosensitive section that detects infrared rays uniform. In particular,
Regarding the pseudo-thermosensitive element, by connecting it to the semiconductor substrate with a member having a higher thermal conductivity (low thermal resistance) than the wiring member of the thermosensitive element in the photosensitive section, it is possible to obtain a uniform temperature by providing a relatively small number of pseudo-thermosensitive elements. Can be realized.

[Brief description of drawings]

FIG. 1 is a plan view showing a structure of a thermal infrared imaging device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a temperature distribution of a photosensitive section in the thermal infrared imaging element of the embodiment.

FIG. 3 is a diagram showing a circuit configuration of a thermal infrared imaging device of the same embodiment.

FIG. 4 is a diagram showing how the temperature of a heat-sensitive element in the thermal-type infrared imaging element of the embodiment changes.

FIG. 5 is a view showing a wiring structure of each cell used in the thermal infrared imaging element of the embodiment.

FIG. 6 is a view showing a cross-sectional structure of each cell used in the thermal infrared imaging element of the same embodiment.

[Explanation of symbols]

11 ... Semiconductor substrate 12 ... Photosensitive area 13 ... Dummy thermosensitive element array 14 ... Vertical scanning circuit 15 ... Horizontal scanning circuit 111 ... Vertical scanning line (row line) 112 ... Horizontal scanning line (column line) 113 ... Vertical MOS transistor 114 ... Horizontal MOS transistor 301, 302 ... Wiring member

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Claims (5)

(57) [Claims] 1. A thermal infrared imaging device comprising a semiconductor substrate and a photosensitive section including a plurality of thermosensitive elements two-dimensionally arranged on the semiconductor substrate, wherein the semiconductor substrate is provided via a first wiring member. Higher than the heat-sensitive element, which is connected to the semiconductor substrate through a second wiring member having a higher thermal conductivity than the first wiring member around the plurality of heat-sensitive elements of the photosensitive section connected to A thermal infrared image pickup device comprising a plurality of pseudo resistance thermosensitive elements arranged in a line. 2. The plurality of pseudo-thermosensitive elements are connected to the same row lines and column lines as the plurality of thermosensitive elements constituting the photosensitive section, and the pseudo-thermosensitive elements and the photosensitive section are arranged in units of row lines. 2. The thermal infrared image pickup device according to claim 1, wherein the heat sensitive device is driven together. 3. The thermal infrared imaging device according to claim 1, wherein the plurality of pseudo-thermosensitive elements are two-dimensionally arranged around the photosensitive portion so as to surround four sides thereof. 4. The heat generation device according to claim 1, wherein the arrangement pitch between the plurality of pseudo heat-sensitive elements is set to be narrower than the arrangement pitch between the plurality of heat-sensitive elements forming the photosensitive section. Infrared imaging device. 5. A thermal infrared imaging device, comprising : a semiconductor substrate; and a plurality of heat-sensitive elements which are two-dimensionally arranged on the semiconductor substrate and generate heat when driven , wherein the plurality of heat-sensitive elements are photosensitive parts. Which is used to read image signals
A sub-group and the image pickup signal arranged so as to surround the outer periphery of the photosensitive section.
And the pseudo-thermosensitive elements that are not used for reading
In addition, the thermal-type infrared imaging device further comprises a driving unit for driving the plurality of heat-sensitive elements.