JP2000295528A - Thermal infrared ray image pickup element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal infrared ray image pickup element that easily and quickly corrects the sensitivity between pixels with high accuracy. SOLUTION: A heating means 41 and a temperature detection means 40 heat up a semiconductor substrate 11 to a prescribed temperature, a voltage is applied between an electrode 30 provided to a diaphragm section 14 with an infrared ray detection section (resistor 16) mounted thereon and the semiconductor substrate 11, an electrostatic force allows the diaphragm section 14 to be in contact with the semiconductor substrate 11 to make the temperature of all pixels of the infrared ray detection section the same as that of the semiconductor substrate 11, an output voltage of each pixel is stored in this case, and the sensitivity of each pixel is corrected according to the output voltage in this thermal infrared ray image pickup element. Since an object at a uniformized temperature is not required different from a conventional image pickup element, the procedure required for sensitivity correction is very easy and quickened, and since the temperature of the pixels can be made the same accurately, the sensitivity can be corrected with high precision.

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 having means for correcting performance.

[0002]

2. Description of the Related Art A thermal infrared imaging device has a structure in which a large number of pixels (for example, tens of thousands to hundreds of thousands of pixels) are arranged on a plane, but the sensitivity of each pixel lacks uniformity. ing. Therefore, if imaging is performed without correcting the sensitivity of each pixel, the captured screen may be different from the actual subject. Therefore, when using a thermal infrared imaging device, it is necessary to correct the sensitivity of each pixel of the device in order to improve image quality. Explaining with reference to a plan view of the thermal infrared imaging device shown in FIG. 3, the thermal infrared imaging device has a thermal infrared sensor 1 having a heat absorbing layer 2 as a pixel, and a large number of pixels arranged in an m-column × n-row array. It is arranged in a shape. A switching circuit unit 3 is formed in each pixel, and a signal of each pixel is read out to the outside via an x address line 4 and a y address line 5 (external circuit is not shown).

In a conventional thermal infrared imaging device, as shown in FIG. 5, the output voltage of each pixel (described as a change in the state of a pixel converted to a voltage signal) is unbalanced for each pixel. Always. For this reason, it is necessary to provide an external signal processing unit such as an amplifier circuit, an A / D conversion unit, and a signal correction storage unit, and to correct the imbalance between pixels each time an image is captured. As a method of correcting the imbalance between pixels, when using a thermal infrared imaging device as an infrared imaging camera, an object having a relatively uniform temperature is placed in front of the infrared imaging camera, and the incident infrared energy at that time is set. There is a method in which the output voltage of each pixel is stored in a storage unit assuming that the pixel values are uniform, and the sensitivity of each pixel is corrected according to the output value at that time. Generally, a metal plate or a black plate close to room temperature is installed in front of the infrared imaging camera, and sensitivity is corrected in accordance with the output voltage of each pixel when capturing the image.

[0004]

However, in the above-described correction method, it is necessary to prepare an object having a uniform temperature and having a size within the field of view of the infrared imaging camera every time the infrared imaging camera is used, and performing the correction. There is. For example, in order to obtain a practically accurate image, it is necessary to perform correction at intervals of about 10 minutes even during use. In addition, when an object having a uniform temperature is placed in front of the camera, it is difficult to maintain a uniform temperature over the entire area, depending on the heat capacity of the object, depending on the environmental temperature. Particularly, in the case of recent infrared cameras, some have a performance with a NETD (noise equivalent temperature difference) of about 0.1 ° C., so that it is very difficult to maintain an accurate uniform temperature suitable for the performance. It will be difficult. Further, when an object having a temperature higher than the ambient temperature is used, the difficulty increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art as described above, and provides a thermal infrared imaging device capable of easily, quickly and accurately correcting the sensitivity between pixels. The purpose is to do.

[0006]

In order to achieve the above object, the present invention is structured as described in the appended claims. That is, according to the first aspect of the present invention, means for contacting and separating the diaphragm on which the infrared detecting unit is mounted from and with the supporting substrate, heating means for heating the supporting substrate, and detecting the temperature of the supporting substrate or the diaphragm. Temperature detection means, storage means for storing the temperature when the diaphragm is brought into contact with the support substrate, and the output signal of the pixel at that time, and the output of each pixel based on the storage value of the storage means. Means for correcting the signal. The above-mentioned temperature indicates the temperature of the object itself (the unit may be either ° C. or K), and does not mean a temperature difference. Further, the storage means and the means for correcting the output signal of each pixel may be provided as an external circuit, but may be formed in an empty area of the element if there is any.

[0007] With the above configuration, by bringing the diaphragm into contact with the support substrate heated to a predetermined temperature by the heating means, all the pixels can be unified to the same predetermined temperature as the temperature of the support substrate. The sensitivity of each pixel can be corrected by detecting the output signal of each pixel at that time. Further, since it is not necessary to prepare an object having a uniform temperature as in the related art, the procedure required for sensitivity correction is extremely easy and quick, and the temperature of each pixel can be set to exactly the same temperature. It can be performed with high accuracy. Further, since the thermal infrared imaging element itself has a heating means and a temperature detecting means, the temperature can be set by the element itself, and the temperature can be set and detected with high accuracy, so that the accuracy can be further improved. Can be done.

Further, in the invention according to claim 2,
Since the diaphragm and the support substrate are electrostatically contacted,
Preparation for imaging can be performed very quickly and easily.

Further, in the invention according to claim 3,
Sensitivity correction can be performed precisely. Even if the temperature characteristics of each pixel are not linear, by detecting outputs at three or more different temperatures, accurate sensitivity correction can be performed even for non-linear characteristics. Becomes possible.

[0010]

According to the present invention, the temperature of each pixel constituting the infrared imaging device can be easily, quickly and accurately set to the same predetermined temperature as the substrate temperature. Therefore, the performance of each pixel can be easily corrected according to the output signal at that time. Further, correction can be performed even when the temperature characteristics of the infrared sensor serving as each pixel are not linear. Therefore, an effect is obtained in that the sensitivity of each pixel of the thermal infrared imaging device can be easily, quickly, and accurately corrected without preparing an object having a uniform temperature as in the related art.

[0011]

1 and 2 are views showing an embodiment of one infrared sensor (pixel) constituting a thermal infrared imaging device according to the present invention. FIG. 1 is a plan view, and FIG. FIG. FIG. 3 is a plan view showing a schematic configuration of a thermal infrared imaging device formed using the above-described sensor.

First, the structure of a pixel will be described with reference to FIGS. Here, a bolometer-type infrared sensor capable of detecting temperature will be described as a sensor (pixel). The bolometer-type infrared sensor utilizes a characteristic in which the electric resistance of a resistor changes according to a temperature change. 1 and 2, reference numeral 11 denotes a semiconductor substrate (for example, a silicon substrate) serving as a support substrate. Reference numeral 12 denotes a diaphragm, which is supported by the beam portion 13 and faces the semiconductor substrate 11 with a small gap 20 (for example, about several μm). On this diaphragm 12, a resistor 16, an interlayer insulating film 17, an interlayer insulating layer 19, a heat absorbing layer 25, and an electrode 30 are formed, and a diaphragm portion 14 is constituted as a whole.
The diaphragm portion 14 is thermally separated from the semiconductor substrate 11 by a gap 20. On the beam portion 13, a wiring 15 for connecting the resistor 16 to the outside and a wiring 31 for connecting the electrode 30 to the outside are formed.
Covered with 7. Further, a temperature detecting means 40 and a heating means 41 are provided on the semiconductor substrate 11. A required number of such pixels are formed in an array on the semiconductor substrate 11 (see FIG. 3). As can be seen from FIG. 2, the resistor 16 is formed on the electrode 30, and the heat absorbing layer 25 is further formed thereon. In FIG. 1, only the heat absorbing layer 25 is actually visible. However, for convenience of explanation, the resistor 16 is shown as shown in the figure, and the electrode 30 and the heat absorbing layer 25 are formed on substantially the same plane. This is indicated by a solid line.

The semiconductor substrate 11 may be formed with a signal processing circuit such as a decoder for x and y addresses, a preamplifier, and the like. A temperature detecting means 40 (for example, a bolometer-type or pn-junction-type temperature sensor) and a heating means 41 (for example, a metal film resistor) are formed using the empty area of the semiconductor substrate 11. Since the heating means 41 heats the entire thermal infrared imaging element so as to have a uniform temperature, it is preferable to dispose the heating means 41 over the whole. Temperature detection means 4
0 may be provided for each pixel, but if the temperature of the entire semiconductor substrate 11 is uniform, one may be provided as a whole. In the drawing, a pixel in which the temperature detecting means 40 exists is shown as an example.

Further, a circuit for applying a voltage between the electrode 30 and the semiconductor substrate 11 and a memory for detecting the temperature and storing an output signal of each pixel at that time (described in detail later) are required. Illustration is omitted. These circuits may be formed in the element if there is an empty area, or may be external circuits.

FIG. 2 shows an example in which the heating means 41 is provided in the semiconductor substrate 11.
Alternatively, it may be formed on the interlayer insulating layer 17 formed below or below the semiconductor substrate 11. Further, the temperature detecting means 40 may be provided anywhere in the element.

FIG. 3 is a plan view of a thermal infrared imaging device using the infrared sensor 1 shown in FIGS. The infrared sensor 1 (pixel) is connected to the heat absorbing layer 2 (25 in FIGS. 1 and 2).
), And a large number of pixels are arranged in an array of m columns × n rows. A switching circuit unit 3 is formed in each pixel, and a signal is read out to the outside via an x address line 4 and a y address line 5. Note that an external circuit, a circuit for correcting the output voltage, and the like are not shown.

Hereinafter, the operation will be described. In the bolometer-type infrared sensor as described above, incident infrared light is absorbed by the heat absorbing layer 25, and a change in the resistance value of the resistor 16 corresponding to a temperature change due to the infrared light is detected (for example, detected as a voltage change). And a signal corresponding to the incident infrared light.

In this embodiment, the temperature detecting means 4
The temperature of the semiconductor substrate 11 is maintained at a predetermined temperature by applying a current to the heating means 41 and heating while detecting the temperature at 0, and in this state, the heat in which the infrared detecting section of each pixel is formed is formed. The diaphragm portion 14 having the separation structure is brought into contact with the semiconductor substrate 11 to be thermally short-circuited, and the temperature of the infrared detecting portion (heat absorbing layer 25, resistor 16) formed on the diaphragm portion 14 is made equal to the substrate temperature. . Note that the thickness of the diaphragm portion 14 is extremely small, for example, about several μm, and its heat capacity is very small. If all the pixels are set to the same temperature in this manner, the same effect can be obtained as in the case where an object having a constant temperature is conventionally placed in front of the infrared camera. The temperature control of the semiconductor substrate 11 as described above can be achieved by feeding back the output of the temperature detecting means 40 and controlling the heating means 41 so that the temperature coincides with a predetermined temperature. Alternatively, a method is also possible in which the heating means 41 is appropriately operated to perform heating, and the temperature at that time is detected by the temperature detecting means 40. As described above, the diaphragm portion 14
Is brought into contact with the semiconductor substrate 11 to bring the temperature to a predetermined value,
When the diaphragm section 14 is separated from the semiconductor substrate 11, the preparation state for imaging is completed.

Next, the function of bringing the diaphragm portion 14 into and out of contact with the semiconductor substrate 11 as described above will be described. In the present embodiment, the diaphragm section 14 and the semiconductor substrate 11 are brought into contact with each other by electrostatic force. That is, the electrode 30 formed on the diaphragm portion 14
An electric field is applied between the substrate and the semiconductor substrate 11 (a voltage application circuit is not shown). For example, when the semiconductor substrate 11 side is grounded and a positive voltage is applied to the electrode side, the diaphragm portion 14 is attracted by electrostatic force, the beam portion 13 is bent, and the diaphragm portion 14 and the semiconductor substrate 11 come into close contact. At this time, the temperature on the semiconductor substrate 11 side is conducted to the diaphragm portion 14 side, and the diaphragm portion 14 having a small heat capacity quickly becomes the same temperature as the semiconductor substrate 11. The temperature at this time is measured by the temperature detecting means 40. The size of the diaphragm portion 14 is, for example, about several tens to several hundreds μm on one side, and
Is about 1 μm to several μm, for example, and can be easily adhered by applying a low voltage.

When the applied voltage is removed, the diaphragm 14 is separated from the semiconductor substrate 11 by the elastic force of the beam 13. Note that a metal layer may be provided on the semiconductor substrate 11 side or a layer of a material having low adhesion to the silicon nitride film may be formed so that the diaphragm portion 14 is easily separated from the semiconductor substrate 11. Further, grooves may be formed in these layers in order to ease the adhesion between these layers and the diaphragm portion 14.

The above description is an example of the case where the semiconductor substrate 11 can be used as an electrode with low resistance (high impurity concentration). However, when the semiconductor substrate 11 has a high resistance value (low impurity concentration). In the case where a support substrate made of an insulating material is used, a second electrode is provided at a position opposing the electrode 30 on the support substrate (a position opposing the diaphragm portion 14 with the gap 20 therebetween). It may be configured to apply a voltage between the electrodes.

Next, a configuration for correcting the performance (sensitivity calibration) of each pixel using the above-described temperature control (means for correcting the output signal of each pixel) will be described. FIG. 4 shows (m-1,
FIG. 9 is a diagram illustrating the concept of output signals at (T−1) and (T2) for the (n−1) -th pixel and the (m, n) -th pixel.
It should be noted that the temperature referred to here indicates the temperature of the object itself (the unit may be C or K), and does not mean a temperature difference. It is assumed that the entire thermal infrared imaging device as shown in FIG. 3 is set to the temperature T1 by the above-described method using the heating means 41, and the diaphragm portion 14 of each pixel is brought into contact with the substrate. At this time, both the (m-1, n-1) th pixel and the (m, n) th pixel have the same temperature T1. At this temperature T1, an output signal V1 of the (m-1, n-1) th pixel and an output signal V1 'of the (m, n) th pixel are obtained. Although the temperature change in the pixel itself is a change in the resistance value of the resistor 16, it is treated here as being converted into a voltage and output. Next, the entire thermal infrared imaging device is set at a temperature T2 (for example, T2> T1), the diaphragm section 14 of each pixel is brought into contact with the substrate, and (m
The output signal V2 of the (−1, n−1) th pixel and (m, n)
An output signal V2 'of the pixel is obtained.

The difference between the above temperatures T1 and T2 (T2-T1)
Is ΔT, and the difference (V2−V1) between the output signals of the pixels is Δ
If V1, (V2′−V1 ′) is ΔV1 ′, then (m−
ΔV1 / ΔT = (V2−V1) / (T2−T1) for (1, n−1) th pixel ΔV1 ′ / ΔT = (V2′−V1 ′) for (m, n) th pixel / (T2−T1) is the output signal change with respect to the temperature change, and this value can be treated as a proportional constant indicating the temperature change of the output signal for each element. The same is performed for all the pixels, the data of all the pixels is stored in the storage unit, and the performance of each pixel is corrected when the infrared camera is used.

Hereinafter, a case where an average value is used will be described as an example of performance correction (calibration) of each pixel. The proportional constant (corresponding to the above △ V1 ′ / △ T) of the (m, n) th pixel obtained as described above is A (m, n), and the average value of the proportional constants of all pixels is A, Consider sensitivity correction for the (m, n) -th pixel. The difference between the output voltage V1 of the (m, n) -th pixel and the average value V of the output voltages of all the pixels at the temperature T1 is (V-V1). Assuming that the output voltage of the (m, n) -th pixel at a certain temperature Tx is Vx, the correction value is [Vx + (V−V1)] × A / A (m, n). Similar correction is performed for other pixels. By performing such correction, the performance correction of all pixels can be performed based on the average value.

Next, a case where performance correction is performed with reference to a certain pixel will be described. For example, if the reference pixel is (1,
The pixel is the 1) th pixel, and the proportional constant of the (1,1) pixel is A0. The difference between the output voltage V1 of the (m, n) -th pixel and the output voltage V0 of the (1, 1) pixel at the temperature T1 is (V0-V1). At a certain temperature Tx, (m,
Assuming that the output voltage of the (n) th pixel is Vx, the correction value is [Vx + (V0−V1)] × A0 / A (m, n). Similar correction is performed for other pixels. By performing such correction, the performance correction of all pixels can be performed based on the average value. As described above, the difference in sensitivity between the pixels can be eliminated.

As for the performance correction of each pixel, a method has been described in which a proportionality constant is obtained from two points of data and the data is corrected based on the proportional constant. However, the relationship between the output signal of the pixel and the temperature is linear. Otherwise, if the set temperature is set to three or more points, the output signal at each temperature is measured, the temperature characteristic curve of each pixel is obtained, and the correction corresponding thereto is performed, so that the performance can be corrected with high accuracy. Further, it is desirable to set the temperatures T1, T2, and the like when performing the performance correction, for example, to values close to the temperature of the subject to be imaged.

The above-described correction does not reach the point where the semiconductor substrate 11 is heated even if infrared light enters through the infrared camera and is irradiated on the infrared sensor.
No environmental impact. Furthermore, since heating and temperature detection are performed using an electrical method, a uniform temperature object for performance correction is not required. Therefore, the infrared camera can be quickly prepared.

Next, a method of manufacturing the device shown in FIGS. 1 to 3 will be described. First, on the semiconductor substrate 11, an oxide film (for example, PSG
Film). Here, a method for forming a sacrificial layer of PSG will be described. A P having a thickness of about 1 μm
An SG oxide film is formed by a CVD method or the like. Since this PSG oxide film is a sacrificial etching layer, it may be polyimide or the like. Lattice grooves (width about 1 μm) in this PSG oxide film
Is formed by etching. The same PSG oxide film is formed thereon by the CVD method, and is etched away except for a part. In this way, the portion that becomes the void 20 (the diaphragm portion 14
A sacrificial layer is formed on the lower part of the beam 13). The oxide film serving as the sacrificial layer may be a single layer having a thickness of about 2 μm. However, if the method of forming a groove and forming a PSG oxide film again as described above is used, a small tunnel (cavity or “ Is formed, and the etching solution permeates through the tunnel when the sacrificial layer is etched, so that the etching rate can be increased.

Next, a film to be a diaphragm, for example, a silicon nitride film is formed on the sacrificial layer by LPCVD. This is the structural material of the beam 13 and the diaphragm 12. An electrode 30 is formed on the diaphragm 12. Any electrode may be used as long as it is a metal film.
Considering the S process, the A1 film is preferable. This electrode 30
An interlayer insulating film 17, for example, a silicon oxide,
Furthermore, the resistor 1 whose electric resistance changes according to a temperature change
6 is formed and patterned if necessary. After an interlayer insulating film 19 is formed thereon, an etching hole 18 is formed. Next, the heat absorption layer 25 is formed. The heat absorbing layer 25
In order to enhance the adhesion of the heat absorbing layer 25 between the semiconductor device and the interlayer insulating layer 19, an amorphous Si layer may be formed. In this case, a gold black film is appropriate as the heat absorbing layer 25. Next, an etching solution is injected from the etching hole 18 and the sacrificial layer of the PSG oxide film is removed by etching, thereby forming a gap 20 and separately forming the diaphragm portion 14.

In the above description, the case where a bolometer type infrared sensor is used as a pixel has been described. However, a pn junction type infrared sensor can be similarly configured.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of an infrared sensor (pixel) used in a thermal infrared imaging device of the present invention.

FIG. 2 is a cross-sectional view showing an embodiment of an infrared sensor (pixel) used in the thermal infrared imaging device of the present invention.

FIG. 3 is a plan view showing an array configuration of a thermal infrared imaging device of the present invention.

FIG. 4 is a characteristic diagram showing states of output signals of two pixels.

FIG. 5 is a characteristic diagram showing variations in output signals of respective pixels in the thermal infrared imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Infrared sensor 2 ... Heat absorption layer 3 ... Switching circuit part 4 ... x address line 5 ... y address line 11 ... Semiconductor substrate 12 ... Diaphragm 13 ... Beam part 14 ... Diaphragm part 15 ... Wiring 16 ... Resistor 17 ... Interlayer insulation Layer 18 Etching hole 19 Interlayer insulating layer 20 Air gap 25 Heat absorbing layer 30 Electrode 31 Wiring 40 Temperature detecting means 41 Heating means

Claims (4)

[Claims] A thermo-infrared sensor in which a diaphragm having a thermal isolation structure is formed with a gap from a support substrate, and a thermal type infrared sensor having an infrared detecting portion formed on the diaphragm is used as a pixel, and an array is formed by a plurality of pixels. In the infrared type infrared imaging device, means for contacting and separating the diaphragm with the support substrate, heating means for heating the support substrate, temperature detection means for detecting the temperature of the support substrate or the diaphragm, the diaphragm and the Storage means for storing the temperature at the time of contact with the support substrate and the output signal of the pixel at that time, and means for correcting the output signal of each pixel based on the storage value of the storage means. A thermal infrared imaging device, characterized in that: 2. The method according to claim 2, wherein the diaphragm contacts the support substrate.
The separating means applies electrostatic force between the electrode formed on the diaphragm and the electrode provided on the support substrate or the support substrate, thereby bringing the diaphragm into contact with the support substrate by electrostatic force. The thermal infrared imaging device according to claim 1, wherein: 3. The means for correcting the output signal of each pixel,
3. The thermal infrared imaging device according to claim 1, wherein an output signal of each pixel is corrected according to at least two different temperatures and an output signal value at each temperature. 4. The infrared detector according to claim 1, wherein said infrared detector is of a bolometer type or a p-type.
The thermal infrared imaging device according to any one of claims 1 to 3, wherein the thermal infrared imaging device is an n-junction infrared sensor.