JPH11344375A - Linear infrared detecting element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear infrared detecting element which removes an offset, which reduces the influence by a temperature drift and whose detecting accuracy is enhanced. SOLUTION: In a linear infrared detecting element, a plurality of bolometer elements 1 are arranged on a substrate, and infrared rays are detected by sequentially selecting the bolometer elements 1. A plurality of first bolometer elements 1d which are provided with a thermal isolation structure used to thermally cut off the substrate from the bolometer elements 1 formed on the substrate and which directly receive the infrared rays and a plurality of second bolometer elements 1c which are provided with a thermal isolation structure used to thermally cut off the substrate from the bolometer elements 1 formed on the substrate and which do not receive any infrared rays constitute the linear infrared detecting element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear infrared detecting element and a method of manufacturing the same, and more particularly to an infrared detecting element which eliminates offsets and eliminates the influence of temperature drift, thereby enabling accurate detection of infrared rays. The present invention relates to a linear infrared detecting element suitable for a camera.

[0002]

2. Description of the Related Art A bolometer element changes its resistance value in accordance with a change in temperature, and is widely used for detecting infrared rays by utilizing its characteristics. The operation of a conventional linear infrared detecting element using a bolometer element as an application example will be described with reference to FIG. The unit cells 31 including the bolometer elements 32 are arranged in a linear array, and the bolometer elements 32 in the unit cells 31 are connected to a ground terminal 34 via a unit cell selection transistor 33. Here, the gate electrode of the unit cell selection transistor 33 is controlled by the shift register 35 so as to be turned on in order from the left in the figure. Thereby, the output terminal 3
6, the bolometer element 32 of any one of the unit cells 31 is selectively connected. The light receiving portion of the bolometer element 32 is in a state of high thermal insulation from the substrate, whereby thermal energy due to infrared radiation is temporarily stored in the bolometer element 32. As a result, the temperature of the bolometer element 32 rises, and a corresponding resistance change occurs. By reading this resistance change from the output terminal 36 to the outside,
Object temperature information can be obtained.

As a read circuit, for example, an integrating circuit 3
7 is used. In this method, a constant voltage is applied to the bolometer element for a fixed time, and the current at this time is integrated by the integration capacitor 39. Actually, the integration capacitor 39 connected in series with the bolometer element 32 is charged to a constant voltage in advance, and after a constant time is supplied with a constant voltage, the remaining voltage of the integration capacitor is read. This residual voltage depends on the resistance value of the bolometer element 32 during the integration period and includes information on the amount of heat radiation received from the subject.

[0004] In this manner, information on the amount of infrared radiation can be electrically read. However, in the linear infrared detecting element using the above-mentioned bolometer element, there is a problem that the offset component of the signal is large and a sufficiently large gain cannot be obtained. The main part of the offset component of this signal is generated by a large change in the bolometer resistance due to a temperature rise due to self-heating of the bolometer element during the integration period. This offset component occupies most of the output signal, but does not include any temperature information of the subject. Therefore, the dynamic range of the amplifier cannot be used effectively, and the signal gain cannot be increased. Further, if the integration time is extended, the temperature resolution is improved accordingly, but the offset amount also increases at the same time, so that a sufficient integration time cannot be secured.

[0005] Another major problem is temperature drift. Although the bolometer element is thermally separated from the substrate, there is actually a small amount of heat exchange with the substrate via the signal readout wiring. Therefore, when the environmental temperature changes and the substrate temperature changes, the element temperature of the bolometer changes with a long time constant. This causes a temperature drift. In order to prevent this, frequent correction of FPN (fixed pattern noise) must be performed during operation, which significantly impairs the operability as an infrared camera.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned disadvantages of the prior art, and in particular, to eliminate offsets and eliminate the effects of temperature drift, thereby improving the accuracy of infrared detection. And a novel linear infrared detecting element and a method of manufacturing the same.

[0007]

SUMMARY OF THE INVENTION The present invention basically employs the following technical configuration to achieve the above object. That is, the first aspect of the linear infrared detecting element according to the present invention is a linear infrared detecting element in which a plurality of bolometer elements are formed and arranged on a substrate, and infrared rays are detected by sequentially selecting these bolometer elements. In the infrared detecting element, a substrate and a bolometer element formed on the substrate have a thermal isolation structure in which the substrate is thermally cut off, and a plurality of first bolometer elements that directly receive infrared rays; And a second bolometer element having a thermal isolation structure in which the bolometer element formed in the second bolometer element is thermally cut off and not receiving infrared rays. An aspect is characterized in that a plurality of the second bolometer elements are provided, and a third aspect is the first and the second bolometer elements in the first bolometer element which do not have a heat separation structure. 4 bolometer element, the third bolometer element and the second bolometer element are connected in series between a first power supply and a second power supply, and a first power supply and a second power supply are connected to each other. Wherein the fourth bolometer element and the first bolometer element are connected in series, and a voltage difference between connection points of the respective bolometer elements is detected.
Further, in a fourth aspect, third and fourth bolometer elements having the same structure which are configured not to receive infrared rays are provided, and the third bolometer element and the fourth bolometer element are disposed between a first power supply and a second power supply.
Bolometer elements are connected in series, the first power supply and the second
The first bolometer element and the second bolometer element are connected in series between the bolometer element and a power supply, and a voltage difference between connection points of the bolometer elements is detected. In a fifth aspect, the first bolometer element is arranged and arranged in a first row, and the second bolometer element is arranged and arranged corresponding to the first bolometer element. The sixth aspect is characterized in that the third and fourth bolometer elements and the substrate are formed integrally thermally. According to a seventh aspect, an infrared reflecting film is provided on the substrate, and in an eighth aspect, the infrared reflecting film is provided in the second bolometer element. The light-receiving side must be provided with light-blocking means to block infrared light Which is characterized, also, the ninth aspect, the substrate on which the bolometer element is formed, the first
A differential amplifier for detection is formed together with a switching transistor for selecting the bolometer element.

In a first aspect of the method of manufacturing a linear infrared detecting element according to the present invention, a plurality of bolometer elements are arranged on a substrate, and infrared rays are detected by sequentially selecting these bolometer elements. In the method for manufacturing a linear infrared detecting element, a first transistor for forming a switching transistor for selecting the bolometer element is formed on a substrate.
A second step of forming a sacrificial layer on the substrate, a third step of forming a film made of a bolometer material on the sacrificial layer and a protective film so as to sandwich the film, A fourth step of etching the film with a protective film and covering the film with a protective film, and a fifth step of forming an infrared absorbing film or an infrared reflecting film or a light shielding film on the bolometer material and patterning the film into a predetermined shape. A sixth step of forming a space by removing the sacrificial layer by etching, and a seventh step of bringing the space to a substantially vacuum state. A second aspect is characterized in that the bolometer elements are manufactured using the same material and in the same process.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The linear bolometer element of the present invention is such that the bolometer element addressed by the shift register at an arbitrary time always forms a bridge circuit, and the bridge circuit removes offset components other than infrared signals. Is configured. The bridge circuit is composed of a bolometer element which is a light receiving element, a bolometer element provided with a light-shielding plate on the bolometer element, and a bolometer element having no thermal isolation structure. And the other is connected to the unit cell selection transistor. Two bolometer elements having the same electrical characteristics are connected in series between the power supply and the ground at any operation timing, and the midpoint potential is configured to be the input of the differential amplifier (FIG. 2). reference).

Since each bolometer element is formed under the same conditions and under the same process, it has the same temperature coefficient of resistance. From the bridge circuit, only a net infrared signal from which offset components due to background radiation and self-heating have been removed is extracted.
Therefore, temperature drift is reduced.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a linear type infrared detecting element according to the present invention. FIG. 1 is a view showing the structure of a specific example of a linear infrared detecting element according to the present invention. In these figures, a plurality of bolometer elements 1 are formed and arranged on a substrate 20, In a linear infrared detecting element configured to detect infrared rays by sequentially selecting the elements 1, the linear infrared detecting element has a thermal isolation structure in which the substrate 20 and the bolometer element 1 formed on the substrate are thermally cut off, A plurality of first bolometer elements 1d for directly receiving infrared rays
And a second bolometer element 1c having a thermal isolation structure in which the substrate 20 and the bolometer element 1 formed on the substrate are thermally cut off and not receiving infrared rays. Is shown, and a third infrared detector having the same structure as described above, which does not receive infrared rays.
And a fourth bolometer element 1a, 1b, the third bolometer element 1a and the second bolometer element 1c are connected in series between a first power supply 6 and a second power supply 5, and 3 is connected to the first power source 6.
And the fourth bolometer element 1b and the first bolometer element 1d between the first power supply 6 and the second power supply 5.
And the fourth bolometer element 1
b is connected to the first power supply 6 side, and the configuration is such that the difference between the voltages at the connection points C1 and C2 of the respective bolometer elements is detected. A first column A in which the first bolometer elements 1d are arranged in alignment, and a second column A in which the second bolometer elements 1c are arranged in correspondence with the first bolometer elements 1d. A linear infrared detecting element having a column B is shown.

Hereinafter, the present invention will be described in more detail. FIG. 1 shows a first specific example of the linear infrared detecting element of the present invention. In this specific example, a bolometer element is used as an infrared detecting element. In this example, unit cells 3, a differential amplifier 8, and a shift register 9
It is composed of

The unit cell 3 includes a bolometer element 1, a unit cell selection transistor 4, a ground terminal 5, and a power supply 6. Each of the bolometer elements 1 has one terminal connected to the input of the differential amplifier 8 and the other terminal connected to the unit cell selection transistor 4. In this specific example, in order to reduce the device area, the unit cell selection transistor 4 and the bolometer element 1 are designed to have a two-story structure in the same cell.

There are two types of bolometer elements included in the unit cell 3. The first type is a bolometer element 1A having a substrate and a heat separation structure, and the other type is a bolometer element 1B having no heat separation structure. is there. The detailed difference in the structure will be described later with reference to FIG. In this specific example, only the upper and lower two unit cells 3A and 3B at the left end of the linear array are bolometer elements having no heat separation structure, and all other unit cells 3C and 3D are bolometer elements having a heat separation structure. Further, the unit cells 3C in a horizontal row above the unit cell array are provided with a light shielding plate 7 for blocking the incidence of infrared rays on the infrared incidence surface.

The unit cell selection transistor 4 is controlled by a shift register 9 so that two vertically adjacent unit cells are paired and scanned in order from the left. Thus, at an arbitrary timing, a total of four bolometer elements 1 of the two leftmost unit cells 3A and 3B and the pair of upper and lower unit cells 3C and 3D selected at that time are connected to the bridge of FIG. Configure the circuit.

The bridge circuit formed at an arbitrary timing will be described with reference to FIG. Two bolometer elements 1a, 1b and two bolometer elements 1
A total of four bolometer elements c and 1d are provided between a power supply (first power supply) 6 and a ground (second power supply) 5 to form a bridge circuit. Point C
1, C2 become the inputs of the differential amplifier 8 and the two midpoints C
1, the potential difference between C2 and differential terminal 8 passes through output terminal 9
Is output to With this configuration, only the thermal energy due to the infrared light S incident on the bolometer element 1d at the lower right in FIG. 1B causes a deviation from the equilibrium point of the bridge circuit, and only the effective infrared signal is transmitted to the outside. Is read. Even if the temperature of the substrate changes, the two midpoint potentials, that is, the voltages at the midpoints C1 and C2 change by the same value in the same direction, so that no temperature drift occurs at the output terminal 9.

Next, the structure of each bolometer element of the present invention will be described with reference to FIG. In FIG. 3A, a cavity 16 is provided for thermally separating the bolometer material 13 from the substrate 20, and the bolometer 16 is evacuated to further ensure thermal separation from the substrate 20. The infrared absorbing film 12 is provided on the infrared S incident light side of the material 13, and the infrared reflecting film 15 is provided on the substrate 20, and the thermal separation from the substrate 20 is further ensured by the interference of these films 12 and 15. Therefore, in the unit cell of FIG. 3A, the thermal energy of the infrared incident light S is effectively absorbed by the infrared absorbing film 12 due to the optical interference between the infrared absorbing film 12 and the infrared reflecting film 15, The heat is applied to the protective film 14.
To the bolometer material 13 covered by the bolometer material, resulting in a temperature change and a change in the resistance value of the bolometer material.

Therefore, this type of unit cell is used for the unit cell 3D. Next, FIG. 3B shows the bolometer elements 1a and 1b of the unit cells 3A and 3B. The difference from the bolometer element of FIG. 1A is that there is no cavity. Therefore, the thermal energy of the incident infrared light is quickly diffused into the substrate 20, and the temperature of the bolometer material hardly changes. Since the resistance value and the temperature coefficient have the same electrical characteristics as those of the bolometer element of FIG. 3A, it is convenient to obtain the reference potentials C1 and C2 of the bridge.

FIGS. 3 (c) and 3 (d) show FIGS. 3 (a) and 3 (b) so that thermal energy of infrared incident light is not applied to the bolometer element.
The light shielding plate 7 is provided on the infrared light incident surface. FIG. 3C shows an example in which the infrared reflecting film 12 is provided above the bolometer material 13. Therefore, the bolometer element having the structure shown in FIGS. 3C and 3D is used as a unit cell 3C.

FIG. 2 shows another embodiment of the present invention, in which a bolometer element 1A with a light-shielding plate 7 having a heat separation structure (FIG. 3D) is used for a unit cell 13A, and a heat separation is performed for a unit cell 13C. Bolometer element having a structure (Fig. 3
(A)), the substrate 2 is provided in the unit cells 13B and 13D.
This is configured using a bolometer element 1B (FIG. 3B) which does not have a thermal isolation structure which is thermally integrated with the bolometer element 1B.

Also in this circuit, the unit cell selecting transistor 4 is controlled by the shift register 9 so that two vertically adjacent unit cells are paired and scanned in order from the left. In this way, at an arbitrary timing, the two leftmost unit cells 13A, 13B and the pair of upper and lower unit cells 13C selected at that time,
A total of four 13D bolometer elements 1 constitute the bridge circuit of FIG.

This bridge circuit formed at an arbitrary timing will be described with reference to FIG. The bolometer elements 11a to 11d are provided between a power supply (first power supply) 6 and a ground (second power supply) 5 to form a bridge circuit, and have two midpoint potentials, that is, midpoints C1 and C2. Is the input of the differential amplifier 8, and the potential difference between the two middle points C1 and C2 is output to the output terminal 9 through the differential amplifier 8, whereby the bolometer element at the lower right of FIG. 11
Only thermal energy due to the infrared S incident light incident on c causes a deviation from the equilibrium point of the bridge circuit, and only a valid infrared signal is read out. Also, even if the temperature of the substrate changes, two midpoint potentials, namely,
Since the potentials of the middle points C1 and C2 are constant, no temperature drift occurs at the output terminal 9, and only a predetermined detection output can be taken out.

Therefore, in this circuit, the bridge circuit
Third and fourth identical structures not receiving infrared light
Bolometer elements 11a and 11b are provided, and the first power supply 6
The third bolometer element 11 is connected between the power supply 5 and the second power supply 5.
a and the fourth bolometer element 11b are connected in series, and between the first power supply 6 and the second power supply 5, the first bolometer element 11d and the second bolometer element 11c are connected in series. , The voltage difference between the connection points C1 and C2 of the respective bolometer elements is detected.

In the method for manufacturing a linear infrared detecting element according to the present invention, a first method in which a switching transistor 4 for selecting the bolometer element is formed on a substrate 20.
And a second step of forming a sacrificial layer (not shown) on the substrate 20, and forming a film 13 made of a bolometer material on the sacrificial layer and a protective film 14 with the film 13 interposed therebetween. A third step, and a film 1 comprising the bolometer material
A fourth step of etching 3 into a predetermined shape and covering the film 13 with a protective film 14, and a fifth step of forming an infrared absorbing film or an infrared reflecting film on the bolometer material and patterning the film into a predetermined shape. And a sixth step of forming a space (cavity) by removing the sacrificial layer and a seventh step of bringing the space into a substantially vacuum state. In this case, the bolometer The devices need to be manufactured using the same material and by the same process.

[0025]

The linear infrared detecting element according to the present invention is constructed as described above, and has the following effects.
The first effect is removal of the offset component. By extracting only a net signal from which offset components due to background radiation and self-heating have been removed, a sufficiently large gain after signal detection can be obtained.

The second effect is a reduction in temperature drift. This eliminates the need to frequently perform FPN correction during operation as in the related art, and improves the operability of the infrared camera.

[Brief description of the drawings]

FIG. 1A is a circuit diagram of a linear infrared detecting element according to the present invention, and FIG. 1B is a diagram for explaining a measurement principle of the present invention.

2A and 2B show another specific example of a linear infrared detecting element according to the present invention, wherein FIG. 2A is a circuit diagram and FIG. 2B is an equivalent circuit diagram thereof.

FIG. 3 is a diagram showing a unit cell structure of the present invention.

FIG. 4 is a circuit diagram of a conventional linear infrared detecting element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1a-1d, 11a-11d Bolometer element 3, 3A-3D, 13A-13D Unit cell 4 Unit cell selection transistor 5 Ground terminal 6 Power supply 7 Shielding plate 8 Differential amplifier 9 Shift register 10 Output terminal 12 Infrared absorbing film 13 Bolometer material 14 Protective film 15 Infrared reflective film 16 Cavity 20 Substrate S Infrared

Claims (11)

[Claims] 1. A linear infrared detecting element in which a plurality of bolometer elements are formed and arranged on a substrate, and infrared rays are detected by selecting these bolometer elements in order. A plurality of first bolometer elements that directly receive infrared rays, and a substrate and a bolometer element formed on the substrate have a thermal isolation structure in which the separated bolometer element is thermally interrupted. A second bolometer element having a heat separation structure and not receiving infrared light, and a linear infrared detection element. 2. The linear infrared detecting element according to claim 1, wherein a plurality of said second bolometer elements are provided. 3. A first bolometer element, wherein third and fourth bolometer elements having no heat separation structure are provided.
The third bolometer element and the second bolometer element are connected in series between a first power supply and a second power supply, and the fourth bolometer is connected between the first power supply and the second power supply. 3. The linear infrared detecting element according to claim 1, wherein the element and the first bolometer element are connected in series, and a difference between voltages at connection points of the respective bolometer elements is detected. 4. A third and fourth bolometer element having the same structure so as not to receive infrared rays, wherein the third and fourth bolometer elements are provided between a first power supply and a second power supply. The first bolometer element and the second bolometer element are connected in series between a first power supply and a second power supply, and a voltage of a connection point of each bolometer element is connected. 2. The linear infrared detecting device according to claim 1, wherein the difference is detected. 5. A first column in which the first bolometer elements are arranged in alignment, and a second column in which the second bolometer elements are arranged corresponding to the first bolometer elements. The linear type infrared detecting element according to any one of claims 1 to 3, further comprising: 6. The linear infrared detecting element according to claim 1, wherein the third and fourth bolometer elements and the substrate are formed integrally thermally. 7. The linear infrared detecting element according to claim 1, wherein an infrared reflecting film is provided on the substrate. 8. The linear infrared detecting device according to claim 1, wherein a light blocking means for blocking incidence of infrared light is provided on a light receiving side of said second bolometer element. element. 9. A differential amplifier for detection is formed on a substrate on which the bolometer element is formed, together with a switching transistor for selecting a first bolometer element. The linear infrared detecting element according to any one of the above. 10. A method for manufacturing a linear infrared detecting element in which a plurality of bolometer elements are arranged on a substrate, and infrared rays are detected by sequentially selecting these bolometer elements, wherein the bolometer element is selected as a substrate. A second step of forming a sacrifice layer on a substrate, a second step of forming a sacrifice layer on a substrate, and a second step of forming a bolometer material film on the sacrifice layer and a protection film so as to sandwich the film. A third step of etching the film made of the bolometer material into a predetermined shape and covering the film with a protective film; and forming an infrared absorbing film, an infrared reflecting film, or a light shielding film on the protective film. A fifth step of patterning into a predetermined shape; a sixth step of forming a space by removing the sacrificial layer; and a step of setting the space to a substantially vacuum state. Method for producing a linear infrared detector characterized by comprising between step. 11. The method according to claim 10, wherein the bolometer elements are manufactured using the same material and in the same process.