JP3417855B2 - Infrared sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an infrared sensor,
More specifically, the present invention relates to a sensor of a type that absorbs infrared light and converts it into heat, by which displacement caused by thermal expansion of an infrared absorption structure is converted into capacitance to detect infrared light.

[0002]

2. Description of the Related Art As a conventional technique relating to a capacitance type infrared sensor, there is one disclosed in Japanese Patent Laid-Open No. 8-193888, for example.

In this system, a member having a bimetal structure in which two kinds of metals having different thermal expansion coefficients are laminated is used as a detection electrode (movable electrode), and the detection electrode and a fixed counter electrode facing the detection electrode (this counter electrode). Serves as a reference for knowing the displacement of the detection electrode, and therefore, may be referred to as a reference electrode in this specification) to form a capacitance (capacitor). When this sensor is irradiated with infrared light, the infrared light absorbing member absorbs the infrared light and converts it into heat, causing a temperature change. As a result, the detection electrode having a bimetal structure is bent (deformed by thermal expansion) due to thermal stress, and the gap between the detection electrode and the reference electrode is changed to cause a capacitance change. Therefore, the infrared light amount should be detected as a capacitance change. You can

[0004]

However, when manufacturing a bimetal structure, the temperature at the time of manufacture and the ambient temperature at the time of actually using the sensor are often different, and the thermal stress is caused by the temperature difference. Occurs, and the detection electrode is likely to warp. Further, when the bimetal structure is formed by a sputtering method or the like, film stress is often generated during the film formation, which also causes warpage. When the detection electrode is warped, the electrode gap is widened and the capacitance value is reduced.
In addition, the widening of the gap reduces the influence of the displacement of the detection electrode on the capacitance value, and reduces the sensitivity.

Further, in the conventional example, since a thick glass substrate is used for the electrode mounting member (electrode supporting substrate) having the electrostatic capacity, the thermal resistance and the thermal capacity are large, and the infrared response time determined by the product of both is long. There were challenges left.

The first object of the present invention is to prevent warpage due to thermal stress of the detection electrode (infrared absorbing structure) due to a temperature difference between the manufacturing temperature of the detection electrode and the ambient temperature actually used. It is to solve the problem and improve the detection sensitivity and detection accuracy of infrared light. Secondly, the thermal resistance and thermal capacity of the infrared sensor are reduced to improve the infrared response.

[0007]

In order to achieve the above-mentioned first object, the following problem solving means is proposed.

The first invention is an electrostatic capacitance type infrared sensor.
And both electrodes that make up the capacitance have a bimetal structure
Of the movable electrode. Of these, one of the electrodes (hereinafter referred to as the detection electrode) is set to more displaced infrared absorption structure that absorbs infrared light of the detected thermal expansion deformation, opposed to the detection electrode The other electrode (hereinafter, referred to as a reference electrode) has a temperature compensation structure that can be displaced in a direction that compensates for the displacement of the detection electrode due to a change in ambient temperature .
In addition, the detection electrodes and the reference electrodes are
The degree and direction of the event are matched.

[0009]

According to this structure, even if the detection electrode is warped due to a change in ambient temperature during manufacturing and during use of the sensor thereafter, the reference electrode is displaced in a direction to compensate (cancel) the warp (displacement). By doing so, the relative initial position (inter-electrode gap) between the detection electrode and the reference electrode can be kept substantially constant, and it is possible to prevent a decrease in the sensitivity of infrared light detection. In addition, the influence of ambient temperature can be eliminated as much as possible to capture the capacitance change due to thermal expansion deformation of infrared light absorption, and the infrared detection accuracy (including quantitative detection of infrared light) can be improved. You can

A second aspect of the invention is to use an electrode that constitutes electrostatic capacitance.
One of these electrodes (detection electrode) is
Bimeta absorbs infrared light of an elephant and displaces due to thermal expansion
And a detection electrode that is opposed to the detection electrode in the initial state.
It is characterized in that it is warped toward the constant electrode (reference electrode) side, and a step or an inclination is provided on the surface of the reference electrode to allow the warpage of the detection electrode to escape.

According to this structure, even if the detection electrode (infrared absorption structure; movable electrode) is warped in the initial state, the direction of the warp is on the reference electrode side, and moreover, on the surface of the reference electrode. Since a space for allowing the warp of the detection electrode to escape (a space for receiving the warp) is ensured, the initial gap between the reference electrode and the detection electrode is made small at each site without the detection electrode contacting the reference electrode. Therefore, it is possible to reduce the relative initial position gap (interelectrode gap) between the detection electrode and the reference electrode and prevent the sensitivity of infrared light from decreasing.

[0013]

According to this structure, even if the member for supporting the detection electrode is an infrared absorbing structure, a double-supported beam supporting structure is formed, so that the infrared absorbing structure has a temperature difference between the time of manufacture and the time of use. As a result, the structure is less likely to warp even when subjected to thermal stress, and the detection electrode and the reference electrode maintain a parallel gap in the initial state. Therefore, it is possible to reduce the relative initial position gap (interelectrode gap) between the detection electrode and the reference electrode and prevent the sensitivity of infrared light from decreasing.

[0015]

[0016]

A third aspect of the present invention is provided with an electrode that constitutes an electrostatic capacitance, and one of the electrodes (detection electrode) has a bimetal structure that absorbs infrared light of an object to be detected and is displaced by thermal expansion. A movable electrode, and means for detecting a change in the capacitance, and means for applying a servo control voltage between the electrodes so that the capacitance has a target value. It is characterized by being prepared.

According to the above structure, even if the detection electrode is warped in the initial state due to the temperature difference between the time of manufacture and the time of use, the detection electrode (movable electrode) and the reference electrode (fixed electrode) are in use.
Since the servo control voltage (electrostatic attraction force) is applied so that the electrostatic capacitance becomes the target value during, the reduction of the capacitance value or the capacitance change due to the warp of the initial state of the detection electrode can be suppressed. . Further, in the present invention, infrared light can be detected from the applied value of the servo control voltage.

The second purpose is to provide the infrared sensors described above .
There is achieved a radiation fin on the substrate for mounting the electrodes of the electrostatic capacity set <br/> only isosamples.

According to this structure, the heat capacity of the sensor portion can be reduced and the infrared response of the sensor can be improved. The substrate on which the sensor is mounted can be further reduced in heat capacity of the entire sensor portion by forming a thin film at the location where the heat radiation fin is provided.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a vertical sectional view of an infrared sensor according to an embodiment of the first invention, and FIG. 2 is a plan view showing the structure of its electrode. As an example, an image sensor using many infrared sensors is illustrated. is doing.

The infrared sensor mainly comprises a substrate 1, one electrode (detection electrode) 2 of the electrostatic capacitance, the other electrode (reference electrode) 3 facing it, and a window portion 4 for transmitting infrared light. Consists of.

The substrate 1 is composed of electrodes 2 and 3 which form a capacitance.
Is mounted on the substrate 1, and the electrodes 2 and 3 of the capacitance are mounted on the substrate 1.
The cap-shaped window portion 4 is fixed so as to cover the arrangement space. A silicon plate is used for the substrate 1, and in order to reduce the heat capacity of the electrostatic capacity part, RIE (Rea
While thinning the electrode attachment part of the capacitance by a method such as ctive Ion Etching),
The radiating fins 5 are processed on the bottom portion (outer bottom surface) of the thinned substrate. Further, a thin film 6 of Pyrex glass having a thickness of several μm is formed on the upper surface of the substrate 1 by the sputtering method.

The detection electrode 2 and the reference electrode 3 formed on the Pyrex glass thin film 6 are both made of a bimetal structure. In this embodiment, as an example, polycrystalline Si is used.
(Silicon) thin film 7 and Al (aluminum) thin film 8
The electrodes 2 and 3 are supported by a Si thin film 7 in a cantilever structure.

The detection electrode 2 and the reference electrode 3 are arranged so that the detection electrode 2 faces the window portion 4 and absorbs infrared light, and a gap (gap) between the detection electrode 2 and the reference electrode 3 is secured. A thin film of Pyrex glass is used as the gap holding member (spacer) 9 for this purpose. In addition, the detection electrode 2
In the above, a thin gold black 10 is formed as an infrared light absorbing material on the Al thin film 8.

In this way, the detection electrode 2 is set so as to be displaced by the infrared absorption structure (bimetal structure) that absorbs infrared light of the object to be detected and undergoes thermal expansion deformation. In addition, the bimetal structure of the detection electrode 2 and the bimetal structure of the reference electrode 3 are configured so as to have the same thermal expansion deformation, and in that sense, the bimetal structure of the reference electrode 3 is changed by a change in ambient temperature. When the detection electrode 2 is displaced, it functions as a temperature compensation structure that can be displaced in a direction that compensates (cancels) this.

The detection electrode 2 and the reference electrode 3 are connected to the detection electrode line 11 and the reference electrode line 12, respectively.

The multilayer film structure having such a capacitance gap is manufactured by using a thin film forming technique such as sputtering, vapor deposition, and CVD, and a sacrifice layer etching technique.

In the infrared sensor according to the present embodiment, the detection electrode 2 and the reference electrode 3 are warped toward the light receiving surface side. This is during the manufacturing process, after the thin film forming process at high temperature. When the temperature is returned to room temperature, thermal stress is generated in the polycrystalline Si thin film 7 and the Al thin film 8 of the bimetal structure due to the difference in thermal expansion coefficient, and when the electrode becomes free after the sacrifice layer etching, thermal expansion occurs. This is because the Al thin film 8 having a large coefficient contracts greatly.

A silicon plate is used for the window portion 4, and after forming a space for the electrode portion by etching, the Pyrex glass layer 6 on the substrate 1 is used to join the substrate 1 by anodic bonding. At that time, the light-receiving portion can be made into a vacuum by bonding in a vacuum atmosphere, and deterioration of responsiveness due to the magnitude of the heat capacity of the gas can be prevented.

Next, the electrode structure will be described with reference to a plan view.
This sensor is a sensor array in which a minute sensor is one pixel and is arranged in a matrix, and an infrared image can be detected. The electrode wire 11 of the detection electrode 2 and the reference electrode 3,
12 are orthogonal to each other through an insulating member 13 and are connected to adjacent sensors.

Al, Au, Pt and the like are suitable as the material of the electrode wire, and Ti, Cr and the like may be used as the intermediate layer in order to enhance the adhesion to the substrate.

Next, the operation principle will be described. The infrared light that has passed through the window 4 is absorbed by the gold black 10 above the detection electrode 2 and converted into heat, and the temperature of the detection electrode 2 changes accordingly.
At this time, the detection electrode (movable electrode) 2 serves as a shield plate for the reference electrode 3 and is not irradiated with infrared light, and is thermally insulated from the detection electrode 2 by the gap holding material 9 having a large thermal resistance. The temperature change of the reference electrode 3 due to infrared light does not occur.

Since the detection electrode 2 has a bimetal structure, the curved state of the detection electrode 2 changes due to the thermal stress caused by absorption of infrared light, and the gap between the reference electrode 3 and the detection electrode 2 changes (in this embodiment, As the amount of infrared light absorption increases, the detection electrode 2 is displaced in the direction of decreasing the gap with the reference electrode 3). Since the capacitance value between the detection electrode 2 and the reference electrode 3 depends on the gap amount, the change in the infrared light amount can be measured by monitoring the capacitance value between the electrodes. The capacitance value C is represented by C = εS / d (here, ε is the dielectric constant of the interelectrode gap, S is the electrode facing area, and d is the interelectrode gap).

For example, let d be the electrode gap at the initial stage of the electrostatic capacitance, and let the gap d be Δ due to the infrared light absorption of the detection electrode 2.
If only d changes,

[0037]

[Equation 1] Initial capacity C = εS / d After displacement C * = εS / (d−Δd) Change amount ΔC = C−C * = εSΔd / d (d−Δ
d) When a constant voltage is applied between the detection electrode 2 and the reference electrode 3 and the capacitance changes, the change in the accumulated charge amount due to the change in the capacitance is measured by current or voltage,
Capacitance can be detected.

In the conventional example, the direction of the warp of the initial position of the detection electrode 2 (the warp due to the thermal stress caused by the temperature difference between the time of manufacture and the time of use) does not hit the reference electrode 3,
Although the structure is curved on the opposite side,
There is a problem that the electrode gap is widened and the initial capacitance value and the capacitance change amount are reduced. On the other hand, in the structure of the present invention, since the reference electrode 3 also has the same bimetal structure as the detection electrode 2, it has the same warped shape in the initial state before being irradiated with infrared light. The gap interval can be made almost equal and small in each part, and the initial capacitance value and the capacitance change amount can be increased. Therefore, it is possible to prevent the sensitivity of the capacitance type infrared sensor from decreasing.

Further, in this structure, the electrodes of the bimetal structure are displaced even when the ambient temperature changes. However, if the reference electrode 3 and the detection electrode 2 have substantially the same shape, both of them have the same displacement with respect to the ambient temperature change. Because of the amount, the gap spacing is kept almost constant and the influence of ambient temperature can be cancelled. Therefore, the detection accuracy of the infrared sensor can be increased without providing a special temperature sensor or temperature compensation circuit.

Further, in this structure, Si, which has a smaller thermal resistance than glass or the like, is used as the material of the substrate 1, the electrode forming portion is further thinned, and the heat radiation fins 5 are processed. The resistance and heat capacity can be reduced, and the infrared response can be improved as compared with the conventional example.

Next, the structural features of the infrared sensor according to the embodiment of the second invention and the method for manufacturing the infrared sensor will be described with reference to FIG. FIG. 3 is a vertical cross-sectional view showing a manufacturing process of an electrostatic capacitance portion which is a main portion of the infrared sensor of this embodiment.

FIG. 3D is a completed view of the electrostatic capacitance section. In this example, the reference electrode 3 is composed of a so-called fixed electrode fixed to the substrate 1, and the detection electrode 2 has a cantilever structure. It is composed of movable electrodes. The infrared absorption structure constituting the detection electrode 2 is composed of the Si thin film 15 and A
1 is composed of a bimetal structure of the thin film 8, but differs from the embodiment of FIG. 1 in that the Al thin film 8 is arranged on the side facing the reference electrode 3 and the Si thin film 15 on the opposite side is arranged.
By doing so, the infrared absorption structure (detection electrode) 2
When the ambient temperature actually used (the temperature after fabrication) is different from the temperature during fabrication, the reference electrode 3 is warped.
It is bent to the side.

On the surface of the reference electrode 3, the above-mentioned detection electrode 2 is formed.
Of the initial state of the detection electrode 2, that is, a plurality of step-like steps are formed from the supporting portion of the detection electrode 2 to the free end side, so that the detection electrode 2 is free from the warpage (stepped space). Has been secured.

In the case of forming the capacitance section of this embodiment, first, as shown in FIG. 3A, the silicon substrate 1 is etched in steps by repeating the photolithography technique, and then is sputtered. After forming the thin film 6 of Pyrex glass, a metal thin film such as Al is formed on the surface by a sputtering method, and the reference electrode 3 is manufactured by this metal thin film.

Next, boron is diffused on the surface of the p to silicon plate 14 to form a p ++ layer (Si thin film) 15, and then an Al thin film 8 to be the detection electrode 2 is formed on the surface and patterned. As shown in FIG. 3B, the silicon plate 14 is applied to the substrate 1 on which the stepped surface-shaped fixed electrode (reference electrode) 3 is formed.
Then, as shown in FIG. 3 (c), selective etching is performed to etch the parts other than the diffusion layer 15 with ethylenediamine-pyrocatechol water. After that, as shown in FIG. 3D, the Si film (boron diffusion layer) 15 with the Al thin film 8 is formed.
Is patterned by RIE or the like to form the detection electrode 2. At that time, the Al thin film 8 having a larger thermal expansion coefficient than Si,
Since the tensile stress is applied, the detection electrode 2 is the substrate 1
Warp to the side. However, in this structure, since the reference electrode 3 is stepped according to the shape of the warp of the detection electrode 2, it is possible to reduce the gap interval at each portion between the detection electrode 2 and the reference electrode 3, and thus the initial stage is reduced. It is possible to increase the electrostatic capacitance value and the amount of capacitance change. Therefore,
Also in this embodiment, it is possible to prevent a decrease in infrared light detection sensitivity.

Although not shown in the drawing, the final product shape of the structure of this embodiment is such that the window 4 as shown in FIG. 1 is attached to the substrate 1 so as to cover the capacitance mounting space. However, on the window 4 side of the bimetal structure of the detection electrode 2, instead of the Al layer (Al thin film) 8 having a large infrared reflection,
Since the silicon layer 15 is formed and the silicon layer 15 in which boron is diffused has an infrared absorption effect, there is an advantage that it is not necessary to form an absorbing material such as gold black on the detection electrode 2.

In the case of the present embodiment, the detection electrode 2 undergoes thermal expansion deformation on the side opposite to the reference electrode 3 as the infrared absorption amount increases.

Even if the surface shape of the reference electrode 3 is changed to a stepped shape and is processed into an inclined shape in accordance with the warped shape of the detection electrode 2 as shown in FIG. 4, the same effect as described above is obtained. Can be played.

Next, regarding the third embodiment of the present invention,
This will be described with reference to the sectional view of FIG. In this structure, the detection electrode 2
Is not supported by a cantilever structure, but is supported by a bilateral structure by a bimetal structure (infrared absorption structure).

Of the electrostatic capacitance, the detection electrode 2 composed of a movable electrode is composed of an electrode plate (for example, a silicon plate) having a thick film thickness which is not easily deformed, and a bimetal structure (beam) 2'supporting it from both sides. Is composed of a beam portion 16 formed by extending the same member as the electrode plate (silicon plate) 2 and an Al thin film 17 formed on the beam portion 16.

In this embodiment, the reference electrode 3 is a fixed electrode formed on the substrate 1 with a Pyrex glass thin film 6 interposed therebetween.

According to this embodiment, since the beam 2'is warped due to the bimetal structure, the electrode plate 2 which is not easily deformed.
By supporting the electrode plate 2 from both sides by a symmetrical beam 2 ', the electrode plate 2 is kept horizontal with respect to the reference electrode 3 against temperature changes while suppressing warping of the beam 2'. Move up and down while keeping it. Therefore, it is possible to suppress the decrease in the capacitance value or the capacitance change due to the warp of the detection electrode 2, and prevent the sensor detection sensitivity from decreasing.

Next , a detection electrode which replaces the bimetal structure is provided.
With the infrared sensor, the problem of initial warpage of bimetal
The lost embodiment will be described with reference to FIG. FIG. 6 is a plan view showing an operating state of the capacitance section of this embodiment.

This sensor is basically a plurality (for example, 2
Detection electrode 2 composed of comb-shaped movable electrodes
1 and a comb-teeth-shaped reference electrode (fixed electrode) 31 that alternately enters the detection electrode 21. Detection electrode 21
Is integrally formed with the beam 21a, and the base 20 of the beam 21a is thinned, and the detection electrode 21 is attached to the frame 19 via the base 20. Detection electrode 2
1, the beam 21a and the frame 19 are made of a conductor such as Si, and the reference electrode 31 and its frame 1
8 is also made of a conductor.

The detection electrode 21 has its beam 21a.
Via a support member 22 made of a material having a large coefficient of thermal expansion such as Al through steps from both sides of the beam 21a in a stepped manner. This stepped support structure causes the support member 22 to undergo thermal expansion as shown in FIG. It is set so that a rotational moment in one direction is generated in. In order to generate such a rotation moment, it is premised that the base 20 has a large degree of freedom in the left-right direction, and in that sense, the base 21 is not provided, and the beam 21a is provided only on the support member 22. Just support it.

When the support member 22 is made of Al having a high light reflectivity, a member having a good infrared light absorption may be applied to the surface thereof, whereby the infrared light of the detection object can be detected. A support member having an infrared absorption structure that absorbs and thermally expands is configured. In this example, the support member 2 is inserted through the window 4 similar to that shown in FIG.
Infrared light is incident on 2.

Next, the operation of this sensor will be described.
When thermal expansion occurs in the support member 22 by infrared absorption, the force generated by the thermal expansion causes the detection electrode 21 to rotate via the beam 21a as shown in FIG. 6 (b) according to the lever principle shown in FIG. Displace.

Due to this rotational displacement, the gap between the detection electrode 21 and the reference electrode 31 of the comb-teeth electrode structure changes, and the capacitance changes.

The reason why the capacitance value changes is shown in FIG. 8 and the calculation formula.

As shown in FIG. 8, the comb-teeth-shaped detection electrode 2
The capacitance C between 1 and the reference electrode 31 is

[0061]

## EQU2 ## It is represented by C = C1 + C2 + C3 + C4 (other, including parasitic capacitance, omitted). Here, when the movable electrode moves to the right, C2 and C4 increase and C1 and C3 decrease. When such an operation is taken, it is apparent that the increasing capacity and the decreasing capacity are offset and the output does not appear, but the capacity changes quantitatively.

Considering C1 and C2 for simplification, assuming that the initial electrode gaps of C1 and C2 are d, and the displacement is Δd,

[0063]

[Number 3] initial capacity C = εS / d + εS / d = ε2S / d ... (1) displacement after the C * = εS / (d- Δd) + εS / (d + Δd) = ε2dS / (d 2 -Δd 2) (2) Change amount ΔC = C−C * = 2εSΔd ² / d (d ² −Δd ² ) (3) As is clear from the above equation, it is understood that the capacitance change is caused by the change amount ΔC.

Also in this structure, due to the thermal stress of the supporting member 22 of the infrared absorption structure, the detection electrode (movable electrode) 21 is offset in the rotational direction due to the temperature change during and after the manufacture. By forming a so-called comb-like structure in which the detection electrode 21 and the reference electrode 31 are alternately inserted, the capacitance value between the detection electrode and the reference electrode increases. The reason for this is that the relationship between the displacement amount and the capacitance value is as shown in FIG. 9 according to the result shown in the equation (2), and therefore the capacitance value after the fabrication increases in either direction. This is because it works in the direction.

Therefore, also in this embodiment, even if an offset occurs in the detection electrode 2 after fabrication, the detection sensitivity of infrared light can be increased.

Next, an infrared sensor according to the third embodiment of the present invention will be described with reference to FIG. The infrared sensor according to the present embodiment relates to an electrostatic servo control type, and FIG.
0 (a) shows the infrared sensor in the initial state before the servo control is carried out, and (b) shows the state where the servo control is carried out.

Detection electrode (movable electrode) 2 in this embodiment
Is a bimetal structure (infrared absorption structure) of Al and polycrystalline Si, and is formed by a thin film forming technique such as a sputtering method on the Si substrate 1 via the Pyrex glass thin film 6 and a sacrifice layer etching technique. It is formed by the structure. The facing reference electrode (fixed electrode) 3 is a thin film of Al or the like, and is fixedly formed on the substrate 1 via a Pyrex glass thin film 6.

When servo control is not performed, the detection electrode 2 has an initial warp (displacement) in a direction away from the reference electrode 3 (Si window portion 4 direction) due to thermal stress after fabrication, as shown in FIG. ) Occurs, but SiO provided on the Si window portion 4
_The free end is pressed down by the projection (stopper member) 23 of the insulating material consisting of ₂ , and the amount of warpage is regulated (reduced).
Has been done.

Next, the operating principle of this sensor will be described.

When a voltage between the reference electrode 3 and the detection electrode 2 is applied, the curved detection electrode 2 is pulled back to the reference electrode 3 side by electrostatic attraction, and a flat plate is formed as shown in FIG. 10 (b). Become a state. The capacitance value at this time is C ₀ .
Here, when the temperature of the detection electrode 2 changes due to infrared absorption, the detection electrode 2 is displaced due to the thermal stress due to the bimetal structure, and the gap changes, so that the capacitance value C _0.
Change from.

The capacitance value at this time is determined by the capacitance value detection circuit 24.
The servo control voltage applied between the detection electrode 2 and the reference electrode 3 is feedback-controlled by the voltage application circuit (servo control voltage application means) 25 so that the capacitance value is always C ₀ .

The infrared light amount can be detected by reading this servo control voltage.

In this method, since infrared light is detected while the detection electrode 2 is forcibly flattened by applying an electrostatic attraction between the electrodes, the capacitance value and the capacitance change due to the warp of the detection electrode 2 The decrease can be suppressed. Therefore, although warpage that occurs during manufacture is allowed to some extent, if the warp becomes too great, it cannot be pulled back by electrostatic attraction. Therefore, even if the electrostatic attraction is applied, it is possible to increase the degree of design freedom by providing the projection 23 that functions as a stopper so that the warp of the detection electrode 2 does not become excessive.

[0074]

As described above, the first invention to the third invention
According to the invention of claim 1, even when an initial warp (thermal stress) due to temperature change during and after manufacturing occurs in the detection electrode that constitutes the electrostatic capacity in the infrared sensor, the capacitance value decreases and the sensitivity is reduced. It is possible to provide at low cost a sensor that prevents deterioration and that exhibits high sensitivity and high responsiveness. Further, according to the first invention, even if the detection electrode is displaced due to a change in ambient temperature during use, the temperature compensation structure is adopted for the reference electrode, so that the influence of the ambient temperature can be eliminated and the infrared light can be eliminated. The detection accuracy can be improved.

In addition, the infrared sensor according to each of the above inventions
If a radiation fin is provided on the substrate that supports the capacitance,
The heat capacity of the entire sensor can be reduced to improve the responsiveness of the sensor.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an infrared sensor according to an embodiment of the first invention.

FIG. 2 is a plan view showing the structure of the electrode of the above embodiment.

FIG. 3 is a vertical cross-sectional view showing a process of manufacturing an electrostatic capacitance portion which is a main portion of an infrared sensor according to an embodiment of the second invention.

FIG. 4 is a vertical sectional view showing a modified example of the infrared sensor according to the embodiment of the second invention.

FIG. 5 is a vertical sectional view of an infrared sensor according to an embodiment of the third invention.

FIG. 6 is a plan view showing an operating state of an infrared sensor according to an embodiment of the fourth invention.

FIG. 7 is an explanatory diagram of a rotation moment applied to the detection electrode according to the embodiment of the fourth invention.

FIG. 8 is an explanatory diagram showing a change in electrostatic capacitance according to the embodiment of the fourth invention.

FIG. 9 is an explanatory diagram showing the relationship between the displacement of the detection electrode and the change in capacitance according to the fourth embodiment of the invention.

FIG. 10 is an explanatory view showing an initial state of the infrared sensor according to the fifth embodiment of the present invention before the servo control is performed and a state where the servo control is performed.

[Explanation of Codes] 1 ... Substrate, 2 ... Detection electrode, 3 ... Reference electrode, 4 ... Window portion, 5
... radiation fins, 20 ... beams, 21 ... comb-teeth-shaped movable electrodes (detection electrodes), 22 ... support members having a large coefficient of thermal expansion,
23 ... Warp restriction stopper, 24 ... Capacitance value detection circuit (electrostatic capacitance detection means), 25 ... Voltage application circuit (servo control voltage application means) 31 ... Comb-shaped fixed electrode (reference electrode).

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-198597 (JP, A) JP-A-8-193888 (JP, A) JP-A-51-84681 (JP, A) International Publication 97/036155 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01J 1/00-1/60 G01J 5/00-5/62

Claims (5)

(57) [Claims] 1. In a capacitance type infrared sensor, both electrodes constituting a capacitance are movable electrodes having a bimetal structure, and one of these electrodes (hereinafter referred to as a detection electrode)
Is set to absorb infrared light of an object to be detected and displaced by thermal expansion, and the other electrode (hereinafter referred to as a reference electrode) facing the detection electrode is the detection electrode due to a change in ambient temperature. Is capable of being displaced in a direction compensating for the displacement of the infrared sensor, and the degree of warpage in the initial state of the detection electrode and the reference electrode is adjusted to the same degree. 2. An electrode forming a capacitance is provided, and one of these electrodes (hereinafter, referred to as a detection electrode) has a bimetal structure which absorbs infrared light of an object to be detected and is displaced by thermal expansion. The detection electrode is composed of a movable electrode, and in the initial state, the detection electrode is warped to the other fixed electrode (hereinafter referred to as reference electrode) side facing the detection electrode, and the detection electrode is warped on the surface of the reference electrode. An infrared sensor characterized by being provided with a step or a slope for escape. 3. An electrode forming a capacitance is provided, one of which is formed of a bimetal structure movable electrode which absorbs infrared light of a detection target and is displaced by thermal expansion, and Means for detecting a change in the capacitance,
An infrared sensor comprising means for applying a voltage for servo control between the electrodes of the capacitance so that the capacitance has a target value. 4. The infrared sensor according to claim 3, further comprising an insulative stopper member arranged to regulate a warp amount of the movable electrode due to a thermal stress when the servo control is not performed. 5. A substrate to which the electrode of the electrostatic capacity is attached is provided, and a radiation fin is provided on the substrate.
5. The infrared sensor according to any one of 1 to 4 .