JP2008026124A - Thermal infrared sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a readily manufacturable thermal infrared sensor having superior detection sensitivity, using a dielectric film whose solid-state properties change depending on the temperature. <P>SOLUTION: In this thermal infrared sensor 100 having an infrared detection part 110, the infrared detection part 110 is equipped with the first electrode part 103a and the second electrode part 103b formed adjacent on a substrate 105, and a conductive layer 106, formed in a state of facing the first electrode part 103a and the second electrode part 103b via the dielectric film 101. The conductive layer 106 includes the third electrode part 106a facing the first electrode part 103a and the fourth electrode part 106b facing the second electrode part 103b. The first capacitor, comprising the first electrode part 103a and the third electrode part 106a and the second capacitor that comprises the second electrode part 103b and the fourth electrode part 106b are connected in series by electrical connections formed by including the third electrode part 106a and the fourth electrode part 106b in the conductive layer 106. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an infrared sensor that detects infrared rays emitted from an object, a human body, and the like, and more particularly, to a thermal infrared sensor that captures infrared rays as changes in physical properties of a dielectric film due to temperature changes.

  An infrared sensor that detects infrared rays radiated from a human body and an object can obtain information on the presence and temperature of the object in a non-contact manner. For this reason, application is expected in various fields such as human body detection in a dark field as a security use and a non-contact thermometer.

  There are many detection methods for infrared sensors, but the mainstream methods that are often used can be broadly divided into two types. One of them is a quantum infrared sensor that utilizes the photoelectric effect of a solid material to directly convert absorbed infrared light into an electrical signal for detection. The other is a thermal infrared sensor that converts a received infrared ray into heat once and detects the temperature change due to the heat using a material having a large change in physical properties due to temperature.

  Since the quantum infrared sensor uses the photoelectric effect based on the solid state transition by infrared absorption as the basic principle of infrared detection, a cooling mechanism using liquid nitrogen or the like is usually required. On the other hand, since the thermal infrared sensor performs detection using heat generated by infrared absorption, it can detect infrared rays even at room temperature, and can realize an inexpensive and small device.

  As such a thermal infrared sensor, there is a sensor using a change in characteristics of a dielectric film. When classified further, a pyroelectric infrared sensor that detects pyroelectric current caused by a temperature change of the ferroelectric film, and a dielectric infrared sensor that detects infrared rays using the temperature change of the relative permittivity of the ferroelectric film. Is known. Among them, the dielectric infrared sensor is superior to the pyroelectric infrared sensor in that it does not require a chopper and does not require polling necessary for improving the pyroelectric effect and is suitable for miniaturization. Since it has characteristics, its practical application is expected.

  The basic structure of a thermal infrared sensor using a dielectric film and the basic operation principle of pyroelectric and dielectric infrared sensors will be described below. First, FIG. 10 is a view showing a cross-sectional structure of a conventional thermal infrared sensor using a dielectric film (see, for example, Patent Document 1).

  The thermal infrared sensor of FIG. 10 is formed using a substrate 17. An insulating film 16 is formed on the substrate 17, and a lower electrode 13, a dielectric film 11, and an upper electrode 12 are formed on the insulating film 16 in this order from the bottom to constitute the infrared detecting unit 10 having a capacitor structure. .

  Note that a part of the substrate 17 is removed from the back side by etching under the infrared detecting unit 10 to be thinned. Furthermore, the portion on which the infrared detecting unit 10 is mounted in the thinned substrate 17 becomes the mounting unit 20, and the mounting unit 20 is connected to the peripheral portion of the substrate 17 by the support unit 18. With such a structure, the infrared detector 10 is thermally insulated from the surroundings.

  In addition, a wiring 15 is connected to the lower electrode 13, and a wiring 14 is connected to the upper electrode 12.

  In the thermal infrared sensor having such a structure, the irradiated infrared ray 19 is absorbed by the infrared detection unit 10 and converted into thermal energy, and the infrared ray is thermally insulated by taking a structure supported by the support unit 18. This contributes to the temperature rise of the detection unit 10.

  Here, in the case of a pyroelectric infrared sensor, a change in pyroelectric charge caused by a temperature change is detected as a minute pyroelectric current. When the temperature does not change, the amount of charge does not change, so it is effective for detecting moving objects that cross the front of the sensor, but means such as a chopper to detect a stationary object It is necessary to modulate the infrared.

  On the other hand, in the case of a dielectric infrared sensor, a change in relative dielectric constant in a dielectric film caused by a temperature change is detected by voltage conversion. FIG. 11 shows an example of a detection circuit in a dielectric infrared sensor.

  In the dielectric infrared sensor of FIG. 11, a variable capacitor 31 whose relative dielectric constant varies with temperature and a reference capacitor 33 whose relative dielectric constant is substantially constant regardless of temperature are electrically connected to each other. More series connected circuits are used. Further, as shown in FIG. 11, the other terminal of the reference capacitor 33 is connected to the voltage source 34, and the other terminal of the variable capacitor 31 is connected to the ground GND (that is, grounded).

  In such a circuit, an electric signal at the output terminal 32 which is a connection point between the variable capacitor 31 and the reference capacitor 33 is detected. The voltage output to the output terminal 32 is a voltage in which the power supply voltage from the voltage source 34 is distributed according to the capacitance values of the variable capacitor 31 and the reference capacitor 33 connected in series. For this reason, when the capacitance of the variable capacitor 31 changes due to a temperature change, the voltage output to the output terminal 32 changes, and the temperature change can be detected as a voltage change.

  Suitable materials for the dielectric infrared sensor include barium titanate-based ferroelectric materials having a high dielectric constant temperature change rate near room temperature. In particular, titanic acid stannic acid in which a part of titanium is substituted with tin and zirconium, respectively. Barium or barium zirconate titanate is effective. Further, in these materials, materials in which a part of barium is replaced with calcium are also effective. As an example of such a material, the relative dielectric constant-temperature characteristic of barium titanate titanate is shown in FIG. FIG. 12 shows the relative dielectric constant-temperature characteristics using the voltage applied to the dielectric film and the electric field strength converted with the thickness of the dielectric film as parameters.

  FIG. 13 shows the ratio of the variable capacitor 31 in FIG. 11 in the case where the infrared rays are started to be irradiated at time T after matching the capacitances of the variable capacitor 31 and the reference capacitor 32 at the room temperature of 300 K before the infrared irradiation. The change in dielectric constant and the output from the output terminal 32 are shown.

  Before the infrared irradiation, the variable capacitor 31 and the reference capacitor 33 have the same capacity. For this reason, a half potential with respect to the power supply voltage by the voltage source 34 is output to the output terminal 32. When infrared irradiation is started, the temperature of the dielectric film increases, and the relative permittivity of the variable capacitor 31 decreases as shown in the characteristics of FIG. For this reason, in the detection circuit of FIG. 11, the voltage is redistributed between the variable capacitor 31 and the reference capacitor 33, and the potential at the output terminal 32 changes. Here, the potential increases.

  By detecting such a change in potential at the output terminal 32, it operates as a dielectric infrared sensor.

  In addition, since the output voltage is maintained according to the amount of irradiation of infrared rays, unlike a pyroelectric infrared sensor, the modulation of infrared rays by a chopper or the like is unnecessary.

  In the pyroelectric infrared sensor, polling is necessary to improve the pyroelectric effect, but in the case of a dielectric infrared sensor, polling is not necessary. For this reason, it has excellent features such as being suitable for miniaturization and is expected to be put to practical use.

The reference capacitor necessary for configuring the detection circuit of FIG. 11 has the same structure as that of FIG. 10 and is shielded to prevent infrared irradiation, or the same structure as the infrared detection unit 10 of FIG. Or the like provided on a substrate that is not thermally insulated.
Japanese Unexamined Patent Publication No. 7-307696

  However, the conventional dielectric infrared sensor described above has the following problems.

  First, a dielectric film used in a conventional dielectric infrared sensor has a relative dielectric constant-temperature characteristic as shown in FIG. As shown here, when the electric field strength applied to the dielectric film is increased, the relative permittivity is decreased, and the temperature change rate of the relative permittivity is also decreased.

  Due to such material-specific characteristics, even if the voltage of the voltage source 34 is increased in the detection circuit of FIG. 11 for the purpose of increasing the output voltage of the dielectric infrared sensor, the detection sensitivity cannot be improved. This is because when the power supply voltage is increased, the temperature change rate of the dielectric constant of the dielectric film is lowered.

  Therefore, in order to improve the detection sensitivity of the dielectric infrared sensor, the thickness of the dielectric film is increased. However, in the conventional thermal infrared sensor, for example, as shown in FIG. 10, when the wiring 14 and the wiring 15 are located at the same height as the lower electrode 13, in order to connect the wiring 14 and the upper electrode 12, It is necessary to cover and connect a step corresponding to the film thickness of the dielectric film 11.

  For this reason, when the film thickness of the dielectric film 11 is increased, the coverage of the wiring 14 is likely to decrease and disconnection is likely to occur, and further, fine patterning becomes difficult. As a result, a problem of yield reduction occurs.

  In addition, when the dielectric film 11 is thickened, the heat capacity of the infrared detecting unit 10 is increased, and the temperature change amount of the dielectric film 11 itself is reduced. Therefore, these solutions have been problems.

  Furthermore, conventionally, a Pt material having a large work function has been used as the upper electrode 12 in order to increase the charge injection barrier with respect to the dielectric film 13. However, the Pt material has a high reflectance in the 8 to 14 μm band, which is the infrared wavelength range to be detected, and there is a problem in that the infrared absorption rate in the infrared detection unit 10 is reduced. This solution was also an issue.

  In view of the above problems, an object of the present invention is to provide a thermal infrared sensor that uses a dielectric film whose material properties change with temperature, has high detection sensitivity, and is easy to manufacture.

  In order to achieve the above object, in the thermal infrared sensor of the present invention having an infrared detection unit, the infrared detection unit includes a first electrode unit and a second electrode unit formed so as to be adjacent to each other on the substrate, A conductive layer formed so as to face the first electrode portion and the second electrode portion with a dielectric film interposed therebetween, and the conductive layer includes a third electrode portion and a second electrode portion facing the first electrode portion. The fourth electrode portion is opposed to the second electrode portion, and the first electrode portion and the third electrode portion are electrically connected by including the third electrode portion and the fourth electrode portion in the conductive layer. The first capacitor made of and the second capacitor made of the second electrode portion and the fourth electrode portion are connected in series.

  According to the thermal infrared sensor of the present invention, since the first electrode portion and the second electrode portion are formed so as to be adjacent to each other on the substrate, wiring for these can be performed on a flat surface. it can. That is, the wiring for electrical connection to the first capacitor and the second capacitor connected in series functioning as the infrared detection unit does not need to cover the step generated due to the film thickness of the dielectric film. Can be formed. For this reason, such wiring connection can be easily and reliably performed.

  In addition, since the third electrode portion and the fourth electrode portion are both included in the same conductive layer as the infrared detecting portion, the two capacitors (the first capacitor connected in series) are electrically connected. 1 capacitor and second capacitor). Since two capacitors are configured and connected in series with the same conductive layer in between, compared to a single capacitor having a similar dielectric film, the electric field strength applied to the dielectric film is It will be reduced to about one half. As a result, even when the dielectric film is thinned, the increase in electric field strength can be mitigated and the temperature change rate of the relative dielectric constant can be suppressed from decreasing. Furthermore, this means that the dielectric film can be thinned while avoiding an increase in electric field strength, and the thermal capacity of the infrared detector becomes smaller than the thinning of the dielectric film, which improves the detection sensitivity. Realize.

  An insulating film is formed on the substrate, the first electrode portion and the second electrode portion are lower electrodes formed on the insulating film, respectively, and the dielectric film is the first electrode portion and the second electrode portion. The conductive layer may be an upper electrode formed on the dielectric film.

  The thermal infrared sensor of the present invention can also be realized as such a configuration. In this case, the wiring to the capacitor constituting the infrared detection unit is connected to each lower electrode (first electrode unit and second electrode unit) formed on the insulating film. Since the upper surface of the insulating film can be made flat, such wiring can be easily and reliably formed.

  Further, an insulating film having a recess is formed on the substrate, the conductive layer is a lower electrode formed on the bottom surface of the recess, and the dielectric film is formed on the conductive layer, and the first electrode portion and Each of the second electrode portions may be an upper electrode formed on the dielectric film.

  The thermal infrared sensor of the present invention can also be realized as such a configuration. In this case, the wiring to the capacitor constituting the infrared detecting unit is connected to each upper electrode (first electrode unit and second electrode unit). Each upper electrode is formed on the dielectric film formed in the recess of the insulating film, and the upper surface of the dielectric film and the upper surface of the insulating film can have a small or no step. is there. For this reason, the connection between the upper electrode and the wiring can be easily and reliably performed.

  Moreover, it is preferable that the surface on the opposite side to the infrared detection part in the insulating film of the part in which the infrared detection part was formed is exposed.

  If it does in this way, since the heat capacity of an infrared detection part is reduced, the detection sensitivity of a thermal type infrared sensor will improve. In other words, the portion corresponding to the back side of the infrared detection unit in the insulating film is structured so as not to be covered with the substrate or other film, so that the substrate or other film is not affected by the infrared detection unit. Since heat can be prevented from escaping, detection sensitivity is improved.

  Moreover, it is preferable that an opening is provided around the infrared detection unit so as to leave at least one support unit for supporting the infrared detection unit.

  If it does in this way, the infrared rays detection part formed on the insulating film can be made into the structure separated from the other part of the thermal type infrared sensor by the opening, and supported only by the support part. As a result, it is possible to improve the heat insulation characteristics of the infrared detection unit with respect to other parts of the thermal infrared sensor, and it becomes difficult for heat to escape from the infrared detection unit, so that the infrared detection sensitivity is improved. In this case, it is preferable that the surface of the support portion opposite to the infrared detection portion is exposed. Thereby, the heat capacity of the infrared detection unit can be further reduced, and the detection sensitivity can be improved.

  In addition, it is preferable that the first electrode portion and the second electrode portion have an electrode area that coincides with each other.

  By doing so, the capacitance values of the first capacitor and the second capacitor match, and the electric field strengths applied to these two capacitors match, so the detection sensitivity of the thermal infrared sensor improves. However, although it is a preferable configuration that the areas of the first electrode portion and the second electrode portion exactly match each other, it is not essential. The approximation is preferable because the capacitance values of the capacitors are close to each other, and the most preferable configuration completely matches.

  The material of the upper electrode is preferably an oxide conductive material.

  The oxide conductive material has a lower infrared reflectance than a material such as Pt. For this reason, since the reflection of infrared rays by the upper electrode can be reduced in this way, the efficiency of infrared absorption in the infrared detection unit can be improved, and as a result, the detection sensitivity of the thermal infrared sensor can be improved. it can.

  The oxide conductive material is more preferably indium tin oxide.

  In this way, the upper electrode can be a low-resistance oxide electrode, and the power consumption in the infrared detector can be reduced, so that the detection sensitivity of the thermal infrared sensor can be improved.

  In addition, it is preferable to further include a heat collecting film formed on the infrared detection unit so as to be in contact with the protective film through the protective film and extending above the periphery of the infrared detection unit through the space.

  If it does in this way, the infrared rays irradiated to the circumference | surroundings of an infrared detection part will be absorbed by a heat collecting film, heat | fever will be generated, and this heat can be utilized for the temperature rise of an infrared detection part. That is, the infrared absorption efficiency can be improved by utilizing infrared rays that are not directly irradiated to the infrared detection unit. Thereby, the detection sensitivity of an infrared sensor improves.

  According to the thermal infrared sensor of the present invention, wiring to the infrared detector can be easily and reliably performed, and the dielectric film can be made thin while avoiding a decrease in the temperature change rate of the relative dielectric constant. . For this reason, it is a thermal infrared sensor with high detection sensitivity and easy manufacture.

(First embodiment)
The thermal infrared sensor according to the first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a cross-section of the main part of a thermal infrared sensor 100 of the present embodiment.

  As shown in FIG. 1, the thermal infrared sensor 100 is formed using a substrate 105 made of silicon having a thickness of 500 μm, for example. On the substrate 105, an insulating film 102 made of, for example, a silicon oxide film or a silicon nitride film having a thickness of 500 nm is formed.

  On the insulating film 102, two lower electrodes 103a and 103b having the same area are formed with a thickness of 200 nm using, for example, Pt as a material. Further, on the insulating film 102, a wiring 104a connected to the lower electrode 103a and a wiring 104b connected to the lower electrode 103b are also formed with a thickness of 200 nm using Pt as a material.

  The lower electrode 103a and the lower electrode 103b are arranged adjacent to each other on the insulating film 102 with a gap, and are covered with the dielectric film 101 including the gap. The dielectric film 101 is formed as a film having a thickness of 500 nm using, for example, barium titanate as a material.

  Further, a conductive layer 106 is formed on the dielectric film 101 over both the lower electrodes 103a and 103b. The conductive layer 106 includes an upper electrode 106 a that faces the lower electrode 103 a through the dielectric film 101, and an upper electrode 106 b that faces the lower electrode 103 b through the dielectric film 101. Since each of them is a part of the same conductive layer 106, the upper electrodes 106a and 106b are naturally connected electrically. The conductive layer 106 is formed to a thickness of 200 nm using, for example, indium tin oxide.

  Here, the lower electrode 103a and the upper electrode 106a, and the lower electrode 103b and the upper electrode 106b form two capacitors with the dielectric film 101 interposed therebetween, and the conductive layer 106 itself serves as a wiring. The infrared detector 110 is connected in series by fulfilling the function. Furthermore, the wiring 104a is connected to the lower electrode 103a, and the wiring 104b is connected to the lower electrode 103b, whereby an electrical connection to the infrared detection unit 110 is formed.

  FIG. 2 shows an equivalent circuit display of this configuration by an electric circuit diagram. The dielectric film 101 of this embodiment has a configuration in which the capacitors 110a and 110b having variable capacitances are connected in series because the relative dielectric constant changes depending on the temperature. Such capacitors connected in series correspond to the variable capacitor 31 in the detection circuit shown in FIG. When applied to the detection circuit of FIG. 11, one of the wirings 104a and 104b is electrically connected to GND, and the other is electrically connected to a reference capacitor 33 (not shown in FIG. 1). As a result, the capacitors 110a and 110b of the infrared detecting unit 110 change according to the change in the relative dielectric constant of the dielectric film 101 due to infrared irradiation, and the change in voltage distribution with the reference capacitor can be detected.

  In the conventional structure shown in FIG. 10, a step corresponding to the film thickness of the dielectric film 101 is generated. Unlike the structure of the thermal infrared sensor 100 described above, the lower electrode 103a and the wiring 104a. Are connected on the flat insulating film 102. Therefore, the lower electrode 103a and the wiring 104a can be easily and reliably connected, and the yield when manufacturing the thermal infrared sensor 100 is improved. In particular, when the lower electrode 103a and the wiring 104a are formed of the same material as in the case of the present embodiment, they can be formed as an integral pattern and the end portion can be used as the lower electrode 103a. The same applies to the lower electrode 103b and the wiring 104b.

  Further, even when a voltage of about 2.5 V is applied to the infrared detector 110, the two capacitors connected in series (see 110a and 110b in FIG. 2) each have a voltage of 1.25 V, which is a half voltage. Will remain applied one by one. For this reason, since the film thickness of the dielectric film 101 is 500 nm as an example, the electric field strength in each capacitor is about 25 kV / cm. That is, the electric field strength is also halved compared to a single capacitor having a dielectric film with a thickness of 500 nm.

  As shown in the example of the relative dielectric constant-temperature characteristic in FIG. 12, the electric field applied to the dielectric film 101 decreases because the relative dielectric constant and the temperature change rate thereof decrease as the electric field strength applied to the dielectric film increases. The smaller the intensity is, the better the sensitivity of the infrared detecting unit 110 is.

  According to the thermal infrared sensor 100, even when the dielectric film 101 having the same film thickness is used, since the plurality of capacitors are connected in series, the actually applied electric field intensity is reduced, and the infrared detection sensitivity is improved. ing. Moreover, since it means that the dielectric film 101 can be thinned without increasing the applied electric field strength, the heat capacity of the infrared detector 110 can be reduced by making the dielectric film 101 thin. This also improves the sensitivity of detecting infrared rays.

  In addition, the conductive layer 106 including the upper electrodes 106a and 106b and on the side irradiated with infrared rays is formed using indium tin oxide having a work function of 4.8 eV, so that the infrared reflectance is reduced. Yes. As a result, the infrared absorption efficiency in the infrared detector 110 is improved, and the detection sensitivity of the thermal infrared sensor 100 is improved. Note that the same effect can be obtained by using an oxide conductive material such as zinc oxide or indium oxide instead of indium tin oxide.

  Further, the substrate 105 where the infrared detection unit 110 is formed is thinned by being removed from the back side (the side opposite to the side where the infrared detection unit 110 is formed) by etching or the like. It has a supported structure. In this way, the infrared detection unit 110 is thermally insulated from the peripheral portion of the substrate 105 and the like.

  In the thermal infrared sensor 100 of the present embodiment, the dielectric film 101 is formed over the lower electrodes 103a and 103b. However, a configuration in which individual dielectric films are formed on the lower electrodes 103a and 103b is also possible.

  Further, in the present embodiment, the single conductive layer 106 is provided so that the upper electrodes 106 a and 106 b are included in the conductive layer 106. However, the upper electrode 106a facing the lower electrode 103a and the upper electrode 106b facing the lower electrode 103b are separately provided, and a wiring or the like is further provided to electrically connect these two upper electrodes. Is also possible.

(First modification according to the first embodiment)
In the thermal infrared sensor 100 shown in FIG. 1, the wirings 104a and 104b are formed using the same material (here, Pt) as the lower electrodes 103a and 103b. However, a wiring material different from that of the lower electrode may be used.

  Such a case will be described below as a first modification of the first embodiment with reference to the drawings. FIG. 3 is a diagram showing a configuration of a thermal infrared sensor 100a according to this modification. Compared with the thermal infrared sensor 100 of the first embodiment shown in FIG. 1, the thermal infrared sensor 100a of FIG. 3 is made of a different material instead of the wirings 104a and 104b made of the same material as the lower electrodes 103a and 103b. This is different in that wirings 121a and 121b are formed. Since the other points are the same, the same reference numerals as those in FIG. 1 are used in FIG.

  In the thermal infrared sensor 100a of FIG. 3, the wirings 121a and 121b are formed using a material having a lower thermal conductivity than Pt which is a material of the lower electrodes 103a and 103b. For example, a TiAlN-based alloy material can be used. In FIG. 3, wirings 121a and 121b are connected in order so as to cover a part of the lower electrodes 103a and 103b, respectively. Also here, regardless of the level difference caused by the dielectric film 101, the connection is made on the flat insulating film 102, and a reliable connection can be easily made. As a result, the thermal infrared sensor 100a having such a structure can be formed with high yield.

  In addition, by using a material having low thermal conductivity for the wirings 121a and 121b, the thermal insulation of the infrared detecting unit 110 is improved, and thus the detection sensitivity of the thermal infrared sensor 100a is improved.

(Second modification of the first embodiment)
The infrared detection unit 110 of the thermal infrared sensor 100 shown in FIG. 1 includes two capacitors connected in series, each including a lower electrode 103a and 103b sandwiching the dielectric film 101 and a conductive layer 106. However, it is also possible to provide an infrared detector having a configuration in which more capacitors are connected.

  Hereinafter, such an example will be described as a second modification of the first embodiment with reference to the drawings. FIG. 4 shows a thermal infrared sensor 100b of this modification. Here, the same components as those of the thermal infrared sensor 100a according to the first modification of the first embodiment shown in FIG. 3 are denoted by the same reference numerals as those in FIG. The differences will be described in detail below.

  As shown in FIG. 4, the thermal infrared sensor 100b has a lower electrode divided into three, that is, lower electrodes 103a, 103b, and 103c, and a conductive layer divided into two, that is, conductive layers 106x and 106y. is doing.

  Here, the two conductive layers 106x and 106y have the same area. The lower electrodes 103a and 103b have the same area, and the lower electrode 103c positioned between them has an area about twice that of the lower electrode 103a or 103b.

  Therefore, about half of the lower electrode 103a and the conductive layer 106y, about half of the remaining conductive layer 106y and about half of the lower electrode 103c, about half of the remaining lower electrode 103c and about half of the conductive layer 106x, and conductive layer The remaining half of 106x and the lower electrode 103b constitute four capacitors with the dielectric film 101 interposed therebetween. The conductive layer 106x functions as two upper electrodes that are electrically connected. Similarly, the conductive layer 106y functions as two upper electrodes. Furthermore, the lower electrode 103 also functions as two electrically connected lower electrodes.

  As described above, the conductive layers 106x and 106y and the lower electrode 103c each function as a wiring, and the four capacitors are all connected in series. The infrared detection unit 110x in this modification has such a configuration.

  This is a difference from the thermal infrared sensor 100a of FIG. 3 having the infrared detection unit 110 having a configuration in which two capacitors are connected.

  Because of this structure, even if a voltage of about 2.5 V is applied to the infrared detector 110, a voltage of 1/4 is applied to each of the four capacitors connected in series. Will stay. For this reason, since the film thickness of the dielectric film 101 is 500 nm here, the electric field strength is about 12.5 kV / cm, respectively.

  That is, the electric field strength in each capacitor configured in the infrared detection unit 110x of the present modification is further halved as compared with the thermal infrared sensor 100a including the infrared detection unit 110 having a configuration in which two capacitors are connected in series. Yes.

  As described above, the electric field strength in the dielectric film 101 is further reduced as compared with the case of the first modification of the first embodiment, which further improves the detection sensitivity of the thermal infrared sensor 100a. Can do.

  In this modification, the wirings 104a and 104b are connected on the insulating film 102 to the lower electrodes 103a and 103b, respectively. Such a connection can be easily and surely performed without being deteriorated by a step caused by the dielectric film 101, so that the manufacturing yield of the thermal infrared sensor 100a is improved.

  Further, the wires 104a and 104b of the thermal infrared sensor 100b are formed using a material different from that of the lower electrode, similarly to the thermal infrared sensor 100a shown in FIG. However, like the thermal infrared sensor 100 shown in FIG. 1, the wirings 104a and 104b can be formed using the same material as the lower electrode.

  As an example of a specific material for the wirings 104a and 104b, an AlCu alloy is used here. Compared with Pt, which normally requires physical processing such as milling, the AlCu alloy is excellent in process workability such as narrow wiring width because it can be chemically etched. For this reason, wiring can be made thin and it is advantageous to the improvement of heat insulation. AlCu alloy is also a stable wiring material. Of course, other materials may be used.

  In the present modification, the infrared detection unit 110x having a structure in which four capacitors having substantially the same electrode area are connected in series has been described. However, an infrared detector having a configuration in which an even number of capacitors exceeding four are connected in series may be provided. For example, when a lower electrode divided into four and an upper electrode divided into three are provided, six capacitors can be connected in series. If it does in this way, when the same voltage is applied, the electric field strength will be 1/6, and it will become a thermal type infrared sensor with still higher detection sensitivity. Similarly, eight or more capacitors may be configured.

  By setting the number of capacitors to an even number, the two wirings can be connected to the infrared detection unit on the insulating film to the lower electrode, and the wiring can be reliably connected.

  The structure of this modification may be considered as a structure in which two units connected in series, each composed of two lower electrodes and two conductive layers functioning as upper electrodes, are provided as a unit. it can.

(Second Embodiment)
Next, a thermal infrared sensor 200 according to a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 5 is a view showing a cross-section of the main part of the thermal infrared sensor 200. As shown in FIG. 5, the thermal infrared sensor 200 of the present embodiment is formed using a substrate 205. On the substrate 205, for example, a first insulating film 202a made of a silicon oxide film and having an air gap 212 is formed. Further, a second insulating film 202b is formed to a thickness of 500 nm, for example, as a laminated film of a silicon oxide film and a silicon nitride film so as to cover the air gap 212 and the first insulating film 202a.

  Further, two lower electrodes 203a and 203b having the same area are formed on the second insulating film 202b. These are formed above the air gap 212 using, for example, Pt as a material so as to have a thickness of 200 nm. A dielectric film 201 made of barium titanate and having a thickness of 500 nm is formed so as to cover the lower electrodes 203a and 203b, and a conductive layer 206 is formed thereon. The conductive layer 206 includes an upper electrode 206a facing the lower electrode 203a via the dielectric film 201, and an upper electrode 206b facing the lower electrode 203b via the dielectric film 201. Since each of them is a part of the same conductive layer 206, the upper electrodes 206a and 206b are of course electrically connected. The conductive layer 206 is formed to a thickness of 200 nm using, for example, an indium tin compound.

  Further, a protective film having a thickness of 300 nm made of a laminated film of a silicon oxide film and a silicon nitride film is formed so as to cover the wirings 204a and 204b and the conductive layer 206, for example.

  Here, two capacitors are formed with the dielectric film 201 sandwiched between the lower electrode 203a and the upper electrode 206a, and the lower electrode 203b and the upper electrode 206b, respectively. At the same time, these two capacitors are connected in series when the conductive layer 206 itself functions as a wiring, and constitutes an infrared detection unit 210. Furthermore, electrical connection to the infrared detection unit 210 is formed by connecting the wirings 204a and 204b.

  From this, as in the thermal infrared sensor 100 of the first embodiment, the voltage (for example, 2.5 V) applied to the infrared detection unit 210 is half of each capacitor (here, 1.V). 25) is applied step by step. For this reason, the electric field intensity is also half that of a single capacitor (25 kv / cm because the thickness of the dielectric film 201 is 500 nm). As a result, as in the case of the first embodiment, the detection sensitivity of the thermal infrared sensor 200 is improved.

  Similarly to the thermal infrared sensor 100 of the first embodiment, the wirings 204a and 204b are connected to the lower electrodes 203a and 203b on the flat second insulating film 202b, respectively. For this reason, the connection of the wiring can be surely formed regardless of the level difference due to the dielectric film 201. As a result, the yield in manufacturing the thermal infrared sensor 200 is improved.

  The infrared detecting unit 210 is supported above the air gap 212 by the support unit 207. For this reason, the heat capacity of the infrared detection unit 210 is reduced, and the heat insulating property with respect to the substrate 205 and the like is improved. From this, the sensitivity of the thermal infrared sensor 200 is improved.

  Further, FIG. 6 schematically shows a planar configuration of the thermal infrared sensor 200. However, illustration of some components is omitted. A cross section taken along line VV ′ in FIG. 6 corresponds to FIG.

  As shown in FIG. 6, the second insulating film 202 b is provided with an opening 212 a that leads to the air gap 212 so as to surround the infrared detection unit 210 while leaving the support unit 207. As a result, the infrared detecting unit 210 is improved in heat insulation from the surroundings even in a plan view, and the infrared detection sensitivity is improved.

  In addition, the surface of the second insulating film 202b where the infrared detection unit 210 is mounted is exposed on the side opposite to the infrared detection unit 210 (here, the surface on the air gap 212 side). That is, the structure is not in contact with other films or substrates. Further, the surface of the support portion 207 opposite to the infrared detection portion 210 is exposed. As a result, the heat capacity of the second insulating film 202b and the support 207 in the portion where the infrared detection unit 210 is mounted is reduced, and the infrared detection sensitivity of the infrared detection unit 210 is improved.

  In the thermal infrared sensor 200 of the present embodiment, the wirings 204a and 204b are formed using the same material as the lower electrodes 203a and 203b. However, as in the first modification of the first embodiment, the wirings 204a and 204b and the lower electrodes 203a and 203b may be formed of different materials.

  Furthermore, as in the second modification of the first embodiment, it is possible to further divide the upper electrode and the lower electrode and configure four or more capacitors connected in series.

  Next, a method for manufacturing the thermal infrared sensor 200 of this embodiment will be described. 7A to 7D are cross-sectional views for explaining the manufacturing process of the thermal infrared sensor 200.

  First, the process of FIG. 7A will be described. First, a first insulating film 202a made of, for example, a silicon oxide film having a thickness of 3 μm is formed on the substrate 205 by P-CVD. Subsequently, a recess 221 having a depth of 2 μm is formed in the first insulating film 202a by dry etching.

  Next, the process of FIG.7 (b) is demonstrated. Here, first, a sacrificial layer 222 made of a polysilicon film having a thickness of 3 μm is formed so as to fill the recess 221 and cover the first insulating film 202a. Thereafter, the sacrificial layer 222 and the first insulating film 202a are polished from the surface by CMP (Chemical Mechanical Polishing), and the sacrificial layer 222 having a thickness of 1.5 μm is embedded in the first insulating film 202a. Form.

  Next, the process of FIG.7 (c) is demonstrated. Here, first, a second insulating film 202b made of a stacked film of a 200 μm thick silicon oxide film and a 300 μm thick silicon nitride film is formed so as to cover the first insulating film 202a and the sacrificial layer 222. Further, for example, wirings 204a and 204b made of Pt having a thickness of 200 μm and lower electrodes 203a and 203b are formed. This is formed by patterning by dry etching after forming a Pt film by sputtering film formation.

  Subsequently, a dielectric film 201 made of barium titanate titanate is formed to a thickness of 500 nm by, for example, a PLD (Pulsed Laser Deposition) method. Further, an indium tin oxide film 206x for forming the conductive layer 206 is formed on the dielectric film 201 with a thickness of 200 nm by a sputtering method.

  Next, the process of FIG.7 (d) is demonstrated. Here, the indium tin oxide film 206x and the dielectric film 201 are patterned using an etching mask to form a structure in which the conductive layer 206 is formed on the lower electrodes 203a and 203b with the dielectric film 201 interposed therebetween. Further, a protective film 211 made of, for example, a 200 nm thick silicon nitride film and a 100 nm thick silicon oxide film is formed so as to cover the entire surface of the substrate 205.

  Subsequently, part of the protective film 211 and the second insulating film 202b is dry-etched using a desired etching mask, and an opening 212a is provided to expose a part of the sacrificial layer 222 to the surface as shown in FIG. . At this time, the support portion 207 is formed.

  Thereafter, the sacrificial layer 222 is removed by exposure to a gas containing, for example, chlorine trifluoride. Thereby, the thermal infrared sensor 200 shown in FIG. 5 is formed.

  In the above description, the PLD method is used as a method for forming the dielectric film 201. However, other formation methods such as spin coating or sputtering may be used. In addition, the dielectric film 201 can be formed by using both the PLD method and the spin coating method.

  In the case of the thermal infrared sensor 100 of the first embodiment, it is necessary to etch away the substrate 105 from the back side below the infrared detection unit 110. However, when manufacturing the thermal infrared sensor 200 of this embodiment, such a process is unnecessary. For this reason, manufacture is easy and the reduction | decrease of the heat capacity regarding the 2nd insulating film 202b of the part which mounts the infrared rays detection part 210 and the improvement of the heat insulation characteristic in the support part 207 are implement | achieved. As a result, the detection sensitivity of the thermal infrared sensor 200 is improved.

(Third embodiment)
The thermal infrared sensor according to the third embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a diagram showing a cross-section of the main part of the thermal infrared sensor 300 of the present embodiment.

  As shown in FIG. 8, the thermal infrared sensor 300 is formed using a substrate 305. On the substrate 305, for example, a first insulating film 302a made of a laminated film of a silicon oxide film and a silicon nitride film is formed to a thickness of 2 μm. A concave portion is provided in the first insulating film 302a, and an air gap 312 is formed by providing the second insulating film 302b above the concave portion.

  The second insulating film 302b has a shape that protrudes toward the substrate 305 on the air gap 312, and a recess having a depth of, for example, 700 nm is formed on the upper surface. A conductive layer 303 made of Pt having a thickness of 200 nm, for example, is provided on the bottom surface of the recess, and a dielectric having a thickness of 500 nm made of barium titanate so as to fill the recess and cover the conductive layer 303. A body film 301 is formed. Here, the surface is flattened so that no step is formed between the upper surface of the second insulating film 302 b other than the concave portion and the upper surface of the dielectric film 301.

  Further, two upper electrodes 306 a and 306 b are formed through the dielectric film 301 so as to face the conductive layer 303. These are made of indium tin oxide, for example, and have the same area.

  Here, the conductive layer 303 includes a lower electrode 303a that faces the upper electrode 306a through the dielectric film 301, and a lower electrode 303b that faces the upper electrode 306b through the dielectric film 101. The lower electrode 303a and the upper electrode 306a, and the lower electrode 303b and the upper electrode 306b constitute two capacitors with the dielectric film 301 interposed therebetween, and are connected in series by the conductive layer 303 that also functions as a wiring. Such two capacitors connected in series function as the infrared detection unit 310.

  Further, the upper electrodes 306a and 306b are connected to the wirings 304a and 304b, respectively, to obtain an electrical connection to the infrared detection unit 310. Since such a connection is performed on the second insulating film 302b and the dielectric film 301 which are flat surfaces, a reliable connection can be easily made. In particular, it is not affected by the film thickness of the dielectric film 301. This facilitates the manufacture of the thermal infrared sensor 300 and improves the yield. For example, an AlCu alloy can be used as the wiring material.

  Further, a protective film 311 made of, for example, a laminated film of a silicon nitride film and a silicon oxide film is formed on the second insulating film 302b so as to cover the upper electrodes 306a and 306b and the wirings 304a and 304b. . This film thickness is, for example, 300 nm.

  Further, a heat collecting film 313 made of resin is formed on the infrared detecting unit 310 so as to be in contact with the protective film 311. The heat collecting film 313 has a larger area than the infrared detection unit 310 and spreads around the infrared detection unit 310, and is positioned above the protective film 311 with a space therebetween in the periphery. Yes. For this reason, the infrared rays irradiated around the infrared detection unit 310 can also be absorbed by the heat collecting film 313 and contribute to the temperature increase in the infrared detection unit 310. That is, the amount of infrared absorption can be increased by the heat collecting film 313, and the detection sensitivity of the thermal infrared sensor 300 can be improved.

  In the thermal infrared sensor 300 described above, the infrared detector 310 is provided with an air gap 312 below, so that thermal insulation with the substrate 305 and the like is enhanced. The second insulating film 302b is provided with an opening so as to leave at least one (here, two) support portions 307 and surround the infrared detection portion 310. The infrared detecting unit 310 is thermally insulated from the surroundings by the same structure as that of the thermal infrared sensor 200 of the second embodiment whose plan view is shown in FIG.

  Further, in the second insulating film 302 b, the back side of the infrared detection unit 310 is exposed toward the air gap 312. That is, it is not covered by other layers. For this reason, the heat capacity in the lower part of the infrared detector 310 is reduced, which contributes to an improvement in detection sensitivity of the thermal infrared sensor 300.

  Note that the wires 304a and 304b of this embodiment are formed of a material different from that of the upper electrodes 306a and 306b. However, like the thermal infrared sensor 100 shown in FIG. 1 and the like, the wires 304a and 304b may be formed of the same material as the upper electrodes 306a and 306b.

  Next, a method for manufacturing the thermal infrared sensor 300 will be described with reference to the drawings. FIGS. 9A to 9D are cross-sectional views illustrating the manufacturing process of the thermal infrared sensor 300.

  First, steps required until a structure shown in FIG. First, a first insulating film 302a made of a silicon oxide film is formed on the entire surface of a substrate 305 made of silicon having a thickness of 500 μm. For example, it is formed to a thickness of 3 μm using the P-CVD method. Next, a recess having a depth of 2.5 μm is formed by dry etching on the second insulating film 302b, and a sacrificial layer 322 made of polysilicon is formed so as to fill the recess. Thereafter, the sacrificial layer 322 and the first insulating film 302a are polished by a CMP method so that the thickness of the sacrificial layer 322 embedded in the recess becomes 2 μm.

  Next, steps required until a structure shown in FIG. An etching mask having a desired pattern is formed over the sacrificial layer 322, and a recessed portion having a depth of 800 nm (having a shape extending toward the opposite side of the substrate 305) having a tapered sidewall is formed by dry etching.

  Thereafter, a second insulating film made of a laminated film of a 200 nm thick silicon oxide film and a 200 nm thick silicon nitride film is formed on the entire surface of the first insulating film 302a and the sacrificial layer 322 by, for example, P-CVD. 302b is formed. Thus, the second insulating film 302b has a recess that covers the bottom and side surfaces of the recess provided in the sacrificial layer 322.

  Next, steps required until a structure shown in FIG. A conductive layer 303 made of Pt having a thickness of 200 nm is formed by patterning on the bottom surface of the recess formed in the second insulating film 302b. On this, a dielectric film 301 made of barium titanate titanate is formed to a thickness of 800 nm by, for example, spin coating. According to the spin coating method, the second insulating film 302b can be formed with good coverage even in the concave portion.

  Further, the top surfaces of the dielectric film 301 and the second insulating film 302b are polished by CMP, and planarized until the dielectric film 301 on the conductive layer 303 has a thickness of 500 nm. As a result, the thickness of the second insulating film 302b constituting the support portion 307 is 300 nm.

  Next, steps required until a structure shown in FIG. On the dielectric film 301 and the second insulating film 302b flattened by the CMP method, for example, upper electrodes 306a and 306b made of indium tin oxide and wirings 304a and 304b made of AlCu alloy are connected to these electrodes, respectively. , Each having a thickness of 200 nm. For this, film formation by sputtering and patterning using a desired etching mask may be used.

  Next, a protective film 311 made of a silicon nitride film having a thickness of 200 nm and a silicon oxide film having a thickness of 100 nm is formed on the entire surface of the substrate 305. Further, the protective film 311 and the second insulating film 302b are dry-etched using an etching mask having a desired pattern so that a part of the sacrificial layer 322 is exposed on the surface. At this time, a support portion 307 is formed. The planar configuration at this time is the same as that of the thermal infrared sensor 200 according to the second embodiment shown in FIG.

  Further, a heat collecting film 313 in contact with the infrared detection unit 310 through the protective film 311 is formed on the protective film 311 by, for example, a photolithography process using a material containing polyimide. As shown in FIG. 8, this has a shape that spreads over the protective film 311 via a space in the vicinity of the infrared detection unit 310.

  Finally, when the sacrificial layer 322 is removed by exposure to a gas containing chlorine trifluoride, the thermal infrared sensor 300 shown in FIG. 8 is formed.

  In the manufacturing method described above, it is not necessary to thin the second insulating film 302b on which the infrared detection unit 310 is mounted by etching from the back surface. For this reason, it is possible to easily reduce the heat capacity of the infrared detection unit 310 and improve the heat insulation characteristics of the support unit 307. For this reason, the detection sensitivity of the thermal infrared sensor 300 is improved.

  In the above description, the PLD method is used as a method for forming the dielectric film 301. However, other formation methods such as spin coating or sputtering may be used. In addition, the dielectric film 301 can be formed by using both the PLD method and the spin coating method.

  The thermal infrared sensor according to the present invention has good detection sensitivity and is easy to manufacture. Therefore, the thermal infrared sensor is useful as a point sensor for human body detection, for example. Moreover, it can use also as a thermal-type infrared image sensor by setting it as the structure which arranged many infrared detection parts.

FIG. 1 is a cross-sectional view showing a structure of a thermal infrared sensor 100 according to the first embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the infrared detector 110 in the thermal infrared sensor 100. FIG. 3 is a cross-sectional view showing the structure of the thermal infrared sensor 100a in the first modification of the first embodiment of the present invention. FIG. 4 is a cross-sectional view showing the structure of a thermal infrared sensor 100b in a second modification of the first embodiment of the present invention. FIG. 5 is a cross-sectional view showing the structure of a thermal infrared sensor 200 in the second embodiment of the present invention. FIG. 6 is a plan view showing the structure of the thermal infrared sensor 200. 7A to 7D are cross-sectional views illustrating the manufacturing process of the thermal infrared sensor 200. FIG. 8 is a cross-sectional view showing a structure of a thermal infrared sensor 300 according to the third embodiment of the present invention. FIGS. 9A to 9D are cross-sectional views illustrating the manufacturing process of the thermal infrared sensor 300. FIG. 10 is a cross-sectional view illustrating the structure of a conventional thermal infrared sensor. FIG. 11 is a basic detection circuit diagram of the dielectric infrared sensor. FIG. 12 is a graph showing the relative dielectric constant-temperature characteristics of barium titanate titanate, which is a dielectric film material. FIG. 13 is an explanatory diagram of the detection operation of the dielectric infrared sensor.

Explanation of symbols

31 Variable capacitor 32 Output terminal 33 Reference capacitor 34 Voltage source 100, 100a, 100b Thermal infrared sensor 101 Dielectric film 102 Insulating film 103a, 103b, 103c Lower electrode 104a, 104b Wiring 105 Substrate 106, 106x, 106y Conductive layer 106a, 106b Upper electrode 107 Support part 110 Infrared detectors 110a, 110b Capacitor 110x Infrared detectors 121a, 121b Wiring 200 Thermal infrared sensor 201 Dielectric film 202a First insulating film 202b Second insulating film 203a, 203b Lower electrode 204a, 204b Wiring 205 Substrate 206 Conductive layer 206a, 206b Upper electrode 206x Indium tin oxide film 207 Support part 210 Infrared detection part 211 Protective film 212 Air gap 212a Opening 221 Recess 222 Sacrificial Layer 300 Thermal infrared sensor 301 Dielectric film 302a First insulating film 302b Second insulating film 303 Conductive layers 303a and 303b Lower electrodes 304a and 304b Wiring 305 Substrate 306a and 306b Upper electrode 307 Support section 310 Infrared detection section 311 Protection Film 312 Air gap 313 Heat collecting film 322 Sacrificial layer

Claims (9)

In a thermal infrared sensor having an infrared detector,
The infrared detector is
A first electrode portion and a second electrode portion formed adjacent to each other on the substrate;
A conductive layer formed to face the first electrode portion and the second electrode portion via a dielectric film;
The conductive layer includes a third electrode portion facing the first electrode portion and a fourth electrode portion facing the second electrode portion,
The first capacitor including the first electrode portion and the third electrode portion is electrically connected by including the third electrode portion and the fourth electrode portion in the conductive layer; and The thermal infrared sensor, wherein the second electrode part and the second capacitor comprising the fourth electrode part are connected in series. In claim 1,
An insulating film is formed on the substrate;
Each of the first electrode portion and the second electrode portion is a lower electrode formed on the insulating film,
The dielectric film is formed on the first electrode portion and the second electrode portion,
The thermal infrared sensor, wherein the conductive layer is an upper electrode formed on the dielectric film. In claim 1,
An insulating film having a recess is formed on the substrate,
The conductive layer is a lower electrode formed on the bottom surface of the recess,
The dielectric film is formed on the conductive layer,
The thermal infrared sensor, wherein the first electrode portion and the second electrode portion are upper electrodes formed on the dielectric film, respectively. In claim 2 or 3,
The thermal infrared sensor, wherein a surface of the insulating film where the infrared detection unit is formed is exposed on a side opposite to the infrared detection unit. In any one of Claims 1-4,
A thermal infrared sensor, wherein an opening is provided around the infrared detection unit so as to leave at least one support unit for supporting the infrared detection unit. In any one of Claims 1-5,
The thermal infrared sensor, wherein the first electrode portion and the second electrode portion have electrode areas that coincide with each other. In claim 2 or 3,
The thermal type infrared sensor, wherein the material of the upper electrode is an oxide conductive material.   8. The thermal infrared sensor according to claim 7, wherein the oxide conductive material is indium tin oxide. In any one of Claims 1-7,
A thermal infrared sensor, further comprising a heat collecting film formed on the infrared detection unit so as to be in contact with the protective film through a protective film and extending above the periphery of the infrared detection unit through a space. .

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