JP2006153675A - Thermopile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problems: difficult to measure a minute area because of projection area of a sensor differs largely to an area projected with a sensor part which is made as an RI ray detection region of the thermopile heretofore wherein, a flat surface of a plano-convex lens is faced to a chip side; the defect of a small output when the sensor part is arranged around the lens, a part of IR ray doesn't incident on the sensor part; difficult of work because of high precision needed at the assembly time; and not easy manufacturing because of tendency of angular misalignment of lens axis. <P>SOLUTION: The spherical surface of the plano-convex lens is positioned to the chip side for the thermopile making the detection region where the sensor part is projected with the plano-convex lens. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermopile having a plurality of sensor units that convert infrared rays of an object into electrical signals and detect them.

The thermopile is a thermocouple composed of two kinds of materials, forming a hot junction on the diaphragm, forming a cold junction on the surrounding heat sink, providing an insulating protective film on the thermocouple, cold junction and hot junction, and A chip configuration is adopted in which an absorption film is installed on the hot junction to form a sensor part.
Infrared rays incident on the absorption film that is the sensor part are converted into heat, causing the temperature of the hot junction to rise, and a voltage proportional to the Seebeck constant of each thermocouple material is generated. In addition, this voltage is also influenced by the number of thermocouples, the absorption film distance from the diaphragm end, and the absorption film area, and the voltage increases as these increase.

  For example, a thermopile having a sensor unit with 4 rows and 4 columns has the same configuration. For example, when it is housed in a TO-5 stem, for example, an outer angle 2.9 mm thermopile chip, for example, an absorption film with a 0.281 mm angle 16 are arranged, and a thermocouple having a size of 0.03 millimeters per set and 16 hot junctions having a length of 0.045 millimeters and a width of 0.023 millimeters are provided below the absorbing film.

  As for the position of the absorption film, for example, the distance between the absorption films at the four central portions of the diaphragm is set to 0.221 mm, and the distance between the other absorption films is set to 0.282 mm. For example, a heat sink is arranged around each absorption film at a distance of 0.0735 millimeters, and a cold junction having the same dimensions as the hot junction is located on the heat sink between the absorption films and the heat sink around the chip. The peripheral heat sink portion is provided with an output signal extraction pad from each detection area. These pads are concentrated on two sides of the thermopile chip to facilitate wire bonding with a stem lead or the like. For the same purpose, the negative voltage output terminals of each detection area are integrated into one common pad.

The thermopile chip is die-bonded to a stem such as TO-5 with an epoxy adhesive or the like, and a lead provided on the stem and a pad provided on a heat sink portion around the chip are electrically connected by a bonding wire. Thereafter, the can and the stem provided with a plano-convex lens whose one surface is a flat surface and the other surface is a spherical surface are welded to the incident window. For example, silicon having a refractive index n of 3.4 is used as the plano-convex lens material. For example, the focal length f is 1.95 millimeters, the center thickness tc is 2 millimeters, and the lens diameter is 6.65 millimeters. The plano-convex lens has a flat side on the chip side as described in JP-A-08-062037, for example, with an epoxy adhesive on a circular entrance window having a diameter of 3.5 mm provided on the can, for example, from the lens principal point H to the chip. The fixed distance is 1.65 mm. This distance is achieved by using a can having a preset can height. Further, the axis of the circular incident window provided on the can and the axis of the outer periphery of the stem are made to coincide with each other by adopting a can / stem fitting structure.
As described above, the thermopile chip sensor unit is projected by the plano-convex lens to form an infrared detection region, and a thermopile that outputs a voltage proportional to the amount of infrared rays in each detection region is completed.

FIG. 5 shows a conceptual cross-sectional view of a conventional thermopile.
FIG. 9 is a conceptual perspective view of the thermopile having the detection area of 4 rows and 4 columns.
FIG. 10 shows the arrangement of the sensor section of the above-mentioned 4 × 4 thermopile chip.
Japanese Patent Application Laid-Open No. 08-062037

  When the conventional plano-convex lens plane is positioned on the chip side, the projected area of the sensor unit located around the lens is extremely large compared to the projected area of the sensor unit located at the center of the lens, and the sensor provided around the lens. In other words, it has a drawback that it is difficult to perform minute measurement at the part.

  For example, the sensor section of the above-mentioned outer angle of 2.9 mm and the angle of 0.281 mm in 4 rows and 4 columns is 0.221 mm in the central four positions, and the distance between the other sensor sections is 0.282 mm. When a silicon plano-convex lens having a focal length of 1.95 mm and a center thickness of 2 mm is installed on the thermopile at a distance of 1.65 mm from the lens principal point H to the chip with the plane as the chip side, the center shown in FIG. Consider a projected image of sensor part diagonal vertices a and b and four corner sensor part diagonal vertices c and d.

  For the sake of simplification, considering the light emitted from each point in the direction parallel to the lens axis, as shown in FIG. 6, the projected point aa of the central sensor portion diagonal vertices a and b at a distance of 100 millimeters from the lens. , Bb is 22.21 millimeters, whereas the distance between the projection points cc, dd of the four corner sensor portions diagonal vertices c, d is 130.19 millimeters, which is the distance between aa, bb, 5. 86 times. Since the area is the square of this, in the conventional method, the projected area of the four corner sensors is 34.3 times the projected area of the center sensor.

  FIG. 7 shows the ray trajectory in the direction parallel to the lens axis at points a, b, c, and d on the conventional thermopile sensor unit. In the figure, the can side wall and the stem are omitted for clarity.

  Furthermore, in the sensor part located in the lens periphery, a part of infrared rays from the detection area was not incident on the sensor part, and there was a disadvantage that the output was low. For example, at the four corner sensor diagonal vertices d in the above-described example, as shown in FIG. 8, the light beam forming an angle of +10 degrees with the lens axis has an angle of 17.42 degrees with respect to the lens spherical normal. Since this is a critical angle of 17.10 degrees or more, total reflection occurs at the lens spherical surface and the light is not emitted to the outside. That is, a light beam having an angle of +10 degrees with respect to the lens axis is not incident on the four corner sensor portion diagonal vertex d from the detection area, and the output is low.

Further, since the distance between the lens and the chip is small, the tolerance value such as the bonding wire height at the time of the thermopile chip assembly is small, and the manufacturing accuracy is high.
That is, in the above-described example, the distance between the lens principal point H and the chip is 1.65 millimeters. However, as shown in FIG. 7, the plane-side principal point H of the plano-convex lens has a lens center thickness tc of the lens material refractive index n. Therefore, the distance between the lens plane and the chip is 1.06 millimeters.

  In addition, when the plano-convex lens is fixed to the circular entrance window on the can, the angle between the lens axis and the axis of the can tends to be high, and the manufacturing accuracy is high. Tools were needed. This occurred because the lens can be held at all angles where the lens spherical surface is in contact with the can circular hole.

  The plano-convex lens spherical surface is positioned on the chip side.

When the plano-convex lens spherical surface is located on the chip side, the ratio of the sensor area projected area around the lens to the projected area of the sensor area located at the center of the lens is smaller than in the conventional technology, and the sensor section located around the lens. This makes it possible to perform micro measurement with
Further, when the plano-convex lens spherical surface is positioned on the chip side, the infrared rays that are not incident on the sensor portion located around the lens due to the total reflection of the lens are also incident on the sensor portion to increase the output.
Further, when the plano-convex lens spherical surface is positioned on the chip side, the distance between the lens and the chip becomes large even if the lens principal point H and the distance between the chips are the same as the conventional one, so that the bonding wire height at the time of the thermopile chip assembly, etc. The allowable value becomes large and the production becomes easy.
Furthermore, when the plano-convex lens spherical surface is positioned on the chip side, when the plano-convex lens is bonded and fixed to the circular entrance window provided on the can, the lens angle and the can are not easily displaced, and the lens can be easily manufactured. Adhesive special jig and angle deviation inspection jig are not required.

A thermopile chip is formed in the order of a thermocouple pattern, an insulating protective film, and an absorption film after forming a diaphragm constituting film on a substrate material, and finally, a diaphragm is formed by etching from the back surface.
A thermocouple pattern, an insulating protective film, an absorption film, and a diaphragm are manufactured using a semiconductor process method such as film formation, exposure, and etching, and a photomask designed in advance so as to obtain a large number of chips is used.
A substrate material on which a large number of thermopile chips are formed is cut with a dicing saw or the like and die-bonded to a stem such as TO-5 with a die bonder or the like. Thereafter, the stem lead and the pad provided on the chip are wire-bonded with a gold wire or the like.
Further, for example, a can and a stem having a spherical surface inside and a plano-convex lens bonded with an epoxy adhesive or the like are welded to a circular incident window. The distance from the lens principal point H to the chip is achieved by using a can having a preset can height.
As described above, the thermopile in which the spherical surface is positioned on the chip side and the chip sensor unit is projected by the plano-convex lens to form the infrared detection region is completed.

  As an embodiment of the present invention, a thermopile having a detection area of 4 rows and 4 columns as described in the background art section, and a chip sensor portion is projected by a plano-convex lens having a spherical surface located on the chip side to form an infrared detection area. An example of the production procedure will be described.

The thermopile chip is manufactured by the following manufacturing procedure as an example.
For example, a substrate material is a silicon wafer having a thickness of 0.4 mm, and a film having a total thickness of, for example, 0.002 mm, such as silicon oxide or silicon nitride, is formed on the silicon wafer by a CVD method or the like. These films become diaphragm constituting films.
Two types of thermocouples having different Seebeck constants, such as nichrome on the one hand and bismuth antimony on the other, are used, and many thermocouple patterns are formed on the silicon wafer. At this time, a semiconductor process method such as film formation, exposure, and etching is used, for example, a nichrome width of 0.006 millimeters, a bismuth antimony width of 0.01 millimeters, and a distance between both of them is 0.007 millimeters. A fine pattern of 0.03 millimeters, contact length 0.045 millimeters, and contact width 0.023 millimeters is formed. A photomask having a pattern designed in advance is used for the exposure process.
As another thermocouple material example, one may be polysilicon and the other may be aluminum.

  Further, for example, a polyimide film having a thickness of 0.002 mm is processed into a predetermined shape by a semiconductor process method such as post-coating exposure and etching as an insulating protective film positioned on the thermocouple, the cold junction, and the hot junction.

Thereafter, a pad made of aluminum or the like is provided as an output extraction pad using a semiconductor process method such as film formation, exposure and etching. This pad is preset to a size such as a length of 0.12 mm and a width of 0.1 mm that can be wire-bonded with a gold wire, an aluminum wire, or the like. Further, nichrome having a high adhesion strength to the silicon wafer is provided in advance on the pad base.
The positive voltage output signal extraction pad from each detection area is set to a point that becomes a heat sink around the chip when the diaphragm is formed in the final chip manufacturing process. These pads are concentrated on two sides of the heat sink around the chip in order to facilitate wire bonding with a stem lead or the like which will be described later. For the same purpose, the negative voltage output terminals of each detection area are integrated into one common pad.

  Subsequently, for example, a 0.001 mm thick absorbing film is formed by a semiconductor process method such as film formation, exposure, and etching. As an example, 16 absorption films having an angle of 0.281 mm are arranged, and the absorption film positions are, for example, 0.221 mm at the four central portions of the diaphragm, and 0.282 mm at other absorption film intervals. The absorption film forming region manufactured using the photomask set to 1 is the thermopile sensor part.

Thereafter, a back surface protection pattern is formed by a semiconductor process technique such as exposure using a photoresist or the like, and plasma etching is performed using a fluorocarbon gas with a high-density plasma etching apparatus or the like to produce a diaphragm. At this time, as the fluorocarbon-based gas, a gas having a structure capable of vertical etching at a low lateral etching speed is selected.
If the back surface protection pattern is set in advance between the absorption films and around the chip, heat sinks are formed between the absorption films and around the chip. As a result, the heat sink is arranged at a position of, for example, a distance of 0.0735 millimeters around each absorption film. When the absorption film size angle is 0.281 millimeters, the diaphragm size is 0.428 millimeters. By setting the cold junction position in the thermocouple pattern photomask, the cold junction is positioned on the heat sink.
When the absorption film size is 0.282 mm and the distance between the absorption films in the central part is 0.221 mm, the heat sink width is 0.074 mm, and a contact having a length of 0.045 mm is provided on the diaphragm end. It is impossible because it is located at a point of 0.045 millimeters. For an absorption film interval of 0.282 mm, the heat sink width is 0.135 mm, and a cold junction can be provided. Therefore, in the case of the example described in the background art section, cold junctions are disposed on the heat sinks on the two sides of each absorption film, and 16 thermocouples are arranged in each absorption film.

  As an example, the 4 × 4 thermopile chips formed on the substrate material described above are made of silicon having a refractive index n of 3.4, a focal length f of 1.95 mm, a center thickness tc of 2 mm, and a lens. Using a plano-convex lens having a diameter of 6.65 millimeters, the distance from the lens principal point H to the tip is 1.65 millimeters, and the assembly is performed in the following procedure.

  A silicon wafer having a thickness of, for example, 0.4 mm, on which a large number of thermopile chips are formed, is attached to a cutting sheet, and then cut into a predetermined size, for example, a corner of 2.9 mm, using a dicing saw or the like. At this time, in consideration of the cutting margin, the chip is arranged on the substrate material with a square of 2.95 mm, for example.

  Next, the cutting sheet is set in a die bonder, and a thermopile chip is die-bonded to a predetermined position using, for example, an epoxy adhesive on a stem such as TO-5.

  After that, for example, a gold wire having a wire diameter of 0.025 mm is used to electrically connect a pad provided on the heat sink portion around the chip and a lead provided on the stem using a device such as a wire bonder.

  Further, for example, a can and a stem having a plano-convex lens bonded with an epoxy adhesive and the like are welded to a circular incident window having a diameter of 3.5 mm with a spherical surface inside. A distance of 1.65 millimeters from the lens principal point H to the tip is achieved by using a can whose height is set in advance. Here, the axis of the circular incident window provided on the can and the axis of the outer periphery of the stem are matched by adopting a can / stem fitting structure.

As described above, the thermopile in which the spherical surface is positioned on the chip side and the chip sensor unit is projected by the plano-convex lens to form the infrared detection region is completed.
FIG. 1 shows a conceptual cross-sectional view of the thermopile of the present invention.

  In the above example, the thermopile described in the background art section, the chip specification, the lens specification, and the like are the same, and only the plano-convex lens holding direction is different.

Now, when the plano-convex lens spherical surface is arranged on the chip side, the projected images of the central sensor part diagonal vertices a and b and the four corner sensor part diagonal vertices c and d shown in FIG. 10 are considered.
Similarly to the problem to be solved by the invention, for the sake of simplification, considering the light emitted from each point in the direction parallel to the lens axis, as shown in FIG. The distance between the projection points a ′ and b ′ of the sensor part diagonal vertices a and b is 21.52 millimeters, and the distance between the projection points c ′ and d ′ of the four corner sensor part diagonal vertices c and d is 41. 90 millimeters. That is, the distance ratio, which was 5.86 times in the prior art, becomes 1.95 times. Since the area is the square of this, in the conventional technique, the projected area of the four corner sensors is 34.3 times the projected area of the center sensor, whereas in the example of the present invention, the projected area is reduced to 3.8 times.
FIG. 3 shows the ray trajectory in the direction parallel to the lens axis at points a, b, c, and d on the thermopile sensor portion of the present invention. In the figure, the can side wall and the stem are omitted for clarity.

Further, when the plano-convex lens spherical surface is arranged on the chip side, the light beam forming an angle of +10 degrees with the lens axis at the diagonal apex d of the four-corner sensor portion in the above example is 12. It has an angle of 73 degrees. Since this is less than a critical angle of 17.10 degrees, it is emitted out of the lens plane. That is, in the prior art, the light beam having an angle of +10 degrees with respect to the lens axis is not incident on the four corner sensor portion diagonal vertex d from the detection area, but in the present invention example, the light is incident and the output is increased.
When the plano-convex lens spherical surface is arranged on the chip side, the spherical-side principal point H of the plano-convex lens is located at the spherical vertex as shown in FIG. 3, and therefore the distance between the lens spherical vertex and the chip is the lens principal point H and the chip. The distance is 1.65 mm, which is the same as the distance. That is, in the prior art, the distance between the lens and the chip was 1.06 millimeters, but in the example of the present invention, the distance is increased by 0.59 millimeters, and the allowable value such as the bonding wire height at the time of the thermopile chip assembly becomes large.
Also, when the plano-convex lens spherical surface is arranged on the chip side, the plano-convex lens plane is adhered and fixed to the inner surface of the can, so there is no mechanical misalignment between the lens axis and the can axis, and the can and lens are bonded. Becomes easy.
In addition, as described in the above chip manufacturing procedure and assembly procedure, the present invention is a lens holding direction change with respect to the can in the final assembly process, and can be easily performed without changing the chip manufacturing process / procedure and assembly process / procedure. it can.
The present invention can also be applied to plano-convex lenses of other specifications such as material silicon, focal length f1.5 mm, center thickness tc 2 mm, and lens diameter 6 mm.

It is a conceptual sectional view showing the structure of the present thermopile. It is a figure which shows the projection position of each point on the sensor of this invention thermopile. It is the figure which showed the locus | trajectory of the lens axis parallel direction light ray of each point on a sensor part in this invention thermopile. It is the figure which showed the locus | trajectory of the light ray which makes an angle of +10 degree | times with the lens axis of the sensor part upper point arrange | positioned around the lens in this invention thermopile. It is a conceptual sectional view showing the structure of a conventional thermopile. It is a figure which shows the projection position of each point on the sensor of the conventional thermopile. It is the figure which showed the locus | trajectory of the lens-axis parallel direction light ray of each point on the sensor part in the conventional thermopile. It is the figure which showed the locus | trajectory of the light ray which makes a +10 degree angle with the lens axis of the sensor part upper point arrange | positioned around the lens in the conventional thermopile. It is a perspective view showing the structure of a 4 × 4 thermopile chip. It is the figure which showed sensor part arrangement | positioning of a 4 row 4 column thermopile chip | tip.

Explanation of symbols

1 Plano-convex lens 2 Thermopile chip 3 Thermopile chip sensor part 4 Can 5 Incident window 6 Stem 7 Lead 8 Bonding wire 9 Hot junction 10 Cold junction 11 Thermocouple 12 Diaphragm component film 13 Insulating protective film 14 Pad 15 Negative voltage output common pad 16 Around heatsink

Claims (1)

  A thermocouple composed of two kinds of materials is used to form a hot junction on the diaphragm, a cold junction on the surrounding heat sink, and an absorption film on the hot junction to form a chip that forms multiple sensors. Further, in the thermopile in which the sensor unit is projected with a plano-convex lens and used as a detection area, the spherical surface of the plano-convex lens is located on the chip side.

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