JP2007127496A - Thermal infrared detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal infrared detector which has high infrared measurement accuracy, is small, is lightweight, and is inexpensive, by cutting off infrared radiation incoming from the surroundings that becomes a disturbance. <P>SOLUTION: The infrared detector 2 is housed in a vacuum vessel 3 having an infrared incoming opening 4. A micro shield 10 is erected on the infrared detector 2 so that pixels, arranged in an array form, are partitioned. The height of the micro shield 10 is set so that it is larger than the thickness, in the direction of connecting the pixels and that infrared radiation from parts other than the infrared incoming opening 4 is cut off. The temperature of the micro shield 10 is kept fixed by an electronic cooling element 7. An external connection terminal 9, which can be electrically connected to the exterior and the infrared detector 2, are connected directly to one bonding wire 19. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal infrared detector that detects infrared radiation from a thermal object and detects a temperature distribution of the thermal object.

  The bolometer-type thermal infrared detector detects a change in temperature of a detection element due to incidence of infrared rays as a change in resistance, and measures the temperature of an object to be measured from the change in resistance. The detection element in the bolometer-type detector has a diaphragm thermally separated from the silicon wafer by a thin beam, and a resistor (bolometer) is formed on the diaphragm. The infrared detection element of the thermal infrared detector is configured by arranging the detection elements in an array, and a two-dimensional infrared image can be obtained.

  As described above, the detector images heat. Usually, infrared rays emitted from a measurement object are imaged and imaged on a detector surface using an optical system. However, when the ambient temperature of the detector changes, in addition to the infrared rays emitted from the measurement object and incident through the optical system, ambient thermal radiation also enters the detector, and the amount of infrared rays from the measurement object and the detection Since the amount of infrared rays from the surroundings of the vessel cannot be discriminated, there is a problem that an infrared image from a measurement object to be originally measured cannot be imaged.

  With respect to this problem, Patent Document 1 discloses a thermal infrared detector provided with a radiation shield that blocks heat radiation from around the detector. FIG. 5 is a conceptual diagram showing a cross-sectional configuration of the thermal infrared detector described in Patent Document 1. FIG. 6 shows a cross-sectional configuration of one pixel of the infrared detection element based on FIG. FIG. 7 is a conceptual diagram schematically showing, and FIG. 7 is an enlarged view of a portion A in FIG.

  As shown in FIG. 5, in the thermal infrared detector 101, the infrared detection element 102 is held in a vacuum container 103 in order to improve thermal separation between the silicon wafer 110 and a diaphragm described later. The infrared detection element 102 is configured by two-dimensionally arranging pixels as detection elements in an array. As shown in FIG. 6, the diaphragm 113 in which the bolometer (resistor) 112 is formed is thermally separated from the silicon wafer 110 by a thin beam 114 with a cavity 121 therebetween.

  The change in the resistance value due to the temperature rise of the diaphragm 113 due to the incidence of the infrared ray 111 is read out by applying a bias current. For this reason, the temperature rise of the sensing element itself due to Joule heat generated by the bias current becomes a problem. This temperature rise far exceeds the temperature rise of the diaphragm 113 due to the incidence of infrared rays from the measurement object. Usually, in order to suppress the temperature rise of the detection element due to the heat generation, the infrared detection element 102 is placed on the electronic cooling element 107 and kept at a constant temperature.

  As described above, since the thermal infrared detector 101 absorbs infrared rays emitted from the measurement object and reads the change in resistance as an electrical signal, the temperature of the vacuum vessel 103 changes due to a change in the external temperature. When infrared radiation is incident on the infrared detection element 102, it is impossible to distinguish between the amount of infrared light incident from the measurement object and the infrared radiation incident from the peripheral portion.

  Therefore, in the technique disclosed in Patent Document 1, metal parts having an opening called a radiation shield 109 are arranged on the front and side surfaces of the infrared detection element 102, and the diaphragm of the optical system is made to coincide with this opening. Infrared radiation incident on the infrared detection element 102 is limited to radiation transmitted through the optical system and radiation from the radiation shield 109. Since the radiation shield 109 is formed on the silicon wafer 110 disposed on the electronic cooling element 107, the temperature is maintained constant.

  Since the radiation shield 109 does not have an opening other than the infrared incident opening with respect to the infrared detection element, an external connection terminal 105 that can be electrically connected to the outside, and the infrared detection element 102 It is necessary to devise a device for electrically connecting the two. As shown in FIG. 7, an internal bonding pad 116 and an external bonding pad 117 are provided on the silicon wafer 110 with the radiation shield 109 interposed therebetween, and an interlayer wiring 120 is provided between the multilayer silicon wafers 110. Then, the bonding pad 115 and the internal bonding pad 116 formed on the infrared detection element 102 are bonded via the first bonding wire 118, and the external bonding pad 117 and the external connection terminal 105 are further bonded to the second bonding wire. By bonding through 119, the external connection terminal 105 and the infrared detection element 102 are electrically connected.

  Further, although different from the above purpose, Patent Document 2 proposes a thermal infrared sensor that has a high detection accuracy and sensitivity of the radiation temperature and can provide a clear image. This thermal infrared sensor is a sensor that uses the pyroelectric effect. FIG. 8 is a cross-sectional view showing an embodiment of the infrared sensor described in Patent Document 2. In FIG. As shown in FIG. 8, 201a, 201b and 201c are thin-film pyroelectric elements having pyroelectric characteristics, and light receiving electrodes 203a, 201a, 201b and 201c are arranged on the infrared light receiving surface side of each upper surface of the pyroelectric thin film elements 201a, 201b and 201c. The sensor elements 201A, 201B, and 201C are configured by including 203b and 203c and lower electrodes 202a, 202b, and 202c on the infrared non-light-receiving surface side of the lower surface. Each of the sensor elements 201A, 201B, and 201C is embedded on the holding layer 204 with a predetermined interval, and the holding layer 204 is held by the substrate 205. Further, on the infrared light receiving surface side of the upper surface of the holding layer 204, a metal infrared light reflecting metal film 208 for reflecting the infrared light 207 incident on the non-arranged areas of the sensor elements 201A, 201B and 201C is provided. ing. The function of the infrared light reflecting metal film 208 is that the infrared rays incident on the sensor element non-arrangement region are absorbed by the holding layer 204, and the temperature rises in this portion, so that heat flows into the sensor element. This is to prevent the detection accuracy from deteriorating.

JP 2000-292253 A Japanese Patent Laid-Open No. 9-218086

  However, the conventional techniques described above have the following problems.

  In the conventional thermal infrared detector described in Patent Document 1, the entire infrared detection element is covered with a radiation shield, and an electron cooling element is used to keep the radiation shield at a constant temperature, thereby preventing radiation from other than the opening. The influence is excluded. Therefore, the vacuum container for storing the components inevitably becomes large, and there is a problem that the thermal infrared detector cannot be reduced in size and weight. Further, since the radiation shield is arranged, in order to connect the infrared detecting element and the external connection terminal, it is necessary to wire the first bonding wire, the interlayer wiring between the silicon wafers, and the second bonding wire. There is a problem that it is expensive.

  Moreover, in the infrared sensor described in Patent Document 2, an infrared light reflecting metal film is provided between the sensor elements, but these are for reflecting infrared rays incident on the sensor element non-arrangement region, If the shape is a film shape, it is sufficiently effective. For this reason, unlike the shield-like one for blocking the infrared rays that are incident from the peripheral portion, it does not deal with the problem of a decrease in temperature measurement accuracy caused by the infrared rays that cause the disturbance.

  The present invention has been made in view of such a problem, and is a thermal infrared detector that is high in infrared measurement accuracy by blocking infrared radiation that is a disturbance incident from a peripheral portion, and is small, lightweight, and low in cost. The purpose is to provide.

  The thermal infrared detector according to the present invention includes an infrared detection element having a plurality of pixels arranged one-dimensionally or two-dimensionally on the surface, an electronic cooling element that controls an operating temperature of the infrared detection element, and the infrared ray A vacuum vessel in which a detection element and the electronic cooling element are housed and an infrared incident opening for allowing infrared rays to enter the infrared detection element is formed, and the infrared detection element partitions the pixels. A micro shield standing on the surface of the infrared element, the micro shield having a height in a direction perpendicular to the surface of the infrared detection element larger than a thickness in a direction connecting the pixels. To do.

  In the present invention, the shield for blocking infrared rays is not provided on the entire infrared detection element, but a microshield is erected on the surface of the infrared detection element so as to partition each pixel. At this time, the height of the microshield is larger than the thickness in the direction connecting the pixels. In this way, by installing the microshield, the infrared light incident on each pixel of the infrared detection element is limited to radiation that has passed through the infrared incident opening and radiation from the microshield, resulting in disturbance from the periphery. Infrared radiation is blocked by the microshield and prevented from directly entering each pixel. Further, since the temperature of the micro shield is kept constant by the electronic cooling element, it is not affected by the temperature change of the outside world, and therefore, the influence of the infrared radiation that becomes a disturbance incident on the infrared detection element is eliminated. For this reason, the detection accuracy of the infrared detector is high. And as seen in the prior art, it is not necessary to enclose the entire infrared detection element with a radiation shield, so that the thermal infrared detector can be reduced in size and weight.

  The microshield can be arranged so as to surround each pixel, or can be arranged so as to surround each pixel in a grid pattern.

  The thermal infrared detector can be a bolometer type in which a bolometer is formed in the heat detection part of the infrared detection element.

  Further, the electronic cooling element can be an electronic cooling element utilizing the Peltier effect.

  An infrared detection element may be formed on a silicon wafer, and a signal readout circuit may be formed inside the silicon wafer. The element constituting the readout circuit can be, for example, a MOS type.

  It is possible to provide an external connection terminal for electrically connecting to the vacuum vessel to the outside, and to directly connect the external connection terminal and the infrared detection element with a single bonding wire. Therefore, the cost can be reduced as compared with the conventional connection means described in Patent Document 1.

  According to the present invention, by arranging the microshield so as to partition the pixels of the infrared detection element, it is possible to block infrared radiation that is a disturbance from other than the measurement target and improve the infrared detection accuracy. . Furthermore, compared with the conventional thermal infrared detector, the thermal infrared detector of the present invention is small in size, light in weight, and low in price.

  Hereinafter, a thermal infrared detector according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a conceptual diagram illustrating a cross-sectional structure of a thermal infrared detector according to the present embodiment, and FIG. 2 illustrates a structure of a pixel of the thermal infrared detector according to the present embodiment as viewed from above. FIG. 3 is a conceptual diagram, and FIG. 3 is a conceptual diagram showing a structure when the one pixel is viewed from the side.

  As shown in FIG. 1, in the thermal infrared detector 1 in the present embodiment, an electronic cooling element 7 using the Peltier effect is disposed on the inner bottom surface of the vacuum vessel 3, and a silicon wafer 6 is disposed thereon. It is glued. The infrared detection element 2 is formed on the silicon wafer 6. On the infrared detection element 2, a microshield 10 is formed so as to surround each pixel constituting the infrared detection element 2. An infrared incident opening 4 is provided in a part of the vacuum vessel 3 above the infrared detection element 2, and a window 5 is welded to the vacuum vessel 3 so as to cover the opening.

  The electronic cooling device 7 releases heat to the flat plate at the bottom of the vacuum vessel 3 while keeping the temperature of the silicon wafer 6 and the infrared detecting element 2 constant. An external connection terminal 9 for electrical connection with the outside is installed in the lower part of the vacuum vessel 3 so as to penetrate the lower part of the vacuum vessel 3. Between the infrared detection element 2 and the external connection terminal 9, wiring for transmitting an input signal for driving the infrared detection element 2 and an output signal from the infrared detection element 2 is provided. A bonding pad (not shown) and the external connection terminal 9 are directly connected by a bonding wire 19. Further, a metal exhaust pipe 8 is connected to the vacuum vessel 3, and the exhaust pipe 8 is connected to a vacuum exhaust device to bring the inside of the vacuum vessel 3 to a predetermined pressure, and then the exhaust pipe 8 is cut off from the outside. Thus, the inside of the vacuum container 3 is sealed.

  Next, a cross-sectional structure of one pixel of the infrared detection element 2 will be described with reference to FIGS. As shown in FIG. 6, two beams 114 are formed on the silicon wafer 110, and the diaphragm 113 on which the bolometer (resistor) 112 is formed is formed between the diaphragm 113 and the silicon wafer 110 by the two beams 114. And supported by a cavity 121 formed therebetween. Accordingly, the diaphragm 113 is thermally separated from the surface of the silicon wafer 110. An infrared reflection film 123 is formed on the silicon wafer 110 below the bolometer (resistor) 112. Further, for example, a MOS type signal readout circuit 122 is provided in the lower layer portion of the silicon wafer 110. The infrared detection element in the present embodiment is configured by two-dimensionally arranging these pixels, and a microshield is formed so as to surround each pixel.

  FIG. 3 is a conceptual diagram when the structure of one pixel in this embodiment is viewed from the side. As shown in FIG. 3, the infrared detector 1 pixel 14 formed on the silicon wafer 6 is partitioned from the adjacent left and right pixels by the microshield 10. The height of the microshield 10 is set so that the infrared detector 1 pixel 14 receives the infrared rays incident through the infrared incident opening, while blocking the radiation 13 from the periphery. Therefore, the height of the microshield 10 is larger than its width.

  FIG. 2 is a conceptual diagram when the pixel structure of the thermal infrared detector is viewed from above. Each pixel constituting the infrared detection element is partitioned in a lattice shape by the microshield 10. The beam 11 extends along the outer periphery of the diaphragm 12, and as described above, a cavity for heat insulation is formed between the diaphragm 12 and the silicon wafer existing on the back surface thereof.

  FIG. 4 shows an example of a method for creating a microshield using a semiconductor manufacturing process. As shown in FIG. 4A, a sacrificial layer 16 is formed on the silicon wafer 6 in order to form a cavity between the diaphragm 12 and the silicon wafer 6. Next, the diaphragm 12 is formed on the formed sacrificial layer 16, and the bolometer 15 serving as a temperature detecting unit is formed on the surface of the portion corresponding to the infrared light receiving unit. Further, the infrared detecting element is covered with a sacrificial layer 16 except for the bolometer 15 portion. Then, a groove 17 for forming a microshield is dug in a part of the sacrificial layer 16. Next, as shown in FIG. 4B, a microshield material is formed in the groove 17. The material of the microshield is, for example, aluminum. Finally, as shown in FIG. 4C, the bolometer 15 and the microshield 10 are formed by etching all the sacrificial layers 16. FIG. 4D is a more detailed view of the diaphragm 12 portion shown in FIG. 4C. The beam 11, the absorption film 18 that absorbs incident infrared rays and generates heat, and infrared rays. A reflecting plate 20 is shown in the figure.

  Next, the operation of the thermal infrared detector according to this embodiment configured as described above will be described. Infrared rays from the measurement object incident through the infrared incident opening 4 are absorbed by the diaphragm 12 constituting the pixel of the infrared detecting element 2, and the temperature of the diaphragm 12 rises. The change in the resistance value of the bolometer (resistance) 15 due to this temperature rise is read out by applying a bias current. However, the temperature of the infrared detection element 2 is kept constant by the electronic cooling element 7 in order to suppress the temperature rise of the infrared detection element 2 itself due to Joule heat generated by the bias current. In addition, the temperature of the vacuum vessel 3 changes due to a change in the temperature of the external environment, and the infrared radiation is incident on the infrared detection element 2, which may degrade the measurement accuracy. For this reason, the microshield 10 is disposed around the pixels constituting the infrared detection element 2, and the infrared radiation from the peripheral portion that is a disturbance is blocked. The temperature of the microshield 10 is also constant by the electronic cooling element 7 through the silicon wafer 6 and the infrared detection element 2, and the infrared radiation that becomes a disturbance is excluded.

  Next, the effect of this embodiment will be described. In the thermal infrared detector according to the present embodiment, since the microshield 10 is arranged around each pixel constituting the infrared detection element 2, infrared radiation that is a disturbance from other than the measurement object is blocked, Infrared measurement accuracy is improved. Further, the detector can be made smaller and lighter than the conventional technology in which the entire infrared detection element is covered with a radiation shield, and the infrared detection element 2 and the external connection terminal 9 are directly connected by a single bonding wire 19. Therefore, it is possible to provide a thermal infrared detector that is less expensive than the prior art.

It is a conceptual diagram which shows the cross-section of the thermal type infrared detector which concerns on embodiment of this invention. It is a conceptual diagram which shows the structure at the time of seeing the pixel of the thermal type infrared detector which concerns on embodiment of this invention from the upper surface. It is a conceptual diagram which shows the structure at the time of seeing one pixel of the thermal type infrared detector which concerns on embodiment of this invention from the side surface. It is a conceptual diagram which shows an example of the production method of the microshield in this embodiment. It is a conceptual diagram which shows the cross-sectional structure of the thermal type infrared detector of patent document 1. It is the conceptual diagram which showed typically the cross-sectional structure of 1 pixel of an infrared rays detection element based on FIG. 2 of patent document 1. FIG. It is an enlarged view of the A section in FIG. It is sectional drawing of the infrared sensor of patent document 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Thermal type infrared detector 2; Infrared detector 3; Vacuum container 4; Infrared incidence opening 5; Window 6; Silicon wafer 7; Electronic cooling element 8; Exhaust pipe 9; Beam 12; Diaphragm 13; Radiation 14; Infrared detector 1 pixel 15; Bolometer 16; Sacrificial layer 17; Groove 18; Absorbing film 19; Bonding wire 20; Reflector 101; Thermal infrared detector 102; ; Vacuum vessel 104; infrared incident opening 105; external connection terminal 106; window 107; electronic cooling element 108; exhaust pipe 109; radiation shield 110; silicon wafer 111; infrared ray 112;
113; Diaphragm 114; Beam 115; Bonding pad 116; Internal bonding pad 117; External bonding pad 118; First bonding wire 119; Second bonding wire 120; Interlayer wiring 121; Cavity 122; Read-out circuit 123; 201B, 201C; sensor element 201a, 201b, 201c; pyroelectric thin film element (thin film)
202a, 202b, 202c; lower electrode 203a, 203b, 203c; light receiving electrode 204; holding layer 205; substrate 207; infrared ray 208; infrared light reflecting metal film

Claims (6)

An infrared detection element having a plurality of pixels arranged one-dimensionally or two-dimensionally on the surface, an electronic cooling element that controls an operating temperature of the infrared detection element, the infrared detection element, and the electronic cooling element are stored. A vacuum vessel formed with an infrared incident opening for allowing infrared rays to enter the infrared detection element, and the infrared detection element is erected on the surface of the infrared element so as to partition the pixels A thermal infrared detector having a microshield, wherein the microshield has a height in a direction perpendicular to the surface of the infrared detection element larger than a thickness in a direction connecting the pixels. 2. The thermal infrared detector according to claim 1, wherein the micro shield is disposed on a surface of the infrared detection element so as to surround the periphery of each pixel. 3. The thermal infrared detector according to claim 1, wherein the thermal detection unit of the infrared detection element is a bolometer type having a bolometer. 4. 4. The thermal infrared detector according to claim 1, wherein the electronic cooling element is a Peltier element. The thermal infrared detector according to any one of claims 1 to 4, wherein the infrared detection element is formed on a silicon substrate, and a signal readout circuit is formed inside the silicon substrate. The vacuum vessel is provided with an external connection terminal for electrical connection to the outside, and the external connection terminal and the infrared detection element are directly connected by a single bonding wire. The thermal infrared detector according to any one of claims 1 to 5.

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