WO2000003214A1 - Bolometer having an increased fill factor - Google Patents

Bolometer having an increased fill factor Download PDF

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Publication number
WO2000003214A1
WO2000003214A1 PCT/KR1998/000200 KR9800200W WO0003214A1 WO 2000003214 A1 WO2000003214 A1 WO 2000003214A1 KR 9800200 W KR9800200 W KR 9800200W WO 0003214 A1 WO0003214 A1 WO 0003214A1
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WO
WIPO (PCT)
Prior art keywords
bolometer
level
conduction line
pair
electrically connected
Prior art date
Application number
PCT/KR1998/000200
Other languages
French (fr)
Inventor
Euisik Yoon
Hyung Kew Lee
Sang Baek Ju
Original Assignee
Korea Advanced Institute Of Science And Technology
Daewoo Electronics Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Korea Advanced Institute Of Science And Technology, Daewoo Electronics Co., Ltd. filed Critical Korea Advanced Institute Of Science And Technology
Priority to PCT/KR1998/000200 priority Critical patent/WO2000003214A1/en
Publication of WO2000003214A1 publication Critical patent/WO2000003214A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
    • G01J5/20—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices

Definitions

  • the present invention relates to an infra-red bolometer; and, more particularly, to a three-level infra-red bolometer.
  • Bolometers are energy detectors based upon a change in the resistance of materials (called bolometer elements) that are exposed to a radiation flux.
  • the bolometer elements have been made from both metals and semiconductors. In metals, the resistance change is essentially due to variations in the carrier mobility, which typically decreases with temperature. Greater sensitivity can be obtained in high-resistivity semiconductor bolometer elements in which the free- carrier density is an exponential function of temperature, but thin film fabrication of semiconductor for bolometers is a difficult problem.
  • Figs. 1 and 2 are a cross sectional and a perspective views illustrating a two-level bolometer 10, disclosed in U.S. Patent No. 5,300,915 entitled "THERMAL SENSOR", the bolometer 10 including an elevated microbridge detector level 11 and a lower level 12.
  • the lower level 12 has a flat surfaced semiconductor substrate 13 , such as a single crystal silicon substrate.
  • the surface 14 of the silicon substrate 13 has fabricated thereon several components of an integrated circuit 15 including diodes, x and y bus lines, connections, and contact pads at the ends of the x and y bus lines, the fabrication following conventional silicon IC technology.
  • the integrated circuit 15 is coated with a protective layer of silicon nitride 16.
  • the valley strip 17 is the area not covered by the elevated detector.
  • the elevated detector level 11 includes a silicon nitride layer 20, a serpentine metallic resistive path 21, a silicon nitride layer 22 over the layers 20 and 21, and an IR absorber coating 23 over the silicon nitride layer 22.
  • Downwardly extending silicon nitride layers 20' and 22' deposited at the same time during the fabrication make up the four sloping support legs for the elevated detector level 11. The number of support legs may be greater or less than four.
  • the cavity 26 between the two levels is ambient atmosphere. During the fabrication process, however, the cavity 26 was originally filled with a previously deposited layer of easily dissolvable glass or other dissolvable material until the layers 20, 20' and 22, 22' were deposited. Subsequently in the process the glass was dissolved out to leave the cavity.
  • FIG. 3 there is a top view depicting the elevated detector level 11 shown in Fig. 1.
  • This drawing is made as though the overlying absorber coating 23 and upper silicon nitride layer 22 are transparent so the serpentine resistive layer path 21 can be shown.
  • the ends of the resistive paths 21a and 21b are continued down the slope area 30 to make electrical contact with pads 31 and 32 on the lower level 12.
  • Fig. 3 shows the nitride window cuts 35, 36 and 37 which are opened through the silicon nitride layers 20 and 22 to provide access to the phosphor- glass beneath for dissolving it from beneath the detector plane.
  • the nitride window cuts 35, 36, 37 to provide this access are narrow and are shared with adjacent pixels on the sides, thus maximizing the area available to the detector and thus maximizing the fill- factor.
  • the four supporting bridges may be short or as long as necessary to provide adequate support and thermal isolation.
  • One of the shortcomings of the above described bolometer is its less than optimum fill factor resulting from the presence of the bridges on same level as the elevated microbridge detector level 11 as shown in Fig. 2, which, in turn, reduces the total area for IR absorbing, i.e., the fill factor.
  • an object of the present invention to provide a three-level infra-red bolometer, each of infra-red bolometer having an increased fill factor.
  • a three-level infra-red bolometer comprising: an active matrix level, the active matrix level including a substrate, at least a pair of connecting terminals and a protective layer covering the substrate, wherein the pair of connecting terminals are formed on top of the substrate; the support level being provided with at least a pair of bridges, each of the bridges including an conduction line formed on top thereof, one end of the conduction line being electrically connected to the respective connecting terminal; an absorption level, the absorption level including a serpentine bolometer element surrounded by an absorber; and at least a pair of posts, each of the posts being placed between the absorption level and the support level and including an electrical conduit surrounded by an insulating material, top end of the electrical conduit being electrically connected to the serpentine bolometer element and bottom end of the electrical conduit being electrically connected to the conduction line, in such a way that each end of the serpentine bolometer element is electrically connected to the respective connecting terminal through
  • Fig. 1 present a schematic cross sectional view illustrating a two-level microbridge bolometer previous disclosed
  • Fig. 2 shows a perspective view setting forth a two-level microbridge bolometer shown in Fig. 1;
  • Fig. 3 produces a top view depicting an elevated detector level in Fig. 1;
  • Fig. 4 shows a perspective view setting forth a three-level infra-red bolometer in accordance with the present invention.
  • Fig. 5 presents a schematic cross section view depicting the three-level infra-red bolometer taken along I - I in Fig. 4.
  • FIGs. 4 and 5 a perspective view illustrating a three-level infra-red bolometer 201 and a schematic cross sectional view thereof taken along I - I in Fig. 4, in accordance with the present invention, respectively. It should be noted that like parts appearing in Figs. 4 and 5 are represented by like reference numerals.
  • the inventive bolometer 201 shown in Figs. 4 and 5 comprises an active matrix level 210, a support level 220, at least a pair of posts 270 and an absorption level 230.
  • the active matrix level 210 has a substrate 212 including an integrated circuit (not shown) , a pair of connecting terminals 214 and a protective layer 216.
  • Each of the connecting terminals 214 made of a metal is located on top of the substrate 212.
  • the protective layer 216 made of, e.g., silicon nitride (SiN ⁇ ) covers the substrate 212.
  • the pair of connecting terminals 214 are electrically connected to the integrated circuit .
  • the support level 220 includes a pair of bridges 240 made of silicon nitride (SiN ⁇ ) , each of the bridges 240 having a conduction line 265 formed on top thereof.
  • Each of the bridges 240 is provided with an anchor portion 242, a leg portion 244 and an elevated portion 246, the anchor portion 242 including a via hole 252 through which one end of the conduction line 265 is electrically connected to the connecting terminal 214, the leg portion 244 supporting the elevated portion 246.
  • the absorption level 230 is provided with a serpentine bolometer element 285 surrounded by an absorber 295 made of a heat absorbing material, e.g., silicon nitride, and an IR absorber coating 297 formed on top of the absorber 295.
  • a heat absorbing material e.g., silicon nitride
  • an IR absorber coating 297 formed on top of the absorber 295.
  • Each of the posts 270 is placed between the absorption level 230 and the support level 220.
  • Each of the post 270 includes an electrical conduit 272 made of a metal, e.g., titanium (Ti) and surrounded by an insulating material 274 made of, e.g., silicon nitride (SiN ) .
  • Top end of the electrical conduit 272 is electrically connected to one end of the serpentine bolometer element 285 and bottom end of the electrical conduit 272 is electrically connected to the conduction line 265 on the bridge 240, in such a way that both ends of the serpentine bolometer element 285 in che absorption level 230 is electrically connected to the integrated circuit of the active matrix level 210 through the electrical conduits 272, the conduction lines 265 and the connecting terminals 214.
  • the resistivity of the serpentine bolometer element 285 is changed, wherein the changed resistivity causes a current and a voltage to vary.
  • the varied current or voltage is amplified by the integrated circuit, in such a way that the amplified current or voltage is read out by a detective circuit (not shown) .
  • the bridges 240 are positioned under the absorption level 230 allowing the absorption level to be fully utilized for IR absorption, which will, in turn, increase the fill factor thereof.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Radiation Pyrometers (AREA)

Abstract

The inventive three-level infra-red bolometer includes an active matrix level (210), a support level (220), a pair of posts (270) and an absorption level (230). The active matrix level (210) includes a substrate (212) having an integrated circuit, a pair of connecting terminals (214) and a protective layer (216) covering the substrate. The support level includes a pair of bridges (240), each of the bridges being provided with a conduction line (265) formed on top thereof, wherein one end of the conduction line is electrically connected to the respective connecting terminal (214). The absorption level (230) includes a serpentine bolometer element (285) surrounded by an absorber (295). Each of posts (270) includes an electrical conduit (272) surrounded by an insulating material (274) and is placed between the absorption level (230) and the bridge (240), in such a way that the serpentine bolometer element (285) is electrically connected to the integrated circuit through the electrical conduits (272), the conduction lines (265) and the connecting terminals (214). In the bolometer of the present invention, the bridge (240) is positioned under the absorption level (230) allowing the absorption level to be fully utilized for IR absorption, which will, in turn, increase the fill factor thereof.

Description

BOLOMETER HAVING AN INCREASED FILL FACTOR
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an infra-red bolometer; and, more particularly, to a three-level infra-red bolometer.
BACKGROUND ART
Bolometers are energy detectors based upon a change in the resistance of materials (called bolometer elements) that are exposed to a radiation flux. The bolometer elements have been made from both metals and semiconductors. In metals, the resistance change is essentially due to variations in the carrier mobility, which typically decreases with temperature. Greater sensitivity can be obtained in high-resistivity semiconductor bolometer elements in which the free- carrier density is an exponential function of temperature, but thin film fabrication of semiconductor for bolometers is a difficult problem.
Figs. 1 and 2 are a cross sectional and a perspective views illustrating a two-level bolometer 10, disclosed in U.S. Patent No. 5,300,915 entitled "THERMAL SENSOR", the bolometer 10 including an elevated microbridge detector level 11 and a lower level 12. The lower level 12 has a flat surfaced semiconductor substrate 13 , such as a single crystal silicon substrate. The surface 14 of the silicon substrate 13 has fabricated thereon several components of an integrated circuit 15 including diodes, x and y bus lines, connections, and contact pads at the ends of the x and y bus lines, the fabrication following conventional silicon IC technology. The integrated circuit 15 is coated with a protective layer of silicon nitride 16. The valley strip 17 is the area not covered by the elevated detector.
The elevated detector level 11 includes a silicon nitride layer 20, a serpentine metallic resistive path 21, a silicon nitride layer 22 over the layers 20 and 21, and an IR absorber coating 23 over the silicon nitride layer 22. Downwardly extending silicon nitride layers 20' and 22' deposited at the same time during the fabrication make up the four sloping support legs for the elevated detector level 11. The number of support legs may be greater or less than four. The cavity 26 between the two levels is ambient atmosphere. During the fabrication process, however, the cavity 26 was originally filled with a previously deposited layer of easily dissolvable glass or other dissolvable material until the layers 20, 20' and 22, 22' were deposited. Subsequently in the process the glass was dissolved out to leave the cavity.
In Fig. 3, there is a top view depicting the elevated detector level 11 shown in Fig. 1. This drawing is made as though the overlying absorber coating 23 and upper silicon nitride layer 22 are transparent so the serpentine resistive layer path 21 can be shown. The ends of the resistive paths 21a and 21b are continued down the slope area 30 to make electrical contact with pads 31 and 32 on the lower level 12. Fig. 3 shows the nitride window cuts 35, 36 and 37 which are opened through the silicon nitride layers 20 and 22 to provide access to the phosphor- glass beneath for dissolving it from beneath the detector plane. The nitride window cuts 35, 36, 37 to provide this access are narrow and are shared with adjacent pixels on the sides, thus maximizing the area available to the detector and thus maximizing the fill- factor. The four supporting bridges may be short or as long as necessary to provide adequate support and thermal isolation.
One of the shortcomings of the above described bolometer is its less than optimum fill factor resulting from the presence of the bridges on same level as the elevated microbridge detector level 11 as shown in Fig. 2, which, in turn, reduces the total area for IR absorbing, i.e., the fill factor.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of the present invention to provide a three-level infra-red bolometer, each of infra-red bolometer having an increased fill factor.
In accordance with one aspect of the present invention, there is provided a three-level infra-red bolometer, the bolometer comprising: an active matrix level, the active matrix level including a substrate, at least a pair of connecting terminals and a protective layer covering the substrate, wherein the pair of connecting terminals are formed on top of the substrate; the support level being provided with at least a pair of bridges, each of the bridges including an conduction line formed on top thereof, one end of the conduction line being electrically connected to the respective connecting terminal; an absorption level, the absorption level including a serpentine bolometer element surrounded by an absorber; and at least a pair of posts, each of the posts being placed between the absorption level and the support level and including an electrical conduit surrounded by an insulating material, top end of the electrical conduit being electrically connected to the serpentine bolometer element and bottom end of the electrical conduit being electrically connected to the conduction line, in such a way that each end of the serpentine bolometer element is electrically connected to the respective connecting terminal through the repective electrical conduit and the respective conduction line. BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, wherein:
Fig. 1 present a schematic cross sectional view illustrating a two-level microbridge bolometer previous disclosed;
Fig. 2 shows a perspective view setting forth a two-level microbridge bolometer shown in Fig. 1;
Fig. 3 produces a top view depicting an elevated detector level in Fig. 1; Fig. 4 shows a perspective view setting forth a three-level infra-red bolometer in accordance with the present invention; and
Fig. 5 presents a schematic cross section view depicting the three-level infra-red bolometer taken along I - I in Fig. 4.
MODES OF CARRYING OUT THE INVENTION
There are provided in Figs. 4 and 5 a perspective view illustrating a three-level infra-red bolometer 201 and a schematic cross sectional view thereof taken along I - I in Fig. 4, in accordance with the present invention, respectively. It should be noted that like parts appearing in Figs. 4 and 5 are represented by like reference numerals.
The inventive bolometer 201 shown in Figs. 4 and 5 comprises an active matrix level 210, a support level 220, at least a pair of posts 270 and an absorption level 230. The active matrix level 210 has a substrate 212 including an integrated circuit (not shown) , a pair of connecting terminals 214 and a protective layer 216. Each of the connecting terminals 214 made of a metal is located on top of the substrate 212. The protective layer 216 made of, e.g., silicon nitride (SiNχ) covers the substrate 212. The pair of connecting terminals 214 are electrically connected to the integrated circuit .
The support level 220 includes a pair of bridges 240 made of silicon nitride (SiNχ) , each of the bridges 240 having a conduction line 265 formed on top thereof. Each of the bridges 240 is provided with an anchor portion 242, a leg portion 244 and an elevated portion 246, the anchor portion 242 including a via hole 252 through which one end of the conduction line 265 is electrically connected to the connecting terminal 214, the leg portion 244 supporting the elevated portion 246.
The absorption level 230 is provided with a serpentine bolometer element 285 surrounded by an absorber 295 made of a heat absorbing material, e.g., silicon nitride, and an IR absorber coating 297 formed on top of the absorber 295. When selecting the material for the bolometer element 285 and the conduction line 265, it is important to consider the fabrication process and the material characteristics. To improve the performance of the bolometer, the bolometer element 285 should have a large temperature coefficient of resistance (TCR) , small thermal conductivity and small 1/f noise. For this reason, titanium was chosen as the material for the bolometer element 285 and the conduction line 265.
Each of the posts 270 is placed between the absorption level 230 and the support level 220. Each of the post 270 includes an electrical conduit 272 made of a metal, e.g., titanium (Ti) and surrounded by an insulating material 274 made of, e.g., silicon nitride (SiN ) . Top end of the electrical conduit 272 is electrically connected to one end of the serpentine bolometer element 285 and bottom end of the electrical conduit 272 is electrically connected to the conduction line 265 on the bridge 240, in such a way that both ends of the serpentine bolometer element 285 in che absorption level 230 is electrically connected to the integrated circuit of the active matrix level 210 through the electrical conduits 272, the conduction lines 265 and the connecting terminals 214. When the infra-red energy is absorbed, the resistivity of the serpentine bolometer element 285 is changed, wherein the changed resistivity causes a current and a voltage to vary. The varied current or voltage is amplified by the integrated circuit, in such a way that the amplified current or voltage is read out by a detective circuit (not shown) .
In the three-level infra-red bolometer 201 of the present invention, the bridges 240 are positioned under the absorption level 230 allowing the absorption level to be fully utilized for IR absorption, which will, in turn, increase the fill factor thereof.
While the present invention has been described with respect to certain preferred embodiments only, other modifications and variations may be made without departing from the scope of the present invention as set forth in the following claims.

Claims

What is claimed is:
1. A three-level infra-red bolometer, the bolometer comprising: an active matrix level, the active matrix level including a substrate and at least a pair of connecting terminals, wherein the pair of connecting terminals are formed on top of the substrate; the support level being provided with at least a pair of bridges, each of the bridges including an conduction line, one end of the conduction line being electrically connected to the respective connecting terminal ; an absorption level, the absorption level including a bolometer element surrounded by an absorber; and at least a pair of posts, each of the posts being placed between the absorption level and the support level and including an electrical conduit surrounded by an insulating material, each end of the bolometer element of the absorption level being electrically connected to the respective connecting terminal through the respective electrical conduit and the respective conduction line.
2. The bolometer of claim 1, wherein each of the bridges is provided with an anchor portion, a leg portion and an elevated portion, the anchor portion including a via hole through which one end of the conduction line is electrically connected to the connecting terminal.
3. The bolometer of claim 1, wherein the pair of connecting terminals are made of a metal.
4. The bolometer of claim 1, wherein the active matrix level further includes a protective layer.
5. The bolometer of claim 4, wherein the protective layer is made of silicon nitride.
6. The bolometer of claim 1, wherein the conduction line is made of a metal.
7. The bolometer of claim 6, wherein the conduction line is positioned on top of the bridges.
8. The bolometer of claim 1, wherein top end of the electrical conduit is electrically connected to one end of the bolometer element and bottom end of the electrical conduit is electrically connected to other end of the conduction line.
9. The bolometer of claim 1, wherein the electrical conduit is made of a metal .
10. The bolometer of claim 1, wherein the bolometer element has a serpentine shape.
11. The bolometer of claim 10, wherein the bolometer element is made of a metal.
12. The bolometer of claim 1, wherein the conduction line, the electrical conduit and the bolometer element are made of the same metal .
13. The bolometer of claim 12, wherein the conduction line, the electrical conduit and the bolometer element are made of a titanium.
14. The bolometer of claim 1, wherein the insulating material and the absorber is made of the same material.
15. The bolometer of claim 14, wherein the absorber and the insulating material are made of silicon nitride,
PCT/KR1998/000200 1998-07-09 1998-07-09 Bolometer having an increased fill factor WO2000003214A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1122526A2 (en) * 2000-01-31 2001-08-08 Nec Corporation Thermal infrared detector provided with shield for high fill factor

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0534768A1 (en) * 1991-09-27 1993-03-31 Texas Instruments Incorporated Uncooled infrared detector and method for forming the same
US5572029A (en) * 1994-06-30 1996-11-05 Walker; William K. Thermal isolation for hybrid thermal detectors

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0534768A1 (en) * 1991-09-27 1993-03-31 Texas Instruments Incorporated Uncooled infrared detector and method for forming the same
US5572029A (en) * 1994-06-30 1996-11-05 Walker; William K. Thermal isolation for hybrid thermal detectors

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1122526A2 (en) * 2000-01-31 2001-08-08 Nec Corporation Thermal infrared detector provided with shield for high fill factor
EP1122526A3 (en) * 2000-01-31 2003-11-19 Nec Corporation Thermal infrared detector provided with shield for high fill factor

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