WO2004020960A1 - Dispositif de detection infrarouge - Google Patents

Dispositif de detection infrarouge Download PDF

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Publication number
WO2004020960A1
WO2004020960A1 PCT/IB2003/003608 IB0303608W WO2004020960A1 WO 2004020960 A1 WO2004020960 A1 WO 2004020960A1 IB 0303608 W IB0303608 W IB 0303608W WO 2004020960 A1 WO2004020960 A1 WO 2004020960A1
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WO
WIPO (PCT)
Prior art keywords
substrate
sensing device
sensor
absorbing material
array
Prior art date
Application number
PCT/IB2003/003608
Other languages
English (en)
Inventor
Steven Verlinden
Original Assignee
Melexis Nv
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 Melexis Nv filed Critical Melexis Nv
Priority to AU2003263389A priority Critical patent/AU2003263389A1/en
Publication of WO2004020960A1 publication Critical patent/WO2004020960A1/fr

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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
    • G01J5/12—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using thermoelectric elements, e.g. thermocouples

Definitions

  • the present invention relates mainly to infrared (IR) sensing devices and particularly to arrays formed of such devices.
  • a known arrangement for detecting IR radiation utilises the heating effect of the radiation to raise the temperature of a target.
  • the target is typically an IR absorbing membrane deposited on an area of a silicon integrated circuit that has been thermally isolated from the bulk of the integrated circuit by reducing its thickness.
  • the difference in temperature between the target and the bulk is determined from the electrical signals generated by one or more thermopile devices arranged with their hot junctions in the target area and their cold junction in the bulk.
  • thermopile devices arranged with their hot junctions in the target area and their cold junction in the bulk.
  • a plurality of thermopiles are connected in series to increase the signal level.
  • the temperature of the target is raised by the incoming IR radiation.
  • the corresponding signal generated by the thermopiles indicates the difference in temperature between the target and the bulk.
  • each IR sensor senses one element or pixel of the IR image.
  • the individual sensors are provided on a common area of thinned silicon. The thinned area is surrounded by a bulk area of non-thinned silicon.
  • the cold junctions of the thermopiles associated with each sensor are located within the common thinned area and not the bulk.
  • the temperature of the .bulk is measured by a thermistor as a datum against which the temperatures of the individual sensors may be referenced in order to determine a signal level and thereby detect a thermal image.
  • the accuracy of the individual signals from the thermopiles associated with each sensor may be affected by local heating of the common thinned area relative to the bulk due to the incoming IR radiation.
  • the temperature of the thinned area local to each target will therefore depend on the thermal conductivity of the thinned area and on the intensity of incoming radiation. This creates distortion and noise in the image when a large amount of radiation is incident upon a particular sensor, neighbouring sensors register artificially raised signal levels due to heat conduction causing local heating relative to the bulk. This phenomenon is known as 'blooming'.
  • a known method of addressing this problem is to deposit a layer of gold or other good heat conductor in a grid or similar pattern such that it isolates each of the individual sensors in the image array from its neighbours.
  • the gold layer acts to conduct heat away from individual sensors and to thereby help keep all reference areas at a common temperature.
  • these heat conducting layers extend partially over the bulk thereby allowing the bulk to function as a heat sink and keeping the temperature of the thinned area as close as possible to that of the bulk.
  • This method is partially successful in achieving this aim, however in some circumstances there are still problems. For example a large local IR intensity can cause substantially the whole of the thinned area to heat up relative to the to the bulk resulting in loss of signal contrast in the array.
  • an infrared (IR) sensing device comprising an array of IR sensors disposed on a suitable substrate characterised in that each IR sensor is disposed on a relatively thin area of substrate and is thermally isolated from every other IR sensor in the array by interspaced relatively thicker areas of substrate.
  • the relatively thick areas of substrate surrounding every sensor act as a heat sink and a thermal barrier between said sensors, thermally isolating the sensors from one another.
  • each IR sensor in the IR sensor array comprises an area of IR absorbing material deposited onto a relatively thin area of substrate and a means for measuring the temperature difference between the IR absorbing material and the thicker areas of substrate interspaced between each relatively thin area of substrate.
  • said substrate has a peripheral portion, being thick compared to the IR absorbing areas wherein circuitry for the operation of the sensor array or for interfacing the sensor array with external circuitry is provided.
  • the means for measuring the temperature difference comprises one or preferably, a plurality of thermopiles, the thermopile or thermopiles having their hot junctions close to the IR absorbing material such that they are at substantially the same temperature as the IR absorbing material and their cold junctions further away from the IR absorbing material in the thicker areas of the substrate interspaced between each and every sensor.
  • thermopiles In order to boost signal strength if a plurality of thermopiles is used, they may preferably connected in series, the hot junction of the thermopile at one end of the series being close to the IR absorbing material such that it is at substantially the same temperature as the IR absorbing material and the cold junction of the thermopile at the other end of the series being further away from the IR absorbing material in the thicker areas of the substrate interspaced between each and every sensor.
  • a plurality of thermistors are additionally provided in the thicker substrate areas interspaced between the sensors.
  • the reference temperature of the cold thermopile junction or junctions for each individual sensor is determined from the temperature of an adjacent or associated thermistor or from an average of the temperatures of a number of adjacent or associated thermistors. Measuring the temperature of the thick substrate surrounding each sensor at a plurality of locations allows a unique temperature to be determined as a cold reference for each sensor. This allows the array to operate with a greater degree of accuracy than arrays of the type described in the prior art as the adverse effects of sensors being heated by heat conduction from neighbouring sensors and thereby having a higher local temperature than the reference temperature of a thermistor in bulk silicon are avoided.
  • the thermistors may be formed by any appropriate conventional techniques onto or into the surface of the substrate.
  • the thermistors may be formed by conventional deposition techniques on the surface of the substrate or alternatively may be formed as a diffusion resistor in the substrate material.
  • the diffusion resistor arrangement provides a more intimate relationship between the thermistor and the substrate and thereby provides a more accurate measurement of the cold junction temperature of the thermopiles.
  • the substrate is preferably a silicon substrate. Most preferably, the area of substrate containing each sensor is thinned by selectively etching the backside of the silicon in line with each sensor. A particularly preferred method for achieving this is Reactive Ion Etching.
  • Figure 1 shows an IR sensor array in accordance with the state of the art
  • Figure 2 shows a cross section along line X-X in Figure 1 ;
  • Figure 3 shows an IR sensor array in accordance with the present invention
  • Figure 4 shows a cross section along line Y-Y in figure 3
  • Figure 5a shows one embodiment for integrating thermistors with the IR array in accordance with the present invention
  • Figure 5b shows an alternative embodiment for integrating thermistors with the IR array in accordance with the present invention.
  • an IR sensing device in accordance with the state of the art comprises a regular array of IR sensors 103 disposed on a suitable substrate 101.
  • Each sensor 103 corresponds to a pixel in an IR image formed by the device.
  • the substrate is comprised of two parts, a thick peripheral portion 106 upon which is disposed supplementary circuitry 102, such as amplifiers and buffers and a thin central portion 107 upon which the array of sensors 103 is disposed.
  • the sensors 103 comprise a layer of IR absorbing material deposited on the thin portion 107 of the substrate and an associated thermopile (not shown) with its hot junction lying close to the IR absorbing material such that it is at substantially the same temperature the IR absorbing material and its cold junction is located in the thin substrate portion 107 surrounding each sensor 103 further from the IR absorbing material than the hot junction.
  • a number of thermopiles connected in series may be substituted for the lone thermopile described above.
  • Suitable means are provided within the substrate for connecting signals generated by the thermopiles to the processing circuitry 102.
  • a reference temperature for the cold junctions of the thermistors is determined by a thermistor 1C4 located on the thick peripheral portion 106 of the substrate.
  • a grid 105 of thermally conducting material typically gold.
  • the grid surrounds each sensor 103, isolating each sensor 103 from its neighbours.
  • the objective of the grid 105 is to conduct absorbed heat throughout the array thereby reducing temperature variations within the array. This does reduce the temperature variation within the array but it introduces noise into any image produced by the array.
  • Figure 2 shows a cross section through Figure 1 along line X-X.
  • the deposited grid 105 is clearly seen on the surface of the substrate 101 , as is the contrast between the thick peripheral portion 106 of the substrate and the thin central portion 107 upon which the sensors 103 are disposed.
  • thermopiles are arranged to lie close to the IR absorbing material in order that they are at substantially the same temperature as the IR absorbing material and the cold junctions are arranged to lie in the thicker substrate areas immediately surrounding the IR absorbing material.
  • the thermopiles are preferably connected in series to increase the magnitude of the signal generated.
  • the substrate 201 has a thick peripheral portion 206 upon which circuitry 202 is provided and a central portion 207 upon which the sensors are disposed.
  • the supplementary circuitry 202 may include such components as amplifiers and buffers and may act as processing or control circuitry for enhancing or otherwise manipulating the signals. Alternatively or additionally, the supplementary circuitry may be used to control individual sensors 203 or to allow the array to interface with other external circuitry.
  • the central portion 207 of the substrate is of variable thickness as can be seen in figure 4 which shows a cross-section along line Y-Y in figure 3.
  • the thinned substrate areas 209 under the sensors 203 and the remaining thicker substrate areas, or walls 208 can be clearly seen.
  • the substrate 201 is etched from the backside to thin down the base material in those areas immediately under and aligned with the infrared absorbing areas. This is normally achieved by reactive ion etching but can alternatively be achieved by any other suitable technique.
  • Each infrared absorbing area is thus over a thin substrate area 209 and will exhibit a farger change in temperature with exposure to infrared radiation than if it were over an area of thicker substrate.
  • the areas of thicker substrate 208 between the infrared absorbing areas act as a thermal barrier or heat sink to reduce the transfer of heat energy from one sensor 203 to the next. This helps to reduce the effect of 'blooming' in the infrared image.
  • thermistors 210 Distributed within the array, in the walls or thicker substrate areas 208 immediately surrounding the IR absorbing areas and close to the cold junctions of the thermopiles are a plurality of thermistors 210.
  • the signals from the thermopiles and the signals from the thermistors 210 are connected to the supplementary circuitry 202 on the peripheral portion of the substrate.
  • the supplementary circuitry 202 determines a specific cold junction temperature for each thermopile by using the signal from a suitably selected thermistor 210 which may typically be the thermistor 210 located closest to the cold junction of the particular thermopile although other thermistors 210 may be selected if desired.
  • the supplementary circuitry 202 is arranged to determine a specific cold junction temperature for each thermopile by averaging the signals from one or more suitably selected thermistors 210.
  • the thermistors 210 may typically be a number of the closest thermistors 210 to the cold junction of the particular thermopile though other selections may be used if desired.
  • thermopile cold junctions allow a more accurate temperature measurement of the temperature of each thermopile cold junction than that provided by a single thermistor in the peripheral portion of the substrate as disclosed in the prior art. This allows the device to compensate for local heating effects as if the temperature of a local area of the array is raised by intense radiation the reference temperature will also be raised. Using individual reference temperatures in this manner reduces noise and distortion in images detected by the array significantly compared to prior art sensors which use only a single reference temperature.
  • the thermistors 210 may be formed by any appropriate conventional techniques onto or into the surface of the substrate.
  • Figure 5A shows an embodiment wherein the thermistor 210 has been formed by a conventional deposition technique on the surface of the substrate.
  • Figure 5B shows an alternative arrangement wherein the thermistor
  • thermopiles 210 and the substrate and thereby provides a more accurate measurement of the cold junction temperature of the thermopiles.

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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

L'invention concerne un réseau de capteurs infrarouges placés sur un substrat (201). Ce substrat est constitué de silicium mais on peut utiliser un autre matériau approprié si on le souhaite. Chaque capteur (203) est constitué d'un matériau à absorption infrarouge ainsi que d'une ou de plusieurs piles thermoélectriques associées (non illustrées). Les soudures chaudes des piles thermoélectriques sont étroitement réalisées au-dessus du matériau à absorption infrarouge de façon à avoir sensiblement la même température que ce dernier Les jonctions froides sont par contre réalisées dans les parties les plus épaisses du substrat (208), aux abords immédiats du matériau à absorption infrarouge. De préférence, les piles thermoélectriques sont connectées en série pour augmenter l'amplitude du signal émis.
PCT/IB2003/003608 2002-08-29 2003-08-29 Dispositif de detection infrarouge WO2004020960A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003263389A AU2003263389A1 (en) 2002-08-29 2003-08-29 Infrared sensing device

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0220048A GB0220048D0 (en) 2002-08-29 2002-08-29 Infrared sensing device
GB0220048.3 2002-08-29

Publications (1)

Publication Number Publication Date
WO2004020960A1 true WO2004020960A1 (fr) 2004-03-11

Family

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Family Applications (1)

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PCT/IB2003/003608 WO2004020960A1 (fr) 2002-08-29 2003-08-29 Dispositif de detection infrarouge

Country Status (3)

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AU (1) AU2003263389A1 (fr)
GB (1) GB0220048D0 (fr)
WO (1) WO2004020960A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009043571A1 (fr) * 2007-09-28 2009-04-09 Pyreos Ltd. Dispositif de détection d'un rayonnement thermique à haute résolution et son procédé de production

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1531423A (en) * 1975-03-13 1978-11-08 Omega Engineering Cold junction compensator
US6372656B1 (en) * 1998-09-25 2002-04-16 Robert Bosch Gmbh Method of producing a radiation sensor

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1531423A (en) * 1975-03-13 1978-11-08 Omega Engineering Cold junction compensator
US6372656B1 (en) * 1998-09-25 2002-04-16 Robert Bosch Gmbh Method of producing a radiation sensor

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009043571A1 (fr) * 2007-09-28 2009-04-09 Pyreos Ltd. Dispositif de détection d'un rayonnement thermique à haute résolution et son procédé de production
US8969811B2 (en) 2007-09-28 2015-03-03 Pyreos Ltd. Device to detect thermal radiation with high resolution method to manufacture and use the device

Also Published As

Publication number Publication date
GB0220048D0 (en) 2002-10-09
AU2003263389A1 (en) 2004-03-19

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