U.S. patent application number 16/947599 was filed with the patent office on 2020-11-26 for thermopile infrared individual sensor for measuring temperature or detecting gas.
This patent application is currently assigned to Heimann Sensor GmbH. The applicant listed for this patent is Heimann Sensor GmbH. Invention is credited to Frank HERRMANN, Wilhelm Leneke, Jorg Schieferdecker, Christian SCHMIDT, Mischa SCHULZE, Marion Simon, Karlheinz Storck.
Application Number | 20200370963 16/947599 |
Document ID | / |
Family ID | 1000005004517 |
Filed Date | 2020-11-26 |
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United States Patent
Application |
20200370963 |
Kind Code |
A1 |
Simon; Marion ; et
al. |
November 26, 2020 |
Thermopile infrared individual sensor for measuring temperature or
detecting gas
Abstract
A thermopile infrared individual sensor includes a housing
filled with a gaseous medium. It has optics and one or more sensor
chips with individual sensor cells with infrared sensor structures
with reticulated membranes, infrared-sensitive regions of which are
each spanned by at least one beam over a cavity in a carrier body.
The thermopile infrared sensor uses monolithic Si-micromechanics
technology for contactless temperature measurements. In the case of
a sufficiently large receiver surface, this outputs a high signal
with a high response speed. A plurality of individual adjacent
sensor cells are combined with respectively one infrared-sensitive
region with thermopile structures on the membrane on a common
carrier body of an individual chip to a single thermopile sensor
structure with a signal output in the housing, consisting of a cap
sealed with a base plate with a common gaseous medium.
Inventors: |
Simon; Marion; (Bad
Schwalbach, DE) ; SCHULZE; Mischa; (Hunstetten,
DE) ; Leneke; Wilhelm; (Taunusstein, DE) ;
Storck; Karlheinz; (Lorch am Rhein, DE) ; HERRMANN;
Frank; (Dohna, DE) ; SCHMIDT; Christian;
(Dresden, DE) ; Schieferdecker; Jorg; (Dresden,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Heimann Sensor GmbH |
Dresden |
|
DE |
|
|
Assignee: |
Heimann Sensor GmbH
Dresden
DE
|
Family ID: |
1000005004517 |
Appl. No.: |
16/947599 |
Filed: |
August 7, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16309513 |
Dec 13, 2018 |
10794768 |
|
|
PCT/EP2017/064429 |
Jun 13, 2017 |
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16947599 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01J 5/045 20130101;
G01J 5/048 20130101; G01J 5/06 20130101; G01J 5/0225 20130101; G01J
2005/065 20130101; G01J 5/14 20130101; G01J 5/12 20130101; G01N
21/3504 20130101; G01J 2005/123 20130101; G01J 5/0014 20130101 |
International
Class: |
G01J 5/00 20060101
G01J005/00; G01J 5/02 20060101 G01J005/02; G01J 5/04 20060101
G01J005/04; G01J 5/14 20060101 G01J005/14; G01N 21/3504 20060101
G01N021/3504; G01J 5/12 20060101 G01J005/12; G01J 5/06 20060101
G01J005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2016 |
DE |
10 2016 111 349.2 |
Claims
1. A thermopile infrared sensor, comprising: a housing filled with
a gas medium, the housing having a base plate and a cap; an optical
unit arranged at an aperture opening in the housing; and a sensor
chip having a plurality of sensor cells, each of the plurality of
sensor cells having a thermopile infrared-sensitive region, the
plurality of sensor cells being arranged on a common carrier body
to form a thermopile sensor structure, wherein sensor cells of the
plurality of sensor cells are interconnected with one another to
form an effective thermopile individual sensor, wherein each sensor
cell of the plurality of sensor cells generates an output signal,
and wherein the output signals of the plurality of sensor cells are
combined to form one output signal of the thermopile infrared
sensor.
2. The thermopile infrared sensor as in claim 1, wherein the sensor
cells of the plurality of sensor cells are connected in series, in
parallel or in a combination of series and parallel circuit to form
the one output signal.
3. The thermopile infrared sensor as in claim 1, wherein the one
output signal is formed by use of preamplifiers or impedance
converters or multiplexers or microcontrollers as a summation
element.
4. The thermopile infrared sensor as in claim 3, wherein each
preamplifier is an impedance converter or a low pass filter.
5. The thermopile infrared sensor as in claim 1, wherein the common
carrier body comprises a plurality of cavities, and wherein each of
the plurality of sensor cells comprises a membrane extending over
one cavity of the plurality of cavities, a central sensitive
portion of the membrane being the thermopile infrared-sensitive
region; a beam structure connecting the central sensitive portion
of the membrane with the carrier body, a hot contact thermocouple
arranged on the central sensitive portion of the membrane, and a
cold contact thermocouple arranged on the carrier body.
6. The thermopile infrared sensor as in claim 5, wherein adjacent
ones of the plurality of cavities are separated by the carrier
body.
7. The thermopile infrared sensor as in claim 1, wherein each of
the plurality of sensor cells further comprises two terminal pads,
and wherein adjacent ones of the plurality of sensor cells are
electrically connected by wire bridges.
8. The thermopile infrared sensor as in claim 5, wherein the beam
structure comprises a first L-shaped beam and a second L-shaped
beam, the first L-shaped beam and the second L-shaped beam being
arranged in a mirrored configuration to form a rectangular beam
structure.
9. The thermopile infrared sensor as in claim 8, wherein the
cavities of the plurality of cavities have generally vertical
walls, and wherein the first L-shaped beam is arranged above the
cavity and proximal to two adjacent ones of the generally vertical
walls of the respective cavity, and wherein the second L-shaped
beam is arranged above the cavity and proximal to two further
adjacent ones of the generally vertical walls of the respective
cavity.
10. The thermopile infrared sensor as in claim 8, wherein the
cavities of the plurality of cavities have inclined walls, and
wherein the first L-shaped beam is arranged above two adjacent ones
of the inclined walls, and wherein the second L-shaped beam is
arranged above to two further adjacent ones of the inclined
walls.
11. The thermopile infrared sensor as in claim 5, wherein the beam
structure of each of the plurality of sensor cells comprises a
first beam; a first outer slot separating the first beam from the
carrier body; a first inner slot separating the first beam from the
membrane; a second beam; a second outer slot separating the second
beam from the carrier body; and a second inner slot separating the
second beam from the membrane.
12. The thermopile infrared sensor as in claim 5, wherein an
absorber layer having a thickness of less than 1 .mu.m is arranged
on the membrane.
13. The thermopile infrared sensor as in claim 1, wherein the gas
medium comprises one or more of xenon, krypton, and argon.
14. The thermopile infrared sensor as in claim 1, wherein the
housing is sealed against its surroundings and wherein an internal
pressure of the gas medium is below standard atmospheric
pressure.
15. The thermopile infrared sensor as in claim 1, wherein the
plurality of sensor cells and a plurality of preamplifiers are
formed from a common substrate.
16. The thermopile infrared sensor as in claim 1, wherein the
sensor chip comprises 2, 4, 9, or 16 sensor cells.
17. The thermopile infrared sensor as in claim 1, wherein the
thermopile infrared sensor is a gas detector.
18. The thermopile infrared sensor as in claim 1, wherein two or
four sensor chips are arranged adjacent to one another in the
housing to form one or more channel for NDIR gas detection.
19. The thermopile infrared sensor as in claim 18, wherein between
adjacent channels is disposed an optical partition wall to prevent
crosstalk between the channels.
Description
TECHNICAL FIELD
[0001] The invention relates to a thermopile individual sensor for
measuring temperature or detecting gas in monolithic silicon
micromechanical technology in a housing filled with a gas medium
and having an optical unit and also one or more sensor chips having
individual sensor cells having infrared sensor structures having
reticulated membranes, the infrared-sensitive regions of which are
each spanned by at least one beam over a cavity in a carrier body
with good thermal conduction.
BACKGROUND
[0002] Thermopile infrared sensors which are produced in silicon
micromechanical technology exist in greatly varying embodiments.
For example, a thermopile sensor chip is described in DE 101 44 343
A1, which, with vertical or nearly vertical walls, has the largest
possible membrane as an IR receiving area, in order to maximize the
signal to be received using an IR-sensitive area on the membrane.
The membrane is spanned over a recess in a silicon carrier body,
which is also formed as a heat sink.
[0003] A further solution is proposed in DE 103 21 639 A1, in which
thermopile elements are provided, the hot ends of which are
positioned on the membrane and the cold ends of which are located
on a silicon carrier body.
[0004] These embodiments share the feature that a homogeneous thin
membrane carries many thermocouples, for example, thermopile
elements, and the sensor chip is housed in a housing having
atmospheric pressure and typically dry air or dry nitrogen. To
obtain the greatest possible signal voltage in thermopile sensor
elements, the thermocouples thereof have to be formed as long as
possible, because thus less heat conduction and therefore a greater
temperature difference is achieved between the hot and cold ends of
the thermocouples.
[0005] Therefore, sufficiently high signal voltages for many
applications cannot be achieved on smaller chip areas and the
signal-to-noise ratio or the detection limit in measuring tasks
does not meet the requirements. If such a chip is used for
detecting gas, for example, the sensitive sensor area alone already
has to be selected as quite large, for example, 1.times.1 mm, or
larger. The sensor chips themselves are then also significantly
larger, which is disadvantageous for the user.
[0006] It is disadvantageous that the signal voltage achieved per
unit of area is not sufficient for many applications; the large
area also has a high time constant (thermal inertia), and this thus
causes an excessively slow reaction time. The required signal
voltage therefore cannot be achieved with low reaction time by
homogeneous, unstructured membranes having many thermocouples.
[0007] A single thermopile sensor is proposed in WO 91 02229 A1, in
which a single free-floating membrane is arranged over a recess in
the chip body, which membrane is connected via the longest possible
beam to a heat sink, i.e., the edge of the chip body. Inclined
walls, which delimit the recess, arise due to the etching method
applied for the production of the recess in the chip body. In this
sensor, larger signals may be achieved on a smaller area because of
the better absorber region on the membrane. However, the thermal
conductivity of the "normal atmosphere" (i.e., air, nitrogen)
enclosing the absorber region prevents the sensor from achieving a
sufficiently high signal. Furthermore, the inclined walls, which
result in a very large and thus quite expensive overall chip with
respect to the sensitive area, are disadvantageous.
[0008] Furthermore, a thermopile infrared sensor in monolithic
silicon micromechanics is proposed in DE 10 2010 042 108 A1, which
can achieve a significantly higher signal voltage on a very small
area, by the sensor chip membrane being provided with slots and an
inner area receiving the IR radiation being suspended on the
absorber region on thin webs, via which a few thermocouples are led
from the silicon edge ("cold" contacts) to the absorber region
("warm" contacts). To enhance the insulation of the inner absorber
area, the sensor element is enclosed in a housing having a medium
of lower thermal conductivity, of significantly less than air.
[0009] In this manner, quite high signal levels may be achieved for
quite small membranes (absorber areas). If one increases the size
of the absorbing area to the 0.5.times.0.5 mm . . . 1.times.1 mm
area typically necessary at least for so-called NDIR gas sensors,
however, the absorber area, which then becomes more and more
sluggish, however results in a long time constant, i.e., the
response speed of the sensor chip sinks and the sensor would be
excessively slow for many applications.
[0010] Thermal sensor structures having thin membrane and slots for
etching out parts of the underlying carrier substrate are also
proposed in U.S. Pat. Nos. 4,472,239 A and 4,654,622 A. In both
cases, the underlying recesses only reach a small depth, which--as
in the above-described solutions--only permits low sensitivities in
the case of cost-effective housing solutions without high vacuum
leak-tightness.
[0011] Thermopile sensor cells are described in DE 199 54 091 A1
and U.S. Pat. No. 6,342,667 B, in which the recess below the sensor
structure is etched free through slot structures in the form of
large triangles in the peripheral region of the membrane or in the
form of a cross in the middle of the membrane. In both cases, this
is performed by a wet etching method, which does not permit large
distances to the heat sink on the periphery to arise due to
inclined walls. The plurality of thermocouples arranged in parallel
prevents large temperature differences between "hot" and "cold"
contacts and thus prevents higher signal sensitivities from being
achieved.
[0012] Cells of infrared radiation sensors are proposed in DE 198
43 984 A1. The recesses of the individual cells have vertical
walls, which go through the entire substrate, wherein the substrate
encloses the recess. A membrane is located above the recess.
However, a plurality of rather short thermocouples is also
provided, which do not permit a high sensitivity. The recesses are
produced by micromechanical solutions, for example, by etching
through an opening in the membrane, wherein the depth of the
etching can be 50-200 .mu.m. The short distance between the sensor
structure on the membrane and the heatsink of at most 200 .mu.m is
disadvantageous here, which has the result, because of the thermal
conductivity of the gas, that a high sensitivity is not
achieved.
[0013] Furthermore, a thermopile sensor cell having thin membrane
and slotted structure is proposed in DE 40 91 364 C1. The absorber
region on the membrane is held via a long beam and a few
thermocouples, wherein holes or slots are located in the membrane.
The beam having the thermocouples and a width of 130 .mu.m is
insulated from the substrate periphery and the absorber region by
slots, which are also wide, however. The carrier substrate located
under the sensor structure is wet-etched from the rear side, which
results in inclined walls in the substrate. The entire arrangement
is provided with a filling having a protective gas.
[0014] In principle, higher temperature differences and
sensitivities may be achieved using such a solution. However, the
wide slots prevent an optimum area utilization (degree of filling)
of the sensor cell. The wet-etched recess in the carrier substrate
has inclined walls going outward, wherein the entire sensor cell is
to be approximately 2.times.2 mm in size. The substrate walls
inclined outward do not permit small sensor cells or cell
intervals. The large structure of the suspended receiving area
results in slower response speed and a high time constant, and
therefore many measuring tasks which require rapid measurements are
not possible.
[0015] In summary, it may be stated that the thermal infrared
sensor cells proposed in the prior art either achieve excessively
low signal levels per unit of area because of a large-area chip
technology without sufficient thermal insulation of the absorber,
or, in the case of sufficiently large sensitive area of the
individual absorber region, have excessively high time constants
and therefore react excessively sluggishly and slowly in a
measuring task.
SUMMARY
[0016] The object of the invention is to specify a thermopile
infrared sensor in monolithic silicon micromechanical technology
for contactless temperature measurements or NDIR gas detection,
which outputs a high signal having high response speed with
sufficiently large receiver area and can be operated under a gas
medium at normal pressure or at reduced pressure and can be
produced without complex technologies for the housing closure in
mass piece counts.
[0017] This is achieved in a thermopile infrared individual sensor
of the type mentioned at the outset in that, in each case, multiple
individual adjacent sensor cells respectively having one
infrared-sensitive region are combined with thermopile structures
on the membrane on a common carrier body of an individual chip to
form an individual thermopile sensor structure having a signal
output in the housing, consisting of a cap sealed with a base
plate, having a common gas medium.
[0018] In a first embodiment of the invention, the signals of
individual sensor cells of each sensor chip are combined to form
one output signal by series circuit, parallel circuit, or in a
combination of series and parallel circuit and led out via a
terminal.
[0019] The cavity under each membrane having the infrared-sensitive
regions preferably has vertical or nearly vertical walls, which are
driven in from the wafer rear side.
[0020] Alternatively, the cavity under each membrane having the
infrared-sensitive regions can have inclined walls, which are
etched out from the front side through the slots in the
membrane.
[0021] The common gas medium is preferably a gas having a
significantly higher molar mass than air, such as xenon, krypton,
or argon under normal atmospheric pressure.
[0022] The gas medium is preferably a gas or gas mixture having a
pressure which is significantly lower than normal atmospheric
pressure.
[0023] In a further embodiment of the invention, the signal of each
of the individual sensor cells of a sensor chip is conducted via an
individual preprocessing channel having an individual preamplifier,
impedance converter, or analog-to-digital converter, wherein some
or all of the individual preprocessing channels of the individual
sensor cells have at least one integrating function or a low-pass
function.
[0024] Furthermore, the preprocessed signals of the individual
sensor cells of a sensor chip are advantageously combined in an
electronic summing circuit, such as a multiplexer and/or
microcontroller, to form an output signal.
[0025] In a refinement of the invention, the signal processing
channels of the individual sensor cells and a summing unit are
housed on the same semiconductor carrier body or on an adjacent
semiconductor chip inside the sensor housing.
[0026] Alternatively, in addition to the signal preprocessing
channels and the summing unit, further electronic signal processing
units, such as temperature or voltage references or for computing
temperatures or gas concentrations are housed on the same
semiconductor carrier body, or on an adjacent semiconductor chip
inside the sensor housing in the common gas medium.
[0027] Furthermore, the thermopile structures consist of
n-conductive and p-conductive polysilicon applied in a CMOS
process, amorphous silicon, germanium, or a mixed form of silicon
and germanium, or of applied thermoelectric thin metal layers made
of bismuth or antimony, to ensure cost-effective manufacturing.
[0028] The invention is particularly advantageously suitable for
use of at least two thermopile infrared individual sensors, each
forming one sensor channel, adjacent to one another under a common
cap on a common bottom plate as a gas detector, wherein a separate
optical filter of different wavelength is provided for each sensor
channel and wherein a partition wall is arranged in each case
between adjacent sensor channels.
[0029] To improve the long-term stability and drift resistance, one
of the sensor channels is equipped with a reference filter.
[0030] The thermopile infrared individual sensors forming sensor
channels are advantageously suitable for employment for NDIR gas
detection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The invention will be described in greater detail hereafter
on the basis of exemplary embodiments:
[0032] FIG. 1A shows the basic structure of a thermopile individual
sensor according to the invention having multiply structured
individual chip in a housing having vertical walls.
[0033] FIG. 1B shows the basic structure of a thermopile individual
sensor according to the invention having multiply structured
individual chip in a housing having inclined walls.
[0034] FIG. 2 shows a top view of an individual chip according to
the invention of the thermopile sensor having an arrangement of the
thermopile sensor chip having four-fold structured sensor cell.
[0035] FIG. 3 shows a top view of an individual chip according to
the invention having nine-fold structured sensor cell, each in
series circuit.
[0036] FIG. 4 shows an embodiment of the thermopile sensor
according to the invention having summation of the signals of the
individual structures via preamplifiers or impedance converters and
electronic summing elements.
[0037] FIG. 5 shows a further thermopile sensor structure according
to the invention having a multichannel sensor, for example, for
detecting gas.
[0038] FIG. 6 shows an enlarged illustration of detail A from FIG.
2.
DETAILED DESCRIPTION
[0039] The schematic structure of a thermopile infrared individual
sensor according to the invention on an individual chip is shown in
FIGS. 1A, 1B. The thermopile individual sensor is constructed on a
common frame-shaped semiconductor carrier body 1, for example made
of silicon, and is located in a sensor housing, consisting of a
bottom plate 2, and also a base plate 3 having electrical terminals
4, which are each connected via a wire bridge 5 having terminal
pads 6 to the frame-shaped semiconductor carrier body 1 (FIGS. 2
and 3), and also a cap 7 having an aperture opening 8 and an
optical unit 9, wherein the sensor housing encloses a gas medium 10
in a leak-tight manner.
[0040] The carrier body 1 is provided with a cavity 11, which is
spanned by a membrane 12 having a sensitive region (absorber
region) and is connected via beams 13 to the frame-shaped
semiconductor carrier body 1, which is used as a heat sink.
[0041] The gas medium 10 is a gas or gas mixture, which has a
thermal conductivity which is lower than that of air or nitrogen,
in order to keep convection from the central sensitive region on
the membrane 12 to the carrier body 1 as low as possible. The gas
medium 10 is preferably a gas having a high molar mass, such as
xenon, krypton, or argon, or a gas having an internal pressure
significantly reduced in relation to normal air pressure. The
sensor housing has to be sealed in this case such that no gas
exchange can occur with the surroundings.
[0042] The sensor chip, consisting of the carrier body 1 of an
individual chip, contains multiple individual cells 18 having a
slotted membrane 12 and a beam structure 13, on which thermocouples
13', such as thermopile structures, are housed, the "hot" contact
14 of which is located on the membrane 12 and the "cold" contact 15
is located on the carrier body 1. Furthermore, a thin absorber
layer 16 (preferably thinner than 1 .mu.m) is located on the
membrane 12, to cause the thermal mass of the sensitive region to
be low and the response speed to be high. Slots 17 are located
between the membrane 12 and the beams 13, and between these and the
carrier body 1, for thermal separation (FIGS. 2, 3, 6).
[0043] The thermocouples of the thermopile structure are produced
from thermoelectric materials known per se of different
thermoelectric polarity. These can be both semiconductor materials
applied in a CMOS process, for example, n-conductive and
p-conductive polysilicon, (doped) amorphous silicon, germanium, or
a mixed form of silicon and germanium, or applied thermoelectric
thin metal layers (for example, bismuth, antimony, inter alia),
wherein the thickness is less than 1 .mu.m in each case.
[0044] The membranes 12 having the beams 13 and the sensitive
region are spanned on the carrier body 1 above the cavities 11.
These cavities 11 can be introduced, for example, by dry etching
(deep RIE) from the wafer rear side and preferably then have
vertical walls (FIG. 1A), or can be driven in through the membrane
12 by etching of sacrificial layers or of the semiconductor
substrate itself from the front side through slots 17 (FIGS. 2 and
3) in the semiconductor substrate to form the carrier body 1. The
inclined walls of the cavity 11 in FIG. 1B are one example of the
latter.
[0045] The advantageous effect according to the invention arises in
that multiple smaller cells 18 (for example, 2, 4, 9, or 16 cells)
having slotted membranes 12 are located closely adjacent on the
area of a thermopile individual sensor, which cells form a
receiving area just as large as known individual element thermopile
chips by interconnection, wherein the gas medium 10 enables high
individual signal levels per cell 18.
[0046] As a result of the relatively small dimensions of the
individual cells 18 and the sensitive regions thereof on the
respective membranes 12, significantly lower time constants and
higher response speeds result than in a non-segmented thermopile
chip of typical size. The summation of the signals of all cells 18
of a thermopile chip in turn results in a significantly higher
signal voltage at equal size of the thermopile chip.
[0047] FIGS. 2 and 3 show the thermopile individual sensor
according to the invention having multiple cells 18 as a top view,
in order to illustrate the arrangement and interconnection of the
individual cells 18 of the thermopile individual sensor. In this
case, each cell 18 acts like an individual thermopile known per se,
except the geometrical area of the individual cells 18 is typically
significantly smaller than in the conventional thermopile
individual sensor.
[0048] Each cell 18 of the thermopile individual sensor has a + and
a - terminal (bond pads 5). All cells 18 formed as a thermopile are
interconnected with one another to form an effective thermopile
individual sensor. Preferably, all cells 18 of a thermopile
individual sensor are connected in series in this case, by
connecting together the respective+ and - terminals like individual
batteries in a battery block. However, a parallel circuit or a
combination of series and parallel circuit is also possible.
[0049] FIG. 2 shows a four-fold cell structuring and FIG. 3 shows a
nine-fold cell structuring.
[0050] A further embodiment of the invention consists of the use of
preamplifiers or impedance converters 19 and/or electronic summing
elements 20 or multiplexers/microcontrollers, instead of the simple
series circuit of the cells 18 (FIG. 4).
[0051] Such a signal electronics unit having preamplifiers or
preamplifiers and low-pass filter 19 and a summing element 20 or a
multiplexer can be housed both on the same substrate as the
thermopile individual sensor, or on a separate chip but in the
housing, or outside the housing. The summation can also take place
in a microprocessor, which processes the pre-amplified, filtered,
and multiplexed signals of the individual cells 18.
[0052] Since the function of the noise-limited low-pass filter or
the downstream microprocessor is sufficiently comprehensible, a
separate illustration was omitted in FIG. 4.
[0053] The summation element 20 preferably consists of a signal
multiplexer for all cells 18 and the downstream A/D converter
having microprocessor, which adds the signals of all cells 18 in a
low-noise manner. The structure of at least a part of the signal
processing is expediently housed in the housing, because then
electrical or electromagnetic interfering influences from the
outside can be suppressed better.
[0054] A further advantage of the integrated preamplifier 19 or
impedance converter per cell 18 consists of the following:
[0055] If more or thinner thermocouples of a cell 18 are connected
in series, the signal thus increases, but the impedance
(thermocouple, resistor) also does. If many (for example, 4, 9, 16,
or also more) cells 18 are connected in series and the signal is
led to the outside without preamplifier or impedance converter,
very high impedances (internal resistances) of the overall
thermopile individual sensor thus result. With increasing
impedance, the risk of noise interference of external interference
sources or an additional noise source indicated by the current
noise of the input circuit of the downstream electronics increases,
which is negligible, inter alia, in the case of lower impedance.
Both effects can reduce the measurement accuracy.
[0056] In particular for NDIR gas detection (NDIR: non-dispersive
infrared technology), it is advantageous to integrate two or more
sensor channels made of one thermopile individual sensor each into
one housing, i.e., two or four thermopile infrared individual
sensors according to the invention are arranged adjacent to one
another in one housing.
[0057] Multiple gases can thus be measured simultaneously. One of
the sensor channels is optionally equipped with a reference filter,
which significantly improves the long-term stability and drift
resistance. The other channel or channels then measure one or more
specific gases.
[0058] As an example of such a multichannel thermopile sensor, FIG.
5 shows a dual thermopile sensor, which is particularly suitable
for NDIR gas detection.
[0059] According to the invention, multiple cells 18 are again
combined to form one thermopile individual sensor (per channel) and
two such thermopile individual sensors 21, 22 are arranged adjacent
to one another under a common cap 26 on a common bottom plate 27,
wherein a separate optical filter 23, 24 is provided for each
channel. In addition, an optical partition wall 25 between adjacent
channels is recommended, which prevents optical crosstalk of the
infrared radiation between adjacent channels. For this purpose, the
partition wall 25 has to absorb the infrared radiation and cannot
transmit it or reflect it.
[0060] In this case, a common ground pin (negative terminal) on the
bottom plate 27 can be associated with each cell 18 and the
positive terminals are each led out via an individual terminal.
Alternatively, multiple channels can be led via a preamplifier and
low-pass filter to a multiplexer and read out in succession via one
output line.
[0061] The combined thermopile individual cells can all also be
located on the same chip, which simplifies the signal processing,
or can be housed on separate individual chips, as shown in FIG. 5.
Depending on the size, 2 to 4, but also 10 or more individual
channels can also be located in one housing. The partition walls 18
can be mounted both on the bottom plate 27, or in the cap 26.
[0062] In addition to the signal processing channels and the
electronic summing unit, further electronic signal processing units
(for example, having temperature or voltage references or a
calculation circuit for computing object temperatures or gas
concentrations) can be housed on the same semiconductor carrier
body 1 inside the sensor housing.
LIST OF REFERENCE NUMERALS
[0063] 1 carrier body [0064] 2 bottom plate [0065] 3 base plate
[0066] 4 terminal [0067] 5 wire bridge [0068] 6 terminal pad [0069]
7 cap [0070] 8 aperture opening [0071] 9 optical unit [0072] 10 gas
medium [0073] 11 cavity [0074] 12 membrane [0075] 13 beam [0076]
13' thermocouples [0077] 14 hot contact [0078] 15 cold contact
[0079] 16 absorber layer [0080] 17 slot [0081] 18 cell [0082] 19
preamplifier or preamplifier and low-pass filter [0083] 20
summation element [0084] 21 thermopile individual sensor [0085] 22
thermopile individual sensor [0086] 23 optical filter [0087] 24
optical filter [0088] 25 partition wall [0089] 26 cap [0090] 27
bottom plate
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