Thermopile infrared individual sensor for measuring temperature or detecting gas

Abstract

The invention relates to a thermopile infrared individual sensor in a housing that is filled with a gaseous medium having optics and one or more sensor chips with individual sensor cells with infrared sensor structures with reticulated membranes, the infrared-sensitive regions of which are spanned by, in each case, at least one beam over a cavity in a carrier body with good thermal conduction. The object of the invention consists of specifying a thermopile infrared sensor using monolithic Si-micromechanics technology for contactless temperature measurements, which, in the case of a sufficiently large receiver surface, outputs a high signal with a high response speed and which can operated in a gaseous medium with normal pressure or reduced pressure and which is producible in mass produced numbers without complicated technology for sealing the housing. This is achieved by virtue of, in each case, combining a plurality of individual adjacent sensor cells (18) with respectively one infrared-sensitive region with thermopile structures (14, 15) on the membrane (12) on a common carrier body (1) of an individual chip to a single thermopile sensor structure with a signal output in the housing, consisting of a cap (12) sealed with a base plate (3) with a common gaseous medium (10).

Claims

1. A thermopile infrared individual sensor 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, infrared-sensitive regions of which are each spanned by at least one beam over a cavity in a carrier body with good thermal conduction, wherein in each case, multiple individual adjacent sensor cells (18) respectively having one infrared-sensitive region are combined with thermopile structures (14, 15) on the membrane (12) on a common carrier body (1) of an individual chip to form an individual thermopile sensor structure having a signal output in the housing, consisting of a cap (12) sealed with a base plate (3), having a common gas medium (10).

2. The thermopile infrared individual sensor as claimed in claim 1, wherein signals of individual sensor cells (18) of each individual 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 (4).

3. The thermopile infrared individual sensor as claimed in claim 1, wherein the cavity (11) under each membrane (12) having the infrared-sensitive regions has vertical or nearly vertical walls, which are driven in from a wafer rear side.

4. The thermopile infrared individual sensor as claimed in claim 1, wherein the cavity (11) under each membrane (12) having the infrared-sensitive region has inclined walls, which are etched out from a front side through slots in the membrane.

5. The thermopile infrared individual sensor as claimed in claim 1, wherein the common gas medium (10) is a gas having significantly higher molar mass than air, such as xenon, krypton, or argon under normal atmospheric pressure.

6. The thermopile infrared individual sensor as claimed in claim 5, wherein the common gas medium (10) is a gas or gas mixture having a pressure which is significantly lower than normal atmospheric pressure.

7. The thermopile infrared individual sensor as claimed in claim 1, wherein a signal of each of the individual sensor cells (18) of a sensor chip is conducted via an individual preprocessing channel (19) having an individual preamplifier, impedance converter, or analog-to-digital converter.

8. The thermopile infrared individual sensor as claimed in claim 7, wherein some or all of the individual preprocessing channels (19) of the individual sensor cells have at least one integrating function or a low-pass function.

9. The thermopile infrared individual sensor as claimed in claim 7, wherein the preprocessed signals of the individual sensor cells of a sensor chip are combined in an electronic summing circuit (20), such as a multiplexer and/or microcontroller, to form an output signal.

10. The thermopile infrared individual sensor as claimed in claim 1, wherein signal processing channels (19) of the individual cells (18) and a summing unit (20) are housed on the same semiconductor carrier body (1) or on an adjacent semiconductor chip inside the sensor housing having common gas medium (10).

11. The thermopile infrared individual sensor as claimed in claim 10, wherein, in addition to the signal preprocessing channels (19) and the summing unit (20), 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 (1), or on an adjacent semiconductor chip inside the sensor housing having common gas medium.

12. The thermopile infrared individual sensor as claimed in claim 1, wherein the thermopile structures (14, 15) 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 thermoelectric thin metal layers made of bismuth or antimony.

13. A method, comprising: Providing at least two thermopile infrared individual sensors, each forming a sensor channel, as claimed in claim 1 adjacent to one another under a common cap (26) on a common bottom plate (27) as a gas detector, wherein a separate optical filter (23, 24) of different wavelength is provided for each channel and wherein a partition wall (25) is arranged in each case between adjacent sensor channels.

14. The method as claimed in claim 13, wherein one of the sensor channels is equipped with a reference filter.

15. The method as claimed in claim 13, wherein the thermopile infrared individual sensors forming sensor channels perform NDIR gas detection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be described in greater detail hereafter on the basis of exemplary embodiments:

[0032] FIG. 1 shows the basic structure of a thermopile individual sensor according to the invention having multiply structured individual chip in a housing a) having vertical walls, b) having inclined walls.

[0033] 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.

[0034] FIG. 3 shows a top view of an individual chip according to the invention having nine-fold structured sensor cell, each in series circuit.

[0035] 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.

[0036] FIG. 5 shows a further thermopile sensor structure according to the invention having a multichannel sensor, for example, for detecting gas.

[0037] FIG. 6 shows an enlarged illustration of detail A from FIG. 2.

DETAILED DESCRIPTION

[0038] The schematic structure of a thermopile infrared individual sensor according to the invention on an individual chip is shown in FIGS. 1a, b. 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.

[0039] 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.

[0040] 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.

[0041] 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 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).

[0042] 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 m in each case.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] FIG. 2 shows a four-fold cell structuring and FIG. 3 shows a nine-fold cell structuring.

[0049] 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).

[0050] 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.

[0051] 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.

[0052] 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.

[0053] A further advantage of the integrated preamplifier 19 or impedance converter per cell 18 consists of the following:

[0054] 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.

[0055] 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.

[0056] 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.

[0057] As an example of such a multichannel thermopile sensor, FIG. 5 shows a dual thermopile sensor, which is particularly suitable for NDIR gas detection.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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

[0062] 1 carrier body [0063] 2 bottom plate [0064] 3 base plate [0065] 4 terminal [0066] 5 wire bridge [0067] 6 terminal pad [0068] 7 cap [0069] 8 aperture opening [0070] 9 optical unit [0071] 10 gas medium [0072] 11 cavity [0073] 12 membrane [0074] 13 beam [0075] 13 thermocouples [0076] 14 hot contact [0077] 15 cold contact [0078] 16 absorber layer [0079] 17 slot [0080] 18 cell [0081] 19 preamplifier or preamplifier and low-pass filter [0082] 20 summation element [0083] 21 thermopile individual sensor [0084] 22 thermopile individual sensor [0085] 23 optical filter [0086] 24 optical filter [0087] 25 partition wall [0088] 26 cap [0089] 27 bottom plate