EP1904837A1

EP1904837A1 - Method for the simultaneous detection of a plurality of different types of atmospheric pollution using gas-sensitive field effect transistors

Info

Publication number: EP1904837A1
Application number: EP06777780A
Authority: EP
Inventors: Peter Biber; Maximilian Fleischer; Stephan Heinrich; Uwe Lampe; Roland Pohle; Elfriede Simon
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-07-15
Filing date: 2006-07-14
Publication date: 2008-04-02
Also published as: WO2007009948A1; DE102005033226A1

Abstract

The invention relates to a gas sensor arrangement for the detection of atmospheric pollution, especially in the air supply of a passenger cabin, said arrangement consisting of at least one silicon chip known in microstructure technology and comprising a plurality of gas-sensitive field effect transistors which read out the gas reactions on sensitive layers in the presence of a target gas, in order to detect at least one target gas respectively characterising a certain type of atmospheric pollution. The inventive gas sensors are economical and robust.

Description

description

METHOD FOR THE SIMULTANEOUS DETECTION OF MULTIPLE DIFFERENT

AIR LOADS WITH GAS-SENSIVE FIELD EFFECT TRANSISTORS

The invention relates to a method for detecting different air loads, which are usually defined by gases or gas groups, in particular for the assessment of a passenger cabin of a motor vehicle air supplied.

Modern air conditioning systems in motor vehicles have features with which the air quality in the passenger cabin can be maintained on average better than the ambient air quality. For this purpose, the quality of the fresh air sucked in for the ventilation of the passenger cabin is determined with a gas sensor. When it temporarily gets worse, measures are taken to prevent this bad air from loading the passenger cabin. In this regard, a ventilation, possibly temporarily with circulating air, a throttling of the air supply to the required minimum or the cleaning of fresh air sucked temporarily by a filter conceivable before it is fed into the passenger cabin.

Previous sensors mainly determine the air quality by detecting the emission of preceding vehicles. In this air pollution, at least one predetermined guide gas can be detected. The exhaust gases of gasoline engines are detected, for example, by the detection of the conductive gas carbon monoxide (CO) and in individual cases by the detection of hydrocarbons (HC) in the volume concentration range of 1 to 200 ppm. The exhaust gases of diesel engines are detected by the detection of nitrogen oxide (NOx), which actually nitrogen dioxide (NO2) is measured, especially in the range of about 0.05-10 ppm by volume. Due to the continuously decreasing emissions of motor vehicles, however, the current burden on the corresponding air quality due to the emission of vehicles in front is also decreasing. At the same time, the pollution of the air quality by odor sources such as manure, Tar work, petrochemicals, sewage treatment plants etc. with accompanying strongly subjective odor impression more and more important. Furthermore, atmospheric ground level ozone (O3) and

Smog, also subjectively very strongly perceptible, require a precise sensory detection of air quality.

A solution for the detection of the air quality by the above mentioned odor sources or by ozone / smog is not known at the moment. In motor vehicle traffic, the exhaust components of other motor vehicles are mainly used as a measure for assessing the air quality. For cost reasons, as well as due to the required durability in long-term operation in motor vehicle environmental conditions only solid-state gas sensors are used.

From EP 0448681 Bl, for example, shows a gas detection, based on the combination of a heated to several 100 ⁰ C ceramic tin oxide conductivity sensor for

CO detection with a operated at temperatures around 100 ⁰ C phthalocyanine conductivity sensor for Nθ2 ~ detection is performed. This combination is limited only to the detection of carbon monoxide and nitrogen oxides and requires efficient heating, which in turn increases costs.

Another variant for the detection of air pollutants is to use a single heated ceramic tin oxide conductivity sensor either on ceramic or micromechanically produced substrates. At this point, the problem arises that such sensors should react to two or more target gases, with the reactions, ie the signal curves, pointing in opposite directions. Thus, a signal generated at the sensor can not be clearly evaluated. It may be related to a reaction to one of the target gases or to a lessening of the reaction to the other target gas. This problem was solved by an intelligent, time transient signal evaluation. It is assumed that the response is faster as the decline of a sensor reaction; see international patent application WO 95/29435.

Another system that can treat air quality in automotive systems consists of two heated oxide ceramic conductivity sensors. The one conductivity sensor should react as selectively as possible to the one target gas, whereas the other one should react as selectively as possible to other target gases.

However, sensors used to date are, despite good sensitivity to the exhaust gases of other vehicles, in particular to the above-mentioned air polluting substances only weakly sensitive and record essentially only the burden of air quality by other vehicles. This weak reaction also occurs only as a superposition of the previous sensor signals and is therefore only weakly evaluated. The additional, separate third and fourth sensor is uneconomical overall for cost and space reasons.

Furthermore, sensors which operate on the basis of semiconducting metal oxides require special control electronics which, on the one hand, consist of a heating control and, on the other hand, of readout electronics for the sensor signal. These sensors are also associated with significant operating costs.

The invention has for its object to provide an improved sensor for assessing the quality of fresh air sucked in the operation of motor vehicles.

The solution to this problem is achieved by the combination of features of claim 1 and claim 19.

Advantageous embodiments are given in the dependent claims.

The invention is based on the finding that an improvement of the conditions in the gas detection by the set of silicon microstructure technology in the manufacture of a gas sensor arrangement can be achieved. This gas sensor arrangement of a plurality of sensors is in contact with the outside air and can be accommodated in an advantageous manner in a corrosion-resistant housing, which is particularly suitable for automobiles. For gas measurement, this housing must have a gas-permeable membrane, so that a measuring gas can reach the gas-sensitive field-effect transistors. The comprehensive integration and miniaturization allows a variety of simultaneous detection capabilities, so that, for example, an air supply control for a passenger cabin, the u. U. additionally to be coupled with an air conditioner, is easy to control.

To stabilize the individual gas-sensitive transistors, in particular for the reproducible measurement of gases, the gas sensors are kept at a constant, identical or different temperature with an electric heater.

It has proved to be particularly advantageous to use the type of field effect transistors for gas detection, which are designed as so-called suspended gate field effect transistors (SGFETs), capacitively-coupled field effect transistors (CCFETs) or gateing gate field effect transistors (FGFETs) , These are characterized by an air gap between the gas-sensitive layer and the signal-receiving Si transducer. However, it is also possible to use FET gas sensors which have a porous gas-sensitive layer, which is located directly on the signal-receiving Si transducer.

As a result of the greater number of gas-sensitive field-effect transistors present in an arrangement, it is possible to detect a plurality of specific target gases. Furthermore, cross sensitivities can additionally be detected. It should be noted that different target gases can also influence each other, which in the electronic Control device of the gas sensor arrangement can be considered.

Selected air pollutants are identified by appropriate target gases. An occurrence of certain different target gases can trigger variable effects on the air supply to the passenger cabin.

In the following, exemplary embodiments will be described with reference to schematic figures which do not limit the invention. The figures show in detail:

FIG. 1 shows a sectional view of a gas sensor arrangement with different gas-sensitive elements

Layers,

FIG. 2 shows a gas sensor arrangement according to FIG. 1 in a spatial representation, wherein only the common gate electrode with three different sensitive layers is shown,

FIG. 3 shows the basic structure of field-effect transistors combined with gas-sensitive layers.

FIG. 4 shows an embodiment of a gas sensor as

Suspended-gate field-effect transistor,

FIG. 5 shows an embodiment of a gas-sensitive field effect transistor as a floating gate field effect transistor,

FIGS. 6, 7, 8 and 9 respectively show recorded gas loads as gas sensor signals as a function of time, partially indicating the influence of varying air humidity, FIG. 6 mainly shows a sensor signal in the detection of NO 2 with phthalocyanine as sensitive

Material,

FIG. 7 shows a result diagram for the carbon monoxide detection with a sensitive layer of Pd / SnO ₂ ,

FIG. 8 shows a result diagram for ammonia detection with a gas-sensitive layer of TiN.

FIG. 9 shows a result diagram in the case of ozone detection with a gas-sensitive layer of KI.

The miniaturization using silicon microstructure technology results in a gas sensor arrangement which, when in contact with the supply air to a passenger compartment, can determine target gases by means of a manifold gas measurement, each of which is representative of certain environmental impacts. The field effect transistors used are preferably field-effect transistors with lifted gate electrode or field-effect transistors with additional floating or sliding potential, or field-effect transistors to which a porous gas-sensitive layer is applied without an air gap. In order to achieve particular advantages, electronics integrated in the silicon-based sensor perform parts of the control of the sensors. These include in particular the control of the sensor heater with a corresponding

Control, the reading and amplification of the sensor signal and the signal processing of the sensor signal with respect to, for example, a linearization, drift compensation, elimination of cross-sensitivities u.ÄÄ.

In addition to the general advantages, the following possibilities arise in connection with the use of a gas sensor arrangement in the air intake for a passenger cabin: The use of various gas-sensitive field-effect transistors in the sensor arrangement enables the simultaneous detection of different gases. For certain groups of air pollutants or air pollutions occurring in motor traffic and in the environment, a characteristic guide or target gas is usually assigned in each case, whereby the presence of the corresponding air pollution can be detected by detection of this one gas. Vehicle exhaust gases are detected, for example, in connection with the target gas NOx or NC> 2. For the exhaust gases of gasoline engines applies that this group of exhaust gases by the target gas carbon monoxide or hydrogen is detectable, whereby the sum of hydrocarbons (HC) is used. For example, odors such as liquid manure can be produced via organic conductive gases or via ammonia

(NH3) are detected. The so-called smog load can be detected via the guide gas or target gas ozone (03). Tar odors as well as petrochemical or foul odors can also be detected. In the vicinity of sewage treatment plants these are in particular the main gas hydrogen sulfide (H2S) or

Thiols.

Through the use of a gas detection array, in addition to the load on the air by other vehicles, further loads on the environment, in particular the ambient air, can be detected. These burdens can be recorded separately and thus appropriate measures can be taken to the respective situation. Thus, for example, could be mainly by other vehicles through the ventilation of a motor vehicle interior loads in the intervening phases, where it is accurately detected when there is no waste gas plume.

In the case of an air pollution by ozone, for example, a continuous low ventilation can be set, which reduces the load in the interior due to the natural ozone depletion or suitable ozone-decomposing filters be applied. The same applies to odors and odor filters.

The invention is associated with general advantages, which is essentially to mention that the components are small and inexpensive to produce. Thus, gas-sensitive field-effect transistors with different gas-sensitive properties can be realized by selecting the sensitive layer. This makes it possible in an integrated form according to the arrangement according to the invention that a large number of gases of interest can be realized. An integration of the evaluation electronics or a part of this electronics in the gas sensor is possible without difficulty and can save costs of the overall system. Due to the small size of the sensor arrangements can be realized with a variety of different individual sensors of different sensitivity without problems and integrated on a common sensor chip. As a result, cross sensitivities are eliminated, measurement accuracy is improved, and / or the measurement range is increased to improve overall sensor reliability. The basic structure of gas sensitive field effect transistors is shown in FIG. A gas-sensitive layer is applied to a conductive gate element, wherein the adsorption of the gas to be detected generates an electrical potential at the sensitive layer, which acts via an air gap directly on the region of a field-effect transistor for signal readout.

FIG. 4 shows an embodiment of a single gas sensor designed as SGFET. Shown are in particular the gate electrode on the air gap 2, 3, 4 side facing the sensitive layer 5,6,7 is applied. In the illustration of Figure 4 in addition a so-called guard ring (guard ring electrode) is provided to improve the signal evaluation. The gas-sensitive layer 5,6,7 on the other side of the air gap 2, 3, 4 opposite element is a field effect transistor, which consists of a so-called gate insulation, wherein in the silicon base body 11, three essential areas of the semiconductor device are provided, source, channel and drain. The field effect transistor is a signal readout element.

FIG. 5 shows an embodiment of a single gas sensor, shown as a so-called FGFET with different structure in relation to the gas sensor according to FIG. 4. In this case, the read-out transistor 8, 9, 10 is not arranged directly at or below the air gap. There is an electrode whose potential is not fixed, which connects the area of air gap and gas-sensitive layer with the region of the read-out signal. This is also known as a floating gate.

A sensor array is created by placing a plurality of individual gas sensitive field effect transistors on a chip. The base is usually a silicon chip. In this case, this silicon chip is in each case equipped with a separate gate, which is provided with the respective sensitive layer. A very advantageous variant provides that a common gate, or a common gate electrode is used, wherein depressions are provided for receiving the sensitive layers. These recesses introduced in the common gate electrode are filled up with the materials of the sensitive layers, as shown in FIG. These sensitive layers 5, 6, 7 are gas-sensitive in this case and generally have a uniform spacing from the top edge of the spacers 12, so that the air gap 2, 3, 4 to be represented assumes the same thickness for three regions shown in FIG. The common gate 1 is then mounted on a readout chip, in which the readout elements are mounted at a distance from the sensitive layer. The readout elements are, as described, the field effect transistors.

An improvement in the response time of the sensors can be achieved if in the gate one or more gas inlet holes are provided. These can be produced in the case of ceramic gate carriers, for example by means of mechanical processing or by means of laser material ablation.

In the case of silicon, erosion is carried out by micromechanical silicon machining. In principle, it should be noted that measuring gas must, of course, come into contact with the gas-sensitive layers.

An arrangement of gas sensors equipped with a plurality of gas-sensitive field effect transistors, in which each field effect transistor is assigned a corresponding gas-sensitive layer, is shown in FIG. The silicon chip 11 contains three read-out transistors 8, 9, 10, whereby signal transmission from the gas-sensitive layers 5, 6, 7 takes place via corresponding air gaps of generally equal size.

FIGS. 6 to 9 show diagrams with measurements on the basis of the sensor arrangements comprising the invention with the associated method with corresponding use. Directly above the respective abscissa in FIGS. 6 to 9, pulsed or staged target gas loads are shown. For FIG. 6, a NO 2 concentration is specified, for FIG. 7 a carbon monoxide / CO concentration, for FIG. 8 an ammonia / NH 3 concentration and for FIG. 9 a stepwise increasing ozone / O 3 concentration.

FIG. 6 shows that, in accordance with the pulse-type nitrogen oxide concentration, the sensor in each case indicates a sensor function linked directly to the appearance of the target gas. The evaluation according to FIG. 6 has been carried out on gas-sensitive layers of phthalocyanine for the detection of nitrogen oxide.

FIG. 7 shows the detection of carbon monoxide, wherein it is likewise recognizable that an increase of a target gas or a target gas concentration directly results in the rise of the sensor signal. Effect larger concentrations larger target gas amplitudes. In this case, Pd / SnO2 has been used as a gas sensitive layer.

FIG. 8 shows the curves in the detection of ammonia on sensitive TiN layers. Here, too, follows

Sensor signal directly to the occurrence of a concentration of target gas.

Figure 9 shows the detection of ozone using a gas-sensitive layer of potassium iodide (KI). Over time, a close correlation between the occurrence of a target gas and the corresponding sensor signal can be recognized.

At least the representations corresponding to 6 and 8 apply to gas sensors, which are heated to about 95 and 6O ⁰ C.

As gas-sensitive layers, therefore, metals, nitrides, organic layers, metal oxides or ionic salts are generally suitable. To be used in particular for the automotive application:

For the detection of nitrogen oxides porphyrin dyes or phthalocyanines or tin oxide layers with noble metal dispersion.

For the detection of carbon monoxide metal oxides with noble metal dispersion, preferably Pd.

For the detection of ammonia nitrides are used, preferably titanium nitride TiN. To detect ozone, sensitive layers of Au or KI are to be used.

The detection of hydrogen sulfide or thiols is achieved with sensitive layers such as silver layers.

If the intrinsic stability of the sensitive layers for the

Normal operation is not sufficient, the gas-sensitive material can be placed in a matrix of a stable, inert body for stabilization. Suitable materials are for example glass or polymer. Typical operating temperatures of the layers are between 40 and 100 ^° C., but preferably 85 ^° C.

The gas sensor assembly is protected by gas-permeable filter from environmental influences such as dust and spray. Here are open-pore polymer filter, preferably from hydrophobic, so water-repellent, polymers such as Teflon with a typical pore diameter between 1 and 10 microns. If interfering gases are to be suppressed, individual gas channels may still be provided with layers selectively filtering the interfering gases, e.g. be based on activated carbon. Strong changes in ambient humidity, which also cause spurious signals, can be detected with moisture stabilizing filters, e.g. on the basis of silicate gel.

Claims

claims

1. Gas sensor arrangement for the detection of air pollution, in particular for the detection of air pollution in the air supply for a passenger cabin consisting of at least one silicon chip shown in microstructure technology with a plurality of gas-sensitive field effect transistors, the gas reactions on sensitive layers at existing target gas read to detect one or more for each - Because a specific air pollution characteristic of target gases, which are each representative of an air pollution.

2. Gas sensor arrangement according to claim 1, which is installed in a protective housing with a gas-permeable membrane.

3. Gas sensor arrangement according to claim 1 or 2 with an electrically controlled heating.

4. Gas sensor arrangement according to one of claims 1 to 3, wherein the field effect transistors are formed as SGFET, CCFET or FGFET.

5. Gas sensor arrangement according to one of claims 1 to 4, wherein in a silicon chip, a control electronics is integrated.

6. Gas sensor arrangement according to one of claims 1 to 5, wherein a plurality of detection channels is used, so that in addition to the air pollution by preceding vehicles and the air pollution is detected by other sources.

7. Gas sensor assembly according to claim 6, wherein the air pollution by other sources includes the detection of one or more odors such as manure, road works, tar / asphalt odor, pet- rochemie, ozone pollution or SMOG.

8. Gas sensor arrangement according to one of claims 1 to 7, wherein a part of the sensors is sensitive to noise, the Represent cross sensitivities for the detection of selected target gases.

9. Gas sensor arrangement according to one of claims 1 to 8, wherein at least one gas-sensitive field effect transistor for Nθ2 ~ detection is present, which has a gas-sensitive layer of a porphyrin dye or phthalocyanine or SnC> 2 with noble metal dispersion.

10. Gas sensor arrangement according to one of claims 1 to 9, wherein at least one gas-sensitive field effect transistor for the detection of carbon monoxide is present, which has a gas-sensitive layer of a metal oxide with a noble metal dispersion, in particular Pd.

11. Gas sensor arrangement according to one of claims 1 to 10, wherein at least one gas-sensitive field effect transistor for the detection of ammonia is present, which has a gas-sensitive layer of a nitride, in particular TiN.

12. Gas sensor arrangement according to one of claims 1 to 11, wherein at least one gas-sensitive field effect transistor for ozone detection is present, which has a gas-sensitive layer of gold or potassium iodide (KI).

13. Gas sensor arrangement according to one of claims 1 to 12, wherein at least one gas-sensitive field effect transistor for the detection of hydrogen sulfide or of thiols is present, which has a gas-sensitive layer of silver.

14. Gas sensor according to one of the preceding claims, wherein the gas-permeable membrane consists of an open-cell hydrophobic polymer.

15. A gas sensor according to claim 14, wherein the polymer is Teflon.

16. Gas sensor according to one of claims 14 or 15, wherein the pore diameter is between 1 and 10 microns.

17. A gas sensor according to any one of the preceding claims, wherein a part of the gas-sensitive channels is protected by an activated carbon-based filter to eliminate unwanted cross-sensitivities of the gas channel.

18. Gas sensor according to one of the preceding claims, in which all or individual channels by a fluctuation of the

Humidity balancing filter is protected on the basis of silicate gel.

19. The use of a gas sensor device, which is constructed according to one of claims 1 to 18, for detecting air pollution in a passenger compartment, wherein representative of diesel exhaust gases, the target gas NOx or NC> 2, or representative of gasoline engine exhaust the target gas

Carbon monoxide or hydrogen or the amount of hydrocarbons is detected, or representative of liquid manure, the target gas ammonia is detected or as a representative of a smog load the target gas ozone (O3) is detected, or on behalf of tar smell aromatic hydrocarbons such as benzene, toluene, Xylene or, as a representative of petrochemical odors, unsaturated and aromatic hydrocarbons or, for the presence of a foul odor, either the conducting gas hydrogen sulfide or thiols is detected, or a combination thereof.

20. Use according to claim 19, wherein selected interfering gases are additionally detected to compensate for cross-sensitivities.