DE3519397A1 - Sensor for gas analysis and detection - Google Patents

Abstract

Semiconductor gas sensor operating according to the calorimeter principle and with a bridge connection (Figures 2, 3). In particular, a plurality of sensors of this type having mutually different characteristics are arranged in the manner of a matrix (Figures 4, 5) to detect one or more individual gases contained in a gas mixture. <IMAGE>

Description

Sensor for gas analysis or detection

The present invention relates to a sensor according to the preamble of claim 1.

From DE-OS 24 07 110 is a gas sensor with a detection used semiconductor element and known with a selective device. The semiconductor element is a field effect transistor with source, drain and one between source and drain extending until reaching the surface of the semiconductor body of the element Canal area. This channel area is located on the surface of this semiconductor body covering a layer of ß-carotene as a selective device. Known is this carotene is a substance that is sensitive to gases and its use leads to this Semiconductor field effect transistor to charge influence in the channel area, to different Conductivity of the field effect transistor and / or to changed threshold voltage.

For the detection of hydrogen, also in hydrogen-containing compounds may be present, are in Appl. Phys. Letters, Vol. 26 (1975), pp. 55-57 gas sensors described, which consist essentially of a MOS transistor, the gate electrode consists of palladium. Palladium is like e.g.

also rhodium a metal that has catalytic action for hydrogen and split off atomic hydrogen from molecular hydrogen compounds able. The atomic hydrogen diffuses through the palladium metal of the gate electrode through to the one between the electrode and Semiconductor surface located Oxide layer of the transistor. The hydrogen absorbed there causes it to develop a dipole layer, the presence of which increases the level of the threshold voltage of the transistor changed.

A gas sensor as described above cannot be used for hydrogen-free Use gases. For a corresponding gas detection, CO detection is preferred in "ESSDERC", Munich, Sept. 1979, in "Int. Vac. Conf.", Cannes, Sept. 1979

1980 and in IEEE Trans. ED 26 (1979), pp. 390-396, a MOS transistor described, whose gate electrode is preferably made of palladium, however, this palladium electrode has a plurality up to the metal oxide interface The use of an NMOS transistor is also used in this context in question. Such transistors with a perforated palladium gate have good sensitivity for carbon monoxide and greatly reduced "cross" sensitivity to hydrogen. In addition to the actual desired sensitivity, a cross-sensitivity is used here the added sensitivity of the sensor with respect to another gas. For known arrangements, the amount of change in the threshold voltage is dependent known from the gas concentration, with a largely linear dependence too is watching. Is considered to be disadvantageous that the response of such Gas sensor is a dynamic process with a certain time delay to the action of the gas in question, e.g. carbon monoxide.

In addition, it should be mentioned that a given cross-sensitivity is a respective sensor can be reduced by additional measures. For example can in the case of a CO sensor as described last, the cross-sensitivity with regard to Hydrogen through an applied special protective layer around be reduced by at least more than an order of magnitude.

It should also be mentioned that the quantitative sensitivity and also the delay time constant are temperature dependent.

Palladium was used in the gas sensors described above In addition, rhodium, platinum and nickel are also known to be hydrogen-permeable. silver has a pronounced selective permeability for oxygen.

It is also a gas sensor (made by Figaro) with sintered tin dioxide known for flammable gases and for some toxic gases, based on a change in resistance of tin dioxide made conductive.

Gas sensors are known under the name "Pellistor", which after the Principle of calorimetry work. A pellistor consists of two platinum resistance wires, on each of which a porous ceramic pill is sintered. On one of the two ceramic pills a catalyst is applied. In the case of catalytic combustion of the to be detected Gas results for the platinum resistance wire with the catalyst coated one Ceramic pill a measurable increase in resistance, namely compared to the second platinum resistance wire, for measuring these two platinum resistance wires in a bridge circuit are inserted.

Calorimetric effects in connection with catalysts are off known in the art. It is the combustion of hydrogen on one Platinum catalyst, the production of NO from NH3 with platinum or platinum-rhodium as Catalyst at 200 to 250O C and from NO2 from NO with a catalyst from Al203-SiO2 gel at 1000 C, in each case with the addition of appropriate oxygen. SO2 can be oxidized to SO3 with oxygen at an elevated temperature with the aid of a platinum catalyst, with the aid of a catalyst made of Fe 2 O 3 and with V205 as a catalyst.

CO can be with the help of palladium at temperatures around or higher than 1500 C oxidize to C02. Using a silver catalyst, at 200 Oxidize methanol to HCH0 up to 4000 C.

Further catalytic processes are from Gmelin's Handbook of Organic Chemistry ", from Winnacker-Küchler," Chemical Technology ", from Ullmans," Encyclopedia of technical chemistry "and from Reich," Thermodynamics ".

Further publications relating to semiconductor sensors are: IEEE Trans. On Biomed. Eng., Vol. BME 19, (1972), pp. 342-351, IEEE Trans. On Biomed. Eng., Vol.BME 19, (1972), p.70-71, Umschau, (1970), p. 651, Umschau, (1969), p. 348, German Patent 1,090,002, U.S. Patent 3,865,550.

In connection with a selective effect for gases, zeolites are known, which are also known as molecular sieves. Such molecular sieves have the property Molecules of certain sizes and smaller to let through and larger molecules at To prevent passage. Numerous examples of usable zeolites are known from: Grubner et al. "Molecular Sieves" VEB Dt. Verl. D. Wissensch., Berlin (1968).

The object of the present invention is to provide one suitable for gas analysis Specify sensor that is relatively simple and in particular despite its high performance has a structure that is technologically easy to manufacture. In particular, the sensor should be such be trained so that he is able to use a predeterminable single gas among others current gases, in particular simultaneously and selectively several individual gases in one To detect gas components contained in the gas mixture or an unknown individual Identify gas in addition to other gases, if appropriate.

This task is achieved with a sensor with the features of claim 1 solved and from the subclaims go further refinements and developments of the invention.

In order to have a simple and technologically easy to implement structure achieve, the invention is based on semiconductor technology and technology, whereby the advantage of the integrated circuit is also made usable here, namely that the respective structure of the two detector elements of an individual detector or the several such individual detectors (with their two structures each) and the inevitably required electronic (amplifier) circuit as an integrated Circuit are constructed on a common substrate, preferably made of silicon.

It can be assumed that at least one is simply conceived Arrangement is not to be realized with a single detector responds to a certain gas.

The training is based on the idea that detectors, which are each sensitive to a plurality of individual gases, but for a respective one of the gases has quantitatively different sensitivity Gas sensor can be built with which you can even detect different gas components simultaneously a gas mixture can perform. According to one feature, this is a system of pattern recognition in the case of a gas sensor comprising several individual detectors applied, which provides the differentiated recognition of the various components.

A sensor according to the invention or a sensor according to the development has one or a plurality of individual detectors with selective means so that one another there are different properties or sensitivities with regard to the gases. Such selective devices are a respective catalyst layer and / or a respective zeolite and / or (heating or cooling) devices to maintain a predetermined other operating temperature of the two structures of the individual detector in question.

A selective device can also consist in that the dynamic Sequence of response (of one structure) of the individual detector concerned, the possibly an individual detector of a plurality of other other individual detectors is the one to be evaluated, a specific gas or

selective detector criterion corresponding to a specific gas component is.

In the present invention, the calorimeter effect becomes the single detectors used, the respective individual detector comprising an electrical bridge circuit, in order to eliminate external temperature influences and the like in a simple manner.

Due to the pattern recognition principle already mentioned above, this is sufficient It is for a gas sensor according to the invention that it has a number of m individual detectors includes. With this one is able to simultaneously detect a number n gases, where n can easily be greater than m. It is there the Cross-sensitivity that would otherwise occur undesirably is positively exploited here. The information about the n individual gases is in the combination of the measurement signals the m single detectors included.

Further explanations of the invention can be found in the following description on exemplary embodiments and developments of the invention.

Figure 1 shows the electrical circuit diagram of a single detector.

Figures 2 and 3 show in section representations of examples of a individual gas detector according to the invention or a single detector of a detector array.

FIG. 4 shows a basic illustration of a detector array.

FIG. 5 shows that used for a further development of the invention Principle of pattern recognition based on a schematic representation.

Figure 1 shows the known circuit structure of a Detector D. With 11 its sensitive detector element and with 12 its insensitive Detector element referred to. With 13 and 14 there are more, usually for one of these Bridge circuit of Figure 1 denotes elements to be used, which are preferably used here are resistors implemented as semiconductor components. A change in electrical Properties of the sensitive detector element 11, namely when an or several gases G will keep the bridge circuit unchanged because of the corresponding Property of the detector element 12 detuned. This is between the connections 15 To obtain output signal of the individual detector D.

FIG. 2 shows a construction example with the two detector elements 11 and 12 of a detector D according to the invention are reproduced. The location of the cut 2 goes through the two detector elements 11 and 12. It is the section drawn through the substrate body 21, this substrate body 21 in the area of the respective detector elements 11, 12 have a recess, in particular in each case has a hole 111, 112 as shown in FIG. Respective proportions of a thin Layer 22 cover each of these in the substrate body to a substantial extent 21 located holes. Such a hole has, for example, a diameter of about 1 mm. The substrate body 21 is made of silicon, for example. Layer 22 has electrical and also thermally insulating property. It consists e.g. of silicon dioxide and / or nitride. The detector element 11 comprises a semiconductor structure 23 and the detector element 12 a semiconductor structure 24. One such structure is a semiconductor component with temperature-dependent properties and with at least two connections. One such structure has a diameter of e.g. 0.2 mm. With 25 and 26 are the respectively denotes an electrical connection of the structures 23 and 24, respectively. For the other electrical connection of the diode 23 can, for example, the catalytic layer 27 and its Terminal 125 can be used if it is made of metal or suitable electrically conductive material.

With 126 belonging to the connection 26 is the other connection of the diode 24 designated. This terminal 126 is one on the surface of the substrate body 21 and the layer 22 applied metal conductor track.

The layer 22 is load-bearing at least for the detector element 12 Element of the respective structure 24, 23. A structure that is only basically similar and its technological production can be found in DE-OS 32 40 180 and 33 33 410.

According to the example chosen, see the above specified combinations for a catalyst and an associated gas the catalytic layer 27 made of palladium, for example. Hydrogen H2 or gas a hydrogen-containing compound that reaches the catalytic layer 27, is burned there, giving off heat. This means that the structure 23 of the Detector element 11 is heated, in comparison to the structure 24, on which hydrogen does nothing. The sensitivity of the structure 23 comparatively the insensitive behavior of the structure 24 leads to a signal S on in the figure 2 connections 15, not shown, of the bridge circuit of FIG. 1.

Due to the thin-layer design in the area of the structure 23 this already speaks to a slight heat supply with such a temperature increase on, so that an easily measurable output signal S at already relatively low Concentration of the acting gas is achieved.

A suitable catalyst material for layer 27 is for CO detection Palladium at a temperature above 150 ° C. For the detection of ammonia vapors ruthenium is also suitable and further examples have already been mentioned above.

By supplying heat or cooling from the outside, a respective, Predeterminable operating temperature can be set, namely one at which a Detector of the type according to the invention is optimal for a gas or gas component in question Has measurement sensitivity. Especially in the event that one or more individual detectors a detector array should be kept at a different operating temperature, than is the case for more of the existing individual detectors, it recommends to integrate a respective heating or cooling element into the structure 23 and 24. It can do this be a heating resistor or a Peltier cooling element, which can be realized in semiconductor technology. At 29 there is a respective heating resistor which is integrated into both the structure 23 and the structure 24 is inserted. For the sake of clarity, are for the two heating resistors 29 power supply lines to be provided are omitted in the illustration of FIG. Both Heating resistors 29 are fed so that the same high operating temperature for both Structures 23 and 24 is set. But it can also be sufficient, just that Heat structure 23 of actually sensitive detector element 11. Instead of the use of additional heating resistors can also be used for heating accordingly large current flow through the respective structure (diode current).

The additional use from above is already of particular importance mentioned zeolites or molecular sieves in a sensor according to the invention. figure 3 shows an embodiment of a single detector D ′ with a layer 227 of FIG Zeolite on a catalytic layer 27. Further details of the embodiment of Figure 3, which have already been described for the embodiment according to Figure 2, have the meaning already described in FIG. 3.

Such a layer 227 made of a zeolite covers the catalytic Layer 27 at least in that area over which the structure 23 of the sensitive detector element 11a extends. Regarding the available offer of zeolites, reference is made to the abovementioned publication "Molecular Sieves".

FIG. 4 shows a basic structure of one of nine individual detectors D1 to D9 existing detector arrays are shown.

These detectors are integrated in or on a substrate body 21 Realized construction, preferably together with the evaluation of a pattern recognition matrix 55.

H1 to Hg are feed lines for heating 29.

The schematic representation of FIG. 5 shows the principle of a gas sensor with a detector array with the individual detectors D1, D2 to Dm. For the individual Have gases or for the gas components G1, G2, G3 ... Gi ... Gn of a gas mixture the individual detectors D1, D2 ... those in the matrix 54 in the respective associated Column of the matrix 54 indicated sensitivities. A pulse sign means high Sensitivity or main sensitivity, a St. Andrew's cross, on the other hand, means clear lower sensitivity and a minus sign stands for insensitivity of the concerned Individual detector compared to the relevant gas component G1, G2 .... The individual detectors the row 52 and the gas components form the column 53 of the matrix 54. It is on it pointed out that such a matrix, for example, only has two individual detectors D1 and D2 owns.

The bottom line contains the individual signal outputs of the individual detectors D1, D2 ..., which supply the respective signals S1, S2 to Sm. For example, the signal S1 is an integral signal for the sensitivities of the individual detector D1 the gas components G1, G2 to Gn. It also contains the information that the single detector D1 is insensitive to the gas components Gi and Gn. The same applies accordingly say the remaining signals S2 to Sm.

If, for example, the gas components G2 and Gn are not available, a distinction is made Then a signal S'1 to be obtained from the signal S1 is that the otherwise on the signal component based on the gas component G2, here even a main sensitivity of the individual detector compared to the gas component G2, in the signal S'1 is missing. The missing the gas component Gn evidently makes no contribution to the present difference from S'l opposite S1. For example, if there is no gas component G2 and Gn occurring signal S'm differs from the signal Sm in that the signal component the main sensitivity to the gas component Gn and the minor sensitivity compared to the gas component G2 are absent.

With 55 a pattern recognition matrix is referred to, which in the manner of a Logic works. As can be seen, the detector signals, i.e. in the in each individual case those actually occurring for a gas component mixture x Signals S1 to Sm supplied. This matrix 55 is able to obtain from the entirety of the supplied signals S1 to Sm, i.e. from the number m signals for the presence respectively.

Absence of individual gas components from one in the pattern recognition matrix programmed number n gas components to close. The number m even be smaller (by a speaking relative number) than the number n. It should be noted that the presence of a non-programmed gas (due to a non residual signal to be assigned) is at least to be determined.

In mathematical terms, the matrix 54 corresponds to the j = n system of equations Si = sum (a. G.) with i from 1 to m j = 1 1J for the signals S1 to Sm.

The aij with j different from i are the cross sensitivities mentioned above.

In the prior art, such detectors have been and are sought to develop that have the lowest possible cross-sensitivities, i.e. with those the matrix elements for i different from j as small as possible compared to the Matrix elements a. with i equal to j. This requires at least one of its own for each gas component Single detector, i.e. m must be equal to or greater than n.

With the invention, on the other hand, the cross-sensitivities are also included i used and evaluated differently from j to an extent that is essential to the invention. at of the invention, cross-sensitivities are just desired, which is what the previous level of development is even directed in the opposite direction. In the exploitation of cross-sensitivities is justified that in the invention, the number m of individual detectors easily can be smaller than the number n of gas components to be detected.

If the aij constant values of the respective sensitivity of the person concerned Single detector Si, including the value zero, results in a linear one System of equations that is solved with the aid of the pattern recognition matrix 55. Provided the a. . a function depending on the presence of the gas component Gj in addition to other gases G ...

is the pattern recognition matrix with the help of appropriate calibration 55 enabled to solve this system of equations as well.

For this purpose, the corresponding calibrations from the individual detectors are used existing detector arrays using each known, different Make gas mixtures. The same applies if the sensitivities aij a Function of the present concentration of the respective gas Gj for j = i and / or of the other gases present is Gj for j X i. The pattern recognition matrix 55 becomes then equipped in such a way that it can perform iterations with their help In this case, too, the clear assignment is possible, i.e. the solution is on known mathematical way with the help of the pattern recognition matrix 55 is to be obtained.

The method of calibration and pattern recognition can also be mathematical can be understood as a way of forming correlation coefficients. In addition the following Example: For each gas component G.

* j, the signals S ij for j from 1 to * n mediated. This i. j values of S ij are stored in a memory of the pattern recognition matrix 5 saved. When measuring the gas mixture to be determined, the correlation coefficients ßj determined according to the following rule: i = m * ß. = Sum S. S 1 = 1 1 1 The correlation coefficient ßj then indicates the proportion of the gas components G. to be determined.

J The pattern recognition matrix 55 is as indicated in column 57 Outputs Al to An for the number n gas components G1 to Gn. At these exits A the individual values for the gas components concerned can be obtained.

11 claims 5 figures

Claims (11)

Claims 1. Sensor for gas analysis or detection with a Semiconductor detector working according to the principle of calorimetry g e k e n n z e i c h n e t by the fact that the semiconductor detector (D) has two on a common The substrate body (21) is provided with detector elements implemented in thin-film technology (11, 12) - that one detector element (11) is different from the other detector element (12) differentiates by the presence of a selective device (27, 127, 227), by means of which this detector element (11) is colorimetrically differentiated in a gas-sensitive manner to the other detector element (12). 2. Sensor according to claim 1, g e k e n n z e i c hn e t characterized, - that the individual detector elements (11, 12) diodes (23, 24) with connections (25, 125; 26, 126) are - that these diodes (23, 24) of one on the surface of the substrate body (21) located layer (22) are held at the location of the diodes (23, 24) in the substrate body (21) located depressions (111, 112) bridged. 3. Sensor according to claim 2, g e k e n n z e i c hn e t characterized, - that the one or more layers (27, 127, 227) of the selective device in the Depressions (111, 112) of the substrate body (21) are applied in such a way that the one of the layers (27, 127) on the diode (11) of the sensitive detector element (23) is applied. 4. Sensor according to claim 1, 2 or 3, g e k e n nz e i c h n e t thereby, that a selective device has a catalyst layer (27, 127). 5. Sensor according to claim 1, 2, 3 or 4, g e k e n nz e i c h n e t in that a selective device selected a layer of a zeolite (227) Thickness owns. 6. Sensor according to one of claims 1 to 5, g e k e n nz e i c h n e t characterized in that the selective device of an individual detector (Di) has a heating or Cooling device (29) to achieve a different from other individual detectors Temperature of this single detector (Di) is. 7. Sensor according to one of claims 1 to 6, g e k e n nz e i c h n e t in that the selective device is a manipulated structure of the grid of the Semiconductor material of the sensitive diode (11) of the given individual detector (Di) is. 8. Sensor, g e k e n n z e i c h n e t, - that for selective Detection of at least one gas (Gj) of a number n different gases (G1, G2, ...) - a number m of individual detectors (D1, D2 ...) is provided in the arrangement of an array (Fig. 4), -that these individual detectors (D1, D2 ...) semiconductor diode arrangements (Fig. 2, 3) according to one of the claims 1 to 7 are, - and that a respective individual detector is different from the other individual detectors differs through its associated selective device (27; 127, 227), wherein at least some of the individual detectors (D1, D2 regarding several of the gases to be detected (G1, G2 ...) for each individual detector have specific sensitivity. 9. Gas sensor according to claim 8, g e k e n n z e i c hn e t thereby, that for the detection of at least one gas (Gj) in a mixture of a number Gases (G1 G2 ...) is included, a number m = 1, 2, ... Single detectors (0) are provided and with these up to n = 1, 2, ... gases can be detected with the number m less than / equal to the number n. 10. Gas sensor according to claim 8 or 9, g e k e n n z e i c h n e t in that all of the detectors provided (D1, 02 ... Dm) are on a single semiconductor substrate body (21) are located (Fig. 4). 11. The arrangement according to claim 10, g e k e n n z e i c hn e t thereby, that on the substrate body (21) also the electronic circuits (55) of the Evaluations are located.