DE3519435A1 - Sensor for gas analysis - Google Patents

Abstract

Sensor for gas detection or analysis comprising a catalytically active layer (32) and a zeolite layer (33), said layer combination forming a selective device (V) of a semiconductor component. A number of sensors (D) of this type having different selective devices is preferably operated as an array together with a pattern recognition matrix (Figures 3 and 4). <IMAGE>

Description

Gas analysis sensor

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. 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 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 2500 C and from N02 from NO with a catalyst made from Al203-SiO2 gel at 1000 C, in each case with the addition of appropriate oxygen. S02 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 detect a (predeterminable specific or unknown) gas, which may be used as a gas component in a gas mixture is present, and in particular for simultaneous selective detection in a gas mixture containing gas components to indicate (single) gas detectors that different responses to or different sensitivity to each other individual gases or vapors.

This object is achieved with detectors that have the features of claim 1 have. Further refinements and developments emerge from the subclaims of the invention.

The present invention is based on the fact that on the one hand zeolites as Molecular sieves with widely differing permeability behavior for gas molecules are available and on the other hand according to the principle of a Capacitance diode, a field effect transistor and the like.

functioning semiconductor components exist, which are classified as gas-sensitive Detectors can be designed and, moreover, also in integrated Technology can also be built together in larger numbers.

In particular, the semiconductor components are MOS semiconductor elements with silicon in particular as the substrate material.

In particular, the silicon technology makes it possible with relatively little Effort and yet the highest precision to build integrated detector arrangements.

A further development of the invention consists in a large number of such Individual detectors with mutually different detection properties as an array to arrange and the measurement results of these individual detectors, at least two of each other different individual detectors, with the help of a Pattern recognition matrix to evaluate logically. Those already mentioned above, which have so far been perceived as annoying Cross-sensitivities of any individual detector are in the invention advantageously when evaluating the output signals of several different from one another Individual detectors used to advantage.

Further explanations of the invention can be found in the following description to embodiments and the development of the invention.

Figures 1 and 2 show examples of a diode and a field effect transistor single detector.

FIG. 3 shows a schematic representation of an integrated detector array and FIG. 4 shows a diagram for pattern recognition.

The capacitance diode 20 of FIG. 1 is on a substrate body 21 made of silicon in particular. At 31 is a gate insulator layer made of e.g. Designated silicon dioxide or silicon nitride. This layer 31 can also be thermal oxide or nitride generated in the surface of the substrate body 21. The next one Layer 32 is an electrode layer, which is used here as a catalytically active layer also part of the selective device V is.

The selective device V also includes that designated by 33 Layer of a zeolite. For example is for main sensitivity to hydrogen and hydrogen-containing compounds, the metal of layer 32 platinum, palladium or another metal of the platinum series that acts as a catalytic layer for hydrogen is to be used. There are numerous different zeolites available for the zeolite layer with different permeability resp.

Pore sizes available for gas molecules. The method of application the zeolite layer 33 depends on the particular zeolite. For a selective device for gases other than hydrogen, e.g. carbon monoxide, it is necessary that the catalytically active layer 32 has holes 34 through which the to be detected Gas can penetrate to the interface between layers 31 and 32. These holes 34 have cross-sections that are large compared to zeolites.

An integrated structure of such diodes is such that several such arrangements shown in Figure 1 side by side on the surface of a larger substrate body 21 are arranged. The individual diodes are the individual detectors with a respective separate connection 35 and the common substrate connection 36. Each individual detector 20 has its zeolite layer 33 and its catalytic acting layer 32, which is for an array, in particular for the yet to be described Pattern recognition, has gas detector properties or provides an output signal, the or

that is different from at least a number of the further individual detectors of the array.

FIG. 2 shows a built up on or in a substrate body 21 Field effect transistor as a single detector 30. With 41 and 42 are a source and referred to as a drain region. Layer 31 is a gate insulator layer, the layer 32 the catalytically active layer and the layer 33 is again a zeolite layer. Here, too, the layers 32 and 33 taken together form the selective device. With 35, 35a and 36 the connections are again referred to.

This also applies to a single field effect transistor detector to the Figure 1 described with regard to an integration of many such detectors in or on a single substrate body 21.

The effect of the gas is indicated by the arrow labeled G.

The sensitivity of a respective individual detector to a respective one Gas and its cross-sensitivities to other gases or gas components is preferably determined by testing and series tests.

On the one hand, only capacitance diodes can be used for a detector array according to Figure 1 and on the other hand field effect transistor detectors according to Figure 2 as integrated array can be used as a gas sensor. However, an array can also be mixed Arrangements according to Figure 1 and Figure 2 included.

E.g. the signal-to-noise ratio for varactor diodes and with field effect transistors even with the same zeolite and the same catalytic Layer have differences from each other.

FIG. 3 shows a basic structure of one of nine individual detectors D1 up to 9 existing detector arrays.

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

It can be provided that the detectors D1 to D9 open individually mutually different temperatures or one or more of these detectors temperature deviating from the other detectors (operated at "room temperature") being held. The indicated power supply lines H1 to Hm The heating current are used for this purpose can also be modulated, which leads to a corresponding characteristic sensitivity or selectivity leads.

The schematic representation of FIG. 4 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'1 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 system of equations j = n Si = sum j = l (aij Gj) with i from 1 to m 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 aij for i different from j as small as possible compared to the Matrix elements aij 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 the 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 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 aij a function depending on the presence of the gas component Gj other existing 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 are a Function of the present concentration of the respective gas Gj for j = i and / or of the other gases Gj present for j £ 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 in a known mathematical way with the aid of the pattern recognition matrix 55 is.

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.

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

The pattern recognition matrix 55 has the outputs indicated in column 57 Al to An for the number n gas components G1 to Gn. Leave A at these outputs the individual values for the gas components concerned decrease.

9 claims 4 figures - blank page -

Claims (9)

Claims 1. Sensor for gas analysis with a zeolite layer not shown in that the respective zeolite layer (33) on one based on the principle of a capacitance diode (20) or a field effect transistor (30) working semiconductor component (Fig. 1, 2) is, - is on the Semiconductor body (21) of the component is a layer sequence composed of an insulator layer (31) and a catalytically active layer (32) is arranged and the zeolite layer (33) is located on this catalytically active layer (32), the zeolite layer (33) and the catalytically active layer (32) together form a selective device (V) form. 2. Sensor according to claim 1, g e k e n n z e i c hn e t in that the catalytically active layer (32) has through holes (34) which are large compared to the pores of the zeolite. 3. Sensor according to claim 1 or 2, g e k e n n z e i c hn e t thereby, that the catalytically active layer (32) made of palladium, platinum or a metal the platinum series. 4. Sensor according to claim 1, 2 or 3, g e k e n nz e i c h n e t thereby, that the insulator layer is an oxide or nitride layer of the material of the semiconductor body (21) is. 5. Sensor according to one of claims 1 to 4, g e k e n nz e i c h n e t in that the semiconductor material is silicon. 6. Sensor, g e k e n 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 of m differently designed individual detectors (Del, D2 ...) is provided in the arrangement of an array (Fig. 3), - that these individual detectors (D1, D2 ...) semiconductor diode arrangements (Fig. 1, 2) according to one of the claims 1 to 5 are, - and that a respective individual detector is different from the other individual detectors differs by its associated selective device (V), - at least individual detectors (D1, D2 ...) with respect to several of the ones to be detected Gases (G1, G2 ...) have specific sensitivity for the respective individual detector. 7. Gas sensor according to claim 6, 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, ... individual detectors (D) 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. 8. Gas sensor according to claim 6 or 7, g e k e n n z e i c h n e t thereby, that all the detectors provided (D1, D2 ... Dm) are on a single one Semiconductor substrate body (21) are located (Fig. 4). 9. Arrangement according to claim 8, 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.