Multi-gas digital cartridge based on a metal oxide MEMS sensor array for detecting patterns related to air composition, and related stabilization method

Abstract

A multi-gas digital cartridge based on a metal oxide MEMS sensor array for detecting patterns related to air composition is disclosed. The sensing elements of the cartridge are stabilized in a manufacturing period of 72 - 100 hours by gas emission and controlled passivation techniques, rather than the current 4 - 6 months required for natural stabilization. The operation of the cartridge is ensured by a process of dynamic scanning and virtualization of the sensing elements performed by applying a control voltage. When stabilized by the method of the present disclosure, this cartridge enables accurate investigation from two different measurement channels using selective chemical filtering separation, as well as pattern recognition and extraction processes based on principal component analysis, for total volatile organic compounds (TVOCs) having spectral profiles grouped in major families (alcohols, ethers, ketones, organic acids, aliphatic hydrocarbons, aromatic hydrocarbons, amines, aldehydes, alkenes, halogenated organic compounds, organic sulfur compounds, organic nitrogen compounds), carbon monoxide (CO), nitrogen dioxide (NO 2 ), formaldehyde (HCHO), ozone (O 3 ), oxygen (O 2 ), ammonia (NH 3 ), sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), hydrogen (H 2 ), hydrogen fluoride acid (HF), hydrogen cyanide (HCN), hydrochloric acid (HCL), chlorine dioxide (ClO 2 ), methyl mercaptan (H 4 S), bromine (Br 2 ) to be selectively detected.

Description

Technical Field

[0001] The present invention relates to a sensor using MEMS technology, having a sensing element made of metal oxide, and belonging to the field of sensors suitable for analyzing the composition of air.

Background Art

[0002] MEMS (Micro Electro Mechanical Systems) technology has been established as a disruptive technology that raises the mechanical dimensions to the same level as those of microelectronics in the field of microelectronics. MEMS technology has dramatically changed the design paradigm of electronic systems and computer systems and can realize electromechanical functions at the nanometer level that could only be achieved by electrical technology before, so it is widely recognized as the most innovative technology in the 21st century. Furthermore, because of its very small size, various levels of system integration are possible, and the device can have comprehensive functions. That is, the device can have analog and digital functions that enable all that is necessary for the interface with the host microcontroller to be incorporated into one device. MEMS is evolving rapidly, and in the prior art, the micro dimensions are shifting to nano dimensions. For this reason, there is already talk about NEMS (Nano electro mechanical systems).

[0003] In this context, the first actual application of MEMS technology was in sensors. This is because the most commonly used sensors in the field of automation, etc., were electromechanical (for example, pressure sensors, motion sensors, acoustic sensors such as microphones).

[0004] Among these, it has become possible to fabricate environmental sensors (such as gas, light intensity, atmospheric pressure, humidity, temperature, etc.) with very convenient dimensions and costs. In particular, the use of MEMS gas sensors makes it possible to realize applications for very wide-ranging and low-cost environmental monitoring. For example, AS-MLV-P2 is a gas component sensor based on MEMS technology manufactured by AMS. Due to its characteristics of low power consumption (34 mW) and long lifespan (10 years), it has found important application fields in the Internet of Things network technology.

[0005] However, the main problems of this type of sensor for gas detection and air composition analysis, especially based on MEMS technology, are low selectivity, as well as baseline drift and progressive sensitivity loss that typically occur during the first six months. Therefore, these devices are not very suitable for providing quantitative information about the concentrations of various pollutants present in the air. Thus, MEMS sensors based on metal oxide technology are mainly used to provide a rough qualitative indicator of the presence of volatile organic compounds (VOCs), which is expressed as a correlation value index or differential value index with respect to the minimum concentration value detected in the past 24 to 72 hours. In fact, in order to overcome the problem of baseline drift, instead of performing static calibration of the device, continuous operation and correction techniques are used, and without this, the device cannot function accurately.

[0006] Furthermore, today's MEMS sensors based on metal oxide technology have extremely limited ability to selectively detect volatile substances and cannot identify and measure specific gases such as methane, ammonia, formaldehyde, nitric oxide, nitrogen dioxide, or ozone. Also, considering the low selectivity of the above sensors, they are particularly sensitive to hydrogen, which is one of the main interfering substances. Therefore, it is difficult to accurately detect the total value of volatile organic compounds (TVOC) expressed in parts per million using these devices.

[0007] To enhance the selectivity of metal oxide MEMS devices, various techniques are used, such as using various materials for the sensing layer or diversifying the temperature of the heater.

[0008] For example, in the patented Triplesensor technology by UST (Umwelt Sensor Technik), by using three different sensing materials on the same heater, the discrimination ability for easily oxidizable gas (CO), hardly oxidizable gas (CH 4 ), and oxidizing gas (NO 2 , O 3 ) is enhanced. However, with this technology, various families of specific pollutants such as organic volatiles (VOC), hydrocarbons, and formaldehyde cannot be discriminated. Furthermore, the measurement of carbon monoxide shows very high cross-sensitivity to highly volatile substances such as alcohol, because only partial selectivity can be achieved by diversifying the sensing materials.

[0009] In addition, attempts have been described in the scientific literature to enhance the selectivity of metal oxide devices by varying or diversifying the temperature of the heater. However, the results obtained are generally only effective in the academic field and last for a short period. This is because the unstable nature of metal oxide devices hinders any attempt to characterize these devices, and their behavior changes significantly during the first 6 to 8 months of their lifespan. This is also the case for the implementation of pattern extraction and discrimination algorithms combined with metal oxide sensor arrays. As the reproducibility of measurements decreases over time, the identification and quantification of substances in gas phases present at low concentrations, such as air quality parameters, are not practical. Therefore, this approach is limited to quality control in the food, chemical, and pharmaceutical industries, where the gas concentration is 10 or 100 times higher and the analysis results are simple qualitative parameters such as "good" or "not good", "yes" or "no". Such analysis results are obtained, for example, by recognizing a specific pattern downstream of the training performed by the user, as in the case of the PEN3 (Portable Electronic Nose) device sold by Airsense.

[0010] Accordingly, the object of this industrial patent application is to propose a multi-gas digital cartridge based on a metal oxide MEMS sensor array for detecting patterns related to air composition. The sensitive elements of the cartridge are stabilized by gas release and controlled passivation techniques in a manufacturing period of 72 - 100 hours instead of the current 4 - 6 months required for natural stabilization. Thereafter, the cartridge is calibrated and guaranteed to operate for 24 months. Note that no further calibration or correction of baseline drift is required for this cartridge. The operation of a single cartridge is guaranteed by the process of dynamic scanning and virtualization of the sensitive elements executed by applying a control voltage. When this cartridge is stabilized by the method of the present disclosure, it is possible to selectively detect many molecules by accurate investigations obtained from two different measurement channels using selective chemical filtering separation, as well as pattern recognition and extraction processes based on principal component analysis. Examples of these molecules include total volatile organic compounds (TVOC) with spectral profiles grouped in major families (alcohols, ethers, ketones, organic acids, aliphatic hydrocarbons, aromatic hydrocarbons, amines, aldehydes, alkenes, halogenated organic compounds, organic sulfur compounds, organic nitrogen compounds), carbon monoxide (CO), nitrogen dioxide (NO 2 ), formaldehyde (HCHO), ozone (O 3 ), oxygen (O 2 ), ammonia (NH 3 ), sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), hydrogen (H 2 ), hydrofluoric acid (HF), hydrogen cyanide (HCN), hydrochloric acid (HCL), chlorine dioxide (ClO 2 ), methyl mercaptan (H 4 S), bromine (Br 2 ). Description of the Invention

[0011] This patent application related to industrial inventions intends to describe and claim an apparatus and method that includes at least a new alternative solution to the currently known solutions and / or satisfies one or more needs recognized in the technical field, particularly inferred from the above. To achieve this objective, the inventors have developed a sensor for analyzing the air composition based on MEMS technology, which has a sensing element of metal oxide and can selectively detect many gas molecules present in the air with high sensitivity and high precision. This sensor is characterized by a construction method described below for fabricating a cartridge equipped with an array of sensing elements having a dual measurement chamber, and an innovative stabilization method realized by an advanced process of accelerated aging and calibration in a controlled environment. By this stabilization method, the manufacturing time can be shortened by up to 72 - 100 hours compared to the 4 - 6 months required to naturally obtain aging and stabilization.

[0012] The multi - gas digital cartridge that is the subject of this industrial patent application is based on an array of sensing elements. This element array is an array that can be adjusted in real - time to respond partially and selectively to substances within a specific range in a specific chemical group with very high accuracy and reproducibility over time, based on a specific molecular size and the tendency of the molecule to increase oxidation and / or reduction. The sensitivity of each element can be changed and adjusted by applying a control voltage that can change the physical parameters of its surface layer, thereby adjusting the sensitivity of the element to various volatile compounds. The application of voltage, i.e., "dynamic scanning", can obtain up to 64 virtual sensing elements, each of which can exhibit a specific partial and selective reaction to a specific range of substances. By combining these reactions, the unique "chemical signature" of multiple different chemical compounds or individual substances in the gas phase can be identified and distinguished.

[0013] To obtain these results, preferably 3 to 5 metal oxide sensors are arranged in the cartridge, and by means of these sensors, at least 3 traces are obtained from two different measurement channels, namely, an active measurement trace and a passive measurement trace extracted from a first measurement channel directly exposed to the air to be analyzed, and a reference trace extracted from a second chemically filtered channel. Both channels are formed by arranging a sensitive element downstream of a chamber formed by two hydrophobic PTFE membranes that enable gas exchange with the environment by means of double diffusion.

[0014] To obtain a chemically filtered channel, at least one sensor is arranged downstream of a multilayer filter arranged between two PTFE membranes. This multilayer filter is formed by a plurality of (preferably 6) layers of fabric impregnated with a chemically absorbent material. Examples of such materials that do not have legal binding force include activated carbon microparticles, potassium iodide, activated carbon impregnated with potassium hydroxide or sodium hydroxide, or activated carbon mixed with molecular sieves such as aluminosilicates, particularly zeolites of types 3A, 4A, 5A, 10X, and 13X. By stacking and combining a plurality of layers of this filtering material, the passage of gas molecules can be selectively adjusted to form a reference channel.

[0015] The sensitive elements involved in the measurements via the two different channels produce specific diverse reactions. Specifically, two sensitive elements belonging to a plurality of different channels, namely, a filtered channel and an unfiltered channel, can supply a signal containing uncorrelated non-redundant information about the composition of the filtered air and the unfiltered air when appropriately modulated by an equivalent periodic signal such as a sine wave signal, a square wave signal, a ramp signal, or a step signal. The filtered channel can allow molecules with low affinity for the composition of the filter material to pass through.

[0016] For example, a channel filtered using a fabric impregnated with micronized activated carbon allows carbon monoxide and hydrogen to pass through, but can completely block ethyl alcohol and solvents. The distinction between hydrogen and carbon monoxide is made by a modulation technique. The information extracted from two modulation sensors is two or four periodic signals to which FFT (Fast Fourier Transform) is applied to extract so-called "features", and this "feature" is the characteristic information of the signal being analyzed, that is, the complex coefficients of A1~An and B1~Bn (n is the order of the FFT applied to the signal).

[0017] The combination of these coefficients can be represented on a histogram graph, and each bar of the histogram represents one of these coefficients. The specific shape of the histogram can be associated with a specific chemical element and indicates its unique "chemical feature".

[0018] In this regard, in order to distinguish between two different substances, the principal components of the "chemical features" are extracted using the PCA algorithm. This result can also be visually represented in a 2D scatter plot, but when the complexity of the compound to be detected increases, a 3D plot visual representation may be required to distinguish all the elements.

[0019] Specifically, the sensor is modulated by applying a variable voltage across the entire heater, thereby changing the temperature of the sensitive layer, or more precisely, dynamically changing the equilibrium of the surface reaction of chemisorbed oxygen. As a result, the resistance Rs measured across the entire sensitive layer fluctuates at a level capable of generating a periodic signal.

[0020] The same appropriately converted periodic voltage is also applied as a bias voltage to a resistor divider for measuring the resistance Rs of a second sensing element driven at a constant voltage, that is, at a temperature, thereby disturbing the dynamic equilibrium of the surface reaction. Also in this case, the resistance Rs becomes a periodic function.

[0021] The functions considered for pattern extraction are as follows: (1) The periodic function Rs1(t), that is, the resistance Rs of the sensing layer of the first sensing element measured by applying a variable voltage V(t)=f(t) to the heater, where this resistance Rs is measured with a constant bias voltage applied to the sensing layer. This control operation is defined as "dynamic scan using temperature modulation". (2) The periodic function Rs2(t), that is, the resistance value obtained from the second sensing element to which a constant voltage V(t)=k is applied, where this resistance Rs is measured by applying a variable voltage proportional to the voltage V(t) that controls the heater of the first sensing element to the sensing layer. This control operation is defined as "controlled bias isotherm". (3) The periodic function Rn(t)=Rs1(t) / Rs2(t) normalized to the isotherm, that is, the ratio of the functions Rs1(t) and Rs2(t).

[0022] Preferably, in order, use the function described in (1), or, if possible, use the function described in (3), and in some cases, use it in combination with the function described in (2).

[0023] By comparative analysis of the obtained signals and subsequent pattern extraction from both channels, it is possible to extrapolate information related to the composition of air based on the differentiated presence of molecules having selective ability for the following: - Total volatile organic compounds (TVOC) having a spectral profile grouped by major families (alcohol, ether, ketone, organic acid, aliphatic hydrocarbon, aromatic hydrocarbon, amine, aldehyde, alkene, halogenated organic compound, organic sulfur compound, organic nitrogen compound); - Carbon monoxide (CO); - Nitrogen dioxide (NO 2 ); - Formaldehyde (HCHO); - Ozone (O 3 ): - Oxygen (O 2 ); - Ammonia (NH 3 ); - Sulfur dioxide (SO 2 ); - Hydrogen sulfide (H2 S); - Hydrogen (H 2 ); - Hydrofluoric acid (HF); - Hydrogen cyanide (HCN); - Hydrochloric acid (HCl); - Chlorine dioxide (ClO 2 ); - Methyl mercaptan (H 4 S); - Bromine (Br 2 )

[0024] Specifically, in a configuration where a total of four sensing elements, namely three sensing elements in the unfiltered channel and one sensing element in the filtered channel, are used, the sensor is managed as follows. - The sensing elements in the filtered channel and the sensing elements in the unfiltered channel are managed by "temperature modulation dynamic scan". - One of the sensing elements in the unfiltered channel is managed according to the modality isotherm of the controlled bias. - The additional sensing elements are managed in the "static mode", that is, using a heater with a bias of constant temperature and constant voltage.

[0025] The final result, that is, the concentration of each pollutant, is determined using the values provided by the sensors managed in the static mode and the sensors managed in the controlled bias isothermal mode. These sensors are individually calibrated by using two-point reference gases with the baseline values obtained by exposing to the reference concentration and chromatographic air (pure synthetic air, that is, air containing no pollutants and CO 2 ), that is, dividing by the average R S value which is the average of the R S values during the scan period.

[0026] These concentration values are appropriately corrected by a series of coefficients obtained from the dynamic pattern recognition process described above, that is, by a series of coefficients obtained as the processing results of the functions Rn(t), Rs1(t), and Rs2(t).

[0027] In addition to the above-described configuration, a configuration modification example that provides two or more integrated MEMS sensors suitable for realizing two different measurement chambers is also conceivable. For example, from this perspective, an integrated MEMS sensor composed of four metal oxide sensing elements installed downstream of the chemical filter can realize the first filtered measurement channel, and each of one or more other integrated sensors composed of four sensing elements made of metal oxide exposed to air can realize the second unfiltered measurement channel. In this configuration, four sensing elements are arranged on the filtered channel, and four to eight sensing elements are arranged on the unfiltered channel, whereby the elements can be diversified. Specifically, it can be diversified into one element using a material for oxidizing the gas, two elements using a material that hardly reduces the gas, and an element using a material for easily reducing the gas.

[0028] Attempts to improve the sensitivity and selectivity of metal oxide sensors using temperature modulation technology have always left unstable results due to passivation by siloxane, aging, microcracks in the surface layer, and high sensitivity to hydrogen independent of the temperature of the sensing element (common background interferents). Instead, the reference measurement channel is differential with respect to common-mode interferents and is not affected by the evolution of individual sensing elements or ongoing aging, so highly reliable and reproducible information can be obtained over a long period of time.

[0029] Another reason for the instability often found in metal oxide-based sensors is that their sensitivity is inversely proportional to the baseline resistance Ra (the resistance value in clean air without chemical contaminants) over time compared to when first powered on.

[0030] This sensitivity gradually stabilizes after 10 - 14 days but gradually decreases in the first 4 - 6 months of the device's life, making it unsuitable for static calibration. For this reason, metal oxide sensors are typically used for differential measurements over 24 - 48 hours, during which the relative minimum point reached in the previous time period is referenced. However, this is generally unreliable, especially in the measurement of absolute concentrations of gases such as total volatile organic compounds (TVOC), carbon monoxide, ozone, methane, nitrogen dioxide, formaldehyde, and ammonia, due to low selectivity and high instability over time, resulting in low reliability.

[0031] Furthermore, the subsequent behavior of the sensor in the stable zone, i.e., when the baseline and sensitivity reach a nearly stable trend after 4 - 6 months, is also greatly affected by the history that occurred in the previous period, i.e., the chemical substances to which the sensor was exposed at this stage, the degree of relative humidity, and the ambient temperature at which the exposure was carried out.

[0032] To overcome this problem, a method has been developed that can accelerate the aging of the sensor to the stable stage in 72 - 100 hours instead of the 4 - 6 months currently required for natural aging. This method can also make the performance uniform among sensors, maintain these sensors in a stable state for at least 24 months, and further achieve reproducibility and uniformity of responses among different production batches.

[0033] This technology can be realized by an environmental fine - tuning chamber that can control temperature with an accuracy of ±0.5°C and relative humidity with an accuracy of ±3%RH. In these chambers, various gaseous substances obtained by mixing the contents of certified cylinders can be supplied, and the temperature of the sensor's micro - heater can be controlled within the range of 100 - 450°C with an accuracy of ±3°C. This is particularly important in the first few hours after the device starts operating because the operation during this time period determines the behavior after stabilization.

[0034] The assumed steps of the method of accelerated aging and calibration in a controlled environment are described below. This method is flexible and adaptable to various operating needs and can be used following an exact order or a combination of all or some of the steps below. A. First, turn on the power and stabilize it at a low temperature. Turn on all the power supplies of the sensing elements simultaneously. B. Maintain the above elements at a temperature of about 120 °C for about 4 hours. This slowly activates the sensing layer of the sensor. C. In this step, it can be observed that the resistance value gradually increases until it reaches the maximum point and then gradually decreases. The maximum point indicates the completion of the first step. a. If the maximum point is not reached, it is necessary to wait for a longer time. The procedure cannot be continued until the resistance value reaches the maximum. D. Then, while supplying chromatographic air (air with no CO or other chemical impurities), expose the inside of the adjustment chamber to a constant temperature of about 20 - 22 °C and a relative humidity of 50% RH to promote the gas emission and stabilization of the materials near the sensing elements. 2 E. While supplying a mixture of reducing gases with passivation characteristics or a mixture of air and CO mixed at a ratio of 5% in the temperature range of 300 - 400 °C, modulate the temperature of the sensing element in a sine wave cycle with a minimum temperature of 150 °C, a maximum temperature of 400 °C, and a cycle duration of about 5 minutes for about 8 - 12 hours. In the low - temperature step, supply chromatographic air to remove chamber contamination and normalize the sensor surface. In this way, controlled passivation and stabilization of the sensitivity of the sensing element can be achieved. 2 F. Leave the sensor at a constant temperature of 320 °C for 12 hours while supplying chromatographic air with a relative humidity of 25%. G. Perform further stabilization of the sensing element and check the uniformity of the resistance RS of all sensors. ​​Elements that do not have the required resistance value are each put into the cycle of step (F), and then new measurements are made on the element until the target value is reached. I. Turn off the power of the sensor with the desired / correct R value. J. In some cases, repeat step (G) over 6 hours to further check the value of resistance RS. K. Keep the adjustment chamber at a temperature of 60 °C and leave the sensor on at a temperature of 350 °C for 2 hours in an environment of chromatographic air flow and relative humidity of 25%. This procedure is aimed at removing contamination of the entire cartridge, especially the absorbent material of the multilayer chemical filter. L. Turn off the sensor over 6 - 12 hours while continuously supplying chromatographic air with a relative humidity of 50% at a temperature of 20 - 22 °C. M. Supply chromatographic air with a relative humidity of 50% to readjust the above - mentioned sensitive element and multilayer chemical filter. N. Turn on the sensor at 400 °C for 30 minutes. O. Turn on the sensor at 250 °C for an additional 30 minutes. P. Leave the sensor on in the operating state and stabilize the sensor over 6 hours. Q. Perform calibration by supplying a specific gas at the required concentration using a certified cylinder / tank according to the needs of the configuration and operating range of the cartridge to be calibrated.

[0035] Among the possible combinations of the above - mentioned steps, in particular, a simplified functional procedure for calibration and accelerated aging of the sensor, including only steps (A), (B), (C), (C)a, (D), (E), (K), (P), (Q) of the method in question, was tested over a period of approximately 100 hours.

Brief Description of the Drawings

[0036] The above - mentioned advantages, as well as other advantages and features of the present invention, will be described with reference to the accompanying drawings. These drawings are merely illustrative and do not limit or restrict the effects of this patent application.

[0037]

Figure 1

Figure 2

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DETAILED DESCRIPTION OF THE INVENTION

[0038] It will soon become apparent that many modifications and variations are possible to the above - described description, without departing from the scope of the invention as set forth in the appended claims (e.g., regarding shape, dimensions, arrangement, and components having equivalent functions, etc.).

[0039] Hereinafter, as a non-limiting or non-binding example regarding the concept of the present invention, the multi-gas digital cartridge 100 according to the present invention will be described. This cartridge includes at least one metal oxide sensor 10 disposed downstream of a selective chemical filter 50 interposed between two hydrophobic PTFE membranes in a first polymer chamber, and at least three metal oxide sensors 11-13 exposed to air in a second polymer chamber belonging to the same cartridge 100.

[0040] Each of the sensitive elements 5 disposed on the filtered sensor and the unfiltered sensor is modulated by the application of a periodic signal such as, for example, a sine wave signal, a square wave signal, or a step signal, and these sensitive elements supply, as an output, a signal containing uncorrelated and non-redundant information regarding the composition of the filtered air and the unfiltered air. At this time, the filtered channel allows only molecules with low affinity for the filtering material components to pass through. Since the physical parameters of these sensitive elements can be changed by modulation, each sensor can be prepared to respond in a specific selective manner to gaseous substances. Further, the detection results obtained by the above-described algorithms and functions can be combined with each other and typically displayed as a histogram graph, a distribution diagram, or, depending on the complexity of the measurement, a three-dimensional graph, and these are used to identify and distinguish the "chemical characteristics" of a plurality of different detected components.

[0041] To achieve the above object, two measurement chambers of appropriate dimensions are fabricated within the polymer chamber 20. Below the polymer chamber 20, a PCB 15 having at least four sensors 10, 11, 12, and 13 is inserted, and all of these sensors are equipped with a sensing element 5 based on metal oxide. The first sensor 10 is disposed in the first measurement chamber, and the other three sensors 11 to 13 are disposed in the second measurement chamber. On the opposite side of the polymer chamber 20, a first film 30 made of PTFE (polytetrafluoroethylene) is inserted into the compartment corresponding to the first sensor 10, followed by the insertion of a selective chemical filter 50. This chemical filter 50 is preferably composed of six layers and includes a fabric impregnated with a chemical absorbent. Non-limiting examples of such chemical absorbents include microactivated carbon, potassium iodide, activated carbon impregnated with potassium hydroxide or sodium hydroxide, or activated carbon mixed with molecular sieves such as aluminosilicates, particularly zeolites of types 3A, 4A, 5A, 10x, and 13x. By stacking and combining various layers of the filtering material, the passage of gas molecules can be selectively adjusted to form a channel for use in reference measurements. The three sensors 11 to 13 exposed to air in the second compartment within the polymer chamber 20 perform active and passive measurements instead.

[0042] As an upper closure of the cartridge 100, a sealing cover 60 having two appropriate openings for the two above-described compartments is provided, and these two openings are further filtered by a second PTFE film 40.

[0043] The cartridge 100 constructed in this way is required to accelerate the stabilization and aging processes, which are due to passivation in the sensing element 5 caused by siloxane, microdestruction of the surface layer, and high reactivity to hydrogen.

[0044] To perform this operation, procedures that are flexible and adaptable to various operational needs have been developed, and this procedure can be executed according to the order of the following steps, or according to all or some combinations of the following steps. (A) First, turn on the power and stabilize it at a low temperature. All the sensing elements will be in the switched-on state simultaneously. (B) Maintain the above-mentioned sensing elements at a temperature of about 120 °C for about 4 hours. This will slowly activate the sensing layer of the sensor. (C) In this step, it can be observed that the resistance value gradually increases until it reaches the maximum point and then gradually decreases. The maximum point indicates the completion of the first step. a. If the maximum point is not reached, it is necessary to wait for a longer time. Until the resistance value reaches the maximum or does not reach the maximum, the next procedure cannot be proceeded with. (D) Then, while supplying chromatographic air (air without any CO 2 or other chemical impurities), expose it to a constant temperature of about 20 - 22 °C and a relative humidity of 50% in the adjustment chamber to promote the gas release and stabilization of the materials near the sensing elements. (E) While supplying a mixture of reducing gas with passivation characteristics, or a mixture of air and 5% CO 2 in the temperature range of 300 - 400 °C, modulate the temperature of the sensing elements in a sine wave cycle with a minimum temperature of 150 °C, a maximum temperature of 400 °C, and a cycle duration of about 5 minutes for about 8 - 12 hours. In the low-temperature step, supply chromatographic air to remove chamber contamination and normalize the sensor surface. In this way, controlled passivation and stabilization of the sensitivity of the sensing elements can be achieved. (F) Leave the sensor at a constant temperature of 320 °C for 12 hours while supplying chromatographic air with a relative humidity of 25%. (G) Perform further stabilization of the sensing elements and check the uniformity of the resistance Rs of all sensors. (H) Elements that do not have the required resistance value are each returned to the above step (F), and then new measurements are made on the element until the target value is reached. (I) Turn off the power supply of the sensor with the desired / correct R value. (J) Optionally, repeat step (G) over 6 hours to further check the value of the resistance Rs. (K) Keep the adjustment chamber at a temperature of 60 °C and leave the sensor on at a temperature of 350 °C for 2 hours in an environment of chromatographic air flow and relative humidity of 25%. This procedure aims to remove the contamination of the entire cartridge, especially the absorbent material of the multilayer chemical filter. (L) Turn off the sensor over 6 - 12 hours while continuously supplying chromatographic air with a relative humidity of 50% at a temperature of 20 - 22 °C. (M) Supply chromatographic air with a relative humidity of 50% to readjust the above - mentioned sensing element and multilayer chemical filter. (N) Turn on the sensor at 400 °C for 30 minutes. (O) Turn on the sensor at 250 °C for an additional 30 minutes. (P) Leave the sensor on in the operating state and stabilize the sensor over 6 hours. (Q) Perform calibration by supplying a specific gas at the required concentration using a certified cylinder / tank according to the needs of the configuration and operating range of the cartridge to be calibrated.

[0045] Among the possible combinations of the above - described steps, in particular, a simplified functional procedure for the calibration and accelerated aging of the sensor including only steps (A), (B), (C), (Ca), (D), (E), (K), (P), (Q) of the target method was tested over a period of approximately 100 hours.

[0046] The cartridge 100 thus prepared has total volatile organic compounds (TVOCs), carbon monoxide (CO), nitrogen dioxide (NO 2 ), formaldehyde (HCHO), ozone (O3 ) Oxygen (O 2 ) Ammonia (NH 3 ) Sulfur dioxide (SO 2 ) Hydrogen sulfide (H 2 S), Hydrogen (H 2 ), Hydrofluoric acid (HF), Hydrogen cyanide (HCN), Hydrochloric acid (HCl), Chlorine dioxide (ClO 2 ), Methyl mercaptan (H 4 S), Bromine (Br 2 ) can be detected.

[0047] It should be obvious to those skilled in the art that the above-described present invention can be modified, added to, or altered without departing from the scope of protection defined by the appended claims.

Claims

1. A multi-gas digital cartridge (100) based on a metal oxide MEMS sensor array for detecting patterns related to air composition, comprising at least two measurement chambers of suitable dimensions fabricated in a polymer chamber (20), below which a PCB (15) is inserted, carrying at least four MEMS sensors (10-13), each with a metal oxide sensitive element (5), in particular at least a first sensor (10) being arranged in the first measurement chamber and at least three other sensors (11-13) being arranged in a second measurement chamber, on the opposite side of the polymer chamber (20) in a compartment facing the first sensor (10), a first membrane (30) made of hydrophobic PTFE (polytetrafluoroethylene) is arranged, downstream of which a selective chemical filter (50) is arranged, the chemical filter preferably consisting of six layers and made of fabric impregnated with a chemical absorbent. The chemical absorbent is, for example, finely divided activated carbon, activated carbon impregnated with potassium iodide, potassium hydroxide or sodium hydroxide, or activated carbon mixed with molecular sieves such as aluminosilicates, particularly zeolites of types 3A, 4A, 5A, 10x and 13x. A sealing cover (60) having appropriate openings facing the measurement chamber is arranged to close the upper side of the cartridge (100). The two openings are further filtered by a second hydrophobic PTFE membrane (40) arranged on top. The cartridge (100) completed through the calibration and stabilization process described below is capable of measuring total volatile organic compounds (TVOCs), carbon monoxide (CO), nitrogen dioxide (NO), and the like, having spectral profiles grouped into the following major families: alcohols, ethers, ketones, organic acids, aliphatic hydrocarbons, aromatic hydrocarbons, amines, aldehydes, alkenes, halogenated organic compounds, organic sulfur compounds, organic nitrogen compounds. ２ ), formaldehyde (HCHO), ozone (O ３ ), oxygen (O ２ ), ammonia (NH ３ ), sulfur dioxide (SO ２ ), hydrogen sulfide (H ２ S), hydrogen (H ２ ), hydrofluoric acid (HF), hydrogen cyanide (HCN), hydrochloric acid (HCL), chlorine dioxide (ClO ２ ), methyl mercaptan (H ４ S), and bromine (Br ２ ) .

2. 2. A multi-gas digital cartridge (100) based on a metal oxide MEMS sensor array for detecting patterns related to air composition according to claim 1, characterized in that the two measurement chambers formed in the polymer chamber (20) comprise two different measurement channels, one of which faces the first sensor (10) filtered by the selective chemical filter (50) and constitutes a reference channel, and the other of which faces the sensors (11-13) exposed to the air to be analyzed and constitutes a channel for performing active and passive measurements.

3. The sensitive elements (5) provided in the sensors (10-13) belonging to a number of different measurement channels are modulated by an equivalent periodic signal, for example a sine wave signal, a square wave signal, a ramp signal or a step signal, in order to detect at their output signals containing uncorrelated and non-redundant information about the composition of the filtered and unfiltered air, the functions considered being, in order of preference, the functions of subparagraph A below or the functions of subparagraph C below, which may be combined, if available, with the functions of subparagraph B below, the resistance Rs of the sensitive layer of the first sensitive element (5) measured by applying a periodic function Rs1(t), i.e. a variable voltage V(t) = f(t) to the heater, the resistance Rs being measured under a constant bias voltage applied to said sensitive layer, this control operation being defined as "temperature modulated dynamic scanning"; a periodic function Rs2(t), i.e. the resistance obtained from the second sensitive element (5) with a constant voltage V(t)=k applied to its heater, the resistance Rs being measured by applying a variable voltage to its sensitive layer proportional to the voltage V(t) controlling the heater of the first sensitive element, this control action being defined as the "control bias isotherm"; - A multi-gas digital cartridge (100) based on a metal oxide MEMS sensor array for detecting patterns related to air composition, according to claim 1, characterized in that the periodic function normalized to the isotherm Rn(t) = Rs1(t) / Rs2(t), i.e. the ratio of the functions Rs1(t) and Rs2(t).

4. The sensitive element (5) provided in the sensor (10-13) is characterized by being managed as follows: the sensitive element (5) in the filtered channel and one of the sensitive elements (5) in the unfiltered channel are controlled by a "temperature-modulated dynamic scan" as defined in the preceding claims, one of the sensitive elements (5) in the unfiltered channel is controlled according to the modality of "isotherm with controlled bias" as claimed in the preceding claim, the further sensitive element (5) is managed using a heater in static mode, i.e. at constant temperature and constant voltage bias; A multi-gas digital cartridge (100) based on a metal oxide MEMS sensor array for detecting patterns related to air composition, as described in claim 1, characterized in that the final result is determined from concentration values ​​appropriately corrected using coefficients obtained from the functions Rn(t), Rs1(t), and Rs2(t).

5. 2. A multi-gas digital cartridge (100) based on a metal oxide MEMS sensor array for detecting patterns related to air composition according to claim 1, characterized in that the measurements obtained from the two measurement channels, i.e. the reference measurement detected by the sensor (10) and the active and passive measurements detected by the sensors (11-13) exposed to the air to be analyzed, are read by dedicated software and suitably displayed for easy visual understanding on a 2D scatter graph or, depending on the complexity of the measurements, on a 3D graph, and each measurement is displayed to identify and identify the "chemical signature" of the detected compound.

6. A method for stabilizing and accelerating aging of MEMS type sensors (10-13) belonging to a multi-gas digital cartridge (100) according to any one of claims 1 to 5, carried out using a temperature and humidity controlled environmental fine-tuning chamber into which various gaseous substances can be supplied / introduced from certified cylinders / tanks, said method being flexible and adaptable to various operational needs, characterized in that it is used according to the following procedure or a combination of all or some of the following steps: (A) First, turn on the power and let it stabilize at a low temperature, while all the sensing elements (5) are switched on. (B) maintaining said sensitive element (5) at a temperature of about 120° C. for about 4 hours to slowly activate the sensitive layer of the sensors (10-13); (C) In this step, a gradual increase in resistance can be observed until a maximum point is reached, and then a gradual decrease thereafter, which indicates the completion of the first step; (C) a. If the maximum point is not reached, it is necessary to wait a longer time and it is not possible to proceed to the next step unless / until the resistance value reaches the maximum; (D) Then, chromatographic air (CO ２ and exposing the material near the sensitive element to a constant temperature of about 20-22°C and a relative humidity of 50% RH while supplying air (air completely free of fluorine and other chemical impurities) to promote outgassing and stabilization of the material near the sensitive element; (E) A mixture of reducing gases with passivating properties, or air and CO in a 5% ratio. ２ While supplying the mixture in the temperature range of 300-400°C, the sensitive element is temperature-modulated in a sinusoidal cycle with a minimum temperature of 150°C and a maximum temperature of 400°C, the cycle lasting approximately 5 minutes, for approximately 8-12 hours, and in the low-temperature step, chromatographic air is supplied to decontaminate the chamber and normalize the sensor surface, thereby achieving controlled passivation and stabilization of the sensitivity of the sensitive element; (F) leaving the sensors (10-13) at a constant temperature of 320°C for 12 hours while supplying chromatography air with a relative humidity of 25%; (G) Further stabilization of the sensor element (5) and uniformity check of the resistances Rs of all sensors (10-13) are carried out; (H) Each element (5) that does not have the required resistance value is returned to step (F) above, after which new measurements are made on that element (5) until the target value is reached; (I) Turn off the sensors (10-13) that have the desired / correct R value; (J) optionally repeating step (G) for 6 hours and further checking the value of resistance Rs; (K) leaving the sensors (10-13) in the "on" state at a temperature of 350°C for 2 hours in an environment with a conditioning chamber kept at a temperature of 60°C, a chromatographic air flow and a relative humidity of 25%, this procedure aimed at decontaminating the entire cartridge, especially the absorbent material of the multi-layer chemical filter; (L) turning off the sensors (10-13) for 6-12 hours while continuously supplying chromatography air with a relative humidity of 50% at a temperature of 20-22°C; (M) supplying chromatography air having a relative humidity of 50% to recondition the sensing element and the multi-layer chemical filter; (N) Turn on sensors (10-13) at 400°C for 30 minutes; (O) Turn on sensors (10-13) at 250°C for another 30 minutes; (P) leaving the sensors (10-13) in an operational, on-state and allowing the sensors (10-13) to stabilize for 6 hours; (Q) A method characterized by carrying out calibration by supplying specific gases at the required concentrations using certified cylinders / tanks according to the needs of the configuration and operating range of the cartridge to be calibrated.

7. 10. A method for stabilizing and accelerated aging of MEMS type sensors (10-13) belonging to a multi-gas digital cartridge (100) according to the preceding claims, characterized in that it comprises only steps (A), (B), (C), (C)a, (D), (E), (K), (P), and (Q) according to claim 6, and is carried out for a total of about 100 hours.

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