阅读说明：本技术 氧化铝掺杂的金属氧化物气体传感器 (Alumina doped metal oxide gas sensor ) 是由 桑吉布·特里帕蒂 沃尔弗拉姆·西门丁格 于 2019-03-12 设计创作，主要内容包括：一种NOx感测器件,包括衬底、位于衬底上的电介质层、位于电介质层内的加热器；一种用于感测NOx的材料,其中气敏材料包括氧化铝(Al<Sub>2</Sub>O<Sub>3</Sub>)掺杂的导电金属氧化物,优选地是氧化钨、氧化锌、氧化锡、氧化铟、氧化钛、氧化铬和氧化铜。(A NOx sensing device includes a substrate, a dielectric layer on the substrate, a heater within the dielectric layer; a material for sensing NOx, wherein the gas sensitive material comprises alumina (Al) 2 O 3 ) Doped conductive metal oxides, preferably tungsten oxide, zinc oxide, tin oxide, indium oxide, titanium oxide, chromium oxide and copper oxide.)

1. A sensing device, comprising:

a substrate;

a dielectric layer on the substrate;

a heater within the dielectric layer;

a material for sensing a gas, wherein the material comprises alumina (Al)₂O₃) A doped conductive metal oxide.

2. The sensing device of claim 1, wherein the sensing device is NO₂A sensing device.

3. The sensing device according to any one of claims 1 or 2, wherein the conductive metal oxide is tin oxide (SnO)₂)。

4. The sensing device according to any one of claims 1 or 2, wherein the conductive metal oxide is any one of the group comprising tungsten oxide, zinc oxide, indium oxide, titanium oxide, chromium oxide and copper oxide.

5. The sensing device of claim 4, wherein the conductive metal oxide comprises a combination of the metal oxides.

6. The sensing device of any preceding claim, wherein the alumina doping concentration within the conductive metal oxide is from 1% to 10%.

7. The sensing device of claim 6, wherein the conductive metal oxide has an alumina doping concentration of 2.6% to 3%.

8. The sensing device of any preceding claim, wherein the material for sensing a gas is NO₂Has high selectivity.

9. A sensing device according to any preceding claim, wherein the capacitance and/or resistance of the material for sensing a gas is sensitive to the presence of a gas.

10. The sensing device of any preceding claim, wherein the heater has an interdigitated configuration.

11. The sensing device of any preceding claim, wherein:

the substrate comprises an etched portion and a substrate portion;

the dielectric layer comprises a dielectric film, and wherein the dielectric film is adjacent to an etched portion of the substrate; and is

The heater is located within the dielectric film.

12. The sensing device of claim 11, wherein the material for sensing a gas is located in one side of the dielectric film.

13. A sensing array device comprising a two-dimensional array of a plurality of sensing devices according to any preceding claim.

14. The sensing array device of claim 13, comprising

At least one sensing device comprising a material for sensing a gas, the material comprising an alumina-doped metal oxide, wherein the metal oxide is a first metal oxide; and

at least one sensing device comprising a material for sensing a gas, the material comprising an alumina-doped metal oxide, wherein the metal oxide is a second metal oxide;

wherein the first metal oxide and the second metal oxide are different metal oxides.

15. The sensing device according to any preceding claim, wherein the sensing device is configured to operate at a temperature of about 200 ℃.

16. The sensing device according to any preceding claim, further comprising an electrode underlying the gas sensing material.

17. The sensing device of claim 16, wherein the electrode is configured to measure the resistance and/or capacitance of the gas sensing material.

18. The sensing device according to any preceding claim, wherein the sensing device is a CMOS based microhotplate, wherein the heater comprises a CMOS interconnect metal and the dielectric layer comprises a CMOS dielectric layer.

19. A method of manufacturing a sensing device, the method comprising:

forming a substrate;

forming a dielectric layer disposed on the substrate;

forming a heater within the dielectric layer; and

forming a material for sensing a gas, wherein the material comprises aluminum oxide (Al)₂O₃) A doped conductive metal oxide.

20. The method of claim 19, wherein the conductive metal oxide is any one of the group consisting of tin oxide, tungsten oxide, zinc oxide, indium oxide, titanium oxide, chromium oxide, and copper oxide.

21. A method of sensing a gas using the sensing device of any one of claims 1 to 18, the method comprising:

measuring a value of a capacitance and/or resistance of a material for sensing a gas, wherein the material comprises alumina (Al)₂O₃) A doped conductive metal oxide.

Technical Field

The present disclosure relates toA gas sensor, particularly but not exclusively for detecting low concentrations of NO at low temperatures₂The metal oxide gas sensor of (1).

Background

Metal Oxide (MOX) gas sensors are typically based on a metal oxide film deposited on or within a suitable substrate on a sensing electrode. The substrate may be a ceramic substrate or, more recently, a silicon substrate. The deposition process may use thin film techniques such as sputtering, atomic layer deposition or chemical vapor deposition, or thick film techniques such as screen printing, drop coating or ink jetting. In the latter case, the film may be deposited in the form of an ink or paste in which the metal oxide particles are held in suspension in a suitable carrier vehicle, which typically includes an organic solvent. It is generally necessary to remove this support from the powder and any organic compounds to leave the metal oxide uncontaminated. Furthermore, the metal oxide particles typically need to be "fired" to form a mechanically strong, stable and porous structure that is attached to the substrate and the sensing electrode.

It has been shown that this will be based on tin oxide (SnO)₂) Are used in various applications, in particular for volatile organic compound (VoC) detection. Metal Oxide (MOX) gas sensors are inexpensive, reliable, easy to manufacture, and can be tuned to target various gases by modifying the functionality of the MOX by adding various noble metal elements (Pd, Pt, Au, Ru, etc.) and adding other MOXs at very low concentrations.

Detection of NO on Metal Oxide (MOX) platforms₂By controlled addition of a catalyst based on a catalyst having tungsten oxide (WO)₃) The characteristics of the various noble metal catalysts of the material. These NOs₂The sensor operates at high temperatures (> 350 ℃) and has a great cross-sensitivity to various other VoCs present in the environment.

NO previously explained₂The sensor has the following disadvantages:

i) low concentration of NO₂Is very difficult to detect;

ii) the sensor must operate at high temperatures (> 350 ℃). This increases the power consumption of the gas sensor and reduces the efficiency;

iii) the noble metal added to the MOX may react with oxygen or moisture, which leads to baseline instability;

iv) the sensor is sensitive to VoC;

v) the sensor has a high baseline resistance (resistance in the absence of any oxidizing/reducing gas) of > 5M Ω. This results in difficulties in providing the appropriate sensor output to the user in ASIC design; and

vi) since the current sensor comprises a noble metal doped MOX as sensing element, siloxanes can be generated during operation. This can poison the sensor.

CN104820068 and CN1746131 relate to gas sensors using noble metal (e.g. platinum) doped metal oxides. US8043566 relates to multi-component gas systems using chemical sensors. US6071476 relates to an exhaust gas sensor having a sensing element with a catalytic layer, and US6047544 relates to a catalyst unit for purifying exhaust gases of an engine.

Disclosure of Invention

The present disclosure relates to low concentration of NO₂(as low as 50ppb) detection using solid state doping techniques with low concentrations of Al₂O₃(< 3%) for metal oxide materials (e.g., SnO₂) And (6) doping. Preferably, in SnO₂Middle doped alumina (Al)₂O₃) To achieve the desired NO₂And (6) detecting. This allows detection of NO at a heater temperature of 200 ℃₂. The cross-sensitivity of the disclosed sensor to various VoCs is greatly reduced. The sensor is sensitive to NO in all gases present in the environment₂Is very selective.

Compared to prior art sensing devices, the disclosed sensing device will have the following advantages:

i) the sensor is capable of operating at relatively low temperatures of about 200 c.

ii) reduced or no cross-sensitivity to VOCs.

iii) the base resistance of the sensor is in the range of a few K Ω. This simplifies the ASIC design and improves the sensor output for the user.

iv) the potential for sensor poisoning is greatly reduced due to the presence of the siloxane. This is because the gas sensing device of the present disclosure does not use a noble metal and has a low operating temperature.

According to an aspect of the present disclosure, there is provided a sensing device including: a substrate; a dielectric layer on the substrate; a heater located within the dielectric layer; and a material for sensing a gas, wherein the material includes aluminum oxide (Al)₂O₃) A doped conductive metal oxide. In other words, the metal oxide material is doped with a predetermined concentration of alumina.

When the material for sensing gas is exposed to the gas at a specific temperature controlled by the heater, the gas reacts or diffuses, thereby modifying an electrical characteristic, such as resistance (or capacitance), of the material for sensing gas.

This provides an advantage of providing a sensing device with high sensitivity to low concentrations of gas at low device operating temperatures. Since no noble metal need be used in the device, cross-sensitivity to VoC is reduced or absent and siloxane poisoning is reduced.

The sensing device may be NO₂A sensing device.

Alternatively, the conductive metal oxide may be tin oxide (SnO)₂). This achieves the desired NO₂And (6) detecting.

Alternatively, the conductive metal oxide may be any one of the group consisting of tungsten oxide, zinc oxide, indium oxide, titanium oxide, chromium oxide, and copper oxide. The use of noble metals in the device is not required, device poisoning due to siloxanes is reduced, and the baseline instability of the device is reduced. In prior art devices, the noble metal can react with moisture or oxygen, which leads to baseline instability.

The conductive metal oxide may include a combination of the metal oxides. Different metal oxides may be sensitive to different gases or have greater sensitivity at different temperatures. This allows selective detection of gas.

The alumina doping concentration may be 1% to 10% within the conductive metal oxide. Preferably, the alumina doping concentration may be 2.6% to 3% (within the conductive metal oxide). Such low doping concentrations achieve the desired NO₂And (6) detecting.

The material for sensing the gas may be for NO₂Has high selectivity. This allows detection of low concentrations of NO₂。

The capacitance and/or resistance of the material used to sense the gas may be sensitive to the presence of the gas. Advantageously, this allows the gas to be detected by measuring the capacitance and/or resistance of the material used to sense the gas.

The heater may have an interdigitated configuration.

According to another aspect of the present disclosure, there is also provided a sensing device as described above, wherein the substrate may comprise an etched portion and a substrate portion; the dielectric layer may include a dielectric film, and the dielectric film may be adjacent to the etched portion of the substrate; and the heater may be located within the dielectric film. The use of a dielectric film provides thermal isolation for the heater and enables the gas sensing device to operate at high temperatures.

The film may be formed by etching back the supporting semiconductor substrate. The film cavity may have near-vertical sidewalls (formed by using Deep Reactive Ion Etching (DRIE)) or may have sloped sidewalls (formed by using an anisotropic or crystallographic etching process such as potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH)). Alternatively, the film can be formed by front-side etching.

The material for sensing the gas may be on one side of the dielectric film.

According to another aspect of the present disclosure, there is also provided a sensing array device comprising a two-dimensional array of a plurality of sensing devices as described above.

The sensing array device may include at least one sensing device comprising a material for sensing a gas, the material comprising an alumina doped metal oxide, wherein the metal oxide is a first metal oxide; and at least one sensing device comprising a material for sensing a gas, the material comprising an alumina-doped metal oxide, wherein the metal oxide is a second metal oxide. The first metal oxide and the second metal oxide may be different metal oxides. This has the advantage that the first metal oxide and the second metal oxide may be sensitive to different gases. This allows the device to sense more than one gas and selectively detect the gas.

The sensing device may be configured to operate at a temperature of about 200 ℃. The advantage is that the sensing device has lower power consumption and higher efficiency than prior art sensing devices. This low operating temperature also reduces the presence of siloxane in the device and thus reduces the likelihood of the sensing device being poisoned by siloxane.

The sensing device may further comprise an electrode underlying the gas sensing material. The electrodes may be configured to measure the resistance and/or capacitance of the gas sensing material. The measurement depends on the presence of gas in the sensing device and is therefore used for detecting gas.

The sensing device may be a CMOS based micro-hotplate, wherein the heater comprises a CMOS interconnect metal and the dielectric layer comprises a CMOS dielectric layer. CMOS technology offers many advantages such as lower cost for large-scale manufacturing, integration of circuits on the same chip, and good device-to-device reproducibility.

The sensing device may also include a passivation layer to protect the device.

According to another aspect of the present disclosure, there is provided a method of sensing a gas using a sensing device as described above, the method comprising:

measuring a value of a capacitance and/or resistance of a material for sensing a gas, wherein the material comprises alumina (Al)₂O₃) A doped conductive metal oxide.

According to another aspect of the present disclosure, there is also provided a method of manufacturing a sensing device, the method including:

forming a substrate;

forming a dielectric layer disposed on the substrate;

forming a heater within the dielectric layer; and

forming a material for sensing a gas, wherein the material comprises alumina (Al)₂O₃) A doped conductive metal oxide.

The conductive metal oxide may be any one of the group consisting of tin oxide, tungsten oxide, zinc oxide, indium oxide, titanium oxide, chromium oxide, and copper oxide.

Drawings

Some preferred embodiments of the present disclosure will now be described, by way of example only, and with reference to the accompanying drawings, in which:

FIG. 1 shows a structure having Al₂O₃A cross section of a gas sensor of a doped metal oxide gas sensing material;

FIG. 2 shows a structure having Al₂O₃A cross-section of an alternative gas sensor of a doped metal oxide gas sensing material, wherein the substrate has no etched portion;

FIG. 3 shows an exemplary flow chart outlining a method of manufacturing a gas sensor; and

FIG. 4 shows a semiconductor device having Al₂O₃Doped SnO₂The sensor of (2) performs a gas function test.

Detailed Description

In general, the present disclosure relates to gas sensing devices that include a gas sensing material that includes alumina (Al)₂O₃) A doped metal oxide gas sensing material. This allows for an increase in, for example, NO to the environment in the event of a decrease in the sensor operating temperature₂The sensitivity of the particular gas. It will be understood that the gas sensing material is a powder and a material carrier mixed together. When it is exposed to a sufficiently high temperature, the material formulation is capable of being converted into a porous sensing structure or sensing layer, which is referred to as a gas sensing material. Generally, the metal oxide material is formed from a formulation that includes a metal oxide powder (particles) and a carrier solvent. When the metal oxide powder and the carrier solvent are mixed together, a paste/ink is formed,which is then deposited on the sensing electrode. After deposition, the carrier solvent evaporates and/or decomposes from the ink/paste at elevated temperatures (e.g., about 300 ℃). This is then followed by a ramp to a higher temperature, for example around 600 ℃, which forms a stable porous sensing material comprising metal oxide. In the present disclosure, the sensing material is doped with aluminum oxide (Al)₂O₃) For NO₂And (6) detecting.

FIG. 1 shows a structure having Al₂O₃A cross-section of a gas sensor of a doped metal oxide gas sensing material. The gas sensor includes a dielectric film 8 supported by a semiconductor substrate 1 having an etched portion and a substrate portion. In general, dielectric film region 8 is immediately adjacent to the etched portion of substrate 1. The dielectric film region 8 corresponds to a region above the cavity of the substrate 1. The heater 2 and heater track (or metallization structure) 3 are embedded within a dielectric layer 5, with the heater 2 being formed within a dielectric film region 8. The electrode 7 is formed on top of the dielectric film 8. The electrode 7 is connected to a gas sensing material 17 which has been grown or deposited on the membrane 8. A passivation layer 6 is formed on top of the dielectric layer 5.

A gas sensing material 17 is disposed on the electrode 7. The electrodes 7 are configured to measure the resistance and/or capacitance of the gas sensing material 17.

The gas sensing material 17 can be alumina (Al)₂O₃) Doped tin oxide (SnO)₂). Alternatively, the gas sensing material can be Al₂O₃Doped metal oxides, e.g. tungsten oxide (WO)₃) Zinc oxide (ZnO), indium oxide (ln)₂O₃) Titanium oxide (TiO), or copper oxide (CuO). The doping concentration is a low doping concentration using solid state doping techniques. The doping concentration is preferably 2.6% to 3% Al₂O₃However, in metal oxide materials, the doping concentration can be 1% to 10% Al₂O₃Any value of (c).

The sensing material 17 is such as to allow the detection of low concentrations of nitrogen dioxide (NO)₂). Due to the low concentration of alumina doping of the metal oxide gas sensing material, the gas sensor is capable of detecting down to, for example, one billionNO at a concentration of 50(ppb)₂. Gas sensor pair NO at a temperature of about 200 deg.C₂Has high selectivity. Around this temperature, the gas sensor has a low sensitivity to the presence of other volatile organic compounds (VoC) and reducing gases. Since the gas sensing material does not include a noble metal and the operating temperature of the gas sensor is low, the possibility of poisoning the gas sensor by siloxane is reduced.

FIG. 2 shows a structure having Al₂O₃A cross-section of an alternative gas sensor of a doped metal oxide gas sensing material. Many of the features of fig. 2 are similar to those of fig. 1 and therefore have the same reference numerals. In the present embodiment, the substrate 1 has no etched portion. The dielectric layer 5 has no dielectric film. The heater 2 and the heater track (or metallization structure) 3 are embedded within a dielectric layer 5. An electrode 7 is formed on top of the dielectric layer 5. The electrode 7 is connected to a gas sensing material 17 which has been grown or deposited on the dielectric layer 5. A passivation layer 6 is formed on top of the dielectric layer 5.

Fig. 3 shows a flow chart outlining a method of manufacturing a gas sensor. The method comprises the following steps:

1. in S100, starting from a semiconductor substrate. The substrate includes an etched portion and a substrate portion. In an alternative embodiment, the substrate is not etched.

2. In S105, a dielectric layer is formed on the substrate. The dielectric layer includes a dielectric film adjacent to the etched portion of the substrate. The heater is formed within the dielectric film. Alternatively, the heater is formed in a dielectric layer on the substrate.

3. In S110, Al is formed using solid powder synthesis₂O₃Doped metal oxide powders. The powder was calcined at 700 ℃ for 4 hours to obtain a suitable NO₂Control of particle size and stability of the assay. The powder is made into a paste by solid loading of, for example, 40% carrier.

4. In S115, the paste is deposited onto the dielectric film at 100 ℃ using an inkjet printer with a dot size of, for example, 220 microns.

5. In S120, the film was electrically annealed at 700 ℃ for 2 hours to obtain the desired film texture. This is followed by gas testing at various temperatures to optimize the sensor drive mode.

In S110, Al is formed using solid state powder synthesis₂O₃Doped metal oxide powders. The method comprises the following steps:

from SnCl precursor gel₄And ammonia solution. For the tin tetrachloride (SnCl)₄Ultrapure) is hydrolyzed with water and the precursor gel is obtained by mixing the hydrolysate with an ammonia solution (ultrapure).

The mixture was repeatedly washed with deionized water to remove unwanted chloride and ammonium ions.

Determination of the SnO of the gel by thermogravimetric analysis₂And (4) content.

Using the results, the amount of alumina required was calculated, and aluminum nitrate (Al (NO) was weighed out separately₃)₃Ultra pure).

Mixing aluminum nitrate Al (NO)₃)₃Dissolved in deionized water.

Mixing Al (NO)₃)₃The solution was mixed with a stoichiometric amount of aqueous ammonia solution to obtain a white precipitate.

The gel is washed with deionized water to remove unwanted nitrate and ammonium ions.

The two precipitated gels were mixed with a stirrer for 30 minutes.

Followed by drying in a drying oven at 150 ℃ overnight to obtain white crystals.

The white crystals were ground thoroughly (wet) in a mortar for 15 minutes.

The powder was calcined in a tube furnace at 800 ℃ for several hours under ambient atmosphere to give a white powder.

FIG. 4 shows a semiconductor device having Al₂O₃Doped SnO₂The sensor of (2) performs a gas function test. Testing four sensor component pairs including methane, NO₂Acetone, toluene, CO, ethanol and H₂Sensitivity of 7 gases. The test was conducted at 15% background relative humidity and 85% background relative humidityCarried out under humidity. The results show that at a heater temperature of about 200 ℃, the sensor couples very low concentrations of NO present in the test chamber₂Is highly selective and insensitive to the other six gases present. Tests were performed in DC mode to correctly understand sensor behavior. Humidity has little or no effect on the selectivity of the sensor and the sensitivity of the sensor.

Reference numerals

1. Semiconductor substrate

2. Embedded heater

3. Heater track or metallization structure

5. Dielectric layer

6. Breathable layer

7. Electrode for electrochemical cell

8. Dielectric film region

17. Sensing material

It will be understood by those skilled in the art that in the foregoing description and the appended claims, positional terms such as "above", "overlapping", "below", "transverse" and the like are formed with reference to conceptual illustrations of the apparatus such as are shown in standard cross-sectional perspective views and in the drawings. These terms are used for ease of reference and are not intended to be limiting. Accordingly, these terms should be understood to refer to the device in the orientation as shown in the drawings.

While the present disclosure has been described in terms of the preferred embodiments set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to these embodiments. Those skilled in the art will be able to make modifications and substitutions in light of the present disclosure which are contemplated to be within the scope of the appended claims. Each feature disclosed or illustrated in this specification may be incorporated in the disclosure, either individually or in any suitable combination with any other feature disclosed or illustrated herein.