The present disclosure generally relates to a gas detection device, particularly, for detecting poisonous gases released from domestic and industrial area. The device is based on specially designed sensors assembly to detect effluent gases with ease.
Background of the Art:
There are so many environmental and health issues because of hazardous and poisonous gases like Carbon Monoxide (CO), Hydrogen Sulphide (H2S), Nitrogen dioxide (NO2), Sulphur dioxide (SO2) and many more. In domestic and industrial areas, there are highly flammable gases such as LPG, Methane, Butane, Propane etc. The emission of nitrogen dioxide (NO2) which has a bad effect on public health and the environment is motivating extensive scientific and technological research in the field of NO2 sensing. The detection of NO2 is quite necessary because of its characteristic pungent odour, toxicity and dangerousness, even at very low concentration. Human being and other living organism are affected by this gas as it can cause mental disorder, incurable diseases that even can cause death, so safety precautions need to be taken. To prevent these issues, we need a gas sensor. Gas sensor is basically used to detect these types of harmful gases.
The gas sensors known in the art have issue associated with them such as substandard detection at room temperature.
US 5624640A discloses a semiconducting metal oxide layer which is deposited on a ceramic substrate and a converter layer is suitably constituted of titanium oxide (TiO) and/or zirconium oxide (Zr02) and/or silicon oxide (Si02) and/or aluminum oxide (AO) and has a platinum content of from 0.01 to 20 weight percent. However, said device shows poor gas response for <180°C operating temperature.
US 2012/0047994 discloses a nitrogenous gas sensor comprises a piezoelectricity plate which has a sensing surface and two transducers. This application however does not disclose the device as disclosed. Further, the detection limit of this device is more than lOOppb. Whereas, the device as developed in the present invention have a detection limit of 10-100ppb.
Further, the gas detection devices in the art are complex to prepare, time consuming and are expensive. Whereas the device of the present disclosure is simple, time reducing and cost efficient.

To resolve the problem existing in the art i.e. inaccurate detection at room temperature and extreme conditions, the inventors the manufacture a device which is efficient in detecting gases poisonous to environment accurately and rapidly.
Summary:
The present disclosure relates to a gas detection device, particularly, for detecting poisonous gases released from domestic and industrial area. The device is based on specially designed sensors assembly to detect effluent gases with ease. Specifically, the present disclosure relates to device for detecting gases, the device comprising;
a substrate (LI) layer;
an insulating layer (L2); wherein said insulating layer is configured on the substrate;
a sensing layer (L3) with a resistance characteristic which changes in the presence of a target gas in ambient air;
wherein the sensing layer is configured to adsorb the target gas on its surface and cause a resistance change across the same; and
an electrode(L4) arranged in a metal-semiconductor-metal pattern; wherein the electrode is configured to provide the electrical connection and measure the change in resistance and confirm the presence of target gas.
The device of the present invention is also manufactured without a substrate.
The present invention provides method of manufacturing said device and uses thereof.
Brief description of drawings:
The disclosure may be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:
Figure 1 (a) shows side view of the gas detection device; (b) shows angle view of the gas detection device; (c) shows top view of the gas detection device;
Figure 2 shows side view of the gas detection device without substrate layer (LI) and substrate layer (L2).
Figure 3 shows flow chart of device analysis;

Figure 4 shows flow chart of device fabrication, characterization and testing;
Figure 5 shows flow chart of device demonstration.
Figure 6 shows circular shape interdigitated pattern.
Figure 7 shows round square shape interdigitated pattern.
Figure 8 shows archimedean spiral shape interdigitated pattern.
Figure 9 shows XRD image of WO3 nanomaterial.
Figure 10 shows Raman spectra of WO3 nanomaterial.
Figure 11 shows FESEM images (a) & (b) WO3 nanoparticles and (c) & (d) WO3-PANI nanocomposite.
Figure 12 shows ED AX analysis of WO3 nanomaterial.
Figure 13 shows sensing mechanism for NO2 gas, (a) and (b) represents the energy band in absence and presence of NO2 gas.
Figure 14 shows sensor response of pure WO3 nanomaterial and WO3-PANI nanocomposite with different NO2 gas concentration.
Figure 15 shows response and recovery for the pure WO3 nanomaterial and WO3-PANI nanocomposite at 100 PPM NO2 gas concentration.
Figure 16 shows sensor response for 100 PPM NO2 gas concentration towards different electrode shape (Shape 1- E-shape interdigitated pattern, Shape 2- Circular interdigitated pattern, Shape 3- Round square pattern, and Shape 4- Archimedean spiral pattern).
Figure 17 shows selectivity of the WO3-PANI nanocomposite-based gas sensor towards different target gasses.
Figure 18 shows repeatability of the gas sensor when exposed to 100 ppm NO2 gas concentration.
Figure 19 shows stability of the WO3-PANI nanocomposite-based gas sensor towards 100 ppm NO2 gas concentration.

Detailed Description:
The present disclosure relates to a gas detection device, particularly, for detecting poisonous gases released from domestic and industrial area. etc. The device of the present invention is selective for gases selected from Carbon Monoxide (CO), Hydrogen Sulphide (H2S), Nitrogen Oxides (NOx), Sulphur Oxides (SOx), Carbon dioxide (CO2), Ammonia (NH3). Specifically, the device of the present disclosure is highly selective for Nitrogen Oxides, preferably Nitrogen Dioxide (N02).
The device of the present disclosure has the ability of detecting the harmful gases both at room temperature as well as at high temperature. Further, said device is reusable as well.
The device, when designed for high temperature, it is based on specially designed sensors assembly to detect effluent harmful gases with ease.
In an embodiment, the present disclosure provides a device for detecting gases, the device comprising;
an insulating layer (L2);
a sensing layer (L3) with a resistance characteristic which changes in the presence of a target gas in ambient air;
wherein the sensing layer is configured to adsorb the target gas on its surface and cause a resistance change across the same; and
an electrode(L4) arranged in a metal-semiconductor-metal pattern; wherein the electrode is configured to provide the electrical connection and measure the change in resistance and confirm the presence of target gas.
In another embodiment, said sensing layer is coated on an insulating layer(L2) of a substrate(Ll).
In an embodiment, the present invention provides a device for detecting gases, the device comprising;
a sensing layer (L3) with a resistance characteristic which changes in the presence of a target gas in an ambient air;

wherein the sensing layer is configured to adsorb the target gas on its surface and cause a resistance change; and
an electrode(L4) arranged in a metal-semiconductor-metal pattern; wherein the electrode is configured to measure the change in resistance and confirm the presence of target gas.In yet another embodiment, said sensing layer is made of polyaniline (PANI) and tungsten trioxide (WO3) nanoparticle.
In another embodiment, said electrode is assembled on the sensing layer.
In an embodiment, said sensing layer is made of polyaniline (PANI) and tungsten trioxide (W03) nanoparticle.
In yet another embodiment, said WO3 is in concentration range of 0.1-25% of PANI.
In one embodiment, the electrode is selected from palladium, gold, platinum and the like.
In another embodiment, substrate is Si-wafer.
In yet another embodiment, the insulating layer is Si02.
In one embodiment said target gas is selected from Carbon Monoxide (CO), Hydrogen Sulphide (H2S), Nitrogen Oxides (NOx), Sulphur Oxides (SOx), Carbon dioxide (CO2), and Ammonia (NH3).
In another embodiment, said target gas is NO2.
In yet another embodiment, the electrode is assembled on sensing layer by masking the same in an interdigitated pattern.
In one more embodiment, said interdigitated pattern is of shape selected from E-shape, circular, round square and Archimedean spiral.
In another embodiment, said E-shape pattern (A) has:
two contact pads (1, 2) with extended arms (la, 2a), respectively; the extended arm 1(a) has three extended arms (lb), (lc) and (Id) and the extended arm (2a) has three extended arms (2b), (2c) and (2d);
In yet another embodiment the extended arms (are in "E" shape and the extended arms (2b), (2c) and (2d) are in a "mirror E" shape.

In an embodiment the arms (lb), (lc), (Id) and (2b), (2c), (2d) face each other in a manner that further extended arms (E) of (1) and further extended arms (Mirror E) of (2) results in a pattern having alternate extensions having a gap of around 0.2 mm.
In another embodiment, the arms are in a pattern:
(2b) | (lb) | (2c) | (lc) | (2d) | (Id).
In yet another embodiment, said circular interdigitated pattern has:
two contact pads (3, 4) facing each other with extended arms (3a, 4a), respectively; the extended arms 3(a) and 4 (a) have points which have further extended arms;
In an embodiment, said points are A and B on extended arm 3(a) and C, D and E on extended arm (4a).
In another embodiment, said point A has the extended arms (3b) and (3c).
In one more embodiment, said point B has extended arms (3d) and (3e).
In another embodiment, said point C has extended arms (4b) and (4c).
In yet another embodiment, said point D has extended arms (4d) and (4e).
In one embodiment, said point E has extended arms (4f) and (4g).
In another embodiment, said round square interdigitated pattern has:
contact pads (5) and (6) facing each other and arms (5a) and (6a) extending respectively from said contact pads;
where said extended arms are coiled with other to form a concentric square. In yet another embodiment, said Archimedean spiral interdigitated pattern has
contact pads (7) and (8) facing each other and arm (7a) and (8a) extending respectively from the contact pads.
In an embodiment, said sensing layer has a detection limit between 10-100 parts per billion (ppb).
In an aspect, the present invention provides a method of manufacturing a device for detecting gases, wherein the method comprises the steps of:

a) synthesizing composite of PANI and WO3;
b) depositing the composite of PANI and WO3 on the insulating layer formed on substrate at a deposition rate of 1500-4000 rpm for 10 sec to 15 min;
In an embodiment, said substrate is oxidized to form an insulating layer;
In an embodiment, said substrate is Si wafer and is 4 inches in diameter and 525 um in
thickness.
In another embodiment, the insulating layer formed in SiCh;
In yet another embodiment synthesis of composite of PANI and WO3 comprises steps of:
dissolving polyaniline powder in N-methyl- 2-pyrolidone (NMP) and stirring the solution for 5 hours; filtering the solution; - adding 1 % WO3, 5% WO3, 10% WO3, and 20% WO3 in filtered solution of undoped PANI in NMP and stirring it for 5 h;
In an embodiment, said deposition is done by using technique selected from Hot press method and spin coating.
In yet another embodiment, the present invention provides a method of detecting a target gas, wherein said method comprises the steps of:
keeping the device of the present invention in a closed gas chamber;
providing the target gas;
a fixed bias voltage of 1-5V have been applied to the device
the source meter measures the resistance of the device and the change in resistance
confirms presence of the gas.
The device of the present disclosure is capable of detecting the minimal amount of harmful gases present in the atmosphere.
The present disclosure provides gas detection device comprising sensing layer made of composite of PANI and Nano particle of Tungsten trioxide (WO3); electrode selected from Palladium , Gold, platinum and the like. By "the like" it is meant for the present specification that metal which similar and chemical and properties and shall behave in similar manner; and a substrate selected from Si wafer and Alumina.

The insulating layer (SiCh) is formed when Si wafer is used as substrate. Otherwise, the sensing layer is directly deposited on the wafer, when the substrate used is selected from Sapphire, Quartz etc.
Polyaniline (PANI), as an intrinsically conducting polymer. It is a cost-effective conductive polymer which can form composite with other metal oxides very easily. Polyaniline have following advantages:
offers ease of its synthesis, low-cost monomer, - tunable properties
high environmental stability.
The tungsten trioxide (WO3) thin films happen to be one of the potential materials in gas sensing owing to its ability to sense hazardous gases such as nitrogen dioxide (NO2). The nano structure W03 is the mesoporous material having an advantage of its increasing specific surface areas.
Some of the important advantages of tungsten trioxide (WO3) are as follow:
low cost, small size,
measurement simplicity,
durability,
ease of fabrication,
low detection limits (< ppm levels).
The combination of PANI and WO3 has the potential to improve sensitivity of detection at room temperature and retain the advantages of its constituents with increased surface functionalities for gas detection. Further, the weight % of PANI in composite is less as it enables detection of small change in the conductivity from which the response time can be improved.
In gas detection device of the present disclosure, Schottky pattern (Metal-Semiconductor-Metal) have been developed which measures the changes in resistance due to adsorption process.
The adsorption process here means the accumulation of negatively charged species such O2", 0", O2- on the sensing layer thereby rendering the sensing layer as negatively charged. Other

gases such as oxidizing or reducing gases when adsorbed on the surface of the device gives rise to charge transfer. Depending on the same, the electronegative species such NO2 or NH3 are attracted to Charge species on the sensing layer and the resistance of the film will change due to formation of such adsorbent layer.
Usually in the field effect transistor detection which is used by most of the sensors known in the art, the focus is mainly on change in capacitance due to change in relative permittivity in adsorption process. The conductivity will change either by resistive sensing approach or capacitive sensing approach. But in resistive sensor very small change in adsorption process can be measured and hence the detection limit is improved.
The device of the present invention represented by Figure 1 (a) (Side view) exhibits four layers. The first layer (LI) is of substrate i.e. Si Wafer; Second layer (L2) is composed of an insulator i.e. SiCh; Third layer (L3) is the sensing layer having composite of PANI and WO3; and Forth layer (L4) represents electrode protrusions.
Figure 1(b) represents angle view of the device of the present invention, where it is clearly shown that the electrode is placed on the surface of the sensing layer.
Figure 1(c) represents top view of the device where the electrode is mounted on such way at the top of the sensing surface L3 that the shape formed is an interdigitated pattern. Two squares i.e. contact pads (1) and (2) have extended arms (la) and (2a) respectively. These arms extend further to divide into three extended arms. The further extended arms of (la) are (lb), (lc) and (Id) Said extended arms are in "E" shape. The further extended arm of (2a) are (2b), (2c) and (2d) Said extended arms are in a "mirror E" shape. These arms face each other in such a manner that further extended arms (E) of (1) and further extended arms (Mirror E) of (2) results in a pattern having alternate extensions having a gap of around 0.2 mm. Particularly, the arms appear to be in following pattern:
(2b) I (lb) I (2c) I (lc) I (2d) I (Id)
The dimensions of (1) and (2) are 2.0mmX2.0mm. The Length of (la) and (2a) are 1.0mm. E and Mirror E shaped extended arms have dimensions of 6.0mm X 0.4mm. Collectively, the arrangement has a dimension of 12.6mm X 3.4mm.

A further embodiment of the present invention in define in Figure 2 (Side view) which exhibits only two layers out the four layers defined earlier. The first layer (L3) is the sensing layer having composite of PANI and WO3; and Forth layer (L4) represents electrode protrusions.
Further, the device of present invention may have other possible shapes and exists in various other possible patterns such as circular, round square, Archimedean spiral etc. (Fig. 6-8).
Figure 6 represents circular shape of interdigitated pattern where the electrode has two contact pads (3) and (4), each having one extended arm (3a) and (4a), respectively. The extended arm (3a) has a ring (3f) at the end. Further, points A and B of extended arm (3a) have two further extended arms in shape of arc. At point A, the extended arms are (3b) and (3c) and at point B, the extended arms are (3d) and (3e). Similarly, points C, D and E of extended arm (4a) have two further extended arms in shape of arc. At point C, the extended arms are (4b) and (4c); at point D, the extended arms are (4d) and (4e) and at Point E the extended arms are (4f) and (4g). This pattern too requires facing of the arms towards each other so as to form a concentric circle.
The diameter of (3a) and (3b) is 1mm. The thickness of all the arms is 0.4mm and the thickness of gap between them is 0.2mm. The diameter of inner circle formed by (3f) is 0.4mm.
Figure 7 represents round square pattern, wherein contact pads (5) and (6) face each other and have extended arms (5a) and (6a). The extended arms are coiled with other to form concentric square.
The contact pads (5) and (6) have a dimension of 1mm X 1mm. Thickness of extended arms (5a) and (6a) is 0.4mm and thickness of gap between them is 0.2mm.
Figure 8 represents Archimedean spiral pattern, wherein contact pads (7) and (8) face each other and have extended arm (7a) and (8a).
The contact pads (7) and (8) have a diameter of 1mm. Thickness of extended arms (7a) and (8a) is 0.4mm and thickness of gap between them is 0.2mm.
The device of the present disclosure has a dimension of 15mmX5mm, wherein the Si wafer has thickness of 525 micron, Si02 layer has layer of thickness of 100 nm, PANI/W03 composite has a thickness of lOnm and electrode as thickness of 50nm.
The present invention has been illustrated through the following examples and it should be construed of limiting the scope of the instant invention.

Examples:
Example 1:
Fabrication of Sensing Layer:
The composite of PANI and WO3 is prepared by using solvent ethylene glycol. The composite (sensing layer) is taken in a concentration of 0.2 to 0.5 molar and mixed with 10 ml of ethylene glycol. Further, a drop of 200 microliters of the sensing layer is used while spin coating. In the spin coating, the spinning is basically done from 1200rpm to 4000 rpm for obtaining a film of 10-100 nm thickness. However, it is pertinent to mention here that the concentration range provided in this example are only for illustration and should not be construed as restricting the scope of invention.
Example 2:
Method of manufacturing and characterization of device:
Si wafer is obtained commercially. The size of the same being lOOnm in diameter and 525 mm in thickness. The Si wafer is then wet oxidized and oxidized layer of the silicon i.e. Silicon dioxide (SiCh) is generated so that an insulating layer is created on the top of the Si- wafer. The insulating layer is formed to generate gap between the metals (substrate and semiconductor -WO3/PANI) for better detection of resistance change.
The composite of PANI/WO3 is deposited on the SiChby conventional method i.e. spin coating system, as discussed in Example 1.
Further, the characterization of the device is done by AFM system, FESEM and HRTEM (for morphology and topography), Photoluminescence, Raman Spectroscopy and UV spectroscopy (for Band gap and defects analysis), XRD (crystalline size measurement and stress analysis), IV source meter with gas sensing chamber (for gas sensitivity, response time).
2.1. Synthesis of WQ3 Nanoparticle
WO3 nanoparticle were synthesized by a hydrothermal process. Na2W04 2H2O, HC1, and NaCl aqueous solution were used as the precursor. In a typical synthesis, 0.850 g of Na2W04 •2H2O and 0.300 g of NaCl were dissolved in 20 mL of deionized water. Subsequently, 12 M HC1 was slowly dropped into the solution with stirring until the pH value of the solution

reached 1.5. Then, the solution was transferred into a Teflon-lined 100 mL capacity autoclave. Hydrothermal reaction was carried out at 200° C for 26 hrs. in an oven. After the autoclave cooled to room temperature, a white product was obtained. At last, W03 nanoparticles were synthesized after repeatedly washing the product with deionized water.
The growth mechanism of the WO3 nanoparticle can be explained according to the following reactions:
Na2W04 + 2HC1 -> H2WO4 + 2NaCl (1)
H2W04^ WO3 (crystal nucleus) + H20 (2)
WO3 (crystal nucleus)-^ WO3 nanoparticle (3)
2.2. Synthesis of polyaniline (PANI)
Polyaniline was synthesized by polymerization of aniline in the presence of hydrochloric acid (acts as a catalyst) using ammonium peroxidisulphate (acts as an oxidizing agent) by chemical oxidative polymerization method. For the synthesis, we took 0.1M of aniline and 1.0M of HC1 in double distilled water. These were stirred in a double wall flask at temperature 0±1° C. The solution (140 ml) of ammonium peroxidisulphate (0.1M in double distilled water) was added drop by drop in the doublewall flask during the stirring. After 6 h, stirring was stopped and the solution was filtered in Butchner funnel and the residual was washed 3-4 times with distilled water in the same funnel. The resultant residual was dried in oven at 70° C for 24 h and grinded in mortar pestle to get powder form of HCl-doped conductive polyaniline. The HCL doped conductive polyaniline powder was insoluble in any organic solvent so it was treated with ammonia solution (NH4OH) to get undoped polyaniline which was soluble in organic solvent like: N-methyl-2-pyrolidone. The undoped polyaniline was washed with methanol to remove the oligomers and the residual was dried in oven at 60° C for 30 h and ground in mortar pestle to get an undoped polyaniline in powder form.
2.3. Synthesis of WQ3-PANI nanocomposite
The undoped polyaniline powder (lOOmg) was dissolved in N-methyl- 2-pyrolidone (NMP). The solution was stirred for 5 h and filtered with a Whatman filter paper having pores of size of few microns. The solution of filtered undoped PANI was poured in a petri dish and dried at 60° C. The WO3 composites with undoped PANI were prepared by adding 1% WO3, 5% WO3,

10% WO3, and 20% W03 in filtered solution of undoped PANI in NMP and stirring it for 5 h. Films of the composite were prepared on substrate by spin coating method at 1500rpm for 30
s.
The WO3/PANI composite of the present application was also deposited using hot press method, the powder mixture was kept in a stainless-steel die (integrated circuit) in hot press machine. Then the mixture has been heated for 15 min duration and at 200 °C operating temperature followed by 5 tones pressure applied for the same time. The temperature of the die was brought down to room temperature by running cold water and then the stress was released. The flexible sensor was then ready for further deposition process (i.e. electrode deposition).
The electrode deposition on the sensing layer was done using shadow mask technology known to a person skilled in the art.
Example 3:
Results and discussion
3.1. Structural Characterization and Growth Mechanism of WO3 Nanoparticle Figure 8 shows the XRD pattern of the WO3 nanomaterial. The diffraction peaks observed at 14.001°, 22.789°, 24.374°, 26.845°, 28.217°, 33.611°, 36.573°, 49.947°, 55.325°, 55.567°, 58.354°, and 63.474° is correspond to the (010), (001), (110), (011), (020), (111), (021), (220), (022), (221), (040), (041) crystal phases of WO3 respectively. All of the peaks can be indexed to the hexagonal phase of WO3 structure (JCPDS 98-003-2001) and no nonstoichiometric tungsten oxides (WO3-X) and tungsten oxide hydrates (WO3 • xH20) were detected, indicating pure WO3 was obtained. Strong diffraction peaks also indicate the good crystallinity of the hydrothermal product.
The Raman spectrum of the pure W03 powder (Fig. 9) shows sharp signals at 154, 239, 665, 809, 934 cm"1 and a very weak peak at 330 cm"1. The signals at 239 and 330 cm"1 correspond to O-W-0 bending modes of bridging oxygen, and the signals at 809 cm"1 and in the 665 cm" 1 range are the corresponding stretching modes. The peak at 934 cm"1 corresponds to the terminal W O bond which forms on tungsten ions with low coordination numbers as in amorphous W03. Rampaul et al. reported the Raman spectrum of sol-gel synthesized W03 films and observed a prominent signal at 924 cm"1 corresponding to amorphous W03, whereas

the Raman peaks corresponding to crystalline W03 at 304, 717 and 807 cm"1 appeared less intense. This reveals the less crystalline nature of the sol-gel derived materials unless they are calcined at a sufficiently high temperature. Habazaki et al. reported the Raman spectra of annealed electrodeposited WO3 films at several temperatures. The intensity of the Raman peaks corresponding to crystalline WO3 increases with annealing temperature and the most intense peak is positioned at 809 cm"1 which agrees well with the present study.
The cross-sectional FESEM images have been obtained at a magnification of 50.00 kX and 25.00 kX for the scale of 200 nm and lum respectively. Fig. 10 shows FESEM images of pure WO3 and PANI- WO3 (10%) composite. The SEM image of composite shows that there is no agglomeration of WO3 particles in PANI matrix and there is a uniform distribution of the WO3 particles in the PANI matrix. Figure 11 reprints the ED AX analysis of W03 nanomaterial and it is clear from the figure is the weight percentage of W is almost 3 time the weight percentage ofO.
3.2 Gas Sensing Analysis
Gas sensing is based on the change of resistance of the material because of the electronic and chemical interaction in-between material and gas. The chemical interaction comprises the target gas adsorption on the surface of catalyst then migration to the surface of zinc oxide, which outcomes in the exploration for the target gas. The sensing mechanism of WO3-PANI nanomaterial-based sensor in the presence of NO2 gas has been shown in figure 12.
In the sensing mechanism when WO3-PANI nanomaterial-based sensor is explicated to air, oxygen species adsorb on material surface to make anions of chemisorbed oxygen (Oads-) by occupying the electrons from conduction band. It further results to form a space charge region, i.e. depletion region, on material surface which outcomes in an increase in sensing material resistance.
02(gas) + e~^ 02"(ads) (4)
02(gas) + 2e~^ 20"(ads) (5)
When this WO3-PANI nanomaterial based sensor is exposed in nitrogen dioxide gas at some operating temperature, the adsorbed NO2 interacts with the oxygen anions present in the surface; the reaction can be explained as follows:
N02(gas) + e~ -> N02"(ads) (6)

N02"(ads)+ 0-(ads)+2e"^NO(gas)+202-(ads) (7)
02"(ads) + 02 -> 20"(ads) (8)
20"(ads) ^02"(ads)+e- (9)
02"(ads)^ 02(gas)+e" (10)
NO(gas)+0" -> N02(gas) + e" (11)
Due to this charge transfer process the concentration of electrons increases. That is why
resistivity of the WO3-PANI nanomaterial based sensor decreases eventually; this mechanism
is used for the detection of N02 gas.
The sensor response with respond and recovery time for different concentration of N02 gas is shown in fig. 13. The response of the sensor was calculated as:
Sensor Response S=Rg/Ra (12)
From the figure it is clear that the sensor is very sensitive even at very low gas concentration. The detection limit was found 50 PPB for WO3-PANI nanocomposite. The highest response was calculated for WO3-PANI nanocomposite at 100 PPM N02 gas concentration. The corresponding respond time and recovery time was found 8 sec and 42 sec respectively. The sensing test was performed twice for a sample and results were very similar. This demonstrates that WO3-PANI nanocomposite gas sensor has the reproducibility.
The gas sensor response for the WO3 nanoparticles and WO3-PANI nanocomposite at 100 PM N02 gas concentrations was found to be 124 and 424 Rg (resistance in gas)/Ra resistance in air respectively (Figure 14). The respond time was measured 18 sec and 8 sec respectively.
The sensor response of the device of the present inventor was observed for different shapes of electrode pattern as shown in figure 15. Among the entire electrode patterns the circular shape interdigitated pattern gave the highest response towards 100 PPM N02 gas concentration. These results confirm that the shape of electrode pattern is also equally important as the sensing layer material.
The device of the present invention was tested for different gases at 100 PPM concentration and it is found that the proposed sensor is very much selective for detection of N02 gas.
The nanocomposite makes the sensor very much suitable for N02 gas detection at room temperature.

The observed sensor response for H2S, NO, NO2, CO, CO2 ad NH3 gas having 100 PPM concentration at room temperature is shown in fig. 16. This demonstrates that the sensor response of device for Nitrogen dioxide (NO2) is 424, while to hydrogen sulfide (H2S), Nitric oxide (NO), carbon monoxide (CO), carbon dioxide (CO2), ammonia (NH3), and, the responses are 40.8, 93, 50, 40, and 65, respectively. The response towards NO2 is 10.39, 4.55, 8.48, 10.6, and 6.52 times higher than that toward H2S, NO, CO, CO2, and NH3, respectively.
To check the repeatability of the sensor, we have repeated the test 4 times for 100 PPM NO2 gas concentration as shown in figure 17. From the response characteristics it was observed that the sensor shows almost same gas response. This confirms that device of the present invention gives the repeatability as well as reproducibility.
The reliability is very much concern issue for any electronic devices, and it depends on the stability of the device. The proposed sensor was tested for different time intervals/days. The sensor response for the 100 PPM NO2 gas concentration for WO3-PANI nanocomposite at room temperature was recorded for 45 days. The obtained results (fig. 18) having the deviation of <3%, which indicates long term stability of the sensor and reusability of the sensor.
Advantages of the present invention:
1. Rapid and accurate detection of the harmful gases present in the environment;
2. Large spectrum of detection. The device can detect the presence of harmful gases from room temperature to higher temperature;
3. The device of the present invention is simple and cost effective.

We claim:

1.A device for detecting gases, the device comprising;
a substrate (LI) layer;
an insulating layer (L2); wherein said insulating layer is configured on the
substrate;
a sensing layer (L3) with a resistance characteristic which changes in the presence
of a target gas in ambient air;
wherein the sensing layer is configured to adsorb the target gas on its surface and
cause a resistance change across the same; and
an electrode(L4) arranged in a metal-semiconductor-metal pattern; wherein the electrode is configured to provide the electrical connection and measure the change in resistance and confirm the presence of target gas.
2. The device as claimed in claim 1, wherein said sensing layer is coated on an insulating layer(L2) of the substrate(Ll).
3. A device for detecting gases, the device comprising;
a sensing layer (L3) with a resistance characteristic which changes in the presence of a target gas in an ambient air;
wherein the sensing layer is configured to adsorb the target gas on its surface and cause a resistance change; and
an electrode(L4) arranged in a metal-semiconductor-metal pattern; wherein the electrode is configured to measure the change in resistance and confirm the presence of target gas.
4. The device as claimed in claims 1 and 3, wherein said electrode is assembled on the sensing layer.
5. The device as claimed in claim 1 and 3, wherein said sensing layer is made of polyaniline (PANI) and tungsten trioxide (WO3) nanoparticle.
6. The device as claimed in claims 1 and 3, wherein said WO3 is in concentration range of 0.1 -25% of PANI.
7. The devices as claimed in claims 1 and 3, wherein the electrode is selected from palladium, gold, platinum and the like.
8. The device as claimed in claim 1, wherein the substrate is Si-wafer.
9. The device as claimed in claim 1, wherein the insulating layer is Si02.

10. The device as claimed in claims 1 and 3, wherein said target gas is selected from Carbon Monoxide (CO), Hydrogen Sulphide (H2S), Nitrogen Oxides (NOx), Sulphur Oxides (SOx), Carbon dioxide (CO2), and Ammonia (NH3).
11. The device as claimed in claim 10, wherein said target gas is NO2.
12. The device as claimed in claims 1-3, wherein the electrode is assembled on sensing layer by masking the same in an interdigitated pattern.
13. The device as claimed in claim 12, wherein said interdigitated pattern is of shape selected from E-shape, circular, round square and Archimedean spiral.
14. The device as claimed in claim 13, wherein said E-shape pattern (A) has:
two contact pads (1, 2) with extended arms (la, 2a), respectively; the extended arm 1(a) has three extended arms (lb), (lc) and (Id) and the extended arm (2a) has three extended arms (2b), (2c) and (2d).
15. The device as claimed in claim 13, wherein the extended arms (are in "E" shape and the extended arms (2b), (2c) and (2d) are in a "mirror E" shape.
16. The device as claimed in claim 15, wherein the arms (lb), (lc), (Id) and (2b), (2c), (2d) face each other in a manner that further extended arms (E) of (1) and further extended arms (Mirror E) of (2) results in a pattern having alternate extensions having a gap of around 0.2 mm.
17. The device as claimed in claim 16, wherein the arms are in a pattern:
(2b) I (lb) I (2c) I (lc) I (2d) I (Id).
18. The device as claimed in claim 13, wherein said circular interdigitated pattern has:
two contact pads (3, 4) facing each other with extended arms (3a, 4a),
respectively;
the extended arms 3(a) and 4 (a) have points which have further extended arms.
19. The device as claimed in claim 18, wherein said points are A and B on extended arm 3(a) and C, D and E on extended arm (4a).
20. The device as claimed in claim 19, wherein said point A has extended arms (3b) and (3c).
21. The device as claimed in claim 19, wherein said point B has extended arms (3d) and (3e).
22. The device as claimed in claim 19, wherein said point C has extended arms (4b) and (4c).

23. The device as claimed in claim 19, wherein said point D has extended arms (4d) and (4e).
24. The device as claimed in claim 19, wherein said point E has extended arms (4f) and (4g).
25. The device as claimed in claim 13, wherein said round square interdigitated pattern
has:
contact pads (5) and (6) facing each other and arms (5a) and (6a) extending respectively from said contact pads;
where said extended arms are coiled with other to form a concentric square.
26. The device as claimed in claim 13, wherein said Archimedean spiral interdigitated
pattern has
contact pads (7) and (8) facing each other and arm (7a) and (8a) extending respectively from the contact pads.
27. The device as claimed in claims 1 and 3, wherein said sensing layer has a detection
limit between 10-100 parts per billion (ppb).
28. A method of manufacturing a device for detecting gases, wherein the method comprises the steps of:
a) synthesizing composite of PANI and WO3;
b) depositing the composite of PANI and WO3 on the insulating layer formed on substrate at a deposition rate of depositing the composite of PANI and W03 on the insulating layer formed on substrate at a deposition rate of 1500-4000 rpm for 10 sec to 15 min.

29. The method as claimed in claim 28, wherein said substrate is oxidized to form an insulating layer;
30. The method as claimed in claim 28, wherein said substrate is Si wafer and is 4 inches in diameter and 525 um in thickness.
31. The method as claimed in claim 28, wherein the insulating layer formed in Si02.
32. The method as claimed in claim 28, wherein synthesis of composite of PANI and WO3 comprises steps of:
dissolving polyaniline powder in N-methyl- 2-pyrolidone (NMP) and stirring the solution for 5 hours;

filtering the solution;
- adding 1% W03, 5% WO3, 10% WO3, and 20% WO3 in filtered solution of
undoped P ANI in NMP and stirring it for 5 h.
33. The method as claimed in claim 28, wherein said deposition is done by using technique selected from Hot press method and spin coating.
34. A method of detecting a target gas, wherein said method comprises the steps of:
keeping the device as claimed in claims 1-27 in a closed gas chamber; providing the target gas; « a fixed bias voltage of 1-5V have been applied to the device
- the source meter measures the resistance of the device and the change in
resistance confirms presence of the gas.