GAS SENSOR

Abstract

A gas sensor is revealed, and the gas sensor comprises a sapphire substrate. An epitaxial oxide sensing layer is disposed on the sapphire substrate and formed by a thin film of single-crystalline gallium oxide series grown by using metal-organic chemical vapor deposition. The material of epitaxial oxide sensing layer include oxygen, gallium, and zinc. Two electrodes are disposed on a portion of the epitaxial oxide sensing layer. When the epitaxial oxide sensing layer senses a gas, a current will be generated and change the resistance. The two electrodes thereon receive the resistance. According to the change of the resistance, the concentration of the gas can be deduced. A heating element is further disposed below the sapphire substrate for providing the temperature required for sensing.

Claims

1. A gas sensor, comprising: a substrate; an epitaxial oxide sensing layer, disposed on said substrate, the material of said epitaxial oxide sensing layer including oxygen, gallium, and zinc; and two electrodes, disposed on a portion of said epitaxial oxide sensing layer; where said epitaxial oxide sensing layer senses a gas for generating current to change a resistance thereof.

2. The gas sensor of claim 1, and further comprising a heating element disposed below a portion of said substrate.

3. The gas sensor of claim 1, wherein said substrate is a sapphire substrate.

4. The gas sensor of claim 1, wherein said epitaxial oxide sensing layer is a single-crystalline thin film.

5. The gas sensor of claim 1, wherein said epitaxial oxide sensing layer is a polycrystalline thin film.

6. The gas sensor of claim 1, wherein the material of said epitaxial oxide sensing layer is zinc gallium oxide (ZnGa.sub.2O.sub.4, ZGO).

7. The gas sensor of claim 1, wherein the application temperature of said epitaxial oxide sensing layer reaches 800 C.

8. The gas sensor of claim 1, wherein said epitaxial oxide sensing layer is annealed in nitrogen or oxygen at 800 C. to 950 C.

9. The gas sensor of claim 1, wherein the material of said two electrodes is selected from the group consisting of titanium/aluminum/titanium and titanium/platinum/gold.

10. The gas sensor of claim 1, wherein said gas is selected from the group consisting of carbon dioxide (CO.sub.2), alcohol, total volatile organic compound (TVOC), and sulfur dioxide (SO.sub.2).

11. The gas sensor of claim 1, wherein said epitaxial oxide sensing layer reacts with said gas to generate current for increasing or decreasing the resistance.

12. The gas sensor of claim 2, wherein the material of said heating element is selected from the group consisting of tungsten and platinum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows a structure diagram of the gas sensor according to an embodiment of the present invention;

[0020] FIG. 2 shows a structure diagram of the gas sensor according to an embodiment of the present invention;

[0021] FIG. 3 shows a gas response diagrams of the gas sensor according to an embodiment of the present invention; and

[0022] FIG. 4 shows a gas response diagrams of the gas sensor according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0023] In order to make the structure and characteristics as well as the effectiveness of the present invention to be further understood and recognized, the detailed description of the present invention is provided as follows along with embodiments and accompanying figures.

[0024] In the following description, figures are used for describing various embodiments according to the present invention in detail. Nonetheless, the concept of the present invention can be embodied in many different forms, instead of being limited to the exemplary embodiments described in the present description.

[0025] To solve the problem of lower sensitivity in the gas sensor according to the prior art, the present invention provides a gas sensor formed by growing a thin film of single-crystalline gallium oxide series using metal-organic chemical vapor deposition. By using zinc gallium oxide (ZnGa.sub.2O.sub.4, ZGO) as the epitaxial oxide sensing layer, the sensitivity of the gas sensor can be improved effectively.

[0026] The present invention provides a gas sensor, which uses a thin film of single-crystalline gallium oxide series using metal-organic chemical vapor deposition as the epitaxial oxide sensing layer. The epitaxial oxide sensing layer is disposed on a portion of a sapphire substrate. The epitaxial oxide sensing layer reacts with the gas to generate ionized electrons for changing the resistance. According to the change of the resistance, the concentration of the gas can be deduced.

[0027] First, please refer to FIG. 1 shows a structure diagram of the gas sensor according to an embodiment of the present invention. As shown in the figure, the present invention provides a gas sensor, which comprises a substrate 10, an epitaxial oxide sensing layer 30, and two electrodes 50. The epitaxial oxide sensing layer 30 is disposed on a portion of the substrate 10. The two electrodes 50 are disposed on a portion of the epitaxial oxide sensing layer 30.

[0028] Please refer to FIG. 2, which shows a structure diagram of the gas sensor according to an embodiment of the present invention. As shown in the figure, the present invention provides a gas sensor, and further comprises a heating element 70 disposed below a portion of the substrate 10.

[0029] The epitaxial oxide sensing layer 30 is used for reacting with gases such as CO.sub.2, alcohol, TVOC, and SO.sub.2. When the gas is absorbed to the epitaxial oxide sensing layer 30, an electron will be captured, as shown in Formula 1. Next, when the temperature is increased, the sensitivity will be increased. Then the reaction rate of chemical absorption is accelerated and hence the absorption state is further stabilized, as shown in Formula 2. As the temperature reaches 100 C., oxidation reactions occur in the epitaxial oxide sensing layer 20, making the gas to lose electrons and thus raising the resistance. As shown in FIG. 3, at 100 C., the epitaxial oxide sensing layer 30 reacts with CO.sub.2, alcohol, TVOC, and SO.sub.2, respectively. The reactions increase the resistance. Next, in Table 1 below, the sensitivities of the epitaxial oxide sensing layer 30 on gases at 100 C. are shown. The highest sensitivity of the epitaxial oxide sensing layer 30 on CO.sub.2 can reach 76.92%; the highest sensitivity of the epitaxial oxide sensing layer 30 on alcohol can reach 52.12%; the highest sensitivity of the epitaxial oxide sensing layer 30 on TVOC can reach 49.61%; and the highest sensitivity of the epitaxial oxide sensing layer 30 on SO.sub.2 can reach 25.79%.

g+e.sup.-.fwdarw.g.sup.(Formula 1)

g.sup.+e.sup.-.fwdarw.2g.sup.(Formula 2)

The symbol g shown in Formula 1 and Formula 2 represents the gas to be detected, such as CO.sub.2, alcohol, TVOC, and SO.sub.2.

TABLE-US-00001 TABLE 1 Sensitivity level LV1 LV2 LV3 LV4 LV5 CO.sub.2 34.05% 45.43% 61.29% 70.66% 76.92% Alcohol 24.18% 32.42% 38.19% 48.77% 52.12% TVOC 19.22% 36.93% 42.03% 43.24% 49.61% SO.sub.2 7.58% 14.82% 17.09% 22.53% 25.79%

[0030] The sensitivity of the epitaxial oxide sensing layer 20 at 150 C. is superior to that at 100 C. As shown in FIG. 4, at 150 C., oxidation reactions occur in the epitaxial oxide sensing layer 30, and the epitaxial oxide sensing layer 30 reacts with CO.sub.2, alcohol, TVOC, and SO.sub.2, respectively. The reactions increase the resistance. Next, in Table 2 below, the sensitivities of the epitaxial oxide sensing layer 30 on gases at 150 C. are shown. The highest sensitivity of the epitaxial oxide sensing layer 30 on CO.sub.2 can reach 84.72%; the highest sensitivity of the epitaxial oxide sensing layer 30 on alcohol can reach 70.92%; the highest sensitivity of the epitaxial oxide sensing layer 30 on TVOC can reach 78.21%; and the highest sensitivity of the epitaxial oxide sensing layer 30 on SO.sub.2 can reach 32.71%. According to the data, it is known that the sensitivity of the epitaxial oxide sensing layer 20 at 150 C. is superior to that at 100 C.

TABLE-US-00002 TABLE 2 Sensitivity level LV1 LV2 LV3 LV4 LV5 CO.sub.2 40.26% 60.58% 65.75% 70.46% 84.72% Alcohol 31.81% 40.00% 58.33% 70.04% 70.92% TVOC 23.69% 51.22% 58.29% 77.89% 78.21% SO.sub.2 7.77% 13.76% 16.20% 25.97% 32.71%

[0031] Next, as shown in Tables 3 to 6, the detection times of the epitaxial oxide sensing layer 30 on CO.sub.2, alcohol, TVOC, and SO.sub.2 at 100 C. and 150 C., respectively, are all less than 10 seconds.

TABLE-US-00003 TABLE 3 Response time Response Alcohol temperature 100 C. 150 C. (C.sub.2H.sub.5OH) Rise Fall Rise Fall Rise Fall time time time time time time 10 cc 2 s 4 s 2 s 2 s 20 cc 2 s 4 s 2 s 3 s 30 cc 3 s 5 s 3 s 4 s 40 cc 5 s 6 s 4 s 4 s 50 cc 6 s 7 s 6 s 5 s

TABLE-US-00004 TABLE 4 Response Response time temperature 100 C. 150 C. CO.sub.2 Rise Fall Rise Fall Rise Fall time time time time time time 10 cc 2 s 3 s 2 s 2 s 20 cc 4 s 5 s 3 s 2 s 30 cc 5 s 6 s 5 s 4 s 40 cc 5 s 7 s 6 s 4 s 50 cc 5 s 7 s 6 s 5 s

TABLE-US-00005 TABLE 5 Response Response time temperature 100 C. 150 C. TVOC Rise Fall Rise Fall Rise Fall time time time time time time 0.5 cc 2 s 1 s 2 s 2 s 1.0 cc 4 s 3 s 3 s 2 s 1.5 cc 5 s 4 s 4 s 4 s 2.0 cc 6 s 5 s 4 s 3 s 2.5 cc 6 s 6 s 4 s 4 s

TABLE-US-00006 TABLE 6 Response time Room temperature 100 C. 150 C. SO.sub.2 Rise Fall Rise Fall Rise Fall time time time time time time 1 cc 4 s 2 s 1 s 3 s 2 s 1 s 2 cc 5 s 3 s 1 s 3 s 2 s 2 s 3 cc 5 s 2 s 2 s 3 s 2 s 2 s 4 cc 5 s 2 s 2 s 3 s 2 s 2 s 5 cc 6 s 2 s 2 s 4 s 2 s 2 s