Adaptive test method and design for low power MOX sensors

Abstract

The present disclosure relates to an adaptive testing method and design for low power MOX sensors. The present disclosure relates to a gas sensor device comprising a plurality of gas sensors. Each of the gas sensors comprises a semiconductor metal oxide (SMO) film, a heater, and a temperature sensor. Each of the SMO films is designed to be sensitive to a different gas concentration range. As a result, the gas sensor device is able to obtain accurate readings for a large range of gas concentration levels. Additionally, the gas sensors are selectively activated and deactivated based on the current gas concentration detected by the gas sensor device. Thus, the gas sensor device is able to save power since the gas sensors are turned on when appropriate rather than continuously.

Description

[0001] Divisional Application Statement

[0002] This application is a divisional application of the Chinese Patent Application No. 201811587644.X, filed on December 24, 2018, entitled “Adaptive Testing Method and Design for Low Power MOX Sensors”, and priority to which is claimed. TECHNICAL FIELD

[0003] The present disclosure relates to a gas sensor device for detecting air quality. BACKGROUND

[0004] Air quality is important to maintaining the health of people. Air pollution can cause various health problems, such as cardiorespiratory disease. Air pollution is not limited to outdoor pollution and can occur indoors, such as in homes, offices, and factories. A wide range of chemical compounds, such as volatile organic compounds (VOCs), can be found in indoor environments. VOCs include compounds such as ethanol, toluene, benzene, formaldehyde, tetrachloroethylene (TCE), and dichloromethane.

[0005] Indoor air pollution can be derived from a variety of different sources, such as air conditioners, building materials, furniture, solvents, paints, and carpets. Indoor air pollution can even be caused by routine activities, such as breathing, cooking, and cleaning.

[0006] The concentration of VOCs can rise to harmful levels as the polluted air accumulates within an enclosed space. In some cases, indoor air pollution can be more harmful to health than outdoor air pollution.

[0007] Some people are particularly sensitive to VOCs and can experience allergic reactions, such as headaches, dizziness, and irritability. However, most people are unable to detect dangerous levels of VOCs. Accordingly, it is important for buildings to be equipped with gas sensors for detecting harmful levels of gases, such as VOCs, to maintain proper air quality. SUMMARY

[0008] The present disclosure relates to an improved gas sensor device for detecting air quality. The gas sensor device can be used for various applications, such as indoor air quality sensors and outdoor air quality sensors. The gas sensor device is capable of accurate readings for a wide range of gas concentration levels. Additionally, the gas sensor device has low power consumption, which makes it ideal for low power devices, such as smartphones and smartwatches.

[0009] The gas sensor device includes a plurality of gas sensors. Each of the gas sensors includes a semiconductor metal oxide (SMO) film, a heater, and a temperature sensor. Each of the SMO films is designed to be sensitive to a different gas concentration range. For example, a first SMO film can be designed to detect a low gas concentration range, a second SMO film can be designed to detect a medium gas concentration range, and a third SMO film can be designed to detect a high gas concentration range. By having each of the SMO films be sensitive to a different gas concentration range, the gas sensor device is able to obtain accurate readings for a large range of gas concentration levels.

[0010] The gas sensor device selectively activates and deactivates the gas sensors based on a current gas concentration detected by the gas sensor device. For example, when a low gas concentration is detected, the gas sensor device can activate a gas sensor having an SMO film designed to detect a low gas concentration range and deactivate all other gas sensors. As a result, the gas sensor device saves power because the gas sensors are turned on when appropriate rather than being left on continuously. BRIEF DESCRIPTION OF DRAWINGS

[0011] In the drawings, like reference numerals identify similar features or elements. The size and relative positions of features in the drawings are not necessarily drawn to scale.

[0012] Figure 1 is a block diagram of a gas sensor device according to an embodiment of the present disclosure.

[0013] Figure 2 is a plot of sensitivity for three different SMO films according to an embodiment of the present disclosure.

[0014] Figure 3 is a top view of a gas sensor device according to an embodiment of the present disclosure.

[0015] Figure 4 is a cross-sectional view of a gas sensor device according to an embodiment of the present disclosure along the axis shown. Figure 3

[0016] Figure 5 is a cross-sectional view of a gas sensor device according to an embodiment of the present disclosure along the axis shown. Figure 3

[0017] Figure 6 is a cross-sectional view of a gas sensor device according to another embodiment of the present disclosure along the axis shown. Figure 3

[0018] Figure 7 is a top view of a gas sensor device according to another embodiment of the present disclosure. ​​​

[0019] Figure 8 is a flowchart of a method of operating a gas sensor device according to an embodiment of the disclosure.

[0020] Figure 9 is a circuit representing a gas sensor device according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0021] In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter can be practiced without these specific details. In some instances, well-known structures and methods of making electronic devices have not been described in detail in order to avoid obscuring the description of the other aspects of the disclosure.

[0022] Unless the context requires otherwise, throughout the present specification and claims, the word "comprise" and variations thereof (such as, "comprises" and "comprising") are to be construed in an open, inclusive sense, that is as "including but not limited to."

[0023] References throughout this specification to "one embodiment" and "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more aspects of the disclosure.

[0024] References throughout this specification to integrated circuits are intended to include integrated circuit components that are built on semiconductor or glass substrates, whether or not those components are coupled together in a circuit or are capable of being interconnected. Throughout this specification, the term "layer" is used in its broadest sense to include films, caps, and the like, and a layer can be composed of multiple sub-layers.

[0025] The present disclosure relates to a gas sensor device that detects various kinds of gases including volatile organic compounds (VOCs). The gas sensor device is capable of obtaining accurate readings for a wide range of concentration levels. Further, the gas sensor device has low power consumption and is ideal for portable devices such as smartphones and smartwatches.

[0026] Figure 1 is a block diagram of a gas sensor device 10 according to one embodiment of the disclosure. The gas sensor device 10 includes a plurality of gas sensors 12, 14, 16 and a processor 18. Although in the embodiment shown in Figure 1Only three gas sensors are shown, but the gas sensor device 10 can include any number of gas sensors.

[0027] Each of the gas sensors 12, 14, 16 is configured to detect one class of gas, such as volatile organic compounds (VOCs). Each of the gas sensors 12, 14, 16 includes a semiconductor metal oxide (SMO) film, a heater, and a temperature sensor. In particular, the gas sensor 12 includes an SMO film 20, a heater 22, and a temperature sensor 24; the gas sensor 14 includes an SMO film 26, a heater 28, and a temperature sensor 30; and the gas sensor 16 includes an SMO film 32, a heater 34, and a temperature sensor 36.

[0028] Each of the SMO films 20, 26, 32 is a material that chemically reacts with various gases in the surrounding environment. For example, the SMO film 20 can include tin oxide (Sn02), zinc oxide (Zn02), and / or indium oxide (In203). Each of the SMO films 20, 26, 32 acts as an active sensor area. When heated to a certain temperature, the SMO films 20, 26, 32 experience a change in resistivity when exposed to certain gases. For example, a tin oxide film experiences a change in resistance when methane gas (CH4), liquefied petroleum gas (LPG), or hydrogen gas (H2) is present when heated to between 100 and 400 degrees Celsius. Accordingly, the presence of a particular gas can be detected based on the current resistivity of the SMO film 20, 26, 32.

[0029] In one embodiment, each of the SMO films 20, 26, 32 is a thin film. For example, each of the SMO films 20, 26, 32 can have a thickness between 90 and 110 nanometers (nm).

[0030] The level of sensitivity of the SMO films 20, 26, 32 is determined by the design of the SMO films 20, 26, 32 for a particular concentration range of gas. Generally, the concentration range of gas to which an SMO film will be sensitive is determined by the number of oxygen sites on the SMO film that are available to react with gas molecules. When all of the oxygen sites of an SMO film are occupied by active gas molecules, the SMO film will be saturated and will not be sensitive to any additional gas molecules present. Thus, an SMO film with a larger surface area film will be able to detect a higher concentration of gas because the SMO film has a larger number of oxygen sites available to react with gas molecules. Conversely, when a large number of oxygen sites of an SMO film are unoccupied, the reactivity of the SMO film will be reduced and experience a smaller change in the presence of gas. Thus, an SMO film with a larger surface is generally not sensitive to low concentrations of gas because the SMO film will have a large number of unoccupied oxygen sites.

[0031] Accordingly, the size or surface area of each of the SMO films 20, 26, 32 determines the range of gas concentrations to which each of the SMO films 20, 26, 32 will be sensitive. SMO films having a larger exposed surface area are generally more sensitive to high concentrations of gas and less sensitive to low concentrations of gas. SMO films having a smaller exposed surface area are generally less sensitive to high concentrations of gas and more sensitive to low concentrations of gas.

[0032] For example, an SMO film having a surface area of 10 square micrometers (pm 2 ) responds well to and is sensitive to gas concentrations in the range of 1 part per billion (PPB) to 1 part per million (PPM), an SMO film having a surface area of 100 pm 2 responds well to and is sensitive to gas concentrations in the range of 1 PPM to 10 PPM, and an SMO film having a surface area of 1000 pm 2 responds well to and is sensitive to gas concentrations in the range of 10 PPM to 100 PPM. Figure 2 is a graph of sensitivity for three different SMO films according to embodiments of the present disclosure. Line 38 represents the response of an SMO film having a surface area of 10 pm 2 , line 40 represents the response of an SMO film having a surface area of 100 pm 2 , and line 42 represents the response of an SMO film having a surface area of 1000 pm 2 .

[0033] Line 38 shows that the SMO film having a surface area of 10 pm 2 has a greater rate of change of resistivity (i.e., slope) for gas concentrations less than 0.8 PPM compared to gas concentrations greater than 0.8 PPM. Thus, the SMO film having a surface area of 10 pm 2 is particularly sensitive to gas concentrations up to approximately 0.8 PPM. Line 40 shows that the SMO film having a surface area of 100 pm 2 has a greater rate of change of resistivity for gas concentrations less than 10 PPM compared to gas concentrations greater than 10 PPM. Thus, the SMO film having a surface area of 100 pm 2 is particularly sensitive to gas concentrations up to approximately 10 PPM. Line 42 shows that the SMO film having a surface area of 1000 pm 2 has a greater rate of change of resistivity for gas concentrations less than 90 PPM compared to gas concentrations greater than 90 PPM. Thus, the SMO film having a surface area of 1000 pm 2 is particularly sensitive to gas concentrations up to approximately 90 PPM.

[0034] Each of the SMO films 20, 26, 32 is designed to be sensitive to different gas concentration ranges. That is, each of the SMO films 20, 26, 32 has a different exposed surface area such that each of the SMO films 20, 26, 32 is sensitive to a different gas concentration range. By making each of the SMO films 20, 26, 32 sensitive to a different concentration range, the gas sensors 12, 14, 16 are able to obtain accurate readings for a large range of gas concentration levels.

[0035] In one embodiment, the SMO film 20 has a first surface area to detect a low gas concentration range, the SMO film 26 has a second surface area greater than the first surface area to detect a medium gas concentration range, and the SMO film 32 has a third surface area greater than the second surface area to detect a high gas concentration range. For example, in one embodiment, the SMO film 20 has a surface area approximately equal to 10 μm 2 , the SMO film 26 has a surface area approximately equal to 100 μm 2 , and the SMO film 32 has a surface area approximately equal to 1000 μm 2 . Accordingly, the gas sensor 12 is able to detect gas concentrations in the range of 1 PPB to 1 PPM, the gas sensor 14 is able to detect gas concentrations in the range of 1 PPM to 10 PPM; and the gas sensor 16 is able to detect gas concentrations in the range of 10 PPM to 100 PPM. Accordingly, the gas sensor device 10 is able to accurately detect and measure gas concentrations in the range of 0 to 100 PPM.

[0036] The heaters 22, 28, 34 heat the SMO films 20, 26, 32, respectively, to a desired temperature. In one embodiment, the heaters 22, 28, 34 are resistive heaters that heat the SMO films 20, 26, 32 using the Joule effect by resistive dissipation of electrical current. As will be discussed in further detail with respect to Figures 3 to 5 FIG. 3, the heaters 22, 28, 34 are located beneath and heat the SMO films 20, 26, 32, respectively.

[0037] As previously discussed, the SMO films 20, 26, 32 should be heated to a particular temperature in order to react with a particular gas. In one embodiment, the heaters 22, 28, 34 heat the SMO films 20, 26, 32, respectively, to the same temperature range in order to sense the same gas.

[0038] The power consumption of the heaters 22, 28, 34 to heat the SMO films 20, 26, 32 depends on the size of the SMO films 20, 26, 32. Generally, the larger the SMO film, the more power is required to heat the SMO film to a desired temperature. For example, if the SMO films 20, 26, 32 have a surface area approximately equal to 10 μm2 100 pm 2 and 1000 pm 2 If the SMO film 20, 26, 32 has a surface area of 100 pm x 100 pm, the heater 22, 28, 34 will consume approximately 5 milliwatts (mW), 15 mW, and 35 mW, respectively, to heat the SMO film 20, 26, 32 to between 300 and 350 degrees Celsius. As will be discussed in further detail with respect to Figure 8 The heaters 22, 28, 34 are selectively activated and deactivated to conserve power, as will be discussed in further detail.

[0039] The temperature sensors 24, 30, 36 measure the current temperature of the SMO film 20, 26, 32, respectively. The temperature sensors 24, 30, 36 are placed proximate to the SMO film 20, 26, 32, respectively, so as to obtain accurate measurements. As will be discussed in further detail below, the temperature sensors 24, 30, 36 are used as feedback control devices for automatically adjusting the heaters 22, 28, 34, respectively, to heat the SMO film 20, 26, 32 to a desired temperature. For example, the temperature sensor 24 can measure the current temperature of the SMO film 20, and the heater 22 can adjust its temperature based on the current temperature of the SMO film 20.

[0040] The processor 18 is coupled to the gas sensors 12, 14, 16. The processor 18 is configured to activate and deactivate each of the gas sensors 12, 14, 16, measure the current resistivity of the SMO film 20, 26, 32, control the heaters 22, 28, 34 to heat the SMO film 20, 26, 32 to a particular temperature, and communicate with the temperature sensors 24, 30, 36 to obtain the current temperature of the SMO film 20, 26, 32. The processor 18 can be any type of controller, microprocessor, or application specific integrated circuit (ASIC) that communicates with and controls the gas sensors 12, 14, 16.

[0041] In one embodiment, the processor 18 reads the current temperature of the SMO film 20, 26, 32 via the temperature sensors 24, 30, 36, respectively; and then controls the heaters 22, 28, 34 based on the current temperature of the SMO film 20, 26, 32, respectively. For example, the processor 18 can receive the current temperature of the SMO film 20 via the temperature sensor 24, and adjust the heater 22 to maintain a desired temperature (e.g., between 300 and 350 degrees Celsius) of the SMO film 20. By adjusting the heaters 22, 28, 34 to a particular temperature, the processor 18 is able to tune the gas sensors 12, 14, 16 (more specifically, the SMO film 20, 26, 32) to be sensitive to a particular gas. In one embodiment, the processor 18 adjusts the heaters 22, 28, 34 to maintain the same temperature range, such that the SMO film 20, 26, 32 is sensitive to the same gas.

[0042] In one embodiment, the processor 18 activates and deactivates each of the gas sensors 12, 14, 16 to conserve power. As previously discussed, the larger the SMO membrane, the more power required to heat the SMO membrane to the desired temperature. Therefore, to conserve power, the processor 18 activates and deactivates the gas sensors 12, 14, 16 depending on which one of the gas sensors 12, 14, 16 is most sensitive to the range of gas concentrations currently present in the surrounding environment. As a result, the gas sensors 12, 14, 16 with larger SMO membranes and high power consumption are not powered when not in use. Further details regarding the activation and deactivation of the gas sensors 12, 14, 16 are discussed below. Figure 8 The activation and deactivation of the gas sensors 12, 14, 16 are discussed in further detail.

[0043] Figure 3 is a top view of a gas sensor device according to an embodiment of the present disclosure. Figure 4 is a cross-sectional view of a gas sensor device along the axis indicated by Figure 3 is a cross-sectional view of a gas sensor device along the axis indicated by Figure 5 is a cross-sectional view of a gas sensor device along the axis indicated by Figure 3 is a cross-sectional view of a gas sensor device along the axis indicated by Together, the above figures are advantageous. It should be noted that the dimensions set forth herein are provided as examples. Other dimensions are contemplated for this embodiment and all other embodiments of the present application. Figures 3 to 5

[0044] The gas sensor device 10 includes an SMO membrane 20, 26, 32; a heater 22, 28, 34; a substrate 44; a first dielectric layer 46; a second dielectric layer 48; a third dielectric layer 50; and a fourth dielectric layer 52.

[0045] For example, the first dielectric layer 46 is formed on the substrate 44 using a deposition or growth process. For example, the substrate 44 can be made of silicon or glass. In one embodiment, the substrate 44 has a thickness in the range of 500 to 600 pm thick. For example, the first dielectric layer 46 can be made of an oxide. In one embodiment, the first dielectric layer 46 has a thickness in the range of 3 to 10 pm.

[0046] For example, the second dielectric layer 48 is formed on the first dielectric layer 46 using a deposition or growth process. For example, the second dielectric layer 48 can be made of silicon nitride. In one embodiment, the second dielectric layer 46 has a thickness in the range of 300 to 550 nm.

[0047] The cavities 56, 58, 60 are formed between the first dielectric layer 46 and the second dielectric layer 48. As shown in Figure 4 ​As best shown in FIG. 1, each of the gas sensors 12, 14, 16 includes a respective cavity. That is, the gas sensor 12 includes a cavity 56, the gas sensor 14 includes a cavity 58, and the gas sensor 16 includes a cavity 60. The cavities 56, 58, 60 can be formed, for example, by patterning a recess 62 in the first dielectric layer 46 and filling the recess 62 with a sacrificial material 54, such as polyimide, using photolithography and etching techniques. The second dielectric layer 48 can then be formed over the first dielectric layer 46 and the polyimide 54. Portions of the polyimide 54 can then be removed, for example, using photolithography and etching techniques. As in Figure 4 As best shown in FIG. 1, the remaining portions of the polyimide 54 provide additional support for portions of the second dielectric layer 48 over the cavities 56, 58, 60. In one embodiment, each of the cavities 56, 58, 60 has a depth in the range of 2 to 5 pm.

[0048] The cavities 56, 58, 60 provide an air gap between the first dielectric layer 46 and the second dielectric layer 48. Because air has a low thermal conductivity, the cavities 56, 58, 60 provide thermal insulation and limit the heat within the gas sensors 12, 14, 16. As a result, less power can be utilized to maintain the temperature of the SMO films 20, 26, 32. Additionally, because polyimide also has a low thermal conductivity, the polyimide 54 provides additional thermal insulation for the gas sensors 12, 14, 16.

[0049] The heaters 22, 28, 34 are formed, for example, using deposition over the second dielectric layer 48. The heaters 22, 28, 34 are directly over the cavities 56, 58, 60, respectively. As previously discussed, in one embodiment, the heaters 22, 28, 34 are resistive heaters that heat the SMO films 20, 26, 32 using the Joule effect by resistive dissipation of electrical current. In this embodiment, the heaters 22, 28, 34 include a resistive layer 64, such as tantalum aluminum. In one embodiment, the resistive layer 64 has a thickness in the range of 100 to 200 nm. Although a single resistive layer is shown in Figure 4 The heaters 22, 28, 34 can include multiple resistive layers. In one embodiment, the heaters 22, 28, 34 include at least one resistive layer on both sides of the SMO films 20, 26, 32, such that at least a portion of the SMO films 20, 26, 32 is sandwiched between two resistive layers.

[0050] The third dielectric layer 50 is formed, for example, using a deposition or growth process over the second dielectric layer 48 and the heaters 22, 28, 34. The third dielectric layer 50 can be made, for example, of silicon nitride. In one embodiment, the third dielectric layer 50 has a thickness in the range of 200 to 400 nm.

[0051] For example, the SMO films 20, 26, 32 are formed on the third dielectric layer 50 using deposition. For example, the SMO films 20, 26, 32 can be formed by forming an SMO layer on the third dielectric layer 50 and patterning the SMO layer using photolithography and etching techniques. As previously discussed, the SMO films 20, 26, 32 are made of a material that chemically reacts with various gases in the surrounding environment. For example, the SMO layer can include tin oxide (Sn02), zinc oxide (Zn02), and / or indium oxide (In203). In one embodiment, the SMO layer (i.e., each of the SMO films 20, 26, 32) has a thickness in the range of 50 to 150 nm.

[0052] As best shown in Figure 3 each of the SMO films 20, 26, 32 has a different upper surface area such that each of the SMO films 20, 26, 32 is sensitive to a different range of gas concentrations. In particular, the SMO film 20 has an exposed upper surface (which has a first surface area), the SMO film 26 has an exposed upper surface (which has a second surface area that is greater than the first surface area), and the SMO film 32 has an exposed upper surface (which has a third surface area that is greater than the second surface area). Accordingly, each of the SMO films 20, 26, 32 is sensitive to a different range of gas concentrations.

[0053] In one embodiment, each of the SMO films 20, 26, 32 includes one or more SMO segments. For example, as shown in Figure 3 the SMO film 20 includes a single SMO segment 66, the SMO film 26 includes two separate SMO segments 68, 70, and the SMO film 32 includes three separate SMO segments 72, 74, 76. In one embodiment, each of the SMO segments has the same surface area.

[0054] As previously discussed, in one embodiment, the SMO film 20 has a first surface area, the SMO film 26 has a second surface area that is greater than the first surface area, and the SMO film 32 has a third surface area that is greater than the second surface area. In this embodiment, the first surface area is the exposed surface area of the SMO segment 66, the second surface area is the combined exposed surface area of the SMO segments 68, 70, and the third surface area is the combined exposed surface area of the SMO segments 72, 74, 76.

[0055] For example, the fourth dielectric layer 52 is formed on the third dielectric layer 50 and the SMO films 20, 26, 32 using a deposition or growth process. For example, the fourth dielectric layer 52 is patterned using photolithography and etching techniques to expose the SMO films 20, 26, 32 such that the SMO films 20, 26, 32 are exposed to the surrounding environment, as Figure 3As shown. For example, the fourth dielectric layer 52 can be made of silicon nitride. In one embodiment, the fourth dielectric layer 52 has a thickness in the range of 300 to 550 nm.

[0056] exist Figures 3 to 6 In the illustrated embodiment, gas sensors 12, 14, and 16 are all formed on the same die. That is, gas sensors 12, 14, and 16 are formed on substrate 44. However, gas sensors 12, 14, and 16 may also be formed on separate dies.

[0057] It should be noted that, for simplicity, processor 18 and temperature sensors 24, 30, and 36 are not shown in the image. Figures 3 to 5 As shown in the figure. In one embodiment, gas sensors 12, 14, 16 and processor 18 are all formed on the same substrate. In another embodiment, processor 18 is formed on a substrate separate from gas sensors 12, 14, 16 and is electrically coupled to gas sensors 12, 14, 16 via interconnects. In one embodiment, temperature sensors 24, 30, 36 are positioned adjacent to SMO films 20, 26, 32, respectively, to obtain accurate measurements. Additionally, although not shown in the figure... Figures 3 to 5 As shown, however, the gas sensor device 10 may include multiple conductive layers that electrically couple SMO membranes 20, 26, 32 and heaters 22, 28, 34 to processor 18 and / or other electrical components.

[0058] Figure 6 It is according to another embodiment of this disclosure along Figure 3 The image shows a cross-sectional view of the gas sensor device with the shaft shown.

[0059] exist Figure 4 In the illustrated embodiment, each of gas sensors 12, 14, and 16 includes a corresponding cavity. That is, gas sensor 12 includes cavity 56, gas sensor 14 includes cavity 58, and gas sensor 16 includes cavity 60. In contrast, in Figure 6 In the illustrated embodiment, gas sensors 12, 14, and 16 share a single cavity 78. Similar to cavities 56, 58, and 60, cavity 78 provides an air gap between the first dielectric layer 46 and the second dielectric layer 48 to provide thermal insulation for gas sensors 12, 14, and 16. As a result, less power can be used to maintain the temperature of SMO films 20, 26, and 32. Using cavity 78 instead of multiple cavities 56, 58, and 60 simplifies the manufacture of the gas sensor device 10. Additionally, cavity 78 provides a larger air gap for increased thermal insulation.

[0060] Figure 7 This is a top view of a gas sensor device according to another embodiment of the present disclosure.

[0061] existFigure 3 In the illustrated embodiment, each of the SMO films 20, 26, 32 includes one or more SMO segments. For example, in the illustrated embodiment, the SMO film 20 includes a single SMO segment 66, the SMO film 26 includes two separate SMO segments 68, 70, and the SMO film 32 includes three separate SMO segments 72, 74, 76. Figure 3 In the illustrated embodiment, the SMO film 20 includes a single SMO segment 66, the SMO film 26 includes two separate SMO segments 68, 70, and the SMO film 32 includes three separate SMO segments 72, 74, 76. In contrast, in the embodiment of FIG. 2, the SMO film 20 includes two separate SMO segments 78, 80, the SMO film 26 includes a single SMO segment 82, and the SMO film 32 includes a single SMO segment 84. Figure 7 In the illustrated embodiment, each of the SMO films 20, 26, 32 includes a single SMO segment. For example, as illustrated, the SMO film 20 includes a SMO segment 80, the SMO film 26 includes a SMO segment 82, and the SMO film 32 includes a SMO segment 84. Accordingly, the manufacturing of the gas sensor device 10 is simplified. Additionally, the SMO films will consume less of the overall surface area of the gas sensor device 10. Figure 7 In the illustrated embodiment, each of the SMO films 20, 26, 32 includes a single SMO segment. For example, as illustrated, the SMO film 20 includes a SMO segment 80, the SMO film 26 includes a SMO segment 82, and the SMO film 32 includes a SMO segment 84. Accordingly, the manufacturing of the gas sensor device 10 is simplified. Additionally, the SMO films will consume less of the overall surface area of the gas sensor device 10.

[0062] Figure 8 is a flowchart of a method 86 of operating a gas sensor device 10 in accordance with an embodiment of the present disclosure Figure 1 The method 86 selectively activates and deactivates the gas sensors 12, 14, 16 based on a current gas concentration detected by the gas sensor device 10.

[0063] In block 88, the gas sensor 12 is on, the gas sensor 14 is off, and the gas sensor 16 is off. In particular, the processor 18 activates the gas sensor 12, deactivates the gas sensor 14, and deactivates the gas sensor 16. When the gas sensor 12 is activated, the heater 22 is on to heat the SMO film 20 to a desired temperature. When the gas sensors 14, 16 are deactivated, the heaters 28, 34 are off.

[0064] As previously discussed, the SMO film 20 detects a low gas concentration range. Accordingly, in block 88, the gas sensor device 10 is configured to detect the low gas concentration range. For example, in embodiments where the SMO film 20 has a surface area approximately equal to 10 μιη2, the gas sensor device 10 is configured to detect gas concentrations in the range of 1 PPB to 1 PPM. 2 In the illustrated embodiment, each of the SMO films 20, 26, 32 includes a single SMO segment. For example, as illustrated, the SMO film 20 includes a SMO segment 80, the SMO film 26 includes a SMO segment 82, and the SMO film 32 includes a SMO segment 84. Accordingly, the manufacturing of the gas sensor device 10 is simplified. Additionally, the SMO films will consume less of the overall surface area of the gas sensor device 10.

[0065] In decision branch 90, the processor 18 determines whether the current gas concentration detected by the gas sensor 12 is greater than a first threshold. If the current gas concentration is not greater than the first threshold, the method 86 returns to block 88. If the current gas concentration is greater than the first threshold, the method 86 moves to block 92.

[0066] In one embodiment, the first threshold is based on the surface area of the SMO film 20. The first threshold is set near or at the upper limit of the gas concentration range to which the SMO film 20 is sensitive. For example, with reference toFigure 2 If the SMO film 20 has a surface area approximately equal to 10 pm 2 , the first threshold can be set to 0.8 PPM.

[0067] In block 92, the gas sensor 12 is off, the gas sensor 14 is on, and the gas sensor 16 is off. In particular, the processor 18 deactivates the gas sensor 12, activates the gas sensor 14, and deactivates the gas sensor 16. When the gas sensor 14 is activated, the heater 28 is turned on to heat the SMO film 26 to the desired temperature. When the gas sensors 12, 16 are deactivated, the heaters 22, 34 are turned off.

[0068] As previously discussed, the SMO film 26 detects a medium gas concentration range. Accordingly, in block 92, the gas sensor device 10 is configured to detect the medium gas concentration range. For example, in embodiments where the SMO film 26 has a surface area approximately equal to 100 pm 2 , the gas sensor device 10 is configured to detect gas concentrations in the range of 1 PPM to 10 PPM.

[0069] In decision branch 94, the processor 18 determines whether the current gas concentration detected by the gas sensor 14 is greater than a second threshold. If the current gas concentration is not greater than the second threshold, the method 86 returns to block decision branch 90. If the current gas concentration is greater than the second threshold, the method 86 moves to block 96.

[0070] In one embodiment, the second threshold is based on the surface area of the SMO film 26. The second threshold is set to be close to the upper limit of the gas concentration range to which the SMO film 26 is sensitive. For example, with reference to Figure 2 If the SMO film 26 has a surface area approximately equal to 100 pm 2 , the first threshold can be set to 8 PPM.

[0071] In block 96, the gas sensor 12 is off, the gas sensor 14 is off, and the gas sensor 16 is on. In particular, the processor 18 deactivates the gas sensor 12, deactivates the gas sensor 14, and activates the gas sensor 16. When the gas sensor 16 is activated, the heater 34 is turned on to heat the SMO film 32 to the desired temperature. When the gas sensors 12, 14 are deactivated, the heaters 22, 28 are turned off.

[0072] As previously discussed, the SMO film 32 detects a high gas concentration range. Accordingly, in block 96, the gas sensor device 10 is configured to detect the high gas concentration range. For example, in embodiments where the SMO film 32 has a surface area approximately equal to 1000 pm 2In an embodiment in which the surface area of the SMO membranes 20, 26, 32 is 1 cm2, the gas sensor device 10 is configured to detect gas concentrations in the range of 10 PPM to 100 PPM. The method then returns to the decision branch 94.

[0073] By selectively activating and deactivating the gas sensors 12, 14, 16 based on the current gas concentration detected by the gas sensor device 10, the gas sensor device 10 is able to obtain accurate readings for a large range of concentration levels. Additionally, the gas sensor device 10 saves power because the heaters 22, 28, 34 are turned on when appropriate, rather than continuously.

[0074] Figure 9 is a representation of the gas sensor device 10 according to an embodiment of the disclosure.

[0075] The circuit includes the gas sensors 12, 14, 16; the processor 18; the switches 100, 102, 104; and the multiplexers 106, 108.

[0076] The SMO membranes 20, 26, 32 of the gas sensors 12, 14, 16 are electrically coupled to the multiplexers 108. Each of the SMO membranes 20, 26, 32 is represented as a resistive element. As previously discussed, each of the SMO membranes 20, 26, 32 acts as an active sensor area. When heated to a certain temperature, the SMO membranes 20, 26, 32 experience a change in resistivity when exposed to certain gases.

[0077] The heaters 22, 28, 34 of the gas sensors 12, 14, 16 are electrically coupled to the multiplexers 106 through the switches 100, 102, 104. Each of the heaters 22, 28, 34 is represented as a resistive element. As previously discussed, in one embodiment, the heaters 22, 28, 34 are resistive heaters that heat the SMO membranes 20, 26, 32 using the Joule effect by dissipating electrical current through resistance.

[0078] The processor 18 is electrically coupled to the multiplexers 106, 108. As previously discussed, the processor 18 is configured to activate and deactivate each of the gas sensors 12, 14, 16, measure the current resistivity of the SMO membranes 20, 26, 32, and control the heaters 22, 28, 34 to heat the SMO membranes 20, 26, 32 to a certain temperature.

[0079] The switches 100, 102, 104 and the multiplexers 106 selectively activate and deactivate the heaters 22, 28, 34. For example, in the embodiment in which the surface area of the SMO membranes 20, 26, 32 is 1 cm2, the gas sensor device 10 is configured to detect gas concentrations in the range of 10 PPM to 100 PPM. The method then returns to the decision branch 94. Figure 8In block 88 of the illustrated method 86, the switch 100 is closed to activate the heater 22, and the multiplexer 106 electrically couples the heater 22 to the processor 18 so that the processor 18 can control the heater 22. Conversely, in block 88, the switches 102, 104 are open to deactivate the heaters 28, 34, and the multiplexer 106 decouples the heaters 28, 34 from the processor 18.

[0080] The multiplexer 108 selectively couples the SMO film 20, 26, 32 to the processor 18 based on which of the gas sensors 12, 14, 16 is currently active or turned on. For example, in block 90 of the illustrated method 86, the multiplexer 108 electrically couples the SMO film 20 to the processor 18 so that the resistivity of the SMO film 20 can be measured and a gas concentration can be detected. Conversely, in block 90, the multiplexer 108 decouples the SMO films 26, 32 from the processor 18. Figure 8 In block 92 of the illustrated method 86, the multiplexer 108 electrically couples the SMO film 26 to the processor 18 so that the resistivity of the SMO film 26 can be measured and a gas concentration can be detected. Conversely, in block 92, the multiplexer 108 decouples the SMO films 20, 32 from the processor 18.

[0081] Various embodiments provide a gas sensor device that detects various kinds of gases including VOCs. The gas sensor device is able to obtain accurate readings for a wide range of concentration levels. Further, the gas sensor device has low power consumption and is ideal for portable devices.

[0082] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above- detaileddescription. In general, the described features, structures, or characteristics can be combined in any suitable manner to form yet other embodiments, including other combinations of features, structures or characteristics. Where the claimed embodiments cannot be practiced by virtue of a patentable device not having been reduced to practice, the claims should not be interpreted as being limited to the disclosed embodiments and equivalents thereof. Accordingly, the claims are not limited to the disclosed embodiments and equivalents thereof.

Claims

1. A gas sensor device, comprising: A first gas sensor, the first gas sensor comprising: First heater; and A first gas-sensitive membrane on the first heater, the first gas-sensitive membrane having a first surface area, the first gas-sensitive membrane comprising a single segment, the first heater being configured to heat the single segment of the first gas-sensitive membrane; and A second gas sensor, the second gas sensor comprising: Second heater; and A second gas-sensitive membrane on the second heater, the second gas-sensitive membrane having a second surface area greater than the first surface area, the second gas-sensitive membrane including a first segment and a second segment spaced apart from the first segment, the second heater being configured to heat the first segment and the second segment of the second gas-sensitive membrane.

2. The gas sensor device according to claim 1, wherein the first gas sensor is configured to detect gas concentration in a first range, the second gas sensor is configured to detect gas concentration in a second range, and the gas concentration in the second range is greater than the gas concentration in the first range.

3. The gas sensor device according to claim 1, further comprising: Substrate; The first dielectric layer on the substrate; A second dielectric layer on top of the first dielectric layer; The first cavity is located between the first dielectric layer and the second dielectric layer, and the first heater is located on the second dielectric layer and directly covers the first cavity; as well as The second cavity is located between the first dielectric layer and the second dielectric layer, and the second heater is located on the second dielectric layer and directly covers the second cavity.

4. The gas sensor device according to claim 3, further comprising: A third dielectric layer on the second dielectric layer, the first heater, and the second heater, wherein the single segment of the first gas-sensitive film and the first and second segments of the second gas-sensitive film are on the third dielectric layer.

5. The gas sensor device according to claim 4, further comprising: A fourth dielectric layer on the third dielectric layer, the fourth dielectric layer including openings that expose a single segment of the first gas-sensitive film and the first and second segments of the second gas-sensitive film to the surrounding environment.

6. A method for operating the gas sensor device according to claim 1, comprising: A first gas sensor is used to measure the gas concentration, the first gas sensor being configured to detect the gas concentration within a first gas concentration range; Determine whether the gas concentration is outside the first gas concentration range; as well as In response to determining that the gas concentration is outside the first gas concentration range, the gas concentration is measured using a second gas sensor, the second gas sensor being configured to detect gas concentrations within a second gas concentration range greater than the first gas concentration range.

7. The method of claim 6, wherein the first gas sensor comprises a first semiconductor metal oxide (SMO) film, and the second gas sensor comprises a second SMO film having a surface area greater than that of the first SMO film.

8. The method of claim 7, wherein the first SMO membrane comprises a single segment, and the second SMO membrane comprises a plurality of segments spaced apart from each other.

9. The method of claim 7, wherein Measuring the gas concentration using the first gas sensor includes heating the first SMO membrane to a temperature, and Measuring the gas concentration using the second gas sensor includes heating the second SMO membrane to the specified temperature.

10. The method of claim 7, wherein the first SMO film and the second SMO film are located on the same substrate.

11. The method of claim 6, further comprising: Activate the first gas sensor and use the first gas sensor to measure the gas concentration in response to the activation of the first gas sensor; as well as In response to determining that the gas concentration is outside the first gas concentration range, the first gas sensor is deactivated and the second gas sensor is activated.

12. A method for operating a gas sensor device according to claim 1, comprising: The first gas sensor is set to the on state, and the first gas sensor is configured to detect the gas concentration within a first gas concentration range; The gas concentration is measured using the first gas sensor; It is determined that the gas concentration is outside the first gas concentration range; In response to determining that the gas concentration is outside the first gas concentration range, the first gas sensor is set to an off state; and In response to determining that the gas concentration is outside the first gas concentration range, the second gas sensor is set to the on state, and the second gas sensor is configured to detect the gas concentration in a second gas concentration range that is different from the first gas concentration range.

13. The method according to claim 12, wherein, The first gas sensor includes a first semiconductor metal oxide (SMO) film, the second gas sensor includes a second SMO film, and the first SMO film and the second SMO film have different surface areas.

14. The method according to claim 13, wherein, The first SMO membrane includes a first number of segments, and the second SMO membrane includes a second number of segments, which is different from the first number of segments.

15. The method according to claim 14, wherein, The second number of segments are spaced apart from each other.

16. The method of claim 13, wherein the first SMO film and the second SMO film are located on the same substrate.

17. The method according to claim 12, wherein the gas concentration in the second gas concentration range is greater than the gas concentration in the first gas concentration range.

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