Gas sensor device and method of manufacturing the same

Abstract

A gas sensor device is configured to measure a predetermined gas of interest and includes a housing including a semiconductor substrate and defining a first cavity, a second closed cavity that is transparent to light, and a third cavity. The second cavity is between the first cavity and the third cavity. The first cavity includes an inlet port for receiving the measured gas and an outlet port for discharging the measured gas. The first cavity also includes a light source and a measurement sensor. The second cavity is configured to act as a gas filter including a volume of the gas of interest that is sealedly disposed in the second cavity, and the third cavity includes a reference measurement sensor disposed therein.

Description

Technical Field

[0001] The invention relates to a gas sensor device, e.g. of the type comprising a light source, a measuring sensor and a reference sensor, configured to measure absorption of electromagnetic radiation emitted by the light source by a measured gas. The invention also relates to a method of manufacturing a gas sensor device, e.g. of the type providing a light source, a measuring sensor and a reference sensor in a manner allowing measurement of absorption of electromagnetic radiation emitted by the measured gas by the light source. Background Art

[0002] In the field of gas sensors, in particular the field of so-called nondispersive infrared (NDIR) gas sensors, it is known to provide a chamber including an inlet for receiving a target gas to be analyzed and an outlet for discharging the gas to be analyzed, the chamber serving as an optical path for light to be absorbed by the target gas. A light source is provided at one end of the chamber, and a pair of electromagnetic radiation detectors are provided at the opposite end of the chamber, thereby providing a signal "arm" and a reference arm. With respect to carbon dioxide, for example, the amount of infrared electromagnetic radiation absorbed by the gas in the chamber is proportional to the concentration of the gas. Therefore, as the concentration increases, the signal output by the detector of the signal arm decreases. The reference arm is used to compensate for the drift of the light source over time and / or temperature, and when used should provide an output that does not change when the gas concentration in the chamber changes. This can be achieved by placing a bandpass filter in front of the reference detector, which allows only wavelengths of electromagnetic radiation that are not absorbed by the target gas to pass to the reference detector. The signal arm can be achieved by providing a bandpass filter in front of the absorption detector to allow only wavelengths of electromagnetic radiation absorbed by the target gas to pass to the absorption detector. The actual signal measured is the difference between the signal arm and the reference arm.

[0003] The typical method of creating a bandpass filter is to use an interference filter, which is usually composed of multiple thin layers of dielectric material with very well controlled thickness and different refractive indices. However, creating multiple thin layers of dielectric material with very well controlled thickness is a cumbersome and expensive process. Moreover, the performance of such filters varies with the incident angle of the received electromagnetic radiation, which means that when a light source with a wide angular spectrum is employed, the system performance is severely degraded.

[0004] Another gas sensor is the so-called Gas Filter Correlation (GFC) spectrometer, which, instead of a filter formed of a plurality of thin layers of dielectric material, employs a rotating filter wheel comprising two or more gas chambers, one of which is filled with an inert gas and the other of which is filled with a target gas or multiple target gases. The filter wheel is placed in the optical path between the light source and the sample chamber. A measurement detector is provided in the optical path so that the sample chamber is arranged between the filter wheel and the measurement detector. GFC spectrometers are expensive to produce and, like the NDIR sensors described above, are relatively large. Summary of the invention

[0005] According to a first aspect of the present invention, there is provided a gas sensor device configured to measure a predetermined gas of interest, the device comprising: a housing comprising a semiconductor substrate and defining a first cavity, a light-transmissive second closed cavity and a third cavity, the second cavity being interposed between the first cavity and the third cavity; wherein the first cavity comprises an inlet port for receiving the gas to be measured, an outlet port for discharging the gas to be measured, a light source and a measurement sensor; the second cavity is configured to act as a gas filter including a certain volume of the gas of interest sealed in the second cavity; and the third cavity comprises a reference measurement sensor disposed therein.

[0006] The reference measurement sensor may be sealingly disposed within the third cavity.

[0007] The second cavity may include a light-transmitting hole defining the first cavity and the third cavity.

[0008] The first cavity may be substantially cylindrical.

[0009] The second cavity may be disposed adjacent to the first cavity.

[0010] The third cavity may be disposed adjacent to the second cavity and outside the first cavity.

[0011] The housing may further include a cover configured to cooperate with the base plate to define the first cavity, the second cavity, and the third cavity.

[0012] The apparatus may further include: a wall extending away from the cover; wherein the wall may cooperate with the base plate to define the first cavity, the second cavity, and the third cavity.

[0013] The wall may be formed integrally with the cover.

[0014] The apparatus may further include: a wall extending away from the base plate; wherein the wall may cooperate with the cover to define the first cavity, the second cavity, and the third cavity.

[0015] The housing may include a reflective inner surface. The substrate may be reflective.

[0016] The substrate may include a first groove and a second groove relative to the first cavity; the light source may be disposed in the first groove and the measurement sensor may be disposed in the second groove.

[0017] The third chamber may include a getter.

[0018] According to a second aspect of the present invention, a method for manufacturing a gas sensor device is provided, the method comprising: providing a substrate including a first area, a second area and a third area; providing a cover; providing a light source and a measurement sensor within the first area of ​​the substrate; providing a reference sensor within the third area of ​​the substrate; configuring the cover; and adhering the cover to the substrate, the substrate and the cover cooperating to define a first cavity defining the first area, a second cavity defining the second area, and a third cavity defining the third area; and providing a certain volume of gas of interest in the second cavity; wherein the cover cooperates with the substrate so that the first cavity includes an inlet for receiving the gas to be measured and an outlet port for exhausting the gas to be measured.

[0019] The cover may include an inner wall; and the method may further include: respectively adhering shielding members to exposed ends of the inner wall; orienting the cover at a non-perpendicular angle relative to the longitudinal axis; rotating the cover about the longitudinal axis; and applying a layer of reflective material in a direction parallel to the longitudinal axis, the shielding member substantially preventing the reflective material from being applied to the inner wall.

[0020] The method may further include adhering the cover to the substrate in an atmosphere of the gas of interest.

[0021] Thus, a gas sensor device and method of manufacturing a gas sensor device can be provided which provides consistent measurement results over time despite changes from noise sources and / or long-term drifts caused, for example, by fluctuations in the intensity of the light source or by aging of the light source or sometimes by temperature. The device is also not dependent on the angle of incidence of the light on the filter. The device and method provide a very compact sensor device which is well suited for manufacture using semiconductor processing techniques or other techniques that allow low-cost mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] At least one embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0023] Figure 1 is a plan view of a gas sensor device constituting an embodiment of the present invention;

[0024] Figure 2 It is along the AA line Figure 1 A cross-sectional view of a gas sensor device;

[0025] Figure 3 It is along the BB line Figure 1 A cross-sectional view of a gas sensor device;

[0026] Figure 4 Is manufacturing Figure 1 A gas sensor device and a flowchart of a method constituting another embodiment of the present invention; and

[0027] Figure 5 is provided during an optically transparent window Figure 1 Schematic diagram of the cover. DETAILED DESCRIPTION

[0028] Throughout the following description, the same reference numerals will be used to identify the same components.

[0029] refer to Figure 1 , 2 3, the gas sensor device 100 includes a substrate layer 102 and a cover 104. The substrate layer 102 is attached to the cover 104 using any suitable method to form the housing 101, the method being, for example, eutectic bonding, glass paste bonding, thermocompression bonding, or bonding using any other suitable adhesive such as benzocyclobutene (BCB). In this example, the substrate layer 102 optionally includes: a first recess 106, which can be a groove formed in a first region of the substrate layer 102; a second recess 108, which can be a groove formed in a second region of the substrate layer 102; and a third recess 110, which can also be a groove formed in a third region of the substrate layer 102.

[0030] The light source 112 is disposed in the first recess 106, and the measurement detector 114 is disposed in the second recess 108. In this example, the light source 112 is configured to emit electromagnetic radiation having a wavelength that can be detected by the measurement detector 114, for example, light in the mid-infrared (MIR) range of the electromagnetic spectrum. In this example, the light source 112 is a MIR light emitting diode (LED). However, the technician will understand that other infrared electromagnetic radiation sources, such as a thermal heater, can be used. In this example, the measurement detector 114 is a photodetector. However, the technician will understand that other types of detectors, such as a thermopile or a bolometer, can be used. The reference detector 116 is the same type as the measurement detector 114 and is disposed in the third recess 110. In this example, circuits (not shown) for driving the light source 112, the measurement detector 114, and the reference detector 116 are integrated onto the substrate layer 102.

[0031] The cover 104 includes a cover layer 118 that provides a peripheral wall 120 that extends substantially vertically away from the cover layer 118 and an inner wall 122 that also extends substantially vertically away from the cover layer 118. In this example, the walls 120, 122 are integrally formed with the cover layer 118. Alternatively, the peripheral wall 120 and the inner wall 122 may be provided on the substrate layer 102. In this example, the cover 104 is attached to the substrate layer 102 and the peripheral wall 120 and the inner wall 122 cooperate with the substrate layer 102 to define a first cavity 124, a second cavity 126, and a third cavity 128. However, in the case where the substrate layer 102 is provided with the walls 120, 122, the walls 120, 122 cooperate with the cover layer 118 to define the first cavity 124, the second cavity 126, and the third cavity 128. The above-mentioned first area of ​​the substrate layer 102 is defined by the first cavity 124 , the second area of ​​the substrate layer 102 is defined by the second cavity 126 , and the third area of ​​the substrate layer 102 is defined by the third cavity 128 .

[0032] In this example, the first cavity 124 is substantially cylindrical in shape and includes an inlet port 130 for receiving a gas of interest to be tested and an outlet port 132 for exhausting the gas to be tested. In this example, the inlet port 130 and the outlet port 132 are disposed in the cover layer 118, although in other examples, the inlet port 130 and the outlet port 132 may be disposed at other locations relative to (e.g., around) the first cavity 124.

[0033] Thus, the light source 112 and the measurement detector 114 reside in the first cavity 124 and the reference detector 116 resides in the third cavity 128. In this example, the light source 112 is disposed at a first side 131 of the first cavity 124, and the measurement detector 114 is disposed at another location around the first cavity 124. In this example, the measurement detector 114 is disposed around the first cavity 124 between the measurement detector 114 and a location on a second side 133 of the first cavity 124 opposite the first side 131 of the first cavity 124, such as between the endpoints of a 90 degree arc extending between the light source 112 and the measurement detector 114, so as to cause light therein to reflect multiple times before reaching the measurement detector 114, and thereby achieve an extended period of time for the light to interact with the target gas despite the limited size of the first cavity 124.

[0034] In this example, the second cavity 126 is positioned adjacent to the first cavity 124 and diametrically opposite to the measurement detector 114. The second cavity 126 is light-transmissive and closed. In this example, the third cavity 128 is adjacent to the second cavity 126 and outside the first cavity 124. The volume of the second cavity 126 is filled with a gas of interest or "target gas" (e.g., carbon dioxide) to be tested, which is hermetically sealed within the second cavity 126. The first wall 134 defines the first cavity 124 and the second cavity 126, and the second wall 136 defines the second cavity 126 and the third cavity 128. The first wall 134 and the second wall 136 are at least partially light-transmissive, so that light emitted from the light source 112 can propagate through the first cavity 124, enter the second cavity 126 and pass through the third cavity 128. It can therefore be seen that the first wall 134 and the second wall 136 include light-transmissive holes that serve as windows. The second cavity 126 filled with the gas of interest serves as a filter for light entering the second cavity 126.

[0035] In this example, the inner surface of the peripheral wall 120 and / or the cover layer 118 is covered by a reflective material (e.g., metal) layer 138. The reflective material layer 138 is used to reflect light emitted by the light source 112, thereby reducing light loss to the peripheral wall 120 of the first cavity 124 and increasing the number of times the light passes through the gas to be measured in the first cavity 124. In some examples, another reflective material layer (not shown) can be applied to the substrate layer 102 only relative to the first cavity 124 or relative to the entire surface of the substrate layer 102 to serve as the inner surface of the housing 101. In some examples, the reflective material layer 138 can be roughened (as can be the case when the reflective material layer is applied to the substrate layer 102) in order to tune and optimize the scattering of light within the housing 101 (e.g., the first cavity 124). In another example, the surface(s) to which the reflective material layer 138 is applied can be roughened before the reflective material layer 138 is applied.

[0036] In operation, a measured gas, which is a predetermined gas of interest, is introduced into the first cavity 124 via the inlet port 130. The measured gas resides in the first cavity 124 until it leaves the first cavity 124 via the outlet port 132. During the time when the gas is being tested, the light source 112 emits infrared light in the MIR range of the electromagnetic spectrum. With the benefit of internal reflection caused by the reflective material layer 138, some of the infrared light emitted into the first cavity 124 is absorbed by any carbon dioxide molecules present in the measured gas. In this regard, some of the other wavelengths of the emitted light incident on the measurement detector 114 and any infrared light not absorbed by the measured gas are converted into electrical measurement signals. Similarly, some of the other wavelengths of the emitted light and any infrared light not absorbed by the measured gas pass through the second cavity 126 via the holes in the inner wall separating the first cavity 124 from the second cavity 126, and the MIR wavelength of the light propagating through the second cavity 126 is at least partially absorbed by the carbon dioxide gas present in the second cavity 126, which acts as a gas filter. The remaining wavelength of light continues to propagate through the second cavity 126 into the third cavity 128 via a hole in the inner wall separating the second cavity 126 from the third cavity 128. The light entering the third cavity 128 is incident on the reference detector 116, where the light incident on the reference detector 116 is converted into a reference electrical signal. The measurement electrical signal and the reference electrical signal are used as a differential signal to determine the amount and / or concentration of carbon dioxide present in the measured gas.

[0037] refer to Figure 4 and Figure 5 , the manufacture of the gas sensor device 100 can be as follows. A first blank silicon substrate and a second blank silicon substrate are grown using any suitable semiconductor growth technique (step 200). The first silicon substrate is used as the substrate layer 102 and the second silicon substrate is used for the cover 104. The cover layer 118 is then adapted (step 202) using, for example, deep reactive ion etching (DRIE) to provide the cover 104 with a peripheral wall 120, a first wall 134 and a second wall 136, an inlet port 130, and an outlet port 132. When placed together with the substrate layer 102, the peripheral wall 120 and the first wall 134 and the second wall 136 are used to define a first cavity 124, a second cavity 126, and a third cavity 128.

[0038] After etching (step 202), shields 300 are placed on the ends of the first wall 134 and the second wall 136 (step 204), which shields 300 can be, for example, a photoresist dry film. Each shield extends substantially vertically away from the first wall 134 and the second wall 136, respectively, and is used to prevent reflective material from reaching the first wall 134 and the second wall 136 during the subsequent deposition stage. In this regard, the cover 104 is oriented at a non-vertical angle relative to the longitudinal axis 302. The cover 104 is then rotated about the longitudinal axis 302, and a thin layer 138 of reflective material (e.g., gold, silver or copper) is applied in a direction parallel to the longitudinal axis 302 (step 206), and the shields 300 substantially prevent the reflective material from being applied to the first wall 134 and the second wall 136, thereby keeping the first wall 134 and the second wall 136 optically transparent and thus providing the light-transmitting holes mentioned above for use as windows. In another example, a light-transmitting hole can be defined by applying a photoresist by spraying to a portion on the first wall 134 and the second wall 136 to include a window. In such an example, a conformal coating of the photoresist may include a modified solvent composition to facilitate application. Once the reflective material layer 138 has been applied, the sprayed area of ​​the photoresist can be removed to complete the formation of the window. On the substrate layer 102, another thin layer of reflective material is optionally deposited (step 208). Similarly, a groove can be optionally etched into the substrate layer 102 using potassium hydroxide (KOH) or DRIE (step 210) to define a first recess 106, a second recess 108, and a third recess 110 to receive a light source 112, a measurement detector 114, and a reference detector 116, respectively. The light source 112, the measurement detector 114, and the reference detector 116 are then integrated on the substrate layer 102 by any suitable technology (e.g., flip-chip bonding or transfer printing) (step 212). Light source 112, measurement detector 114, and reference detector 116 may be electrically connected to other circuitry by wire bonding or using vias such as through silicon vias.Substrate layer 102 and lid 104 are then brought together and bonded together using, for example, wafer bonding (step 214).

[0039] In order to fill the second cavity 126 with the gas of interest (in this example, carbon dioxide), the bonding can be performed using an atmosphere of the target gas. If a hermetically sealed cavity without the presence of the target gas is required elsewhere in the gas sensor device 100, a getter can be provided in the cavity where the target gas is not required (e.g., the third cavity 128) to remove the target gas.

[0040] Alternatively, hermetic sealing of the cavity where the unwanted target gas is located can be avoided during the wafer bonding process by allowing the target gas to escape (e.g., by providing a small hole that can be closed later using any suitable filler). In this example, the activation temperature of the getter is higher than the temperature used in the bonding process, and the getter is activated after the bonding process by exposing the cavity housing to the getter activation temperature. Alternatively, the getter can be reactivated when a getter with such an activation temperature cannot be used.

[0041] It will be appreciated by those skilled in the art that the above implementations are merely examples of various implementations that are conceivable within the scope of the appended claims. Indeed, it will be appreciated that while in this example the shield is applied to the ends of the walls 120, 122 of the cover layer 118, in alternative examples where the walls 120, 122 are provided for the substrate layer 102, the shield is applied to the ends of the walls 120, 122 of the substrate layer 102. Likewise, while the circuitry for driving the light source 112, the measurement detector 114, and the reference detector 116 is described above as being integrated into the substrate layer 102, the skilled artisan will appreciate that the circuitry for one or more of these devices may be provided elsewhere, for example, on a separate integrated circuit die that is wire-bonded to one or more of the respective devices 112, 114, 116.

[0042] As mentioned above, a thermal heater can be used as an infrared electromagnetic radiation source. In such examples, at least from the perspective of energy saving, it is desirable to provide a thermal heater for the first cavity 124, the second cavity 126, and the third cavity 128 in a separate cavity. In this regard, the cover layer 118 can be formed with an additional wall so that when the cover layer 118 is in contact with the substrate layer 102 to form the gas sensor device 100, an additional cavity for accommodating the thermal heater is provided, which is arranged adjacent to the first cavity 124 and outside the other cavities 126, 128. Of course, in other examples as described above, the substrate layer 102 may include an additional wall instead of the cover layer 118. For example, an additional cavity may be formed so that the thermal heater is contained in a vacuum to avoid convection cooling. The additional wall may be configured to include another window to allow electromagnetic radiation emitted by the thermal heater when in use to propagate into the first cavity 124. The thermal heater may include a resistor formed on the film, for example, the resistor is used to heat the film. In other examples, for example, in the case where the temperature of the film needs to be monitored, the film may optionally include one or more thermopiles.

[0043] It should be understood that, unless otherwise expressly stated, references to "infrared" herein are intended to be references to electromagnetic energy having a wavelength in the range of 700 nm to 1 mm (such as 760 nm to 1 mm or 700 nm to 1500 nm), including electromagnetic radiation in the near infrared region, mid infrared region, and far infrared region.

Claims

1. A gas sensor device configured to measure a predetermined gas of interest, the device comprising: A housing, the housing comprising a semiconductor substrate and defining a first cavity, a second cavity and a third cavity, wherein the second cavity is a light-transmitting closed cavity and is located between the first cavity and the third cavity; in The first chamber includes an inlet port for receiving the gas to be measured, an outlet port for discharging the gas to be measured, a light source and a measurement sensor; The second chamber is configured to act as a gas filter including a volume of the gas of interest sealedly disposed in the second chamber; and The third chamber includes a reference measurement sensor disposed therein.

2. The device according to claim 1, characterized in that The second cavity includes a light-transmitting hole defining the first cavity and the third cavity.

3. The device according to claim 1, characterized in that The first cavity is cylindrical.

4. The device according to claim 1 or claim 2 or claim 3, characterized in that The second cavity is disposed adjacent to the first cavity.

5. The device according to claim 1 or claim 2 or claim 3, characterized in that The third cavity is disposed adjacent to the second cavity and outside the first cavity.

6. The device according to claim 1 or claim 2, characterized in that The housing further includes a cover configured to cooperate with the base plate to define the first cavity, the second cavity, and the third cavity.

7. The apparatus of claim 6, further comprising: a wall extending away from the cover; in The wall cooperates with the base plate to define the first cavity, the second cavity, and the third cavity.

8. The device according to claim 7, characterized in that The wall is integrally formed with the cover.

9. The apparatus of claim 6, further comprising: a wall extending away from the base; in The wall cooperates with the cover to define the first cavity, the second cavity, and the third cavity.

10. The device according to claim 1 or claim 2, characterized in that The housing includes a reflective inner surface.

11. The device according to claim 1 or claim 2, characterized in that The substrate includes a first groove and a second groove relative to the first cavity, the light source is disposed in the first groove and the measurement sensor is disposed in the second groove.

12. The device according to claim 1 or claim 2, characterized in that The third chamber includes a getter.

13. A method of manufacturing a gas sensor device, the method comprising: providing a substrate including a first region, a second region, and a third region; Provide a cover; providing a light source and a measurement sensor in the first region of the substrate; providing a reference sensor within the third region of the substrate; configuring the cover; as well as adhering the cover to the substrate, the substrate and cover cooperating to define a first cavity defining the first region, a second cavity defining the second region, and a third cavity defining the third region; as well as providing a volume of a gas of interest in the second chamber to act as a gas filter for the third chamber; in The cover cooperates with the base plate so that the first cavity includes an inlet port for receiving a gas to be measured and an outlet port for exhausting the gas to be measured.

14. The method according to claim 13, characterized in that: The cover comprises an inner wall; and the method further comprises: adhering shielding members to the exposed ends of the inner walls, respectively; orienting the cover at a non-perpendicular angle relative to the longitudinal axis; rotating the cover about the longitudinal axis; and A layer of reflective material is applied in a direction parallel to the longitudinal axis, the shield preventing the reflective material from being applied to the inner wall.

15. The method of claim 13 or claim 14, further comprising: The cover is adhered to the substrate in an atmosphere of the gas of interest.

Images