Gas sensor

Abstract

A sensor assembly and a method of manufacturing a sensor assembly. The sensor comprises a gas sensor, and the gas sensor comprises a gas sensing range; and a package comprising one or more walls, where the walls define a volume to accommodate the gas sensor, and where one wall comprises an opening defining an inlet to the package. The package includes a deflecting surface within the volume, where, in use, the deflecting surface is configured to deliver gas molecules to a gas sensing range.

Description

TECHNICAL FIELD

[0001] The present application relates to gas concentration and composition sensors. BACKGROUND

[0002] Thermal conductivity gas sensors are widely used in many applications due to their low cost, small size, ability to measure a variety of gases and large concentration range.

[0003] When used to detect leaks of hazardous gases, one stringent requirement for any gas sensor is fast response time. The sensor should detect the leak as soon as possible so that the system can react and prevent potentially devastating consequences such as explosions, poisoning or severe malfunctions.

[0004] However, the response time of any system depends only partly on the type and technology of the sensor used therein. The response time also depends to a large extent on the time it takes for the gas to reach the sensor’s sensing area. The sensor is usually located in a package and / or housing. The speed of transport of gas molecules towards the sensor housing or package can be accelerated by providing a fan, a blower or by making use of convection and buoyancy, etc. However, once the gas molecules have reached the aperture in the gas sensor housing or package, the time it takes for these molecules to reach the sensor’s sensing area depends on the gas diffusion.

[0005] EP2952886B1 relates to a method of manufacturing a gas sensor package. US8916408B2 relates to a lead frame based pre-molded package. US9708174B2 relates to a manufacturing process of a packaged device. SUMMARY

[0006] The present disclosure relates to a sensor assembly comprising a thermal conductivity gas sensor and a package surrounding the thermal conductivity gas sensor.

[0007] The thermal conductivity gas sensor is responsive to a flow, and therefore, it is beneficial to prevent the flow of gas to the sensing area so that the sensor’s reading can be determined by the presence and / or concentration of the target gas only. This means that the gas molecules, and in particular the target gas molecules, can only reach the sensing area by diffusion.

[0008] In order to enable a fast, accurate response of the sensor, it is an object of the present invention to reach a concentration of target gas molecules in the sensing area that is representative for the response as quickly as possible (e.g. at least more than 50% of the target gas concentration outside the package, or more preferably more than 90%).

[0009] The fast sensor response can depend on the “volume displacement time”, i.e. the time it takes for the gas filling the internal volume of the sensor assembly to reach the same composition as the outside environment by gas diffusion, or e.g. at least more than 50% of the target gas concentration outside the package, or more preferably more than 90%.

[0010] In the case of a sensor detecting a leak of a hazardous gas, the sensor can be configured to output a sensor response when the target gas concentration in the sensing region reaches the sensor's detection threshold for the target gas. This means that for applications where accurate measurement of the target gas concentration is required, the system response time can be reduced.

[0011] The sensor assembly in the present disclosure aims to improve the system response time and / or the volume displacement time while avoiding signal interference caused by parasitic flow.

[0012] Generally, the sensor assembly comprises a sensor with a sensing range and a package surrounding the sensor. The package can protect the sensor from unwanted contamination or interference while ensuring that the sensor effectively interacts with the environment to reliably operate. According to the present disclosure, the package of the sensor assembly aims to improve the response time of the system and the accuracy of the sensor by preferentially directing diffusing gas molecules, including target gas molecules, into the sensing region and / or reducing the impact of any potential parasitic gas flow on the sensor response.

[0013] The package of the disclosed sensor assembly, in particular the inlet and the internal volume, is configured to minimize the impact of the response time and / or parasitic flow.

[0014] The diffusion time of the gas from the inlet to the sensing range can depend on the position and size of the inlet relative to the sensing range, the obstruction of the features within the package, and the resulting internal free volume, all of which can be configured and arranged to more effectively direct the diffusion of gas molecules to the sensing range, thereby determining a preferential diffusion region within the package and / or reducing the impact of parasitic flow on the accuracy of the sensor reading.

[0015] The sensor assembly can be used with a gas concentration or composition sensor and a leak detector. The target gas can be H2. The principles disclosed herein can be applied to any gas composition or concentration sensor, as fast response time is required in any case. The disclosed sensor assembly is particularly useful for devices detecting hazardous gases, such as H2. Indeed, as the leakage of any hazardous gas can lead to fatal consequences, fast response time is an important requirement.

[0016] Aspects and preferred features are set out in the accompanying claims.

[0017] According to a first aspect of the disclosure, there is provided a sensor assembly comprising:

[0018] a gas sensor comprising a gas sensing range;

[0019] The package comprises one or more walls, wherein the walls define a volume that houses the gas sensor, and wherein one wall comprises an aperture that defines an inlet to the package, and the package comprises a deflection surface within the volume, wherein, in use, the deflection surface is configured to deliver gas molecules to the sensing region.

[0020] The deflection surface can facilitate preferential diffusion of gas molecules to the sensing region.

[0021] The volume can be closed, i.e. it is surrounded and enclosed by the walls, but for any inlet that allows diffusion of gas into the volume. The volume can be referred to as the internal volume.

[0022] The deflection surface can extend to the sensing region of the gas sensor.

[0023] Diffusion here refers to diffusion of gas that is distinct from gas flow, including turbulent and laminar flow.

[0024] Generally, diffusion is a phenomenon that is driven by a concentration gradient. When a diffusing molecule of the target gas reaches the inlet of the package, a concentration gradient is formed between the region close to the inlet and the rest of the interior of the package, including the sensing region.

[0025] For steady state measurements, the system response time can be determined by the time it takes for the sensor to detect a change in concentration, i.e. when the concentration in the sensing region reaches a certain percentage of the concentration outside the package. For example, the response time“T50” or“T90” is often defined as the time it takes to measure 50% or 90% of the concentration outside the package. For hazardous gas and / or leak detection measurements, the system response time can depend on the time it takes for the concentration of the target gas to reach a predetermined absolute limit or threshold value in the sensing region. The absolute limit can be the lower detection limit of the sensor for the target gas, or a predetermined concentration below a predetermined threshold value, such as the lower explosive limit, so that the system can take countermeasures or issue a warning signal before a catastrophic event occurs.

[0026] In order for the response of the sensor to be accurate, so that the signal of the sensor truly represents the concentration and / or presence of the target gas, the sensing region is preferably not exposed to any gas flow, and gas molecules can only reach the sensing region by diffusion. This is because any gas flow can interfere with the response of the sensor.

[0027] A larger inlet can be provided to allow a large number of molecules to enter the interior of the package per unit time, thereby increasing the volumetric displacement rate of gas into the package, so that a large number of molecules are available for diffusion of the gas to various parts of the package. The width of the inlet can be between 100 microns and 1 mm. For example, the width of the inlet can be at least 500 microns. This can reduce the response time of the sensor. However, the inlet to the package, in addition to providing an entry point for gas molecules, can create a discontinuity in the package, which can affect the sensor itself. A larger inlet can increase turbulence and / or cause parasitic flows to occur within the package, which can also reach the sensing range, thereby affecting the accuracy of the sensor. A larger inlet can also cause the sensor to be damaged during handling and assembly (e.g. soldering to a printed circuit board) and be more susceptible to foreign matter.

[0028] The inlet can be laterally spaced from the sensing range so as not to overlap with the sensing range. The inlet can be in a non-overlapping relationship with the sensing range of the sensor. This means that the inlet is either provided on a wall that does not face the sensing range or, if provided on a wall that faces the sensing range, the projection of the inlet on the surface of the sensor does not overlap with the sensing range.

[0029] This further ensures that the sensing range is not directly exposed to the external environment, thereby avoiding interference of the sensing range by any dust, dirt or any foreign matter that can affect the accuracy of the response of the sensor. An inlet that does not overlap with the sensing range can reduce the effect of any turbulence and / or parasitic flows on the accuracy of the sensor readings.

[0030] The deflection surface can be configured to reduce the average distance of gas diffusion from the inlet to the sensing range.

[0031] As used herein, "main internal volume" or "effective volume" can refer to the portion of the enclosed or internal volume of the package in which the sensor is located.

[0032] One or more walls of the package can be configured to define a preferential diffusion region and a peripheral region within the volume.

[0033] "Preferential diffusion volume" or "preferential diffusion region" as used herein means, respectively, a volume or region in the main internal volume, starting from the inlet, at least partially defined by the deflection surface, ending with the sensing range. The preferential diffusion region can include a path that defines the physically shortest distance between the gas sensor inlet and the sensing range.

[0034] It can be appreciated that the walls defining the internal volume can define the preferential diffusion region together with the deflection surface.

[0035] In preferred embodiments, the preferred diffusion region can provide a shortest diffusion path from the inlet to the sensing range, and / or a diffusion path that is not significantly affected by parasitic flow. In certain embodiments, the shortest diffusion path can be the shortest physical path between the inlet and the sensing range, which can include physical packaging tolerances and constraints.

[0036] The wall can include one or more outer walls, and can additionally include one or more inner walls. The deflection surface can be part of an inner wall of the one or more walls that extends from the one or more outer walls. The deflection surface can be a surface of an inner wall that extends from the outer wall into or toward the enclosed volume and toward the sensing range.

[0037] The deflection surface can be integral with one of the outer walls. In other words, the deflection surface can be a surface of the outer wall that faces into the interior of the volume.

[0038] The deflection surface can be oriented toward the inlet. Alternatively, the deflection surface can be proximate to the inlet. The deflection surface can extend toward the inlet and / or toward the sensing range, and proximate to the shortest path between the inlet and the sensing range.

[0039] The deflection surface can form a non-zero or non-parallel angle with respect to the outer wall or with respect to an outer surface of the outer wall from which the deflection surface extends. This can direct gas diffusing into the package to the sensing range and reduce diffusion of gas to areas of the enclosed volume that are distal from the sensing range. The deflection surface can form an obtuse angle facing the inlet with respect to an outer surface of the wall from which the deflection surface extends.

[0040] The inner wall containing the deflection surface can be oriented to at least partially exclude one or more regions of the primary interior volume from the preferred diffusion region, which one or more regions are peripheral with respect to the region between the inlet and the sensing range, and / or to at least partially shield the sensing range from turbulent and / or parasitic flow.

[0041] The package can include a bottom wall on which the sensor is located, a top wall opposite the bottom wall, and one or more side walls.

[0042] The inner wall containing the deflection surface can extend from the top wall and / or the bottom wall.

[0043] The inner wall containing the deflection surface can extend between two side walls, and can have one or more ends that are in contact with one, both, or neither of the two side walls. The inner wall containing the deflection surface can obstruct diffusion of target gas molecules to peripheral regions of the interior volume of the package.

[0044] The interior volume can be comprised of two or more different or separate volumes. A first volume of the two or more volumes can enclose the preferred diffusion region, and a second volume of the two or more different volumes can enclose the peripheral region.

[0045] The inner wall comprising a deflecting surface can be configured to divide the enclosed volume into two or more different volumes or regions. This reduces the effective volume of the package into which gas can diffuse.

[0046] The package can further comprise additional inner walls at least partially defining the main interior volume, and excluding components of the enclosed volume from the target gas diffusion, or hindering diffusion of target gas molecules to peripheral regions of the enclosed volume.

[0047] The portion of the main interior volume from which target gas diffusion is excluded or reduced can be, for example, a peripheral void adjacent to the outer wall, or a portion of the volume occupied by other features of the sensor, such as pads, electrical connections, and / or other features of the device.

[0048] The inner wall comprising a deflecting surface can at least partially divide the enclosed volume, and / or reduce the effective volume of the enclosed volume into which gas can diffuse. When the interior volume is divided by the inner wall, a main interior volume and one or more peripheral interior volumes adjacent to the main interior volume can be defined. The peripheral interior volumes can not house the sensor, but can house other components of the sensor assembly. The interior peripheral volumes can be at least partially filled with the same or different suitable material as the inner wall.

[0049] The deflecting surface can be integral with one of the outer walls. The deflecting surface can be monolithically formed with one of the outer walls. In these cases, the outer wall comprising the deflecting surface has a first thickness in a region corresponding to the deflecting surface, and a second thickness in a region not corresponding to the deflecting surface, the second thickness being different from the first thickness, measured in a direction perpendicular to the outer surface of the outer wall.

[0050] The outer wall can comprise a first region having a first thickness and a second region having a second thickness. The first and second thicknesses can be thicknesses measured in a direction perpendicular to the outer surface of the outer wall. The first thickness can be much greater than the second thickness. The first thickness can be at least twice the second thickness.

[0051] A first outer wall of the outer walls can have a first portion having a first thickness and a second portion having a second thickness. In other words, one of the outer walls can have multiple thicknesses, or two or more regions having different thicknesses. The first and second thicknesses can be thicknesses measured in a direction perpendicular to the outer surface of the outer wall.

[0052] In some embodiments, one or more of the outer walls can have different thicknesses at different locations, in particular they can have a greater thickness at locations corresponding to the peripheral regions of the enclosed volume.

[0053] In some embodiments, one or more of the outer walls have different thicknesses at different locations, in particular they have a smaller thickness in the region where the inlet is provided, so that the length of the diffusion path through the inlet is shortened and diffusion of gas molecules from the outside to the inside of the package is faster.

[0054] A first one of the outer walls can have a first thickness, and a second one of the outer walls can have a second thickness. In other words, different ones of the outer walls can have different thicknesses. The first thickness and the second thickness can be thicknesses measured in a direction perpendicular to the respective outer surface. The first wall can have a thickness equal to the first thickness, and the second wall can have a thickness equal to the second thickness.

[0055] The walls of the package (both outer and / or inner, if any) can be configured so that the enclosed volume has at least partially a similar shape or profile as the gas sensor. In other words, at least part of the shape of the inner volume can match the shape of the gas sensor.

[0056] In some embodiments, the thickest region of one or more of the outer walls can be immediately adjacent to the sensor, so as to match the volume occupied by the sensor, and separated from the sensor by only the minimum offset or gap required for manufacturing and positioning the sensor. In other words, part of the inner wall can follow part of the perimeter of the sensor.

[0057] The distance between the wall or walls closest to the gas sensor and the gas sensor can be less than 100 micrometers. More preferably, the distance between the one or more walls and the gas sensor can be less than 50 micrometers.

[0058] For a commercial standard package with the same external shape and dimensions suitable for a MEMS device, the package in the present disclosure can be described as having a reduced internal volume, where diffusion of the target gas is limited or delivered to the sensing range through a preferred diffusion volume.

[0059] The one or more walls can comprise a single hole forming the inlet configured to fluidically connect the enclosed volume of the sensor assembly with the external environment. In other words, the one or more walls can not comprise an outlet, and gas diffuses in and out of the package only through the single hole.

[0060] The inlet can be circular.

[0061] The inlet can be provided on a top outer wall of the package. The inlet can be provided on a side outer wall of the package.

[0062] An inlet or aperture can comprise an elongate slot in an outer wall, such as a top wall or a side wall of one or more walls. The length of the inlet can be up to 3mm. The inlet can be formed in a first wall, which can be located opposite a second wall of the one or more walls in which the gas sensor is located. The inlet can be formed in a first wall, which can be located adjacent to a second wall of the one or more walls in which the gas sensor is located. The slot can extend in a transverse direction. The width of the slot in a first direction can be greater than the width of the gas sensor in the same direction. A large aperture can help to improve the response time and / or volume displacement time of the sensor.

[0063] The package can comprise two or more inlets.

[0064] The shape and / or size of a first inlet of the two or more inlets can be the same as a second inlet of the two or more inlets.

[0065] Alternatively, the shape and / or size of a first inlet of the two or more inlets can be different to a second inlet of the two or more inlets.

[0066] The sensor assembly can comprise at least two inlets formed in a single wall of the one or more walls. The two or more inlets can be formed in a first wall of the one or more walls in which the gas sensor is located opposite a second wall. The two or more inlets can be formed in a first wall of the one or more walls in which the gas sensor is located adjacent to a second wall. The at least two inlets can be spaced apart from each other in a transverse direction.

[0067] The at least two inlets can be formed in different walls of the one or more walls.

[0068] The one or more walls can comprise a top wall opposite a base wall, and one or more side walls extending between the top wall and the base wall. The gas sensor can be formed on the base wall.

[0069] The sensor assembly can further comprise a barrier wall or portion located between the inlet and the gas sensor. The barrier wall can extend from an outer wall or an inner wall. The barrier wall can extend from the top wall towards the inlet, or from a region above or below the inlet. The barrier wall is arranged such that gas molecules diffusing from the inlet towards the sensing region must diffuse around the barrier, as the direct diffusion path from the inlet to the sensing region is blocked by the barrier wall. The barrier wall is particularly useful when the package contains multiple inlets and / or the inlets extend in a transverse direction. In these cases, some parasitic flow can enter the package, and the barrier wall can prevent the parasitic flow from reaching the sensing region and affecting the signal provided by the sensor.

[0070] The sensor assembly can comprise a foreign matter collection region between the inlet and the barrier wall, in which foreign matter can be collected rather than being pushed around the barrier wall with the gas molecules.

[0071] The isolation wall can direct gas molecules around the isolation wall to diffuse to the sensing range, i.e. to the preferred diffusion area. In these embodiments, the preferred area can not contain the shortest physical diffusion path relative to a diffusion area without the isolation wall. On the other hand, such a diffusion area can still be defined as a preferred diffusion area, as it can avoid parasitic flows from affecting the sensor's sensing range.

[0072] In some embodiments, the sensor can comprise a substrate or a mold supporting the sensing range. The inlet can be located above a surface of the substrate or mold providing the sensing range. The isolation wall can extend from the substrate of the sensor so that, in use, it can deflect gas molecules diffusing within the package, thereby directing them to the preferred diffusion area and, in turn, to the sensing range.

[0073] In other embodiments, the inlet can be located on an outer wall of the side wall, such that the distance between the bottom wall on which the sensor is located and the most distant edge of the inlet in the direction of the thickness of the sensor is less than the thickness of the sensor in the same direction. This can prevent residual gas flows from reaching the sensing area. In these cases, the side wall of the substrate or mold or the side wall facing the inlet can act as the isolation wall.

[0074] In another aspect of the disclosure, a sensor assembly is provided, comprising:

[0075] a gas sensor comprising a gas sensing range;

[0076] a package comprising one or more walls, wherein the walls define a volume containing the gas sensor, and wherein one wall comprises an aperture defining an inlet of the package;

[0077] wherein the inlet is laterally spaced from the gas sensing range, and the package further comprises an isolation wall located within the volume between the inlet and the gas sensing range

[0078] The isolation wall can extend at least from one outer or inner wall of the package.

[0079] The isolation wall can be configured to at least partially define a first area and a second area of the volume, wherein the gas sensor can be located within the first area, and the inlet can be located within the second area.

[0080] The isolation wall can be configured to reduce gas flow between the inlet and the gas sensing range.

[0081] The isolation wall can be arranged in such a way that gas molecules diffusing from the inlet to the sensing range are forced to diffuse around the isolation wall, as the direct diffusion path from the inlet to the sensing range is blocked by the isolation wall. The isolation wall is particularly useful when the package contains multiple inlets and / or the inlet is laterally elongated. In these cases, some parasitic flows can enter the package, and the isolation wall can avoid the parasitic flows from reaching the sensing range and affecting the signal provided by the sensor.

[0082] The package can include two or more inlets. The two or more inlets can be formed on separate walls of the package.

[0083] A first inlet of the two or more inlets can be laterally spaced apart from a second inlet of the two or more inlets in a first direction. The isolation wall can extend along the first direction.

[0084] The first opening can be located on a side wall and the second opening can be located on another side wall, e.g., an opposite side wall. In other words, a first inlet of the two or more inlets can be formed on a first side wall of the package and a second inlet of the two or more inlets can be formed on a second side wall opposite the first side wall.

[0085] Alternatively, a first inlet of the two or more inlets can be formed on a first side wall of the package and a second inlet of the two or more inlets can be formed on a top wall of the package.

[0086] The inlets can extend laterally along the first direction and the isolation wall can extend along the first direction.

[0087] Such a package can allow for fast displacement but can let residual or parasitic gas flow into the internal volume. The presence of the isolation wall can protect the sensing region from the residual or parasitic flow and limit the gas diffusion volume to the volume immediately adjacent to the sensor.

[0088] The walls of the package can include a top wall opposite the bottom wall and one or more side walls extending between the top wall and the bottom wall and the gas sensor can be formed on the bottom wall.

[0089] The isolation wall can extend from a first side wall of the one or more side walls to a second side wall of the one or more side walls opposite the first side wall.

[0090] The isolation wall can extend from the bottom wall and in contact with both opposite side walls so that gas molecules can diffuse out of the isolation wall around the top end of the isolation wall. The isolation wall can extend from the top wall and in contact with both opposite side walls so that gas molecules can diffuse out of the isolation wall around the bottom end of the isolation wall.

[0091] The isolation wall can extend between both opposite side walls so that gas molecules can diffuse out of the isolation wall around both the top and bottom ends of the isolation wall.

[0092] Alternatively, the isolation wall can extend from the top wall to the bottom wall. This allows gas molecules to diffuse out of the isolation wall around both the top and bottom ends of the isolation wall.

[0093] The outer wall of the package can comprise a first region having a first thickness and a second region having a second thickness. The first and second thicknesses can be thicknesses measured in a direction perpendicular to the outer surface of the outer wall. The first thickness can be substantially greater than the second thickness. The first thickness can be at least twice the second thickness.

[0094] The first portion of the outer wall can have a first thickness and the second portion can have a second thickness. In other words, one wall of the outer wall can have multiple thicknesses, or two or more regions having different thicknesses. The first and second thicknesses can be thicknesses measured in a direction perpendicular to the outer surface of the outer wall.

[0095] In some embodiments, one or more of the outer walls have different thicknesses at different locations, in particular they have a greater thickness at a region corresponding to a peripheral region of the enclosed volume.

[0096] In some embodiments, one or more of the outer walls have different thicknesses at different locations, in particular they have a greater thickness at a region corresponding to a peripheral region of the enclosed volume.

[0097] A first outer wall of the outer wall can have a first thickness and a second outer wall of the outer wall can have a second thickness. In other words, different walls of the outer wall can have different thicknesses. The first and second thicknesses can be thicknesses measured in a direction perpendicular to the respective outer surface. The first wall can have a thickness equal to the first thickness and the second wall can have a thickness equal to the second thickness.

[0098] As mentioned above, the walls of the package in the region where the sensor is located can at least partially match the shape of the sensor.

[0099] The isolation wall can define a collection region for retaining any foreign matter. In other words, the sensor assembly can comprise a foreign matter collection region between the inlet and the isolation wall. Any foreign matter can be collected in the foreign matter collection region rather than being pushed around the isolation wall along with the gas molecules.

[0100] It will be appreciated that even though the inner side of the inner or outer wall of the sensor assembly package of the present disclosure shown herein is planar, this is by no means a limitation. At least in appropriate cases, some curved or stepped walls or any other suitable geometrically shaped walls can be used to improve the effect of the present invention.

[0101] It will be appreciated that any of the inner walls or partition walls can or can not comprise the same material as the outer wall. It will also be appreciated that the outer wall can or can not be made of the same material. In some embodiments, at least a portion of the outer wall can comprise a gas permeable membrane, which can act as a first inlet to prevent ingress of foreign particles such as dust into the enclosed volume of the package. In other embodiments, the inlet can be equipped with a filter to prevent ingress of foreign particles such as dust into the enclosed volume, for example a metal mesh filter, a paper filter, a charcoal filter, and the like.

[0102] The inner walls and / or partition walls can be made of a polymeric material that is deposited on the device after fabrication, for example by spin coating and patterning of a thick coating of SU-8 or PDMS.

[0103] The package of the sensor assembly can employ a standard MEMS package that is commercially available, typically in the shape of a cuboid with an open internal volume. They are readily available and low cost. It will be appreciated, however, that this is not a limitation and the package can be different, i.e. not based on a standard package. The package can have any suitable shape, including a cuboid, a parallelepiped, a sphere, an ellipsoid, a cylinder, a prism, a dome, and the like.

[0104] The package in the present disclosure can consist of at least two parts. The walls of the package can comprise a first part and a second part. The first part and the second part can together define a volume. The first part can comprise a package substrate having a cavity to house the gas sensor.

[0105] In some preferred embodiments, the first part can comprise a lower wall of the package on which the sensor is located. In preferred embodiments, the first part can comprise a PCB board (referred to as a chip-on-board (CoB)).

[0106] The second part can comprise a structure that encloses the sensor when located on the first part. The second part can be a bottomless cuboid-like structure, a cylindrical-like structure, a dome-like structure, or any other suitably shaped structure.

[0107] The second part can comprise a top wall of the package. In certain embodiments, the second part is a lid. The lid can be flat or at least partially convex or concave with respect to the enclosed volume so as to cooperate with the rest of the walls of the package, accommodate bulky features or components, and / or further reduce the enclosed volume.

[0108] Further parts can be provided, for example, the first part and / or the second part can consist of two or more sub-parts to provide a modular package to accommodate different sizes of sensors and / or different application requirements.

[0109] The first and second portions can be secured to one another in any suitable manner known in the art, for example, bonded together using a suitable bonding material.

[0110] In another aspect of the disclosure, a sensor module is provided, comprising the housing and the sensor assembly described above. The housing can house other components and elements of the sensor module, such as a printed circuit board (PCB), a microcontroller, and other electronic components. For example, the sensor assembly can be mounted on a printed circuit board, which is then mounted within the housing. The housing or the sensor assembly can have a filter mounted at one or more of the holes or openings. The housing can have means to establish electrical connections between the components within the housing and the outside world.

[0111] The package of the sensor assembly can comprise a single hole, and the housing can comprise two or more holes. The two or more holes of the housing can form an inlet and an outlet of the housing. In this way, a flow of gas molecules can be established between the inlet and the outlet of the housing, thereby allowing the housing to complete a volume displacement in a short time, which in turn ensures that the target gas molecules reach the package of the sensor assembly quickly. The package can be equipped with one inlet to avoid parasitic flow reaching the sensing area, or multiple inlets or one elongated inlet in combination with a barrier to prevent any parasitic flow from reaching the sensing area.

[0112] The package can comprise two or more holes, and the housing can comprise one hole. In other words, the gas can only enter and exit the housing through a single hole. In a preferred embodiment, the single hole of the housing can extend laterally in at least one direction to allow for a rapid change in concentration within the housing.

[0113] According to another aspect of the disclosure, a method of manufacturing a sensor assembly is provided, the method comprising:

[0114] forming a gas sensor comprising a gas sensing region,

[0115] forming a package comprising one or more walls, wherein the walls define a volume that houses the gas sensor, and wherein one of the walls comprises a hole that defines an inlet of the package, and

[0116] wherein the package comprises a deflection surface located within the volume, wherein, in use, the deflection surface is configured to deliver gas molecules to the sensing region.

[0117] According to a further aspect of the disclosure, a method of manufacturing a sensor assembly is provided, the method comprising:

[0118] forming a gas sensor comprising a gas sensing region,

[0119] forming a package comprising one or more walls, wherein the walls define a volume that houses the gas sensor, and wherein one of the walls comprises a hole that defines an inlet of the package, and

[0120] wherein the inlet is laterally spaced apart from the gas sensing region, and wherein the package further comprises a partition wall within the volume and between the inlet and the gas sensing region.

[0121] The package can be made by moulding. Alternatively, the package can be made by additive manufacturing techniques, 3D printing and any other suitable method. BRIEF DESCRIPTION OF DRAWINGS

[0122] Some embodiments of the present disclosure will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0123] Figure 1 (a) shows a top view of a known gas sensor package;

[0124] Figure 1 (b) shows a perspective view of the internal volume of the package shown in Figure 1 (a) as part of a gas sensor assembly;

[0125] Figure 1 (c) shows a simulated diffusion path for the internal volume shown in Figure 1 (b);

[0126] Figure 1 (d) shows the normalised concentration of target gas in the internal volume shown in Figure 1 (b) at the inlet (triangle) and the sensor sensing region (circle) as a function of time as the target gas molecules move by diffusion as shown in Figure 1 (c);

[0127] Figure 2 (a) shows a top view of a gas sensor assembly;

[0128] Figure 2 (b) shows a top view of a gas sensor assembly;

[0129] Figure 2 (c) shows the normalised concentration of target gas in the inlet (triangle) and the sensor sensing region (circle) as a function of time for the gas sensor assembly shown in Figure 2 (a) as the target gas molecules move by diffusion;

[0130] Figure 3 (a) shows a top view of a gas sensor package;

[0131] Figure 3 (b) shows a top view of a gas sensor assembly;

[0132] Figure 4 Figure 4 (a) shows a top view of a gas sensor package;

[0133] Figure 5 Figure 5 (a) shows a top view of a gas sensor package;

[0134] Figure 6 Figures 6 (a) to 6 (f) show top views of a gas sensor assembly;

[0135] Figure 7 (a) shows a perspective view of the internal volume of a gas sensor package of a gas sensor assembly;

[0136] Figure 7(b) shows the simulated diffusion path for the internal volume shown in Figure 7(a);

[0137] Figure 7(c) shows the normalised concentration of target gas in the sensor sensing region over time for the gas sensor assembly shown in Figure 7(a) with the target gas molecules moving by diffusion as shown in Figure 7(b);

[0138] Figure 8(a) shows a perspective view of the internal volume of a gas sensor package of a gas sensor assembly;

[0139] Figure 8(b) shows the simulated diffusion path for the internal volume shown in Figure 8(a);

[0140] Figure 8(c) shows the normalised concentration of target gas in the sensor sensing region over time for the internal structure of the gas sensor assembly shown in Figure 8(a) with the target gas molecules moving by diffusion as shown in Figure 8(b);

[0141] Figure 9 Figures 9(a) to 9(e) show plan views of gas sensor assemblies;

[0142] Figure 10 Figures 10(a) and 10(b) show cross-sections of gas sensor assemblies;

[0143] Figure 11 Figures 11(a) and 11(b) show cross-sections of gas sensor assemblies;

[0144] Figure 12 Figures 12(a) and 12(b) show cross-sections of gas sensor assemblies;

[0145] Figure 13 Figures 13(a) to 13(d) show plan views of gas sensor assemblies;

[0146] Figure 14 Figures 14(a) to 14(d) show cross-sections of gas sensor assemblies made up of at least two parts;

[0147] Figure 15 Figures 15(a) and 15(b) show cross-sections of gas sensor modules. DETAILED DESCRIPTION

[0148] Figure 1(a) shows a plan view of a known gas sensor package. The package is generally cuboid in shape and has side walls as shown in Figure 1(a) and a circular inlet.

[0149] Figure 1(b) shows a perspective view of the internal volume of a gas sensor assembly, which includes a package (not shown except for the bottom wall), as shown in Figure 1(a). A gas sensor is located in the internal volume. The gas sensor includes a sensing region formed on a substrate. The package defines the internal volume, into which gas can enter through an inlet. Figure 1(c) shows a simulated diffusion path for the internal volume of Figure 1(b). This shows that most gas molecules entering the package will diffuse around the periphery of the internal volume before reaching the sensitive region of the gas sensor. Figure 1(d) shows the normalized concentration of a target gas at the inlet (triangle) and the sensing region (circle) as a function of time for the internal volume of the sensor assembly shown in Figure 1(b). The response time of the sensor is the time required for the normalized concentration of the target gas at the sensing region to reach 90% of the concentration of the target gas in the external environment. This depends on the sum of the time required for the target gas to reach the inlet and the time required for the target gas to reach the sensing region from the inlet.

[0150] Figure 2(a) shows a top view of a package 100 of a gas sensor assembly according to an embodiment of the disclosure. Figure 2(b) shows a top view of an internal volume 120 of a gas sensor assembly according to an embodiment of the disclosure, which has a package with a smaller internal volume than the sensor package shown in Figure 1(a) because one of the walls 115a is thicker than the walls shown in Figure 1(a). The gas sensor assembly includes a gas sensor 105, which has a gas sensitive region 110. In this example, the package 100 is cuboid shaped, but it will be appreciated that the package can have other shapes. The package 100 includes opposing bottom and top walls (not shown, which extend parallel to the plane of the page). The gas sensor 105 is located on the bottom wall of the package. The package includes four side walls 115, which extend between the top and bottom walls to define an enclosed volume 120, in which the gas sensor 105 is located. The package 100 of the sensor assembly includes a region 125 in which the gas sensor 105 is connected to the package by wire bonds. An inlet 130 is located in the top wall of the package. The inlet 130 includes a hole through the top wall, which allows fluid to diffuse from outside the package into the internal volume 120.

[0151] As an example, for a MEMS sensor, the package can be a cuboid with a base of 2x2mm to 5x5mm, and a typical inlet can be a circle with a diameter of less than 1mm, for example 200-500 microns. It is known that the wall thickness of sensor packages can be in the range 100-200 microns, and the package in the present disclosure can have one or more walls with a thickness of 250-1000 microns.

[0152] In the illustrated example, the inlet 130 is formed laterally spaced from the sensing region 110 and the bond wires, such that the inlet is not located over the sensing region 110 or the bond wires. This reduces the disturbance of the sensing region by any residual or parasitic flow, as well as the damage to the bond wires and sensing region by turbulent or bulk flow of the gas to be sensed.

[0153] In certain examples, the sensor package 100 has a single inlet 130 and can have no outlet. This reduces the bulk flow (including laminar and turbulent flow) into the sensor package 100. This increases the relative influence of gas diffusion on the measurements made by the gas sensor 105, thereby increasing the sensitivity of the gas sensor 105 to gas concentration or composition, and reducing the noise caused by bulk gas flow.

[0154] In the example shown in Figure 2(a), the thickness of one of the side walls 115a is increased significantly relative to the known device shown in Figure 1(a) and the other walls of the Figure 2(a) device, such that the internal volume 120 within the package is reduced relative to the internal volume of the Figure 1(a) example package. Figure 2(c) shows the results of a simulation of target gas diffusion, namely the normalised concentration of target gas at the inlet 130 510 and the normalised concentration of target gas at the gas sensitive region 110 520. As can be seen, increasing the thickness of the wall reduces the time taken for gas to diffuse to the gas sensitive region 110, compared to the known device shown in Figures 1(a) to 1(d). In this example, the thickness of the increased thickness side wall 115a is twice or more than the thickness of the other side walls 115b, 115c, 115d. For example, the thickness of the side wall 115a can be between 250-1000 microns, for example 400 microns. Figure 2(a) and 2(b) In the example shown, the sensor 105 is located between the increased thickness side wall 115a and the inlet 130, and therefore the increased thickness side wall 115a reduces the enclosed volume of the shortest path between the inlet 130 and the gas sensitive region 110. This reduces the average distance that gas must diffuse from the inlet 130 to be detected at the gas sensitive region 110. In this example, the thickness of the increased thickness side wall 115a is twice or more than the thickness of the other side walls 115b, 115c, 115d. For example, the thickness of the side wall 115a can be between 250-1000 microns, for example 400 microns.

[0155] In the examples described in this specification, the internal walls and the walls of increased thickness can reduce the enclosed volume by about 10% to 50% compared to the known device shown in Figures 1(a) to 1(d).

[0156] The simulations described herein are performed by software that models diffusion of a substance by solving the Fick’s law and the relevant partial differential equations within a finite volume of air of given size and boundary conditions.

[0157] The package size modelled is 3x3mm with an inlet and housing a silicon chip. However, the package can be larger or smaller. The internal volume is modelled as air at 25°C and atmospheric pressure. As such, the simulations are not intended to be a model of a real-world device, but rather a model of the diffusion of a gas within a given volume of air.Figure 1(b) , 2(b) , 7(a) and 8(a), the internal volume is divided into a dense grid, providing a fixed-point three-dimensional framework for solving the mass transport equation for gas diffusion.

[0158] The response time T90 of the sensor can be evaluated by simulating the time required for the gas concentration to reach 90% of the inlet concentration Co over the sensitive area of the device. Although the results have been normalized, the numerical values used represent a typical gas concentration of 1% of the gas concentration Co in air. The gas diffusion coefficient Do = 10 -5 m 2 / s is assumed, which is consistent with the typical diffusion coefficients of gases such as water (vapor) and hydrogen (H2) under standard conditions. By changing the diffusion coefficient value at each required temperature, the effect of temperature variation in the range of -40°C to 125°C can be calculated.

[0159] As shown in Figure 1(c) , 7(b) and 8(b), the path of gas diffusion within the package is determined. By plotting the concentration vector as a function of time, the fastest diffusion path can be inferred and the range where a gas diffusion bottleneck can exist is determined. This is well demonstrated by Figure 1(c), which shows that the concentration front first passes through the inlet, then extends along the mold edge, and finally crosses the mold to reach the sensitive range.

[0160] Figure 2(c) shows that by thickening the side wall 115a of the package 100, the improvement in T90 is more than 200% (from 1.05 s to 0.3 s). This improvement is due to the fact that the gas is forced to flow directly to the gas sensitive range 110 of the device, rather than simultaneously diffusing to the right of the device. In other words, the lower right diffusion path shown in Figure 1(c) is blocked.

[0161] Figure 3(a) shows a top view of the side wall of a gas sensor package 100 according to an embodiment of the present disclosure, and Figure 3(b) shows a top view of an example gas sensor assembly having the package shown in Figure 3(a). The gas sensor package is similar to that shown in Figure 2(a) and thus has similar reference numerals. In this embodiment, the side wall 115 has different thicknesses. If the thickness t is defined as the first thickness, at least a portion of the side wall has a thickness t xIn the examples of Figures 3(a) and (b), the entire thickness of sidewall 115a is greater than t. Sidewall 115c has a region of thickness t and a region of thickness greater than t. The portion of sidewall 115c with a thickness greater than thickness t is located away from inlet 130. In the example shown, inlet 130 is located between the portion of sidewall 115c without increased thickness and the gas-sensitive area 110. It is understood that while sidewall 115c in the example of Figure 3(a) has a region of thickness t and a region of thickness greater than t, other sidewalls may also have a region of thickness t and a region of thickness greater than t. Generally, a sidewall may have at least a first portion of a first thickness and a second portion of a second thickness, wherein the second thickness is substantially greater than the first thickness.

[0162] Compared to a package where all sidewalls have a thickness of t, the portion of sidewall 115 with a thickness greater than t reduces the enclosed volume associated with the shortest path between inlet 130 and gas sensing range 110. This reduces the average distance gas travels from inlet 130 before being detected in gas sensing range 110. In this example, the thickness of the portion of sidewall 115c with increased thickness is twice the thickness of the portion without increased thickness. In some examples, the thickness of the portion of sidewall 115c with increased thickness is more than twice the thickness of the portion without increased thickness. The thickness of sidewall 115c is tapered, so the thickness change does not occur abruptly. This avoids blind spots and corners that create turbulence between the inlet and sensing area and provides a surface 115s, which is a deflecting surface extending toward the sensing area, to preferentially deliver target gas molecules entering the package to the sensing range, rather than to the peripheral region of the corner between walls 115c and 115b. In this embodiment, the deflecting surface 115s is integral with the outer wall 115c.

[0163] Figure 4 and Figure 5 A top view of a gas sensor assembly according to a further embodiment of the present invention is shown. Figure 4In the example of FIG. 1 1, the inner wall 135 is located inside the package. The inner wall 135 divides the interior volume of the package into a main interior volume containing the gas sensor and a peripheral interior volume, thereby reducing the volume containing the gas sensor. This can be used to reduce the enclosed volume, moving it away from the shortest path between the inlet 130 and the gas sensitive range 1 10, thereby reducing the average distance that a gas must diffuse from the inlet 130 to be detected in the gas sensitive range 1 10. The inner wall 135 can be in contact with both the top and bottom walls of the package, thereby completely excluding gas diffusion into the peripheral interior volume of the package. The inner wall 135 can be in contact with one or neither of the top and bottom walls of the package, thereby providing an obstacle to gas diffusion into the peripheral interior volume, such that the number of molecules diffusing into the peripheral interior volume per unit time is lower than the number of molecules diffusing into the main interior volume per unit time. In this case, the deflection surface 1 15s is contained in the inner wall 135 and preferentially passes diffusing gas molecules to the sensing range.

[0164] In the present example, the inner wall extends between two adjacent side walls 1 15b, 1 15c, although it could extend between two opposite side walls or any other side walls.

[0165] In Figure 5 In the example of the gas sensor assembly of FIG. 12, one end of the inner wall 140 extends from only one side wall 1 15c and the other end of the inner wall 140 is not connected to any side wall. The inner wall 140, and in particular the deflection surface 1 15s as part of the inner wall 140, can deflect any gas, thereby preventing or reducing gas diffusion to the area between the inner wall 140 and the side walls 1 15c, 1 15b. This increases diffusion along or close to the shortest path between the inlet 130 and the gas sensitive range 1 10, thereby reducing the average distance that a gas must diffuse from the inlet 130 to be detected in the gas sensitive range 1 10. The inner wall 140 is preferably in contact with both the top and bottom walls of the package, such that the only diffusion path towards the peripheral interior volume is on the side of the inner wall. The inner wall 140 can be in contact with one or neither of the top and bottom walls of the package, thereby still being able to obstruct most of the diffusion paths towards the peripheral interior volume, while still being able to provide some additional diffusion paths between the inner wall 140 and the top and / or bottom walls of the package.

[0166] Figure 6 (a) to (f) show different embodiments of gas sensor assembly packages according to the present disclosure.

[0167] Figure 6 (a) shows a gas sensor package similar to that shown in FIG. 3(a).

[0168] Figure 6 (b) shows a gas sensor package similar to that shown in FIG. 3(b). Figure 6The gas sensor package shown in (a) is similarly packaged, but the thicker portion of the sidewall 115 extends over a greater length of the sidewall 115c, and the deflection surface 115s is adjacent to the inlet 130. This further reduces the enclosed volume away from the shortest path between the inlet 130 and the gas sensitive region 110, thereby reducing the average distance that gas must diffuse from the inlet 130 to be detected in the gas sensitive region 110.

[0169] Figure 6 (c) shows a gas sensor package similar to that shown in Figure 6 (a), however, both opposing sidewalls 115a, 115c have regions of different thickness, rather than one sidewall having a constant thickness.

[0170] Figure 6 (d) shows a gas sensor package similar to that shown in Figure 6 (a), but the central region of the sidewall 115c has increased thickness between two regions of no increased thickness. Two deflection surfaces 115sl and 115s2 deflect gas to discourage or reduce diffusion to regions away from the central region and away from the inlet. This increases diffusion along or near the shortest path between the inlet 130 and the gas sensitive region 110, thereby reducing the average distance that gas must diffuse from the inlet 130 to be detected in the gas sensitive region 110.

[0171] Figure 6 (e) shows a gas sensor package similar to that shown in Figure 6 (a), however in this example, two inlets 130a, 130b are located within the package. This allows more gas to be diffused into the package, but also allows residual gas to flow into the package. The sidewall 115c adjacent to the second inlet 130b has a region of increased thickness. The portion of the sidewall 115c of increased thickness is away from the inlet 130a, which is located between the portion of the sidewall 115a of no increased thickness and the gas sensitive region 110. The thickened portion of the sidewall 115c reduces the enclosed volume away from the shortest path between the second inlet 130b and the gas sensitive region 110. This reduces the average distance that gas must diffuse from the inlet 130b to be detected in the gas sensitive region 110.

[0172] Figure 6 (f) shows a gas sensor package similar to that shown in Figure 6(a) and (b) show similar gas sensor packages. In this example, the gas sensor package comprises multiple chips, for example, a system consisting of sensor 105 and ASIC readout chip 170. A second electrical connection region 175 is formed for the ASIC readout chip. The additional chip (in this case, ASIC readout chip 170) reduces the internal volume, thereby shortening the average diffusion distance to the gas sensitive region 110 and shortening the sensor response time.

[0173] In the example shown, the side walls are configured to reduce the enclosed volume within the package.

[0174] It will be apparent that, Figure 6 The side walls of the packages shown in (a) to (f), or in other words, the internal volumes they define, at least partially match the shape of the sensor and, if present, the shape of other components of the sensing assembly. In other words, the side walls are configured such that the distance between the side walls and the components within the package is reduced. In some examples, the distance between the gas sensor 105 and the side walls can be less than 100 microns or less than 50 microns.

[0175] Figure 7(a) shows a perspective view of a gas sensor assembly internal volume. The internal space 120 is similar to that shown in Figure 1(b) and so similar reference numerals are provided. In this case, the package comprises two inlets 130a and 130b. The package (not shown, other than the bottom wall) defines an internal volume into which gas can enter from the two inlets. There can be a barrier wall opposite the sensing region and close to the two inlets, although other examples can not comprise a barrier wall. Figure 7(b) shows simulated diffusion paths for the internal volume 120 shown in Figure 7(a). Most of the gas will diffuse to the periphery of the volume before reaching the sensitive region of the gas sensor. The presence of two inlets or apertures can allow some residual gas flow within the internal volume of the package during operation and so a barrier wall can be provided between the two inlets and the sensing region to reduce any residual gas flow to the sensing region. Figure 7(c) shows that, due to the presence of the second inlet, the T90 (0.19s) is reduced relative to the T90 reported in Figure 1(d).

[0176] Figure 8(a) shows a perspective view of a gas sensor assembly internal volume according to an embodiment of the disclosure. The gas sensor assembly is similar to that shown in Figures 2 and Figure 9 and so similar reference numerals are provided. The internal volume 120 shown in Figure 8(a) can be defined by Figure 9The encapsulation in (a) defines where the two inlets 130a, 130b are provided through the top wall of the encapsulation, allowing for increased diffusion into the interior volume of the encapsulation. Both side walls 115a, 115c adjacent to the first inlet 130a and the second inlet 130b, respectively, have regions of increased thickness. The portions of the side walls 115a, 115c with increased thickness are distal from the inlets 130a, 130b, while the inlets 130a, 130b are between the portions of the side walls 115a, 115c with no increased thickness and the gas sensitive range 110. The thickened portions of the side walls 115a, 115c reduce the enclosed volume near the shortest path between the inlets 130a, 130b and the gas sensitive range 110. This reduces the average distance that a gas molecule diffusing from the inlets 130a, 130b is detected at the gas sensitive range 110 before it is detected. The deflection surfaces 115sl and 115s2 preferentially direct gas molecules diffusing within the encapsulation to the gas sensitive range 110. If there is any parasitic flow that can enter the interior volume and reach the gas sensitive range 110 of the gas sensor, thereby adversely affecting the accuracy of the sensor, the (optional) isolation wall can reduce this parasitic flow.

[0177] Figure 8(b) shows the diffusion paths for the interior volume shown in Figure 8(a), and Figure 8(c) shows the change in concentration of the sensing region over time for the interior volume shown in Figure 8(a). As can be seen, the increased thickness of the side wall portions, the deflection surfaces, and the two inlets instead of a single inlet further shorten the T90 (0.155 seconds).

[0178] In examples with a single inlet, including two inlets can have similar effects to increasing the inlet range. Enlarging the inlet or increasing the number of inlets can shorten the response time.

[0179] Figure 9 Figures (a) through (e) show various embodiments of gas sensor assemblies according to the present disclosure, with multiple inlets or laterally extending inlets.

[0180] Figure 9(a) shows a gas sensor package similar to that in Figure 8(a). In this example, two inlets 130a, 130b are provided in the package. This can increase diffusion into the package, but will also allow residual gas to flow into the package. The side walls 115a and 115c adjacent to the first inlet 130a and the second inlet 130b respectively have regions of increased thickness. The portions of the side walls 115a, 115c with increased thickness are distal from the inlets 130a, 130b, while the inlets 130a, 130b are located between the portions of the side walls 115a, 115c with no increased thickness and the gas sensitive region 110. The thickened portions of the side walls 115a, 115c reduce the enclosed volume in the vicinity of the shortest path between the inlets 130a, 130b and the gas sensitive region 110. This reduces the average distance that gas diffuses from the inlets 130a, 130b to be detected in the gas sensitive region 110.

[0181] Figure 9 (b) shows a gas sensor package similar to that in Figure 9 (a), however in this example the inlets are replaced by elongate slot inlets 150 through the top wall of the package. This allows an increased number of gas molecules to enter the internal main volume per unit time.

[0182] Figure 9 (c) shows a gas sensor package similar to that in Figure 9 (a), however in this example the inlets are replaced by elongate slot inlets 150 through the top wall of the package. This allows an increased number of gas molecules to enter the internal main volume per unit time.

[0183] Figure 9 (d) shows a sensor package similar to that shown in Figure 9 (c). In this example, the sensor assembly includes a barrier wall 160 between the inlets 150 and the sensing region 110. The barrier wall 160 can extend from the top wall of the package to the gas sensor 105. The barrier wall 160 reduces the parasitic gas flow from the elongate inlets 150 to the gas sensitive region 110, while still allowing gas to diffuse towards the gas sensitive region 110. In certain embodiments, the barrier wall 160 can extend from the base of the sensor to the top wall, so that in use it can deflect gas molecules diffusing within the package. The barrier wall 160 is located laterally between the inlets 150 and the gas sensitive region 110.

[0184] Figure 9 (e) shows a sensor package similar to that shown in Figure 10(d) shows a similar package for a gas sensor package. In this further example, the package has an elongated inlet located in a side wall rather than a top wall. An isolation wall 160 can extend from the top wall to the bottom wall of the package and / or to the sensor. The isolation wall 160 is located between the inlet 150 and the gas sensitive range 110. The isolation wall 160 reduces the parasitic gas flow from the elongated inlet 150 to the gas sensitive range 110 while still allowing gas to diffuse to the gas sensitive range 110.

[0185] Figure 9 (a) shows a cross section of a gas sensor assembly having a package 100 as shown in FIGS. 2 through Figure 9 The sensor package can be similar to the package shown in FIGS. 2 through Figure 10 In this example, the thickness of the two side walls 115a, 115c shown increases at the lower portion of the side walls. This reduces the enclosed volume within the package 100, thereby shortening the average diffusion distance and improving the sensor response time. The sensor 105 is provided with electrical connections 180.

[0186] Figure 9 (b) shows a cross section of a gas sensor assembly having a package similar to the package shown in FIGS. 2 through Figure 9 The sensor package can be similar to the package shown in FIGS. 2 through Figure 11 In this example, the thickness of one side wall 115c increases gradually near the upper portion of the side wall, while the thickness of the other side wall 115a increases gradually near the lower portion of the side wall. This reduces the enclosed volume within the package 100, thereby shortening the average diffusion distance and improving the sensor response time. The thickness of the side walls can vary vertically and horizontally in general.

[0187] Figure 10 (a) shows a cross section of a gas sensor assembly. The sensor package can be similar to the package shown in FIGS. 2 through Figure 11 In this example, the inlet 150 is formed in the side wall 115c of the package. In this example, the inlet 150 is located below the upper surface of the sensor 105 and the gas sensitive range 110, so the gas sensitive range is located above the inlet 150. In this example, the side wall of the gas sensor 105 or the side wall facing the inlet 150 can also act as an isolation wall. This reduces the parasitic gas flow on the sensitive range 110. The inlet 150 is formed as a hole through the package side wall 115c. The side wall 115c having the inlet has a region with a thickened area above the inlet 150 and away from the inlet 150. The side wall 115a opposite the inlet 150 and away from the inlet 150 has a region with a thickened area at the lower portion of the side wall.

[0188] Figure 11(b) shows a cross-section of a gas sensor assembly with an additional gas sensor package. The sensor package can be similar to the one shown in Figures 2 to Figure 9 (a) and is therefore provided with similar reference numbers. In this example, the inlet 150 is formed in the side wall 115c of the package and the isolation wall 160 is formed between the inlet 150 and the sensing range. The inlet 150 can extend laterally as shown in Figure 9 (e). The isolation wall 160 extends from the top wall to the bottom wall of the package and is at least partially located opposite the inlet to prevent parasitic flow from reaching the sensitive range of the gas sensor 105.

[0189] Laminar or turbulent parasitic flow or residual flow reaching the sensitive range can adversely affect and disturb the sensor measurements. In embodiments with multiple inlets, the likelihood of residual gas flow into the package is particularly high, as one hole can act as an inlet and the other hole as an outlet, and / or in embodiments with elongated slot inlets, particularly in the presence of a large gas flow outside the package, for example in order to reduce the time required for target gas molecules to reach the sensor package.

[0190] The isolation wall 160 extending into the package between the inlet and the sensing area prevents parasitic gas flow from reaching the gas sensitive range 110. The isolation wall 160 will guide gas molecules to diffuse around it to avoid diffusing parasitic flow to the sensing area and one or more deflection walls as shown in Figure 12 (e) direct gas molecules to the sensing area as the preferred diffusion area.

[0191] The isolation wall 160 can also extend from the bottom wall as shown in Figure 12 (b). The isolation wall 160 can help to avoid foreign objects and dust from reaching the sensing range. These particles and dust can collect at or below the bottom of the isolation wall 160 instead of passing the isolation wall with the gas molecules as shown in Figure 12 (a). In these cases, the package can be equipped with a foreign object collection section 165 as shown in Figure 13 (a) and 12(b). As mentioned above, the provision of one or more inlets in a non-overlapping relationship with the sensing range also helps to prevent particles and dust from entering the sensing range. These features can also be used in combination.

[0192] Figure 13 (a) to 13(d) show top views of sensor assemblies according to embodiments of the present disclosure.

[0193] Figure 13(a) The package shown has two holes 130a, 130b on opposite side walls, and a barrier 160 between the area where the two holes are provided and the sensing range 110. The barrier 160 can divide the interior space into a first area where the sensor 105 is located and a second area where the holes 130a and 130b are located. An air flow can be formed between the two holes 130a and 130b. The barrier 160 extends in approximately the same direction as the air flow, but this is not a limiting condition, the barrier 160 can be at an angle to the direction of the air flow. Gas molecules can diffuse to the sensing range around the barrier 160, while the parasitic air flow does not significantly affect the sensing range. Figure 13 (b) The package in Figure 13 (a) is similar, but in this case there is a hole 130a in one side wall and a hole 130b in the other side wall.

[0194] Figure 13 (c) and 13(d) show a package where there is only one opening 150 in the side wall, instead of two openings, and the opening extends in the transverse direction. A barrier 160 is located opposite the entrance 150 to protect the sensing area from any parasitic flow. The barrier 160 is located between the entrance 150 and the sensing area 110. As Figure 13 (d) shows that the barrier 160 is arranged in such a way that the volume in which the sensor 105 is located is smaller than Figure 14 (c).

[0195] Figure 11 (a) to 14(d) show cross sections of sensor packages further exemplified according to the present disclosure. In each embodiment, the package can be composed of two or more parts. The sensor package can be similar to the one shown in Figure 14 Figs. 2 to 13, and thus have similar reference numbers.

[0196] Figure 14 (a) and 14(b) describe a package having a first part 190 which is a bottom wall, e.g. a substrate or a PCB board. In this example, the sensor 105 is formed on the upper surface of the bottom or lower wall. A second part 195 of the package surrounds the sensor 105 from the sides and from the top.

[0197] Figure 14 (a) shows a sensor package where one side wall is thicker than the opposite side wall, as for the sensor package shown in Fig. 2(a).

[0198] Figure 14 (b) shows a sensor package where one side wall is thicker than the opposite side wall, as for the sensor packages shown in Figs. 2(a) and Figure 14 (a) shows a sensor package similar to the one shown in Fig. 2(a). Figure 14 (b) shows a sensor package having a tilted top wall which comprises a deflection surface. Figure 14(a) and Figure 14 (b) the side walls of the package are thicker, which helps to transport gas molecules to the sensing area.

[0199] Figure 14 (c) and 14(d) describe a package with a first portion 190, which is a package substrate, having a top surface with a cavity. A sensor 105 is located on the substrate, within the cavity. In the example shown, each wall of the substrate formed by the cavity has a different thickness to help transport gas molecules to the sensing range of the sensor 105. A second portion 195 of the package encloses the top of the sensor. In some examples, the walls of the second portion 195 can be different in thickness. In Figure 15 (d) the first portion is made up of two or more sub-portions; this provides a modular package that can be adapted to sensors of different sizes and / or different application requirements

[0200] Figure 10 (a) shows a cross-section of a gas sensor module. The gas sensor module includes a gas sensor assembly, which includes a package 100 and a housing 200 in which the sensor assembly is located. In this example, the gas sensor package 100 is similar to that shown in Figure 15 (a) and therefore has similar reference numbers, but it will be understood that any other gas sensor package described herein can be implemented within the housing 200. In this example, the housing 200 is cuboid in shape, but it will be appreciated that the housing can be other shapes. The housing 200 includes opposing bottom and top walls and four side walls extending between the top and bottom walls to define an enclosed volume 220 in which the gas sensor package 100 is located. The gas sensor assembly 100 is located on the bottom wall of the housing and is enclosed by the housing 200. In this example, the gas sensor assembly has a single inlet 130 and the housing 200 has two apertures 230a, 230b located on the top wall of the housing 200. In this way, gas molecules to be sensed can flow quickly into the housing 200 (one aperture as an inlet 230a and the other aperture as an outlet 230b), but must diffuse into the sensor package 100, thereby reducing parasitic flow that affects the sensor 105. In this way, the housing 200 can quickly fill with gas, thereby improving the response time of the sensor. In this example, the housing 200 has two apertures, but there can be more than two apertures. The apertures can be located on the same side of the housing 200 or on different sides.

[0201] Figure 15 (b) shows a cross-section of another example of a gas sensor module. The sensor assembly can be similar to that shown in ​(a) the illustrated analog, and thus have like reference numerals. In this example, the gas sensor package 100 has two holes 130a and 130b, and the housing has a single inlet 230. In this example, the gas to be detected must diffuse into the housing 200 and then into the package 100, as there is no substantial flow within the housing 200. In this case, it takes longer for the gas to fill the housing 200, but once the housing 200 is filled with gas, the gas diffuses into the sensor package 100 more quickly due to the presence of more than one hole in the sensor package 100. It should be noted that there can be more than two holes in the sensor package 100.

[0202] The skilled person will appreciate that in the foregoing description and in the appended claims, terms such as "above", "overlapping", "below", "side", and the like, refer to conceptual drawings of the device, such as shown in the standard sectional views and the accompanying drawings. These terms are used for ease of reference and are not intended to be limiting. Thus, these terms are to be understood as referring to the device in the orientation shown on the accompanying drawings.

[0203] While the present disclosure has been described in terms of the preferred embodiments above, it is to be understood that those skilled in the art will be able to alter and modify the preferred embodiments without departing from the scope of the present disclosure. Accordingly, it is to be understood that the present disclosure is not to be limited by the preferred embodiments described above. Modifications and alternative methods will occur to those skilled in the art upon reading the preceding description, and it is the intent of the inventor(s) to encompass those modifications and alternative methods in the scope of the claims. Each feature disclosed in this specification, and / or shown in the accompanying drawings, is presented alone or in any appropriate combination with each of the other features disclosed and / or shown in the specification and / or drawings. The disclosure is not to be limited in terms of the construction of the specification or claims or appropriate combinations of disclosed and / or shown features.

[0204] Reference Numbers

[0205] 100 gas sensing package

[0206] 105 gas sensor

[0207] 110 gas sensitive range

[0208] 115 package side wall

[0209] 120 enclosed volume

[0210] 125 wire bonding area

[0211] 130 package inlet

[0212] 135 inner wall

[0213] 140 inner wall

[0214] 150 inlet

[0215] 160 internal partition wall

[0216] 165 foreign object collection portion

[0217] 170 ASIC readout chip

[0218] 175 electrical connection area

[0219] 180 electrical connection

[0220] 190 first portion

[0221] 195 second portion

[0222] 200 housing

[0223] 220 enclosed volume

[0224] 230 housing aperture

Claims

1. A sensor assembly, comprising: A gas sensor, which includes a gas sensing range; The package includes one or more walls, wherein the one or more walls define a volume for housing the gas sensor, and one of the walls includes an aperture defining an entrance to the package, and wherein the package includes a deflecting surface within the volume, wherein in use, the deflecting surface is configured to deliver gas molecules to the gas sensing range.

2. The sensor assembly of claim 1, wherein the inlet is laterally offset from the gas sensing range, and in use, the deflection surface is configured to reduce the average distance that gas travels from the inlet into the gas sensing range.

3. The sensor assembly of claim 1 or 2, wherein the one or more walls of the encapsulation are configured to define a preferred diffusion region and a peripheral region within the volume.

4. The sensor assembly of claim 3, wherein the volume is formed by two or more different volumes, and wherein a first volume of the two or more different volumes surrounds the preferred diffusion region, and wherein a second volume of the two or more different volumes surrounds the peripheral region.

5. The sensor assembly of claim 1 or 2, wherein the one or more walls comprise one or more outer walls of the encapsulation and an inner wall extending from one of the outer walls, and the deflection surface is part of the inner wall.

6. The sensor assembly of claim 1 or 2, wherein the one or more walls comprise one or more outer walls of the package, and the deflection surface is integrally formed with one of the outer walls.

7. The sensor assembly of claim 5, wherein the deflecting surface forms an obtuse angle with respect to an outer wall extending from the deflecting surface facing the inlet.

8. The sensor assembly of claim 5, wherein the one or more outer walls include a first region having a first thickness and a second region having a second thickness.

9. The sensor assembly of claim 8, wherein the first thickness is at least twice the second thickness.

10. The sensor assembly of claim 8, wherein the first outer wall of the one or more outer walls has the first thickness, and the second outer wall of the one or more outer walls has the second thickness.

11. The sensor assembly of claim 8, wherein, The first outer wall of the one or more outer walls includes a first portion having the first thickness and a second portion having the second thickness.

12. The sensor assembly according to claim 1 or 2, wherein, The shape of the volume at least partially matches the shape of the gas sensor.

13. The sensor assembly of claim 12, wherein, The distance between one of the one or more walls and the gas sensor is less than 100 micrometers.

14. The sensor assembly of claim 13, wherein, The distance between one of the one or more walls and the gas sensor is less than 50 micrometers.

15. The sensor assembly according to claim 1 or 2, wherein, The hole includes a groove on one of the one or more walls, and the groove extends in the lateral direction.

16. The sensor assembly according to claim 1 or 2, wherein, The sensor assembly includes at least two inlets on a first wall of the one or more walls, and the two inlets are laterally spaced apart from each other.

17. The sensor assembly according to claim 1 or 2, wherein, The one or more walls include a single hole forming the entrance.

18. The sensor assembly according to claim 1 or 2, wherein, The one or more walls include a top wall opposite the bottom wall, and one or more side walls extending between the top wall and the bottom wall, and The gas sensor is located on the bottom wall, and The entrance is formed on one of the sidewalls.

19. The sensor assembly of claim 18, wherein the distance between the top surface of the gas sensor and the bottom wall of the package is greater than the distance between the top edge of the inlet and the bottom wall of the package.

20. The sensor assembly of claim 16, further comprising an isolation wall located between the inlet and the gas sensing range.

21. The sensor assembly of claim 1 or 2, wherein the package includes a first portion and a second portion, the first portion and the second portion together defining a volume, and the first portion includes a substrate having a cavity, wherein the gas sensor is located in the cavity.

22. A sensor module comprising a sensor assembly and a housing according to any one of the preceding claims, wherein the sensor assembly is located within the housing.

23. The sensor module of claim 22, wherein the housing includes two or more holes.

24. The sensor module of claim 22, wherein the package of the sensor assembly includes a single aperture.

25. The sensor module of claim 22, wherein the package of the sensor assembly includes two or more holes, and wherein the housing includes a single hole.

26. A method of manufacturing a sensor assembly, the method comprising: To form a gas sensor that includes a gas sensing range; An encapsulation is formed comprising one or more walls, wherein the one or more walls define a volume for housing the gas sensor, and one of the walls includes an aperture defining an inlet to the encapsulation, and the encapsulation includes a deflecting surface within the volume, wherein, in use, the deflecting surface is configured to deliver gas molecules to the gas sensing range.

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