MEMS device

Abstract

A micro-electromechanical systems (MEMS) device 50, and methods of manufacture, comprising: a first substrate 51; a second substrate 52 attached to the first substrate; an inner sealed chamber 56 and

Description

TECHNICAL FIELD The present disclosure relates to MEMS devices comprising a sealed chamber which is fluidically isolated from the external environment. Examples of MEMS devices according to the present disclosure include resonators, gyroscopes, accelerometers, and differential environmental sensors provided with fluid sensors (e.g. gas sensors and / or humidity sensors) or particle sensors. BACKGROUND MEMS devices such as resonators, gyroscopes, accelerometers, and differential environmental sensors provided with fluid sensors (e.g. gas sensors and / or humidity sensors) or particle sensors, may require a sealed cavity which is fluidically isolated from the external environment in order to function reliably. A cavity or chamber may be defined by a first substrate and a second substrate bonded to each other. Once the bonding process is complete, successive steps of the manufacturing process of MEMS devices, for example dicing, or otherwise handling the MEMS devices, may cause, to an otherwise intact bonding layer, damage such as a crack which may propagate across the bonding layer and compromise a seal of the chamber and, in turn, the functionality of the MEMS device. The yield of the manufacturing process may be particularly affected by this kind of damage which may result in high costs of production. The lifetime of the MEMS devices may also be affected. MEMS devices may also be affected by micro leaks which are difficult to detect at production and / or calibration stage but may become significant during the lifetime of the devices. SUMMARY The present disclosure is directed to a MEMS device of improved reliability. Aspects and preferred features are set out in the accompanying claims. Described herein is a MEMS device comprising: a first substrate, a second substrate attached to the first substrate, a first bonding region between the first substrate and the second substrate, and a second bonding region. The second bonding region may be adjacent the first bonding region. The first bonding region and the second bonding region are arranged to form an inner sealed chamber and an outer chamber. The inner sealed chamber is bounded by the first bonding region, and the outer chamber is bounded by the first bonding region and the second bonding region. As used herein, the term “adjacent” refers to an arrangement in which the first and second bonding regions are next to one another but not in contact to one another, or an arrangement where the first and second bonding regions are next to one another and in contact to one another at one or more locations. The first substrate and / or the second substrate may comprise a semiconductor material such as silicon. In some examples, the first substrate and / or the second substrate may comprise glass. It will be understood that the bonding regions described herein refer to regions of the device comprising a bonding material, adhesive, and / or other type of material or layer (also referred to as an intermediate layer). The bonding region may be formed (e.g. deposited, printed, patterned, or the like) on a surface between the substrates (e.g. on one or more surfaces of one or more of the substrates). The material forming the bonding region is suitable to form a fluidically sealed cavity or chamber. That is: the first bonding region fluidically isolates the inner sealed chamber from the outer chamber, and the second bonding region may fluidically isolate (seal) the outer chamber from the external environment. In some examples, the first bonding region and / or the second bonding region comprise at least one of a glass frit, a polymer, an alloy (such as a metal alloy or a silicon-gold alloy), a metal, and any other suitable material known in the art. Preferably, the first bonding region and the second bonding region comprise a same material. The second bonding region may be between the first substrate and the second substrate. The second bonding region may be adjacent the first bonding region. The outer chamber may comprise an aperture which may maintain the outer chamber in fluidic communication with the external atmosphere. Alternatively, the aperture may be sealed or the outer chamber may not be provided with an aperture. Preferably the outer chamber is an outer sealed chamber which is fluidically isolated from the external atmosphere. A sealed chamber may house at least part of one or more of the functional components of the MEMS device. For example, the inner sealed chamber may comprise vacuum to improve the performance of the device. One or more of the sealed chambers may comprise an internal atmosphere, e.g. a controlled atmosphere, such as vacuum, an inert gas, or a mixture of gases of a known composition, at a specific pressure. For example, the internal atmosphere (e.g. specific gas or vacuum) may be configured to support the functioning and / or longevity of one or more functional components housed in the sealed chamber(s). Advantageously, if a seal of a sealed chamber becomes compromised, for example during production of the MEMS device and / or during the lifespan of the MEMS device, the controlled internal atmosphere can be preserved due to the additional layer of protection provided by the presence of two sealed chambers. The one or more sealed chambers may also comprise a getter material to help maintain the chamber in vacuum or low pressure. For example, the outer sealed chamber may be adjacent to the external environment. If material at either the first bonding region or the second bonding region becomes damaged, e.g. during dicing of one or both of the substrates during manufacturing, and / or due to degradation over the life of the device, the additional seal means that the functioning of the device may remain unaffected. The yield of the manufacturing process and / or the lifespan of the MEMS device may, therefore, be increased. In this way, production costs and / or replacement costs may be reduced. The internal atmosphere of the outer sealed chamber may, preferably, be the same as the internal atmosphere (e.g. controlled internal atmosphere) of the inner sealed chamber. In some examples, the internal atmosphere of the outer sealed chamber may be different from the internal atmosphere of the inner sealed chamber. For example, the internal atmosphere of the outer sealed chamber may be the same as the external (e.g. environmental) atmosphere. An external solicitation may damage the seal of the outer chamber without affecting the seal of the inner sealed chamber. In some examples, the internal atmosphere of the inner sealed chamber is the same, or substantially the same, as the internal atmosphere of the outer sealed chamber. Advantageously, if the internal atmosphere of both sealed chambers is the same, or substantially the same, the total composition of the internal atmosphere may remain substantially unchanged if either seal becomes compromised. In some examples, the inner sealed chamber may be provided with a pressure and / or a chemical sensor for monitoring the atmosphere of the inner sealed chamber, so as to promptly reveal any change in the controlled atmosphere of the inner sealed chamber. This may be particularly beneficial in applications requiring a high degree of reliability of the MEMS device, e.g. when the device is used in critical applications and a malfunction needs to be promptly revealed to put in place mitigating actions. For example, the MEMS device may be a differential gas sensor used to detect leaks of hazardous gases. In use, the internal atmosphere of the inner sealed chamber may be monitored, for example continuously or periodically, through such dedicated sensor or sensing element. When a failure of the seal of the outer sealed chamber, for example due to a manufacturing issue, incorrect handling of the MEMS device, or aging of the MEMS device, is detected, it can be assumed that the seal of the first or internal sealed chamber may also likely be compromised and an appropriate action may be taken. In some examples, the outer sealed chamber comprises a continuous gap between the first bonding region and the second bonding region around a whole perimeter of the first bonding region. In other words, the first bonding region and the second bonding region may each form a closed shape, with the first bonding region inside the second bonding region and with the first bonding region not in contact with the second bonding region. In this way, the probability of a crack or defect in one of the two bonding regions propagating to the other is minimised, and the reliability of the MEMS device may be increased. The outer chamber, which may be a sealed chamber, may be interposed between the internal sealed chamber and the external atmosphere. In some examples, the first bonding region is arranged to be in contact with the second bonding region at least at a first contact region and a second contact region. For example, the outer chamber may be sealed by the second bonding region, and a portion of the first bonding. In other words, the outer chamber may extend only partially around the inner sealed chamber. The inner sealed chamber may also be bounded by the second bonding region. For example, the outer chamber may be partly, predominantly, or entirely, adjacent to an edge of the first and / or second substrate so that the outer chamber is interposed between the inner sealed chamber and the external environment in a region that is particularly vulnerable to seal damage, e.g. during dicing of the substrate(s), while also reducing the total footprint of the device relative to the case where the bonding regions are completely separated. The first substrate may be bonded to the second substrate by the first and / or the second bonding region(s). In some examples, the MEMS device comprises a third substrate disposed between the first substrate and the second substrate. At least one of the inner sealed chamber and the outer chamber may be additionally bounded by the third substrate. For example, the third substrate may be bonded to the first or second substrate by the first bonding region. This arrangement may allow the fabrication of more complex MEMS devices, in some implementations. In some examples, the MEMS device according to the present disclosure is a differential environmental sensor. In some examples, the MEMS device (e.g. differential environment sensor) comprises a sensing region (also referred to as a sensing portion), and a reference region (also referred to as a reference portion). The sensing region is where the interaction between a target stimulus (e.g. a target gas) and the sensor takes place in order to produce a sensor output. The reference region may comprise a reference chamber, which may be formed by the inner sealed chamber, such that the reference chamber is fluidically isolated from the external environment by the bonding regions, as described herein. The outer chamber may be provided adjacent the inner sealed chamber to provide protection to the sela of the inner sealed chamber. The MEMS device (e.g. differential environment sensor) according to the present disclosure may, therefore, provide reliable and accurate sensing (e.g. of fluids such as gases) by providing a reliably sealed reference chamber. When differential sensor readings are collected, any sensor changes due to unwanted parasitic effects, such as temperature or electronic noise, may be reduced or cancelled out. This may allow more accurate sensor readings to be obtained, and may increase the sensitivity of the environmental sensor. The reference region may not to be in contact with the target stimulus. The sensing region and the reference region are otherwise identical, in preferred implementations. In some examples, the environmental sensor comprises a first substrate or sensor substrate. The sensing region may comprise a sensing area of the sensor substrate, and the reference region may comprise a reference area of the sensor substrate. For easier manufacturability of the environmental sensor, the sensing area and the reference area may be provided on a surface of the sensor substrate. The sensing region may comprise a sensing chamber arranged to be in fluid communication with an external environment. For example, the MEMS device (e.g. environmental sensor) may comprise a second substrate, such as a cap (which may correspond to the second substrate described herein), defining an inner sealed chamber and an outer chamber as described herein, so as to fluidically isolate the reference region from the external environment. The outer chamber may also be referred to as an outer reference chamber and the inner sealed chamber may also be referred to as an inner reference chamber. In preferred implementations, the outer chamber is an outer sealed chamber. The cap may define the sensing chamber. The sensing chamber may be provided with one or more holes such that the sensing region is maintained in fluid communication with the external environment. In some examples, the holes may be provided in a third bonding region located between the cap and the first substrate, in the sensing region. This may simplify the production process as no holes in the cap may be required to be created. Preferably, the one or more holes are in non-overlapping relation with the sensing area to reduce the probability of external material impacting the accuracy of the sensor measurements. In some examples, the one or more holes may be provided with a filter. The sensing chamber and the reference chamber may be of the same shape and / or size. One or both reference chamber(s) may be under vacuum (e.g. at a pressure of or below 1 kPa), or may be filled with a fluid (e.g. a gas or a gas mixture) of controlled composition and pressure. For example, the reference chamber may be filled with dry air or nitrogen at atmospheric pressure (-100 kPa) or at other pressure, higher or lower than atmospheric pressure. In some examples, the MEMS device (e.g. environmental sensor) comprises: a substrate comprising a sensing cavity, within the sensing region, and a reference cavity, within the reference region; a dielectric layer disposed over the substrate, wherein the sensing cavity defines a sensing membrane in the dielectric layer, and wherein the reference cavity defines a reference membrane in the dielectric layer. The MEMS device (e.g. environmental sensor) further comprises a first heating element on or within the sensing membrane, and a second heating element on or within the reference membrane. The sensor substrate provided with a dielectric layer may also be defined as a sensor die. In some examples, the sensing membrane may correspond to a sensing area of the device, and the reference membrane may correspond to a reference area of the device. It is desirable that, when a cap with one or more holes in the sensing chamber is provided, the one or more holes are laterally displaced (e.g. in a non-overlapping relation) with respect to the sensing membrane. This enables more effective protection of the sensing membrane. It will be understood that the sensing chamber and the reference chamber may enclose an area larger than the respective membranes, or the respective sensing and reference areas. The dielectric layer may comprise any suitable material, for example silicon oxide, silicon nitride, aluminium oxide or a combination of these materials. Each heating element may be a resistive element or resistor, a diode, a transistor or any other suitable element known in the art. The heating element may comprise platinum, tungsten, titanium, single crystal silicon, polysilicon, and / or another suitable material. The type of heating element, its shape and the material it is made of are not limited and any heating element known in the art may be used in the implementation of the sensors described herein. The heating element may function as a sensing element. In preferred examples, the two heating elements are identical heating elements. The environmental sensor may be a thermal conductivity sensor (e.g. a thermal conductivity gas sensor), wherein the sensor responds to changes in the thermal conductivity of fluid (e.g. gas) around it due to change in fluid composition. For such a sensor type, preferably, the reference area may be isolated from the external environment while the sensing area may be exposed to the environment. The environmental sensor may be a catalytic sensor (e.g. a catalytic gas sensor) comprising, in the sensing area, a heating element and a catalyst, where, at high temperature, the catalyst catalyses the combustion of a target fluid (e.g. gas) causing an increase in temperature that can be measured either by the heating element or by a separate temperature sensor. In some examples, both the sensing area and the reference area may have a catalyst and the reference area may be isolated from the external environment while the sensing area may be exposed to the external environment. The environmental sensor may be a resistive or capacitive sensor comprising, in the sensing area, a heating element and a sensing material whose resistance or capacitance changes in the presence of a target fluid (e.g. gas). In some examples, both reference and sensing areas may be provided with the same sensing material and the reference area may be isolated from the external environment. The environmental sensor may further comprise a circuit chip, such as an applicationspecific integrated circuit (ASIC), to control and operate the sensor. Also described herein is a method of manufacturing a MEMS device, the method comprising: attaching a first substrate to a second substrate, forming a first bonding region between the first substrate and the second substrate, and forming a second bonding region. The second bonding region may be adjacent to the first bonding region. The first bonding region and the second bonding are arranged to form an inner chamber and an outer chamber, the inner chamber being bounded by the first bonding region, and the outer chamber being bounded by the first bonding region and the second bonding region. Forming the first bonding region and / or the second bonding region may comprise applying a bonding material, adhesive, and / or other type of material or layer (also referred to as an intermediate layer). For example, forming the bonding region(s) may comprise depositing, printing, and / or patterning a material on a surface between the substrates (e.g. on one or more surfaces of one or more of the substrates). The material forming the bonding region is suitable to form a fluidically sealed cavity or chamber. That is: the first bonding region fluidically isolates (seals) the inner chamber from the outer chamber, and the second bonding region provides a seal which can fluidically isolate (seal) the outer chamber from the external environment. The outer chamber may still be fluidically connected to the external environment through an aperture in the outer chamber, as described above In some examples, the first bonding region and / or the second bonding region comprise at least one of a glass frit, a polymer, an alloy (such as a metal alloy or a silicon-gold alloy), a metal, and any other suitable material known in the art. The second bonding region may be formed between the first substrate and the second substrate. Preferably, the first bonding region and the second bonding region comprise a same material. In some examples, the method comprises applying heat and / or pressure to one or both of the first bonding region and the second bonding region. The method may comprise, during attachment of the first substrate to the second substrate, exposing the first substrate and the second substrate to a first (e.g. controlled) atmosphere. Examples of the first atmosphere include an inert gas, such as nitrogen or argon, or a gas mixture such as dry air or any other suitable controlled atmosphere, including vacuum. Exposing the substrates to the first atmosphere during their attachment results in the sealed chamber(s) comprising internal atmospheres corresponding to the first atmosphere. In some examples, it may be desirable that the inner sealed chamber and the outer chamber of the device contain different internal atmospheres. For example, the outer chamber may comprise an aperture such that the outer chamber is in fluid communication with the external environment. The method may further comprise (following attachment of the first substrate to the second substrate) exposing the attached first and second substrates to a second atmosphere, different from the first atmosphere, and closing the aperture. Exposing the outer chamber (having the aperture) to the second atmosphere, after the inner chamber has been sealed by attaching the first and second substrates, and then closing the aperture of the outer chamber, results in the inner chamber and the outer chamber being sealed with different internal atmospheres. For example, one of the two sealed chambers may enclose a first controlled atmosphere (e.g. an inert gas, such as nitrogen or argon, or a gas mixture such as dry air or any other suitable controlled atmosphere, including vacuum) of a controlled composition and pressure and the other may enclose a different (in composition and / or pressure) controlled atmosphere. The method may comprise providing the inner sealed chamber with a monitoring sensor or sensing element (e.g. a thermal conductivity sensor, a chemical sensor, or other sensing element) to monitor the atmosphere of the inner sealed chamber. It will be understood that one or more of the methods described herein may be suitable for manufacturing a MEMS device as described herein. Additionally described herein is a method of manufacturing a MEMS device, the method comprising: attaching a first substrate to a second substrate while the first substrate and the second substrate are exposed to a first atmosphere; and forming a bonding region between the first substrate and the second substrate; wherein the first substrate, the second substrate, and the bonding region define a first chamber and a second chamber, the first chamber being sealed, and wherein the second chamber comprises an aperture such that the second chamber is in fluid communication with an external environment; wherein the method further comprises, following attachment of the first substrate to the second substrate: exposing the attached first and second substrates to a second atmosphere, different from the first atmosphere; and closing the aperture. It will be understood that the above method of manufacturing the MEMS device provides a MEMS device having first and second sealed chambers comprising different internal atmospheres. In some examples, the first chamber and the second chamber may form a reference chamber and a lifetime monitoring chamber of a differential environmental sensor as described herein. The device may further comprise a sensing chamber, and the sensing chamber may be in fluid communication with the external environment As described herein, the first chamber and the second chamber may collectively form part of a reference region of the device, and the sensing chamber may form part of a sensing region of the device. Further described herein is a MEMS device comprising a first substrate, and a second substrate attached to the first substrate. The MEMS device comprises a first bonding region between the first substrate and the second substrate, and a second bonding region between the first substrate and the second substrate. The first bonding region and the second bonding region may be arranged to form a first chamber and a second chamber. The first chamber may be sealed. The first chamber is bounded by the first bonding region and the second chamber is bounded by the second bonding region. The second bonding region is a discontinuous bonding region such that the second chamber is in fluid communication with an external environment For example, the discontinuous bonding region may comprise one or more holes (e.g. openings or apertures) in the bonding region (e.g. in the bonding material or other material as described herein) to enable gas or other fluids to enter and / or exit the second chamber. In some examples, the first chamber is a reference chamber and forms part of a reference region of the MEMS device, and the second chamber is a sensing chamber and forms part of a sensing region of the MEMS device. For example, the MEMS device may be a differential environmental sensor as described herein. In some examples, the MEMS device further comprises a further bonding region. The further bonding region may be adjacent the first bonding region. The further bonding region and the first bonding region may be arranged to form a chamber (referred to as an outer first chamber) bounded by the first bonding region and the further bonding region, such that the first chamber is an inner first chamber. The outer first chamber may be a sealed chamber. The outer first chamber may provide protection against the effects of the inner sealed chamber becoming compromised, as described herein and above. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of example only, with reference to the following drawings: Figure 1 illustrates examples of a MEMS device having a first substrate, a second substrate, an inner sealed chamber, and an outer sealed chamber according to the present disclosure; Figure 2 illustrates examples of a MEMS device comprising a sealed aperture according to the present disclosure; Figure 3 illustrates examples of a MEMS device having an outer sealed chamber formed by a first bonding region in contact with a second bonding region according to the present disclosure; Figure 4 illustrates examples of a MEMS device having an outer chamber having apertures according to the present disclosure; Figure 5 illustrates examples of a MEMS device comprising a third substrate according to the present disclosure; Figure 6 illustrates examples of a differential environmental sensor according to the present disclosure, the differential environmental sensor comprising a reference chamber having an inner sealed chamber and an outer sealed chamber; Figure 7 illustrates examples of a differential environmental sensor comprising a third substrate according to the present disclosure; Figure 8 illustrates examples of a differential environmental sensor comprising an outer reference chamber formed by a first bonding region in contact with a second bonding region according to the present disclosure; Figure 9 illustrates examples of a differential environmental sensor having an outer chamber having apertures according to the present disclosure; Figure 10 illustrates examples of a differential environmental sensor having an inner reference chamber and an outer reference chamber comprising a sealed aperture according to the present disclosure; Figure 11 illustrates examples of a differential environmental sensor having a sensing chamber and a sealed reference chamber according to the present disclosure; Figure 12 illustrates an example of a method of manufacturing a MEMS device according to the present disclosure; Figure 13 illustrates an example of a method of manufacturing a MEMS device having chambers comprising different internal atmospheres according to the present disclosure; Figure 14 illustrates an example of a MEMS device comprising a first chamber and a second chamber, the second chamber being bounded by a discontinuous bonding region, according to the present disclosure; and Figure 15 illustrates an example of a MEMS device comprising an inner first chamber, an outer first chamber, and a second chamber, the second chamber being bounded by a discontinuous bonding region, according to the present disclosure. DETAILED DESCRIPTION Described herein is a MEMS device, and a method of manufacturing a MEMS device, having an inner sealed chamber and an outer chamber. The outer chamber may be a sealed chamber, such that if the seal of one chamber becomes compromised, for example during manufacture, use, or due to degradation over time, of the device, the presence of the additional chamber may mitigate any effect on the functioning of the device. In some examples, the outer chamber, bounded by a bonding region, may act as a barrier to provide protection for the inner chamber. Additionally described herein is a method of manufacturing a MEMS device having a first sealed chamber and a second sealed chamber, the first and second sealed chambers comprising, following exposure to first and second atmospheres, respectively, different internal atmospheres. Further described herein is a MEMS device having a first chamber, which may be a sealed chamber, and a second chamber that is bounded by a discontinuous bonding region and is, therefore, in fluid communication with an external environment. The first chamber may be a reference chamber, and the second chamber may be a sensing chamber. For example, the MEMS device may be a differential environmental sensor. MEMS device having an inner sealed chamber and an outer chamber Figures 1A to 1C depict examples of a MEMS device according to the present disclosure. Figures 1A shows a cross-section of an example of MEMS device 50 according to the present disclosure. The MEMS device 50 comprises a first substrate 51, a second substrate 52, a first bonding region 54, and a second bonding region 55. The above features cooperate to form an inner sealed chamber 56 and an outer chamber 57, which are shown, in top view, and without the second substrate 52, in Figure 1C. Figure 1B, shows a MEMS device 50 where the second substrate 52 is provided with a cavity so that the inner sealed chamber 56 partially extends through the cavity in the second substrate 52. The device 50 of Figure 1B has the same top view shown in Figure 1C. In the examples illustrated in Figure 1, as well as Figures 2 and 3, the outer chamber is a sealed chamber. Features housed in the inner sealed chamber 56 are not shown for the MEMS device, for the sake of clarity. The first bonding region 54 and the second bonding region 55 are separate from each other so that any damage or defect localised in either of them is less likely to propagate to the other, so that the internal atmosphere of the inner sealed chamber 56 is less likely to change, so affecting the functioning of the MEMS device. The inner sealed chamber 56 and the outer sealed chamber 57 may, preferably, have a same controlled internal atmosphere. In some cases, the outer sealed chamber 57 may partially extend through the second substrate 52, to form, at least in part, a hollow space, as shown at the right hand side of Figures 2B and 2C. Such hollow space may extend all around the inner sealed chamber 56 but this is not limiting, and the hollow space may extend only partially the inner sealed chamber 56. In some examples, differently to what is shown in Figures 1A and 1B, the outer sealed chamber 57 may be provided with an aperture 57a which, for example, at some stage of the manufacturing process or in use, may fluidically connect the external chamber to an external atmosphere. The aperture is shown on the left hand side of Figures 2A and 2B, but its location is not limited. The aperture 57a may be sealed in the finished device with a seal 58, as shown in Figures 2A and 2B, or with a further substrate 59, as shown in Figure 2C. Any other suitable sealing means may be used. This configuration may allow to produce a device where the internal atmosphere of the outer sealed chamber 57 is different from the internal atmosphere of the inner sealed chamber 56. This may provide an opportunity of manufacturing more complex MEMS devices. It will be understood that the position and the dimension of the aperture 57a are not limited. Figure 1C is representative of the top view of the inner and outer sealed chambers 56 and 57 of Figures 2A to 2C. Figures 3A to 3C depict further examples of the MEMS device according to the present disclosure. The devices 50 shown in Figures 3A to 3C differ from those of Figures 1 and 2, in that the second bonding region 55 does not form a closed shape, as it can be clearly appreciated in Figures 3D to 3F, which show example top views of the device 50 without the second substrate 52. As it can be seen, the second bonding region 55 contacts the first bonding region 54 at least at two contact regions so that the seal of the inner sealed chamber 56 is formed, in part, by the second bonding region 55 and in part by a portion of the first bonding region 54 comprised between the two contact regions. Similarly, the seal of the outer sealed chamber 57 is formed, in part, by the second bonding region 55 and, in part by a further portion of the first bonding region 54 extending between the two contact regions. In this way, the two bonding regions are separated specifically at locations which are more likely to be exposed to external solicitations which may result in damage of the first bonding region 54, for example, locations where the first substrate 51 has been diced or otherwise exposed to conditions which may affect the first bonding region 54. This configuration advantageously results in a device of potentially reduced footprint with respect to the devices shown in Figures 1 and 2. While Figure 3 gives a limited number of examples of the arrangement of the outer sealed chamber, others are also possible, for example where the outer sealed chamber 57 extends to varying degrees around the inner sealed chamber 56. It is also possible that the outer sealed chamber 57 is formed of separate portions at two or more different locations, as long as the outer sealed chamber 57 is interposed between the inner sealed chamber 56 and the external environment. In examples shown in Figures 4A to 4C, the MEMS device 50 may be provided with an outer chamber 57 which has three apertures 57a, 57b and 57c. That is, in the examples illustrated in Figures 4A to 4C, the outer chamber is not sealed. Aperture 57a is on top of the outer chamber 57 and is parallel to the first substrate. Lateral apertures 57b and 57c are substantially perpendicular, or at any suitable angle different from zero, to the first substrate 51. In these examples, the second bonding region 55 does not form a closed shape and is separate from the first bonding region 54. It will be understood that, in these examples, the portion 62 laterally limiting the outer chamber 57, as shown in the cross-section (Figure 4A), may comprise the same material as the second substrate 52 or it may comprise a different material. The portion 62 may be formed, e.g. deposited, printed or the like, on the first substrate, partially or completely surrounding the inner sealed chamber, especially in those regions more susceptible of seal damage. In examples where the portion 62 is formed, e.g. deposited, printed or the like, on the first substrate, it will be understood that the second bonding region 55 may form an integral part of the portion 62 or it may be formed by an adhesion promoting layer or the like. Portion 62 may be adjacent to, and separate from, the inner sealed chamber 56. The extension of the portion 62 in a direction parallel and / or perpendicular to the first substrate 51 is not limited and may be chosen so to provide protection of the first bonding region 54 at specific locations. It should be noted that it is not necessary to have all three apertures 57a, 57b, 57c. In some examples, the MEMS device 50 may have only one aperture, or a combination of two or more apertures. Figure 5 shows yet further example of the MEMS device 50, in cross section. Differently from the previous examples, the MEMS device 50 of Figures 4A to 4D is provided with a third substrate 53 which, together with the first substrate 51 and the first bonding region 54, defines the inner sealed chamber 56. The outer chamber 57 (which may be a sealed chamber) is defined by the second substrate 52, the third substrate 53, the first substrate 51 and the first and second bonding regions 54 and 55. This configuration may offer extra flexibility to manufacture complex devices. Figure 6A depicts a cross-section of an example where the MEMS device is a differential environmental sensor 100, such as a fluid sensor, a gas sensor, a particle sensor and the like. The differential environmental sensor 100 (also referred to herein as an “environmental sensor” or a “sensor”) comprises a first substrate 101, a second substrate 102 (also referred to herein as a “cap”), a bottom substrate 111 and a dielectric layer 120. The dielectric layer 120 is provided on a first surface of the first substrate 101. The first substrate 101 is further provided with a sensing cavity 119 and a reference cavity 116, which are closed, at the bottom, by the bottom substrate 111. In other implementations (not shown) the sensing cavity 119 and the reference cavity 116 may be completely defined in the first substrate 101 and the bottom substrate 111 may not be provided. The sensing cavity 119 and the reference cavity 116 define, in the dielectric layer 120, respectively, a first or sensing membrane 121 and a second or reference membrane 122, each membrane provided with a respective heating element 123, 124. As it can be seen, the sensor 100 has two substantially symmetrical regions, the region on the right hand side of Figures 5A being a sensing region and the region on the left hand side of Figure 5A being a reference region. The area of the first membrane 121 provided with the heating element 123 is a sensing area. The area of the second membrane 122 provided with the heating element 124 is a reference area. The sensor 100 further comprises a sensing chamber 109 and a reference chamber or inner sealed chamber 106. An outer sealed chamber 107 similar to those shown in Figure 1B and 1C is also provided. The inner sealed chamber 106 may comprise a controlled internal atmosphere and may fluidically isolate the reference region (comprising the reference area) from the external environment. The outer sealed chamber 107 is interposed between the inner sealed chamber 106 and the external environment to provide extra protection to the inner sealed chamber 106, as described above. The inner sealed chamber 106 may be in fluidic communication with the reference cavity 116, for example through one or more holes or apertures (not shown) provided in the reference membrane. In this way, the reference cavity 116 may have an internal atmosphere which is the same as the internal atmosphere of the inner sealed chamber 106. The sensing chamber 109 is provided with a hole 118 which fluidically connects the sensing region (comprising the sensing area) to the external environment. An additional bonding region 114 is located between the first and second substrates 101 102 on the sensing chamber 109 side of the sensor. The sensing chamber 109 may be in fluidic communication with the sensing cavity 119, for example through one or more holes or apertures (not shown) provided in the sensing membrane. In this way, the heating element 123 may be exposed to a larger amount, e.g. a larger mass, of a target stimulus, for example a target gas, and the overall sensitivity of the differential sensor may be increased. The sensor 100 is operated and controlled by a controller or readout circuit (not shown). In this case, the heating element 123 may function as a heating and sensing element and interact with a target stimulus (e.g. a target gas), to provide a sensing reading. A sensor output may be based on a differential signal obtained using a signal returned by the heating element 123 and a signal returned by the heating element 124, which is not exposed to the target stimulus. The heating elements 123 and 124 are otherwise exposed to the same, or as close as possible, environmental conditions. In some cases, the membranes 121 and 122 may be provided with separate sensing elements (not shown) in thermal contact with the respective heating elements 123 and 124. The presence of the heating (and / or sensing) element in the inner sealed chamber 106 enables the obtaining of differential measurements which are not significantly affected by common mode effects, since common mode effects affect both heating elements and are therefore cancelled in a differential measurement. The heating element 123 is affected by a target stimulus, so that the sensor output is indicative of the target stimulus and substantially free of common mode effect contributions. Any damage to the seal of the inner sealed chamber 106, which would expose the reference area to the target stimulus, could severely affect the reliability of the sensor. In some examples, the sensor 100 may be provided with bonding regions located between the first substrate 101 and the bottom substrate 111, so as to define an inner sealed cavity and an outer cavity, which may be a sealed cavity or a cavity having an aperture, as described above in connection with the inner sealed chamber and the outer chamber. Figure 6B shows a differential environmental sensor similar to the one shown in Figure 6A. In this case, the outer sealed chamber 107 has an aperture 107a, which opens on the top surface of the cap, and which is sealed by a seal 108. In this configuration it is possible to have a different controlled internal atmosphere in the outer sealed chamber 107 with respect to the inner sealed chamber 106. Figure 6C further shows that the external sealed chamber may extend, at least in part through the second substrate 102, and may (or may not) be provided with an aperture 107a, as described above. Figure 6D depicts a top view of the environmental sensor 100 of Figures 6A to 6C where the first bonding region 104 and the second bonding region 105 are separate, to avoid propagation of damage from one bonding region to the other. Figure 6D further shows the third bonding region 114 which is located between the first substrate 101 and the second substrate 102 and bounds the sensing chamber 116. Figure 7A and 7B show two further examples of the environmental sensor 100 where a third substrate 103 is provided similarly to the examples shown in Figures 5A to 5D. In Figures 8A to 8F, examples (in cross-section and top view, without the cap) of the differential environmental sensor 100 are shown, where the first bonding region 104 does not form a closed shape. A few, non-limiting examples of how the internal sealed chamber 106 and the external sealed chamber 107 are arranged, in top view, are depicted in Figures 8D to 8F. Figure 8C also shows that, when present, the aperture 107a of the outer sealed chamber may be closed by a further substrate 159. The sensor 100 examples of Figures 9A to 9C have an outer chamber 107 with an aperture 107a, open on the top surface of the second substrate 102 and one further lateral aperture 107b, as shown in Figure 9B, or two lateral apertures 107b and 107c, as shown in Figure 9C. Apertures 107b and 107c are substantially perpendicular, or at any suitable angle different from zero, to the first substrate 101. It will be understood that the position and size of any of the apertures is not limited. In these examples, the second bonding area 105 does not form a closed shape and it may or may not be separate from the first bonding region 104. It will be understood that, in these examples, the portion 162 laterally limiting the outer chamber 107, as shown in the cross-section (Figure 9A), may comprise the same material as the second substrate 102, or it may comprise a different material. The portion 162 may be formed, e.g. deposited, printed or the like, on the first substrate, so as to partially or completely surround the inner sealed chamber 106, especially in those regions more susceptible of seal damage. In examples where the portion 162 is formed, e.g. deposited, printed or the like, on the first substrate 101, it will be understood that the second bonding region 105 may form an integral part of the portion 162 or it may be formed by an adhesion promoting layer or the like. Portion 162 may be adjacent to, and may be separate from, the inner sealed chamber 106. The extension of the portion 162 in a direction parallel and / or in a direction perpendicular to the first substrate 101 is not limited and may be chosen so to provide protection of the first bonding region 104 at specific locations. It should be noted that many different configurations of the sensor 100 may be provided. For example, a device 100 may have the top view of either figure 9B or 9C, and the cross-section of Figure 8A. A further example of a differential environmental sensor 200, according to the disclosure, may be seen in Figures 10A, in cross-section, and 10B in top view. Similarly to the differential environmental sensor 100, the differential environmental sensor 200 is provided with a sensing region. The sensor 200 further comprises a first reference region adjacent to the sensing region and a second reference region adjacent to the first reference region. It will be appreciated that the three regions described above may be arranged, with respect to each other, in any suitable way, for example, the sensing region may be located between the first reference region and the second reference region. The sensing region comprises a sensing chamber 209, a sensing cavity 219, a sensing membrane 221 and a heating element 223. In use, the first and the second reference regions are fluidically isolated from the external environment, and the sensing region is exposed to the external environment, including a target stimulus. The second reference region, comprising a second reference membrane 226, a heating element 225, a second reference cavity 229 and a second reference chamber 227, may be provided to be used as a lifetime monitoring structure during the operation of the sensor. If the first reference region, comprising an inner sealed chamber 206 and an outer sealed chamber 207 is sealed in a controlled atmosphere, and the second reference region comprising the second reference sealed chamber 227 is sealed in vacuum (or in a different controlled atmosphere to the one of the internal sealed chamber), then this configuration may be used to (indirectly) monitor for leaks in the seal of the inner sealed chamber 206, during operation, over the lifetime of the device (sensor). It will be understood that the internal atmosphere of the second reference sealed chamber 227 may be suitably provided through an aperture in the second reference region, which may be successively sealed through a seal 228. During operation of the sensor, leaks in the seal of the second reference sealed chamber 227 may be detected by monitoring (e.g. periodically) the vacuum level within the vacuum sealed second reference region. This may be achieved by measuring the temperature of the heating element 225 provided to membrane 226 (or the temperature of a temperature sensing element placed in the vicinity of such heating element 226) for a given power level applied to the heating element 225. In the presence of a leak, the temperature of the heating element 225 would gradually decrease (compared to the value expected when no leak is present). This may provide an indication that the seal of the internal sealed chamber 206 (e.g. sealed in dry air), and / or of the external sealed chamber 207, may have failed too, since they have been used for the same period of time and in similar conditions, and, therefore, the heating element 224, provided to membrane 222, may no longer provide a reliable reference to the heating element 223, provided to membrane 221 in the sensing region, for a differential measurement. It will be understood that, while the second reference region may preferably be sealed in a vacuum, in other embodiments it may be sealed in any other suitable atmosphere that is different from the external atmosphere, to which the sensing region is exposed, or air. For example, it may be sealed in low pressure air, high pressure air, hydrogen, helium, argon and / or carbon dioxide or any other suitable gas or combination of gases at any suitable pressure. Different pressures or gases may be used as long as they behave in a significantly different way from air, or the external atmosphere, with respect of their interaction with the heating element 225. Preferably the heating elements 223, 224 and 225 are substantially identical. A change in pressure and / or composition of the internal atmosphere of the second reference sealed chamber 227 may be detected by any suitable means known in the art, e.g. a pressure sensor, a gas sensor or the like. The internal atmosphere within the second reference region may be chosen such that a comparatively small change in such internal atmosphere may produce a comparatively high signal, as returned, for example, by the heating element 225, with respect to a change of similar quantity in the internal atmosphere of the first reference region, which may produce a weaker signal, as returned, for example, by the heating element 224. In this way the heating element 225 within the second reference region may detect leaks more effectively as compared to the heating element 224 within the first reference region. For example, the second reference region may be in a vacuum, while the first reference region may be filled with dry air or nitrogen at a pressure of 100kPa. In this case, a small change, such as a small increase, in the pressure of the internal atmosphere within the second reference region, may mean a larger change in the applied bias, e.g. the applied power, required to keep the heating element 225 at a target temperature with respect to a similar change in the internal atmosphere of the first reference region, which may require only a small change in the applied bias, e.g. the applied power, required to keep the heating element 224 at the target temperature. Figure 10B shows a top view of the differential environmental sensor 200 of Figure 10A where it is shown that the first bonding region 204 of the first reference region and the bonding region 230 of the second reference region are both separated from one another and from the second bonding region 205 so that the internal sealed chamber 206 and the second reference chamber 227 are in a similar arrangement. MEMS device having first and second sealed chambers having different internal atmospheres Figure 11 illustrates an example of a MEMS device 300 comprising a first sealed chamber 306 and a second sealed chamber 327. In the particular example illustrated in Figure 11, the MEMS device 300 is a differential environmental sensor. The differential environmental sensor of Figure 11 is similar to the differential environmental sensor 200 of Figure 10, except that the first sealed chamber 306 and the second sealed chamber 327 are separated by only one bonding region 304. Optionally, e.g. in the case of a differential environmental sensor as illustrated in Figure 11, the MEMS device 300 may further comprise a sensing chamber 309, and the first sealed chamber 306 may be referred to as a first reference chamber, and the second sealed chamber 327 may be referred to as a second reference chamber. It will be appreciated that the three regions described above may be arranged, with respect to each other, in any suitable way, for example, the sensing region may be located between the first reference region and the second reference region. The sensing region comprises a sensing chamber 309, a sensing cavity 319, a sensing membrane 321 and a heating element 323. In use, the first and the second reference regions are fluidically isolated from the external environment, and the sensing region is exposed to the external environment, including a target stimulus. The second reference region, comprising a second reference membrane 326, a heating element 325, a second reference cavity 329 and a second reference chamber 327, may be provided to be used as a lifetime monitoring structure during the operation of the sensor. If the first reference region, comprising a first sealed reference chamber 306 is sealed in a controlled atmosphere, and the second reference region, comprising a second sealed reference chamber 327, is sealed in vacuum (or in a different controlled atmosphere to the one of the first sealed reference chamber), then this configuration may be used to (indirectly) monitor for leaks in the seal of the first sealed reference chamber 306, during operation, over the lifetime of the device (sensor). It will be understood that the internal atmosphere of the second reference sealed chamber 327 may be suitably provided through an aperture in the second reference region, which can be successively sealed through a seal 328. During operation of the sensor, leaks in the seal of the second sealed reference chamber 327 may be detected by monitoring (e.g. periodically) the vacuum level within the vacuum sealed second reference region. This may be achieved by measuring the temperature of the heating element 325 provided to membrane 326 (or the temperature of a temperature sensing element placed in the vicinity of such heating element 326) for a given power level applied to the heating element 325. In the presence of a leak, the temperature of the heating element 325 would gradually decrease (compared to the value expected when no leak is present). This may provide an indication that the seal of the first reference sealed chamber 306 (e.g., sealed in dry air), may have failed too, since they have been used for the same period of time and in similar conditions, and, therefore, the heating element 324, provided to membrane 322, may no longer provide a reliable reference to the heating element 323, provided to membrane 321 in the sensing region, for a differential measurement. It will be understood that, while the second reference sealed region 327 may preferably be sealed in a vacuum, in other embodiments it may be sealed in any other suitable atmosphere that is different from the external atmosphere, to which the sensing region is exposed, or air. For example, it may be sealed in low pressure air, high pressure air, hydrogen, helium, argon and / or carbon dioxide or any other suitable gas or combination of gases at any suitable pressure. Different pressures or gases may be used as long as they behave in a significantly different way from air, or the external atmosphere, with respect of their interaction with the heating element 325, as explained above. Preferably the heating elements 323, 324 and 325 are substantially identical. A change in pressure and / or composition of the internal atmosphere of the second reference sealed chamber 327 may be detected by any suitable means known in the art, e.g. a pressure sensor, a gas sensor or the like. In some examples, the heating element 325 may be used as a Pirani sensor, where a power loss varies with changes in pressure. Figure 11B shows a top view of the differential environmental sensor of Figure 11A where it is shown that the first bonding region 304 of the first reference region, the bonding region 305 of the second reference region, and the bonding region 314 of the sensing region are all arranged in a similar way so that it may be assumed that they age in a similar fashion. Methods Figure 12 provides a schematic representation of a method of manufacture 800 which may be used to produce, for example, the MEMS devices 50, 100, and 200. In a step S802, the method 800 comprises attaching a first substrate to a second substrate. In a step S804, the method 800 comprises forming a first bonding region between the first substrate and the second substrate and a second bonding region, adjacent to the first bonding region, wherein the first bonding region and the second bonding are arranged to form an inner chamber and an outer chamber, the inner chamber being bounded by the first bonding region, and the outer chamber being bounded by the first bonding region and the second bonding region. It will be understood that the steps S802, S804 of the method 800 may be performed in any order. Attaching the first and second substrates may comprise bonding the two substrates through either or both bonding regions. Many bonding techniques and bonding materials are known in the art. Some bonding techniques require an intermediate layer, or bonding region, to be arranged between the two substrates e.g. wafers, to be bonded together. These include adhesive bonding, glass frit bonding, eutectic bonding, metal thermocompression bonding and the like. The intermediate layers, depending on the technique, may comprise polymers (such as polyimides, resists, benzocyclobutenes, epoxies), glass frit, eutectic alloys, metals (e.g. aluminium, copper and gold). In general, a bonding process is a step in the manufacturing process, which may happen at wafer level, where a bonding region (or a precursor thereof) is formed on either or both substrates. Forming the bonding region may comprise lithography or screen printing. It may further comprise one or more heating and / or curing processes. The two substrates are then aligned and brought in contact with each other while heat and pressure are suitably applied in order to modify the bonding material structure and properties so as to bond the two substrates via the bonding region. The method 800 may comprise, during attachment of the first substrate to the second substrate, exposing the first substrate and the second substrate to a first atmosphere which will define the controlled internal atmosphere of the inner sealed chamber. Attaching the first substrate to the second substrate may comprise applying heat and / or pressure to one or both of the first bonding region and the second bonding region, e.g. through the first and / or the second substrate. In some implementations of the method, the outer chamber may comprise an aperture such that the outer chamber is in fluid communication with an external environment. This allows, following attachment of the first substrate to the second substrate, exposing the attached first and second substrates to a second atmosphere, different from the first atmosphere, and closing the aperture. The second atmosphere may define the internal controlled atmosphere of the external sealed chamber. Figure 13 provides a schematic representation of a method of manufacture 900 which may be used, for example, to produce the MEMS devices 300. In a step S902, the method 900 comprises attaching a first substrate to a second substrate while the first substrate and the second substrate are exposed to a first atmosphere. In a step S904, the method 900 comprises forming a bonding region between the first substrate and the second substrate, wherein the first substrate, the second substrate, and the bonding region define a first chamber and a second chamber, the first chamber being sealed, and wherein the second chamber comprises an aperture such that the second chamber is in fluid communication with an external environment. In a step S906, the method 900 comprises, following attachment of the first substrate to the second substrate, exposing the attached first and second substrates to a second atmosphere, different from the first atmosphere. In a step S908, the method 900 comprises closing the aperture. It will be understood that the steps S902, to S908 of the method 900 may be performed in any order. Attaching the first and second substrates may comprise bonding the two substrates through either or both bonding regions. Many bonding techniques and bonding materials are known in the art. Some bonding techniques require an intermediate layer, or bonding region, to be arranged between the two substrates e.g. wafers, to be bonded together. These include adhesive bonding, glass frit bonding, eutectic bonding, metal thermocompression bonding and the like. The intermediate layers, depending on the technique, may comprise polymers (such as polyimides, resists, benzocyclobutenes, epoxies), glass frit, eutectic alloys, metals (e.g. aluminium, copper and gold). In general, a bonding process is a step in the manufacturing process, which may happen at wafer level, where a bonding region (or a precursor thereof) is formed on either or both substrates. The two substrates are then aligned and brought in contact with each other while heat and pressure are suitably applied in order to modify the bonding material structure and properties so as to bond the two substrates via the bonding region. MEMS device having a discontinuous bonding region Figure 14 shows an example of a MEMS device 400 comprising a discontinuous bonding region 414. In the particular example illustrated in Figure 14, the MEMS device 400 is a differential environmental sensor. Figure 14A is a cross-section of the sensor 400 comprising a first substrate 401, a dielectric layer 420 and a second substrate 402. The sensor 400 has a sensing region, on the right hand side and a reference region on the left hand side of Figure 14A. The sensing region comprises a sensing chamber 409, a sensing cavity 419, the sensing cavity 419 defining, in the dielectric layer 420, a sensing membrane 421 provided with a heating element 423. The reference region comprises a reference chamber 406, a reference cavity 416, the reference cavity 416 defining, in the dielectric layer 420, a reference membrane 422 provided with a heating element 424. A bottom substrate 411 closes the cavities 416 and 419. In some examples, the cavities 416 and 419 are entirely defined in the first substrate 401 and the bottom substrate 411 may not be provided. The reference region further comprises a first bonding region 404. The reference region is sealed so as to be fluidically isolated from the external environment. The sensing region comprises a second bonding region 414. The sensing region is in fluidic communication with the external environment through one or more holes provided in the second bonding region 414. In other words, the second bonding region 414 is discontinuous. The second bonding region 414 may be provided with a plurality of holes, as shown, in top view, in Figure 14B, or the second bonding region 414 may be provided with one hole, two holes or any suitable number of holes. It will be understood that the number and size of the holes are not limited. The number and size of the holes may be chosen so as to ensure, at least, fast displacement time of the gas in the sensing region and structural stability of the device 400. Figure 15 shows another example of the differential environmental sensor 400. The sensor 400 of Figure 15 differs from the sensor 400 of figure 14 in that the reference region of the sensor 400 of Figure 15 comprises an inner sealed chamber 406 and an outer chamber 407. The inner sealed chamber and the outer chamber are defined by the first bonding region 404 and a further bonding region 405. The outer chamber 407 may be an outer sealed chamber. The outer sealed chamber and the inner sealed chamber may have the same controlled atmosphere or different controlled atmospheres. Alternatively, the outer chamber 407 may be in fluidic communication with the external atmosphere. The outer chamber 407 and the second bonding region 405, provide protection of the seal of the inner sealed chamber 406, as described above. It will be understood that, while the Figures show, in top view, the bonding regions as having a substantially square or rectangular shape, this is in no way limiting and other suitable shapes may be used, for example circular, polygonal or rectangular with rounded corners. Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the disclosure, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

1. A MEMS device comprising:a first substrate;a second substrate attached to the first substrate;a first bonding region between the first substrate and the second substrate; anda second bonding region adjacent the first bonding region;wherein the first bonding region and the second bonding region are arranged to form an inner sealed chamber and an outer chamber, the inner sealed chamber being bounded by the first bonding region, and the outer chamber being bounded by the first bonding region and the second bonding region.

2. The MEMS device according to claim 1, wherein the outer chamber comprises a continuous gap between the first bonding region and the second bonding region around a whole perimeter of the first bonding region.

3. The MEMS device according to claim 1, wherein the first bonding region is arranged to be in contact with the second bonding region at least at a first contact region and a second contact region.

4. The MEMS device according to any one of the preceding claims, wherein the inner sealed chamber is bounded by the second bonding region.

5. The MEMS device according to any one of the preceding claims, wherein the outer chamber is a sealed chamber.

6. The MEMS device according to any one of the preceding claims, wherein at least part of the outer chamber is adjacent to an edge of the first and / or second substrate.

7. The MEMS device according to any one of the preceding claims, comprising a third substrate disposed between the first substrate and the second substrate,wherein at least one of the inner sealed chamber and the outer chamber is bounded by the third substrate.

8. The MEMS device according to any one of the preceding claims, wherein the outer chambers is a sealed chamber and an internal atmosphere of the inner sealed chamber is substantially the same as an internal atmosphere of the outer sealed chamber.

9. The MEMS device according to any one of claims 1 to 7, wherein an internal atmosphere of the inner sealed chamber is different from an internal atmosphere of the outer chamber.

10. The MEMS device according to any one of the preceding claims, comprising a pressure sensor and / or a chemical sensor disposed in the inner sealed chamber.

11. The MEMS device according to any one of the preceding claims, wherein the first bonding region and the second bonding region comprise a same material.

12. The MEMS device according to any one of the preceding claims, wherein at least one of the first bonding region and the second bonding material comprises a glass frit.

13. The MEMS device according to any one of the preceding claims, comprising a sensing region and a reference region, wherein the inner sealed chamber forms a reference chamber.

14. The MEMS device according to claim 13, wherein the sensing region comprises a sensing chamber arranged to be in fluid communication with an external environment.

15. A method of manufacturing a MEMS device, the method comprising: attaching a first substrate to a second substrate; andforming a first bonding region between the first substrate and the second substrate, and a second bonding region adjacent to the first bonding region;wherein the first bonding region and the second bonding are arranged to form an inner chamber and an outer chamber, the inner chamber being bounded by the first bonding region, and the outer chamber being bounded by the first bonding region and the second bonding region.

16. The method according to claim 15 comprising, during attachment of the first substrate to the second substrate, exposing the first substrate and the second substrate to a first atmosphere.

17. The method according to claim 15 or 16, wherein attaching the first substrate to the second substrate comprises applying heat and / or pressure to one or both of the first bonding region and the second bonding region.

18. The method according to any one of claims 15 to 17, wherein the outer chamber comprises an aperture such that the outer chamber is in fluid communication with an external environment; andwherein the method further comprises, following attachment of the first substrate to the second substrate:exposing the attached first and second substrates to a second atmosphere, different from the first atmosphere; andclosing the aperture.

19. A method of manufacturing a MEMS device, the method comprising:attaching a first substrate to a second substrate while the first substrate and the second substrate are exposed to a first atmosphere; andforming a bonding region between the first substrate and the second substrate;wherein the first substrate, the second substrate, and the bonding region define a first chamber and a second chamber, the first chamber being sealed, and wherein the second chamber comprises an aperture such that the second chamber is in fluid communication with an external environment;wherein the method further comprises, following attachment of the first substrate to the second substrate:exposing the attached first and second substrates to a second atmosphere, different from the first atmosphere; andclosing the aperture.

20. A MEMS device comprising:a first substrate;a second substrate attached to the first substrate;a first bonding region between the first substrate and the second substrate; anda second bonding region between the first substrate and the second substrate;wherein the first bonding region and the second bonding region are arranged to form a first chamber and a second chamber, the first chamber being sealed and being bounded by the first bonding region and the second chamber being bounded by the second bonding region; andwherein the second bonding region is a discontinuous bonding region such that the second chamber is in fluid communication with an external environment.

21. The MEMS device according to claim 20, wherein the first chamber is a reference chamber and forms part of a reference region of the MEMS device; and wherein the second chamber is a sensing chamber and forms part of a sensing region of the MEMS device.

22. The MEMS device according to claim 20 or 21, wherein the first chamber is an inner first chamber and wherein the MEMS device further comprises a further bonding region adjacent the first bonding region, wherein the first bonding region and the further bonding region are arranged to form an outer first chamber, the first chamber being bounded by the first bonding region and the further bonding region.

23. The MEMS device according to claim 22, wherein the outer first chamber is a sealed chamber.34

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