Patent Description:
The sensing of environmental parameters in the ambient atmosphere, such as noise, sound, temperature and gases, e.g. environmental gas components, gains more and more importance in the implementation of appropriate sensors within mobile devices, home automation, such as smart home, the automotive sector, etc. With the evermore extensive use of sensors, there is also a particular need to be able to provide such sensors, e.g. for sensing the environmental air quality, and their components as inexpensively as possible, but nevertheless the achieved reliability and accuracy of the sensors should be as high as possible.

In the field of monitoring the air quality in our environment, there are several types of existing gas-sensing concepts, for example, NDIR sensors (NDIR = non-dispersive infrared), chemical sensors, catalytic bead (pellistor) sensors and photo-acoustical sensors (PAS sensors, PAS = photoacoustic spectroscopy). An often used sensor principle is based on the excitation of gas molecules in a medium by (e.g. infrared) light with a certain wavelength. However, currently available NDIR or PAS systems are relatively expensive due to their complex setups or special components even if the NDIR or PAS devices offer a relatively high sensitivity together with a relatively cheap set of components. Furthermore, chemical sensors are showing a relatively poor selectivity compared to single-wavelength or filter containing optical systems.

A typical optical sensor, e.g. a PAS or NDIR sensor, comprises a radiation source, filter elements for a wavelength selection, a detector and the sample area (interaction area) where the light between the light source and the detector interacts with the environmental medium.

<CIT> relates to a method for manufacturing an emitter package for a photoacoustic sensor assembly, an emitter package for a photoacoustic sensor assembly and a photoacoustic emitter assembly with such an emitter package.

<CIT> relates to an emitter package for a photoacoustic sensor.

<CIT> relates to sensors for detection of gas, in particular sensors for detection of CO2 , and methods for manufacturing a sensor.

The inventors of the present application have recognized that depending on the target gas (the gas to be measured), e.g. CO<NUM>, a parasitic content of this gas (or of another gas) inside the emitter (PAS) package or the detector (NDIR) package would affect the sensitivity of such a sensor toward the target gas. The presence of a parasitic gas, such as CO<NUM>, e.g. in the emitter or detector, forms relatively easy due to temperature steps, such as bake and reflow process steps, applied to the gas sensor system during the manufacturing process.

Thus, it is an object of the herewith disclosed principle to provide an improved optical radiation device package, e.g. comprising an optical radiation source as part of a PAS sensor or an optical radiation detector as part of an NDIR sensor, for achieving improved operating characteristics of the optical radiation device and of the sensor device comprising the optical radiation device.

Such a need can be solved by the acoustically tight optical radiation device package according to claim <NUM>.

Further specific implementations of the package are defined in the dependent claims.

According to an embodiment, an optical radiation device package comprises a base structure having arranged thereon the optical radiation device, an optically (IR, UV or visible radiation) transparent lid element bonded to the base structure defining a cavity between the base structure and the lid element, wherein the optical radiation device is arranged in the cavity, and a bond structure in a bonding region between the base structure and the lid element. The bond structure is arranged to provide an adhesive bond between the base structure and the lid element, and the bond structure comprises a diffusion layer having a gas diffusive material or gas diffusive structure for providing an gas diffusion path between the closed cavity and the surrounding atmosphere. According to an embodiment, the optical radiation device is an optical radiation emitter or an optical radiation detector.

Thus, the present concept as described in the different embodiments can be used in physical gas sensors, such as in photoacoustic spectroscopy (PAS) and non-dispersive infrared (NDIR) gas sensors. According to embodiments, the present concept improves a sub-component of these systems, such as the emitter (for a PAS sensor) or the detector (for the NDIR sensor).

Thus, the present disclosure describes a design of a package that has a defined diffusion path to allow an out-diffusion of gases inside an emitter (for a PAS sensor) or a detector (for an NDIR sensor). A defined exchange with the ambient air will be used to further dilute the gas inside the emitter/detector package. Thus, only a (highly) reduced amount of a gas remains in the package of the optical radiation device.

According to embodiments, the package may comprises an acoustically tight gas diffusion path, e.g. with an acoustically tight bond structure. Thus, the package may be arranged to be acoustically tight. Further, the bond structure may comprise a diffusion layer having a "parasitic" gas diffusive material or parasitic gas diffusive structure for providing an acoustically tight parasitic gas diffusion path between the cavity and the surrounding atmosphere. Any gas which negatively influences or affects the operation of the optical radiation device may be regarded as a parasitic gas, i.e. a gas or gas composition, which has a negative effect to the functionality of the optical radiation structure.

An acoustically tight package may ensure that the cavity is acoustically isolated from the sample area (interaction area) in the measurement cell of a sensor device. Moreover, acoustical influences or interferences from the environment, e.g. in the frequency range of the periodically chopped radiation emitted from the (PAS) radiation source, may be sufficiently attenuated and suppressed, i.e. acoustically kept away from the cavity of the package.

Once the gas (or parasitic gas) is fully driven out and/or at the same level (equilibrium) with the ambient gas concentration (or ambient parasitic gas concentration), the device can be calibrated. A further increase of gas, e.g. due to operation, will be avoided due to the constantly given diffusivity of the package.

According to embodiments, the package uses a highly gas permeable layer (diffusion layer) in the interface (having a high gas diffusivity) of a cavity package which is typically closed by an optical filter (lid element). This diffusion layer can be integrated in front-end or back-end on the filter or on the cavity package directly. To seal off the package, an adhesive layer is commonly used. According to embodiments, there could be also filter particles directly integrated into the adhesive to modify its diffusion properties.

Thus, embodiments of the package having the high gas diffusivity interface can achieve the following technical effects.

The package can avoid that an elevated amount of the gas, e.g. a parasitic gas such as CO<NUM>, is present inside the emitter package during the sensor calibration, wherein an elevated amount of the gas can quickly diffuse out of the package. Thus, it can be prevented that a gas will cause a drift of the sensor toward lower concentrations detected in case of an emitter in a PAS system, for example. Thus, it can be avoided that a gas (e.g. CO<NUM>) inside the PAS emitter package would reduce the radiation output by light absorption. Thus, the gas sensitivity of the PAS sensor is not lowered as it can be avoided that less radiation reaches the interaction area of the sensor cell.

Moreover, it can be avoided during assembling and operating the emitter, e.g. a ceramic emitter, that the air pressure within the sealed cavity becomes too low due to curing the lid adhesive (filter adhesive) at a high temperature as the air pressure falls within the cavity on cooling.

In case, UV cured adhesive are used for the lid (filter) attachment and a contamination occurred due to uncured adhesive material in the (ceramic) cavity, interfering shifts in the (ceramic) emitter output signal can be avoided as the (parasitic) gas content, e.g. CO<NUM>, which results from the contamination, can easily diffuse to the environment.

Moreover, the package can avoid that an elevated amount of the (parasitic) gas, e.g. CO<NUM>, is present inside the detector package during the sensor calibration, wherein an elevated amount of the gas can quickly diffuse out of the package. Thus, it can be prevented that a gas will cause a drift of the sensor toward higher concentrations in a detector of a NDIR system. Thus, it can be avoided that a gas, e.g. a parasitic gas, such as CO<NUM>, inside the NDIR detector package would reduce the received radiation due to light absorption. Thus, the gas sensitivity (CO<NUM> sensitivity) is not lowered as it can be avoided that less radiation reaches the radiation detector.

In the following, embodiments of the present disclosure are described in the following in more detail while making reference to the accompanying drawings in which:.

In the following description, embodiments are discussed in further detail using the figures, wherein in the figures and the specification identical elements and elements having the same functionality and/or the same technical or physical effect are provided with the same reference numbers or are identified with the same name. Thus, the description of these elements and of the functionality thereof as illustrated in the different embodiments are mutually exchangeable or may be applied to one another in the different embodiments.

In the following description, embodiments are discussed in detail, however, it should be appreciated that the embodiments provide many applicable concepts that can be embodied in a wide variety of semiconductor devices. The specific embodiments discussed are merely illustrative of specific ways to make and use the present concept, and do not limit the scope of the embodiments.

In the following description of embodiments, the same or similar elements having the same function have associated therewith the same reference signs or the same name, and a description of such elements will not be repeated for every embodiment. Moreover, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

In the description of the embodiments, terms and text passages placed in brackets (next to a described element or function) are to be understood as further explanations, exemplary or optionally configurations, exemplary additions and/or exemplary alternatives of the described element or function.

It is understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or intermediate elements that may be present. Conversely, when an element is referred to as being "directly" connected to another element, "connected" or "coupled," there are no intermediate elements. Other terms used to describe the relationship between elements should be construed in a similar fashion (e.g., "between" versus "directly between", "adjacent" versus "directly adjacent", and "on" versus "directly on", etc.).

For facilitating the description of the different embodiments, some of the figures comprise a Cartesian coordinate system x, y, z, wherein the x-y-plane corresponds, i.e. is parallel, to a main surface region (= a reference plane = x-y-plane), wherein the direction vertically up with respect to the reference plane (x-y-plane) corresponds to the "+z" direction, and wherein the direction vertically down with respect to the reference plane (x-y-plane) corresponds to the "-z" direction. In the following description, the term "lateral" means a direction parallel to the x- and/or y-direction or a direction parallel to (or in) the x-y-plane, wherein the term "vertical" means a direction parallel to the z-direction.

<FIG> shows a schematic cross-sectional view through an package <NUM> for an optical radiation device <NUM> (<NUM>-<NUM>, <NUM>-<NUM>) according to an embodiment. As exemplarily shown in <FIG>, the package <NUM> for the optical radiation device <NUM> comprises a base structure <NUM> having arranged thereon the optical radiation device <NUM>, a lid element <NUM> (e.g. optically transparent for IR, UV or visible radiation) bonded to the base structure <NUM> and defining a cavity <NUM> between the base structure <NUM> and the lid element <NUM>. The package <NUM> further comprises a bond structure <NUM> in a bonding region <NUM> between the base structure <NUM> and the lid element <NUM>.

The bond structure <NUM> is arranged to provide an adhesive bond between the base structure <NUM> and the lid element <NUM>. The bond structure <NUM> comprises a diffusion layer <NUM>-<NUM> having a gas diffusive material or gas diffusive structure for providing a gas diffusion path <NUM> between the closed cavity <NUM> and the surrounding atmosphere <NUM>. According to an embodiment, the optical radiation device <NUM> may be formed as an optical radiation emitter <NUM>-<NUM> or an optical radiation detector <NUM>-<NUM>.

According to an embodiment, the package <NUM> may comprise an acoustically tight gas diffusion path <NUM>, e.g. with an acoustically tight bond structure <NUM>. Thus, the package <NUM> may be arranged as an acoustically tight package <NUM>. According to a further embodiment, the bond structure <NUM> may comprise a diffusion layer <NUM>-<NUM>, <NUM>-<NUM> having a parasitic gas diffusive material or parasitic gas diffusive structure for providing an acoustically tight parasitic gas diffusion path <NUM> between the cavity <NUM> and the surrounding atmosphere <NUM>.

In the context of the present description, the term "acoustically tight" may define a condition of the package <NUM> and, for example, of the bond structure <NUM> of the package <NUM>, wherein a first order low frequency (roll-off corner frequency or high-pass corner frequency) is (about) <NUM> (or between <NUM> and <NUM>,<NUM>). A first order low frequency (roll-off corner frequency) of (about) <NUM> (within ± <NUM>%) may result in an attenuation of <NUM> dB (equals a factor of <NUM>) at a target frequency of <NUM> (within ± <NUM>), for example.

Thus, the acoustically tight package <NUM> may ensure that the cavity <NUM> is acoustically isolated from the sample area (interaction area) in the measurement cell of a sensor device (see <FIG>, for example). The periodically chopped radiation emitted from the (PAS) radiation source may be sufficiently attenuated and suppressed, i.e. acoustically kept away from the sample area (interaction area) in the measurement cell of a sensor device, to ensure that the gas measurements are not compromised.

Moreover, acoustical influences or interferences from the environment, e.g. in the frequency range of the periodically chopped radiation emitted from the (PAS) radiation source, may be sufficiently attenuated and suppressed, i.e. acoustically kept away from the cavity <NUM> of the package <NUM>. Thus, the cavity <NUM> of the package <NUM> may be acoustically isolated from the environment, e.g. from external noise.

In the context of the present description, the term "parasitic" gas may relate to any gas or gas composition, which affects or (negatively) influences the operation of the optical radiation device. Thus, a parasitic gas may be any gas or gas composition, which may have a negative effect to the functionality of the optical radiation structure.

According to an embodiment, the optical radiation device <NUM> may be an IR emitter (e.g. a MEMS heater) and, thus, part of a PAS gas detector (see <FIG>, for example) for detecting a target gas GTAR, wherein the bond structure <NUM> is arranged to provide the diffusion path <NUM> for a (parasitic) gas GCAV (from or to the cavity <NUM>) through the bond structure <NUM>. According to a further embodiment, the optical radiation device <NUM> may be a laser or LED, e.g. a blue ray laser with an emission wavelength of <NUM> (CWL = continuous wave laser), for example.

According to an embodiment, the optical radiation device <NUM> may be (alternatively) an optical radiation detector and part of a NDIR gas detector (e.g. a thermopile, see <FIG>, for example) for detecting a target gas GTAR, wherein the bond structure <NUM> is arranged to provide the diffusion path <NUM> for a parasitic gas GCAV through the bond structure <NUM>.

Embodiments of the present disclosure are described with respect to gases or gas components, e.g., in the environmental air. However, the description of the different embodiments is equally applicable to liquids or liquid components in the environmental medium. Thus, the general term "fluid" may relate to a liquid or a gas. Moreover, the description with respect to a gas or gas component is equally applicable to a liquid or liquid component.

Thus, a target gas or target gas component is the gas or gas component to be detected or sensed and may comprise at least one of CO, CO<NUM>, O<NUM>, NOX, methane, etc., for example. The present concept is equally applicable to sense a target liquid or a target liquid component in the environmental medium. In the context of the embodiments, the target gas GTAR and the parasitic gas GCAV may relate to the same gas or gas component or may relate to different gases or different gas components. According to an exemplarily embodiment, the target gas or target gas component to be detected or sensed and the (parasitic) gas GCAV may relate to gases or gas components having similar absorption lines (which are reactive on similar bands).

To summarize, the gas (or parasitic gas) GCAV may relate to any gas content in the cavity <NUM> which may affect an operating parameter, e.g. the sensitivity, of the optical radiation device <NUM> or of a sensor device which comprises the optical radiation device <NUM>. Thus, the gas GCAV may be the target gas to be sensed or another component, e.g. water vapor, which will also vent out through the diffusion path <NUM>. According to an exemplarily embodiment, the target gas or target gas component GTAR to be detected or sensed may comprise CO (carbon monoxide), for example, wherein the (parasitic) gas GCAV may comprise CO<NUM> (carbon dioxide), because CO and CO<NUM> have similar absorption lines (bands). Moreover, according to a further exemplarily embodiment, the target gas or target gas component to be detected or sensed may comprise CO<NUM> (carbon dioxide), for example, wherein the (parasitic) gas GCAV may comprise CO (carbon monoxide).

According to an embodiment, the bond structure <NUM> is arranged to have a permeability for the gas GCAV for providing a gas exchange (of gas GCAV) through the diffusion path <NUM> between the cavity and the surrounding environment with a diffusion time constant TD which is below <NUM>, <NUM>, <NUM> or <NUM> seconds or between <NUM> and <NUM>, <NUM>, <NUM>, or <NUM> seconds.

The diffusion time constant TD is, in the context of the present description, the time duration until the gas GCAV is fully driven out of the package and/or at the same level (equilibrium) with the ambient gas concentration, such as the concentration of the gas GCAV in the environment. The diffusion time constant TD of the gas GCAV is based on the gas diffusivity or gas permeability along the diffusion path <NUM> through the bond structure <NUM>. As the bond structure <NUM> comprises the diffusion layer having a gas diffusive material or a gas diffusive structure (for the gas GCAV), the bond structure <NUM> allows the transmission of the gas GCAV in both directions, i.e., both into and out of the cavity <NUM> (to allow a gas exchange of the gas GCAV).

In general, the term "gas permeability" or "gas diffusivity" refers to the permeability of the interface <NUM> to gas. The higher the gas diffusivity of the interface, for example, the better the interface can transport gas to the outside or release it back to the inside. The higher the gas diffusivity of the interface <NUM>, the shorter is the diffusion time constant TD.

According to an embodiment, the bond structure <NUM> comprises the diffusion layer <NUM>-<NUM> and the adhesive layer <NUM>-<NUM> in the bonding region for providing the adhesive bond between the base structure <NUM> and the lid element <NUM>. The diffusion layer <NUM>-<NUM> may be formed as a layer which is highly permeable for the gas GCAV, for providing the diffusion path <NUM> of the gas GCAV through the bond structure <NUM>, i.e., from the cavity <NUM> to the surrounding environment.

The diffusion layer <NUM>-<NUM> may comprise a gas diffusive material or a gas diffusive structure for the gas GCAV (e.g. in form of very thin pores or capillary tubes with an effective pore size or tube diameter in a range of about <NUM> and <NUM>) for providing the diffusion path <NUM> between the close cavity <NUM> and the surrounding atmosphere. The adhesive layer <NUM>-<NUM> may be formed as a double-sided tape which is attached to a side (surface region) of the diffusion layer <NUM>-<NUM>, e.g., a PTFE layer or a PTFE impregnated adhesive materials, polymers, such as polyamide or cellulose acetate, or ceramic materials. The bond structure (bondline) <NUM> may comprise a typical overall thickness between (around) <NUM> and <NUM>, for example.

The package <NUM> may comprise an exemplary lateral extension "X" between <NUM> and <NUM>, between <NUM> and <NUM> or of about <NUM>. The (lateral) thickness X<NUM> of the wall <NUM> may be in a range of about <NUM> to <NUM>.

In case of a bond structure <NUM> comprising the diffusion layer <NUM>-<NUM> and the adhesive layer <NUM>-<NUM>, the diffusion layer <NUM>-<NUM> may comprise a thickness t<NUM>-<NUM> in a range between <NUM> and <NUM> or between <NUM> and <NUM>, wherein the adhesive layer <NUM>-<NUM> may comprise a (vertical) thickness t<NUM>-<NUM> of about <NUM> to <NUM>. The diffusion layer <NUM>-<NUM> and the adhesive layer <NUM>-<NUM> may comprise a (lateral) width w<NUM>-<NUM>, w<NUM>-<NUM> of about <NUM> to <NUM> which corresponds to the (lateral) wall thickness X<NUM>. In case the bond structure <NUM> comprises the adhesive layer <NUM>-<NUM> with the filler particles, the (lateral) thickness t<NUM>-<NUM> of the adhesive filler layer <NUM>-<NUM> is in a range between <NUM> and <NUM>.

Thus, according to an embodiment, the bond structure <NUM> may comprises the diffusion layer <NUM>-<NUM> and the adhesive layer <NUM>-<NUM> in the bonding region <NUM> for providing the diffusion path <NUM> between the cavity <NUM> and the surrounding environment and for providing the adhesive bond between the base structure <NUM> and the lid element <NUM>. According to an embodiment, the bond structure <NUM> may further comprise a further adhesive layer <NUM>-<NUM>, wherein the diffusion layer <NUM>-<NUM> having a gas diffusive material is sandwiched between the adhesive layer <NUM>-<NUM> and the further adhesive layer <NUM>-<NUM>. According to a further embodiment, the bond structure <NUM> comprises a stack of a plurality of alternating adhesive layers <NUM>-<NUM> and (sandwiched) gas diffusive layers <NUM>-<NUM>.

According to an embodiment, at least one of the base structure <NUM> and the lid element <NUM> may further comprise a supporting structure <NUM>, e.g. in form of a merlon-like structure for mechanically stabilizing the diffusion layer <NUM>-<NUM>.

According to an embodiment, the bond structure <NUM> may comprise an adhesive layer <NUM>-<NUM> in the bonding region <NUM> for providing the adhesive bond between the base structure <NUM> and the lid element <NUM>. The adhesive layer (filler adhesive) <NUM>-<NUM> may comprise gas diffusive filler particles <NUM> for providing the diffusion path <NUM> through the bond structure <NUM>. According to an embodiment, the adhesive layer <NUM>-<NUM> may comprise a PTFE material or a PTFE impregnated adhesive for providing the diffusion path <NUM> of the gas GCAV through the bond structure <NUM>.

Based on the size and quantity (density) of the gas diffusive filler particles <NUM> in the adhesive layer <NUM>-<NUM> and based on the dimensions of the adhesive layer <NUM>-<NUM>, the diffusion time constant TD can be set to a requested value. Thus, the more filler particles <NUM> in the adhesive layer <NUM>-<NUM> and the greater the dimension (e.g. the vertical cross-sectional area) of adhesive layer <NUM>-<NUM>, the shorter is the (set) diffusion time constant TD.

According to an embodiment, the adhesive layer <NUM>-<NUM> may comprise a gas diffusion section <NUM> for providing the gas diffusion path <NUM> through the bond structure <NUM>. According to an embodiment, the diffusion section <NUM> may be formed as at least one (or a plurality of) channel(s) <NUM> through the adhesive layer <NUM>-<NUM> and comprises a gas diffusive material.

According to a further embodiment, the diffusion section <NUM> in the adhesive layer <NUM>-<NUM> may comprise a gas diffusive filler material or gas diffusive filler particles embedded in the adhesive layer <NUM>-<NUM>. Thus, a part (section) of the adhesive layer <NUM>-<NUM>, which laterally extends through the bond structure <NUM>, comprises the gas diffusive filler material or gas diffusive filler particles and forms the diffusion path <NUM>.

Further, a plurality of gas diffusion sections <NUM> of the adhesive layer <NUM>-<NUM>, which laterally extend through the bond structure <NUM>, may comprise the gas diffusive filler material or gas diffusive filler particles and may form the diffusion path <NUM>.

In the following description of <FIG>, essentially additions, differences or alternatives to the embodiments as shown in <FIG> are discussed in detail. Thus, the above description with respect to <FIG> is equally applicable to the further embodiments as described below. As elements having the same structure and/or function are provided with the same reference numbers or name, a detailed description of such elements will not be repeated for every embodiment.

<FIG> show further schematic cross-sectional views through further possible implementations of the package <NUM> for an optical radiation device <NUM> according to further embodiments. The further illustrations of the package <NUM> in <FIG> should show (and clarify) that the following evaluations of the present concept for the package <NUM> for an optical radiation device <NUM> are equally applicable to different configurations (designs) of the respectively bonded base structure <NUM> and lid element <NUM> and to different positions of the bonding region <NUM> with the bond structure <NUM> between the base structure <NUM> and the lid element <NUM>.

To be more specific, as shown in <FIG>, the base structure (basis element) <NUM> may comprise the (vertically extending) side walls <NUM>. As shown in <FIG>, the lid element <NUM> may comprise the (vertically extending) side walls <NUM>. As shown in <FIG>, the base structure <NUM> and the lid element may each comprises a part of the (vertically extending) side walls <NUM>. In each case, the bonding region <NUM> with the bond structure is formed between the base structure <NUM> and the lid element <NUM>. Thus, the lid element <NUM> is placed (arranged) on top of the base structure <NUM>.

Moreover, the following evaluations of the present concept for the package <NUM> are also applicable to configurations with further "intermediate elements" in the base structure <NUM>, the lid element <NUM> and/or the side walls <NUM> as far as the intermediate elements are bonded to the base structure <NUM>, the lid element <NUM> and/or the side walls <NUM> and provide for the package <NUM>.

Moreover, the bond structure <NUM> may be formed (placed) at any height position of the side walls <NUM>, e.g. at a top position as shown in <FIG>, at a bottom position as shown in <FIG> or at an intermediate position as shown in <FIG>. Moreover, the bond structure <NUM> may be circumferentially arranged in the side walls <NUM> and parallel to the lateral (reference) plane, for example, for facilitating the manufacturing process.

As shown in <FIG>, the side wall <NUM> of the package <NUM> is arranged between and adhesively fixed (bonded) to the base structure (base element) <NUM> and the lid element (lid structure) <NUM>. As shown in <FIG>, a further bond structure <NUM> may be arranged in a further bond region <NUM> between the side wall <NUM> and the base structure <NUM> wherein the bond structure <NUM> is arranged in the bond region <NUM> between the side wall <NUM> and the lid element <NUM>. The bond region <NUM> and the further bond region <NUM> are vertically spaced from each other. Thus, the further bond region <NUM> may be formed (placed) at a bottom position of the side wall(s) <NUM> as shown in <FIG>. Alternatively, a least one (or both) of the bond region <NUM> and the further bond region <NUM> may be placed at an intermediate position of the side wall(s) <NUM>.

As shown in <FIG>, the further bond structure <NUM> may be arranged in a further bond region <NUM> between the side wall <NUM> and the base structure <NUM>, wherein the bond structure <NUM> is arranged in the bond region <NUM> between the side wall structure <NUM> and the lid element <NUM>. The bond region <NUM> and the further bond region <NUM> are vertically spaced from each other. Thus, the further bond region <NUM> may be formed (placed) at a bottom position of the side wall(s) <NUM>. Alternatively, a least one (or both) of the bond region <NUM> and the further bond region <NUM> may be placed at an intermediate position of the side wall(s) <NUM>.

According to a further embodiment, the bond structure <NUM> and the further bond structure <NUM> may form together the diffusion paths <NUM>, <NUM>-<NUM>. Thus, the further bond structure <NUM> may comprise an adhesive layer <NUM>-<NUM> in the further bonding region <NUM> for providing the adhesive bond. According to a further embodiment, the adhesive layer <NUM>-<NUM> of the further bond structure may comprise gas diffusive filler particles <NUM> for providing a further diffusion path <NUM>-<NUM> through the bond structure <NUM>. According to an embodiment, the adhesive layer <NUM>-<NUM> may comprise a PTFE material or a PTFE impregnated adhesive for providing the further diffusion path <NUM>-<NUM> of the target gas GTAR through the further bond structure <NUM>.

According to a further embodiment, the further bond structure <NUM> may comprise a diffusion layer <NUM>-<NUM> having a gas diffusive material or gas diffusive structure for providing a further gas diffusion path <NUM>-<NUM> between the closed cavity <NUM> and the surrounding atmosphere. The further bond structure <NUM> may comprise the adhesive layer <NUM>-<NUM> in the further bonding region <NUM> for providing the adhesive bond.

Thus, the further bond structure <NUM> may comprise the same arrangement and function as the bond structure <NUM> for providing the further gas diffusion path <NUM>-<NUM>.

Thus, the embodiments as discussed with respect to <FIG> and <FIG> describe a design of a package <NUM> that has a defined gas diffusion path <NUM> (<NUM>-<NUM>) to allow an out-diffusion of gases inside an optical radiation device <NUM>, e.g. an emitter (PAS) <NUM>-<NUM> or a detector (NDIR) <NUM>-<NUM>. A defined exchange with the ambient atmosphere, e.g. environmental air, will be used to further and further dilute the gas GCAV inside the emitter / detector package <NUM>.

The package <NUM> may be part of a gas sensor device (see <FIG> and <FIG>). Once the gas GCAV is fully driven out and/or at the same level as (in an equilibrium with) the ambient gas concentration, the sensor device can be calibrated. A further increase of gas GCAV (e.g. due to operation) will be avoided due to the constantly given diffusivity of the package <NUM> through the bond structure <NUM> providing the diffusion path <NUM> between the cavity <NUM> and the surrounding atmosphere.

Depending on the material and geometry selection for the bond structure <NUM>, quick diffusion time constants (seconds / minutes) can be achieved by the interface layer stack which forms the bond structure <NUM>. A gas GCAV will diffuse quickly inside the emitter / detector package <NUM> and can be calibrated out as it will be present in the sensor cell (sensor device) and in the emitter / detector package <NUM> in equal amount.

According to the described embodiments, the package <NUM> uses a highly gas permeable structure or layer ("diffusion structure or layer" <NUM>) in the interface (= bond structure = interface having a high gas diffusivity) <NUM> of the cavity package <NUM>. The cavity <NUM> is enclosed by the base structure <NUM> and the lid element (lid structure) <NUM>, wherein the lid element <NUM> may form or comprise an optical filter, for example. This diffusion layer (of the bond structure) <NUM> can be integrated in front- or backend on the lid structure (e.g. a filter) <NUM> or base structure <NUM> of the cavity package <NUM> directly. To seal off the package <NUM>, the bond structure <NUM> may comprise an adhesive layer (or layer stack). Alternatively, there could be filler particles directly integrated into the adhesive layer to modify its diffusion properties.

In the following description, further alternative embodiments are discussed in detail. Thus, the above description with respect to <FIG> and <FIG> is equally applicable to the further embodiments as described below. As elements having the same structure and/or function are provided with the same reference numbers or name, a detailed description of such elements will not be repeated for every embodiment.

<FIG> show schematic cross-sectional views through an acoustically tight optical radiation device package according to further embodiments together with an enlarged sectional view of the bond structure. As shown in <FIG>, the bond structure <NUM> may comprises (at least) the diffusion layer <NUM>-<NUM> and the adhesive layer <NUM>-<NUM> in the bonding region <NUM> for providing the diffusion path <NUM> between the cavity <NUM> and the surrounding environment and for providing the adhesive bond between the base structure <NUM> and the lid element <NUM>.

As shown in <FIG>, the diffusion layer <NUM>-<NUM> is attached to the lid element <NUM>, wherein the adhesive layer is attached to the wall element <NUM> of the base structure <NUM>. Further, the opposing surfaces of the diffusion layer <NUM>-<NUM> and the adhesive layer <NUM>-<NUM> are attached to each other to form the bond structure <NUM>.

As shown in <FIG>, the diffusion layer <NUM>-<NUM> is attached to the wall element <NUM> of the base structure <NUM>, wherein the adhesive layer is attached to the lid element <NUM>. Further, the opposing surfaces of the adhesive layer <NUM>-<NUM> and of the diffusion layer <NUM>-<NUM> are attached to each other to form the bond structure <NUM>.

As shown in <FIG> the bond structure <NUM> may be formed as a triple stack with adhesive layers <NUM>-<NUM> and <NUM>-<NUM> of both sides of the diffusion layer <NUM>-<NUM>. Thus, according to <FIG>, the bond structure <NUM> may further comprise the further adhesive layer <NUM>-<NUM>, wherein the diffusion layer <NUM>-<NUM> having a gas diffusive material is sandwiched between the adhesive layer <NUM>-<NUM> and the further adhesive layer <NUM>-<NUM>.

As shown in <FIG>, the bond structure <NUM> may comprise a stack of a plurality of alternating adhesive layers <NUM>-<NUM>, <NUM>-<NUM> and diffusion layers <NUM>-<NUM>. As exemplarily shown in <FIG>, each diffusion layer <NUM>-<NUM> is sandwiched between two adhesive layers <NUM>-<NUM>, <NUM>-<NUM>, for example.

<FIG> shows a schematic cross-sectional view through an optical radiation device package according to a further embodiment together with an enlarged sectional view of the bond structure. As shown in <FIG>, at least one of the base structure <NUM> and the lid element <NUM> may further comprise a supporting structure <NUM>, e.g., in the form of a merlon- or pinnacle-like structure or of bumps, for mechanically stabilizing the diffusion layer <NUM>-<NUM>. The supporting or stabilization structure may be part of the base structure <NUM> or the lid element <NUM> or of both. In <FIG>, the stabilization structure <NUM> is shown as part of the base structure <NUM> on top of the wall elements <NUM>. The stabilization structures <NUM> are arranged to avoid a deflection of the lid element <NUM> (having an optical filter, for example) in case the diffusion layer <NUM>-<NUM> comprises a (relatively) soft and deformable material, e.g., a foam-like material.

To summarize, if the diffusion layer <NUM>-<NUM> comprises, for example, a soft foam-like material, the merlon-like structures around the package frame (between the base structure <NUM> and the lid element <NUM>) are arranged to stabilize the assembly by offering direct mechanical contact between the base structure <NUM> and the adhesive layer <NUM>-<NUM> which is attached to the lid element <NUM>, for example, or between the base structure <NUM> and the lid element <NUM>.

Alternatively, the merlon-like structures may be formed at the lid element and may provide direct mechanical contact to the adhesive layer <NUM>-<NUM> which is attached to the top side of the wall elements <NUM> of the base structure <NUM>, or directly to the wall elements <NUM> of the base structure <NUM>.

<FIG> shows a schematic 3D view of an package <NUM> for an optical radiation device <NUM> together with an enlarged cross-sectional view of the bond structure <NUM> according to a further embodiment.

As shown in <FIG>, the adhesive layer <NUM>-<NUM> comprises a gas diffusion section <NUM> for providing the gas diffusion path <NUM> through the bond structure <NUM>. According to the embodiment, the diffusion section <NUM> may be formed as at least one channel <NUM> or a plurality of channels <NUM> through the adhesive layer <NUM>-<NUM> and comprises a gas diffusive material. According to a further embodiment, the diffusion section <NUM> may comprise a gas diffusive filler material or gas diffusive filler particles embedded in the adhesive layer <NUM>-<NUM>. Thus, the section <NUM> of the adhesive layer <NUM>-<NUM>, which laterally extends through the bond structure <NUM>, comprises the gas diffusive filler material or gas diffusive filler particles and forms the diffusion path <NUM>. Further, a plurality of sections of the adhesive layer <NUM>-<NUM>, which laterally extend through the bond structure <NUM>, may comprise the gas diffusive filler material or gas diffusive filler particles and may form the diffusion path <NUM>.

To summarize, the diffusion layer <NUM>-<NUM> does not fully surround the interface (bond structure) <NUM> but is partially formed as a section <NUM> of the bond structure <NUM>. By introducing the diffusion section(s) <NUM> in the adhesion section (layer) <NUM>-<NUM>, at least one or a plurality of diffusion channels <NUM> are formed through the adhesion layer(s) <NUM>-<NUM>.

<FIG> shows a schematic cross-sectional view through an acoustic type optical radiation device package <NUM> according to a further embodiment together with an enlarged view of the bond structure <NUM>.

As exemplarily shown in <FIG>, the adhesive layer (filler adhesive) <NUM>-<NUM> of the bond structure <NUM> may comprise gas diffusive filler particles <NUM> (filler particles which are diffusive for the gas GCAV) for providing the diffusion path <NUM> through the bond structure <NUM>. According to an embodiment, the adhesive layer <NUM>-<NUM> may comprise a PTFE material or a PTFE impregnated adhesive for providing the diffusion path <NUM> of the gas GCAV through the bond structure <NUM>. Based on the amount and quantity (density) of the gas diffusive filler particles <NUM> in the adhesive layer <NUM>-<NUM>, and based on the dimensions of the adhesive layer <NUM>-<NUM>, the diffusion time constant TD can be set to a predefined value. Thus, the more filler particles in the adhesive layer <NUM>-<NUM> and the greater the dimension (e.g., the vertical cross sectional area) of the adhesive layer <NUM>-<NUM>, the shorter is said diffusion time constant TD.

To summarize, the adhesive layer <NUM>-<NUM> of the bond structure <NUM> may comprise diffusion time enhancing filter particles <NUM>, e.g., in a standard adhesive material. The filler particles <NUM>, e.g., PTFE material, allow a quicker diffusion of the gas GCAV by having a shorter effective path length of the glue interface (bond structure) <NUM> to the outside (ambient atmosphere).

Thus, according to the above embodiments, the package <NUM> uses a highly gas permeable structure or layer based on the filler particles <NUM> in the bond structure (interface) <NUM> of the cavity package <NUM>. As further indicated above, the present concept can be used in physical gas sensors, such as in photoacoustic spectroscopy (PAS) and non-dispersive infrared (NDIR) sensors. The following evaluations are outlined in connection with a PAS gas sensor, however, the following evaluations are equally applicable to an NDIR gas sensor.

In the following, some technical effects of the package <NUM> for an optical radiation device <NUM> in form of an optical radiation source <NUM>, e.g. as part of a PAS sensor, are summarized. The following evaluations are correspondingly applicable to the package <NUM> for an optical radiation device <NUM> in form of an optical radiation detector for a NDIR gas detector.

According to embodiments, a potential method to improve the emitter performance is to make one element (the bond structure <NUM>) of its construction 'breathable', i.e. allow exchange of gas, but not compromise acoustic tightness. An adhesive <NUM>-<NUM> used to retain the lid element <NUM>, which forms or comprises an IR filter, in place can be used wherein the adhesive may contain a PTFE or a similar gas exchanging / high permeability filler material. This structure allows the exchange of gas (parasitic gas GCAV) far more readily through the adhesive material.

The high gas permeability material suspended in the adhesive <NUM>-<NUM> allows to provide an cavity <NUM>, but still allow the transmission of gas both into and out of the emitter cavity <NUM>. The gas exchanging material does not necessarily need to form a solid pathway between interior and exterior if the adhesive already has some ability to allow gas exchange, it needs to have a much higher rate of gas permeability. An improved gas transmission may also occur along the interfaces between the adhesive and the more gas permeable filler.

The high gas permeability material in the adhesive <NUM>-<NUM> would allow equalization of (atmospheric) pressure between the IR emitter interior <NUM> and the gas measurement chamber (see <FIG>, for example) in which it sits. It would also allow any gas, e.g. CO<NUM>, generated from curing materials to escape. If the diffusion time of gas through the material (bond structure <NUM>) is chosen to be much slower than that of the gas, e.g. CO<NUM>, entering the measurement chamber (see <FIG>, for example), the gas, e.g. CO<NUM>, measurement should not be affected.

As well as UV curing, the high gas permeability impregnated adhesive <NUM>-<NUM> could potentially be cured by thermal means, since the adhesive material's breathability would allow pressure inside the ceramic cavity to equalize on cooling.

However, the gas exchange through the high gas permeability material <NUM>-<NUM> may not be fast enough during thermal curing (during the manufacturing process) to overcome internal air pressure changes, so that a slow ramp in heating may applied. Thus, it can be ensured that the adhesive <NUM>-<NUM> will not be pushed out of the joint between the base structure <NUM>, e.g. a ceramic cavity, and the lid element <NUM>, e.g. an IR filter, by internal air pressure, creating voids in the adhesive <NUM>-<NUM>.

As exemplarily shown in <FIG>, the package may be formed as a ceramic cavity emitter package <NUM> and may comprise the optical radiation device <NUM> in form of an IR emitter (e.g. a MEMS heater) <NUM>-<NUM>. Thus, the package <NUM> may be part of a PAS gas detector for detecting a target gas GTAR. According to an embodiment, the packaged emitter <NUM>-<NUM> is formed as a MEMS heater die on the base structure <NUM>. The die is connected via wire-bonds <NUM> to a processing circuit (e.g. an ASIC). The light (radiation) emitted from the MEMS heater die <NUM>-<NUM> is transmitted to and through the transparent lid element <NUM>. The lid element <NUM> may comprise or form an IR filter (band-pass filter). The IR filter may be formed as a silicon IR filter so that filtered IR light emerges from the IR filter. The adhesive material <NUM>-<NUM> of the bond structure <NUM> retains the lid element (filter) <NUM> on the sidewalls of the (ceramic) cavity package <NUM>.

According to the embodiment of <FIG>, the package <NUM> may comprise an acoustically tight gas diffusion path <NUM>, e.g. with an acoustically tight bond structure <NUM>. Thus, the package <NUM> may be arranged as an acoustically tight package <NUM>. According to a further embodiment, the bond structure <NUM> may comprise a diffusion layer having a parasitic gas diffusive material or parasitic gas diffusive structure for providing an acoustically tight parasitic gas diffusion path <NUM> between the cavity <NUM> and the surrounding atmosphere <NUM>.

<FIG> shows a schematic block diagram of a fluid (= gas or liquid) sensing device <NUM> having the package <NUM> for an optical radiation device <NUM> according to a further embodiment. The fluid sensor <NUM> may comprise the package <NUM> for an optical radiation device <NUM>.

According to an embodiment, the fluid sensor <NUM> may be formed as a PAS gas detector (fluid detector) <NUM>-<NUM>, wherein the optical radiation device <NUM> is an IR emitter or a laser or LED <NUM>-<NUM> and part of the PAS gas detector <NUM>-<NUM> for detecting a target gas GTAR. The bond structure <NUM> of the package <NUM> is arranged to provide the diffusion path <NUM> for a gas GCAV through the bond structure <NUM>. According to an embodiment, the bond structure <NUM> of the package <NUM> may be arranged to provide an acoustically tight diffusion path <NUM> for a parasitic gas GPAR through the bond structure <NUM>.

According to a further embodiment, the fluid sensor <NUM> may be formed as an NDIR gas detector <NUM>-<NUM>, wherein the optical radiation device <NUM> is an optical radiation detector <NUM>-<NUM>, e.g., a thermopile detector, for detecting a target gas GTAR, wherein the bond structure <NUM> is arranged to provide the diffusion path <NUM> for a gas GCAV through the bond structure <NUM>.

<FIG> shows a schematic block diagram of a fluid (gas or liquid) sensing device <NUM>-<NUM> in the form of a PAS gas sensor having the package <NUM> for an optical radiation device <NUM> according to a further embodiment.

As shown in <FIG>, the PAS gas sensor <NUM>-<NUM> comprises a light source <NUM>-<NUM> which is arranged in the package <NUM>, e.g. an the acoustically tight package <NUM>. The light source <NUM>-<NUM> may comprise an infrared emitter or a laser diode, for example. The light source <NUM>-<NUM> may be periodically chopped. The package <NUM> comprises an optical filter, which is, for example, part of the lid element <NUM>, for a wavelength selection. The gas sensor device <NUM> further comprises a sample area (interaction area) <NUM> where the light or radiation R between the light source <NUM>-<NUM> and the detector <NUM> interacts with the environmental medium. The optical filter <NUM> is arranged to filter the wavelength related to a specific gas, e.g., a wavelength λ = <NUM> for CO<NUM>. The detector <NUM> may be formed, for example, as a (capacitive or piezoelectric) MEMS microphone. In the interaction area <NUM>, the molecules of the target gas GTAR, e.g. CO<NUM> molecules, absorb the light R emitted from the light source <NUM>-<NUM> and filtered by the optical filter <NUM>. The light absorption causes a periodic local change of temperature in the interaction area <NUM>, which results in corresponding pressure changes in the interaction area <NUM>. The periodic pressure changes are detected by the acoustic detector <NUM>, e.g., a MEMS microphone, which is optimized for low frequency operation. The acoustic detector <NUM> may be read out by means of an ASIC <NUM>, for example. Moreover, the closed interaction area may be accessible through a fluid port <NUM> for fluid (gas or liquid) diffusion.

Thus, embodiments may relate to a PTFE impregnated adhesive to secure of the lid element <NUM>, e.g. an IR filter, to the base structure <NUM> defining a cavity <NUM>, e.g. a ceramic cavity, on the PAS gas sensor <NUM>-<NUM>, e.g. a PAS CO<NUM> sensor.

<FIG> shows a schematic block diagram of a fluid (gas or liquid) sensing device in the form of an NDIR gas sensor <NUM>-<NUM> having the package <NUM> for an optical radiation device <NUM> according to a further embodiment.

According to <FIG>, the NDIR sensor device <NUM>-<NUM> comprises a radiation source <NUM>, the package <NUM> for the detector <NUM>-<NUM>, the package <NUM> comprises the lid element <NUM> having filter element for a wavelength selection and the sample area (interaction area) <NUM> which is accessible by means of a gas inlet/outlet <NUM>. In the interaction area <NUM>, the light R between the light source <NUM> and the detector <NUM> interacts with the environmental medium, e.g. the target gas GTAR.

Thus, the main components of the NDIR sensor <NUM>-<NUM> are an infrared IR source <NUM>, the sample chamber or light tube <NUM>, the light filter <NUM> and the infrared detector <NUM> in the package <NUM>. The IR light R is directed through the sample chamber <NUM> towards the packaged detector <NUM>. The target gas GTAR in the sample chamber <NUM> causes an absorption of a specific wavelength and the intensity change at this wavelength is measured by the detector <NUM> to determine the target gas concentration. The optical filter <NUM> in front of (upstream to) the detector is arranged to eliminate all light except the wavelength that the target gas molecules can absorb.

In the following, different technical implementations and technical effects of the optical radiation device package and the fluid sensor device <NUM> are summarized below. According to an embodiment, the bond structure <NUM> of the package <NUM> may be arranged to provide an acoustically tight diffusion path <NUM> for a parasitic gas GPAR through the bond structure <NUM>.

Embodiments describe an improvement to existing cavity packages for gas sensing, which often contain a certain amount of the target gas interfering with the IR radiation as gas GCAV. According to the embodiments, a defined gas ventilation path <NUM> is provided inside the cavity package <NUM>, wherein the cavity package <NUM> allows gas GCAV (parasitic gas) to penetrate at a specific rate. The cavity package <NUM> may be acoustically tight but also allows gas GCAV (parasitic gas) to penetrate at a specific rate. The ventilation path <NUM> can be formed as one or more separate (diffusion) layers or a diffusion material <NUM>-<NUM> embedded into existing adhesive layers <NUM>-<NUM> and/or <NUM>-<NUM>.

The package <NUM> for an optical radiation device <NUM> may provide a drift stabilization of a gas sensing device <NUM>, e.g., a PAS system <NUM>-<NUM> or a NDIR system <NUM>-<NUM> for gas sensing.

The package <NUM> according to the above embodiments is inexpensive to manufacture, wherein there is no need to have the gas content fully settled and under control prior to calibration of the gas sensor device. The bond structure <NUM> can inexpensively be integrated in the package. Moreover, the package <NUM> provides a defined acoustical tightness for the gas sensor device <NUM>, e.g., a PAS sensor <NUM>-<NUM> or an NDIR sensor <NUM>-<NUM>, so that the package <NUM> can be inexpensively integrated into the measurement cell. Moreover, the package <NUM> can be formed to have high mechanical robustness as well as high resilience to temperature cycles.

Claim 1:
An optical radiation device package (<NUM>), comprising:
a base structure (<NUM>) having arranged thereon the optical radiation device (<NUM>; <NUM>-<NUM>, <NUM>-<NUM>),
an optically transparent lid element (<NUM>) bonded to the base structure (<NUM>) defining a cavity (<NUM>) between the base structure (<NUM>) and the lid element (<NUM>), wherein the optical radiation device (<NUM>; <NUM>-<NUM>, <NUM>-<NUM>) is arranged in the cavity (<NUM>), and
a bond structure (<NUM>) in a bonding region (<NUM>) between the base structure (<NUM>) and the lid element (<NUM>), wherein the bond structure (<NUM>) is arranged to provide an adhesive bond between the base structure (<NUM>) and the lid element,
characterized in that the bond structure (<NUM>) comprises a diffusion layer (<NUM>-<NUM>, <NUM>-<NUM>) having a gas diffusive material or gas diffusive structure for providing a gas diffusion path (<NUM>) between the cavity (<NUM>) and the surrounding atmosphere (<NUM>).