Patent Description:
The detection of environmental parameters in the ambient atmosphere is becoming increasingly important in the implementation of appropriate sensor systems, for example within mobile devices, but also in the implementation in home automation, such as smart home, and, for example, in the automotive sector. However, with the ever more extensive use of sensor systems, there is also a particular need to be able to produce such sensor systems as inexpensively as possible and, thus, as cost effectively as possible. However, the resulting reliability and accuracy of the sensor systems should nevertheless be maintained or should be even increased.

In particular, the field of monitoring the air quality and/or the gas composition in our environment is receiving more and more attention. However, typical gas sensors are rather expensive to manufacture and/or rather bulky.

<CIT> relates to a gas sensor. The gas sensor comprises a substrate having a cavity for providing an optical interaction path for an interaction of a filtered IR (IR = infrared) radiation with a target gas in the cavity; a thermal emitter arranged for emitting a broadband IR radiation, wherein the thermal emitter is optically coupled to the cavity; a wavelength selective structure arranged for filtering the broadband IR radiation emitted by the thermal emitter; an IR detector arranged to provide a detector output signal based on a signal strength of the filtered IR radiation having traversed the optical interaction path in the cavity and being received by the IR detector.

<CIT> relates to a biosensor chip combining surface plasmon and electrochemical detection. The biosensor comprises a waveguide configured to receive an optical radiation, and to propagate the optical radiation along the length of the waveguide as a surface plasmon-polariton (SPP) wave with its transverse electric field substantially perpendicular to the width of the waveguide, and to emit the propagated optical radiation away from the waveguide and towards a detector.

Generally, there is a need in the art for an approach to implement an improved monolithic fluid sensor system and an improved method for manufacturing the monolithic fluid sensor system.

Such a need can be solved by the monolithic fluid sensor system according to independent claim <NUM> and by a method for manufacturing a monolithic fluid sensor system according to independent claim <NUM>.

Specific implementations of the monolithic fluid sensor system and the method for manufacturing the monolithic fluid sensor system are defined in the dependent claims.

According to an embodiment a monolithic fluid sensor system comprises:.

Thus, embodiments provide a monolithic fluid sensor system and a method for manufacturing such a monolithic fluid sensor system, wherein the sensor system comprises a sensor arrangement and a reference sensor arrangement which are monolithically arranged, i.e., the respective substrates or semiconductor substrates (wafers or semiconductor wafers) are bonded (fusion bonded or wafer bonded on wafer-level) to each other for providing the resulting monolithic fluid sensor system.

The monolithic fluid sensor system and a method for manufacturing such a monolithic fluid sensor system provide for an inexpensive monolithic on-chip integration of a selective and efficient fluid sensor system for the industrial sector.

Embodiments of the present monolithic fluid sensor system and the method for manufacturing the monolithic fluid sensor system are described in detail with respect to the drawings and figures, 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 are to be understood as further explanations, exemplary configurations, exemplary additions and/or exemplary alternatives,.

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 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 first main surface region of a substrate (e.g. a sensor substrate = 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.

In the following, a monolithic fluid sensor system <NUM> is described with respect to <FIG>, <FIG> and <FIG> according to an embodiment. <FIG> shows a schematic plan view (top view) of a monolithic fluid sensor system <NUM> according to an embodiment. <FIG> shows different schematic 3D representations of different exemplarily waveguide types for the monolithic fluid sensor system according to an embodiment. <FIG> shows exemplary schematic cross-sectional views of a strip waveguide and a slot waveguide together with a simulation of the respective evanescent fields at the resonance wavelength λ<NUM> according to an embodiment. <FIG> show schematic cross-sectional views of the monolithic fluid sensor system of <FIG>.

As shown in <FIG>, the monolithic fluid sensor system <NUM> comprises a sensor arrangement (sensor path) <NUM>, a cover substrate <NUM>, a reference sensor arrangement (reference path) <NUM>, and a reference cover substrate <NUM>.

The sensor arrangement <NUM> comprises a thermal radiation emitter <NUM>, an optical filter structure <NUM>, a waveguide structure <NUM> and a thermal radiation detector <NUM> on a first main surface region <NUM>-<NUM> of the sensor substrate <NUM>.

The cover substrate <NUM> comprises a recess, e.g. a depression or hollow, <NUM>, which is arranged in a first main surface region <NUM>-<NUM> of the cover substrate <NUM>. The cover substrate <NUM> further comprises a through-opening, e.g. a ventilation opening or ventilation hole, <NUM> between the recess <NUM> in the first main surface region <NUM>-<NUM> and a second main surface region <NUM>-<NUM> of the cover substrate. The first main surface region <NUM>-<NUM> of the cover substrate <NUM> is bonded, e.g., wafer bonded or fusion bonded on wafer-level, to the first main surface region <NUM>-<NUM> of the sensor substrate <NUM>, wherein the sensor arrangement <NUM> is arranged below the recess <NUM> of the cover substrate <NUM>.

The recess <NUM> in the first main surface region <NUM>-<NUM> of the cover substrate <NUM> forms a (structured) cavity <NUM> for the sensor arrangement (reference path) <NUM>, and wherein the through-opening <NUM> forms a fluidic connection to the environment for enabling exchange of fluids between the sensor cavity <NUM> and the environment. The through-opening <NUM> in the cavity <NUM> of the sensor path <NUM> provides for an interaction (in the cavity <NUM>) with the environmental gas. As exemplarily shown in <FIG>, the cover substrate <NUM> may comprises at least one (or a plurality) of through-opening(s) <NUM>.

The reference sensor arrangement <NUM> comprises a reference thermal radiation emitter <NUM>, a reference optical filter structure <NUM>, a reference waveguide structure <NUM>, a reference thermal radiation detector <NUM> on a first surface region <NUM>-<NUM> of the reference sensor substrate <NUM>.

The reference cover substrate <NUM> comprises a reference recess <NUM>, wherein the reference recess <NUM> is arranged in a first main surface region <NUM>-<NUM> of the reference cover substrate <NUM>. The first main surface region <NUM>-<NUM> of the reference cover substrate is bonded, e.g. wafer bonded or fusion bonded on wafer-level, to the first main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>. The reference recess <NUM> in the first main surface region <NUM>-<NUM> forms a hermetically closed (e.g. sealed) cavity (= structured cavity) <NUM> for the reference sensor arrangement (reference path) <NUM>. The reference cover substrate does not comprise a through opening and constitutes therefore a hermetic cavity <NUM> without an exchange of fluids between the reference sensor cavity <NUM> and the environment.

According to an embodiment, the waveguide structure <NUM> of the sensor arrangement <NUM> may (optionally) comprise a first waveguide portion <NUM>-<NUM> and a second waveguide portion <NUM>-<NUM>, which are optically arranged between the thermal radiation emitter <NUM> and the thermal radiation detector <NUM>. Thus, the thermal radiation emitter <NUM> (through a first and second optical filter structure portion <NUM>-<NUM>, <NUM>-<NUM>) couples into the two waveguide portions <NUM>-<NUM>, <NUM>-<NUM>, which lead to the thermal radiation detector <NUM>. The two waveguide portions <NUM>-<NUM>, <NUM>-<NUM> may have (parallel to the reference plane) a L-shape or an arc shape, so that the two waveguide portions <NUM>-<NUM>, <NUM>-<NUM> each lead to the thermal radiation detector <NUM>.

According to the embodiment, the reference waveguide structure <NUM> of the reference sensor arrangement <NUM> may (optionally) comprise a first reference waveguide portion <NUM>-<NUM> and a second reference waveguide portion <NUM>-<NUM>, which are optically arranged between the reference thermal radiation emitter <NUM> and the reference thermal radiation detector <NUM>. Thus, the reference thermal radiation emitter <NUM> couples (through a first and second optical filter structure portion <NUM>-<NUM>, <NUM>-<NUM>) into the two waveguide portions <NUM>-<NUM>, <NUM>-<NUM>, which lead to the reference thermal radiation detector <NUM>. The two reference waveguide portions <NUM> may have (parallel to the reference plane) a L-shape or an arc shape, so that the two reference waveguide portions <NUM> each lead to the reference thermal radiation detector <NUM>.

According to an embodiment, the elements <NUM>, <NUM>, <NUM>, <NUM> of the sensor arrangement <NUM> and the corresponding reference elements <NUM>, <NUM>, <NUM>, <NUM> of the reference sensor arrangement <NUM> have the same structural setup (composition) and functionality with the exception of the through-opening(s) <NUM> in the cover substrate <NUM> which are not present in the reference cover substrate <NUM>.

According to an embodiment, the monolithic fluid sensor system <NUM> further comprises a bottom substrate <NUM> (see <FIG>), wherein a first main surface region <NUM>-<NUM> of the bottom substrate <NUM> is bonded, e.g. fusion bonded or wafer bonded, to the second main surface region <NUM>-<NUM> of the sensor substrate <NUM>. The monolithic fluid sensor system <NUM> further comprises a reference bottom substrate <NUM>, wherein a first main surface region <NUM>-<NUM> of the reference bottom substrate <NUM> is bonded, e.g. fusion bonded or wafer bonded, to the second main surface region <NUM>-<NUM> of the reference senor substrate <NUM>.

Thus, the sensor substrate <NUM> is sandwiched (in a stacked configuration) between the cover substrate <NUM> and the bottom substrate <NUM>, wherein the reference sensor substrate <NUM> is sandwiched (in a stacked configuration) between the reference cover substrate <NUM> and the reference bottom substrate <NUM>.

According to an embodiment, the sensor substrate <NUM> and the reference sensor substrate <NUM> are arranged to form a common system substrate <NUM>, wherein the cover substrate <NUM> and the reference cover <NUM> substrate are arranged to form a common cover substrate <NUM>, and wherein the bottom substrate <NUM> and the reference bottom substrate <NUM> are arranged to form a common bottom substrate (spacer substrate) <NUM>. Thus, the top main surface region <NUM>-<NUM> of the sensor substrate <NUM> may form a common system plane of the monolithic fluid sensor system <NUM>.

The term "common substrate" may be also referred to an one-piece substrate or one-piece wafer or, also, as an one piece semiconductor substrate or one-piece semiconductor wafer, or, also, as an one piece glass substrate or one-piece glass wafer.

According to a further embodiment, the sensor substrate <NUM> and the reference sensor substrate <NUM> may be arranged to form separate system substrates, wherein the cover substrate <NUM> and the reference cover substrate <NUM> may be are arranged to form separate cover substrates, and wherein the bottom substrate <NUM> and the reference bottom substrate <NUM> may be arranged to form separate bottom substrates. These substrates may be processed as separated substrates or may be singulated (diced) at the dicing line DL, shown in <FIG>. Thus, the solutions for the reference complete system <NUM> and the sensor complete system <NUM> can both get divided on different layouts regarding production.

The sensor arrangement <NUM> and the reference sensor arrangement <NUM> may be formed on different substrates and, thus, may be provided as a sensor chip and a reference sensor chip, which may be placed next to each other in the application. Furthermore, the sensor chip and the reference sensor chip may be fixed or bonded to each other, e.g. by means of chip-stacking, for providing the monolithic fluid sensor system.

The monolithic fluid sensor system <NUM> is arranged for sensing an amount or a concentration of a target fluid or a target fluid component in the surrounding atmosphere, e.g. an environmental medium. In the present context, the term fluid may related to a liquid or a gas. In case, the environmental medium relates to environmental air, the target fluid may relate to a target gas or a target gas component which is present in the environmental air. Such a target gas or a target gas component may be at least one of CO, CO<NUM>, O<NUM>, NOx, and methane, for example. The present concept is equally applicable to sense a target liquid or a target liquid component in the environmental medium.

As shown in <FIG>, the monolithic fluid sensor system <NUM> comprises the sensor arrangement <NUM>, which is in fluidic communication with the environmental atmosphere, and the reference sensor arrangement <NUM>, which is arranged in the hermetically closed cavity <NUM>.

According to embodiments of the present disclosure, the monolithic fluid sensor system <NUM> performs a fluid measurement by means of the sensor arrangement <NUM> as well as a reference measurement by means of the reference sensor arrangement <NUM>. During the fluid measurement, filtered thermal radiation R<NUM>, which is emitted by the thermal radiation emitter <NUM> and filtered by the optical filter structure <NUM>, is guided via the waveguide structure <NUM> to the thermal radiation and detector <NUM>. The sensor arrangement <NUM> is in fluidic connection to the environmental atmosphere comprising the target fluid to be detected and/or sensed.

The reference sensor arrangement <NUM> is arranged to perform a reference measurement by guiding a reference thermal radiation R'<NUM>, which is emitted by the reference thermal radiation emitter <NUM> and filtered by the reference optical filter structure <NUM>, via the reference waveguide structure <NUM> to the reference thermal radiation detector <NUM>.

In the following, some general technical aspects of the elements of the sensor arrangement <NUM> and of the reference sensor arrangement <NUM> are described.

Sensor arrangement <NUM>: The thermal radiation emitter <NUM> may comprise a semiconductor strip <NUM>-<NUM> for emitting a broadband thermal radiation R, e.g., a broadband IR radiation, at least partially in a main radiation emission direction parallel to the first main surface region <NUM>-<NUM> of the sensor substrate <NUM>. Thus, the thermal radiation emitter <NUM> may be formed as a doped poly-Si wire emitter. At least a part of the emitted thermal radiation is in the IR wavelength range between <NUM>,<NUM> and <NUM>, or between <NUM> and <NUM>. Thus, the emitted thermal radiation is infrared (IR) radiation or comprises infrared (IR) radiation.

The semiconductor strip <NUM>-<NUM> may form a black body radiator (= thermal radiation emitter) and may be configured to have in an actuated condition an operating temperature in a range between <NUM>° K and <NUM>° K or between <NUM>° K and <NUM>° K. Thus, according to an embodiment, a free standing (isolated) highly n-doped polysilicon wire <NUM>-<NUM> is provided as the thermal radiation emitter <NUM>, that emits broadband IR radiation proportionally to the Planck's radiation law.

According to an embodiment, the thermal radiation emitter <NUM> may be connected via a first and a second buried conductor <NUM>-<NUM>, <NUM>-<NUM> to a first and a second terminal (metal pads) <NUM>-<NUM>, <NUM>-<NUM>. The first and second terminal (metal pads) <NUM>-<NUM>, <NUM>-<NUM> may be electrically connected (by means of wire bonding) to a power source for providing the thermal radiation emitter <NUM> with electrical energy to bring the thermal radiation emitter <NUM> in the actuated condition. The cover substrate <NUM> may comprise openings or holes <NUM>-<NUM>, <NUM>-<NUM> for contacting (wire bonding) the metal pads <NUM>-<NUM>, <NUM>-<NUM>.

The sensor arrangement <NUM> further comprises the optical filter structure <NUM> (with the first and second optical filter structure portions <NUM>-<NUM>, <NUM>-<NUM>) on the top main surface region <NUM>-<NUM> of the sensor substrate <NUM>. The optical filter structure <NUM> may comprises a semiconductor material and is configured to filter the broadband thermal radiation R (= broadband IR radiation) emitted by the thermal radiation emitter <NUM> and to provide a filtered (= narrowband) IR radiation R<NUM> (= filtered thermal radiation) having a center wavelength λ<NUM> for achieving a maximum interaction or absorption of the filtered thermal radiation R<NUM> with the target fluid. Thus, the optical filter structure <NUM> adjusts the filtered thermal radiation R<NUM> to match the absorption spectrum of the target fluid (target medium). The optical filter structure <NUM> of the sensor arrangement <NUM> may be formed as an optical resonator structure having a narrow transmission band with the center wavelength λ<NUM>. According to an embodiment, the optical filter structure <NUM> may comprise at least one of a photonic crystal structure (photonic filter) and/or a Bragg filter structure as wavelength selective optical element(s) for providing the filtered (= narrowband) IR radiation R<NUM> having the center wavelength λ<NUM>.

The sensor arrangement <NUM> further comprises the waveguide structure <NUM> (with the two parallel waveguide portions <NUM>-<NUM>, <NUM>-<NUM>) on the main top surface region <NUM>-<NUM> of the sensor substrate <NUM>. The filtered narrowband IR radiation R<NUM> having the center wavelength λ<NUM> is at least partially coupled into the waveguide structure <NUM>, wherein a mode of the filtered IR radiation R<NUM> propagates in the waveguide <NUM>. The waveguide structure <NUM> may comprise a semiconductor material and is configured to guide the filtered IR radiation having the center wavelength λ<NUM> (e.g. by total reflection). The guided IR radiation R<NUM> comprises an evanescent field component, i.e., a field component outside the waveguide <NUM>, for interacting with the surrounding atmosphere comprising the target fluid, i.e., a target liquid or a target gas.

As shown in the schematic plane view of <FIG>, the waveguide structure <NUM> may comprise a multi-slot waveguide with seven strips, for example. The multi-slot waveguide may comprise of at least two (<NUM> to n) strips of high refractive index materials nH separated by a sub-wavelength-scale slot region having a low-refractive index nL and surrounded by the environmental medium, e.g. air, having a low-refractive-index nAIR. The multi-slot waveguide is an optical waveguide that guides strongly confined light (= the filtered thermal radiation R<NUM>) in the slot region. Thus, a multi-slot waveguide may be used because the orientation and the strength of the evanescent field accumulated due to the overlapping fields between the at least two strips of the multi-slot waveguide.

The filtered IR radiation R<NUM> guided by the waveguide structure <NUM> comprises an evanescent field component E for interacting with the surrounding atmosphere having the target fluid, wherein the interaction of the evanescent field component E with the surrounding atmosphere results in a reduction of the transmitted thermal radiation R<NUM> due to absorption of the guided radiation R<NUM> which is a measure for the target fluid concentration in the surrounding atmosphere or medium.

<FIG> shows different schematic 3D representations of different exemplarily waveguide types for the monolithic fluid sensor system according to an embodiment. According to further embodiments, other waveguide types, e.g., at least one of a slab waveguide, a strip waveguide, a slot waveguide, a slot-array waveguide and a multi-slot waveguide, etc., may be used for the waveguide structure <NUM>.

<FIG> shows exemplary schematic cross-sectional views of a strip waveguide and a slot waveguide together with a simulation of the respective evanescent fields "E" at the filtered (resonance) wavelength λ<NUM> according to an embodiment.

To summarize, the sensor arrangement <NUM> of the monolithic fluid sensor system <NUM> may comprise a so-called multi-slot waveguide <NUM>, wherein in the multi-slot waveguide, an electromagnetic mode propagates in the infrared wavelength range, wherein a significant part of the mode, i.e. the evanescent field E, propagates outside the waveguide structure <NUM>. Due to the specific design of the multi-slot waveguide, a large portion of the mode propagates in the slots between two strips or slabs of the waveguide. Thus, an evanescent field proportion of several <NUM>% is possible in multi-slot waveguides.

As further shown in <FIG>, the sensor arrangement <NUM> further comprises the thermal radiation detector or IR detector (= IR receiver) <NUM> on the top main surface region <NUM>-<NUM> of the sensor substrate <NUM>, wherein the waveguide structure <NUM> is optically arranged between the thermal radiation emitter <NUM> and the thermal radiation detector <NUM>. The thermal radiation detector <NUM> may comprise at least one of a pyroelectric temperature sensor, a piezoelectric temperature sensor, a pn junction temperature sensor, a piled diode and a resistive temperature sensor.

According to an embodiment, the thermal radiation detector <NUM> may be connected via a first and a second buried conductor <NUM>-<NUM>, <NUM>-<NUM> to a first and a second terminal (metal pads) <NUM>-<NUM>, <NUM>-<NUM>. The thermal radiation detector <NUM> is further configured to provide a detector output signal SOUT based on a radiation strength (= signal strength) of the filtered IR radiation R received from the waveguide structure <NUM>. The thermal radiation detector <NUM> may provide the detector output signal SOUT between the first and second detector terminal <NUM>-<NUM>, <NUM>-<NUM>. The cover substrate <NUM> may comprise openings or holes <NUM>-<NUM>, <NUM>-<NUM> for contacting (wire bonding) the metal pads <NUM>-<NUM>, <NUM>-<NUM>.

According to an embodiment, the elements of the sensor arrangement <NUM> and the reference elements of the reference sensor arrangement <NUM> may have the same structural setup and (principal) functioning. Thus, the above evaluations of the elements (i.e. the thermal radiation emitter <NUM>, the optical filter structure <NUM>, the waveguide structure <NUM> and the thermal radiation detector <NUM>, respectively) of the sensor arrangement <NUM> are equally applicable to the corresponding elements (i.e. the reference thermal radiation emitter <NUM>, the reference optical filter structure <NUM>, the reference waveguide structure <NUM> and the reference thermal radiation detector <NUM>, respectively) of the reference sensor arrangement <NUM>.

Reference sensor arrangement <NUM>: The reference thermal radiation emitter <NUM> may comprise a reference semiconductor strip <NUM>-<NUM> for emitting a reference broadband thermal radiation R, e.g., a broadband IR radiation, at least partially in a main radiation emission direction parallel to the first main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>. Thus, the reference thermal radiation emitter <NUM> may be formed as a doped poly-Si wire emitter.

According to an embodiment, the reference thermal radiation emitter <NUM> may be connected via a first and a second buried conductor <NUM>-<NUM>, <NUM>-<NUM> to a first and a second terminal (metal pads) <NUM>-<NUM>, <NUM>-<NUM>. The first and second terminal (metal pads) <NUM>-<NUM>, <NUM>-<NUM> may be electrically connected (by means of wire bonding) to a power source for providing the reference thermal radiation emitter <NUM> with electrical energy to bring the reference thermal radiation emitter <NUM> in the actuated condition. The reference cover substrate <NUM> may comprise openings or holes <NUM>-<NUM>, <NUM>-<NUM> for contacting (wire bonding) the metal pads <NUM>-<NUM>, <NUM>-<NUM>.

The reference sensor arrangement <NUM> further comprises the optical filter structure <NUM> (with the first and second optical filter structure portion <NUM>-<NUM>, <NUM>-<NUM>) on the top main surface region <NUM>-<NUM> of the reference sensor substrate <NUM> for filtering the broadband thermal radiation (= broadband IR radiation) emitted by the thermal radiation emitter <NUM> and to provide the filtered (= narrowband) IR radiation R<NUM> (= filtered thermal radiation) having a center wavelength λ<NUM>.

The reference sensor arrangement <NUM> further comprises the reference waveguide structure <NUM> (with the two, parallel reference waveguide portions <NUM>-<NUM>, <NUM>-<NUM>) on the main top surface region <NUM>-<NUM> of the reference sensor substrate <NUM>. The filtered narrowband IR radiation R<NUM> having the center wavelength λ<NUM> is at least partially coupled into the waveguide structure <NUM>, wherein a mode of the filtered IR radiation R<NUM> propagates in the waveguide <NUM>. The waveguide structure <NUM> may comprise a multi-slot waveguide. According to further embodiments, other waveguide types, e.g., at least one of a slab waveguide, a strip waveguide, a slot waveguide, a slot-array waveguide and a multi-slot waveguide, etc., may be used for the waveguide structure <NUM>.

The reference sensor arrangement <NUM> further comprises the thermal radiation detector or IR detector (= IR receiver) <NUM> on the top main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>, wherein the reference waveguide <NUM> is optically arranged between the reference thermal radiation emitter <NUM> and the reference thermal radiation detector <NUM>. The thermal radiation detector <NUM> may comprise at least one of a pyroelectric temperature sensor, a piezoelectric temperature sensor, a pn junction temperature sensor, a piled diode and a resistive temperature sensor. The reference thermal radiation detector <NUM> is further configured to provide a reference detector output signal SOUT-REF based on a radiation strength (= signal strength) of the filtered IR radiation R<NUM> received from the reference waveguide structure <NUM>. The thermal radiation detector <NUM> may provide the detector output signal SOUT via a first and a second buried conductor <NUM>-<NUM>, <NUM>-<NUM> to a first and second detector terminal <NUM>-<NUM>, <NUM>-<NUM>.

In the following, the technical effect of commonly using the sensor arrangement <NUM> and the reference sensor arrangement <NUM> are described. In order to suppress specific environmental impacts on the measurement, the reference cover substrate <NUM> is configured to provide the hermetically closed cavity <NUM> for the reference sensor arrangement <NUM>. For example, an influence of an ambient fluid on the guided radiation, e.g. on an evanescence field of the guided radiation, guided by the reference waveguide structure <NUM>, may be suppressed or reduced by physically blocking the fluid with the reference cover substrate <NUM> from the reference sensor arrangement <NUM>. Other environmental impacts, for example a temperature, may still influence the reference measurement and the sensor measurement.

The reference measurement of the guided radiation with reduced environment impacts may be used in order to determine an information about unsuppressed environmental effects, e.g. temperature or humidity, or an impact of said effects on the guided radiation that are not or only to a limited amount influenced by the reference cover substrate <NUM>. This information may be used to correct other sensor measurements of the sensor arrangement <NUM> that are impacted by the environment in the same, or approximately same, manner as the reference measurement of the reference sensor arrangement <NUM>. Consequently, a reference measurement with the reference sensor arrangement <NUM>, using a similar setup to the sensor arrangement <NUM> may be used to correct or adapt the measurement results of the sensor arrangement <NUM>.

Moreover, not only environmental influences may be determined or compensated in that way. With the reference measurement, and for example an evaluation of a measurement trend over time, sensor parameters or a sensor condition, for example aging of the sensor arrangement <NUM> and/or fluctuations of the supply voltage, may be determined or taken into account for a compensation or improvement of other measurements of the sensor arrangement <NUM>.

<FIG> show different schematic cross-sectional views through different sections and elements of the sensor arrangement <NUM> and the reference sensor arrangement <NUM> of the monolithic fluid sensor system of <FIG> according to the embodiment.

The monolithic fluid sensor system <NUM> comprises the sensor arrangement <NUM> on the sensor substrate <NUM>, the cover substrate <NUM>, the reference sensor arrangement <NUM> on the reference sensor substrate <NUM>, and a reference cover substrate <NUM>.

As shown in <FIG> the sensor substrate <NUM> and, accordingly, the reference sensor substrate <NUM> may optionally comprise a plurality of (stacked) layers e.g., a first insulating (= dielectric) layer <NUM>, a second insulating (= dielectric) layer <NUM> and a semiconductor substrate layer <NUM>. The first dielectric layer <NUM> may comprise nitride material, e.g. SiN, the second dielectric layer <NUM> may comprise an oxide material, e.g. BOX = buried oxide, such as SiO<NUM>, and the semiconductor substrate layer <NUM> may comprise silicon. Thus, the first main surface region of the first dielectric layer <NUM> forms the top main surface region <NUM>-<NUM> of the sensor substrate <NUM> and the top main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>, respectively, e.g. on the complete semiconductor substrate layer <NUM>.

As further shown in <FIG> the cover substrate <NUM> and, accordingly, the reference cover substrate <NUM> may optionally comprise a plurality of (stacked) layers e.g., a first insulating (= dielectric) layer <NUM>, a second insulating (= dielectric) layer <NUM> and a semiconductor substrate layer <NUM>. The first dielectric layer <NUM> may comprise nitride material, e.g. SiN, the second dielectric layer <NUM> may comprise an oxide material, e.g. BOX = buried oxide, such as SiO<NUM>, and the semiconductor substrate layer <NUM> may comprise silicon. Thus, the first main surface region of the first dielectric layer <NUM> forms the top main surface region <NUM>-<NUM> of the cover substrate <NUM> and the top main surface region <NUM>-<NUM> of the reference cover substrate <NUM>, respectively, e.g. on the complete semiconductor substrate layer <NUM>.

The first insulating layer <NUM>, <NUM> may comprise a thickness between <NUM> to <NUM>, between <NUM> and <NUM>, or about <NUM>. The second insulating layer <NUM>, <NUM> may comprise a thickness between <NUM> to <NUM>, between <NUM> and <NUM>, or about <NUM>.

The semiconductor structures or elements of the sensor arrangement <NUM> and the reference sensor arrangement <NUM> may comprise a semiconductor element layer, e.g. having a Poly-Si material, on the first insulating layer <NUM>. The semiconductor element layer may comprise a thickness between <NUM> to <NUM>, between <NUM> and <NUM>, or about <NUM>. This semiconductor element layer is provided with an uniform height to form and define at least partially the thermal emitter <NUM>, <NUM>, the optical filter structure <NUM>, <NUM>, the waveguide structure <NUM>, <NUM> and the thermal detector <NUM>, <NUM> of the sensor arrangement <NUM> and the reference sensor arrangement <NUM>.

The thermal heater (Poly heater) <NUM>, <NUM> may be doped with a dopant, e.g. phosphor, for providing the heating property, and doping the thermal detector <NUM>, <NUM> with a dopant, e.g. phosphor, for providing the thermal detector <NUM>, <NUM> with an absorbing property for the thermal radiation (IR radiation).

Thus, the sensor arrangement <NUM> and the reference sensor arrangement <NUM> of the monolithic fluid sensor system <NUM> can be manufactured based on inexpensive CMOS processes.

As further shown in <FIG>, the first main surface region <NUM>-<NUM> of the cover substrate <NUM> is bonded, e.g., wafer bonded or fusion bonded on wafer-level, to the first main surface region <NUM>-<NUM> of the sensor substrate <NUM>, wherein the sensor arrangement <NUM> is arranged below the recess <NUM> of the cover substrate <NUM>. The first main surface region <NUM>-<NUM> of the bottom substrate <NUM> is bonded, e.g. fusion bonded or wafer bonded, to the second main surface region <NUM>-<NUM> of the sensor substrate <NUM>. The first main surface region <NUM>-<NUM> of the reference cover substrate is bonded, e.g. wafer bonded or fusion bonded on wafer-level, to the first main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>, wherein the reference sensor arrangement <NUM> is arranged below the reference recess <NUM> of the reference cover substrate <NUM>. The first main surface region <NUM>-<NUM> of the reference bottom substrate <NUM> is bonded, e.g. fusion bonded or wafer bonded, to the second main surface region <NUM>-<NUM> of the reference senor substrate <NUM>. Thus, the sensor substrate <NUM> is sandwiched (in a stacked configuration) between the cover substrate <NUM> and the bottom substrate <NUM>, wherein reference sensor substrate <NUM> is sandwiched (in a stacked configuration) between the reference cover substrate <NUM> and the reference bottom substrate <NUM>. The respective bonding areas (bonding regions) <NUM> between the bonded substrates are indicated in <FIG>.

The enlarged schematic cross-sectional view through the monolithic fluid sensor system <NUM> in <FIG> along the section line "AA" of <FIG> shows the reference thermal radiation detector (= IR receiver) <NUM> and (a part of) the reference waveguide structure <NUM> on the top main surface region <NUM>-<NUM> of the reference sensor substrate <NUM> and in the reference sensor cavity <NUM> below the recess <NUM> in the first main surface region <NUM>-<NUM> of the reference cover substrate <NUM>.

As shown in <FIG>, a cavity <NUM> is arranged in the sensor substrate <NUM> (i.e. in the second dielectric layer <NUM> and the semiconductor layer <NUM>) vertically below the reference thermal radiation detector <NUM>. The formation of the cavity <NUM> in the reference sensor substrate <NUM> below the thermal radiation detector <NUM> reduces the heat transfer from the reference thermal radiation detector <NUM> into the adjacent material so that the detection efficiency of the reference thermal radiation detector <NUM> can be increased.

The explanations with respect to <FIG> equally apply to the thermal radiation detector (= IR receiver) <NUM> on the sensor substrate <NUM> of the sensor arrangement <NUM>.

The enlarged cross-sectional view of <FIG> along the section line "BB" of <FIG> shows the portion of the reference multi-slot waveguide <NUM> having six strips on the top main surface region <NUM>-<NUM> of the reference sensor substrate <NUM> and in the reference sensor cavity <NUM> below the recess <NUM> in the first main surface region <NUM>-<NUM> of the reference cover substrate <NUM>. The reference recess <NUM> in the first main surface region <NUM>-<NUM> in the reference cover substrate <NUM> forms a hermetically closed cavity <NUM> for the reference sensor arrangement <NUM>. Thus, the reference cover substrate <NUM> hermetically closes (seals) the cavity <NUM> without a fluid exchange between the reference sensor cavity <NUM> and the environment.

The enlarged schematic cross-sectional view through the monolithic fluid sensor system <NUM> in <FIG> along the section line "CC" of <FIG> shows the portion of the multi-slot waveguide having six strips on the top main surface region <NUM>-<NUM> of the sensor substrate <NUM> and in the sensor cavity <NUM> below the recess <NUM> in the first main surface region <NUM>-<NUM> of the cover substrate <NUM>. As shown in <FIG>, the through-opening(s) <NUM> between the recess <NUM> in the first main surface region <NUM>-<NUM> and a second main surface region <NUM>-<NUM> of the cover substrate forms a fluidic connection to the environment for enabling exchange of fluids between the sensor cavity <NUM> and the environment.

The enlarged schematic cross-sectional view through the monolithic fluid sensor system <NUM> in <FIG> along the section line "DD" of <FIG> shows the semiconductor strip <NUM>-<NUM> of the thermal radiation emitter <NUM> on the top main surface region <NUM>-<NUM> of the sensor substrate <NUM> and in the sensor cavity <NUM> below the recess <NUM> in the first main surface region <NUM>-<NUM> of the cover substrate <NUM> and, further, the reference semiconductor strip <NUM>-<NUM> of the reference thermal radiation emitter <NUM> on the top main surface region <NUM>-<NUM> of the reference sensor substrate <NUM> and in the reference sensor cavity <NUM> below the reference recess <NUM> in the first main surface region <NUM>-<NUM> of the reference cover substrate <NUM>.

Optionally, a cavity <NUM>, <NUM> may be also arranged vertically below the thermal radiation emitter <NUM> and the reference thermal radiation emitter <NUM> (= emitter <NUM>, <NUM>). The formation of a cavity <NUM>, <NUM> in the substrate <NUM>, <NUM> below the emitter <NUM>, <NUM> reduces the heat transfer from the emitter <NUM>, <NUM> into the adjacent material so that the emission efficiency of the emitter <NUM>, <NUM> can be increased.

The first insulating (= dielectric) layer <NUM> and the second insulating (= dielectric) layer <NUM> can be seen as an insulating layer stack to decouple the waveguide structures <NUM>, <NUM> from the substrate <NUM>, <NUM> and to provide a membrane for the emitter structure <NUM>, <NUM> and detector structure <NUM>, <NUM> as the substrate is removed under these structures" or on the substrate itself.

The enlarged schematic cross-sectional view through the monolithic fluid sensor system <NUM> in <FIG> along the section line "EE" of <FIG> shows the second terminal (metal pads) <NUM>-<NUM>, <NUM>-<NUM> for the thermal radiation emitter <NUM> on the sensor substrate <NUM> and the reference thermal radiation emitter <NUM> on the reference sensor substrate <NUM>, e.g. on the one-piece substrate <NUM> (<NUM>, <NUM>). According to an embodiment, the thermal radiation emitter <NUM>, <NUM> may be connected via a first and second buried conductor <NUM>-<NUM>, <NUM>-<NUM> to the first and second terminals <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>, <NUM>-<NUM> (terminals <NUM>-<NUM> and <NUM>-<NUM> are not shown in <FIG>). The cover substrate <NUM> and reference cover substrate <NUM>, respectively, comprises openings or holes <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> (openings <NUM>-<NUM> and <NUM>-<NUM> are not shown in <FIG>) for contacting, e.g. wire bonding, the metal pads <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>, <NUM>-<NUM>.

Summary of the above embodiments: The described approach of the present monolithic fluid sensor system <NUM> provides an efficient utilization of the emitter radiation based on a thermal emitter. This can be achieved when using waveguides. Using waveguides may entail coupling losses, which is a known effect. However, using two waveguides which are each guided to a detector results in an increase in the area for interaction with the gas to be sampled. The detector takes advantage from being heated from both sides.

Moreover, a reference measurement of the guided radiation may be used to determine an information about unsuppressed environmental effects, e.g. temperature or humidity, or an impact of side effects on the guided radiation. This information may be used to correct other sensor measurements of the sensor arrangement that are impacted by the environment in the same, or approximately same, manner as the reference measurement of the reference sensor arrangement. Consequently, a reference measurement with the reference sensor arrangement, using a similar setup to the sensor arrangement may be used to correct or adapt the measurement results of the sensor arrangement.

Such an approach synergistically combines the following exemplary aspects:.

The waveguide structure <NUM>, <NUM> according to examples of the disclosure, e.g. a twin WG (for example a waveguide structure comprises a first and second waveguide section) may provide for more area for interacting with an analyte, i.e. a larger interacting area with the surrounding fluid, e.g. gas to be sampled. Additionally, the detector may be heated from more than one, e.g. both sides.

<FIG> shows a principle flowchart of a method <NUM> for manufacturing the monolithic fluid sensor system <NUM> according to an embodiment, such as the monolithic fluid sensor system <NUM> of <FIG>, <FIG> and <FIG>.

The method <NUM> for manufacturing a monolithic fluid sensor system <NUM> may comprise.

According to an embodiment, the method steps of providing <NUM> the sensor arrangement <NUM>, of bonding <NUM> the first main surface region of the cover substrate <NUM> to the first main surface region of the sensor substrate <NUM>, of providing <NUM> the reference sensor arrangement <NUM>, and of bonding <NUM> the first main surface region of the reference cover substrate <NUM> to the first main surface region of the reference sensor substrate <NUM> are conducted on wafer level.

Thus, the sensor substrate <NUM> may be a sensor wafer, the cover substrate <NUM> may be a cover wafer, the reference sensor substrate <NUM> may be a reference sensor wafer, and the reference cover substrate <NUM> may be a reference cover wafer. Further, the respective substrates may be singulated (= diced) parts (= chips) of an associated wafer.

Wafer bonding is a bonding and packaging technology on wafer-level for the fabrication, for example, of microelectromechanical systems (MEMS), ensuring a mechanically stable and hermetically closed connection between the bonded areas (regions) of the bonded wafers. The term wafer bonding my relate to bonding techniques, such as direct bonding, surface activated bonding, anodic bonding, eutectic bonding, glass frit bonding adhesive bonding thermos-compression bonding, reactive bonding, transient liquid phase diffusion bonding, etc..

According to embodiments, the term wafer bonding may especially relate fusion bonding (= direct bonding). Fusion bonding describes a wafer bonding process without any "additional" intermediate layers, i.e. in addition to the (optional) first insulating (= dielectric) layer <NUM>, <NUM> (e.g. a nitride material, such as SiN), the (optional) second insulating (= dielectric) layer <NUM>, <NUM> (e.g. an oxide material, e.g. BOX = buried oxide, such as SiO<NUM>), and the semiconductor substrate layer <NUM>, <NUM> (e.g. a silicon layer). The bonding process is based on chemical bonds between two surfaces of any material possible meeting the bonding requirements, such as between opposing nitride layers <NUM>, <NUM>, oxide layers <NUM>, <NUM> or semiconductor layers <NUM>, <NUM>. The procedural steps of the direct bonding process of wafers any surface may divided into <NUM>. wafer preprocessing, <NUM>. pre-bonding at room temperature and <NUM>. annealing at elevated temperatures, for example.

As exemplarily shown in <FIG>, the method <NUM> for manufacturing a monolithic fluid sensor system <NUM> may further comprise the step <NUM> of providing a bottom substrate <NUM> and bonding a first main surface region <NUM>-<NUM> of the bottom substrate <NUM> to the second main surface region <NUM>-<NUM> of the sensor substrate <NUM>, and the step <NUM> providing a reference bottom substrate <NUM> and bonding <NUM> a first main surface region <NUM>-<NUM> of the reference bottom substrate <NUM> to the second main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>.

Thus, the bottom substrate <NUM> may be a bottom wafer and the reference bottom substrate <NUM> may be a reference bottom wafer. Further, the respective substrates may be singulated (= diced) parts (= chips) of an associated wafer.

According to a further embodiment, the sensor substrate <NUM> and the reference sensor substrate <NUM> are arranged to form a common system substrate <NUM>, wherein the cover substrate <NUM> and the reference cover substrate <NUM> are arranged to form a common cover substrate <NUM>, and wherein the bottom substrate <NUM> and the reference bottom substrate <NUM> are arranged to form a common bottom substrate <NUM>.

According to an embodiment, the bonding steps <NUM>, <NUM>, <NUM>, <NUM> may be conducted with the common system substrate <NUM>, the common cover substrate <NUM> and the common bottom substrate <NUM>. The term "common substrate" may be also referred to an one-piece substrate or one-piece wafer or, also, as an one piece semiconductor substrate or one-piece semiconductor wafer, or, also, as an one piece glass substrate or one-piece glass wafer.

The method <NUM> for manufacturing a monolithic fluid sensor system <NUM> may further comprise the step <NUM> of conducting the steps of providing a bottom substrate and bonding and the steps of providing a reference bottom substrate and bonding on wafer level.

According to a further embodiment, the sensor substrate <NUM> and the reference sensor substrate <NUM> may arranged to form separate system substrates, wherein the cover substrate <NUM> and the reference cover substrate <NUM> are arranged to form separate cover substrates, and wherein the bottom substrate <NUM> and the reference bottom substrate <NUM> are arranged to form separate bottom substrates. These substrates may be singulated (diced) at the dicing line DL, shown in <FIG>.

In the following, a further embodiment of the monolithic fluid sensor system <NUM> is described with respect to <FIG>. <FIG> shows a schematic cross-sectional view of a monolithic fluid sensor system according to a further embodiment. <FIG> shows an exploded view of the different substrates (wafers - before the bonding process) of the monolithic fluid sensor system <NUM> according to the further embodiment.

Also referring to in <FIG>, <FIG> and <FIG>, the monolithic fluid sensor system <NUM> comprises the sensor arrangement (sensor path) <NUM>, the cover substrate <NUM>, the reference sensor arrangement (reference path) <NUM>, and the reference cover substrate <NUM>. The sensor arrangement <NUM> comprises the thermal radiation emitter <NUM>, the optical filter structure <NUM>, the waveguide structure <NUM> and the thermal radiation detector <NUM> on the first main surface region <NUM>-<NUM> of the sensor substrate <NUM>.

The cover substrate <NUM> comprises the recess, e.g. depression or hollow, <NUM>, which is arranged in the first main surface region <NUM>-<NUM> of the cover substrate <NUM>. The cover substrate <NUM> further comprises the through-opening, e.g. a ventilation opening or ventilation hole, <NUM> between the recess <NUM> in the first main surface region <NUM>-<NUM> and the second main surface region <NUM>-<NUM> of the cover substrate. The first main surface region <NUM>-<NUM> of the cover substrate <NUM> is bonded, e.g., wafer bonded or fusion bonded on wafer-level, to the first main surface region <NUM>-<NUM> of the sensor substrate <NUM>, wherein the sensor arrangement <NUM> is arranged below the recess <NUM> of the cover substrate <NUM>.

The recess <NUM> in the first main surface region <NUM>-<NUM> of the cover substrate <NUM> forms the (structured) cavity <NUM> for the sensor arrangement (reference path) <NUM>, wherein the through-opening <NUM> forms the fluidic connection to the environment for enabling exchange of fluids between the sensor cavity <NUM> and the environment. The through-opening <NUM> in the cavity <NUM> of the sensor path <NUM> provides for an interaction (in the cavity <NUM>) with the environmental gas.

The reference sensor arrangement <NUM> comprises the reference thermal radiation emitter <NUM>, the reference optical filter structure <NUM>, the reference waveguide structure <NUM>, the reference thermal radiation detector <NUM> on the first surface region <NUM>-<NUM> of the reference sensor substrate <NUM>.

The reference cover substrate <NUM> comprises the reference recess <NUM>, wherein the reference recess <NUM> is arranged in the first main surface region <NUM>-<NUM> of the reference cover substrate <NUM>. The first main surface region <NUM>-<NUM> of the reference cover substrate is bonded, e.g. wafer bonded or fusion bonded on wafer-level, to the first main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>. The reference recess <NUM> in the first main surface region <NUM>-<NUM> forms the hermetically closed (e.g. sealed) cavity (= structured cavity) <NUM> for the reference sensor arrangement (reference path) <NUM>. The reference cover substrate <NUM> does not comprise a through opening to the environment and constitutes therefore a hermetic cavity <NUM> with no exchange of fluids possible between the reference sensor cavity <NUM> and the environment.

According to an embodiment, the waveguide structure <NUM> of the sensor arrangement <NUM> may (optionally) comprise a first waveguide portion <NUM>-<NUM> and a second waveguide portion <NUM>-<NUM>, which are optically arranged between the thermal radiation emitter <NUM> and the thermal radiation detector <NUM>. Thus, the thermal radiation emitter <NUM> couples into the two waveguide portions <NUM>-<NUM>, <NUM>-<NUM>, which lead to the thermal radiation detector <NUM>. The two waveguide portions <NUM>-<NUM>, <NUM>-<NUM> may have (parallel to the reference plane) a L-shape or an arc shape, so that the two waveguide portions <NUM>-<NUM>, <NUM>-<NUM> each lead to the thermal radiation detector <NUM>.

According to the embodiment, the reference waveguide structure <NUM> of the reference sensor arrangement <NUM> may (optionally) comprise a first reference waveguide portion <NUM>-<NUM> and a second reference waveguide portion <NUM>-<NUM>, which are optically arranged between the reference thermal radiation emitter <NUM> and the reference thermal radiation detector <NUM>. Thus, the reference thermal radiation emitter <NUM> couples into the two waveguide portions <NUM>-<NUM>, <NUM>-<NUM>, which lead to the reference thermal radiation detector <NUM>. The two reference waveguide portions <NUM> may have (parallel to the reference plane) a L-shape or an arc shape, so that the two reference waveguide portions <NUM> each lead to the reference thermal radiation detector <NUM>.

According to an embodiment, the elements <NUM>, <NUM>, <NUM>, <NUM> of the sensor arrangement <NUM> and the corresponding reference elements <NUM>, <NUM>, <NUM>, <NUM> of the reference sensor arrangement <NUM> have the same structural setup (composition) and functionality with the exception of the through-opening(s) in the cover substrate which are not present in the reference cover substrate.

As shown in <FIG>, the cavity <NUM> is arranged in the sensor substrate <NUM> (i.e. in the second dielectric layer <NUM> and the semiconductor layer <NUM>) vertically below the reference thermal radiation detector <NUM>. Further, the bonding areas (bonding regions) <NUM> between the bonded substrates (wafers) are shown in <FIG>.

As further shown in <FIG>, the monolithic fluid sensor system <NUM> further comprises a bottom substrate <NUM> (= <NUM> and/or <NUM>), wherein the second main surface region <NUM>-<NUM> of the reference cover substrate <NUM> is bonded (= wafer bonded or fusion bonded) to the second main surface region <NUM>-<NUM> of the sensor substrate <NUM>, and wherein the first main surface region <NUM>-<NUM> of the bottom substrate <NUM> is bonded to the second main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>. Thus, the sensor substrate <NUM> is sandwiched between the cover substrate <NUM> and the reference cover substrate <NUM>, and wherein the reference sensor substrate <NUM> is sandwiched between the reference cover substrate <NUM> and the bottom substrate <NUM>.

As shown in exploded view of the different substrates (wafers - before the bonding process) of the monolithic fluid sensor system <FIG>, the different substrates and wafer, respectively may be positioned and oriented with respect to each other and, then, mechanically connected by means of wafer bonding, e.g. direct or fusion bonding. Thus, a reduced footprint can be achieved due to the (possible) stacking of the sensing system <NUM> and the reference sensor system <NUM> on wafer level via bonding.

The resulting wafer stack (of <FIG>) may be singulated (diced) at the dicing line DL for providing the singulated (diced) monolithic fluid sensor systems <NUM> having the sensor arrangement <NUM> and the reference sensor arrangement <NUM>, wherein the monolithic fluid sensor system <NUM> can be placed in the application, for example.

<FIG> shows a schematic flowchart of a further method <NUM> for manufacturing the monolithic fluid sensor system <NUM> according to a further embodiment, such as the monolithic fluid sensor system <NUM> of <FIG>.

The method <NUM> for manufacturing a monolithic fluid sensor system <NUM> may further comprise the step <NUM> of bonding (e.g. wafer bonding or fusion bonding) the second main surface region <NUM>-<NUM> of the reference cover substrate <NUM> to the second main surface region <NUM>-<NUM> of the sensor substrate <NUM>, and the step <NUM> of providing a bottom substrate <NUM> and of bonding <NUM> a first main surface region <NUM>-<NUM> of the bottom substrate <NUM> to the second main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>.

According to an embodiment, the method steps of providing and bonding are conducted on wafer level by means of wafer bonding. To be more specific, the method steps of providing <NUM> the sensor arrangement <NUM>, of bonding <NUM> the first main surface region of the cover substrate <NUM> to the first main surface region of the sensor substrate <NUM>, of providing <NUM> the reference sensor arrangement <NUM>, of bonding <NUM> the first main surface region of the reference cover substrate <NUM> to the first main surface region of the reference sensor substrate <NUM> and of bonding <NUM> the second main surface region of the reference cover substrate <NUM> to the second main surface region of the sensor substrate <NUM>, and the step <NUM> of providing a bottom substrate <NUM> and bonding a first main surface region of the bottom substrate <NUM> to the second main surface region of the reference sensor substrate <NUM> are conducted on wafer level.

Thus, the sensor substrate <NUM> may be a sensor wafer, the cover substrate <NUM> may be a cover wafer, the reference sensor substrate <NUM> may be a reference sensor wafer, the reference cover substrate <NUM> may be a reference cover wafer, and the bottom substrate (spacer substrate) <NUM> may be a bottom wafer (spacer wafer).

The resulting wafer stack (of <FIG>) may be singulated (diced) at the dicing line DL for providing the singulated (diced) monolithic fluid sensor systems <NUM> having the sensor arrangement <NUM> and the reference sensor arrangement <NUM>, wherein the monolithic fluid sensor systems <NUM> can be placed in the application, for example.

In the following, a further embodiment of the monolithic fluid sensor system <NUM> is described with respect to <FIG>. <FIG> shows a schematic cross-sectional view of the monolithic fluid sensor system <NUM> according to a further embodiment. <FIG> shows an exploded view of the different substrates (wafers - before the bonding process) of the monolithic fluid sensor system <NUM> according to the further embodiment.

Again referring to in <FIG>, <FIG> and <FIG>, the monolithic fluid sensor system <NUM> comprises the sensor arrangement (sensor path) <NUM>, the cover substrate <NUM>, the reference sensor arrangement (reference path) <NUM>, and the reference cover substrate <NUM>. The sensor arrangement <NUM> comprises the thermal radiation emitter <NUM>, the optical filter structure <NUM>, the waveguide structure <NUM> and the thermal radiation detector <NUM> on the first main surface region <NUM>-<NUM> of the sensor substrate <NUM>.

As shown in the monolithic fluid sensor system <NUM> of <FIG>, the reference sensor substrate <NUM> and the reference cover substrate <NUM> are flipped when compared to the arrangement of the reference sensor substrate <NUM> and the reference cover substrate <NUM> in the monolithic fluid sensor system <NUM> in <FIG>.

As shown in <FIG>, the cavity <NUM> is arranged in the sensor substrate <NUM> (i.e. in the second dielectric layer <NUM> and the semiconductor layer <NUM>) vertically below the reference thermal radiation detector <NUM>.

As further shown in <FIG>, the monolithic fluid sensor system <NUM> further comprises a spacer substrate <NUM>, wherein the first main surface region <NUM>-<NUM> of the spacer substrate <NUM> is bonded (= wafer bonded or fusion bonded) to the second main surface region <NUM>-<NUM> of the sensor substrate <NUM>, and wherein the second main surface region <NUM>-<NUM> of the spacer substrate <NUM> is bonded (= wafer bonded or fusion bonded) to the second main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>.

Thus, the spacer substrate <NUM> is sandwiched between the sensor substrate <NUM> and the reference sensor substrate <NUM>, wherein the sensor substrate <NUM> is sandwiched between the spacer substrate <NUM> and the cover substrate <NUM>, and wherein the reference sensor substrate <NUM> is sandwiched between the spacer substrate <NUM> and the reference cover substrate <NUM>.

Thus, the sensor substrate <NUM> may be a sensor wafer, the cover substrate <NUM> may be a cover wafer, the reference sensor substrate <NUM> may be a reference sensor wafer, the reference cover substrate <NUM> may be a reference cover wafer, and the spacer substrate <NUM> may be a spacer wafer.

The method <NUM> for manufacturing a monolithic fluid sensor system <NUM> may comprise:.

The method <NUM> for manufacturing a monolithic fluid sensor system <NUM> may further comprise the step <NUM> of providing a spacer substrate <NUM> and bonding <NUM> a first main surface region <NUM>-<NUM> of the spacer substrate <NUM> to the second main surface region <NUM>-<NUM> of the sensor substrate <NUM>, and the step <NUM> of bonding the second main surface region <NUM>-<NUM> of the spacer substrate <NUM> to the second main surface region <NUM>-<NUM> of the reference sensor substrate <NUM>.

According to an embodiment, the method steps of providing and bonding are conducted on wafer level by means of wafer bonding. Thus, the sensor substrate <NUM> may be a sensor wafer, the cover substrate <NUM> may be a cover wafer, the reference sensor substrate <NUM> may be a reference sensor wafer, the reference cover substrate <NUM> may be a reference cover wafer, and the bottom substrate <NUM> may be bottom wafer.

In the following, embodiments and technical aspects of the present disclosure are described and summarized which may be used alone or in combination with the features and functionalities described herein.

Embodiments of the present disclosure relate in general to the field of monolithic fluid sensor systems <NUM> and methods <NUM> for manufacturing such monolithic fluid sensor systems. In particular, embodiments relate to a fusion-bond or wafer-bond based wafer-level package for a mid-infrared gas sensor system <NUM>.

The monolithic fluid sensor system <NUM> uses (for the sensor path <NUM> and the reference path <NUM>): a thermal emitter <NUM>, <NUM> having a narrow-band wavelength filter <NUM>, <NUM> integrated in a waveguide <NUM>, <NUM>, said waveguide and a detector <NUM>, <NUM>, e.g. pyro detector or alternatively a piezo or thermal diode-based detector. The waveguide <NUM>, <NUM> serves for guiding the emitted radiation and having it interact with the environment. The result is a specific absorption of the radiation, which subsequently allows detecting a target gas concentration, e.g. the CO<NUM> concentration, in the ambient air by means of spectroscopy, for example.

In summary, radiation is coupled into an optical waveguide <NUM>, <NUM> and filtered. For determining a CO<NUM> concentration, a narrow-band filtering of the wavelengths in the waveguide <NUM>, <NUM> around a wavelength of <NUM> is provided, which corresponds to the absorption of CO2 in air. In order for this wavelength region to be emitted at a sufficiently strong power, an emitter temperature of about <NUM>-<NUM> is set.

The monolithic fluid sensor system <NUM> ensures a very high efficiency of the power transmission, or intensity at which waves in the filtered wavelength region are provided, emanating from the thermal emitter <NUM>, <NUM>. This is achieved even if (already) "small" influences, like impure filter structures or defects at the waveguide <NUM>, <NUM>, may result in a coupling loss. Since a waveguide <NUM>, <NUM> has the characteristic of directing the radiation along its path, the radiation introduced can be guided specifically by its shape, which offers the possibility of not only increasing the intensity at which the radiation impinges on the detector <NUM>, <NUM>, but also ensuring the most efficient usage of a single black (or full) radiator (thermal emitter) as the radiation source <NUM>, <NUM>, and a more effective usage of the electrical power to be provided for the radiator.

By making use of the waveguide characteristic mentioned, a reference measurement can be conducted at the same time, without abandoning optimization of the transmission intensity. A reference measurement would support signal evaluation when measuring individual gas concentrations (background noise is taken into consideration).

Based on the monolithic fluid sensor system <NUM>, it can be shown that both the requirements to a reference measurement (i.e. the reference and actual measurements have an equal behavior when external influences change, variations of the input voltage, for example at the emitter, should apply to both to the same extent), and also an increase in the intensity of the transmission of radiation from the emitter to the detector can be realized within a single overall system, i.e. the monolithic fluid sensor system <NUM>.

The emitter(s) <NUM>, <NUM> couples into four waveguides <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>, <NUM>-<NUM> (= two pairs of waveguides <NUM>, <NUM>) which lead to two detectors <NUM>, <NUM>. The four waveguides are formed in an L-shape or arc shape, for example, meaning that two waveguides each lead to one detector. The scheme of the waveguides can be varied in different variations (e.g. slab, strip, slot, etc.).

In the monolithic fluid sensor system <NUM>, one detector <NUM> serves as a reference, a further detector <NUM> for measuring the ambient gas. The reference path <NUM> on a Si wafer <NUM> is prevented from interacting with the environment by means of a silicon cover <NUM>. Both the Si wafer <NUM> and the Si cover wafer <NUM> of the reference path <NUM> as well as the Si wafer <NUM> and the Si cover wafer <NUM> of the sensing path <NUM> comprise a passivation against potential absorption of the basic material substrate from SiO<NUM> and Si<NUM>N<NUM>. These layers <NUM>, <NUM> and <NUM>, <NUM> are also present as a top layer of the bonding areas <NUM>, thereby selecting the bond method to be fusion bonding, for example. Fusion bonding allows a pure wafer bond in the case of SiO<NUM>-SiO<NUM> and Si<NUM>N<NUM>- Si<NUM>N<NUM>, as long as, in the case of a nitride layer, its thickness is between <NUM> and <NUM> (resulting in a design rule).

The detectors <NUM>, <NUM> are supported on membranes (= dielectric layers <NUM>, <NUM>), e.g. formed of Si<NUM>N<NUM>, meaning that they are exposed by means of a "bosch" etching in order to thermally insulate the same from the substrate <NUM> and the contact pads (the same applies for the emitter).

In order to produce hermetic bonding, the electrically conductive contacts <NUM>-#, <NUM>-# and <NUM>-#, <NUM>-# to the emitter <NUM>, <NUM> and the detector <NUM>, <NUM> are at least partly buried, i.e. comprise buried conductors. In order to provide for a complete wafer-level package, the bottom of the Si wafer "supporting the system" may be terminated by means of a Si bottom wafer or spacer wafer <NUM>.

In the monolithic fluid sensor system <NUM>, the described approach of arranging the waveguides <NUM>, <NUM> is aimed to achieve the best possible utilization of the solid angle of radiation and the surface of the emitter <NUM>, <NUM>. Thus, the monolithic fluid sensor system <NUM> allows to make use of the radiation of the emitter <NUM>, <NUM> in the lateral direction. Additionally, using a "true" reference path <NUM> would save algorithms for interpreting measuring results to a certain extent.

The monolithic fluid sensor system <NUM> provides an efficient utilization of the emitter radiation, which supports the monolithic approach based on a thermal emitter <NUM>, <NUM> in connection with waveguides <NUM>, <NUM>. Even if the utilization of waveguides may entail coupling losses (which is a known effect). The utilization of two (parallel) waveguides <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>, <NUM>-<NUM> in the sensor path <NUM> and the reference path <NUM>, which are each guided to a respective detector <NUM>, <NUM> results in an increase in the area for interaction with the fluid (= gas or liquid) to be sampled. The detector <NUM>, <NUM> takes advantage from being heated from both sides.

The monolithic fluid sensor system <NUM> can implemented as a single chip or a package. The hermitic sealing of the bond regions and the cavities can be achieved by means of wafer bonding the respective wafer (substrates) at the dedicated bonding regions <NUM>.

Additional embodiments and aspects are described which may be used alone or in combination with the features and functionalities described herein.

According to an embodiment, the monolithic fluid sensor system <NUM> comprises a sensor arrangement <NUM> having a thermal radiation emitter <NUM>, an optical filter structure <NUM>, a waveguide structure <NUM> and a thermal radiation detector <NUM> on a first main surface region of a sensor substrate <NUM>, a cover substrate <NUM>, wherein a recess <NUM> is arranged in a first main surface region of the cover substrate <NUM> and a through-opening <NUM> is arranged between the recess <NUM> in the first main surface region and a second main surface region of the cover substrate <NUM>, wherein the first main surface region of the cover substrate <NUM> is bonded to the first main surface region of a sensor substrate <NUM>; <NUM>, and wherein the sensor arrangement <NUM> is arranged below the recess <NUM> of the cover substrate <NUM>, a reference sensor arrangement <NUM> having a reference thermal radiation emitter <NUM>, a reference optical filter structure <NUM>, a reference waveguide structure <NUM> and a reference thermal radiation detector <NUM> on a first main surface region of a reference sensor substrate <NUM>, and a reference cover substrate <NUM>, wherein a reference recess <NUM> is arranged in a first main surface region of the reference cover substrate <NUM>, wherein the first main surface region of the reference cover substrate <NUM> is bonded to the first main surface region of the reference sensor substrate <NUM>, and wherein the reference recess <NUM> in the first main surface region of the reference cover substrate <NUM> forms a hermetically closed cavity <NUM> for the reference sensor arrangement <NUM>.

According to an embodiment, the elements of the sensor arrangement <NUM> and the reference elements of the reference sensor arrangement <NUM> have the same structural setup.

According to an embodiment, the monolithic fluid sensor system <NUM> further comprises a bottom substrate <NUM>; <NUM>, wherein a first main surface region of the bottom substrate <NUM>; <NUM> is bonded to the second main surface region of the sensor substrate <NUM>, and a reference bottom substrate <NUM>; <NUM>, wherein a first main surface region of the reference bottom substrate <NUM>; <NUM> is bonded to the second main surface region of the reference sensor substrate <NUM>.

According to an embodiment, the sensor substrate <NUM> and the reference sensor substrate <NUM> are arranged to form a common system substrate <NUM>, wherein the cover substrate <NUM> and the reference cover substrate <NUM> are arranged to form a common cover substrate <NUM>, and wherein the bottom substrate <NUM> and the reference bottom substrate <NUM> are arranged to form a common bottom substrate <NUM>.

According to an embodiment, the sensor substrate <NUM> and the reference sensor substrate <NUM> are arranged to form separate system substrates, wherein the cover substrate <NUM> and the reference cover substrate <NUM> are arranged to form separate cover substrates, and wherein the bottom substrate <NUM> and the reference bottom substrate <NUM> are arranged to form separate bottom substrates.

According to an embodiment, the monolithic fluid sensor system <NUM> further comprises a bottom substrate <NUM>, wherein the second main surface region of the reference cover substrate <NUM> is bonded to the second main surface region of the sensor substrate <NUM>, and wherein the first main surface region of the bottom substrate <NUM> is bonded to the second main surface region of the reference sensor substrate <NUM>.

According to an embodiment, the monolithic fluid sensor system <NUM> further comprises a spacer substrate <NUM>, wherein the first main surface region of the spacer substrate <NUM> is bonded to the second main surface region of the sensor substrate <NUM>, and wherein the second main surface region of the spacer substrate <NUM> is bonded to the second main surface region of the reference sensor substrate <NUM>. The first main surface region of the cover substrate <NUM> is bonded to the first main surface region of a sensor substrate <NUM>, and the first main surface region of the reference cover substrate <NUM> is bonded to the first main surface region of the reference sensor substrate <NUM>.

According to an embodiment, a method <NUM> for manufacturing a monolithic fluid sensor system <NUM> comprises providing <NUM> a sensor arrangement having a thermal radiation emitter, an optical filter structure, a waveguide structure and a thermal radiation detector on a first main surface region of a sensor substrate, bonding <NUM> a first main surface region of a cover substrate to the first main surface region of a sensor substrate, wherein the cover substrate comprises a recess in the first main surface region and comprises a through-opening between the recess in the first main surface region and a second main surface region of the cover substrate, providing <NUM> a reference sensor arrangement having a reference thermal radiation emitter, a reference optical filter structure, a reference waveguide structure and a reference thermal radiation detector on a first main surface region of a reference sensor substrate, and bonding <NUM> a first main surface region of the reference cover substrate to the first main surface region of the reference sensor substrate, wherein the reference cover substrate comprises a reference recess in the first main surface region, wherein the reference recess in the first main surface region of the reference cover substrate forms a sealed cavity for the reference sensor arrangement.

According to an embodiment, the method steps (-) of providing <NUM> a sensor arrangement, (-) of bonding <NUM> a first main surface region of a cover substrate to the first main surface region of a sensor substrate, (-) of providing <NUM> a reference sensor arrangement, and (-) of bonding <NUM> a first main surface region of the reference cover substrate to the first main surface region of the reference sensor substrate are conducted on wafer level.

According to an embodiment, the method <NUM> further comprises the steps of providing <NUM> a bottom substrate and bonding a first main surface region of the bottom substrate to the second main surface region of the sensor substrate, and Providing <NUM> a reference bottom substrate and bonding <NUM> a first main surface region of the reference bottom substrate to the second main surface region of the reference sensor substrate.

According to an embodiment, the sensor substrate and the reference sensor substrate are arranged to form a common system substrate, wherein the cover substrate and the reference cover substrate are arranged to form a common cover substrate, and wherein the bottom substrate and the reference bottom substrate are arranged to form a common bottom substrate, wherein the method <NUM> further comprises conducting <NUM> the steps of providing a bottom substrate and bonding and the steps of providing a reference bottom substrate and bonding on wafer level.

According to an embodiment, the sensor substrate and the reference sensor substrate are arranged to form separate system substrates, wherein the cover substrate and the reference cover substrate are arranged to form separate cover substrates, and wherein the bottom substrate and the reference bottom substrate are arranged to form separate bottom substrates.

According to an embodiment the method <NUM> further comprises bonding <NUM> the second main surface region of the reference cover substrate to the second main surface region of the sensor substrate, and providing <NUM> a bottom substrate and bonding <NUM> a first main surface region of the bottom substrate to the second main surface region of the reference sensor substrate.

According to an embodiment the method <NUM> further comprises providing <NUM> a spacer substrate and bonding <NUM> a first main surface region of the spacer substrate to the second main surface region of the sensor substrate, and bonding <NUM> the second main surface region of the spacer substrate to the second main surface region of the reference sensor substrate.

According to an embodiment the method steps of bonding are conducted on wafer level by means of wafer bonding.

Although some aspects have been described as features in the context of an apparatus it is clear that such a description may also be regarded as a description of corresponding features of a method. Although some aspects have been described as features in the context of a method, it is clear that such a description may also be regarded as a description of corresponding features concerning the functionality of an apparatus.

Depending on certain implementation requirements, embodiments of the control circuitry can be implemented in hardware or in software or at least partially in hardware or at least partially in software. Generally, embodiments of the control circuitry can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer.

In the foregoing detailed description, it can be seen that various features are grouped together in examples for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed examples require more features than are expressly recited in each claim. Rather, as the following claims reflect, subject matter may lie in less than all features of a single disclosed example. Thus the following claims are hereby incorporated into the detailed description, where each claim may stand on its own as a separate example. While each claim may stand on its own as a separate example, it is to be noted that, although a dependent claim may refer in the claims to a specific combination with one or more other claims, other examples may also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of each feature with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended. Furthermore, it is intended to include also features of a claim to any other independent claim even if this claim is not directly made dependent to the independent claim.

Claim 1:
Monolithic fluid sensor system (<NUM>) for sensing a fluid in the environment, comprising:
a sensor arrangement (<NUM>) having a thermal radiation emitter (<NUM>), an optical filter structure (<NUM>), a waveguide structure (<NUM>) and a thermal radiation detector (<NUM>) on a first main surface region (<NUM>-<NUM>) of a sensor substrate (<NUM>) a cover substrate (<NUM>), wherein a recess (<NUM>) is arranged in a first main surface region (<NUM>-<NUM>) of the cover substrate (<NUM>) and a through-opening (<NUM>) is arranged between the recess (<NUM>) in the first main surface region (<NUM>-<NUM>) and a second main surface region (<NUM>-<NUM>) of the cover substrate (<NUM>), wherein the first main surface region (<NUM>-<NUM>) of the cover substrate (<NUM>) is bonded to the first main surface region (<NUM>-<NUM>) of the sensor substrate (<NUM>; <NUM>), and wherein the sensor arrangement (<NUM>) is arranged below the recess (<NUM>) of the cover substrate (<NUM>),
wherein the recess (<NUM>) forms a cavity (<NUM>) and wherein the through-opening (<NUM>) forms a fluidic connection from the cavity to the environment,
a reference sensor arrangement (<NUM>) having a reference thermal radiation emitter (<NUM>), a reference optical filter structure (<NUM>), a reference waveguide structure (<NUM>) and a reference thermal radiation detector (<NUM>) on a first main surface region (<NUM>-<NUM>) of a reference sensor substrate (<NUM>), and
a reference cover substrate (<NUM>), wherein a reference recess (<NUM>) is arranged in a first main surface region (<NUM>-<NUM>) of the reference cover substrate (<NUM>), wherein the first main surface region (<NUM>-<NUM>) of the reference cover substrate (<NUM>) is bonded to the first main surface region (<NUM>-<NUM>) of the reference sensor substrate (<NUM>), and wherein the reference recess (<NUM>) in the first main surface region (<NUM>-<NUM>) of the reference cover substrate (<NUM>) forms a hermetically closed cavity (<NUM>) for the reference sensor arrangement (<NUM>).