Heat emitter with embedded heating element

Abstract

The present disclosure relates generally to a heat emitter with embedded heating elements. The heat emitter (1) comprises a free-standing film (2) supported by a substrate (3), wherein the free-standing film (2) comprises in a lateral extension a central section (2-1), a conductive intermediate section (2-2) and a border section (2-3), wherein the conductive intermediate section (2-2) laterally surrounds the central section (2-1) and is electrically isolated from the central section (2-1), the conductive intermediate section (2-2) comprises an electrically conductive semiconductor material enclosed in an insulating material, and wherein the border section (2-3) at least partially surrounds the intermediate section (2-2) and is electrically isolated from the conductive intermediate section (2-1), wherein a perforation (4) is formed through the border section (2-3).

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to emitters, for example infrared emitters with embedded heating elements. The present disclosure also relates to MEMS infrared radiation sources with embedded heating elements and plasmonic structures. Embodiments thus relate to techniques for providing infrared (IR) radiation sources, i.e. IR or thermal emitters. BACKGROUND

[0002] When sensing environmental parameters in the ambient atmosphere, such as noise, sound, temperature and gases, for example environmental gas components are increasingly important when implementing appropriate sensors within the mobile device, home automation such as smart home, and automotive industry. Harmful gas concentrations can arise due to pollution and / or malfunctions of certain devices. However, the health of humans or animals is strongly influenced by air quality. Therefore, gas detection in the ambient atmosphere by cheap, always available and connected sensors will be a topic in the future.

[0003] In monitoring the air quality in our environment, there are various types of gas sensing concepts, for example, non-dispersive infrared (NDIR) sensors, chemical sensors and photoacoustic sensors (PAS = photoacoustic spectroscopy). Frequently used sensor effects are based on the excitation of gas molecules in a medium by a certain wavelength of (infrared) light. However, currently available NDIR or PAS systems are relatively expensive due to their complex setup or special components. Furthermore, chemical sensors show a relatively poor selectivity compared to single wavelength or filter containing optical systems. Typical optical sensors, for example PAS sensors, comprise a radiation source, a filter element for wavelength selection, a detector and a sample region at which the light between the light source and the detector interacts with the ambient medium.

[0004] Current thermal emitters for infrared or mid-infrared radiation are typically small bulbs or MEMS emitters with metallic heating elements, such as tungsten or platinum. Surface micromachined or MEMS emitters with metallic heaters are typically limited to operating temperatures below 600°C for preventing performance degradation. This leads to a significant reduction of the optical output power. Metallic conductors typically have a very low emissivity, further leading to a reduction of the output. The thermal mass of current current emitters is high, leading to a slow switching speed. Furthermore, the thermal resistance is low, leading to a reduced energy efficiency (= less temperature rise per watt of input power).

[0005] With the increasing use of gas sensors, there is a particular need to be able to produce such gas sensors with thermal emitters as cheap as possible, thus cost-efficiently. However, the reliability and accuracy of the gas sensors should still be maintained or even improved.

[0006] Generally, in the field of sensors, there is a need to provide a thermal emitter, e.g. for a gas sensor or a fluid sensor, with a relatively high thermal resistance (= low thermal mass) to achieve a relatively high energy efficiency (= high increment of optical output power per increment of input electrical power = high increment of temperature per Watt input power) and which can be operated at a high operating temperature.

[0007] Such a need can be solved by a thermal emitter according to the technical solution described in the technical solution. Further, a specific implementation of a fluid sensor is defined in the technical solution.

[0008] Thus, the present disclosure describes a possible thermal emitter, which can be part of a MEMS gas or fluid sensor capable of sensing at least one component of the ambient atmosphere at the same time. The thermal emitter for infrared or mid-infrared radiation can be used in any MEMS device with an IR radiation source. SUMMARY

[0009] According to one embodiment, the thermal emitter can comprise a free-standing membrane supported by a substrate, wherein the free-standing membrane comprises in a lateral extension a central section, a conductive intermediate section and a border section, wherein the conductive intermediate section laterally surrounds the central section and is electrically isolated from the central section, the conductive intermediate section comprising an electrically conductive semiconductor material enclosed in an insulating material, and wherein the border section at least partially surrounds the intermediate section and is electrically isolated from the conductive intermediate section, wherein a perforation is formed through the border section.

[0010] According to another embodiment, the MEMS gas or fluid sensor can comprise the above described thermal emitter for emitting thermal radiation, a measurement volume with a target gas or a target fluid and providing an optical interaction path for the emitted thermal radiation, and an acoustic transducer or a (direct) thermal detector for providing a detector output signal based on an optical interaction of the emitted thermal radiation with the target gas or the target fluid in the measurement volume.

[0011] Further embodiments are described in the technical solution. BRIEF DESCRIPTION OF DRAWINGS

[0012] In the following, embodiments will be described in the following description that will be presented in the order of description and illustrations. It should be understood, of course, that the following description can be not limitative of the embodiments and should not be interpreted in that way. The implementation can also provide other embodiments, as an example, based on consideration of the description.

[0013] Figure 1a A schematic top 3D view of a thermal emitter according to one embodiment is shown;

[0014] Figure 1b A schematic (lateral) temperature profile of a thermal emitter according to one embodiment is shown;

[0015] Figure 2a schematic bottom 3D view of a thermal emitter according to one embodiment is shown;

[0016] Figure 3a a schematic partial top view of a thermal emitter according to one embodiment is shown;

[0017] Figure 3b a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown along the dashed intersection line A of the thermal emitter; Figure 3a a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown along the dashed intersection line B of the thermal emitter;

[0018] Figure 4a a schematic partial top view of a thermal emitter according to one embodiment is shown;

[0019] Figure 4b a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown along the dashed intersection line A of the thermal emitter; Figure 4a a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown along the dashed intersection line B of the thermal emitter;

[0020] Figure 5a a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown having a fully embedded plasma structure;

[0021] Figure 5b a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown having a partially embedded plasma structure;

[0022] Figure 5c a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown having an at least partially exposed plasma structure;

[0023] Figure 5d a schematic partial cross-sectional view of a thermal emitter according to one embodiment is shown having a plasma resonator;

[0024] Figure 6a a schematic cross-sectional view of a MEMS gas or fluid sensor according to one embodiment is shown; and

[0025] Figure 6b a schematic cross-sectional view of a MEMS gas or fluid sensor according to one embodiment is shown.

[0026] Before the embodiments are discussed in further detail using the accompanying drawings, it has to be pointed out that in the drawings and in the specification identical elements and elements having the same function and / or the same technical or physical effect are generally provided with the same reference signs or are identified with the same names, such that the description of these elements and their function can be exchanged between the different embodiments or can be applied to each other in the different embodiments. DETAILED DESCRIPTION

[0027] In the following description, numerous specific details are discussed in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that embodiments of the application can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the examples described herein. Additionally, features of the different embodiments described herein can be combined with each other, unless specifically noted otherwise.

[0028] However, it will be apparent to one skilled in the art that other embodiments can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the examples described herein. Additionally, features of the different embodiments described herein can be combined with each other, unless specifically noted otherwise.

[0029] It is to be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other terms of relationship are to be interpreted similarly (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” and “on” versus “directly on,” etc.).

[0030] For ease of description of different embodiments, the drawings include a Cartesian coordinate system x, y, z, wherein the x-y plane corresponds to (i.e., is parallel to) the first major surface area of the substrate (= reference plane = x-y plane), wherein the direction vertically upwards with respect to the reference plane (x-y plane) corresponds to the “+z” direction, and wherein the direction vertically downwards with respect to the reference plane (x-y plane) corresponds to the “-z” direction. In the following description, the term “lateral” refers to a direction parallel to the x and / or y direction, i.e., parallel to the x-y plane, wherein the term “vertical” refers to a direction parallel to the z direction.

[0031] In the following description, the thickness of an element generally indicates the vertical dimension of such element. In the figures, different elements are not necessarily drawn to scale. Thus, the thickness of certain elements (e.g., the thickness of a stand-alone film, a semiconductor substrate, an insulating layer, a heavily doped semiconductor layer, and / or a disc-shaped heat spreader structure) can not be drawn to scale.

[0032] Figure 1a A schematic top 3D view (= three-dimensional view) of a heat emitter 1 according to one embodiment is shown. In the following, the heat emitter 1 is described with reference to the schematic top 3D view of Fig. 1. Figure 1aIn the middle, the drawing plane is essentially parallel to the x-y plane. The heat emitter 1 comprises a free-standing film 2 supported by a substrate 3, wherein the free-standing film 2 comprises in a lateral extension a central section 2-1, a conductive (= electrically conductive) intermediate section 2-2, and a border section 2-3, wherein the conductive intermediate section 2-2 laterally surrounds the central section 2-1 and is electrically isolated from the central section 2-1. The conductive intermediate section 2-2 comprises a conductive (= electrically conductive) semiconductor material encapsulated in an insulating material. The border section 2-3 at least partially surrounds the intermediate section 2-2 and is electrically isolated from the conductive intermediate section 2-2, wherein a perforation 4 is formed through the border section 2-3.

[0033] In other words, the free-standing film 2 supported by the substrate 3 can be divided (= partitioned) into three sections, the (inner) central section 2-1, the conductive intermediate section 2-2, and the (outer) border section 2-3, which are supported (e.g. arranged on or at) by the substrate 3, for example. According to one embodiment, the border section 2-3 can be mechanically bonded to the substrate 3, wherein the central section 2-1, the intermediate section 2-2, and at least a part of the border section 2-3 of the free-standing film 2 are arranged on a cavity 6 (see Figure 2 ) in the substrate 3.

[0034] The central section 2-1 and the border section 2-3 can comprise one or more layers. In case of multiple layers, the layers of the central section 2-1 can comprise the same material, or alternatively different materials, for example. The same applies to the border section 2-3. The intermediate section 2-2 can comprise multiple layers, for example at least two layers, such that the electrically conductive semiconductor layer is encapsulated in an insulating material layer, for example.

[0035] Thus, the free-standing film 2 is divided into at least three sections, namely the central section 2-1, the conductive intermediate section 2-2, and the border section 2-3, and is supported by the substrate 3. When the conductive intermediate section 2-2 is encapsulated (= passivated) in an insulating material, the conductive intermediate section 2-2 is electrically isolated from the central section 2-1 and the border section 2-3. The substrate 3 can comprise a bulk semiconductor substrate 7 and an optional insulating layer 8, wherein the insulating layer 8 can form a main surface area 3-1 of the substrate 3 to which the free-standing film 2 is mechanically attached. Further, the insulating layer 8 can comprise an opening 8-1 for at least partially or completely exposing the cavity 6 (see Figure 2 ) from the back side.

[0036] Based on the construction of the thermal emitter 1, such radiation sources for gas sensors or fluid sensors can be requested from a system aspect, such as small and compact, low cost, high radiation output, high energy efficiency, high switching speed, high lifetime and bandwidth. Due to the thermal emitter 1 having a relatively high thermal resistance (= low thermal mass), a relatively high energy efficiency (= high temperature increment per watt of input power) can be achieved, wherein due to its specific setup, the thermal emitter 1 can be operated at a relatively high operating temperature.

[0037] According to one embodiment, the free-standing membrane 2 of the thermal emitter 1 can extend as a layer stack parallel to the main surface area 3-1 of the substrate 3, wherein the layer stack can comprise an electrically conductive semiconductor layer encapsulated in an insulating layer, the insulating layer having an insulating material (see also, for example, WO 2019 / 1 1 1 1 1 A1 ). Figure 3b , Figure 4b , Figure 5b In other words, the layer stack forming the conductive intermediate section 2-2 parallel to the main surface area 3-1 of the substrate 3 can comprise a plurality of layers, for example, at least two layers. The conductive intermediate section 2-2 can comprise an electrically conductive semiconductor layer encapsulated in an insulating layer in the form of an insulating encapsulation layer, wherein the electrically conductive semiconductor layer provides a current path that is heated to an operating temperature during electrical activation of the thermal emitter 1, and wherein the insulating encapsulation layer provides electrical insulation to the adjacent environment and elements and provides high thermal conductivity for heat generated by the electrically conductive semiconductor layer to the environment.

[0038] According to one embodiment, the conductive intermediate section 2-2 forms a branched current path separated by the central section 2-1. As Figure 1a exemplarily shown in Fig. 2, the conductive intermediate section 2-2 can form a ring-shaped heating element that generates heat during an activated state (= intermediate section 2-2 energized) which can also be spread into / through the central section 2-1. Thus, the central section 2-1 and the intermediate section 2-2 can together form a final heating structure or heating element for emitting or dissipating heat in the form of thermal (e.g., infrared) radiation into the measurement cavity. Thus, the heated ring-shaped conductive intermediate section 2-2 can provide a relatively uniform temperature distribution in the heating structure.

[0039] According to another embodiment, the conductive intermediate section 2-2 can also comprise one of a circular, square, oval and elliptical shape (or any convex polygon), wherein this list of shapes of the conductive intermediate section 2-2 is not considered to be exhaustive.

[0040] According to one embodiment, the electrically conductive semiconductor layer is mostly (e.g., at least 80%, 90% or 95%) or completely encapsulated (= hermetically sealed or passivated) in the insulating material to prevent oxidation of the electrically conductive semiconductor layer during the activated state.

[0041] According to one embodiment, the conductive intermediate section 2-2 of the stand-alone film 2 comprises a heavily doped semiconductor layer 10 encapsulated in an insulating material. The doping concentration of the heavily doped semiconductor layer can be in the range of 10 18 to 10 20 doping atoms / cm 3 to achieve an electrical conductivity of the material of the heavily doped semiconductor layer of the conductive intermediate section 2-2 in the range of 10 S / m to 1000 S / m. The doping concentration can be chosen to achieve an electrical conductivity of the material of the heavily doped semiconductor (e.g. Si) layer in the range of 250 S / m to 350 S / m and (approximately) 300 S / m in the cold (= deactivated) state and in the range of 80 S / m to 120 S / m and (approximately) 100 S / m in the hot (= activated) state of the conductive intermediate section 2-2 of the stand-alone film 2.

[0042] Based on the resulting (e.g. homogenous distributed) electrical conductivity of the material of the heavily doped semiconductor layer of the conductive intermediate section 2-2, a homogenous heat distribution and thus a homogenous heat dissipation can be achieved in the conductive intermediate section 2-2.

[0043] According to one embodiment, the conductive semiconductor material of the conductive intermediate section 2-2 can comprise poly- or mono-crystalline silicon and the insulating material can comprise silicon nitride. Other materials can be used. More specifically, the insulating material can comprise, for example, silicon nitride (Si x N y ), silicon oxide (SiO2), silicon oxynitride (Si2N2O), a plastic (e.g. a polymer) or a ceramic (e.g. AI2O3) for operation under harsh conditions. However, this list of insulating materials for covering the conductive semiconductor layer should not be considered exhaustive. The conductive semiconductor material can comprise, for example, silicon (Si) (such as poly-silicon (poly-Si), amorphous silicon (a-Si) or mono-crystalline silicon), gallium nitride (GaN), gallium arsenide (GaAs) or aluminum nitride (AIN). However, this list of materials for the conductive semiconductor layer should not be considered exhaustive.

[0044] According to one embodiment, the conductive intermediate section 2-2 of the stand-alone film extends between at least two edge regions 5-1, 5-2... 5-n of the stand-alone film 2. As Figure 1a illustrated, the laterally opposite edge regions 5-1, 5-2 can traverse or bridge the boundary section 2-3 to reach a respective wiring structure or contact pad 11. The wiring structure 11 can be arranged to provide a bonding area for external electrical connections to a control and / or power supply unit, for example by means of bonding wires. The wiring structure 11 can comprise a copper, aluminum, tungsten, gold, platinum and / or titanium material or a layered stack of at least two of these materials to provide a low contact resistance.

[0045] According to another embodiment, the conductive intermediate section 2-2 can comprise n conductor arms or extensions 2-2-n between at least two edge regions 5-1, 5-2...5-n of the free-standing film 2, where n is an integer and n≥2. Thus, a Y-shaped conductive intermediate section 2-2 has n = 3 arms (e.g., two input arms and one output arm, or vice versa), while an X-shaped conductive intermediate section 2-2 has n = 4 arms (e.g., two input arms and two output arms, or vice versa), etc. The plurality of arms 2-2-n of the conductive intermediate section (2-2) and the associated edge regions 5-n of the free-standing film 2 can be symmetrically arranged with respect to a center line or symmetry line (e.g., AA or BB) passing through the center point of the center section 2-1. The plurality of arms 2-2-n and the edge regions 5-n can be arranged with an angular offset or angular difference C, where C = 360° / n.

[0046] According to one embodiment, the perforations 4 in the border region 2-3 form a vent or a plurality of vents in the free-standing film. The perforations 4 form a venting path through the border section 2-3. The vent(s) of the perforations 4 allow for a gaseous or fluidic venting between the ambient atmospheres at both sides of the free-standing film 2, i.e., adjacent to the main surface regions 2-A, 2-B. An atmospheric pressure difference between the ambient atmospheres at both sides of the free-standing film 2 can be leveled or balanced.

[0047] Furthermore, the vent holes of the perforations 4 together with the insulating material 12 of the border section 2-3 allow for a thermal isolation or decoupling of the heating structure of the free-standing film 2, i.e., the intermediate section 2-2 and the adjacent center section 2-1, from the substrate 2 (= bulk Si), thereby avoiding that the substrate 2 acts as a heat sink. The venting and thermal isolation function of the border section 2-3 of the free-standing film 2 is very effective, since the free-standing film 2 can be arranged on a cavity in the substrate 3, i.e., the free-standing film 2 can span the cavity in the substrate 3 (see Fig. 2). Figure 2 ).

[0048] According to one embodiment, the center section 2-1 of the free-standing film is a disc-shaped heat spreader structure with a high thermal conductivity material, e.g., κ≥30 W / m K at 298°C.

[0049] With the center section 2-1 being sufficiently thermally coupled with the intermediate section 2-2, the high thermal conductivity material of the center section 2-1 allows for a nearly uniform heat distribution in the center section 2-1 and, thus, a nearly uniform heat dissipation of the conductive intermediate section 2-2 from the center section 2-1 during the active state (= intermediate section 2-2 energized), wherein the achieved temperature (heat) is only slightly reduced in the center section 2-1. The center section 2-1 can comprise a semiconductor material (e.g., silicon) or a metal. For example, bulk silicon has a thermal conductivity of κ≥148 W / m K, the thermal conductivity of polysilicon at 298°C is K > 30 W / m K, the thermal conductivity of aluminum at 293°C is K > 237 W / m K, the thermal conductivity of copper at 293°C is K > 401 W / m K, the thermal conductivity of gold at 300°C is K > 315 W / m K, and the thermal conductivity of tungsten at 293°C is K > 173 W / m K.

[0050] Typically, the heat sink structure 2-1 has a form of a disc or a square. However, other structures, e.g. with perforations or recesses, are possible. The shape of the heat sink structure 2-1 can typically be related to the shape of the membrane itself. Thus, a disc-shaped membrane can be used, which does not have edges with different thermal boundary conditions, since the isotherms (= same radius) can be adapted to have the same thermal boundary conditions resulting from the membrane clamping.

[0051] Further, the outer periphery shape (outline) of the heat sink structure 2-1 is typically adapted to the inner periphery shape of the conductive intermediate section 2-2, where both elements are arranged with a minimal lateral distance (e.g. 1 to 5 pm to achieve a tight thermal coupling between them. The heat sink structure 2-1 and the conductive intermediate section 2-2 are typically separated by an insulating section, which can comprise a dielectric material.

[0052] According to one embodiment, the heat emitter forms a MEMS IR emitter operating at an operating temperature in the range between 800°C and 1100°C.

[0053] According to one embodiment, the heat emitter 1 can be implemented by a surface micromachined IR emitter (MEMS emitter) with a layer stack of a free-standing membrane 2 and a packaging (= passivation) (e.g. Si x N y ) layer to prevent the conductive intermediate section 2-2 from being oxidized by the heating layer with a polysilicon or monocrystalline silicon material. A possible material for the conductive intermediate section 2-2 is heavily doped (polysilicon), which allows the heat emitter 1 to operate at high temperatures (e.g. ~ 1000°C), where the radiant output “P out ” (= emitted power) of the heat emitter 1 depends on the 4th power of the temperature “T” generated in the conductive intermediate section 2-2 and the heat sink structure 2-1:

[0054]

[0055] Based on the described construction of the thermal emitter 1, e.g. based on MEMS technology, such a radiation source for a gas sensor can provide many requirements from a system aspect, such as small and compact size, low cost, high radiation output, high energy efficiency, high switching speed, high lifetime and bandwidth. The thermal emitter 1 can be arranged with silicon microphone technology, such that due to the reduced thickness of the conduction intermediate section 2-2, such a thermal emitter system can have a very low thermal mass. This also leads to a high thermal resistance. Due to the thermal emitter 1 having a relatively high thermal resistance (= low thermal mass), a relatively high energy efficiency (= high temperature increment per watt of input power) and a high switching speed can be achieved, wherein the thermal emitter 1 can be operated at a relatively high operating temperature due to its specific setup.

[0056] Using polysilicon as a heater material, the reliability at high operating temperatures can be improved, wherein the thermal emitter 1, i.e. the conduction intermediate section 2-2, is less prone to electromigration effects compared to metals.

[0057] Furthermore, Figure 1a Some exemplary lateral dimensions of the different elements of the free-standing membrane 2 are shown parallel to the x-axis. The lateral width (diameter) w 2-1 may be between 100 pm and 1600 pm, between 200 pm and 800 pm or between 300 pm and 600 pm or about 400 pm + / - 40 pm. The lateral width w 2-2 may be between 25 pm and 400 pm, between 50 pm and 200 pm or between 75 pm and 125 pm or about 100 pm + / - 10 pm. The lateral width w 2-3 may be between 25 pm and 400 pm, between 50 pm and 200 pm or between 75 pm and 125 pm or about 100 pm + / - 10 pm.

[0058] According to one embodiment, the boundary section 2-3 of the free-standing membrane 2 can comprise a semiconductor layer encapsulated in an insulating material or comprise an insulating material layer. According to one embodiment, the center section 2-1 of the free-standing membrane 2 can comprise a semiconductor layer encapsulated in an insulating material or comprise an insulating material layer.

[0059] According to one embodiment, the thermal emitter 1 can further comprise a plasmonic structure on the center section 2-1 and the conduction intermediate section 2-2 of the free-standing membrane 2, wherein the plasmonic structure is at least partially encapsulated in an insulating material and wherein the plasmonic structure forms a bandpass filter for the IR radiation emitted by the free-standing membrane during operation of the thermal emitter. According to one embodiment, the plasmonic structure can form a plasmonic resonator for the emitted IR radiation.

[0060] Figure 1b A schematic (lateral) temperature profile of the individual membrane 2 of the thermal emitter 1 according to one embodiment is shown. In Figure 1b , the exemplary temperature profile P belongs to the thermal emitter 1 of Figure 1a and is associated with different sections of the individual membrane 2 of the thermal emitter 1 during the activated state (= energizing of the intermediate section 2).

[0061] The depicted temperature profile P shows the temperature T (°C = y-axis) as a function of the distance (x-axis) from the center of the individual membrane 2. Thus, the temperature profile P can indicate the thermal distribution depending on the lateral distance from the conductive intermediate section 2-2.

[0062] As shown in Figure 1b , the temperature profile P originates from the annular conductive intermediate section 2-2 (= heating element). The highest temperature T MAX can be reached at the annular portion of the heating element 2-2, while the temperature T can slightly decrease by ΔT towards the central portion of the individual membrane 2 (i.e. the inside of the disc-shaped central section 2-1). In the central section 2-1, the temperature T is within a temperature range ΔT, wherein ∆T depends on the thermal conductivity of the material of the central section 2-1, i.e. the higher the thermal conductivity of the material of the central section 2-1, the smaller ∆T. Based on the configuration of the thermal emitter 1, the temperature decrease ΔT can be less than 15%, 10% or 5% of the temperature T MAX at the annular portion of the heating element 2-2. Furthermore, the temperature T can rapidly decrease as the lateral distance from the annular conductive intermediate section 2-2 towards the peripheral portion of the individual membrane 2 (i.e. in the boundary section 2-3) decreases.

[0063] The thermal isolation function of the boundary section 2-3 of the individual membrane 2 allows to a large extent the thermal decoupling of the intermediate section 2-2 of the individual membrane 2 from the substrate 2 (e.g. bulk Si), which results in a rapid decrease of the temperature T in the boundary section 2-3 having the perforations 4 in the insulating material 12.

[0064] Upon activation of the intermediate section 2-2 of the thermal emitter 1, heat (temperature T increase) is generated in the intermediate section 2-2 and spreads into the thermally conductive central section 2-1. This heat (approximately T MAX ) can be emitted or dissipated by the conductive intermediate section 2-2 and the central section 2-1 in the form of thermal (e.g. infrared) radiation.

[0065] Figure 2A schematic bottom 3D view of the heat emitter 1 is shown. According to an embodiment, the central section 2-1, the intermediate section 2-2 and the at least partially border section 2-3 of the free-standing film 2 can be arranged on a cavity or recess 6 in the substrate 3. Further, the free-standing film 2 can cover the cavity 6 in the substrate 3, wherein the border section 2-3 of the free-standing film 2 is attached to the substrate 3. The substrate 3 may, for example, comprise a bulk semiconductor substrate 7, e.g. a bulk silicon.

[0066] In the following, several different possible implementations of the heat emitter 1 are exemplarily described. In the current description of embodiments, identical or similar elements having identical structures and / or functions are provided with identical reference signs or identical names, wherein a detailed description of these elements will not be repeated in each embodiment. Thus, the above description with respect to Figures 1a-1b and Figure 2 applies equally to the other embodiments as described in the following. In the following description, essential differences (e.g. additional elements) of the embodiments as shown above and the resulting technical effect(s) are discussed in detail.

[0067] Figure 3a A schematic partial top view of the heat emitter 1 is shown, wherein Figure 3b A schematic cross-sectional partial view of the heat emitter 1 along the dashed intersection line A of the heat emitter of Figure 3a is shown. The intersection line A is parallel to the y-axis.

[0068] According to an embodiment of the heat emitter 1, the central section 2-1 of the free-standing film 2 can comprise a first portion 10-1 of the semiconductor layer 10 encapsulated in the insulating material 12. Further, the conductive intermediate section 2-2 of the free-standing film 2 can comprise a second portion 10-2 of the semiconductor layer 10 encapsulated in the insulating material 12. The insulating material 12 can comprise a first insulating material layer 12-1 arranged on a first main surface area 10-A of the semiconductor layer 10, a second insulating material layer 12-2 arranged on a second main surface area 10-B of the semiconductor layer 10, and a dielectric split line 12-3 of the insulating material 12 arranged laterally between the first portion 10-1 and the second portion 10-2 of the semiconductor layer 10 to electrically separate these two portions.

[0069] Further, the border section 2-3 of the free-standing film 2 can comprise a third portion 10-3 of the semiconductor layer 10 encapsulated in the insulating material 12 or can comprise the insulating material layer 12-2. Optionally, a further dielectric split line 12-3 of the insulating material 12 can be arranged laterally between the second portion 10-2 and the third portion 10-3 of the semiconductor layer 10 to electrically separate the two portions (in case the third portion 10-3 is present).

[0070] At least the second portion 10-2 of the semiconductor layer 10 is heavily doped. Optionally, the first portion 10-1 and the third (optional) portion 10-3 of the semiconductor layer 10 are also heavily doped.

[0071] Therefore, the independent film 2 of the thermal emitter 1 can extend between the first insulating material layer 12-1 and the second insulating material layer 12-2 of the insulating material 12 as a layer stack including semiconductor layers 10 (partial 10-1, 10-2 and optional 10-3).

[0072] The insulating material 12 can form passivation of the semiconductor layer 10 (= heating element) (parts 10-1 and / or 10-2) of the independent film 2. The heating element itself can be integrated into the independent film (= carrier film) 2, thereby resulting in improved thermal properties of the thermal heater 1.

[0073] like Figures 3a-3b As shown, the wiring structure 11 is arranged at the edge region 5-1 of the independent membrane 2 to provide a bonding area, for example, for external electrical connections to control and / or power supply units via bonding wires. The wiring structure 11 may comprise a layered stack of gold, platinum, and / or titanium materials, or at least two of these materials, to provide low contact resistance. Figure 3b As illustrated, the wiring structure 11 may include a metal layer stack, which includes a Ti layer 11-1 on a second portion 10-2 of the semiconductor layer 10 in the conductive intermediate section 2-2, a Pt layer 11-2 on the Ti layer 11-1, and an Au layer 11-3 on the Pt layer 11-2.

[0074] Since the central section 2-1 is thermally coupled to the intermediate section 2-2, the high thermal conductivity of the central section 2-1 allows for a nearly uniform heat distribution in the central section 2-1, and thus allows for a nearly uniform heat dissipation of the intermediate section 2-2 together with the central section 2-1 in the active state (when the intermediate section 2-2 is energized).

[0075] like Figures 3a-3b As shown, the substrate 3 may include a bulk semiconductor substrate 7 and an optional insulating layer 8, with the independent film 2 mechanically attached to the insulating layer 8. According to another embodiment, the optional insulating layer 8 may be omitted, wherein the second insulating material layer 12-2 of the independent film may also be directly attached to the semiconductor substrate 7.

[0076] like Figures 3a-3b As shown, the (vertical) thickness d of semiconductor layer 10 (and portions 10-1, 10-2, and optionally 10-3) 10between 200 nm and 2000 nm, between 400 nm and 1300 nm or between 500 nm and 800 nm, or approximately 660 nm + / - 60 nm (= between 600 nm and 720 nm). Alternatively, the (vertical) thickness d 10 between 80 nm and 1200 nm, between 160 nm and 700 nm or between 250 nm and 400 nm, or approximately 330 nm + / - 30 nm (= between 300 nm and 360 nm).

[0077] The (vertical) thickness d 12 Each can be between 50 nm and 400 nm, between 100 nm and 300 nm or between 120 nm and 160 nm, or approximately 140 nm + / - 10 nm (between 130 nm and 150 nm).

[0078] The (vertical) thickness d8 of the insulating layer 8 can be between 500 nm and 8000 nm, between 1000 nm and 4000 nm or between 1800 nm and 2600 nm, or approximately 2200 nm + / - 200 nm (= between 2000 and 2400 pm).

[0079] The (vertical) thickness d7 of the bulk substrate 7 is each between 50 pm and 1000 pm, between 100 pm and 750 pm or between 200 pm and 300 pm, or approximately 250 pm + / - 25 pm (= between 225 pm and 275 pm).

[0080] The contact pad 11 can comprise a metal layer stack having a (vertical) thickness d 11-1 a Ti layer 11-1 of approximately 400 nm + / - 40 nm, a (vertical) thickness d 11-2 a Pt layer 11-2 of approximately 100 nm + / - 10 nm and a (vertical) thickness d 11-3 an Au layer 11-3 of approximately 50 nm + / - 5 nm.

[0081] The above values and / or value ranges apply equally to the other embodiments described herein.

[0082] Figure 4a A schematic partial top view of the thermal emitter 1 is shown, wherein Figure 4b A schematic partial cross-sectional view of the thermal emitter 1 along Figure 4a A schematic cross-sectional partial view of the thermal emitter along the dashed intersection line B of the thermal emitter 1. The intersection line A is parallel to the x-axis.

[0083] As Figures 4a-4bAs shown, the border section 2-3 of the independent film 2 can comprise the combined insulating material layers 12-1 and 12-2 with the perforations 4 to provide the ventilation and thermal isolation functions.

[0084] As shown, the substrate 3 can comprise a bulk semiconductor substrate 7 and an optional insulating layer 8 to which the independent film 2 is mechanically attached. According to another embodiment, the optional insulating layer 8 can be omitted, wherein the second insulating material layer 12-2 of the independent film can also be directly connected to the semiconductor substrate 7. Thus, the border section 2-3 of the independent film 2 can comprise only the insulating material 12, e.g. the insulating material layers 12-1 and 12-2. Figures 4a-4b

[0085] A schematic partial cross-sectional view of a thermal emitter 1 with a fully embedded plasma structure 9 is shown. Figure 5a The arrangement of the thermal emitter 1 of Figure 5a The difference between the arrangement of the thermal emitter 1 of Figure 3b The plasma structure 9 can comprise a plasma material (metallic or metalloid material or dielectric material) exhibiting a negative real dielectric constant, e.g. gold, silver or silicon.

[0086] The thermal emitter 1 can emit light as a black body emitter with a broad emission spectrum (e.g. between 0.25 pm and 3 pm), e.g. the inclusion of the plasma structure 9 at the heating element (central section 2-1 and / or conductive intermediate section 2-2 of the independent film 2) can enhance the radiation in the desired wavelength range. Thus, the thermal emitter 1 can be configured to emit thermal radiation (e.g. infrared radiation) in a predetermined wavelength spectrum into a measurement cavity of e.g. a gas sensor or a fluid sensor. The specific wavelength of the emitted thermal radiation can be related to a gas or fluid to be detected (i.e. a so-called analyte or target gas / fluid).

[0087] By embedding the plasma structure 9 in the insulating material 12, desorption of the material of the plasma structure 9 into the base material, loss of adhesion forces or diffusion / alloying can be prevented. The thermal emitter 1 (heating structure) can be provided with an enhanced emission in the desired wavelength range, wherein long-term stability, long lifetime, high efficiency and small chip size can be achieved.

[0088]

[0089] Figure 5b ​A schematic cross-sectional partial view of a thermal emitter with a partially embedded plasma structure is shown. Figure 5b The arrangement of the thermal emitter 1 according to Figure 5a The arrangement of the thermal emitter 1 according to

[0090] As shown in any one of Figure 5b The plasma structure 9 can be arranged directly on the central section 2-1 of the free-standing film 2 and / or optionally on the conductive intermediate section 2-2. Thus, the plasma structure 9 is encapsulated between the insulating material 12 and the respective portions 10-1 and / or 10-2 of the semiconductor layer 10.

[0091] Figure 5c A schematic cross-sectional partial view of a thermal emitter with at least partially exposed plasma structure 9 is shown according to one embodiment. Figure 5c The arrangement of the thermal emitter 1 according to Figures 5a-5b The arrangement of the thermal emitter 1 according to The plasma structure 9 can be arranged directly on the central section 2-1 of the free-standing film 2 and / or optionally on the conductive intermediate section 2-2. Thus, the plasma structure 9 is encapsulated between the insulating material 12 and the respective portions 10-1 and / or 10-2 of the semiconductor layer 10.

[0092] Figure 5d A schematic partial cross-sectional view of a thermal emitter 1 with a plasma resonator 9-1 is shown according to another embodiment. As shown in any one of Figures 5a to 5c The thermal emitter 1 can comprise a plasma structure 9 adjacent to a first major surface area 10-A of the semiconductor layer 10, wherein a reflective layer 9-2 is arranged on the opposite side of the semiconductor layer 10, i.e. adjacent to a second major surface area 10-B of the semiconductor layer 10. The reflective layer 9-2 can comprise a reflective material (e.g. a metal) on the bottom side of the film 2. The reflective material for the plasma is typically a low ohmic material.

[0093] Figure 6a A schematic cross-sectional view of a MEMS gas sensor or MEMS fluid sensor 20 is shown according to one embodiment. The above evaluations with respect to the thermal emitter 1 apply equally to the Figure 6athermal emitter (= radiation source) 1. In the present context, embodiments can relate to the detection and sensing of a gas or a gas component that can be present in the ambient atmosphere, for example. However, the concept is generally applicable to the detection and sensing of a fluid or a fluid component, wherein the term fluid can generally relate to a liquid or a gas. In case the ambient medium relates to ambient air, the target fluid can relate to a target gas or a target gas component that is present in the ambient air (= ambient atmosphere). The present invention is equally applicable to sensing a target liquid or a target liquid component in an ambient medium, an ambient gas or an ambient liquid.

[0094] According to one embodiment, the MEMS gas sensor 20 can be arranged as a PAS sensor (PAS = photoacoustic spectroscopy), can comprise a thermal emitter 1 for emitting thermal radiation 22, and can comprise a measurement volume 24 with an optical interaction path 26 for the emitted thermal radiation 22 with a target gas G T and providing a detector output signal S T based on the optical interaction of the emitted thermal radiation 22 with the target gas G OUT in the measurement volume, and can comprise an acoustic transducer 28 or a thermal detector for providing the detector output signal S T . As shown, the thermal emitter 1 and the acoustic transducer 28 are arranged inside a mutual measurement volume (= cavity) 24. Figure 6a

[0095] The photoacoustic principle provides a very high selectivity as well as a relatively inexpensive set of components, e.g. the (infrared) emitter 1, optional filter 9 and detector 28. The PAS principle shows a good sensitivity to carbon dioxide as a target gas, for example.

[0096] The cavity 24 is arranged for providing an optical interaction path 26 for the interaction of the thermal radiation 22 with a target gas G T in the cavity 24 with a center wavelength λ0, wherein the cavity 24 is accessible to an ambient gas comprising the target gas component, e.g. through at least one inlet opening 30 in the housing 32. The gas sensor 20 can be formed as a MEMS gas sensor (MEMS = microelectromechanical system) in a PAS configuration. The cavity 24 can be formed as a waveguide or a reflective housing 36, wherein a reflective coating such as a metal layer on the shaped structural housing wall (= cavity wall) can guide the emitted radiation through the interaction path by means of reflection. As shown, the cavity 24 is formed by the housing 32. Figure 6a

[0097] The specific wavelength of the emitted radiation 22 can be targeted to a respective gas or gas component to be detected (i.e. a so-called analysis gas or target gas G TThe transmitter structure 1 can be configured to emit thermal radiation 22 intermittently or periodically. Therefore, the ambient gas (including the target gas) inside the measurement cavity 24 absorbs the intermittently emitted thermal radiation, and thus, in response to the emitted thermal radiation, the gas is intermittently or periodically heated and cooled. The absorption of the gas inside the measurement cavity 24, and the associated heating and cooling, can produce alternating pressure increases and decreases within the cavity 24. These pressure changes can be detected by an acoustic transducer 28 (e.g., a MEMS microphone). The amount of thermal radiation absorbed by the gas and the associated pressure changes within the cavity 24 can depend on the type of gas inside the cavity 24, and can vary with the corresponding target gas G. T It varies depending on its concentration. Each target gas G T This can include a characteristic absorption spectrum, i.e., it can cause a characteristic pressure change in response to the emitted thermal radiation 22. The characteristic absorption spectrum can also be referred to as a gas-specific fingerprint. Therefore, the acoustic transducer 28 can record what may be a corresponding target gas G. T The characteristic signal allows the acoustic transducer 28 to detect and identify the corresponding target gas G. T .

[0098] According to one embodiment, the gas sensor 20 may optionally include processing circuitry or a controller 34 for providing an excitation signal S1 (e.g., time-varying or pulsed) to the IR transmitter 1, and for reading out and optionally processing the corresponding output signal S of the acoustic transducer 28. OUT And used to provide the gas sensor output signal S 34 Gas sensor output signal S 34 Having the target gas component G in the ambient gas in cavity 24 T Information related to concentration. Processing circuit 34 can be formed by an ASIC (ASIC = Application-Specific Integrated Circuit).

[0099] Figure 6b A schematic cross-sectional view of another example of a gas sensor or fluid sensor 20' according to one embodiment is shown. The above evaluations relating to the thermal emitter 1 are equally applicable. Figure 6b 1. Thermal emitter (=radiation source)

[0100] According to one embodiment, the MEMS gas sensor 20' can be arranged as an NDIR sensor (NDIR = non-dispersive infrared). The MEMS gas sensor 20' may include a thermal emitter 1 for emitting thermal radiation 22, and may include a target gas G. T The measurement volume 24 provides a light interaction path 26 for the emitted thermal radiation 22 and may include a (direct) thermal detector 28' for measuring the target gas G in the measurement volume based on the emitted thermal radiation 22 and the target gas G in the measurement volume.T of the optical interaction to provide a detector output signal S OUT As shown in Fig. 1, the thermal emitter 1 and the detector 28 can be arranged outside the cavity 24. Figure 6b

[0101] The NDIR gas sensor 20' specifically measures the abundance or concentration of a target gas G T in the sample chamber 24. If a gas is present in the interaction path 26 from the infrared light source 1 to the detector 28', in a non-dispersive system, the IR radiation 22 with a center wavelength λ0is absorbed by the target gas GTif it falls into the absorption spectrum of the target gas GT. The degree of absorption depends on the concentration of the target gas GTin the ambient gas or is a measure thereof.

[0102] The cavity 24 can be formed as a waveguide or a reflective housing 32, wherein a reflective coating such as a metal layer on the shaped structural housing wall (= cavity wall) can guide the emitted radiation through the interaction path by means of reflection. The cavity 24 is accessible to ambient gases including the target gas component, e.g. through at least one entrance opening 30 in the housing 32.

[0103] Additional embodiments and aspects are described that can be used individually or in combination with the features and functions described herein.

[0104] According to one embodiment, the thermal emitter comprises a free-standing membrane supported by a substrate, wherein the free-standing membrane comprises in a lateral extension a center section, a conductive intermediate section, and a border section, wherein the conductive intermediate section laterally surrounds the center section and is electrically isolated from the center section, the conductive intermediate section comprising an electrically conductive semiconductor material enclosed in an insulating material, and wherein the border section at least partially surrounds the intermediate section and is electrically isolated from the conductive intermediate section, wherein a perforation is formed through the border section.

[0105] According to one embodiment, the free-standing membrane extends as a layer stack parallel to a main surface area of the substrate, wherein the layer stack comprises an electrically conductive semiconductor layer enclosed in an encapsulation layer with an insulating material.

[0106] According to one embodiment, the conductive intermediate section forms a branched current path split by the center section.

[0107] According to one embodiment, the conductive intermediate section of the free-standing membrane comprises a heavily doped semiconductor layer enclosed in an insulating material, wherein the electrically conductive semiconductor material comprises polysilicon or monocrystalline silicon, and wherein the insulating material comprises silicon nitride.

[0108] According to one embodiment, the conductive intermediate section of the free-standing membrane extends between two laterally opposite edge regions of the free-standing membrane.

[0109] ​According to one embodiment, the conductive intermediate section of the free-standing film comprises a plurality of conductor arms extending between a plurality of associated edge regions of the free-standing film, wherein the plurality of arms and edge regions of the conductive intermediate section of the free-standing film are symmetrically arranged with respect to a line of symmetry passing through a center point of the center section.

[0110] According to one embodiment, the center section and the intermediate section of the free-standing film are arranged on a cavity in a substrate.

[0111] According to one embodiment, the free-standing film covers a cavity in a substrate, wherein the boundary section of the free-standing film is attached to the substrate.

[0112] According to one embodiment, the substrate comprises a bulk semiconductor substrate and an insulating layer, wherein the insulating layer forms a main surface area of the substrate to which the free-standing film is attached.

[0113] According to one embodiment, the perforations in the boundary section form a vent or a plurality of vents in the free-standing film.

[0114] According to one embodiment, the boundary section of the free-standing film comprises a semiconductor layer encapsulated in an insulating material or comprises a layer of insulating material.

[0115] According to one embodiment, the center section of the free-standing film comprises a semiconductor layer encapsulated in an insulating material or comprises a layer of insulating material.

[0116] According to one embodiment, the center section of the free-standing film is a disc-shaped heat spreader structure having a high thermal conductivity K > 30 W / m K, e.g. at 298°C.

[0117] According to one embodiment, the heat emitter further comprises a plasmonic structure on the center section and the conductive intermediate section of the free-standing film, wherein the plasmonic structure forms a bandpass filter for the IR radiation emitted by the free-standing film during operation of the heat emitter.

[0118] According to one embodiment, the plasmonic structure forms a plasmonic resonator for the emitted IR radiation.

[0119] According to one embodiment, the heat emitter forms a MEMS IR emitter operating at a temperature in the range between 800°C and 1100°C.

[0120] According to one embodiment, a MEMS gas or fluid sensor can comprise a thermal emitter for emitting thermal radiation as described above, a measurement volume having a target gas or a target fluid and providing an optical interaction path for the emitted thermal radiation, and an acoustic transducer or a (direct) thermal detector for providing a detector output signal based on the optical interaction of the emitted thermal radiation with the target gas or the target fluid in the measurement volume.

[0121] Although some aspects have been described in the context of devices, it is clear that such aspects can also be implemented in a corresponding manner in a method. Although some aspects have been described in the context of methods, it is clear that such aspects can also be implemented in a corresponding manner in a device.

[0122] In the foregoing Detailed Description, it can be seen that various features are grouped together in examples for the purpose of streamlining the disclosure. The methods of this disclosure should not be construed as reflecting an intention that the examples require more features than are explicitly recited in each technical solution. Rather, the subject matter can be less than all of the features of a single disclosed example. Thus, the following technical solutions are hereby incorporated by reference into the Detailed Description, where each technical solution can stand as an independent example. Although each technical solution can stand alone as a separate example, it should be noted that while a technical solution can refer to a particular combination of one or more other technical solutions, other examples can include combinations of the technical solution with the subject matter of other technical solutions, or combinations of each feature with other technical solutions. Such combinations are presented in this document unless otherwise contradicted by context. Further, it is intended that a feature of one technical solution be included in any other technical solution, even if that technical solution does not explicitly include the feature.

[0123] Although specific embodiments have been illustrated and described herein, it will be appreciated that various alterations and / or modifications can be made to the specific embodiments without departing from the scope of the embodiments. The application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that the embodiments be limited only by the claims and their equivalents.

Claims

1. A heat emitter (1) comprising: a free-standing membrane (2) supported by a substrate (3), wherein the free-standing membrane (2) comprises in a lateral extension a central section (2-1), an electrically conductive intermediate section (2-2) and a border section (2-3), wherein the electrically conductive intermediate section (2-2) laterally surrounds and is electrically isolated from the central section (2-1), the electrically conductive intermediate section (2-2) comprising an electrically conductive semiconductor material encapsulated in an insulating material, and wherein the border section (2-3) at least partially surrounds and is electrically isolated from the electrically conductive intermediate section (2-2), wherein perforations (4) are formed through the border section (2-3) as ventilation holes.

2. The heat emitter according to claim 1, wherein the free-standing membrane (2) extends as a layer stack parallel to a main surface area (3-1) of the substrate (3), wherein the layer stack comprises an electrically conductive semiconductor layer encapsulated in an encapsulation layer with the insulating material.

3. The heat emitter according to claim 1 or 2, wherein the electrically conductive intermediate section (2-2) forms a branched current path separated by the central section (2-1).

4. The heat emitter according to claim 1, wherein the electrically conductive intermediate section (2-2) of the free-standing membrane (2) comprises a heavily doped semiconductor layer encapsulated in the insulating material, wherein the electrically conductive semiconductor material comprises polysilicon or monocrystalline silicon, and wherein the insulating material comprises silicon nitride.

5. The heat emitter according to claim 1, wherein the electrically conductive intermediate section (2-2) of the free-standing membrane (2) extends between two laterally opposite edge regions (5-1, 5-2) of the free-standing membrane (2).

6. The heat emitter according to claim 1, wherein the electrically conductive intermediate section (2-2) of the free-standing membrane (2) comprises a plurality of conductor arms (2-2-1, 2-2-2,..., 2-2-n) extending between a plurality of associated edge regions (5-1, 5-2,..., 5-n) of the free-standing membrane (2), wherein the plurality of arms (2-2-1, 2-2-2,..., 2-2-n) and the edge regions (5-1, 5-2,..., 5-n) of the electrically conductive intermediate section (2-2) of the free-standing membrane (2) are symmetrically arranged with respect to a line of symmetry (AA) through a center point of the central section (2-1).

7. The heat emitter according to claim 1, wherein the central section (2-1) and the electrically conductive intermediate section (2-2) of the free-standing membrane (2) are arranged on a cavity (6) in the substrate (3).

8. The heat emitter according to claim 7, wherein the free-standing membrane (2) covers the cavity (6) in the substrate (3), wherein the border section (2-3) of the free-standing membrane (2) is attached to the substrate (3).

9. The thermal emitter according to claim 1, wherein the substrate (3) comprises a bulk semiconductor substrate (7) and an insulating layer (8), wherein the insulating layer (8) forms a main surface area (3-1) of the substrate (3), to which the free-standing membrane (2) is attached to the main surface area (3-1) of the substrate (3).

10. The thermal emitter according to claim 1, wherein the perforations (4) in the border section (2-3) form a vent or a plurality of vents in the free-standing membrane (2).

11. The thermal emitter according to claim 1, wherein the border section (2-3) of the free-standing membrane (2) comprises a semiconductor layer encapsulated in an insulating material or comprises an insulating material layer.

12. The thermal emitter according to claim 1, wherein the center section (2-1) of the free-standing membrane (2) comprises a semiconductor layer encapsulated in an insulating material or comprises an insulating material layer.

13. The heat emitter according to claim 1, wherein the central section (2-1) of the free-standing film (2) is a heat sink structure having a thermal conductivity of K > 30 W / m K at 298 °C of a high thermal conductivity material of K.

14. The thermal emitter according to claim 1, further comprising a plasmonic structure (9) on the center section (2-1) and the electrically conductive intermediate section (2-2) of the free-standing membrane (2), wherein the plasmonic structure (9) forms a bandpass filter for the IR radiation emitted by the free-standing membrane (2) during operation of the thermal emitter.

15. The thermal emitter according to claim 14, wherein the plasmonic structure (9) forms a plasmonic resonator (9-1) for the emitted IR radiation.

16. The thermal emitter according to claim 1, wherein the thermal emitter forms a MEMS IR emitter with an operating temperature in the range between 800 °C and 1100 °C.

17. A MEMS gas or fluid sensor, comprising: a thermal emitter for emitting thermal radiation according to any of the preceding claims 1 to 15; a measurement volume with a target gas or a target fluid and providing an optical interaction path for the emitted thermal radiation, and an acoustic transducer or a direct thermal detector for providing a detector output signal based on an optical interaction of the emitted thermal radiation with the target gas or target fluid in the measurement volume.

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