Light emitting devices with heater structure and associated manufacturing process

Abstract

A light emitting device (100; 300; 400) comprising: a heater structure (140) configured to emit light when a predefined current flows through the heater structure (140), wherein the heater structure is arranged on a heater support structure (130); an upper portion (150) of a cavity disposed vertically between the heater support structure (130) and a cover structure (160); a lower portion (120) of the cavity disposed vertically between the heater support structure (130) and at least a portion of a support substrate (110); an optical filter structure configured such that light passing through the optical filter structure has a spectral maximum at a desired optical wavelength when the optical filter structure is implemented through the cover structure (160) or is arranged between the lower portion (120) of the cavity and a back surface of the light emitting device (100; 300; 400), wherein the optical filter structure comprises a plurality of semiconductor layers of a filter layer stack and a plurality of insulating layers or cavity layers of the filter layer stack arranged alternately; and Side walls of the upper section (150) and the lower section (120), wherein side walls of the upper section (150) or the lower section (120) on which the filter structure is arranged are formed by an oxide layer, wherein the heater support structure (130) comprises a plurality of holes connecting the upper portion (150) of the cavity and the lower portion (120) of the cavity, and wherein a pressure in the cavity is less than 100 mbar.

Description

Area

[0001] Examples relate to concepts for generating light and applications thereof, and in particular to light emitting devices, optical filter structures, methods for forming light emitting devices, and methods for forming optical filter structures. background

[0002] Light emitting devices, e.g., light emitting devices for gas sensing applications, may need to be optimized with respect to various objectives, such as cost, manufacturing complexity, or power consumption.

[0003] WO 2006 / 031 125 A1 discloses a sealed infrared radiation source comprising an emitter membrane which is excited by an electrical current passed through the membrane, the membrane thus comprising an electrical conductor, the membrane being mounted between a first and a second housing part, at least one of which is transparent in the IR range, and each housing part defining a cavity between the membrane and the respective housing part on each side of the membrane, the housing parts being at least partially electrically conductive and a first of the housing parts being electrically coupled to a first end of the electrical conductor and insulated from the second end of the electrical conductor, the second housing part being electrically coupled to a second end of the electrical conductor and insulated from the first end of the electrical conductor.

[0004] JP 2007-86038 A discloses a light source unit that emits light in a wavelength range including the absorption wavelength of the detection target gas, a light-receiving element unit that receives light emitted from the light source unit, and a detection target gas provided between the light source unit and the light-receiving element unit. A gas cell opening that introduces a gas to be detected near the slab-type photonic crystal, and a slab-type photonic crystal having a periodic refractive index structure in a two-dimensional plane are provided. The light emitted from the light source unit, incident from the direction intersecting the slab-type photonic crystal, is emitted toward the light-receiving element side, and the slab has a resonant peak with respect to the absorption wavelength of the gas to be detected.Optical gas sensor, characterized in that the periodic structure of the refractive index of a photonic crystal is designed. US 2008 / 0 124 565 A1 discloses a material for forming a conductive structure for a micromechanical current-driven device, consisting of an alloy containing approximately 0.025% manganese and the balance nickel. The data demonstrate that the alloy possesses advantageous mechanical and electrical properties. In particular, the sheet resistance of the alloy is actually lower and more stable than the sheet resistance of the pure metal. Accordingly, when used for conductive lines in a photonic device, the NiMn alloy lines can deliver current to heat the photonic device while generating less heat in the lines themselves and providing more stable performance.

[0005] DE 10 2014 114 873 A1 discloses a semiconductor device for emitting frequency-adjusted infrared light, comprising a lateral emitter structure and a lateral filter structure. The lateral emitter structure is configured to emit infrared light with an emitter frequency distribution. Furthermore, the lateral filter structure is configured to filter the infrared light emitted by the lateral emitter structure, thereby providing frequency-adjusted infrared light with an adjusted frequency distribution. The frequency range of the adjusted frequency distribution is narrower than a frequency range of the emitter frequency distribution. Furthermore, a lateral air gap is arranged between the lateral emitter structure and the lateral filter structure.

[0006] EP 3 096 345 A1 discloses an infrared radiator having a metallized membrane that emits infrared light during operation. The membrane comprises a two-dimensional array of through-holes sized at infrared wavelengths and, on each side, a thin metal layer also comprising an array of through-holes. The through-holes are arranged as a two-dimensional periodic array, and each of the through-holes has a cross-section with a maximum and a minimum dimension smaller than each wavelength of the emitted infrared light. The peak wavelength of the emitted infrared light is proportional to the periodicity of the through-holes. At least one of the metal layers is connected to an electrical power source that supplies an electrical current that heats at least one of the metal layers, thereby emitting a narrow-band and highly directional beam of infrared light.The membrane is mounted on a membrane carrier, and both are made of a material that can withstand temperatures of more than 400 °C. Summary

[0007] There may be a need to provide an improved concept for light emitting devices and / or optical filters that may enable light emitting devices and / or optical filters with lower power consumption and / or at lower cost.

[0008] Such a need may be met by the subject matter of the claims.

[0009] Some examples relate to a light emitting device. The light emitting device comprises a heater structure configured to emit light when a predefined current flows through the heater structure. The heater structure is arranged on a heater support structure. The light emitting device comprises an upper portion of a cavity arranged vertically between the heater support structure and a cover structure. The light emitting device comprises a lower portion of the cavity arranged vertically between the heater support structure and at least a portion of a support substrate. The heater support structure comprises a plurality of holes connecting the upper portion of the cavity and the lower portion of the cavity. A pressure in the cavity is less than 100 mbar.The light emitting component further comprises an optical filter structure configured such that light passing through the optical filter structure has a spectral maximum at a desired optical wavelength when the optical filter structure is implemented through the cover structure or arranged between the lower portion of the cavity and a rear surface of the light emitting component. The optical filter structure comprises a plurality of semiconductor layers of a filter layer stack and a plurality of insulating layers or cavity layers of the filter layer stack, which are arranged alternately. The light emitting component further comprises sidewalls of the upper portion and the lower portion. Sidewalls of the upper portion or the lower portion, on which the filter structure is arranged, are formed by an oxide layer.

[0010] Some examples relate to a method of forming a light emitting device. The method includes forming a patterned sacrificial layer over a heater support structure. A heater structure is disposed on the heater support structure. The method includes forming an insulation layer on the patterned sacrificial layer. The method includes removing a portion of the insulation layer until the patterned sacrificial layer is exposed to obtain a smooth surface. The method includes forming a cap structure on the smooth surface. Forming the cap structure includes forming an optical filter structure. The method includes forming at least one hole through the cap structure to the patterned sacrificial layer. The method includes removing the patterned sacrificial layer to obtain a cavity between the heater support structure and the cap structure.The method comprises sealing the at least one hole at ambient pressure of less than 100 mbar. Short description of the drawings

[0011] Some examples of devices and / or methods are described below solely by way of example and with reference to the accompanying drawings in which Fig. Figure 1 shows a schematic cross-section of part of a light emitting device; Fig. Figure 2 shows a schematic plan view of a heater support structure arranged within a cavity; Fig. 3-4 show a schematic cross-section of examples of light emitting devices; Fig. 5 shows a diagram of a reflectivity of a back reflector on a silicon substrate; Fig. 6 shows a schematic cross-section of a gas sensor device; Fig. 7 shows a flowchart of a method for forming a light emitting device; Fig. Figure 8 shows a schematic cross-section of an optical filter structure; Fig. 9 shows a diagram of a transmissivity of an optical (multilayer) filter structure on a silicon substrate; and Fig. 10 shows a flow diagram of a method for forming an optical filter structure. Detailed description

[0012] Various embodiments will now be described in more detail with reference to the accompanying drawings, in which some embodiments are illustrated. In the figures, the thickness of lines, layers, and / or regions may be exaggerated for clarity.

[0013] Accordingly, while other examples of various modifications and alternative forms are susceptible of further disclosure, some examples thereof are shown by way of example in the figures and are described in detail herein. It should be understood, however, that examples are not intended to limit the particular forms disclosed. Other examples may be intended to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure. Throughout the description of the figures, like reference numerals refer to like or similar elements, which may be implemented identically or in modified form compared to one another while providing the same or similar functionality.

[0014] It is understood that when an element is described as being "connected" or "coupled" to another element, the elements may be connected or coupled directly or through one or more intermediate elements. When two elements A and B are connected with an "or," this should be understood to disclose all possible combinations, i.e., only A, only B, and both A and B. Alternative wording for the same combinations is "at least one of A and B." The same applies to combinations of more than two elements.

[0015] The terminology used herein is intended to describe specific examples and is not intended to be limiting. Whenever a singular form such as "a," "an," and "the" is used, and the use of only one element is neither explicitly nor implicitly defined as mandatory, further examples may include the plural forms to implement the same functionality. Similarly, where functionality is described below as being implemented using multiple elements, further examples may implement the same functionality using a single element or processing entity.It is further understood that the terms "comprises," "comprising," "having," and / or "comprising," as used herein, indicate the presence of specified features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0016] Unless otherwise defined, all terms used herein (including technical and scientific terms) are used in their ordinary sense, to which the examples belong.

[0017] Fig. 1 shows a schematic cross-section of a light emitting device 100. The light emitting device comprises a heater structure (e.g., a light-emitting structure) 140 configured to emit light when a predefined current flows through the heater structure 140. The heater structure is arranged on (e.g., on a front side or a back side) a heater support structure 130. The light emitting device comprises an upper portion 120 of a cavity arranged vertically between the heater support structure 130 and a cover structure 160. The light emitting device comprises a lower portion 150 of the cavity arranged vertically between the heater support structure 130 and at least a portion of a carrier substrate 110. The heater support structure 130 comprises a plurality of holes 132 connecting the upper portion 120 of the cavity and the lower portion 150 of the cavity. A pressure (e.g.,an air pressure or ambient pressure) within the cavity is less than 100 mbar (or less than 10 mbar, less than 1 mbar, less than 0.1 mbar, less than 0.01 mbar).

[0018] Because the heater support structure is disposed within the cavity (e.g., at a low pressure, e.g., near vacuum) and due to the plurality of holes within the heater support structure, heat conduction to walls of the cavity (e.g., via the heater support structure or through air / gas within the cavity) can be reduced. In this way, power loss of the light emitting device 100 due to heat conduction can be reduced, and power consumption of the light emitting device 100 can be reduced, enabling more compact dimensions of the light emitting device and / or improved emission efficiency.

[0019] For example, the heater support structure 130 may correspond to a membrane structure. For example, the heater support structure may be spanned between (side) walls of the cavity. For example, the heater support structure 130 may be detached / separated from lateral surfaces of the cavity, e.g., from a bottom surface (e.g., formed by the support substrate 110) and a ceiling surface (e.g., formed by the cover structure 160) of the cavity. For example, the support structure may be attached (only) to the lateral / vertical walls of the cavity. For example, the heater support structure 130 may extend in a first lateral direction and in a second lateral direction. The second lateral direction may be orthogonal (aligned) to the first lateral direction.The heater support structure 130 may be connected to (or connect to) walls of the cavity on both sides in the first lateral direction and on both sides in the second lateral direction. This may improve stability of the heater support structure. For example, the heater support structure 130 may have a vertical thickness of less than 20 µm (or less than 15 µm or less than 10 µm). For example, the heater support structure 130 may have a patterned oxide layer. For example, the heater support structure 130 may have a lateral length and a lateral width each at least 5 µm (or at least 10 µm, at least 50 µm, at least 100 µm) greater than a lateral length and a lateral width of the cavity. For example, the heater support structure 130 may laterally overlap the cavity on all lateral sides.

[0020] For example, the plurality of holes 132 may extend vertically through the heater support structure 130. For example, the plurality of holes 132 may correspond to a plurality of trenches extending through the heater support structure 130. For example, the plurality of holes 132 may allow air or gas flow between the lower portion 120 and the upper portion 150 of the cavity. For example, the plurality of holes 132 achieves substantially equal pressure in the lower portion 120 and the upper portion 150 of the cavity. For example, a lateral width / diameter of the holes of the plurality of holes 132 may be greater than 500 nm (or greater than 1 µm, greater than 2 µm, greater than 5 µm). For example, a lateral width / diameter of the holes of the plurality of holes 132 may be less than 10 µm (or less than 8 µm, less than 5 µm, less than 2 µm).

[0021] For example, the plurality of holes 132 may have an elongated lateral shape. For example, the elongated lateral shape may have a lateral length at least 4 times (or at least 5 times, at least 8 times, at least 10 times) as large as a lateral width of the elongated lateral shape. The elongated lateral shape may block / extend a heat path toward edges of the heater support structure. The elongated lateral shape of a hole of the plurality of holes may be aligned parallel to an edge of the heater support structure (e.g., an edge of the heater support structure 130 attached to a wall of the cavity).

[0022] For example, the plurality of holes 132 may be arranged in a plurality of rows of holes. For example, the holes of a row of the plurality of rows of holes may have an elongated lateral shape that is aligned parallel to the row. For example, rows of the plurality of rows of holes may be aligned parallel to an edge of the heater support structure. The plurality of rows of holes may be separated by a plurality of strips of the support structure that are arranged laterally parallel to the plurality of rows of holes (as shown, for example, in Fig. 2). A width of the holes of a row of the plurality of rows of holes arranged between two adjacent strips of the plurality of strips may be less than 60% (or less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, less than 5%) of a width of each of the adjacent strips. For example, the plurality of rows of holes and the plurality of strips may be arranged alternately. For example, two adjacent strips of the plurality of strips may be laterally connected by lateral connecting bars made of solid material that separate holes of a row of the plurality of rows of holes arranged between the two adjacent strips. The plurality of holes arranged in a plurality of rows of holes may obstruct a heat path toward an edge of the heater support structure.For example, holes of adjacent rows of the plurality of rows of holes may have a lateral offset of more than 20% (or more than 30%, more than 40%, more than 50%) of a length of a hole of the adjacent rows. For example, the lateral offset of holes of a row of the plurality of rows of holes may be measured parallel to an orientation of the row (e.g., parallel to a lateral direction of a maximum extension of the row). The lateral offset may further define a heat path toward an edge of the heater support structure (e.g., as further shown in FIG. Fig. 2) block / extend.

[0023] For example, the plurality of holes 132 may be arranged and formed such that, from a center of the heater support structure 130 to a nearest edge of the support structure, a path along the heater support structure is at least 20% (or at least 30%, at least 40%, at least 50%, at least 80%, at least 100%, at least 200%, at least 400%) longer than a direct straight path from the center of the heater support structure to the nearest edge of the support structure. For example, the center of the heater support structure may correspond to a lateral geometric center of the heater support structure, or a lateral point of the heater support structure located at a lateral geometric center of the heater structure. For example, the center of the heater support structure may correspond to a lateral point of the heater support structure 130 where heat absorbed by the heater structure 140 is greatest.A longer path can reduce heat conduction toward an edge of the heater support structure. For example, the plurality of holes can form a repeating pattern to reduce thermal conductivity of the support structure compared to a solidly structured support structure.

[0024] For example, the lower portion 120 and the upper portion 150 may be separated by the heater support structure 130. For example, the lower portion 120 of the cavity may form a cavity within the support substrate. For example, the lower portion 120 of the cavity and the upper portion 150 of the cavity may be arranged (vertically, directly) adjacent to the heater support structure 130. For example, the upper portion 150 of the cavity may be arranged (directly) adjacent to the cover structure 160. For example, the support substrate 110 may form at least one (or all) of the sidewall(s) of the lower portion 120 of the cavity. Alternatively or additionally, an oxide layer may form at least one (or all) of the sidewall(s) of the lower portion 120 of the cavity. For example, an oxide layer may form the sidewalls of the upper portion 150 of the cavity.For example, a sidewall of the (lower or upper portion of the) cavity may correspond to a wall of the cavity extending between the heater support structure 130 and one of the cover structure 160, a lateral surface of the support structure, an optical filter structure, and a reflector structure.

[0025] For example, a bottom surface of the lower portion 120 of the cavity (e.g., a surface within the lower portion 120 of the cavity located on a side of the lower portion opposite the heater support structure 130) may be formed by one of the support substrate, a reflector structure, and an optical filter structure. For example, the cavity may be an evacuated cavity (e.g., comprising a vacuum or a gas).

[0026] For example, the lower portion 120 of the cavity may have a vertical height of more than 1 µm (or more than 10 µm, more than 50 µm, more than 100 µm, more than 200 µm, more than 400 µm). For example, the lower portion 120 of the cavity may have a vertical height of less than 600 µm (or less than 500 µm, less than 200 µm, less than 100 µm, less than 50 µm, less than 20 µm, less than 10 µm). For example, the upper portion 150 of the cavity may have a vertical height of greater than 0.05 µm (or greater than 0.1 µm, greater than 0.5 µm, greater than 1 µm, greater than 2 µm, greater than 5 µm). For example, the lower portion 150 of the cavity may have a vertical height of less than 15 µm (or less than 10 µm, less than 8 µm, less than 5 µm, less than 3 µm, less than 2 µm, less than 1 µm, less than 0.5 µm).For example, the upper portion of the cavity may have a lateral width of at least 5 times (or at least 10 times, at least 20 times, at least 50 times, at least 80 times) as large as an (average, vertical) thickness of the upper portion of the cavity.

[0027] For example, a (quasi-)vacuum may be formed in the cavity. For example, a gas pressure in the cavity may be greater than 0.001 mbar or greater than 0.01 mbar. For example, a gas pressure in the upper portion 150 of the cavity may be equal to a gas pressure in the lower portion 120 of the cavity. The cavity may be filled with air or with a gas that has a lower thermal conductivity than air (e.g., radon, xenon, or argon).

[0028] For example, the cover structure 160 may form a substantially planar surface on a front surface of the light emitting device, which may enable light emitting devices with reduced dimensions. For example, the cover structure 160 may form a planar surface (a surface with a height variation of less than 10 µm) over more than 70% (or more than 80%, more than 90%) of the surface of the cover structure (or over more than 70% (or more than 80%, more than 90%) of a front surface of the light emitting device 100). For example, the cover structure may form a (front) ceiling of the light emitting device. For example, the cover structure 160 may include at least one semiconductor layer and / or at least one metal layer. For example, the cover structure may form at least a portion of a front surface of the light emitting device 100.For example, the cover structure 160 may be a (silicon) oxide (chemical symbol SiO. 2 ) layer on a lateral surface facing away from the support structure 110.

[0029] The light-emitting device comprises an optical filter structure configured such that light passing through the optical filter structure exhibits a spectral maximum at a desired optical wavelength when the optical filter structure is implemented through the cover structure or disposed between the lower portion of the cavity and a backside surface of the light-emitting device (e.g., adjacent to the lower portion 120 of the cavity or at the backside surface of the carrier substrate). Integrating an optical filter structure into the cover structure may enable further integration of components onto the carrier substrate, enabling more compact dimensions of the light-emitting device.

[0030] For example, the optical filter structure may have a transmissivity of greater than 70%, or greater than 80%, greater than 90%, at the desired optical wavelength, and transmissivity of less than 20% (or less than 10%, less than 5%) at optical wavelengths at least 5% (or at least 10%) greater or less than the desired optical wavelength. For example, the desired optical wavelength may be within an infrared spectrum. For example, the desired optical wavelength may be between 1 µm and 10 µm (or, for example, between 4 µm and 5 µm, or, for example, between 4.2 µm and 4.5 µm). For example, the desired optical wavelength may correspond to an optical wavelength absorbed by a sample gas in a gas detector. For example, the optical filter structure may have a thickness of less than 25 µm (or less than 20 µm, less than 15 µm, less than 10 µm, less than 5 µm, less than 3 µm).For example, the optical filter structure may have a thickness of more than 1 µm (or more than 2 µm, more than 5 µm, more than 10 µm).

[0031] The optical filter structure comprises a plurality of semiconductor layers of a filter layer stack and a plurality of insulating layers (e.g., silicon oxide or silicon nitride layers) or cavity layers of the filter layer stack (e.g., arranged (positioned) alternately with the semiconductor layers of the plurality of semiconductor layers). For example, the optical filter structure may comprise a Bragg filter with different polysilicon layers and / or insulating layers (e.g., layers comprising silicon oxide or silicon nitride). A multilayer optical filter structure may enable a filter structure with a reduced thickness compared to other optical filter concepts, enabling more compact dimensions of the light emitting device. For example, the plurality of semiconductor layers may comprise fewer than 15 (or fewer than 12, fewer than 10, fewer than 8) semiconductor layers.For example, the plurality of semiconductor layers may comprise an increasing number of semiconductor layers to achieve a more pronounced separation of the desired wavelength from adjacent wavelengths (e.g., to separate an optical wavelength absorbed by carbon dioxide from optical wavelengths absorbed by water). Fig. 8 shows an example of an optical filter structure. For example, an upper layer of the plurality of semiconductor layers and a lower layer of the plurality of semiconductor layers may vertically enclose the plurality of insulation layers or cavity layers. For example, the filter structure may laterally overlap the cavity.

[0032] A thickness of the semiconductor layers of the plurality of semiconductor layers may be less than 2 µm (or less than 1.5 µm, less than 1 µm, less than 0.8 µm) and a thickness of the insulating layers or the cavity layers of the plurality of insulating layers or cavity layers may be less than 4 µm (or less than 3 µm, less than 2 µm, less than 1.5 µm, less than 1 µm, less than 0.8 µm) so that light passing through the filter layer stack has a spectral maximum at the desired optical wavelength.

[0033] For example, the light emitting device may further comprise a reflector structure configured to reflect at least 70% (or at least 80%, at least 90%, at least 95%) of the light within a desired spectral range (e.g., at the desired optical wavelength or in a range extending from 95% of the desired wavelength to 105% of the desired wavelength) that is emitted (vertically) toward the reflector structure by the heater structure (as shown in Fig. 3 or Fig. 4), e.g., at the desired wavelength. The reflector structure can reflect light emitted toward a side of the light emitting device that is not intended to emit light, resulting in reduced power consumption and less heat generated by the heater structure. For example, the reflector structure can be arranged on a rear side of the carrier substrate (as in Fig. 3). Alternatively, the reflector structure may be arranged between the lower portion of the cavity and the support structure, e.g., adjacent to the lower portion 120 of the cavity (e.g., as shown in Fig. 4). Alternatively, the reflector structure may be implemented by the cover structure 160. For example, the reflector structure may be arranged on an opposite side of the heater structure 140 with respect to the optical filter structure.

[0034] A layer of metal (e.g., aluminum, 80 to 90% reflection) can be used as a backside reflector. For example, the reflector structure can comprise a metal film (e.g., aluminum). Alternatively, a dielectric layer stack can be used. An example of a dielectric layer stack can be found in Fig. 5. For example, the reflector structure may comprise a plurality of semiconductor layers of a reflector layer stack and a plurality of insulating layers or cavity layers of the reflector layer stack arranged / positioned alternately with the semiconductor layers of the plurality of semiconductor layers. A multilayer reflector structure may enable a reflector structure with improved reflectivity compared to other reflector concepts.A thickness of the semiconductor layers of the plurality of semiconductor layers may be less than 2 µm (or less than 1.5 µm, less than 1 µm, less than 0.8 µm) and a thickness of the insulating layers or cavity layers of the plurality of insulating layers or cavity layers may be less than 4 µm (or less than 3 µm, less than 2 µm, less than 1.5 µm, less than 1 µm, less than 0.8 µm), such that at least 70% (or at least 80%, at least 90%, at least 95%) of the light vertically incident on the reflector layer stack is reflected within the desired spectral range or at a desired optical wavelength (e.g., at the desired optical wavelength of the optical filter structure). For example, a thickness of layers of the reflector layer stack may differ from a thickness of layers of the filter layer stack, e.g.,to achieve different optical properties for the reflector layer stack and the filter layer stack.

[0035] For example, the light emitting device may include a heater wiring structure connecting the heater structure 140 to a contact pad structure or a heater trigger circuit. For example, the heater wiring structure may include one or more conductive layers, one or more vias, and / or one or more wires. Portions of the heater wiring structure disposed on the support structure 130 may have a resistivity of less than 50% (or less than 40%, less than 20%, less than 10%, less than 5%) of a resistivity of the heater structure (e.g., due to an increased concentration of implanted ions). Reduced resistivity may result in reduced thermal conduction. For example, the heater wiring structure may include two or more contact structures disposed on a surface of the cover structure 160.

[0036] The flow of the predefined current through the heater structure 140 may cause Joule heating of the heater structure 140 and may thereby result in the emission of thermal radiation by the heater structure 140, for example. For example, the heater structure 140 may be configured to emit infrared light (e.g., light having a wavelength in the range of 700 nm to 1 mm), visible light (e.g., light having a wavelength in the range of 400 nm to 700 nm), and / or a combination thereof. For example, the heater structure 140 may be configured to emit light with a spectrum having a maximum intensity at a wavelength greater than 700 nm and less than 1 mm (e.g., between 4 µm and 5 µm, or between 4.2 µm and 4.5 µm).

[0037] For example, the heater structure 140 may be arranged on or below the heater support structure 130 (e.g., at a front or a back of the heater support structure). For example, the heater structure 140 may be arranged within the upper portion 150 of the cavity or within the lower portion 120 of the cavity. For example, at least a portion of the heater structure 140 may have a meander shape or a ring shape. In this way, a length of the heater structure 140 may be increased. Thereby, an electrical resistance value of the heater structure 140 and thereby a Joule heating of the heater structure 140 due to the flow of the predefined current may be increased. In this way, an intensity of the emission of light may be increased. For example, the heater structure 140 may comprise polysilicon. Alternatively, the heater structure 140 may comprise doped, monocrystalline silicon.

[0038] For example, the flow of the predefined current can be generated by applying a voltage to the electrical contacts of the heater structure 140. For example, the predefined current can be less than 10 mA (or less than 1 mA, less than 0.1 mA, less than 0.01 mA, or less than 1 µA). The predefined current can be supplied by a supply circuit, a control circuit, or a heater driver circuit implemented on the carrier substrate 110, or by an external supply circuit. The light emitting device can further comprise a heater driver circuit (e.g., implemented on and / or at least partially in the carrier substrate) configured to provide the predefined current to the heater structure to cause light emission by the heater structure. The heater driver circuit can be implemented on the carrier substrate, e.g., on the carrier substrate or at least partially in the carrier substrate 110.The control circuit integrated on the carrier substrate can further reduce a size of the light emitting device.

[0039] For example, the light-emitting device may further include a package structure including the support substrate 110, the heater support structure 130, the heater structure 140, the cavity, and the cover structure 160. For example, the package structure may not be in direct contact with the cover structure 160. For example, the package structure may be arranged at a distance of at least 500 nm (or at least 1 µm, at least 10 µm) from the cover structure. For example, at least 50% (or at least 70%, at least 80%, at least 90%) of the cover structure 160 is not shielded by the package structure.

[0040] For example, the carrier substrate 110 may be a semiconductor substrate (e.g., a silicon-based substrate (chemical symbol Si)) or a glass substrate. A semiconductor substrate may be a semiconductor wafer or a semiconductor chip, or a part of a semiconductor wafer or a semiconductor chip, for example. For example, a glass substrate may be a silica-based substrate (e.g., SiO 2)-based glass substrate, a borosilicate-based glass substrate, an aluminosilicate-based glass substrate, or an oxide-based glass substrate. A glass substrate may be a glass wafer, a glass lid wafer, or a glass lid, or a part of a glass wafer, a glass lid wafer, or a glass lid, for example. The front surface of the carrier substrate 110 may be the surface of the carrier substrate 140 facing toward the heater support structure 130, and the back surface of the carrier substrate 110 may be the surface of the carrier substrate 140 facing away from the heater support structure. For example, the front surface of the light emitting device 100 may be the surface of the light emitting device at least partially formed by the cover structure.For example, the back surface of the light emitting device 100 may correspond to the back surface of the carrier substrate 110 or an outwardly facing surface of a reflector substrate arranged on the back surface of the carrier substrate 110.

[0041] For example, a vertical direction may be measured orthogonal to the front or back surface of the support substrate 110, and a lateral direction may be measured parallel to the front or back surface of the support substrate 110.

[0042] For example, the light-emitting device 100 can be an element of a photoacoustic gas sensor, a photoacoustic spectroscopy system, a thermal flow sensor, or a mobile device (e.g., a smartphone or a tablet computer). For example, the light-emitting device 100 can be a light source of a gas detection device. The light-emitting device 100 can be used to implement any other gas sensor principle where emitted optical radiation is used to trigger a sensor effect (e.g., a photoacoustic effect), such as NDIR (non-dispersive infrared) sensor systems, for example.

[0043] Fig. 2 shows a schematic top view of an example of a heater support structure 130 arranged within a cavity. The heater support structure 130 of Fig. 2 comprises a plurality of holes 132 arranged in a plurality of rows of holes, and a plurality of strips 134. For example, the holes 132 of the plurality of rows of holes comprise an elongated lateral shape aligned parallel to the row. In the example of Fig. 2, two adjacent strips of the plurality of strips 134 are laterally connected by lateral connecting rods 136 made of solid material that separate holes 132 of one row of the plurality of rows of holes arranged between adjacent strips. The plurality of rows of holes 132 and the plurality of strips 134 are arranged alternately. Holes 132 of adjacent rows of the plurality of rows of holes comprise a lateral offset of more than 20% of a length of a hole of the adjacent rows. Fig. 2 may show a schematic drawing of a patterned oxide spanning a cavity in a silicon substrate.

[0044] It can be mentioned that the Fig. The structure shown in Figure 2 can (significantly) reduce thermal losses. Lateral thermal conductivity can be guided in a serpentine pattern. This allows thermal losses to be kept at a very low level. A bandpass filter can be placed over a structure of this support and a thermal emitter (highly doped silicon resistors). This way, the filter can provide intrinsic sealing of the emitter / filter unit with an evacuated cavity.

[0045] Further details and aspects of the support structure 130 will be mentioned in connection with the proposed concept or one or more of the examples described above (for example Fig. 1). The support structure 130 may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0046] Fig. 3 shows a schematic cross section of a light emitting device 300. The light emitting device 300 can be similar to that described in connection with Fig. 1. The light emitting device 300 comprises a heater structure (e.g., a light-emitting structure) 140 configured to emit light when a predefined current flows through the heater structure 140. The heater structure is arranged on a heater support structure 130. The light emitting device 300 comprises an upper portion 120 of a cavity arranged vertically between the heater support structure 130 and a cover structure 160 comprising an optical filter structure. The light emitting device 300 comprises a lower portion 150 of the cavity arranged vertically between the heater support structure 130 and at least a portion of a carrier substrate 110. The light emitting device 300 further comprises a reflector structure 170 arranged on a backside surface of the carrier substrate 110. Fig. 3 may represent a schematic diagram of an emitting unit for IR (infrared) spectral sensors.

[0047] Further details and aspects of the light emitting device 300 will be mentioned in connection with the proposed concept or one or more of the examples described above (for example Fig. 1 to 2). The light emitting device 300 may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0048] Fig. 4 shows a schematic cross-section of a light emitting device 400. The light emitting device 400 can be similar to that described in connection with Fig. 1. The light emitting device 400 comprises a heater structure (e.g., a light-emitting structure) 140 configured to emit light when a predefined current flows through the heater structure 140. The heater structure is arranged on a heater support structure 130. The light emitting device 400 comprises an upper portion 120 of a cavity arranged vertically between the heater support structure 130 and a cover structure 160 comprising an optical filter structure. The light emitting device 400 comprises a lower portion 150 of the cavity arranged vertically between the heater support structure 130 and at least a portion of a support substrate 110. The light emitting device 400 further comprises a reflector structure 170 arranged between the lower portion 120 of the cavity and the support substrate 110. Fig. 4 can show a schematic cross-section of a backside filter on a silicon substrate as a pure micromechanically manufactured surface design.

[0049] Further details and aspects of the light emitting device 400 are mentioned in connection with the proposed concept or one or more of the previously described examples (for example Fig. 1 to 3). The light emitting device 400 may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0050] Fig. Figure 5 shows a reflectivity diagram of a back reflector on a silicon substrate (made of silicon and air or vacuum) with an average reflectivity of 97.7% (at a wavelength of 1 to 10 micrometers). The back reflector can be implemented similarly to a reflector structure used in conjunction with one of the Fig. 1, Fig. 3 and Fig. 4. The diagram shows a reflectivity (on a scale of 0 to 1) on the y-axis and a wavelength in micrometers on the x-axis. Graph 502 shows a reflectivity of a multilayer reflector structure for a wavelength range between 1 µm and 10 µm. The multilayer reflector structure of Fig. 5 comprises 5 silicon layers, each with a thickness between 200 and 1000 nm and 5 cavity layers comprising air, each with a thickness between 400 nm and 1000 nm.

[0051] Further details and aspects of the reflector (structure) are mentioned in connection with the proposed concept or one or more of the examples described above (for example Fig. 1 to 4). The reflector (structure) 130 may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0052] Fig. Figure 6 shows a schematic cross-section of a (linear, non-dispersive) gas sensor device 600. The gas sensor device 600 comprises a (broadband) infrared source 602 (e.g. a light emitting device as used in conjunction with one of the Fig. 1, Fig. 3 and Fig. 4), a lens 604, a measuring chamber 606 with a gas inlet 608 and a gas inlet 610, dual filter 612 and a dual element detector 614. Fig. Figure 6 may show a schematic diagram of a linear, non-dispersive gas sensor with an optical path length in the range of centimeters.

[0053] Further details and aspects of the gas sensor device 600 are mentioned in connection with the proposed concept or one or more of the examples described above (for example Fig. 1 to 5). The gas sensor device 600 may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0054] Fig. 7 shows a flowchart of a method 700 for forming a light emitting device. The method includes forming 710 a patterned sacrificial layer over a heater support structure 130. A heater structure 140 is arranged on the heater support structure 130. The method includes forming 720 an insulation layer on the patterned sacrificial layer. The method includes removing 730 a portion of the insulation layer until the patterned sacrificial layer is exposed to obtain a smooth surface. The method includes forming 740 a cover structure on the smooth surface. The method includes forming 750 at least one hole through the cover structure to the patterned sacrificial layer. The method includes removing 760 the patterned sacrificial layer to obtain a cavity between the heater support structure 130 and the cover structure.The method includes sealing 770 the at least one hole at an ambient pressure of less than 100 mbar (or less than 10 mbar, less than 1 mbar, less than 0.1 mbar, less than 0.01 mbar).

[0055] The method 700 may enable the light emitting device to be formed such that the cavity has a pressure of less than 100 mbar, enabling improved thermal insulation between the heater structure and walls of the cavity.

[0056] For example, forming 710 the patterned sacrificial layer may include forming an unpatterned sacrificial layer, e.g., depositing the unpatterned sacrificial layer, and subsequently patterning the unpatterned sacrificial layer to obtain the patterned sacrificial layer. For example, patterning the unpatterned sacrificial layer may include removing portions of the unpatterned sacrificial layer based on a mask configured to shield portions of the sacrificial layer from an etching process. For example, the patterned sacrificial layer may be carbon-based and / or comprise carbon (chemical symbol C).

[0057] For example, forming 720 the insulation layer may comprise depositing the insulation layer onto the patterned sacrificial layer. For example, the insulation layer may comprise silicon oxide. For example, the insulation layer may be formed with a thickness at least 50% (or at least 80%, at least 100%, at least 150%) greater than a thickness of the patterned sacrificial layer, enabling a subsequent chemical mechanical polishing step.

[0058] For example, a portion of the insulation layer may be removed by chemical mechanical polishing the insulation layer until the patterned sacrificial layer is exposed to obtain the smooth surface. The chemical mechanical polishing may enable the formation of the smooth surface, which may enable formation of a substantially planar cap structure. For example, the chemical mechanical polishing may use the exposure of the patterned sacrificial layer as a trigger to stop the chemical mechanical polishing. For example, removing 730 the portion of the insulation layer may further comprise removing a portion of the patterned sacrificial layer, e.g., a portion of the patterned sacrificial layer that extends farther from the carrier substrate than the insulation layer after removing the portion of the insulation layer.For example, the smooth surface may correspond to a surface formed by a remaining portion of the insulating layer (after removal 730 of the insulating layer portion) and (a remaining portion of) the patterned sacrificial layer (e.g., after removal of a portion of the patterned sacrificial layer during removal 730 of the insulating layer portion). For example, a level of the smooth surface (a height / thickness of the front surface of the light-emitting device at the smooth surface) may deviate vertically by less than 2 µm (or less than 1 µm, less than 500 nm, less than 200 nm) across the smooth surface.

[0059] For example, forming 740 the cap structure may include depositing or attaching one or a plurality of layers (e.g., semiconductor layers or metal layers) onto the insulation layer and the patterned sacrificial layer. Forming 740 the cap structure may include forming an optical filter structure (e.g., as shown in Fig. 10).

[0060] For example, forming 750 the at least one hole may comprise etching the at least one hole through the cover structure. For example, if the cover structure (e.g., an optical filter structure) comprises a plurality of semiconductor layers and a plurality of sacrificial / insulating layers (e.g., silicon layers and carbon and / or silicon oxide layers), forming 750 the at least one hole may comprise etching the at least one hole through a mutual etching process using the same etchant as used to etch the plurality of semiconductor layers and the plurality of sacrificial layers / the plurality of insulating layers. For example, forming the at least one hole may comprise a hole with a diameter of more than 100 nm (or more than 200 nm, more than 500 nm) and less than 5 µm (or less than 2 µm, less than 1 µm, less than 750 nm).

[0061] The method includes removing 760 the patterned sacrificial layer to obtain a cavity between the heater support structure 130 and the cover structure. For example, removing 760 the patterned sacrificial layer may comprise etching the patterned sacrificial layer, e.g., using a dry etching process and / or an isotropic etching process. For example, if the patterned sacrificial layer is carbon-based, removing 760 the patterned sacrificial layer may comprise plasma etching (e.g., using an oxygen plasma) of the patterned sacrificial layer. For example, removing 760 the patterned sacrificial layer may remove the patterned sacrificial layer and a plurality of sacrificial layers of the optical filter structure (used as a cover structure) using a mutual etching process, e.g., using the same etchant.For example, the resulting cavity may correspond to an upper portion of a cavity, as shown in . Fig. 1 is shown.

[0062] For example, the method may further comprise forming the heater support structure 130. For example, forming the heater support structure may include depositing an unstructured heater support structure and structuring the unstructured heater support structure (e.g., a plurality of holes extending through the heater support structure) to obtain the heater support structure. For example, the heater support structure may comprise a single layer (e.g., a single insulating layer). For example, the heater support structure may comprise or be insulating material, e.g., an oxide (e.g., silicon oxide, SiO2) or a nitride (e.g., silicon nitride (Si 3 N 4)). For example, the method may further comprise forming a further cavity (e.g., into the carrier substrate or between walls of insulating material) and forming a sacrificial layer in the further cavity. Forming the heater support structure 130 may form the heater support structure at least on the sacrificial layer such that the heater support structure laterally overlaps the sacrificial layer. Alternatively, forming the heater support structure may form the heater support structure (directly) on a carrier substrate.

[0063] For example, the method may comprise forming (e.g., etching) a cavity beneath the heater support structure (e.g., a lower portion of a cavity, further comprising the cavity between the heater support structure and the cover structure as an upper portion of the cavity, as described in connection with Fig. 1), before forming the patterned sacrificial layer or after removing the patterned sacrificial layer. The cavity under the heater support structure (e.g., a lower portion of a cavity, as in Fig. 1) may improve insulation between the heater structure and the walls of the cavity. For example, forming the cavity under the heater support structure may comprise etching the cavity under the heater support structure through a plurality of holes extending vertically through the heater support structure (e.g., as described in connection with Fig. 1). For example, forming the cavity under the heater support structure 130 (e.g., by an (isotropic) etching process) may form the cavity under the heater structure 130 into the support substrate. Alternatively, forming the cavity under the heater substrate may comprise removing (e.g., by an ashing process) a sacrificial layer (e.g., carbon) contained in the cavity under the heater support structure 130. For example, forming the cavity under the heater support structure may use the heater support structure as a mask during an etching process (e.g., in a Venetian etching process). For example, forming the cavity under the heater support structure may be implemented similarly to removing 760 the patterned sacrificial layer.

[0064] For example, the method may further comprise forming (e.g., depositing and patterning) the heater structure and / or a heater wiring structure. For example, the heater structure may comprise polysilicon or a (highly doped) monocrystalline silicon.

[0065] For example, sealing 770 the at least one hole may comprise depositing an oxide layer by a high-density plasma deposition process to seal the at least one hole. For example, sealing 770 the at least one hole may form a (silicon) oxide layer over (all or part of) the cap structure. Sealing 770 the at least one hole may seal the at least one hole by forming (e.g., depositing using high-density plasma) a sealing layer (e.g., a (silicon) oxide or a (silicon) nitride) that seals the at least one hole.

[0066] Further details and aspects of the method 700 will be mentioned in connection with the proposed concept or one or more of the examples described above (for example, Fig. 1 to 6). The method 700 may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0067] Fig. Figure 8 shows a schematic cross-section of an optical filter structure 800 (e.g., an optical bandpass filter structure). For example, the optical filter structure may be implemented similarly to an optical filter structure as described in connection with Fig. 1. The optical filter structure comprises a plurality of semiconductor layers 802 (e.g., silicon layers) of a filter layer stack. The optical filter structure comprises a plurality of cavity layers 804 of the filter layer stack, which are arranged / positioned alternately (vertically) to the semiconductor layers of the plurality of semiconductor layers. A thickness of the semiconductor layers of the plurality of semiconductor layers is less than 2 µm (or less than 1.5 µm, less than 1 µm, less than 0.8 µm) and a thickness of the cavity layers of the plurality of cavity layers is less than 4 µm (or less than 3 µm, less than 2 µm, less than 1.5 µm, less than 1 µm, less than 0.8 µm), such that light passing through the filter layer stack has a spectral maximum at a desired optical wavelength.

[0068] A multilayer optical filter structure comprising a plurality of cavity layers may provide a construction of optical (bandpass) filters with improved filtering properties at a reduced thickness, enabling more compact dimensions of a light emitting device, for example.

[0069] For example, the plurality of semiconductor layers 802 may include fewer than 15 (or fewer than 12, fewer than 10, fewer than 8) semiconductor layers. The plurality of semiconductor layers 802 may include more than 4 (or more than 6, more than 8) semiconductor layers. For example, one cavity layer of the plurality of cavity layers 804 may be arranged (directly, vertically) adjacent to two adjacent semiconductor layers of the plurality of semiconductor layers 802. For example, one semiconductor layer of the plurality of semiconductor layers 802 may be arranged (directly, vertically) adjacent to at least one cavity layer of the plurality of cavity layers 804. For example, a pressure within the plurality of cavity layers may be less than 100 mbar (or less than 10 mbar, less than 1 mbar, less than 0.1 mbar, less than 0.01 mbar).Using a low pressure (or near vacuum) within the plurality of cavity layers can further improve the optical properties of the optical filter structure. For example, a (quasi-)vacuum can be formed in the plurality of cavity layers 804. For example, the plurality of cavity layers 804 can be mutually connected. For example, a gas pressure in the plurality of cavity layers 804 can be greater than 0.001 mbar or greater than 0.01 mbar. The plurality of cavity layers 804 can be filled with air or with a gas that has a lower thermal conductivity than, e.g., air (e.g., radon, xenon, or argon). For example, the plurality of cavity layers 804 can be connected to a cavity of a light emitting device (e.g., as introduced in connection with. Fig. 1) which comprises an optical filter structure.

[0070] For example, the optical filter structure may further include a plurality of semiconductor pillars (pillars) connecting adjacent layers of the plurality of semiconductor layers 802 and extending through the cavity layers of the plurality of cavity layers 804 disposed between the adjacent semiconductor layers of the plurality of semiconductor layers. For example, one semiconductor pillar of the plurality of semiconductor pillars may be connected to at least two (or at least 3, at least 4, at least 8) of the semiconductor layers of the plurality of semiconductor layers. For example, one semiconductor pillar of the plurality of semiconductor pillars may be connected to all of the semiconductor layers of the plurality of semiconductor layers 802.For example, a semiconductor pillar of the plurality of semiconductor pillars may be formed to connect adjacent semiconductor layers of the plurality of semiconductor layers 802. For example, the plurality of semiconductor pillars may penetrate the plurality of semiconductor layers. For example, a semiconductor pillar of the plurality of semiconductor pillars may have a plurality of subsections arranged within the plurality of cavity layers 804. For example, the plurality of subsections may laterally overlap (e.g., at least partially share a common lateral position at vertically different cavity layers of the plurality of cavity layers). The plurality of pillars may stabilize and hold the plurality of semiconductor layers 802 apart. For example, a (maximum or average) lateral distance between the semiconductor pillars (e.g.,adjacent columns) of the plurality of semiconductor columns may be less than 150 µm (or less than 100 µm, less than 80 µm) and / or greater than 110 µm (greater than 20 µm, greater than 30 µm, greater than 40 µm). For example, the plurality of semiconductor columns may be arranged in a grid or a plurality of rows of semiconductor columns. For example, each row of semiconductor columns may comprise two or more semiconductor columns of the plurality of semiconductor columns. For example, a (maximum or average) lateral distance between the plurality of rows (e.g., adjacent rows) of semiconductor columns may be less than 150 µm (or less than 100 µm, less than 80 µm). For example, a (maximum or average) lateral distance between adjacent semiconductor pillars in a row of semiconductor pillars may be less than 150 µm (or less than 100 µm, less than 80 µm).

[0071] To build a mechanically stable filter, a structure of silicon pillars can be used. These pillars can be placed on the patterned oxide layer (e.g., the heater support structure shown in Fig. 2) and can penetrate the bandpass filter. Due to their distance of several tens of micrometers, they could (only) negligibly modify the simulated transmission spectrum.

[0072] Further details and aspects of the optical filter structure 800 will be mentioned in connection with the proposed concept or one or more of the previously described examples (for example Fig. 1 to 7). The optical filter structure 800 may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0073] Fig. Figure 9 shows a diagram of the transmissivity of an optical (multilayer) filter structure on a silicon substrate (fabricated from silicon and vacuum). An example infrared filter stack can be calculated using silicon and vacuum for alternating optical layers. The thicknesses of individual layers are well within the processing capabilities of state-of-the-art layer deposition and etching. For example, a dry-etchable sacrificial layer, such as carbon, can be used. Fig. Figure 9 shows a simulated transmission spectrum 902 for a silicon / vacuum layer stack - enhanced for the carbon dioxide absorption band (roughly at 4.2 to 4.4 micrometers). Fig. 9 may further show a spectrum of an IR transmission filter (with a target peak at 4.3 micrometers). The x-axis shows a wavelength in micrometers, the y-axis shows a transmissivity. Graph 902 shows a transmissivity of an optical filter structure comprising a plurality of semiconductor (silicon) layers and a plurality of cavity (vacuum) layers for different wavelengths, with a main transmissivity peak of >0.8 at wavelengths between 4.2 µm and 4.4 µm.

[0074] Further details and aspects of the optical filter structure will be mentioned in connection with the proposed concept or one or more of the examples described above (for example Fig. 1 to 8). The optical filter structure may have one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0075] Fig. 10 shows a flowchart of a method 1000 for forming an optical filter structure. For example, the optical filter structure may be implemented similarly to an optical filter structure used in conjunction with at least one of Fig. 1 and Fig. 8. The method 1000 for forming the optical filter structure may be implemented similarly to a method for forming the light emitting device described in connection with Fig. 7. The method 1000 comprises forming 1010 a plurality of semiconductor layers (e.g., silicon layers) and a plurality of sacrificial layers (e.g., carbon layers) of an interlayer stack. The plurality of sacrificial layers are arranged / positioned alternately with the semiconductor layers of the plurality of semiconductor layers. The method 1000 further comprises forming 1020 at least one hole through the interlayer stack to at least a lowermost sacrificial layer of the plurality of sacrificial layers. The method 1000 comprises removing 1030 the plurality of sacrificial layers to obtain a filter layer stack comprising the plurality of semiconductor layers and a plurality of cavity layers arranged / positioned alternately with the semiconductor layers of the plurality of semiconductor layers.A (maximum or average) thickness of the semiconductor layers of the plurality of semiconductor layers is less than 2 µm (or less than 1.5 µm, less than 1 µm, less than 0.8 µm) and a (maximum or average) thickness of the cavity layers of the plurality of cavity layers is less than 4 µm (or less than 3 µm, less than 2 µm, less than 1.5 µm, less than 1 µm, less than 0.8 µm), so that light passing through the filter layer stack has a spectral maximum at a desired optical wavelength.

[0076] The method may enable the formation of the optical filter structure with a plurality of cavity layers, enabling a construction of optical (bandpass) filters with improved filtering properties at a reduced thickness.

[0077] For example, forming 1010 the plurality of semiconductor layers and the plurality of sacrificial layers may comprise alternately depositing (individual) semiconductor layers of the plurality of semiconductor layers and depositing (individual) sacrificial layers of the plurality of sacrificial layers. For example, forming 1010 the plurality of semiconductor layers and the plurality of sacrificial layers may comprise forming a first semiconductor layer of the plurality of semiconductor layers, forming a sacrificial layer of the plurality of sacrificial layers on the first semiconductor layer, and forming a second semiconductor layer of the plurality of semiconductor layers on the sacrificial layer (and repeating the formation of the sacrificial layer and the second semiconductor layer until the plurality of semiconductor layers and the plurality of sacrificial layers are formed). For example, the plurality of sacrificial layers may be carbon-based, e.g., may be carbon.

[0078] For example, forming 1020 the at least one hole may include etching the at least one hole through a mutual etching process using the same etchant as used to etch the semiconductor layers and to etch the sacrificial layers. The mutual etching process may reduce a number of processing steps required to fabricate the optical filter structure. For example, the etchant may be configured / selected to etch both semiconductor layers of the plurality of semiconductor layers and sacrificial layers of the plurality of sacrificial layers.

[0079] For example, removing 1030 the plurality of sacrificial layers may include etching the plurality of sacrificial layers, e.g., using a dry etching process and / or an isotropic etching process. For example, if the plurality of sacrificial layers are carbon-based, removing 1030 the plurality of sacrificial layers may include plasma etching (e.g., using an oxygen plasma) of the plurality of sacrificial layers. For example, the interlayer stack may become the filter layer stack after removing the plurality of sacrificial layers.

[0080] For example, the method may further comprise sealing the at least one hole by forming (e.g., depositing using high-density plasma) a sealing layer (e.g., a (silicon) oxide or a (silicon) nitride) that seals the at least one hole. Sealing the at least one hole may comprise depositing an oxide layer by a high-density plasma deposition process. Sealing the at least one hole may comprise fabricating the optical filter structure having a plurality of cavity layers at a pressure of less than 100 mbar (or less than 10 mbar, less than 1 mbar, less than 0.1 mbar, less than 0.01 mbar). For example, sealing the at least one hole may seal the at least one hole at an ambient pressure of less than 100 mbar (or less than 10 mbar, less than 1 mbar, less than 0.1 mbar, less than 0.01 mbar).For example, a pressure within the plurality of cavity layers may be less than 100 mbar (or less than 10 mbar, less than 1 mbar, less than 0.1 mbar, less than 0.01 mbar) after sealing the at least one hole. For example, the at least one hole may correspond to at least one hole as described in connection with . Fig. 7. For example, sealing the at least one hole may seal the at least one hole of the optical filter structure and the light emitting device of Fig. 7 seal.

[0081] Further details and aspects of the method 1000 for forming the optical filter structure are mentioned in connection with the proposed concept or one or more of the previously described examples (for example Fig. 1 to 10). The method 1000 for forming the optical filter structure may include one or more additional optional features corresponding to one or more aspects of the proposed concept or one or more examples described above or below.

[0082] Examples may provide an emitting unit (e.g., a light emitting device) for infrared light with a defined spectral distribution.

[0083] A constantly growing number of publications and concepts deal with the detection and characterization of chemicals in gases and other fluids. The progressive miniaturization of components in these measurement systems is paving the way for the opening of new markets.

[0084] A prominent example may be the measurement of carbon dioxide concentrations in enclosed environments. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) provided some insight into the role of demand-controlled ventilation for buildings. "Carbon dioxide-based demand-controlled ventilation... could potentially become as widespread as thermostatic control is today..."

[0085] Measurements of carbon dioxide concentration in a ventilated room as a function of time with ventilation rate as a parameter can detect the build-up of CO 2 in buildings and vehicles over time. In buildings, with a ventilation rate of 3.5 l / s per person, a concentration of CO 2increase steadily over time and exceed 2500 ppm (parts per million) over time. At a ventilation rate of 7.5 l / s and 15 l / s, an equilibrium of carbon dioxide can be established at approximately 1000 ppm and / or 750 ppm. In vehicles (based on measurements of carbon dioxide concentration in a luxury car with stopped ventilation as a function of time, occupancy as a parameter), the carbon dioxide level can also increase over time, approaching 10000 ppm with 4 people in the vehicle after 2000s of seconds (or 8000 ppm with 3 people, 6000 ppm with 2 people, and 4000 ppm with 1 person).

[0086] Acceptable CO2 levels are in the range of 600 ppm. Symptoms of stiffness and odors occur between 600 and 1000 ppm, and general drowsiness is associated with the range of 1000 and 2500 ppm. For example, carbon dioxide concentration in vehicles makes ventilation a safety concern. On the other hand, fuel efficiency can be one of the driving factors in vehicle automation. Studies estimate a reduction in fuel consumption of up to 0.9 l / 100 km when sensor-controlled on-demand ventilation is used instead of conventional ventilation systems.

[0087] Heating in residential and public buildings is a major contributor to carbon dioxide emissions in temperate countries. In Germany, the associated energy consumption is currently approximately 7000 kWh per person per year. This may correspond to carbon dioxide emissions of approximately 3.5 tons (assuming oil or natural gas as the main energy source). Although heating buildings may only account for one-third of total energy consumption in Germany, carbon dioxide emissions for heating buildings are already well above the level of 2 tons per person per year, which is acceptable in light of global warming. Reducing the effort required to heat buildings may be linked to gas-tight construction and demand-controlled ventilation as a basis for efficient thermal insulation.

[0088] There may be a need for sensor-driven air quality management. There are at least two sensing approaches that are promising candidates for widespread use in buildings: non-dispersive infrared (NDIR) sensing systems and photoacoustic sensors. While both systems demonstrate sufficient resolution and key performance parameters, some improvements may be needed, e.g., with regard to sensor dimensions, power consumption, and cost.

[0089] Non-dispersive infrared CO 2 -Sensor systems (NDIR): In recent decades, a wide range of sensing principles for gas detection have been investigated. From this variety, optical sensing, as used in non-dispersive infrared (NDIR) CO 2 sensors, provide long-term stability and cross-response to other gas types. Fig. Figure 6 shows a schematic diagram of a linear, non-dispersive gas sensor with an optical path length in the range of centimeters.

[0090] One of the targeted research topics for NDIR sensors has potentially been the improvement and reduction of the optical path lengths required for carbon dioxide detection in the 100 ppm range. Some studies have shown individual components of NDIR sensors as integrated parts of a silicon chip. In principle, all components have been demonstrated separately as silicon chips. However, the improved use of silicon's physical properties with regard to infrared waveguiding and spectral filtering is rarely utilized in more than one component.

[0091] Reducing the system dimensions and overall power consumption of infrared emitters can be a key challenge toward monolithically integrated gas sensors. Improved thermal insulation and filtering can be used in some examples.

[0092] Examples may include an emitting unit (e.g., a light emitting device 100 of Fig. 1) for infrared light with a defined spatial and spectral distribution. At least some examples can combine an integrated infrared emitter and a spectral filter as a single unit for emitting a spectrum of choice. This unit can be (at least partially) thermally isolated from the surrounding material by evacuated cavities. The main components can be shown in Fig. 1, Fig. 3 and / or 4. As shown in Fig. 1, Fig. 3 and / or 4, for example, the infrared light emitter can be placed directly in a trap (e.g., a cavity) that primarily allows a spectrum of choice to pass through a filter sandwich. A structured support (e.g., a heater support structure 130 made of Fig. 1) can be used to reduce thermal losses.

[0093] At least some examples provide an infrared-emitting device that combines an emitter and a bandpass filter in a manner that can result in reduced thermal and radiation losses. An evacuated cavity can surround the emitter (e.g., the heater structure). The filter (e.g., the optical filter structure or the cover structure) can be used to seal the cavity. In this way, a structured support can be used, which can reduce lateral thermal conductivity.

[0094] At least some examples provide an infrared-emitting device (e.g., the light-emitting device) with an integrated bandpass filter (optical filter structure) on a silicon substrate (support substrate). At least some examples provide a patterned support layer (heater support structure) for reducing lateral thermal losses. At least some examples may include a backside reflector (reflector structure) for improved emission efficiency, e.g., fabricated from a silicon / air stack. Some examples may include pillar mounting of a filter stack on an oxide support.

[0095] The examples shown above can be designed such that parts are omitted, such as an emitting unit without a filter system. Furthermore, other elements can be combined. One example is a back reflector on the silicon substrate, as shown in Fig. 4 is shown.

[0096] The aspects and features mentioned and described together with one or more of the examples and figures described in detail above may further be combined with one or more of the other examples to replace a similar feature of the other example or to additionally incorporate the feature into the other example.

[0097] The description and drawings only illustrate the principles of the disclosure. Furthermore, any examples provided herein are expressly intended to be for educational purposes only to assist the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to advance the art. All statements herein regarding principles, aspects, and examples of the disclosure, as well as specific embodiments thereof, are intended to include equivalents thereof.

[0098] Furthermore, it should be understood that the disclosure of multiple steps, processes, operations, procedures, or functions disclosed in the specification or claims should not be construed as being in that particular order unless explicitly or implicitly stated otherwise, e.g., for technical reasons. Therefore, the disclosure of multiple steps or functions does not limit them to a particular order unless those steps or functions are not interchangeable for technical reasons. Furthermore, in some examples, a single step, function, process, or procedure may include or be broken down into multiple sub-steps, functions, processes, or procedures. Such sub-steps may be included and be part of the disclosure of that single step unless expressly excluded.

Claims

[1] A light emitting device (100; 300; 400) comprising: a heater structure (140) configured to emit light when a predefined current flows through the heater structure (140), wherein the heater structure is arranged on a heater support structure (130); an upper portion (150) of a cavity disposed vertically between the heater support structure (130) and a cover structure (160); a lower portion (120) of the cavity disposed vertically between the heater support structure (130) and at least a portion of a support substrate (110); an optical filter structure configured such that light passing through the optical filter structure has a spectral maximum at a desired optical wavelength when the optical filter structure is implemented through the cover structure (160) or is arranged between the lower portion (120) of the cavity and a back surface of the light emitting device (100; 300; 400), wherein the optical filter structure comprises a plurality of semiconductor layers of a filter layer stack and a plurality of insulating layers or cavity layers of the filter layer stack arranged alternately; and Side walls of the upper section (150) and the lower section (120), wherein side walls of the upper section (150) or the lower section (120) on which the filter structure is arranged are formed by an oxide layer, wherein the heater support structure (130) comprises a plurality of holes connecting the upper portion (150) of the cavity and the lower portion (120) of the cavity, and wherein a pressure in the cavity is less than 100 mbar. [2] The light emitting device according to claim 1, wherein the plurality of holes are arranged and formed such that from a center of the heater support structure to a nearest edge of the heater support structure, a path along the heater support structure is at least 20% longer than a direct straight path from the center of the heater support structure to the nearest edge of the heater support structure. [3] The light emitting device according to any one of the preceding claims, wherein the plurality of holes has an elongated lateral shape. [4] The light emitting device according to any one of the preceding claims, wherein the plurality of holes are arranged in a plurality of rows of holes, wherein the plurality of rows of holes are separated by a plurality of strips of the heater support structure arranged laterally parallel to the plurality of rows of holes, and wherein a width of the holes of a row of the plurality of rows of holes arranged between two adjacent strips of the plurality of strips is less than 60% of a width of each of the two adjacent strips. [5] The light emitting device according to claim 4, wherein holes of adjacent rows of the plurality of rows of holes have a lateral offset of more than 20% of a length of a hole of the adjacent rows of holes. [6] The light emitting device according to any one of the preceding claims, wherein the heater support structure (130) extends in a first lateral direction and in a second lateral direction, the second lateral direction being orthogonal to the first lateral direction, and wherein the heater support structure (130) is connected to walls of the cavity on both sides in the first lateral direction and on both sides in the second lateral direction. [7] The light emitting device according to any one of the preceding claims, further comprising a reflector structure configured to reflect at least 70% of the light within a desired spectral range emitted toward the reflector structure by the heater structure. [8] The light emitting device according to claim 7, wherein the reflector structure is arranged on a back side of the carrier substrate or is implemented by the cover structure (160). [9] The light emitting device according to one of claims 7 or 8, wherein the reflector structure comprises a plurality of semiconductor layers of a reflector layer stack and a plurality of insulation layers or cavity layers of the reflector layer stack arranged alternately with the semiconductor layers of the plurality of semiconductor layers. [10] The light emitting device according to any one of the preceding claims, further comprising a heater wiring structure connecting the heater structure (140) to a contact pad structure or a heater driver circuit, wherein portions of the heater wiring structure disposed on the heater support structure (130) have a resistivity of less than 50% of a resistivity of the heater structure. [11] The light emitting device according to any one of the preceding claims, further comprising a heater driver circuit configured to provide the predefined current to the heater structure to cause light emission by the heater structure, wherein the heater driver circuit is implemented on the carrier substrate. [12] A method (700) of forming a light emitting device, the method comprising: Forming (710) a patterned sacrificial layer over a heater support structure (130), wherein a heater structure (140) is arranged on the heater support structure (130); forming (720) an insulating layer on the patterned sacrificial layer; removing (730) a portion of the insulation layer until the patterned sacrificial layer is exposed to obtain a smooth surface; Forming (740) a cover structure on the smooth surface, wherein forming (740) the cover structure comprises forming an optical filter structure (800); Forming (750) at least one hole through the cover structure to the patterned sacrificial layer; Removing (760) the structured sacrificial layer to obtain a cavity between the heater support structure (130) and the cover structure; and Sealing (770) the at least one hole at an ambient pressure of less than 100 mbar. [13] The method of forming the light emitting device according to claim 12, wherein the portion of the insulating layer is removed by chemical mechanical polishing of the insulating layer until the patterned sacrificial layer is exposed to obtain the smooth surface.

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