Patent Description:
The sensing of environmental parameters in the ambient atmosphere, such as sound, noise, temperature, gases, etc., with MEMS-based devices gains more and more importance in the implementation of appropriate sensors within mobile devices, home automation, such as smart-home, and the automotive sector.

In gas sensor systems based on the photoacoustic principle, for example, a broad-band radiator in the infrared range (e.g. <NUM> to <NUM>) is required for exciting gas molecules of different types. In PAS sensor systems (PAS = photoacoustic spectroscopy), planar, non-insulated radiators are generally used for generating the required excitation lines. However, only a small amount of the electrical power is transferred into the emitted optical power (optical energy).

A further application case is a radiation heater used for inducing thermal phase transitions in phase transition materials, such as GeSbTe (GST). For generating the phase transition in GST materials, usually a tungsten heater is used which is in direct contact to the material. This has a negative impact on the potentially achievable cooling rate and, thus, on the amorphization of the GST material.

<CIT> relates to mid-infrared (MIR) hyperspectral spectroscopy systems and method thereof. The MIR spectroscopy systems comprise a hierarchical spectral dispersion. The hierarchical spectral dispersion is derived by employing at least two diffractive lens arrays, located on either side of a test sample, each receiving input radiation having an input spectral range and distributing the input radiation into a plurality of output signals, each having a fraction of the spectral range of the input radiation. As a result, the signal multiplication factor of the two arrays is multiplied in a manner that mitigates the propagation of wavelength harmonics through the system.

<CIT> relates to an infrared incandescent lamp. The infrared incandescent electric lamps have an oval-shaped quartz envelope, with two parallel tungsten filaments, extending the length of the lamp, and are mounted within said envelope.

XP <NUM><NUM><NUM> relates to electrical and optical characteristics of vacuum-sealed polysilicon microlamps. The silicon-filament vacuum-sealed incandescent light source has been fabricated using IC technology and subsurface micromachining. The incandescent source consists of a heavily doped p+ polysilicon filament coated with silicon nitride and enclosed in a vacuum-sealed cavity in the siliconchip surface. The filament is formed beneath the surface and later released using sacrificial etching to obtain a microstructure that is protected from the external environment. The filament is electrically heated to reach incandescence at a temperature near <NUM>.

Therefore, there is a need in the field of IR radiation sources to implement an IR radiation source having improved characteristics, e.g. an improved efficiency, when compared to current IR radiation sources.

Such a need can be solved by the IR radiation source according to independent claim <NUM>.

Further, specific implementations of the IR radiation source are defined in the dependent claims.

According to an embodiment, an IR (infrared) radiation source comprises the features according to claim <NUM>.

According to the IR radiation source with filament heating elements in a vacuum chamber, an increased efficiency can be achieved when compared to current IR radiation sources, wherein the IR radiation source according to the embodiments can be manufactured as an integrated application on a wafer, e.g. a Si wafer, wherein the manufacturing process is in principle CMOS compatible.

To be more specific, in case of a PAS sensor system, the suggested filament radiation heater comprises a high radiation yield when compared to the electrical power used, resulting in an increased efficiency.

When generating the phase transition in a GST material, the utilization of the suggested filament radiation heater allows a faster cooling rate of the material since the heat source and the GST material are spatially separated (spaced).

In the following, embodiments of the present disclosure are described in more detail with reference to the figures, in which:.

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

In the following description, embodiments are discussed in detail, however, it should be appreciated that the embodiments provide many applicable concepts that can be embodied in a wide variety of semiconductor devices. The specific embodiments discussed are merely illustrative of specific ways to make and use the present concept, and do not limit the scope of the embodiments. In the following description of embodiments, the same or similar elements having the same function have associated therewith the same reference signs or the same name, and a description of such elements will not be repeated for every embodiment. Moreover, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

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

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

<FIG> shows a schematic cross-sectional view of an IR (infrared) radiation source <NUM> according to an embodiment. The vertical schematic cross-sectional view is parallel to the x-z-plane (= vertical plane).

The IR radiation source <NUM> comprises a sealed cavity structure <NUM>, e.g. in form of an encapsulation structure, enclosing a vacuum chamber <NUM> having low atmospheric pressure, e.g. a low internal atmospheric pressure, such as a near vacuum condition. The sealed cavity structure comprises a thermally and electrically insulating material <NUM>, <NUM> or a corresponding material combination for enclosing, such as encapsulating and sealing, the vacuum chamber <NUM>.

The IR radiation source <NUM> further comprises a plurality of heating filaments <NUM> extending in the vacuum chamber <NUM> between opposing electrode regions <NUM>, <NUM> at opposing wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>. According to the embodiment, the heating filaments <NUM> are electrically connected in parallel, wherein the heating filaments <NUM> and the electrode regions <NUM>, <NUM> have a highly electrically conductive material. The highly electrically conductive material of the heating filaments <NUM> and the electrode regions <NUM>, <NUM> may comprise a specific electrical resistance (= electrical resistivity) below <NUM> mOhm cm, e.g. between <NUM> mOhm cm and <NUM>,<NUM> mOhm cm.

The IR radiation source <NUM> further comprises an optical isolation structure <NUM> adjacent to the vacuum chamber <NUM> (and the sealed cavity structure <NUM>) for optically confining the IR radiation and providing a predominant propagation direction of the IR radiation <NUM>.

To be more specific, the optical isolation structure <NUM> may be arranged adjacent (e.g. parallel) to at least one, to a plurality or to all side wall regions <NUM>-<NUM>,. <NUM>-<NUM>, for example, of the vacuum chamber <NUM> for optically confining the IR radiation <NUM> generated by the IR radiation source <NUM> in an activated condition, i.e. in an energized condition of the heating filaments <NUM>, and for providing a predominant propagation direction of the IR radiation <NUM> in the sealed cavity structure <NUM> and for providing a predominant emission direction of the IR radiation <NUM> from the sealed cavity structure <NUM>.

In case, the vacuum chamber <NUM> comprises a rectangular footprint, the sealed cavity structure <NUM> and the vacuum chamber <NUM> may be regarded, for example, as a rectangular parallelepiped or cuboid having three pairs of opposing side faces or side wall regions <NUM>-<NUM>,. <NUM>-<NUM>. The opposing side wall regions <NUM>-<NUM>, <NUM>-<NUM> extend parallel to the x-y-plane, the opposing side wall regions <NUM>-<NUM>, <NUM>-<NUM> extend parallel to the y-z-plane, and the opposing side wall regions <NUM>-<NUM>, <NUM>-<NUM> extend parallel to the x-z-plane. However, as described below in further embodiments, the vacuum chamber <NUM> may comprise a rectangular, square, circular, elliptic, etc. footprint shape and comprises the correspondingly shaped side wall regions, wherein the heating filaments <NUM> are enclosed in sealed cavity structure <NUM>.

As exemplarily shown in <FIG>, the optical isolation structure <NUM> of the IR radiation source <NUM> may comprise at least one reflector element <NUM>-1a,. , <NUM>-<NUM> (= <NUM>-#) for optically confining the IR radiation <NUM> and providing a predominant propagation direction of the IR radiation <NUM>. Thus, the further reflector elements <NUM>-1a,. , <NUM>-<NUM>, as optionally shown in <FIG>, are only shown for illustrating the different implementation options of the optical isolation structure <NUM>, wherein the different isolation elements of the optical isolation structure <NUM>-1a,. , <NUM>-<NUM> are described below in more detail. According to an embodiment, the optical isolation structure may comprise (at least) one, a plurality or all reflector elements <NUM>-1a,. , <NUM>-<NUM> (as shown in <FIG>) for optically confining and/or directing the IR radiation <NUM>.

The reflector element <NUM>-1a may be formed as a cavity (optical reflector) in the insulating material layer <NUM> and is arranged adjacent and parallel to the first side wall region <NUM>-<NUM> of the vacuum chamber <NUM>. The reflector element <NUM>-1b may be formed as a metallization layer (optical reflector) on the insulating material layer <NUM> and is arranged adjacent and parallel to the first side wall region <NUM>-<NUM> of the vacuum chamber <NUM>.

The reflector element <NUM>-2a may be formed as a cavity (optical reflector) in the substrate <NUM> (or in the insulating material layer <NUM>) and is arranged adjacent and parallel to the second side wall region <NUM>-<NUM> of the vacuum chamber <NUM>. The reflector element <NUM>-2b may be formed as a metallization layer (optical reflector) on the substrate <NUM> or in the insulating material layer <NUM> and is arranged adjacent and parallel to the second side wall region <NUM>-<NUM> of the vacuum chamber <NUM>.

The reflector element <NUM>-<NUM> may be formed as a trench (optical reflector) in the insulating material layer <NUM> and is arranged adjacent and parallel (or inclined) to the third side wall region <NUM>-<NUM> of the vacuum chamber <NUM>. The reflector element <NUM>-<NUM> may be formed as a trench (optical reflector) in the insulating material layer <NUM> and is arranged adjacent and inclined (or parallel) to the fourth side wall region <NUM>-<NUM> of the vacuum chamber <NUM>.

The reflector element <NUM>-<NUM> (see for example <FIG>) may be formed as a trench (optical reflector) in the insulating material layer <NUM> and is arranged adjacent and parallel to the fifth side wall region <NUM>-<NUM> (parallel to the x-z-plane - see for example <FIG>) of the vacuum chamber <NUM>. The reflector element <NUM>-<NUM> (see for example <FIG>) may be formed as a trench (optical reflector) in the insulating material layer <NUM> and is arranged adjacent and parallel to the sixth side wall region <NUM>-<NUM> (parallel to the x-z-plane - see for example <FIG>) of the vacuum chamber <NUM>. Thus, the optical isolation structure <NUM> may comprise at least one of the cavities <NUM>-1a, <NUM>-2a, of the trenches <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and/or of the metal films <NUM>-1b, <NUM>-2b for defining the optical path of the generated IR radiation <NUM>.

Moreover, the IR radiation source <NUM> further comprises contact pads <NUM> and vias <NUM> for electrically connecting the top-electrode region <NUM> and comprises the contact pad <NUM> and the via <NUM> for contacting the opposing electrode region <NUM> (at opposing wall regions of the vacuum chamber <NUM>). The contact pads <NUM>, <NUM> may be provided for an external connectivity of the IR radiation source <NUM>. The contact pads <NUM>, <NUM> may be arrange in the same plane as the metallization layer <NUM>-1b.

As further shown in <FIG>, the IR radiation source <NUM> may be arranged on a substrate <NUM>, wherein the substrate <NUM> may comprise a semiconductor material, such as silicon, or a glass material, etc..

The present concept for implementing the IR radiation source <NUM> (radiation heater) results in a high efficient radiation heater <NUM> by using the heating filaments <NUM> of a material with a high melting point, wherein the material may comprise or consist of carbon, graphene, polysilicon or tungsten, for example. The arrangement of the heating filaments <NUM> in the vacuum chamber <NUM> of the sealed cavity structure <NUM> provides a thermal isolation of the heating filaments <NUM>. The material for the heating filaments <NUM> and the opposing electrode regions <NUM>, <NUM> (top and bottom electrodes) is highly electrically conducting and may be chosen to be transparent for the generated IR radiation in the energized condition of the heating filaments <NUM>.

The IR radiation source <NUM> using the plurality of heating filaments <NUM> allows the utilization of different materials for the heating elements <NUM>, i.e. the heating filaments <NUM>, between the opposing electrode regions <NUM>, <NUM>, resulting in an optimization of the characteristics of the IR radiation source <NUM>. Thus, the emission spectrum of the IR radiation source <NUM> may be optimized based on the same material used for the heating filaments <NUM> and the opposing electrode regions <NUM>, <NUM>. A high working temperature in the energized condition of the heating filaments <NUM>, e.g. by using carbon with a melting temperature TM = <NUM> at a good vacuum level (e.g. near vacuum) in the vacuum chamber <NUM> results in a high light intensity of the generated IR radiation <NUM>, for example.

The vertical arrangement of the heating filaments <NUM> between the opposing electrode regions <NUM>, <NUM> at opposing wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM> allows for an electrical parallel connection of the heating filaments <NUM> resulting in a relatively low operation voltage needed for operating the filaments <NUM>, such as to bring the filaments <NUM> in a glowing (= annealing or red heat) condition. Based on the specific arrangement of the IR radiation source <NUM>, a high light intensity (IR radiation intensity) at a reduced chip area can be achieved by the IR radiation heater <NUM> when compared to state of the art infrared heaters.

Furthermore, the modular layout of the IR radiation source <NUM> according to the embodiments is easy to adapt to specific applications, e.g. to PAS or GST applications. Furthermore, the manufacturing process of the IR radiation source <NUM> is easily integratable in a CMOS manufacturing process flow. Moreover, current CMOS manufacturing processes allow to achieve a high mechanical stability, a high temperature homogeneity and a high vacuum stability of the IR radiation source <NUM>.

To summarize, the IR radiation source <NUM> according to embodiments, provides a broad-band IR source with a high opto-electrical efficiency. Further, the structure and setup of the IR radiation source <NUM> allows to implement a manufacturing process which is compatible with current CMOS process flows.

The vertical current flow through the heating filaments <NUM> which have a high aspect ratio and are arranged in an electrical parallel connection by means of the top and bottom plate electrodes <NUM>, <NUM>, respectively, results in a compact device <NUM> with a high radiation density at a (relatively) low operating voltage.

Moreover, the materials for the heating filaments <NUM> may be selectively chosen to comprise a high melting point, a sufficient electrical conductivity, a CMOS process compatibility, and the possibility of having a high aspect ratio deposition. Exemplary materials for the heating filaments <NUM> are, for example, carbon, graphene, polysilicon or tungsten. The above indicated materials are suited for this application due their high melting point, low expansion coefficient and sufficient (high) conductivity, and their technological manufacturability in high aspect ratios and different/various geometries.

For providing a thermal isolation and a diffusion isolation (barrier) of the vacuum chamber <NUM> (filament cavity) of the sealed cavity structure <NUM>, an insulating material, such as silicon nitride (Si<NUM>N<NUM>) or titanium nitride (TiN) may be used, for example. These materials have a large band gap and a low thermal conductivity. Furthermore, these materials have a high density to (long-term) prevent hydrogen or oxygen diffusion into the vacuum chamber <NUM>. Furthermore, these materials have a low thermal expansion coefficient and are compatible to CMOS process flows.

The optical isolation structure <NUM> (with at least one reflection element <NUM>-#) may form a light pipe for confining the generated IR radiation <NUM> and providing a predominant propagation direction and emission direction of the generated IR radiation <NUM>. Thus, the optical isolation structure <NUM> may comprise at least one or a plurality of trenches, cavities and/or metal films for defining the optical path of the generated IR radiation <NUM>.

The IR radiation source <NUM>, which is implemented according to the different embodiments, uses the fact that the radiation yield increases by T<NUM> (Boltzmann Law), so that a material for the heating filaments <NUM> having a high melting point (temperature of destruction) contributes to a high IR radiation yield. The IR radiation emission of the heating filaments <NUM> is generated by the interaction between the current flow (electrons) through the heating filaments <NUM> and the material of the heating filaments <NUM>. Thus, a high current flow and a corresponding geometry in form of the heating filaments <NUM> favors and supports the IR radiation emission of the IR radiation source <NUM>. A relatively low temperature (i.e. a temperature as low as possible) in the connection area, i.e. at the opposing electrode regions <NUM>, <NUM>, may be achieved by the utilization of a highly electrically conductive material, e.g. with a specific electrical resistance (electrical resistivity) below <NUM> mOhm cm.

The resistance can be adjusted based on the material of and the geometry for the heating filaments <NUM> based on the Ohm's Law (R = ρ × I/A). Therefore, the opposing electrode regions <NUM>, <NUM> for parallel connecting the heating filaments <NUM> may comprise the highest possible conductivity (due to the same material as the heating filaments <NUM>, the same conductivity) and a relatively large area.

Moreover, the efficiency of the IR radiation source <NUM> is further increased as the annealing or glowing region, i.e. the vacuum chamber <NUM>, loses a very small amount of energy due to a very low heat conduction and heat convection to adjacent regions or the environment. Thus, the IR radiation source <NUM> allows due to its specific structure that essentially all or at least a predominant amount of the generated IR radiation is used and consumed for the intended utilization of providing and emitting the IR radiation <NUM> (and is not emitted and radiated in an unused way).

Moreover, the IR radiation source <NUM> allows for a high thermal stability and a manageable technological manufacturability.

Based on the design and the structure of the IR radiation source <NUM> according to the embodiments, the emitted radiation amount (radiation portion) is at high temperatures (red to yellow glowing heating elements <NUM>) very high and can be directed and bundled by the optical isolation structure <NUM>, such as by means of the optical reflectors <NUM>-# and optional further optical elements, such as lenses. Thus, the usable energy of the IR radiation source <NUM> is increased due to the reduced convection and heat conduction to adjacent regions. Moreover, the emitted radiation is minimally absorbed by materials (substances) outside the intended energy flow, thus resulting in reduced (low) convection losses. As a consequence, the present heater system in form of the IR radiation source <NUM> achieves a high system inertia, which results in a high threshold frequency (cut-off frequency) for on- and off-switching operations.

According to an embodiment, the heating filaments <NUM> and the electrode regions <NUM>, <NUM> comprise the same highly electrically conductive material having a melting temperature or melting point higher than <NUM>°, <NUM>° or <NUM>° Celsius. Thus, the conductive material of the heating filaments may comprise carbon, graphene, polysilicon or tungsten for providing the high annealing (soak) temperature.

According to to the present invention, the opposing electrode regions <NUM>, <NUM> of the heating filaments <NUM> are formed as plate electrodes. The heating filaments may have a length (between the opposing electrode regions) between <NUM> and <NUM> (or between <NUM> and <NUM>) and have an aspect ratio (diameter to depth) of <NUM>:<NUM> up to <NUM>:<NUM>. This corresponds to a thickness of the filaments <NUM> of about <NUM> to <NUM>. The spacing between the filaments <NUM> is in the range between <NUM> and <NUM>.

According to embodiments of the IR radiation source <NUM>, the IR radiation <NUM> is generated in or with the filaments <NUM> located in an evacuated cavity (the vacuum chamber) <NUM>, wherein the filaments <NUM> are connected by the top and bottom electrode <NUM>, <NUM> (= the opposing electrode regions <NUM>, <NUM>). Moreover, the electrode regions <NUM>, <NUM> are connected to contact pads <NUM>, <NUM> and vias <NUM>, <NUM> for an external connectivity.

According to an embodiment, the insulator material of the sealed cavity structure <NUM> is optically transparent to the IR radiation <NUM>, i.e. for the radiation <NUM> generated by the heating filament(s) <NUM> in an excitation condition in the vacuum chamber <NUM>.

According to an embodiment, the insulating material <NUM>, <NUM> of the sealed cavity structure <NUM> comprises a first insulating layer <NUM> having a silicon nitride material enclosing the vacuum chamber <NUM> of the sealed cavity structure <NUM>. The first layer <NUM> may have a thickness of at least <NUM>,<NUM>, e.g. between <NUM> and <NUM>.

According to an embodiment, the insulating material <NUM>, <NUM> of the sealed cavity structure <NUM> further comprises a second insulating layer <NUM> comprising a silicon dioxide material for enclosing the first layer <NUM>. The second layer <NUM> may have a thickness of at least <NUM>, e.g. between <NUM> and <NUM>.

According to an embodiment, the insulating material <NUM>, <NUM> of the sealed cavity structure <NUM> further comprises a third insulating layer <NUM>, e.g. a passivation layer, comprising a titanium nitride material. The third layer may have a thickness between <NUM> and <NUM>, e.g. about <NUM> nanometers.

Thus, according to embodiments, the thermal isolation of the vacuum chamber <NUM> and of the heating filaments <NUM> which are arranged therein, is achieved by a silicon oxide housing having a thickness of at least <NUM>.

Furthermore, according to an embodiment, the low atmospheric pressure in the vacuum chamber <NUM> comprises a cavity pressure less than <NUM> mbar (<NUM> Torr or <NUM> Pa) or less than <NUM> mbar (<NUM> Torr or <NUM> Pa). Thus, the vacuum in the vacuum chamber <NUM> may be in a range of <NUM> mbar or below and long-term stable. This can be achieved by the SiN encapsulation, wherein the SiN material (having a thickness of roughly <NUM>) is a diffusion barrier, even for hydrogen.

Thus, the vacuum chamber may comprise a reduced low atmospheric pressure (vacuum or near vacuum) with an atmospheric pressure of about or below <NUM> mbar or <NUM> mbar. The internal atmospheric pressure in the cavity chamber may, therefore, be in a range between <NUM> mbar and <NUM> mbar. The reduced atmospheric pressure in the vacuum chamber <NUM> may be achieved based on the process pressure during the position of the different layers for forming the sealed cavity structure <NUM> and sealing the vacuum chamber <NUM>, such that the cavity chamber has said reduced atmospheric pressure.

According to an embodiment, the optical isolation structure <NUM> forms an optical waveguide structure for providing an optical path with the predominant propagation direction of the IR radiation <NUM> in the sealed cavity structure <NUM>. According to an embodiment, the optical isolation structure may comprise optical reflector elements <NUM>-# for providing the optical path for the IR radiation <NUM> in the sealed cavity structure <NUM>.

According to an embodiment, the optical reflector elements <NUM>-# of the optical isolation structure <NUM> comprise a metallization layer adjacent to the side wall region of the sealed cavity structure <NUM>, and/or the optical reflector elements <NUM>-# of the optical isolation structure <NUM> may comprise a cavity in the substrate <NUM> or a trench in the insulating material <NUM>, <NUM> of the sealed cavity structure <NUM> or adjacent to the sealed cavity structure <NUM>.

According to an embodiment, the sealed cavity structure <NUM>, i.e. at least on optical reflector element <NUM>-# of the optical isolation structure <NUM>, is arranged on the substrate <NUM>, wherein the optical isolation structure <NUM> may be formed as a metallization layer on a surface region <NUM>-A of the substrate <NUM> adjacent to a side wall region of the sealed cavity structure <NUM>. Additionally or alternatively, the optical isolation structure <NUM>, i.e. at least one optical reflector element <NUM>-# of the optical isolation structure <NUM>, may be formed as a cavity in the substrate <NUM> adjacent to the side wall region of the sealed cavity structure <NUM>. According to an embodiment, the cavity <NUM>-# may be formed by means of a SON process (SON = silicon on nothing), which is also called as a venezia process, in the substrate <NUM> (semiconductor substrate or Si wafer) adjacent to the side wall region of the sealed cavity structure <NUM>.

According to an embodiment, the cavities of the optical isolation structure <NUM> may comprise a thickness of about <NUM> - <NUM>, wherein the trenches of the optical isolation structure <NUM> comprise a width of about <NUM> - <NUM>.

According to an embodiment, the IR radiation source <NUM> may further comprise an optical element <NUM>-# for guiding the IR radiation <NUM>, wherein the optical element <NUM>-# comprises a lens and/or prism-element at an radiation output area (radiation outlet) of the sealed cavity structure <NUM>.

According to the embodiments of the IR radiation source <NUM>, an undesired and unintended emission of IR radiation is prevented, in that the radiator cavity <NUM> (vacuum chamber) itself is enclosed by optical isolation structures, such as cavities (with a thickness of <NUM> to <NUM>) and trenches (with a width of <NUM> to <NUM>) in the surrounding silicon oxide layers <NUM> and/or in the substrate <NUM>, such as a semiconductor wafer, except for the intended radiation output location and radiation emission direction.

The specific arrangement of the optical isolation structure <NUM> forms a kind of an optical waveguide structure for providing an optical path with a predominant propagation direction of the IR radiation in the sealed cavity structure and a predominant emission direction of the generated IR radiation from the IR radiation source <NUM>. Thus, the optical isolation structure <NUM> may comprise at least or a plurality of trenches, cavities and/or metal films for defining the optical path of the generated IR radiation <NUM>.

Thus, an optical isolation of the generated IR radiation may be achieved by the IR radiation source according to the embodiments described herein.

In the present description of embodiments, the same or similar elements having the same structure and/or function are provided with the same reference numbers or the same name, wherein a detailed description of such elements will not be repeated for every embodiment. Thus, the above description with respect to <FIG> is equally applicable to the further embodiments as described below. In the following description, essentially the differences, e.g. additional, changed or replaced elements, to the embodiment as shown in <FIG> and the technical effect(s) resulting therefrom are discussed in detail.

With respect to the arrangement and geometry of the heating filaments <NUM> in the vacuum chamber <NUM>, it is now referred to the exemplary schematic plane views (parallel to the x-y-plane) in <FIG> of the vacuum chamber <NUM> with circular heating filaments <NUM> according to an embodiment.

As shown in <FIG>, the heating filaments <NUM> may be arranged as a rectangular mxn array in a square or rectangular vacuum chamber <NUM>, i.e. in a vacuum chamber <NUM> having a square or rectangular footprint parallel to the x-y-plane. The array of heating filaments <NUM> may have a plurality with mxn heating filaments, with m is an integer ≥ <NUM> (m = <NUM>, <NUM>, <NUM>, <NUM>. ) and with n is an integer ≥ <NUM> (n = <NUM>, <NUM>, <NUM>, <NUM>. The top and bottom electrode contacts <NUM>, <NUM> are arranged at diagonally opposing portions of the electrode regions <NUM>, <NUM>. The reflector elements <NUM>-<NUM>, <NUM>-<NUM> may be formed as optical reflectors adjacent and parallel to the third and fourth side wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>. The reflector elements <NUM>-<NUM>, <NUM>-<NUM> may be formed as optical reflectors adjacent and parallel to the fifth and sixth side wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>.

As shown in <FIG>, the heating filaments <NUM> may be arranged as a rectangular 2xn array in a square or rectangular vacuum chamber <NUM>, i.e. in a vacuum chamber <NUM> having a rectangular footprint parallel to the x-y-plane. The array of heating filaments <NUM> may have a plurality with 2xn heating filaments, with m = <NUM> and with n is an integer ≥ <NUM> (m = <NUM>, <NUM>, <NUM>, <NUM>. The top and bottom electrode contacts <NUM>, <NUM> are arranged at opposing portions of the electrode regions <NUM>, <NUM>. The reflector elements <NUM>-<NUM>, <NUM>-<NUM> may be formed as optical reflectors adjacent and parallel to the third and fourth side wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>. The reflector elements <NUM>-<NUM>, <NUM>-<NUM> may be formed as optical reflectors adjacent and parallel to the fifth and sixth side wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>.

As shown in <FIG>, the heating filaments <NUM> may be arranged in a line arrangement in a square or rectangular vacuum chamber <NUM>, i.e. in a vacuum chamber <NUM>, having a square or rectangular footprint parallel to the x-y-plane. The line of heating filaments <NUM> may have a plurality of n heating filaments, with n is an integer ≥ <NUM> (n = <NUM>, <NUM>, <NUM>, <NUM>. The top and bottom electrode contacts <NUM>, <NUM> are arranged at diagonally opposing portions of the electrode regions <NUM>, <NUM>. The reflector elements <NUM>-<NUM>, <NUM>-<NUM> may be formed as optical reflectors adjacent and parallel to the third and fourth side wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>. The reflector elements <NUM>-<NUM>, <NUM>-<NUM> may be formed as optical reflectors adjacent and parallel to the fifth and sixth side wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>.

As shown in <FIG>, the heating filaments <NUM> may be arranged in a circular arrangement in a circular vacuum chamber <NUM>, i.e. in a vacuum chamber <NUM>, having a circular footprint parallel to the x-y-plane. The line of heating filaments <NUM> may have a plurality of n heating filaments, with n is an integer ≥ <NUM> (n = <NUM>, <NUM>, <NUM>, <NUM>. The top and bottom electrode contacts <NUM>, <NUM> are arranged at opposing portions of the electrode regions <NUM>, <NUM>. The reflector elements <NUM>-<NUM>, <NUM>-<NUM> may be formed as optical reflectors adjacent and parallel to the first and second side wall regions <NUM>-<NUM>, <NUM>-<NUM> of the vacuum chamber <NUM>.

The above explanation should make clear that the shape of the vacuum chamber <NUM> and the geometrical arrangement or alignment of the heating filaments <NUM> therein includes a large number of different implementations, wherein the implementations as shown <FIG> for the vacuum chamber <NUM> and the heating filaments <NUM> is not to be regarded as exhaustive. To be more specific, according to further embodiments, the shape (footprint) of the vacuum chamber <NUM> may also comprise one of a circular, square, oval and ellipse shape (or any convex polygon shape), for example.

<FIG> show different exemplary, schematic cross-sectional views (vertical = parallel to the x-z-plane) of the IR radiation source <NUM> with different configurations of the optical isolation structure for providing a lateral and/or vertical emission direction from the IR radiation source <NUM>.

As shown in <FIG>, the IR radiation source <NUM> may comprise the (laterally extending) optical reflector elements <NUM>-1a, <NUM>-2a, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-1a, <NUM>-2a, and further comprises the (vertically extending) optical reflector element (trench) <NUM>-<NUM> which is laterally arranged to the vacuum chamber <NUM>. The IR radiation source <NUM> may further comprise the (vertically extending) optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>. Thus, the resulting emission direction of the generated IR radiation is lateral (in parallel to the x direction) of the IR radiation source <NUM>.

As shown in <FIG>, the IR radiation source <NUM> may comprise the (laterally extending) optical reflector element <NUM>-2a, and further comprises the (vertically extending) optical reflector elements (trenches) <NUM>-<NUM>, <NUM>-<NUM> which are laterally arranged to the vacuum chamber <NUM>, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>. The IR radiation source <NUM> may further comprise the (vertically extending) optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>. Thus, the resulting emission direction of the generated IR radiation is vertical (in parallel to the z direction) of the IR radiation source <NUM>.

As shown in <FIG> the IR radiation source <NUM> may comprise the (laterally extending) optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, and further comprises the (vertically extending) optical reflector elements (trenches) <NUM>-<NUM>, <NUM>-<NUM> which are laterally arranged to the vacuum chamber <NUM>. The optical reflector element (trench) <NUM>-<NUM> is arranged parallel to the y-z-plane, wherein the optical reflector element (trench) <NUM>-<NUM> is arranged with an inclined angle, e.g. <NUM>° (e.g. between <NUM> and <NUM>°) with respect to the x-y-plane. The IR radiation source <NUM> may further comprise the (vertically extending) optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>. Thus, the resulting emission direction of the generated IR radiation is lateral (in parallel to the z direction) of the IR radiation source <NUM>.

As shown in <FIG>, the IR radiation source <NUM> may comprise the (laterally extending) optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, and further comprises the optical reflector elements (trenches) <NUM>-<NUM>, <NUM>-<NUM> which are laterally arranged to the vacuum chamber <NUM> and are arranged with an inclined angle, e.g. <NUM>° (e.g. between <NUM> and <NUM>°) with respect to the x-y-plane. The IR radiation source <NUM> may further comprise the (vertically extending) optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>, wherein the vacuum chamber <NUM> with the heating filaments <NUM> is sandwiched between the optical reflector elements <NUM>-<NUM>, <NUM>-<NUM>. Thus, the resulting emission direction of the generated IR radiation is lateral (in parallel to the z direction) of the IR radiation source <NUM>.

Instead of the laterally extending optical reflector elements in form of cavities and the vertically or inclined extending optical reflector elements in form of trenches, it is pointed out to the fact that at least one, a plurality or all of these optical reflector elements are also formable by means of reflective metallic layers.

In the following, a summary of some implementations of the IR radiation source <NUM> according to the above embodiments and the resulting technical effects are provided in the following.

According to embodiments, the IR radiation source <NUM> comprises heating filaments <NUM> which are arranged and sealed in a vacuum chamber <NUM>, wherein the material of the heating filaments <NUM> comprises at least the conductivity of highly doped polysilicon. The material for the heating filaments may, for example, comprise carbon, graphene, polysilicon or tungsten or other suitable highly conductive, CMOS process flow compatible materials.

The heating filaments <NUM> may be manufactured in high aspect ratios between large area electrodes (plate electrodes with a narrow alignment of the heating filaments, wherein the electrodes and heating filaments are homogeneously connected. A low expansion coefficient of the material of the heating filaments <NUM> supports the mechanical stability of the IR radiation source <NUM>, wherein the heating filaments <NUM> comprise an elastic material which is stable in the case of vibrations. The high melting temperature of the filament material provides for a high radiation yield, especially due to the low atmospheric pressure (near vacuum) in the vacuum chamber. The low atmospheric pressure in the vacuum chamber <NUM> also provides for an energy optimization of the radiator source <NUM>. According to embodiments, the vacuum chamber <NUM> (cavity) having the low atmospheric pressure (good vacuum) fits to the manufacturing of the heat elements, e.g. by etching an SiO sacrificial layer by means of HF (hydrofluoric acid) and a sealing, e.g. as sputter sealing, under vacuum. Further, carbon has a good etching selectivity to HF.

For achieving a reliable isolation of the vacuum chamber <NUM> for avoiding a later diffusion of gases into the cavity, the housing of the vacuum chamber <NUM> comprises a SiN/TiN. barrier against H2, O2, etc. This insulator combination provides a device passivation with a final furnace anneal. The thermal isolation of the vacuum chamber <NUM> may be achieved by housing the vacuum chamber <NUM> into thick SiO layers.

The optical isolation of the vacuum chamber <NUM> may be achieved by cavities and/or unfilled trenches, which optimally provide for a low heat conduction loss. Also, metal layers and trenches filled with metal are possible for at least partially providing the optical isolation.

For further increasing (optimizing) the radiation output, the optical isolation structure forms an optical waveguide structure for providing an optical path with a predominant propagation direction of the IR radiation in the sealed cavity structure and a predominant emission direction from the IR radiation source. In this connection, waveguide materials and optical elements, such as lenses, prisms, etc., can be used to provide a localized radiation output.

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

According to an embodiment, an IR (infrared) radiation source comprises a sealed cavity structure enclosing a vacuum chamber having a low atmospheric pressure, wherein the sealed cavity structure comprises a thermally and electrically insulating material for enclosing the vacuum chamber, a plurality of heating filaments extending in the vacuum chamber between opposing electrode regions at opposing wall regions of the vacuum chamber, wherein the heating filaments are electrically connected in parallel, and wherein the heating filaments and the electrode regions have a highly electrically conductive material, and an optical isolation structure adjacent to the vacuum chamber for optically confining the IR radiation and providing a predominant propagation direction of the IR radiation.

According to an embodiment, the heating filaments and the electrode regions comprise the same highly electrically conductive material having a melting temperature higher than <NUM>° Celsius.

According to an embodiment, the conductive material of the heating filaments comprises carbon, graphene, polysilicon or tungsten.

According to an embodiment, the opposing electrode regions of the heating filaments are formed as planar electrodes.

According to an embodiment, the heating filaments have a length between <NUM> and <NUM> micrometers and have an aspect ratio of <NUM>:<NUM> up to <NUM>:<NUM>.

According to an embodiment, the insulator material of the sealed cavity structure is optically transparent to the IR radiation.

According to an embodiment, the insulating material of the sealed cavity structure comprises a first insulating layer having a silicon nitride material enclosing the vacuum chamber of the sealed cavity structure, and wherein the insulating material of the sealed cavity structure further comprises a second insulating layer comprising a silicon dioxide material for enclosing the first layer.

According to an embodiment, the insulating material of the sealed cavity structure further comprises a third insulating layer comprising a titanium nitride material.

According to an embodiment, the low atmospheric pressure in the vacuum chamber comprises a cavity pressure less than <NUM> mbar (<NUM> Torr or <NUM> Pa) or less than <NUM> mbar (<NUM> Torr or <NUM> Pa).

According to an embodiment, the optical isolation structure forms an optical waveguide structure for providing an optical path with the predominant propagation direction of the IR radiation in the sealed cavity structure.

According to an embodiment, the optical isolation structure comprises optical reflector elements for providing the optical path for the IR radiation.

According to an embodiment, the optical reflector elements of the optical isolation structure comprise a metallization layer adjacent to the side wall region of the sealed cavity structure, or wherein the optical reflector elements of the optical isolation structure comprise a cavity in a substrate or a trench in the insulating material adjacent to the sealed cavity structure.

According to an embodiment, the sealed cavity structure is arranged on a substrate, wherein the optical isolation structure is formed as a metallization layer on a surface region of the substrate adjacent to a side wall region of the sealed cavity structure, or wherein the optical isolation structure is formed as a cavity in the substrate adjacent to the side wall region of the sealed cavity structure.

According to an embodiment, the cavities of the optical isolation structure comprise a thickness of about <NUM> - <NUM> and/or wherein the trenches of the optical isolation structure comprise a width of about <NUM> - <NUM>.

According to an embodiment, the IR radiation source further comprises an optical element for guiding the IR radiation, wherein the optical element comprises a lens and/or prism-element at an radiation output area of the sealed cavity structure.

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

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

Claim 1:
IR (infrared) radiation source (<NUM>) comprising:
a sealed cavity structure (<NUM>) enclosing a vacuum chamber (<NUM>) having a low atmospheric pressure, wherein the sealed cavity structure (<NUM>) comprises a thermally and electrically insulating material (<NUM>, <NUM>) for enclosing the vacuum chamber (<NUM>),
opposing plate electrodes (<NUM>, <NUM>),
a plurality of heating filaments (<NUM>) vertically extending in the vacuum chamber (<NUM>) between the opposing plate electrodes (<NUM>, <NUM>) at opposing wall regions (<NUM>-<NUM>, <NUM>-<NUM>) of the vacuum chamber, wherein the heating filaments (<NUM>) are electrically connected in parallel, and wherein the heating filaments (<NUM>) and the plate electrodes (<NUM>, <NUM>) have a highly electrically conductive material, and
an optical isolation structure (<NUM>) adjacent to the vacuum chamber (<NUM>) for optically confining the IR radiation (<NUM>) and providing a predominant propagation direction of the IR radiation (<NUM>).