Micro-heating element with at least one heatable base, as well as a micro-heating element and a method for manufacturing the micro-heating element.

Abstract

Micro-heating element (1) with a heatable base (2) which is partially freestanding on a support substrate (5) by means of recesses (6) and connected to the support substrate (5) only by several connecting webs (3), wherein the base (2) and the connecting webs (3) are made in one piece and are made of glass, and wherein each connecting web (3) has a depth (T) in a transverse direction to the main plane of the base (2) or the support substrate (5) which is greater than a width (B) of the connecting web (3) parallel to the main plane of the base (2) or the support substrate (5), characterized in that the base (2) and the connecting webs (3) are made of glass and several connecting webs (3) have at least one section with a width (B) which is greater than a width of the adjacent recess (6) and / or a distance to an adjacent connecting web (3),or the cross-sectional area and / or cross-sectional geometry varies along the main extent between the base (2) and the surrounding support substrate (5).

Description

[0001] The invention relates to a micro-heating element with at least one base that can be heated by a heating element, which is partially exposed on a support substrate by means of recesses and is connected to the support substrate only by several connecting webs. The invention further relates to a micro-heating element for such a micro-heating element and to a method for manufacturing the micro-heating element.

[0002] Micro-heating elements are components of microsystems technology that enable the heating of defined areas of a substrate, the wafer, through thermal decoupling from the rest of the substrate. This thermal decoupling is achieved by creating recesses in the substrate to isolate specific structures.

[0003] The power consumption of a micro-heating element can be reduced through a suitable design, for example by isolating the heating surfaces in silicon wafers, which are connected to the rest of the wafer only by thin connecting bridges. To maintain mechanical stability, these connecting bridges cannot be arbitrarily thin, so the sensors typically consume several tens of milliwatts per heating element at an operating temperature above 200°C.

[0004] Another approach involves placing the sensor element on a dielectric thin-film membrane, beneath which the silicon has been etched away. This achieved power consumption of just over 10 mW.

[0005] The thermal conductivity of membranes is relatively high, as heat is dissipated radially in all directions.

[0006] Additionally, mechanical stresses arise when the membrane is heated due to thermal expansion. The mechanical stability of thin-film membranes is comparatively low.

[0007] Conventional designs based on thin-film technology typically have connecting webs with a significantly greater width than thickness in order to achieve a minimum cross-section that provides sufficient stability. In thin-film technology, the thickness can only be increased by a few micrometers, so a large width is required to increase the cross-section.

[0008] In the manufacturing processes commonly used in practice, this results in relatively wide connecting bridges with a very low height, with the connecting bridges extending radially from the heating surface.

[0009] In practice, however, this geometry often proves to be disadvantageous, as on the one hand the area consumption is large and on the other hand the mechanical stability of the heating element, especially the connecting webs, is low when subjected to force or oscillating or cyclic loading in a transverse direction to the main extension plane.

[0010] In practice, for example in gas sensors, an optimized sensor design with low power consumption is of fundamental importance. Micromechanical structures, so-called "micro-hotplates," ensure thermal decoupling of the active sensor area from the housing, thus significantly reducing power consumption. These structures are created by exposing the front surface of the hotplates (reactive ion etching (RIE)). Nevertheless, micro-heating elements, which are used, for example, in MEMS gas sensors, typically still require high heating power and are therefore not standardly installed in portable devices such as smartphones.

[0011] In principle, it is essential to ensure low thermal conductivity of the connecting bridges to minimize heat loss. Furthermore, the required surface area of ​​the micro-heating element, including the connecting bridges, should be kept as small as possible to reduce the footprint and achieve a low heat capacity for the heating element.

[0012] DE 692 12 936 T2 describes an infrared sensor for non-contact measurement of object temperature, comprising a bridge structure on which a heat-sensitive section is formed. The infrared receiver section is connected to the silicon substrate solely by one-piece mounting sections. To minimize heat loss due to conduction, the thickness of the infrared receiver section and the mounting sections, as well as the width of the mounting sections, are small.

[0013] To prevent a delay in the heat transfer from a microcoil to an object and to generate heat precisely, a cover glass is used to close a chamber which carries a printed coil on the opposite side, according to KR 10 1 165 303 B1.

[0014] US Patent 2021 / 0246016A1 relates to an emitter, for example, an infrared source combined with a glass cover, for protecting devices used to detect environmental parameters such as noise, sound, temperature, and gases in mobile devices from contamination and malfunction. A laser beam is used to weaken the glass substrate in a recessed area where a subsequent recess is to be created. For this purpose, the focus of the laser beam can be variably adjusted to a specific point on the glass substrate.

[0015] DE 695 10 432 T2 relates to an infrared radiation sensor with a light-receiving part that is supported by a bridge structure spanning a hollow part of a substrate, which has a width in the range of 3 to 30 µm and a thickness in the range of 2 to 5 µm.

[0016] CN 1 04 817 054 A discloses a micro-heating element with a bridge structure for reducing heat conduction and heat dissipation of the micro-heating element and for compensating for the voltage.

[0017] From US patent 2017 / 0001857A1, a sensor element with connecting bridges is known that links a chip and a frame. The connecting bridges can have a section with a width greater than the width of the adjacent recess.

[0018] Furthermore, US patent 2020 / 0209175A1 shows a MEMS device with a heating element for heating a MEMS sensor to a specific temperature before operation. A central section carrying the heating element is connected to the circumferential section by a connecting section whose width varies.

[0019] The object of the invention is to provide a micro-heating element with compact dimensions for low surface area while simultaneously offering good thermal insulation or low thermal conductivity compared to the surrounding substrate and improved mechanical strength. Furthermore, a semiconductor element constructed in this way and a method for manufacturing such a micro-heating element are to be developed.

[0020] The first-mentioned problem is solved according to the invention with a micro-heating element according to the features of claim 1. Further embodiment of the invention can be found in the dependent claims.

[0021] According to the invention, a micro-heating element is provided in which the base, bounded by recesses, and the connecting webs are made of glass in one piece, wherein each connecting web has a depth in a transverse direction to the main plane of the base or the support substrate that is greater than a width of the connecting web parallel to the main plane of the base or the support substrate, and wherein the base and the connecting webs are made of glass and several connecting webs have at least one section with a width that is greater than a width of the adjacent recess and / or a distance to an adjacent connecting web, or the cross-sectional area and / or cross-sectional geometry varies along the main extent between the base and the surrounding support substrate in order to enable a geometry adapted to the action of the external forces along the entire extent of the connecting webs.Preferably, the connecting webs are axially symmetric or point-symmetric with respect to a surface normal through the base.

[0022] The base, exposed in the glass substrate by the cutouts, is thus connected to the surrounding substrate only by several connecting webs, which, for example, extend in a straight line. Each connecting web has a cross-sectional area with its greatest extent perpendicular to the plane of the substrate. The cross-sectional areas of different connecting webs can be of different sizes and / or geometries. Preferably, to achieve homogeneous thermal and mechanical properties, the cross-sectional area is either constant along the length of the connecting webs or has a continuously changing shape.

[0023] Due to their greatest extent perpendicular to the plane of the support substrate, the forces acting on the support, in practice often vibrations, are not transmitted to the base, or only to a very small degree. Thus, by making the connecting webs comparatively narrow but with a large material thickness, matching, for example, that of the adjacent support substrate, a geometry optimally adapted to the occurring mechanical forces is achieved.

[0024] Furthermore, the cross-sectional area can be reduced even further compared to connecting bridges known from the prior art, without any undesirable reduction in mechanical strength. As a result of the reduced cross-sectional area, lower heat capacity and thermal conductivity are achieved, thus improving the performance characteristics and energy consumption of the micro-heating element. The narrow width of the connecting bridges also reduces the surface area required for them, allowing a greater number of heating elements to be produced for a given substrate area.

[0025] The micro-heating element according to the invention therefore leads to a reduction in the required heating power in conjunction with higher mechanical stability.

[0026] It has already proven particularly advantageous if at least some of the connecting webs do not merely extend radially along a straight line, but if at least some of the connecting webs follow a curved or spiral course around the base, at least in sections, or if at least some of the connecting webs have at least an arc, a curve or an angle and thereby one or more changes in direction.

[0027] This allows for a surprisingly simple and significant extension of the connecting webs in the direction of their main extension between the base and the surrounding support substrate, without increasing the footprint or the area required by the connecting webs on the support substrate. Such an extension of the connecting webs, which leads to a corresponding reduction in heat conduction, is made possible by the fact that the mechanical stability is significantly increased according to the invention, so that the connecting webs not only have a comparatively small width, but can also be extended without undesirably reducing their load-bearing capacity.

[0028] Another particularly promising embodiment of the invention is achieved by having several adjacent connecting webs have a parallel orientation, at least partially. The connecting webs preferably have several sections angled relative to each other, each of which runs parallel to the corresponding sections of the adjacent connecting webs. This allows for a particularly compact design, and multiple changes in direction can be easily implemented. This makes it possible to create at least some connecting webs in which several sections of the same connecting web, angled relative to each other, run parallel to one another.

[0029] Due to the manufacturing process, various cross-sectional contours of the connecting webs can be realized, thereby further improving the mechanical stability relative to the cross-sectional area. For example, the connecting webs can have a U- or T-profile. It is generally advantageous if the connecting webs exhibit the thermal and mechanical properties of the surrounding support material.

[0030] It has already proven particularly advantageous if at least some connecting webs enclose a circumferential section of the base of more than 90°, in particular more than 180° or 270°.

[0031] It has also been shown that the comparatively long connecting bridges allow for limited elasticity of the connecting bridges, so that the base can be moved relative to the surrounding support substrate without impairment, thus preventing damage to the micro-heating element not only during deflections in the direction of the surface normal, but also during tilting movements.

[0032] An advantageous aspect of the invention is also the smallest possible distance between the adjacent connecting webs, wherein several connecting webs have at least one section in which this distance is less than the respective cross-sectional width of the adjacent connecting webs, thereby achieving optimal use of space.

[0033] In particular, at least some connecting bridges may be enclosed in a labyrinthine manner by neighboring connecting bridges.

[0034] The object of the invention is further achieved by a method for producing a micro-heating element in that the connecting webs and the recesses between the connecting webs are introduced in a single process step by etching the glass substrate, wherein modifications with optionally different parameters are introduced beforehand by laser radiation in areas of the recesses to be produced and optionally also in the areas of the connecting webs to be produced, so that during the etching treatment the etching progress in the areas of the recesses to be produced is greater than in the areas of the connecting webs to be produced, so that in the area of ​​the recesses, perforations of the substrate are produced due to the anisotropic material removal, while in the areas of the connecting webs to be produced, the material removal during the etching treatment does not produce any perforations.

[0035] The invention is thus based on laser-induced deep etching for the production of micro-heating plates with connecting bridges made of glass, which possess the thermal and mechanical properties of the solid material.

[0036] The invention allows for various embodiments. To further illustrate its basic principle, one of these is shown in the drawing and described below. This shows in Fig. 1 a top view of a micro heating element with a base and four connecting struts according to the state of the art; Fig. 2 a top view of a micro-heating element according to the invention with four angled connecting struts; Fig. 3 a top view of a variant of the micro-heating element according to the invention with four multiply angled connecting struts; Fig. 4 a top view of a variant of the micro-heating element according to the invention with different connecting webs; Fig. 5 a representation cut along line IV-IV of the in Fig. 2 micro-heating elements shown; Fig. 6 different web profiles of the micro heating element in cross-section.

[0037] A micro-heating element 1 according to the invention, for a micro-heating element 1 of microsystems technology that can be used in particular as a sensor, is described below with reference to the Fig. 1 to 6 explained in more detail, whereby Fig. 1 shows an embodiment known from the prior art.

[0038] The micro-heating element 1 has a heatable base 2, which in the prior art is realized by four diagonally extending connecting webs 3, which are freed by recesses 6.

[0039] In the prior art, the connecting webs have a rectangular cross-sectional area (not shown) with a large width and a very low height, taking into account requirements for mechanical stability on the one hand, and for low thermal conductivity and the associated thermal energy losses during operation of the heating element on the other.

[0040] By the invention, as in the Fig. As shown in Figures 2 to 6, where the base 2 is produced in a glass support substrate 5 by laser-induced deep etching, cross-sectional shapes of the connecting webs 3 can be realized in which each connecting web 3 has a depth T in a transverse direction to the main plane of the base 2 or the support substrate 5 that is greater than a width B of the connecting web 3 in the main plane of the base 2 or the support substrate 5. This allows for improved mechanical stability of the connecting webs 3 according to the invention compared to those shown in Figures 2 to 6. Fig. The connecting bridges 3 shown in Figure 1 not only reduce the width B of the connecting bridges 3, but also further reduce the cross-sectional area of ​​the connecting bridges 3 according to the invention in order to achieve a lower heat capacity and heat conduction, thereby improving the usage characteristics and reducing the energy requirement for heating the micro-heating element 1.

[0041] Due to the small width of the connecting bridges 3, the area requirement F2 or F3 of the connecting bridges 3 according to the invention is also reduced compared to the area requirement F1 according to the prior art, so that a larger number of electronic elements, for example semiconductor elements, can be produced for a given carrier substrate area.

[0042] Furthermore, the reduced width B and the angled geometry of the connecting webs 3 allow for improved thermal decoupling of the base 2 from the support substrate 5 with the same surface area compared to the prior art. Alternatively, identical thermal decoupling can be achieved on a smaller area F2 or F3.

[0043] According to the invention, adjacent connecting webs 3 extend in several mutually angled sections A1, A2, each parallel to the corresponding sections of the adjacent connecting webs 3. This allows for a particularly compact design, with multiple changes in direction being easily achievable. This makes it possible to realize at least some connecting webs 3 in which several mutually angled sections A1, A2 of the same connecting web 3 run parallel to each other.

[0044] At the in Fig. In the variant shown, the individual connecting webs 3 are labyrinthinely enclosed by multiple bends 8 from their respective neighboring connecting webs 3, resulting in an even greater overall length of each individual connecting web 3 and a length that is greater than that shown in Fig. 2. Recognizable area requirement F2 results in reduced area requirement F3.

[0045] Additionally, in Fig. Figure 4 shows another variant in which the connecting bridges have 3 different forms and have areas with a curved course along their main extent.

[0046] Due to the manufacturing process according to the invention, in which the connecting webs 3 and the recesses 6 between the connecting webs 3 are produced in a single process step by etching the glass substrate, wherein modifications are introduced in areas of the recesses 6 to be produced by laser radiation, such that the anisotropic etching progress in the areas of the recesses 6 to be produced is greater than in the areas of the connecting webs 3 to be produced, a perforation of the support substrate 5 occurs only in the area of ​​the recesses 6 to be produced. It is generally advantageous that the connecting webs 3 have the thermal and mechanical properties of the surrounding glass substrate.

[0047] However, the connecting webs 3 can also be partially removed by introducing modifications with differing parameters in the area of ​​the connecting webs 3 to be created, so that glass material is also removed in the area of ​​the connecting webs 3 without creating any perforations in the connecting webs 3. This allows, as in the Fig. 5 and Fig. Figure 6 shows an example of how to introduce U-shaped or V-shaped recesses 7 into the connecting webs 3 or achieve T-shaped cross-sectional shapes of the connecting webs 3 in order to further reduce the cross-sectional area and thus the heat conduction with almost unchanged mechanical stability. REFERENCE MARK LIST 1 micro heating element 2 Basis 3 connecting bridge 4 heating surface 5 Carrier substrate 6 Exclusion 7. Further Study 8 Angle T depth B Width F1, F2, F3 Space requirement A1, A2 section

Claims

[1] Micro-heating element (1) with a heatable base (2) which is partially freed on a support substrate (5) by means of recesses (6) and is connected to the support substrate (5) only by several connecting webs (3), wherein the base (2) and the connecting webs (3) are made in one piece and are made of glass and wherein each connecting web (3) has a depth (T) in a transverse direction to the main plane of the base (2) or the support substrate (5) which is greater than a width (B) of the connecting web (3) parallel to the main plane of the base (2) or the support substrate (5), characterized by, that the base (2) and the connecting webs (3) are made of glass and several connecting webs (3) have at least one section with a width (B) that is greater than a width of the adjacent recess (6) and / or a distance to an adjacent connecting web (3), or the cross-sectional area and / or cross-sectional geometry varies along the main extent between the base (2) and the surrounding support substrate (5). [2] Micro-heating element (1) with a heatable base (2) which is partially freed on a support substrate (5) by recesses (6) and is connected to the support substrate (5) only by several connecting webs (3), wherein each connecting web (3) has a depth (T) in a transverse direction to the main plane of the base (2) or the support substrate (5) which is greater than a width (B) of the connecting web (3) parallel to the main plane of the base (2) or the support substrate (5), characterized by, that the base (2) and the connecting webs (3) are made of glass and several connecting webs (3) have at least one section with a width (B) that is greater than a width of the adjacent recess (6) and / or a distance to an adjacent connecting web (3), or the cross-sectional area and / or cross-sectional geometry varies along the main extent between the base (2) and the surrounding support substrate (5), wherein the recesses (6) and / or the connecting webs (3) are produced by introducing modifications by laser radiation and subsequent etching treatment, wherein the etching progress in the areas of the previously introduced modifications is greater than in the areas without the modifications, such that perforations of the support substrate (5) have been created in the area of ​​the recesses (6). [3] Micro heating element (1) according to claim 1 or 2, characterized by, that several adjacent connecting bridges (3) have a parallel orientation at least in sections. [4] Micro-heating element (1) according to at least one of the preceding claims, characterized by , that individual connecting webs (3) run at least partially in a curved or spiral shape and / or have an arc, a curve and / or a bend (8) [5] Micro heating element (1) with a base (2) comprising a heating surface (4) freed by recesses (6) and having only several connecting webs (3) for electrical contact, by which the heating surface (4) is connected to the support substrate (5), characterized by, that the support substrate (5), the connecting webs (3) and the base (2) are integrally connected and made of glass, wherein each connecting web (3) has a depth (T) in a transverse direction to the main plane of the base (2) or the support substrate (5) that is greater than a width (B) of the connecting web (3) parallel to the main plane of the base (2) or the support substrate (5), and several connecting webs (3) have at least one section with a width (B) that is greater than a width of the adjacent recess (6) and / or a distance to an adjacent connecting web (3), or the cross-sectional area and / or cross-sectional geometry varies along the main extent between the base (2) and the surrounding support substrate (5). [6] Method for manufacturing a micro heating element (1) in which a heatable base (2) on a support substrate (5) is partially exposed by recesses (6) and is connected to the support substrate (5) only by several connecting webs (3), characterized by, that the recesses (6) between the connecting webs (3) are introduced in a single process step by etching the glass support substrate (5), wherein modifications are introduced beforehand by laser radiation in areas of the recesses (6) to be produced, so that anisotropic material removal occurs during the etching treatment in the areas of the recesses (6) to be produced and the etching progress is greater than in the areas of the connecting webs (3) to be produced and perforations of the support substrate (5) are created in the area of ​​the recesses (6) and several connecting webs (3) have at least one section with a width (B) that is greater than a width of the adjacent recess (6) and / or a distance to an adjacent connecting web (3), or the cross-sectional area and / or cross-sectional geometry varies along the main extent between the base (2) and the surrounding support substrate (5). [7] Method according to claim 6, characterized by , that in the areas of the recesses to be produced (6) on the one hand and the areas of the connecting webs to be produced (3) on the other hand, modifications with different parameters are introduced, so that during the etching treatment the etching progress in the areas of the recesses to be produced (6) is greater than in the areas of the connecting webs to be produced (3), so that in the area of ​​the recesses (6) perforations of the support substrate (5) are created and in the areas of the connecting webs to be produced (3) support substrate material is removed without perforations being created.

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