Ceramic substrate material, method for production and utilisation of the same and antenna or antenna array

p0001The invention relates to a method for producing a ceramic substrate material having a first layer and optionally a further layer, said first layer of at least a first component of a crystalline ceramic material and / or a glass material as the matrix and a second component made of a crystalline ceramic material which is present in the matrix. The invention further relates to a ceramic substrate material having a first layer and optionally a further layer, said first layer of at least a first component consists of a crystalline ceramic material and / or a glass material as the matrix. Moreover, the present invention relates to the use of such a ceramic substrate material, and an antenna or an antenna array.

p0002A single- or multilayer ceramic substrate materials form important starting materials for microelectronic components, in particular for telecommunications. A layer in this case represents a layer or a film of the substrate material with a large extension in two directions in space and a comparatively small extension in the third, the first two spatial directions running perpendicular to the direction of the space. Typically, a sintered layer of an LTCC substrate has a thickness of 140 microns.

p0003From glass-ceramic materials both low dielectric constant materials as well as materials with moderately high dielectric constant (ε be_r) Or relative permittivity (also referred to as dielectric constant or relative permittivity) manufactured. As ceramic, a ceramic material is designated, the first is a glass composition that prior to crystallization sinters upon subsequent annealing at temperatures up to 1000 ° C to form a dense mass, so that a partially or completely crystalline material.

p0004An important and cost-effective technology for the manufacture of microelectronic substrates with high coating density is the so called "Low Temperature Cofired Ceramics" technology, hereinafter referred to as LTCC technology. The LTCC technology is a technology for the manufacture of multilayer circuits on the basis of sintered ceramic carriers. It can be produced on the substrates traces, capacitors, resistors and coils. These elements are applied by screen printing or photochemical processes to the respective unfired layer. The unfired ceramic films are individually patterned and then stacked and laminated. A defined sintering profile is applied with a peak temperature of about 850 ° C to 900 ° C to solidify the structure.

p0005Mono- or multi-layer substrates for electronic devices are often provided with materials having a low dielectric constant, when a high speed of electronic signals to be reached by the substrate at high frequencies. In a low dielectric constant or permittivity is achieved that the largest possible part of the RF signal, for example. An antenna, radiated and injected some energy into the material and is thus consumed wastefully.

p0006In the document <patcit id="pcit0001" dnum="DE10043194A1"><text>DE 100 43 194 A1</text></patcit> is a glass ceramic mass containing at least one oxide ceramic containing barium, titanium and at least one rare earth metal comprises at least one and described glass material contains at least one oxide with boron. The glass material further comprises an oxide with at least one tetravalent metal and an oxide with at least one rare earth metal. This glass ceramic mass compacted at a temperature of below 850 ° C and is suitable for use in microwave technology. In particular, through the oxide of the rare earth, it is possible to tune the dielectric material properties of the glass material to the dielectric material properties of the oxide ceramic. It being understood that the higher the amount of lanthana in the glass material is, the higher the permittivity of the glass material. Moreover, the composition of the oxide ceramic and the glass material is selected so that crystallization products are formed during the compaction (for example, by reactive liquid phase sintering), and particularly after compaction (at higher temperatures). This crystallization products sustainably influence the dielectric material properties of the glass ceramic mass, so that the glass ceramic mass can be used in microwave technology. In this way, can be obtained, for example, at a low compression temperature a glass ceramic mass with a relatively high permittivity of about 15 and with a finish of 350th This in<patcit id="pcit0002" dnum="DE10043194A1"><text>DE 100 43 194 A1</text></patcit> however described material is not suitable for applications at high frequencies.

p0007The publication <patcit id="pcit0003" dnum="DE4234349C2"><text>DE 42 34 349 C2</text></patcit> is a composite ceramic with low dielectric constant is known, in which a plurality are dispersed mullite bubbles of which is selected from the group consisting of a glass matrix and a borosilicate glass-ceramic matrix based on aluminum silicate. These mullite bubbles are typically produced in that Aluminiumborsilikatblasen be heated. The mullite bubbles typically have a diameter of up to about 50 microns. The preparation of these materials is very complex. Furthermore, can be expected with a non-planar surface characteristics, which excludes in particular the use of thin-film technology in this area with structural dimensions in the micrometer scale.

p0008In the document <patcit id="pcit0004" dnum="US5108958A"><text>US 5,108,958</text></patcit> A ceramic material composition for electronic applications described, the hollow, thin-walled, fireproof ceramic bubbles (ceramic bubbles) which are evenly distributed in a refractory ceramic matrix. The ceramic bubbles are made of a material having a dielectric constant of less than 9th The known material composition has a low dielectric constant, a low dissipation factor and a thermal expansion coefficient that can be adjusted to that of the IC chip. The ceramic bubbles comprise for example aluminum borosilicate, mullite or a mixture of both. The diameters of the bubbles are between about 1 to 50 microns and have a wall thickness of about 0.05 to about 0.5 .mu.m. As a matrix material alumina, aluminum phosphate, mullite, cordierite, forsterite, or steatite be used. The crystallites of which is arranged in the walls of bubbles compounds form a network structure with cavities in the walls of the bubbles. The size of these cavities is approximately 0.5 microns. The preparation and the handling of such material composition is also time-consuming. In addition, the height of the dielectric constant is influenced by whether the ceramic bubbles are otherwise destroyed break during the production of a component or.

p0009In clear script <patcit id="pcit0005" dnum="EP0234896A2"><text>EP 0234896 A2</text></patcit> is a material disclosed with a low dielectric constant, which is suitable as VLSI elements of circuits of thick film technology. From the publication it appears that the dielectric constant of an insulating material with a layer of hollow glass microspheres through the large volume of air in the spheres already at a small proportion of the balls, that is, above a proportion 10 to 15% by volume in the layer significant to a reducing the dielectric constant leads. Above a proportion of 45 to 50% by volume of glass microspheres in the film, however, the structural strength and the thermal resistance of the resulting insulating layers is adversely affected.

p0010Also, the embedding of hollow microspheres in a dielectric composition is in block letters <patcit id="pcit0006" dnum="US4867935A"><text>US 4,867,935</text></patcit> disclosed. These are hollow microspheres of a ceramic, which is embedded in a ceramic matrix. This publication also discloses the disadvantages of using hollow microspheres. This may break during the manufacturing process, so that the desired reduction of the dielectric constant is not reached. In the document<patcit id="pcit0007" dnum="US4867935A"><text>US 4,867,935</text></patcit> is thereby fixed, in that the hollow ceramic microspheres are dispersed at high speeds in a milled mixture, so that a slip is formed with a viscosity in the range of about 500 to 1500 cps this problem. However, this is a rather complex production process.

p0011Further disadvantages of a layer with microspheres disclosed the document <patcit id="pcit0008" dnum="US4867935A"><text>US 4,867,935</text></patcit> also, that at too high a proportion (about 40%) of the microspheres, the air-tightness of the resulting ceramic product deteriorates. In addition, the surface roughness of the layer can be problematic during subsequent processing of the layer. In contrast, at a too low a proportion of the microspheres will not achieve the desired reduction of the dielectric constant.

p0012The publication <patcit id="pcit0009" dnum="DE10042653A1"><text>DE 100 42 653 A1</text></patcit> is a ceramic multilayer circuit comprises at least two superposed ceramic layers are known which differ in their dielectric constant. For producing such a ceramic multi-layer circuit by means of LTCC method is proposed, ceramic green sheets for stacking and subsequent sintering in the stacked condition above each other, but which have the same raw material as the remaining layers in comparison to these a lowered crystallization temperature. This these layers crystallize early and thus freeze a high porosity. The areas with a high porosity have a reduced dielectric constant. The lowered crystallization temperature can be achieved in that the ceramic raw material is comparatively finely ground prior to casting and drying the material or nuclei are added. The described method has the disadvantage that the LTCC process has to be changed and additional layers are used, which have a different shrinkage characteristics as the other layers may.

p0013The document <patcit id="pcit0010" dnum="GB2266181A"><text>GB 2266181 A</text></patcit> is described with an intermediate layer of insulating material, which reduces the capacity of the circuits and increase the operating speed of a semiconductor integrated circuit. The interlayer insulating layer has a glass matrix containing aluminum or tantalum particles. These can be etched away by an etchant such as NaOH or KOH, are such that a layer is formed, uniformly distributed in the cavities. The disadvantage of this method is that it is only suitable for very thin layers having a thickness of less than 1 micron. Such thin layers are used in semiconductor circuits, for use on antennas are not suitable. Due to the lack of bonding of the particles to each other, the etching of a thicker layer is not possible.

p0014It is therefore an object of the present invention to provide a simple and inexpensive, and safe method for producing a ceramic substrate material for thick-film applications in the range of layer thicknesses above several ten microns, preferably with layer thicknesses of about 20 to about 30 microns, indicate that a substrate material having a produces low dielectric constant. The task is also to provide a corresponding thick ceramic substrate material which allows the use of LTCC technology. Moreover, the object is to specify a suitable use of such a ceramic substrate material. In addition, the object is to provide an antenna or an antenna array having a thick substrate material that are easy and inexpensive to produce.

p0015The stated object is achieved by a method for producing a ceramic substrate material in which an etching step is performed such that are etched in the first layer selectively coat portions of the crystals and / or crystal agglomerates of the second component to form a cavity structure in the first layer , Preferably, the cavity structure is a pore or tube structure. The structure of the cavities depends on the structure or three-dimensional shape in which the sheath portions of the second component are present, which are preferably formed from one or more transition or intermediate phases. The transitional and intermediate phases preferably have relative to the structure and / or composition of the crystalline second component to a minor change crystal structure, which may also be regions amorphous, and / or a slightly altered composition. In the composition of the mantle areas may also have components of the matrix. The composition and / or structure of the shell portions can vary over a certain range. The cladding region of a crystal or crystal agglomerate, which is composed of multiple crystals thus comprises the grain boundary area of ​​each crystal or crystal agglomerate, but may also be in addition to the stoichiometric composition of the second component extending into the crystal. The expansion of the cladding region depends also on the duration of etching and the etchant used.

p0016The specified method is a very simple and cost-effective and easily controllable method to a ceramic substrate material to produce with a low dielectric constant. It also expresses not with the above-mentioned disadvantages in the use of hollow microspheres, and takes the LTCC process unchanged. In addition, be prepared by the selective etching of the cladding regions layers having a greater thickness in the range of several 10 .mu.m, preferably etch layer thicknesses of between about 20 microns and about 30 microns, since the mantle areas of the crystals and / or crystal agglomerates connect the adjacent crystals and crystal agglomerates together and so the etchant penetrates into the layer during the etching along the mantle areas.

p0017The porosification, that is, the etching step, in which the cavity structure is produced in the matrix layer of the body, makes it possible to produce a dielectric constant that is located between the air (about 1) and the remaining glass ceramic or crystalline ceramic. This resulting dielectric constant in the porosified areas ε_r, Which is composed of the dielectric constant of the remaining material after the etching the etched layer and the dielectric constant of the cavity structure can be achieved up to the second

p0018The present invention utilizes the knowledge that a material, ie the material with a higher dielectric constant, in multiphase materials with not only two structurally and completely different from its constituent materials, but with materials that are closer by their composition and structure together ( second component on the one hand and the mantle areas of the crystals and crystal agglomerates of the second component on the other hand), which differ in their etching behavior, can be etched. In the etched-out areas after the etching step is air with a dielectric constant of about 1 before. The two materials must be selectively etchable this.

p0019In a preferred embodiment, the etching step is preferably performed by means of an appropriate mask, in a predetermined area of ​​the first layer and / or up to a predetermined depth of the first layer only in the predetermined area and / or up to the predetermined depth of the first layer to generate a hollow structure in the first layer. Hereby is achieved a locally reduced dielectric constant, namely in the region of the opening of the etch mask to a predetermined depth of the first layer, and a locally reduced dissipation factor or a local reduction of the thermal conductivity is present. Further defined mechanical predetermined breaking points can be introduced. Here, the etching depth is primarily controlled by the process parameters of temperature, concentration of the etching medium and the time of action of the etching medium. For example, can be achieved with a process time of 6 hours by a phosphoric acid etching agent based on a depth of the cavity structure in the first layer of 20 microns.

p0020In a further preferred embodiment, the matrix and the second component prior to the etching step, forming a glass-ceramic material. This material can be good in terms of the required crystal size and distribution of the second component and the cladding region of the crystals and crystal agglomerates in the first layer, and thus the subsequent structure of the etched cavity structure control. The ceramic material can be easily processed using LTCC technology. In addition, the respective tapes (tapes) are commercially available.

p0021In a further embodiment, the second component contains Al₂O₃Crystallites and / or of Al₂O₃ various aluminum-based crystalline compound and / or an alumina-based crystalline compound and surrounding mantle areas which contain as the boundary transition layer crystals and / or crystal agglomerates of the second component, ie, inter alia Al₂O₃Crystallites and / or of Al₂O₃ various aluminum-based crystalline compound and / or an alumina-based crystalline compound made. The shell portions of the specified components of the second component or the sheath ranges given are particularly easy using the preferred wet chemical etching process, preferably by means of an etching based on phosphoric acid. The phosphoric acid-based etchant to other etching steps, where other structures are produced, used, so that the handling of this etchant is known in the production.

p0022In a particularly preferred embodiment, the substrate material comprises at least two layers, wherein the at least two layers are first prepared as a LTCC by the LTCC technology, and then in the first layer, a cavity structure is produced. Construction of the two LTCC layers includes, as described above, so that the porosification made at least one sintering step in the sintered first layer. In this embodiment is advantageous in that the substrate can be produced with the usual in ceramic multilayer technology litigation with internal components and vias initially, which are not affected by the etching process. Thus, the range of the dielectric constant of 3-4, which has hitherto been realized by means of organic RF materials developed for ceramics which are produced by LTCC technology.

p0023Furthermore, it is possible with conventional methods of thin and thick film technology functional layers on the porosified material and without interruption over the transition betwe apply hen porosified and not porosified material.

p0024The above object is also achieved by a ceramic substrate material, wherein the first layer contains a second component of a further crystalline ceramic material, wherein the mantle areas of the crystals and / or crystal agglomerates of the second component is at least partially etched such that a cavity structure is present. This ceramic substrate material is simple and inexpensive to manufacture. In addition, the substrate material, thickness of the first layer is preferably several 10 microns, in some areas the desired low resulting dielectric constant of up to 2 in.

p0025Especially preferred is the hollow structure, which is a pore or tube structure. This can be manufactured easily.

p0026The second component preferably contains Al₂O₃Crystallites and / or of Al₂O₃ various aluminum-based crystalline compound and / or an alumina-based crystalline compound, preferably with a total amount of at most 40% by volume of the first layer, and the cladding regions. By this proportion of the second component or the corresponding part of the skirt areas of the crystals and / or crystal agglomerates of the second component, a sufficient strength of the ceramic substrate material after the etching, and at the same time achieve a low dielectric constant in the etched regions of the first layer. The aluminum and alumina based compounds that contain the shell portions of the second component, is also can be easily etched with a phosphoric acid-based etchant.

p0027Particularly preferably, the etched cavity structure is present only in a predetermined area of ​​the first layer and extends to a predetermined depth in the first layer. This leads to an advantageous reduction in the local dielectric constant, the dissipation factor or to a local reduction in the thermal conductivity.

p0028In the etched areas, the resulting dielectric constant is ε_r, Preferably between about 10 and 1, more preferably between about 5 and 1. The local reduction of ε_r is advantageous because for a radar sensor, in particular in the range of 80 GHz, the distribution network should have a high dielectric constant to minimize radiation effects.

p0029Particularly preferably, the ceramic substrate material on at least two layers which are produced by LTCC technology. The LTCC technology simplifies the manufacture of the ceramic substrate material. The method is cost.

p0030The inventive use of an above-mentioned ceramic substrate material involves the application for an antenna or an antenna array, in particular for high frequencies in the range of 80 GHz.

p0031According to the invention the object is achieved by an antenna or an antenna array with a substrate material according to the invention indicated above.

p0032In the conventional antennas or antenna arrays typically a Rogers tape is stuck in an LTCC cavity and associated metallization overlying the two areas by wire bonding. In a preferred embodiment of an antenna according to the invention or an inventive antenna array has contrast in each of its elements in the first layer in regions, an etched cavity structure and the metallization overlying extending from the area of ​​the etched cavity structure into a region where no etched cavity structure present. The metallization can be embodied here as a thick film or thin film metallization. The advantage of such an antenna or an antenna array is that a wire bonding connection between the metallisations is no longer necessary and thereby the reliability of the overall structure is increased, since a combination of materials required and the number of bonding adhesive bodies is reduced. In addition, the AVT (<u>A</u>ufbau- and <u>V</u>heiress manure<u>t</u>echnology) simplified because no bonding step is necessary.

p0033Other objects, features, advantages and applications of the invention will become apparent from the following description of an embodiment with reference to an in <figref idrefs="f0001">figure 1</figref> specified diagram. Further, the structure of an antenna according to the invention using a schematic sectional drawing in will<figref idrefs="f0002">figure 2</figref> shown. All described and / or illustrated features form by themselves or in any combination form the subject matter of the present invention, irrespective of their summary in the individual claims or their reference

Examples

p0034A substrate material having a first layer comprising a sintered glass-ceramic, for. Example, a LTCC tape having a composition of 30% SiO₂, 40% Al₂O₃, 4% CaO, 9% PbO, 2% B₂O₃ + Rest - known as the Produktbezeichung DP951, the composition 30% SiO₂, 20% Al₂O₃, 3% CaO, 5% of SrO, 17% BaO, 5% ZnO + residue - known as "Tape-Heraeus" - or composition of about 50% Al₂O₃About 15% B₂O₃, About 15% La₂O₃+ Residue, which is known under the product name of the DP943 Fa. Hereaus, for porosification is at a temperature of 110 ° C in a suitable etching solution (for example, for DP951, "Heraeus Tape" DP943 and phosphoric acid) added. The porosification may alternatively be carried out using KOH (potassium hydroxide solution) of a concentration of about 40% at a temperature in the range of 80 ° C.

p0035In the diagram of <figref idrefs="f0001">figure 1</figref> Illustrated curve shows the dependence of the depth of penetration of the etching solution of phosphoric acid in the volume of the glass ceramic DP951 having a composition of 30% SiO₂, 40% Al₂O₃, 4% CaO, 9% PbO, 2% B₂O₃ + Moiety has at an etching temperature of 110 ° C or 90 ° C and therefore the depth of the cavity structure produced in the first layer in microns on the Y-axis from the plotted on the X-axis etching time in hours, as the depth of penetration by the etching time can be controlled. For example, at an etching temperature of 110 ° C, a penetration depth of 15 microns is achieved with an etching time of four hours.

p0036In <figref idrefs="f0002">figure 2</figref> is shown in section of the construction of an antenna according to the invention. In a first layer 10, a porosified area 12 is provided with the etched cavity structure having a low dielectric constant. The porosified area 12 merges seamlessly with the other, non-porosified regions 11 of the first layer 10th On the surface of a metallized layer (metallization) 20 is arranged, which is formed above the porosified region 12 as an antenna structure 22nd Above the remaining portions 11 of the first layer 10, the metallized layer is formed as a conductor track 25th The metallization to the antenna structure 22 and the conductor track 25 may be applied simultaneously in a metallization step without additional bonding.