Abstract:
A radiofrequency assembly includes a module with an antenna assembly formed in a semiconductor integrated circuit. The semiconductor integrated circuit can carry out at least one of the following functions: transmitting an electromagnetic signal, and receiving an electromagnetic signal. The radiofrequency assembly further includes a horn-like structure with a base portion adapted to fit on the module. The horn-like structure has an extending horn-shaped portion an input opening that encloses the antenna assembly when the horn-like structure is fitted on the module.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a National Stage Entry into the United States Patent and Trademark Office from International PCT Patent Application No. PCT/NL2014/050276, having an international filing date of Apr. 28, 2014, and which relies for priority on Netherlands Patent Application No. 1040185, filed Apr. 26, 2013, the entire contents of both of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a module comprising an antenna assembly formed in a semiconductor integrated circuit. The module may functionally constitute, for example, a radar device. 
       BACKGROUND OF THE INVENTION 
       [0003]    Analog and digital integrated circuits (ICs) are typically designed and manufactured in silicon, GaAs, GaN or SiGe processes, which may be of the BiCMOS or CMOS type. These ICs can be mass-produced, for example, on 8 or 12 inch wafers. After production of a wafer, the wafer is diced to separate the ICs from each other, typically through sawing. 
         [0004]    Dicing process is a relatively rough process: a diamond saw cuts through a wafer. As silicon is quite brittle, cracks may form relatively easily and extend into electronic circuitry. The electronic circuitry may then become defective: it is not capable of operating according to desired specifications, or even not capable of operating at all. 
         [0005]    A standard way of preventing cracks forming into the electronic circuitry is by placing a “seal-ring” around all circuitry. A seal-ring is a ring consisting of (nearly) all doping- and metal-layers placed around the electronic circuitry. Silicon-nitride is usually placed as last layer on top of all circuitry (except bump-pads and bond-pads as they need to be electrically connected to the outside world) to prevent moisture getting into the silicon. The seal-ring also has an opening in the silicon-nitride as a silicon-nitride layer is also quite brittle (similar to glass), again to prevent cracks from entering the IC. 
         [0006]    This seal-ring is therefore an essential part of the mass-production process of silicon chips in order to realize a high reliability and a high yield. 
         [0007]    With integration of RF electronics on silicon, proposals of implementing antennas on silicon have come up. Antennas are used in all electronic equipment (from GSM, GPS, DECT, Bluetooth to radar systems) to convert electrical energy to electromagnetic energy and vice-versa. However, when these antennas are placed inside a seal-ring, the seal-ring can short the electromagnetic field of the antenna. This reduces radiation efficiency and affects the radiation pattern of the antenna. Some antenna-on-silicon designs simply ignore production process requirements by leaving out the seal-ring, resulting in lower yields or reliability problems or breakdown after some time in the application. Other designs implement antennas in special post-production processes thus increasing overall costs. 
         [0008]    Modern IC processes require a minimum and maximum use of metal per given silicon-area for reproducibility of the etching process and the chemical-mechanical-polishing used in the back-end processing. Usually a defined metal-filling (called tiling) using minimum sized structures fulfils the metal density requirement without disturbing overall performance too much. 
         [0009]    When antennas are placed on the silicon, testing becomes an issue as DC-voltage, output power and matching can no longer be measured. 
         [0010]    When the abovementioned problems are solved, antennas can be integrated side-to-side a complete radar. Even if the antenna is not integrated on the silicon but in the package the overall “module” can be seen as a single device. Antennas usually have a size close to lambda/4 or lambda/2, where lambda is the wavelength in the material or in free-space. For 60 GHz the free-space wavelength is 5 mm, and antenna can thus be 1.25 mm or smaller pending the dielectric constant of the material. 
         [0011]    Single antennas usually have a relatively wide radiation pattern, which can be as wide as ±60 degrees in azimuth and ±60 degrees in elevation. For some applications this beam-width is too wide. Narrower beam-widths can be realized with antenna arrays: multiple antennas in a row, column or matrix driven with the proper phase and amplitude for each antenna. This can be done on the silicon, but results in a new design (usually resulting in a much larger silicon area to accommodate the extra antennas) and thus a new, expensive mask-set. Economy of scales may be difficult to reach if the market consists of a large number of applications with low quantities. It would be much nicer if a low-cost, easy to mass-produce, auto-aligned structure can be made that allows defining the radiation pattern after the silicon is produced. 
         [0012]    Parabolic dish antennas and horn antennas have been known to provide well defined gains and (narrow) beam-widths. However, a special heavy and expensive launcher used to launch the electromagnetic wave into a waveguide or horn antenna. For satisfactory performance the waveguide should also be aligned with the horn antenna. 
       SUMMARY OF THE INVENTION 
       [0013]    There is a need for a solution that allows achieving a desired radiation pattern with integrated antennas at relatively low cost and suitable for mass production. 
         [0014]    In accordance with an aspect of the invention, there is provided a radiofrequency assembly that includes: 
         [0015]    a module comprising an antenna assembly formed in a semiconductor integrated circuit and arranged to carry out at least one of the following functions: transmitting an electromagnetic signal, and receiving an electromagnetic signal; and 
         [0016]    a horn-like structure including:
       a base portion adapted to fit on the module;   an extending horn-shaped portion having an input opening that encloses the antenna assembly when the horn-like structure is fitted on the module.       
 
         [0019]    The base portion may include an inner circumference that matches with an outer circumference of the module. 
         [0020]    The base portion may include L-shaped edges that engage with edge portions of the module. 
         [0021]    The antenna assembly that is enclosed by the input opening of the extending horn-shaped portion may include various antennas. 
         [0022]    The antennas may be located off center with respect to the input opening. 
         [0023]    The antenna assembly may include at least one transmitter antenna and at least one receiver antenna. 
         [0024]    The antenna assembly may include various receiver antennas for an angle of arrival measurement. 
         [0025]    In addition, solutions are provided to avoid a seal ring from significantly influencing an electro-magnetic-field, and solutions for testing a radiofrequency module with integrated antennas. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0026]      FIG. 1  is a schematic top view of an integrated circuit with integrated antennas. 
           [0027]      FIG. 2  is a perspective view of a portion of the integrated circuit near a base of an antenna. 
           [0028]      FIG. 3  is another perspective, semi-transparent view of this portion of the integrated circuit. 
           [0029]      FIG. 4  is yet another perspective, semi-transparent view of this portion of the integrated circuit. 
           [0030]      FIG. 5  is a schematic cross-sectional view of a radar assembly that comprises a horn-like structure, which is mounted on a module in which the integrated circuit is embedded. 
           [0031]      FIG. 7  is a completed version of  FIG. 1  in which an input opening of the horn-like structure is indicated. 
           [0032]      FIG. 8  is a diagram of angle-of-arrival measurements results that have been obtained. 
           [0033]      FIGS. 9   a,    10   a,    11   a  are schematic perspective views of several different horn-like structures. 
           [0034]      FIGS. 9   b,    10   b,    11   b  are diagrams of measured radiation patterns of the horn-like structures illustrated in  FIGS. 9   a,    10   a,  and  11   a,  respectively. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]      FIG. 1  illustrates an example of an integrated circuit (IC)  100 .  FIG. 1  provides a schematic top view of the integrated circuit  100 . The integrated circuit  100  comprises three antennas  101 ,  102 , and  103 . A first antenna  101  is located near one side of the integrated circuit  100 . A second antenna  102  and a third antenna  103  are located near an opposite side of the integrated circuit  100 . The integrated circuit  100  comprises electronic circuits  104 , which may include analog circuits as well as digital circuits. 
         [0036]    The integrated circuit  100  further comprises two seal rings: an inner seal ring  105  and an outer seal ring  106 . These seal rings  105 ,  106  prevent cracks from occurring in the electronic circuits  104  in a dicing process as explained hereinbefore. The inner seal ring  105  may comprise all doping layers in combination with all metal layers. The outer seal ring  106  may also comprise all doping layers and all metal layers. In the example of  FIG. 1 , the inner seal ring  105  and the outer seal ring  106  are non-overlapping. In an alternative embodiment, such seal rings may partially overlap along at least one side of the integrated circuit  100 . 
         [0037]    The first antenna  101  is coupled to a center bond pad  111  that has two neighboring side bond pads: a left side bond pad and a right side bond pad. Similarly, the second antenna  102  is coupled to a center bond pad  112 , which has two neighboring side bond pads: a left side bond pad and a right side bond pad. The third antenna  103  is coupled to a center bond pad  113 , which has two neighboring side bond pads: a left side bond pad and a right side bond pad. The aforementioned neighboring side bond pads may be coupled to signal and the inner seal-ring  105 . In some applications, it may be useful to avoid metal layers in an area around an antenna.  FIG. 1  illustrates such areas around the three antennas  101 ,  102 , and  103  by means rectangles in broken lines. 
         [0038]    The inner seal ring  105  comprises an opening  121  near a base of the first antenna  101 . The opening  121  extends to a top metal layer and a via layer that is associated with this top metal layer, which layers form part of the inner seal ring  105 . A connection between the first antenna  101  and the center bond pad  111  passes through this opening  121  in the inner seal ring  105 . The inner seal ring  105  comprises similar openings  122  and  123  near a base of the second antenna  102  end near a base of the third antenna  103 , respectively. 
         [0039]    The integrated circuit  100  illustrated in  FIG. 1  may functionally form, for example, a radar device, such as, a Frequency Modulated Continuous Wave (FMCW) radar device. In FMCW radar devices, a transmitter and a receiver operate simultaneously. Isolation between the transmitter and the receiver, including antennas, is therefore important. If there is insufficient isolation, this will significantly impair radar performance, in particular in terms of detection range. In  FIG. 1 , the first antenna  101  may be, for example, a transmitter antenna. The second and third antennas  102 ,  103  may then be receiver antennas. In this configuration, the isolation between the transmitter antenna and the receiver antennas can be sufficient for satisfactory radar performance. The use of two receiver antennas, the second and third antennas  102 ,  103 , allows determining an angle-of-arrival of reflections in a radar mode setup. 
         [0040]    The integrated circuit  100  may be embedded in a module  140  as described in, for example, patent publication WO 2014/049088. This will be described in greater detail hereinafter. 
         [0041]      FIG. 2  illustrates in greater detail a portion of the integrated circuit  100  near the base of the first antenna  101 .  FIG. 2  provides a perspective view of this integrated circuit portion.  FIG. 2  clearly illustrates that the left side bond pad and the right side bond pad are coupled to the inner seal ring  105 .  FIG. 2  further clearly illustrates the opening  121  in the inner seal ring  105 , which comprises an opening in the top metal layer that forms part of the inner seal ring.  FIG. 2  further illustrates tiling areas  209  and  210  adjacent to the first antenna  101 . These tiling areas  209  and  210  comprise patches formed in a metal layer that ensure a presence of metal in this layer within a desired use range. 
         [0042]      FIG. 3  illustrates another perspective, semi-transparent view of the portion concerned of the integrated circuit  100 , in a direction from the outside towards the inside. The first antenna  101  is electrically coupled to the center bond pad  111  by means of a path formed in the top-metal layer. It should be noted that electrical coupling may be DC or AC. The opening  121  in the inner seal ring  105  is also clearly visible.  FIG. 3  further illustrates openings  307  in a nitride layer that covers the integrated circuit  100 .  FIG. 3  further illustrates that the inner seal ring  105  comprises a pile-up of different layers  308 , which lie underneath the path in the top metal layer, which electrically couples the first antenna  101  to the center bond pad  111 . These layers  308  within the inner seal ring  105  are not affected by the opening  121  in this example. 
         [0043]      FIG. 4  shows yet another perspective, semi-transparent view of the portion concerned of the integrated circuit  100 , in a direction from the inside towards the outside. 
         [0044]    For testing purposes, several solutions can be envisaged. A first solution is to add bond pads or bump pads, or a combination of such pads, on which a signal of interest is present. Standard integrated circuit testing methods can be used to place probes on these pads. Accordingly, a DC levels can then be measured, as well as radiofrequency signal properties, such as, for example, frequency, amplitude, power, and spurious components. However, radiofrequency measurements may be influenced by antenna radiation. This influence can be accounted for by establishing reference measurement results and correlating actual measurement results with the reference measurements results. Accordingly, functionality and performance of a device-under-test can be determined. 
         [0045]    A second solution can be to provide the integrated circuit  100  with on-chip measurements circuits. A DC voltage can be measured with an on-chip analog-to-digital converter. Preferably, a proper isolation circuit is provided so as to prevent that radiofrequency performance is adversely affected. The frequency of a radiofrequency signal can be measured indirectly by means of on-chip frequency dividers, which provide a frequency-divided signal whose frequency can be measured. An output power can be measured by means of an on-chip power sensor. Such a power sensor may have a large bandwidth. Any spurious component within the bandwidth of the power sensor will be measurable. Matching of an antenna to a circuit can be measured by an on-chip measurement of power reflected by the antenna. 
         [0046]    An integrated antenna, such as the first, the second, or the third antenna  101 ,  102 ,  103 , has a radiation pattern that is relatively wide, such as, for example, ±60 degrees. A narrower radiation pattern may be desired. In principle, this can be achieved by means of an array of integrated antennas. However, this is a relatively costly solution. An integrated antenna for electromagnetic signals in the millimeter wave range is relatively large. That is, a relatively large integrated circuit area is required to form an integrated antenna. In the example illustrated in  FIG. 1 , the three antennas  101 ,  102  and  103  already occupy an area that is similar in size as the area that the electronic circuitry  104  occupies. 
         [0047]    A more cost-efficient solution for obtaining a relatively narrow radiation pattern is to place a horn like structure on an integrated circuit with integrated antennas, or on a module in which such an integrated circuit is embedded. The horn like structure preferably comprises a base portion that fits on the integrated circuit, or the module, whichever applies. The base portion may comprise an inner circumference that matches with an outer circumference of the integrated circuit, or the module, whichever applies. An extending horn-shaped portion of the horn like structure is disposed with respect to the base portion so that the extending horn-shaped portion is suitably disposed with respect to the integrated antennas or on the horn like structure is mounted on the integrated circuit, or the module, whichever applies. 
         [0048]      FIG. 5  illustrates a radar assembly  1000  that comprises a horn-like structure  1010 , which is mounted on the module  140  in which the integrated circuit  100  is embedded.  FIG. 5  provides a schematic cross-sectional view of this assembly  1000 . The module  140  comprises an epoxy layer  1008  that covers the integrated circuit  100 . The module  140  further comprises a substrate  1009  on which the integrated circuit  100  is mounted by means of, for example, gluing. This substrate  1009  may be in the form of, for example, a printed circuit board. Bonding wires may electrically couple the integrated circuit  100  to the substrate  1009 . The module  140  is mounted on a main printed circuit board  1006  by means of, for example soldering. 
         [0049]    The horn-like structure  1010  comprises a base portion  1011  and an extending horn-shaped portion  1012 . The base portion  1011  fits on the module  140 . The base portion may comprise an inner circumference that matches with an outer circumference of the module. More specifically, the base portion  1011  may comprise L-shaped edges that engage with edge portions of the module  140  as illustrated in  FIG. 5 . 
         [0050]    Dimensions of the module  140  may vary within a range of, for example, 50 μm. The base portion is designed to account for these tolerances so as to ensure a proper fit. The extending horn-shaped portion of the horn like structure is suitably disposed with respect to the base portion  1011  as will be discussed hereinafter.  FIG. 5  thus illustrates a solution that allows automatic alignment and robustness, which are required for mass-production consumer-like products. 
         [0051]    The horn-like structure  1010  may be mounted on the printed circuit board  1006  by means of, for example, screws  1003  and  1004 . The radar assembly  1000  may be attached to a casing by means of screws  1001  and  1002  in a flange of an upper section of the extending horn-shape portion  1012 . Instead of screws  1001 - 1004 , clips or any other suitable fastening element can be used. 
         [0052]      FIG. 6  further illustrates the radar assembly  1000  by providing a schematic top view thereof. It is noted that the schematic cross-sectional view of  FIG. 5  corresponds with a cross-section along line B-B′ indicated in  FIG. 6 . The module  140  is represented by means of dotted lines.  FIG. 6  illustrates that the extending horn-shaped portion  1012  has an input opening  1020 , which faces the module  140 . This input opening  1020  may be smaller than the module  140 , but should preferably be larger than an area within which the three antennas  101 ,  102 , and  103  are present. That is, the input opening should  1020  enclose the three antennas  101 ,  102 , and  103 . 
         [0053]      FIG. 7  is a completed version of  FIG. 1  in which a rectangle  130  formed by dotted lines represents the input opening  1020  of the extending horn-shaped portion  1012  illustrated in  FIG. 6 . As an example, let it be assumed that the module  140  has a dimension of 7 by 7 mm. In this example, the input opening may be, for example, 5 by 5 mm. The outer seal ring  106  can be regarded as a circumference of the integrated circuit  100 , which may be, for example, 3 by 3 mm. 
         [0054]    In  FIG. 6 , it can be seen that the three antennas  101 ,  102 , and  103  antennas are located somewhat off-centre, rather than exactly in the centre of the input opening of the extending horn-shaped portion. Surprisingly, this does not significantly affect performance. For example, an angle of arrival can be determined with sufficient precision by means of the second and third antennas  102 ,  103 , which are the two receiver antennas. It has been found an off-centered integrated antenna can provide satisfactory performance in particular if the following general rule is observed. The integrated antenna has a distance with respect to a nearest boundary of the input opening that is at least λ/2, whereby λ denotes a wavelength of interest, typically the wavelength at which the aforementioned radar device operates. 
         [0055]      FIG. 8  illustrates angle-of-arrival measurements results obtained with an integrated circuit, which has been provided with a horn-like structure. More specifically,  FIG. 8  illustrates a mono-pulse radar characteristic obtained with a sum-and-difference method. In  FIG. 8 , a vertical axis  901  represents a difference pattern. A horizontal axis  902  represents an angle from which a reflection is received. Curve  903  represents a measured characteristic. Curve  904  shows a theoretical characteristic, which has been calculated based on theory.  FIG. 8  thus shows that it is feasible to measure an angle of arrival with a radar assembly wherein multiple integrated antennas are within an opening end of a horn-like structure as illustrated in  FIGS. 5 and 6 . 
         [0056]    An advantage of the solution described hereinbefore is that it is possible to obtain a wide variety of different radiations patterns on the basis of a same integrated circuit, as the one illustrated in  FIG. 1 . A desired radiation pattern can be obtained by placing on the integrated circuit a horn-like structure that has a particularly shaped and sized extending horn-shaped portion. The extending horn-shaped portion is shaped and sized so that a desired radiation pattern is obtained. According to theory on horn-antennas, a beam width, which can be characterized by a 3 dB reduction of maximum antenna gain, depends on an antenna aperture, which corresponds to a width of the extending horn-shaped portion. More specifically, the product of these parameters, antenna aperture and beam-width, is constant. This holds both for azimuth and for elevation. 
         [0057]    Accordingly, a desired radiation pattern can be obtained by placing on the integrated circuit a horn-like extension having appropriate apertures. There is thus no need to design the integrated circuit for a specific radiation pattern. Moreover, it is relatively easy to modify a radiation pattern of a radar assembly as the one illustrated in  FIGS. 5 and 6 . It is sufficient to replace the hornlike extension by another horn-like extension. The solution described hereinbefore can thus be more cost efficient than entirely relying on an antenna array for obtaining a desired radiation pattern. In addition, the solution based on a horn-like structure obviates the need for a so-called launcher, which is typically used to convert signals from a cable connector assembly to a waveguide assembly. The horn-like structure can be regarded as functionally replacing such a launcher. 
         [0058]      FIGS. 9   a,    10   a,  and  11   a  illustrate several horn-like structures that can be placed on an integrated circuit with integrated antennas as the one illustrated in  FIG. 1 .  FIGS. 9   b,    10   b  and  11   b  illustrate measured radiation diagrams of the horn-like structures illustrated in  FIGS. 9   a,    10   a,  and  11   a,  respectively. In  FIGS. 9   b,    10   b  and  11   b,  curves  601 ,  701  and  801 , respectively, represent a radiation pattern in azimuth direction. Curves  602 ,  702 ,  802 , respectively, represent a radiation pattern in elevation direction. These figures clearly show that different radiation patterns can be obtained with different horn-like structures. These figures further confirm that the product of the aforementioned parameters, antenna aperture and beam-width, is constant. 
         [0059]    Numerous different materials are suitable for making a horn-like structure like the one illustrated in  FIGS. 5 and 6 , as well as like those illustrated in  FIGS. 9   a,    10   a,  and  11   a.  For example, a horn-like structure may be made of standard copper-plated FR4 epoxy. Various other materials are also suitable: metal, plastic, in various combinations, plastic coated with metal, 3D-printed forms comprising metal, plastic or plastic coated with metal, plastic with a metal-tape or metal-spray, etc. Pure plastic may also be suitable if the plastic has an appropriate design and dielectric constant. 
         [0060]    A horn-like structure may be open, that is, without any filling. However, a horn-like structure may be filled with a dielectric material. In fact, the horn-like structure may comprise a horn-shaped block of dielectric material. Surfaces of such a horn-shaped block may be provided with a metal coating by means of, for example, spraying. A dielectric filling material can be given a particular shape that forms a lens-like structure. This can contribute to obtaining a desired radiation pattern, such as, for example, a relatively narrow beam in a particular direction. 
         [0061]    It should be noted that robustness depends on a combination of weight and size of, on the one hand, a horn-like structure and, on the other hand, a module comprising an integrated circuit. For example, the module illustrated in  FIG. 5  may weigh less than 1 g. The horn-like structure may have a similar weight. 
         [0062]    The detailed description hereinbefore with reference to the drawings is merely an illustration of the invention and the additional features, which are defined in the claims. The invention can be implemented in numerous different ways. In order to illustrate this, some alternatives are briefly indicated. 
         [0063]    The invention may be applied in numerous types of products or methods related to transmitting or receiving electromagnetic signals, or both. Radar applications are merely an example. As another example, the invention may be applied to in telecommunication devices, which may comprise antennas formed an integrated circuit. 
         [0064]    A horn-like structure need not necessarily have a rectangular shape as in the examples presented hereinbefore. For example, a horn-like structure may have a round shape, an elliptical shape, a hexagonal shape, or an octagonal shape, or any other type of angular shape. 
         [0065]    A horn-like structure need not necessarily enclose three integrated antennas as in the examples presented during before. In principle, a horn-like structure may enclose any number of integrated antennas. A horn-like structure may enclose an array of antennas. Beam-steering is also possible with an array of antennas enclosed in a horn-like structure. 
         [0066]    The solutions presented in this application are valid for different types of polarizations: horizontal, vertical, circular or any combination of these polarizations. Inserts in a back portion of a horn-like structure can be used to modify a polarization. 
         [0067]    A horn-like structure can be manufactured in numerous different fashions, such as, for example, using standard plastic molding, 3D-printing, or even by hand. 
         [0068]    The remarks made hereinbefore demonstrate that the detailed description with reference to the drawings is an illustration of the invention rather than a limitation. The invention can be implemented in numerous alternative ways that are within the scope of the appended claims. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. Any reference sign in a claim should not be construed as limiting the claim. The word “comprising” does not exclude the presence of other elements or steps than those listed in a claim. The word “a” or “an” preceding an element or step does not exclude the presence of a plurality of such elements or steps. The mere fact that respective dependent claims define respective additional features, does not exclude combinations of additional features other than those reflected in the claims.