Abstract:
A millimeter wave transceiver including a plate forming an interposer having its upper surface supporting an interconnection network and having its lower surface intended to be assembled on an electronic device; at least one integrated circuit chip assembled on the upper surface of the interposer; at least one antenna including at least one track formed on the upper surface of the interposer; and at least one block attached under the plate and including in front of each antenna a cavity having a metalized bottom, the distance between each antenna and the bottom being on the order of one quarter of the wavelength, taking into account the dielectric constants of the interposed materials.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to transceiver systems capable of operating with millimeter waves and capable of issuing and receiving signals from devices arranged at distances greater than one meter, for example, on the order of 10 meters. 
         [0003]    2. Description of the Related Art 
         [0004]    In a system operating with millimeter waves, for example, at a frequency on the order of 60 GHz, the available powers are such that antenna arrays providing directional beams, often called phased arrays, are employed. In such arrays, each antenna transmits a signal which is phase-shifted with respect to that of the other antennas or is capable of receiving a signal which is phase-shifted with respect to that of the other antennas. 
         [0005]    At 60 GHz, the wavelength in air is 5 mm. The largest dimension of antennas currently is on the order of half the wavelength, that is, 2.5 mm, and each antenna is separated from the surrounding antennas by a distance at least of the same order of magnitude. 
         [0006]    Accordingly, it is in practice impossible to arrange the antenna array on the integrated circuit chip which contains the electronic circuits capable of providing, receiving, processing, and amplifying the high-frequency signals of the antennas. This would indeed result in prohibitive chip dimensions. 
         [0007]    Known devices have often used antennas assembled on individual substrates inserted in a ceramic block, also intended to receive the integrated processing circuit. This makes the system relatively complex, all the more as the track lengths between each of the elements should be made the shortest possible to avoid stray radiations and interferences. Further, some of these systems force the card manufacturer to provide relatively complicated devices to reprocess the transmitted/received signals. 
       BRIEF SUMMARY 
       [0008]    One embodiment of the disclosure is a system forming a single assembly comprising a circuit of high-frequency signal transmission-reception, and advantageously processing and amplification, and an array of transceiver antennas of minimum bulk. 
         [0009]    One embodiment of the disclosure is to a system which is particularly adapted to being simply assembled on a printed circuit board. 
         [0010]    One embodiment of the disclosure is a millimeter wave transceiver comprising: a plate forming an interposer having its upper surface supporting an interconnection network and having its lower surface intended to be assembled on an electronic device; at least one integrated circuit chip assembled on the upper surface of the interposer; at least one antenna comprising at least one track formed on the upper surface of the interposer; and at least one block attached under the plate and comprising in front of each antenna a cavity having a metalized bottom, the distance between each antenna and the bottom being on the order of one quarter of the wavelength, taking into account the dielectric constants of the interposed materials. 
         [0011]    According to an embodiment, each of the antennas is totally or partly surrounded with a peripheral conductive track on the upper surface of the interposer, said track being connected to a network of through vias in contact or in quasi-contact with a metallization of the block. 
         [0012]    According to an embodiment, the interposer is a silicon plate. 
         [0013]    According to an embodiment, the upper surface is coated with an encapsulation resin. 
         [0014]    According to an embodiment, the bottom and the peripheral conductive tracks are grounded. 
         [0015]    According to an embodiment, the electronic device is a printed circuit board and the interposer is assembled on the board by bumps. 
         [0016]    The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]      FIG. 1  is a simplified cross-section view of a portion of an integrated transceiver system; 
           [0018]      FIG. 2  is a simplified cross-section view of an antenna portion of the transceiver system of  FIG. 1 ; 
           [0019]      FIG. 3  is a top view of an antenna element; and 
           [0020]      FIG. 4  is a general top view of a transceiver system. 
       
    
    
       [0021]    For clarity, the same elements have been designated with the same reference numerals in the different drawings and, further, as usual in the representation of integrated circuits, the various drawings are not to scale. 
       DETAILED DESCRIPTION 
       [0022]      FIG. 1  is a very simplified cross-section view of an electronic device that includes a millimeter wave transceiver assembly  2  mounted on a printed circuit board  4 . This assembly  2  comprises an integrated circuit chip  1  comprising various circuits for processing and amplifying high-frequency signals transmitted/received by antennas. On its lower side, the chip comprises an assembly of conductive and insulating layers, not shown, forming interconnection levels for the interconnection of the various chip components and the connection of these components to the outside. 
         [0023]    Chip  1  is assembled on an interposer plate  3 . This plate is topped with an interconnection network, not shown, comprising insulating layers, metal tracks on one or more levels, and vias. The assembly of chip  1  on interposer plate  3  is for example performed via conductive pillars  5 , for example, made of copper. 
         [0024]    In interposer  3 , which for example is a silicon or glass plate, are formed insulated conductive through vias  8 , a single one being shown, which are connected by the interconnection network to pads of chip  1 . Metallizations  20 , actually comprising, in practice, an assembly of metallizations to which (welded) conductive bumps  21  are attached, are formed on the lower side of the interposer plate. The conductive bumps  21  are attached to conductive pads  22  on a surface of the printed circuit board  4  in order to electrically couple the transceiver  2  to other circuits of the electronic device that are also mounted on the printed circuit board (not shown). 
         [0025]    On the upper surface of interposer plate  3  are arranged antennas  30  formed of conductive tracks according to any antenna configuration suitable for the transmission and/or the reception of millimeter waves. Although a single antenna appears in the cross-section view of  FIG. 1 , it should be understood that there is a number of transmitting antennas and a number of receiving antennas which are connected by metallization levels, not shown, to appropriate terminals of chip  1  so that, in operation, each of these antennas is excited with a given phase-shift with respect to the other antennas. 
         [0026]    An antenna  30  transmits, when excited, a high-frequency radiation, upwards as well as downwards. To improve the efficiency of the antenna and avoid stray radiations, the beam that this antenna sends downwards is sent back up. To achieve this, it is provided to arrange under antenna assemblies a block  32  comprising, directly under each antenna  30 , a recess  34  coated with a metallization  36  having its bottom  38  forming a reflector. This reflector should be arranged at a vertical distance on the order of λ/4 from the antenna, X, being the wavelength of the radiation. Of course, distance λ/4 should take into account the fact that the space between the antenna and the reflector comprises the thickness of the interposer plate  3 , having a dielectric constant on the order of 12 if this interposer is made of silicon, and an air gap having a dielectric constant equal to 1, as well as possibly, a small insulator thickness between the antenna and the interposer. The thickness of the interposer plate is accurately known and the height of the recess in block  32  is also accurately determined. 
         [0027]    As a numerical example, for a silicon interposer having a 120-μm thickness, the recess height will be 400 μm for a 60-GHz frequency, which results in an operating bandwidth on the order of 13 GHz. 
         [0028]      FIG. 2  is a cross-section view of a portion of the assembly described herein comprising, on the upper side of interposer plate  3 , antennas  30 . A portion of a block  32  comprising several recesses has been shown. Block  32  is advantageously made of silicon and may be manufactured and attached by any known means to the lower surface of the interposer. Especially, technologies developed in the field of the manufacturing and assembly of MEMS (Micro-Electro-Mechanical-System) may be used. Preferably, the upper surface of block  32  in contact with interposer  3  is also coated with a metal layer  40  and the periphery of each antenna region is surrounded with a conductive track  42 . Surrounding track  42  is connected by a network of conductive vias  44  to lower layer  40  (these vias are effectively in contact with layer  40  or are separated therefrom by a small distance as compared with the wavelength of the antenna radiation—this is called a quasi-contact). Thus, the downward radiation of antenna  30  reflects on reflector  38  but cannot diverge to create parasitic waves, especially in the interposer, due to the tight network of vias which surrounds the area separating the antenna from its reflector, forming a Faraday cage. Thus, any influence of an antenna  30  on the neighboring antennas and/or on integrated circuit chip  1  is avoided. A double network of tracks and vias has been shown in  FIG. 2 . A simple surrounding line  42  and a single network of vias  44  may also be used. 
         [0029]      FIG. 3  is a top view of an antenna  30  surrounded with a track  42  connected by regularly distributed vias  44  to the upper surface metallization of block  32 . Preferably, the surrounding track and metallizations  36 ,  38 ,  40  are grounded. Bumps  21  shown in  FIG. 1  may be attached to interposer  3  after installation of block(s)  32 . Block(s)  32  will have a thickness smaller than the bump diameter so that, when the system is arranged on a printed circuit board, there is no contact between these blocks and the printed circuit board. 
         [0030]    Thus, chip  1 , interposer plate  3 , and bumps  21  form an assembly ready to be delivered by a manufacturer to a system assembler which assembles the above-mentioned assembly on another electronic device, for example, a printed circuit board on which metallizations capable of receiving bumps  21  are formed. The upper surface of this assembly is preferably encapsulated in an insulating body  25 , for example, made of resin, to protect the product and possibly mark it ( FIG. 1 ). 
         [0031]    According to an advantage of the above-described system, the connections between the chip and the antennas may have well-determined minimum lengths. 
         [0032]      FIG. 4  is a general view of the system. It shows, in its central portion, integrated circuit  1  and connection pads of this circuit intended to be connected to the above-mentioned through vias  8 . Antennas  30 , by the number of  16  in the shown example, are arranged on either side of integrated circuit  1 . As indicated, each of these antennas is surrounded with a conductive track  42  periodically connected by vias  44  to a corresponding conductive track formed under interposer  3 . A block  32  may be provided under each of the antenna assemblies or a single block may be provided under the entire interposer plate. 
         [0033]    This top view shows that each of the antennas is insulated from the neighboring ones and from the environment by the via network. 
         [0034]    Of course, the present disclosure is likely to have various alterations which will occur to those skilled in the art, especially as concerns the shape of the antennas. Further, the various metallization levels formed on the interposer, and especially the metallizations intended to connect the integrated circuit to each of the antennas, have not been described in detail. Indeed, these are common layouts. What matters is for all the metallizations to be arranged on a same surface of an interposer and thus to have a minimum dimension. 
         [0035]    Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present disclosure. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. 
         [0036]    The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.