Abstract:
A thin-film, radio frequency terminator is provided that includes a mounting flange and a thin-film termination chip mounted on a surface of the mounting flange. The mounting flange grounds the termination chip. The termination chip includes a substrate, a terminal, a metallization layer including a resistor pad electrically connecting the terminal to the mounting flange, and a cover. The terminator has a low physical profile but provides high power handling capability.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to radio frequency (RF) power electronics. More specifically, the present invention relates to a thin-film RF power terminator. 
         [0003]    2. Related Art 
         [0004]    Terminators provide electrical resistance to present an electrical load to an RF transmitter and an associated transmission line. Additionally, terminators prevent a signal from being reflected back from the end of the transmission line and causing interference. Often, terminators are used in wireless communications networks. For example, a terminator can be incorporated in a transmitter circuit of a wireless node (e.g., a base station, a relay station, a mobile device, etc.). Unfortunately, terminators often have bulky configurations that create design challenges, particularly when the terminators must handle significant (e.g., 1000 Watts or greater) power loads. As such, there is a need to provide high-power RF terminators that have a lower profile while providing sufficient power handling capability. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention relates to a high-power, thin-film radio frequency power terminator. The terminator includes a mounting flange and a thin-film termination chip mounted on a surface of the mounting flange. The mounting flange provides a ground terminal for the termination chip. The termination chip is manufactured using thin-film manufacturing techniques, and includes a substrate, a terminal, a metallization layer including a resistor pad electrically connecting the terminal to the mounting flange, and a cover. Advantageously, the terminator has a low physical profile but provides high power handling capability. 
         [0006]    The present disclosure also relates to a method for manufacturing a thin-film radio frequency power terminator. The method includes the steps of forming a thin-film termination chip, and mounting the termination chip to a mounting flange so that the mounting flange grounds the termination chip. The step of forming the thin-film termination chip could include forming a substrate, forming a metallization layer including a resistor pad on the substrate, soldering a terminal to the metallization layer, and mounting a cover on the substrate and the metallization layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The foregoing features of the invention will be apparent from the following Detailed Description of the Invention, taken in connection with the accompanying drawings, in which: 
           [0008]      FIG. 1  is a top view showing the terminator of the present invention; 
           [0009]      FIG. 2  is a side view of the terminator shown in  FIG. 1 ; 
           [0010]      FIG. 3  is a perspective view of the termination chip shown in  FIG. 1 ; 
           [0011]      FIG. 4  is a sectional view of the termination chip shown in  FIG. 1 , taken along line  4 - 4  of  FIG. 3 ; 
           [0012]      FIGS. 5-6  are graphs showing performance characteristics of the terminator shown in  FIG. 1 ; and 
           [0013]      FIG. 7  is a flowchart showing method steps for manufacturing the terminator shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The present invention relates to a thin-film, high-power radio frequency terminator, as discussed in detail below in connection with  FIGS. 1-7 . 
         [0015]      FIG. 1  is a top view showing the terminator of the present invention, indicated generally at  10 . The terminator  10  includes a termination chip  14  that is mounted on a mounting flange  12 . As seen in  FIG. 1 , both the termination chip  14  and the mounting flange  12  have rectangular shapes, but of course, other shapes and/or geometries can be provided. A terminal  16  protrudes from the termination chip  14  and is electrically connectable to an RF circuit. The profile of the mounting flange  12  is greater than that of the termination chip  14  (e.g., mounting flange  12  is wider than the termination chip  14 ) to accommodate mounting holes  18  on opposite sides of the termination chip  14 . As indicated in  FIG. 1 , the terminator  10  could have a resistance of 50 ohms, but of course, other resistances and/or impedances are possible. 
         [0016]      FIG. 2  is a side view of the terminator  10 , showing the termination chip  14  and the mounting flange  12 . The termination chip  14  can have a substantially hexahedral shape, and the terminal  16  protrudes from one of the surfaces while the other five surfaces of the termination chip  14  can be substantially smooth and flush. This flush design is achieved by a metallization stackup of the termination chip  14 , which will be described in further detail below. As shown, a bottom surface of the termination chip  14  includes a bottom metallized layer  25  which is mounted on a top surface of the mounting flange  12 . For example, the termination chip  14  can be high temperature soldered to the mounting flange  12 . The mounting holes  18  extend through the mounting flange  12 , from the top surface to a bottom surface of the mounting flange  12 . Thus, the mounting holes  18  can receive attachment means (e.g., screws, bolts, etc.) for mounting the terminator  10  to a mounting surface (e.g., to a circuit board). The mounting flange  12  is made of a material with strong thermal conductive properties, such as copper, and the mounting flange  12  can be nickel plated. As such, while the mounting flange  12  serves to ground the RF signal receivable by the termination chip  14 , the mounting flange  12  also acts as a heat dissipating element, transferring heat from the termination chip  14  to the mounting surface. 
         [0017]      FIG. 3  is a top perspective view of the termination chip  14 . The termination chip  14  includes a substrate possessing strong dielectric properties (e.g., an aluminum nitride (AlN) substrate)  22  and a cover  20 , with a metallization layer  24  therebetween. The metallized bottom layer  25  is provided on the bottom surface of the termination chip  14  to facilitate soldering of the chip  14  to the mounting flange  12  of  FIGS. 1-2 . The cover  20  can be an alumina ceramic cover with information (e.g., indicia) printed on it. The cover  20  can be sized and shaped in accordance with the AlN substrate  22 , so that the AlN substrate  22 , the metallization layer  24 , and the cover  20  together form a hexahedron having substantially smooth and flush surfaces. When assembled, the termination chip  14  can have a thickness of 60 mils, and possess a dielectric constant of 8.8. Of course, other thicknesses and dielectric constants are possible. As will be discussed in further detail below, the termination chip  14  is formed through multiple thin-film deposition processes to create an advantageous topology and metallization stackup. 
         [0018]      FIG. 4  is a sectional view of the termination chip  14 , taken along line  4 - 4  as seen in  FIG. 3 . More particularly,  FIG. 4  shows a top view of the AlN substrate  22  and the metallization layer  24  of the termination chip  14 . The metallization layer  24  includes a metallization pad  32  for receiving the terminal  16 . The terminal  16  can be a pure silver terminal that is high temperature soldered to the metallization pad  32 . It is noted that no additional processes need to be performed on the pure silver terminal  16 . Metallized circuit traces  26  are formed on the AlN substrate  22  for electrically connecting the terminal  16  to a thin-film resistor pad  28 . Those in the art will appreciate that the geometry of the metallized circuit traces  26  and the pad  28  shown in  FIG. 4  is exemplary, and the geometry of the metallized circuit traces  26  and the pad  28  can be dictated by desired termination characteristics, operating frequencies, etc. The resistor pad  28  can be electrically coupled to a metallization strip  29  disposed at or near an outer edge of the termination chip  14 . The resistor pad  28  can be generally trapezoidal in shape as shown in  FIG. 4 , and is electrically connected between the traces  26  and the metallization strip  29 . Of course, other shapes for the resistor pad  28  are possible. 
         [0019]    As seen in  FIG. 4 , the AlN substrate  22  includes metallized vias  30  (shown in phantom lines) positioned beneath the the metallization strip  29 . The metallized vias  30  extend through the AlN substrate  22  (e.g., from a top surface of the AlN substrate  22  to a bottom surface of the AlN substrate  22 ) and electrically connect the metallization strip  29  on the top side of the AlN substrate  22  to the metallized layer  25  formed on the opposite side of the AlN substrate  22 , which is then soldered to the copper mounting flange  12 . As such, the metallization layer  24  (e.g., the metallization pad  32 , the circuit traces  26 , the resistor pad  28 , and the metallization  29 ) and the metallization layer  25  formed on the opposite side of the AlN substrate  22  together, through the vias  30 , provide electrical continuity from the terminal  16  to the copper mounting flange  12 . Thus, because the metallization has continuity through the resistor pad  28  to ground (the ground is the mounting flange  12 ), the termination chip  14  can serve as the heart from which all the electrical and thermal performance is derived, and the terminator  10  can effectively terminate a 1000 Watt RF power load. 
         [0020]      FIG. 5  is a graph showing chip performance. More particularly,  FIG. 5  is a graph of return loss as measured as the amount of power lost in the chip as a reflection back to the circuit, and not terminated to ground. As can be seen, signal loss is graphed (in decibels) as a function of operated frequency (in GHz). 
         [0021]      FIG. 6  is a graph known to those in the art as a “Smith Chart” for illustrating the impedance of the terminator  10 . The Smith Chart is a normalized way of representing the phase of the impedance, by simultaneously showing the Real and Complex portions of the impedance of the terminator  10 . 
         [0022]      FIG. 7  is a flowchart showing method steps for manufacturing the terminator  10 . The terminator  10  is formed through a multiple thin-film deposition process, which creates the topology and the metallization stackup required to create the final chip configuration. The method  40  includes a forming process  42  for forming the termination chip  14 , and a mounting step  44  for mounting the termination chip  14  to the mounting flange  12 . The forming process  42  includes four sub-steps, i.e., sub-steps  42   a - 42   f . Step  42   a  includes forming the substrate  22  (e.g., an AlN substrate  22 ). Step  42   b  includes forming the metallization pad  32 , the metallized circuit traces  26  and the resistor pad  28  on the AlN substrate  22 . In step  42   b , the metallization  29  can also be formed on the AlN substrate  22 . In step  42   c , a printed protective epoxy is provided which covers to the substrate  22 . In step step  42   d , individual termination chips are singulated from a multiple chip array substrate. In step  42   e , additional plating is electrolytically deposited on the chips. Also, such plating could involve plating of the mounting flange  12 . Step  42   f  includes high temperature soldering the terminal  16  to the metallization pad  32 . In step  42   g , the alumina ceramic cover is fastened on top of the AlN substrate  22  the the metallization layer  24 . For example, the alumina ceramic cover can be attached with high temperature epoxy (e.g., black thermoset epoxy) to cover the top of the termination chip  14 . In step  44 , the termination chip  14  is mounted to the mounting flange  12 . When mounting the termination chip  14  to the mounting flange  12 , the termination chip  14  can be high temperature soldered to the mounting flange  12 . 
         [0023]    Having thus described the invention in detail, it is to be understood that the foregoing description is not intended to limit the spirit or scope thereof. What is desired to be protected is set forth in the following claims.