Abstract:
A high frequency arrangement is provided that includes an integrated high frequency circuit, a first bond pad, which is electrically connected by a first electrical supply line, in particular a bond wire and/or a solder bump, to a housing terminal and/or another circuit, wherein the first bond pad adjoins a dielectric so that the first bond pad forms a first capacitance with the dielectric and an electrically conductive region of the integrated high-frequency circuit, and the first capacitance and the first supply line, which has an inductance, influence a (tuned) first resonant frequency associated with the high-frequency circuit.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on German Patent Application No. 102005008195, which was filed in Germany on Feb. 23, 2005, and which is herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high frequency arrangement. 
     2. Description of the Background Art 
     As the operating frequency of high frequency circuits increases, the assembly technology, which is to say the electrical and mechanical connection of a semiconductor chip to its housing and terminals or to other semiconductor chips, has an increasing influence on the functionality of the high-frequency circuit. The electrical and mechanical connections create parasitic inductances and capacitances that can degrade the electrical properties of the high frequency circuit. 
     One possible reason for this degradation is the inductances of the supply lines, such as bond wires or solder bumps or the like, which are needed to connect to the high-frequency circuit. 
     One conventional solution for this problem is the use of what is known as a “virtual ground.” For example, instead of what is called a “single-ended” (non-symmetrical) amplifier arrangement, a differential amplifier design is used in which the symmetry point of the amplifier circuit experiences no voltage fluctuations. Accordingly, when the amplifier circuit is powered from the symmetry point, a suitable circuit design makes it possible to ignore supply line inductances. 
     Associated with the symmetrical solution is the necessity to drive loads symmetrically or to make the initially differential output signal asymmetrical. The measurement effort for measuring the electrical characteristic quantities must be matched to the differential system. The complexity of symmetrical systems is greater as compared to non-symmetrical systems. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to reduce the influence of inductances of supply lines to a high frequency circuit on its electrical characteristics as much as possible. 
     Accordingly, a high frequency arrangement is provided such as is used for a region above 1 GHz. The high frequency arrangement has a high frequency circuit on a semiconductor chip and an electrical supply line. The electrical supply line to the semiconductor chip connects the high-frequency circuit to a housing terminal and/or another circuit. In this regard, the electrical supply line has an inductance that may be parasitic. The supply line to the semiconductor chip is a bond wire and/or a solder bump, for example. 
     In an embodiment of the present invention, a series-resonant circuit can be connected in parallel to the electrical supply line. In particular, the series-resonant circuit is damped, because this series-resonant circuit itself has a (real) resistive component. The series-resonant circuit has a resonant frequency that is matched to a requirement of the high frequency circuit in this context. An embodiment of the invention provides that the series-resonant circuit can be composed of a supply line acting as an inductance and a bond pad having a capacitance. 
     Another embodiment of the invention provides a high frequency arrangement with an integrated high frequency circuit, a first bond pad, and a first electrical supply line. Here, the bond pad is electrically connected by the first electrical supply line, in particular a bond wire and/or solder bump, to a housing terminal and/or another circuit. In this regard, a variety of housing types, such as, for example, surface-mounted packages (SMD) or flip-chip housings, can be used as the housing. 
     The first bond pad adjoins a dielectric. In this regard, the first bond pad forms a first capacitance with the dielectric and an electrically conductive region of the integrated high-frequency circuit. The capacitance depends on the thickness of the dielectric and the geometry of the bond pad as well as on their tolerances. 
     The first capacitance and the first supply line, which has an inductance, influence a first resonant frequency, which is associated with the high-frequency circuit. This resonant frequency is preferably tuned to an operating frequency of the high-frequency circuit within the scope of typical manufacturing tolerances. 
     In a further embodiment of the invention, a second bond pad can be conductively connected to the electrically conductive region, so that a significant DC current can flow through the second bond pad between the bond pad and the high-frequency circuit. The second bond pad can be electrically connected to the housing terminal and/or the additional circuit by a second supply line for connection in parallel with the first bond pad and with the first supply line. 
     In yet a further embodiment of the invention, a third bond pad can be provided that is electrically connected to the housing terminal and/or the additional circuit by a third supply line for connection in parallel, especially to compensate for production tolerances on the geometry of the first bond pad and a thickness of the dielectric. Preferably the third bond pad can be located adjacent to the first bond pad or the second bond pad. 
     In this context, the third bond pad adjoins a dielectric. This dielectric preferably has the same material composition and, within the scope of the manufacturing tolerance, the same material thickness as the dielectric that adjoins the first bond pad. Alternatively, different dielectrics may also be used. The third bond pad forms a second capacitance with the dielectric and the electrically conductive region of the integrated high-frequency circuit. In this context, the second capacitance and the second supply line, which has an inductance, influence a second resonant frequency associated with the high-frequency circuit. This second resonant frequency is preferably different from the first resonant frequency and differs therefrom by less than 10%, especially preferably by less than 5%. 
     Additional parallel circuits, comprised of additional lines and additional bond pads adjoining dielectrics, influence additional resonant frequencies. The number of parallel circuits depends advantageously on the manufacturing tolerance of the geometry of the bond pads and the thickness of the dielectric. The parallel-connected individual resonant circuits also produce coupled resonances formed by the interconnection of the individual resonant circuits among one another. 
     A further embodiment of the invention provides for the first capacitance to differ from the second capacitance by virtue of a different geometry, for example, by a different surface area. If a number of supply lines are connected in parallel to one another, each capacitance can have a different geometry from any other capacitance of a series-resonant circuit, so that the individual resonant circuits are detuned relative to one another. 
     The conductive region can be conductively connected to a semiconductor region of an active, integrated component of the integrated high-frequency circuit. The semiconductor region is, for example, a drain region of a high-frequency field-effect transistor. The semiconductor region can be an emitter of a high-frequency bipolar transistor or of a high-frequency tetrode, which is conductively connected to the conductive region, for example through a metal area or a junction or boundary surface between different dopant concentrations. 
     The high-frequency circuit can be designed such that at least the second line forms a negative electrical feedback, in particular a negative current feedback, for the integrated high-frequency circuit, which can be reduced for at least the first resonant frequency by the parallel connection with the first bond pad and the first line. 
     In a further embodiment of the invention, provision is made that the dielectric has silicon dioxide and preferably has a thickness less than 100 nm, but especially preferably a thickness of 50 nm. 
     While it is possible for the conductive region adjoining the dielectric to have a doped semiconductor, according to an embodiment of the invention the conductive region has a metal. For example, the conductive region includes aluminum or a silicide. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
         FIG. 1  is a cross-section through a terminal region of a semiconductor chip; 
         FIG. 2  is a circuit diagram for a high frequency amplifier; 
         FIGS. 3   a  through  3   c  show examples of various emitter circuits; and 
         FIG. 4  is a gain-vs-frequency diagram. 
     
    
    
     DETAILED DESCRIPTION 
     First, for  FIG. 2 , an achievable power gain of an output driver for 5 GHz in SiGe technology is examined. In this context, the output driver is a SiGe npn heterobipolar transistor Q 1  with an emitter size of 20×1 μm 2  per emitter finger and a number NE of emitter fingers, hereinafter referred to as “finger count,” in a common-emitter circuit. A supply line (Lp) required for electrically contacting the emitter E can scarcely be implemented with a reactive component Lp of less than 0.1 nH, regardless of whether it is in the form of solder bumps or bond wires. 
     A parallel connection of a number n of inductances Lp of a given inductance which are not coupled to one another has an overall inductance on the order of the individual inductance divided by the factor n. Conversely, each of NE emitter fingers connected overall to an inductance of 0.1 nH experiences an effective inductance of NE times 0.1 nH. 
     However, an inductance Lp in the emitter branch represents a negative feedback and reduces the achievable gain (G). In the case under consideration, above a finger count of approximately 16 and a frequency of approximately 1 GHz, the power gain G drops by 3 dB when the finger count is doubled. The circuit in  FIG. 2  with NE=128 emitter fingers serves as an example. 
     In this context, the high-frequency signal is fed into the circuit for amplification through the input EIN. The input EIN is DC decoupled from the base B of the transistor Q 1  by a capacitor C 1 . The components—current source IB, voltage source V 2 , transistors Q 2  and Q 3 , and the inductance L 2 —serve to set the operating point of the high-frequency transistor Q 1 . 
     The collector K of the high-frequency transistor Q 1  is connected to the output AUS of the circuit and DC decoupled by an additional capacitor C 2 . In addition, the collector K of the high-frequency transistor Q 1  is, in turn, connected to an additional inductance L 1  and a voltage source V 1  for setting the operating point and is HF decoupled. 
     The emitter E of the high-frequency transistor Q 1  has a real resistive component, which is indicated as a resistor R. The emitter E of the high-frequency transistor Q 1  is connected to a bond pad  32 , which is schematically represented in the circuit diagram of  FIG. 2  as a rectangle. The bond pad  32  is connected to a terminal of the housing of the high-frequency arrangement by a supply line formed of a bond wire, which forms a parasitic inductance Lp. 
       FIG. 1  shows a terminal of the emitter E via bond pads  31 ,  32 , and  33  in a schematic cross-sectional view. Bond wires  51 ,  52 ,  53  with the typical bond structure  41 ,  42 ,  43  are bonded on to the respective bond pads. The bond structure  41 ,  42 ,  43  and the bond wires  51 ,  52 ,  53  each act as an inductance here. In addition, the bond structure  41 ,  42 ,  43  as well as the bond wires  51 ,  52 ,  53  each have an ohmic resistance. 
     The middle bond pad  32  of the bond pads  31 ,  32 ,  33  shown in  FIG. 1  is connected to the emitter E of the high-frequency transistor Q 1  (see  FIG. 2 ) in an electrically conductive manner by metal connections  02 ,  001  and  002 , which have aluminum, for example, wherein the metal connections  02 ,  001 , and  002  have a low resistance value. 
     The bond pad  31  on the right is separated from an electrically conductive region  11  by a dielectric  21 . In this example embodiment, the dielectric  21  has silicon dioxide, but can, for example, also be made of borosilicate glass. In this example embodiment, the electrically conductive region  11  has a metal, preferably the metal used in the wiring level  001 , for example aluminum. The conductive region  11  is connected to the emitter E through the metal connections  01 ,  001  and  002 . Naturally, additional metal connections not shown in  FIG. 1  may also be necessary. 
     The left-hand bond pad  33  is wired in a manner analogous to the right-hand bond pad  31 . In contrast to the right-hand bond pad  31  of  FIG. 1 , the left-hand bond pad  33  has a smaller area of overlap with a conductive region  13 , so that it likewise forms a capacitance, but with a different value, presupposing that the dielectrics  21  and  23  do not compensate for the difference in areas of overlap. The manufacturing tolerance of the dielectric thickness can preferably be compensated for by different capacitances. The left-hand conductive region  13  is also connected to the emitter E by metal connections  03 ,  001 ,  002 . 
       FIGS. 3   a ,  3   b , and  3   c  show different types of connections to the emitter E.  FIG. 3   a  shows the idealized connection with a bond wire having no reactance, which represents only a comparison value and cannot be implemented technically.  FIG. 3   b  shows the connection through a bond wire which forms a parasitic inductance Lp of 0.1 nH. 
     An example embodiment of the invention is shown in  FIG. 3   c . While the supply line inductance represents a DC path for supplying the device to be contacted, the device to be contacted is preferably connected in an essentially reactance-free manner through a series-resonant circuit connected in parallel to the line inductance, with reduced reactance at the resonant frequency of said series-resonant circuit. 
     In the example embodiment in  FIG. 3   c , five damped resonant circuits formed of the capacitances C 3 , C 4 , C 5 , C 6 , and C 7  and the associated inductances L 3 , L 4 , L 5 , L 6 , and L 7 , each having slightly different resonant frequencies at approximately 5 GHz, are connected in parallel to the bond inductance Lp. The ohmic resistive component of the bond wires is omitted in  FIGS. 3   b  and  3   c  to simplify the representation. The capacitances C 3 , C 4 , C 5 , C 6 , and C 7  have, for example, a structure analogous to  FIG. 1 , while the inductances L 3 , L 4 , L 5 , L 6 , and L 7  are formed by bond wires  51 ,  52 ,  53 . 
       FIG. 4  shows the corresponding achievable power gains. The parallel connection of the aforementioned resonant circuits to the supply line inductance increases the power gain in the example by more than an order of magnitude. In the example, the necessary resonant circuits can be implemented in an especially simple manner by capacitances located under the bond pads and having areas of 80×100 μm 2 , 90×100 μm 2 , 100×100 μm 2 , 110×100 μm 2 , and 120×100 μm 2 , with silicon dioxide 50 nm thick as the dielectric, and with the aforementioned bond pads as inductances. 
       FIG. 4  shows the gains G (dB) of the circuit variants in  FIGS. 3   a ,  3   b , and  3   c  plotted over frequency f (Hz).  FIG. 4  shows that for the example embodiment in  FIG. 3 , the gain G approaches the ideal case of  FIG. 3   a , but only for the required operating frequency in the range of 5 GHz. As a result of the multiple parallel connection of series resonances, multiple maxima are produced in the vicinity of the operating frequency of 5 GHz, optimizing a wider frequency band with regard to the gain G (dB) than a single series resonance. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.