Wire-bond transmission line RC circuit

Disclosed are apparatus and associated methodology providing for fixed components that exhibit tailorable variations in frequency response depending on the applied frequencies over the components useful frequency range. The presently disclosed subject matter provides improved operational characteristics of generally known transmission line capacitor devices by providing a parallel resistive component constructed as a portion of the dielectric separating electrodes corresponding to a capacitor.

FIELD OF THE SUBJECT MATTER

The presently disclosed subject matter relates to wire-bond transmission line resistor-capacitor (RC) circuits. In particular, the presently disclosed subject matter relates to improvements in such wire-bond devices that provide for fixed components that exhibit tailored variations in frequency response depending on the applied frequencies over the component's useful frequency range.

BACKGROUND OF THE SUBJECT MATTER

Transmission line capacitor circuits may be used in various forms including for DC blocking when placed in series with a transmission line, for RF and source bypassing when in shunt with a transmission line or RF source, and for impedance matching among other applications. Such devices operate by passively adjusting the impedance characteristic of the signal pathway and have applicability in a broad range of applications including optical transceiver modules, broadband receivers, Transmit Optical Sub-Assemblies (TOSA), Receive Optical Sub-Assemblies (ROSA), and various other high frequency devices.

Known wire-bond transmission line capacitive devices have been developed that respond to many of such uses but have not provided a device that meets current desirable operational requirements such as the ability to tailor responses over the usable frequency range of the device. It would be advantageous, therefore, if a device could be developed that could be tailored to provide differing responses from the device over the device's useful frequency range.

SUMMARY OF THE SUBJECT MATTER

In view of the recognized features encountered in the prior art and addressed by the presently disclosed subject matter, improved apparatuses and methodologies have been developed that provide for tailoring differing responses over the useful operating frequency of the device.

In accordance with one aspect of an exemplary embodiment of the presently disclosed subject matter, a parallel connected RC circuit has been provided wherein the primary response of the device operating at relatively lower frequencies is tailored to that of the RC time-constant, while at higher frequencies the device response is based more on the capacitive component. In some embodiments of the presently disclosed subject matter, a layer of resistive material is placed between some or all of the area between electrodes corresponding to a capacitor structure to form a parallel resistor-capacitor (RC) structure.

In accordance with another aspect of presently disclosed subject matter, a parallel RC circuit may be configured in some instances based on the structure of a transmission line. In exemplary selected embodiments, such transmission line may include a backside ground.

In accordance with additional aspects of exemplary embodiments of the presently disclosed subject matter, the transmission line RC circuit may be provided with wire-bond pad structures. In yet further embodiments, the transmission line structure may be provided on various substrates, each providing additional advantageous characteristics to the completed structure. In particularly advantageous embodiments, the layer of resistive material may be laser trimmed to provide exact desired resistive values.

One presently disclosed exemplary embodiment relates to an RC circuit component for insertion in a transmission line, such circuit component comprising a monolithic substrate, a capacitor, and a thin-film resistor. Preferably, such monolithic substrate has a top surface; such capacitor is supported on such substrate top surface and has first and second electrodes separated at least in part by a dielectric layer; and such thin-film resistor is received at least in part between such capacitor first and second electrodes, and connected in parallel with such capacitor. The frequency response of such RC circuit component exemplary embodiment depends on the applied frequencies over the component's useful frequency range.

In some variations of such exemplary embodiment, such monolithic substrate may have opposing first and second longitudinal ends; and such component may further comprise a pair of wire bond pads supported on such substrate top surface respectively at such first and second longitudinal ends thereof, and with such wire bond pads coupled respectively with such first and second electrodes of such capacitor.

In other alternatives, such thin-film resistor may comprise a layer of resistive material trimmed to provide an exact desired resistive value for tailoring the frequency response of such component. Per further variations thereof, such layer of resistive material may comprise at least one of tantalum nitride (TaN), nickel-chromium alloys (NiCr), and ruthenium oxide (RuO2), and have sheet resistance up to about 1000.

For other variations, such substrate may comprise at least one of fused silica, quartz, alumina, and glass.

In yet other alternative exemplary embodiments, such monolithic substrate may have a bottom surface; and such component further may comprise a ground electrode received on such substrate bottom surface. In others, such first and second electrodes may at least partially overlap; and such resistor may be received in such overlap. For other alternatives, such dielectric layer may comprise at least one of silicon oxynitride (SiON) and barium titanate (BaTiO3). For yet others, the values of such capacitor and resistor may be chosen such that the impedance at each of such pair of wire bond pads is about 50Ω.

In another presently disclosed exemplary embodiment, a wire-bond transmission line RC circuit may preferably comprise a monolithic substrate having a top surface, a bottom surface, and opposing first and second longitudinal ends; a capacitor supported on such substrate top surface and having a first electrode, and a second electrode at least partially overlapping such first electrode so as to define an electrode overlap area therebetween, such capacitor further comprising a dielectric layer received in at least part of such electrode overlap area; a pair of wire bond pads, supported on such substrate top surface respectively at such first and second longitudinal ends thereof, and coupled respectively with such first and second electrodes of such capacitor; and a thin-film resistor. Per such embodiment, preferably such thin-film resistor is received at least in part in such electrode overlap area, and connected in parallel with such capacitor, and with such thin-film resistor comprising a layer of resistive material formed to provide a determined resistive value for selectively tailoring the frequency response of such RC circuit over the circuit's useful frequency range.

Per variations of such exemplary embodiment, such wire-bond transmission line RC circuit may further comprise a ground electrode received on such substrate bottom surface. In further such variations, such layer of resistive material may comprise at least one of tantalum nitride (TaN), nickel-chromium alloys (NiCr), and ruthenium oxide (RuO2), and have sheet resistance up to 100Ω. Further, such substrate may comprise at least one of fused silica, quartz, alumina, and glass, while such dielectric layer may comprise at least one of silicon oxynitride (SiON) and barium titanate (BaTiO3).

In other alternatives, the capacitance value of such capacitor and the resistive value of such resistor may be chosen such that the impedance at each of such pair of wire bond pads is about 50Ω.

It is to be understood from the complete disclosure herewith that the presently disclosed subject matter equally encompasses corresponding and/or associated methodology. For example, one presently disclosed exemplary embodiment of such encompassed methods relates to methodology for tailoring the frequency response of an RC circuit component for insertion in a transmission line, such circuit component comprising the type having a monolithic substrate having a top surface, a capacitor supported on such substrate top surface and having at least partially overlapping first and second electrodes separated at least in part by a dielectric layer, with a signal pathway through such circuit component, such methodology comprising including a thin-film resistor received at least in part between the capacitor first and second electrodes, and connected in parallel with such capacitor; and forming the resistive value of such resistor so as to passively adjust the impedance characteristic of the circuit signal pathway for selectively tailoring the frequency response of such RC circuit component over the circuit component's useful frequency range.

Per some variations of the foregoing exemplary embodiment, such methodology may further comprise selecting the capacitance value of such capacitor and the resistive value of such resistor so that the primary response of the RC circuit component operating at relatively lower frequencies is tailored to that of the RC time-constant, while at higher frequencies the RC circuit component response is based more on the capacitive component, so that the fixed RC circuit component has tailored variations in frequency response depending on the applied frequencies over the circuit component's useful frequency range.

In other presently disclosed variations, such monolithic substrate may have opposing first and second longitudinal ends; and such methodology may further comprise providing a pair of wire bond pads supported on such substrate top surface respectively at said first and second longitudinal ends thereof, and with said wire bond pads coupled respectively with the first and second electrodes of such capacitor.

In other presently disclosed alternatives, such step of forming the resistive value may comprise providing a layer of resistive material trimmed to provide an exact desired resistive value for tailoring the frequency response of such RC circuit component. Per further such variations, such layer of resistive material may comprise at least one of tantalum nitride (TaN), nickel-chromium alloys (NiCr), and ruthenium oxide (RuO2), and has sheet resistance up to about 100Ω.

In other presently disclosed variations, such substrate may comprise at least one of fused silica, quartz, alumina, and glass; and such monolithic substrate may have a bottom surface, so that such methodology also may further comprise providing a ground electrode received on such substrate bottom surface.

Pet yet other alternatives, such dielectric layer may comprise at least one of silicon oxynitride (SiON) and barium titanate (BaTiO3). Also, the capacitance value of such capacitor and the resistive value of such resistor may be chosen such that the impedance at each of said pair of wire bond pads is about 50Ω.

Still further, per presently disclosed alternative methodologies, such monolithic substrate may have a bottom surface; and such step of forming the resistive value may comprise providing a layer of resistive material trimmed to provide an exact desired resistive value for tailoring the frequency response of such RC circuit component; and such methodology may further comprise providing a ground electrode received on such substrate bottom surface.

Still further, it is to be understood that different embodiments, as well as different presently preferred embodiments, of the presently disclosed subject matter may include various combinations or configurations of presently disclosed features, steps, or elements, or their equivalents (including combinations of features, parts, or steps or configurations thereof not expressly shown in the figures or stated in the detailed description of such figures). Additional embodiments of the presently disclosed subject matter, not necessarily expressed in the summarized section, may include and incorporate various combinations of aspects of features, components, or steps referenced in the summarized objects above, and/or other features, components, or steps as otherwise discussed in this application. Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the remainder of the specification.

Repeat use of reference characters throughout the present specification and appended drawings is intended to represent same or analogous features or elements.

DETAILED DESCRIPTION OF THE SUBJECT MATTER

As discussed in the Summary of the Subject Matter section, the presently disclosed subject matter is particularly concerned with improvements to wire-bond parallel connected RC devices that provide for tailored fixed components that exhibit variations in frequency response depending on the applied frequencies over the component's useful frequency range.

Selected combinations of aspects of the disclosed technology correspond to a plurality of different embodiments of the presently disclosed subject matter. It should be noted that each of the exemplary embodiments presented and discussed herein should not insinuate limitations of the presently disclosed subject matter. Features or steps illustrated or described as part of one embodiment may be used in combination with aspects of another embodiment to yield yet further embodiments. Additionally, certain features may be interchanged with similar devices or features not expressly mentioned which perform the same or similar function.

Reference is made hereafter in detail to the presently preferred embodiments of the subject parallel wire-bond transmission line RC circuit. Referring to the drawings,FIG. 1illustrates a previously known transmission line capacitor100constructed on substrate102. Capacitor100is provided with wire-bond pads104,106positioned at opposite ends108,110, respectively of substrate102. A relatively small value capacitor is formed by the overlapping arrangement of electrodes112,114, which electrodes are coupled to wire-bond pads104,106, respectively. In such known construction, the capacitor may have a value of 2 pF and the substrate may be constructed from fused silica. Known similar devices provide for constructing substrates of quartz, alumina, glass and other substances. For example,FIGS. 7 and 8also illustrate characteristics of a known device similar to that illustrated inFIG. 1but constructed on an alumina substrate.

FIGS. 2 and 3illustrate characteristics of the known device ofFIG. 1withFIG. 2illustrating response curves for the device whileFIG. 3illustrates an equivalent circuit300for the device ofFIG. 1.

In accordance with such known device, capacitor100may correspond to a silicon oxynitride (SiON) capacitor having a first electrode112thereof coupled to wire bond pad104on fused silica substrate102. Capacitor100also includes a second electrode114at least partially below first electrode112and separated therefrom via a SiON layer (not seen in this view). Electrode114is coupled to wire bond pad106. A backside electrode116functions as a ground plane for the assembled device.

With reference toFIG. 2, there are illustrated graphic response curves200related to the device illustrated inFIG. 1. Those of ordinary skill in the art will appreciate that the notations S11and S21represent reflection and forward transmission coefficients, respectively, for the transmission line circuit100. As illustrated inFIG. 2, the forward transmission coefficients S21and reflected coefficients S11for a high frequency structural simulator (HFSS) simulated model of device100and for that of the equivalent circuit illustrated inFIG. 3, track exactly and are thus illustrated together with common respective S11and S21notations. As illustrated inFIG. 2, the frequency scale of such example corresponds to 100-30,000 MHz so that the resonance point as illustrated by the dip in the S11line is about 15,425 MHz. Of special interest is the fact that the forward transmission coefficient S21line is virtually flat over the entire useful operating range after rising rapidly from the lower frequency operating range according with the value of the capacitor.

With reference toFIG. 3, there is illustrated an equivalent circuit diagram for the exemplary device illustrated inFIG. 1. As noted above and illustrated inFIG. 2, the response curves for the equivalent circuit track exactly the HFSS simulation of the circuit. In such example, transmission line302had a width of 0.24 mm and a length of 0.584 mm while transmission line304had a width of 0.2 mm and a length of 0.4 mm. Capacitor312had a value of 1.931 pF, an equivalent series resistance314of 0.013Ω, and an equivalent series inductance322of 0.011 nH. The transmission line structure produced a characteristic impedance (Z0) of 50Ω at both the input port316and output port318.

With reference toFIG. 4, an exemplary embodiment of an internal configuration of a transmission line400including a thin-film resistor422and parallel connected capacitor426in accordance with the presently disclosed subject matter is illustrated. From a comparison with the device illustrated inFIG. 1and that ofFIG. 4constructed in accordance with the presently disclosed subject matter, it will be noticed that the internal components have some similarities but with the exception of the inclusion of thin-film resistor422. Thus, generally, transmission line400is constructed on a top surface430of substrate402and includes a first electrode412thereof coupled to wire bond pad404positioned on one longitudinal end408of substrate402, and a second electrode414below first electrode412and at least partially overlapped by first electrode412.

First electrode412is at least partially separated from second electrode414by SiON layer428and also at least partially separated from second electrode414by thin-film resistor422. Electrode414is coupled to wire bond pad406at a second longitudinal end410of substrate402. A backside electrode416is provided on a bottom surface432of substrate402and functions as a ground plane for the assembled device.

As with the device illustrated inFIG. 1, substrate402may also be constructed from fused silica. Thin-film resistor422may correspond to a tantalum nitride (TaN) layer having 25 to 100Ω sheet resistance. It should be appreciated, however, by those of ordinary skill in the art that other resistive materials may be used in addition to or in place of TaN. Other suitable materials include, but are not limited to, nickel-chromium alloys (NiCr) and ruthenium oxide (RuO2). Such thin-film resistors may be trimmed using laser techniques well known in the art to provide precision resistor values for use with the presently disclosed subject matter. Likewise, it should be appreciated that materials other than SiON may be used for the dielectric material for capacitor426including, but not limited to, barium titanate.

With reference toFIG. 5, there are illustrated graphic response curves500related to the exemplary device illustrated inFIG. 4. From an inspection ofFIG. 5, it will be noticed that the forward transmission coefficient S21for both a HFSS simulated model and for that of the equivalent circuit illustrated inFIG. 6, track exactly and are thus illustrated as a single line S21. Similarly, the reflection coefficients S11for a HFSS simulated model and that of the equivalent circuit also track exactly and are illustrated as single line S11.

An inspection ofFIG. 5shows that the resonance frequency for the device illustrated inFIG. 4is slightly higher on the frequency scale than that illustrated in the curves200ofFIG. 2. As with the curves illustrated inFIG. 2, the frequency scale of such example corresponds to 100-30,000 MHZ so that the resonance point is about 16,200 MHz. Of interest here is the fact that the forward transmission coefficient S21is seen to gradually increase at the lower end of the operating range of the exemplary device, according to the RC (Resistor Capacitor) product, before flattening out in the mid to upper operating frequency ranges. Such response is due to the inclusion of thin-film resistor422which provides the desired tailorable variations in frequency response in dependence on the applied frequencies and particular construction of the capacitive and resistive components over the component's useful frequency range.

With reference toFIG. 6, there is illustrated an equivalent circuit diagram600for the device illustrated inFIG. 4. In such example, transmission line602had a width of 0.203 mm and a length of 0.239 mm while transmission line604had a width of 0.194 mm and a length of 0.269 mm. Capacitor612had a value of 2.502 pF, an equivalent series resistance622of 0.428Ω, and an equivalent series inductance614of 1.283e-3 nH. Parallel connected resistor620had a value of 20.617Ω. The transmission line structure produced a characteristic impedance (Z0) of 50Ω at both the input port616and output port618.

FIG. 7illustrates graphic response curves700related to an embodiment of the previously known device ofFIG. 1constructed using an alternative substrate material, for example, in such case, alumina. As may be seen by comparison with the graph ofFIG. 2wherein the substrate was made of fused silica, the reflection coefficient S11overall has a steeper slope and the resonance frequency is slightly higher. The forward transmission coefficient S21rises significantly faster at the lower frequencies than did that of the graph ofFIG. 2and thereafter remains substantially flat for the entire useful operating frequency range. Again in both a modeled and equivalent circuit, the S11and S21values track exactly and are thus illustrated inFIG. 7as single lines. It should be noted that the frequency range associated with the graphs ofFIG. 7as well as that ofFIG. 8described herein, correspond to a range of 100 to 50000 MHz.

FIG. 8illustrates an equivalent circuit diagram800for the device illustrated inFIG. 1using an alumina substrate. As noted above and illustrated inFIG. 7, the response curves for the equivalent circuit track exactly a simulation of the circuit. In such example, transmission line802had values of Z=46.174Ω and L=6.03° while transmission line804had values of Z=40.51Ω and L=26.415°. Capacitor812had a value of 2.416 pF, an equivalent series resistance814of 0.401Ω and an equivalent series inductance822of 0.022 nH. The transmission line structure produced a characteristic impedance (Z0) of 50Ω at both the input port816and output port818.

FIG. 9illustrates graphic response curves900related to an embodiment of the presently disclosed subject matter illustrated inFIG. 4constructed using an alumina substrate. As may be seen by comparison with the graph ofFIG. 5wherein the substrate was made of fused silica, the reflection coefficient S11overall has a steeper slope and the resonance frequency is slightly higher. The forward transmission coefficient S21rises slightly faster at the lower frequencies than did that of the graph ofFIG. 5and thereafter remains substantially flat for the entire useful operating frequency range. Again, in both the HFSS modeled and equivalent circuit, the S11and S21values track exactly and are thus illustrated inFIG. 7as single lines.

FIG. 10illustrates an equivalent circuit diagram1000for the exemplary device illustrated inFIG. 4but using an alumina substrate. As noted above and illustrated inFIG. 9, the response curves for the equivalent circuit track exactly a simulation of the circuit. In such example, transmission line1002had values of Z=49.186Ω and L=20.924° while transmission line1004had values of Z=49.023Ω and L=25.192°. Capacitor1012had a value of 2.646 pF, an equivalent series resistance1014of 0.389Ω, and an equivalent series inductance1022of 0.021 nH. Parallel resistor1024had a value of 2Ω and had an equivalent series inductance1026of 0.01 nH. The transmission line structure produced a characteristic impedance (Z0) of 50Ω at both the input port1016and output port1018.