Patent Publication Number: US-2023136967-A1

Title: Monolithic microwave integrated circuit device with internal decoupling capacitor

Description:
FIELD 
     The disclosure relates to monolithic microwave integrated circuit (MMIC) devices, and in particular to MMIC devices having an operating frequency between 26.5 GHz and 40 GHz. 
     BACKGROUND 
       FIG.  1    is a plan view of a conventional MMIC RF transistor amplifier  400  according to embodiments of the present inventive concepts. As shown in  FIG.  1   , the MMIC RF transistor amplifier  400  includes an integrated circuit chip  430  that is contained within a package  410 . The package  410  may comprise a protective housing that surrounds and protects the integrated circuit chip  430 . The package  410  may be formed of, for example, a ceramic or plastic material. 
     The package  410  includes an input lead  412  and an output lead  418 . The input lead  412  may be mounted to an input lead pad  414  by, for example, soldering. One or more input bond wires  420  may electrically connect the input lead pad  414  to an input bond pad on the integrated circuit chip  430 . The integrated circuit chip  430  includes an input feed network  438 , an input impedance matching network  450 , a first RF transistor amplifier stage  460 , an intermediate impedance matching network  440 , a second RF transistor amplifier stage  462 , an output impedance matching stage  470 , and an output feed network  482 . The package  410  also includes a decoupling network  490  for supplying DC bias voltage to the gate (VG) and drain (VD). The decoupling network  490  may include a plurality of capacitors. The function of the decoupling network  490  is to provide stable operation when multiple stages are connected to the same gate and drain supply voltages. 
     The package  410  further includes an output lead  418  that is connected to an output lead pad  416  by, for example, soldering. One or more output bond wires  490  may electrically connect the output lead pad  416  to an output bond pad on the integrated circuit chip  430 . The first RF transistor amplifier stage  460  and/or the second RF transistor amplifier stage  462  may be implemented using any of the RF transistor amplifiers according to embodiments of the present inventive concepts. 
     An RF transistor amplifier may be designed to operate in a wide variety of different frequency bands. For example, RF transistor amplifiers may be configured to operate in at least one of the 0.6-2.7 GHz, 3.4-4.2 GHz, 5.1-5.8 GHz, 12-18 GHz, 18-27 GHz, 27-40 GHz or 40-75 GHz frequency bands or sub-portions thereof. 
     An important figure of merit for high frequency MMIC amplifiers is video bandwidth. Video Bandwidth (VBW) indicates the ability of a nonlinear power amplifier (PA) to maintain a low-level Adjacent Channel Leakage Ratio (ACLR) or Intermodulation Distortion (IMD) products as a function of the frequency spread or spacing (Δf) of an input signal. 
     In the most general case, the input signal consists of a multicarrier signal, such as an orthogonal frequency division multiplexing (OFDM) signal, or a wideband signal such as a wideband code division multiple access (WCDMA) signal. In this case, ACLR should be plotted against the bandwidth of the input signal. 
     For the simplest case, the input signal consists of a two-tone signal. In that case, IMDn (e.g., IMD3, IMD5, etc.) may be plotted against the two-tone spacing (Δf) of the signal. Conventionally, VBW is characterized by a plot of IMD3 vs two-tone spacing. VBW is a particularly important design requirement for wireless transmission systems in which wideband or multichannel signals are amplified using PAs prior to transmission. Examples of such transmission systems include satellite communication systems (Satcom) and wideband TV broadcasting systems. 
     When a PA is excited with two tones (e.g., f1, f2), the resulting output usually consists of combinations of different harmonics at frequencies n×f1±m×f2. Where n and m are the integers 1, 2, 3, etc. The frequencies at 2f2-f1 and 2f1-f2 are referred to as the upper and lower IM3 tones. The harmonics at frequency f2-f1 is a low frequency signal close to DC, referred to as the VBW frequency. 
     SUMMARY 
     A power amplifier according to some embodiments includes a submount, a monolithic microwave integrated circuit (MMIC) die on the submount, the MMIC die including an RF transistor configured to operate at frequencies greater than 26.5 GHz, and an internal decoupling capacitor on the submount and connected to a drain of the RF transistor. The internal decoupling capacitor has a capacitance greater than 2 nF. 
     The power amplifier may include a multi-stage amplifier including a first stage and a second stage. The RF transistor may include a first RF transistor in the first stage of the power amplifier and the power amplifier further may include a second RF transistor in the second stage of the power amplifier. The internal decoupling capacitor may be further connected to a drain of the second RF transistor. The power amplifier may include a third stage having a third RF transistor, and the internal decoupling capacitor may be further coupled to a drain of the third RF transistor. 
     The internal decoupling capacitor may include a single layer capacitor, and the RF transistor may include a Group III-nitride based high electron mobility transistor. The internal decoupling capacitor may have a capacitance of 10 nF or less and/or may have a voltage rating greater than 50 V. 
     The power amplifier may have a peak output power greater than 37 dBm at an operating frequency between 26.5 GHz and 40 GHz. The power amplifier may have a peak output power greater than 37 dBm at an operating frequency between 27 GHz and 31 GHz. The power amplifier may have a intermodulation distortion product of less than −20 dB over a tone spacing from 0.1 GHz to 300 MHz. The power amplifier may have a video bandwidth greater than 300 MHz at an operating frequency between 26.5 GHz and 40 GHz. 
     The internal decoupling capacitor may include a first decoupling capacitor, and the power amplifier may include a second internal decoupling capacitor coupled to a drain of the RF transistor. The second internal decoupling capacitor may have a capacitance greater than 2 nF. The second internal decoupling capacitor may be a single layer capacitor. 
     The power amplifier may include a multi-stage amplifier including a first stage and a second stage. The RF transistor may include a first RF transistor in the first stage of the power amplifier and the power amplifier further may include a second RF transistor in the second stage of the power amplifier. The first internal decoupling capacitor and the second internal decoupling capacitor may be further connected to a drain of the second RF transistor. The power amplifier may include a third stage having a third RF transistor, and the first and second internal decoupling capacitors may be further connected to a drain of the third RF transistor. The first and second internal decoupling capacitors may be on opposite sides of the RF transistor on the submount. 
     A method of forming a power amplifier according to some embodiments includes mounting a monolithic microwave integrated circuit (MMIC) die on a submount, the MMIC die including an RF transistor configured to operate at frequencies greater than 26.5 GHz, mounting an internal decoupling capacitor on the submount, wherein the internal decoupling capacitor has a capacitance greater than 2 nF, and connecting the decoupling capacitor to a drain of the RF transistor. 
     The internal decoupling capacitor may include a first internal decoupling capacitor, and the method may further include mounting a second internal decoupling capacitor on the submount and connecting the second internal decoupling capacitor to the drain of the RF transistor. The second internal decoupling capacitor has a capacitance greater than 2 nF. 
     The power amplifier may include a multi-stage amplifier including a first stage and a second stage. The RF transistor includes a first RF transistor in the first stage of the power amplifier and the power amplifier may further include a second RF transistor in the second stage of the power amplifier. The method may further include connecting the internal decoupling capacitor to a drain of the second RF transistor. 
     A power amplifier according to some embodiments includes a submount, a monolithic microwave integrated circuit (MMIC) die on the submount, the MMIC die including an RF transistor configured to operate at frequencies greater than 26.5 GHz, an input matching circuit coupled to a gate of the RF transistor, and an output matching circuit coupled to a drain of the RF transistor, and an internal decoupling capacitor on the submount and connected to the drain of the RF transistor, wherein the internal decoupling capacitor has a capacitance greater than 2 nF. 
     Additional features, advantages, and aspects of the disclosure may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the disclosure and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the disclosure as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure, are incorporated in and constitute a part of this specification, illustrate aspects of the disclosure and together with the detailed description serve to explain the principles of the disclosure. No attempt is made to show structural details of the disclosure in more detail than may be necessary for a fundamental understanding of the disclosure and the various ways in which it may be practiced. In the drawings: 
         FIG.  1    is a schematic illustration of a conventional MMIC amplifier including a GaN HEMT transistor. 
         FIG.  2    is a schematic layout of a conventional multistage MMIC. 
         FIG.  3    is a schematic circuit diagram of a conventional multistage MMIC. 
         FIG.  4    is a schematic block diagram of a conventional multistage MMIC. 
         FIG.  5    is a graph of IMD3 versus frequency spacing for a conventional multistage MMIC. 
         FIG.  6    is a schematic block diagram of a MMIC device according to some embodiments. 
         FIG.  7 A  is a schematic circuit diagram of a multistage MMIC according to some embodiments. 
         FIG.  7 B  is a schematic layout of a multistage MMIC according to some embodiments. 
         FIGS.  8 A and  8 B  illustrate packaged MMICs according to some embodiments. 
         FIG.  9    is a graph of IMD3 versus frequency spacing for a MMIC according to some embodiments. 
         FIG.  10    is a flowchart of operations for forming a MMIC according to some embodiments. 
         FIGS.  11 A- 11 C  are schematic block diagrams of multi-amplifier circuits in which RF transistor amplifiers incorporating transistor devices according to embodiments may be used. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Embodiments of the inventive concepts are explained more fully with reference to the non-limiting aspects and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of some embodiments may be employed with other aspects as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the aspects of the disclosure. The examples used herein are intended merely to facilitate an understanding of ways in which the disclosure may be practiced and to further enable those of skill in the art to practice the aspects of the disclosure. Accordingly, the examples and aspects herein should not be construed as limiting the scope of the disclosure, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the another element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the another element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the another element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. 
     The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Since a field effect transistor (FET), such as a Group III-nitride high electron mobility transistor (HEMT), used in a MMIC power amplifier, is a current source, the resulting signal will be in the form of currents at the mentioned harmonic frequencies. If the VBW currents are not well terminated, a low frequency voltage swing on top of the DC bias voltage demodulates the main signal, resulting in additional distortion on top of the normal IM3 components which in turn affects the VBW of the PA. 
     Having a high VBW in a high-power PA may allow for higher data rates to be transmitted using a single PA in a wireless communication system. To obtain a good VBW, it is desirable for a PA to be decoupled at DC or the VBW frequency, with a wideband resonance free low impedance at the drain, and possibly the gate. Decoupling is conventionally achieved via a capacitor network including a plurality of capacitors coupled to the drain terminals of transistors in a PA. The capacitor network typically includes an on-chip component, an in-package, or internal, component and an off-package component. The on-chip component of the decoupling network provides RF matching and initial decoupling. The internal component, which includes capacitors provided within the package but not on-chip, provides most of the decoupling. Additional decoupling may be provided by the off-package component, which may include capacitors mounted on a printed circuit board (PCB) on which the package is mounted. 
       FIG.  2    is a schematic layout, and  FIG.  3   , which is a schematic circuit diagram of a conventional package MMIC based PA, including an internal VBW decoupling circuit, with larger components located on a PCB. The PA illustrated in  FIGS.  2  and  3    includes three amplification stages provided by three HEMT field effect transistors (FETS), namely FET 1 , FET 2 , and FET 3 . An RF input provides an input RF signal via an input matching network to FET 1 . An RF output signal is output by FET 3 . Each FET has a gate biased by a gate bias signal Vg 1 , Vg 2 , Vg 3  and a drain biased by a drain bias signal Vd 1 , Vd 2 , Vd 3 . An on-chip decoupling and match circuit includes capacitors C 1  and C 2  coupled to the gates and drains of each FET. In a conventional approach, the on-chip capacitor (C 1 ) is located on the MMIC die. C 2  is the first internal capacitor and is located close to the MMIC die  10 . C 2  has a typical capacitance of about 50 pF to 100 pF. The second capacitor (C 3 ) is typically located off-chip either within the package or on the printed circuit board (PCB) and has a typical capacitance of about 500 pF to 1000 pF. This arrangement is illustrated schematically for a single-stage PA in  FIG.  4   . As shown therein, a MMIC  10  includes a field effect transistor  60  formed on a MMIC chip (or die)  10 . The MMIC die  10  is packaged within a package  30  and mounted on a PCB  40 . An input RF signal is applied to the FET  60  through an input impedance matching circuit  50 . An output impedance matching circuit  70  is coupled to the output of the FET  60 . A gate bias voltage signal VG is applied to the input of the FET  60 , and a drain bias voltage signal VD is applied to the output (drain) of the FET  60 . An on-chip decoupling capacitor C 1  and a first off-chip decoupling capacitor C 2  are connected to the drain of the FET  60 . The on-chip decoupling capacitor C 1  is provided on the chip substrate  30 , while the internal decoupling capacitor C 2  is provided within the package  30 . Additional decoupling capacitors may be provided outside the package  30 , such as on a PCB  40 . C 2  is provided internal to the package  30  and connected with wire bonds. The goal is to place C 2  close to the MMIC die  10  to reduce inductance which add to the impedance. 
     An example plot of IMD3 as a function of two-tone frequency separation (Δf) of an input signal is for a conventional GaN HEMT MMIC is shown in  FIG.  5   , where the dashed line represents upper IMD3 (+IMD3) and the solid line represents lower IMD3 (−IMD3). As seen in  FIG.  5   , the IMD3 characteristic increases substantially above −25 dBc at a frequency separation of about 50 MHz, indicating that the device has a VBW of about 50 MHz. 
     Some embodiments provide a single layer decoupling capacitor that is coupled the drain of the FET. The single layer decoupling capacitor may be an internal capacitor. In particular, the single layer on-chip decoupling capacitor may have a capacitance that is large enough for operation at KA band frequencies (26.5 GHz to 40 GHz). For example, a single layer internal decoupling capacitor according to some embodiments may have a capacitance of 2 nF or greater. In some embodiments, the internal decoupling capacitor may have a capacitance of 10 nF or less. 
     In some embodiments, multiple single layer internal decoupling capacitors may be coupled to a MMIC FET. For example, single layer internal decoupling capacitors may be coupled on opposite sides of a MMIC die  10 . Moreover, the single layer internal decoupling capacitors may be coupled to drains of FETs in multiple stages of a MMIC power amplifier, rather than providing separate decoupling capacitors for the different stages of the amplifier. 
     An example arrangement according to some embodiments is illustrated schematically for a single-stage PA including a single stage internal decoupling capacitor in  FIG.  6   . As shown therein, a packaged MMIC  130  includes a field effect transistor  160  formed on a MMIC chip or die  100 . An input RF signal is applied to the FET  160  through an input impedance matching circuit  150 . An output impedance matching circuit  170  is coupled to the output of the FET  160 . A gate bias voltage signal VG is applied to the input of the FET  160 , and a drain bias voltage signal VD is applied to the output (drain) of the FET  160 . An internal decoupling capacitor DCC is provided in the MMIC package  130  and is connected to the drain of the FET  160 . The internal decoupling capacitor DCC has a capacitance of 2 nF or greater. 
       FIG.  7 A  is a schematic circuit diagram and  FIG.  7 B  is a schematic layout diagram of a multistage PA including dual single stage on-chip decoupling capacitors according to some embodiments. As shown therein, a packaged MMIC amplifier  130  includes first, second and third stage field effect transistors  260 A,  260 NB,  260 C formed on a MMIC die  100 . An input RF signal is applied to the first stage FET  260 A through an input impedance matching circuit  250 . The output of the first stage FET  260 A is coupled to the input of the second stage FET  260 B through a first interstage impedance matching circuit  255 A. The output of the second stage FET  260 B is coupled to the input of the third stage FET  260 C through a second interstage impedance matching circuit  255 B. An output impedance matching circuit  270  is coupled to the output of the third stage FET  260 A. A gate bias voltage signal VG is applied to the respective inputs of the FETs  260 A,  260 B,  260 C, and a drain bias voltage signal VD is applied to the outputs (drains) of the FETs  260 A,  260 B,  260 C. A first internal decoupling capacitor DCC 1  is connected to the drains of the FETs  260 A,  260 B,  260 C on a first side of the FETs  260 A,  260 B,  260 C and a second internal decoupling capacitor DCC 2  is connected to the drains of the FETs  260 A,  260 B,  260 C on a second side of the FETs  260 A,  260 B,  260 C, opposite the first side. The internal decoupling capacitors DCC 1 , DCC 2  are provided within the same package as the MMIC die  100 , and each of the internal decoupling capacitors DCC 1 , DCC 2  has a capacitance of 2 nF or greater. 
       FIG.  8 A  is a schematic side view of a packaged MMIC RF transistor amplifier  130 A. As shown in  FIG.  8 A , packaged RF transistor amplifier  130 A includes a MMIC die  100  packaged in an open cavity package  610 A. The package  130 A includes metal gate leads  622 A, metal drain leads  624 A, a metal submount  630 , sidewalls  640  and a lid  642 . 
     The submount  630  may include materials configured to assist with the thermal management of the package  130 A. For example, the submount  630  may include copper and/or molybdenum. In some embodiments, the submount  630  may be composed of multiple layers and/or contain vias/interconnects. In an example embodiment, the submount  630  may be a multilayer copper/molybdenum/copper metal flange that comprises a core molybdenum layer with copper cladding layers on either major surface thereof. In some embodiments, the submount  630  may include a metal heat sink that is part of a lead frame or metal slug. The sidewalls  640  and/or lid  642  may be formed of or include an insulating material in some embodiments. For example, the sidewalls  640  and/or lid  642  may be formed of or include ceramic materials. 
     In some embodiments, the sidewalls  640  and/or lid  642  may be formed of, for example, Al 2 O 3 . The lid  642  may be glued to the sidewalls  640  using an epoxy glue. The sidewalls  640  may be attached to the submount  630  via, for example, braising. The gate lead  622 A and the drain lead  624 A may be configured to extend through the sidewalls  640 , though embodiments of the present inventive concepts are not limited thereto. 
     The MMIC die  100  is mounted on the upper surface of the metal submount  630  in an air-filled cavity  612  defined by the metal submount  630 , the ceramic sidewalls  640  and the ceramic lid  642 . The gate and drain terminals of MMIC die  100  may be on the top side of the structure, while the source terminal is on the bottom side of the structure. 
     The gate lead  622 A may be connected to the gate terminal of MMIC die  100  by one or more bond wires  654 . Similarly, the drain lead  624 A may be connected to the drain terminal of MMIC die  100  by one or more bond wires  654 . The source terminal may be mounted on the metal submount  630  using, for example, a conductive die attach material (not shown). The metal submount  630  may provide the electrical connection to the source terminal  126  and may also serve as a heat dissipation structure that dissipates heat that is generated in the RF transistor amplifier die  100 . 
     The heat is primarily generated in the upper portion of the MMIC die  100  where relatively high current densities are generated in, for example, the channel regions of the unit cell transistors. This heat may be transferred though the source vias  146  and the semiconductor layer structure of the device to the source terminal and then to the metal submount  630 . 
     A decoupling capacitor DCC 2  is mounted on the submount  30  alongside the MMIC die  100  and is attached to the drain of the MMIC die  100  via a wirebond  656 . 
       FIG.  8 B  is a schematic side view of another packaged MMIC RF transistor amplifier  130 B. The MMIC transistor amplifier  130 B differs from the MMIC RF transistor amplifier  130 A in that it includes a different package  610 B. The packaged MMIC RF transistor amplifier  130 B includes a metal submount  630 , as well as metal gate and drain leads  622 B,  624 B. The packaged MMIC RF transistor amplifier  130 B also includes a plastic overmold  660  that at least partially surrounds the RF transistor amplifier die  100 , the leads  622 B,  624 B, and the metal submount  630 . 
     A measured plot of IMD3 as a function of two-tone frequency separation (Δf) of an input signal is for a GaN HEMT MMIC  210  is shown in  FIG.  9   , where curve  902  represents upper IMD3 (+IMD3) and curve  904  represents lower IMD3 (−IMD3). As seen in  FIG.  9   , the IMD3 characteristic remains below −22 dBc at a frequency separation of above 300 MHz, indicating that the device has a VBW of about at least about 100 MHz. 
       FIG.  10    illustrates operations for forming a packaged MMIC power amplifier according to some embodiments. Referring to  FIG.  10   , a method of forming a packaged MMIC power amplifier includes mounting a high electron mobility transistor (HEMT) configured to operate at frequencies greater than 26.5 GHz on a submount (block  1002 ), and mounting an internal decoupling capacitor on the submount, wherein the internal decoupling capacitor has a capacitance greater than 2 nF (block  1004 ). The method further includes connecting the internal decoupling capacitor to a drain of the HEMT (block  1006 ). 
     The internal decoupling capacitor may include a first internal decoupling capacitor, and the method may further include forming a second internal decoupling capacitor in the package, wherein the second internal decoupling capacitor has a capacitance greater than 2 nF, and connecting the second decoupling capacitor to the drain of the HEMT. The power amplifier may be a multi-stage amplifier including a first stage and a second stage, where the HEMT includes a first HEMT in the first stage of the power amplifier and a second HEMT in the second stage of the power amplifier. The method may further include connecting the internal decoupling capacitor to a drain of the second HEMT. 
     Devices as described herein may be used in amplifiers that operate in a wide variety of different frequency bands. In some embodiments, the RF transistor amplifiers incorporating transistor devices as described herein may be configured to operate at frequencies greater than 1 GHz. In other embodiments, the RF transistor amplifiers may be configured to operate at frequencies greater than 2.5 GHz. In still other embodiments, the RF transistor amplifiers may be configured to operate at frequencies greater than 3.1 GHz. In yet additional embodiments, the RF transistor amplifiers may be configured to operate at frequencies greater than 5 GHz. In some embodiments, the RF transistor amplifiers may be configured to operate in at least one of the 2.5-2.7 GHz, 3.4-4.2 GHz, 5.1-5.8 GHz, 12-18 GHz, 18-27 GHz, 27-40 GHz or 40-75 GHz frequency bands or sub-portions thereof. 
     Although embodiments of the inventive concepts have been discussed above with respect to HEMT devices, it will be understood that the inventive concepts described herein may be applied to other types of semiconductor devices, such as MOSFETs, DMOS transistors, GaAs MMICs, CMOS, and/or laterally diffused MOS (LDMOS) transistors. 
     RF transistor amplifiers incorporating transistor devices described herein can be used in standalone RF transistor amplifiers and/or in multiple RF transistor amplifiers. Examples of how the RF transistor amplifiers according to some embodiments may be used in applications that include multiple amplifiers will be discussed with reference to  FIGS.  11 A- 11 C . 
     Referring to  FIG.  11 A , an RF transistor amplifier  1000 A is schematically illustrated that includes a pre-amplifier  1010  and a main amplifier  1030  that are electrically connected in series. As shown in  FIG.  11 A , RF transistor amplifier  1000 A includes an RF input  1001 , the pre-amplifier  1010 , an inter-stage impedance matching network  1020 , the main amplifier  1030 , and an RF output  1002 . The inter-stage impedance matching network  1020  may include, for example, inductors and/or capacitors arranged in any appropriate configuration in order to form a circuit that improves the impedance match between the output of pre-amplifier  1010  and the input of main amplifier  1030 . While not shown in  FIG.  11 A , RF transistor amplifier  1000 A may further include an input matching network that is interposed between RF input  1001  and pre-amplifier  1010 , and/or an output matching network that is interposed between the main amplifier  1030  and the RF output  1002 . The RF transistor amplifiers according to embodiments may be used to implement either or both of the pre-amplifier  1010  and the main amplifier  1030 . 
     Referring to  FIG.  11 B , an RF transistor amplifier  1000 B is schematically illustrated that includes an RF input  1001 , a pair of pre-amplifiers  1010 - 1 ,  1010 - 2 , a pair of inter-stage impedance matching networks  1020 - 1 ,  1020 - 2 , a pair of main amplifiers  1030 - 1 ,  1030 - 2 , and an RF output  1002 . A splitter  1003  and a combiner  1004  are also provided. Pre-amplifier  1010 - 1  and main amplifier  1030 - 1  (which are electrically connected in series) are arranged electrically in parallel with pre-amplifier  1010 - 2  and main amplifier  1030 - 2  (which are electrically connected in series). As with the RF transistor amplifier  1000 A of  FIG.  9 A , RF transistor amplifier  1000 B may further include an input matching network that is interposed between RF input  1001  and pre-amplifiers  1010 - 1 ,  1010 - 2 , and/or an output matching network that is interposed between the main amplifiers  1030 - 1 ,  1030 - 2  and the RF output  1002 . 
     As shown in  FIG.  11 C , the RF transistor amplifiers according to some embodiments may also be used to implement Doherty amplifiers. As is known in the art, a Doherty amplifier circuit includes first and second (or more) power-combined amplifiers. The first amplifier is referred to as the “main” or “carrier” amplifier and the second amplifier is referred to as the “peaking” amplifier. The two amplifiers may be biased differently. For example, the main amplifier may comprise a Class AB or a Class B amplifier while the peaking amplifier may be a Class C amplifier in one common Doherty amplifier implementation. The Doherty amplifier may operate more efficiently than balanced amplifiers when operating at power levels that are backed off from saturation. An RF signal input to a Doherty amplifier is split (e.g., using a quadrature coupler), and the outputs of the two amplifiers are combined. The main amplifier is configured to turn on first (i.e., at lower input power levels) and hence only the main amplifier will operate at lower power levels. As the input power level is increased towards saturation, the peaking amplifier turns on and the input RF signal is split between the main and peaking amplifiers. 
     As shown in  FIG.  11 C , the Doherty RF transistor amplifier  1000 C includes an RF input  1001 , an input splitter  1003 , a main amplifier  1040 , a peaking amplifier  1050 , an output combiner  1004  and an RF output  1002 . The Doherty RF transistor amplifier  1000 C includes a 90° transformer  1007  at the input of the peaking amplifier  1050  and a 90° transformer  1005  at the input of the main amplifier  1040 , and may optionally include input matching networks and/or an output matching networks (not shown). The main amplifier  1040  and/or the peaking amplifier  1050  may be implemented using any of the above-described RF transistor amplifiers according to embodiments. 
     The RF transistor amplifiers according to embodiments may be formed as discrete devices, or may be formed as part of a Monolithic Microwave Integrated Circuit (MMIC). A MMIC refers to an integrated circuit that operates on radio and/or microwave frequency signals in which all of the circuitry for a particular function is integrated into a single semiconductor chip. An example MMIC device is a transistor amplifier that includes associated matching circuits, feed networks and the like that are all implemented on a common substrate. MMIC transistor amplifiers typically include a plurality of unit cell HEMT transistors that are connected in parallel. 
     A transistor device according to some embodiments may be utilized in power semiconductor devices and/or applications. In some embodiments, the power semiconductor devices may be utilized for a power module that may include structure optimized for state-of-the-art wide band gap power semiconductor devices such as Gallium Nitride (GaN) or other Group III-nitride materials, Silicon Carbide (SiC), and the like, which are capable of carrying high amounts of currents and voltages and switching at increasingly faster speeds in comparison with established technologies. The power devices may include Wide Band Gap (WBG) semiconductors, including Gallium Nitride (GaN), Silicon Carbide (SiC), and the like, and offer numerous advantages over conventional Silicon (Si) as a material for the power devices. Nevertheless, various aspects of the disclosure may utilize Si type power devices and achieve a number of the benefits described herein. 
     A transistor device according to some embodiments may be utilized in radio frequency (RF) applications. In particular, a transistor device according to some embodiments may be utilized in wireless base stations that connect to a wireless device. In further aspects, the transistor device may be utilized in in wireless communication devices. 
     In aspects, the dimensions of z and/or d may be critical in order to address extreme temperature ranges, humidity ranges, and/or a host of other environmental conditions; operation at or near rated currents and voltages over extended periods of time; and address manufacturing issues such as insufficiently optimized wire bonding processes as well as others. 
     Although embodiments of the inventive concepts have been described in considerable detail with reference to certain configurations thereof, other versions are possible. The field plates and gates can also have many different shapes and can be connected to the source contact in many different ways. Accordingly, the spirit and scope of the invention should not be limited to the specific embodiments described above.