Abstract:
Implementations of semiconductor devices may include: a plurality of drain fingers and a plurality of source fingers interdigitated with one another; at least one gate; and at gate bus formed to completely surround the plurality of drain fingers and the plurality of source fingers; wherein the gate bus is mechanically and electrically coupled to the at least one gate.

Description:
BACKGROUND 
     Technical Field 
       [0001]    Aspects of this document relate generally to guard rings to protect semiconductor devices. More specific implementations involve using guard rings in cascode devices. 
       Background 
       [0002]    Conventionally, gallium nitride (GaN) devices are used in high power/high frequency applications. These devices include source, drain, and gate regions where the source and drain regions are often arranged in an interdigitated fashion. 
       SUMMARY 
       [0003]    Implementations of semiconductor devices may include: a plurality of drain fingers and a plurality of source fingers interdigitated with one another; at least one gate; and at gate bus formed to completely surround the plurality of drain fingers and the plurality of source fingers; wherein the gate bus is mechanically and electrically coupled to the at least one gate. 
         [0004]    Implementations of semiconductor devices may include: a depletion mode (D-mode) transistor having one or more source fingers, one or more drain fingers and one or more gates; and a gate bus surrounding the one or more source fingers and the one or more drain fingers of the D-mode transistor; wherein the gate bus couples with the one or more gates of the D-mode transistor; wherein the gate bus is a first guard ring of the D-mode transistor. 
         [0005]    Implementations of semiconductor devices may include one, all, or any of the following: 
         [0006]    The D-mode transistor may be a gallium nitride (GaN) high electron mobility transistor (HEMT). 
         [0007]    The gate bus may be formed from one selected from the group of an ohmic metal, a gate metal, and a field plate. 
         [0008]    A channel under the first guard ring may be depleted during one of operation or non-operation of the device. 
         [0009]    A channel under the first guard ring may be active during operation of the device. 
         [0010]    The semiconductor device further includes at least one additional guard ring surrounding an outer perimeter of the first guard ring. 
         [0011]    A channel between the first guard ring and the at least one additional guard ring may be active during operation of the device. 
         [0012]    A second guard ring may be coupled to one of a group comprising the gate, the source and a substrate of the device. 
         [0013]    A second guard ring may be floating relative to the drain fingers and the source fingers. 
         [0014]    Implementations of semiconductor devices may include: a depletion mode (D-mode) transistor having one or more source fingers, one or more drain fingers and one or more gates; an enhanced mode (E-mode) transistor having one or more source pads, one or more drain pads and one or more gate pads; and a gate bus formed as a guard ring of the D-mode transistor; wherein the one or more gate pads of the D-mode transistor couple with the source pads of the E-mode transistor and an electrical ground. 
         [0015]    Implementations of semiconductor devices may include one, all, or any of the following: 
         [0016]    The D-mode transistor may be a gallium nitride (GaN) high electron mobility transistor (HEMT). 
         [0017]    The E-mode transistor is a silicon (Si) field effect transistor (FET). 
         [0018]    The semiconductor device further including a second guard ring surrounding an outer perimeter of the first guard ring. 
         [0019]    The D-mode transistor is coupled to a first conductive lead frame and the E-mode transistor is coupled to a second conductive lead frame. 
         [0020]    The semiconductor device further including a pin out from each of the drain of the D-mode transistor and the gate and the source of the E-mode transistor. 
         [0021]    The source of the D-mode transistor may be coupled to the drain of the E-mode transistor. 
         [0022]    The source of the D-mode transistor and the drain of the E-mode are coupled together through a wire bond. 
         [0023]    The foregoing and other aspects, features, and advantages will be apparent to those artisans of ordinary skill in the art from the DESCRIPTION and DRAWINGS, and from the CLAIMS. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Implementations will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and: 
           [0025]      FIG. 1  is a cross-sectional view of a conventional guard ring structure; 
           [0026]      FIG. 2  is top view of another conventional guard ring structure; 
           [0027]      FIG. 3  is a top view of an implementation of a guard ring structure; 
           [0028]      FIG. 4A  is a top view of another implementation of a guard ring structure; 
           [0029]      FIG. 4B  is an enlarged view of a gate pad from  FIG. 4A ; 
           [0030]      FIG. 5A  is a top view of another implementation of a guard ring structure; 
           [0031]      FIG. 5B  is an enlarged view of a corner from the device in  FIG. 5A ; 
           [0032]      FIG. 6  is a view an implementation of a guard ring protecting a device; 
           [0033]      FIG. 7  is a top view of a cascode device using an implementation of a guard ring structure. 
       
    
    
     DESCRIPTION 
       [0034]    This disclosure, its aspects and implementations, are not limited to the specific components, assembly procedures or method elements disclosed herein. Many additional components, assembly procedures and/or method elements known in the art consistent with the intended gallium nitride semiconductor device structure will become apparent for use with particular implementations from this disclosure. Accordingly, for example, although particular implementations are disclosed, such implementations and implementing components may comprise any shape, size, style, type, model, version, measurement, concentration, material, quantity, method element, step, and/or the like as is known in the art for such gallium nitride semiconductor device structures and implementing components and methods, consistent with the intended operation and methods. 
         [0035]    Examples of conventional semiconductors having guard rings may be in found in U.S. Patent Publication No. 2013/0126888 to Kizilyalli et al., entitled “Edge Termination by Ion Implantation in GAN,” published May 23, 2013, and filed Nov. 21, 2011 and U.S. Pat. No. 9,165,999 to Kentaro Ikeda, entitled “Nitride Semiconductor Device,” issued Oct. 20, 2015 and filed Mar. 15, 2013, the disclosures of each which are hereby incorporated entirely herein by reference. 
         [0036]    Referring to  FIG. 1 , a semiconductor device  2  having conventional guard ring structure is illustrated. This device has an elevated field region. The gate  4  structure and the source  6  structure of this device are located on positively and negatively doped regions of the device  2 . The guard ring  8  is formed through ion implantation at the edge of the device to form a resistive layer. 
         [0037]    Referring to  FIG. 2 , another semiconductor device  9  having a conventional guard ring structure is illustrated. This guard ring structure  10  is formed by a layer of isolation between the device region  12  and the guard ring  14 , isolating the device from the two dimensional electron gas (2DEG). 
         [0038]    Referring now to  FIG. 3 , an implementation of a semiconductor device  16  having a guard ring structure is illustrated. A first guard ring  18  is formed around a device region  20 . The device region  20  includes a plurality of drain fingers  22  and a plurality of source fingers  24  interdigitated with one another. In this implementation there are two gates  26 , however, in other implementations, a single gate may be used. A gate bus  28  is mechanically and electrically coupled to the gates  26  and functions as a first guard ring  18 . The first guard ring  18  completely surrounds the device region/die  20 . The first guard ring  18  can be coupled to the substrate through ohmic/electrical contacts. The channel under the first guard ring  18  may be either depleted or an active 2DEG during the operation of the device. A second guard ring  30  is also illustrated. Multiple guard rings may be used in implementations of semiconductor devices having guard rings as described here. By non-limiting example, additional guard rings may be connected to the gate, the source, or the substrate of the device. The guard rings may also be floating guard rings, floating relative to the drain, source and gate of the device. The channel present between the guard rings  18  and  30  may be either depleted or an active 2DEG. The device may be a high electron mobility transistor (HEMT) formed from gallium nitride (GaN) or any other suitable semiconductor known in the art. 
         [0039]    Referring now to  FIG. 4A , another implementation of a semiconductor device  34  having guard rings  36  is illustrated. The device may be a depletion mode (D-mode) transistor  38  having one or more source fingers  40 , one or more drain fingers  42  and one or more gates  44 . A gate bus  36  surrounds the one or more source fingers and the one or more drain fingers. The gate bus  36  couples with the one or more gates  44  of the D-mode transistor. An enlarged view of the gate  44  and guard ring  36  is illustrated in  FIG. 4B . The guard ring  36  is grounded through the gate  44  which may reduce the capacitance between the source and the substrate of the device. 
         [0040]    Referring to now to  FIG. 5A , an implementation of a semiconductor device  46  having multiple guard rings is illustrated. An enlarged view of the corner of the device is illustrated in  FIG. 5B . The gate bus acts as the first guard ring  48  and is coupled to the gates  50  of the device  46  as previously described in other implementations. In addition, a second  52  and third  54  guard ring are illustrated. The second  52  and third guard ring  54  may be coupled to the source and/or the substrate of the device. The layers used for the guard rings may be any suitable metal known in the art such as metals used for ohmic, gate, or field plate applications. Referring to  FIG. 6 , multiple guard rings may physically protect the device  56  as well. The gallium nitride epitaxial layer  58  can easily be damaged during sawing. Here, the second guard ring  60  blocked the transfer of a crack or chipping defect  59 , occurring during sawing, into the device. 
         [0041]    Referring now to  FIG. 7 , an implementation of a cascode device  62  having a gate  64  connected guard ring  66  is illustrated. A depletion mode (D-mode) transistor  68  is surrounded by a first guard ring  66  coupled to the gate  64 . The D-mode transistor may be a GaN HEMT. A second guard ring  76  is surrounding an outer perimeter of the first guard ring  66 . The D-mode transistor is coupled to a conductive lead frame  78  having leads coming out from the drain  80 . More specifically, the lead frame  78  is connected to the gate pad  64 , the drain pad  80  has a separate pin-out, and the gate and source of the silicon metal oxide semiconductor field effect transistor (Si-MOSFET)  86  are electrically connected. The D-mode transistor  68  is coupled to an enhancement mode (E-mode) transistor  70 . The transistors may be coupled through wire bonds. The E-mode transistor may be a silicon (Si) field effect transistor (FET). The source  72  of the D-mode transistor is coupled to the substrate  74  of the E-mode transistor. The E-mode transistor  70  is coupled to a second conductive lead frame  82 . The gate  84  and the source  86  of the E-mode transistor may have lead outs to connect to other devices. During operation of this implementation of a cascode device, the gate  64  of D-mode transistor  68  is connected to the ground. Having the gate  64  connected to the guard ring  66  may help to keep the potential at the guard ring constant (0V) and may effectively protect the device  62 . The built-up charges between the source and the substrate can be significantly reduced. 
         [0042]    Implementations of GaN devices like those disclosed herein may be manufactured by those of ordinary skill in the art using a wide variety of processing methods and techniques using the principles disclosed herein. 
         [0043]    In places where the description above refers to particular implementations of gallium nitride semiconductor devices and implementing components, sub-components, methods and sub-methods, it should be readily apparent that a number of modifications may be made without departing from the spirit thereof and that these implementations, implementing components, sub-components, methods and sub-methods may be applied to other gallium nitride semiconductor devices.