Abstract:
Embodiments of apparatuses, articles, methods, and systems for a monolithic microwave integrated circuit with a substrate having a diamond layer are generally described herein. Other embodiments may be described and claimed.

Description:
FIELD 
     Embodiments of the present invention relate generally to the field of integrated circuits, and more particularly to a monolithic microwave integrated circuit with a diamond layer. 
     BACKGROUND 
     Monolithic microwave integrated circuits (MMICs) are integrated circuits designed to operate in millimeter-wave and microwave frequency ranges (e.g., 1 gigahertz (GHz) to 300 GHz). A gallium nitride (GaN)—based MMIC typically includes an active layer of aluminum gallium nitride/GaN (AlGaN/GaN) disposed on a suitable buffer layer. The buffer layer is, in turn, disposed on a silicon carbide (SiC) substrate. Active devices may be disposed on the AlGaN/GaN layer opposite the SiC substrate. 
     After MMIC fabrication is completed, the SiC substrate must be thick enough, e.g., greater than approximately 50-75 micrometers (μm), to prevent unacceptable transmission losses in transmission lines coupled to the active devices. At such a thickness, the flexibility of employing different types of materials for the substrate is limited. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
         FIG. 1  is a cross-section view of a MMIC in accordance with various embodiments of the present invention; 
         FIG. 2  is a flowchart illustrating operations involved in manufacturing a MMIC in accordance with various embodiments of the present invention; 
         FIG. 3  is a flowchart illustrating process operations involved in the provisioning of a diamond and active layer wafer in accordance with various embodiments of the present invention; 
         FIG. 4  is a cross-section view of an MMIC in various formative phases that correspond to the process operations discussed in  FIG. 3  in accordance with various embodiments of the present invention; 
         FIG. 5  is a flowchart illustrating process operations involved in front-end processing of the MMIC in accordance with various embodiments of the present invention; 
         FIG. 6  is a cross-section view of the MMIC in various formative phases that correspond to the process operations discussed in  FIG. 5  in accordance with various embodiments of the present invention; 
         FIG. 7  is a flowchart illustrating process operations involved in back-end processing of the MMIC in accordance with various embodiments of the present invention; 
         FIG. 8  is a cross-section view of the MMIC in various formative phases that correspond to the process operations discussed in  FIG. 7  in accordance with various embodiments of the present invention; and 
         FIG. 9  is a signaling system in accordance with various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific devices and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. 
     Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. 
     The phrase “in one embodiment” is used repeatedly. The phrase generally does not refer to the same embodiment; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise. 
     For the purposes of the present invention, the phrases “A/B” and “A and/or B” mean (A), (B), or (A and B). For the purposes of the present invention, the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). For the purposes of the present invention, the phrase “(A)B” means (B) or (A and B), that is, A is an optional element. 
       FIG. 1  is a cross-section view of a MMIC  100  in accordance with various embodiments of the present invention. The MMIC  100  may have a substrate, which includes a diamond layer  106 . The MMIC  100  may also have a buffer layer  108  coupled to an active layer  110  at a first side of the active layer  110 . The buffer layer  108  may be a very thin layer, e.g., less than 2 μm, configured to facilitate the coupling of the active layer  110  to the diamond layer  106 . In various embodiments, the buffer layer  108  may be constructed of one or more semiconductor materials, e.g., Si, gallium arsenide (GaAs), GaN, AlGaN, etc. The active layer  110  may also be constructed of one or more semiconductor materials, which may complement the materials used in the buffer layer  108 . The semiconductor materials of the active layer  110  may include, but are not limited to, GaAs GaN, AlGaN, etc. 
     Active components  112  may be coupled to a second side of the active layer  110  and electrically coupled to a passive component, e.g., capacitor  116 , through a conductive path such as a bridge  120 . An active component, as used herein, may refer to a solid-state device that has gain, directionality, and/or control characteristics determined by reference to a particular embodiment. An active component may include, but is not limited to, a transistor, e.g., a field-effect transistor (FET), a bipolar junction transistor (BJT), a heterojunction bipolar transistor (HBT), etc. The active components may operate in any frequency range, including, but not limited to, millimeter-wave and microwave frequency ranges (e.g., 1 gigahertz (GHz) to 300 GHz). 
     The MMIC  100  may have a dielectric polymer layer  124  coupled to the second side of the active layer  110  in a manner to encompass the components disposed at the second side of the active layer  110 . The dielectric polymer layer  124  may include a low dielectric constant (k) material such as, but not limited to, polyimide, benzocyclobutene (BCB), etc. 
     A transmission line  128  may be coupled to a top surface of the dielectric polymer layer  124  and electrically coupled to the capacitor  116  through a via  132  through the dielectric polymer layer  124 . A ground layer  136 , also referred to herein as a ground plane, corresponding to the transmission line  128 , may be coupled to an opposite side of the MMIC  100 . The ground layer  136  may be electrically coupled to the active components  112  by vias  140  through the diamond layer  106 , the buffer layer  108 , and the active layer  110 . 
     The dielectric polymer layer  124  may have a sufficient thickness, e.g., approximately 10-100 μm, to provide low transmission losses through the transmission line  128 . This may, in turn, allow for the thickness of the diamond layer  106  to be relatively thin, e.g., approximately 25 μm or less. Providing the diamond layer  106  with a thickness in this range may, among other things, enable the diamond layer  106  to function as a substrate with desired characteristics, e.g., heat transfer characteristics, appropriate rigidity, etc. A thick diamond layer, e.g., a thickness greater than 75 μm, may be prohibitively expensive and too rigid for some embodiments. 
     The active layer  110  may have a thickness of approximately 5 μm or less. Providing the active layer  110  with a thickness in this given range may, among other things, provide efficient transfer of thermal energy to a nearby heatsink, e.g., the diamond layer  106 . 
       FIG. 2  is a flowchart  200  illustrating operations involved in the manufacturing of a MMIC, such as MMIC  100 , in accordance with various embodiments of the present invention. 
     At block  204  a wafer having a diamond layer, a buffer layer, and an active layer may be provided.  FIG. 3  is a flowchart  300  depicting process operations involved in the provisioning of this wafer in accordance with some embodiments.  FIG. 4  is a cross-section view of the MMIC in various formative phases that correspond to the process operations discussed in flowchart  300  in accordance with some embodiments. 
     At block  208 , a front end of the MMIC may be processed. The front end, as used herein, may refer to the side of the MMIC having an active layer.  FIG. 5  is a flowchart  500  depicting process operations involved in the front-end processing in accordance with some embodiments.  FIG. 6  is a cross-section view of the MMIC in various formative phases that correspond to the process operations discussed in flowchart  500  in accordance with some embodiments. 
     At block  212 , a back end of the MMIC may be processed. The back end, as used herein, may refer to the side of the MMIC opposite the front end.  FIG. 7  is a flowchart  700  depicting process operations involved in the back-end processing in accordance with some embodiments.  FIG. 8  is a cross-section view of the MMIC in various formative phases that correspond to the process operations discussed in flowchart  700  in accordance with some embodiments. 
     In various embodiments, the operations depicted by the flowchart  200  may be performed by different entities. For example, in one embodiment, a first entity may perform the operation at block  204 , while another entity performs the operations at blocks  208  and  212 . In other embodiments, one entity may perform all of the operations. 
     Reference numbers referring to process operations of  FIGS. 3 ,  5 , and  7  are shown in parentheses in  FIGS. 4 ,  6 , and  8 , respectively. 
     Referring now to the provisioning of the wafer as detailed in  FIGS. 3 and 4  in accordance with some embodiments, at block  304 , a first handle  400  may be provided. The first handle  400  may include a buffer layer, e.g., Si layer  404 , on a layer of silicon oxide (SiO)  408 . At block  308 , a diamond layer  412  may be deposited on the first handle  400 . As used herein, deposited may include any process that grows, coats or otherwise transfers a material onto a surface. 
     In some embodiments, the diamond layer  412  may be deposited through the use of a chemical vapor deposition (CVD) technique. This may enable providing the diamond layer  412  with a thickness in the range approximately 25 μm or less as discussed above. 
     At block  312 , a second handle  416  may be deposited on the diamond layer  412 . The second handle  416  may be a layer of polycrystalline Si (poly Si) that is approximately 500 μm in some embodiments. 
     At block  316 , at least a portion of the first handle  400  may be removed, e.g., through an etching process, and the MMIC may be flipped over. In this embodiment, only the SiO layer  408  is removed, while the Si layer  404  buffer is left. 
     At block  320 , an active layer  420  may be deposited on the Si layer  404 . 
     Front-end processing of the MMIC may be performed as detailed in  FIGS. 5 and 6  in accordance with some embodiments. At block  504 , active/passive components  600  may be formed at a first side of the active layer  420 . Formation of the active/passive components  600  may include a variety of operations including, but not limited to: device isolation; metal plating/evaporation; nitride depositions for passivation; formation of ohmic contacts, gates, capacitors, routing lines; etc. 
     At block  508 , a dielectric polymer  604  may be deposited to encompass the active/passive components  600  disposed at the first side of the active layer  420 . In some embodiments, the dielectric polymer  604  may be deposited by spin-on and cure techniques. 
     A via  606  may be formed through the dielectric polymer  604  to provide a conductive path from various elements of the active/passive components  600 , e.g., a capacitor, to the surface of the dielectric polymer  604 . The via  606  may be formed after the dielectric polymer  604  has been deposited through etching and plating techniques; by plating a tall via first, spinning the dielectric polymer material on top, and then planarizing; or by some other technique. 
     At block  512 , a transmission line  608  may be formed on top of the dielectric polymer  604  and electrically coupled to the active/passive components  600  through the via  606 . 
     Back-end processing of the MMIC may be performed as detailed in  FIGS. 7 and 8  in accordance with some embodiments. At block  704  at least a portion of the second handle  416  may be removed. In this embodiment, the entire second handle  416  may be removed. In some embodiments, the second handle  416  may be removed earlier in the sequence, e.g., at the provisioning of the wafer at block  204 . 
     At block  708 , a via  804  may be formed through the diamond layer  412 , Si layer  404 , and active layer  420  to provide a conductive path to various elements of the active/passive components  600 , e.g., to sources of active devices. In various embodiments, sections of the via  804  may be formed in iterative stages intermixed with the layer depositioning operations. The via  804  may be plated after formation. 
     At block  712 , a ground layer  808  may be deposited on the diamond layer  412  as shown. 
     In various embodiments, MMICs having a thin diamond layer as taught herein (e.g., MMIC  100 ) may be formed through process operations that vary from those depicted in  FIGS. 3-8 . 
       FIG. 9  illustrates a signaling system  900  in accordance with various embodiments of the present invention. The system  900  may include a controller  904  coupled to a MMIC  908 . The MMIC  908 , which may be substantially interchangeable with any of the MMICs described in other embodiments of the present invention, may include circuit components configured to perform a variety of transmit/receive functions for the signaling system  900 . These functions include, but are not limited to, microwave mixing, power amplification, low-noise amplification, high-frequency switching, etc. 
     The controller  904 , which may be a digital controller in some embodiments, may control the MMIC  908  to transmit/receive signals via a signaling medium  912 . The signaling medium  912  may be a wireless medium, a wired medium, or a wire-like medium (e.g., optical fiber). 
     The signaling system  900  may be a device capable of transmitting/receiving signals in a variety of military/civilian applications. For example, the signaling system  900  may be a radar, a wireless communication device (e.g., a mobile device such as a mobile phone or a wireless network infrastructure device such as a base station); a wired/wire-like communication device, etc. 
     Although the present invention has been described in terms of the above-illustrated embodiments, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This description is intended to be regarded as illustrative instead of restrictive on embodiments of the present invention.