Abstract:
A method includes forming one or more capacitors over a substrate. The method also includes forming a transformer at least partially over the substrate. The transformer is adjacent to at least one of the one or more capacitors. At least a portion of the transformer is formed at a same level over the substrate as the one or more capacitors. The method further includes coupling the one or more capacitors and the transformer to at least one embedded integrated circuit die. The one or more capacitors, the transformer, and the at least one embedded integrated circuit die form at least part of a light emitting diode (LED) driver.

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/278,809 filed on Oct. 13, 2009, which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to lighting systems. More specifically, this disclosure relates to an integrated driver system architecture for light emitting diodes (LEDs). 
       BACKGROUND 
       [0003]    Light emitting diodes (LEDs) are becoming more and more popular due to their low energy usage and their long operational lifespan. LEDs are typically controlled using LED drivers. There is interest in integrating LED drivers to minimize their form factor, provide improved system packing density, and reduce costs. 
         [0004]    Integration, however, presents its own challenges. Integration generally involves reducing the overall form factor of an LED driver system by increasing the packing density of its components and optimizing the performance of the components to run at higher performance levels. This is done while taking a holistic view of the overall system&#39;s form factor when considering the underlying component matrix. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    For a more complete understanding of this disclosure and its features, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0006]      FIGS. 1 through 4  illustrate an example formation of capacitive structures and other structures in an integrated LED driver system according to this disclosure; and 
           [0007]      FIG. 5  illustrates an example power supply unit incorporating an integrated LED driver system according to this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]      FIGS. 1 through 5 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the invention may be implemented in any type of suitably arranged device or system. 
         [0009]    In accordance with this disclosure, an LED driver system is provided with tight three-dimensional integration of its components. This structure can be formed while avoiding packaging-related volume overhead. Various categories of components may be included in the integrated LED driver system, such as line voltage transistor devices, isolation transformers, high-frequency switching devices, rectification devices, smoothing devices (capacitances), control and intelligence devices, optical and thermal sensors, wireless or wired control interfaces (such as radio interfaces), and over-voltage suppression devices. Various ones of these components, such as integrated circuits, power diodes, and transistors, could be implemented in one or more discrete dies that are embedded into the integrated LED driver system. 
         [0010]    Passive energy storage elements in this type of three-dimensional integration scheme may represent the largest components by volume of the integrated LED driver system. Thus, these components can take the lead in the set of considerations of overall system volume arrangement. The following describes one example of a process for forming an integrated LED driver system. 
         [0011]      FIGS. 1 through 4  illustrate an example formation of capacitive structures and other structures in an integrated LED driver system according to this disclosure. As shown in  FIG. 1 , the process begins with a wafer level substrate  102 , which is used to deliver mechanical strength during subsequent layer build-up processing steps. The wafer level substrate  102  could include a printed circuit board (PCB) with embedded metal or other conductive layers and with exposed vias at its surface, and vias can also be run through the substrate  102  as heat pipes. As particular examples, the wafer level substrate  102  may be formed from a silicon, copper, aluminum, or FR4 (glass reinforced epoxy laminate) resin board, optionally with interconnects already processed and in place in the substrate  102 . Also, pre-formed metal or other conductive layers may be fabricated using a typical wafer process flow or a PCB processing flow. 
         [0012]    A capacitor  104  is formed over the substrate  102 . For example, a set of capacitors  104  can be formed on top of the wafer level substrate  102  using a multi-layer buildup process flow. In particular embodiments, the formation of the capacitors  104  could involve using a single wafer processing deposition tool with three or more chambers. Two chambers may respectively include shadow masking metal or other conductive masks representing an anode and a cathode of a capacitor  104 . A third chamber can be used to deposit a dielectric layer, such as a dielectric layer formed by chemical vapor deposition (CVD) or plasma-enhanced chemical vapor deposition (PECVD) of SiO 2 , SiON, or AlOx material. The wafer level substrate  102  can be processed though each chamber sequentially multiple times to form multiple conductive layers  106   a - 106   m  and multiple dielectric layers  108   a - 108   n.  In particular embodiments, there could be between five and one hundred layers of conductive and dielectric material. The conductive layers  106   a - 106   m  form interleaved layers of the capacitor&#39;s cathode and anode. 
         [0013]    After formation of the stack of layers as shown in  FIG. 1 , the anodes and cathodes of the capacitor  104  are exposed to enable formation of electrical contacts  110   a - 110   b  as shown in  FIG. 2 . This could include, for example, performing a single lithographic and physical etch step to expose the cathodes and anodes to metalized or other electrical contacts suitable for use with a large-value capacitor. This etch could also open up vias  111   a - 111   b  to the metal or other conductive layers of the wafer level substrate  102  underlying the capacitor  104 . This processing flow can result in a high density, high voltage capacitor with the minimal cost of a single contact mask and a single metal/conductive mask. The electrical contacts  110   a - 110   b  could be formed using any suitable material(s), such as a redistribution layer (RDL) of metal. 
         [0014]    Another mask and metal/conductive layer could optionally be used as a redistribution layer definition plating electroplating mask. This could be done to provide the LED driver with de-coupled system power plane rails, each at various voltages throughout the system. In each isolated case, there could be a capacitor for smoothing and/or decoupling the voltage between the rails. Thus, several types of capacitors are envisioned and can be processed at the same time, where they are already isolated from one other by the deposited dielectric layers.  FIG. 3  illustrates one example of this, where two capacitors  104   a - 104   b  are separated from one another by an inter-dielectric layer (IDL)  112  (formed by portions of the dielectric layers  108   a - 108   n ). 
         [0015]      FIG. 3  also illustrates a bottom portion  114  of a transformer&#39;s windings, which are formed within a dielectric layer  116 . The bottom portion  114  of the transformer is coupled to one of the capacitors  104   b.    FIG. 3  further illustrates the results obtained using both: 
         [0016]    an etch mask used to define (i) vias that may be filled to link the electrodes of the capacitor terminals and (ii) vias used to contact the underlying substrate conductive interconnect; and 
         [0017]    an etch mask used to define (i) vias that contact the capacitors&#39; “fins,” (ii) redistribution conductive material connected to the capacitors, and (iii) conductive material to connect the underlying substrate interconnect. In particular embodiments, the lower portion of the transformer windings can be formed within the substrate  102 . After that, the capacitors  104   a - 104   b  can be formed. The dielectric layer  116  could be formed at the same time that the dielectric layers  108   a - 108   n  are formed, or the dielectric layer  116  could be formed separately. Vias through the dielectric layers  108   a - 108   n  and  116  can be formed, and the electrical contacts for the capacitors  104   a - 104   b,  the redistribution conductive material, and electrical contacts for the transformer windings can all be formed at the same time. 
         [0018]    Inductive elements can also be fabricated, such as to provide a transformer core. Several transformer core processing options are available. For example, in low-current LED driver systems, a ferromagnetic core can be formed by electroplating. In mid-current LED driver systems, a ferromagnetic core can be formed by discrete core fabrication and wafer level embedding. Interconnects can be fabricated using epoxy build-up and plating metal/conductive material to close the turns around the transformer. These structures are depicted in more detail in  FIG. 4 , which shows a completed transformer  118  with an embedded ferromagnetic material core torroid  120 . In addition, transistors, diodes, and other discrete devices can be selected and placed into the system as one or more embedded dies  122  within pre-formed cavities in one or more epoxy layers  124 - 126 . These devices can be subsequently wired up with a final set of interconnect layers and contacts, bumps, or bonding areas formed on top. 
         [0019]      FIG. 5  illustrates an example power supply unit (PSU)  500  incorporating an integrated LED driver system according to this disclosure. As shown in  FIG. 5 , the PSU  500  includes or is coupled to an AC source  502 , which provides a suitable AC voltage signal. A super-junction transient voltage suppressor  504  suppresses voltage transients in the AC voltage signal. A complementary bridge rectifier  506  performs rectification on the AC voltage signal. The bridge rectifier  506  in this example is formed by diodes, which could represent VHP700 power diodes. A micro-electro-mechanical (MEMS) capacitor  508  is coupled across the bridge rectifier  506 . A complementary H-bridge  510  formed by transistors is coupled to the capacitor  508  and a transformer  512 . A high voltage (HV) bootstrap circuit  514  controls the transistors in the H-bridge  510 . An electro-static discharge (ESD) protection circuit  516  is coupled across the transformer  512  and a complementary bridge rectifier  518 . The bridge rectifier  518  is again formed by diodes, such as PVIP25 or ABCD5 power diodes. A MEMS capacitor  520  is coupled across the bridge rectifier  518  and a system load  522 , such as one or more light emitting diodes. 
         [0020]    In the PSU  500  of  FIG. 5 , the capacitors  508  and  520  and the transformer  512  could be formed as shown in  FIGS. 1-4 . Also, the remaining components  504 - 506 ,  510 ,  514 ,  516 - 518  could be implemented using one or more embedded dies  122 . In this way, the PSU  500  shown in  FIG. 5  can implement the architecture shown in  FIG. 4 , allowing the architecture in  FIG. 4  to drive one or more LEDs or some other system load  522 . 
         [0021]    Note that the description above has described the use of particular materials, such as silicon, copper, and epoxy. This is for illustration and explanation only. Each component shown in the figures could be formed in any suitable manner and from any suitable material(s). 
         [0022]    It may be advantageous to set forth definitions of certain words and phrases that have been used within this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more components, whether or not those components are in physical contact with one another. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. 
         [0023]    While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.