Patent Publication Number: US-10788367-B2

Title: Integrated circuit using photonic bandgap structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/800,009 filed Oct. 31, 2017, the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Individual discrete components are typically fabricated on a silicon wafer before being cut into separate semiconductor die and assembled in a package. The package provides protection against impact and corrosion, holds the contact pins or leads which are used to connect from external circuits to the device, and dissipates heat produced in the device. 
     Wire bonds may be used to make electrical connections between an integrated circuit and the leads of the package with fine wires connected from the package leads and bonded to conductive pads on the semiconductor die. The leads external to the package may be soldered to a printed circuit board. Modern surface mount devices eliminate the need for drilled holes through circuit boards and have short metal leads or pads on the package that can be secured by reflow soldering. 
     Many devices are encapsulated with an epoxy plastic that provides adequate protection of the semiconductor devices and mechanical strength to support the leads and handling of the package. Some integrated circuits have no-lead packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) devices that physically and electrically couple integrated circuits to printed circuit boards. Flat no-lead devices, also known as micro leadframe (MLF) and small outline no-leads (SON) devices, are based on a surface-mount technology that connects integrated circuits to the surfaces of printed circuit boards without through-holes in the printed circuit boards. Perimeter lands on the package provide electrical coupling to the printed circuit board. 
     A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction. This creates an internal electric field which reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axis aligns to the field. While the term “insulator” implies low electrical conduction, “dielectric” is typically used to describe materials with a high polarizability which is expressed by a number called the relative permittivity (εr). The term insulator is generally used to indicate electrical obstruction while the term dielectric is used to indicate the energy storing capacity of the material by means of polarization. 
     Permittivity is a material property that expresses the force between two point charges in the material. Relative permittivity is the factor by which the electric field between the charges is decreased or increased relative to vacuum. Relative permittivity is also commonly known as dielectric constant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an example integrated circuit (IC) package that includes photonic filter structure formed by a photonic collimating structure. 
         FIGS. 2A-2C  is a frequency dispersion plot illustrating a band gap in a photonic bandgap structure having a hexagonal lattice. 
         FIG. 3  is an example of another photonic bandgap structure having a square lattice. 
         FIG. 4  is a plot illustrating a portion of the electromagnetic frequency spectrum vs. wavelength. 
         FIG. 5  illustrates a simulation of an example photonic waveguide formed by a photonic bandgap structure. 
         FIG. 6  is a cross section of an example encapsulated package that includes another example of a photonic filter structure. 
         FIG. 7  is a top view of an example leadframe. 
         FIGS. 8A-8C  illustrate formation of a photonic filter structure using an additive manufacture process to encapsulate an IC. 
         FIGS. 9A-9B  illustrate a top and bottom view of an example IC package containing a photonic filter structure. 
         FIG. 10  is a flow chart illustrating an example process for formation of an encapsulated package with a photonic filter structure within the encapsulation material. 
         FIGS. 11-12  are a cross sectional views of an alternative embodiments. 
         FIG. 13  illustrates a simulation of another example photonic waveguide. 
         FIG. 14  is a cross sectional view of another example encapsulated package that includes a photonic waveguide formed by a resonant structure coupled to a filter structure. 
         FIG. 15  is a cross sectional view of another example encapsulated package that includes a multilayer photonic filter structure. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Like elements in the drawings are denoted by like reference numerals for consistency. 
     The epoxy encapsulant for semiconductor chips/packages has typically served the primary purpose of providing environmental and mechanical protection for the integrated circuit (IC). Previously, in order for an additional package function to be added, it must be added before or after the encapsulation step. Performing additional packaging steps may increase cost and limit functionality on the processes that can be performed. In a method described herein for encapsulating an IC, a structure to perform an additional package function may be created during the process of encapsulation. 
     A spectrometer is a scientific instrument originally used to split light into an array of separate colors, called a spectrum. Spectrometers were developed in early studies of physics, astronomy, and chemistry. The capability of spectroscopy to determine chemical composition drove its advancement and continues to be one of its primary uses. 
     In physics, a photon represents an energy packet, or “quanta” of electromagnetic waves. A photon is massless, has no electric charge, and is a stable particle. In the momentum representation of the photon, a photon may be described by its wave vector which determines its wavelength and direction of propagation. 
     Prior spectrometry sensors require open packaging to allow photons to be able to strike the sensor surface. This leaves the delicate sensor open to the environment or at least more easily accessible. The sensor may be discrete from the processing IC in many implementations. 
     Additive manufacturing has enabled the deposition of patterned materials in a rapid and cost efficient manner. By utilizing additive manufacturing, control structures may be integrated directly into the encapsulation material of an IC. As described herein, a spectrometer sensor may be fabricated on an IC die that is included within an encapsulated package. A filter structure may be provided by the implementation of multi-material photonic bandgap (PBG) structures within the encapsulation material to allow sensing of a selected frequency band of photon energy that falls on the encapsulated package. 
       FIG. 1  is an example encapsulated integrated circuit (IC) package  100  that includes a filter structure formed by a photonic collimating structure  150  within the encapsulant material  120 . As will be described in more detail below, filter structure  150  may be configured to selectively filter frequency bands from electromagnetic energy that falls on a surface of encapsulated package  102 . For example, filter region  151  may allow a first band of energy to pass, filter region  152  may allow a second band of energy to pass, and filter region  153  may allow a third band of energy to pass. One or more sensors fabricated on IC die  102 , such as sensors  111 - 113 , may then sense the energy present in a selected band of the total electromagnetic energy that falls on each sensor to thereby produce spectrometric data that may be used by processing circuitry on IC die  102 , or be provided to processing circuitry located in another package. 
     IC die  102  may be attached to a die attach pad (DAP)  104  of a leadframe that includes a set of contacts  105 . DAP  104  may also be referred to as a “thermal pad.” IC die  100  may also be referred to as a “chip.” IC die  102  may be fabricated using known or later developed semiconductor processing techniques. IC die  102  may include an epitaxial (epi) layer on the top surface in which are formed various semiconductor transistor devices and interconnects. One or more conductive layers may be formed on the epi layer and patterned into interconnect traces and bond pads. A set of bond wires  106  may be attached to contacts  105  and bond pads located on the surface of IC die  106  using known or later developed wire bonding techniques. In this example, IC package  100  is a quad-flat no-leads (QFN) package; however, in other embodiments various known or later developed packaging configurations, such as DFN, MLF, SON, flip chips, dual inline packages (DIP), etc, may be fabricated using the techniques described herein to form an encapsulated package with a photonic bandgap structure included within the encapsulant material. 
     In this example, a solid encapsulant material  120  surrounds and encapsulates IC die  102 . A portion of the encapsulation material may include a matrix of interstitial nodes such as indicated at  121  that may be filled with a material that is different from encapsulation material  120 . In this example, nodes  121  are arranged in a three dimensional array of spherical spaces that are in turn separated by a lattice of encapsulation material  123 . Encapsulation material  123  may be the same or different as solid encapsulation material  120 . 
     In some embodiments, the structure formed by the matrix of nodes  121  and lattice  123  may be referred to herein as a “photonic bandgap structure.” A photonic bandgap (PBG) structure formed by periodic nodes  121  may effectively filter photonic energy that falls on package  100  by selectively blocking a frequency band from passing while allowing other electromagnetic photons to pass. In other embodiments, the structure formed by the matrix of nodes  121  and lattice  123  may be referred to herein as a “photonic wave collimator structure.” A photonic wave collimator (PWC) structure formed by periodic nodes  121  may effectively filter photonic energy that falls on package  100  by selectively allowing only a certain frequency band of energy to pass. 
     The PBG works by destructively diffracting energy at a certain band of frequencies. The PWC works by constructively diffracting energy at a certain band of frequencies. It is actually the same phenomenon, just turned on its head. A PWC structure may pass a single band due to the fact that the photonic crystal is designed to work at a narrow band. Just as the PBG can only block a narrow band, the PWC can only pass a narrow band. 
     In this example, PWC structure  150  may be designed to form a separate photonic wave collimator to each of the three sensors  111 - 113 . Each photonic wave collimator  151 ,  152 ,  153  may be designed to allow only a single band of electromagnetic energy received from broad band electromagnetic signal  140  to pass to a corresponding sensor  111 - 113 . In this example, a spectrometer may be provided that may sense energy in three different energy bands of signal  140 . 
     A different spectrometer may be provided by using the same IC die  102 , and forming PWC regions with different parameters during the encapsulation process. In this manner, several different devices may be fabricated to sense different bands by using a same version of IC die. Only the encapsulation process needs to be modified to change the spectral sensing parameters by selecting the node and lattice parameters of the photonic wave collimating regions. 
     While three sensors are illustrated here for clarity, another embodiment may have a larger array of sensors to provide a spectrometer with more precision. 
     In this example, a broadband electromagnetic signal  140  is impinging on encapsulated package  100 . In this example, signal  140  may be an optical signal or a radio frequency signal (RF), for example. For illustrative purposes only, signal  140  is illustrated as having a spectrum of six frequency bands to better illustrate how signal  140  may be separated into different bands by photonic filter structure  150 . In reality, the frequencies of a broadband signal are mixed together. Signal  140  may have a broader spectrum or a narrower spectrum than what is included in PWC structure  150 , for example. 
     Solid encapsulant material  120  is usually an epoxy based material that provides mechanical protection and seals IC die  102  from environmental gases and liquids. 
     In this example, lattice  123  may be in contact at various places across the entire upper surface of IC die  102 . As mentioned above, lattice  123  may be formed from the same material as solid encapsulation material  120 , or it may be formed using a different material by using an additive manufacturing process. The array of nodes  121  may be formed with one or more different materials. For example, some of the nodes, such as nodes  121 , may be filled with a first material and some of the nodes  121  may be filled with different types of material. There may be a number (N) of different materials that are used to fill N different sets of nodes within encapsulation material  123 . Node material may be a polymer or other material that has different intrinsic material properties from the lattice material  123 . For example, the node material may have various different intrinsic material properties from the lattice material, such as permittivity, permeability, conductivity, etc. 
     For example, certain nodes  121  may be filled with a high dielectric material, while other nodes  121  are filled with a low dielectric material. In some embodiments, node material  121  may be air, some other gas, or even a vacuum. 
     In the example of  FIG. 1 , lattice  123  forms a square three dimensional (3D) array of spherical nodes. In other embodiments, a differently shaped lattice may be formed to produce other shapes of arrays and nodes  121 , such as: triangular, rectilinear, hexagonal, round nodes, elongated nodes, tubes, etc. 
     In some embodiments, die attachment  125  may be a thin layer of adhesive material. In other embodiments, die attachment  125  may include a portion that is also a photonic bandgap structure. 
     A photonic crystal is an artificially manufactured structure, or material, with periodic constitutive or geometric properties that are designed to influence the characteristics of electromagnetic wave propagation. When engineering these crystals, it is possible to isolate these waves within a certain frequency range. Conversely it may be more helpful to consider these waves as particles and rely on the wave-particle duality throughout the explanation. For this reason, reference to “propagation” herein may refer to either the wave or the particle movement through the substrate. Propagation within this selected frequency range, referred to as the band gap, is attenuated by a mechanism of interferences within the periodic system. Such behavior is similar to that of a more widely known nanostructure that is used in semiconductor applications, a photonic crystal. The general properties and characteristics of photonic structures are known, for example, see: “Fundamental Properties of Phononic Crystal,” Yan Pennec and Bahram Djarari-Rouhani, Chapter 2 of “Phononic Crystals, Fundamentals and Applications” 2015, which is incorporated by reference herein. See also “Self-Collimating Phenomena in Photonic Crystals,” Hideo Kosaka et al, 1999. 
     Photonic crystals may be formed by a periodic repetition of inclusions in a matrix. The dielectric properties, shape, and arrangement of the scatterers may strongly modify the propagation of the electromagnetic waves in the structure. The photonic band structure and dispersion curves can then be tailored with appropriate choices of materials, crystal lattices, and topology of inclusions. 
     Similarly to any periodic structure, the propagation of electromagnetic waves in a photonic crystal is governed by the Bloch or Floquet theorem from which one can derive the band structure in the corresponding Brillouin zone. The periodicity of the structures, that defines the Brillouin zone, may be in one (1D), two (2D), or three dimensions (3D). 
     The general mechanism for the opening of a band gap is based on the destructive interference of the scattered waves by the inclusions. This necessitates a high contrast between the properties of the materials. In periodic structures, this is called the Bragg mechanism and the first band gap generally occurs at a frequency which is about a fraction of c/a, where “c” is a typical velocity of light, and “a” is the period of the structure. 
     Photonic bandgap structures may be designed and modeled using simulation software available from various vendors. For example, physics-based systems may be modeled and simulated using COMSOL Multiphysics® simulation software from COMSOL®. “Multiphysics” and “COMSOL” are registered trademarks of COMSOL AB. HFSS (High Frequency Structure Simulator) is available from Ansys. CST (Computer Simulation Technology) offers several simulation packages. 
       FIG. 2A  is a frequency dispersion plot illustrating a band gap in a photonic bandgap structure having a hexagonal lattice.  FIG. 2B  illustrates a single cell  230  of the hexagonal matrix and illustrates Brillouin zone  231  for the hexagonal cell.  FIG. 2C  illustrates a larger portion of a hexagonal photonic crystal  232  formed by a 3D matrix of nodes as indicated at  233 .  FIG. 3  is an example of another photonic bandgap structure having a square lattice. 
     The x-axis of  FIG. 2A  represents the periphery of Brillouin zone  231  of photonic crystal  232  as defined by points Γ, M, and K. The y-axis represents the angular frequency of acoustic energy propagating in photonic crystal  232  in units of ωα/2πC. The various plot lines represent propagation paths through Brillouin zone  231 . Region  235  represents a photonic band gap in which the propagation of waves falling within the defined band of frequencies is blocked by interference produced by the crystal lattice. 
     The width and the frequency range covered by a photonic bandgap depends on the periodic spacing of the nodes  233 , which may be represented by lattice constant “a” as indicated at  336  in  FIG. 3 , and the relative difference between the dielectric constant of the lattice material and the dielectric constant of the nodes. For example, the frequency range covered by photonic bandgap  235  may be shifted to a higher frequency range for larger relative differences between the dielectric constant of the lattice and the dielectric constant of the nodes, while the photonic bandgap  235  may be shifted to a lower frequency range for smaller relative differences between the dielectric constant of the lattice and the dielectric constant of the nodes. 
       FIG. 4  is a plot illustrating a portion of the electromagnetic frequency spectrum vs. wavelength for an example dielectric solid material. The velocity (v) of an electromagnetic wave in a vacuum is approximately equal to the speed of light (c) in a vacuum, which is approximately 3×10 8  m/s. The velocity of an electromagnetic wave through a solid material is defined by expression (1), where ε r  is the relative permittivity of the solid material, which may also be referred to as the “dielectric constant” of the material
 
 v=c /√{square root over (ε r )}  (1)
 
     The photonic wavelength (λ) may be determined using expression (2), where the velocity (v) in dielectric materials is usually on the order of 1-2.5×10 8  m/s for dielectric constant values in the range of approximately 1-10, and f is the frequency of the photon.
 
lambda (λ)= v/f   (2)
 
     For electromagnetic signals in the GHz to low THz frequency range, for example, the corresponding wavelengths in encapsulant material  120  may be in the range of several microns to several hundred microns, as indicated at  400 . The opening of wide photonic band gaps requires two main conditions. The first one is to have a large physical contrast, such as density and speed of propagation of the wave movements, between the nodes and the lattice. The second condition is to present a sufficient filling factor of the nodes in the lattice unit cell. The forbidden band gap occurs in a frequency domain given by the ratio of an effective propagation velocity in the composite material to the value of the lattice parameter of the periodic array of nodes. Referring to  FIG. 3 , as a rule of thumb the lattice dimension  336  may be selected to be about one half of the wavelength of the center of the target photonic bandgap. 
     While the effect of dielectric constant (εr) is described above, other intrinsic properties of a material may be evaluated during the design of a PBG structure, such as permeability, conductivity, etc. 
       FIG. 5  illustrates a simulation of an example PBG waveguide  540  formed by an example photonic bandgap structure  550 . This example illustrates a how photons of a particular frequency may move through a waveguide region  540  of a PBG structure  550  while being blocked from another region. As described above, a photonic bandgap structure may be formed within encapsulation material  123  by inserting a matrix of nodes  121  with a periodic spacing. In this example, the x-axis node spacing  554  is approximately equal to the y-axis node spacing  556 . The z-axis node spacing (not shown) is also approximately the same as node spacing  554 ,  556  in this example. 
     The node spacing  554 - 556  in this example may be selected to be approximately one half the wavelength of a selected frequency of electromagnetic radiation represented by photons  552  that should be guided by bandgap structure  550 . In this manner, electromagnetic energy in the form of photons  552  that falls within the bandgap frequency range of PBG structure  550  may be guided through PBG waveguide  540  is illustrated by signal vector  541 . 
       FIG. 6  is a cross sectional view of encapsulated package  600  that includes an embodiment of a spectrometer that uses filter structure  650  that is formed within the encapsulation material  120  by a multilayer PBG structure. In this example, filter structure  650  may be implemented in only a limited portion of encapsulation material  120 , but still provide an effective filter for electromagnetic energy that falls on package  600 . In this example, filter structure  650  includes six layers that are designed to provide a photonic bandgap at six different frequency bands, however, in other embodiments a larger or a smaller number of layers may be implemented to provide a smaller or larger number of bandgaps. 
     In this example, a broadband electromagnetic signal  640  is impinging on encapsulated package  600 . In this example, signal  640  may be an optical signal or a radio frequency signal (RF), for example. For illustrative purposes only, signal  640  is illustrated as having a spectrum of six frequency bands, such as band  641 ,  642 ,  643 , to correspond to the six bandgaps provided by the six layer filter structure  650 . Signal  640  may have a broader spectrum or a narrower spectrum than what is included in multilayer filter structure  650 , for example. 
     Assuming the bandgap of each of the six layers of filter structure  650  is designed cover a different portion of the spectrum and all six together can block the entire spectrum, then no portion of signal  640  would reach any of sensors  111 - 113 . However, in this example, a waveguide region may be formed in selected layers of filter structure  650  to allow energy in a selected band to flow through filter structure  650 . For example, a waveguide region  651  may be formed in one layer of filter structure  650  to allow frequencies in a selected band, such as the band indicated at  641 , to flow through the filter structure and be sensed by sensor  111 . Another waveguide region  652  may be formed in another layer of filter structure  650  to allow frequencies in another selected band, such as the band indicated at  642 , to flow through the filter structure and be sensed by sensor  112 . Similarly, waveguide region  653  may be formed in another layer of filter structure  650  to allow frequencies in another selected band, such as the band indicated at  643 , to flow through the filter structure and be sensed by sensor  113 . In this example, a spectrometer may be provided that may sense energy in three different energy bands in signal  640 . 
     A different spectrometer may be provided by using the same IC die  102 , and forming waveguide regions in different layers of filter structure  650  during the encapsulation process. In this manner, several different devices may be fabricated to sense different bands by using a same type of IC die. Only the encapsulation process needs to be modified to change the spectral sensing parameters by selecting which layers to place wave guide regions. In some embodiments, waveguide regions may be placed in several layers to allow a sensor to sense energy for more than one band. 
     While three sensors are illustrated here for clarity, another embodiment may have a larger array of sensors to provide a spectrometer with more precision. 
     While a filter structure  650  is illustrated herein that has approximately contiguous bandgaps, another embodiment may use a filter structure in which the bandgaps are not contiguous. In that case, electromagnetic energy that is not blocked by any bandgap in the bandgap structure may be sensed by an underlying sensor. In some embodiments, a separate portion of the filter over each sensor may be tailored to have no bandgap in the frequency range to be sensed by each sensor. 
       FIG. 7  is a top view of an example QFN leadframe  700  that may be used to support IC  100  in  FIG. 1 , for example. Other types of packages may use a leadframe strip that has a different known or later developed configuration. Lead frame strip  700  may include one or more arrays of individual lead frames. Lead frame strip  700  is usually fabricated from a copper sheet that is etched or stamped to form a pattern of thermal pads and contacts. Lead frame strip  700  may be plated with tin or another metal that will prevent oxidation of the copper and provide a lower contact surface that is easy to solder. An IC die may be attached to each individual lead frame. 
     Each individual leadframe may include a die attach pad, such as die attach pads  104 . Each individual lead frame also includes a set of contacts that surround the die attach pad, such as contacts  105 . A sacrificial strip of metal connects all of the contacts together and provides mechanical support until a sawing process removes it. An IC die, also referred to as a “chip,” is attached to each die attach pad during a packaging process. Wire bonding may then be performed to connect bond pads on each IC chip to respective contacts on the lead frame. The entire lead frame strip  700  may then be covered with a layer of mold compound using an additive process as described in more detail below to encapsulate the ICs. Lead frame strip  700  may then be singulated into individual packaged ICs by cutting along cut lines  728 ,  729 . 
       FIGS. 8A-8C  are cross sectional views illustrating fabrication of the example IC package  100  of  FIG. 1 . IC die  102  may be attached by die attach layer  842  to a die attach pad  104  of a leadframe that may be part of a leadframe strip similar to leadframe strip  700  shown in  FIG. 7  that includes a set of contacts  105 . IC die  102  may be fabricated using known or later developed semiconductor processing techniques. IC die  102  may include an epitaxial (epi) layer  841  on the top surface in which are formed various semiconductor transistor devices and interconnects. One or more conductive layers may be formed on the epi layer and patterned into interconnect traces and bond pads  843 . A set of bond wires  106  may be attached to contacts  105  and bond pads  843  located on the surface of IC die  102  using known or later developed electrical connection techniques. In this example, IC package  100  is a quad-flat no-leads (QFN) package; however, in other embodiments various known or later developed packaging configurations, such as DFN, MLF, SON, flip chip, dual inline packages (DIP), etc, may be fabricated using the techniques described herein to form an encapsulated package with a PBG waveguide formed within the encapsulant material. 
       FIG. 8B  is a cross sectional view illustrating partial formation of encapsulation material  120 . Additive manufacturing processes are now being used in a number of areas. The International Association for Testing Materials (ASTM) has now promulgated ASTM F7292-12a “Standard Terminology for Additive Manufacturing Technologies” 2012 which is incorporated by reference herein. Currently, there are seven families of additive manufacturing processes according to the ASTM F2792 standard, including: vat photopolymerization, powder bed fusion, binder jetting, material jetting, sheet lamination, material extrusion, directed energy deposition. Hybrid processes may combine one or more of these seven basic processes with other manufacturing processes for additional processing flexibility. Recent process advances allow additive manufacturing of 3D structures that have feature resolution of less than 100 nm, such as direct laser lithography, multi-photon lithograph, two-photon polymerization, etc. 
     In this example, a vat photopolymerization process may be used in which leadframe strip and the ICs attached to it, such as IC die  102 , are lowered into a vat of liquid photopolymer resin. A light source, such as a laser or projector, may then expose selected regions of the liquid photopolymer resin to initiate polymerization that converts exposed areas of the liquid resin to a solid. In this manner, layers of encapsulant material  120  may be formed in selected shapes. For example, encapsulant material that forms lattice  123  may be the same or different as the solid encapsulant material  120 . Nodes  121  may be formed with any selected lattice spacing. 
       FIG. 8C  is a cross sectional view illustrating further partial formation of encapsulation material  120  around IC die  102 . Additional layers of liquid encapsulation material  120  have been exposed and converted to a solid. Selective exposure of the liquid resin allows lattice  123  to be formed with nodes  121 , as described with regard to  FIG. 1 . A small portion of filter structure  150  is illustrated in  FIG. 8C . Waveguide region  651  may be formed in this example by omitting nodes  123  from the encapsulation material in the region that forms waveguide  651 . 
     As each layer of encapsulation material is added, the lattice and/or node parameters may be altered to form a multilayer filter structure in which each layer provides a different bandgap. 
     The leadframe strip may be submerged in different vats at different times in order to allow different materials to form the nodes  121  within lattice  123 . 
     Additional layers of resin may be exposed and hardened to form the final outside encapsulation layer illustrated in  FIG. 1 . The leadframe strip may then be sawed or otherwise separated into individual encapsulated IC packages. 
     In another embodiment, other additive manufacturing processes may be used to form encapsulation material  120 . For example, a powdered bed diffusion process may be used in which a powdered material is selectively consolidated by melting it together using a heat source such as a laser or electron beam. 
     In another embodiment, a material jetting process may be used in which droplets of material are deposited layer by layer to produce a PBG waveguide within an encapsulation structure as described herein. However, bond wires  106  may require extra care to avoid disrupting the droplet streams. 
     In another embodiment, bond wires are not initially bonded to contacts  105  and bond pads  843 . In this example, a material jetting process may be used in which droplets of material are deposited layer by layer to produce a photonic bandgap structure as described herein. As part of the material jetting process, a conductive material may be deposited to form the bond wires between contacts  105  and bond pads  843 . In some embodiments, a sintering process may be done by heating the encapsulated leadframe  700  assembly to further solidify the bond wires. The leadframe strip  700  may then be sawed or otherwise separated into individual encapsulated IC packages. 
     In another embodiment, IC die  102  is not initially attached to die attach pad  104  of a leadframe that may be part of a leadframe strip similar to leadframe strip  700  shown in  FIG. 7 . In this example, a vat photopolymerization process may be used in which the leadframe strip is lowered into a vat of liquid photopolymer resin. A light source, such as a laser or projector, may then expose selected regions of the liquid photopolymer resin to initiate polymerization that converts exposed areas of the liquid resin to a solid. In this manner, layers of encapsulant material  120  may be formed in selected shapes. In this manner, a photonic bandgap structure  126  as shown in  FIG. 1  may be fabricated on top of die attach pad  104  to isolate a later attached IC die from die attach pad  104 . Spaces may be left above each contact  105  for later attachment of bond wires. A set of bond wires  106  may be attached to contacts  105  and bond pads  643  located on the surface of IC die  106  using known or later developed wire bonding techniques. Additional layers of resin may be exposed and hardened to form an additional photonic structure as described with regard to  FIGS. 8A-8C , for example. The leadframe strip may then be sawed or otherwise separated into individual encapsulated IC packages. 
     In another embodiment, the photonic bandgap structure may be fabricated using a lattice material that includes filler particles diffused throughout the lattice material in place of the explicitly formed nodes as described above, such as nodes  121 . In this case, the filler particles are selected to have a size and material composition that will influence the characteristics of electromagnetic wave propagation, as described above. The filler material may be a polymer or other material that has different intrinsic material properties from the lattice material, in a similar manner as the difference between nodes  121  and lattice material  123 . In some embodiments, the filler material may have a higher dielectric constant than the lattice material, while in other embodiments the filler material may have a lower dielectric constant than the lattice material, for example. 
     In another embodiment, multiple photonic bandgaps may be formed by using two or more types of fillers. For example, a portion of the filler material may have a high dielectric constant, while another portion of the filler material may have a low dielectric constant. In some embodiments, different size filler particle may be used in different regions or in a same region to form multiple bandgaps. In some embodiments, a different number of filler particles per unit volume may be used in different regions to form different bandgaps. 
     In this case, the filler dispersion may not be perfectly crystalline, but there will be a statistical mean separation of the filler particle that may lend itself to a bandgap based on the statistical mean separation distance of the filler particles. 
     An additive manufacturing process may be used to encapsulate an IC die using two or more different polymers, such as one with filler particles and one without filler particles to form the PBG structures as described herein or other configurations of PBG structures. 
     Alternatively, a selective molding process may be used in which one area of the encapsulation is molded with first polymer having either no filler particles or a first configuration of filler particles (size, material, number of particles per unit volume, etc.) and other areas are molded with a polymer having a different filler particle configuration to form a PBG structure as described herein or other configurations of PBG structures. 
       FIGS. 9A-9B  are top and bottom views of an example IC package  900  that includes a PBG waveguide provided by a photonic bandgap structure within the encapsulant material as described herein. IC  900  is an illustration of a quad-flat no-leads (QFN) IC package that was encapsulated using additive manufacturing process to form PBG waveguide structures within the encapsulation material as described herein.  FIG. 9A  illustrates a top side and  FIG. 9B  illustrates a bottom side of QFN package  900 . Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON (small-outline no leads), is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. Flat no-lead is a near chip scale plastic encapsulation package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB. Flat no-lead packages include an exposed thermal pad  904  to improve heat transfer out of the IC (into the PCB). Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package, and a ball grid array. 
     QFN package  900  includes a set of contacts  905  arrayed around the perimeter of the package on the bottom side. Thermal pad  904  has an exposed surface on the bottom side of QFN  900 . An integrated circuit die (not shown) is mounted to the other side of thermal pad  904 . The entire assembly is encapsulated in an encapsulation material  920  using a manufacturing process as described herein to form a photonic filter structure. While a QFN is illustrated in  FIG. 9A-10B , other embodiments may use other types of integrated circuit packages. 
       FIG. 10  is a flow diagram illustrating fabrication of the example encapsulated package of  FIG. 1 . In one embodiment, as described above in more detail, an IC die may be fabricated that has one or more broadband spectral sensors, such as sensor  111 - 113  as illustrated in  FIG. 6 , as indicated at  1000 . The IC die may be fabricated using known or later developed semiconductor processing techniques. The IC die may include an epitaxial (epi) layer on the top surface in which are formed various semiconductor transistor devices and interconnects. One or more conductive layers may be formed on the epi layer and patterned into interconnect traces and bond pads. A set of bond wires may be attached to the contacts and bond pads located on the surface of the IC die using known or later developed wire bonding techniques. 
     An example of the IC die may be encapsulated to form an encapsulated package that includes a filter structure that passes only a selected frequency band of energy to the one or more sensors on the IC die, as indicated at  1002 . The filter structure may be any of the photonic filter structures described herein or later developed structures, such as photonic wave collimating structure, such as filter structure  150  as shown in  FIG. 1 ; a multilayer filter structure, such as filter structure  650  as shown in  FIG. 6 , etc. A band(s) may be selected by selective placement of waveguides in the multiple layers, as described above in more detail. A waveguide region may be formed during the encapsulation process by simply omitting nodes from the region that forms the waveguide. As described above in more detail, the filter structure is formed within the encapsulation material of the package. 
     The encapsulated package may then be used to detect spectral energy in the selected band(s) defined by the filter structure, as indicated at  1003 . 
     Another example of the same version of the IC die may be encapsulated to form an encapsulated package that includes a filter structure that passes a different selected frequency band of energy to the one or more sensors on the IC die, as indicated at  1004 . The filter structure may be any of the photonic filter structures described herein or later developed structures. A band(s) may be selected by selective placement of waveguides in the multiple layers, as described above in more detail. As described above in more detail, the filter structure is formed within the encapsulation material of the package. 
     The encapsulated package may then be used to detect spectral energy in the selected band(s) defined by the filter structure, as indicated at  1005 . 
     In this manner, several different versions of spectrometer devices may be manufactured using a common IC die by merely changing the filter structure parameters during the encapsulation process. 
     In each case, a first portion of the encapsulation material may be solid and a second portion of the encapsulation material may include nodes filled with a second material to form a photonic bandgap structure. As described above in more detail, an additive manufacturing process may be used to create a lattice and fill the periodically spaced nodes in the lattice with a different type of material, or with several different types of material in different locations. A waveguide may be formed during the encapsulation process by simply omitting nodes from the region that forms the waveguide. 
     In another embodiment, the encapsulation process indicated at box  1002 ,  1004  may be done using a selective molding process in which one area of the encapsulation is molded with first polymer having either no filler particles or a first configuration of filler particles (size, material, number of particles per unit volume, etc.) and other areas are molded with a polymer having a different filler particle configuration diffused within the polymer to form a photonic filter structure as described herein or other configurations of photonic filter structures. 
     As discussed above in more detail, various types of IC packages may be formed in this manner. For example, a quad-flat no-leads (QFN) package is illustrated in  FIG. 1 . However, in other embodiments various known or later developed packaging configurations, such as DFN, MLF, SON, flip-chips, dual inline packages (DIP), etc, may be fabricated using the techniques described herein to form an encapsulated package with a PBG waveguide included with the encapsulant material. 
       FIG. 11  is a cross sectional view of an example encapsulated package  1100  that includes a multilayer filter structure  1150 . In this example, IC die  1102  includes two broadband emitter circuits  1111 ,  1112 . Emitter devices  1111 ,  1112  may be optical or RF emitters, for example. While two emitters are illustrated in this example, another embodiment may have only a single emitter, or three or more emitters. 
     Filter structure  1150  may be fabricated during encapsulation of IC die in a similar manner as described above with regard to  FIGS. 8A-8C . By selectively placing waveguide regions  1151 ,  1152  in a selected bandgap layer(s) of multilayer filter structure  1150 , a particular band may be selected to be emitted by each emitter device  1111 ,  1112  of package  1100 , as indicated at  1141 ,  1142 . 
     In another embodiment, another type of photonic filter structure may be used in place of filter structure  1150 , such as a photonic wave collimating structure similar to PWC structure  150 , for example. 
       FIG. 12  is a cross sectional view of encapsulated package  1200  that includes an embodiment of a spectrometer that uses filter structure  1250  that is formed within the encapsulation material  120  by a PBG structure that includes PBG regions  1251  and  1253 . PBG region  1251  may be designed to block a first frequency band, while PBG region  1253  may be designed to block a different second frequency band. 
     In this example, a broad spectrum electromagnetic signal  1240  is impinging on encapsulated package  1200 . In this example, signal  1240  may be an optical signal or a radio frequency signal (RF) that is similar to signal  640  as shown in  FIG. 6 , for example. In this example, the spectrum of signal  1240  is illustrated as having six frequency bands each approximately equal in size to the bandgap provided by PBG regions  1251 ,  1253 . 
     In this example, IC die  1202  includes three broad spectrum sensors  111 - 113  as shown in  FIG. 6 . IC die may be the same or similar as IC die  102  shown in  FIG. 6 . In this example, a photonic waveguide region is provided to allow signal portion  1242  of electromagnet signal  1240  to reach sensor  112 . Similar portions  1241 ,  1243  of electromagnetic signal  1240  are provided to PBG regions  1251  and  1253 . PBG region  1251  may block a first band of portion  1241  and PBG region  1253  may block a second band of portion  1243 . 
     In this manner, a magnitude value may be measured by sensor  112  for broad spectrum signal  1240  as represented by portion  1242 . A magnitude value may be measured by sensor  111  that indicates the magnitude of signal  1240  minus the first band of energy. Similarly, a magnitude value may be measured by sensor  113  that indicates the magnitude of signal  1240  minus the second band of energy. Processing circuitry on IC die  1202  or on another system coupled to IC die  1202  may then easily calculate a value for the magnitude of the first band and of the second band. 
     A different spectrometer may be provided by using the same IC die  1202 , and forming PBG regions with different bandgap, or multiple bandgaps for filter structure  1250  during the encapsulation process. In this manner, several different devices may be fabricated to sense different bands by using a same type of IC die. Only the encapsulation process needs to be modified to change the spectral sensing parameters by selecting which bandgap to implement. In some embodiments, multiple bandgaps may be included in a PBG region to allow a sensor to sense energy for more than one band. 
     While three sensors are illustrated here for clarity, another embodiment may have a larger array of sensors to provide a spectrometer with more precision. 
       FIG. 13  illustrates a simulation of another example photonic waveguide  1340  formed within a photonic structure  1350 . Photonic structure  1350  is similar to photonic structure  550  as illustrated in  FIG. 5  in that an array of nodes  1321  within a lattice material  1323  form an approximately periodic structure. However, in this example photonic waveguide region  1340  may be populated with nodes  1322 . Nodes  1322  may be the same as nodes  1321 , or they may be different in intrinsic properties, shape, spacing, etc. 
     In this example, a continuous lattice may be provided that steers the photon energy  1341  by curving the lattice in the direction of travel. The nodes  1322  in the “pathway” do not improve propagation but do steer it. In this manner, the space in the path of the photons may be warped as opposed to creating a hallway for them to bounce down. This may be analogous to a boat on a river; the river (curved lattice) is already flowing in a certain direction and pulls the boat (photon) in that direction. 
     An additive process as described above in more detail with reference to  FIGS. 8A-8C  may be used to place the array of nodes to form the curved lattice during encapsulation of an encapsulated package. 
     Nodes  1322  within photonic waveguide region  1340  may configure such that they do not provide a bandgap to the frequency of photonic signal  1341  so that photonic signal  1341  may propagate through photonic waveguide region  1340 . 
     Nodes  1321  may also be configured such that they do not provide a bandgap to the frequency of photonic signal  1341 . However, the photonic energy of photonic signal  1341  may be directed along photonic waveguide region by curving the lattice of photonic structure  1350  to maintain an approximately smooth wall of nodes  1321  along the edge of phonic waveguide region  1340 . Similarly, nodes  1322  are arranged in a curved manner to provide a pathway for phonons  1341 . Photonic structure  1350  may be referred to as a “resonant structure” that acts as a bandpass structure as opposed to a bandgap structure. 
       FIG. 14  is a cross sectional view of another example encapsulated package  1400  that includes a photonic waveguide  1440  formed by a resonant structure  1450 . In this example, resonant structure  1450  is implemented in a similar manner as resonant structure  1350  as shown in  FIG. 13  and relies on warping the lattice structure to guide phonon stream  1441  from a transmitter on IC die  102  to a receiver on IC die  103 . 
     As described in more detail above, a photonic filter structure  1452  may be included in the encapsulation material package  1400  that may be designed to pass only a certain band or range of frequencies out of or into a sensor or emitter  1411  located on IC die  1402 . In this example, photonic filter structure  1451  is a multilayer filter structure that may be similar to filter structure  650  shown in  FIG. 6 . In other embodiments, other types of photonic filter structures may be included, such as waveguide structure  150  as shown in  FIG. 1  or structure  1250  as shown in  FIG. 12 . 
       FIG. 15  is a cross sectional view of another example encapsulated package  1500  that includes a multilayer photonic filter structure  1550 . This example may be similar to multilayer photonic structure  650  as shown in  FIG. 6 , except that in this case one or more layers of the multilayer filter structure may be omitted in some portions of the filter structure. 
     In this example, a broadband electromagnetic signal  640  is impinging on encapsulated package  1500 . In this example, signal  640  may be an optical signal or a radio frequency signal (RF), for example. For illustrative purposes only, signal  640  is illustrated as having a spectrum of six frequency bands, such as band  641 ,  642 ,  643 , to correspond to the six bandgaps provided by the six layer filter structure  1550 . Signal  640  may have a broader spectrum or a narrower spectrum than what is included in multilayer filter structure  1550 , for example. 
     Assuming the bandgap of each of the six layers of filter structure  1550  is designed cover a different portion of the spectrum and all six together can block the entire spectrum, then no portion of signal  640  would reach any of sensors  111 - 113 . However, in this example, a one or more layers of bandgap material may be omitted in selected portions of filter structure  1550  to allow energy in a selected band to flow through filter structure  1550 . For example, a layer  1551  may be omitted from filter structure  1550  to allow frequencies in a selected band, such as the band indicated at  641 , to flow through the filter structure and be sensed by sensor  111 . Another layer region  1552  may be omitted in another portion of filter structure  1550  to allow frequencies in another selected band, such as the band indicated at  642 , to flow through the filter structure and be sensed by sensor  112 . Similarly, layer  1553  region  1553  may be omitted in another portion of filter structure  1550  to allow frequencies in another selected band, such as the band indicated at  643 , to flow through the filter structure and be sensed by sensor  113 . In this example, a spectrometer may be provided that may sense energy in three different energy bands in signal  640 . 
     A different spectrometer may be provided by using the same IC die  102 , and omitting different layers of filter structure  1550  during the encapsulation process. In this manner, several different devices may be fabricated to sense different bands by using a same type of IC die. Only the encapsulation process needs to be modified to change the spectral sensing parameters by selecting which layers to omit. In some embodiments, several layers may be omitted to allow a sensor to sense energy for more than one band. 
     While three sensors are illustrated here for clarity, another embodiment may have a larger array of sensors to provide a spectrometer with more precision. 
     While a filter structure  1550  is illustrated herein that has approximately contiguous bandgaps, another embodiment may use a filter structure in which the bandgaps are not contiguous. In that case, electromagnetic energy that is not blocked by any bandgap in the bandgap structure may be sensed by an underlying sensor. 
     In some embodiments, a separate portion of the filter over each sensor may be tailored to have no bandgap in the frequency range to be sensed by each sensor. 
     Other Embodiments 
     In some embodiments, the lattice material may have a relatively low dielectric constant value and the node material may have relatively high dielectric constant value. In other embodiments, the lattice material may have relatively high dielectric constant value and the node material may have a relatively low dielectric constant value. In some embodiments, the node material may be air, another gas, or a vacuum, for example. 
     While photonic structures using materials with different permittivities were described herein, other embodiments may use materials having differences in other intrinsic properties, such as permeability, conductivity, etc. 
     In some embodiments, a portion of the nodes may be formed with one kind of material, while another portion of the nodes may be formed with a different material. Several different types of material may be used to form different sets of nodes within the photonic bandgap structure to thereby tailor the performance of the photonic bandgap structure. 
     In some embodiments, a portion of the nodes may be formed with one lattice constant, while another portion of the nodes may be formed with a different lattice constant. Several different lattice constants may be used to form different sets of nodes within the photonic bandgap structure to thereby tailor the performance of the photonic bandgap structure 
     The nodes may be fabricated using various materials, such as: various polymers such as polyurethane, polyacrylates, etc., ceramic materials, metals, gases such as natural air, nitrogen etc. In some cases, a vacuum may be left and therefore no material would be used for some lattice nodes. 
     In some embodiments, the photonic structure may be symmetric in 3D, while in other embodiments the photonic structure may be asymmetric with different lattice spacing in different directions. 
     In some embodiments, the photonic structure may have a bandgap that is effective in all directions, while in other embodiments the photonic structure may have a bandgap in one direction but not in another direction, for example. 
     in another embodiment, an IC die may be partially or completely surrounded by a photonic bandgap structure in the form of an enclosure that surrounds the IC, such as a box shaped or spherical shaped enclosure that is formed within the encapsulation material by selective placement of nodes within the encapsulation material. 
     Another embodiment may include packages that are entirely encased in mold compound, such as a dual inline package (DIP). 
     In another embodiment, the PBG structure may be made with ferroelectric or magnetic material. In this case, a field bias may be applied to the PBG structure using coils or plates located on the IC die or adjacent to the IC die to tune the bandgap. The amount of bias may be controlled by control circuitry located on the IC die, or by control circuitry that is external to the IC die. 
     In this description, the term “couple” and derivatives thereof mean an indirect, direct, optical, and/or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, and/or through a wireless electrical connection. 
     Although method steps may be presented and described herein in a sequential fashion, one or more of the steps shown and described may be omitted, repeated, performed concurrently, and/or performed in a different order than the order shown in the drawings and/or described herein. Accordingly, embodiments are not limited to the specific ordering of steps shown in the drawings and/or described herein. 
     Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.