Abstract:
Embodiments of methods/apparatus according to the application can include radiographic imaging device comprising an imaging array of pixels or a plurality of photosensors including a first side to receive light from a scintillator and a second side to pass second light responsive to impingement of the scintillator light and a reflective layer configured to reflect third light responsive to impingement of the second light. Exemplary photosensors can absorb a prescribed amount of the scintillator light received through a first transparent side and the third light received through a second transparent side. Exemplary reflective arrangements can be selected based upon scintillotor emission characteristics and/or photosensor absorption characteristics. Embodiments of radiographic detector arrays and methods can reduce photosensor thickness to reduce noise, reduce image lag and/or increase charge capacity. Embodiments can maintain the quantum efficiency of a reduced thickness photosensor.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of diagnostic imaging and more particularly relates to methods and/or systems for digital radiographic detectors. 
     BACKGROUND OF THE INVENTION 
     Traditionally, flat panel image sensors for digital radiographic (DR) applications employ a scintillator to convert incoming X-ray radiation to visible light and a flat-panel image sensor to convert the visible light into an electrical signal. The pixel of a flat-panel image sensor comprises a photo-sensor and a readout element. Examples of photo-sensors include PIN photodiodes, MIS photo-sensors, photo-transistors and photo-conductors. Such conventional DR image sensors generally use amorphous-Silicon (a-Si) for the photo-sensors and readout elements. Further, such related art DR image sensors can be used for radiographic applications, fluoroscopic applications and/or volume image reconstruction applications. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an aspect of this application to address in whole or in part, at least the foregoing and other deficiencies in the related art. 
     It is another aspect of this application to provide in whole or in part, at least the advantages described herein. 
     In one aspect of the disclosure, photosensor components of a flat panel DR detector (FPD) can provide improved quantum efficiency (QE) (e.g., in a prescribed wavelength band, for a 550-700 nm wavelength band or overall photosensor QE) when a light-transmissive back-contact and a reflective optical mechanism is used beneath the photosensor. The photosensors can be top-illuminated photosensors. 
     In another aspect, embodiments of a photosensor can provide a reflective optical mechanism that can include a reflective layer, one or more dielectrics with thickness(es), a dielectric film, a reflective organic layer and optical property/properties to increase or optimize overall quantum efficiency in conjunction with scintillator emission characteristics and photosensor characteristics. The reflective layer can operate to improve photosensor performance characteristics such as by reducing cross-talk between pixels or the like. 
     In another aspect, embodiments of the application can reduce a thickness of semiconductor material portions of photosensors to reduce lag, increase charge capacity and/or decrease dark current. 
     In another aspect, embodiments of the application can provide an optical reset unit to reset photosensors by passing reset light through a reflective layer or optical reflector mechanism. 
     In one embodiment, a radiographic imaging system can include a scintillator, a plurality of photosensitive elements including a first side to receive first light from the scintillator and including a second side to pass second light responsive to impingement of the first light, a reflective layer receiving the second light from the plurality of photosensitive elements and configured to reflect third light responsive to impingement of the second light, and a substrate on the second side of the plurality of photosensitive elements, wherein photosensitive element characteristics of the plurality of photosensitive elements are selected to absorb a prescribed amount of the first light received through the first side and the third light received through the second side, wherein the reflectivity of the reflective layer is greater than 50%. 
     In yet another embodiment, a method for operating a radiographic imaging apparatus for capturing a plurality of x-ray images of an object, the method can include providing a scintillation screen for receiving incident radiation and responding by emitting excited radiation at a first band of wavelengths, providing an array of photosensors including a first light-transmissive side and a second light-transmissive side, the first light-transmissive side for receiving first light at the first band of wavelengths from the scintillator, the second side for passing second light responsive to impingement of the first light, providing a reflective layer for receiving the second light from the array of photosensors and for reflecting third light responsive to impingement of the second light, and providing a substrate over the second side for supporting the array of photosensitive elements, the array of photosensors absorbing a prescribed amount of the first light received through the first side and absorbing a prescribed amount of the third light received through the second side, wherein the reflectivity of the reflective layer is greater than 50%. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a further understanding of the invention, reference will be made to the following detailed description of the invention which is to be read in connection with the accompanying drawing, wherein: 
         FIG. 1  is a diagram that shows the construction of an exemplary embodiment of an x-ray detector in accordance with the application. 
         FIG. 2  is a diagram that shows the construction of another exemplary embodiment of a DR detector in accordance with the application. 
         FIG. 3  schematically illustrates an exemplary embodiment of a photosensor having a transparent top electrode/contact and a transparent bottom electrode/contact according to the application; 
         FIG. 4  is a diagram that shows a cross-section view of an exemplary embodiment of a reflector unit according to the application; 
         FIGS. 5A ,  5 B,  5 C are diagrams that show a cross-section view of exemplary embodiments of reflective layers according to the application. 
         FIG. 6  is a diagram that shows an imaging panel that can be used in a flat panel radiographic imager incorporating embodiments of the application. 
         FIG. 7  is a sectional view of an exemplary embodiment of an X-ray detector with an optical reset unit beneath a reflector layer in accordance with the application. 
         FIG. 8  is a diagram that shows a top view of an exemplary reflective layer according to the application. 
         FIG. 9  is a diagram that shows a graph of normalized percent emission per nm of wavelength as a function of wavelength for an exemplary representative scintillator. 
         FIG. 10  is a diagram that shows a graph of normalized percent emission per nm of wavelength as a function of wavelength for another exemplary representative scintillator. 
         FIG. 11  is a diagram that shows a graph of light absorption in a related art amorphous silicon PIN photodiode. 
         FIG. 12  is a diagram that shows a graph including relative quantum efficiency of an amorphous silicon photosensor as a function of amorphous silicon intrinsic layer thickness for exemplary scintillator screens. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following is a description of exemplary embodiments according to the application, reference being made to the drawings in which the same reference numerals identify the same elements of structure in each of the several figures, and similar descriptions concerning components and arrangement or interaction of components already described are omitted. Where they are used, the terms “first”, “second”, and so on, do not necessarily denote any ordinal or priority relation, but may simply be used to more clearly distinguish one element from another. 
     One objective of embodiments of apparatus and/methods thereof according to the application is to increase the photo-sensitivity of flat-panel image sensors used for digital radiography. Flat panel image sensors for DR applications use a scintillator to convert incoming X-ray radiation to visible light and a flat-panel image sensor to convert the visible light into an electrical signal. A pixel of a flat-panel image sensor includes a photo-sensor and a readout element. Examples of photo-sensors include PIN photodiodes, MIS photo-sensors, photo-transistors and photo-conductors. The photo-sensors can be illuminated from one side. The spectral quantum efficiency (QE) of the photo-sensors depends on the optical properties and thicknesses of the insulating layers overlying the photo-sensor, the carrier generation caused by light absorption in each of the semiconducting layers, and the optical properties of the layers underlying the photo-sensor. As an example, in a PIN photodiode, approximately 80% of the photons incident on the photodiode are optically transmitted to the amorphous silicon semiconductor. A portion of these incident photons will be absorbed in the semiconductor layers and portion will be absorbed by the back-side contact. At wavelengths&gt;550 nm and typical a-Si semiconductor thicknesses of 500 nm, a significant portion of the incident photons penetrate and pass through the a-Si layers and are absorbed in the metallic back contact; and accordingly, these photons do not generate free carriers. Backside contact metals, such as Mo and MoW, are highly absorptive. 
     To increase absorption of the light by the photosensor, a thickness is increased. However, as a total number of charge traps in the photosensor (e.g., a-Si) are increased, a dark current and/or an image lag, which depend on the total number of charge traps, also increase. Further, light output by the scintillator is dependent on the characteristics of the scintillator, and light absorption in the photosensor is dependent on the absorption characteristics of a material comprising the photosensor. 
     In one embodiment, a pixel for a DR detector can comprise a photosensor including a light-transmissive front and back (e.g., first and second) sides, read out electronics and a reflector capability corresponding to the light-transmissive back side to improved quantum efficiency in the pixel. For example, improved quantum efficiency in photosensors can be obtained in the red spectrum when a light-transmissive back-contact is used for the photodiode and a reflective layer is used beneath the photodiode. 
       FIG. 1  shows construction of an exemplary embodiment of an x-ray detector in accordance with the application. As shown in  FIG. 1 , an x-ray detector  100  can include a scintillator  120 , an imaging array  130 , a reflective layer  140  and a substrate  150 . X-rays  160  are incident on the scintillator  120 . The x-rays  160  are converted into visible light  180  therein. A protective layer  122  can be provided at the scintillator  120  to protect the scintillator  120 . The imaging array  130  can include photosensors PS and read out electronic RO, which can include data lines, scan lines, amplifiers, transistors and the like. As shown in  FIG. 1 , the photosensors PS can form a continuous layer and the read out electronics RO can be vertically integrated below the photosensors PS. As shown in  FIG. 1 , the photosensors PS can include an optically transmissive back-side contact and/or electrode. At least some of the light rays  180  can impinge the individual photosensors PS. The light rays  180  not only impinge on the photosensors PS, but also a portion are absorbed and a portion pass completely through. The backside reflective layer  140  can be positioned to redirect reflected light  185  that passed through the photosensors PS back to the photosensors PS to increase the amount of light  180  absorbed by the photosensors PS. 
     As shown in  FIG. 1 , the light rays  180  can impinge a first side of the photosensors PS and the reflected light  185  can impinge a second side (e.g., an opposite side) of the photosensors PS. For example, reflected from the reflective layer  140 , the reflected light  185  can reach the relevant photosensors PS so as to contribute to signal generation by the x-ray detector  100 . The substrate  150  (e.g., a glass substrate) can be provided underneath the reflective layer  140 . In one embodiment, an optically transmissive insulating layer (e.g., dielectric layer)  145  can be between the reflective layer  140  and the photosensor PS to reduce or prevent interference therebetween (e.g., alloy formation). The substrate  150  can act as a support or substrate for the x-ray detector  100 . 
       FIG. 2  shows the construction of another exemplary embodiment of an x-ray detector in accordance with the application. As shown in  FIG. 2 , read out electronics RO 1  can be disposed in the same layer or co-planar with photosensors PS 1 . In one embodiment, the photosensors PS 1  can include an optically transmissive back-side contact and/or electrode. Examples of the photosensors PS 1  can include, but are not limited to PIN photodiodes, MIS photo-sensors, photo-transistors and photo-conductors. 
     Photosensors PS, PS 1  can include transparent conductive electrodes and/or contacts.  FIG. 3  is a diagram that shows cross-sectional view of an exemplary embodiment of photosensor structure  300  that can pass light impinging on a top (e.g., first) electrode and/or a bottom (e.g., second) electrode. As shown in  FIG. 3 , a flat panel DR image sensor of the indirect conversion type can include a scintillator screen (not shown) in front of the image sensor. 
     As shown in  FIG. 3 , an amorphous-Si based photodiode structure can be used for the photosensor PS, PS 1 . Top and bottom electrodes  312 ,  314  can be transparent or light-transmissive formed of material such as ITO or ZnO:Al electrodes. Both a p-type region  322  and an n-type region  324  of a PIN photodiode  310  can include doped hydrogenated amorphous silicon (a-Si:H). An undoped a-Si:H layer  325  can be used as an intrinsic layer. Semiconductor layers in the exemplary photodiode structure  300  of  FIG. 3  can be formed using a multi-chamber plasma-enhanced chemical vapor deposition (PECVD) system at relatively low temperatures (e.g., 150° C.-300° C.). In one embodiment, exemplary dimensions for the photodiode structure  300  can include a Si nitride layer, e.g., about 170 nm, a ITO layer, e.g., about 40 nm can form the top electrode; the PIN photodiode can include the p-type region  322  e.g., about 15 nm, i-type layer  325  e.g., about 600 nm, and an n-type region  324  e.g., about 40 nm; and the ITO layer  324 , e.g., about 100 nm can form the bottom electrode. In one embodiment, dimensions of a pixel having transparent top and bottom electrodes can range between 100 μm×100 μm to 200 μm×200 μm. 
     Alternatively, both a p-type region  322  and an n-type region  324  of the photodiode  310  can include doped hydrogenated nanocrystalline silicon (nc-Si:H). Such doped nc-Si:H layers can have higher conductivity and/or lower optical adsorption in the visible range relative to a-Si:H or amorphous silicon carbide (a-SiC:H). 
     Embodiments of an imaging array, flat panel detector or x-ray imaging system and/or methods for using the same according to the application can use a photosensor structure sensitive to light impinging on a top (e.g., first) electrode and/or a bottom (e.g., second) electrode, in combination with an optically reflecting mechanism (e.g., between the glass substrate and the photo-sensor or below the glass substrate and the photosensor), can increase quantum efficiency of single side illuminated (e.g., top-illuminated) photosensors in electromagnetic imaging systems such as digital radiographic imaging systems. 
       FIG. 4  is a diagram that shows an exemplary embodiment of a reflector structure according to the application. As shown in  FIG. 4 , a reflector structure  400  can include a reflective layer  410  and an optional insulating layer  420  provided when interactions between the reflective layer  410  and a corresponding photosensor are undesirable or to improve characteristics of the reflector structure. 
     The reflector layer  410  in a pixel can correspond, for example, to a first level of metallization (e.g., gate metal) of a pixel or to an additional metal level selected for overall high reflectivity or high reflectivity in a wavelength band of interest. A wavelength band can be a single wavelength. The reflector layer  410  can be a metal such as aluminum. 
     In one embodiment, the reflective structure  400  can be an optical dielectric stack with thickness of one or more layers chosen to increase or optimize reflection at a particular band of wavelengths to increase or optimize overall quantum efficiency of the top-side illuminated photosensor. Alternatively, the reflective structure  400  can be a dielectric film (e.g, SiO 2 , Si 3 N 4 ) with a thickness and optical property/properties to increase or optimize overall quantum efficiency. In another embodiment, the reflective structure  400  can be an organic layer or a photoacrylic selected for its reflective characteristics. In exemplary embodiments, the quantum efficiency can be based on the scintillator emission characteristics and the photosensor/photo-diode characteristics, and then the reflectivity characteristics of the reflective structure  400  can be determined to increase or optimize overall quantum efficiency. In one embodiment, an improvement in photosensor QE is larger at longer wavelengths. 
     In one embodiment, the reflector layer  400  can be configured to improve performance, for example, by increasing a spatial resolution or decreasing cross-talk between pixels (e.g., photosensors) or increasing an angular spread of emergent light from a scintillator in a DR imaging array. As shown in  FIG. 5A , a reflector layer can include a reflective control layer being a diffuse reflector  510 . The diffuse reflector  510  can increase (e.g., linearly, nonlinearly) the reflective light  185  angle as the incident light  180  angle differs from perpendicular. 
     In another embodiment, the reflector layer  400  can be configured to include a reflective control layer to increase a spatial resolution or decrease cross-talk between pixels (e.g., photosensors) in a DR imaging array. As shown in  FIG. 5B , the reflective control layer can be a layer  520  that can include a light absorbing pattern  525  to increasingly capture reflected light  185  as the incident light  180  angle differs from perpendicular. The light absorbing pattern  185  can be intermittent or continuous stripes aligned to rows or columns or a grid (e.g., to match a 2D layout of the pixels). Alternatively, the reflector layer  520  can include a reflecting pattern (not shown) to redirect the reflected light  185  as the incident light  180  angle differs from perpendicular. Alternatively as shown in  FIG. 5C , the reflective control layer can be a reflector layer  530  that can include a diffused light absorbing material  530  to increasingly capture reflected light  185  as the reflected light  185  travels farther through the reflective layer  530 . The layers  510 ,  520 ,  530  can operate to improve performance of a photosensor or imaging array. In one embodiment, the layers  510 ,  520 ,  530  can replace or supplement the optional insulating layer  420 . 
     Digital detectors or flat panel detectors can be reset after an exposure image is captured. Related art FPDs can be reset using electrical charges (e.g., switching voltage across the diode during a reset period) or optically reset. Embodiments according to the application can provide an increase in efficiency, a decrease in a reset or bias voltage and/or an increase in consistency to reset operations (e.g., photosensor reset) because the photosensor can be reduced in thickness or contain fewer traps. 
       FIG. 6  shows a block diagram of circuitry for a flat panel imager that can incorporate embodiments of a pixel and/or imaging array according to embodiments of the application. As shown in  FIG. 6 . a flat panel imager  10 , can include a sensor array  12 . The a-Si based sensor array includes m data lines  14  and n row select or gate lines  16 . Each pixel comprises an a-Si photodiode  18  connected to a TFT  20 . Each photodiode  18  is connected to a common bias line  22  and a drain  24  of its associated TFT. Gate lines  16  are connected to gate drivers  26 . Bias lines  22  carry bias voltages applied to photodiodes  18  and TFTs  20 . TFTs  20  are controlled by their associated gate lines  26  and when addressed, transfer stored charge onto data lines  14 . During readout, a gate line is turned on for a finite time (approximately 10 to 100 ms), allowing sufficient time for TFTs  20  on that row to transfer their pixel charges to all the m data lines. Data lines  14  are connected to charge amplifiers  28 , which operate in parallel. In general, charge amplifiers  28  are divided into a number of groups, with each group typically having 64, 128, or 256 charge amplifiers. The associated charge amplifiers in each group detect the image signals, and clock the signals onto multiplexer  30 , whence they are multiplexed and subsequently digitized by an analog to digital converter  32 . The digital image data are then transferred over a coupling to memory. In some designs, a correlated double sampling (CDS) circuit  34  may be disposed between each charge amplifier  28  and multiplexer  30  to reduce electronic noise. Gate lines  16  are turned on in sequence, requiring approximately a few seconds for an entire frame to be scanned. Additional image correction and image processing are performed by a computer  36  and the resulting image is displayed on a monitor  38  or printed by a printer  40 . 
       FIG. 7  is a sectional view of an optically reset FPD that can incorporate embodiments of a pixel and/or imaging array according to embodiments of the application. Optical reset of photosensors can be more efficient and/or more uniform. As shown in  FIG. 7 , underneath the substrate  150  there is provided an optical reset unit  710 . The optical reset unit  710  can includes a plurality of light sources (not shown), for example light emitting diodes that can emit light  720  in a spectral range that is suitable for resetting the photosensors PS. The photosensors PS can be reset by using of the light  720 . The reflective layer  140  can be configured to pass sufficient quantities of the reset light  720  to reset the photosensors PS, PS 1 . In one embodiment, the reflective layer  140  can include holes sufficient to pass the reset light  720 .  FIG. 8  is a diagram that shows a top view of an exemplary reflective layer according to the application. As shown in  FIG. 8  for example, arranged holes  810  can comprise a small amount of the surface area of the reflective layer  140  (e.g., &lt;10%, &lt;5%, or &lt;2%). Alternatively, the reflective layer  140  does not have holes, but can be transparent to the reset light  720  or pass a prescribed amount (e.g., &gt;25%, &gt;50%, or &gt;75%) of the incident reset light  720  impinging on a bottom surface thereof. In one embodiment, the reset light can be ultraviolet. 
       FIG. 9  is a diagram that shows a normalized percent emission per nm of wavelength as a function of wavelength for an exemplary representative scintillator. A graph  910  shows a normalized percent emission per nm of wavelength as a function of wavelength for a representative CsI scintillator (e.g., the integral of the % emission over wavelength is 100%). As shown in  FIG. 9 , there is significant emission at wavelengths&gt;600 nm, where the a-Si absorption falls off. 
       FIG. 10  is a diagram that shows a normalized percent emission per nm of wavelength as a function of wavelength for an exemplary representative scintillator. A graph  1010  shows a normalized percent emission per nm of wavelength as a function of wavelength for a representative GOS scintillator (e.g., the integral of the % emission over wavelength is 100%). 
       FIG. 11  shows the light absorption in a representative related art PIN photodiode with 500 nm thick amorphous silicon, an ITO transparent electrode top contact and a MoW back contact. The absorption in the a-Si is shown in a first curve  1110  and the light that is transmitted through the a-Si and then absorbed in the MoW back contact is shown in a second curve  1120  in  FIG. 11 . There is significant energy at wavelengths&gt;600 nm that is transmitted through the a-Si and absorbed in the MoW. In exemplary embodiments, photosensors according to the application transmit more light through the PIN photodiode. 
       FIG. 12  shows the relative quantum efficiency of an amorphous silicon PIN photodiode as a function of amorphous silicon intrinsic layer thickness calculated for emission spectra  1210  of an exemplary CsI scintillator screens and emission spectra  1220  of an exemplary GOS scintillator screens. For amorphous silicon intrinsic layer thicknesses less that 1 um, light transmission through the amorphous silicon and subsequent absorption in the MoW back contact reduces the quantum efficiency. As shown in  FIG. 12 , by 500 nm, the loss is ˜8% for CsI emission spectra and by 250 nm the loss is 25%. Thin a-Si thicknesses are desirable for reducing the dark current, reducing the image lag caused by trapping, and/or increasing the charge capacity. For related art PIN photodiodes with a metal (e.g., MoW, Mo) or light absorbing backside contact, the signal-to-noise is selected with or optimized with a 500 nm intrinsic layer thickness. For exemplary PIN photodiodes including light transmissive electrodes and including an embodiment of a reflective layer, a reduced thickness such as 250 nm thickness would result in about the same quantum efficiency as the 500 nm related art photodiode, but could include reduced noise, reduced image lag and/or higher charge capacity. Alternatively, according to embodiments, a thickness of the intrinsic layer or semiconductor layers of the photosensor can be less than 200 nm, 300 nm, 350 nm or 400 nm. 
     Embodiments of reflector layers and methods for using the same are based on characteristics of scintillator materials and photosensor materials. Embodiments of reflective layers can be selected, for example, to increase quantum efficiency based on emission characteristics of the scintillator and absorption characteristics of photodiodes in the FPR. In one embodiment, scintillator properties can include at least one of scintillator thickness, scintillator composition, scintillator x-ray absorption coefficient, and scintillator light emission spectra. In one embodiment, photosensor characteristics can include at least one of photosensitive element area, photosensitive element pitch, photosensitive element sensitivity, or characteristics for each of photosensor layers therein can include absorption coefficient as a function of wavelength, index of refraction as a function of wavelength, or thickness. In one embodiment, characteristics of reflector layers can include at least one of spectral reflectance or angular distribution of reflected light. An optional an optically transparent dielectric formed between a reflective layer and the photosensors can be a dielectric with characteristics of absorption coefficient as a function of wavelength or index of refraction as a function of wavelength. 
     In one embodiment, absorption of reflected light can be at least 15%, at least 25%, or at least 35% of total absorption of photosensors in the DR detector for light between 550 nm to 700 nm or absorption of reflected light increases an absorption of the photosensors for at least one wavelength of the light between 550 nm to 700 nm by more than a prescribed amount such as 10% or 20%. A thickness of photosensors can be configured to pass at least 50% of at least one wavelength of the impinging light from the scintillator, which can be between 400-700 nm. Embodiments of reflective layer can be selected to preferentially reflect a prescribed band of wavelengths or include a reflection coefficient is highest for wavelength selected between 550-650 nm or 500-700 nm. 
     It is gradually commonly recognized that the screening, image-guided interventional whether in regular x-ray radiographic or CT imaging should reduce or minimize the associated X-ray exposure risk to the subjects and operators. As photosensor thickness decreases, an x-ray dose can be reduced. X-ray low dose medical imaging will be very attractive if the same or better image quality can be achieved compared to what current medical X-ray technology can do but with less X-ray dose. 
     It should be noted that the present teachings are not intended to be limited in scope to the embodiments illustrated in the figures. 
     While the invention has been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, the various pixel embodiments can be used in radiation imaging systems. An example radiation imaging system can include a plurality of the various pixel embodiments in an array, driving circuits, readout circuits, and a phosphor screen. A radiation source can also be included. Further, DR image sensors/methods embodiments can be used for radiographic applications, fluoroscopic applications, mobile imaging system applications and/or volume image reconstruction applications. 
     In addition, while a particular feature of an embodiment has been disclosed with respect to only one of several implementations, such feature can be combined with one or more other features of the other implementations and/or other exemplary embodiments as can be desired and advantageous for any given or particular function. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of −2 and the maximum value of 10, that is, any and all sub-ranges having a minimum value equal to or greater than −2 and a maximum value equal to or less than 10, e.g., 1 to 5. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” As used herein, the term “connected” means electrically connected either directly or indirectly with additional elements in between. As used herein, the term “one or more of” or “and/or” with respect to a listing of items such as, for example, “A and B” or “A and/or B”, means A alone, B alone, or A and B. The term “at least one of” is used to mean one or more of the listed items can be selected. 
     Further, in the discussion and claims herein, the term “on” used with respect to two materials, one “on” the other, means at least some contact between the materials, while “over” means the materials are in proximity or near each other, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither “on”, “above”, below”, “over” nor “under” implies any directionality as used herein. The term between as used herein with respect to two elements means that an element C that is “between” elements A and B is spatially located in at least one direction such that A is proximate to C and C is proximate to B or vice versa. The term “conformal” describes a coating material in which angles of the underlying material are preserved by the conformal material. Further, in the discussion and claims herein, the term “exemplary” indicates the description is used as an example, rather than implying that it is an ideal. 
     The invention has been described in detail with particular reference to exemplary embodiments, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein. While the present invention has been described with reference to a number of specific embodiments, it will be understood that the true spirit and scope of the invention should be determined only with respect to claims that can be supported by the present specification. Further, while in numerous cases herein wherein systems and apparatuses and methods are described as having a certain number of elements it will be understood that such systems, apparatuses and methods can be practiced with fewer than the mentioned certain number of elements. Also, while a number of particular embodiments have been set forth, it will be understood that features and aspects that have been described with reference to each particular embodiment can be used with each remaining particularly set forth embodiment. For example, aspects and/or features of embodiments variously described herein can be specifically interchanged or combined.