[0001] This application claims priority to U.S. Provisional Application No.: 61/096,121, filed September 11, 2008, the disclosures of which are herein expressly incorporated by reference in their entirety.

[0002] The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION [0003] The present invention relates to plasma deposition. BACKGROUND

[0004] Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

[0005] OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

[0006] One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as "saturated" colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

[0007] One example of a green emissive molecule is tris(2-phenylpyridine) indium, denoted Ir(ppy) ₃ , which has the structure of Formula I:

[0008] In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

[0009] As used herein, the term "organic" includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. "Small molecule" refers to any organic material that is not a polymer, and "small molecules" may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the "small molecule" class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a "small molecule," and it is believed that all dendrimers currently used in the field of OLEDs are small molecules. [0010] As used herein, "top" means furthest away from the substrate, while "bottom" means closest to the substrate. Where a first layer is described as "disposed over" a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is "in contact with" the second layer. For example, a cathode may be described as "disposed over" an anode, even though there are various organic layers in between.

[0011] As used herein, "solution processible" means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form. [0012] A ligand may be referred to as "photoactive" when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as "ancillary" when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

[0013] As used herein, and as would be generally understood by one skilled in the art, a first "Highest Occupied Molecular Orbital" (HOMO) or "Lowest Unoccupied Molecular Orbital" (LUMO) energy level is "greater than" or "higher than" a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A "higher" HOMO or LUMO energy level appears closer to the top of such a diagram than a "lower" HOMO or LUMO energy level.

[0014] As used herein, and as would be generally understood by one skilled in the art, a first work function is "greater than" or "higher than" a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a "higher" work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a "higher" work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions. [0015] More details on OLEDs, and the definitions described above, can be found in US Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

[0016] A method of fabricating an organic device is provided. An electrically insulating layer is grown over a first surface of a flexible conductive substrate. The flexible conductive substrate is then placed on an electrode of a deposition chamber, such that the electrically insulating layer is in contact with the electrode and prevents electrical contact between the electrode and the flexible conductive substrate. A layer is deposited by a plasma process over the substrate while the electrically insulating layer is in contact with the electrode of the deposition chamber.

[0017] Layers that may be plasma deposited over the flexible conductive substrate include a planarizing layer, a layer of an active matrix transistor, an electrode, and an encapsulation layer. The layer may be plasma deposited before or after an organic layer. The organic device may be any of a variety of organic devices, including organic light emitting devices and organic transistors.

[0018] The conductive substrate may be a metal foil. The conductive substrate may comprise a material selected from the group consisting of stainless steel, aluminum, titanium, graphite, iron and alloys thereof. The metal foil preferably has a thickness of 10 μm to 150 μm.

[0019] The electrically insulating layer preferably has a thickness of 0.2 μm to 10 μm. The electrically insulating layer may comprises material selected from the group consisting of electrically insulating oxides and nitrides. The electrically insulating layer may comprise a material selected from the group consisting of SiO ₂ , Ta ₂ Os, TiO, SiOF, SiOC, Al ₂ O ₃ , Si ₃ N ₄ , AlN, TiN, and TiAlN. The electrically insulating layer may comprise a material selected from the group consisting of TiC, SiC, Si and GaN. The electrically insulating layer may comprise a polymeric material. [0020] Examples of plasma process that may be used include plasma-enhanced chemical vapor deposition and sputter deposition.

[0021] The electrically insulating layer preferably has an electrical resistance of at least 10 ^{" 6} Ω-cm. The electrically insulating layer preferably has a thermal conductivity of at least 0.7 W/m-°K at 25 ⁰ C. [0022] The flexible conductive substrate may comprise a metal that forms an electrically insulating metal oxide. In this situation, the electrically insulating layer may be provided by baking the flexible conductive substrate to form the electrically insulating oxide. The electrically insulating layer may be provided by exposing the flexible conductive substrate to a reactant to form the electrically insulating oxide. BRIEF DESCRIPTION OF THE DRAWINGS [0023] FIG. 1 shows an organic light emitting device.

[0024] FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer

[0025] FIG 3 shows different substrate structures that can be used to reduce or prevent arcmg duπng plasma deposition.

[0026] FIG 4 shows one of the substrates of FIG. 3 disposed in a plasma deposition chamber DETAILED DESCRIPTION

[0027] Generally, an OLED composes at least one organic layer disposed between and electrically connected to an anode and a cathode When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an "exciton," which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non- radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable [0028] The initial OLEDs used emissive molecules that emitted light from their smglet states ("fluorescence") as disclosed, for example, in U S. Pat No 4,769,292, which is incorporated by reference in its entirety Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

[0029] More recently, OLEDs having emissive mateπals that emit light from tπplet states ("phosphorescence") have been demonstrated Baldo et al , "Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices," Nature, vol 395, 151-154, 1998; ("Baldo-I") and Baldo et al , "Very high-efficiency green organic light-emitting devices based on electrophosphorescence," Appl. Phys Lett , vol. 75, No 3, 4-6 (1999) ("Baldo-II"), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in US Pat. No 7,279,704 at cols. 5-6, which are incorporated by reference [0030] FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, and a cathode 160. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in US 7,279,704 at cols. 6- 10, which are incorporated by reference. [0031] More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m- MTDATA doped with F.sub.4-TCNQ at a molar ratio of 50: 1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to

Thompson et al., which is incorporated by reference in its entirety. An example of an n- doped electron transport layer is BPhen doped with Li at a molar ratio of 1 : 1 , as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg: Ag with an overlying transparent, electrically-conductive, sputter- deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

[0032] FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an "inverted" OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

[0033] The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non- limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an "organic layer" disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2. [0034] Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties. [0035] Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. patent application Ser. No. 10/233,470, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing. [0036] Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfmders, micro-displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C, and more preferably at room temperature (20-25 degrees C). [0037] The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures. [0038] The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in US 7,279,704 at cols. 31 -32, which are incorporated herein by reference.

[0039] When fabricating devices, including OLEDs, transistor, and other types of devices, it is often desirable to use a flexible substrate. Metal foils are preferred because metal foils may be durable at the low thicknesses needed for flexibility, and may also have sufficient resistance to water permeation at these low thicknesses to avoid undesirable exposure of the device to water. Some preferred metals include stainless steel, aluminum, titanium, iron and alloys thereof. Graphite is another preferred material. The materials mentioned herein as preferred for use as flexible substrates are conductive. Conductivity of a flexible substrate may be desired for device operation, or it may be incidental to device operation. Other conductive substrates may also be used.

[0040] It is often desirable to use a plasma process to deposit a layer for a device. Plasma- enhanced chemical vapor deposition (PE-CVD) is a well-known technique for the deposition of materials in the semiconductor industry. The most common applications of PE-CVD involve the use of a semiconductor wafer as the substrate, particularly a silicon wafer. Layers used in OLED fabrication that may be deposited by a plasma process include electrodes and planarizing layers. The layers of an active matrix transistor may also be deposited by plasma deposition, and such transistors may be use in conjunction with OLEDs or with other devices. Plasma processes may also be used to deposit layers in other types of devices.

[0041] Plasma deposition involves applying power in the deposition chamber to generate the plasma. The power involved can be quite high. For example, some equipment has power ranges of 50 - 2000 W. Other equipment may have other voltage ranges

[0042] The use of a conductive substrate may cause problems when used with plasma processes. These problems may be particularly pronounced for devices that may be degraded by heat, such as an organic light emitting device, or more generally many organic devices, because plasma processes such as PE-CVD may result in heat sufficient to cause degradation. Such heat may be removed by placing the substrate in contact with a heat sink. In a PE-CVD chamber, the substrate should be between the two electrodes of the chamber so that a voltage difference may be used to form the plasma. Thus, one of the electrodes may be used as a heat sink by placing the substrate in contact with the electrode. [0043] The substrate onto which a layer is being deposited by plasma deposition may be located between the electrodes used to generate the voltage that generates the plasma. The substrate may experience significant heating during plasma deposition. One way to remove such heat in order to avoid damage is to place the substrate directly onto one of the electrodes during deposition, such that the electrode acts as a heat sink. However, when this is done with a conductive substrate, there may be arcing during plasma deposition due to the applied voltage. Such arcing is undesirable because it may damage the device being fabricated, and may lead to device performance that is less than expected.

[0044] As used herein, "conductive substrate" means that a substrate upon which a device is fabricated is made primarily of an electrically conductive material such as metal. The "substrate" is the part upon which the rest of the device is fabricated, and is generally much thicker than the rest of the device and provides most of the structural integrity to the device. A metal foil or a metal plate are examples of metal substrates. Coatings are generally not substrates, but the part upon which the coating is deposited may be a substrate. Thus, a metal coating on a silicon wafer would not be considered a "metal substrate" for purposes of this application.

[0045] The inventors have observed practitioners putting tape on the electrode and / or the substrate prior to deposition to avoid such arcing. While using tape in this way may reduce or prevent arcing, it introduces other problems. Any adhesive on the tape, or the tape itself, may introduce impurities into the chamber. If the tape is adhered to the substrate, it generally needs to be subsequently removed, which may damage a flexible substrate, which is generally thin in order to achieve flexibility, and it may leave an undesirable residue. In addition, tape may interfere with the ability of the electrode to act as a heat sink, and it may do so in a non-uniform way, depending on how the tape was applied. [0046] A method of fabricating a device is provided, that allows for the use of a flexible, conductive substrate in conjunction with a plasma process, that reduces or prevents arcing while allowing an electrode of the plasma chamber to act as a heat sink. An organic device may be fabricated using the method. An electrically insulating layer is provided over a first surface of a flexible conductive substrate. The electrically insulating layer is grown over the first surface. As used herein, "grown" includes deposition, including solution deposition techniques, and formation by a reaction such as oxidation or other reaction of the first surface. "Grown" includes any deposition technique from a liquid or gaseous phase, as well as deposition techniques involving small solid particulates. "Grown" excludes adhesion to the first surface, as with tape. The flexible conductive substrate is placed on an electrode of a deposition chamber, such that the electrically insulating layer is in contact with the electrode and prevents electrical contact between the electrode and the flexible conductive substrate. A layer is then deposited by a plasma process over the substrate while the electrically insulating layer is in contact with the electrode of the deposition chamber.

[0047] A conductive substrate is considered "in contact with" an electrode of a plasma- enhanced chemical vapor deposition chamber if there is sufficient physical contact to allow for significant heat transfer from the conductive substrate to the electrode. Generally, simply setting a conductive substrate on an electrode will result in contact. A conductive substrate may be considered in contact with the electrode even if there is a thin electrically insulating layer disposed between the conductive substrate and the electrode that may block any electrical conductive path while still allowing for heat transfer.

[0048] The method may be used with a wide variety of layers deposited by a plasma process. Such layers include a planarizing layer deposited over the flexible conductive substrate, a layer that is part of an active matrix transistor over the substrate, electrodes and encapsulating layers. The organic layers of an organic light emitting device may be deposited over the substrate after a layer is deposited by a plasma process. Examples of layers that may be deposited by a plasma process before the organic layers of an organic light emitting device include a planarizing layer, a layer of an active matrix transistor, and the bottom electrode of the OLED. The organic layers of an organic light emitting device may be deposited over the substrate before a layer is deposited by a plasma process. Examples of layers that may be deposited by a plasma process after the organic layers of an organic light emitting device include the top electrode of the OLED and an encapsulation layer for the OLED. Similarly, a layer may be deposited using a plasma process using the method before or after depositing the organic layers of an organic thin-film transistor.

[0049] Preferred flexible conductive substrates include metal foils and graphite. Preferred metal foils include stainless steel, aluminum, titanium, graphite, iron and alloys thereof. Flexible conductive graphite suitable for use as a substrate includes Pyrolytic Graphite Sheet (PGS), type EYG, available from Panasonic. [0050] For a flexible metal substrate, it is preferred that the thickness is 10 μm to 150 μm. At lower thicknesses, the metal may not have sufficient structural integrity and / or moisture resistance. At higher thicknesses, some flexibility may be lost.

[0051] The electrically insulating layer preferably has a thickness of 0.2 μm to 10 μm. A thickness of less than 0.2 μm may not provide an ideal amount of electrical insulation. A thickness of greater than 10 μm may provide decreasing marginal benefit in terms of electrical insulation, while undesirably decreasing thermal conductivity. In addition, many flexible conductive foils have, as a result of the fabrication process, spikes on their surface that are several microns high. The electrically insulating layer is preferably thick enough to cover these spikes. Note that this does not mean that the electrically insulating layer needs to be thicker than the height of the spikes - the objective is to cover the metal foil sufficiently to reduce or prevent electrical contact between the metal foil and an underlying electrode, and not necessarily to planarize the metal foil.

[0052] Preferably the electrically insulating layer has an electrical resistance of at least 10 ^"6 Ω-cm. Much higher electrical resistances may be used, for example up to 10 ^"4 Ω-cm or higher at 25°C. At the upper end of the range, additional electrical resistivity, while marginally useful, may result in undesirable tradeoffs in other properties. Preferably the electrically insulating layer has a heat conductivity of at least 0.7 W/m-°K at 25 ⁰ C. Much higher heat conductivities may be used, up to 600 W/m-°K and higher at 25°C. At the upper end of the range, additional heat conductivity, while marginally useful, may result in undesirable tradeoffs in other properties. Increasing thickness of the electrically insulating layer will generally increase electrical resistance while decreasing heat conductivity, and it is preferred that the electrically insulating layer has both an electrical resistance of at least 10 ^"6 Ω-cm at 25°C and a heat conductivity of at least 0.7 WAn- ⁰ K at 25°C. [0053] Preferred materials for the electrically insulating layer include electrically insulating oxides and nitrides. Examples of such materials include SiO ₂ , Ta ₂ Os, TiO, SiOF, SiOC, Al ₂ O ₃ , Si ₃ N ₄ , AlN, TiN, and TiAlN. Other preferred electrically insulating materials include TiC, SiC, Si and GaN. Other preferred electrically insulating materials include polymeric material. Polyimide is a preferred polymeric material. [0054] The flexible conductive substrate may comprises a metal that forms an electrically insulating metal oxide, and the electrically insulating layer may be provided by baking the flexible conductive substrate to form the electrically insulating oxide. [0055] The flexible conductive substrate may comprises a metal that forms an electrically insulating metal oxide, and the electrically insulating layer may be provided by exposing the flexible conductive substrate to a reactant to form the electrically insulating oxide.

[0056] The electrically insulating layer may be provided by a number of other methods, including vapor deposition and chemical vapor deposition. Plasma processes may be used.

[0057] Plasma processes that may be used in the method described include plasma- enhanced chemical vapor deposition and sputter deposition.

[0058] It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore includes variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting.