LOW PRESSURE VAPOR PHASE DEPOSITION OF ORGANIC THIN FILMS
Methods for preparing organic thin films on substrates, the method comprising the steps of providing a plurality of organic precursors in the vapor phase, and reacting the plurality or organic precursors at a sub-atmospheric pressure. Also included are thin films made by such a method and apparatuses used to conduct such a method. The method is well-suited to the formation of organic light emitting devices and other display-related technologies.
This application is a continuation of U.S. application Ser. No. 10/427,933, filed May 2, 2003, which is a divisional of U.S. application Ser. No. 10/125,400, filed Apr. 19, 2002, which is a continuation of U.S. application Ser. No. 09/736,090, filed on Dec. 13, 2000, which is a continuation of U.S. application Ser. No. 09/663,143, filed on Sep. 15, 2000, which is a continuation of U.S. application Ser. No. 08/972,156, filed on Nov. 17, 1997, the subject matter of which are incorporated by reference herein in their entireties.
GOVERNMENT RIGHTSThis invention was made with Government support under Contract No. F49620-92-J-05 24 (Princeton University), awarded by the U.S. Air Force OSR (Office of Scientific Research). The Government has certain rights in this invention.
FIELD OF THE INVENTIONThe present invention relates to the fabrication of optical quality thin films, and more particularly to the low pressure fabrication of such thin films for application in non-linear optical devices and organic light emitting devices.
BACKGROUND OF THE INVENTIONThe field of organic electroluminescence is a rapidly growing technology. Spurred by potential application to displays, organic light emitting devices (OLEDs) are capable of achieving external quantum efficiencies of over 3%, and operational lifetimes on the order of 10,000 hours at video brightness. Both small molecule and polymer-based OLEDs are known, but polymer based devices have a general advantage of simple and inexpensive fabrication by spin-on deposition techniques. In contrast, small molecule devices are usually fabricated by thermal evaporation in vacuum, which is usually a more expensive process than spin-on deposition. Examples of OLED structures and processing techniques are provided in published PCT application WO 96/19792, incorporated herein by reference.
The use of organic vapor phase deposition (OVPD) has made progress towards the low cost, large scale deposition of small molecular weight organic layers with numerous potential photonic device applications such as displays. The OVPD process is described in U.S. Pat. No. 5,554,220 to Forrest et al.; S. R. Forrest et al., “Intense Second Harmonic Generation and Long-Range Structural Ordering in Thin Films of an Organic Salt Grown by Organic Vapor Phase Deposition,” 68 Appl. Phys. Lett. 1326 (1996); and P. E. Burrows et al., “Organic Vapor Phase Deposition: a New Method for the Growth of Organic Thin Films with Large Optical Non-linearities,” 156 J. of Crystal Growth 91 (1995), each of which is incorporated herein by reference.
The OVPD process uses carrier gases to transport source materials to a substrate, where the gases condense to form a desired thin film. The OVPD technique has been used, for example, to deposit films of the optically non-linear organic (NLO) salt, 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST), from volatile precursors 4′-dimethylamino-N-methyl-4-stilbazolium iodide (DASI) and methyl p-toluensulfonate (methyltosylate, MT), which are transported by carrier gases to a heated substrate. In this process, DASI thermally decomposes to form 4-dimethylamino-4-stilbazole (DAS), which subsequently reacts with MT to form DAST on the substrate.
Because of its capability for controlled codeposition of materials with radically different vapor pressures, OVPD is believed to be the only method for the precise stoichiometric growth of multi-component thin films. However, the OVPD process is conducted at atmospheric pressure, and films grown at or near atmospheric pressure are often rough and have non-uniform surface morphologies due to gas phase nucleation and a diffusion-limited growth process.
SUMMARY OF THE INVENTIONThe present invention makes use of low pressure deposition techniques to produce organic thin films having superior surface properties. In one aspect, the present invention comprises a method for preparing an organic thin film on a substrate, the method comprising the steps of providing a plurality of organic precursors, the organic precursors being in the vapor phase; and reacting the plurality of organic precursors at a sub-atmospheric pressure in the presence of the substrate to form a thin film on the substrate. In another aspect , the present invention includes organic films made by such a method. In yet another aspect, the present invention includes an apparatus designed to facilitate the reaction of organic precursors at sub-atmospheric pressures to form an organic film on a substrate.
One advantage of the present invention is that it provides multi-component organic thin films wherein the amount of each component in such films can be controlled accurately and precisely.
Another advantage of the present invention is that it provides uniform organic thin films having smooth surfaces.
Another advantage of the invention is that it provides a low pressure organic vapor phase deposition method and apparatus for the growth of thin films of organic light emitting materials and optically non-linear organic salts.
Another advantage of the invention is that it provides a low pressure organic molecular beam deposition method and apparatus for the formation of thin films of organic light emitting materials and optically non-linear organic salts.
Yet another advantage of the invention is that it provides a method and apparatus for the uniform deposition of organic materials over large substrate areas.
The present invention provides a method and apparatus for the growth of organic thin films on substrates while under sub-atmospheric pressures. The method of the invention is herein identified as low pressure organic vapor deposition (LPOVPD). The LPOVPD method of the present invention allows for the accurate and precise control of the deposition of multi-component organic thin films. In addition, the thin films of the present invention are characterized by superior surface properties such as low surface roughnesses.
A LPOVPD reactor 10 in accordance with an embodiment of the present invention is schematically shown in
Inert gas is delivered from tank 24 through a regulator valve 26 and into tubing 28 for delivery through at least two flow paths, 30 and 38, and into reactor tube 12. One flow path 30 includes a series connected pressure regulator 32, flow meter 34 and quick switching valve 35 from which the carrier gas is delivered into end 20 of reactor tube 12. The second flow path 38 includes a series connected pressure regulator 40, flow meter 42 and quick switching valve 39 from which the carrier gas flows into a bubbler 46, which contains a second organic precursor material 48. To facilitate the temperature control of second organic precursor material 48, bubbler 46 is partially immersed in bath 50 within container 52. Inert gas from tank 24 bubbles through the second organic precursor 48 and through tubing 54 to carry vapor of the second organic precursor 48 into reactor tube 12. During this process, tube 54 must be maintained at a sufficiently high temperature to avoid recondensation of the volatilized second organic precursor 48 as it travels from the bubbler to the reactor.
The amount of any precursor entering reactor tube 12 is controlled by processing parameters such as the temperature and flow rate of the carrier gas and the temperature of the reactants. The LPOVPD method provides precise metering of the precursors or reactants independently of their vapor pressure or chemical nature using pressure mass flow controllers. The present method thus permits the combination of materials with widely different characteristics in ratios necessary for the production of desired films.
The precursor streams are capable of being turned on and off almost instantly by employing quick switching valves 35 and 39. These valves direct the precursor streams into reactor 12 or into a by-pass line (not shown), so that at any given time, different precursor streams may be entering the reactor 12 for the deposition of films of different compositions and characteristics. Valve 39 also regulates the admittance of carrier gas into bubbler 46. Valves 35 and 39 thus allow the rapid change of reactant streams entering the reactor 12, for changing the nature and the composition of the grown films. It is thus possible, for example, to grow ABAB, ABCABC, ABABCAB, and ABCDABCD-type films, where each letter denotes a different molecular layer or composition.
A vacuum pump 66 and control throttle valve 68 are attached to reactor 10 at the exhaust 62. Most of the organic vapors not deposited onto substrate 58 are condensed in a trap 64 placed upstream from pump 66. Trap 64 contains liquid nitrogen or a neutral, fluorocarbon oil, for example. Throttle valve 68 regulates the pressure in reactor 10. An appropriate pressure gauge is connected to the reactor (not shown) with electronic feedback to the control throttle valve 68 to maintain a desired pressure in the reactor.
Vacuum pump 66 provides a pressure of about 0.001-100 Torr in reactor tube 12. The actual pressure for any combination of acceptor, donor, and single component layers is experimentally determined with reference to the temperatures required to volatilize the precursor materials, the wall temperature to prevent condensation of the precursor materials, and the reaction zone temperature gradient. The optimal choice of pressure is unique to the requirements of each deposited organic layer. For example, optimal pressures for the deposition of single component layers such as tris-(8-hydroxyquinoline) aluminum (Alq3) or N—N′-diphenyl-N,N-bis(3-methylphenyl) 1,1′-biphenyl-4,4′ diamine (TPD) are about 0.1-10 Torr.
The substrates on which the thin films of the present invention are deposited are typically selected from those materials that are commonly encountered in semiconductor and optics manufacturing. Such materials include, for example, glass, quartz, silicon, gallium arsenide and other III-V semiconductors, aluminum, gold and other precious and non-precious metals, polymer films, silicon dioxide and silicon nitride, indium-tin-oxide and the like. For high quality optical thin films, it is preferable to use substrates that provide crystalline interactions with the deposited organic film to induce epitaxial growth. To achieve such epitaxial growth, it is often necessary to coat substrates with non-polar organics having crystalline structures similar to the film to be deposited.
In addition, as an organic thin film is deposited onto substrate 58, it is often desirable to control the temperature of the substrate. Independent control of substrate temperature is accomplished, for example, by contacting substrate 58 with temperature-control block 60, which has channels therein for the circulation of materials such as water, gas, freon glycerin, liquid nitrogen, and the like. It can also be heated by the use of resistance or radiant heaters positioned on or near the block 60.
Reactor 20 of
The method of the present invention is used to deposit a wide variety of organic thin films from the reaction of vapor precursors. As used herein, “reaction” refers to a chemical reaction in which precursor reactants form a distinct reaction product, or alternatively, it merely refers to a combination or mixture of precursor materials, or where precursor materials form a donor-acceptor or guest-host relationship. For example, in accordance with the present invention, the following NLO materials are formed as thin films by the reaction of the listed precursors:
In another example relating more specifically to light emitting materials used to make OLEDs, the precursors consist of, for example, tetrathisferlvalene (TFF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The mixing step results in the charge transfer complex TTF-TCNQ which deposits onto a substrate. In another example relating to OLEDs, 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM) is added into a high flow rate carrier gas stream while Alq3 is added into a lower flow rate carrier gas stream. These streams are then mixed in a central reactor tube, thus providing the desired dilution of the guest molecule in the host matrix film to form a single luminescent layer. Other guest molecule examples in Alq3, hosts are 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP), Rubrene, DCM2, Coumarin, etc. As a variation, multiple dopants can be added into a single host to achieve efficient broad color conversion.
In another example, a bilayer light emitting device consisting of a hole transporting layer (“HTL”) such as TPD; α-4,4′-bis[N-(1-naphthyl)-N-Phenyl-amino]biphenyl (α-NPD); or MTDATA, layered onto the surface of a light emitting layer (“EL”) such as Alq3, bis-(8 hydroxyquinoline) aluminum oxyphenyl ((Alq3)′-OPh) or doped combinations of these layers, is grown by sequentially growing the HTL and EL to desired thicknesses. This is followed by growing additional layers onto the organics, or by growth on metallic contact layers using organometallic sources such as trimethyl-indium, trimethyl-gallium, and the like.
In addition to the apparatus and method described with reference to
Bubbler 74 is included for containing a first precursor material 75. The bubbler 74 is placed into, container 76 and immersed in a temperature controlled bath 80. A high purity inert carrier gas 78 bubbles through first precursor 75, and carries respective vapors through heated tubing 79 and into vacuum chamber 71 by way of injector 82. Once inside chamber 71, the precursor vapors form a molecular beam 83 that impinges on substrate 85. Substrate 85 is provided with a means for providing temperature control such as coolant port 81, for example.
Vacuum chamber 71 optionally is provided with at least one Knudsen or K-cell 86, which contains a second precursor material 88. K-cell 86 is a uniformly heated and controlled oven for the effusion of evaporants under vacuum. For example, K-cell 86 is heated to crack DASI or other precursor and sublime the resulting DAS, such that it is injected into reactor 70 as a molecular beam 89. Alternatively, K-cell 86 simply sublimes a single component substance such as Alq3. Alternatively, K-cell 86 is fitted with a carrier gas inlet used to dilute the concentration of the molecular species being sublimed or evaporated into the gas stream by thermalization. This dilution process is particularly useful in achieving precise doping levels of guest-host systems such as DCM-Alq3 by controlling the temperatures of bath 80 and Knudsen cell 86 as well as the flow of carrier gas 78 to bubbler 74.
Molecular beams 83 and 89 impinge on substrate 85 to deposit an organic thin film, the thickness of which is monitored by quartz crystal 93. Sample holder 90 rotates to ensure a uniform deposition and reaction of precursor materials. The deposition of precursor materials is further controlled by shutters 87, which are used to interrupt molecular beams 83 and 89.
Reactor 70 also optionally includes a cooled shroud 91 to help keep the pressure of vacuum chamber 71 to a minimum for re-evaporated precursor materials. Also preferably included is a partition 92 to keep precursor materials from migrating and thus contaminating each other.
Reactor 70 is embellished with many of the same attributes of the LPOVPD reactor shown in
The apparatus of
Each of the chambers 150, 152, an 154 in the example of
As an example, curtain 120 is comprised of TPD vapors, curtain 120′ is comprised of Alq3 vapors and curtain 120″ is comprised of vapors such as a polypyrrole or metallorganic compounds that produce a conductive surface. If desired, control or tuning of the color of light emitted by an OLED can be effected by suitable doping of the Alq3 layer with an additional RGD device 108 in the chamber 152 that produces a curtain 120′″ of dopant vapor.
The apparatus of
The present invention is further described with reference to the following non-limiting examples.
Example 1Using the apparatus of
Glass substrates were placed within the reactor tube 12 at a location where the temperature was approximately 220° C. The first layer deposited on the ITO surface was TPD, a hole transporting material. Specifically, TPD vapor was carried from crucible 14 to substrate 28 via nitrogen carrier gas. The TPD growth conditions included a source temperature of 200±5° C., a nitrogen carrier gas flow rate of 100 sccm, a reactor pressure of 0.50 Torr and a growth time of 20 minutes. At a nitrogen flow rate of 100 sccm, the Reynolds number of the system was ˜500, indicating operation well within the laminar flow regime. The TPD layer was grown to a thickness of between 100-300 Å.
After deposition, the temperature near the TPD crucible was reduced, and the corresponding nitrogen flow was shut off. Next, an electron transporting layer of Alq3 was grown by turning on a separate nitrogen line to carry Alq3 vapor from crucible 14N into chamber 12. The Alq3 growth conditions included a source temperature of 247±8° C., a nitrogen flow rate of 50 sccm, a pressure of 0.65 Torr and a growth time of 10 minutes. During the deposition of both the TDP and Alq3, the substrate was maintained at 15° C. using a water cooled stainless steel substrate holder. The TPD layer was grown to a thickness of between 700-1100 Å.
After deposition of the Alq3 layer, the substrate was removed from the reactor and a Mg:Ag top contact was applied by thermal evaporation. The contact was completed with the evaporation of a 1000 Å thick protective Ag layer.
The use of low pressures during deposition resulted in organic layers having smooth and uniform surfaces. For example, the TPD and Alq3 layers were measured via atomic force microscopy to have RMS roughnesses of 6-8 Å and 9-11 Å, respectively. The resulting OLED devices exhibited current-voltage characteristics wherein I∝V at low voltages and I∝V9 at higher voltages. The turn-on voltage, VT, at which the power law dependence of I on V changed, was about 6V.
Example 2An NLO film was prepared using the apparatus shown in
The present invention makes use of low pressure deposition techniques to produce organic thin films having superior surface properties and accurate and precise compositions. Although various embodiments of the invention are shown and described herein, they are not meant to be limiting. For example, those of skill in the art may recognize certain modifications to these embodiments, which modifications are meant to be covered by the spirit and scope of the appended claims.
The subject invention as disclosed herein may be used in conjunction with co-pending applications: “High Reliability, High Efficiency, Integratable Organic Light Emitting Devices and Methods of Producing Same”, Ser. No. 08/774,119 (filed Dec. 23, 1996), now U.S. Pat. No. 6,046,543; “Novel Materials for Multicolor LED's”, Ser. No. 08/850,264 (filed May 2, 1997), now U.S. Pat. No. 6,045,930; “Electron Transporting and Light Emitting Layers Based on Organic Free Radicals”, Ser. No. 08/774,120 (filed Dec. 23, 1996), now U.S. Pat. No. 5,811,833; “Multicolor Display Devices”, Ser. No. 08/772,333 (filed Dec. 23, 1996), now U.S. Pat. No. 6,013,982; “Red-Emitting Organic Light Emitting Devices (LED's)”, Ser. No. 08/774,087 (filed Dec. 23, 1996), now U.S. Pat. No. 6,048,630; “Driving Circuit For Stacked Organic Light Emitting Devices”, Ser. No. 08/792,050 (filed Feb. 3, 1997), now U.S. Pat. No. 5,757,139; “High Efficiency Organic Light Emitting Device Structures”, Ser. No. 08/772,332 (filed Dec. 23, 1996), now U.S. Pat. No. 5,834,893; “Vacuum Deposited, Non-Polymeric Flexible Organic Light Emitting Devices”, Ser. No. 08/789,319 (filed Jan. 23, 1997), now U.S. Pat. No. 5,844,363; “Displays Having Mesa Pixel Configuration”, Ser. No. 08/794,595 (filed Feb. 3, 1997), now U.S. Pat. No. 6,091,195; “Stacked Organic Light Emitting Devices”, Ser. No. 08/792,046 (filed Feb. 3, 1997), now U.S. Pat. No. 5,917,280; “High Contrast Transparent Organic Light Emitting Device Display”, Ser. No. 08/821,380 (filed Mar. 20, 1997), now U.S. Pat. No. 5,986,401; “Organic Light Emitting Devices Containing A Metal Complex of 5-Hydroxy-Quinoxaline as a Host Material”, Ser. No. 08/838,099 (filed Apr. 15, 1997), now U.S. Pat. No. 5,861,219; “Light Emitting Devices Having High Brightness”, Ser. No. 08/844,353 (filed Apr. 18, 1997), now U.S. Pat. No. 6,125,226; “Organic Semiconductor Laser”, Ser. No. 60/046,061 (filed May 9, 1997), “Organic Semiconductor Laser”, Ser. No. 08/859,468 (filed May 19, 1997), now U.S. Pat. No. 6,111,902; “Saturated Full Color Stacked Organic Light Emitting Devices”, Ser. No. 08/858,994 (filed May 20, 1997), now U.S. Pat. No. 5,932,895; “An Organic Light Emitting Device Containing a Hole Injection Enhancement Layer”, Ser. No. 08/865,491 (filed May 29, 1997), now U.S. Pat. No. 5,998,803; “Plasma Treatment of Conductive Layers”, Serial No. PCT/US97/10252; (filed Jun. 12, 1997), now U.S. national phase application Ser. No. 09/202,152, filed May 5, 1999; Patterning of Thin Films for the Fabrication of Organic Multi-Color Displays”, Serial No. PCT/US97/10289 (filed Jun. 12, 1997), now U.S. national phase application Ser. No. 09/202,152, filed Jun. 14, 1999; “Double Heterostructure Infrared and Vertical Cavity Surface Emitting Organic Lasers”, Ser. No. 60/053,176 (filed Jul. 18, 1997), now U.S. Pat. No. 5,874,803; “Oleds Containing Thermally Stable Asymmetric Charge Carrier Materials”, Ser. No. 08/929,029 filed (Sep. 8, 1997), “Light Emitting Device with Stack of Oleds and Phosphor Downconverter”, Ser. No. 08/925,403 (filed Sep. 9, 1997), now U.S. Pat. No. 5,874,803, “An Improved Method for Depositing Indium Tin Oxide Layers in Organic Light Emitting Devices”, Ser. No. 08/928,800 (filed Sep. 12, 1997), now U.S. Pat. No. 5,981,306, “Azlactone-Related Dopants in the Emissive Layer of an Oled” (filed Oct. 9, 1997), Ser. No. 08/948,130, “A Highly Transparent Organic Light Emitting Device Employing A Non-Metallic Cathode”, (filed Nov. 3, 1997), now U.S. Pat. No. 6,030,715, Attorney Docket No. 10020/40 (Provisional), now U.S. Provisional Application No. 60/064,005, and “A Highly Transparent Organic Light Emitting Device Employing a Non Metallic Cathode”, (filed Nov. 5, 1997), Attorney Docket No. 10020/44, now U.S. Ser. No. 08/964,863, each co-pending application being incorporated herein by reference in its entirety. The subject invention may also be used in conjunction with the subject matter of each of co-pending U.S. patent application Ser. No. 08/354,674, now U.S. Pat. No. 5,707,745, Ser. No. 08/613,207, now U.S. Pat. No. 5,703,436, Ser. No. 08/632,322, now U.S. Pat. No. 5,757,026 and Ser. No. 08/693,359 and provisional patent application Ser. Nos. 60/010,013, to which non-provisional U.S. application Ser. No. 08/779,141 filed Jan. 6, 1997 claimed benefit, now U.S. Pat. No. 5,986,268; 60/024,001, to which non-provisional U.S. application Ser. No. 08/789,319 filed Jan. 23, 1997 claimed benefit, now U.S. Pat. Nos. 5,844,363 and 60/025,501, to which non-provisional U.S. application Ser. No. 08/844,353 filed Apr. 18, 1997 claimed benefit, now U.S. Pat. No. 6,125,226, each of which is also incorporated herein by reference in its entirety.
Claims
1. An apparatus for the physical vapor deposition of an organic small molecule material on a substrate, said apparatus comprising:
- (a) a deposition chamber;
- (b) at least one flow path in fluid communication with said deposition chamber, said flow path comprising: (i) a carrier gas source, (ii) an organic small molecule material source containing a non-polymeric organic small molecule material that forms a non-polymeric organic thin film of the organic small molecule material, and (iii) a flow controller;
- (c) a substrate holder disposed within said deposition chamber; and
- (d) a vacuum pump in fluid communication with said deposition chamber and adapted to provide a pressure ranging from 0.001 torr to 100 torr within said deposition chamber;
- wherein the deposition chamber has walls that may be heated to a temperature sufficiently high to avoid re-condensation of volatilized organic small molecule material, without decomposing the volatilized organic small molecule material, and
- wherein the non-polymeric organic thin film remains non-polymeric after deposition.
2. The apparatus of claim 1, further comprising a roll-to-roll substrate delivery system.
3. The apparatus of claim 1, wherein the non-polymeric organic small molecule material forms a uniform non-polymeric organic thin film.
4. The apparatus of claim 1, wherein the organic small molecule material comprises Alq3.
5. The apparatus of claim 1, wherein said flow controller includes a pressure regulator.
6. The apparatus of claim 1, wherein said flow controller includes a flow meter.
7. The apparatus of claim 1, wherein said flow controller includes a switching valve.
8. The apparatus of claim 1, wherein said deposition chamber has heated walls.
9. The apparatus of claim 1, wherein said deposition chamber is provided with one or more radiant heat sources.
10. The apparatus of claim 1, further comprising a heater substantially surrounding said deposition chamber.
11. The apparatus of claim 10, wherein said heater is a multi-zone heater/cooler temperature controller that heats and cools.
12. The apparatus of claim 1, wherein the substrate holder is cooled.
13. The apparatus of claim 12, wherein the substrate holder comprises a temperature-control block.
14. The apparatus of claim 1, wherein said organic small molecule material source is an open container holding said organic small molecule material.
15. The apparatus of claim 14, wherein said open container is heated.
16. The apparatus of claim 1, wherein said apparatus comprises two or more flow paths.
17. An apparatus for physical vapor deposition of a film comprising an organic small molecule material on a substrate, said apparatus comprising:
- a deposition chamber;
- means for heating said deposition chamber;
- means for introducing vapors of non-polymeric organic small molecule materials including a source containing the organic small molecule materials, wherein the organic small molecule materials form a non-polymeric organic thin film that remains non-polymeric after deposition, into said deposition chamber;
- means for cooling a substrate within said deposition chamber; and
- means for maintaining the pressure in said reaction chamber at a pressure ranging from 0.001 torr to 100 torr;
- means for heating the deposition chamber walls to a temperature sufficiently high to avoid re-condensation of vapors of the organic small molecule materials, without decomposing the organic small molecule materials.
18. The apparatus of claim 17, further comprising means for moving the substrate through the deposition chamber.
19. A method for preparing an organic thin film on a substrate, said method comprising the steps of: providing a plurality of organic precursors, said organic precursors being in the vapor phase; and reacting said plurality of organic precursors at a sub-atmospheric pressure in the presence of said substrate to form said thin film on said substrate.
Type: Application
Filed: Aug 27, 2009
Publication Date: Apr 29, 2010
Inventors: Stephen R. Forrest (Princeton, NJ), Paul E. Burrows (Princeton Junction, NJ), Vladimir S. Ban (Princeton, NJ)
Application Number: 12/548,555
International Classification: C23C 16/44 (20060101); C23C 16/00 (20060101);