Abstract:
An evaporator device for coating substrates, in particular for applying an aluminum layer of OLEDs. To attain high evaporator tube temperatures, such as are required for example for the vaporization of materials with low vapor pressure, the heating system is placed into the interior of the evaporator tube. The thermal losses are thereby minimized and higher tube temperatures are possible at comparably coupled-in heating power.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
       [0001]     This application claims priority under 35 U.S.C. §119 from European Patent Application No. 050 16 364 filed Jul. 28, 2005, incorporated herein by reference in its entirety.  
         [0002]     The invention relates to an evaporator device.  
         [0003]     Modern flat-screen displays comprise liquid crystal elements (LCDs) or plasma elements for the rendering of images or characters.  
         [0004]     Flat-screen displays have also recently been produced which utilize organic light-emitting diodes (OLEDs) as color pixels.  
         [0005]     Compared to the known structural elements, a great advantage of the OLEDs is their high degree of efficiency of more than 16% (Helmuth Lemme: OLEDs—Senkrechtstarter aus Kunststoff, Elektronik February 2000, p. 98, right column, 2nd paragraph, No. [5]: Yi He; Janicky, J.: High Efficiency Organic Polymer Light-Emitting Heterostructure Devices, Eurodisplay 99, VDE-Verlag Berlin, Offenbach). Therewith the OLEDs are situated far above the quantum efficiency of the LEDs comprised of inorganic III-V semiconductors.  
         [0006]     OLEDs, further, have low weight, a wide angle of radiation, and produce colors of more intense brightness and can be applied in a broad temperature range from −40° C. to 85° C. Of advantage is also that they can be operated at less than 5 Volts and have low electric energy consumption, which makes the OLEDs especially suitable for installation in battery-operated apparatus.  
         [0007]     The OLEDs can be produced by means of OVPD technology (OVPD=Organic Vapor Phase Deposition), such as is described in U.S. Pat. No. 5,554,220 or DE 101 28 091 C1. Therein the organic materials are applied onto an electrode located on glass. This electrode can be, for example, an ITO electrode (ITO=Indium Tin Oxide) which had previously been vapor deposited onto glass.  
         [0008]     Onto the OLED layer generated in this way further materials, in particular metals, which assume the function of control electrodes, can be applied. Since OLEDs are heat sensitive, precautions must be taken to prevent the heat effect onto the OLEDs from becoming too strong.  
         [0009]     As a rule, the heating sets for the evaporation of metals are disposed around an evaporator tube (DE 38 17 513 C2, DE 101 28 091 C1). The heating sets are vertical heating rods or coil heaters (DE 102 56038 A1, U.S. Pat. No. 4,880,960). Of disadvantage in heating systems located outside of the evaporator tube are their high thermal losses. When coating OLEDs with metals, where for the evaporation of the metals temperatures of more than 1200° C. must be generated, such heating sets have a negative effect on the OLEDs due to their heat radiation.  
         [0010]     Furthermore is known an evaporator device for coating substrates, which comprises an evaporator with a heating system (U.S. Pat. No. 5,157,240 A). However, this evaporator device does not have a linear distributor opening.  
         [0011]     From EP 0 581 496 A an evaporator device is also known, which serves for coating substrates. However, a linear distributor opening also does not exist here.  
         [0012]     U.S. Pat. No. 6,117,498 A discloses a coating device with a vacuum chamber. In the center of this chamber is located an electric resistance heater in the form of a tantalum sheet. A linear distributor opening is not provided in this coating device.  
         [0013]     In addition, a metal evaporator device is known with a cylindrical tube as the evaporator. This tube comprises a rod-shaped resistance heater (DE 41 33 615 A). This device also does not include a linear distributor opening.  
         [0014]     The invention addresses the problem of providing an evaporator device in which high-boiling substances are converted into the gas phase, without too high a heat radiation reaching the substrate to be coated.  
         [0015]     This problem is solved with an evaporator device according to the present invention.  
         [0016]     The invention, consequently, relates to an evaporator device for coating substrates, in particular for applying an aluminum layer onto OLEDs. To attain high evaporator tube temperatures, such as are necessary for example for the evaporation of materials having low vapor pressure, the heating system has been placed into the interior of the evaporator tube. The thermal losses are thereby minimized and higher tube temperatures are possible at comparably coupled-in heating power.  
         [0017]     The advantage attained with the invention comprises in particular that the heating power remains within the evaporator tube and is not radiated outwardly. Hereby only a low power loss occurs, and very high evaporator temperatures can be generated. It is additionally possible to improve the thermal insulation of the evaporator tube against the outside, since the insulation can be directly in contact on the evaporator tube since an outside heater is omitted. Furthermore, a more homogeneous decoupling of the heating energy is attained through the improved symmetry of the structure. In the known evaporators no heating set could be provided in front of the outlet opening for the vapor. This led to some extent to the condensation of evaporation material in the proximity of the outlet opening.  
         [0018]     The invention is illustrated in conjunction with the drawings and will be explained in the following in further detail. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0019]      FIG. 1  is a cross section through an evaporator device.  
         [0020]      FIG. 2  is a perspective view of a portion of the inner wall of an evaporator tube.  
         [0021]      FIG. 3  is a perspective view of a portion of the outer wall of the evaporator tube.  
         [0022]      FIG. 4  is a perspective view of an evaporator tube with heating elements extending within the evaporator tube.  
         [0023]      FIG. 5  is a perspective view of an evaporator tube with a heating device in contact on an evaporator bar. 
     
    
     DETAILED DESCRIPTION  
       [0024]      FIG. 1  shows a longitudinal section through an evaporator device  1  comprised of a lower housing part  2  and an upper housing part  3 . The upper housing part  3  is herein placed onto the lower housing part  2 . The lower and the upper housing part  2 ,  3  are held together with connection clamps  4 ,  5  and a connection pin  6 . While the lower housing part  2  rests on a base  25 , the upper housing part  3  is closed off by a cover  26 . Instead of connection clamps  4 ,  5 , a simple plug connection may also be provided.  
         [0025]     In the interior of the upper housing part  3  is located an evaporator tube  19  which includes several nozzles  30 ,  31 ,  32 ,  33  disposed linearly one below the other, through which vapor can escape from the evaporator tube. This vapor is deposited on the surface of a substrate  7 , which can be moved into the plane of drawing past the evaporator device  1 .  
         [0026]     Beneath the evaporator tube  19  is provided a crucible  8  on which rests the evaporator tube  19  via a taper  48 . The crucible  8  is heated via an electric heating means whose power supply lines are denoted by  9  and  10 . The heating means may be, for example, a, not shown, heating coil wound about the crucible  8 . The crucible interior  11  is filled with a material to be vaporized. On the underside of crucible  8  is located a heat sensor  12 , via which the temperature of the crucible  8  is measured. This heat sensor  12  is connected via an electric terminal  13  with a control system, not shown in  FIG. 1 , with which the temperature of the crucible  8  can be controlled.  
         [0027]     An insulating layer  14  is provided about the crucible  8 . About the crucible  8 , in turn, at least one shielding tube  45  is placed. The termination to the outside is formed by a cooling tube  46 , which is formed by concentric walls  54 ,  55 .  
         [0028]     The evaporator tube  19  is also encompassed by a tubular insulating layer  15 , which is encompassed by a shielding tube  28 . The concentric cylindrical walls  56 ,  57  following thereon form a cooling space  58  between them.  
         [0029]     The evaporator tube  19  terminates at its upper end with an opening  16 , which can be closed by means of a plunger  17  and a rod  18 .  
         [0030]     The cooling spaces  58  and  46  are separately controllable cooling spaces through which may flow a cooling means.  
         [0031]     To prevent condensation on the evaporator tube  19  of the vapor rising from the crucible  8 , a heating means  22  is provided on the inside of the evaporator tube  19 . This heating device is preferably an electric heater  22 , which in  FIG. 1  is only shown schematically. It may be comprised for example of rod-shaped heating rods, which are retained by electrically insulating spacer blocks  23 ,  24 .  
         [0032]     Through this inner heating means  22  very high temperatures can be reached in the interior  21  of the evaporator tube  19 , such that even materials with low vapor pressure cannot condense.  
         [0033]     The heating rods do not need to be disposed symmetrically in the evaporator tube, such that through the skillful geometric disposition of the heating rods it is possible to heat even those sites at which high thermal losses occur, such as for example at the outlet openings  30  to  33  of the evaporator tube  19 .  
         [0034]     Instead of on the interior surface of the evaporator tube  19 , the heating rods can also be located as a grouping in its center.  
         [0035]      FIG. 2  shows a perspective cut-out of the inside of the evaporator tube  19  with the insulating layer  15 . Evident are several nozzles  30  to  33  disposed linearly one above the other, from which the vapor can escape from the inside to the outside. The nozzles  30  to  33  consequently form a linear distributor system, through which the vapor impinges perpendicularly onto the surface of the substrate  7 .  
         [0036]     On both sides of the nozzles  30  to  33  run two heating elements  35 ,  36  formed in the shape of meanders, which are connected with the inside wall of the evaporator tube  19  via electrically insulating spacer blocks  37  to  40  and  41  to  44 , respectively. The power source supplying the heating elements  35 ,  36  with electric energy is not shown in  FIG. 2 .  
         [0037]      FIG. 3  shows a perspective cut-out of the outside of the evaporator tube  3  with the evaporator tube  19  and the insulating layer  15 . The insulating layer  15  encompasses the inner tube  19  nearly completely leaving open a wedge-form window  47 . In this window  47  the nozzles  30  to  33  are disposed linearly one above the other, these nozzles  30  to  33  increasing in size toward the outside in the manner of inverse embrasures. The enlargements are denoted by  50  to  53 .  
         [0038]     For the better shielding of the inner tube  19  and of the insulating layer  15  still further shielding tubes (cf.  28  in  FIG. 1 ) may be provided. In this case, these must have windows which adjoin the window of the insulating layer  15 . Such shielding tubes have thermal conductivities of different magnitudes, the thermal conductivity preferably increasing from the inside to the outside.  
         [0039]      FIG. 4  shows a perspective view of the evaporator tube  19  with the insulating layer  15 , with heating elements  60  to  62  being carried through the center of the evaporator tube  3 . These heating elements  60  to  62  extend through the centers  63 ,  64  of two parallel Y-shaped carriers  65 ,  66 , each with three webs  72  to  74  and  75  to  77 , respectively. The carrier  66  is disposed in the lower region of the evaporator tube above the crucible, while the upper carrier  65  is disposed closely beneath the upper end of the evaporator tube  19 .  
         [0040]     To avoid possible contact between the heating elements  60  to  62 , they are separated by electrically insulating spacers  70 ,  71  in the form of a triangle disposed in the vertical direction and at a certain spacing one from the other.  
         [0041]     In addition to the inner heating rods  60  to  62 , outer heating rods  78  to  80  can also be provided, which are carried through the ends of webs  72  to  74  and  75  to  77 , respectively. The heating rods  78  to  80  in this case extend further via spacer blocks  83 ,  84  along the inner wall  90  of evaporator tube  19 . It is understood that the heating rods  78  to  80  can also be provided without the heating elements  60  to  62 .  
         [0042]     Carriers can also be installed which have even more webs, which also permits accommodating more heating elements. At one end of the web several heating elements can also protrude and run along the tube wall whereby the heating power can still be further increased.  
         [0043]     It is understood that the carriers and the heating elements must be comprised of materials having high thermal resistance.  
         [0044]      FIG. 5  shows a further disposition of an inner heating system for an evaporator tube  90 . The evaporator tube  90  is here encompassed by an insulating layer  91 , which, in turn, is encompassed by a metal shielding sheet  92 . A cooling tube  93  encompasses the shielding sheet  92 , with this cooling tube  93  having two concentric walls  94 ,  95  between which extend separating webs  96  to  98 . Together with the walls  94 ,  95 , these separating webs  96  to  98  form channels through which a cooling fluid can flow. A nozzle bar  99  with nozzles  30  to  32  is flanged onto the ends  100 ,  101  of the evaporator tube  90 . Directly behind the nozzle bar  99  is located an inner heater  102  comprised of several heating rods  103  to  105  disposed in a circle. These heating rods  103  to  105  are braced by inner and outer holding rings  106 ,  107 . Since the nozzle bar  99  projects outwardly, a very small radiation area of width b is formed in connection with the special inner heater  102 .