Abstract:
A method of making a charge containing element including the steps of depositing and patterning a dielectric material on a surface wherein the dielectric material includes a metallo-organic component and a liquid component; and decomposing by laser light the deposited dielectric material to substantially evaporate the liquid component to cause the metallic portion of the metallo-organic component to react with oxygen causing the dielectric material to have charge-holding properties.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to forming a charge-containing element, which is useful as a capacitor on a printed circuit board.  
         BACKGROUND OF THE INVENTION  
         [0002]    Ceramic oxide layers are diverse in their properties. Apart from their unusually high mechanical strength, high wear and abrasion resistance, and high corrosion resistance, they can be considered to be dielectric, ferroelectric, piezoelectric, or optoelectronic materials. They can also be utilized in both electrical and thermal insulation applications. These ceramic oxides can be crystalline or amorphous.  
           [0003]    Layers of ceramic materials can be manufactured using physical vapor deposition (PVD) and chemical vapor deposition (CVD), laser ablation, dip and knife coating of a ceramic precursor material, and metallo-oxide decomposition (MOD) as shown by Mir et al in commonly-assigned U.S. Pat. No. 4,880,770.  
           [0004]    However the above-mentioned processes are time consuming, involving numerous steps for realization of the final product. In addition, the above mentioned processes are not discreet enough to selectively deposited the dielectric materials in the desired configuration or location.  
           [0005]    Formation of dielectric material normally requires high temperature processing. This high temperature processing restricts the choice of substrates that can be selected for use. Capacitors are multilayer coatings comprised of an arrangement of conductive, dielectric, and conductive layers in sequence. There is a need for forming dielectric materials on a substrate in many applications such as capacitive devices. Capacitors are essentially materials with high dielectric constants. Dielectric (which is essentially electrically non-conducting) characteristic of ceramic materials are well known and getting increasing importance as the field of solid state electronics continues to expand rapidly. The principal applications for ceramic dielectrics are as capacitive elements in electronic circuits and as electrical insulation. For these applications, the properties of most concern are the dielectric constant, dielectric loss factor, and dielectric strength. The principal characteristics of a capacitor are that an electric charge can be stored in that capacitor and the magnitude of the charge which can be stored is dependent primarily on the nature of the material, grain size, and the impurity distribution at the grain boundaries.  
           [0006]    As mentioned earlier, there are problems with conventional deposition methods. It is felt that the method of delivery of the metallo-organic precursor requires the development a novel approach in order to reduce the time required to manufacture dielectric components and reduce the waste involved during conventional manufacturing processes.  
           [0007]    Ink jet printing is commonly utilized for delivery of liquid ink onto a receiver. An ink jet printhead made from a piezoelectric material is used to selectively eject ink droplets onto a receiver to form an image. Within the printhead, the ink may be contained in a plurality of channels and energy pulses are used to actuate the printhead channels causing the droplets of ink to be ejected on demand or continuously, through orifices in a plate in an orifice structure. The delivery of metallo-organic precursor material in a liquid state can be made utilizing ink jet printers utilizing suitable printheads onto selected substrates.  
           [0008]    In one representative configuration, a piezoelectric ink jet printing system includes a body of piezoelectric material defining an array of parallel open topped channels separated by walls. In the typical case of such an array, the channels are micro-sized and are arranged such that the spacing between the adjacent channels is relatively small. The channel walls have metal electrodes on opposite sides thereof to form shear mode actuators for causing droplets to expel from the channels. An orifice structure comprising at least one orifice plate defining the orifices through which the ink droplets are ejected, is bonded to the open end of the channels. In operation of piezoelectric printheads, ink is directed to and resides in the channels until selectively ejected therefrom. To eject an ink droplet through one of the selected orifices, the electrodes on the two side wall portions of the channel in operative relationship with the selected orifice are electrically energized causing the side walls of the channel to deflect into the channel and return to their normal undeflected positions when the applied voltage is withdrawn. The driven inward deflection of the opposite channel wall portions reduces the effective volume of the channel thereby increasing the pressure of the ink confined within the channel to force few ink droplets, 1 to 100 pico-liters in volume, outwardly through the orifice. Operation of piezoelectric ink jet printheads is described in detail in U.S. Pat. Nos. 5,598,196; 5,311,218; 5,365,645, 5,688,391, 5,600,357, and 5,248,998.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the present invention to provide an improved method of making a patterned charge-containing element.  
           [0010]    It is another objective of the present invention to provide a method of depositing and patterning a dielectric material on a conductive portion of a substrate to form a patterned charge-containing element.  
           [0011]    In one aspect, these and other objects of making patterned charge-containing elements are achieved by a method comprising the steps of:  
           [0012]    (a) depositing and patterning a dielectric material on a surface by a precision precursor delivery head wherein the dielectric material includes a metallo-organic component and a liquid component; and  
           [0013]    (b) thermally decomposing by laser light the deposited dielectric material to substantially evaporate the liquid component to cause the metallic portion of the metallo-organic material to react with oxygen causing the dielectric material to have charge-holding properties wherein the dielectric material includes a metallo-organic component and a liquid component.  
           [0014]    It is a further object of the present invention to provide a method of depositing and patterning by a precision precursor delivery head, which responds to electrical signals to provide the dielectric material at predetermined positions.  
           [0015]    It is still a further object of the present invention to provide a conductive portion over a substrate and forming the patterned dielectric material on such conductive portions.  
           [0016]    It is still another object of the present invention to provide a method of converting the dielectric material at predetermined positions to electrically conductive material using a Nd-YAG laser source having wavelength 1.06 μm.  
           [0017]    The present invention is particularly suitable to provide a dielectric layer for a multilayer capacitor, flexible capacitor, capacitor integrated to circuit boards, camera body, cellular phone, personal digital assistant, pace maker, hand held electronic devices, and related components.  
           [0018]    This invention provides a convenient way to have fully completed solid state reactions to produce desired chemistries in material layer. It is easy to control various crystallographic phases of the material by simplified doping methods.  
           [0019]    It is an advantage of the present invention that the dielectric layer can be made using a low cost ink jet printer, which permits controlled and selective delivery of the metallo-organic precursor having high degree of thickness uniformity, and ability to deposit in a cost effective manner.  
           [0020]    This invention overcomes many of the problems that are associated with conventional methods of fabricating printed circuit boards, multilayer capacitors, flexible capacitors, capacitors integrated onto circuit boards, and protective coatings on metals, alloys, polymers, organics, inorganics, composites, glasses, paper, photographic film, magnetic media, or ceramic substrates or combinations thereof both flexible and rigid in form. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a perspective of a single-head precision precursor delivery and curing system for a rigid or flexible substrate showing deposition of precursor droplets;  
         [0022]    [0022]FIG. 2 is a perspective of a single-head precision precursor delivery and curing system for a rigid or flexible substrate as shown in FIG. 1, showing sequential laser curing method following deposition of droplets;  
         [0023]    [0023]FIG. 3 is a perspective of a simultaneous single-head precursor delivery and laser curing arrangement; and  
         [0024]    [0024]FIG. 4 is a perspective of a dual-head precursor delivery system for depositing precursor droplets on both sides of a flexible or rigid substrate. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    This invention refers to a dielectric layer, which can be used in an article having electrical capacitive properties in which selectively the electrical charges can be trapped or discharged on demand. The present invention has particular applicability in forming an article, which has identified elements. Since a dielectric material frequently is used to make use of its capacitive properties, articles formed by the present invention can be used in capacitors that can be individually addressed. When addressed such a capacitor can be discharged.  
         [0026]    Turning now to FIG. 1, there is shown a perspective of a single-head precision precursor delivery and curing system  100 , which in many respects is identical to an ink jet printer, and can be used in accordance with the present invention.  
         [0027]    The precursor is deposited in the form of droplets  50  along the precursor delivery head direction  80  on a substrate (receiver)  10  by means of a delivery nozzle  30  located in a precursor delivery head  20 . It will be understood that the substrate  10  can be a printed circuit board, which has other components that are either formed prior to or after making capacitors. The droplets  50  are generally deposited onto conductive portions  11  of the substrate  10 . The substrate  10 , which moves along the substrate (receiver) direction  70 , can be flexible or rigid and the substrate  10  can be generally made from polymers, polymeric composites, paper, photographic film, magnetic media, or ceramic substrates or combinations thereof. A flexible substrate  10  can have a thickness in the range of 0.1 to 10.0 mils, preferably 1 to 5 mils. Furthermore, the flexible substrate 10 can be wound around a mandrel that is at least 1 millimeter in diameter. Those substrates  10 , which are thicker than 10.0 mils or cannot be wrapped around a mandrel having at least 1-millimeter diameter, are considered rigid substrates. The precursor delivery head  20  is mounted on at least one guide rail  40 , or preferably more than one, guide rails  40  for precursor delivery head direction  80  of the precursor delivery head  20 . The guide rails  40  are driven by a motor (not shown) which in turn causes the precursor delivery head  20  to travel from one edge of the substrate  10  to the other while the substrate (receiver) direction  70  is traverse to that of precursor delivery head  20 . An edge guide  60  is provided for properly locating and guiding the substrate  10 .  
         [0028]    [0028]FIG. 2 shows a partial perspective of the precursor delivery and curing system  100  of FIG. 1, wherein an alternative embodiment of sequential laser assisted thermal curing process following deposition of precursor droplets is accomplished. FIG. 2 shows an IR laser source  90 , like CO 2 , which produces a laser beam  95  and that is used to thermally cure the deposited precursor droplet  50  to form the cured dielectric element  55  after it is being deposited on the conductive portion  11  of the substrate  10 . These cured dielectric elements  55  form capacitors. FIG. 1 shows a substrate (receiver) direction  70 , whereas, alternatively, the substrate  10  can be translated on X-Y translation stage  65  through X-movement direction  72  and Y-movement direction  75  as shown in FIG. 2. A second IR laser source like Nd-YAG (not shown) having 1.06 μm wavelength can also be used to transform the cured dielectric element  55 , to electrically conductive element  58 . Alternatively, the second IR laser source can be the one and the same laser source  90  needed for curing the droplets to form the cured dielectric element  55  using different laser operating parameters.  
         [0029]    [0029]FIG. 3 shows another alternative embodiment of precursor delivery and curing method. FIG. 3 shows simultaneous single-head precursor delivery and laser curing system  200  wherein the precursor droplet delivery step is immediately followed by precursor curing step to form cured dielectric element  55  which is followed by the final laser transformation process to form electrically conductive element  58 . A laser housing  92  is mounted on a at least one guide rail  45 , or preferably more than one guide rails  45 , in close proximity to a precursor delivery head  20 . An IR laser beam  95  transforms the cured dielectric element  55  to electrically conductive element  58 .  
         [0030]    [0030]FIG. 4 shows a two-sided precursor delivery system for rigid or flexible substrate  300  for depositing precursor droplets  52 ,  52 A on conductive portions top side  12  and conductive portions bottom side  12 A of the top and bottom surfaces or sides respectively of a rigid or flexible substrate  15 ,  15 A; top and bottom sides respectively. Identical precursor delivery heads  22 ,  22 A are spaced apart such that the precursor droplets  52 ,  52 A top and bottom sides respectively are deposited from delivery nozzles  32 ,  32 A respectively, on the conductive portions top side  12  and conductive portions bottom side  12 A of both sides of the substrate  15 ,  15 A top and bottom sides respectively. The precursor delivery heads  22 ,  22 A are mounted on at least one guide rail  42 ,  42 A respectively, or preferably more than one guide rails  42 ,  42 A. The substrate  15 ,  15 A is translated through flexible receiver movement direction  85 . The next steps of thermal curing by a laser  90  and laser transformation from dielectric to conductive elements are the same as described hereinbefore.  
         [0031]    As will be described later in this disclosure through the impingement of infrared radiation upon the droplet  50 , cured element  55 , and electrically conductive element  58  can be formed. The formation of the electrically conductive element  58  on the surface of the substrate  10  or the flexible substrate  15 ,  15 A is a feature of this invention by selectively discharging certain ones of the elements. Each cured and electrically conductive element  55  and  58 , respectively on the substrate  10  or flexible substrate  15 ,  15 A is in effect a capacitor which can be used to accept stored charge or discharge stored charge depending on the configuration of the electrical connections.  
         [0032]    Capacitors made in accordance with the present invention can have a multi-layer structure in which one of the coatings is electrically conductive and one or more of the other layers are dielectrics that can hold the charge and can be selectively converted to have electrically conductive areas or regions by altering the chemical composition of those regions.  
         [0033]    The present invention makes use of ceramic materials, which can be used, in capacitive elements in electronic circuits and as electrical insulation. For these applications, the properties of most concern are the dielectric constant, dielectric loss factor, and dielectric strength. The principal characteristics of a capacitor is that an electric charge can be stored in that capacitor and the magnitude of the charge which can be stored is dependent primarily on the nature of the material, grain size, and the impurity distribution at the grain boundaries. The elements of FIGS. 2 and 3 can use a ceramic material which has a surface region changed from a dielectric to a conductor by the application of laser light as will be described later.  
         [0034]    According to the present invention one or more dielectric layers are formed for storing the electrical charges that can utilize any ceramic oxides or any material having a high dielectric constant. A dielectric layer can, for example, be formed on a conductive layer wherein the dielectric layer is formed by the thermal decomposition of an organic component of the dissolved metallo-organic component and a reaction of the metallic portion of the material with oxygen thereby causing the dielectric layer to have charge holding properties.  
         [0035]    Oxide ceramics are commonly prepared by solid state reactions and sintering of metal oxide/carbonate mixtures. Since they usually are physical mixtures, they require prolonged grinding/heating cycles to complete the solid state reactions. Sometimes, it is even extremely difficult to have fully completed solid state reactions. This difficulty has led to considerable interests in the preparation of materials by chemical methods for achieving stoichiometric control, “atomic level” homogeneity and for reduction of processing times and temperatures. One of such chemical methods of coating and producing ceramic or other metal or alloy structures, particularly in thick and thin layer form is Metallo-Organic-Decomposition (MOD). Metallo-Organic-Decomposition is a convenient non-vacuum technique for the deposition of various types of inorganic layers. It includes coating a precursor solution (such as, metal carboxylates, metal alkoxides etc.) containing the desired cations in the desired proportions onto a substrate followed by solvent removal and thermal decomposition. MOD is a simple technique for layer deposition with low cost equipment requirements, and permits excellent control of overall stoichiometry, high uniformity of thickness and composition, and ability to coat irregular substrate shapes in a cost effective manner.  
         [0036]    Any material with high dielectric constant can be utilized for storage of electric charge, hence capacitor material. In the present invention, only zirconium oxide material is chosen for experimental purposes and cited as examples through which reduction in practice is established.  
         [0037]    Three zirconia precursor materials were selected for coating on some rigid electrically insulating ceramic materials, such as alumina, and also on some flexible insulating materials, such as flexible polyimide polymer substrate.  
         [0038]    These are: (a) Zirconium 2-Ethylhexanoate, 90% zirconium content (packaged under nitrogen), bought from Gelest, Inc.; (b) Zirconium Octoate (in mineral spirits), 6% zirconium content, bought from Pfaltz &amp; Bauer, Inc.; (c) Zirconium Tetra-n-butoxide (in N-Butanol), 80% zirconium content, bought from Pfaltz &amp; Bauer, Inc. These precursor materials were normally diluted with toluene in 50:50 proportion before depositing onto a substrate, because experience showed that undiluted precursors were difficult to deposit. After depositing the precursor droplets on the substrates using the precursor delivery head, those droplets were cured using an IR laser before they were selectively treated with a Nd-YAG laser for converting the cured element to electrically conductive element. The curing process may be described as converting the liquid droplets to dry droplets by thermally driving out the liquid component of the precursor and oxidizing the precursor in ambient air to form a dielectric oxide.  
         [0039]    Converting certain thickness of the dielectric element (zirconia) to an electrically conductive element was done adopting the method used by Ghosh, et. al in commonly-assigned U.S. Pat. No. 5,889,234, the disclosure of which is incorporated by reference herein. A dielectric element having electrically conductive surface is made by modifying the chemical composition of the surface using infrared laser energy. Through the impingement of infrared laser radiation upon the surface of the element, an electrically conductive element is produced on the surface. In such manner, the entire surface can be made electrically conductive or a particular pattern can be traced. A Nd-YAG laser with a wavelength of 1.06 μm was utilized. As an integral part of the element, the conductive surface layer will not delaminate from the element. Further, because the modified surface region and the element are both a zirconia, the coefficients of thermal expansion of the element and the modified surface region will be closely matched. These types of laser assisted chemical changes were made on zirconia or its composites coated on electrically conductive metallic and electrically non-conductive polymeric or plastic substrates as described above. This type of multilayer structure forms the basis for element formation as described earlier. In the case of flexible polyimide polymer substrates the surface opposite to the laser treated electrically conductive surface can be coated with some conductive metallic or alloy layers by PVD, CVD, Sol-Gel and, and dip-coating methods. Suitable electrodes were configured so that the novel capacitor is effective.  
         [0040]    This invention can be used in articles having a dielectric layer on a very thin polymer, composites, or ceramic substrates which are generally electrically non-conductive flexible material layer where elements can be fully or selectively converted to either electrically conductive or electrically insulating elements by altering the chemical composition of those regions, thus forming a flexible or rigid capacitor.  
         [0041]    This invention also provides a method of fabricating the above mentioned articles at a low temperature so that the substrates are not adversely affected by the process of formation of the article.  
         [0042]    The above described precursor materials for formation of zirconia layer were doped with a precursor, which translated to yttria, a crystal modifying dopant. The doping was done through Y-Acetylacetonate. The amount of dopant controls the crystalline phase, and for example, an appropriate amount of dopant to produce 0, 9, 30 mole % yttria were added and thoroughly mixed with Zirconium 2-Ethylhexanoate, Zirconium Octoate, and Zirconium Tetra-n-butoxide, before they were coated on the substrates.  
         [0043]    The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
                                         PARTS LIST                                 10   substrate (receiver)        11   conductive portion        12   conductive portion top side        12A   conductive portion bottom side        15   flexible substrate (flexible receiver) top side        15A   flexible substrate (flexible receiver) bottom side        20   precursor delivery head        22   precursor delivery head top side        22A   precursor delivery head bottom side        30   delivery nozzle        32   delivery nozzle top side        32A   delivery nozzle bottom side        40   guide rail for precursor delivery head        42   guide rail for precursor delivery head top side        42A   guide rail for precursor delivery head bottom side        45   guide rail for laser        50   droplet        52   droplet top side        52A   droplet bottom side        55   cured dielectric element        58   electrically conductive element        60   edge guide        65   X-Y translation stage        70   substrate (receiver) direction        72   X-movement direction        75   Y-movement direction        80   precursor delivery head direction        85   flexible receiver movement direction        90   laser source        92   laser housing        95   laser beam       100   single head precision precursor delivery and curing system       200   precision precursor simultaneous delivery and curing system       300   two-sided precursor delivery system for rigid or flexible substrate