Patent Publication Number: US-2010119730-A1

Title: Apparatus and method for forming a thin film electronic device on a thermoformed polymeric substrate

Description:
TECHNICAL FIELD 
     The present invention is related to an apparatus and method for fabricating an electronic device on a polymeric substrate using heat processable inks. 
     BACKGROUND 
     Electronic device fabrication by conventional methods typically involves use of high resolution photolithography processes to form multilayer devices. These high-resolution processes require substantial investment in equipment to achieve precise layer-to-layer alignments on substrates that are relatively flat and rigid. 
     The processes and requirements of conventional photolithographic techniques are less successful when fabricating devices on flexible, stretchable substrates, especially when the substrate is a polymer. Fabrication of electronic devices, such as thin film transistors, on flexible substrates generally requires relaxed registration tolerance between device layers. In particular, polymer substrates may be prone to distortion, such as shrinkage and/or expansion, due to thermal processing, and/or to absorption or desorption of water or other solvents, making layer to layer alignment difficult using conventional fabrication techniques. 
     It is desirable to form electronic devices on substrates that are flexible or stretchable. It is also desirable to fabricate such devices using low-cost polymeric substrates that are subject to a significant degree of distortion during electronic device fabrication. The present invention fulfils these and other needs, and offers other advantages over the prior art. 
     SUMMARY 
     Embodiments of the present invention are directed to an apparatus and method for fabricating an electronic device or devices on a polymeric substrate. According to various embodiments, fabrication methods of the present invention involve positionally constraining a polymer substrate on a platen, and heating the constrained polymer substrate to at least a glass transition temperature of the polymer substrate. A heat processable ink is applied to the constrained polymer substrate to form at least a portion of a layer of an electronic device thereon. 
     Other embodiments of the present invention involve positionally constraining a polymer substrate on a platen, applying a heat processable ink to the constrained polymer substrate while the polymer substrate is at a temperature below a glass transition temperature of the polymer substrate, and heating the constrained polymer substrate with the heat processable ink to at least a glass transition temperature of the polymer substrate to form at least a portion of a layer of an electronic device thereon. 
     Embodiments of the present invention involve positionally constraining a polymer substrate on a platen and heating the constrained polymer substrate to a temperature lower than, but near, a glass transition temperature of the polymer. A heat processable ink is applied to the constrained polymer substrate while at this temperature. The constrained polymer substrate with the heat processable ink is heated to at least a glass transition temperature of the polymer substrate to form at least a portion of a layer of an electronic device thereon. 
     According to other embodiments of the present invention, apparatuses for forming at least a portion of an electronic device on a polymer substrate include a platen configured to receive the polymer substrate, and an arrangement configured to constrain the polymer substrate on the platen. A heat source is provided to heat the constrained polymer substrate to at least a glass transition temperature of the polymer substrate. A printer is configured to apply a heat processable ink to the constrained polymer substrate to form at least a portion of a layer of the electronic device thereon. 
     In some embodiments, the printer is configured to apply the heat processable ink to the constrained polymer substrate while the polymer substrates is at a temperature below a glass transition temperature of the polymer substrate. The constrained polymer substrate with the heat processable ink is heated by the heat source to at least a glass transition temperature of the polymer substrate to form at least a portion of a layer of an electronic device thereon. 
     In other embodiments, a heat source is provided to heat the constrained polymer substrate to a temperature lower than, but near, a glass transition temperature of the polymer substrate, and the printer is configured to apply the heat processable ink to the constrained polymer substrate while at this temperature. The same or different heat source is provided to heat the constrained polymer substrate with the heat processable ink to at least a glass transition temperature of the polymer substrate to form at least a portion of a layer of an electronic device thereon. 
     The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram showing various processes for forming electronic devices on a polymer substrate in accordance with embodiments of the present invention; 
         FIG. 2  is a diagram of an apparatus for forming electronic devices on a polymer substrate in accordance with embodiments of the present invention; 
         FIG. 3  is a diagram of a platen and an arrangement for heating a polymer substrate constrained on the platen in accordance with embodiments of the present invention; 
         FIG. 4A  is a diagram of a curved structure of a platen that facilitates thermoforming of a polymer substrate constrained on the platen in accordance with embodiments of the present invention; 
         FIGS. 4B and 4C  show structured elements or features that may be incorporated into a platen in accordance with embodiments of the present invention; 
         FIG. 5  is a diagram of an arrangement for constraining a polymer substrate on a platen in accordance with embodiments of the present invention. 
         FIG. 6  is a diagram of an arrangement for constraining a polymer substrate on a platen in accordance with other embodiments of the present invention. 
         FIG. 7  is a diagram of an arrangement for constraining a polymer substrate on a platen in accordance with further embodiments of the present invention; and 
         FIG. 8  is a diagram of an apparatus for forming electronic devices on a polymer substrate in accordance with embodiments of the present invention. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It is to be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     In the following description of the illustrated embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration, various embodiments in which the invention may be practiced. It is to be understood that the embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     The present invention is directed to fabricating electronic devices and, more particularly, to fabrication techniques and apparatuses that use heat processable inks applied to a polymer substrate to form an electronic device thereon. According to embodiments of the present invention, a polymer substrate is positionally constrained and subject to heating to at least a glass transition temperature of the polymer substrate, but preferably below the melting temperature of the substrate. Heat processable inks are applied to the positionally constrained polymer substrate to form one or more layers that define an electronic device or a portion thereof. The layers of the electronic device formed on the polymer substrate may include one or more of an electrically conductive layer, an electrically non-conductive layer, and a semiconductor layer, for example. 
     Conventional fabrication techniques, in contrast, typically limit heating of a polymer substrate to a temperature below the glass transition temperature of the substrate. When the glass transition temperature is reached or exceeded, the substrate suffers distortion typically due to shrinkage. For example, heating an unconstrained polymeric film to temperatures at or exceeding the glass transition temperature will cause the film material to become substantially non-planar due to thermal shrinkage. 
     Since polymer substrate distortion occurs during the sintering of a first layer printed on the substrate using conventional techniques, subsequent layers require positional adjustment to ensure proper registration that accounts for substrate shrinkage. Positional adjustments made to the substrate between fabrication phases introduces registration errors. Properly repositioning the heated polymer substrate to ensure proper registration for building additional electronic device layers is further complicated when substrate shrinkage is not uniform in both X and Y directions. Biaxial oriented films, for example, exhibit different shrinkage in the X and Y direction. 
     Positionally constraining the polymer substrate according to the present invention provides for forming of a multiplicity of electronic device structures and layers on the polymer substrate without having to remove or disturb the polymer substrate from its positionally constrained configuration. Heating, printing, sintering, drying, and cooling processes, for example, may be conducted while the polymer substrate is constrained on a platen and without removing the substrate from the platen between these fabrication phases. 
     Positionally constraining the polymer substrate in accordance with the present invention advantageously facilitates application of heat processable inks to the polymer substrate at elevated temperatures, such as at or above a glass transition temperature of the polymer substrate. As such, low cost polymer films that typically have glass transition temperatures of less that 155° C. may readily be used. Sintering of heat processable inks, such as silver nanoparticle ink, is a time-temperature process. Higher processing temperatures achievable in accordance with the present invention sinter the ink faster than at lower processing temperatures associated with conventional fabrication approaches. It is understood that heat processable inks may be applied to the polymer substrate at a variety of process temperatures, below or above a glass transition temperature of the polymer substrate. 
     Turning now to  FIG. 1 , there is shown a flow diagram of various processes for forming electronic devices on a polymer substrate in accordance with embodiments of the present invention. According to  FIG. 1 , a polymer substrate is positionally constrained  11  on a platen. The constrained polymer substrate is heated  13  to at least a glass transition temperature of the polymer substrate. A heat processable ink is applied  15  to the constrained polymer substrate to form at least a portion of a layer of an electronic device thereon. Heating and constraining the polymer substrate according to embodiments of the present invention provides for thermoforming of the polymer substrate to assume a shape of the platen, which may be flat, curved shape, and/or include one or more structured elements or features. 
     Positionally constraining  11  the polymer substrate may involve producing a vacuum or an electrostatic charge to positionally constrain the polymer substrate on the platen. Positionally constraining  11  the polymer substrate may involve mechanically constraining the polymer substrate on the platen. A curved platen may be particularly advantageous to facilitate mechanical clamping. 
     Heating  13  the constrained polymer substrate may involve infrared heating of the constrained polymer substrate. According to one approach, the polymer substrate may be positionally constrained  11  on a heat absorptive structure of the platen that is thermally insulated from other portions of the platen, and heating  13  the constrained polymer substrate may involve heating the heat absorptive structure of the platen to at least a glass transition temperature of the substrate while other portions of the platen are at a temperature below the glass transition temperature, such as ambient temperature. According to other approaches, the platen structure may be heated using a suitable heat source (e.g., oven heated or integral electrical or fluidic heating elements), and need not include a separate or integral heat absorptive structure. 
     One or more additional heat processable inks may be applied to the constrained polymer substrate without removal of the polymer substrate from the platen to form at least a portion of one or more additional layers of the electronic device thereon. The heat processable inks preferably include inks that comprise electrically conductive particles or electrically non-conductive particles. For example, a suitable heat processable ink is a silver nanoparticle ink. The heat processable ink or inks applied to the polymer substrate may be subject to a drying process while the polymer substrate is positionally constrained on the platen. 
     Other embodiments of the present invention involve positionally constraining a polymer substrate on a platen, applying a heat processable ink to the constrained polymer substrate while the polymer substrate is at a temperature below a glass transition temperature of the polymer substrate, and heating the constrained polymer substrate with the heat processable ink to at least a glass transition temperature of the polymer substrate to form at least a portion of a layer of an electronic device thereon. Further embodiments of the present invention involve positionally constraining a polymer substrate on a platen and heating the constrained polymer substrate to a temperature lower than, but near, a glass transition temperature of the polymer. A heat processable ink is applied to the constrained polymer substrate while at this temperature. The constrained polymer substrate with the heat processable ink is heated to at least a glass transition temperature of the polymer substrate to form at least a portion of a layer of an electronic device thereon. 
       FIG. 2  is a diagram of an apparatus for forming electronic devices on a polymer substrate in accordance with embodiments of the present invention. The apparatus shown in  FIG. 2  includes a platen  12  configured to receive the polymer substrate  30 . The platen  12  may be substantially flat. The platen  12  may also be curved, and may include a simple or complex curve (e.g., single or multiple deflection points). The platen  12  may include one or more structured elements. Structured elements of the platen  12  may include non-planer shapes that impart functionality to the thin film electronic device, such as a mechanical tactile function for an electronic keypad. Alternatively, structured elements may aid further processing of the device with surface features that enhance traction, assisting the formation of a vacuum or enabling handling or packaging or the device. 
     An arrangement  32  is configured to constrain the polymer substrate  30  on the platen  12 . A heat source  50  is configured to heat the constrained polymer substrate  30  to at least a glass transition temperature of the polymer substrate. A printer  40  is configured to apply heat processable ink to the constrained polymer substrate  30  to form at least a portion of a layer of the electronic device thereon. 
     In some embodiments, the heat source  50  is configured to heat the constrained polymer substrate  30  to a temperature below a glass transition temperature of the polymer substrate  30 , and the printer  40  is configured to apply the heat processable ink to the constrained polymer substrate  30  while at this temperature. The constrained polymer substrate  30  with the heat processable ink is heated by the heat source  50  (or other heat source) to at least a glass transition temperature of the polymer substrate  30  to form at least a portion of a layer of an electronic device thereon. 
     In other embodiments, the heat source  50  is provided to heat the constrained polymer substrate  30  to a temperature lower than, but near, a glass transition temperature of the polymer substrate  30 , and the printer  40  is configured to apply the heat processable ink to the constrained polymer substrate  30  while at this temperature. The same or different heat source  50  is provided to heat the constrained polymer substrate  30  with the heat processable ink to at least a glass transition temperature of the polymer substrate  30  to form at least a portion of a layer of an electronic device thereon. 
       FIG. 3  illustrates an arrangement for heating a polymer substrate  30  constrained on the platen  12  in accordance with embodiments of the present invention. In general, the arrangement shown in  FIG. 3  allows a thin film polymer substrate to be heated to a high temperature quickly, while constraining the shape of the polymer substrate as the temperature of the substrate reaches and exceeds the glass transition temperature, T g , of the substrate. The arrangement of  FIG. 3  provides a structure that dictates and controls the shape of the polymer substrate  30 . 
     According the arrangement shown in  FIG. 3 , a platen  12  supports a heat absorptive structure  102  configured to receive a polymer substrate. A thermal insulator  104  is preferably disposed between the heat absorptive structure  102  and the supporting surface of the platen  12 . The thermal insulator  104  may be formed from a variety of thermally insulating materials, such as rubber, plastic foam, ceramic materials, fiberglass or wood. The platen  12  further includes an arrangement  32  configured positionally constrain the polymer substrate  30  on the heat absorptive structure  102  of the platen  12 . 
     Although shown substantially flat, the heat absorptive structure  102  and, preferably, the thermal insulator  104  may be curved, as is shown in  FIG. 4A  (e.g., convex or concave). The curve imparted to the heat absorptive structure  102  and thermal insulator  104  may be simple (e.g., a single point of deflection) or complex (e.g., multiple points of deflection).  FIGS. 4B and 4C  show a heat absorptive structure  102  that incorporates one or more structured elements. The heat absorptive structure  102  shown in  FIG. 4B , for example, incorporates a series of dimples or depressions  105  that may impart functionality to the thin film electronic device, as discussed previously.  FIG. 4C  shows a heat absorptive structure  102  that incorporates grooves  107  that may facilitate or enhance positional constraining of the edge of the substrate during thermoforming and other fabrication processes, for example. 
     According to various embodiments, the heat absorptive structure  102  may include an infrared (IR) absorber or other heat absorptive structure or material having a low coefficient of thermal expansion (e.g., quartz with a backside coating of carbon black). Use of a heat absorptive material having a low coefficient of thermal expansion is desirable, so that thermal shrinkage of the polymer substrate  30  will be minimized. The surface of the heat absorptive structure  102  adjacent the thermal insulator  104  may be coated with carbon to enhance the absorption of IR energy, for example. Inclusion of the thermal insulator  104  reduces conduction of thermal energy away from the heat absorptive structure  102 . When IR radiation is present, the polymer substrate material  30  softens. A constraining force is applied to the heated polymer substrate  30  vis-à-vis the constraining arrangement  32  so that the substrate  30  takes the shape of the heat absorptive structure  102 . 
     Infrared sintering of heat processable inks, such as silver nanoparticle inks, can now take place at temperatures that exceed the glass transition temperature, T g , of the polymer substrate material  30 . When cooled, the polymer substrate material  30  retains the shape of the heat absorptive structure  102  and, preferably, the constraining arrangement  32 , since both structures as shown in the embodiment of  FIG. 3  are substantially smooth and planer. The non-planer area of the polymer substrate  30  can be trimmed and recycled. 
       FIG. 5  is a diagram of an arrangement for constraining a polymer substrate on a platen in accordance with embodiments of the present invention. The constraining arrangement  32  shown in  FIG. 5  includes a porous metal (e.g., aluminum) platen  12 . For example, the platen  12  may include perforations  70  or pores distributed through the platen  12 . The perforations  70  may be situated at various locations of the platen  12 , but are typically disposed proximate a peripheral edge of the platen  12 . 
     A vacuum source  72  is fluidly coupled to the perforation  70 . When the vacuum source  72  is turned on, a negative pressure condition is created at the surface of the platen  12  proximate the perforations  70 . When a polymer substrate  30  is situated on the platen  12  such that portions of the substrate  30  cover, or are immediately proximate to, the perforations  70 , the negative pressure condition provides a constraining force that positionally restrains the polymer substrate  30  on the platen  12 . After processing of the polymer substrate  30 , the vacuum  72  is removed or a positive pressure is generated to facilitate removal of the polymer substrate  30  from the platen  12 . 
       FIG. 6  is a diagram of an arrangement for constraining a polymer substrate on a platen in accordance with other embodiments of the present invention. According to the configuration shown in  FIG. 6 , an electrostatic pinning arrangement  32  is employed to positionally constrain a polymer substrate  30  on a platen  12 . The constraining arrangement  32  of  FIG. 6  includes the platen  12  coupled to ground and a positive electrode  80  coupled to a generator  82  that typically includes a voltage control. 
     Application of a voltage potential between the electrodes  80  and the grounded platen  12  by the generator  82  creates an electrostatic field, the strength of which may be adjusted by the voltage control. When the polymer substrate  30  is situated on the platen  12  and the generator  82  is active, the electrostatic field creates a surface charge imbalance between the platen  12  and the polymer substrate  30 . The surface charge imbalance results in attractive forces that positionally constrain the substrate  30  on the platen  12 . Deactivation of the generator  82  after processing facilitates removal of the polymer substrate  12  from the platen  12 . 
       FIG. 7  is a diagram of an arrangement for constraining a polymer substrate on a platen in accordance with further embodiments of the present invention. According to the configuration shown in  FIG. 7 , a mechanical constraining arrangement  32  provides for positionally constraining a polymer substrate  30  on a platen  12 . A retention apparatus  90  provides for mechanical engagement between the retention apparatus and edge portions of the polymer substrate  30 . Engagement between the retention apparatus  90  and the edge portions of the polymer substrate  30  results a compressive force that constrains the substrate  30  to the platen  12 . 
     A variety of mechanical arrangements are contemplated. For example, the retention apparatus  90  may include a number of edge members that are configured to engage at least a portion of a number peripheral edge portions of the polymer substrate  30 . In some configurations, the edge members of the retention apparatus  90  may pivot or rotate in and out of engagement with the polymer substrate  30 . In other configurations, the edge members of the retention apparatus  90  may be movable in a plane normal to the plane of the polymer substrate  30 , and engage the polymer substrate  30  by raising and lowering the edge members. Movement of the retention apparatus  90  may be computer controlled or effected manually. Individual edge members may be movable independent of, or in concert with, one another. 
       FIG. 8  is a diagram of an apparatus for forming electronic devices on a polymer substrate in accordance with embodiments of the present invention. The apparatus shown in  FIG. 8  includes a platen  12  and a constraining arrangement  32  of a type previously described. A polymer substrate  30  is shown constrained on the platen  12 . A platen support  19  extends from the platen  12  and is coupled to a positioning system  16 . The positioning system  16  facilitates movement of the platen support  19  and, therefore, platen  12  in a multiplicity of directions, including along an x-axis and a y-axis as shown in  FIG. 8 . 
     The positioning system  16  may include a motorized linear positioning table  14  and two or more motors  18 ,  20  arranged for moving the platen  12  in an x-direction and a y-direction. Other motors may be arranged for moving the platen  12  in a z-direction if desired. The positioning system  16 , which may include a controller  22 , is preferably coupled to a system controller  46 . A suitable linear motor  20  for moving the platen  12  along the y-axis is Trilogy Linear Motor Model T3DS43-2NCJS. A suitable linear motor  18  for moving the platen  12  along the x-axis is Trilogy Linear Motor Model T2DS43-2NCJS. A suitable motorized linear positioning table  14  is Parker Daedal Model 500000ET. A suitable positioning system controller  22  is a Delta Tau UMAC position controller. 
     A printer  40  is shown situated above the platen  12 . The printer  40  includes a printhead  42  that is shown positioned proximate a polymer substrate  30  that is positionally constrained on the platen  12 . The printer  40  is configured to apply heat processable inks  44  to the polymer substrate  30 , such as inks that include electrically conductive particles and those that include electrically non-conductive particles. Suitable printers  40  include various inkjet printers, such as those that employ a piezoelectric inkjet head and support electronics. One such printer  40  is a Spectra SE-128 jetting assembly, which provides for 128 individually addressable inline nozzles and a 30 picoliter drop volume. 
     The positioning system  16  may be aided by one or more cameras that facilitate registration of the platen  12  relative to the printhead  42 . One or more cameras may be deployed to provide a camera-based registration system. A suitable vision-based registration system is the Legend 530 Machine Vision Sensor System, available from DVT Corporation. In the configuration shown in  FIG. 8 , one camera  60  is situated on the same linear axis as the printhead  42 . Another camera  62  may be situated at a fixed position relative to the platen  12 . 
     A heat source  50  is situated proximate the printer  40 . The heat source  50  is preferably an IR heat source, such as an IR lamp that can focus high intensity infrared energy on specific target areas (e.g., using an elliptical reflector). A suitable IR heat source is Model IR 5194-04 (4 inch, 2000 W IR lamp) available from Research Inc. of Eden Prairie, Minn., which is powered by a Research Incorporated 5420 ma Power controller. An optional ultraviolet lamp (not shown) may also be included, such as a 254 nm “germicidal” UV lamp. 
     The system controller  46  is communicatively coupled to the printer  40 , positioning system  16 , and cameras  60 ,  62 . The system controller  46  executes programmed instructions for fabricating electronic device structures on the polymer substrate  30  in accordance with the present invention. 
     For example, the system controller  46  coordinates movement of the platen  12  along the y-axis so as to position the polymer substrate  30  under the printer  40  and under the heat source  50  in accordance with the programmed instructions. In accordance with a preferred fabrication approach, the polymer substrate  30  is situated on the platen  12 , and the constraining arrangement  32  is activated. Placement of the polymer substrate  30  onto and from the platen  12  may be effected manually or by use of a computer controlled pick-and-place machine as is known in the art. With the polymer substrate  30  constrained on the platen  12 , the platen  12  is moved under the heat source  50 . 
     The temperature of the polymer substrate  30  is preferably raised to at least the glass transition temperature of the polymer substrate  30  and, more preferably, above T g  of the polymer substrate  30 . As previously discussed, the platen  12  may include a heat absorptive structure that is thermally insulated from other portions of the platen  12 , thereby allowing for rapid heating of the polymer substrate  30  to the desired processing temperature, while other portions of the platen  12  remain at ambient temperature. After heating the polymer substrate  30  to at least T g , the platen  12  is moved underneath the printer  40 , and heat processable inks are applied to the constrained polymer substrate  30  to form at least a portion of one or more layers of an electronic device thereon. As was previously discussed, heat processable inks may be applied to the constrained polymer substrate  30  while heated at a temperature lower than T g  (e.g., near T g ) and the constrained polymer substrate  30  with the heat processable inks may subsequently be heated at a temperature of at least T g . 
     The apparatus shown in  FIG. 8  may be controlled to implement a sub-process of a process of fabricating thin film electronic devices components by drop on demand printing. In particular, the apparatus of  FIG. 8  may be controlled to implement a sub-process of sintering metallic nanoparticles on a thermoformed polymeric substrate, such as sintering silver nanoparticle inks to form conductive circuits on a thermoformed polymeric substrate. 
     The system of  FIG. 8  may be used to fabricate electronic devices via deposition of liquids via an inkjet printhead in patterns that define each of the layers of the device. In the following discussion, an illustrative process of building a bottom gate, bottom contact thin film transistor (TFT) using the system of  FIG. 8  is described. It is understood that other devices may be fabricated with this system and processes, and that the some of the described processes may be excluded and others included. In the process flow described below, it is assumed that all material solutions and image files are already prepared. The image files may contain features needed for multiple devices. 
     Processes for building an all-additive TFT from solution according to this non-limiting illustrative example include the following:
     1. Situate polymer substrate  30  on the platen  12 .   2. Clean the substrate surface.   3. Register the position of the lower left corner of the substrate  30  with Camera  60 .   4. Deposit the Gate Layer.
       4.1. Preheat and thermoform the substrate  30  using heat source  50  and constraining arrangement  32  (via vacuum, electrostatic pinning or mechanically).   4.2. Re-register the position of the lower left corner of the substrate  30  with Camera  60 .   4.3. Inkjet print the gate layer using printer  40 .   4.4. Measure and record the overall size of the printed image.   4.5. Dry and sinter the Silver (Ag) gate layer.   
       5. Deposit the Dielectric Layer.   6. Deposit the Source-Drain Layer.   7. Deposit the Semiconductor Layer.   8. Remove substrate  30  and electronic device formed thereon from the platen  12 .   

     The apparatus shown in  FIG. 8  was used to perform several experiments, various processes of which are described below. Polymer substrates used in the experiments included PEN and PET films. The PEN film used in the experiments was PEN film Q65F 5 mil A5072, available from Teijin DuPont Films. The PET films used in the experiments were PET film-1 (2 mil PET) and PET film-2 (5 mil ST504 PET). The heat processable ink used in the experiments was Silver Ink AG-IJ-G-100-S1, available from Cabot Corporation. 
     The platen  12  was of a construction shown in  FIG. 3 , having a quartz glass plate with a backside coating of carbon black and a thermal insulator (e.g., pine wood). A porous aluminum platen  12  was constructed to facilitate the use of vacuum to constrain the substrate. The polymer substrate  30  was placed on the platen  12  and a vacuum was created to positionally constrain the substrate  30  on the platen  12 . The substrate  30  was heated to a temperature at or above the glass transition temperature of the substrate  30  using an IR lamp  50  by way of four passes at 2″/second, 100% power (1″ advance per pass). 
     The constrained substrate  30  was moved under the printer  40 . An image was printed on the substrate  30  using the following settings:
     i) Horizontal Pixel Increment 11 or Saber angle 5.19 degrees   ii) Pulse Amplitude 100V   iii) Fire pulse width 5 μSeconds   iv) Rise and fall time 1.5 μSeconds   v) Velocity 2″/sec   vi) Acceleration 4″/Seĉ2   vii) Meniscus vacuum 5 to 6 inches H2O.   

     After printing, the silver nanoparticle ink was sintered using the IR lamp  50  by way of 8 passes at 2″/second, 100% power. (1/2″ advance/pass). Following sintering, the substrate  30  was removed from the platen  12  for visual inspection and to measure electrical properties of the printed image. 
     Experiments using the PEN, PET film-1, and PET film-2 substrates  30  demonstrated that the substrates  30  took on the shape of the platen  12  and that silver ink was fully dried. Electrical measurements revealed very good electrical characteristics for the printed structures. 
     Fabricating electronic devices on thin film polymeric substrates in accordance with the present invention provides several advantages over conventional fabrication approaches. For example, thermoforming a polymer substrate to a planar (flat or curved) surface allows process temperatures that exceed the glass transition temperature of the substrate to be utilized to sinter heat processable inks, such as silver nanoparticle ink. Using a platen or mold that can heat quickly by IR radiation results in substantially shorter cure times. Better conductivities are achievable when the ink transforms from a wet blue film to a dry silver film at a higher process temperature (e.g., temperatures at or above T g  of the polymer substrate). Substrate shrinkage is reduced since the substrate is thermoformed to a quartz sheet, for example, of the platen. The substrate need not be removed from the platen between processing phases, thereby reducing or eliminating re-alignment errors associated with conventional fabrication approaches. 
     The foregoing description of the various embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. For example, embodiments of the present invention may be implemented in a wide variety of applications. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.