Abstract:
Thin film light-activated power switches, photovoltaic devices and methods for making a micro-fluid ejected electronic device. One such thin film light-activated power switch includes a micro-fluid ejected photoactive device having a first electrode, a second electrode, and a P-N junction between the first electrode and second electrode provided by an n-type organic material and a p-type organic material. The first electrode of the photoactive device is electrically connected to a gate of a micro-fluid ejected transistor device. A power source is connected to the source of the transistor. An electronic device is connected to the drain of the transistor and to the second electrode of the photoactive device. Activation of the photoactive device provides a low voltage signal to the gate of the transistor to provide power from the power source to the electronic device.

Description:
FIELD OF THE DISCLOSURE  
       [0001]     The disclosure is directed to micro-fluid ejected electronic devices and in particular to micro-fluid ejected photovoltaic switching devices and methods for making the devices.  
       BACKGROUND AND SUMMARY  
       [0002]     Semiconductor electronic devices such as transistors, capacitors, resistors, solar cells, and the like are typically made using elaborate equipment by processes including, but not limited to, photolithography, vacuum deposition, chemical vapor deposition, oxidation, etching, masking, dopant diffusion, and the like. Many of the foregoing process steps are relatively slow and difficult to control. Furthermore, the equipment required to make such devices on a large scale is expensive and often requires clean room environments.  
         [0003]     As the uses of semiconductor and electronic devices continue to grow and diversify, there is a continuing need for faster, more economical production processes for electronic devices.  
         [0004]     With regard to the foregoing needs, exemplary embodiments of the disclosure provide a thin film light-activated power switch, a photovoltaic device and a method for making a micro-fluid ejected electronic device. One such thin film light-activated power switch includes a micro-fluid ejected photoactive device having a first electrode, a second electrode, and a P-N junction between the first electrode and second electrode provided by an n-type organic material and a p-type organic material. The first electrode of the photoactive device is electrically connected to a gate of a micro-fluid ejected transistor device. A power source is connected to the source of the transistor. An electronic device is connected to the drain of the transistor and to the second electrode of the photoactive device. Activation of the photoactive device provides a low voltage signal to the gate of the transistor to provide power from the power source to the electronic device.  
         [0005]     Another exemplary embodiment of the disclosure provides a method for making a micro-fluid ejected electronic device. The method includes depositing a source conductor and a drain conductor on a substrate by a micro-fluid ejection process. A polymeric semiconductor material is deposited on at least a portion of the source conductor and at least a portion of the drain conductor by a micro-fluid ejection process. An electrically insulating material is deposited over the semiconductor material and the source conductor and drain conductor by a micro-fluid ejection process. A gate conductor is deposited on at least a portion of the insulating material by a micro-fluid ejection process. A first electrode is deposited in electrical communication with the gate conductor over the gate conductor and insulating material by a micro-fluid ejection process. An n-type organic material is deposited on the first electrode by a micro-fluid ejection process. A p-type organic material is deposited on the n-type organic material by a micro-fluid ejection process. An at least translucent second electrode is deposited on the p-type organic material by a micro-fluid ejection process.  
         [0006]     A further exemplary embodiment of the disclosure provides a photovoltaic device made by a micro-fluid ejection process. The device includes a substrate, a micro-fluid ejected conductor deposited on the substrate, a micro-fluid ejected n-type organic material deposited on the conductor, a micro-fluid ejected p-type organic material deposited on the n-type organic material to provide a P-N junction, and a micro-fluid ejected at least translucent electrode deposited on the p-type organic material.  
         [0007]     An advantage of at least some of the foregoing embodiments is that an electronic switching device may be provided using relatively inexpensive equipment. Such a switching device has an advantage with regard to types of substrates that may be used and ease of layout changes for electronic components of the switching device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Further advantages of the exemplary embodiments may become apparent by reference to the detailed description when considered in conjunction with the elements through the several views, and wherein:  
         [0009]      FIGS. 1 and 2  are schematic illustrations of a switching device according to the disclosure;  
         [0010]      FIG. 3  is a perspective view, not to scale, of a greeting card containing a switching device according to the disclosure;  
         [0011]      FIG. 4  is a schematic illustration of a process for depositing conductive, semiconductive, and insulating material on a substrate according to the disclosure; and  
         [0012]      FIG. 5  is a schematic illustration of a switching device according to another exemplary embodiment of the disclosure. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0013]     With reference to  FIGS. 1 and 2 , there are shown schematic drawings of a switching device  10  according to an exemplary embodiment of the disclosure. The switching device  10  includes a photovoltaic component  12  and a transistor component  14 . The switching device  10  may be used to activate a load  16  such as an electronic display, motor, or the like that is connected to a power source  18 . When light is present, the photovoltaic component  12  is activated and sends an electrical signal via conductor  20  to power a gate  22  of the transistor component  14 . When light is no longer present, the photovoltaic component  12  is no longer activated hence no electrical signal is sent to the gate  22  of the transistor component  14 . Since the gate  22  is not activated, there will be no current flowing from a source region  24  to a drain region  26  providing an open circuit configuration with respect to the load  16 .  
         [0014]     While not desiring to be bound by theory, in the presence of light, it is believed that the photovoltaic component  12  generates a negative electrical charge that is applied to the gate  22  of the transistor component  14 . The negative electrical charge on the gate  22  of the transistor component  14  repels electrons downward providing a relatively electron rich region in the transistor component  14 , which allows current to flow from the source region  24  to the drain region  26 . Since the photovoltaic component  12  generates a low voltage, there is not enough energy generated by the photovoltaic component  12  to power the load  16  directly. Accordingly, the switching device  10  includes the power source  18  that is the main source of power for the load  16 .  
         [0015]     An advantage of the switching device  10  described above, could be that the device  10  may be used to activate devices such as electroluminescence displays that need high voltage to operate. The foregoing device  10  allows high voltage to flow to the load  16  only when light is present, thus not draining batteries or other power sources  18  when the load  16  is not needed.  
         [0016]     An example of a load  16  powered by the switching device  10  described above is illustrated in  FIG. 3 . The switching device  10  is deposited onto a card stock providing a greeting card  28  by a micro-fluid ejection process. In this case, the load  16  is an electroluminescent display or liquid crystal display  30  on an inside flap  32  of the greeting card  28 . The display  30  is powered by a battery or batteries  36 . When the card  28  is opened, light activates the photovoltaic component  12  sending an electrical signal to the gate  22  of the transistor component  14  thereby completing the circuit from the batteries  36  to the display  30 . When the card  28  is closed, the circuit is opened and the power to the display  30  is terminated. The foregoing switching device  10  may also be adapted to complete the circuit from the batteries in the absence of light and to open the circuit in the presence of light.  
         [0017]     A process for making the switching device  10  will now be described. Each of the photovoltaic component  12  and transistor component  14  may be deposited on a single substrate in spaced-apart locations, on separate substrates, or as shown in  FIG. 4 , the photovoltaic component  12  and transistor component  14  may be combined in a single location on a substrate  40 . Both the photovoltaic component  12  and the transistor component  14  are made of organic semiconductor materials that may be ejected onto the substrate by a micro-fluid ejection device.  
         [0018]     A micro-fluid ejection head  40  may be used to eject conductive, semiconductive, and insulative fluids  42  onto a substrate  44  as shown in  FIG. 4 . In a first step of the process, two conductive, non-contacting traces are deposited using a conductive ink onto the substrate  44  to provide the source region  24  and drain region  26  of the transistor ( FIG. 5 ). The substrate  44  may be a flexible or rigid substrate  44  made of a non-conducting material such as paper, plastic film, fiberglass, ceramic, glass, natural or synthetic rubber, and the like. For a flexible switching device  10 , the substrate  44  may be a coated or uncoated paper substrate. The conductive ink providing the source region  24  and drain region  26  may include silver particles, copper particles, carbon particles, and the like, and may be deposited by the micro-fluid ejection process described above. The thickness of the source region  24  and drain region  26  may range from about 20 nm to about 10 microns.  
         [0019]     Next, a polymeric semiconductor layer  46  is deposited by a micro-fluid ejection process onto the substrate  44  so that it covers the source region  24  and the drain region  26 . It will be appreciated that conductive leads  48  and  50  ( FIG. 1 ), not covered by the polymeric semiconductor layer  46 , may be provided for providing electrical contact to the source region  24  and drain region  26 . The polymeric semiconductor layer  46  may include an n-type or p-type polythiophene material as the polymeric semiconductor layer  46 , and may be deposited with a thickness ranging from about 20 nm to about 10 microns.  
         [0020]     A first insulating layer  52  is then deposited by a micro-fluid ejection process on the polymeric semiconductor layer  46 . The first insulating layer  52  has a thickness ranging from about 20 nm to about 10 microns and may be made from an epoxy or acrylic dielectric material or may be a hydrated silicon dioxide that is ejected from a micro-fluid ejection device as an opal fluid.  
         [0021]     A conductive trace providing the gate  22  and containing a conductive lead is then deposited onto a portion of the insulating layer  52 . As with the source region  24  and drain region  26 , the conductive trace providing the gate  22  may be deposited with a conductive ink, as described above using a micro-fluid ejection process. The gate has a thickness ranging from about 20 nm to about 10 microns.  
         [0022]     In order to provide the photovoltaic component  12 , a second insulating layer or substrate  54  is deposited using a micro-fluid ejection process over the gate  22  and first insulating layer  52 . The second insulating layer  54  may be made of the same material as the first insulating layer  52  and may be deposited using a similar micro-fluid ejection process.  
         [0023]     A conductive layer  56  is deposited on the gate  22  and second insulating layer  54  using a micro-fluid ejection process. The conductive layer  56  may also be made of a conductive ink as described above. The thickness of the conductive layer  56  may range from about 20 nm to about 10 microns. The conductive layer  56  may also provide the conductor  20  for electrical contact with a conductive trace providing the gate  22 .  
         [0024]     The photovoltaic component  12  includes an n-type semiconductor layer  58  in contact with a p-type semiconductor layer  60 . The n-type semiconductor layer  58  may be provided by the polythiophene material described above having perfluoroarene groups attached thereto. The thickness of the n-type semiconductor layer  58  may range from about 20 nm to about 10 microns. A micro-fluid ejection process may be used to deposit the n-type semiconductor layer  58 .  
         [0025]     The p-type semiconductor layer  60  is then deposited on at least a portion of the n-type semiconductor layer  58  to provide a P-N junction for the photovoltaic component  12 . The p-type semiconductor layer  60  includes pentacene which is inherently a p-type semiconductor material. As with the n-type semiconductor layer  58 , the p-type semiconductor layer  60  may be deposited using a micro-fluid ejection process.  
         [0026]     Finally, a top electrode layer  62  is deposited onto the p-type semiconductor layer  60  by a micro-fluid ejection process. Top electrode layer  60  is deposited with a thickness that enables light to penetrate the electrode layer and activate the P-N junction of the photovoltaic component  12 . For example, a silver ink may be deposited by a micro-fluid ejection process with a thickness ranging from about 20 nm to about 10 microns to provide a substantially transparent (“translucent”) top electrode layer  62 . In the alternative, at least translucent conductive materials selected from indium tin oxide, zinc oxide, aluminum- or boron-doped zinc oxide, cadmium sulfide, cadmium oxide, tin oxide and fluorine-doped tin oxide may be used as the top electrode layer  62 .  
         [0027]     Organic semiconductor materials and methods for making semiconductor devices using such materials are described for example in U.S. Pat. No. 6,608,323, the disclosure of which is incorporated herein by reference. Drop on demand printing techniques are described for example in U.S. Pat. No. 6,503,831, the disclosure of which is incorporated herein by reference.  
         [0028]     Having described various aspects and embodiments herein and several advantages thereof, it will be recognized by those of ordinary skill that the disclosed embodiments are susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.