Patent Publication Number: US-2011069093-A1

Title: Electrophoretic display device

Description:
BACKGROUND 
     1. Related Applications 
     This application is related to copending applications entitled, “ELECTROPHORETIC DISPLAY DEVICE”, filed **** (Atty. Docket No. US29334) 
     2. Technical Field 
     The present disclosure relates to display devices and, more particularly, to an electrophoretic display device. 
     3. Description of Related Art 
     Electrophoretic effects are well known among scientists and engineers, wherein charged particles dispersed in a fluid or liquid medium move under the influence of an electric field. As an example of the application of the electrophoretic effects, engineers try to realize displays by using charged pigment particles that are dispersed and are contained in dyed solution arranged between a pair of electrodes. Under the influence of an electric field, the charged pigment particles are attracted to one of the electrodes, so that desired images will be displayed. The dyed solution in which charged pigment particles are dispersed is called electrophoretic ink, and the display using the electrophoretic ink is called an electrophoretic display (abbreviated as EPD). It is desirable to provide a new type of electrophoretic display device that can display images in purer colors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the electrophoretic display device. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic, cross-sectional view showing an electrophoretic display device in accordance with an exemplary embodiment. 
         FIG. 2  is a schematic, planar view of the electrophoretic display device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     Referring to  FIG. 1 , an electrophoretic display device  10  includes a lower substrate  20 , an electrophoretic ink layer  30 , and an upper substrate  40 . The electrophoretic ink layer  30  is arranged between the lower substrate  20  and the upper substrate  40 , and is electrically connected to the upper substrate  40 . 
     The lower substrate  20  can be made of plastic, or glass. A plurality of thin-film transistors (TFTs)  22  are located on the lower substrate  20 , and a plurality of pixel electrodes  23  are connected between the electrophoretic ink layer  30  and the plurality of the TFTs  22 , therein, each pixel electrode  23  is connected between one TFT  22  and the electrophoretic ink layer  30 . 
     A transparent electrode  42  is formed between the upper substrate  40  and the electrophoretic ink layer  30 , which corresponds to a display surface of the upper substrate  40  to be viewed by a person such as an operator. In the embodiment, the transparent electrode  42  is grounded and is used as a common electrode and can be made of indium tin oxide. 
     The electrophoretic ink layer  30  includes a plurality of tubular cavities  302 . In the exemplary embodiment, the tubular cavities  31  are substantially parallel to each other and are substantially perpendicular to the lower substrate  20  and the upper substrate  40 , and are arranged in a matrix pattern. 
     Each tubular cavity  302  is electrically connected between one pixel electrode  23  and the transparent electrode  42 . Each tubular cavity  302  contains suspension fluid  304  and charged pigment particles  306  dispersed in the suspension fluid  304 . The charged pigment particles  306  include black particles, red particles, green particles, and blue particles. 
     Applying a voltage to the pixel electrodes  23  forms a corresponding electric field between the pixel electrode  23  and the transparent electrode  42 , the charged pigment particles  306  are driven to move to or away from the transparent electrode  42  to form images displayed on the electrophoretic display device  10 . 
     Referring to  FIG. 2 , the tubular cavities  302  are arranged in a matrix pattern and three tubular cavities  302   r ,  302   g , and  302   b  constitute a pixel unit  308 . Each of the tubular cavities  302   r ,  302   g , and  302   b  contain red, green, and blue particles, respectively, and all of the tubular cavities  302  contain black particles. The manner of arrangement of the three tubular cavities  302   r ,  302   g , and  302   b  are not limited. For example, as shown in  FIG. 2 , the tubular cavities  302   r ,  302   g , and  302   b  are arranged from left to right in the pixel in the upper left corner, while the cavities  302   b ,  302   r , and  302   g  are arranged from left to right in the pixel in the lower right corner. 
     The black particles have charge polarity opposite to charge polarity of the red particles, green particles, blue particles, in the embodiment, the red, green, and blue particles are positively charged and the black particles negatively charged. When a positive voltage is applied to the pixel electrode  23 , the red, green, and blue particles are driven to move toward the transparent electrode  42 . The black particles are driven to move toward the pixel electrodes  23 , then the tubular cavities  302   r ,  302   g , and  302   b  display red, green, and blue respectively viewed by a person from the display surface. When a negative voltage is applied to pixel electrode  23 , the black particles are driven move toward the transparent electrode  42 , and the red, green, and blue particles are driven to move toward the pixel electrodes  23 , then the tubular cavities  302   r ,  302   g , and  302   b  display black viewed by a person from the display surface. 
     Referring to  FIG. 1  again, in the embodiment, the electrophoretic display device  10  also includes a gate driver  50  and a source driver  60 . 
     Each TFT  22  includes a control terminal  221 , a first path terminal  222 , and a second path terminal  223 , which terminals are connected to the gate driver  50 , the source driver  60 , and the pixel electrode  23 , respectively. The gate driver  50  is used to turn on or off the TFT  22 , the source driver  60  is used to provided power to the pixel electrode  23  connected to the TFT  22  that is turned on. 
     When the gate driver  50  turns on a TFT  22  the pixel electrode  23  connected to the TFT  22  is connected to the source driver  60  through the TFT  22 . The source driver  60  applies a voltage to the pixel electrode  23  and causes the particles of the tubular cavity  302  corresponding to the pixel electrode  23  to move. The tubular cavity  302  thus displays corresponding color accordingly. For example, if a TFT  22  connected to the tubular cavity  302   r  is turned on and the source driver  60  applies a positive voltage to the pixel electrode  23 , the red particles are driven to move toward the transparent electrode  42  and the tubular cavity  302   r  displays red color. If the source driver  60  applies a negative voltage to the pixel electrode  23 , the black particles are driven to move toward the transparent electrode  42  and the tubular cavity  302   r  displays black. 
     Each pixel unit  308  can display different colors by applying different voltages to the cavities  302   r ,  302   g , and  302   b . The pixel unit  308  can thus display different colors by combining the colors displayed by the tubular cavities  302   r ,  302   g , and  302   b . For example, if tubular cavities  302   r ,  302   g , and  302   b  of a pixel unit  308  displays red, green, and blue, respectively, then the pixel unit  308  displays a mixed color combined with red, green, and blue. If the tubular cavities  302   r ,  302   g , and  302   b  of a pixel unit  308  display red, green, and black respectively, the pixel unit  308  displays a mixed color combined only with red and green. If the tubular cavities  302   r ,  302   g , and  302   b  of a pixel unit  308  display red, black, and black respectively, the pixel unit  308  displays red. If the tubular cavities  302   r ,  302   g , and  302   b  of a pixel unit  308  all display black, then the pixel unit  308  displays black accordingly. 
     In the embodiment, the tubular cavities  302   r ,  302   g , and  302   b  can display colors of different levels by applying voltages with different amplitude. If the gate driver  50  turns on a TFT  22  connected to the tubular cavity  302  and the source driver  60  applies voltage with different amplitude to the pixel electrode  23 . A different amount of particles are driven toward the transparent electrode  42  corresponding to the different voltage amplitude, and the tubular cavity  302  displays color of different level accordingly. 
     In other embodiments, a pulse width modulation driving method may be used. Specifically, by applying driving pulses of different pulse widths to the cavities  302   r ,  302   g , and  302   b , different amount of particles are driven toward the transparent electrode  42 . In yet another embodiment, a pulse rate modulation driving method may be used. Specifically, by applying different numbers of driving pulses to each cavity  302   r ,  302   g , and  302   b , in a finite driving period that is the same for each of the cavities  302   r ,  302   g , and  302   b , different amount of particles are driven toward the transparent electrode  42 . 
     Referring to  FIG. 1  again, in the embodiment, the electrophoretic display device  10  further includes a signal converting unit  70  and a display port  80 . The display port  80  is used to connect with and receive display signal from a computer or other electronic devices. The signal converting unit  70  is connected between the display port  80 , the gate driver  50 , and the source driver  60 . The signal converting unit  70  is used to convert the display signal from the display port  80  to a control signal. In general, the display signal transmitted from the computer or other electronic devices includes clock signal and RGB signal. The signal converting unit  70  converts the clock signal to a scan signal and transmits the scan signal to the gate driver  50 . The signal converting unit  70  also converts the RGB signal to an analog RGB signal and transmits the analog RGB signal to the source driver  60 . 
     The gate driver  50  turns on corresponding TFTs according to the scan signal, and the source driver applies corresponding voltage to the pixel electrodes through the TFT that is turned on. Therefore, as described above, each pixel unit  308  displays corresponding color and all of pixel unit  308  form an image corresponding to the display signal. 
     While various embodiments have been described and illustrated, the disclosure is not to be constructed as being limited thereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the disclosure as defined by the appended claims.