Patent Publication Number: US-7898721-B2

Title: Method and device for adjusting driving voltage of microelectromechanical optical device

Description:
BACKGROUND 
     The invention relates to a driving voltage adjusting device and in particular to method and device for adjusting driving voltage of a microelectromechanical optical (MEMO) device and a display using the same. 
     Current thin film technology has enabled the development of sophisticated integrated circuits. This semiconductor technology has also been leveraged to create microelectromechanical structures. Microelectromechanical structures, comprising microsensors, microgears, micromotors, and other microengineered devices, are typically capable of motion or applying force. Currently, microelectromechanical devices are being developed for a wide variety of applications as they provide the advantages of low cost and extremely small size (on the order of microns). For example, microelectromechanical optical (MEMO) devices are employed in display technology. 
     A microelectromechanical optical device, such as an interferometric modulator, comprises an actuator operated by vibration or movement. The actuator, however, may suffer from increased mechanical stress or deterioration of organic material properties when the microelectromechanical optical device is operated for a long time or under various ambient temperature conditions, lowering the performance of thereof and reducing reliability due to an unsuitable driving voltage. 
       FIG. 1  illustrates an interferometric modulator  100 . As shown in  FIG. 1 , the interferometric modulator  100  comprises a transparent substrate  101  and an actuator  107  disposed thereon. The actuator  107  comprises a plurality of top electrodes  102 , a bottom electrode  104 , and a plurality of posts  106 . Each top electrode  102  may be a stack layer disposed on the transparent substrate  101 . For example, the top electrode  102  may comprise an indium tin oxide (ITO) layer and an overlying chromium layer. An insulating layer (not shown), such as a silicon oxide or aluminum oxide layer, is formed on each top electrode  102 . The bottom electrode  104  acts as a mechanical layer for the actuator  107 , comprising aluminum or nickel. The top and bottom electrodes  102  and  104  are separated by the posts  106  comprising, for example, photoresist materials, to form air gaps g therebetween. 
     Visible light may pass through the air gaps g from the transparent substrate  101  and be reflected from the bottom electrode  104 , inducing interference. Visible light with various wavelengths may be formed by the interference and air gaps g to provide visible light with different colors. If a voltage (driving voltage) is applied between one of the top electrodes  102  and the bottom electrode  104 , two electrodes  102  and  104  may make contact, as the right side of the interferometric modulator  100  shown in  FIG. 1 . When this occurs, light cannot pass through the air gap g, resulting in formation of a dark region. As mentioned, when the interferometric modulator  100  is operated under different ambient temperatures, the width of the air gap g may vary with the deteriorated organic material properties of the post  106 . Here, the ambient temperature indicates that the environment temperature of the location where the interferometric modulator  100  is situated. That is, the ambient temperature may vary with different climates or locations. The varied width of the air gap g induces an unstable driving voltage between the top and bottom electrodes  102  and  104 . Additionally, the unstable driving voltage may also be induced because the mechanical stress of the bottom electrode (mechanical layer)  104  is increased with increased operating time of the interferometric modulator  100 . 
     SUMMARY 
     A method and device for adjusting driving voltage of a microelectromechanical optical (MEMO) device and a display using the same are provided. An embodiment of a driving voltage adjusting device for a microelectromechanical optical device comprises a parameter generator for outputting a parameter and a driving device for outputting an adjusting driving voltage to the microelectromechanical optical device according to the parameter. 
     The parameter generator can be a temperature sensor or timer and the parameter can be temperature or time. 
     An embodiment of a method for adjusting a driving voltage of a microelectromechanical optical device is provided. A parameter is generated. The driving voltage of a microelectromechanical optical device is adjusted according to the parameter. 
     An embodiment of a display comprises a microelectromechanical optical device, a parameter generator for outputting a parameter, and a driving device for outputting an adjusting driving voltage to the microelectromechanical optical device according to the parameter. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Method and device for adjusting driving voltage of microelectromechanical optical device will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, given by way of illustration only and thus not intended to be limitative of the invention. 
         FIG. 1  is a cross-section of an interferometric modulator. 
         FIG. 2   a  is a block diagram of a display of an embodiment of the invention. 
         FIG. 2   b  is a block diagram of a display of an embodiment of the invention. 
         FIG. 3  is a flowchart of a method for adjusting a driving voltage of a microelectromechanical optical device of an embodiment of the invention. 
         FIG. 4   a  is a graph showing the relationship between the ambient temperature and the driving voltage of the interferometric modulator. 
         FIG. 4   b  is a graph showing the relationship between the operating time and the driving voltage of the interferometric modulator. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 2   a  and  2   b  illustrate two embodiments of a display  10  of the invention. The display  10  comprises a microelectromechanical optical device  11  and a driving voltage adjusting device  18 . The microelectromechanical optical device  11 , such as an interferometric modulator, activated by vibration or movement, serves as a display device. The driving voltage adjusting device  18  comprises a driving device  12  and a parameter generator. In some embodiments, the parameter generator may comprise a temperature sensor  14  (as shown in  FIG. 2   a ) or a timer  16  (as shown in  FIG. 2   b ). Moreover, the parameter generator is employed to generate a parameter. If the temperature sensor  14  serves as the parameter generator, the parameter is temperature. Conversely, if the timer  16  serves as the parameter generator, the parameter is time. Here, the temperature parameter indicates the ambient temperature of the microelectromechanical optical device  11  and the time parameter the operating time thereof. 
     The driving device  12  outputs an adjusting driving voltage V 1  to the microelectromechanical optical device  11  according to the parameter thereby adjusting the driving voltage. The driving device  12  comprises a storage unit  121  and a control unit  123 . The storage unit  121  is employed to store a look up table. Here, if the temperature sensor  14  serves as the parameter generator, the look up table is a temperature look up table and comprises different ambient temperature conditions of the microelectromechanical optical device  11  and corresponding driving voltages thereof. Conversely, if the timer  16  serves as the parameter generator, the look up table is a time look up table and comprises different operating time conditions of the microelectromechanical optical device  11  and corresponding driving voltages thereof. The temperature look up table is depicted by a graph of the relationship between the ambient temperature and the driving voltage of the interferometric modulator, as shown in  FIG. 4   a . Moreover, the time look up table is depicted by a graph of the relationship between the operating time and the driving voltage of the interferometric modulator, as shown in  FIG. 4   b . The control unit  123  outputs an adjusting driving voltage V 1  to the microelectromechanical optical device  11  according to the temperature look up table and the temperature parameter T 1  generated by the temperature sensor  14  or according to the time look up table and the time parameter t 1  generated by the timer  16 . 
     Note that the driving voltage adjusting device  18  may comprise the temperature sensor  14  and the timer  16 . In this case, the storage unit  121  must store the temperature and time look up tables. Moreover, the control unit  123  may control the driving voltage according to the temperature parameter T 1  generated by the temperature sensor  14  or the time parameter t 1  generated by the timer  16 . 
       FIG. 3  shows a flowchart of a method for adjusting a driving voltage of a microelectromechanical optical device  11  of an embodiment of the invention. In step S 11 , a look up table is stored. For example, a temperature look up table comprising different ambient temperature conditions of the microelectromechanical optical device  11  and the corresponding driving voltages thereof (as shown in  FIG. 4   a ) or a time look up table comprising different operating time conditions of the microelectromechanical optical device  11  and the corresponding driving voltages thereof (as shown in  FIG. 4   b ) is stored in the storage unit  121  of the driving device  12 . In step S 13 , a parameter is generated by a parameter generator. For example, a temperature parameter T 1  is generated by detecting the ambient temperature of the microelectromechanical optical device  11  using the temperature sensor  14  or a time parameter ti generated by counting the operating time of the microelectromechanical optical device  11  using the timer  16 . In step S 15 , the driving voltage of the microelectromechanical optical device  11  is adjusted according to the parameter and the relative look up table. For example, an adjusting driving voltage V 1  is output to the microelectromechanical optical device  11  by acquiring the temperature parameter T 1  and the temperature look up table or acquiring the time parameter t 1  and the time look up table using the control unit  123  of the driving device  12 , thereby controlling the driving voltage of the microelectromechanical optical device  11 . 
     In this embodiment, for example, the driving voltage of the microelectromechanical optical device  11  (interferometric modulator) is about 5V when the display  10  is operated at room temperature (25 C). When the operating environment of the display  10  is changed, the temperature sensor  14  detects the ambient temperature (for example, 45 C) and then outputs the temperature parameter T 1 . Thereafter, the control unit  123  of the driving device  12  outputs an adjusting driving voltage V 1  to the microelectromechanical optical device  11  according to the temperature parameter T 1  and the temperature look up table (as shown in  FIG. 4   a ) stored in the storage unit  121 , thereby adjusting the driving voltage to 4.5 V. 
     Moreover, the driving voltage of the microelectromechanical optical device  11  (interferometric modulator) is about 5V during initial operation of the display  10 . When the operating time of the display  10  is increased, the timer  16  counts the operating time of the microelectromechanical optical device  11  (for example, 400 hr) and then outputs the time parameter t 1 . Thereafter, the control unit  123  of the driving device  12  outputs an adjusting driving voltage V 1  to the microelectromechanical optical device  11  according to the time parameter t 1  and the time look up table (as shown in  FIG. 4   b ) stored in the storage unit  121 , thereby adjusting the driving voltage to 4.4 V. 
     Accordingly, a suitable driving voltage can be output to drive the microelectromechanical optical device when the ambient temperature or operating time of the display  10  is changed. That is, the microelectromechanical optical device can be stably operated, thereby increasing reliability and retarding device deterioration. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.