Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-10-18
2001-12-04
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000, C359S295000, C359S224200, C359S230000
Reexamination Certificate
active
06327071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to drive methods of an array-type light modulation element manufactured by micromachining for changing the transmission factor of light by the electromechanical operation and a flat-panel display using the array-type light modulation element and in particular to alternating current (AC) drive of the array-type light modulation element and the flat-panel display.
2. Description of the Related Art
An electromechanical light modulation element for executing light modulation by causing a flexible thin film manufactured by micromachining to perform the mechanical operation by an electrostatic force is known. For example, the light modulation element comprises a flexible thin film made up of a transparent electrode and a diaphragm placed on a fixed electrode on a light waveguide plate via a support.
In the light modulation element, a predetermined voltage is applied across both electrodes, thereby generating an electrostatic force between the electrodes for bending the flexible thin film toward the fixed electrode. The optical characteristic of the element itself changes accordingly and light passes through the light modulation element. On the other hand, the applied voltage is set to zero, whereby the flexible thin film is elastically restored and the light modulation element shields light. Light modulation is thus executed.
By the way, to deform or elastically restore the light modulation element by an electrostatic force, the relationship between applied voltage Vgs and displacement of the flexible thin film shows a hysteresis characteristic. Therefore, the relationship between the applied voltage Vgs and light transmission factor T also shows a hysteresis characteristic as shown in FIG.
30
.
According to the hysteresis characteristic, when the light modulation element is in an OFF state (fight shield), it holds the OFF state if Vgs is Vth(L) or less, and if Vgs becomes Vth(H) or more, the light modulation element holds an ON state. When Vgs is Vth(H) or more, the light modulation element remains in the ON state, and if Vgs becomes Vs(L) or less, the light modulation element becomes saturated to the OFF state. If the polarity of Vgs is negative, the characteristic symmetrical with respect to the vertical axis of the positive polarity results.
However, in the example in the related art, using the characteristic, the light modulation elements are placed in two dimensions and matrix drive is executed, whereby two-dimensional light modulation elements can be formed. As the matrix drive, simple matrix drive and active matrix drive are available and in either drive method, from the above-described modulation element, the matrix can be driven with one polarity of the voltage applied to the modulation element and a DC voltage component is applied to the modulation element.
However, in drive of applying the DC component, if the inside of the flexible thin film is formed of an insulator, there is a possibility that in the structure of electrode-insulator-electrode structure, a parasitic internal electric field, etc., may occur because of an insulation failure caused by migration of the insulator or occurrence/trap of spatial charges, causing the operation to become unstable. For liquid crystal, etc., an AC-drive system is adopted to avoid instability of drive of applying the DC component; particularly, to make the insulator of macromolecule, etc., the possibility that an unstable state will be entered is large.
SUMMARY OF THE INVENTION
To the end, in this invention, there is provided an array-type light modulation element drive method comprising the steps of arranging electromechanical light modulation elements for executing light modulation by displacement operation of a flexible section by an electrostatic force and elastic restoration operation of the flexible section like a two-dimensional matrix, selecting each pixel according to a scan electrode signal, and giving a data signal to a pixel electrode for driving the pixel, wherein an AC signal is applied to electrode of the light modulation element for executing AC drive of the light modulation element.
In the array-type light modulation element drive method, AC drive is adopted, whereby unstable operation caused by occurrence of an internal electric field or an insulation failure caused by migration of an insulator involved in drive with a DC component added can be eliminated.
In this invention, the AC drive of the light modulation element is provided by dividing a basic period of the scan drive signal into an odd frame and an even frame and the polarity of the drive signal is inverted in the odd and even frames.
In the array-type light modulation element drive method, for example, if the drive signal in the odd frame is of positive polarity and the drive signal in the even frame is of negative polarity, the applied voltage to a modulation element becomes AC drive in total of one frame period, and balance can be held.
In this invention, the AC drive of the light modulation element is AC drive in a simple matrix structure of pixels.
In the array-type light modulation element drive method, the light modulation elements in a simple matrix with n rows x m columns can be AC-driven.
In this invention, the AC drive of the light modulation element is AC drive in an active matrix structure of pixels.
In the array-type light modulation element drive method, the light modulation elements in an active matrix with n rows x m columns can be AC-driven.
In this invention, the active matrix structure is any of a mechanical conductive switch type active matrix structure, a mechanical switch type active matrix structure, or a semiconductor switch type active matrix structure.
In the array-type light modulation element drive method, an active matrix with n rows×m columns of mechanical conductive switch type, mechanical switch type, semiconductor switch type, etc., can be AC-driven.
In this invention, the AC drive of the simple matrix structure is to set voltage across electrodes in an even frame, Veven, to the difference between applied voltage maximum value max and voltage across electrodes in an odd frame, Vodd.
In the array-type light modulation element drive method, the polarity of the drive voltage in the even frame can be inverted with respect to the drive voltage in the odd frame in one period for executing AC drive.
According to this invention, there is provided a drive method of a flat-panel display comprising an array-type light modulation element, a surface light source placed facing the array-type light modulation element, and a phosphor disposed on the opposite side to the surface light source with the array-type light modulation element between, the method comprising the steps of driving the array-type light modulation element by a drive method as claimed in any one of claims
1
to
6
and causing the phosphor to emit light for producing display by light emitted from the array-type light modulation element.
In the flat-panel display drive method, the electromechanical array-type light modulation element is AC-driven and the phosphor is caused to emit light for producing display by light source light passing through the array-type light modulation element, so that it is made possible to drive the flat-panel display stably with high definition.
In this invention, the surface light source is a light source for emitting ultraviolet rays for exiting the phosphor.
In the flat-panel display drive method, ultraviolet rays emitted from the surface light source can be allowed to pass through the light modulation element or shielded by the light modulation element for exiting the phosphor to emit light.
REFERENCES:
patent: 5078479 (1992-01-01), Vuilleumier
patent: 5212582 (1993-05-01), Nelson
patent: 5629794 (1997-05-01), Magel et al.
patent: 5708521 (1998-01-01), Jeon et al.
patent: 5710656 (1998-01-01), Goossen
patent: 5745281 (1998-04-01), Yi et al.
Ben Loha
Fuji Photo Film Co. , Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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