JP3726642B2 - Electrostatic actuator, switching element, switching device, image display device, image display apparatus, and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical switching element suitable for optical communication, optical computation, an optical storage device, an optical printer, an image display device, an electrostatic actuator thereof, an image display device using the same, and a control method thereof.
[0002]
[Prior art]
Several methods for expressing multicolor are known. One of them is a three-plate method often used in projectors, etc., which prepares light valves such as a plurality of liquid crystal panels corresponding to each of the three primary colors of light, red, green and blue. Images of different colors are formed separately and synthesized on a screen to express multicolor. A direct-view liquid crystal panel uses a color filter system that can display dots of three primary colors. In this method, three liquid crystal cells having different colors to be expressed are used to express one pixel in multi-color, and multi-color is expressed by spatial color mixture. The other is called a field sequential method, a field sequential method, or a color sequential method, in which light of different colors (usually light of three primary colors) is irradiated in order to represent each color image. Multi-color is expressed by temporal color mixing of human eyes.
[0003]
Compared to parallel additive color mixing using color filters, this frame sequential method can express multi-color with one cell or switching element, so a high-resolution image can be obtained, and the driver circuit that drives the switching element becomes smaller. Since the color filter is not necessary, the image display device can be reduced in size and a high-quality image can be expressed. Furthermore, since the illuminance, brightness, or time for each color can be easily adjusted, there are many advantages such as easy adjustment of the color balance.
[0004]
[Problems to be solved by the invention]
However, in the frame sequential method, since it is necessary to rewrite an image for each color, it is necessary to take time to write the image of that color in a light valve such as a liquid crystal before irradiating light of that color. That is, in an active matrix type liquid crystal panel, it is necessary to rewrite data of liquid crystal cells arranged in the horizontal direction for each horizontal scanning line (address line), and there are 500 or more scanning lines in one frame (screen). . Accordingly, it is necessary to perform an operation in which an image is displayed by applying a certain color of light, and then the light is blocked by a shutter or the like, and the light of the next color is applied after rewriting one frame. For this reason, it is difficult to realize an image display device that displays a compact and bright image because the light use efficiency is lowered. Further, if an attempt is made to display a high-quality image that does not generate flicker or the like, it is time-consuming. A control circuit and a light valve with high resolution are required. On the other hand, it has been studied to divide one frame into a plurality of fields and display them in different colors in order, but this is not a fundamental solution.
[0005]
Furthermore, if a multi-tone screen is to be expressed by time division, a screen with higher temporal resolution is required. On the other hand, if the liquid crystal is used as a light valve, the response speed is about several milliseconds, so that it is difficult to express a multi-tone image by the frame sequential method.
[0006]
For this reason, a device having a response speed faster than that of liquid crystal is demanded. One of them is a device that modulates incident light by moving an optical element having a reflection function or a transmission function substantially in parallel by an actuator. The evanescent light is extracted by bringing the extraction surface of the switching unit into contact with the total reflection surface of the light guide unit, which the applicant of the present application has applied for and can transmit light by total reflection, and about one wavelength or less of the optical element. One of them is an optical switching device capable of modulating and controlling light at a high speed by a minute movement of.
[0007]
FIG. 1 shows an outline of the above-described frame sequential method (color sequential method) projector 80 as an example of an image display device using an image display device (optical switching device) that performs switching by evanescent light. The projector 80 includes a white light source 81, a rotary color filter 82 that splits the light from the white light source 81 into three primary colors and makes the light incident on the light guide plate (light guide) 1 of the image display unit (light switching unit) 55, An image or image display unit 55 that modulates and emits light of each color and a projection lens 86 that projects the emitted light 85 are provided. Then, the modulated light 85 for each color is projected onto the screen 89 and mixed with time to output a multi-tone multicolor image. The projector 80 further includes a control circuit 84 that controls the image display unit 55 and the rotating color filter 82 to display a color image. The image display unit 55 includes a light guide 1 and an image display device (light switching device) 50 described in detail below. Data φ for displaying a color image from the control circuit 84 is an image display device. 50.
[0008]
As described above, the projector 80 shown in FIG. 1 includes the light source 81 that supplies light for projection to the light guide 1 that transmits light while totally reflecting the light, and the lens 85 that projects the light emitted from the light guide 1. And an image display device 50 that modulates the projection light supplied to the light guide 1. The evanescent light leaks from the light guide 1 by the image display device 50. An image is displayed by controlling the light.
[0009]
Figure 2 shows the Eva Ne An outline of an image display device (evanescent light switching device) 50 that modulates light using a cent wave (evanescent light) is shown. The image display device 50 is a switching device (optical switching device) in which a plurality of optical switching elements (optical switching mechanisms) 10 are two-dimensionally arranged, and each optical switching element 10 alone transmits all the light 2 introduced. An optical element (switching unit) 3 capable of modulating light by approaching and separating from a light guide plate (light guide) 1 that can be reflected and transmitted, and an actuator 6 that drives the optical element 3 are provided. Then, the layer of the optical element 3 and the layer of the actuator 6 are stacked on the semiconductor substrate 20 on which the drive circuit for driving the actuator 6 and the digital storage circuit (storage unit) are built, and are integrated as one image display device. Has been.
[0010]
The image display device 50 of this example using evanescent light will be described in more detail with reference to FIG. Describing based on the individual optical switching elements 10, the optical switching element 10a shown on the left side of FIG. 2 is in the on state, and the optical switching element 10b shown on the right side is in the off state. The optical element 3 has a surface (contact surface or extraction surface) 3a that is in close contact with the surface (total reflection surface) 1a of the light guide plate 1 that functions as a waveguide, and the surface 3a is in close contact with the total reflection surface 1a. A V-shaped reflecting prism (microprism) 4 that extracts the leaked evanescent wave and reflects it in a direction substantially perpendicular to the light guide plate 1 inside, and a support structure 5 that supports the V-shaped prism 4; It has.
[0011]
The actuator 6 is of a type that electrostatically drives the optical element 3. For this purpose, the movable electrode 9 that is mechanically connected to the support structure 5 of the optical element 3 and moves with the optical element 3, and the movable electrode 9 is totally reflected. The upper electrode (first fixed electrode) 7 disposed so as to be driven in the direction of the surface 1a (hereinafter, upward or in the first direction) and the movable electrode 9 are all disposed at a position facing the upper electrode 7. A lower electrode (second fixed electrode) 8 is provided so as to be driven in a direction opposite to the reflecting surface 1a (hereinafter, downward or second direction).
[0012]
The semiconductor substrate 20 is provided with a drive circuit 21 for driving the optical element 3 by supplying a voltage to these electrodes 9, 7 and 8. For example, the upper electrode 7 is biased to a high potential, the lower electrode 8 is biased to a low potential (ground potential), and a low potential and a high potential are supplied to the movable electrode 9 as drive voltages, whereby the optical element 3 is totally reflected by electrostatic force. It can be moved to a first position in contact with the surface 1a and a second position away from the total reflection surface 1a.
[0013]
As shown in FIG. 2, the illumination light 2 is supplied from the light source to the light guide plate 1 at an angle at which it is totally reflected by the total reflection surface 1a, and all the interfaces inside it, that is, the optical element section (light switching section). ) The light is repeatedly totally reflected on the side 1a facing 3 and the upper surface (outgoing surface), and the light guide plate 1 is filled with light. Accordingly, in this state, the illumination light 2 is macroscopically confined inside the light guide plate 1 and propagates through the light without loss. On the other hand, microscopically, in the vicinity of the totally reflecting surface 1a of the light guide plate 1, the illumination light 2 is once leaked from the light guide plate 1 by a very small distance of the wavelength of light, and the course is changed. The phenomenon of returning to the inside of the light guide plate 1 again occurs. The light leaking from the surface 1a is generally called an evanescent wave. The evanescent wave can be extracted by bringing another optical member closer to the total reflection surface 1a at a distance of about the wavelength of light or less. The optical switching element 10 of this example utilizes this phenomenon to modulate, that is, switch (on / off) the light transmitted through the light guide plate 1 at high speed.
[0014]
For example, in the optical switching element 10a of FIG. 2, since the optical element 3 is in the first position in contact with the total reflection surface 1a of the light guide plate 1, an evanescent wave can be extracted by the surface 3a of the optical element 3. For this reason, the angle of the light 2 extracted by the microprism 4 of the optical element 3 is changed to become outgoing light 2a. The emitted light 2a is used as projection light 85 of the projector 80 shown in FIG. On the other hand, in the optical switching element 10b, the optical element 3 is moved to a second position away from the light guide plate 1. Therefore, no evanescent wave is extracted by the optical element 3, and the light 2 does not exit from the inside of the light guide plate 1.
[0015]
An optical switching element using an evanescent wave functions as a device capable of switching light alone, but as shown in FIG. 2, a configuration in which these can be arranged side by side in a one-dimensional or two-dimensional direction, or even in a three-dimensional manner. It has become. In particular, by arranging two-dimensionally in a matrix or array, a video device or image display unit 55 that can display a planar image in the same manner as a liquid crystal or DMD can be provided. In the image display device 50 using evanescent light, the moving distance of the optical element 3 serving as a switching unit is on the order of submicrons, so that it can be used as a light modulation device having a response speed one digit or more faster than that of liquid crystal. It is possible to provide a projector 80 or a direct-view type image display device capable of high-speed operation using the. Furthermore, the optical switching element 10 using evanescent light can turn on and off light almost 100% with submicron order motion, and can express a very high contrast image. For this reason, it is easy to increase the temporal resolution, and a high-contrast image display apparatus can be provided.
[0016]
Further, in this optical switching device 50, the image display device 50 having a configuration in which the actuators 6 and the optical elements 3 arranged in an array are stacked on the semiconductor integrated substrate 20 on which a drive circuit and the like are built is provided in one chip. It is possible. That is, the image display unit 55 can be supplied by assembling the image display device 50 and the light guide 1 which are a micromachine or an integrated device in which a microstructure such as the actuator 6 and the optical element 3 is constructed on the semiconductor substrate 20. By incorporating the projector, it is possible to provide a projector capable of displaying a high-contrast image with high operation speed and high resolution.
[0017]
FIG. 3 schematically shows how the drive circuits 21 are arranged in an array or matrix on the semiconductor substrate 20 in accordance with the layout of the switching element 10. The address signal φa is supplied to these drive circuits 21 via address lines 44 in which the drive circuits 21 of the light modulation units arranged in the row direction (left and right direction in FIG. 3) are connected in parallel by the address line driver circuit 45. They are sequentially supplied in the direction (vertical direction in FIG. 3). Further, the data line driver circuit 46 supplies data of each drive circuit 21 via the data line 41 in which the drive circuits 21 of the light modulation units arranged in the column direction are connected in parallel. Then, the data signal φd is latched in the corresponding drive circuit 21 by the address signal φa supplied in synchronization with the data signal φd supplied to the data line 41, whereby a signal for driving the actuator 6 is transferred to the movable electrode 9. To be supplied. On the other hand, bias voltages of high voltage Vh and low voltage Vg are supplied to the upper electrode 7 and the lower electrode 8 of each switching element 10 through voltage supply lines 47 and 48, and the movable electrode 9 is supplied from the drive circuit 21. The optical element 3 which is a switching unit is moved by the driving voltage supplied to, and the incident light is on / off controlled.
[0018]
Therefore, the drive circuit 21 needs a storage element that holds the supplied data signal φd until the data signal is supplied at the next timing. The drive circuit 21 shown in FIG. 4A is a circuit using a capacitor 22 inserted in parallel with the optical switching element 10 as a sample hold. The switching element 23 serving as a gate is controlled to be turned on and off by an address signal φa. The data signal φd supplied at a proper timing is held in the capacitor 22.
[0019]
In FIG. 2, an evanescent light switching element having upper and lower electrodes, that is, a first fixed electrode 7 and a second fixed electrode 8 is described as an example, but the movable electrode 9 is moved to the first position. A switching element of the type driven by elasticity is also possible, an example of which is shown in FIG. The actuator 6 of the optical switching element 10 of this example is provided with a second fixed electrode 8 that drives the movable electrode 9 downward, that is, to the second position. Therefore, when ON 10a, the optical element 3 is driven to the first position by the elasticity of the movable electrode 9, and contacts the total reflection surface 1a of the light guide. When it is off 10b, the optical element 3 is driven to the second position by the electrostatic force of the actuator 6 and moves away from the total reflection surface 1a of the light guide.
[0020]
The optical switching element 10 shown in FIG. 5 can also be made into a device that displays an image by arranging it in a matrix or array as shown in FIG. And it can drive by the drive circuit 21 shown to Fig.4 (a). However, as described above, in the frame sequential method, it is necessary to rewrite an image for each color. Therefore, in order to omit the operation of applying the next color light after rewriting one frame, a two-stage memory as shown in FIG. 4B is required. The drive circuit 21 shown in FIG. 4B is a two-memory type drive circuit proposed by the applicant of the present application. This drive circuit 21 is a loop-connected set of so-called SRAM circuit forms. In addition to the capacitor 22, another memory is configured by the inverters 24a and 24b. Therefore, data signal φd supplied from data lines 41a and 41b by address signal φa is once stored in a memory constituted by inverters 24a and 24b. Thereafter, the switching element 25 is operated by the frame sequential signal φs supplied in synchronization with the frame rewrite timing and the like, and the data signal φd latched in the memory is supplied to the capacitor 22 and the optical switching element 10 which are sample and hold. The optical switching element 10 is driven by the data signal φd.
[0021]
As described above, the drive circuit provided with two storage elements can latch the next image data while displaying an image, and the entire screen can be rewritten in one clock. . Therefore, in the image display apparatus that displays multi-colors by the above-described frame sequential (color sequential) method, an effect such as an improvement in light utilization efficiency can be obtained, and a bright high-resolution image can be displayed.
[0022]
However, it is necessary to dispose two storage elements, a switching element for transferring and latching data to them, and a control wiring for controlling them on the semiconductor substrate. Therefore, if the switching element 10 is miniaturized, there is a high possibility that it is difficult to arrange these elements and wiring. In addition, even if it is possible to build a circuit by applying a miniaturization rule to a semiconductor substrate at a high manufacturing cost, an actuator or an optical element is manufactured when manufacturing an actuator and an optical element on a semiconductor substrate on which a circuit is formed. If there is a defect in the optical element, an expensive semiconductor substrate is wasted and the manufacturing cost of the image display device becomes very high. Therefore, it is clear that a device having a plurality of memories per switching element is desirable in order to support the frame sequential method, but there is a trade-off relationship between miniaturization and cost reduction of the device. A configuration that satisfies the above is not disclosed.
[0023]
Therefore, in the present invention, by storing the state of the switching element without increasing the number of storage elements, the switching device can be adapted to the field sequential method, and can be reduced in size and cost, and an electrostatic actuator suitable for the switching device. It is another object of the present invention to provide an image display device and an image display apparatus using these. Moreover, it aims at providing the control method suitable for these electrostatic actuators, a switching device, and an image display device.
[0024]
It is another object of the present invention to provide a compact and bright image display device capable of displaying a multi-tone multicolor image by a frame sequential method.
[0025]
[Means for Solving the Problems]
Therefore, in the present invention, since the movable electrode moves to the first and second positions by the driving potential, it is used as a switching means, and the movable electrode is held at the position where the movable electrode is driven. The potential is automatically supplied. That is, in the electrostatic actuator that drives the switching unit that can move to the first position of the present invention and the second position separated from the first position by the electrostatic force acting between the electrodes, the switching unit is driven. Movable electrode and this movable electrode The direction of the first position or the direction of the second position opposite to each other Arranged to drive to A fixed potential is supplied The fixed electrode and the movable electrode are in contact with each other at the first or second position where the fixed electrode is disposed. Is electrically connected to the movable electrode Holding electrode and Driving means capable of applying a driving potential having a different polarity to the movable electrode; and holding means capable of applying a holding potential having the same polarity as the driving potential when the movable electrode contacts the holding electrode to the holding electrode; Have
--
[0026]
With the electrostatic actuator of the present invention, the driving means capable of applying a driving potential having a different polarity to the movable electrode, and the holding electrode having the same polarity as the driving potential when the movable electrode is in contact with the holding electrode By providing holding means capable of applying a potential, for example, when the movable electrode is driven to the first position by the first driving potential, the first driving potential from the holding electrode that contacts at the first position. Can be supplied. For this reason, even if the driving potential is not supplied from the driving means, the state can be maintained. Conversely, even when driven to the second position by the second drive potential, the second drive potential can be supplied from the holding electrode in contact with the second position, and the drive means can drive the drive potential. Even if is no longer supplied, the state can be maintained.
[0027]
As described above, the actuator is not limited to the actuator having the first fixed electrode and the second fixed electrode for driving the movable electrode in the first and second directions, but the movable electrode itself may be used. The present invention can also be applied to an actuator provided with an elastic means for driving at a position of 2 and the fixed electrode being an actuator provided to drive the movable electrode in the direction of the second position.
[0028]
Therefore, in the electrostatic actuator of the present invention, it is possible to provide the driving means with a driving mode in which a driving potential is applied to the movable electrode and a holding mode in which the movable electrode is opened. By setting the holding mode in the drive mode and setting the holding means in the drive mode until the reset mode appears The state of the actuator is maintained. For this reason, the actuator itself can be used as one memory.
[0029]
By simultaneously shifting from the holding mode to the drive mode and from the reset mode to the set mode with the same clock, the movable electrode and the destination holding electrode are at the same potential, so there is no short circuit and a large current flows. Absent. However, in the reset mode, a large current does not flow even if the drive mode and the set mode are not synchronized by opening the holding electrode. In addition, since the holding electrode to which the movable electrode moves does not have to have the same potential, the electrostatic force of the holding electrode does not become a resistance.
[0030]
Therefore, the actuator of the present invention includes a driving process in which driving voltages having different polarities are applied to the movable electrode, a holding process in which the movable electrode is opened, and the movable electrode when the movable electrode is in contact with the holding electrode. It has a setting process for applying a holding voltage having the same polarity as the driving voltage, and a resetting process for applying no holding voltage to the holding electrode, and the control is performed by a control method characterized in that the setting process is performed between the driving processes. be able to. With this control method, as described above, the electrostatic actuator itself can be used as a memory. That is, by performing the setting process during the driving process, the potential of the movable electrode is maintained through the holding electrode even if the process proceeds to the holding process. State is maintained or maintained. On the other hand, since the potential of the movable electrode is not applied from the holding electrode during the reset process, the movable electrode moves according to the drive voltage in the drive process. Therefore, during the reset process, the gate for writing data to the memory is in an open state, and the movable electrode is moved by the drive voltage, and by moving to the set process, the moved position of the movable electrode is changed to the selected drive voltage. The state is stored in the electrostatic actuator.
[0031]
As described above, in the electrostatic actuator of the present invention, the electrostatic actuator itself can be used as a memory. Therefore, by preparing one memory in the drive circuit, therefore, when controlling in units of screens, it is retained. In the process, the data is sequentially stored in the memory by the scanning lines, and the movable electrode can be moved by one clock so as to reflect the data supplied at the color sequential timing in the subsequent driving process.
[0032]
That is, the electrostatic actuator of the present invention can be controlled in the same manner as the switching element controlled by the drive circuit having the two memories described above, by providing only one memory or sample hold. Furthermore, by adopting the present invention, two memories and switches and drive lines for transferring data to these memories become unnecessary in the drive circuit. Therefore, the circuit as the driving means can be extremely simplified and can be compactly integrated. Further, in a device in which driving means are arranged in an array or the like, it is not necessary to provide a connection line (scanning line or data line) for performing control for transferring data between memories to the driving means. Therefore, it is possible to provide an electrostatic actuator that can cope with the frame sequential method and can be further reduced in size and cost.
[0033]
By combining the electrostatic actuator of the present invention and the switching unit driven by the electrostatic actuator, a compact switching element using the electrostatic actuator as a memory function can be provided at low cost. In addition, the switching unit can be a switching element that modulates light at the first or second position, one of which is an optical switching element using evanescent light that has been filed by the present applicant. . That is, the switching element further includes a light guide unit having a total reflection surface capable of transmitting the input light by total reflection, and the switching unit extracts the evanescent light leaking from the total reflection surface at the first position. The present invention can be applied to.
[0034]
Furthermore, it is possible to provide a switching device (image display device) capable of displaying an image by arranging a plurality of these switching elements in an array, and the actuator of the switching element constituting each pixel has one memory. Since it operates as a function, it is very easy to provide two memory functions. Since only one set of capacitor or SRAM serving as a sample and hold is provided in the driving means in order to incorporate two memory functions, the circuit configuration as the driving means is simplified and compact, A semiconductor device can be provided at low cost. Therefore, the yield can be improved and the product cost can be reduced. A compact image display device having two memory functions for each pixel can be provided.
[0035]
In this image display device, it is possible to apply a holding voltage to the electrostatic actuators of switching elements arranged in an array at the same timing, and to reset and set the same, after supplying display data, the same It becomes possible to switch the display of the full screen at the timing. Therefore, in the surface sequential display method in which the light for each color is irradiated in order, it is possible to instantaneously switch the screen for each color, the light use efficiency can be improved, and a bright image can be displayed.
[0036]
It is also possible to reset and set by applying a holding voltage to the electrostatic actuators of switching elements arranged in a line at the same timing. Such an image display device can be applied to the field sequential display method in the same manner as described above, and can set the timing for setting or resetting pixels for each scanning line separately from the timing for supplying data. . Accordingly, the pixel display time can be defined at the timing of setting or resetting, and the state of the pixel can be controlled flexibly which cannot be realized by a conventional image display device.
[0037]
Then, it is possible to provide an image display apparatus according to the present invention such as a projector having these image display devices and means for inputting / outputting projection light to / from the image display devices, as described above. The image display device can be made compact and low in cost, and can be adapted to high-speed frame sequential display. Therefore, it is possible to provide an image or video display device that is low-cost, compact, and capable of displaying a brighter image.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 6 schematically shows an optical switching unit according to an embodiment of the present invention. The switching unit 55 of this example is a unit that adopts evanescent light as described above with reference to FIG. 5 and includes a light guide (light guide) 1 and a switching device 50. The switching device 50 is an image display device in which the switching elements 10 are two-dimensionally arranged in an array, and each switching element 10 is composed of an optical element 3 that is a switching unit and an actuator mechanism 6 that drives the semiconductor element. The configuration is laminated on the substrate 20.
[0039]
A circuit 21 for driving each actuator mechanism 6 is formed on the semiconductor substrate 20. Hereinafter, the actuator mechanism 6 and the drive circuit 21 will be referred to as an actuator 60. As described with reference to FIG. 5, the actuator mechanism 6 of the present example includes the movable electrode (intermediate electrode) 9 and the fixed electrode 8 for driving the movable electrode 9 to the off position (second position). ing. The movable electrode 9 has elasticity, and is driven to the ON position (first position) by this elasticity. Therefore, the actuator 60 of this example is an electrostatic drive type actuator that drives the movable electrode 9 and the optical element 3 connected thereto by the electrostatic force generated by the drive voltage supplied to the movable electrode 9 by the drive circuit 21. is there.
[0040]
The detailed configuration of the optical switching element 10 of this example and the mechanism for turning on and off the light have been described in detail with reference to FIG. The optical switching element 10 constituting the image display device 50 of this example includes holding electrodes 62 positioned on both sides of the fixed electrode 8 as one of the actuator mechanisms 6. Therefore, as shown in the switching element 10b of FIG. 6, when the actuator mechanism 6 moves to the second position below, the optical element 3 moves away from the total reflection surface 1a, the switching element 10 is turned off, and the movable electrode 9 The dimples 13 projecting downward from both ends of the contact with the holding electrode 62, and the holding electrode 62 and the movable electrode 9 are electrically connected. Therefore, in this example, the dimple 13 protruding downward from the movable electrode 9 has a function of preventing the movable electrode 9 from coming into contact with the fixed electrode 8 and short-circuiting, and the movable electrode 9 and the holding electrode 62 are electrically connected. It has the function to do. On the other hand, as shown in the switching element 10a of FIG. 6, when the actuator mechanism 6 moves to the first upper position, the optical element 3 comes into contact with the total reflection surface 1a, the switching element 10 is turned on, and the movable electrode 9 is turned on. Is away from the holding electrode 62.
[0041]
Furthermore, the optical switching element 10 of this example includes a holding circuit 65 that controls the voltage supplied to the holding electrode 62 in addition to the driving circuit 21, and is a circuit that constitutes the actuator 60 that drives each optical element 3. It is one. The holding circuit 65 supplies a voltage when the movable electrode 9 is driven in the direction of the fixed electrode 8 to the holding electrode 62 at an appropriate timing. In the following, the fixed electrode 8 is fixed to a low voltage (ground potential) Vg, and the movable electrode 9 is moved to the fixed electrode 8 side by supplying a high voltage Vh (indicated by + in the drawing) to the movable electrode 9. The movable electrode 9 is driven to the light guide 1 side (first position) by driving to the second position and supplying a low potential Vg (also indicated by G in the figure). Therefore, the holding circuit 65 of this example supplies the holding voltage of the high voltage Vh to the holding electrode 62 at an appropriate timing. Hereinafter, a state in which the holding voltage is supplied to or applied to the holding electrode 62 is referred to as a set mode.
[0042]
Furthermore, the holding circuit 65 has a function of holding the holding electrode 62 in an open state (indicated by Z in the figure) by opening the holding electrode 62 from the high potential or low potential supply side. Hereinafter, the state in which the holding electrode 62 is opened is referred to as a reset mode. In addition to the mode (drive mode) in which the drive voltage 21 of the movable electrode 9 supplies the low potential Vg and the high potential Vh, the drive circuit 21 in this example has a holding mode in which the potential is undefined by opening the movable electrode 9. I have. As will be described later, the actuator mechanism 6 can be used as a memory by combining the set and reset modes with the drive and hold modes.
[0043]
This will be described in more detail with reference to the timing charts shown in FIGS. The timing chart shown in FIG. 7 is an example of changing from black display (off position, second position) to white display (on position, first position). The potential of the fixed electrode 8 is held at the ground potential Vg (G), and at time t1, the high potential Vh (+) is supplied from the drive circuit 21 to the movable electrode 9, and the movable electrode 9 moves to the off position. At this time, the holding electrode 62 is open Z, and the potential is indefinite. However, the movable electrode 9 is moved by the electrostatic force of the movable electrode 9 and the fixed electrode 8, and the optical element 3 is driven to the second position by the actuator mechanism 6. Therefore, time t1 is the timing for writing data. The movable electrode 9 is in contact with the holding electrode 62 at the second position. However, since the holding electrode 62 is open Z, the electric potential hardly flows though the potential becomes high.
[0044]
At time t <b> 2, the high potential + is supplied from the holding circuit 65 to the holding electrode 62 and becomes the same potential as the movable electrode 9. Further, since the movable electrode 9 and the holding electrode 62 are electrically connected, the potential of the movable electrode 9 is held thereafter even when the movable electrode 9 is opened. Therefore, this timing is locked.
[0045]
For this reason, even if the movable electrode 9 becomes open Z at time t3, the substantial potential of the movable electrode 9 is held by the holding electrode 62. Therefore, the actuator composed of the movable electrode 9, the fixed electrode 8 and the holding electrode 62 serves as a memory, and the state of the movable electrode 9 can be stored without preparing an element serving as a memory in the drive circuit 21.
[0046]
On the other hand, when the holding electrode 62 is opened at time t4, the potentials of the movable electrode 9 and the holding electrode 62 become indefinite. In many cases, since the electric charge is held as it is when it is completely open, the same state as at time t3 is preserved. On the other hand, when new data is written to the movable electrode 9 at time t5, an operation corresponding to the new data is performed. In this example, when the low potential G is supplied from the drive circuit 21 to the movable electrode 9 at time t5, the movable electrode 9 is moved upward by the spring elasticity of the movable electrode itself or a member supporting the movable electrode 9 (first side). The switching element 10 is turned on.
[0047]
At the timing of locking at time t6, the potential of the holding electrode 62 becomes the high potential +. However, since the movable electrode 9 is not in contact with the holding electrode 62, the potential of the movable electrode 9 is not affected. Even when the movable electrode 9 becomes open Z at time t7, the potential of the holding electrode 62 is not applied, and the ON state is maintained by the elasticity of the movable electrode 9.
[0048]
In the optical switching element 10 of this example, the time t1 to t3 and the time t5 to t7 are drive modes in which a G or + drive potential is applied to the movable electrode 9, and the time t3 to t5 and the time t7 and subsequent are movable. This is a holding mode in which the electrode 9 is open Z. From time t2 to t4 and after time t6 correspond to the set mode in which the holding electrode 62 becomes the holding potential (high potential in this case), and from time t4 to t6 correspond to the reset mode in which the holding electrode 62 becomes open Z. . A driving voltage is applied to the movable electrode 9 in the driving mode, and then the holding potential is supplied to the holding electrode 62 in the set mode after the movable electrode 9 moves. By such a control method, the holding voltage corresponding to the drive voltage for moving to the position is supplied to the movable electrode 9 from the holding electrode 62 at the moved position. Therefore, even if the drive voltage is not supplied from the drive circuit 21 (holding mode), the position of the movable electrode 9 can be held until the holding voltage is not supplied (reset mode).
[0049]
As described above, the actuator 60 of this example and the optical switching element 10 using the actuator 60 include the actuator mechanism 6 that can be used as switching for supplying a voltage for holding the movable electrode itself to the movable electrode 9. The position of the movable electrode 9 moved by the drive circuit 21 can be latched on the actuator mechanism 6 side. Therefore, if an element to be a memory, such as a storage capacitor or an SRAM, is prepared in the drive circuit 21, the movable electrode 9 is opened so that the state of the movable electrode 9 is not affected and the next memory is inserted into the memory. Data can be latched.
[0050]
The timing chart shown in FIG. 8 is an example in which the color of the pixel formed by the optical switching element changes from black display (second position) to black display (second position). Also in this example, when a high potential + that is black is supplied to the movable electrode 9 at time t11, black display is performed. At time t12, the holding potential + is supplied to the holding electrode 62, and the movement of the movable electrode 9 is performed. Locked. Therefore, even when the potential of the movable electrode 9 becomes indefinite Z at time t13, the state of the movable electrode 9 is maintained. Further, even if the holding electrode 62 becomes open Z at time t14, if the charge at the previous timing is stored, the potential of the movable electrode 9 is maintained at the high potential +, and the state of the switching element 10 is maintained. Is done. Then, when the high potential + which is displayed black again is written at time t15 during reset, the switching element 10 is displayed black and is locked again at time t16, and the movable electrode 9 is opened Z at time t17. Even then, there is no change in the states of the actuator mechanism 6 and the optical switching element 10.
[0051]
The timing chart shown in FIG. 9 is an example in which the color of the pixel formed by the optical switching element changes from white display (first position) to black display (second position). In this example, when the low potential G that is white display is supplied to the movable electrode 9 at time t21, white display is performed. Even if the holding potential + is supplied to the holding electrode 62 at time t22, the movable electrode 9 is The movement is locked by the elasticity of the movable electrode 9 without being affected by the influence. Therefore, even when the potential of the movable electrode 9 becomes indefinite Z at time t23, the state of the movable electrode 9 is maintained. On the other hand, when the high potential + that is displayed in black is written at time t25, the switching element 10 is displayed in black, and when the holding potential + is supplied to the holding electrode 62 at time t26, the state is locked in that state. Even if the movable electrode 9 becomes open Z at t27, the states of the actuator mechanism 6 and the optical switching element 10 are not changed.
[0052]
The timing chart shown in FIG. 10 is an example in which the color of the pixel formed by the optical switching element changes from white display (first position) to white display (first position). Also in this example, when the low potential G that is white display is supplied to the movable electrode 9 at time t31, white display is performed, and even if the holding potential + is supplied to the holding electrode 62 at time t32, the movable electrode 9 The movement is locked by the elasticity of the movable electrode 9 without being affected. Therefore, even when the potential of the movable electrode 9 becomes indefinite Z at time t33, the state of the movable electrode 9 is maintained. Even when the holding electrode 62 becomes open Z at time t34, the state of the switching element 10 is held because the state of the movable electrode 9 is maintained by its own elasticity. When the low potential G for white display is written again at time t35 during reset, the switching element 10 maintains white display, and the state does not change even if it is locked again at time t36. Even if the movable electrode 9 becomes open Z at time t37, the states of the actuator mechanism 6 and the optical switching element 10 are not changed.
[0053]
As shown in these timing charts, in the optical switching element 10 of this example, the state of the movable electrode 9 at that time is maintained by supplying the holding potential to the holding electrode 62 in all states. Can do. In this example, the holding electrode 62 is opened in the reset mode. On the other hand, it is also possible to apply a reverse potential to the holding electrode 62 at the time of resetting. FIG. 11 shows a timing chart when such control is performed. In this example, the black display is changed to the black display. However, in the case of applying a reverse polarity potential in the reset mode, the holding electrode 62 holds the holding electrode 62 unless the holding potential is applied to the holding electrode 62 at the writing timing. There is a possibility that an excessive current flows in the electrode 62. Therefore, first, at time t41, the high potential + is supplied to the movable electrode 9, and the holding potential + is also supplied to the holding electrode 62 to lock the writing simultaneously. Even when the movable electrode 9 becomes open Z at time t43, the state of the movable electrode 9 is maintained by the holding potential supplied from the holding electrode 62. On the other hand, when the reset mode is entered at time t44, since the holding electrode 62 becomes low potential G, the potential of the movable electrode 9 also temporarily becomes low potential G and moves in the direction of white display. When a high potential + that causes black display is written to the electrode 9, black display is again performed. Since the holding electrode 62 is also at the holding potential +, the state is locked.
[0054]
Except for the case where the black display is changed to the black display, the white display for only one clock in the reset mode does not cause a problem. Further, white display in the reset mode when black display continues leads to a decrease in contrast, but this influence can be almost eliminated by shortening the reset time. That is, the extraction efficiency of evanescent light depends on the distance between the extraction surface 3a of the prism 4 and the total reflection surface 1a, so that writing can be performed before the distance between the extraction surface 3a and the total reflection surface 1a is reduced to the distance for evanescent coupling. In this case, the reset mode time is very short, and a reduction in contrast can be prevented. Further, in the reset mode, the contact between the holding electrode 62 and the movable electrode 9 is once removed, and the polarity of the movable electrode 9 can be changed during that time, so that the pixels are not short-circuited via the holding electrode 62. Therefore, the holding electrode 62 does not need to be electrically independent for each pixel, and can be made common to all pixels.
[0055]
Thus, the state of the actuator mechanism 6 can be locked by supplying the holding potential to the holding electrode in the set mode without necessarily opening the holding electrode in the reset mode. In the above example, the state is locked using the elasticity of the movable electrode 9 in the on position (first position), but it is also possible to lock using the holding electrode.
[0056]
FIG. 12 is an example in which the present invention is applied to the optical switching element 10 having the upper and lower fixed electrodes 7 and 8 shown in FIG. 2, and the movable electrode 9 is located at the second position driven by the fixed electrode 8. In addition to the holding electrode 62 that contacts when the movable electrode 9 moves, a holding electrode 61 that contacts when the movable electrode 9 moves to the first position driven by the fixed electrode 7 is provided. A holding potential is supplied from the holding circuit 65 to the holding electrodes 61 and 62 at an appropriate timing. Hereinafter, similarly to the above, it is assumed that the lower electrode 8 is fixed at the low potential G and the upper electrode 7 is fixed at the high potential +. Therefore, when the movable electrode 9 is at the low potential G, the movable electrode 9 is driven in the direction of the upper electrode 7. Accordingly, the lower holding electrode 61 is supplied with the low potential G as the holding potential. On the other hand, since the movable electrode 9 is driven in the direction of the lower electrode 8 when the movable electrode 9 is at the high potential +, the lower holding electrode 62 is supplied with the high potential + as the holding potential.
[0057]
FIG. 13 shows an example of a timing chart for controlling the switching element 10. This timing chart is an example of changing from black display (second position) to white display (first position). First, at time t51, the drive mode is set, and a high-potential + drive voltage for black display is applied. When supplied to the movable electrode 9, the movable electrode 9 moves to the second position and contacts the lower holding electrode 62. When the set mode is entered at time t52 and the respective holding voltages are supplied to the holding electrodes 61 and 62, the movable electrode 9 is in contact with the lower holding electrode 62, so that it has the same high potential as the driving voltage. Contact is made with the + holding potential, and no current flows between them, and the state is locked. At time t53, when the holding mode is set and the movable electrode 9 is open Z, the same potential as the driving voltage is supplied from the holding electrode 62, and the movable electrode 9 does not move. Even when the reset mode is entered at time t54 and the holding electrode 62 becomes open Z, the charge is stored, so that the state of the movable electrode 9 is held.
[0058]
On the other hand, at time t55, when the drive mode is entered and the drive voltage of the low potential G that is white display is supplied to the movable electrode 9, the movable electrode 9 moves in the direction of the upper fixed electrode 7 and the upper holding electrode. 61 is contacted. When the set mode is entered at time t56 and the respective holding voltages are supplied to the holding electrodes 61 and 62, since the movable electrode 9 is in contact with the upper holding electrode 62, the same low potential as the driving voltage is obtained. Contact is made with the holding potential of G, no current flows between them, and the state is locked. At time t57, even if the holding mode is set and the movable electrode 9 is opened Z, the movable electrode 9 does not move because the same potential as the drive voltage is supplied from the holding electrode 61.
[0059]
In this way, by providing holding electrodes in the moving direction of the movable electrode 9, it is possible to select the holding or locking potential using the movable electrode 9 as a selection means, and the state of the movable electrode can be changed. Can be locked and memorized. Then, by eliminating the holding potential of the holding electrode, the movable electrode becomes movable, so that the lock can be reset and the next driving voltage can be reflected.
[0060]
In FIGS. 6 and 12, an image of supplying the holding voltage to the holding electrode in units of pixels is illustrated. However, in the image display device 55 in which the optical switching elements 10 are two-dimensionally arranged in an array, a line is used. The holding voltage can be controlled in units of (scanning lines) or the entire screen, and the holding circuit 65 does not have to be built in the area of each actuator 60 or the switching element 10. The timing for turning on / off the holding voltage is preferably controlled in units of scanning lines or screens because it controls the timing at which the data latched in the drive circuit 21 is reflected on the pixel level.
[0061]
In FIG. 14, as the switching element 10 provided with the actuator 60 of this example, the driving circuit 21 when the switching elements shown in FIG. 6 are two-dimensionally arranged in an array to constitute the image display device 50, and the fixed electrode 8 Further, an example of a configuration for supplying a voltage to the holding electrode 62 is shown. This figure corresponds to FIG. 3 described above. In this example, in addition to the voltage supply line 48 for supplying a bias voltage to the fixed electrode, each scanning line in which the drive circuit 21 is arranged in the horizontal direction is shown. The holding electrodes 62 are divided into groups so that the holding potential can be output from the holding circuit 65 through the voltage supply line 69. Therefore, in the device 50 of this example, the voltage of the holding electrode 62 can be controlled for each scanning line. That is, the holding voltage can be supplied to the holding electrode 62 in synchronization with each scanning line, and the state of the switching element 10, that is, the pixel can be reset or set with one clock for each scanning line. Of course, the pixel state of the entire screen can be reset or set in one clock.
[0062]
As described above, by using the image display device 50 that can set or reset the state of the pixel with one clock for each scanning line or each screen, several very beneficial effects can be obtained. For example, in the projector 80 shown in FIG. 1, a plurality of colors (usually red, green, and blue) are sequentially input to the image display unit 55 by the rotating color filter 82, and the light 85 modulated into an image for each color is generated. Emitted. Therefore, the control circuit 84 for displaying a color image gives the image display unit 55 data φd for displaying the color image and an address (scanning) signal φa for latching the data φd in the memory of each pixel. Is supplied to the drive circuit 21. Further, the driving voltage is output from the driving circuit 21 by the frame sequential signal for displaying each pixel with the latched data, and the color rotation filter moves in synchronization with the frame sequential signal, so that the light of each color is displayed on the image of each color. It can be output almost synchronously with irradiation, and the loss of irradiation time can be made almost zero.
[0063]
That is, a signal φs that is the same as or synchronized with the frame sequential signal is supplied to the holding circuit 65, and the state of the pixel supplied from the drive circuit 21 is locked to the pixel itself, that is, the switching element 10. Thus, while the image is fixed, the pulsed address signal φa is sequentially supplied in the column direction via the address line 44, and the corresponding data signal φd is supplied by the data line 41. As a result, when an address line for one frame (screen) is scanned, one frame of data is newly latched in the memory of each drive circuit 21. At this time, if a system in which one frame is divided into a plurality of fields and displayed in order is employed, data for one field is stored.
[0064]
Next, when the frame sequential signal is turned on, a new drive voltage is supplied from the drive circuit 21 to the actuator mechanism 6 of each pixel, whereby the next image appears. In other words, the next screen display is switched in one clock. Therefore, images with different colors can be displayed by irradiating or supplying light of different colors to the image display unit 55 in accordance with the switching timing of the screen display. Further, while the light of the color is supplied and the image of the color is displayed, the image data of the next color is latched by the drive circuit 21 in the order of the scanning lines in accordance with the address signal φa as described above. . Then, by the next frame sequential signal, the image display is switched in synchronization with the timing at which the light of the next color is irradiated according to the data of all the drive circuits 21 constituting the screen.
[0065]
As described above, in the image display unit 55 of this example, the optical switching element itself has a memory function, so that only one element serving as a memory is prepared in the drive circuit 21, and an image can be switched in one clock. it can. Therefore, when irradiating light of different colors, it is not necessary to turn off the light source and secure a time for writing each image. Furthermore, since the optical switching element 10 whose response speed is about an order of magnitude shorter than that of the liquid crystal is adopted as the light modulation element, light of different colors is sequentially transmitted without being blocked by a shutter or the like almost continuously. Can be irradiated. Therefore, an extra mechanism such as a shutter is not necessary in the surface sequential driving method in which light of each color is irradiated in order, and an image display device with very high temporal resolution can be provided. Therefore, it is possible to provide an image display device capable of expressing a multi-tone multicolor image by a frame sequential method. By adopting the frame sequential method, as described above, one pixel can be expressed in multiple colors by one optical switching element, so that a compact and high-resolution image display device can be provided.
[0066]
In order to realize such a field sequential method, only one memory as described above with reference to FIG. 4A is prepared and operated in the switching element or drive circuit constituting each pixel. Just do it. For this reason, in the image display apparatus of this example, it is possible to provide an image display apparatus that can express a very compact and multi-tone image.
[0067]
Further, since light of each color can be irradiated almost continuously, an image display device that can display a bright image with high light use efficiency can be provided. Since the screen is not rewritten with interlace or non-interlace during display, it is possible to display a very high quality image without occurrence of flicker.
[0068]
Further, more flexible pixel control can be performed by supplying a holding voltage to the upper electrode and the lower electrode in units of scanning lines. For example, when an image of one color is composed of a large number of frames, the switching timing of the frames can be controlled in units of lines, and image control that can be called a line sequential method can be performed. Further, it is not necessary to provide a scanning line for supplying a set or reset signal to the drive circuit and to add a circuit element for setting or reset in the drive circuit in order to perform such control. Accordingly, the present invention provides an image display device that can control the timing of reading and writing of pixel data, and further the display timing, while being a compact and low-cost device with a very simple configuration. Can do.
[0069]
In this example, an example is described in which an electrostatic actuator is used as a switching element that performs light modulation. However, the present invention is not limited to an optical element that is driven by an electrostatic actuator or a device that uses the optical element. Can be applied. The present invention can be applied to any device provided with an electrostatic actuator in which a movable electrode is driven by a fixed electrode, and is not limited to a light modulation device, but a switching device for other uses such as a microvalve. The present invention can also be applied to a device that can freely control the switching timing with a simple and compact configuration.
[0070]
【The invention's effect】
As described above, in the present invention, in the electrostatic actuator using the electrostatic force that works between the fixed electrode and the movable electrode, by providing the holding electrode that can lock the state of the movable electrode, The actuator mechanism of the electric actuator, that is, the drive mechanism itself composed of electrodes can be used as one memory, and at least one set of memory prepared on the drive circuit side can be reduced.
[0071]
In a microdevice having a structure in which microactuators are stacked on a semiconductor substrate, it is an important issue to increase the degree of integration of the microactuators, and the area occupied by the drive circuit in the semiconductor substrate is also reduced. For this reason, it is necessary to further improve the degree of integration on the semiconductor substrate side, which increases the manufacturing cost and decreases the yield. In particular, in a device having a structure in which a macro actuator and further switching optical element layers are stacked on a semiconductor substrate, the substrate side is wasted due to the yield of each layout layer, and the optical element layer and actuator layer The yield of an expensive highly integrated semiconductor substrate depends on the yield. Therefore, even if the degree of integration of the semiconductor substrate is increased, if the cost is greatly increased, the influence on the product cost is very large.
[0072]
On the other hand, by applying the present invention, it is possible to add a function as a memory without increasing the cost on the semiconductor substrate side. For this reason, not only can the yield of the semiconductor substrate be improved, but it is also possible to minimize the influence of the loss associated with the yield of the actuator layer or the optical element layer, and one or more memories can be provided for each pixel at low cost. A highly functional switching device provided can be provided. Then, by using the optical switching device (image display device) according to the present invention, it is possible to provide an image display apparatus that can display a bright high-resolution image while being compact at a low cost.
[Brief description of the drawings]
FIG. 1 shows an example of a projector as an image display device.
FIG. 2 is a diagram showing an outline of an evanescent light switching element.
FIG. 3 is a diagram illustrating a configuration of an image display device in which drive circuits are arranged in an array.
4 is a circuit diagram showing an example of a drive circuit shown in FIG. 3;
FIG. 5 is a diagram showing an outline of a type of optical switching element in which a movable electrode is driven only by a lower fixed electrode.
FIG. 6 is a diagram showing an outline of an evanescent light switching element including an electrostatic actuator according to the present invention.
7 is a timing chart showing the movement of the switching element shown in FIG. 6, and shows a state of transition from black display to white display. FIG.
8 is a timing chart showing the movement of the switching element shown in FIG. 6, and shows a state of transition from black display to black display.
9 is a timing chart showing the movement of the switching element shown in FIG. 6, and shows a state of transition from white display to black display.
10 is a timing chart showing the movement of the switching element shown in FIG. 6, and is a diagram showing a transition from white display to white display. FIG.
11 is a timing chart showing the movement of the switching element shown in FIG. 6, and shows an example in which the holding voltage is different.
FIG. 12 is a diagram showing an outline of an evanescent light switching element including an electrostatic actuator different from the above.
13 is a timing chart showing the movement of the switching element shown in FIG. 12, and is a diagram showing a transition from black display to white display.
FIG. 14 is a diagram showing a configuration of an image display device in which switching elements having electrostatic actuators according to the present invention are arranged in an array.
[Explanation of symbols]
1 Light guide plate
2 Illumination light
3 Optical elements
4 Microprism
5 V type support structure
6 Actuator mechanism
7 Fixed electrode on
8 Lower fixed electrode
9 Movable electrode
10 Optical switching element
20 Semiconductor substrate
21 Drive circuit (drive unit)
22 Sample hold
23 Switching element
41 data lines
42 Address line
45 Address line driver circuit
46 Data line driver circuit
47 Voltage supply line to fixed electrode on
48 Voltage supply line to the lower fixed electrode
50 Optical switching devices (image display devices)
55 Image display unit
60 Electrostatic actuator
61 Holding electrode on
62 Lower holding electrode
65 Holding circuit
69 Voltage supply line to holding electrode

Claims (9)

An electrostatic actuator that drives a switching unit that can move to a first position and a second position away from the first position by an electrostatic force acting between the electrodes,
A movable electrode for driving the switching unit;
A fixed electrode that is arranged to drive in the direction of the first position or the direction of the second position, which is a direction approaching or separating from the movable electrode, and to which a fixed potential is supplied;
A holding electrode that is in electrical communication with the movable electrode by contacting the movable electrode at the first or second position;
Drive means capable of applying drive potentials having different polarities to the movable electrode;
An electrostatic actuator comprising: a holding unit capable of applying a holding potential having the same polarity as the driving potential when the movable electrode is in contact with the holding electrode. In claim 1,
Elastic means for driving the switching unit to the first position;
The fixed actuator is disposed so as to drive the movable electrode in the direction of the second position, and the holding electrode is in contact with the movable electrode at the second position. In claim 1,
The fixed electrode includes a first fixed electrode that drives the movable electrode in the direction of the first position, and a second fixed electrode that drives the movable electrode in the direction of the second position. ,
The electrostatic actuator includes: a first holding electrode that contacts the movable electrode at the first position; and a second holding electrode that contacts the movable electrode at the second position. In any one of Claims 1 thru | or 3,
The driving means can select a driving mode for applying the driving potential to the movable electrode and a holding mode for opening the movable electrode,
The electrostatic actuator is capable of selecting a set mode in which the holding potential is applied to the holding electrode and a reset mode in which the holding potential is not applied to the holding electrode.   5. A light guide unit including a total reflection surface capable of transmitting the introduced light by total reflection, the electrostatic actuator according to claim 1, and the electrostatic actuator using the electrostatic actuator. A switching unit that is driven to be able to contact and separate from a reflecting surface and can modulate light at the first or second position, and the switching unit is configured to perform the total reflection at the first position. Switching element that extracts evanescent light leaking from the surface.   A switching device in which a plurality of the switching elements according to claim 5 are arranged in an array.   An image display device in which a plurality of the switching elements according to claim 5 are arranged in an array.   8. An image display device comprising: the image display device according to claim 7; and means for inputting / outputting projection light to / from the image display device. A control method for an electrostatic actuator that drives a switching unit movable to a first position and a second position away from the first position by an electrostatic force acting between electrodes,
The electrostatic actuator is driven in the direction of the first position or the direction of the second position, which is a movable electrode that drives the switching unit, and a direction in which the movable electrode approaches or separates from the movable electrode. A fixed electrode to which a fixed potential is supplied, a holding electrode that is electrically connected to the movable electrode by contacting the movable electrode at the first or second position, and a movable electrode Driving means capable of applying drive potentials having different polarities, and holding means capable of applying a holding potential having the same polarity as the driving potential when the movable electrode is in contact with the holding electrode. Have
A driving step of applying driving voltages having different polarities to the movable electrode;
A holding step of opening the movable electrode;
A setting step of applying a holding voltage having the same polarity as the driving voltage when the movable electrode is in contact with the holding electrode to the holding electrode;
And a resetting step in which the holding voltage is not applied to the holding electrode, and the setting step is performed between the driving steps.

Images