JP2008539455A - Miniature electromechanical device having deflectable reflective surfaces and electrode surfaces perpendicular to each other - Google Patents

Abstract

  The present invention relates to a microelectromechanical device having at least one pixel element 132. The pixel element 132 includes a support structure 134, at least one deflectable reflective surface 135 supported on the support structure, and at least one deflectable electrode surface 146, 148. The electrode surfaces 146, 148 are substantially perpendicular to the deflectable reflective surface and can be electrostatically attracted by upright bars 160, 170 disposed between the pixel elements 132, and the upright bars are the pixels. Compared to the second side of the tilt axis of the element 132, a larger portion of the electrode surfaces 146, 148 is attracted on the first side of the tilt axis of the pixel element 132. The invention also relates to a method for operating a micro electromechanical device.

Description

  The present invention relates to the modulation of electromagnetic radiation, and more particularly to a method of addressing a microelectromechanical device for modulating said radiation.

  Micro-electromechanical systems (MEMS) can include movable / deflection mirrors or pixels fabricated on a wafer substrate by microelectronic processing techniques. Electrostatic electromotive force is most commonly used for micromirror deflection. In order to generate a force, a voltage may be generated between the two electrodes. In this case, one electrode can be placed under the micromirror and the other electrode can be assigned to the mirror.

  For example, a spatial light modulator (SLM) having an actuator (micromirror or reflective element) array used for a mask writing device or a chip manufacturing device can be loaded with a special pattern. Can be in an addressed or non-addressed state before each stamp is printed. See, for example, US Pat. No. 6,373,619. This pattern can typically be a subset of the pattern to be printed on each mask or chip. Each actuator can be deflected or moved by static electricity generated by applying a voltage between the actuator and the address electrode disposed below the actuator, and then can be shifted to a predetermined deflection state. Is triggered to print the stamp.

  Loading an SLM in analog mode is conventionally performed by applying a single potential to the mirrors or pixel elements and individually addressing at least one electrode assigned under each of the mirrors. As a result, a desired SLM pattern was formed. In analog mode, the SLM mirror can be set to many different states, for example 64 or 128 states, which range from a totally undeflected state to a maximum deflected state. In this case, the maximum deflection state can be defined as the maximum extinction state of incident electromagnetic radiation, and the minimum deflection state can be defined as a complete reflection state of incident electromagnetic radiation. In a digital SLM, the maximum deflection state is defined as the reflected electromagnetic beam deflecting out of the target plane, and the minimum deflection state is defined as the complete reflection of incident electromagnetic radiation. A digital spatial light modulator can operate in a deflection mode, whereas an analog spatial light modulator operates in a diffraction mode. Between these two modes, the degree to which the individual elements are deflected is significantly different, and analog elements are usually only a few fractions of a degree, but in the case of digital elements, several degrees of deflection. Is made.

  However, as the thickness of the micromirror increases, crosstalk between mirrors begins to become a problem when the mirrors are individually addressed by the prior art.

  Accordingly, it is an object of the present invention to provide a microelement addressing method in which the above problems are solved or at least mitigated, thereby facilitating the use of thicker pixel elements in microelectromechanical devices. Is to do.

  This object has been achieved, inter alia, by a spatial light modulator comprising at least one pixel element according to the first aspect of the invention. In that case, the pixel element includes a support structure, at least one deflectable surface supported by the support structure, and at least one electrode surface that can be deflected, the electrode surface being deflectable. The pixel element is electrostatically attractable by an upright bar that is substantially perpendicular to the reflective surface and disposed between the pixel elements, and the upright bar is compared to a second side of the oblique axis of the pixel element. The larger part of the electrode surface is attracted on the first side of the oblique axis.

  In accordance with another embodiment of the present invention, a method of operating a spatial light modulator including at least one pixel element adapted to generate two or more multiple modulation states includes a first bias voltage applied to a first upright bar. And an application of an address voltage to at least one of the pixel elements, wherein the first upstanding bar can electrostatically attract the deflection electrode surface of the pixel element.

Other features, objects, and advantages of the present invention will become apparent from the appended claims and from the detailed description of the preferred embodiment presented below and the accompanying drawings of FIGS. The illustrated embodiments are merely illustrative and do not limit the invention.
The following detailed description is made with reference to the figures. The preferred embodiments for clarifying the invention are not intended to limit the scope of the invention as defined in the claims. Those skilled in the art will appreciate that various equivalent variations can be made to the following description.

  FIG. 3 is a schematic side view of a state of a prior art actuator arrangement or pixel element 300. Such an actuator structure 300 may be, for example, a micromirror structure of a spatial light modulator (SLM). The actuator structure shown in FIG. 3 includes a substrate 313, a first electrode 312, a second electrode 314, a support structure 311, and a movable element 310. The substrate is made of a semiconductor material and includes one or more multiple CMOS circuits. The first and second electrodes are made of a conductive material, such as gold, copper, silver, aluminum, alloys of these materials and / or alloys of other conductive materials. The electrodes can be connected to a steering circuit such as the CMSO circuit described above.

  The support structure 311 is preferably made of a relatively rigid material, such as single crystal silicon, but of course can be made of a material that is not significantly rigid. The movable element 310 is preferably made of a material having good optical properties, such as aluminum. However, if a material is selected that does not have the desired properties, it can be coated with one or more other materials having more favorable properties to create a sandwich structure.

  The electrostatic force can deflect the movable element 310. When a different potential acts on the movable element 310 and one of the first electrode 312 and the second electrode 314, an electrostatic force is generated. When a first potential is applied to the movable element 310 and a second potential is applied to the first and second electrodes, an electrostatic force is generated when the first and second potentials are equal, but these electrostatic forces are balanced. Therefore, the movable element will not be deflected. However, even when an equal potential is applied to the first and second electrodes, the movable element may be deflected. This is because the attracting area between the movable element / first electrode and the attracting area between the movable element / second electrode are unequal, or the distance between the movable element / first electrode and the distance between the movable element / second electrode. This is because of inequality. Two equal attractive forces are equalized with each other.

  In FIG. 3, the actuator structure is shown as having two electrodes, a first electrode 312 and a second electrode 314. However, only the first or second electrode is required for deflection of the movable element. There are several reasons for having more than one electrode. One reason is that in order to deflect the mirror in two different directions, two electrodes spaced apart from each other are required. Other reasons will become clear from the following description of the method of the present invention.

  FIG. 1 is a perspective view showing an embodiment of a pixel element (mirror structure) 132 according to the present invention. The pixel element includes a deflectable reflecting surface 135, a support 134, a cavity 131, a base 136, a first leg 142, and a second leg 144. The pixel element 132 may have at least one cross section that is equal in thickness to the original substrate, and in this embodiment, the original substrate thickness is from the deflectable reflective surface 135 to the bottom surfaces of the legs 142, 144. 145, 147 and / or the bottom surface 143 of the base 136. The original substrate may be an SOI (Silicon On Insulator) substrate, a silicon substrate, or some other semiconductor substrate. This gives the mirror structure good mechanical properties such as high rigidity. In other words, the mirror surface is substantially rigid while in the deflecting position.

  The support 134 may be a thin columnar object. These supports support the deflectable reflecting surface 135 and the first and second legs 142 and 144, respectively, and at the same time function as hinges. In the case of the embodiment shown in FIG. 1, the support 134 is arranged such that the axis of rotation is located substantially in the center of the structure. In another embodiment, the axis of rotation may be located off-center, which is achieved by displacing the support from the center position. The rotation axis of the deflectable reflecting surface 135 may be parallel to the reflecting surface 135.

  Base 136 and support 134 may be referred to as a hidden hinge. In another embodiment, the base 136 is minimized so that only the support 134 can be referred to as a hidden hinge. The cross section of the support may be polygonal, for example triangular or quadrangular. Base 136 may be attached to support 134. The bottom surface 143 of the base 136 can be attached to another surface, for example, a wafer having a steering circuit. The legs 142 and 144 can have electrode surfaces 146 and 148 that are substantially perpendicular to the reflective surface 135 of the mirror. The void 131 can be formed by an isotropic etching process. The mirror structure 132 can be doped. This doping is preferably done before defining the void 131 and the support 134. That is, the substrate used to define the mirror structure is doped. In this embodiment, electrode surface 148 can be used to rotate pixel element 132 clockwise. The electrode surface 146 may be used to rotate the pixel element 132 counterclockwise. The bottom surface 143 of the base 136 may be located at a different level from the bottom surfaces 145 and 147 of the legs 144 and 142, respectively.

  The electrode surfaces 146 and 148 are electrostatically attracted by upright bars 160 and 170. These upright bars 160, 170 can be placed between individual pixel elements.

  FIG. 2 is a schematic plan view of an embodiment in accordance with the present invention that addresses a spatial light modulator that includes an upstanding bar 210. As can be seen in FIG. 2, the pixel element columns 230 are separated by the upright bars 210. In the embodiment shown in FIG. 2, the pixel element can be deflected to the right or left. Of course, the upright bars may be arranged so as to separate the rows of pixel elements instead of the columns. In such embodiments, the pixel elements will be deflected up or down in the figure. With an appropriate hinge configuration, the upright bar can also be placed between both rows and columns of pixel elements. In such an embodiment, the pixel element can be freely deflected in any of the four possible deflection directions, ie up, down, left, right. In embodiments with upright bars between both the column and row of pixel elements, one type of upright bar, i.e. one of the bars separating the row or column, must be discontinuous, but otherwise. , All bars will be set to the same potential. The discontinuities of the upright bars in one row coincide in one embodiment with the intersections with the upright bars of the other row, i.e. the bars propagating in a perpendicular direction.

  First and second bias voltages can be set for every other upright bar. In the embodiment shown in FIG. 2, for example, the first bias voltage is 10V and the second bias voltage is 0V. As can be easily understood, since the setting of the first and second bias voltages can be selected in any way, a specific purpose in question can be achieved. 2 is that pixel elements are addressed in a checkerboard fashion, in other words, every row of pixel elements is alternately addressed to 0-5V and 5-10V. Also, every column pixel element is set to 0-5V and 5-10V alternately. This implies that a particular pixel element, for example pixel element 260, is set to the first address interval, in this case 5-10V. This pixel element 260 is adjacent to the pixel element of the second address interval, in this case 0-5V.

In connection with the above, by setting every other upright bar to the first bias voltage, in this case 10V, and to the second bias voltage, in this case 0V, the checkerboard address of the pixel element The effect of deflecting the alternating row of pixel elements in a first direction, eg clockwise, and in the opposite direction, eg counter-clockwise will be obtained.
In order to prevent tilting of the upright bar while attracting the pixel elements by static electricity, the upright bar could be reinforced by a perpendicular bar support 220. As shown in FIG. 2, the bar support 220 can support the upright bar against the inclination in both the clockwise direction and the counterclockwise direction. As shown in FIG. 2, when the upstanding bars separate the columns of pixel elements, the bar support 220 extends in the direction between the rows of pixel elements. The embodiment of FIG. 2 can prevent the upright bar from tilting in the clockwise direction and the counterclockwise direction. In another embodiment, the upright bar is supported only on one side, but still the tilting of the upright bar can be prevented.

  The upright bars 210, 160, and 170 have a height that is less than or equal to the height of the pixel element 132 in one embodiment. As shown in FIG. 1, the upright bars 160 and 170 are approximately half the height of the pixel element 132. In order to deflect the deflectable reflective surface 135, the area of the electrode surfaces 146, 148 that can electrostatically attract the upright bars 160, 170, ie, opposite the upright bars, is above the tilt axis of the pixel element. Thus, the lower portion of the tilt axis can be made larger. The position of the tilt axis can be changed according to the shape of the structure. In other words, the shorter the length of the support structure for obtaining a predetermined distance between the deflectable reflecting surface 135 and the bottom surfaces 145 and 147, the lower the position of the tilt axis is in the pixel element. Will be located. The same area of the electrode surface opposite the upright bar above and below the tilt axis will consequently not rotate. In other words, the electrostatic forces from the areas above and below the tilt axis will be equalized with each other.

  In an embodiment having an inclined axis located at half the distance between the deflectable reflective surface 135 and the bottom surface 145, the upright bar is located at any height below the deflectable reflective surface. You may do it. An upright bar having a height just below the deflectable reflective surface 135 is such that the height of the pixel element 132 is between the upright bars 160, 170 and the electrode surface 146 to obtain a predetermined deflection. Let the applied voltage difference be greater than an upright bar with half the height. In order to obtain a predetermined deflection, the upright bars 160 and 170 having the top surfaces 162 that are flush with the inclined axis can minimize the potential difference between the upright bars 160 and 170 and the electrode surfaces. Any electrode that is below the tilt axis of the pixel element reduces the effective electrostatic attraction surface, thus reducing the electrostatic force that deflects the pixel element. In that case, it was assumed that the upright bar covers the entire width of the electrode surfaces 146, 148, in other words, the shape of the electrode surface is equal to the upright bar. If the shape of the electrode surface and the upright bar is different, the electrostatic attractive force between the electrode surface and the upright bar will be affected.

In FIG. 1, the upright bar is shown having a substantially flat top surface 162, 172. By providing the top surface shape which is not flat, the scattered light will be further reduced. Examples of such shape of the top surface of the upright bar are tapered or pyramidal.
The top surfaces 162, 172 of the upright bars can be coated with a non-reflective material, and one example of such a non-reflective material is Ti (titanium) or Ta (tantalum). The non-reflective coating may also be a stack of suitable materials.
The top surfaces 162, 172 of the upright bar can be displaced in a direction perpendicular to the at least one deflectable surface 135 by twice the pi / irradiation electromagnetic radiation wavelength, in other words, the top surface of the upright bar is The reflected electromagnetic radiation from the upright bar can be displaced 180 degrees out of phase with the electromagnetic radiation from the at least one deflectable reflecting surface.

  In another embodiment, the top surface of every other upright bar can be displaced perpendicular to the at least one deflectable reflective surface by four times the pi / irradiation electromagnetic radiation wavelength, and also the remaining upright bars The top surface could be displaced vertically by at least 4 times -pi / irradiation electromagnetic radiation wavelength with respect to at least one deflectable reflective surface. In other words, the top surface of every other upright bar has the reflected electromagnetic radiation from the upright bar 90 degrees out of phase with the electromagnetic radiation reflected from the at least one deflectable reflective surface, and the remaining upright bars. The top surface of the bar may be displaced vertically so that the reflected electromagnetic radiation from the top surface of the upright bar is -90 degrees out of phase with the reflected electromagnetic radiation from the at least one deflectable reflecting surface. .

The upright bar can be made of a semiconductor material, a metal material, or any other conductive material.
While the invention has been described through a number of preferred embodiments, it is to be understood that these embodiments are for illustrative purposes and are not intended to limit the invention. It will be apparent to those skilled in the art that various modifications and combinations of modifications can be made without departing from the spirit of the invention and the scope of the claims.

1 is a schematic perspective view of an embodiment of a pixel element of the present invention used in a spatial light deflector. FIG. The schematic plan view of one Example of the address to the spatial light deflector of this invention. 1 is a schematic side view of an actuator structure or pixel element according to the prior art.

Explanation of symbols

131 Cavity 132 Pixel Element, Mirror Structure 134 Support Structure 135 Deflective Reflection Surface 136 Base 142 First Leg 143 Base Bottom 144 144 Second Leg 145 Second Leg Bottom 146, 148 Electrode Surface 147 First Leg Bottom 160, 170 Upright bar 162, 172 Upright bar top surface 210 Upright bar 220 Upright bar support 230 Pixel element 240 Spatial light deflector 260 Pixel element

Claims (19)

In a micro electromechanical device (MEMS) comprising at least one pixel element, the pixel element (132) comprises:
A support structure (134);
At least one deflectable reflective surface (135) supported by the support structure (134);
At least one electrode surface (146, 148) that is deflectable, the electrode surface (146, 148) being substantially perpendicular to the deflectable reflecting surface (135), and the electrode surface (146, 148) Can be electrostatically attracted by an upright bar (160, 170) disposed between the pixel elements (132), and the upright bar can be compared to a second side of the tilt axis of the pixel element (132). A microelectromechanical device comprising at least one pixel element that attracts a larger portion of the electrode surface (146, 148) towards the first side of the tilt axis of the pixel element (13).   The microelectromechanical device of claim 1, wherein at least one of the upstanding bars has a surface substantially parallel to the electrode surface.   3. A microelectromechanical device according to claim 1 or 2, wherein columns and / or rows of the pixel elements are separated by the upright bars.   4. Every other upright bar of the upright bars is set to a first bias voltage and the other upright bars are set to a second bias voltage. Ultra-small electromechanical device.   The micro electromechanical device according to any one of claims 1 to 4, wherein the upright bar has a height equal to a position of an inclined axis.   The deflection direction of the pixel element can be changed by changing the range of voltage applied to the pixel element, while the first and second bias voltages of the first and second upright bars are fixed. The micro electromechanical device according to any one of claims 1 to 5.   The micro-electromechanical device according to any one of claims 1 to 6, wherein at least one upright bar is displaced perpendicular to the other upright bar. A method of operating a microelectromechanical device including at least one pixel element adapted to generate two or more multiple modulation states, the method comprising:
Applying a first bias voltage to the first upright bar;
Applying an address voltage to at least one of the pixel elements, and wherein the first upright bar is capable of electrostatically attracting a deflectable electrode surface of the pixel element. How to operate.   The method further includes applying a second bias voltage to at least one second upright bar, wherein at least one of the first and second upright bars electrostatically attracts the deflectable electrode surface of the pixel element. The method according to claim 8, which is possible.   10. A method according to claim 8 or claim 9, wherein the first and second upstanding bars have surfaces that are substantially parallel to the edge of the pixel element.   11. A method according to any one of claims 8 to 10, wherein at least two adjacent columns of the pixel elements are separated by the upstanding bar. Further, every other upright bar of the upright bars is set to the first bias voltage,
12. A method according to any one of claims 8 to 11 including the task of setting another upright bar to the second bias voltage.   The upright bar is more of the electrode surface (146, 148) on the first side of the tilt axis of the pixel element (132) than on the second side of the tilt axis of the pixel element (132). 13. A method according to any one of claims 8 to 12, wherein a large portion is attracted.   Further, the deflection direction of the pixel element is changed by changing the range of the voltage applied to the pixel element, while the first and second bias voltages of the first and second upright bars are fixedly maintained. 14. A method as claimed in any one of claims 8 to 13, comprising the work of:   15. A method as claimed in any one of claims 8 to 14, wherein the deflectable electrode surface is substantially perpendicular to the deflectable reflective surface of the pixel element.   10. A method according to claim 8 or claim 9, wherein the upright bar has a height equal to the position of the tilt axis.   17. A method according to any one of claims 8 to 16, wherein at least one upstanding bar is displaced perpendicularly to the other upstanding bar.   The microelectromechanical device of claim 1, wherein the microelectromechanical device (MEMS) is a spatial light modulator (SLM). The method of claim 8, wherein the microelectromechanical device is a spatial light modulator (SLM).

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