WO2002013168A1 - Ecran plat de micromecanique - Google Patents

Ecran plat de micromecanique Download PDF

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Publication number
WO2002013168A1
WO2002013168A1 PCT/IL2000/000475 IL0000475W WO0213168A1 WO 2002013168 A1 WO2002013168 A1 WO 2002013168A1 IL 0000475 W IL0000475 W IL 0000475W WO 0213168 A1 WO0213168 A1 WO 0213168A1
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WO
WIPO (PCT)
Prior art keywords
flipper
force
electrode
pixel
voltage
Prior art date
Application number
PCT/IL2000/000475
Other languages
English (en)
Inventor
Amichai Heines
Original Assignee
Flixel Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from PCT/IL1999/000488 external-priority patent/WO2000052674A1/fr
Application filed by Flixel Ltd. filed Critical Flixel Ltd.
Priority to AU2000264660A priority Critical patent/AU2000264660A1/en
Priority to TW089119362A priority patent/TW523608B/zh
Publication of WO2002013168A1 publication Critical patent/WO2002013168A1/fr

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • G09F9/37—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • G09F9/37—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements
    • G09F9/372—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements the positions of the elements being controlled by the application of an electric field
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • G09F9/37—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements
    • G09F9/375—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements the position of the elements being controlled by the application of a magnetic field

Definitions

  • the invention relates to visual display systems and in particular to flat-panel displays produced using micro-machining techniques. BACKGROUND OF THE INVENTION
  • Flat-panel video displays are ubiquitous components of many consumer, industrial and military products and devices. They are found in computer laptops, automobile dashboards, microwave ovens and a myriad of other machines and devices with which man interacts.
  • Active-matrix liquid-crystal displays dominate the market for high quality high- resolution flat-panel displays. However, these displays are relatively expensive and the amount of power they consume when operating is relatively large in comparison to the amount of power readily available from many battery driven devices.
  • a flat-panel display of a first type has pixels each of which comprises a liquid crystal cell formed on a silicon substrate.
  • Light which may be ambient light or light from an appropriate light source, illuminates the pixels.
  • Transmittance of the liquid crystal in each pixel for the light determines how bright the pixel appears.
  • the transmittance of the liquid crystal is controlled by voltage on electrodes in the pixel.
  • a pattern of pixels having varying levels of brightness is formed on the display to produce an image by controlling the voltage on the electrodes in each pixel of the display. Images provided by this type of display generally suffer from low brightness and low contrast.
  • a flat panel display hereinafter referred to as a "micro-mechanical display", of a second type, has pixels each of which comprises at least one movable structure micro- machined on a silicon substrate. The position of the at least one moveable structure in each pixel controls how bright the pixel appears by controlling an amount of light that the pixel reflects or diffracts.
  • the position of the at least one moveable element is controlled by electrostatic forces between the at least one moveable element and electrodes in the pixel that are generated by applying appropriate voltages to the electrodes.
  • the voltages are relatively high and moving the at least one moveable element requires a relatively large expenditure of energy.
  • brightness and image contrast are dependent upon viewing angle, as measured with respect to the normal to the plane of the display, and decrease as the viewing angle increases.
  • a micro-mechanical display in which the at least one moveable structure in pixels in the display comprises a plurality of parallel flexible reflecting ribbons is described in US Patent 5,841,579 to D. M. Bloom et al, which is incorporated herein by reference.
  • the flexible ribbons in a pixel of the display are normally located parallel to the plane of the substrate on which the pixel is formed at a small distance above the plane.
  • the ribbons are controllable to be depressed towards the substrate by electrostatic forces that are generated by voltages applied to electrodes in the pixel.
  • the pixels in the display are illuminated with light from a suitable light source so that light is incident on the pixels at a given angle with respect to the plane of the display.
  • the plurality of ribbons in the pixel form a diffraction grating that diffracts some of the incident light at an angle such that the pixel appears bright to a user of the display.
  • the plurality of ribbons in the pixel reflect the incident light at a different angle such that light from the pixel does not reach the eye of the user and the pixel appears dark.
  • An appropriate pattern of bright and dark pixels forms the image on the display.
  • the patent describes methods for using pixels of the type described to produce a flat- panel displays that provide color images. Another type of micro-mechanical display is described in US patent 5,636,052 to S.C.
  • the at least one moveable element in a pixel is a membrane.
  • the membrane is flexibly supported so that it is parallel to the substrate with a small air gap between the two.
  • Light that is incident on the pixel is reflected by both the substrate and the membrane.
  • the height of the air gap determines whether the reflected light from the membrane and the substrate interfere constructively or destructively and therefore if the pixel appears bright or dark respectively.
  • An addressable electrode in the pixel when charged attracts the membrane towards the substrate thereby controlling the height of the air gap and therefore whether the pixel is bright or dark.
  • relatively high voltages on the order of tens of volts, must be applied to the addressable electrode.
  • micromechanical devices presents a stiction phenomena.
  • Various methods of reducing or counteracting stiction in micromechanical devices are described, for example, in "Adhesion of Polysilicon Microbeams in Controlled Humidity Ambients", by M.P. de Boer, et al., Mat. Res. Soc. Symp Proc, Vol. 518, pp. 131-136, 'Stiction in Surface Micromachining", Niels Tas, et al, J. Micromech. Microene.. 6 (1996) pp.
  • An aspect of some embodiments of the present invention is related to providing a micro-mechanical flat-panel display that uses ambient light and provides high-contrast images at substantially all viewing angles with respect to the plane of the display.
  • An aspect of some embodiments of the present invention is related to providing a flat- panel display that operates with low power consumption.
  • An aspect of some embodiments of the present invention is related to providing a flat- panel display that operates using electrical power supplied at low voltages, such as 5 volts or less.
  • a high voltage is used, such as 50 volts.
  • the device uses a combination of high and low voltages, in which the addressing uses low voltages and the pixel flipping uses high voltages.
  • An aspect of some embodiments of the present invention relates to providing a flat- panel display that provides black and white and/or gray level images.
  • An aspect of some embodiments of the present invention relates to providing a flat- panel display that provides color images.
  • An aspect of some embodiments of the present invention relates to providing a micromechanical flat-panel display formed on a substrate and having pixels that comprise a moveable element.
  • the moveable element is formed in the shape of a thin planar panel having first and second relatively large face surfaces and thin edges.
  • the panel hereinafter referred to as a "flipper”
  • the flipper is hinged to the substrate in such a way that it is rotatable from one to the other of two limiting positions about an axis of rotation that is parallel to the surface of the substrate.
  • the limiting positions are hereinafter referred to as “on” and “off positions.
  • the flipper is, for example, at least partly formed from a conducting material. In the on position the first face surface faces a user looking at the display and is visible to the user.
  • the second face surface of the flipper faces the substrate, facing away from the user, and is not visible to the user.
  • the second face surface faces the user and is visible to the user while the first face surface faces the substrate.
  • the plane of the flipper is close to and substantially parallel to the surface of the substrate.
  • the flipper rotates through approximately 180° about the axis of rotation to rotate between on and off positions.
  • an aspect of some embodiments of the invention relates to overcoming stiction in a planar-electrode device using a levitation electrode.
  • the levitation electrode is raised higher than a movable element whose stiction is to be broken.
  • the electrode may be the same height or even slightly lower, and still generate a net levitating force on the movable element, to break its stiction and levitate the element over the surface of the device.
  • a levitation electrode is provided substantially perpendicular to the planer electrode and/or the moving part.
  • the voltage may be applied to the levitation electrode at least at the start of motion of the moving part in order to free it of the stiction.
  • the device is a flipper pixel as described herein and the levitation electrode comprises one or more electrodes which extend in a direction perpendicular to the substrate.
  • An aspect of some embodiments of the invention is related to structure and method for reducing friction in flippers.
  • a force is applied to a flipper in a direction perpendicular to its face.
  • the force causes the flipper to rotate about the hinge.
  • this force also causes the appendage to be pushed against the inner surface of the hinge.
  • This problem may exist independently of the shape of the hinge or the appendage. However, for rectangular shapes (which are generally the easiest to produce, especially in microstructures) the problem is more pronounced.
  • a counter force is applied to the appendage to reduce the force with which it is pressed against the hinge or to keep it from being pressed against the hinge altogether.
  • This force may be an electrical force supplied, for example by an electrified electrode that generates an electric field or by a magnetic field.
  • the field is permanent. In others, it is activated only during part or all of the time during which the flipper is being flipped. Optionally, different fields are applied at different parts of the flipping procedure.
  • the field is applied by applying a voltage to one or more electrodes that underlay the appendage. These voltages are of a polarity to draw the appendage away from the hinge during flipping.
  • the electrode is electrified to the opposite polarity to draw the appendage away from the hinge.
  • the friction reducing force is applied only at or near the hinge, such that it does not substantially reduce the flipping forces. This is generally not problematic, since the flipping moment is very small near the hinge, so that substantial forces may be applied without impeding the flipping.
  • both the flipping and friction reducing forces are electrical, mixed electrical, mechanical or magnetic forces can be used in some embodiments of the invention.
  • magnetic or mechanical forces are used for flipping, electric fields could be used to reduce the friction.
  • permanent or transient magnetic forces can be used to counteract friction in electrically actuated flippers.
  • a visual display comprising a plurality of pixels each of which comprises: there is thus provided, in accordance with an exemplary embodiment of the invention, a method of rotating a flipper from a first position about a hinge, wherein an appendage of the flipper is contained within the hinge, comprising: applying a first force over at least a first portion of the flipper such that the flipper rotates about the hinge from the first position; and applying a second force on a second portion of the flipper in a direction opposite that of the first force, said second force being configured and located to reduce or remove pressure of the appendage against the hinge.
  • the flipper has a first surface having a surface area and wherein the first force is applied over substantially the entire surface area.
  • the second portion of the flipper is a portion adjacent the hinge.
  • the first force comprises a mechanical force.
  • the first force comprises an electrical force.
  • the first force comprises a magnetic force.
  • the second force comprises an electrical force.
  • the flipper is at a first voltage and the second force is generated by a difference in voltage between the flipper and an electrode.
  • the electrode is grounded.
  • the electrode is at a voltage having an opposite polarity from that of the flipper.
  • the electrode is at a voltage having a same polarity as that of the flipper.
  • the electrode voltage is a pulsed voltage.
  • the electrode voltage is a substantially constant voltage.
  • the second force comprises a magnetic force.
  • the magnetic force is induced by a permanent magnet.
  • the magnetic force is initiated by an electromagnet.
  • the second force is a constant force.
  • the second force is an intermittent force.
  • the flipper has a size of less than about 1 square mm.
  • a visual display comprising a plurality of pixels each pixel comprising: a flipper having first and second sides and at least one appendage; at least one hinge holding said at least one appendage and defining a rotation axis about which said flipper is rotatable; at least one first electrode, which is so positioned and energized at a first voltage different from a voltage of the flipper, to be operative to apply a first force to said flipper, said first force causing the flipper to rotate about the rotation axis and also causing the at least one appendage to be urged towards a surface of the hinge; and at least one second electrode, which is so positioned that when it is energized at a second voltage different from the flipper voltage, is operative to apply a second force to said flipper, said second force counteracting the first force substantially only in the vicinity of the hinge.
  • the second electrode is positioned on an opposite side of the flipper, from the hinge.
  • the appendage is a portion of the flipper outboard of a hole formed in the flipper.
  • the appendage has a rectangular cross section.
  • the appendage is held in an opening in the hinge having a substantially rectangular cross-section.
  • FIGs. 1A-1C show schematic perspective views of a micro-machined pixel with a flipper in three different positions, in accordance with an exemplary embodiment of the present invention
  • Figs. 2A-2D show schematic side views of the pixel shown in Figs. 1A-1C and illustrate how electrostatic forces control movement and position of the flipper, in accordance with an exemplary embodiment of the present invention
  • FIGS. 3A and 3B show schematic side views of a variation of the pixel shown in Figs. 1A-1C, in accordance with an exemplary embodiment of the present mvention, in which the structure of the pixel has been simplified in order to illustrate how electrostatic forces control movement and position of the flipper;
  • Fig. 4 shows schematically another pixel structure in accordance with an exemplary embodiment of the present invention.
  • Fig. 5 shows schematically a portion of a flat-panel display comprising a two dimensional array of pixels, in accordance with an exemplary embodiment of the present invention
  • Figs. 6A-6D show schematically construction and operation of a multi-flipper pixel in accordance with an exemplary embodiment of the present invention
  • FIG. 7 shows another multi-flipper pixel, constructed in accordance with an exemplary embodiment of the present invention
  • Fig. 8A-8N illustrate schematically a micro-machining fabrication process for producing the pixel shown in Figs 1 A-IC, in accordance with an exemplary embodiment of the present invention
  • Figs. 9A and 9B show schematically a perspective view and a cross-section view respectively of another pixel, constructed in accordance with an exemplary embodiment of the present invention
  • Figs. 10A and 10B show schematically perspective views of another pixel and a flipper respectively, constructed in accordance with an exemplary embodiment of the present invention
  • Fig. 11 shows schematically another pixel, in accordance with an exemplary embodiment of the present invention.
  • Figs. 12A-12L illustrate schematically a micro-machining fabrication process for producing the pixel shown in Figs 9A-9B;
  • Fig. 13 A is a schematic illustration corresponding to Fig. 1A and showing a levitation electrode for a flipper pixel in accordance with an exemplary embodiment of the invention
  • Fig. 13B is a sectional view along a line A-A in Fig. 13 A;
  • FIGs. 14A-14F which correspond to some of Figures 8C-8M, illustrate a method of manufacturing a pixel having a levitation electrode, in accordance with an exemplary embodiment of the invention
  • Figs. 15A-15E illustrate a method of manufacturing a pitted nub, in accordance with an exemplary embodiment of the invention
  • Figs. 15F-15G illustrate an alternative method of forming a rounded nub, in accordance with an exemplary embodiment of the invention
  • Fig. 16 illustrates a display device including a vibration generator, in accordance with an exemplary embodiment of the invention
  • Figs. 17A and 17B illustrate a flipper with integral springs in respective top view and side views thereof, in accordance with an exemplary embodiment of the invention
  • Figs. 17C and 17D illustrate steps in manufacturing an integral flipper spring in accordance with an exemplary embodiment of the invention
  • Fig. 18A is a schematic circuit diagram of a touch input device, in accordance with an exemplary embodiment of the invention.
  • Fig. 18B is a side cross-sectional view of a micro-mechanical touch input device in accordance with an exemplary embodiment of the invention.
  • Fig. 19 is a schematic circuit diagram for a flipper-pixel, in accordance with an exemplary embodiment of the invention.
  • Fig. 20 is a schematic illustration of a flip-chip configuration for a device in accordance with an exemplary embodiment of the invention
  • Fig. 21 is a perspective view of an alternate embodiment of a pixel
  • Fig. 22 is a side view of a pixel incorporating a feature of Fig. 21, showing electric field lines at the start of a flipping of a pixel
  • Fig. 20 is a schematic illustration of a flip-chip configuration for a device in accordance with an exemplary embodiment of the invention
  • Fig. 21 is a perspective view of an alternate embodiment of a pixel
  • Fig. 22 is a side view of a pixel incorporating a feature of Fig. 21, showing electric field lines at the start of a flipping of a pixel
  • Fig. 23 shows a perspective view of an alternative pixel construction in accordance with an embodiment of the invention.
  • FIGs. 1A-1C show schematic perspective views of a pixel 20 for use in a micromechanical display, in accordance with an embodiment of the present invention.
  • Components and elements of pixel 20 shown in Figs. 1A-1C and in the other figures are not necessarily to scale and relative dimensions in the figures have been chosen for convenience and clarity of presentation.
  • Pixel 20 may be formed on a silicon substrate 22 using micro-machining techniques.
  • pixel 20 comprises a flipper 24, first and second side electrodes 26 and 28 respectively and a central electrode 30.
  • a thin layer 23 of insulating material separates electrodes 26, 28 and 30 from substrate 22.
  • a thin planar region of substrate 22 that is contiguous with insulating layer 23 may be a good conductor.
  • flipper 24 is in an on position and in Fig. IC flipper 24 is in an off position.
  • flipper 24 is shown in a position intermediate the on and off positions.
  • Flipper 24 is may be formed in the shape of a thin rectangular planar panel having two relatively large surfaces, a first face surface 40 shown in Fig.
  • Flipper 24 may be formed with mounting holes 32 and 34.
  • U brackets 36 and 38 loop through mounting holes 32 and 34 respectively and loosely bracket flipper 24 to central electrode 30 so that flipper 24 is rotatable back and forth between the on and off positions of flipper 24.
  • first face surface 40 (Fig. 1A) may be treated so that it is white.
  • Second face surface 42 (Figs. IB and IC) may be treated so that it is black.
  • First electrode 26 may be treated so that its surface is black and second electrode 28 may be treated so that its surface is white.
  • a portion 29 (Fig. 1A) of the surface of central electrode 30 that is visible when flipper 24 is in the on position is treated so that it is white.
  • a portion 31 of central electrode 30 that is visible when flipper 24 is in the off position (Fig. IC) is treated so that it is black. Black colored surfaces are shown shaded and white colored surfaces are shown without shading.
  • flipper 24 When flipper 24 is in the on position shown in Fig 1A, flipper 24 covers substantially completely first electrode 26 and portion 31 (Fig. IC) of electrode 30 that are black. Substantially all surfaces in pixel 20 that are visible are white and pixel 20 appears white. With flipper 24 in the off position shown in Fig. IC, flipper 24 substantially completely covers electrode 28 and portion 29 (Fig. 1A) of central electrode 30 that are white. As a result, substantially all surfaces in pixel 20 that are visible are black and the pixel therefore appears black.
  • regions and elements of pixel 20 that are described as being treated to be black or white can be treated to display colors other than black or white.
  • regions and elements of pixel 20 that are white can be treated to have a color that is one of the primary RGB colors. Pixel 20 in the on position will therefore display one of the RGB colors accordingly and in the off position the pixel 20 will be black.
  • Pixels 20 treated to have different ones of the RGB colors are useable, in accordance with an exemplary embodiment of the present invention, to provide a color flat-panel display.
  • Motion of flipper 24 between on and off positions is controlled, in accordance with an embodiment of the present invention, by electrostatic forces between flipper 24 and first and second electrodes 26 and 28.
  • flipper 24 and U brackets 36 and 38 can be made from a conducting material such as polysilicon or aluminum.
  • Flipper 24 may be in conductive electrical contact with central electrode 30 and/or U brackets 36 and 38.
  • voltage on flipper 24 is always substantially equal to voltage applied to central electrode 30.
  • conductive electrical contact between flipper 24 and electrode 30 is achieved as a result of physical contact between regions of flipper 24 and regions of electrode 30 and U brackets 36 and 38.
  • flipper 24 may be substantially isolated from conductive electrical contact with first and second electrodes 26 and 28. Conductive electrical contact between flipper 24 and first electrode 26 may be prevented when flipper 24 is in the on position respectively by providing first electrode 26 with insulation nubs 44. Insulation nubs 44 on first electrode 26 are shown in Figs. IB and IC. Conductive electrical contact between flipper 24 and second electrode 28 may be prevented when flipper 24 is in the off position by providing flipper 24 with insulation nubs 45 on face surface 40 shown in Fig. 1 A. Insulation nubs 44 and 45 may be formed from a material that is a poor conductor. In some embodiments of the present invention, an insulating coating is used to cover insulation nubs 44 to make them non-conductive.
  • Insulation nubs 44 and 45 not only prevent electrical contact between flipper 24 and electrodes 26 and 28 respectively, they also reduce stiction forces between flipper 24 and electrodes 26 and 28. Insulation nubs 44 and 45 prevent direct physical contact between flipper 24 and first and second electrodes 26 and 28.
  • flipper 24 When flipper 24 is in the on position (Fig. 1A), flipper 24 rests on insulation nubs 44 of electrode 26 and does not make direct contact with first electrode 26. Because insulation nubs 44 are poor conductors, flipper 24 is substantially electrically isolated from first electrode 26. Little or no current flows between flipper 24 and electrode 26 even if a potential difference exists between electrode 26 and electrode 28.
  • flipper 24 rests on insulation nubs 45 on face surface 40 of flipper 24 and flipper 24 is substantially electrically isolated from second electrode 28.
  • FIGs. 2A-2D illustrate schematically how electrostatic forces generated by applying voltages to electrodes 26, 28 and 30 control movement of flipper 24, in accordance with an embodiment of the present invention.
  • views of pixel 20 are shown in profile facing the short edge of flipper 24.
  • the conducting layer of substrate 22 that is contiguous with insulating layer 23 is grounded. This is indicated in Figs. 2A-2D and in other figures that follow, by showing substrate 22 as grounded.
  • the conducting layer acts as a ground plane for pixel 20.
  • Fig. 2A shows pixel 20 with flipper 24 in the on position corresponding to the position of flipper 24 shown in Fig. 1 A, in which pixel 20 is white.
  • flipper 24 rests on central electrode 30 and insulation nubs 44, only one of which is shown, of first electrode 26.
  • central electrode 30 is shown charged to a positive voltage "+VL" and electrodes 26 and 28 are grounded. (The choice of sign for the voltage is arbitrary and a positive voltage is assumed for convenience.) Because flipper 24 is in contact with central electrode 30, flipper 24 is also at +NL- As a result, flipper 24 has a net positive charge distribution indicated schematically in Fig. 2A by plus signs.
  • the positive charges on flipper 24 induce negative charges, shown schematically by minus signs, on first electrode 26. Electrostatic attraction between the positive and negative charges prevents flipper 24 from moving away from first electrode 26 and flipper 24 is locked in the on position. Since insulation nubs 44 are substantially non-conducting, substantially no current flows between central electrode 30 and first electrode 26 through flipper 24. As a result, with flipper 24 locked in the on position substantially no energy is dissipated in pixel 20. It should be noted that whereas in Fig. 2 A first electrode 26 is shown grounded, first electrode 26 does not necessarily have to be grounded for an attractive electrostatic force to exist between flipper 24 and first electrode 26. As long as there is a potential difference between flipper 24 and electrode 26 there is an attractive force between them. In accordance with an embodiment of the present invention, voltages other than those shown in Fig. 2A, can be used to lock flipper 24 in the on position if they provide required voltage differences between the electrodes and the flipper.
  • Second electrode 28 may be grounded and central electrode 30 to voltage +VL- A voltage +Vr, applied to central elecfrode 30 to lock flipper 24 in an on or off position is hereinafter referred to as a "locking voltage".
  • flipper 24 is "unlocked" from the on position and flipped to the off position by applying a same voltage to central electrode 30 and first electrode 26 and grounding elecfrode 28.
  • Charges on electrodes 26 and 30 and on flipper 24 (as a result of being in contact with electrode 30) resulting from the applied voltages induce charges on electrode 28 that are opposite in sign to the charges on electrodes 26, 30 and flipper 24.
  • the charges on electrodes 26, 28 and 30 and flipper 24 generate electrostatic forces that operate to lift flipper 24 away from first electrode 26 and flip it to second elecfrode 28.
  • the voltage applied to central elecfrode 30 and first electrode 26 is chosen large enough so that the electrostatic forces are strong enough to overcome stiction and the force of gravity acting on the mass of flipper 24.
  • a constant voltage is applied.
  • the voltage may be varied over the course of movement of the flipper. For example, a higher voltage may be provided at the beginning of the movement to overcome stiction.
  • Fig. 2B schematically shows charge distributions on central elecfrode 30 and first electrode 26 in which both central electrode 30 and first elecfrode 26 are raised to a same positive potential +Vp (chosen positive for convenience) in order to flip flipper 24 from the on position to the off position.
  • the positive charges on cenfral elecfrode 30, first electrode 26 and flipper 24 induce negative charge on second electrode 28.
  • An electrostatic field that results from the positive and negative charges generates a force that acts on flipper 24 in a direction indicated by arrow 25. Force 25 lifts flipper 24 away from first electrode 24 and rotates flipper 24 away from first electrode 24 towards second electrode 28, so that flipper 24 flips to the off position.
  • Flipper 24 may be similarly flipped from the off position back to the on position, in accordance with an embodiment of the present invention, by applying voltage +Vp to central electrode 30 and second electrode 28.
  • This is schematically illustrated in Fig. 2C in which positive charge distributions are produced on flipper 24 and second electrode 28 by the application of +Vp to central electrode 30 and second elecfrode 28.
  • the positive charge distributions induce a negative charge distribution on first elecfrode 26.
  • An electrostatic field that results from the charge distributions generates a force on flipper 24 in a direction indicated by arrow 27.
  • Fig. 2D shows schematically an alternate way of flipping flipper 24 between on and off positions, in accordance with an embodiment of the present invention.
  • flipper 24 is shown in the off position with cenfral electrode 30 and second electrode 28 grounded.
  • First elecfrode 26 is charged to a positive potential Np.
  • a resultant positive charge distribution on first electrode 26 induces a negative charge distribution on flipper 24 and on second elecfrode 28.
  • the positive and negative charge distributions generate a net force on flipper 24 that operates in a direction indicated by arrow 29 to lift flipper 24 away from second electrode 28 and rotate flipper 24 towards first electrode 26.
  • the present inventors have simulated electrostatic fields generated by voltages applied to electrodes 26, 28 and 30 of pixel 20 in the configurations shown in Figs. 2C and 2D on a computer using the ANSYS finite elements analysis program (available from Ansys, Inc., Houston TX USA). Forces 27 and 29 shown respectively in Figs 2C and 2D were determined from the simulated electrostatic fields. The inventors found that force 27 is equal to force 29 if the magnitude of Vp is the same in both cases. For the same voltage Vp, the method of flipping flipper 24 shown in Fig. 2C and the method for flipping flipper 24 shown in Fig. 2D generate a same "flipping force". A voltage Vp used to flip flipper 24 between on and off positions is hereinafter referred to as a "flipping voltage".
  • Fig. 2C and 2D methods of flipping flipper 24 may be understood from consideration of a pixel 50 shown in Figs. 3 A and 3B, which is an "idealized" version of pixel 20.
  • Figs. 3A and 3B show pixel 50 in a side view equivalent to the side view of pixel 20 shown in Figs. 2A-2D. In both Figs. 3A and 3B flipper 24 is in the off position.
  • Pixel 50 comprises substantially the same components as pixel 20. In pixel 50 however, insulation nubs 44 and 45 are omitted. Central elecfrode 30 has been "shrunk" to an electrical contact point 30 used for connecting flipper 24 to a power source. U brackets 36 and 38 are replaced by hinges 52, only one of which is shown in the perspective of Figs 3 A and 3B, that enable flipper 24 to flip back and forth between on and off positions.
  • First and second electrodes 26 and 28 and flipper 24 are substantially the same size.
  • Flipper 24 is assumed to be coated with an insulating coating (not shown) that substantially isolates flipper 24 from first and second electrodes when flipper 24 is in the on and off positions respectively.
  • Subsfrate 22 is grounded so that the conducting layer of substrate 22_that is contiguous with insulating layer 23 functions as a ground plane of pixel 50.
  • flipper 24 and second electrode 28 are both raised to a positive voltage +Np (positive for convenience of presentation only) and first electrode 26 is grounded.
  • the voltage configuration shown in Fig. 3A is the same as the voltage configuration of electrodes, 26, 28 and 30 and flipper 24 of pixel 20 shown in Fig. 2C.
  • flipper 24 and second electrode 28 are grounded and first electrode 26 is raised to Np.
  • the voltage configuration shown in Fig. 3A is the same as the voltage configuration of electrodes, 26, 28 and 30 and flipper 24 of pixel 20 shown in Fig. 2C.
  • flipper 24 and second electrode 28 are grounded and first electrode 26 is raised to Np.
  • 3B is the same as the voltage configuration of electrodes, 26, 28 and 30 and flipper 24 of pixel 20 shown in Fig. 2D. Plus and minus charge distributions on electrodes 26, 28, 30, flipper 24 and on the boundary between insulating layer 23 and substrate 22 of pixel 50 are shown schematically by plus and minus signs.
  • first electrode 28 and flipper 24 may be considered to function as a single conductor.
  • none of the deposited positive charge resides (in the idealized geometry of pixel 50) at the boundary between second electrode 28 and flipper 24.
  • the charge resides, as shown in Fig. 3 A, on the outside surfaces of the volume of the "single conductor" formed by second electrode 28 and flipper 24.
  • the positive charge in second electrode 28 is concentrated at a boundary region 54 between second electrode 28 and insulating layer 23.
  • the positive charge in flipper 24 is concentrated on face surface 42 (only an edge of which is shown in the perspective of Fig. 3 A) of flipper 24.
  • the positive charge in second electrode 28 induces a negative charge in the conducting layer of subsfrate 22.
  • the negative charge in substrate 22 is concentrated at a boundary region 56 between substrate 22 and insulating layer 23. Except for edge effects, the electrostatic field generated by the charges at the boundary regions 54 and 56 of insulating layer 23 is confined to a volume of insulating layer 23 between the charges and has little effect outside this volume.
  • Second electrode 28, the conducting layer of substrate 22 and the region of insulating layer 23 between them function as a thin parallel plate condenser.
  • the amount of positive charge on second elecfrode 28 can be estimated from the capacitance of the parallel plate condenser, which is determined by dimensions of second electrode 28 and insulating layer 23 and the dielectric constant of the material of insulating layer 23.
  • FIG. 3B A similar analysis of the charge distributions shown in Fig. 3B leads to a same conclusion as that reached for the charge distributions shown in Fig. 3A.
  • An electrostatic field in the space above flipper 24 and first electrode 26 in Fig. 3B is a function substantially only of the shapes and relative positions of first elecfrode 26 and flipper 24 and on the voltage difference Vp between them.
  • force 29 in Fig. 3B that operates to lift flipper 24 away from second electrode 28 and towards first elecfrode 26 is substantially only a function of the shapes and relative positions of first electrode 26 and flipper 24 and Vp.
  • first electrode 26 and flipper 24 are the same in Fig. 3 A and 3B. Except for being of opposite polarity, the potential difference between flipper 24 and first electrode 26 are the same. As a result, the electrostatic fields generated in the space above flipper 24 and first electrode 26 in Figs. 3A and 3B are identical except for polarity. Therefore forces 27 and 29 in Figs. 3A and 3B that act to lift flipper 24 away from second electrode 28 are identical. Applying the results of the analysis for the "ideal" pixel 50 to pixel 20 shown in Figs. 2C and 2D leads to the conclusion that forces 27 and 29 and therefore the methods for flipping flipper 24 shown in Figs. 2C and 2D respectively are substantially the same.
  • the deposited and induced charges on flipper 24, first elecfrode 26 and second electrode 28 in the various voltage configurations that are used to rotate flipper 24 between on and off states are generally concentrated close to the axis of rotation of flipper 24. Therefore, forces that act on flipper 24 are also concentrated near to the axis of rotation of flipper 24. As a result, most of the torque that rotates flipper 24 is generated by forces that act on relatively short lever arms. In addition, the strength of the forces are substantially proportional to inverse squares of distances between points on flipper 24 and points on electrode 26 or 28 to which flipper 24 is to be rotated.
  • first and second electrodes 26 and 28 are substantially coplanar, as shown in pixels 20 and 50, maximizes the concentration of charge near to the axis of rotation of flipper 24.
  • a coplanar geometry for electrodes 26 and 28 maximizes distances between points on the two elecfrodes.
  • first and second electrodes 26 and 28 are angled so that the angle between their planes is less than 180°.
  • Fig. 4 shows a pixel 60, in accordance with an embodiment of the present invention, in which an angle ⁇ between the planes of first and second electrodes 26 and 28 is less than 180°.
  • ⁇ is between 140° and 180°.
  • ⁇ is between 150° and 180°.
  • the area of pixel 20, or other pixel in accordance with some embodiments of the present invention is optionally a square millimeter or less.
  • flipper 24 is less than 1000 microns long and 500 microns wide. These dimensions provide a square pixel 1-mm on a side.
  • flipper 24 is less than 100 microns long and 50 microns wide, which provides a square pixel approximately 100 microns on a side.
  • a pixel of this size is suitable for providing a black and white (two level) display having a resolution of 250 DPI.
  • flipper 24 is formed from polysilicon and has dimensions 1 x 14 x 83 microns, resulting in a pixel having dimensions approximately 28 x 83 microns. Electrodes 26, 28 and 30 may also be formed from polysilicon and are optionally 0.5 microns thick. Insulation nubs 44 and 45 are for example, about 1.5 microns high. For these dimensions and materials, the inventors have determined that flipper 24 can be flipped between on and off positions in a time on the order of 12 milliseconds using a flipping voltage substantially equal to five volts. A locking voltage of about 2.5 volts locks flipper 24 into an on or off position.
  • Pixels 20 that are 28 x 83 microns can be used, in accordance with an embodiment of the present invention, to provide a black and white or gray level flat-panel display.
  • a flat-panel display comprising pixels 20 of this size has a resolution of 300 DPI in a first dimension and approximately 900 DPI in a second dimension.
  • pixels 20 of this size can be used to provide a flat-panel color display, in accordance with an exemplary embodiment of the present invention.
  • a flat-panel color display the areas of pixel 20 that are treated to be white in Figs 1A-1C are treated to have one of the RGB colors.
  • Each pixel of the flat-panel color display is a "super pixel", substantially square and approximately 83 microns on a side, comprising three pixels 20, each of which has a different RGB color.
  • pixels 20 have been described as being white, black or one of the RGB primary colors, surfaces of pixels 20 can be treated to have other colors or finishes, in accordance with other embodiments of the present invention.
  • Fig. 5 shows schematically part of a black and white flat-panel display 62 comprising a plurality of rectangular pixels 20, in accordance with an embodiment of the present invention.
  • the positions of flippers 24 in pixels 20 are controlled by row and column control lines 64 and 66 respectively.
  • Each row control line 64 is connected to first electrode 26 of each pixel 20 in a row of pixels in flat-panel display 62.
  • Each column control line 54 is connected to cenfral electrode 30 in each pixel 20 in a column of pixels in flat-panel display 62.
  • Second elecfrodes 28 in all pixels 20 are permanently grounded.
  • each super pixel 64 would comprise three pixels 20 in a column of pixels shown in Fig. 5, so as to form a substantially square super pixel.
  • Each one of the pixels 20 in a super pixel would display instead of white in the on position a different one of the RGB colors.
  • a flipper 24 of a pixel 20 is flipped from on to off using the method described in the discussion of Fig. 2B in which both cenfral electrode 30 and first electrode 26 are charged to a flipping voltage.
  • Flipper 24 is flipped from off to on using the method described in the discussion of Fig. 2D, in which central electrode 30 is grounded and a flipping voltage is applied to first electrode 26.
  • Flipper 24 is locked in an on position or an off position using the method shown in Fig. 2A in which central electrode 30 is charged to a locking voltage and first and second electrodes 26 and 28 are grounded.
  • setting flipper 24 of a pixel 20 to an on or off position is also referred to as setting or turning pixel 20 to on or off respectively.
  • pixels 20 are set to on or off, as required to form the image, row by row.
  • Setting pixels 20 in a row to on or off begins with all row control lines 64 of flat panel display 62 grounded and all column control lines 66 of flat panel display 62 raised to a locking voltage.
  • Column control lines 66 of pixels 20 in the row that are to be set to on are then grounded and column control lines 66 of pixels 20 in the row that are to be set to off are left at the flipping voltage.
  • Row control line 64 of the row is then set to the flipping voltage.
  • flip time that it takes a flipper 24 to flip between an on and off position.
  • Flippers 24 of pixels 20 in the row that have their column control lines 66 set to zero remain in the on position if they are in the on position or flip to on if they are in the off position.
  • Flippers 24 of pixels 20 in the row that have their column control lines 66 set to the flipping voltage stay in the off position if the are already in the off position or flip to the off position if they are in the on position.
  • all column control lines 66 in flat-panel display 62 are set to the locking voltage for a short period of time. This assures that all pixels 20 in other rows whose flippers 24 may have begun to dislodge from their respective on and off positions during the time that the row of pixels was being set, as a result for example of a vibration in flat-panel display 62, are safely returned to their positions. In this way pixels 20 in flat-panel display 62 are never left unlocked long enough for a pixel 20 to change its state unintentionally. (During the time that each row is being set some of the row control lines 66 are grounded leaving many pixels 20 unlocked.)
  • all column control lines 66 are raised to the locking voltage to lock the pixels in the on and off states to which they have been set.
  • the time it takes to form an image on flat panel display 62 is substantially equal to the number of rows in flat-panel display 62 times the flip time of the pixels in the flat-panel display.
  • an image is formed in a time that is much shorter than the time it takes to form an image in flat-panel display 62.
  • the image is formed in a time substantially equal to the flip time of pixels 20 in the display rather than in a time substantially equal to a product of the flip time and the number of rows in the display.
  • each pixel 20 with addressable switches.
  • the addressable switches are controllable to connect central electrode 30 and first elecfrode 26 of the pixel to ground or to a voltage output of a display power source independently of each other.
  • each pixel 20 is individually controllable and the setting of a pixel 20 to on or off in the display is uncoupled from the setting of other pixels in the display.
  • the voltage output of the power supply is such that it can be set to ground or to appropriate locking and flipping voltages. When the voltage output is set to the locking or flipping voltage, the power source can substantially simultaneously charge elecfrodes 26 and 30 of all pixels 20 in the display to the locking or flipping voltage in a time substantially less than the flip time of the pixels.
  • the voltage output of the power supply is grounded. All the addressable switches in the display are addressed using an appropriate scanning procedure and controlled to connect first electrode 26 and central electrode 30 of pixels 20 to ground or to the power source. For pixels 20 that are to be set to on, central electrode 30 is connected to ground and first electrode 26 is connected to the output of the power source. For pixels 20 that are to be set to off, both central electrode 30 and first electrode 26 are connected to the voltage output. The voltage output is then raised to the flipping voltage, which causes all pixels 20 in the display to flip to their desired on or off state substantially simultaneously. First electrodes 26 of all pixels 20 are then connected to ground, all central electrodes of pixels 20 are connected to the voltage output and the voltage output is set to the locking voltage. This locks all pixels 20 in the on or off states to which they were set.
  • Scanning and setting the switches occur in a time that is very short compared to the flip time of pixels 20.
  • the total time required to set and lock pixels 20 in their appropriate on or off states so as to form the image is substantially equal to the flip time of pixels 20.
  • pixels 20 can be used to form a flat-panel display, in accordance with some embodiments of the present invention, in which pixels 20 are individually and/or simultaneously controllable to be switched on and off. These configurations will readily occur to persons of the art.
  • an array of pixels 20 that are individually and/or simultaneously controllable is formed as a mono- block in a process that integrates layers of electronic and mechanical components to form a single unit.
  • a pixel comprises more than one flipper.
  • a pixel that has a single flipper has two states, an on and off state
  • a pixel, in accordance with an embodiment of the present invention, comprising a plurality of "N" flippers has (N+l) states.
  • a multi-flipper pixel can therefore display a greater variety of colors than a pixel having a single flipper.
  • Figs. 6A-6D show schematically a perspective view of a multi-flipper pixel 160, in accordance with an embodiment of the present invention.
  • Pixel 160 comprises two flippers, a first flipper 162 and a second flipper 164.
  • Multi-flipper pixel 160 has three states, first, second and third states, that are shown in Figs. 6A-6C respectively.
  • Fig. 6D shows an exploded plan view of pixel 160 in the second state, which is shown in Fig. 6B.
  • Multi-flipper pixel 68 comprises a substrate 22 having an insulating layer 23.
  • First and second lateral electrodes 26 and 28 and first, second, third and fourth central electrodes 171, 172, 173 and 174 are formed on insulating layer 23.
  • First, second, third and fourth central electrodes 171, 172, 173 and 174 are most clearly shown in Fig. 6A and Fig. 6D.
  • First flipper 162 is coupled to pixel 160 by a pair of brackets 176, each of which loops through a different mounting hole 178 in first flipper 162.
  • One of brackets 176 is anchored to second central electrode 172 and the other to third central electrode 173.
  • Brackets 176 are optionally formed from a conducting material.
  • First flipper 162 is in electrical contact with second and third central electrodes 172 and 173 and brackets 176. Electrical contact may be achieved by physical contact of regions of first flipper 162 with regions of second and third central electrodes 172 and 173 and brackets 176.
  • Second flipper 164 is coupled to pixel 160 by a pair of brackets 180 that loop through mounting holes 182 in second flipper 164.
  • One of brackets 180 is anchored to first electrode 171 and the other to fourth electrode 174.
  • Brackets 180 may be formed from a conducting material.
  • Second flipper 164 is in electrical contact with first and fourth central electrodes 171 and 174 and brackets 180. Electrical contact may be achieved by physical contact of regions of second flipper 164 with regions of first and fourth cenfral electrodes 171 and 174 and brackets 180.
  • first flipper 162 may be formed with clearance slots 184 that are large enough so that no part of flipper 162 makes electrical contact with first and fourth cenfral electrodes 171 and 174 or any part of brackets 180.
  • second flipper 164 may be formed with clearance slots 186 that are large enough so that no part of second flipper 164 makes electrical contact with second and third central electrodes 172 and 173 or any part of brackets 176.
  • Brackets 176 and 180 are optionally covered with a layer of insulating material to assist in prevention of undesirable electrical contact with first and second flippers 162 and 164 respectively.
  • First and second flippers 162 and 164 are optionally electrically isolated from each other and from first and second lateral electrodes 26 and 28 by appropriately placed non-conductive insulation nubs (not shown) or by layers of insulating material deposited on their surfaces.
  • Mounting holes 178 and clearance slots 184 of flipper 162 and mounting holes 182 and clearance slots 186 of flipper 164 are most clearly shown in exploded plan view 6D.
  • a control line 190 is connected to second and third cenfral electrodes 172 and 173 for applying voltage to second and third central electrodes 172 and 173 and thereby to first flipper 162. Connections between control line 190 and second and third central electrodes 172 and 173 are shown in Fig. 6A and Fig. 6D.
  • a control line 192 is connected to first and fourth central electrodes 171 and 174 for applying voltage to first and fourth central electrodes 171 and 174 and thereby to second flipper 164. Connections between control line 192 and first and fourth electrodes 171 and 174 are shown in Fig. 6C and Fig. 6D.
  • First lateral electrode 26 is connected to a control line 194 and second lateral electrode 28 is optionally permanently grounded.
  • First and second lateral electrodes 26 and 28 and each of the face surfaces of flippers 162 and 164 of pixel 160 are optionally freated to display one of the RGB colors.
  • pixel 160 displays a different one of the RGB colors in each one of its three different states.
  • Exposed surfaces of first and second lateral electrodes 26 and 28 and face surfaces of first and second flippers 162 and 164 are labeled in each of Figs. 6A-6C with the RGB color that they display.
  • Fig 6 A which shows pixels 160 in a first state
  • pixel 160 displays a substantially saturated red color.
  • second and third states of pixel 160 which are shown respectively in Figs.
  • pixel 160 displays a substantially saturated blue and green color respectively.
  • the choice of colors for face surfaces of flippers 162 and 164 and electrodes 26 and 28 are chosen by way of example and other color choices are possible and can be advantageous.
  • the face surfaces of flippers 162 and 164 can be treated so that they display different levels of gray. Instead of displaying one of the RGB colors in each of its states, pixel 160 will then display a different gray level in each of its states.
  • first second and third states are accomplished in a manner similar to the way in which pixel 20 is switched between on and off states.
  • flippers 162 and 164 are grounded and first lateral electrode 26 is raised to a flipping voltage.
  • first lateral electrode 26, second flipper 164 and second lateral electrode 28 are grounded while first flipper 162 is raised to the flipping voltage.
  • first and second lateral elecfrodes 26 and 28 are grounded and first and second flippers 162 and 164 are raised to the flipping voltage.
  • Pixel 160 is switched from second state to first state (Fig. 6B to Fig. 6 A) by raising second flipper 164 to the flipping potential while grounding first lateral elecfrode 26 and first flipper 162.
  • first and second lateral electrodes 26 and 28 are grounded and voltages are applied to first and second flippers 162 and 164 so that appropriate small voltage differences are generated between adjacent lateral electrodes and flippers.
  • FIG. 7 shows schematically a perspective view of another multi-flipper pixel 200, in accordance with an embodiment of the present invention.
  • Pixel 200 comprises two flippers 202 and 204.
  • Multi-flipper pixel 200 is shown in a second state similar to the second state of multilayer pixel 160 shown in Fig. 6B.
  • Flipper 202 is coupled to a first cenfral electrode 206 by two box hinges 208 that capture mounting extensions 210 (only one of which is shown) that protrude from flipper 202.
  • flipper 204 is coupled to a second central electrode 212 by two box hinges 214 that capture mounting extensions 216 (only one of which is shown).
  • Flipper 202 is formed with clearance slots 218 that enable flipper 202 to clear both sets of box hinges 208 and 214 when flipper 202 is flipped from the position in which it is shown in Fig. 7 to a position in which it lies on top of flipper 204.
  • Flipper 204 has similar clearance slots 220.
  • Figs. 8A-8I illustrate schematically a fabrication procedure, in accordance with an embodiment of the present invention, for forming pixel 20 shown in Figs 1 A - IC.
  • Fig. 8A shows a first step in the fabrication process in which a subsfrate 22, optionally formed from a silicon wafer, is covered with a thin insulating layer 23, formed from a material such as silicon nitride.
  • Fig. 8B shows a next step in the fabrication procedure in which insulating layer 23 is covered with a layer 80 of conducting material, such as polysilicon or a metal such as aluminum. Conducting layer 80 is then etched to form first and second electrodes 26 and 28 and central electrode 30, which electrodes 26, 28 and 30 are shown after they are formed in Fig. 8C.
  • conducting material such as polysilicon or a metal such as aluminum.
  • Second and central electrodes 26, 28 and 30, and exposed surfaces of substrate 22 are then covered with a sacrificial layer 82 shown in Fig. 8D from an appropriate material such as silicon dioxide.
  • Insulation nub wells 81 and insulation nub holes 83 are then etched into sacrificial layer 82.
  • Insulation nub wells 81 are blind holes in sacrificial layer 82 that do not penetrate all the way to second elecfrode 28.
  • Insulation nub holes 83 are through holes that penetrate all the way to first electrode 26.
  • Insulation nub wells 81 are used to form insulation nubs 45 (Fig. 1A) on flipper 24 whereas insulation nub holes 83 are used to form insulation nubs 44 on first electrode 26.
  • conducting material such as polysilicon or aluminum is then deposited on sacrificial layer 82.
  • Conducting layer 84 is then etched, for example, to the depth of sacrificial layer 82 to form flipper 24 with mounting holes 32 and 34, as shown in Fig. 8F.
  • insulation nub holes 83 are filled with the material of layer 84 that form insulation nubs 44 on first electrode 26.
  • a second sacrificial layer 86 is then deposited on the formed flipper 24 and exposed surface of sacrificial layer 82.
  • Sacrificial layer 86 may, for example, be formed from silicon dioxide if polysilicon is used as a material for flipper 24 and a polymer if aluminum is used as a material for flipper 24.
  • the shape of sacrificial layer 86 follows contours of surfaces on which it is deposited.
  • sacrificial layer 86 has a step 85 in the vicinity of an edge 87 of flipper 24 and depressions 89 over mounting holes 32 and 34.
  • Fig. 8H shows schematically a cross-section of the layers of pixel 20 that are shown in Fig. 8G, which cross-section is taken along a line A - A in Fig. 8G. The plane of the cross-section passes through the center of a depression 89.
  • flipper 24 appears to have two disconnected parts, a large part 91 and a small part 93.
  • Small part 93 hereinafter referred to as "axle part 93" is a part of flipper 24 that loops through U-bracket 38 of pixel 20 (Figs.
  • body part 91 is part of the body of flipper 24.
  • Axle part 91 is not separate from body part 93 but appears so because the plane of the cross-section passes through mounting hole 34 (Fig. 8F) of flipper 20.
  • sacrificial layer 86 Following deposition of sacrificial layer 86, four holes 90 are "drilled" through sacrificial layers 86 and 82 all the way to the surface of central electrode 30 using methods known in the art, such as by plasma or other etching. The tops of two of holes 90 are shown in Fig. 81. Two other holes 90 are drilled through sacrificial layers 86 and 82 at the locations of each of depressions 89 and are not shown in the perspective of Fig. 81.
  • Fig. 8J shows schematically two holes 90 and layers of pixel 20 in a cross-section view along line A - A in Fig. 81.
  • Holes 90 and depressions 89 are used as molds for forming parts of the "legs" of U brackets 36 and 38 (Figs. 1A-1C) that loop through mounting holes 32 and 34 of flipper 24.
  • the locations of holes 90 determine where on central electrode 30 the legs of U-brackets 36 and 38 are anchored. Holes 90 are not flush with regions of layer 86 that cover axle part 93 but are displaced from these regions. Technical limitations in the accuracy of placement of holes 90 may require that holes 90 be distanced from regions of layer 86 that cover axle part 93 to prevent these regions being damaged in the process of forming holes 90.
  • Sacrificial layer 86 serves to physically isolate axle part 93 (and body part 91) from a next conducting layer 92, shown in Figs.
  • Fig. 8L shows layer 92 in a cross-section taken along line A - A of Fig. 8K.
  • Layer 92 may for example be formed from polysilicon.
  • Layer 92 is etched away to form upper parts of brackets 36 and 38. (The lower parts of U-brackets 36 and 38 are formed by holes 90 and depressions 89 into which the material of layer 90 is deposited).
  • Sacrificial layers 86 and 82 are then eroded away using methods known in the art to leave a fully formed pixel 20 shown in Fig. 8M.
  • a cross- section of pixel 20 along line A - A in Fig. 8M is shown in Fig. 8N.
  • Brackets 36 and 38 in Figs. 8M and 8N show some details resulting from the manufacturing process illustrated in Figs. 8 A - 8L that were not shown in brackets 36 and 38 in previous figures. Among these details are external shoulders 97 shown in Figs 8M and 8N and internal shoulders 99 shown in Fig. 8N. Shoulders 97 and 99 result from the positioning of holes 90 which was discussed in the description of Figs. 81 and 8 J.
  • the uneven widths of the legs of U-brackets 36 and 38, which are shown in Fig 8M result from differences in the size of holes 90 and the parts of U-brackets 36 and 38 that are formed by etching away material of layer 92. In previous figures the shapes of U-brackets 36 and 38 were simplified and these details were not shown in the interests of clarity of presentation.
  • axle part 93 falls below shoulders 99 shown in Fig 8N undesirable "play" in the position of flipper 24 is increased.
  • axle part 99 falls below a shoulder 99 flipper 24 can get jammed under the shoulder and be prevented from rotating freely.
  • the height of shoulders 99 is determined by the thickness of sacrificial layer 82. In order to prevent flipper 24 from falling below a shoulder 99 the thickness of sacrificial layer 82 in the production process shown in Figs. 8 A - 8N must be less than the thickness of layer 91 from which flipper 24 is formed.
  • brackets 36 and 38 are produced using a method in which the height of shoulders 99 is not determined by the thickness of sacrificial layer 82 or brackets different from brackets 36 and 38 are used to couple flipper 24 to central electrode 30.
  • a relatively thick sacrificial layer 82 can be used, for example, in order to increase the space between flipper 24 and first elecfrode 26 and second electrode 28 when flipper 24 is in the on and off position respectively in order to decrease stiction.
  • a possible manufacturing procedure for producing brackets 36 and 38 with "low' shoulders is discussed at the end of the discussion of Fig. 12L.
  • FIGS. 9A-11 Other pixels and brackets for mounting flippers to pixels, in accordance with embodiments of the present invention are shown in Figs. 9A-11. Pixels and brackets shown in Figs. 9A - 11 are produced using fabrication procedures that are variations of the procedure illustrated in Figs. 8A-8I.
  • Figs. 9A-9B schematically show a pixel 100 comprising a flipper 24, in accordance with an embodiment of the present invention.
  • pixel 100 which is shown in a perspective view, is very similar to pixel 20. The only difference is in the construction of the brackets that couple flipper 24 to elecfrode 30.
  • flipper 24 is coupled to electrode 30 by U brackets 36 and 38 each of which has two legs that attach the U bracket to electrode 30.
  • flipper 24 is coupled to electrode 30 with brackets 102 and 104 each of which has a single leg 106 that attaches the bracket to electrode 30.
  • Each of brackets 102 and 104 has a second leg 108 that does not extend all the way to electrode 30.
  • Gap 110 is best seen in a profile view of pixel 100 taken along a line B - B shown in Fig. 9 A. Gap 110 is made small enough so that flipper 24 does not slip out or shake loose from brackets 102 and 104. Brackets 102 and 104 are smaller than brackets 36 and 38 because brackets 102 and 104 are anchored to cenfral pixel 30 at one location whereas brackets 36 and 38 are anchored to cenfral pixel 30 at two locations.
  • brackets 102 and 104 with respect to brackets 36 and 38 is advantageous.
  • surfaces of a pixel in accordance with an exemplary embodiment of the present invention, are treated to give the pixel a first and second color, e.g. black and white
  • the flipper of the pixel is turned to an on position, for example, and all exposed surfaces of the pixel are freated to give them the first color.
  • the pixel flipper is then turned to the off position and all exposed surfaces of the pixel in the off position are treated so that they have the second color. Surfaces that are exposed in both the on and the off position of the flipper therefore have the second color.
  • brackets used to couple a flipper to a pixel are exposed in both the on and off positions of the flipper and therefore the size of brackets that are used to couple a flipper to a pixel are reduced, in some embodiments of the invention.
  • Figs. 10A-10B schematically show perspective views of another pixel 120 comprising a flipper 122, in accordance with an embodiment of the present invention.
  • flipper 122 has mounting holes 124 and an edge 126 having slots 128 that merge with mounting holes 124.
  • flipper 122 is coupled to central elecfrode 30 by optionally identical brackets 129 and 130.
  • Bracket 130 is cut away in Fig 10A to show its construction.
  • Each of brackets 129 and 130 comprises a septum 132 and a rim 134. Septa 132 of brackets 129 and 130 fit in slots 128 of flipper 122 and prevent movement of flipper 122 in a direction parallel to edge 126.
  • Rims 134 of brackets 129 and 130 prevent flipper 122 from detaching from brackets 129 and 130.
  • each of brackets 129 and 130 may be anchored to central electrode 30 at only one location.
  • one end of each of rims 134 is anchored to central electrode 30 and a small space 133 separates most of each septum 132 and each of the other end of a rim 134 from central electrode 30.
  • Insert 135 in Fig 10A shows a schematic profile view of bracket 134 and central electrode 30 that illustrates the manner in which bracket 129 is attached to central electrode 30.
  • Fig. 11 schematically shows a perspective view of another pixel 140 comprising flipper 142, in accordance with an exemplary embodiment of the present invention.
  • Flipper 142 has protuberances 144 at opposite ends of edge 146 of the flipper.
  • Protuberances 144 are held in socket brackets 148.
  • Socket brackets 148 comprise a back panel 150 and a rim 152.
  • Back panel 150 prevents flipper 142 from shifting laterally in a direction parallel to edge 146.
  • Rims 152 prevent flipper 142 from separating from socket brackets 146.
  • Each of brackets 148 is optionally anchored to central electrode 30 at one location by a "foot" 149, only one of which is shown in Fig. 11.
  • a small space 151 separates most of the body of a bracket 148 from central elecfrode 30.
  • socket brackets 148 comprise only rims 152. Rims 152 prevent flipper 142 from shifting laterally in a direction parallel to edge 146 as a result of contact of rims 150 with the short edges of flipper 142.
  • pixels and flippers shown in Figs. 1A-11 are rectangular, pixels having shapes other than rectangular, in accordance with exemplary embodiments of the present invention, are possible and can be advantageous.
  • pixels can be formed in accordance with exemplary embodiments of the present invention in which the pixels are diamond shaped or hexagonal. A flipper for a diamond shaped pixel would be triangular and cover half the area of the pixel. A flipper for an hexagonal shaped pixel would cover half the hexagonal area of the pixel.
  • Figs. 12A - 12K illustrate schematically a process for forming pixel 100 shown in Figs. 9A and 9B.
  • Figs. 12A - 12K show cross-sectional views taken along a line A - A shown in Fig. 9 A of a process for forming and etching layers required to produce pixel 100.
  • insulating layer 23 is deposited on substrate 22.
  • a layer 80, shown in Fig. 12B, of conducting material is then deposited on insulating layer 23.
  • Layer 80 is etched to form first, second and central electrodes 26, 28 and 30 respectively which are shown in Fig. 12C.
  • Fig. 12D elecfrodes 26, 28 and 30 and exposed surfaces of insulating layer 23 are covered with sacrificial layer 82.
  • Sacrificial layer 82 is covered with a layer 84 of conducting material, which is shown in Fig. 12E.
  • Layer 84 is etched to produce flipper 24 shown in Fig.
  • flipper 24 appears to have two disconnected parts, an axle part 93 and a body part 91, however this is only an artifact of the choice of cross-sectional cut.
  • sacrificial layer 82 are etched away as shown in Fig. 12G to lay bare regions 228 and 229 of central electrode 30.
  • a relatively thin sacrificial layer 226 is then deposited on all exposed surfaces of pixel 100.
  • Sacrificial layer 226 is then etched to uncover a small region 230, shown in Fig. 121, of central electrode 30.
  • Sacrificial layer 226 serves to physically isolate axle part 93 (and body part 91) from a next conducting layer 232, shown in Fig 12J, that is deposited on pixel 100.
  • Region 230 that is uncovered when sacrificial layer 226 is etched, serves as an area of cenfral elecfrode 30 to which conducting layer 232 bonds strongly.
  • Conducting layer 232 is etched to form bracket 104 and all sacrificial layers are eroded away to form pixel 100 shown in Fig. 12K and also in Figs. 9A and 9B.
  • Some embodiments may not include nubs (which reduce the area of contact) or the nubs may not reduce stiction by a sufficient amount.
  • the following description contemplates various methods of counteracting and/or avoiding stiction, in accordance with various exemplary embodiments of the invention. However, it is noted that some embodiments of the invention will utilize more than one or none of the following described methods. It is expected that some combinations of methods will interact in a synergistic manner, drastically reducing stiction.
  • the flipper-pixels are encased in a sealed environment.
  • This environment may include desiccant materials, as well as dry gasses, such as nitrogen.
  • the flipper may move in a vacuum.
  • the sealed environment comprises a flat layer of glass or another transparent material which is suspended over the flipper plane by a plurality of support elements protruding between the flippers, at the periphery of the display and/or replacing individual flippers.
  • groups of pixels or the whole display are in a single sealed cell.
  • one or more levitation electrodes are provided adjacent the flippers to assist in overcoming the stiction forces by applying an extra force beyond that applied by the plane electrodes.
  • Fig. 13A illustrates a pixel 300 including a levitation elecfrode 302, in accordance with an embodiment of the invention. Except for elecfrode 302, Fig. 13A corresponds exactly to pixel 20 shown in Fig. 1 A.
  • Fig. 13B is a sectional view along a line A-A of pixel 300, showing levitation electrode 302 and showing lines of an electric field generated by the levitation electrode and an optional corresponding electrode 304 on the other side of the flipper.
  • levitation electrode 302 exerts levitation forces perpendicular to flipper 24 and at its end, where they have a greater leverage for flipping the flipper and overcoming stiction. Once the flipper is levitated, these extra forces are not needed and can be shut off. In a typical configuration, these levitation forces will tend to obstruct the flipping, and, so, are optionally shut off so that they do not adversely affect the flipping. It should be noted that similar, albeit smaller, perpendicular forces can be achieved even if the elecfrode 302 is shorter, at the level of the flipper or even slightly below.
  • Fig. 13B shows an embodiment in which the levitation forces directly raise the flipper.
  • other forces vectors can be used to overcome the stiction.
  • the levitation forces may be used to move flipper 24 in the plane of the flipper, thereby breaking the flipper's adhesion to the substrate below it.
  • a particular levitation electrode is shown.
  • the electrodes can be solid or ribbed.
  • the height of the electrode may vary, for example, the levitation elecfrode can be at the height of the flipper.
  • the electrode is 6 microns from the base of the flipper.
  • the location of the electrode can vary.
  • a levitation electrode may be situated along the outside edge of the flipper (as shown), along its side and/or at a corner of the flipper (near the outside edge or near the hinge).
  • an opening may be defined in the flipper and the levitation elecfrode placed in the opening.
  • the flipper is slotted from the outside edge towards its middle and a levitation electrode protrudes through the slot.
  • the levitation electrode may be suspended above the flipper, for example attached to an under surface of a transparent cover.
  • the levitation electrodes are wired together and work in concert, so that precise alignment of the levitation elecfrodes and the flipper-pixels is not required.
  • the levitation electrode may be located at, adjacent or above the hinge area, for example to be symmetric with respect to the hinge.
  • a planar levitation electrode is shown, in some exemplary embodiments of the invention, the electrode can be non-planar, for example being columnar.
  • the elecfrode may border the flipper on two or three sides.
  • Another parameter of the electrode which may be controlled is its length (along the length of the pixel edge - opposite the hinge). Although an electrode which is as long as the flipper is shown, shorter electrodes may be provided, for example, elecfrodes between 30% and 80% of the dimension of the flipper.
  • Another parameter which may be controlled is the symmetry of placement of the elecfrode relative to the flipper shape, the flipper hinge and other levitation electrodes. In some cases it is desirable that the force lines be generated in a certain direction which is oblique to the flipper motion. Alternatively or additionally, non-symmetrical positioning may be used to reduce the effects of levitation electrodes of one pixel on another pixel. Alternatively or additionally to the position being asymmetrical, the size and/or shape of single elecfrodes may also be asymmetric. Also the activation (voltage, timing) of the electrodes (for example as described below) may be different for different electrodes and or pixels.
  • Fig. 13B two levitation electrodes are shown, one on each side of the pixel.
  • levitation electrodes are shared between pixels.
  • a possible arrangement is to alternate levitation electrodes every other pixel. If corner levitation electrodes are used a saving of a factor of two or four in the number of levitation elecfrodes can be achieved. It is noted that a line or other grouping of levitation electrodes may be wired together to be activated simultaneously.
  • a different levitation elecfrode is electrified (or a different electrification profile is used), depending on the type of flipper movement, e.g., left, right and/or speed.
  • a same electrification may be used for different flipper movements, for example if the elecfrode is alongside the side of the flipper (perpendicular to the hinge), rather than its edge, any electrification of the electrode will cause the flipper to levitate, thereby breaking the stiction.
  • several electrodes are operated in concert in order to overcome the stiction, for example as shown in Fig. 13B.
  • a levitation electrode may, in some embodiments of the invention, comprises a plurality of sub-electrodes, which may be arranged, for example, vertically or horizontally.
  • the sub-electrodes may be electrified in parallel or in series.
  • the sub- electrodes may be electrified with different voltages.
  • the voltage on the levitation elecfrode is varied during its application, for example, using a timing circuit.
  • One possible type of variation is to modify the voltage as a function of the expected position of the flipper. For example, as the flipper moves, the voltage is reduced (e.g., until it is zero).
  • different elecfrodes or parts of the electrode are electrified as a function of the flipper position.
  • the electrification is modified as a function of the stiction forces, which can be measured in a laboratory, for example, for setting the timing circuit.
  • the electrification is varied responsive to the flipping speed, for example a higher voltage being used if higher flipping rates are required. The variation in voltage may be continuous or it may be stepped, for example depending on the control electronics used.
  • the timing of levitation electrodes is synchronized with the flipping of flippers.
  • the levitation electrodes are activated to break stiction prior to activating the flipping electrodes. The amount of force provided may be only sufficient to break the stiction or it may be enough to actually lift the flipper a certain amount.
  • the levitation electrode and flipping electrodes have an overlapping activation, to apply a maximum force against stiction.
  • the levitation elecfrode is used to cause vibrations or otherwise flexing of the flipper and/or associated structures.
  • the levitation electrodes may be activated before the flipping electrodes, which are activated in a manner timed to utilize the effect of the levitation electrodes .
  • levitation elecfrodes may be activated to break stiction on a plurality of pixels (or the entire device) simultaneously, with the flipping electrodes being activated only for selected ones of the pixels.
  • different amounts of force are applied by different levitation electrodes and/or flipping electrodes for different pixels. This reflects differences in stiction and/or friction for different flippers.
  • a levitation electrode for a flipping-type pixel.
  • levitation electrodes may also be advantageously used in other pixel types, for example as described in the prior art or even in the instant pixels in scales larger than one millimeter square.
  • a levitation electrode breaks the stiction and a functional electrode causes the element to change state.
  • a stiction counter-acting electrode may be used in other MEMS devices, for example to assist in the initiation of the motion of rotors or other moving, bending or flexing elements which adhere to the substrate or other micro-mechanical structures.
  • Such elements may be smaller (in their maximum dimension) than 5 millimeters, 1 millimeter, 0.1 millimeter, 0.01 millimeter or even 0.005 millimeters, depending on the application. Alternatively, larger elements are provided.
  • a stiction-countering elecfrode may be used in a electrostatic motor or to loosen up a beam-type sensor.
  • Figs. 14A-14F which correspond to some of figures 8C-8M, illustrate steps in manufacturing a pixel, having levitation electrodes, in accordance with an embodiment of the invention. This method is only exemplary and many other manufacturing methods and variations thereof will occur to a person skilled in the art.
  • Fig. 14A corresponds to Fig. 8C and shows a pixel 310 having two electrode bases 312 formed along with electrodes 28, 30 and 26.
  • Fig. 14B corresponds to Fig. 8D and shows anchor vias 314 formed along side vias 81 and 83 for allowing an upper electrode layer formed later to contact electrode bases 312.
  • Fig. 14C corresponds to Fig. 8F and shows second electrode portions 316 formed above layer 82 and in a same plane as flipper 24. It should be noted that elecfrode portions 316 contact electrodes bases 312 through vias 314.
  • Fig. 14D is a side view of Fig. 14C, showing only the electrodes, in which layer 82 is transparent, showing the bridging of electrode layers 312 and 316 through vias 314.
  • Fig. 14E is a rendering of Fig. 14C, in which layer 82 is transparent, showing the double levitation electrode structure.
  • Fig. 14F corresponds to Fig. 8M and shows the final structure, in which three elecfrode layers are deposited, including a top elecfrode portion 318.
  • the levitation elecfrodes may be designed to have a minimal shadowing effect on pixel 300, by being low, narrow and perforated. In other embodiments, only one of these features is used.
  • the levitation electrodes may be made reflecting, to reflect the surface color of the adjacent flipper and/or substrate.
  • transparent levitation electrodes are used. In the embodiments where the elecfrodes are formed above the flipper, they may be comprised of transparent conductive polymer deposited on a transparent cover.
  • the amount of stiction between a flipper and a substrate is reduced by providing electrically insulating nubs between them, to reduce the area of stiction.
  • This and other techniques described below may also be provided using nubs on the flipper instead of or in addition to nubs on the subsfrate, on the same side of the flipper or possibly one type of bump on either side of the flipper.
  • a low stiction coating is used between the flipper and the subsfrate.
  • the coating also servers a visual function, for example providing a reflective
  • Silicon Nitride which, depending on the thickness of the layer, is either reflecting or absorbing.
  • the coating may be applied over nubs 44 (Fig. 8M) or underneath them.
  • Silicon Nitride Alternatively to Silicon Nitride, other materials or groups of materials may be used to provide the dual insulation-color functions. Other materials may also be selected, for example based on having the property of varying their optical characteristics based on chemical and/or physical variations in the material and/or its crystal structure. Silicon Nitride coating is described, for example in "Fabrication of Micromechanical Device for Polysilicon Films with Smooth Surfaces", by Guckel, in Sensors and Actuators 20 (1989) 117-122, the disclosure of which is incorporated herein by reference.
  • such materials may also be used to coat the hinge (38 in Fig. 8M), to reduce stiction and/or friction.
  • surface area reducing techniques as described below for nubs may also be applied to the hinge.
  • the tips of nubs 44 are manufactured to have a minimal sized contact area with the flipper, for example using an isofropic etch to make them small, as described for example in "Stiction in Surface Micromachining", by Tas, in L
  • the nubs may be pitted (e.g., have one or more cavities formed at their top), further reducing the contact area.
  • Figs. 15A-15E illustrate an exemplary method of manufacturing a pitted nub, in accordance with an embodiment of the invention
  • a silicon subsfrate 330 is provided, coated with a nitride layer 331 and an elecfrode layer 332, such as for elecfrode 24.
  • a sacrificial oxide layer 334 is formed on the electrode, with a via 335 therein.
  • a polysilicon layer 336 is formed which fills via 335.
  • layer 336 is patterned to remove it except in the vicinity of via 335.
  • layer 336 is etched to remove it down to the level of layer 334 or even slightly below. This removal is optionally achieved using an isofropic wet etch, although other methods known in the art may be used.
  • layer 336 is further etched to form a pit 338 in the top of a formed nub 340. Thereafter, a layer of Silicon Nitride may be deposited.
  • the nubs are formed closer to, rather than further from hinge 38, to allow a greater leverage for levitation electrodes and flipping electrodes against stiction.
  • the nubs may be formed far from the hinge to allow the flipper to sag and/or vibrate.
  • Figs. 15F-15G illustrate an alternative method of forming a rounded nub, in accordance with an embodiment of the invention.
  • a nitride layer 331 is deposited on a silicon substrate 330.
  • a polysilicon layer 342 is deposited and then a photoresist layer 344 is deposited above.
  • other materials than polysilicon may be used, for example oxide or other materials known in the art.
  • the photo-resist layer is patterned, as shown in the Fig. and then an isofropic etch is used to undercut polysilicon 342 (or other materials used) underneath, forming a narrow nub-stub (shown dotted as element 343). Then, in Fig.
  • a layer of polysilicon 346 is deposited for the elecfrodes, and, coating the nub-stub, a small-tip nub is formed, which tip is smaller than the process dimensions. Thereafter, a layer of nitride may be deposited.
  • a layer of nitride may be deposited.
  • active methods of reducing stiction may be used.
  • One active method is to vibrate the flipper and/or other associated pixel structures so that stiction is broken or at least so that during the vibration stiction is reduced sufficiently for levitation electrodes or flipping electrodes to break the stiction. This may require timing the electrification of these elecfrodes to the modes of the vibration. However, it may not be required in all embodiments.
  • the induced vibration may include a component in the direction of flipper motion or it may be wholly perpendicular to the flipper motion.
  • the effected vibration may have a component in the direction of the flipper motion.
  • the vibration is generated by electrifying electrodes in a periodic or other manner to induce the vibrations, for example, the levitation electrodes (or the flipping electrodes) may be switched on and off at a resonance frequency of the flipper (or other pixel structures), thereby increasing the vibration amplitude until the stiction is broken.
  • This vibration may be combined with DC forces.
  • special vibration causing elements may be provided to generate the vibratory motions.
  • the vibration of the flipper is a side effect of the flipping of the current or other flippers, so that the flipper are usually vibrating.
  • the device is constructed with a reduced inter-pixel damping, so that vibration of one flipper is coupled to vibration of other flippers.
  • damping is provided to decouple the flippers.
  • the vibrations may be locally generated, for example, by providing a piezoelectric material associated with a pixel or groups of pixels.
  • a piezoelectric material associated with a pixel or groups of pixels.
  • remote generation of vibrations by a single or a few sources, is utilized.
  • Fig. 16 illustrates a display device 350 on a substrate 351 including a vibration generator 352, in accordance with an embodiment of the invention.
  • flippers in a display area 360 are excited by a piezoelectric material 356 sandwiched between an electrode 354 and an electrode 358 at a periphery of the display device.
  • the vibrations are optionally only activated at the start of a flipping cycle. However, if desired they may be activated continuously.
  • the pixel element which is vibrated is the flipper.
  • the flipper may be made of a suitable flexible material. Alternatively, a plurality of apertures may be formed in the flipper or the flipper made hollow, to support such flexing.
  • energy storage in the flipper is provided using one or more springs attached to the flipper and optionally formed integral with the flipper.
  • Figs. 17A and 17B illustrate a flipper 370 with integral springs 372 in a top view and a side view thereof, in accordance with an embodiment of the invention.
  • a pair of nubs 374 are shown near the hinge, to enhance the flexing of the flipper.
  • the springs may be formed along any part of the edge of the flipper, or even in the middle of the flipper, if they extend beyond the flipper plane. Additionally, other numbers of springs may be used, for example one or three.
  • the springs are shown as being formed by extensions of the sheathing of flipper 370 without an internal support. In an embodiment of the invention, the sheathing is formed of Silicon Nitride.
  • Figs. 17C and 17D illustrate steps in manufacturing an integral flipper spring 372 in accordance with an embodiment of the invention.
  • a polysilicon layer 380 is sandwiched between a nitride layer 376 and a nitride layer 378. Then the flipper is covered with a photo resist layer and a hole is formed in the photo resist layer adjacent spring 372.
  • a wet etch may then be used to etch polysilicon layer 380 underneath nitride layer 376 while the photo resist layer protects the rest of the pixels from the etching
  • Fig. 17D shows the resulting springs in which layer 380 is etched away in spring 372.
  • the spring are used to enhance the effects of vibration, for example amplitude, energy storage, and or coupling of vibration modes.
  • the nubs may be formed to enhance the transfer of vibration, especially increasing the vibration amplitude, to the flipper.
  • the flipper must flex in order to be in contact with both the nubs and the springs, against the substrate.
  • a touch input device is associated with the flipper-pixels.
  • the touch sensitive area is above the flippers, so that the display functions as a touch screen.
  • the flippers may be used to generate a display for other types of touch input devices, such as touch-pads.
  • the area contacted by a finger is generally above the flippers, in some embodiments, at least some of the electronics and/or sensors associated with acquiring the touch input are at or below the flippers.
  • the resolution of the touch input is lower than that of the display, however, this is not essential.
  • the spatial resolution may be uniform. However, in some embodiments, non-uniform spatial touch resolution may be provided.
  • Various types of input technologies may be used, including, but not limited to capacitance based sensing, resistance based sensing, and SAW (surface acoustic wave) based sensing.
  • Fig. 18 A is a schematic circuit diagram for a passive type touch input device 400, in which a touch position is detected by a switch or a sensor at a touched location, in accordance with an embodiment of the invention.
  • a plurality of row electrodes 404 (formed in the substrate) cross a plurality of column elecfrodes 402 similarly formed on the substrate at a plurality of switches 406.
  • switches 406 When a switch is closed, for example as a result of pressure on the touch screen, the relevant row and column electrodes are shorted (or the resistance between them lowered) and this shorting can be detected using standard circuitry at the periphery of the device.
  • other types of pressure detection and/or switch closure detection circuitry may be used.
  • Fig. 18B is a schematic side view of device 400, showing a plurality of support elements 408 which space a transparent cover 410 from switches 406.
  • support element 408 When pressure is applied top cover 410, as shown for example by a reference 414, support element 408 is pushed down, thereby urging a row electrode 404 against a column electrode 402.
  • Flipper pixels can be disposed in areas 412 between the support columns.
  • row electrode 404 is suspended over column electrode 402 (or vice-versa) using a double suspension beam, connected to the subsfrate on either side of the column elecfrode.
  • switches 406 are shown as forming protrusions in the device surface (e.g., of the flipping elecfrodes), this is not essential and they can be flush, for example being formed in depressions.
  • Support elements 408 may be separate elements deposited onto of the row electrodes
  • cover 410 may be attached to cover 410.
  • a switch 406 is formed at a lower spatial resolution than the flipper, for example one switch every 50 linear pixels. Thus, some pixels may be replaced by switches. Alternatively, the switches (and support elements) are formed between pixels, or by reducing the sizes of neighboring pixels rather than removing them entirely.
  • they may be larger than a pixel.
  • a standard pixel may be created, which pixel is suitable for both flipping and touch detection.
  • a support element is deposited or otherwise attached over the pixel, that pixel serves as a switch 406, otherwise, the pixel remains a flippable pixel.
  • Fig. 19 is a schematic circuit diagram of a circuit for driving a flipper-pixel, in accordance with an embodiment of the invention. In an embodiment of the invention, this circuitry is implemented as a thin film, for example as used in thin film transistors, deposited under the flipper pixels, however, this is not essential.
  • This circuit can be used to translate column and row driving signals into an activation of the flipper.
  • a similar circuit may be used to activate the levitation electrodes, if any.
  • the following logic is used (and implemented using the circuitry shown and/or other driving and device control circuitry):
  • a word line is selected and all the data lines (for a row) are brought to an appropriate potential (when left is selected, right is grounded and vice-versa);
  • the data lines potentials cause one capacitor in each pixel to be charged, which charging turns on a thin film transistor (TFT);
  • the activated thin film transistor connects the middle electrode to the appropriate voltage, or ground, based on which capacitor was charged;
  • the middle electrode stays at that voltage until the capacitor discharges below the TFT on voltage.
  • line scanning is described, individual pixel scanning and other scanning methods known in the art may be used.
  • the circuitry for example as shown in Fig. 19, is deposited under the flippers.
  • the flippers can be manufactured using aluminum on glass technology, which is, in some variations thereof, similar to silicon processes, except that aluminum is used instead of polysilicon as a conductor and a polymer is used as the sacrificial layers.
  • other micromachining technologies may be used for constructing a device in accordance with an exemplary embodiment of the invention.
  • circuitry for the display as a whole e.g., peripheral-area circuitry
  • circuitry for the display as a whole may be provided using flip-chip bonding techniques.
  • integrated circuits can be attached to the face of the display device.
  • FIG. 20 illustrates an exemplary device 500 in which a pixel area 502 is connected by a plurality of lines 506 to driving circuitry.
  • a pixel area 502 is connected by a plurality of lines 506 to driving circuitry.
  • one set of lines are shown connected to a chip 510, while a second set of lines are shown as terminating at flip-chip bump-pads 508, which a flip-chip containing driving circuitry can be attached to.
  • flip-chip bonding wire bonding may be used.
  • a pixel In passive addressing, it is usually desired that a pixel has a step-like response to voltage, so that selectivity of the pixels to be flipped will be high.
  • stiction is used to provide such a step response.
  • the combination of levitation electrodes and flipping electrodes is required to flip a pixel, the elecfrodes being activated in series or in parallel.
  • other stiction reduction methods such as vibration may be used.
  • separate sets of row and column electrodes are provided for flipping and levitation uses.
  • the levitation electrodes may be electrified as groups or as a single unit for the whole display.
  • the above devices may be manufactured using many different technologies.
  • the pixels are manufactured using aluminum on glass technology. It should be noted that by using non-silicon substrates, larger display devices may be achieved. Further, by using flexible substrates, flexible display devices can be manufactured. Possibly, each pixel is stiffened, for example by depositing metal or silicon layers, so that the display device bends between pixels rather than at pixels.
  • Fig. 21 shows a pixel 900, in accordance with an embodiment of the invention.
  • Pixel 900 is very similar to the pixel shown in Fig. 4 and most of the elements have the same reference numbers as in that figure.
  • the main difference between Figs. 21 and 4 is that cenfral elecfrode 30 does not run the entire length of the pixel. Rather, portions 902 and optionally 904, of the cenfral elecfrode are separated from it.
  • these electrodes are separately electrified from the portion of electrode 30 that is connected to hinges 38.
  • portions 902 and 904 are separately electrified from portion 30 and optionally from each other.
  • portions 902 and 904 are symmetrically placed and electrified along the length of the axis of rotation of the flipper. This helps to avoid twisting of the flipper.
  • Some embodiments of the invention include only separate portion(s) 902 (inboard of the hinges). Other embodiments include only separate portions 904 (outboard of the hinges). Still other embodiments include both sections 902 and 904.
  • Fig. 22 is a version of Fig. 13B, in which one or more of the portions 902 and 904 is electrified with a voltage that has a different voltage level from the voltage on section 30 and thus, on flipper 24.
  • a study of Fig. 13B shows that the electric field that results from the voltages applied to the respective elements causes an overall upward force on the flipper 24, such that the portion of flipper 24 that is within the hinges is forced upward toward the hinge.
  • This upward force is the same force that, applied to the rest of the flipper caused the flipper to flip. However, it does cause an increase in the friction between the hinge and the portion of the flipper within the hinge.
  • any voltage difference (independent of whether portions 902 and 904 have the same or different polarity than flipper 24) between portions 902/904 and flipper 24 will pull the flipper down, or at least reduce the upward force on the left edge of flipper 24.
  • FIG. 23 is a variant of Fig. 8C.
  • electrode 902 is split lengthwise into elecfrodes 902A and 902B. This splitting allows for different voltages to be applied at the two electrodes and/or for voltages to be applied at different times. The present inventors believe that the additional degrees of freedom available from such splitting may allow for lower wear of the elements in flipping, taking into account a more sophisticated analysis of the flipping dynamics and providing a fine tuning of the balance of pressures, for example attracting the flipper sideways as well as downwards. Furthermore, it should be noted that only a central portion 902 is shown in Fig. 23.
  • portions 904 or use 904 without 902 While, for stability, it may be desirable to include portions 904 or use 904 without 902, this is not absolutely necessary.
  • portions 30 of the hinge do not really have any function, other than to hold the hinge and electrify the flipper. Thus, portions 30 may be made much shorter than shown in either Figs. 21 or 23, allowing for lower voltages on portions 902/904 to give a desired amount of force. In some embodiments of the invention, a constant voltage may be applied to portions
  • the voltage may be pulsed on during the flipping.
  • portions 902/904 may be grounded, at least during the flipping operation.
  • portions 902/904 and flipper 24 While an electric field should be made to exist between portions 902/904 and flipper 24 an electrical connection between them should be avoided. This can be easily provided by forming a very thin oxide, nitride or other insulating layer on the portions, it can also be provided by the thickness of portions 902/904 being less than that of portions 30, such that flipper 24 does not contact portions 902/904.
  • electrodes 902/904 can be used with any of the embodiments shown and not only with those illustrated in Figs. 21-23.
  • the use of a force at the hinges that pulls the flipper away from the hinge is applicable to any flipper, such as for example a pop-up mirror described at www.mdl.sandia.gov/micromachine/images6.html and zoomed images available from that site on the date of filing of the present application, that uses a force on the flipper to rotate the flipper around a hinge.
  • the rotating force need not be electrical, as in the above embodiments, but can be magnetic or mechanical (as in the pop-up mirror).
  • force on the flipper at the hinge need not be electrical, rather is can be magnetic (fixed or pulsed) provided by a fixed magnet or an electromagnet. Magnetic force could be supplied by a spiral printed conductor combined with a micro-machined electromagnet or magnetic materials deposited using methods known in the art.
  • a pixel in accordance with an exemplary embodiment of the present invention may comprise different combinations of features and elements of the exemplary embodiments of the present invention described above.
  • a pixel might omit features and/or elements comprised in the described exemplary embodiments.
  • features and/or elements shown only in different ones of the described exemplary embodiments may be combined.
  • entirely different pixel structures may be used.
  • the manufacturing methods described above may be considerably varies and for some embodiments of the invention, a completely different methodology of manufacture may be used to produce devices according to the invention. The scope of the invention is limited only by the following claims.

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Abstract

L'invention concerne un procédé pour faire pivoter un dispositif de basculement autour d'une charnière à partir d'une première position, un appendice dudit dispositif se trouvant à l'intérieur de ladite charnière. Ce procédé consiste à appliquer une première force sur au moins une première partie du dispositif de basculement, de sorte que ce dernier pivote autour de la charnière à partir de la première position, et à appliquer une seconde force sur une seconde partie du dispositif de basculement dans une direction opposée à celle de la première force, cette seconde force étant développée et localisée dans le but de réduire ou de supprimer la pression de l'appendice contre la charnière.
PCT/IL2000/000475 1999-09-08 2000-08-06 Ecran plat de micromecanique WO2002013168A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU2000264660A AU2000264660A1 (en) 2000-08-06 2000-08-06 Micro-mechanical flat-panel display
TW089119362A TW523608B (en) 2000-08-06 2000-09-20 Method of rotating a flipper and visual display

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IL1999/000488 WO2000052674A1 (fr) 1999-03-04 1999-09-08 Ecran d'affichage micromecanique a entree tactile et source de vibrations

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US7495198B2 (en) 2004-12-01 2009-02-24 Rafael Advanced Defense Systems Ltd. System and method for improving nighttime visual awareness of a pilot flying an aircraft carrying at least one air-to-air missile
US7888644B2 (en) 2005-03-08 2011-02-15 Rafael Advanced Defense Systems Ltd. System and method for wide angle optical surveillance

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