ARRAY OF ELECTROSTATICALLY ACTUATED BINARY DEVICES AND METHODS OF MANUFACTURE

Abstract: Electrostatically actuated binary device arrays have electrostatically attractable flaps to change state. The flaps have plural electrode regions as do the stators to which they are attractable. A method of manufacture of an array assures reproducibility and accuracy. The arrays can be used for alpha-numeric or visual image display, for switching matrices, and for memories.

Description: -/- ARE-AY OF ELECTROSTATICALLY ACTUATED BINARY DEVICES AND METHODS OF MANUFACTURE Background of the Invention This invention relates to electrostatically controllable electromechanical binary devices for use as an array in visual displays, switching matrices, memories, and the like. The prior art contains various examples of electrostatic display elements. One type of device such as is shown in U.S. 1,984,683 and 3,553,364 includes light valves having flaps extending parallel with the approaching light, with each flap electrostatically divertable to an oblique angle across the light path for either a transmissive or reflective display. U.S. 3,897,997 discloses an electrode which is electrostatically wrapped about a curved fixed electrode to affect the light reflective character of the fixed electrode. Further prior art such as is described in ELECTRONICS, 7 December 1970, pp. 78-83 and I.B.M. Technical Disclosure Bulletin, Vol. 13, No. 3, August 1970, uses an electron gun to electrostatically charge selected portions of a defor able material and thereby alter its light transmissive or reflective properties. Additional instruction in the area of electrostatically controlled elements useable for Additional instruction in the area of electrostatically controlled elements useable for display purposes can be gained from the following U.S. patents: 4,336,536 Kalt et al 4,266,339 Kalt 4,234,245 Toda et al ' 4,229,075 Ueda et al 4,208,103 Kalt et al 0 4,160,583 Ueda et al 4,160,582 Yasuo 4,105,294 Peck 4,094,590 Kalt 4,065,677 Micheron et al 5 3,989,357 Kalt 3,897,997 Kalt 888,241 Kuhl ann The present invention proceeds from material disclosed in Simpson U.S.. 4,248,501, and Simpson et ^ ai 4,235,522, the disclosure of which is incorporated herein by reference. Of background interest are: .R. Aiken: "An Electrostatic Sign - - The Distec System", Society for Information 5 Display, June 1972, pp. 108-9; J.L. Bruneel et al: "Optical Display Device Using Bistable Elements", Applied Physics Letters, Vol. 30, no. 8, 15 April 1977, pp.382-3, and R.T. Gallagher: "Microshutters Flip to 0 Form Characters in Dot-Matrix Display", Electronics, 14 July 1983, pp. 81-2. This application is related in subject matter to our copending U.S. applications S.N. 642,752, 642,996, and 683,619. The disclosures of these 5 applications are incorporated herein by reference. Summary of the Invention The present invention provides an electrostatically controllable electromechanical binary device for light reflective or light transmissive display arrays, switching matrices, memories, and the like. Each binary element in the array can be controlled individually. The invention will be described in the context of use as a visual display, including black and white and multi-color alpha-numeric and pictorial displays. A display element (pixel) of the invention has a stator including stationary electrodes and an adjacent moveable flap electrostatically controllable between a position removed from the stationary electrodes and a position overlying the stationary electrodes. In a preferred embodiment, the stator has a flat surface normal to the light path, with a curled flap, when attracted, uncurling to roll adjacent to and covering the stationary electrodes on the flat stator surface. The display element can control light transmission or can affect light reflection qualities for a light reflective device. It is two-state or binary. It can be latched in either state. The display elements or pixels of the present invention are provided with conductive electrode regions on both the stator and the flap. When used as a two dimensional array of pixels one of the regions is designated as an X electrode, and another is designated as a Y electrode. All X electrodes in a row are connected together as are Y electrodes in a column. That pixel at the intersection of the column and the row is actuated to change status. In a preferred embodiment, one of either the X or Y regions is located on the flap and the other on the stator. Both the flap and stator have further electrode regions designated hold-down which serve to latch the actuated pixel in the actuated status after the X and Y electrodes are de-energized. A manufacturing method for making arrays of a myriad of small pixels, each independently addressable, is useable with photo-etch techniques or with direct printing of conductive inks. Brief Description of Drawings Figure 1 is a plan view of the flap member of an electrostatically operated binary element according to the present invention. Figure 2 is a plan view of the stator member. Figure 3 is a view of the assembly in section taken along line III-III of Figures 1 and 2. Figure 4 is a partial view in section of the substrate for an array of the binary elements of Figures 1-3. Figure 5 is a schematic view of a fixture for making the array. Figure 6 is a schematic view of two fixtures for making the array. Figure 7 is an. enlarged partial view of an unfinished binary element of the array. Figure 8 is a view in section along line VIII-VIII of Figure 7 showing the finished element. Detailed Description Figure 1 shows the configuration of one repeat of a pattern of conductive regions separated by gaps of chevron shape on the moveable flap 10. The flexible substrate 11 is a film such as polyethylene terephthalate (PET), sold as "MYLAR". The conductive regions 12, 14, and 16, as well as the conductor leads 17 and X are formed in the pattern shown in Figure 1 by direct printing with conductive ink or by photo- etching away portions of a conductive coating such as aluminum which has been vacuum deposited on the substrate 11. Region 12 is a hold-down region electrically connected to region 16. Region 14 is the X region and is integral with conductive lead X for electrical connection. Region 16 is a hold-down region and is integral with conductive lead 17. After formation of the conductive pattern, a slot (ndicated by dashed line 18) is cut, preferably by a laser beam, to free the flap on three sides. Figure 2 shows the conductive regions separated by gaps of chevron shape on the stator member 20. The PET substrate 21 is provided with conductive regions 22, 24, and 26 as well as conductive leads Y and 27 in the manner described for the flap 10. Region 24 is the Y region and is integral with lead Y. Hold-down regions 22 and 26 are integral with lead 27. Figure 3 is a section taken along line III-III after superposition of stator member 20 (Figure 2) over flap member 10 (Figure 1). Since the slot 18 has been cut, such as by laser beam, the flap ιo is now free to curl as is shown. When actuated to flatten the flap, the X region 14 of the flap 10 will underlie hold-down region 22 of the stator 20; Y region 24 of the stator will overlie hold-down region 16 of the flap; and hold-down region 26 of the stator will overlie hold-down region 16 of the flap. The following is a description of a procedure for manufacturing arrays of display elements (pixels) as shown in Figures 1 - 3. An array for display of a full-size page of printed matter can, for example, be on the order of 10.8 X 14.0 inches and have 540 X 630 = 340,200 pixels for 70 lines of 90 characters, each character being 6 X 9 pixels. Each pixel in the array of this example is 22 mils (thousanths of an inch) high and 20 mils wide. Each pixel is a superposition of the patterned substrates of Figures 1 to 3 overlying a channel approximately 15 mils deep defined by parallel walls about 3 mils thick formed on a flat sheet of rigid material such as glass. Figure 4 is a sectional view showing a sheet 40 of glass 12 X 16 X .125 to which a 15 mil coating of photo-etch resist polymer 42 has been applied. The resist coating is exposed to a source columnated (parallel) light 46 through a negative mask 44 having a photographically generated opaque grid 45 representing the pattern of resist to be retained. T e exposed areas of resist 42 are susceptible to etchant or solvent for removal whereas the unexposed areas 43 will remain after etching to form the 3 X 15 mil walls of the 20 mil wide channels. A converse resist which becomes etch resistant where exposed may be used with a converse mask. The channel pattern of walls can be formed by other techniques than photo-etching. Mass production could justify injection molding dies to mold or cast the walls and substrate 40 as an integral piece of appropriate thermoplastic polymer. Figure 5 is a sectional view showing a sheet 52 of 0.06 mil thick polyethylene terephtalate (PET) film (MYLAR) wrapped about a mandrel or fixture 50 of metal or glass. The very thin PET film can be held flat by surface tension of a liquid or by electrostatic force. The film is aluminized on both sides by well known vacuum vapor deposition techniques. The held film is stress relieved by heating to about 212°F. Figure 6 is a sectional view showing a similar fixture 60 to which is clamped a clear. uncoated sheet 62 of 0.06 mil PET film which has been stretched in tension in one direction indicated by the double-headed arrow. While held on fixture 60, uniaxially stressed sheet 62 is laminated to stress-free alu inized sheet 52 held on fixture 50. One method of laminating sheet 62 to sheet 52 is to stress relieve PET sheet 52 while maintaining an electrical potential between the aluminum coatings 53 and 54. Doing so renders the PET.an electret with a permanent electrostatic charge. The charge is sufficient to adhere sheets 52 and 62 together. The laser beam cutting performed in a later step serves to weld together the edges of sheets 52 and 62 when they are cut into flaps 10. The laminate of tensioned film 62 and stress relieved aluminized film 52 is bonded to the top surfaces of the walls 73 of resist polymer which remain after the photoetching step described in connection with Figure 4. The result is shown in Figure 7 which is an enlargement. Channel walls 73 typically are 3 mils thick, 15 mils high, and separated by the 20 mil width of a pixel. The extremely thin aluminized coatings 53 and 54 are found on each surface of film sheet 52. The substrate 0 is the sheet of glass upon which the photo-etched channel pattern was formed. A photo-etch resist is sprayed onto the upper surface of sheet 52 of the laminate. The pattern of conductive regions of the flap is projected by the well known step-and-repeat photographic technique widely used in integrated circuit manufacture. The aluminum coating 53 is then etched to produce the conductive pattern of Figure 1 at each of the 340,200 pixel locations in the array. A programmed laser beam cutting device then cuts a slot around three sides of the flap 10 to free it. The cutting line is indicated by dashed line 18 in Figure 1. The lamination of stressed PET film 62 to stress relieved PET film 52 causes the now free flap 10 to curl as is shown in Figure 8. Using a fixture essentially identical with that of Figure 5, a third 0.06 mil thick film 84 of PET is stress relieved. Film 84 is provided with a transparent coating 82 which is slightly electrically conductive on the outer surface (the lower surface of 84 in Figure 8) and with an indium-tin oxide coating 86 which is a transparent, excellent electrical conductor on the inside surface (the upper surface of sheet 84 in Figure 8). Using the fixture, the coated, stress relieved sheet 84 is bonded to the upper surface of sheet 52 of the flap laminate 52, 62 as is shown in Figure 8. Using the photo-etch technique described for formation of the conductive region pattern for the flap 10, the transparent, conductive indium-tin oxide coating 84 is coated with resist, exposed in the pattern shown in Figure 2 and etched to form the stator conductive regions 22, 24, 26 also shown in Figures 2 and 3. A sheet of glass 88 or transparent non-conductive polymer is added for protection and strength to complete the assembly of the array. Of course, a photo-etched indium-tin oxide coating on the glass sheet 88 can be used in substitution for the separate PET sheet 84 described above. The above described technique of making the array, because electrode regions are determined by optical or printing techniques, assures not only identity of reproduction among arrays, but also exact registry of the several electrode regions of each element of the array. Consequently, the size of a pixel can be extremely small, limited only by materials considerations. Considering again Figures 1 to 3, it can be seen that the X leads of each pixel in an array are integral with the X leads of the neighboring pixels of each row. Similarly, the Y leads among neighboring pixels of each column are integral. Thus, at both side edges of the array, the X lead for each row is accessible and the Y lead for each column appears at the top and bottom edges. It is significant that no cross-overs or "plate-throughs" (conductors which pass through the substrate) are required. All conductive elements and their interconnections are purely two dimensional. A pixel at a particular X-Y address in the array can be actuated independently of all other pixels. Application of an electrical drive potential to the X lead for the selected row partially will attract all flaps 10 in that row because the X electrode areas 14 are energized. Application of an electrical drive potential to the Y lead for the selected column will cause no attraction of any pixel in the column other than the one at the desired address. This is because the Y electrode areas 24 are too remote from the other flaps 10 of the selected column. That of the selected pixel is, by virtue of partial actuation of all X electrodes 14 in its row, sufficiently proximate the Y electrode 24 to be attracted toward it. Thus, only the pixel at the selected address is actuated. All hold-down regions 12, 16 of the flaps 10 are interconnected as are all hold-down regions 22, 26 of the stators 20. Application of an electrical potential between the flap and stator hold-down leads will cause the just actuated pixel to remain actuated (flattened) after extinction of the X and Y drive potentials. Each pixel subsequently, previously, or concurrently addressed will also remain actuated until the hold-down potential is extinguished. The array can be operated in the converse by starting with all pixels actuated, extinguishing the hold-down potential, energizing all X and Y columns and rows, and then extinguishing the X and Y potentials in sequence for each selected pixel.. Restoration of the hold-down potential serves to preserve the unaffected status of pixels not addressed. This mode of operation is well suited to forming dark characters on a light (silver) field or, for characters which emit light from an illumination source behind the array. As is perhaps most easily seen in Figure 1-3, the gaps between adjacent electrode regions are oblique to the direction of flap movement. The chevron shape of the gaps provides a symmetry of electrostatic force to uncurl the flaps 10 without skewing. The oblique or chevron shape insures that the energized regions of the stator and flap have some overlap at the start of uncurling to initiate movement. It should be noted that the gap forming the distal (to the right in Figure 3) demarcation of discrete X electrode region 14 of the flap is congruent with the gap for the distal demarcation of the proximal stator hold-down electrode region 22, and thereby the proximal demarcation of the discrete Y electrode region 24 of the stator is congruent with the proximal demarcation of the distal hold-down electrode region 16 of the flap. This geometry assures that, when the stator and flap are in registry with each other, the X electrode region 14 and the stator proximal electrode region 22 align for maximum electrostatic force and that the Y electrode region 24 of the stator similarly aligns with the distal hold-down electrode region 16 of the flap. Pixel arrays according to the present invention can be used as capacitance switching arrays to reduce by a large factor the number of external leads required to control a display array.

Claims: WHAT IS CLAIMED IS: 1) An electrostatically actuated binary element comprising; a stator member having plural electrode regions, and an electrostatically attractable flap member having one end fixed with respect to the stator member and having plural electrode regions, the flap member having a permanent mechanical bias away from the stator, the bias being insufficient to overcome the electrostatic force acting on the flap when an electrical potential is applied between a stator electrode region and a flap electrode region proximate said stator electrode region. 2) The element of claim 1 wherein each of the •electrode regions of both the flap member and the stator member are separated from adjacent electrode regions by a gap oblique with respect to the direction of flap movement. 3) The element of claim 2 wherein said gap is of chevron shape. 4) An electrostatically actuated binary element comprising; a* stator member having plural electrode regions, and an electrostatically attractable flap member having one end fixed with respect to the stator member and having plural electrode regions, the flap member having a permanent mechanical bias away from the stator, the bias being insufficient to overcome the electrostatic force acting on the flap when an electrical potential is applied between a stator electrode region and a flap electrode region proximate said stator electrode region to cause the flap member to overlie the stator member. 5) The element of claim 4 wherein at least one gap on the flap member is congruent with a gap on the stator member when the flap member has been actuated to overlie the stator member. 6) An electrostatically actuated binary element comprising; a stator member having plural electrode regions separated from each other by gaps of chevron shape, an electrostatically attractable flap member having one end fixed with respect to the stator member and having plural electrode regions separated from each other by gaps of chevron shape, at least one gap on the flap member being located to be congruent with a gap on the stator member when the flap element is actuated, the flap member having a permanent mechanical bias away from the stator member, the bias being insufficient to overcome the electrostatic force acting on the flap when an electrical potential is applied between a stator electrode region and a flap electrode region proximate said stator electrode region to cause the flap to be attracted to and to overlie the stator member. 7) The element of claim 6 wherein the stator member has at least three electrode regions. 8) The element of claim 6 wherein the flap member has at least three electrode regions. 9) An electrostatically actuated binary element comprising; a flap member free on three edges and having plural electrode regions, and a stator member associated with the flap member, the stator having plural stator electrode regions, the flap member having a permanent mechanical bias away from the stator member. 10) An array of columns and rows of electrostat¬ ically actuated binary elements, each element comprising; a flap member free on three edges, having a permanent mechanical bias to curl, and having at least first, second, and third flap electrode regions, and a stator member " in registry with the flap member and away from which the flap curls, the stator having at least first, second, and third stator electrode regions, the flap members being formed on a first substrate, the stator members being formed on a second substrate, and the first and second substrates being superposed in registry. 11) The array of claim 10 wherein the second stator electrode and the second flap electrode regions are separated from their adjacent regions by gaps of chevron shape. 12) A method of making an array of rows and columns of binary elements, each element comprising an electrostatically attractable flap having plural electrode regions and a stator having plural electrode regions, the method comprising the steps of: a) forming on a substrate a plurality of parallel channels comprising upstanding straight walls separated by the width of the binary elements, b) to a stress-free first polymeric film having a conductive coating on both faces, laminating to one face a second polymeric film while said second film is held in uniaxial tension, c) bonding the exposed face of the second film of the laminate to the tops of the walls of the channels, d) either prior to step (b) or following step (c) forming in the conductive coating on the exposed face of the first film, at the location of each element, the electrode regions for that flap, e) freeing the flaps by cutting through the laminate around the three marginal edges of each flap, f) superposing a sheet of non-conductive material on the exposed face of the laminate, and g) either before or after step (f) forming on the sheet of non-conductive material, at the location of each element, the electrode regions for that stator. 13) The method of claim 12 wherein the channels formed in step (a) are formed by the steps of: 1) coating a rigid substrate with a photo-resist polymeric compound, 2) exposing the- photo-resist polymeric compound to light through a mask having a pattern for the desired channels, 3) dissolving away those portions of the resist not rendered insoluable by the exposure to light to thereby leave channel walls of polymer originating with the photo-resist compound. 14) The method of claim 12 wherein the first film of step (b) is polyethylene terephthalate having a vacuum deposited aluminum coating on both faces, and wherein the first film is rendered stress-free by stress-relieving at an elevated temperature. 15) The method of claim 12 wherein the second film of step (b) is polyethylene terephthalate. 16) The method of claim 12 wherein the electrode regions of step (d) are formed subsequent to step (c) by photo-etching the conductive coating on the exposed face of the first film of the laminate. 17) The method of claim 12 wherein the electrode regions of step (d) are formed prior to step (b) by printing with a conductive coating ink. 18) The method of claim 12 wherein the sheet of material of step (f) is a third film of polyethylene terephthalate. 19) The method of claim 12 wherein the third film has a transparent conductive coating on the face away from the face superposed on the laminate. 20) The method of claim 19 wherein the transparent conductive coating is photo-etched in the pattern of the stator electrodes after step (f). 21) The method of claim 19 wherein the pattern of the stator electrodes is formed in the transparent coating by printing prior to step (f). 22) The method of making an array of rows and columns of binary elements, each element comprising an electrostatically attractable flap having plural electrode regions and a stator having plural electrode regions, the method comprising the steps of: a) forming on a substrate a plurality of parallel channels comprising upstanding straight walls separated by the width of the binary elements, b) to a stress-free first film of polyethylene terephthalate having a vacuum deposited coating of aluminum on both faces, laminating a second film of polyethylene terephthalate while said second film is held in uniaxial tension, c) bonding the exposed face of the second film of the laminate to the tops of the walls of the channels, d) photo-etching the aluminum coating on the exposed face of the first film of the laminate to form the electrode regions of the flap, e) freeing the flaps by cutting through the laminate around the three marginal edges of each flap, f) superposing a third film of polyethylene terephthalate on the exposed face of the laminate, the exposed face of the third film having a transparent conductive coating, g) photo-etching the transparent conductive coating of the third film to form the electrode regions of the stator. 23) An array of columns and rows of electrostat¬ ically actuated binary elements comprising: a first planar member having at the location of each binary element at least three stator electrode regions separated from each other by gaps, a planar second member underlying the first member, the second member having an electrostatically attractable flap free on three edges at the location of each binary element, each flap having at least three electrode regions separated from each other by gaps, the flaps having a permanent mechanical bias away from the stator member, the bias being insufficient to overcome the electrostatic force acting on the flap when an electrical potential is applied between a stator electrode region and a flap electrode region proximate said electrode region to cause the flap to be attracted to the stator member. 24) The array of claim 23 wherein at least one of the gaps between the stator electrode regions for each element, and at least one of the gaps between the electrode regions of each flap are congruent when the element is actuated. 25) The array of claim 23 wherein all of the gaps between adjacent stator electrode regions and all of the gaps between adjacent flap electrode regions are of chevron shape. 26) The array of claim 23 wherein each binary element has first, second, and third stator electrode regions separated by gaps of chevron shape, and first, second, and third flap electrode regions separated by gaps of chevron shape, all of the first and third stator electrode regions being electrically connected together, the second stator electrode regions of all elements for each column of stators of the array being connected together and to an input lead for the column, all of the first and third flap regions being connected together. the second flap electrode regions for each row of flaps of the array being connected together and to an input lead for the row, whereby a selected element of the array is actuated when an electrical potential is applied between the second electrode regions of the column and the second electrode regions of the row for that element. 27) An electrostatically actuated binary element comprising an electrostatically attractable flap having plural electrode regions and a stator having plural electrode regions, the electrode regions being arranged serially in the direction of flap movement and being separated by oblique gaps, the flap having a permanent mechanical bias away from the stator, the bias being insufficient to overcome the electrostatic force when an electrical potential is applied between a stator electrode region and a flap electrode region proximate said stator electrode region to cause the flap to be attracted to the stator. 28) An array of columns and rows of independently selectable electrostatically actuated electrical switching devices, each device comprising a stator having discrete electrode regions, and an electrostatically attractable flap having discrete electrode regions, the stator having first, second, and third electrode regions, the first and third regions being electrically connected together, the second stator electrode region of each of the devices in a column of the array being connected together and connected to an input lead for that column. the flap having a first electrode region located to be aligned with the first electrode region of the stator, and a second electrode region located to be aligned with both the second and third electrode regions of the stator, the first flap electrode region of each flap in a row of the array being connected together and to a row input lead, the second flap electrode for each flap in the array being connected to an output lead, the flaps having a permanent mechanical bias away from the stator, the bias being insufficient to overcome the electrostatic force acting up on the flap when an electrical potential is applied between the row input lead and the column input lead for the selected device.

Inventors: SIMPSON GEORGE R, SULLIVAN HERBERT W, SIMPSON, GEORGE, R., SULLIVAN, HERBERT, W.
Applicants: SIMPSON GEORGE R, SULLIVAN HERBERT W, SIMPSON, GEORGE, R., SULLIVAN, HERBERT, W.
Application year: 1985
Main classification: G09F9
IPC codes: G09F9