EP0783762A1 - Source de lumiere pour enregistreur de film dotee d'une cathode a emission par effet de champ - Google Patents

Source de lumiere pour enregistreur de film dotee d'une cathode a emission par effet de champ

Info

Publication number
EP0783762A1
EP0783762A1 EP95935200A EP95935200A EP0783762A1 EP 0783762 A1 EP0783762 A1 EP 0783762A1 EP 95935200 A EP95935200 A EP 95935200A EP 95935200 A EP95935200 A EP 95935200A EP 0783762 A1 EP0783762 A1 EP 0783762A1
Authority
EP
European Patent Office
Prior art keywords
print head
light
field emission
head according
emission devices
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP95935200A
Other languages
German (de)
English (en)
Inventor
Michael L. Reisch
Joseph Delpico
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Polaroid Corp
Original Assignee
Polaroid Corp
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
Application filed by Polaroid Corp filed Critical Polaroid Corp
Publication of EP0783762A1 publication Critical patent/EP0783762A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/08—Electrodes intimately associated with a screen on or from which an image or pattern is formed, picked-up, converted or stored, e.g. backing-plates for storage tubes or collecting secondary electrons
    • H01J29/085—Anode plates, e.g. for screens of flat panel displays
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/30—Cold cathodes, e.g. field-emissive cathode
    • H01J1/304—Field-emissive cathodes
    • H01J1/3042—Field-emissive cathodes microengineered, e.g. Spindt-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J31/00—Cathode ray tubes; Electron beam tubes
    • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
    • H01J31/10—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes
    • H01J31/12—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes with luminescent screen
    • H01J31/123—Flat display tubes
    • H01J31/125—Flat display tubes provided with control means permitting the electron beam to reach selected parts of the screen, e.g. digital selection
    • H01J31/127—Flat display tubes provided with control means permitting the electron beam to reach selected parts of the screen, e.g. digital selection using large area or array sources, i.e. essentially a source for each pixel group

Definitions

  • the present invention relates generally to electrophotographic printing and film recording apparatus, such as light emitting optical printers. More particularly, the invention relates to apparatus for printing images by exposing a photosensitive recording medium to light generated by a field emission electron source.
  • Optical printers make use of a variety of exposure devices such as lasers, light emitting diodes (“LED” 's), spacial light modulators (“SLM” 's), and cathode ray tubes (“CRT” 's). All have been applied to expose photographic film as the photosensitive recording medium.
  • LED light emitting diodes
  • SLM spacial light modulators
  • CRT cathode ray tubes
  • a single emitter light source the laser for example, or light shutter can be used.
  • These exposure devices require two orthogonal mechanical motions to scan and expose the photosensitive recording medium.
  • Increased mechanical motions require a control system with a precision to govern and synchronize the mechanical motions which, in turn, raise complexity and cost of the optical printer.
  • the first method is a line scan method which uses the LED's or the SLM's configured into linear arrays. These are made long enough to span the width of the photosensitive recording medium so that an entire line is exposed at once.
  • the line scan method is more compact and faster than the single emitter light source but still requires mechanical motion to transport the photosensitive recording medium past the linear array.
  • Line arrays using LED's to form an image on the recording media are useful for high speed printing but are further limited by available colors of the LED's. Blue LED's, for example, are not made in arrays and are expensive.
  • the second method uses the CRT; a light spot is generated by focusing an electron beam which excites a cathode luminescent luminophor screen. Deflecting the beam with either electrostatic or magnetic fields allows scanning of the spot across a CRT face plate coated with a luminophor to translate absorbed electron beam energy into emitted luminescent radiation. The luminescent radiation is focused on the photosensitive recording medium to create an image thereon.
  • CRT's can be used in two ways: area raster scan and line scan. Area raster scan is when the beam is deflected in two directions. Line scan is as previously described where the beam is moved across one line at a time. Line scan types are more compact but, again, need a mechanical scan motion along one direction to expose the film. The area raster type eliminates the mechanical scan motion but requires additional complex electronics to control the beam in two directions.
  • Spot diameter formed on the CRT face plate primarily determines printer resolution.
  • a size of the electron beam as well as the face plate determine the spot diameter.
  • the beam is tightly focused so that the spot size is essentially dependent on the face plate and an amount of light piping, or internal light reflection introduced by the face plate.
  • the luminophor To minimize the spot on the face plate requires the luminophor to have particles which are small and have a uniform size. In addition, the thickness of the luminophor layer and the particular size distribution in the face plate must be extremely uniform to minimize spot intensity variations. Face plates fabricated from polycrystalline thin film fluorescent materials are used to improve spot size and reduce intensity variations, however this technique results in reduced optical output due to light piping in the thin film as well as higher manufacturing costs.
  • the beam in the CRT is formed by a high performance electron gun.
  • the beam must be continuously refocused to insure that the spot size is kept constant as the beam scans across the screen. This is achieved by dynamic focusing electronics which add additional expense to the exposure device.
  • the aforementioned and other objects are achieved by the invention which provides a field emission print head for an optical printer.
  • the print head projects light onto a photosensitive recording medium in the optical printer to record an image thereon.
  • the print head comprises a plurality of field emission devices, each having a first and a second electrode separated by insulation means; illuminescent means; and a third electrode.
  • the plurality of field emission devices are divided into groups where each group defines a single spot for printing purposes.
  • Each of the groups is addressable to alternate between an operative mode and an inoperative mode. In the operative mode, the groups emit electrons therefrom. In the inoperative mode, the group remains inactive without emitting electrons.
  • Each of the field emission devices have the first electrode which is adapted to have a first electrical potential applied thereto and has a protrusion extending therefrom.
  • the first electrode is common to all of the field emission devices in the group.
  • the insulation means is secured to a top surface of the first electrode and has a void overlying the protrusion.
  • the insulation means has a high dielectric strength to inhibit electrical conduction from the first electrode to the second electrode.
  • the second electrode is secured to the insulation means in a position opposed to the first electrode.
  • the second electrode is adapted to have a second electrical potential applied thereto and is operable to switch the field emission device between the operative mode and the inoperative mode.
  • the operative mode is achieved when a difference between the first electrical potential and the second electrical potential exceeds a threshold voltage thus causing protrusion to emit the electrons due to electron tunneling.
  • the inoperative mode is achieved when the threshold voltage is not exceeded.
  • the illuminescent means is separated from the field emission devices along a plane parallel to the field emission devices. It is laid out in spots corresponding to the aforementioned groups of field emission devices where the spots are fabricated from a luminophor which generates light upon excitement by the electrons.
  • the third electrode is also spaced apart from said field emission devices providing a platform upon which the illuminescent means is fixed.
  • the third electrode being light transmissive and adapted to have an electrical potential applied thereto which is selectable to greatly exceed said second electrical potential thus attracting said electrons into engagement with the illuminescent means.
  • the illuminescent means then emits light to project the image onto the photosensitive recording medium.
  • the invention provides methods in accord with the apparatus described above.
  • the aforementioned and other aspects of the invention are evident in the drawings and in the description that follows.
  • Figure 2 shows a perspective view of a detail of a print head in the system of Figure 1;
  • Figure 3A shows a view similar to that of Figure 2 of an electron emission structure also indicating trajectories and circuit structure
  • Figure 3B is a graph of a cathode current versus cathode gate voltage for the print head
  • Figure 4 shows a perspective and detail view of a print head in accordance with the invention as shown in Figure 1 ;
  • Figure 5A shows a top view of a portion of a fiber optic phase plate for use with the invention.
  • Figure 5B shows a profile of the face plate of Figure 5A for use with the invention.
  • FIG. 1 shows an optical printer 10 according to the present invention which is for recording electronic images onto a photosensitive recording medium 14.
  • the photosensitive recording medium 14 is an integral film, such as that described in commonly assigned United States Patent No. 4,563,411 entitled "Copolymeric Mordants and Photographic Products and Processes Containing Same" and issued to Irena Y. Bronstein-Bonte on January 7, 1986. Though this is the preferred embodiment, various other photosensitive recording media can be substituted without detriment to the invention.
  • the photosensitive recording medium 14 is fed into the printer 10 by conveyancing systems well known in the art and is drawn through the printer 10 by rollers 16 driven by drive motor 18. As the photosensitive recording medium 14 is pulled through the printer 10, a processor 19 transfers image data to a print head 20. The print head 20 then projects light (indicated by arrows) onto the photosensitive recording medium 14 such that a coherent image is formed thereon.
  • the print head 20 is a solid state thin film electron source which generates an electric field for luminescent excitation of luminophor materials thus producing light.
  • the print head 20 is shown as a line array for imaging a single line on the photosensitive recording medium 14.
  • An area device utilizing a plurality of line arrays can also be used and should be considered an alternative embodiment of the invention.
  • the luminophor material is one which translates at least a portion of absorbed energy into emitted luminescent radiation.
  • the luminophor is a phosphor based material.
  • the light is transmitted to the photosensitive recording medium 14 by the print head 20. The light then passes through a lens 21.
  • the lens 21 can be a conventional lens or as in the preferred embodiment can be an array of graded index rods, or grinrods. In the case of contact printing, the lens 21 would be removed and a light transmissive faceplate would be used. Such a faceplate is later herein described.
  • FIG. 2 illustrates a basic construction of a field emission cathode ray tube ("CRT") as applied to the print head 20 of the invention.
  • a cathode tip, or cone 26 emits electrons as shown by the dashed line which impinge a face plate 36 coated with a luminophor film 34 so as to excite the luminophor film 34 and emit light.
  • the print head 20 is fabricated with an array of the cones 26 deposited on a back plane 22. These operate at room temperature. Each cone 26 has a sharp radius at its apex such that electron tunneling is enabled when a positive voltage is applied to the gate film.
  • the back plane 22 is generally a glass substrate upon which the field emission CRT is fabricated.
  • a cathode 24 forms a next layer on the back plane 22 such that the cathode 24 extends over an entire surface of the back plane 22.
  • the cathode 24 has the aforementioned array of cones 26 deposited thereon such that centers of the cones range in distance from each other from three micrometers to ten micrometers, and are electrically connected at their bases.
  • the cones 26 are separated from each other by an insulator 28 which is deposited over all surfaces of the cathode 24 which do not have a cone 26 protruding therefrom.
  • the insulator 28 is fabricated from any of numerous materials having a high dielectric strength. In the preferred embodiment, the insulator 28 is silicon dioxide.
  • a gate 30 Spaced in a same plane with the apex of the cones 26 is a gate 30 which is separated from the cathode 24 by the insulator 28 and is made of an electrically conductive metal.
  • the gate 30 is etched with an aperture 40 for each of the cones 26 such that the apex of the cone 26 protrudes through the gate 30.
  • a positive potential at the gate 30 relative to the cathode 24 produces an intense electric field at the apex of the cone 26.
  • the field strength is sufficient to initiate electron tunneling from the apex of the cone 26 to a space around the cone 26.
  • Field strengths of 10 9 to 10 10 volts per meter are typical for gate voltages of 80-100 volts with respect to the cathode 24.
  • An anode 34 is spaced apart from and above the cones 26 and has a potential significantly higher than that of the gate 30 such that once electronic tunneling is initiated, electrons are drawn up towards the anode 34 as shown by the dashed line.
  • a thin film of luminophor 32 is coated on the anode 34 such that as the electrons impinge upon the luminophor 32, the luminophor 32 is excited and produces a light.
  • the light can be varied in wavelength dependent upon the choice of luminophor 32 and is often one of red, green, or blue depending on a spot color required in the print head.
  • the luminophor film 32 is made of a broad spectrum phosphor which is used to produce an essentially white light.
  • the white light is passed through the anode which is transmissive to light and is transmitted by a face plate 36.
  • Color in this embodiment, is produced by using a color filter 38.
  • Figure 3 A illustrates that as a voltage V g is placed across the gate 30 and the cathode 24 through a resistance R g , a current i-, is produced therebetween. Similarly, a voltage V a is placed between the anode 34 and the cathode 24 through resistance R a and a current -a is produced.
  • the resistor R g Due to a minimal attraction of electrons to the gate 30, the resistor R g is not actually required. The attraction is minimal because V g is small, approximately 50 volts, relative to V a which is on the order of 200 volts. In fact, the current i g is produced from leakage through the insulator 28 and from stray electrons from the cathode 24. Therefore, since - g is minimal compared to i * , - a can be ignored in the above equation thus leaving i, ⁇ • * . This current flow causes an attraction of electrons emitted from the cone 26 due to the electron tunneling to be drawn towards the anode 34 as shown by the dashed lines.
  • V g The choice of the gate voltage, V g , is not arbitrary but is instead used to switch sections of cones on and off. If V g is less than a threshold value, V TH , tunneling is not enabled and the electron flow is not created. But as V g rises, the threshold value is exceeded and tunneling in the cone 26 causes the emission of the electrons. This is graphically seen in Figure 3B where once the threshold voltage, V TH , is exceeded the cathode current increases exponentially with the electron field. This characteristic allows for easy switching of individual cones or sections of cones between on and off, thus multiplexing is enabled.
  • an operating voltage, V OP producing an operating cathode current, lop*
  • the operating voltage is chosen to produce sufficient electron flux, to cause sufficient brightness levels in the phosphor while keeping the cathode current below an amount which will burn out the phosphor.
  • Groups of these field emitting cones 26 work together to create a single spot for printing purposes.
  • a single spot forming group is commonly on the order of 10 4 cones per square millimeter. This density ensures redundancy and uniformity of emission.
  • Each spot forming group is composed of plural adjacent cones 26 placed sufficiently closely together so that outer portions of each electron beam overlap. This overlap has an additive effect, causing the fields from adjacent cones 26 to form an electron flux that is relatively uniform.
  • cones may be placed approximately five micrometers apart to form an extended array of electron emitters which collectively constitute a beam for depositing one charge spot.
  • Figure 4 shows a print head 20 for multi-color printing that includes multiple arrays of spot forming groups as previously described.
  • the print head 20 consists of the back plane 22 which carries the gate 30 and the cathode 24 field emission structure.
  • the face plate 36 with red, green, and blue luminophor stripes and a common anode 34.
  • the gates are three electrically independent rows 42 of film which control the red, green, and blue luminophor stripes.
  • Beneath the gate films running in an orthogonal direction are cathodes in columns 42 which are also electrically isolated.
  • the cathodes consist of field emitters which are defined at the intersection of a gate and cathode structure and are shown in detail in Figure 4.
  • electron flux is confined exclusively to the areas at the intersections and are addressable by rectangular coordinates to selectively activate individual areas.
  • the areas define pixels and would be approximately 100 square micrometers per a 200 dot per inch printer.
  • Each pixel consists of 600 or more cones 26.
  • the pixels are addressed sequentially one row at a time using pulse width modulation.
  • the gate-to-anode spacing is on the order of 200 to 2000 micrometers providing good proximity focusing of the electrons. This is accomplished in the preferred embodiment by utilizing thin film technology.
  • the print head can be used as shown for imaging one line at a time or may be run together with additional single line print head structures to form an area printing device which conveys an entire image at once.
  • Figure 5 shows a print head 20 for multi-color printing where like numbers represent like objects.
  • time delay multiplexing is utilized to increase print speeds.
  • the print head 20' consists of the back plane 22' which carries the gate 30' and the cathode 24' field emission structure. Above that is the face plate 36' with red, green, and blue luminophor stripes and a common anode 34'.
  • the gates are three sets of electrically independent rows of film which control the red, green, and blue luminophor stripes. Beneath the gate films running in an orthogonal direction are cathodes in columns 42 which are also electrically isolated.
  • the cathodes consist of field emitters which are defined at the intersection of a gate and cathode structure as previously described. Thus, electron flux is confined exclusively to the areas at the intersections and are addressable by rectangular coordinates to selectively activate individual areas.
  • this embodiment repeats rows of colors such that there are two rows 50 for imaging red, two rows 52 for green, and two rows 54 for blue.
  • a signal sent to the a first row of a single color would then be repeated in the second row at a time delayed in accordance with a speed that the photosensitive recording medium is being moved thereby intensifying the color associated with that row.
  • a faster transport system could be utilized since a single color need only be exposed for one half of the exposure time necessary for a single row of colors. Therefore, the print speed has been approximately doubled.
  • a photosensitive recording medium is introduced into the optical printer where a first row of red is exposed. Since there are two consecutive rows 50 of red the exposure time as compared to a single row is decreased by one half. The second row having received the same print data as the first row, only delayed in time, then exposes the same line again for the color red.
  • the photosensitive recording medium by its nature integrates the two exposures to form one line fully exposed in red. The same process is repeated for the rows of green 52 and blue 54 thus producing a fully exposed line.
  • the number of rows of color may again be increased to three rows or more each time increasing possible print speed as compared to the single row embodiment. In the case of three rows the print speed is increased by a factor of three.
  • a fiber optic face plate is used instead of clear glass for the face plate 36.
  • the fiber optic face plate is particularly useful for direct contact printing on low ASA film. Fibers which have high numeric aperture are used to capture a large fraction of the light emitted by a top surface of the luminophor 32.
  • Pixels 46 are defined by spots of luminophor 32 which are deposited on the faceplate 36 as a thin film material secured by a lithographic process. In the preferred embodiment, the pixels 46 are offset with respect to each other to increase spacing between the pixels 46 thereby reducing crosstalk between the pixels 46.
  • An optical reflector 48 is then secured over the pixels 46 to prevent light piping.
  • the optical reflector 48 is commonly a thin film layer of a reflective metal such as 0.25 micrometers of aluminum which is used in the preferred embodiment.
  • the optical reflector 48 ensures that the light is directed to the top surface of the luminophor and coupled into the fibers.
  • the aluminum must be thin enough so that energetic electrons reach the luminophor, yet it must be of sufficient thickness so that it acts as an efficient reflector of light.

Landscapes

  • Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)

Abstract

Tête d'impression utilisant un tube cathodique à émission par effet de champ pour une imprimante optique permettant d'imprimer sur des surfaces photosensibles. Une pluralité de petits ensembles électroniques constitués de cônes (26) émetteurs cathodiques dans une ouverture anodique forment un espace qui est inférieur au libre parcours moyen des électrons dans une atmosphère ambiante et les ensembles sont de préférence étroitement espacés de manière à former un faisceau en colonne. De préférence, une troisième électrode accélère et nettoie le faisceau qui est séparé de la cathode (24). Ledit faisceau est ensuite incident sur un film (34) luminophore qui est excité, générant ainsi de la lumière. La lumière est transmise à travers une plaque avant émettrice (36), telle qu'une plaque à fibres optiques, où elle est incidente sur le matériau photosensible. Des transmissions multiples d'une seule couleur permettant d'accélérer l'impression par intégration des temps de propagation sont également décrites.
EP95935200A 1994-09-30 1995-09-29 Source de lumiere pour enregistreur de film dotee d'une cathode a emission par effet de champ Withdrawn EP0783762A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US31662694A 1994-09-30 1994-09-30
US316626 1994-09-30
PCT/US1995/012477 WO1996010835A1 (fr) 1994-09-30 1995-09-29 Source de lumiere pour enregistreur de film dotee d'une cathode a emission par effet de champ

Publications (1)

Publication Number Publication Date
EP0783762A1 true EP0783762A1 (fr) 1997-07-16

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP95935200A Withdrawn EP0783762A1 (fr) 1994-09-30 1995-09-29 Source de lumiere pour enregistreur de film dotee d'une cathode a emission par effet de champ

Country Status (3)

Country Link
EP (1) EP0783762A1 (fr)
CA (1) CA2200957A1 (fr)
WO (1) WO1996010835A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6475789B1 (en) 1996-10-01 2002-11-05 University Technology Corporation Human telomerase catalytic subunit: diagnostic and therapeutic methods
US7646149B2 (en) 2003-07-22 2010-01-12 Yeda Research and Development Company, Ltd, Electronic switching device
CN100583350C (zh) * 2006-07-19 2010-01-20 清华大学 微型场发射电子器件

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Publication number Priority date Publication date Assignee Title
JPS59214672A (ja) * 1983-05-21 1984-12-04 Nec Home Electronics Ltd 電子写真式プリンタ
FR2568394B1 (fr) * 1984-07-27 1988-02-12 Commissariat Energie Atomique Dispositif de visualisation par cathodoluminescence excitee par emission de champ
FR2607623B1 (fr) * 1986-11-27 1995-02-17 Commissariat Energie Atomique Source d'electrons polarises de spin, utilisant une cathode emissive a micropointes, application en physique des interactions electrons-matiere ou electrons-particules, physique des plasmas, microscopie electronique
JPH01200975A (ja) * 1988-02-05 1989-08-14 Oki Electric Ind Co Ltd 気体放電型光プリントヘッド
US5004956A (en) * 1988-08-23 1991-04-02 Westinghouse Electric Corp. Thin film electroluminescent edge emitter structure on a silcon substrate
JPH05314891A (ja) * 1992-05-12 1993-11-26 Nec Corp 電界放出冷陰極およびその製造方法

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Title
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Also Published As

Publication number Publication date
WO1996010835A1 (fr) 1996-04-11
CA2200957A1 (fr) 1996-04-11

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