Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
  • H01J3/02—Electron guns
  • H01J3/021—Electron guns using a field emission, photo emission, or secondary emission electron source
  • H01J3/022—Electron guns using a field emission, photo emission, or secondary emission electron source with microengineered cathode, e.g. Spindt-type
• • 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
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/02—Manufacture of electrodes or electrode systems
  • H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
  • H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/02—Manufacture of electrodes or electrode systems
  • H01J9/14—Manufacture of electrodes or electrode systems of non-emitting electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2201/00—Electrodes common to discharge tubes
  • H01J2201/30—Cold cathodes
  • H01J2201/304—Field emission cathodes
  • H01J2201/30403—Field emission cathodes characterised by the emitter shape
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2329/00—Electron emission display panels, e.g. field emission display panels

Definitions

• the present claimed invention relates to the field of flat panel displays. More specifically, the present claimed invention relates to a flat panel display and methods for forming a flat panel display having row metal which provides good conductivity and which resists damage in subsequent process steps.
• a Cathode Ray Tube (CRT) display generally provides the best brightness, highest contrast, best color quality and largest viewing angle of prior art computer displays.
• CRT displays typically use a layer of phosphor which is deposited on a thin glass faceplate. These CRTs generate a picture by using one to three electron beams which generate high energy electrons that are scanned across the phosphor in a raster pattern. The phosphor converts the electron energy into visible light so as to form the desired picture.
• prior art CRT displays are large and bulky due to the large vacuum envelopes that enclose the cathode and extend from the cathode to the faceplate of the display. Therefore, typically, other types of display technologies such as active matrix liquid crystal display, plasma display and electroluminescent display technologies have been used in the past to form flat panel displays.
• a thin flat panel display commonly referred to as a field emission display (FED) which uses the same process for generating pictures as is used in CRT devices.
• FEDs use a backplate including a matrix structure of rows and columns of electrodes.
• the backplate is formed by depositing a cathode structure (electron emitting) on a glass plate.
• the cathode structure includes emitters that generate electrons.
• the backplate typically has an active area surface within which the cathode structure is deposited. Typically, the active area surface does not cover the entire surface of the glass plate and a thin strip is left around the edges of the glass plate.
• the thin strip is referred to as a border or a border region.
• Conductive traces extend through the border to allow for electrical connectivity to the active area surface. These traces are typically covered by a dielectric film as they extend across the border so as to prevent shorting.
• Prior art flat panel displays include a thin glass faceplate (anode) having a layer of phosphor deposited over the surface of the faceplate. A conductive layer is deposited on the glass or on the phosphor. The faceplate is typically separated from the backplate by about 1 millimeter. The faceplate includes an active area surface within which the layer of phosphor is deposited. The faceplate also includes a border region.
• the border is a thin strip that extends from the active area surface to the edges of the glass plate.
• the faceplate is attached to the backplate using a glass sealing structure.
• This sealing structure is typically formed by melting a glass frit in a high temperature heating step. This forms an enclosure which is pumped out so as to produce a vacuum between the active area surface of the backplate and the active area surface of the faceplate.
• Prior art cathodic structures are typically formed by depositing a first layer of metal over a glass plate (first metal layer). This first metal layer is then masked and etched so as to form rows of conductive strips (row metal). Typically, a resistive layer formed of silicon carbide (SiC), cermet, or a combination of SiC and cermet is deposited over the row metal. A dielectric layer is then deposited. A second layer of metal is then deposited over the surface of the cathodic structure. A series of mask and etch steps are then performed so as to form a columns of conductive strips (column metal). The mask and etch steps also form openings in the column metal which extend through the dielectric layer so as to expose portions of the resistive layer.
• first metal layer is then masked and etched so as to form rows of conductive strips (row metal).
• a resistive layer formed of silicon carbide (SiC), cermet, or a combination of SiC and cermet is deposited over the row metal.
• Emitters are formed over the exposed portions of the row metal and within the openings in the column metal by a series of deposition and etch steps. Individual regions of the cathode are selectively activated by applying electrical current to selected conductive strips of row metal and selected conductive strips of column metal so as to generate electrons which strike the phosphor so as to generate a display within the active area surface of the faceplate.
• the first metal layer of a FED is typically formed of an alloy of nickel (approx. 92%) and vanadium (approx. 8%).
• a nickel vanadium alloy is used since it gives a good electrical bond with the overlying resistive layer and because it is resistant to damage and contamination in subsequent process steps.
• the resistivity of the nickel vanadium layer is approximately 55 micro-ohms-centimeter. This high resistivity causes signal delay. Signal delay causes decreased performance and inconsistent display quality.
• nickel vanadium alloy is expensive.
• a FED with row metal which minimizes signal delay and which meets signal propagation and other performance criteria and process compatibility criteria.
• a FED is needed which has row metal which is easy to deposit and etch and which can be formed using current processing techniques.
• processing methods for forming a FED with row metal which has low resistivity and which forms a good bond with a resistive layer are required.
• processing methods are needed for forming a FED with row metal which is resistant to damage during subsequent processing steps. The present invention meets the above needs.
• the present invention provides a field emission display (FED) which includes an improved cathodic structure.
• the cathodic structure includes row metal which is highly conductive.
• the row metal is formed using aluminum which is overlain by a thin cladding layer.
• a faceplate is formed by depositing luminescent material within an active area surface formed on a glass plate.
• a cathodic structure is formed within an active area on a backplate. Walls are attached to either the faceplate or the backplate.
• a glass sealing material is placed within the border of the faceplate.
• the backplate is then placed over the faceplate such that the walls and the glass frit are disposed between the faceplate and the backplate.
• the assembly is then sealed by thermal processing and evacuation steps so as to form a complete FED.
• the cathodic structure includes a row of metal strips aligned roughly parallel to each other (herein referred to as "row metal"). Each strip includes a layer of aluminum overlain by a layer of cladding material. A resistive layer overlies the row metal. A dielectric layer overlies the resistive layer. Column metal overlies the dielectric layer. Column metal is a row of strips of conductive material which are aligned roughly parallel to each other. Openings which extend through the column metal and through the dielectric layer expose portions of the resistive layer. Emitters are formed within the openings in the column metal and the dielectric layer such that they are electrically coupled to the resistive layer.
• electrical current is applied to one or more strips of the row metal and to one or more strips of column metal such that emitters disposed over the strips of row metal to which current is applied and within openings in the strips of column metal to which current is applied are engaged such that they emit electrons. These electrons strike the phosphor deposited on the faceplate so as to produce a visible display.
• row metal The use of aluminum and cladding material to form row metal gives row metal segments which are highly conductive due to the high conductivity of aluminum.
• row metal is formed which maintains good electrical conductivity with overlying structures even after high temperature process steps.
• a cladding material which forms a good bond with the overlying resistive layer is used.
• a refractory metal such as tantalum is used as a cladding material.
• aluminum is deposited, masked and etched to form aluminum strips.
• a cladding layer of tantalum is then deposited over the aluminum strips.
• An etch is then performed so as to remove some or all of the tantalum between adjacent strips of aluminum and tantalum.
• the aluminum and the cladding layer are deposited sequentially in a vacuum deposition chamber.
• the resulting structure is then masked and etched to form strips having aluminum overlain by the cladding layer.
• the sequential deposition process gives a more uniform cladding layer since oxidation between the aluminum layer and the cladding layer is avoided and since contamination that may occur from masking, etching, and photoresist removal steps is avoided.
• the present invention produces a structure which has favorable conductivity characteristics and which has conductivity characteristics which are consistent throughout the row metal.
• the row metal is not damaged in process steps subsequent to the step of depositing the cladding layer.
• the favorable conductivity characteristics are consistent throughout the row metal as a result of the cladding layer's resistance to damage in subsequent process steps.
• tantalum and other refractory metals resists damage when exposed to etchant chemicals and processing chemicals such as alkaline and acidic solutions which are commonly used in subsequent process steps.
• Aluminum is desirable as a conductor since it is commonly used in electronic circuit devices and because it is inexpensive and it has good conductivity.
• FIGURE 1 A is a side cross sectional view illustrating a step for depositing a layer of aluminum on a glass plate in accordance with the present claimed invention.
• FIGURE IB is a side cross sectional view illustrating etching of an aluminum strip in accordance with the present claimed invention.
• FIGURE 1C is a side cross sectional view illustrating the deposition of a cladding layer in accordance with the present claimed invention.
• FIGURE ID is a side cross sectional view illustrating the structure of Figure 1C after a mask and etch step in accordance with the present claimed invention.
• FIGURE IE is a top view illustrating row metal strips in accordance with the present claimed invention.
• FIGURE IF is a side cross sectional view illustrating the deposition of a resistive layer in accordance with the present claimed invention.
• FIGURE 1G is a side cross sectional view illustrating the deposition of a dielectric layer in accordance with the present claimed invention.
• FIGURE 1H is a side cross sectional view illustrating the deposition of a metal layer in accordance with the present claimed invention.
• FIGURE II is a side cross sectional view of the structure of Figure 1H after mask and etch steps and emitter formation steps in accordance with the present claimed invention.
• FIGURE 1 J is a top view illustrating a completed cathodic structure in accordance with the present claimed invention.
• FIGURE IK is a side cross sectional view illustrating an embodiment having a favorable sidewall profile in accordance with the present claimed invention.
• FIGURE 2 is a diagram illustrating a method for forming a field emission display in accordance with the present claimed invention.
• FIGURE 3 is a cross sectional view illustrating a method for forming a field emission display in accordance with the present claimed invention.
• FIGURE 4 is a diagram illustrating steps for forming a field emission display in accordance with the present claimed invention.
• a faceplate which has one or more layers of phosphor deposited thereon is coupled to a backplate onto which a cathodic structure is formed.
• the cathodic structures includes emitters such as emitter 140 of Figure II and emitter 340 of Figure 3 which emit electrons that strike the phosphor layers on the faceplate so as to emit visible light and form a visible display.
• Backplate 100 of Figures 1A-1 J includes a cathodic structure which includes row metal formed of a layer of aluminum over which a layer of cladding material is deposited.
• Figure 2 shows a process 201 for forming a FED.
• backplate 100 is formed by first depositing an aluminum layer over the backplate 100.
• Figure 1A shows backplate 100 which includes glass plate 101 over which aluminum layer 102 is deposited.
• aluminum layer 102 is deposited by a sputter deposition process.
• FIG. 1B shows the structure of Figure 1 A after mask and etch steps have etched aluminum layer 102 of Figure 1 A so as to form aluminum strip 103.
• a cleaning step such as an ion cleaning step or a sputter etch may be used to clean the surface of the aluminum.
• a sputter etch using an argon plasma is used to clean the surface of the aluminum.
• FIG. 1C shows the structure of Figure IB after the deposition of cladding layer 104.
• cladding layer 104 is deposited by a sputter deposition process. If required, a cleaning step such as an ion cleaning step or a sputter etch may be used to clean the surface of the aluminum prior to the step of depositing the cladding layer. In one embodiment, a sputter etch using an argon plasma is used to clean the surface of the aluminum.
• cladding layer 104 is formed of a refractory metal.
• tantalum is used since it makes good electrical contact with overlying resistive layers and since it does not interdifluse with aluminum.
• tantalum is compatible with all of the subsequent process steps and process chemicals which are typically used.
• tantalum is resistant to process chemicals and is easy to process.
• Mask and etch steps are then performed as shown by step 213 of Figure 2. These mask and etch steps form row metal strips such as row metal strip 108 which extends across active area 20 as shown in Figure IE. With reference to Figure ID, the mask and etch steps remove the cladding material which overlies glass plate 101 and the cladding material which is deposited over the side surfaces of aluminum strip 106. This leaves cladding layer 107 which overlies aluminum strip 106 so as to form row metal strip 108. A wet etch could be used to etch both the cladding layer and the aluminum.
• a reactive ion etch process is used to etch the aluminum and the cladding layer.
• a first etch using flouring plasma is used to etch through the cladding layer. This etch stops on aluminum.
• the etch of the aluminum is then performed using a chlorine plasma.
• the etch is followed with a fluorine gas rinse to remove residual chlorine.
• an etch process is used to yield a structure which has side surfaces that are sloped, rather than running vertically.
• Figure IK shows row metal strip 198 formed by etching aluminum layer 196 and cladding layer 197 using an etch process such that side surface 191 and side surface 192 are sloped. This structure allows for good step coverage of subsequent overlying layers. In addition, this structure is favorable for stress purposes, resulting in less damage to the cathodic structure upon subsequent thermal processing steps.
• a resistive layer is then deposited as shown by step 214 of Figure 2.
• silicon carbide SiC
• Figure IF shows the structure of Figure ID after resistive layer 110 is deposited.
• Resistive layer 110 overlies row metal strip 108.
• resistive layer 110 overlies cladding layer 107 and surrounds the sides of aluminum layer 106.
• resistive layer 110 is formed by depositing a first layer of silicon carbide having a thickness of approximately 2000 angstroms which is nitrogen doped to tailor it's resistivity to the requirements of the system.
• a thin layer of Cermet is then deposited over the SiC layer to complete the resistive layer.
• the layer of Cermet has a thickness of approximately 500 angstroms.
• Cermet is a resistive material sold commercially by Pure Tech Incorporated of Carmel, NY which is formed from silicon dioxide (SiO2) and chromium (Cr).
• a dielectric layer is deposited over the resistive layer as shown by step 216 of Figure 2.
• a dielectric layer having a thickness of approximately 1500 angstroms is deposited.
• Figure 1G shows the structure of Figure IF after dielectric layer 120 is deposited over resistive layer 110.
• silicon dioxide is used to form dielectric layer 120.
• column metal is formed by depositing a layer of metal over the surface of backplate 100.
• chromium is used to form column metal.
• Figure 1H shows the structure of Figure 1G after a layer of metal 128 is deposited. The layer of metal is then masked and etched as shown by step 220 of Figure 2.
• emitter openings are etched. Emitter openings may be etched by any of a number of known etch methods. In one embodiment, damage tracks are used to locate emitter openings which are then etched. Emitters are then formed within emitter openings as shown by step 224 of Figure 2.
• Figure II shows the structure of Figure 1H after mask and etch steps have etched row metal strips, shown generally as row metal strip 130, after etching emitter openings, and after emitters, shown generally as emitter 140 are formed in backplate 100. Gates (not shown) and other required structures and circuits are also formed to complete the backplate.
• Figure 1J shows backplate 100 after completion of steps 210-214, 216, 218, 220, 222, and 224 of Figure 2 as shown in Figures 1 A- II.
• the completed cathodic structure formed over glass plate 101 includes column metal strips, shown generally as column metal strip 130.
• column metal strips 130 have a thickness of approximately 1500 angstroms.
• Column metal strips, shown generally as column metal strip 130 extend out of active area 20 for connection to electronic circuits.
• row metal strips, shown generally as row metal strip 108 extend out of active area 20 for connection to electronic circuits.
• the cladding layer overlies the sides of each aluminum strip.
• an aluminum layer is deposited, as shown by step 210 of Figure 2, and masked and etched, as shown by step 211.
• the photoresist used in the etch process is then stripped.
• the layer of cladding material is deposited, as shown by step 212 and the cladding layer is masked and etched as shown by step 213.
• the mask and etch steps only remove some or all of that portion of the cladding layer which overlies the glass plate between each aluminum strip (so as to prevent contact between aluminum strips). Thus the sides of each aluminum strip are not exposed.
• the resistor layer is then deposited over the cladding layer as shown by step 214.
• the dielectric layer is then deposited and column metal is masked and etched as shown by steps 216, 218 and 220. As shown by steps 222 and 224, emitter openings are etched and emitters are formed.
• Figure 3 shows a backplate in which, cladding material is left overlying the top and sides of each of aluminum strip, shown generally as aluminum strip 306.
• Cladding shown generally as cladding layer 307, seals each of aluminum strips 306 so as to form row metal strips shown generally as row metal strip 308. Since the sides of each aluminum strip 306 are sealed with cladding, the aluminum strip 306 is protected from damage in subsequent process steps.
• deposition of aluminum and cladding material is performed sequentially.
• Figure 4 shows a process for forming a FED using a sequential aluminum and cladding deposition process.
• an aluminum layer is deposited as shown by step 410 which is followed by a layer of cladding material as shown by step 411.
• this process is performed by sequentially depositing the aluminum layer and the cladding layer in a vacuum deposition chamber by sputter deposition methods.
• the sequential deposition of the aluminum and cladding layers prevents oxidation and contamination of the aluminum interface between the aluminum and cladding layers.
• the aluminum and cladding layers are then etched as shown by step 412.
• a first etch using flourine plasma is used to etch through the cladding material. This etch stops on the aluminum layer.
• the aluminum layer is then etched using a chlorine plasma. The etch is followed with a fluorine gas rinse to remove residual chlorine.
• the photoresist mask is then removed.
• the resistor layer is then deposited as shown by steps 416 and 418. First a layer of silicon carbide is deposited as shown by step 416. Next, a layer of Cermet is deposited as shown by step 418.
• the structure is then completed by depositing a dielectric layer, depositing, masking and etching column metal, and etching emitter openings and forming emitters as shown by steps 419-423.
• tantalum as a cladding material prevents significant interdiSusion of the aluminum and tantalum. Even after the high temperature cycles in the fabrication process, there is little if any interdiffusion. Consequently there is no increase in the resistivity resulting from interdifiusion. This provides good horizontal and vertical electrical conductivity.
• the improved horizontal and vertical conductivity of the present invention reduces signal propagation delay and allows for the production of brighter displays having faster refresh rates.
• any of a number of other materials could be used if those materials meet the criteria of easy to process, not interdiftusing with aluminum, make good electrical contact with the aluminum layer, make good electrical contact with the overlying resistor layer, and they are compatible with subsequent process steps and processing chemicals.
• Other refractory metals which may meet the above requirements include molybdenum, tungsten, and titanium.
• other materials which may meet the above requirements include niobium, nickel, chromium, metal suicides, and composite films such as tantalum nitride, titanium-tungsten, and metal suicides.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
• Electrodes For Cathode-Ray Tubes (AREA)

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• 1997
  • 1997-09-17 US US08/932,318 patent/US5894188A/en not_active Expired - Lifetime
• 1998
  • 1998-09-10 WO PCT/US1998/018786 patent/WO1999014780A1/en not_active Ceased
  • 1998-09-10 JP JP2000512225A patent/JP4255616B2/ja not_active Expired - Fee Related
  • 1998-09-10 EP EP98945990A patent/EP1016113B1/en not_active Expired - Lifetime
  • 1998-09-10 DE DE69839124T patent/DE69839124T2/de not_active Expired - Lifetime
  • 1998-09-10 KR KR1020007002527A patent/KR20010023850A/ko not_active Withdrawn
  • 1998-10-29 US US09/183,601 patent/US6019657A/en not_active Expired - Lifetime
• 1999
  • 1999-11-09 US US09/437,346 patent/US6225732B1/en not_active Expired - Lifetime

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