Field emission device and field emission display

A field emission device includes an insulating substrate, a number of first electrode down-leads, a number of second electrode down-leads, and a number of electron emission units. The first electrode down-leads are set an angle relative to the second electrode down-leads to define a number of cells. Each electron emission unit is located in each cell and includes a first electrode, a second electrode, and a plurality of electron emitters. The second electrode extends surrounding the first electrode. The plurality of electron emitters located on and electrically connected to at least one of the first electrode and the second electrode. A field emission display is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201010612598.1, filed on Dec. 29, 2010 in the China Intellectual Property Office, disclosure of which is incorporated herein by reference. This application is related to applications entitled, “FIELD EMISSION DISPLAY”, filed Jun. 9, 2011 Ser. No. 13/156,513; and “FIELD EMISSION DEVICE AND FIELD EMISSION DISPLAY”, filed Jun. 9, 2011 Ser. No. 13/156,523

BACKGROUND

1. Technical Field

The present disclosure relates to a field emission device and a field emission display.

2. Description of Related Art

Field emission displays (FED) can emit electrons under the principle of a quantum tunnel effect opposite to a thermal excitation effect, which is of great interest from the viewpoints of low power consumption.

A field emission display, according to the prior art usually includes a transparent plate, an insulating substrate opposite to the transparent plate, a number of supporters, and one or more grids located on the insulating substrate. Each grid includes a pixel unit. The pixel unit includes a rectangular first electrode, a rectangular second electrode spaced from and parallel to the first electrode, at least one electron emitter connected to the first electrode, and a phosphor layer located on the second electrode. However, the brightness of the field emission display is relatively low.

What is needed, therefore, is to provide a field emission display having relatively high brightness.

DETAILED DESCRIPTION

References will now be made to the drawings to describe, in detail, various embodiments of the present field emission device and field emission display. In some embodiments, only one pixel unit is shown.

Referring toFIGS. 1 and 2, a field emission display200of one embodiment includes an insulating substrate202, a number of substantially parallel first electrode down-leads204, a number of substantially parallel second electrode down-leads206, and a number of pixel units220.

The first electrode down-leads204and the second electrode down-leads206are located on the insulating substrate202. The first electrode down-leads204are generally set at an angle to the second electrode down-leads206to form a grid. A cell214is defined by two substantially adjacent first electrode down-leads204and two substantially adjacent second electrode down-leads206of the grid. One of the pixel units220is located in each cell214. InFIG. 1, the lengthwise direction of the first electrode down-lead204is defined as an X direction, and the lengthwise direction of the second electrode down-leads206is defined as a Y direction.

The insulating substrate202is configured to support the first electrode down-leads204, the second electrode down-leads206, and the pixel units220. The shape, size, and thickness of the insulating substrate202can be chosen according to need. The insulating substrate202can be made of material such as ceramic, glass, resin, or quartz. In one embodiment, the insulating substrate202is a square glass substrate with a thickness of about 1 millimeter and an edge length of about 1 centimeter.

The first electrode down-leads204are located equidistantly apart. A distance between two adjacent first electrode down-leads204can range from about 50 micrometers to about 2 centimeters. The second electrode down-leads206are located equidistantly apart. A distance between two adjacent second electrode down-leads206can range from about 50 micrometers to about 2 centimeters. Suitable orientations of the first electrode down-leads204and the second electrode down-leads206are set at an angle with respect to each other. The angle can range from about 10 degrees to about 90 degrees. In one embodiment, the angle is 90 degrees, and the cell214is a square area.

The first electrode down-leads204and the second electrode down-leads206are made of conductive material such as metal or conductive slurry. In one embodiment, the first electrode down-leads204and the second electrode down-leads206are formed by applying conductive slurry on the insulating substrate202using screen printing process, the conductive slurry being composed of metal powder, glass powder, and binder. The metal powder can be silver powder, the glass powder has a low melting point, and the binder can be terpineol or ethyl cellulose (EC). The conductive slurry can include about 50% to about 90% (by weight) of the metal powder, about 2% to about 10% (by weight) of the glass powder, and about 8% to about 40% (by weight) of the binder. In one embodiment, each of the first electrode down-leads204and the second electrode down-leads206is formed with a width in a range from about 30 micrometers to about 100 micrometers and with a thickness in a range from about 10 micrometers to about 50 micrometers. However, it is noted that dimensions of each of the first electrode down-leads204and the second electrode down-leads206can vary corresponding to the dimension of each cell214.

The pixel unit220includes a first electrode212, a second electrode210, an electron emitter208, and a phosphor layer218. The first electrode212and the second electrode210are located on the insulating substrate202and spaced from each other. The first electrode212is used as a cathode electrode and electrically connected to the second electrode down-lead206. The second electrode210is used as an anode electrode and electrically connected to the first electrode down-lead204. The electron emitter208is located on the first electrode212and spaced from the second electrode210. The phosphor layer218is located on a surface of the second electrode210. In one embodiment, the electron emitter208is suspended above the insulating substrate202. One end of the electron emitter208is electrically connected to the first electrode212. The other end of the electron emitter208extends from the first electrode212toward the second electrode210and is used as an electron emission portion222. The electron emission portion222is spaced from the second electrode210. The electron emitted from the electron emitter208can bombard the phosphor layer218to light.

The second electrode210can be a planar conductor, such as a metal layer, an indium-tin oxide (ITO) layer, or a conductive slurry layer. In one embodiment, the second electrode210is cuboid. The size of the second electrode210can be selected according to the size of the cell214. The second electrode210can have a length along the Y direction in a range from about 30 micrometers to about 15 millimeters, a width along the X direction in a range from about 20 micrometers to 10 millimeters, and a thickness in a range from about 10 micrometers to about 500 micrometers. In one embodiment, the second electrode210has a length along the Y direction in a range from about 100 micrometers to about 700 micrometers, a width along the X direction in a range from about 50 micrometers to about 500 micrometers, and a thickness in a range from about 20 micrometers to about 100 micrometers.

The first electrode212can be a planar conductor. In one embodiment, the first electrode212has a rectangular cross section. At least part of the first electrode212surrounds the second electrode210. The first electrode212can be L-shaped, U-shaped, C-shaped, semicircular-shaped, or ring-shaped. In one embodiment, the first electrode212is U-shaped and includes a first portion2121, a second portion2123, and a third portion2125. The first portion2121and the second portion2123are located on opposite sides of the second electrode210. The third portion2125connects the first portion2121and the second portion2123such that the first electrode212surrounds the second electrode210. The first electrode212and the second electrode210can be formed by screen printing the conductive slurry on the insulating substrate202. As mentioned above, the conductive slurry forming the first electrode212and the second electrode210is the same as the conductive slurry forming the electrode down-leads204,206.

The phosphor layer218is located on the second electrode210and exposed to the electron emission portion222of the electron emitter208. In one embodiment, the phosphor layer218is located on the entire top surface of the second electrode210. The phosphor layer218can be white phosphor layer, red phosphor layer, green phosphor layer, or blue phosphor layer. The phosphor layer218can be formed2by printing, coating, or depositing. The thickness of the phosphor layer218can be selected according to need. In one embodiment, the thickness of the phosphor layer218is in a range from about 5 micrometers to about 50 micrometers.

The electron emitter208is located on the first electrode212. The electron emitter208can be a linear emitter such as silicon wire, carbon nanotubes, carbon fibers, or carbon nanotube wires. The lengthwise direction of the electron emitter208can be parallel to the surface of the insulating substrate202. The electron emission portion222of the electron emitter208points to the second electrode210and spaced from the second electrode210by a distance in a range from about 2 micrometers to about 500 micrometers. In one embodiment, the distance between the electron emission portion222and the second electrode210is in a range from about 50 micrometers to about 300 micrometers. In one embodiment, the electron emission portion222can extend above the phosphor layer218.

In one embodiment, the electron emitter208includes a number of carbon nanotube wires evenly spaced from and in parallel with each other. All the carbon nanotube wires are arranged to form L-shaped, U-shaped, C-shaped, semicircular-shaped, or ring-shaped to surround the second electrode210or positioned on opposite sides of the second electrode210. The length of the carbon nanotube wires can be in a range from about 10 micrometers to about 1 centimeter. The distance between each two adjacent carbon nanotube wires can be in a range from about 10 micrometers to about 500 micrometers. One end of the carbon nanotube wire is fixed on the first electrode212by a fixing electrode224or conductive adhesive (not shown). The carbon nanotube wire can be a substantially pure structure of the carbon nanotubes, with few impurities. The carbon nanotube wire is a free standing structure.

The carbon nanotube wire includes a plurality of successive carbon nanotubes joined end to end by van der Waals attractive force therebetween. The carbon nanotubes in the carbon nanotube wire can be single-walled, double-walled, or multi-walled carbon nanotubes. The carbon nanotube wire can be untwisted or twisted. The untwisted carbon nanotube wire includes a plurality of carbon nanotubes substantially oriented along a same direction (i.e., a direction along the length of the untwisted carbon nanotube wire). The carbon nanotubes are parallel to the axis of the untwisted carbon nanotube wire. The twisted carbon nanotube wire includes a plurality of carbon nanotubes helically oriented around an axial direction of the twisted carbon nanotube wire.

The electron emitter208can be formed by disposing and heating a carbon nanotube slurry layer or disposing and cutting a carbon nanotube film. The carbon nanotube slurry layer includes a number of carbon nanotubes, a glass powder, and an organic carrier. The organic carrier is volatilized during the heating process. The glass powder can be melted and solidified to form a glass layer to fix the carbon nanotubes on the first electrodes212during the heating and cooling process.

In one embodiment, the electron emitter208is made by the steps of:

step (a), providing at least one carbon nanotube film;

step (b), placing the at least one carbon nanotube film on the first electrode212and the second electrode210to cover all the first electrodes212and the second electrodes210; and

step (c), breaking the carbon nanotube film to form a number of carbon nanotube wires spaced from and parallel with each other.

In step (a), the carbon nanotube film can be drawn from a carbon nanotube array. Examples of carbon nanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang et al. The carbon nanotube film includes a plurality of successive and oriented carbon nanotubes joined end-to-end by van der Waals attractive force therebetween. The carbon nanotube film is a free-standing film. The term “free-standing film” means that the film can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity.

In step (b), when two or more carbon nanotube films are stacked on the first electrode212and the second electrode210, the aligned directions of the carbon nanotubes in two adjacent carbon nanotube films is the same. All the carbon nanotubes of the carbon nanotube film extend from the first electrode212to the second electrode210. In one embodiment, less than five carbon nanotube films are stacked on the first electrode212and the second electrode210.

Furthermore, the carbon nanotube films are treated with a volatile organic solvent in step (b). The organic solvent is applied to soak the entire surface of the carbon nanotube film. During the soaking, adjacent parallel carbon nanotubes in the carbon nanotube film will bundle together, due to the surface tension of the organic solvent as it volatilizes, and thus, the carbon nanotube film will be shrunk into untwisted carbon nanotube wire. The organic solvent can be ethanol, methanol, acetone, dichloroethane, or chloroform.

In step (c), the carbon nanotube film can be cut by a laser beam, an electron beam, or can be broken by heat. In one embodiment, the carbon nanotube film is cut by a laser beam. The laser beam can be moved along the first electrode down-leads204to remove the carbon nanotubes between the first electrode down-leads204and the first electrode212. The laser beam can be moved along the second electrode down-leads206to break the carbon nanotubes between the first electrode212and the second electrode210. The power of the laser beam can be in a range from about 10 W to about 50 W. The scanning speed of the laser beam can be in a range from about 0.1 mm/sec to about 10,000 mm/sec. The width of the laser beam can be in a range from about 1 micrometer to about 400 micrometers.

Furthermore, the field emission display200can include a plurality of insulators216sandwiched between the first electrode down-leads204and the second electrode down-leads206to avoid short-circuiting. The insulators216are located at every intersection of the first electrode down-leads204and the second electrode down-leads206for providing electrical insulation therebetween. In one embodiment, the insulator216is a dielectric insulator.

Further the field emission display200can include a driving circuit (not shown) to drive the field emission display200to display. The driving circuit can control the pixel units220via the electrode down-leads204,206to display a dynamic image. The field emission display200can be used in a field of advertisement billboard, newspaper, or electronic book. In use, the field emission display200should be sealed in a vacuum.

Referring toFIG. 3, a field emission display300of one embodiment includes an insulating substrate302, a number of substantially parallel first electrode down-leads (not shown), a number of substantially parallel second electrode down-leads306, and a number of pixel units320. The field emission display300is similar to the field emission display200except that the second electrode310has a bearing surface3102inclined to the insulating substrate302, and the phosphor layers318are located on the bearing surface3102and exposed to the electron emitter308.

The bearing surface3102can be flat or curved. If the bearing surface3102is flat, an angle α between the bearing surface3102and the surface of the insulating substrate302can be greater than 90 degrees and less than 180 degrees. In one embodiment, the angle α between the bearing surface3102and the surface of the insulating substrate302is in a range from about 120 degrees to about 150 degrees. If the bearing surface3102is curved, the bearing surface3102can be a convex surface or a concave surface. The bearing surface3102can intersect with the insulating substrate302or can be spaced from the insulating substrate302.

In one embodiment, the second electrode310extends along the Y direction. The width along the X direction of the second electrodes310decreases along a direction away from the insulating substrate302so that the second electrode310has two flat bearing surfaces3102adjacent to and exposed to the electron emitter308on the two sides of the second electrode310. Two phosphor layers318are respectively located on the two bearing surfaces3102and exposed to the electron emission portion322. The angle γ between the two bearing surfaces3102can be in a range from about 30 degrees to about 120 degrees. In one embodiment, the angle γ between the two bearing surfaces3102can be in a range from about 60 degrees to about 90 degrees. Because the phosphor layers318are located on the bearing surface3102of the second electrode310so that the phosphor layer318has a relative larger area and bombarded easily by the electron emitted from the electron emitter308. Thus, the brightness of the field emission display300is improved.

The second electrode310can be formed by screen printing a number of stacked conductive slurry layers repeatedly. The width along the X direction of the conductive slurry layer decreases gradually. Because of the high flowability of the conductive slurry, two inclines can be formed to be used as the bearing surface3102.

Referring toFIGS. 4 and 5, a field emission display400of one embodiment includes an insulating substrate402, a number of substantially parallel first electrode down-leads404, a number of substantially parallel second electrode down-leads406, and a number of pixel units420. InFIGS. 4 and 5, only one pixel unit420is shown. The field emission display400is similar to the field emission display200except that the first electrode412is used as an anode electrode, the second electrode410is used as a cathode electrode, the electron emitter408is connected to the second electrode410, and the phosphor layer418is located on a top surface of the first electrode412.

The phosphor layer418can have the same shape as the first electrode412. In one embodiment, two phosphor layers418are respectively located on top surfaces of the first portion4121and the second portion4123of the first electrode412. The electron emitter408is located on a top surface of the second electrode410and includes a number of electron emission portions422. The electron emission portions422of the electron emitter408are divided into a first group and a second group. The first group of electron emission portions422points to the first portion4121. The second group of electron emission portions422points to the second portion4123. In one embodiment, the electron emitter408includes a number of carbon nanotube wires in parallel with each other and across the top surface of the second electrode410. The first ends of the carbon nanotube wires point to the first portion4121and the second ends of the carbon nanotube wires point to the second portion4123. Furthermore, a phosphor layer418can be located on a top surface of the third portion4125and part of the electron emission portions422points to the third portion4125. Because both the first portion4121and the second portion4123are located on two sides of the second electrode410and have phosphor layers418located thereon, and the electron emission portions422of the electron emitter408point to the first portion4121and the second portion4123respectively, the brightness and uniformity of the field emission display400is further improved.

Referring toFIG. 6, a field emission display500of one embodiment includes an insulating substrate502, a number of substantially parallel first electrode down-leads (not shown), a number of substantially parallel second electrode down-leads506, and a number of pixel units520. InFIG. 6, only one pixel unit520is shown. The field emission display500is similar to the field emission display400except that both the first portion5121and the second portion5123have bearing surfaces5122inclined to the insulating substrate502, and two phosphor layers518are respectively located on the two bearing surfaces5122of the first electrode512.

In one embodiment, the width along the X direction of the first portion5121decreases along a direction away from the insulating substrate502so that the first portion5121has a flat bearing surface5122adjacent to and exposed to the electron emitter508. The width along the X direction of the second portion5123decreases along a direction away from the insulating substrate502so the second portion5123has a flat bearing surface5122adjacent to and exposed to the electron emitter508. The angle α between the bearing surface5122and the surface of the insulating substrate502can be in a range from about 120 degrees to about 150 degrees. In one embodiment, the angle α is about 135 degrees. Because both the first portion5121and the second portion5123have bearing surfaces5122and phosphor layers518located thereon, and the electron emission portions522of the electron emitter508points to the first portion5121and the second portion5123respectively, the brightness and uniformity of the field emission display500is further improved.

Furthermore, the width along the Y direction of the third portion (not shown inFIG. 6) can decrease along a direction away from the insulating substrate502so that the third portion has a flat bearing surface adjacent to and exposed to the electron emitter508. The electron emitter508can have some electron emission portions522pointing to the third portion.

Referring toFIG. 7, a field emission display600of one embodiment includes an insulating substrate602, a number of substantially parallel first electrode down-leads604, a number of substantially parallel second electrode down-leads606, and a number of pixel units620. InFIG. 7, only one pixel unit620is shown. The field emission display600is similar to the field emission display200except that the first electrode612surrounds the second electrode610, and the electron emitter608includes a number of carbon nanotube wires located on the first electrode612and arranged surrounding the second electrode610.

In one embodiment, the second electrode610is located in the middle of the cell614and has the same shape same as the cell614. The second electrode610is electrically connected to the first electrode down-leads604by a conductive line6104which can be formed with the second electrode610together by printing conductive slurry. The first electrode612extends around the second electrode610. An insulator (not shown) can be located between the first electrode612and the conductive line6104or a gap can be formed on the first electrode612at the intersection of the first electrode612and the conductive line6104. All of the electron emission portions622of the of the electron emitter608point to the phosphor layer618on the top surface of the second electrode610. The shape of the second electrode610and the first electrode612can be C-shaped, round, square, or rectangular.

Referring toFIG. 8, a field emission display700of one embodiment includes an insulating substrate702, a number of substantially parallel first electrode down-leads704, a number of substantially parallel second electrode down-leads706, and a number of pixel units720. InFIG. 8, only one pixel unit720is shown. The field emission display700is similar to the field emission display600except that first electrode712is used as anode electrode, the second electrode710is used as cathode electrode, the electron emitter708includes a number of crossed carbon nanotube wires located on the second electrode710, and the phosphor layer718is located on surface of the first electrode712and extends surrounding the second electrode710.

In one embodiment, the second electrode710is located in the middle of the cell714and has a shape same as the shape of the cell714. A gap is formed on the first electrode712at the intersection of the first electrode712and the conductive line7104.

The electron emitter708is located on the second electrode710and has a number of electron emission portions722pointing to the phosphor layer718around the electron emitter708. The electron emitter708can be formed by cross laying two carbon nanotube films or a number of carbon nanotube wires and cutting by laser.

Referring toFIGS. 9 and 10, a field emission display800of one embodiment includes an insulating substrate802, a number of substantially parallel first electrode down-leads804, a number of substantially parallel second electrode down-leads806, and a number of pixel units820. InFIGS. 9 and 10, only one pixel unit820is shown. The field emission display800is similar to the field emission display200except that both the first electrode812and the second electrode810have the electron emitter808and the phosphor layer818located thereon.

In one embodiment, the electron emitter808includes a number of carbon nanotube wires located on the first portion8121, the second portion8123, and the second electrode810. Two phosphor layers818are located on the first portion8121, the second portion8123, and the second electrode810to cover the electron emitter808. The carbon nanotube wires on the first portion8121and the second portion8123extend to the second electrode810and have a number of electron emission portions822pointing to the phosphor layers818on the second electrode810. The carbon nanotube wires on the second electrode810respectively extend to the first portion8121and the second portion8123and have a number of electron emission portions822pointing to the phosphor layers818on the first portion8121and the second portion8123. Both the first electrode812and the second electrode810can be used as an anode or cathode. In one embodiment, an alternating voltage can be supplied to the first electrode812and the second electrode810so the first electrode812and the second electrode810can be used as the anode and cathode alternately in the emission display800. Thus, the field emission display800can have an improved lifespan.

It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Any elements described in accordance with any embodiments is understood that they can be used in addition or substituted in other embodiments. Embodiments can also be used together. Variations may be made to the embodiments without departing from the spirit of the disclosure. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.