GB2440783A

GB2440783A - Improved field emission backplate

Info

Publication number: GB2440783A
Application number: GB0615615A
Authority: GB
Inventors: Mervyn John Rose
Original assignee: QUANTUM FILAMENT TECHNOLOGIES
Current assignee: QUANTUM FILAMENT TECHNOLOGIES
Priority date: 2006-08-07
Filing date: 2006-08-07
Publication date: 2008-02-13
Also published as: GB0615615D0; EP2050116A1; WO2008017809A1

Abstract

A field emission backplate 5a used in a field emission device such as a display device, and an associated method of manufacture. A field emission backplate 5a comprises a substrate 10a, a cathode metal layer 11a upon which is deposited an amorphous semiconductor layer 15a comprising hydrogenated amorphous silicon. The backplate 5a is exposed to laser irradiation so as to form a plurality of conductive or conducting particulates or particles 20a within the amorphous silicon layer 15a. The surface 25a may be substantially flat or planar, or may comprise a plurality of tips.

Description

* 1 2440783

IMPROVED FIELD EMISSION BACKPLATE

FIELD OF INVENTION

The present invention relates to a field emission

backplate, to a field emission device such as a display device, and to an associated method of manufacture. In particular, though not exclusively, the invention relates to a field emission display device comprising a field emission backplate having a plurality of conducting particulates formed or provided within the backplate. *a. p. p.

BACKGROUND TO INVENTION S..

:. Flat panel displays are of immense importance in electronics. Active Matrix Liquid Crystal Displays (AMLCD) have challenged the dominance of Cathode Ray Tube (CRT) technology. AMLCD devices are non-emissive and require complex lithography. Filters and matching spectral backlights are required to produce colour.

Further, there are many light losses and inherent complexity in AMLCD devices because of the non-linear nature of liquid crystal materials. This results in a display that is less bright than CRTs with a smaller colour gamut and poorer viewing angle and contrast.

Also, due to the non-emissive nature of such displays, inefficient use of input electrical power is made, often with over 70% of energy being lost as non-useful energy.

Field Emission Displays (FEDs) are also known. GB 2 378 569 A (The University Court of the University of Dundee) discloses a field emission backplate comprising a planar backplate substantially comprising an amorphous semiconductor based material, and a plurality of grown tips substantially comprising a crystalline semiconductor based material formed on the backplate member.

GB 2 378 570 A (The University Court of the University of Dundee) discloses a method of forming a S.

field emission backplate comprising:

providing a planar body of amorphous semiconductor I..

based material upon a substrate; and laser crystallising at least a portion of the amorphous semiconductor based material; wherein upon crystallising the amorphous semiconductor based material a plurality of emitter sites

are formed. GB 2 378 570 A also discloses a field

emission backplate comprising a plurality of emitter sites formed by laser crystalligatin of a planar body or thin film of amorphous semiconductor based material.

GB 2 389 959 A (The University Court of the University of Dundee) discloses a field emission device comprising a field emission backplate, the backplate being made substantially from semiconductor based material and comprising a plurality of emitter tips, the field emission device further comprising at least one electro-luminescerit material, the at least one material having a fluorescent material chemically attached thereto.

The content of the aforementioned documents is incorporated herein by reference.

Known field emission devices suffer from a number of disadvantages such as: ease of manufacture, predictability of manufacture, quality of manufacture, predictability of technical characteristics.

::* It is an object of at least one embodiment of at least one aspect of the present invention to obviate or S..

at least mitigate one or more disadvantages in the prior art.

S

SW(ARY OF INVENTION According to a first aspect of the present invention there is provided a field emission backplate comprising a plurality of conductive or conducting particulates or particles, wherein the conducting particulates are provided within the backplate.

The field emission backplate may comprise a layer of amorphous semiconductor material.

Each conducting particulate may comprise a point or locality e.g. of crytallisation, e.g. a "crystallite", within the layer of amorphous semiconductor material.

The conducting particulates may each comprise semiconductor and/or metallic material.

The amorphous semiconductor material may comprise amorphous silicon or an alloy thereof, e.g. hydrogenated amorphous silicon, Si:H.

The layer of amorphous semiconductor material may be provided on a substrate.

The substrate may be made from glass, or alternatively from a ceramic or metallic material.

Filaments or pathways, e.g. conductive or conducting filaments, may be provided between the conducting particulates, at least in use. Such filaments may provide a means for electron transport through the backplate to emitter sites on a surface of the backplate, which surface may comprise a surface of the amorphous semiconductor material.

The filaments may be considered as spatial instabilities or spatlo-temporal features, e.g. formed as

a consequence of intense internal electric field

confinement between conducting particulates.

In use, upon application of an electric field across the backplate, the filaments may be formed and may provide a transport network for electrons to the emitter sites.

In use, electrons may move through the filaments between conducting particulates and to an emitter site.

The electrons may move, in use, by electron transport or under certain conditions ballistically, e.g. if the dimension of the conducting particulates are sufficiently small, and/or the space between the conducting particulate is sufficiently small.

In one embodiment the surface of the amorphous semiconductor material is substantially flat.

In an alternative embodiment the surface of the amorphous semiconductor material is substantially non-flat or roughened, comprising a plurality of tips, e.g. microtips. S.

The emitter sites may be provided anywhere upon or ::* 15 across the surface. For example, in the alternative embodiment the emitter sites may be provided on the tips and between adjacent tips.

According to a second aspect of the present invention there is provided a field emission backplate comprising a field emission backplate according to the first aspect of the present invention.

The device may be a vacuum device, wherein each emitter site acts as an electron emission source of the device, in use.

The device may further comprise a substrate, an evacuated space and a transparent window, wherein the field emission backplate is formed upon the substrate and the evacuated space is located between the field emission backplate and the transparent window.

The field emission device may alternatively comprise an electro-luminescent material or (wide band-gap) light emitting material into which electrons from the emission sites are emitted, in use.

Such a field emission device may further comprise a substrate, the light emitting material, and a transparent window, wherein electrons from the emission sites are emitted into the light emitting material.

The light emitting material may be a light emitting polymer.

The electro-lumjnescent or light emitting material may have a fluorescent material chemically attached thereto.

The transparent window may be a thin film transparent metal.

One surface of the light emitting material may be disposed on a surface of the field emission backplate, and the transparent window may be disposed on another surface of the light emitting material.

Preferably the device is a display device.

The emitter or emission sites of the field emission backplate may be of a density of at least 100 per square micron.

According to a third aspect of the present invention there is provided a method of manufacturing a field emission backplate comprising: providing a backplate material; and processing the material so as to at least partially form a plurality of conductive or conducting particulates or particles within the backplate material.

The at least partial formation of the conducting particulates may be termed conditioning" of the backplate.

Preferably the step of providing a backplate :* material comprises: providing a planar body of amorphous semiconductor material upon a substrate.

* Preferably the step of processing the material :* comprises: laser crystallising at least a portion of the amorphous semiconductor material, such that the plurality of conducting particulates are formed.

The method may comprise the step of selecting a level of hydrogenation of the amorphous semiconductor material such that when laser irradiated a surface of the amorphous semiconductor material remains substantially flat or planar.

Alternatively, the method may comprise the step of: selecting a level of hydrogenation of the amorphous semiconductor material such that when laser irradiated a surface of the amorphous semiconductor material becomes substantially non-flat or roughened, e.g. comprising a plurality of tips, e.g. microtips.

The planar body of amorphous semiconductor based material may be provided by depositing a thin film of material upon a substrate, e.g. by Plasma Enhanced Chemical Vapour Deposition (PECVD).

The semiconductor based material may be silicon or an alloy thereof.

The step of performing laser crystallising may be carried out at a wavelength of around 525 nm to 540 rim, e.g. substantially 532 nm. The step of laser i, crystallising may use an excimer laser or Nd:YAG laser at I..

a suitable wavelength thereof. This stop may be carried out in air, vacuum or an inert gas atmosphere.

The excimer laser may be a KrF laser.

According to a fourth aspect of the present invention there is provided a field emission backplate comprising a plurality of conducting particulates, wherein a surface of the backplate is substantially flat or planar.

According to a fifth aspect of the present invention there is provided a method of forming a field emission backplate comprising the step of: providing a backplate material; depositing a layer on the backplate so as to at least partially form a plurality of conducting part iculates.

Preferably the backplate material comprises an amorphous semiconductor material, e.g. a layer of such.

Advantageously the conducting particulates are provided within the backplate material.

The conducting particulates may comprise a plurality of points or locations, e.g. crystallites.

The conducting particulates may be conductively interconnected by filaments, e.g. which allow electron transportation between emitter sites, in use, when a voltage is applied across the backplate.

* The layer may comprise a metallic layer. I.'

S

The metallic layer may comprise aluminium.

* In one implementation deposition of the layer is the

I

sole mechanism for forming the conducting particulates.

In another implementation deposition of the layer is one of a number of mechanisms for forming the conducting particulates. For example, another mechanism of the number of mechanisms may be laser irradiation of the backplate. The another mechanism may preferably be carried out after or alternatively before deposition of the layer.

According to a sixth aspect of the present invention there is provided a field emission backplate formed by the method of the fifth aspect of the present invention.

According to a seventh aspect of the present invention there is provided a field emission device comprising a field emission backplate according to the fourth or the sixth aspects of the present invention.

According to an eighth aspect of the present invention there is provided a field emission backplate comprising a plurality of emitter or emission sites, wherein a surface of the backplate is substantially flat or planar.

It will be appreciated that features of any one aspect of the present invention hereinbefore described, :: 15 may be shared with or be common with any other aspect of * the present invention hereinbefore described, whether solely or in combination.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, which are: Figure 1(a) a schematic side view of a substrate in a first step in a

method of manufacture of a field

emission backplate according to a first embodiment of the present invention; Figure 1(b) a schematic side view of the substrate of Figure 1(a) in a second step in the method of manufacture; Figure 1(c) a schematic side view of the substrate of Figure 1(a) in a third step in the method of manufacture;

Figure 2 a schematic side view of a field

emission device comprising a

field emission backplate formed

according to the method of * Figures 1(a) to 1(c); **.

Figure 3(a) a schematic side view of a substrate in a first step in a

method of manufacture of a field

emission backplate according to a second embodiment of the present invention; Figure 3(b) a schematic side view of the substrate of Figure 3(a) in a second step in the method of manufacture; Figure 3(c) a schematic side view of the substrate of Figure 3(a) in a third step in the method of manufacture; Figure 4(a) a schematic side view of a substrate in a first step in a

method of manufacture of a field

emission backplate according to a third embodiment of the present invention; Figure 4(b) a schematic side view of a substrate of Figure 4(a) in a second step in the method of * manufacture; Figure 4(c) a schematic side view of the substrate of Figure 4(a) in a third step in the method of manufacture; Figure 4(d) a schematic side view of the substrate of Figure 3(a) in an alternative third step in the method of manufacture; Figures 5(a) to 5(e) a series of side cross-sectional views showing a method of

forming a field emission

backplate according to a fourth embodiment of the present invention; and Figures 6(a) to 6(c) a series of side cross-sectional views showing a method of

forming a field emission

backplate formed according to a fifth embodiment of the present invention including the use of a planarising agent.

DETAILED DESCRIPTION OF DRAWINGS

Referring initially to Figures 1(a) to 1(c), there is shown a sequence of diagrams showing steps in a method of manufacture of a field emission backplate, generally designated 5a, according to a first embodiment of the p. , present invention. The backplate 5a comprises a p substrate lOa, which may be made of any suitable material, e.g. glass, ceramic or metal. Upon the substrate l0a is deposited a cathode metal layer ha, e.g. molybdenum, chromium, aluminium, or the like. Upon the cathode metal layer ila is deposited an amorphous semiconductor layer iSa. In this instance the amorphous semiconductor comprises hydrogenated amorphous silicon, which is preselected to have a relatively high hydrogen content, for example, of the order of 18%.

With reference to Figure 1 (b), the backplate 5a is exposed to laser irradiation so as to form a plurality of conductive or conducting particulates or particles 20a within the amorphous silicon layer iSa. The conducting particulates 20a can typically comprise semiconductor material, e.g. crystallised semiconductor material, and metallic material, e.g. from metal layer ha.

Referring to Figure 1(c), in use, when an electrical signal is applied across the backplate 5a, electronic transportation occurs between conducting particulates 20a due to filaments 21a therebetween. Electron transportation towards an electron emission surface 25a :*. of the backplate 5a allows electrons to be emitted from emission sites 26a anywhere on the surface 25a.

:. 15 It is noted in this embodiment that the surface 25a is substantially flat or planar. It is believed that *:*::* this is an effect of preselection of the hydrogen content of the amorphous silicon layer 15a.

In summary, in this first embodiment the layer 15a

of thin film amorphous silicon of a high hydrogen content is provided on the cathode metal layer ha or thin film metal. The backplate 5a is then processed, for example, with an excimer laser, resulting in changes in the internal structure (production of conducting particulates 20a), whilst maintaining a planar surface 25a. In use, application of an external electric field induces a high internal electric field inducing filamentary conduction

within the layer iSa or film, and subsequent field

emission of electrons.

With reference to Figure 2, there is illustrated a

field emission device, generally designated 100,

according to an embodiment of the present invention. In this device 100, the backplate 5a (or cathode backplate) is mounted on a holder 105 and placed in a vacuum chamber with a counter electrode 115 (i.e. an anode), which comprises strips of indium ten oxide, or other transparent conductor. The anode 115 strips are coated with a low or high voltage phosphor. Cathode 120 and anode 125 are held apart using spacers 130. Typically the spacers 130 are in the range of microns to millimetres. Between spacers 130 is evacuated space 110.

The vacuum chamber is then evacuated to a suitable base *:::* pressure. A1ternatively a sealed vacuum device can be prepared.

The device 100 is now in a field emission display

configuration. Application of an electric field across the cathode 120 and anode 125 results in a threshold flow voltage being overcome, and an emission current in excess of microamps measured. Energetic electrons are released from surface 25a of the backplate 5a (cathode 120) at the emitter sites 26a, and travel through the space 110 towards the phosphor typically in a conical distribution, or orthogonal depending on the nature of the filament, and if moving ballistic. Such electrons induce light emission in the counter electrode anode 125 so as to form an activated pixel.

Turning now to Figures 3 (a) to 3 (c), there is shown a series of diagrams showing steps in a method of manufacturing a field emission backplate according to a second embodiment of the present invention. Like parts are indicated by the same numerals, as in Figures 1(a) to 1(c), but suffixed with the letter "b" instead of the letter "a" With reference firstly to Figure 3 (a), in this case the amorphous silicon layer is preselected to have a * *.. * ***

relatively low hydrogen content, for example, around 10%.

Referring now to Figure 3(b), in this case laser irradiation produces a non-flat or roughened surface 25b, *:*::-forming a plurality of tips 27b, which may produce enhanced field emission. it is believed that these tips are produced due to the preselected hydrogen content of the amorphous silicon layer l5a.

Referring to Figure 3(c), in use, electron emission is produced from emission sites across surface 25b, not only regions associated with the tips 27b.

In summary, in the second embodiment the layer 15b

of thin film amorphous silicon with "standard" hydrogen content in the region of 8% to 10%, is provided on the metal cathode layer lib of a thin film metal, e.g. aluminium, chromium, molybdenum, etc. The backplate 5b is processed with an excimer laser resulting in changes in internal structure (formation of conducting particles 20b), and changes in surface morphology and roughness.

In use, application of an external electric field induces

a high internal electric field inducing filament

conduction within the layer 15a of film and subsequent

field emission of electrons.

The field emission backplate 5b may be used in the

device 110 of Figure 2 in place of the backplate 5a of the first embodiment.

Turning now to Figures 4(a) to 4(c), there is shown a series of diagrams showing steps in a method of manufacturing of a field emission backplate according to a third embodiment of the present invention. Like parts again are designated by the same numerals as in Figures 1 (a) to 1 (C) , but suffixed with the letter "c" instead of with the letter "a".

Referring to Figure 4(b), a layer 30c, for example of metal, particularly for example, aluminium, and which may be patterned, is deposited upon the amorphous silicon layer l5c. Typically the further layer 30c is of the order of 50 nm in thickness. Deposition of the further layer 30c causes material of layer 15c to transfer to the further layer 30c, and for material of further layer 30c to transfer to the layer iSa. In other words, semiconductor to flow to the metal and vice versa, e.g. silicon to flow to aluminium and aluminium to flow to silicon. This gives rise to creation of conducting particulates 20c, which typically comprise a mixture of silicon and aluminium.

Referring to Figure 4(c), the further layer 30c can be removed and surface 25c exposed. As shown in Figure 4(c), the surface 25c may be roughened and provide a plurality of tips 27b similar to the embodiment of Figures 3(a) to 3(c) It will be appreciated that in other implementations a semiconductor material other than silicon can be used, and also a metal other than aluminium can be used. S...

It will also be appreciated that between the steps illustrated in Figures 4(b) and 4(c) the backplate 5c may further be irradiated by a laser or heated in other ways, e.g. rapid thermal annealing or vacuum thermal annealing, for example, while the further layer 30c is still on the backplate 5c. Such laser irradiation, preferably after deposition of the layer 30c, or alternatively, before deposition of the layer 30c, is believed to assist in "conditioning" the backplate 5c and efficient formation of the crystallites 20c.

In summary, in the third embodiment of Figures 4(a) to 4(c), the layer 15c of thin film amorphous silicon containing hydrogen is provided on the metal cathode layer lic comprising a thin film metal, e.g. molybdenum, chromium, or the like, and coated with layer 30a comprising an ultra thin layer of metal, such as aluminium, and thereafter optionally and beneficially processed, e.g. with an excimer laser resulting in changes in internal and external structure, and mixed phase conducting particulates 20c (possibly crystallites) or "islands" are formed. Application of an external electric field produces a high internal electric field, which induces filamentary conduction within the layer l5c

and subsequent field emission of electrons.

With reference to Figures 4(d) there is shown a ".. modification to the third embodiment, wherein the backplate 5c is vacuum annealed at a predetermined pressure, for example, at 10.6 mbar, for a predetermined time period, for example, of the order of 30 minutes.

The layer 30c is then evaporated off to expose the islands or tips 27c.

It will be appreciated that in this embodiment, laser irradiation may a1so occur.

Referring now to Figures 5(a) to 5(e) there is shown a fourth embodiment of the field emission backplate 5d forming a three terminal device having self-aligned gates for each tip 27d. This field emission backplate 5d is constructed in a manner illustrated in Figures 5(a) to 5(e) In Figure 5(a) there is shown a backplate 5d formed of a substrate lOa, metal cathode layer lid and a thin film of amorphous silicon 15d. The thin film silicon 15d is conditioned" in the manner described hereinbefore with reference to Figures 3(a) to 3(c) or Figures 4(a) to 4 (d) The first step of forming the self aligned gates involves forming by deposition a thin SiN (Silicon Nitride) insulator 238d, using PEVCD, upon the exposed surface of silicon completely encapsulating each of the tips 27d as is illustrated in Figure 5(b) The second step of the process, the results of which are shown in Figure 5(c), involves a layer of metal 240d, . in this case chromium, being deposited on top of the SiN layer 238d by thermal evaporation. * *.

In the third step of the process, the plate arrangement is then etched by plasma means, in this case using CF (Freon) gas. This results in the top of each tip 27d losing its metal and the SiN insulator layer 238d being exposed, as is shown in Figure 5(d) As is shown in Figure 5(c), the SIN insulator 238d is then etched leaving a supporting metal ring 241d around the exposed tip 27d, which acts as a gate.

The resultant emission backplate Sd can be used to

form a field emission device that is completely

lithography free. Further electron emission is controllably limited to emission sites 26d on tips 27d.

Referring to Figure 6(a) to 6(c), the aforementioned process can be improved by applying a planarising agent 237e, that is a liquid which upon heating or solvent evaporation, becomes a thin planar film, to the backplate Se after the second step of the process resulting in an arrangement as illustrated in Figure 6(a) . This shows the planarising agent 237e coating the backplate Se leaving the tips 27e standing proud.

:. The step of etching the arrangement by plasma means * S..

thus results in the arrangement shown in Figure 6 (b).

:. 15 The SiN insulator is then etched as before, leaving a space between the metal layer and the tip 27e as is shown in Figure 6 Cc). By utilising the planarising agent * *.

*: 237e in this way, the underlying silicon backplate structure is protected from corrosive etch effects. The planarising agent can then be removed, resulting in a metal gate surrounding each tip.

Devices such as those detailed in the embodiments are suitable for many display applications due to their having low power consumption and being relatively simple to fabricate. Emission being confined to the tips 27d;27e is beneficial to the provision of low voltage operation. Such devices may also be used as the cathodes for high power transistors for microwave amplifiers in the satellite and mobile communication markets.

It will be appreciated that the embodiments of the present invention hereinbefore described are given by way of example only, and are not meant to be limiting thereof in any way. Indeed, various modifications may be made to the disclosed embodiments without departing from the scope of the invention. For example, it will be understood that any of the disclosed embodiments may comprise one or more of the features provided in the

summary of invention. * * * *.* **I* * * **.. * * * ***

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I * *. p * * * **

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Claims

CLAIMS

1. A field emission backplate comprising a plurality of conductive or conducting particulat.es or particles, wherein the conducting particulates are provided within the backplate.

2. A field emission backplate as claimed in claim 1, wherein the field emission backplate comprises amorphous semiconductor material such as a layer of amorphous semiconductor material.

S

3. A field emission backplate as claimed in either of.

claims 1 or 2, wherein each conducting particulate..** * S.S comprises a point or locality such as of crytallisation, * such as a crystallite, within the layer of amorphous semiconductor material.

4. A field emission backplate as claimed in claim 2 or claim 3 when dependent upon claim 2, wherein the conducting particulates each comprise semiconductor and/or metallic material.

5. A field emission backplate as claimed in any of

claims 2 to 4, wherein the amorphous semiconductor material comprises amorphous silicon or an alloy thereof such as hydrogenated amorphous silicon, Si:H.

6. A field emission backplate as claimed in any of

claims 2 to 5, wherein the layer of amorphous semiconductor material is provided on a substrate.

7. A field emission backplate as claimed in claim 6, wherein the substrate is made from glass, a ceramic material or metallic material. * * * * * S. *e **S. * S

8. A field emission backplate as claimed in any of ***

S

claims 2 to 7, wherein filaments or pathways, such as *...

conductive or conducting filaments, are provided between *5..

the conducting particulates, at least in use.

9. A field emission backplate as claimed in claim 8, wherein the filaments provide a means for electron transport through the backplate to emitter sites on a surface of the backplate, which surface comprises a surface of the amorphous semiconductor material.

10. A field emission backplate as claimed in either of claims 8 or 9, wherein the filaments are spatial instabilities or spatlo-temporal features, optionally formed as a consequence of intense internal electric

field confinement between conducting particulates.

11. A field emission backplate as claimed in any of claims 8 to 10, wherein in use, upon application of an electric field across the backplate, the filaments are formed and provide a transport network for electrons to the emitter sites.

12. A field emission backplate as claimed in any of * claims 8 to 11, wherein in use, electrons move through *::.: I...

the filaments between conducting particulates and to an **

S

emitter site (s) . *e.. * * *.S.

13. A field emission backplate as claimed in claim 12, .: wherein the electrons move, in use, by electron transport or under certain conditions ballistically, such as if the dimension of the conducting particulates are sufficiently small, and/or the space between the conducting particulate is sufficiently small.

14. A field emission backplate as claimed in any of claims 2 to 13, wherein a surface of the amorphous semiconductor material is substantially flat.

15. A field emission backplate as claimed in any of claims 2 to 13, wherein a surface of the amorphous semiconductor material is substantially non-flat or roughened, comprising a plurality of tips, such as microtips.

16. A field emission backplate as claimed in either of claims 14 or 15, wherein the emitter sites are provided anywhere upon or across the surface. * S * * * S. *.

17. A field emission backplate as claimed in claim 16 when dependent upon claim 15, wherein the emitter sites * *.

are provided on the tips and between adjacent tips. * S...

18. A field emission device comprising a field emission backplate according to any of claims 1 to 17.

19. A field emission device as claimed in claim 18, wherein the device is a vacuum device, wherein emitter Sites act as an electron emission source of the device, in use.

20. A field emission device as claimed in claim 19, wherein the device further comprises a substrate, an evacuated space and a transparent window, wherein the field emission backplate is formed upon the substrate and the evacuated space is located between the field emission backplate and the transparent window.

21. A field emission device as claimed in claim 18, wherein the field emission device comprises an electro-luminescent material or (wide band-gap) light emitting material into which electrons from the emission sites are emitted, in use. * * * * S. **

22. A field emission device as claimed in claim 21, * S S...

wherein the device further comprises a substrate, the *e.

S

light emitting material, and a transparent window, wherein electrons from the emission sites are emitted into the light emitting material.

23. A field emission device as claimed in either of claims 21 or 22, wherein the light emitting material is a light emitting polymer.

24. A field emission device as claimed in any of claims 21 to 23, wherein the electro-luminescent or light emitting material has a fluorescent material chemically attached thereto.

25. A field emission device as claimed in claim 20 or claim 22 or claims 23 or 24 when dependent upon claim 22, wherein the transparent window is a thin film transparent metal.

26. A field emission device as claimed in any of claims 21 to 24 or claim 25 when dependent upon claim 21, wherein one surface of the light emitting material is disposed on a surface of the field emission backplate, and the transparent window is disposed on another surface.* . of the light emitting material. ::.::

S 5S

27. A field emission device as claimed in any of claims *.: 18 to 26, wherein the device is a display device.

28. A field emission device as claimed in any of claims 18 to 27, wherein the emitter or emission sites of the field emission backplate are of a density of at least 100 per square micron.

29. A method of manufacturing a field emission backplate comprising: providing a backplate material; and processing the material so as to at least partially form a plurality of conductive or conducting particulates or particles within the backplate material.

30. A method of manufacturing a field emission backplate as claimed in claim 29, wherein the step of providing a backplate material comprises: providing a planar body of amorphous semiconductor material upon a substrate.

31. A method of manufacturing a field emission backplate * : as claimed in either of claims 29 or 30, wherein the step::.: S...

of processing the material comprises: laser crystallising 5S at. least a portion of the amorphous semiconductor material, such that the plurality of conducting * S..

particulates are formed.

32. A method of manufacturing a field emission backplate as claimed in any of claims 29 to 31, wherein the method comprises the step of selecting a level of hydrogenation of the amorphous semiconductor material such that when laser irradiated a surface of the amorphous semiconductor material remains substantially flat or planar.

33. A method of manufacturing a field emission backplate as claimed in any of claims 29 to 31, wherein the method comprises the step of: selecting a level of hydrogenation of the amorphous semiconductor material such that when laser irradiated a surface of the amorphous semiconductor material becomes substantially non-flat or roughened, optionally comprising a plurality of tips, such as microtips.

34. A method of manufacturing a field emission backplate as claimed in claim 30 or any of claims 31 to 33 when dependent upon claim 30, wherein the planar body of amorphous semiconductor based material is provided by *** depositing a thin film of material upon a substrate, such as by Plasma Enhanced Chemical Vapour Deposition (PECVD) . S... *5S*

35. A method of manufacturing a field emission backplate as claimed in claim 30 or any of claims 31 to 34 when dependent upon clam 30, wherein the semiconductor based material is silicon or an alloy thereof.

36. A method of manufacturing a field emission backplate as claimed in claim 31 or any of claims 32 to 35 when dependent upon claim 31, wherein the step of performing laser crystallising is carried out at a wavelength of around 525 nm to 540 nm, or substantially 532 rim.

37. A method of manufacturing a field emission backplate as claimed in claim 31 or any of claims 32 to 36 when dependent upon claim 31, wherein the step of laser crystallising uses an excirner laser or Nd:YAG laser.

38. A method of manufacturing a field emission

backplate as claimed in claim 31 or any of claims 32 to 36 when dependent upon claim 31, wherein the step of performing laser crystallising is carried out in air, vacuum or an inert gas atmosphere. S... * *.

39. A method of manufacturing a field emission backplate * as claimed in claim 37, wherein the excimer laser is a KrF laser.

S S... *** * . *5

40. A field emission backplate comprising a plurality of conducting particulates, wherein a surface of the backplate is substantially flat or planar.

41. A method of forming a field emission backplate

comprising the step of: providing a backplate material; depositing a layer on the backplate so as to at least partially form a plurality of conducting particulates.

42. A method of forming a field emission backplate as claimed in claim 41, wherein the backplate material comprises an amorphous semiconductor material, such as a layer of such.

43. A method of forming a field emission backplate as claimed in either of claims 41 or 42, wherein the conducting particulates are provided within the backplate material. * S * * S S. * *S*5 * *5S*

44. A method of forming a field emission backplate as **.

claimed in any of claims 41 to 43, wherein the conducting *,* particulates comprises a plurality of points or *S.. * S **S.

locations, such as crystallites.

45. A method of forming a field emission backplate as claimed in any of claims 41 to 44, wherein the conducting particulates are conductively interconnected by filaments, which optionally allow electron transportation between emitter sites, in use, when a voltage is applied across the backplate.

46. A method of forming a field emission backplate as claimed in any of claims 41 to 45, wherein the layer comprises a metallic layer.

47. A method of forming a field emission backplate as claimed in claim 46, wherein the metallic layer comprises aluminium.

48. A method of forming a field emission backplate as claimed in any of claims 41 to 47, wherein deposition of * : ** S. the layer is the sole mechanism for forming the * S S...

conducting particulates. S.. *.. * * * *5

49. A method of forming a field emission backplate as * .*.

claimed in any of claims 41 to 47, wherein deposition of...

the layer is one of a number of mechanisms for forming the conducting particulates.

50. A method of forming a field emission backplate as claimed in claim 49, wherein another mechanism is laser irradiation of the backplate.

51. A method of forming a field emission backplate as claimed in either of claims 49 or 50, wherein the another mechanism is carried out after or before deposition of the layer.

52. A field emission backplate formed by the method of any of claims 41 to 51.

53. A field emission device comprising a field emission backplate according to claim 52.

54. A field emission backplate comprising a plurality of emitter or emission sites, wherein a surface of the * S *.., backplate is substantially flat or planar. S.. * *. *e

54. A field emission backplate comprising a plurality of emitter or emission sites, wherein a surface of the....

backplate is substantially flat or planar.

55. A field emission backplate as hereinbefore described with reference to the accompanying drawings.

56. A field emission device as hereinbefore described with reference to the accompanying drawings.

57. A method of manufacturing a field emission backplate as hereinbefore described with reference to the accompanying drawings. * * a ** ** * *.** S..

S S.. * * * 5' . * . * 5* S.. * -. S.