A FIELD EMISSION CATHODE STRUCTURE FOR A FIELD EMISSION ARRANGEMENT

Abstract

The present disclosure generally relates to field emission cathode structure for a field emission arrangement, specifically adapted for enhance reliability and prolong the lifetime of the field emission arrangement by arranging a getter element underneath a gas permeable portion of the field emission cathode structure. The present disclosure also relates to a field emission lighting arrangement comprising such a field emission cathode structure and to a field emission lighting system.

Claims

1. A field emission cathode structure for a field emission arrangement, comprising: a substrate having a first and a second side; a getter element arranged on top of the first side of the substrate and covering a portion of the first side of the substrate; an at least partly permeable structure arranged on top of at least a portion of the getter element; and an electron emission source arranged to cover a portion of the at least partly permeable structure, wherein the getter element is sandwiched between the substrate and the at least partly permeable structure.

2. The field emission cathode structure according to claim 1, wherein the electron emission source comprises a plurality of nanostructures.

3. The field emission cathode structure according to claim 2, wherein the plurality of nanostructures comprises at least one of ZnO nanostructures and carbon nanotubes.

4. The field emission cathode structure according to claim 3, wherein the plurality of ZnO nanostructures is adapted to have a length of at least 1 um.

5. (canceled)

6. The field emission cathode structure according to claim 1, wherein the at least partly permeable structure encapsulates the getter element.

7. The field emission cathode structure according to claim 1, wherein the getter element is formed by arranging a layer of a getter material onto the portion of the substrate.

8. The field emission cathode structure according to claim 7, wherein the getter material is non-evaporable getter material.

9. The field emission cathode structure according to claim 7, wherein the getter material comprises at least one of tantalum (Ta), zirconium (Zr), titanium (Ti), hafnium (Hf), and/or their alloys.

10. The field emission cathode structure according to claim 7, wherein a thickness of the layer of getter material is about 20-100 m.

11. The field emission cathode structure according to claim 1, wherein the substrate is planar.

12. The field emission cathode structure according to claim 11, wherein the substrate is a wafer.

13. The field emission cathode structure according to claim 12, wherein the wafer is a silicon wafer.

14. The field emission cathode structure according to claim 1, wherein the getter element and the electron emission source are electrically connected.

15. The field emission cathode structure according to claim 1, wherein the at least partly permeable structure is gas permeable.

16. The field emission cathode structure according to claim 1, wherein the at least partly permeable structure is formed from a grid structure.

17. The field emission cathode structure according to claim 16 when dependent on claim 2, wherein the grid structure is net shaped and the plurality of nanostructures are arranged onto bars comprised with the net shaped grid structure.

18. A field emission lighting arrangement, comprising: an evacuated chamber; a field emission cathode structure according to claim 1, the field emission cathode arranged within the evacuated chamber; an anode structure arranged within the evacuated chamber; and a light emission member provided with an electron-excitable light emitting material, the light emission member arranged within the evacuated chamber, wherein the getter element is adapted to be activated prior to operation of the field emission lighting arrangement.

19. The field emission lighting arrangement according to claim 18, wherein a voltage level applied between the field emission cathode and the anode structure is selected to be between 5-15 kV.

20. (canceled)

21. The field emission lighting arrangement according to claim 18, wherein the field emission lighting arrangement is formed as a lighting chip.

22. A field emission lighting system comprising a plurality of field emission lighting arrangements according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The various aspects of the present disclosure, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0038] FIG. 1 illustrates a perspective view of a chip based field emission light source according to prior-art,

[0039] FIGS. 2A-2C conceptually illustrates a first exemplary embodiment of the present disclosure; and

[0040] FIGS. 3A and 3B show alternative embodiments of the present disclosure.

DETAILED DESCRIPTION

[0041] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the present disclosure are shown. This present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present disclosure to the skilled addressee. Like reference characters refer to like elements throughout.

[0042] Referring now to the drawings and to FIG. 1 in particular, there is provided a perspective view of a field emission light source 100 according to prior-art, exemplified to have an essentially elliptical shape and arranged to emit light e.g. within the visible and/or UV light spectrum. Other shapes are feasible, such as being essentially rectangular; however an elliptical (or circular or similarly rounded) shape has advantages, for example in terms of avoiding electrical phenomena as arcing and parasitic currents. Such phenomena may otherwise become an issue when high electrical fields are applied and corners or edges are present. The field emission light source 100 comprises a wafer 102 provided with a plurality of ZnO nanorods 104 having a length of at least 1 um, the wafer 102 and plurality of ZnO nanorods 104 together forming a field emission cathode. It may also, as an alternative, be possible to substitute the ZnO nanorods 104 for carbon nanotubes (CNT, not shown). The field emission light source 100 further comprises an anode structure arranged in close vicinity of the field emission cathode. In any of the figures only one singular device is shown but the wafer may contain large numbers of such devices.

[0043] The distance between the field emission cathode and the anode structure in the current embodiment is achieved by arranging a spacer structure 110 between the field emission cathode and the anode structure, where a distance between the field emission cathode and the anode structure preferably is between 100 um to 5000 um. A cavity formed between the field emission cathode and the anode structure is evacuated, thereby forming a vacuum between the field emission cathode and the anode structure.

[0044] The anode structure comprises a transparent substrate, such as a planar glass structure 114. Other transparent materials are equally possible and within the scope of the invention. Examples of such materials are sodalime like glass, borosilicate glass, quartz and sapphire. The transparent structure 114 is in turn provided with a phosphor layer 116, converting electron energy into photons. The exact properties of the phosphor material will determine the photon wavelengths. The phosphor layer 116 may be deposited by a number of commercially available standard methods, e.g. spraying, screen-printing and the like. Other methods are equally possible ad within the scope of the present disclosure. On top of the phosphor is a conductive layer 118, forming the anode electrical contact. Suitable materials for this layer are for example Aluminum and Silver.

[0045] The thickness of this layer is selected so that a) it is thin enough for electrons of the selected energy to pass through the layer without any significant loss of energy and b) at the same time thick enough to give an as high reflectance as possible, thus reflecting photons generated in the phosphor layer directed towards the conductive layer 118 back and through the glass 114 (unless reflection occur.) The conductive layer 118 may be deposited by a number of methods, sputtering and evaporation serving as two examples.

[0046] In some embodiments where the field emission light source 100 is specifically adapted for emitting visible light, it may also be possible to use a transparent conductive oxide (TCO) layer as the conductive layer, such as an indium tin oxide (ITO) layer. The thickness of such an ITO layer is selected to allow maximum transparency with a low enough electrical resistance. A typical transparency is selected to be above 90%. Using an ITO layer is generally not suitable for UV applications.

[0047] The phosphor material 116 is capable of conversion of electron energy to photons. The phosphor material 116 may, as mentioned above, be adapted to convert electrons to UV or visible light. Examples of phosphor materials suitable for UV light generation comprise for example LuPO3:Pr3+, Lu2Si2O7:Pr3+, LaPO4:Pr3+, YBO3:Pr3+ and YPO4:Bi3+. Other similar materials may be equally feasible.

[0048] The field emission light source 100 further comprises a getter element 120. The getter element 120 is arranged adjacently to the nanostructures 114 at a bottom surface of the cavity formed by the spacer structure 110 surrounding the nanostructures 114 and the getter element 120. The getter element 120 is a deposit of reactive material that is provided for completing and maintaining the vacuum within the cavity 112, as has been discussed above.

[0049] In FIG. 1, the getter element 120 is exemplified as a thin sheet being placed along the side of the spacer element. It may also be deposited as a suitable alloy. To avoid short electrical breakdown and parasitic surface currents the anode and cathode contacting elements (not shown) are placed as well away from the getter element 120 and each other (not explicitly shown). The getter element 120 further is mechanically attached, e.g. to the wafer 102. In FIG. 1 the getter element 120 is shown as being directly arranged at a top surface of the wafer 102, however it has been previously known to also position the getter element 120 in a specially designed cavity arranged at the surface of the wafer 102. Even though the introduction of a cavity may be useful from an attachment perspective, such a solution adds to the cost, complexity and size of the to the field emission light source 100. A typical getter may be HPTF foils, by SAES Getters of Italy.

[0050] Turning now to FIGS. 2A-2C, where it is conceptually illustrated an embodiment of the present disclosure. In FIG. 2A, the field emission light source 200 is exemplified to have an essentially circular shape and is shown as a lighting chip. It should however be understood that in line with the above discussion the field emission light source 200 may be differently shaped, e.g. to be elliptical or rectangular. Also the field emission light source 200 may be arranged to emit light e.g. within the visible and/or UV light spectrum.

[0051] In comparison to the prior-art solution as shown in FIG. 1, the field emission light source 200 as shown in FIG. 2 additionally comprises an at least partly permeable structure. The permeable structure is in FIG. 2 exemplified as a wire mesh 202, comprising a plurality of wires 204 and 206 arranged to form a rectangular spaced structure. In a possible embodiment of the present disclosure a diameter of the wires 204, 206 is selected to be between 20 um and 200 um. A distance between the wires may additionally be selected such that open area portion for the wire mesh 202 is between 40% and 90%, thereby allowing rest gas molecules to pass through the wire mesh 202.

[0052] In accordance to the present disclosure, the wire mesh 202 is provided with a plurality of nanostructures 104 as discussed above. The wire mesh 202 will thus form at least partly protruding structures for the nanostructures 104, providing the first electrical field amplifying effect as discussed above. A detailed view of the nanostructures 104 arranged at the wire mesh 202 is provided in FIG. 2B.

[0053] The field emission light source 200 also comprises a getter element 208. However in line with the concept of the present disclosure, the getter element 208 is arranged beneath the wire mesh 202, as detailed in FIG. 2C, between a surface of a top side 210 the substrate 102 and the wire mesh 202. Accordingly, the getter element 208 will be sandwiched between the substrate 102 and the wire mesh 202.

[0054] The getter element 208 is preferably arranged at the same electrical potential as the wire mesh 202, resulting in that the getter will preferably accept positively charged ions, that would to larger extent otherwise risk adsorption on the cathode tips and thus risk quenching the cathode current.

[0055] In FIG. 3A there is shown a slightly different possible implementation of the present disclosure, as compared to the illustration shown in FIGS. 2A-2C. Specifically, the at least partly permeable structure is formed from an electrically conductive sheet material 302, provided with a plurality of via holes 304. The number of via holes 304 and a diameter of the via holes 304 may be controlled for achieving a desirable permeability of the electrically conductive sheet material 302, such as e.g. between 40%-90%. The first field amplification will occur on the edges of the openings.

[0056] In a corresponding manner, the illustration provided in FIG. 3B shows a further different possible implementation in accordance to the present disclosure, as compared to the illustration shown in FIGS. 2A-2C. Specifically, the at least partly permeable structure comprises a plurality of bars 308 arranged essentially in parallel with each other. The bars 308 are exemplified to have a diameter greatly extending the diameter of the wires 204, 206 as shown in FIG. 2. The bars 308 are in in turn provided with protrusions 310 onto which the nanostructures 104 are provided. In a similar manner as discussed above, the bars 308 are preferably arranged to have a distance them between that allows the permeability and thus access to the getter element 210 to be e.g. between 40%-90%.

[0057] It should be understood that the wires 204, 206 or the bars 308 not necessarily must be completely straight as illustrated in the drawings. Rather, they may be formed to be curved or slightly waved without departing from the scope according to the present disclosure. Additionally, it may be possible to only use e.g. parallel wires (i.e. not formed as a wire mesh), thus only arranged in one direction such as only including the wires 204 and not the wires 206. Further alternatives for forming the at least partly permeable structure is possible and within the scope of the present disclosure.

[0058] In summary, the present disclosure relates to a field emission cathode structure for a field emission arrangement, comprising a substrate having a first and a second side, a getter element arranged on top of the first side of the substrate and covering a portion of the first side of the substrate, an at least partly permeable structure arranged on top of at least a portion of the getter element, and an electron emission source arranged to cover a portion of the at least partly permeable structure.

[0059] In accordance to the present disclosure there is provide a possibility to position the getter element underneath an at least partly permeable structure comprised with the field emission cathode, whereby the rest gas molecules as discussed above are allowed to pass through the at least partly permeable structure comprised with the field emission cathode.

[0060] Although the figures may show a specific order of method steps, the order of the steps may differ from what is depicted. In addition, two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps. Additionally, even though the present disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

[0061] Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed present disclosure, from a study of the drawings, the disclosure, and the appended claims. Furthermore, in the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.