FIELD EMISSION LIGHT SOURCE

Abstract

The present invention generally relates to a field emission light source and specifically to a miniaturized field emission light source that is possible to manufacture in large volumes at low cost using the concept of wafer level manufacturing, i.e. a similar approach as used by IC's and MEMS. The invention also relates to a lighting arrangement comprising at least one field emission light source. The field emission light source comprises: a field emission cathode (106) comprising a plurality of nanostructures (104) formed on a substrate; an electrically conductive anode structure (108) comprising a first wavelength converting material (118) arranged to cover at least a portion of the anode structure, wherein the first wavelength converting material is configured to receive electrons emitted from the field emission cathode and to emit light of a first wavelength range, and means for forming an hermetically sealed and subsequently evacuated cavity (106) between the substrate of the field emission cathode and the anode structure, including a spacer structure (302, 110) arranged to encircle the plurality of nano structures, wherein the substrate for receiving the plurality of nanostructures is a wafer (102′).

Claims

1. A field emission light source configured to emit UV light, comprising: a field emission cathode comprising a plurality of ZnO nanostructures formed on a substrate; an electrically conductive anode structure comprising a first wavelength converting material arranged to cover at least a portion of the anode structure, wherein the first wavelength converting material is configured to receive electrons emitted from the field emission cathode and to emit light of a first wavelength range, and means for forming an hermetically sealed and subsequently evacuated cavity between the substrate of the field emission cathode and the anode structure, including a spacer structure arranged to encircle the plurality of nanostructures, wherein: the substrate for receiving the plurality of nanostructures is a wafer suitable for a modular manufacturing process, the spacer structure is arranged to set a predetermined distance between the anode structure and the field emission cathode, and the spacer is selected to have a thermal expansion matching the wafer and the anode structure.

2. (canceled)

3. The field emission light source according to claim 1, further comprising a second wavelength converting material.

4. The field emission light source according to claim 1, further comprising a second wavelength converting material arranged remotely from the first wavelength converting material.

5. The field emission light source according to claim 4, further comprising a dome shaped structure arranged on an outside of the anode structure, wherein the second wavelength converting material is formed on at least a portion of an inside of the dome shaped structure.

6. The field emission light source according to claim 1, wherein a light outcoupling side of at least one of the substrate of the field emission cathode and the anode substrate comprises light extraction nanostructures.

7. The field emission light source according to claim 3, wherein the first wavelength converting material comprises a phosphor material, and the second wavelength converting material comprises quantum dots generating light at a second wavelength range when receiving light at the first wavelength range, where the second wavelength range is at least partly higher than the first wavelength range.

8. The field emission light source according to claim 7, wherein the first wavelength range is between 350 nm and 550 nm, preferably between 420 nm and 495 nm.

9. The field emission light source according to claim 7, wherein the second wavelength range is between 470 nm and 800 nm, preferably between 490 nm and 780 nm.

10. The field emission light source according to claim 1, wherein the wafer is a metallic alloy.

11. The field emission light source according to claim 1, wherein the plurality of nanostructures have a length of at least 1 um.

12. The field emission light source according to claim 1, wherein the spacer structure is configured to form a distance between the substrate of the field emission cathode and the anode structure to be between 100 um and 5000 um.

13. The field emission light source according to claim 1, wherein a distance between the field emission cathode and the anode structure is dependent on a desired operational point of the field emission light source.

14. The field emission light source according to claim 1, wherein the wafer comprises a recess, and at least a portion of the plurality of nanostructures are formed at a bottom surface of the recess.

15. The field emission light source according to claim 3, further comprising a third wavelength converting material, emitting light within a third wavelength range.

16. The field emission light source according to claim 1, wherein the first wavelength converting material comprises zinc sulfide (ZnS) and the first wavelength converting material is configured to absorb electrons and emit blue light, or the first wavelength converting material comprises a mono crystalline phosphor layer.

17. The field emission light source according to claim 1, wherein the wafer is a silicon waver, and logic functionality for controlling the field emission light source is formed with the silicon wafer.

18. The field emission light source according to claim 1, wherein the wafer is manufactured from a metal material.

19. (canceled)

20. The field emission light source according to claim 1, further comprising a getter arranged adjacently to the nanostructures.

21. A lighting arrangement, comprising: a field emission light source according to claim 1, a power supply for supplying electrical energy to the field emission light source for allowing emission of electrons from the plurality of nanostructures towards the anode structure, and a control unit for controlling the operation of the lighting arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0049] FIG. 1 illustrates a perspective view of a field emission light source according to a currently preferred embodiment of the invention;

[0050] FIGS. 2a and 2b provides exemplary implementations of arranging a first and a second wavelength converting material at an anode structure of the field emission light source of FIG. 1,

[0051] FIG. 3 illustrates an alternative implementation of a field emission light source according to the invention;

[0052] FIGS. 4a-4d provides further alternative embodiments of the field emission light source according to the invention,

[0053] FIG. 5 illustrates an alternative implementation of a field emission light source according to the invention,

[0054] FIG. 6 shows a diagram with a reflectance curve for a conductive anode layer,

[0055] FIG. 7 illustrates a currently preferred implementation of a field emission light source according to the invention, and

[0056] FIG. 8 illustrates a lighting arrangement comprising a plurality of field emission light sources arranged adjacently to each other.

DETAILED DESCRIPTION

[0057] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention 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 invention to the skilled addressee. Like reference characters refer to like elements throughout.

[0058] Referring now to the drawings and to FIG. 1 in particular, there is illustrated a field emission light source 100 according to a preferred embodiment of the invention. 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 and plurality of ZnO nanorods 104 together forming a field emission cathode 106. In a possible embodiment the ZnO nanorods may be selectively arranged onto spaced protrusions (not shown). It may also, as an alternative, be possible to substitute the ZnO nanorods 104 for carbon nanotubes (CNT, not shown). Other emitter materials are equally possible and within scope of the invention. The field emission light source 100 further comprises an anode structure 108 arranged in close vicinity of the field emission cathode 106.

[0059] The distance between the field emission cathode 106 and the anode structure 108 in the current embodiment is achieved by arranging a spacer structure 110 between the field emission cathode 106 and the anode structure 108, where a distance between the field emission cathode 106 and the anode structure 108 preferably is between 100 um to 5000 um. The cavity 112 formed between the field emission cathode 106 and the anode structure 108 is evacuated, thereby forming a vacuum between the field emission cathode 106 and the anode structure 108.

[0060] The anode structure 108 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 quartz and sapphire. The transparent structure 114 is in turn provided with an electrically conductive and at least partly transparent anode layer, typically a transparent conductive oxide (TCO) layer, such as an indium tin oxide (ITO) layer 116. The thickness of the layer 116 is selected to allow maximum transparency with a low enough electrical resistance. In a preferred embodiment the transparency is selected to be above 90%. The layer 116 may be applied to the glass structure 114 using any conventional method known to the skilled person, such as sputtering or deposition by solvent, or screen-printing. As will be discussed below, the electrically conductive anode layer 116 may take different shapes and forms depending on the implementation at hand.

[0061] In accordance to the present embodiment, the layer 116 is provided with a first 118 and a second 120 wavelength converting material. With further reference to FIGS. 2a and 2b, the wavelength range converting materials 118, 120 may be formed onto the layer 116 in different ways. In FIG. 2a the second wavelength converting material 120 is formed directly adjacent to and on top of the ITO layer 116, and the first wavelength converting material 118 is formed directly adjacently and on top of the second wavelength converting material 120. This embodiment, i.e. shown in FIG. 2a, may be advantageous as it allows for a simplified manufacturing process where the different layers (i.e. layer 116, second wavelength converting material 120 and then the first wavelength converting material 118) subsequently are arranged onto the glass structure 114. It should be noted that the glass structure 114 not necessarily has to be planar.

[0062] In a possible embodiment, the glass structure 114 may be selected to form a lens for the field emission light source (e.g. being outward bulging), thereby possibly further enhancing the light extraction and mixing of light emitted from the field emission light source. It may also be possible to provide the glass structure with an anti-reflective coating. With reference to FIG. 3, an outward bulging structure has the additional advantage of at the same time allowing for an improved uniformity of the electrical field on the cathode as well as giving a uniform distribution of the electrons onto the first wavelength converting layer, thus improving the overall uniformity of the emitted light.

[0063] Turning now again to FIG. 1, nano-patterning and/or roughening the exiting surface of the glass structure 114 through which the generated light is coupled out may be used. It may further be possible to reduce lateral optical modes leaking into the glass substrate and increase the light outcoupling. These patterns may include, but are not limited, to nanopillars, nanocones, and/or nanospheres. An example on such light extracting features is ZnO nanorods, typically 0.1-5 um high, 0.1-5 um wide and separated by 0.1-5 μm. In addition, nanoparticles may be placed between the glass and the wavelength converting layer.

[0064] However, as an alternative it may be possible to allow for a “patched” formation of the first 118 and the second 120 wavelength converting materials onto the ITO layer 116, as is shown in FIG. 2b. As may be seen, in this implementation the first 118 and the second 120 wavelength are formed in layered patches at least partly overlapping each other. In the illustrated embodiment, the patches are formed as at least partly overlapping circles, however any type of forms are possible and within the scope of the invention.

[0065] With reference again to FIG. 1, the nanostructures 104 can be grown on a wafer by a number of techniques. As the wafer material may be chosen for example to match thermal expansion coefficients of the other wafer materials, it is not necessarily an optimum material to use for nanostructure formation. Thus, a first step may be the preparation of the wafer 102, for example by applying a thin layer of a metal onto the wafer 102 in order to facilitate this growth. One technique involves allowing the wafer 102 to pass through a hydrothermal growth process for forming a plurality of ZnO nanorods 104. Other techniques for preparation and nanostructure growth are possible and within the scope of the invention.

[0066] During operation of the field emission light source 100, a power supply (not shown) is controlled to apply a voltage potential between the field emission cathode 106 and the ITO layer 116. The voltage potential is preferably between 0.1-20 kV, depending for example on the distance between the field emission cathode 106 and the anode structure 108, the sharpness, height and length relationship of the plurality of ZnO nanorods 104 and the desired performance optimization.

[0067] Electrons will be released from the outer end of the ZnO nanorods 104 and accelerated by the electric field towards the anode structure 108. Once the electrons are received by the first wavelength converting material 118, a first wavelength light will be emitted. The light with the first wavelength range will impinge onto the second wavelength converting material 120, generating light within the second wavelength range. Some parts of the light within the first wavelength range will together with light within the second wavelength range pass through the ITO layer 116 and through the glass structure 114 and thus out from the field emission light source 100.

[0068] With reference to FIG. 3, there is shown an alternative embodiment of a field emission light source 300. In a similar manner as in relation to the field emission light source 100 of FIG. 1, the field emission light source 300 comprises a wafer 102′. A difference in comparison to the wafer 102 provided in relation to the field emission light source 100 is that the wafer 102′ comprises a recess 302. The nanostructures 104 are in the illustrated embodiment formed at a bottom surface 304 of the recess 302. The spacer 110 is provided to separate the anode structure 108 from the field emission cathode 106, forming an evacuated cavity 306. The height of the spacer 110 combined with the depth of the recess 302 creates the distance (D) between the field emission cathode 106 and the anode structure 108. The distance, D, may as mentioned above be selected to optimize the operational point of the field emission light source. In a possible embodiment the distance, D, is selected (in relation to the height of the nanostructures 112) such that the outer ends of the nanostructures 112 (almost) comes in direct contact with the first wavelength converting material 118.

[0069] In general relation to the invention and as illustrated in FIG. 3, the first wavelength converting material comprises zinc sulfide (ZnS) configured to absorb electrons emitted by the nanostructures 104 and to emit blue light.

[0070] In the illustrated embodiment, the field emission light source 300 is further provided with light extracting elements 308 adapted to enhance light extraction out of the field emission light source 300. The light extraction elements 308 reduces the amount of trapped photons emitted from the first wavelength converting material 118 and thus improves the overall efficiency of the field emission light source 300.

[0071] The field emission light source 300 is further provided with a dome shaped structure 310 arranged at a distance from the glass structure 114. The inside surface of the dome shaped structure 310 facing the glass structure 114 and the light extracting elements 308 are provided with the second wavelength converting material 120. As discussed above, the second wavelength converting material 120 may comprise quantum dots (QDs) configured to absorb e.g. blue light emitted by the first wavelength converting material 118 and to emit e.g. green and/or yellow/orange and/or red light. Some portions of the blue light will pass through the second wavelength converting material 120, mix with the e.g. green and red light emitted by the second wavelength converting materials 120 and is thus be provided as white light emitted out from the field emission light source 300. One advantage with such an arrangement is that the second wavelength converting material will be subjected to less heat and therefore may be chosen also from materials that exhibit some temperature quenching in their light emission characteristics.

[0072] In the illustrated embodiment, a control unit 312 is shown as integrated with the wafer 102′. The functionality of the control unit 312 may thus be formed in direct adjacent contact with the field emission cathode 106, possibly simplifying the control of the field emission light source 300. The control unit 312 and the remaining portions of the field emission cathode 106 are preferably manufactured in a combined process, such as in a combined CMOS process.

[0073] It is desirable to form an electrical interconnection pad (not shown) connected to the TCO/ITO layer 116 of the anode 108 for allowing the field emission light source 300 to be operated by means of and connected to a power supply (not shown). A separate electrical connection is in such a case provided between the cathode 106 and the power supply. In relation to the manufacturing process, it may be preferred to connect a bonding wire (not shown) between the interconnection pad of the TCO/ITO layer 116 and a dedicated and isolated portion of the wafer 102, the isolated portion forming a further interconnection pad for receiving the bonding wire. As such, the power supply may more easily be connected to the anode 108 and the cathode 106 of the field emission light source 300. In relation to e.g. a LED light source, the bonding wire may be selected to be in comparison much thinner. The reason for this is that the operational current of the field emission light source 300 is in comparison generally several orders of magnitude lower.

[0074] As discussed briefly above, it may be possible, and within the scope of the invention, to shape the top and bottom surfaces of the recess 302 to optimize both the uniformity of the electrical field on the nanostructures 112 and the corresponding uniformity of emitted electrons onto the anode 108. This may be achieved by allowing the bottom surface of the recess 302, to be formed such that the distance D will be (slightly) smaller at the center of the recess 302, or by allowing the top surface of the cavity (formed together with the anode 108) to be slightly recessed so that the distance D will be (slightly) larger at center of the cavity 302. The concept of shaping the overall structure/shape of the field emission cathode 106 in spatial relation to the anode 108 is further elaborated in EP 2784800, which is fully incorporated by reference. The protrusion is preferably circular as seen from the top.

[0075] Turning now to FIG. 4a which partially shows an alternative implementation of the field emission light source 300 as shown in FIG. 3. As a comparison, in FIG. 4a, an inverted approach to the field emission light source 400 is shown, where the nanostructures 104 of the field emission cathode 106 are arranged as a transmissive field emission cathode. Within the context of the present invention, the nanostructures 104 are, during operation emitting electrons in a direction towards an anode 402, formed from for example a metal material, such as for example aluminum, copper, steel or other similar materials.

[0076] Specifically, in accordance to the invention, a parabolic or near parabolic recess is arranged at the bottom wafer 402, forming a cavity 404 between the field emission cathode 106 and the bottom wafer 402. A surface 406 of the recess is arranged to be reflective, for example by means of the metal material forming the anode 402. One advantage with such an arrangement is that the heat transfer from the anode may be greatly enhanced.

[0077] In addition, the first wavelength converting material 118 is provided at the lower part of the recess/cavity 404. Thereby, during operation of the field emission light source 400, the electrons emitted from the field emission cathode 106 will be received by the first wavelength converting material 118. As a result of the reception of the electrons, the first wavelength converting material 118 will emit light (omnidirectional). The part of the light emitted downwards will in turn be reflected by the reflective surface 406 of the recess of the anode 402. The light will be reflected in a direction (back) towards the transmissive field emission cathode 106. Thus, light will be allowed to pass through the field emission cathode 106 and out from the field emission light source 400.

[0078] As discussed above, the light emitted from the first wavelength converting material 118 will be extracted/directed, e.g. by means of the parabolic recess, towards a second wavelength converting material 120 (not shown). At the second wavelength converting material 120, the received light will typically be converted to a higher wavelength range as compared to the wavelength range of light emitted from the first wavelength converting material 118.

[0079] In case of using a metal material for forming the anode 402, it may be necessary to further insulate the field emission cathode 106 from the anode 402. In such a scenario, an insulating layer 408 may be arranged in between the field emission cathode 106 and the anode 402. The thickness of the insulating layer may be selected depending on the voltage potential provided between the between the field emission cathode 106 and the anode 402 during operation of the field emission light source 400.

[0080] In a similar manner as discussed above in relation to FIG. 3, it may in accordance to the invention be possible to also shape the bottom or the top of the cavity for the purpose of improvements in relation to the uniformity of light emitted by the field emission lighting source 400 by forming a uniform reception of electrons from the cathode 106 towards the anode 108

[0081] In a further alternative embodiment of the invention, with further reference to FIG. 4b, a field emission light source 400′ similar to the field emission light source 400 of FIG. 4a is provided. The field emission light source 400′ differs from field emission light source 400 of FIG. 4a in that the insulating layer 408 is substituted with an insulating spacer 410. However, in a similar manner as discussed above in relation to FIG. 4a, the insulating spacer 410 has a parabolic shape such that the cavity 404 is formed between the anode 402 and the field emission cathode 106. The insulating spacer 410 may in some implementations provide a further electrical separation between the anode 402 and the field emission cathode 106. It is however preferred to at least partly arrange a reflective coating (such as a separate reflective layer, e.g. being a metal layer) onto a portion of the parabolic inside surface forming the cavity 404.

[0082] Turning again to FIG. 3, there may in accordance to the invention be possible to substitute the positioning of the conductive anode layer 116 and the first wavelength converting layer 118. That is, in accordance to the alternative embodiment shown in FIG. 4c, the first wavelength converting material is arranged directly adjacent to the glass structure 114. Accordingly, electrons emitted from the field emission cathode 106 in a direction towards the anode structure 108 will be received by the conductive anode layer 116, where the conductive layer 116 is arranged to have a voltage potential substantially differing from the field emission cathode 106 (i.e. in the range of kV). However, due to the inherent energy comprised with the electrons, they will at least party pass though the conductive anode layer 116 and impinge onto the first wavelength converting material 118. The present embodiment may in some instances be preferred as the conductive anode layer 116 at least partly “screens” the first wavelength converting material 118 from direct contact with high energy/velocity electrons emitted from the field emission cathode 106, thereby possibly improving the lifetime of the first wavelength converting material 118. The conductive anode layer 116 may in some instances comprise a transparent conductive material (TCO), for example comprising ITO. However, it may also be possible, and within the scope of the invention to form the conductive anode layer 116 from a metal layer, for example deposited onto the first wavelength converting material 118 and the glass structure 114. Such a metal layer is preferably selected for optimizing the amount of electrons passing through the metal layer, i.e. elements with low density, with a desired amount of light emitted from the first wavelength converting material 118. Such a layer should also at the same time exhibit a high reflectance so that light emitted from the first wavelength converting material 118 is directly reflected back and out of the structure. Such a layer will in addition also enhance the heat transfer capability of the structure.

[0083] In FIG. 4d there is provided a perspective view of a field emission light source 400″, having an essentially elliptic shape. An elliptical (or circular or similarly rounded) shape has advantages, for example in terms of avoiding electrical phenomena as arcing and parasitic currents. These may otherwise become an issue when high electrical fields are applied and corners or edges are present. The field emission light source 400″ shows similarities to the field emission light source 100 in FIG. 1, with the addition of a getter 412. To achieve and sustain a vacuum of 1×10.sup.−4 Torr or better, it is highly desirable to use the getter 412. The getter 402 is arranged adjacently to the nanostructures 114 at a bottom surface of the cavity 112 formed by the spacer structure 110 surrounding the nanostructures 114 and the getter 402. The getter is a deposit of reactive material that is provided for completing and maintaining the vacuum within the cavity 112. It is preferred to select the getter 410 to at least partly provide to the extraction of light out from the field emission light source 400″. Thus, it is preferred to form the getter from a material having reflective properties. In addition, it is preferred that the surface from which the nanostructures 114 are provided is also arranged to be reflective. The activation of the getter 412 will generally take place once the device is sealed which in turn impose requirements on the temperature budget of the process once the getters have been placed in the device. In a similar manner as discussed above in relation to FIG. 3a, the control unit 312 may be integrated with the wafer 102. The functionality of the control unit 312 may thus be formed in direct adjacent contact with the nanostructures 114 of the field emission cathode for controlling the field emission light source 400″.

[0084] In an embodiment of the invention, with further reference to FIG. 5, a field emission light source 500 is provided. In FIG. 5, the first wavelength converting material 118 is arranged directly adjacent to the glass structure 114, thus sandwiched between the glass structure 114 and the conductive anode layer 116. In a similar manner as in regards to FIG. 4c, during operation, electrons will pass though the conductive anode layer 116 and impinge onto the first wavelength converting material 118. The conductive anode layer 116 is in such an embodiment preferably selected to be reflective, thereby reducing any light generated at the first wavelength converting material 118 be emitted “back” towards the cathode structure 106, thereby improving the overall light output from the field emission light source 500.

[0085] When using an anode with a layer of a conductive reflective layer, several aspects are of importance. The layer should be thin enough, so that electrons, impacting on the anode will pass through the layer without losing any significant portion of the energy; if that happens this energy will not be converted into photons and is lost resulting in an overall reduced energy efficiency.

[0086] On the other hand the layer must be thick enough so that the reflectance has reached an acceptable level; if it is too low, a significant portion of the photons will be absorbed or transmitted back towards the cathode and even if they would all be reflected back the overall losses would be significant.

[0087] There are two preferred metals for this, layer namely Ag (Silver) and Al (Aluminum). Of the two the latter is lower cost, a lighter element (allowing for thicker layers and has high reflectance both for UVC light and visible light, and is easier to implement as its oxide is thin, essentially transparent to visible light.

[0088] The energy used for consumer applications should be less than 10 kV and preferably less than 8.5 kV or soft X-rays generated by Brehmsstrahlung will be able to escape the lamp (it is otherwise absorbed by the anode glass). However these levels are to some extent depending on glass thickness, thus higher voltages can be allowed if a thicker glass is used.

[0089] On the other hand the energy must be high enough to penetrate the conductive and reflecting layer. A preferred range for consumer applications is thus 5-8 kV and 5-15 kV for industrial applications (where some soft X-rays can be accepted).

[0090] The operating energy (operating voltage is primarily set by the nanostructure detailed geometry (height, width/minimum radius, distance) and the distance between the cathode and the anode. The latter is determined by the cathode nanostructure height and the thickness of the spacer element. The dimensions of the spacer element therefore becomes critically important and may be used to set the operating voltage as it is desired to keep the nanostructure geometry constant since this process is much more tedious to modulate in an accurate way as compared to changing the spacer thickness for different application requirements.

[0091] For Aluminum the thickness of the reflective and electrically conductive layer is determined to be in the range of 50-100 nm. A reflectance curve is shown in FIG. 6. As can be seen the reflectance reaches its steady maximum value above 50 nm. Allowing for some thickness variation over the surface a target value should be set to 60-70 nm as the low end and 90-110 nm as the high end, all depending on the exact desired operating voltage, in turn determined by the application.

[0092] It should be noted that higher operating voltages may be beneficial since, using a given input power requirement, a higher voltage leads to lower current densities. The current density is directly related to the intensity degeneration of the phosphor through, where a subjected accumulated charge is considered the primary cause for this degeneration. The lifetime is usually set by a 30% reduction of the initial intensity. A secondary benefit of using a higher energy is that the efficiency usually increases with higher voltages, likely because the photons are generated deeper into the cathodoluminescent crystallite and a lower fraction of electrons (especially secondary electrons) reach the surface of the crystallite where a non-radiative recombination process will occur.

[0093] FIG. 7 illustrates a currently preferred implementation of a field emission light source 700 according to the invention. In the illustrated embodiment, the field emission light source 700 comprises a circular glass wafer 702 arranged at the bottom and a circular anode glass substrate 704 arranged at the top. A spacer 706 of a glass material and form as a glass ring is arranged between the glass wafer 702 and the anode glass substrate 704.

[0094] The glass wafer 702 is provided with a field emission cathode 708 comprising a plurality of nanostructures. A connecting element 710, for example provided using an ITO patch is provided for allowing electrical connection to the field emission cathode 708, i.e. extending beyond and outside the “wall” of the spacer 706.

[0095] The anode glass substrate 704 is provided with a first wavelength converting material 712, where the first wavelength converting material 712 is sandwiched between the anode glass substrate 704 and a metal layer 714 functioning as an electrically conductive anode. An ITO patch 716 is again provided for allowing electrical connection to the anode layer 714 and extending beyond and outside the wall of the spacer 706.

[0096] The field emission light source 700 may for example be manufactured by modularly arranging the components on top of each other in a high vacuum heated environment. Sealing of the glass component is preferably achieved as discussed above. The functionality of the field emission light source 700 is comparable to the field emission light sources 100 and 500 as discussed above.

[0097] Furthermore, in a possible embodiment of the invention, with further reference to FIG. 8, a lighting arrangement 800 may be formed by a plurality of adjacently arranged filed emission light sources 100/300/400/400′/400″/500/700 as discussed above. The field emission light sources 100/300/400/400′/400″/500/700 may be powered by a common power source 302, in turn controlled using a control unit 804. The control unit 804 may be configured to receive an indication of a desired intensity level from a user interface 806. In addition, a sensor 808 may be electrically connected to the control unit 804. The control unit 804 may be configured to control the power supply 802 depending on the desired intensity level and an intermediate intensity level measured using the sensor 808. The lighting arrangement 800 may additionally be provided with a lens structure 810 for mixing light emitted by the plurality of field emission light sources 100/300/400/400′/400″/500/700.

[0098] In summary, the present invention relates to a field emission light source, comprising a field emission cathode comprising a plurality of nanostructures formed on a substrate, an electrically conductive anode structure comprising a first wavelength converting material arranged to cover at least a portion of the anode structure, wherein the first wavelength converting material is configured to receive electrons emitted from the field emission cathode and to emit light of a first wavelength range, means for forming an hermetically sealed and subsequently evacuated cavity between the substrate of the field emission cathode and the anode structure, and a spacer structure arranged to encircle the plurality of nanostructures, wherein the cavity is evacuated and the substrate for receiving the plurality of nanostructures is a wafer.

[0099] Although the figures may show a specific order of method steps, the order of the steps may differ from what is depicted. Also 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 invention 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.

[0100] Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed invention, 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.