Optical device processing

Abstract

There is disclosed a stack for processing a device layer on a rigid substrate, comprising: a rigid substrate layer; a first conductive layer on the rigid substrate layer; an electric debond adhesive layer on the first conductive layer; a second conductive layer on the electric debond adhesive layer.

Description

[0001] OPTICAL DEVICE PROCESSING

[0002] The present application relates to a method of processing a device layer on a glass substrate , a method of debonding a device layer from a glass substrate , and a device stack including a glass substrate for holding a device layer for processing .

[0003] Plastic electronics such as liquid crystal , LC , cells are generally processed while mounted to a carrier such as glass , and then demounted for use . Demounting an LC cell from a glass carrier after processing , while achieving good quality, is a challenge .

[0004] Removing a processed LC cell from a glass substrate whilst achieving a good quality LC cell for further use typically requires being able to demount or debond the LC cell from the glass substrate with zero , or close to zero , peel force .

[0005] Examples current methods for debonding require a thermal debond layer , so as to allow demount with zero peel force . One side of the substrate of a cell is temporarily attached to a thermal release adhesive , and one side of the substrate is temporarily attached to an ultra violet (UV) release adhesive . The thermal debond method uses an adhesive containing thermally activated microspheres . This adhesive often has a thickness variation that can cause problems or mura in liquid crystal cells .

[0006] There is provided an improved technique .

[0007] Figs . 1 (a) to 1 (d) show a representation of an example adhesive layer ;

[0008] Figs . 2 (a) and 2 (b) show a representation of an adhesive layer for j oining and debonding two metallic layers ;

[0009] Figs . 3 (a) to 3 ( c) show a representation of an example of a device carrier for processing a liquid crystal , LC , cell including a glass substrate ; Fig . 4 shows a representation of an example of debonding a glass substrate of a device carrier for an LC layer ;

[0010] Fig . 5 shows a representation of an example of a headset incorporating a liquid crystal , adaptive optical lens ;

[0011] Fig . 6 shows a representation of an example of a system for operating the headset of Fig . 5 ; and

[0012] Fig . 7 shows schematically a representation of an example apparatus .

[0013] There is provided a stack for processing a device layer on a rigid substrate , comprising : a rigid substrate layer ; a f irst conductive layer on the rigid substrate layer ; an electric debond adhesive layer on the f irst conductive layer ; a second conductive layer on the electric debond adhesive layer .

[0014] The stack may further comprise an ultra violet debond adhesive on the second conductive layer , and a backplane photolithographic layer on the ultra violet debond adhesive .

[0015] The stack may further comprise a refractive index changing material layer on the backplane photolithographic layer .

[0016] The stack may further comprise a top plate on the refractive index changing material .

[0017] The stack may further comprise an ultra violet bond adhesive layer on the top plate , and a further rigid substrate layer on the ultra bond adhesive layer .

[0018] The electric bond adhesive layer may comprise a membrane between two adhesive layers .

[0019] The membrane may permit movement of release agents from one adhesive layer to the other when a voltage is applied across the f irst and second conductive layers , to reduce an adhesive force between one of the conductive layers and the rigid substrate layer . There is provided a method of debonding a device from a rigid substrate , a f irst conductive layer connecting a rigid substrate layer to an electric debond adhesive , and a second conductive layer connecting the device to the electric debond adhesive , the debonding method comprising : applying an electric potential between the f irst and second conductive layers ; and peeling the f irst conductive material from the electric debond adhesive .

[0020] The device may be bonded on an opposing side to a further rigid substrate with an ultra violet adhesive , the debonding method further comprising exposing the further rigid substrate to ultra violet light and peeling the further rigid substrate from the device .

[0021] The electric debond adhesive may comprise a layer between two adhesive layers , applying the electric potential causes release agents to move from one adhesive layer to the other adhesive layer to cause a low adhesive force in the one adhesive layer .

[0022] There is provided a method of processing a device layer on a rigid substrate , comprising af f ixing the device to the rigig substrate by : forming a f irst conductive layer on the glass substrate ; forming an electric debond adhesive layer on the f irst conductive layer ; forming a second conductive layer on the electric debond adhesive layer .

[0023] The method of claim 11 , the electric debond adhesive layer being adhesive tape .

[0024] The second conductive layer may be a layer of the device .

[0025] The f irst conductive layer may be a sputtered metal .

[0026] The method may further comprise forming an ultra violet debond adhesive on the second conductive layer , and forming a backplane photolithographic layer on the ultra violet debond adhesive .

[0027] The method may further comprise forming a liquid crystal, LC, layer on the backplane photolithographic layer.

[0028] The method may further comprise forming a top plate on the liquid crystal layer, forming an ultra violet bond adhesive layer on the top plate, and forming a further glass layer on the ultra bond adhesive layer.

[0029] Forming the electric debond adhesive layer may comprise forming a membrane between two adhesive layers.

[0030] There is provided an assembly comprising: a device layer having been formed in a stack comprising an electric debond adhesive layer affixing a rigid substrate to the device layer; and at least one further optical element.

[0031] The at least one further optical element may comprise at least one of : a waveguide, a luminance adjustment component, a lens, an image generation device, a reflection-reduction layer, or a protective layer.

[0032] There is provided apparatus comprising: a device layer having been formed in a stack comprising an electric debond adhesive layer affixing a rigid substrate to the device layer; and at least one processor; and at least one storage comprising instructions, the instructions configured to, with the at least one processor, cause the apparatus to control one or more properties of the LC layer.

[0033] The apparatus may be configured to be mounted on a human head with the optical device cell stack positioned in a field of view of an eye of the human head.

[0034] The apparatus may further compriseg a first lens comprising a first one of the LC layer and first electrode and a second lens comprising a second one of the LC layer and first electrode. The f ield of view of the eye may be a f irst f ield of view of a f irst eye , and the f irst lens may be conf igured to be positioned in the f irst f ield of view, in use , and the second lens is conf igured to be positioned in a second f ield of view, of a second human eye of the human head, in use .

[0035] The apparatus may be at least one of an augmented reality display device , a virtual reality display device or a mixed reality display device .

[0036] In the above , many dif ferent aspects have been described . It should be appreciated that further aspects may be provided by the combination of any two or more of the aspects described above .

[0037] Various other aspects are also described in the following detailed description and in the attached claims .

[0038] In the following description, examples are described of processing an LC layer on a glass substrate stack , in line with current processes . In theory, any substrate material could be used that is rigid enough to pass through a display production line and survive the high temperatures that are typically used . The substrate may therefore be a rigid plastic , which then would not be suitable for the display substrate in use . In general , therefore , a rigid substrate may be used to mount the LC layer for processing , and the LC layer i s then removed from the rigid substrate for use . In general , a rigid substrate is a substrate which provides a substrate for the processing of the LC cell , and which rigid substrate is removed before the LC cell is deployed on a plastic cell for a use implementation . The rigid substrate is robust for withstanding the procedures - including high temperatures - which are applied using the processing procedures for the LC layer .

[0039] With reference to Figs . 1 (a) to 1 (d) there is illustrated the operation of an electric debond adhesive in examples . Fig. 1(a) illustrates an example electric adhesive tape 2, or electric peeling tape, prior to use. Two special adhesive layers 6 and 12, of exemplary thickness 55um, are separated by a non-woven material layer 8 or membrane of exemplary thickness 40um. Release liners 4,14 are connected to each of the special adhesive layers 6,12, in the example a paper release liner 4 and a PET release liner 14.

[0040] For use, the release liners 4,14 are removed, to expose sides of the special adhesive layers 6,12. Reference numeral 22 denotes an electric peeling tape ready to be deployed. As illustrated in Fig. 1(b) , a plurality of release agents 16n are provided in special adhesive layer 6, and a plurality of release agents 18n are provided in special adhesive layer 12.

[0041] As shown in Fig. 1(c) a voltage 20 is applied to or across the special adhesive layers 6,12.

[0042] As shown in Fig. 1(d) , following the application of this voltage the plurality of release agents 18n move across the nonwoven layer 8 or membrane from the special adhesive layer 12 to the special adhesive layer 6, and substantially all of the release agents are positioned in the special adhesive layer 6.

[0043] As substantially all the release agents have moved to the special adhesive layer 6, the special adhesive layer 6 may be readily removed from any layer to which it is attached.

[0044] Preferably the effect of the movement of release agents is reversible when the voltage is removed. Hence whilst not shown in Fig. 1(d) , preferably the voltage 20 remains applied whilst the special adhesive layer 6 is readily removed from any layer to which it is attached.

[0045] With reference to Figs. 2 (a) and 2 (b) , there is illustrated an example in which the electric peeling tape 22 is provided between two conductive layers, affixing the two conductive layers. The two conductive layers comprise a first conductive layer 24 and a second conductive layer 26. The voltage circuit 20 is connected to each of the conductive layers.

[0046] When no voltage is applied as shown in Fig. 2 (a) , the electric peeling tape has an adherence force of 40N to each of the conductive layers. An example overall thickness of the electric peeling tape is 25mm.

[0047] When the voltage is applied, then the adherence force changes at each side of the electric peeling tape 22. The applied voltage may be a DC voltage. At an anode side, adjoining the second conductive layer 24, the adhesive force reduces to 0.5N. At the cathode side, adjoining the first conductive layer 26, the adhesive force remains at 4 ON. The much- reduced adhesive force with the second conductive layer 24, means the second conductive layer 24 can be readily peeled off as shown in Fig. 2 (b) . Although not shown in Fig. 2 (b) , preferably the voltage remains applied for completion of this peeling operation.

[0048] With reference to Figs. 3 (a) to 3 (c) , there is illustrated the applicability of the described technique in manufacturing an LC cell for implementation on a plastic substrate.

[0049] With reference to Fig. 3 (a) , a first conductive layer 7, for example a sputtered metal layer, is formed on a glass substrate layer 9. An electric debond adhesive layer 5 is formed on the first conductive layer 7. A second conductive layer 3, for example an aluminium (Al) laminated PET layer 3, is formed on the electric debond adhesive layer 5. In practice, the layers 3 and 7 may be part of an adhesive tape which includes the electric debond adhesive 5. The layers 3,5,7 of Fig. 3 (a) may be equivalent to the layers 6,8,12 of Fig. 1(a) .

[0050] Next a backplane is built.

[0051] With reference to Fig. 3 (b) , an ultra violet (UV) debond adhesive layer 13 is formed on the aluminium (Al) laminated PET layer 3 . A backplane / photolithographic layer 11 is formed on the ultra violet (UV) debond adhesive layer 13

[0052] The liquid crystal , LC, cell is then assembled .

[0053] With reference to Fig . 3 ( c) , a l iquid crystal cell layer 19 is formed on the backplane / photolithographic layer 11 . A top plate layer 17 is formed on the LC cell layer 19 . An ultraviolet debond adhesive layer 15 is formed on the top plate layer 17 . A second glass substrate layer 21 is formed on the ultra violet debond adhesive layer 15 .

[0054] The structure of the backplane and the liquid crystal cell is illustrative and not limiting . In one simple example the backplane layer 11 and the top plate layer 17 may be electrodes . However the backplane layer may be an array of thin f ilm transistors (TFTs ) made up of multiple layers , rather than a single electrode layer .

[0055] The LC cell is then processed whilst sandwiched in the glass substrate .

[0056] After processing , the LC cell i s removed from the glass substrate , for af f ixing to a plastic substrate for implementation .

[0057] In accordance with the technique described herein, and as shown in Fig . 4 , a voltage cell 21 represents a potential applied across the layers 3 and 5 , to separate the layer 7 as denoted by arrow 23 .

[0058] The technique described with reference to Figs . 1 and 2 is used .

[0059] The UV bond adhesive layer 13 is provided to adhere the backplane layer 11 to the Al laminated PET layer 3 . After removal of the f ist glass substrate , the UV debond adhesive layer 13 can then be removed by exposure to UV light , and then the UV debond adhesive layer 13 peeled to remove it and the Al laminated PET layer 3 . The UV debond adhesive layer 13 is an example of an adhesive layer, and in general the layer 13 is a debond adhesive layer, and is not necessarily a UV debond adhesive layer.

[0060] In this example an electric debond adhesive layer is omitted from the upper stack because the zero peel force requirement is only needed for one side of the stack to remove the first glass layer. If the glass layer is removed from the lower stack first, then removal of the LC cell from the second glass layer can be peeled with a (non-zero) force, for example using a UV-debond adhesive with the UV debond adhesive layer 15 or a low peel -force PSA. In example arrangements, therefore, the electric debond adhesive layer is only provided in the stack which is first debonded.

[0061] It may also be that the opaque nature of the electrode layers needed for the electric debond structure prevents inspection tools and alignment camera's from seeing into the patterned features, so a transparent adhesive is preferable on one side.

[0062] The process of forming the glass substrate stacks may comprise printing and laminating to the glass substrate if adhesive layer is a tape.

[0063] Note the terms 'upper' and 'lower' are used for simplicity, and in the described examples the lower glass substrate is the substrate which is first removed from the overall stack. In alternatives the upper glass substrate may be first removed. The stack comprising the glass substrate which is first removed includes the electric debond adhesive layer 5 in addition to the double- sided UV adhesive.

[0064] Fig. 4 illustrates a debonding or demounting process that is applied to the lower stack, or more generally the first stack, to remove the glass substrate 9. As noted above, the need to have a zero or near-zero peel force applies to the first stack removed. The second stack removed - in this example the upper stack - can be removed by the same process ( if it is formed with an electric debond adhesive layer) . Alternatively it can be removed by peeling from the UV bond adhesive layer 15 . The glass substrate 21 can be peeled from a double- sided UV debond adhesive layer 15 with a suf f iciently low peel force to prevent damage to the LC cell . This peel force does not need to be a zero or near- zero peel force as with the f irst peel . The UV debond adhesive layer 15 can then be removed by exposure to UV light , and then the UV debond adhesive layer 15 peeled to remove it and the glass substrate 21 .

[0065] The UV debond adhesive layer 15 is an example adhesive layer , and in general the layer 15 is a debond adhesive layer , and is not necessarily a UV debond adhesive layer .

[0066] The LC layer 19 is left with the top plate 17 and the backplane 11 , and this structure removed from the glass is then available for use in plastic implementations . A device may be formed on plastic substrates using the LC cell ( the LC layer and LC substrates ) debonded from the glass substrates .

[0067] There is thus provided a method for releasing the LC cell from the glass substrate carrier after processing is complete , while achieving good quality . A good quality LC cell is obtained, with a uniform cell gap . This is achieved while enabling use of TAG , PEN, PET etc .

[0068] There is described an exemplary arrangement where an LC cell is debonded from a glass substrate . In general , the invention may apply to debonding any structure from a glass substrate , and anything sandwiched between two glass carriers .

[0069] There is described an exemplary arrangement where an LC cell is debonded from a glass substrate . In general , the invention may apply to debonding any structure from a rigid substrate such as a glass substrate , and anything sandwiched between two rigid or glass carriers . The processed liquid crystal cell or device described above may, for example , function as or be used within a switchable lens device or a beam steering device . For example , a device may be or comprise an adaptive optical lens comprising a liquid crystal device according to any of the examples herein . Such a device may be or comprise a headset , which may be referred to as a head-mounted display (HMD) .

[0070] The processed liquid crystal device described above is useful in a wide range of applications , including ophthalmic lenses ( such as spectacle lenses ) , virtual reality (VR) , mixed reality (MR) and augmented reality (AR) headsets ; optical proj ectors ; photographic devices ; and communication devices .

[0071] An LC optical lens device may be used for the push lens and / or the pull lens or a combined push / pull lens of an augmented reality (AR) headset such as e . g . that shown in Fig . 5 .

[0072] The headset 40 comprises a support frame 42 supporting optical components arranged in optical series in front of the user eye .

[0073] At least one optical component such as one or more of the optical components shown in Fig . 5 may be considered to correspond to or be part of an assembly, which may be considered to be a display stack , comprising at least one liquid crystal cell according to examples herein . In examples , such as that of Fig . 5 , such an assembly includes a stack of liquid crystal cells according to examples herein . In the example of Fig . 5 , the push lens 48a includes at least one stack of liquid crystal cells , the pull lens 48b includes at least one stack of liquid crystal cells , and the assembly includes the push lens 48a , the waveguide 50 , the pull lens 48b , the variable dimmer device 46 , which is an example of a luminance adj ustment component , and the front window / lens 44 .

[0074] Liquid crystal cells of a stack may be aligned along a common optical axis . In some cases , though, optical axes of at least two of the liquid crystal cells of a stack may be offset from each other in a direction parallel to a plane of a radial electrode pattern of at least one of the liquid crystal cells, provided that light traversing the assembly traverses the liquid crystal cells of the stack. Fig. 5 only shows the optical components for one half of the headset for clarity of representation, but a matching set of optical components is also provided for the other half of the headset.

[0075] The waveguides 50 of the headset respectively display left- and right perspectives of one or more virtual reality objects, by which the user perceives the one or more virtual reality objects as 3D objects. Alternatively, other mechanisms may be employed to display the left / right perspectives of the one or more virtual reality objects, such as e.g. laser projection.

[0076] The degree to which the user's left and right eyes need to rotate relative to each other such that the left and right perspectives of a virtual reality object are simultaneously directed onto the foveas (which are the parts of the retina responsible for sharp central vision necessary for activities for which visual detail is of primary importance) of respective left and right eyes of the user determines the distance at which the user perceives the virtual reality object to be. This mechanism is referred to as vergence.

[0077] The LC optical lens device described above may be used as an adaptive lens device to control the location at which the user's eyes perceive the left / right perspectives of a displayed virtual reality object in focus (i.e. not blurred) , which location may be referred to as a focal plane. In other words, the LC optical lens device described above may be used as an adaptive lens device to control the degree to which the lenses in the user's eyes need to adapt to perceive the left and right perspectives of the virtual reality object in focus (i.e. not blurred) . This adaptation mechanism of the lenses in the user ' s eyes is known as accommodation .

[0078] The LC optical lens device described above may be used to produce optical images ( real or virtual ) of the left / right perspectives of a virtual reality obj ect substantially at the distance from the user ' s eyes at which the user perceives the virtual reality obj ect to be located through the vergence mechanism discussed above . This may allow the user to perceive a focussed 3D image of the virtual reality obj ect without disrupting the vergence-accommodation ref lex, by which the focussing action of the lenses in the user ' s eyes (accommodation) is unconsciously linked to the above-mentioned rotation of the left and right eyes relative to each other (vergence) . In other words , the LC optical lens device may be used to avoid or reduce the strain on the user ' s eyes that can arise from a conf lict between the vergence and accommodation mechanisms ( referred to as the vergence-accommodation conf lict ) . For example , the LC optical lens device may be switchable between a positive focal power and a negative focal power .

[0079] Hence , a liquid crystal device according to examples herein may provide a lower complexity and / or higher quality system to actively adj ust focus to compensate for focal dif ferences between a virtual obj ect and a real -world environment visible to a user of a headset through the optical components mounted in front of each eye . This for example allows the perceived and actual image depth to be brought together in a consistent manner , improving user comfort .

[0080] In Fig . 5 , the headset 40 permits transmission of light from a real -world environment around the headset 40 at least partly through the optical components and into the user ' s eyes . In this example , the optical components are at least partly transparent . On a bright day, the luminance of the environment may be signif icantly higher outdoors than indoors , such as around 100 times higher . This can lead to a virtual obj ect appearing washed out and dif f icult to see when the user operates the headset outdoors , unless the luminance of the light transmitted from the environment to the user is appropriately controlled . In Fig . 5 , the variable dimmer device 46 controls the amount of light transmitted through the optical components and towards the eyes , e . g . so as to reduce the luminance of light from the environment transmitted towards the user in bright conditions , and may be used to provide ambient dimming to dim ambient light transmitted through the headset 40 .

[0081] The variable dimmer device 46 may provide so- called global dimming , in which the luminance of the light from the environment is adj usted by substantially the same amount within an extent of a plane of the variable dimmer device 46 facing the user (e . g . to reduce the luminance of the light by substantially the same amount across an entire surface area of the variable dimmer device 46 ) . In other words , global dimming can allow the luminance of the light transmitted through the variable dimmer device 46 to be controlled in a substantially spatially uniform manner (e . g . so as to provide a substantially spatially uniform reduction in the luminance across a f ield of view of the user) .

[0082] The variable dimmer device 46 may also or alternatively provide local dimming , in which the variable dimmer device 46 is adj ustable to control the luminance of the light transmitted from the environment on an area-by-area basis (where an area may correspond to a single pixel or a plurality of pixels ) . Local dimming may involve adj usting the luminance across less than all of the surface area of the variable dimmer device 46 , such as within a sub-area which is smaller than the surface area of the variable dimmer device 46 . In other cases , though, local dimming may involve adj usting the luminance across the entire surface area of the variable dimmer device 46 but by dif ferent amounts in at least two portions of the surface area . Although not shown in Fig. 5, it is to be appreciated that the headset 40 may be configured to obtain luminance data, e.g. from a light sensor of the headset 40, indicative of the luminance of the light within the environment of the headset 40. For example, if a first side 49a of the headset 40 is configured to face the user, with the headset 40 mounted on the head of the user, the headset 40 may include a light sensor to detect the luminance of light at a second side 49b of the headset 40, opposite to the first side 49a. The variable dimmer device 46 may be controlled at least partly based on the luminance data, so as to adjust the luminance of light transmitted from the second side of the headset 40 towards the user, to improve the visibility of the virtual object displayed to the user by the headset 40.

[0083] In the example of Fig. 5, a first lens comprising at least one liquid crystal cell stack of the examples herein (the push lens 48a) is located between the waveguide 50 and the eye, with the headset 40 in use. Light representative of the virtual object is generated and transmitted to the waveguide 50, which directs the light through the push lens 48a and into the eye. The push lens 48a has a focusing effect to focus the light representative of the virtual object so that the object appears in focus to the user. For example, the virtual object may be generated so that it is in focus at a focal plane of infinity. The push lens 48a may then bring the virtual object into focus at a focal plane which is closer to the user than infinity, to allow the user to focus on the virtual object more comfortably. The focal plane at which the virtual object is to be brought into focus, and hence the focusing power to be applied by the push lens 48a, may be determined based on eye tracking data, e.g. obtained by a suitable sensor as discussed further below, which is indicative of a direction in which the eye of the user is looking. Prior to use of the headset 40 , the external environment may appear in focus to the user . However , in the absence of the pull lens 48b , light from the external environment would be at least partly transmitted through the waveguide 50 and through the push lens 48a and would therefore be subj ect to the focusing ef fect provided by the push lens 48a . This would distort the external environment as viewed by the user through the headset 40 . To compensate for the distortion introduced by the push lens 48a , the headset 40 of Filg . 10 includes a second lens ( the pull lens 48b) positioned at an opposite side of the waveguide 50 to the push lens 48a . The pull lens 48b applies an appropriate focusing ef fect to light from the environment traversing the pull lens 48b to at least partially compensate for or otherwise reduce the focusing ef fect introduced by the push lens 48a . For example , the push and pull lenses 48a , 48b may provide opposite focusing ef fects to each other , e . g . with substantially equal magnitudes but opposite signs . As an example , one of the push and pull lenses 48a , 48b may provide a positive focusing power and the other one of the push and pull lenses 48a , 48b may provide a negative focusing power , which may be substantially equal in magnitude .

[0084] In examples at least one lens of examples herein ( such as at least one of the push lens 48a and the pull lens 48b , and in some cases both the push and pull lenses 48a , 48b) each includes a so- called doublet of liquid crystal cells according to examples herein . A doublet is a stack of two liquid crystal cells . The focusing ef fect of a liquid crystal -based lens may depend on the polarization of the light incident on the lens . Rather than using a separate polarizer component , using a doublet such as this may provide an appropriate focusing ef fect with improved light transmission ; in some examples this is achieved by positioning one liquid crystal cell of the doublet orthogonal to the other liquid crystal cell of the doublet , with respect to the respective orientation of polarization that each liquid crystal cell is configured to modify light for.

[0085] Fig. 5 shows an example of a push lens 48a and a pull lens 48b in combination with various other optical components. It is to be appreciated that a liquid crystal cell in accordance with examples herein can be used in combination with different optical component (s) than those shown in Fig. 5, to provide further flexibility in functionality. This may further reduce the size and / or weight of apparatus including the liquid crystal cell and / or improve optical performance of the apparatus. For example, an assembly, such as a display stack, including a liquid crystal cell in accordance with examples herein may include a reflection-reduction layer (such as an anti-reflection (AR) coating) , which may be laminated to another optical component of the assembly, such as the front window / lens 44, and / or a protective layer (such as a hard coat) to protect the assembly from damage, e.g. due to abrasion, and / or wear due to exposure to environmental conditions.

[0086] In examples, the liquid crystal device comprises electrical terminals electrically connected to the busbars. The electrical terminals for example allow a potential difference to be applied across the busbars, and thus across each set of concentric rings. As explained above, the electrical potential applied to an electrical terminal can be controlled by a suitable control system .

[0087] With reference to Fig. 6, a system 55 according to some examples comprises a processor operating on the basis of computer program code stored in a memory 52 to control an image generation driver chip 53 to cause an image generation system to generate images of left / right perspectives of one or more virtual reality objects, by which the user may perceive 3D images of the virtual reality objects, and display the images via the waveguide 50. Although not shown in Fig. 6, it is to be appreciated that there may be two waveguides: one to display an image of a left perspective of a virtual reality object to a left eye and another to display an image of a right perspective of a virtual reality object to a right eye, as discussed further with reference to Fig. 6. There may further be two image generation systems: one to generate the image of the left perspective of the virtual reality object and another to generate the image of the right perspective of the virtual reality object (although in some cases a single image generation system may generate both images or an image generation system may generate a single image to be displayed to both eyes) . An image generation system is discussed further below with reference to Fig. 7. Inputs from sensors feed into the processor to enable the processor to control positions at which the virtual reality objects are displayed by the waveguides 50, for seamless overlay of the one or more virtual reality objects into the user's view of the user's real environment .

[0088] Based on inputs fed into the processor 51 from one or more sensors 54 sensing the movement of the user's eyes and / or based on the content being displayed by the waveguides 50, the processor 51 controls the adaptive lens driver chip 38 to achieve the optical focussing power (Dioptres) required to achieve the above-described generation of optical images of the display output of the waveguides at a distance from the user's eyes at which the virtual content that the user is determined to be looking at (e.g. through tracking of the user's eyes) is intended to be perceived by the user (through the vergence mechanism described above) . A driver chip is an example of a controller, which may be implemented in hardware, e.g. via suitably configured circuitry. In some cases, a driver chip may include or be considered to implement at least one processor. Fig. 7 illustrates schematically hardware architecture of an apparatus 60 according to further examples. The apparatus 60 comprises at least one liquid crystal cell stack in accordance with examples herein. In Fig. 7, the apparatus 60 is configured to be mounted on human head, e.g. a head of a user, with a liquid crystal cell stack positioned in a field of view of an eye of the head, in use. In the example of Fig. 7, the apparatus 60 is an AR headset for displaying a virtual image to a wearer of the headset, and may be similar to or the same as the headset 40 of Fig. 5. In other examples, though, apparatus including a similar hardware architecture to the apparatus 60 of Fig. 7 may be configured for a different purpose, may include additional components and / or may omit at least one of the components illustrated in Fig. 7.

[0089] The apparatus 60 of Fig. 7 includes an optical system 62, an image generation system 64, at least one processor 66, storage 68, at least one sensor 70, a user input / output interface 72, a communications system 74 and at least one further hardware system 76. Components of the apparatus 60 are connected to each other via at least one bus 78, which may be or include any suitable interface or bus for transferring data between the illustrate components.

[0090] The optical system 62 includes a first assembly and a second assembly, which in this example are a first display stack 62a and a second display stack 62b, respectively. The first display stack 62a comprises a first set of optical components, e.g. arranged as a stack of layers. The apparatus 60 is configured to permit at least partial transmission of light from an external environment through the first display stack 62a and towards a first eye of the user, with the apparatus 60 in use and mounted on the head. In other words, where the apparatus 60 has a first side configured to face the user, in use (e.g. the first side 49a of Fig. 5) , the first display stack 62a is arranged for directing light from the second side towards the first eye (in this case, through the first display stack 62a) . The first display stack 62a in this case includes the optical components shown in Fig. 5, i.e. the push lens 48a, the waveguide 50, the pull lens 48b (where the push and pull lenses 48a, 48b are each an example of a liquid crystal device according to examples herein) , the variable dimmer device 46 and the front window / lens 44. The push lens 48a and / or the pull lens 48b of the first display stack 62a may be considered to be a first lens comprising a first at least one of the liquid crystal cell stacks according to examples herein. The first lens is configured to be positioned in a first field of view of a first eye, e.g. the first eye of a user, in use.

[0091] In Fig. 7, the second display stack 62b comprises a second set of optical components, which in this example is the same as the first set of optical components but configured to transmit light towards a second eye of the user, with the apparatus 60 in use. In other words, the second display stack 62b is arranged to direct light from the second side of the apparatus 60 towards the second eye. Hence, in this example, the push lens and / or the pull lens of the second display stack 62b may be considered to be a second lens comprising a second at least one of the liquid crystal cell stacks according to examples herein. The second lens is configured to be positioned in a second field of view of a second eye, e.g. the second eye of the user, in use. It is to be appreciated that the first lens may be visible to solely the first eye or to both the first and second eye, in use, and the second lens may be visible to solely the second eye or to both the first and second eye, in use.

[0092] A spatial arrangement of elements of the second display stack 62b in at least one layer of the stack may mirror the spatial arrangement of corresponding elements of the first display stack 62a in the corresponding layer of the stack of the first optical arrangement 62a as reflected in a sagittal plane of the apparatus 60 (which may be referred to as a longitudinal plane of the apparatus 60, and e.g. separates left and right sides of the apparatus, with the apparatus in use) . In other cases, though, the first and second display stacks 62a, 62b may have a different structure from each other. It is to be appreciated that the optical system 62 may include further components, e.g. further optical components, not shown in Fig. 7.

[0093] The apparatus 60 also includes an image generation system 64 to generate an image of a virtual object to be displayed to the user of the apparatus 60 so that the virtual object appears to the user to be overlaid on top of the external environment, which is at least partly visible to the user through the optical system 62. The image generation system 64 may be or include a display device to generate an image (e.g. of a virtual object) for display by the apparatus 60 to the user. The display device may be a liquid crystal display (LCD) device, a light emitting diode (LED) display device such as an organic light emitting diode (OLED) display device, an electroluminescent (EL) display device and so forth. In the example of Fig. 7, the image generation system 64 is in optical communication with the optical system 62. For example, the image generation system 64 may be housed by the support frame 42 if the apparatus 60 is in the form of the headset 40 of Fig. 5. Light generated by the image generation system 62 representing the virtual object may be transmitted to the optical system (e.g. to a waveguide such as the waveguide 50 shown in Fig. 5) either directly (e.g. without traversing another optical component) or via at least one further optical component. In some cases, the image generation system may include two display devices, a first one for the first eye and a second one for the second eye, e.g. if it is desired to display a first image to the first eye and a second image to the second eye. In other examples, a single display device may be used to generate an image to be displayed to both the f irst and second eyes .

[0094] In the example of Fig . 7 , the image generation system 64 is shown as a separate system from the optical system 62 . In other examples , though, the image generation system may form part of the optical system . For example , an assembly, such as a display stack , of the optical system may include an image generation system, such as a display device .

[0095] The at least one processor 66 of the apparatus 60 may be a single processor or a plurality of processors of one or more types . Components of the at least one processor 66 may be implemented using suitably programmed hardware , e . g . in the form of circuitry . The at least one processor 66 may include a central processing unit (CPU) , a graphics processing unit (GPU) and / or a neural processing unit (NPU) , which may be referred to as a neural network accelerator .

[0096] In some examples , apparatus , such as the apparatus 60 of Fig . 7 , includes driving circuitry connected to at least one electrical connection connected to the electrode patterns of the liquid crystal cell stack to apply a potential dif ference across one or more electrode sets of the liquid crystal cells of the liquid crystal cell stack . The potential dif ference applied ( such as a magnitude and / or timing of the potential dif ference applied) may be determined by the at least one processor 66 and / or by the driving circuitry, such as by a controller implemented by at least a portion of the driving circuitry, based on the instructions stored in the storage .

[0097] If the potential dif ference is determined by the driving circuitry, the determination of the potential dif ference may be instigated by instructions received from the at least one processor , such as instructions indicative that a virtual obj ect is to be displayed and that one or more electrode sets are thus to be activated so that the virtual obj ect appears in focus to the user . In this way, the driving circuitry may be agnostic to the at least one processor from which the instructions are received . In other words , the operation of the driving circuitry may for example be independent of the at least one processor used to control the driving circuitry, such that the same ef fect can be achieved irrespective of the at least one processor coupled to the driving circuitry (provided the at least one processor provides an appropriate indication to the driving circuitry to cause the driving circuitry to determine a suitable potential dif ference) .

[0098] The potential dif ference may be applied to the electrical connection ( s ) by at least one driver of the driving circuitry, such as the adaptive lens driver chip 38 of Fig . 6 , which is an example of a driver . Application of a potential dif ference by the at least one driver may be considered to amount to so- called "driving" of the electrode pattern ( s ) , via the electrical connection ( s ) . The driving circuitry may be in the form of at least one system-on-a- chip ( SoC) .

[0099] The storage 68 may be or include computer-useable volatile and / or non-volatile memory . The storage 68 may comprise random access memory (RAM) and / or read-only memory (ROM) . The storage 68 may be removable or non- removable from the apparatus 60 . The storage 68 stores instructions for controlling the apparatus 60 in accordance with examples herein, e . g . to activate one or more electrode sets of the liquid crystal cells of the liquid crystal cell stack . Activation of an electrode set for example refers to applying a potential dif ference between at least two connectors connected to the electrode set . The instructions may be in the form of computer- readable and / or executable instructions , e . g . computer program instructions . Although the storage 68 is shown as a separate component to the at least one processor 66 in Fig . 7 , in some cases the storage 68 may be or include internal storage of the at least one processor 66 , in which cases the at least one processor 66 and the storage 68 may be at least partly integrated into the same system or component .

[0100] The at least one sensor 70 in this example is conf igured to obtain eye tracking data of the apparatus , in use , which for example indicates a direction in which at least one eye of the user is looking , as the skilled person will appreciate . Eye tracking data may be obtained for each eye , or the eye tracking data may be obtained for a single eye or for a combination of both eyes of the user . Suitable sensors for obtaining eye tracking data include a camera 70a for obtaining images of at least one eye of the user , an inertial measurement unit ( IMU) 70b for determining an orientation of the apparatus 60 and at least one position sensor 70c such as a global positioning system (GPS ) sensor to determine a location of the apparatus 60 . As the skilled person will appreciate , an IMU 70b may include at least one accelerator or gyroscope for use in determining the orientation of the apparatus 60 . The focusing ef fect of the at least one liquid crystal cell may be controlled based on the eye tracking data , e . g . so as to reduce user eye strain as described further above .

[0101] The apparatus 60 also includes a user input / output interface 72 via which a user can interact with the apparatus 60 to control aspects of the apparatus 60 . For example , the user input / output interface 72 may be or include an input device such as a button, a touchscreen, a slider , a controller or any other suitable device for communicating user requests to the apparatus 60 to control the apparatus 60 .

[0102] The apparatus 60 includes a communications system 74 for receiving data from a remote system, e . g . via a suitable telecommunications network , such as a wireless network , or via some other type of network or connection . The communications system 74 may include an input / output interface , such as a Bluetooth connector , a universal serial bus (USB) connector or a network connector , for receiving the data from the remote system .

[0103] The apparatus 60 of Fig . 7 includes at least one further hardware system 76 such as a power source , e . g . a battery, for providing electrical power to the electrical components of the apparatus 60 .

[0104] Some examples have been described above for the example of an optical focussing device , but the same techniques have application in other areas such as e . g . beam steering optics .

[0105] Further examples relate to a method of operating a liquid crystal device according to any of the examples herein .

[0106] The term "substantially" used herein may be considered to mean that two elements that are "substantially" the same are : the same within manufacturing tolerances , the same within measurement uncertainties and / or are within 5% of each other .

[0107] Examples herein refer to a liquid crystal (LC) material . A liquid crystal material is an example of a material with a switchable refractive index, or a refractive index changing material .

[0108] The described device , assembly and apparatus has use in example implementations other than tuneable lens and optical components . Other example implementations include , but are not limited to : image generation systems , read only memory, network connections , USB , Bluetooth systems etc . , methods of powering and associated techniques . In addition to any modif ications explicitly mentioned above , it will be evident to a person skilled in the art that various other modif ications of the described embodiment examples may be made within the scope of the invention .

[0109] In addition to any modif ications explicitly mentioned above , it will be evident to a person skilled in the art that various other modif ica ions of the described embodiment may be made withing the scope of the invention .

[0110] The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features , to the extent that such features or combinations are capable of being carried out based on the present specif ication as a whole in the light of the common general knowledge of a person skilled in the art , irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims . The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features .

Claims

CLAIMS1 . A stack for processing a device layer on a rigid substrate , comprising : a rigid substrate layer ; a f irst conductive layer on the rigid substrate layer ; an electric debond adhesive layer on the f irst conductive layer ; a second conductive layer on the electric debond adhesive layer .2 . The stack of claim 1 , further comprising an ultra violet debond adhesive on the second conductive layer , and a backplane photolithographic layer on the ultra violet debond adhesive .3 . The stack of claim 2 , further comprising a refractive index changing material layer on the backplane photolithographic layer .4 . The stack of claim 3 , further comprising a top plate on the refractive index changing material .5 . The stack of claim 4 , further comprising an ultra violet bond adhesive layer on the top plate , and a further rigid substrate layer on the ultra bond adhesive layer .6 . The stack of any one of claims 1 to 5 , in which the electric bond adhesive layer comprises a membrane between two adhesive layers .7 . The stack of claim 6 in which the membrane permits movement of release agents from one adhesive layer to the other when a voltage is appl ied across the f irst and second conductive layers , to reduce an adhesive force between one of the conductive layers and the rigid substrate layer .

278. A method of debonding a device from a rigid substrate, a first conductive layer connecting a rigid substrate layer to an electric debond adhesive, and a second conductive layer connecting the device to the electric debond adhesive, the debonding method comprising: applying an electric potential between the first and second conductive layers; and peeling the first conductive material from the electric debond adhesive.

9. The method of claim 8, the device being bonded on an opposing side to a further rigid substrate with an ultra violet adhesive, the debonding method further comprising exposing the further rigid substrate to ultra violet light and peeling the further rigid substrate from the device.

10. The method of claim 8 or claim 9, the electric debond adhesive comprises a layer between two adhesive layers, applying the electric potential causes release agents to move from one adhesive layer to the other adhesive layer to cause a low adhesive force in the one adhesive layer.

11. A method of processing a device layer on a rigid substrate, comprising affixing the device to the rigig substrate by: forming a first conductive layer on the glass substrate; forming an electric debond adhesive layer on the first conductive layer; forming a second conductive layer on the electric debond adhesive layer.

12. The method of claim 11, the electric debond adhesive layer being adhesive tape.

13. The method of claim 11 or claim 12, the second conductive layer being a layer of the device.

14. The method of any one of claims 11 to 13, the first conductive layer being a sputtered metal .

15. The method of any one of claims 11 to 14, further comprising forming an ultra violet debond adhesive on the second conductive layer, and forming a backplane photolithographic layer on the ultra violet debond adhesive.

16. The method of claim 15, further comprising forming a liquid crystal, LC, layer on the backplane photolithographic layer .

17. The method of claim 16, further comprising forming a top plate on the liquid crystal layer, forming an ultra violet bond adhesive layer on the top plate, and forming a further glass layer on the ultra bond adhesive layer.

18. The method of any one of claims 11 to 18, wherein forming the electric debond adhesive layer comprises forming a membrane between two adhesive layers.

19. An assembly comprising: a device layer having been formed in a stack comprising an electric debond adhesive layer affixing a rigid substrate to the device layer; and at least one further optical element.

20. The assembly of claim 19, wherein the at least one further optical element comprises at least one of : a waveguide, a luminance adjustment component, a lens, an image generation device, a reflection-reduction layer, or a protective layer .

21. Apparatus comprising: a device layer having been formed in a stack comprising an electric debond adhesive layer affixing a rigid substrate to the device layer; andat least one processor; and at least one storage comprising instructions, the instructions configured to, with the at least one processor, cause the apparatus to control one or more properties of the LC layer.

22. The apparatus of claim 21, configured to be mounted on a human head with the optical device cell stack positioned in a field of view of an eye of the human head.

23. The apparatus of claim 22 further comprising a first lens comprising a first one of the LC layer and first electrode and a second lens comprising a second one of the LC layer and first electrode.

24. The apparatus of claim 23 wherein the field of view of the eye is a first field of view of a first eye, and the first lens is configured to be positioned in the first field of view, in use, and the second lens is configured to be positioned in a second field of view, of a second human eye of the human head, in use.

25. The apparatus according to any one of claims 21 to 24, the apparatus being at least one of an augmented reality display device, a virtual reality display device or a mixed reality display device.

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