WO2023096776A2

WO2023096776A2 - Laser cutting methods for multi-layered glass assemblies having an electrically conductive layer

Info

Publication number: WO2023096776A2
Application number: PCT/US2022/049914
Authority: WO
Inventors: Sergio Tsuda
Original assignee: Corning Incorporated
Priority date: 2021-11-29
Filing date: 2022-11-15
Publication date: 2023-06-01
Also published as: WO2023096776A3

Abstract

A method including the steps of focusing a laser beam; translating the multi-layered glass assembly and the laser beam relative to each other; and exposing the at least one electrically conductive layer, wherein the induced absorption produces at least one defect line on a surface of the multi-layered glass assembly such that the at least one electrically conductive layer is substantially damage-free after the at least one defect line is produced and a laser cut is initiated in the multi-layered glass assembly.

Description

LASER CUTTING METHODS FOR MULTI-LAYERED GLASS ASSEMBLIES HAVING AN ELECTRICALLY CONDUCTIVE LAYER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No, 63/283,998, filed November 29, 2021, the content of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] The present disclosure relates generally to laser cutting methods for multilayered glass assemblies, having an electrically conductive layer. These types of multilayered glass assemblies are used as smart windows or displays included in televisions, monitors, and other electronic devices.

[0003] The area of laser processing materials encompasses a wide variety of applications that involve cutting, separating, drilling, milling, welding, melting, etc.

Among these applications, one that is of particular interest is cutting different types of substrates included in multi-layered glass assemblies. From process development and cost perspectives there are many opportunities tor improvement in cutting multi-layered glass assemblies. It is of great interest to have faster, cleaner, cheaper, repeatable and reliable methods of glass cutting compared to what is currently practiced today.

[0004] Among several alternative technologies, laser cuting and separation has been successfully demonstrated using different approaches. Techniques include removal of material between the boundaries of the desired part, (or parts) and its matrix, creation of defects within bulk materials to weaken or seed the materials with cracking initiation points along the perimeter of the desired profile followed by a secondary breaking step; and propagation of an initial crack by thermal stress separation. These laser cuting and separating processes have demonstrated several potential economic and technical advantages. Such advantages includes providing improved precision, good edge finishes and low residual stresses compared to competing technologies (e.g. mechanical scribing and breaking, high pressure water jet, and ultrasonic milling).

[0005] For multi-layered glass assemblies that include a liquid crystal layer, there are further difficulties in assuring that the electrically conductive layer is minimally damaged during laser processing. The electrically conductive layer which typically comprises indium -tin-oxide (ITO). Light that goes through these types of multi-layered glass assemblies change polarization as the light traverses the liquid crystal layer and polarizers, allowing control of how much light goes through the structure. When light polarization is aligned with the polarizers, the transmission is maximized. When light polarization is rotated to 90 degrees angle relative to the polarizer axis (crossed polarization), transmission is reduced to a minimum and no light goes through.

[0006] For various types of multi-layered glass assemblies, access to the electrically conductive layer (e.g. ITO layer) is necessary to enable active control of the device. For various applications, the electrically conductive layer is exposed by creating an offset edge cut between glass layers. One glass layer overhangs another by a small distance, exposing the electrically conductive layer, enabling access, physical contact and welding of electrical connectors in the multi-layered glass assembly.

[0007] Creating an offset between the edges of the two glass layers may be challenging, but it is doable. Either by offsetting the glass layers during assembly or by cutting one of the glass edges after assembly, electrodes are exposed. A main challenge in cutting one of the glass layers to expose the electrical contact layer is to avoid introducing damage to the electrically conductive layer and its substrate while cutting the other glass layer. The gap between both glass layers is typically very small (sub-micron to a few microns depending on design). In general, the methods to achieve this type of cutting are either mechanical, such as precision saws, or mechanical scribe and break (MS&B) or lasers. The challenge is to selectively modify only the desired layer without causing significant damage or changes to the other layers in the multi-layered glass assembly.

[0008] To lower production cost of smart devices, the devices are fabricated in large sheets with multiple units that are separated at the final stages of the process. The offset cutting of edges, to expose the electrodes/terminals, is even more challenging in this configuration. When a mechanical method is used, in addition to damaging the electrically conductive layer, the use of a scoring wheel requires physical contact with the sheet. As such, multi-layered glass assembly has to be flipped or somehow accessed from both sides by separate w heels. This increases the chances of catastrophic failure and loss of the entire sheet during handling. [0009] For laser cutting, the challenge of cutting from both sides still exists, but there are strategies that allow cutting from one side only. However, not all laser methods can cut without damage to the electrically conductive layer. For example, while laser ablation can definitely cut the glass, the process is slow and generates significant debris, heat, edge chipping and cracking. Also, laser ablation will more than likely damage the electrically conductive layer.

[0010] Accordingly, there is a continuing need for improved laser processes for multilayered glass assemblies.

SUMMARY

[0011] Disclosed herein are various methods of cutting multi-layered glass assemblies with one or more lasers.

[0012] According to various aspects of the disclosure methods of laser cutting a multilayered glass assembly having at least one glass layer and at least one electrically conductive layer includes the steps of focusing a laser beam, oriented along a beam propagation direction, and directed into the multi-layered glass assembly such that an induced absorption is generated within the multi-layered glass structure, translating the multi-layered glass assembly and the laser beam relative to each other; and exposing the at least one electrically conductive layer, wherein the induced absorption produces at least one defect line on a surface of the multi-layered glass assembly such that the at least one electrically conductive layer is substantially damage-free after the at least one defect line is produced and a laser cut is initiated in the multi-layered glass assembly...

[0013] Additional steps for the methods disclosed of laser cutting disclosed herein include further comprising cutting at least two glass layers such that an outermost edge of one glass layer is offset with respect to an outermost edge of the other glass layer; controlling the direction of crack propagation with the laser beam; creating a crack in a surface of the glass layer that generates a separation path; exposing the at least one electrically conductive layer such that there is an overhang of a glass layer in the multilayered glass assembly with respect to the at least one electrically conductive layer; separating the multi-layered glass assembly along a contour; and separating the multi-layered glass assembly along the contour includes directing the laser beam into the multi-layered glass assembly along or near the contour to facilitate separation of the multi-layered glass assembly along the contour.

[0014] Additional aspects of the disclosure include the laser beam being generated from a Bessel beam laser, and preferably a CPC Bessel beam laser; the at least one electrically conductive layer being an indium-tin-oxide (ITO) layer, or comprises ITO or a material equivalent to ITO; the impedance of the at least one electrically conductive layer after the at least one defect line has been produced being substantiall y the same as the impedance of the at least one electrically conductive layer before the at least one defect line has been produced; the at least one defect line comprising a plurality of defects spaced apart by a distance between 5 micron and 10 microns; at least one defect line extending at least 250 microns; the multi-layered glass assembly comprising cladding and core layers with different coefficients of thermal expansion, with a total of three or more layers; the laser beam having a wavelength and the multi-layered glass assembly is substantially transparent at the wavelength; the distance between each of the plurality of defects being substantially equidistant; at least one of the plurality of defects having a damage width of about 60 pm; the at least one of the plurality of defects having a damage width of about 50 pm; the at least one of the plurality of defects having a damage width of about 30 pm; the at least one of the plurality of defects having a damage width of about 25 pm; the at least one defect line being produced such that the at least one electrically conductive layer has an impedance of between 10 ohms and 15 ohms.

[0015] Additional aspects, features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0016] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary', and are intended to provide an overview' or framework to understanding the nature and character of the claims. The accompanying draw ings are included to provide a further understanding, and are incorporated in and constitute a part of this specification, lire drawings illustrate embodiments, and together with the description serve to explain principles and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 illustrates a configuration of one embodiment of a multi-layered glass assembly in accordance with one or more aspects of the present disclosure;

[0018] FIGs. 2A and 2B are illustrations of the positioning of the laser beam defect line and formation of a defect line in a region of induced nonlinear absorption along the laser beam defect line in accordance with one or more aspects of the present disclosure

[0019] FIG. 3 is an illustration of an optical assembly for laser processing according to one embodiment in accordance with one or more aspects of the present disclosure

[0020] FIG. 4 illustrates a cutting method for a multi-layered glass assembly in accordance with one or more aspects of the present disclosure;

[0021] FIG. 5 illustrates different cutting methods for a multi-layered glass assembly in accordance with one or more aspects of the present disclosure;

[0022] FIGs. 6A-6C illustrate Bessel beam optics and the application of a Bessel beam on a multi-layered glass assembly in accordance with one or more aspects of the present disclosure;

[0023] FIG. 7 schematically illustrates a method of evaluating the conductivity of electrically conductive layers included in multi-layered glass assemblies in accordance with one or more aspects of the present disclosure;

[0024] FIG. 8A illustrates laser focal height measured for the electrically conductive layer shown in FIG. 8B in accordance with one or more aspects of the present disclosure

[0025] FIG. 8B illustrates damage to an electrically conductive layer caused by a Bessel beam laser in accordance with one or more aspects of the present disclosure;

[0026] FIG. 9A illustrates the positioning of a laser with respect to different surfaces in accordance with one or more aspects of the present disclosure;

[0027] FIG. 9B is a photograph of an edge of a top glass layer after separation in accordance with one or more aspects of the present disclosure;

[0028] FIGs. 10A-10D are photographs of surfaces of glass layers in accordance with one or more aspects of the present disclosure; [0029] FIG. 1 1 illustrates the impact on glass layers and corresponding edges after using a Bessel beam laser in accordance with one or more aspects of the present disclosure;

[0030] FIG. 12A illustrates the positioning of a laser with respect to different surfaces in accordance with one or more aspects of the present disclosure;

[0031] FIG. I2B illustrates the impact on glass layers and corresponding edges after using a Bessel beam laser in accordance with one or more aspects of the present disclosure;

[0032] FIG. 13A illustrates the positioning of a laser with respect to different surfaces in accordance with one or more aspects of the present disclosure;

[0033] FIG. 13B illustrates methods of offset cutting of a multi-layered glass assembly using a Bessel beam layer with crack propagation control in accordance with one or more aspects of the present disclosure; and

[0034] FIG. 14 schematically illustrates defects after cuting multi-layered glass assemblies when using a standard Bessel beam laser compared to a Bessel beam with crack propagation control in accordance with one or more aspects of the present disclosure;

[0035] The figures are not necessarily to scale. Like numbers used in the figures may be used to refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

DETAILED DESCRIPTION

[0036] Various exemplar}' embodiments of the disclosure will now be described with particular reference to the drawings. Exemplary embodiments of the present disclosure may take on various modifications and alterations without departing from the spirit and scope of the disclosure. Accordingly, it is to be understood that the embodiments of the present disclosure are not to be limited to the following described exemplary embodiments, but are to be controlled by the features and limitations set forth in the claims and any equivalents thereof.

[0037] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0038] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

[0039] Spatially related terms, including but not limited to, “lower,” “upper,” “beneath,”

“below,” “above,” and “on top,” if used herein, are utilized for ease of description to describe spatial relationships of an element(s) to another. Such spatially related terms encompass different orientations of tire device in use or operation in addition to the particular orientations depicted in the figures and described herein. For example, if an object depicted in the figures is turned over or flipped over, portions previously described as below or beneath oilier elements would then be above those other elements.

[0040] Cartesian coordinates may be used in some of the Figures for reference and an not intended to be limiting as to direction or orientation.

[0041] For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” “top,” “bottom,” “side,” and derivatives thereof, shall relate to the disclosure as oriented w ith respect to the Cartesian coordinates in the corresponding Figure, unless stated otherwise. However, it is to be understood that the disclosure may assume various alternative orientations, except where expressly specified to the contrary.

[0041] For the purposes of describing and defining the subject matter of the disclosure it is noted that the terms “substantially” and “generally” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation.

[0042] Embodiments described herein relate to methods for cutting arbitrary shapes articles of optically transparent materials, particularly multi-layered glass assemblies drawn from glass sheets having an electrically conductive layer. The materials are preferably substantially transparent to the selected laser wavelength (i.e., absorption less than about 10% and preferably less than about 1% per mm of material depth).

[0043] A goal of cutting is to provide precision cutting and then separation of arbitrary shaped articles both with and without internal holes or slots out of multi -layered glass assemblies. The process cuts these multi-layered glass assemblies in a controllable fashion with negligible debris, minimal defects, and low subsurface damage to the edges of the cut and separated parts. Minimal defects and low subsurface damage at the edges of the multilayered glass assembly preserves assembly strength and prevents part failure upon external impacts. The laser cutting method is well suited to materials that are transparent to the selected laser wavelength. Demonstrations of the cutting method have been made using multi-layered glass assemblies of between 0.7 mm and 1 .2 mm in thickness, but it is conceived that any thickness may be cut using the disclosed methods.

[0044] Subsurface damage, which includes small microcracks and material modifications caused by a cutting process and which are oriented roughly perpendicular to a cut surface, is a concern for the edge strength of glass and other brittle materials.

[0045] As used herein, subsurface damage refers to the maximum size (e.g. length, width, diameter) of structural imperfections in the perimeter surface of the part separated from the substrate or material subjected to laser processing in accordance with the present disclosure. Because the structural imperfections extend from the perimeter surface, subsurface damage may also be regarded as the maximum depth from tire perimeter surface in which damage from laser processing in accordance with the present disclosure occurs. The perimeter surface of the separated part may be referred to herein as the edge or the edge surface of the separated part. The structural imperfections may be cracks or voids and represent points of mechanical weakness that promote fracture or failure of the part separated from the substrate or material. By minimizing the size of subsurface damage, the methods disclosed herein improve the structural integrity and mechanical strength of articles separated from the multilayered glass assembly with minimal damage to the electrically conductive layer contained therein.

[0046] lire depth of subsurface damage can be measured by using a confocal microscope to look at the cut surface, the m icroscope having an optical resolution of a few nm. Surface reflections are ignored, while cracks are probed within the material, the cracks showing up as bright lines. The microscope is focused into the material until there are no more ‘‘sparks,” collecting images at regular intervals. The images are manually processed by looking for cracks and tracing them through the depth of the glass to determine a maximum depth (typically measured in microns) of subsurface damage. There are typically many thousands of microcracks, so typically only the largest microcracks are measured. This process is typically repeated on about 5 locations of a cut edge. Although the microcracks are roughly perpendicular to the cut surface, any cracks that are directly perpendicular to the cut surface may not be detected by this method.

[0047] With the methods described herein, sub-surface damage is minimized and limited to a small region m the vicinity of the edge. Sub-surface damage may be limited to a depth relative to the surface of an edge of 100 pm or less, or 75 pm or less, or 60 pm or less, or 50 pm or less, and the cuts may produce only low debris. Cutting of a transparent mult! -layered glass assembly with a laser in accordance with the present disclosure may also be referred to herein as drilling, laser drilling or laser processing.

[0048] The fundamental step of the laser cuting methods disclosed herein is to create a defect line that delineates the desired shape of a part and establishes a path of least resistance for crack propagation and hence separation and detachment of the shaped part from its surrounding substrate. The defect line can include of a series of spaced defects (also referred to as spots, perforations, holes, or damage tracks) that are formed by a laser. These laser cutting methods can be tuned and configured to enable manual or mechanical separation, partial separation or total separation of articles of desired shapes out of the original multilayered glass assembly.

[0049] In the first step, the material (e.g. object or workpiece) to be processed is irradiated with an ultra-short laser beam that is condensed into a high aspect ratio line focus (referred to herein as a laser beam defect line) that penetrates the substrate. Within this volume of high energy density laser irradiation, the material is modified via nonlinear effects It is important to note that optical intensity above a critical threshold is needed to induce nonlinear absorption. Below the critical intensity threshold, the material is transparent to the laser radiation and remains in its original state. By scanning the laser over a desired line or path we create a defect line (a few microns wide) consisting of a series of defect lines. The defect line defines the perimeter or shape of a part to be separated in a subsequent processing step.

[0050] The selection of a laser source is predicated on the ability to induce nonlinear absorption in transparent materials, including formed multi-layered glass assemblies. Nonlinear absorption includes multi-photon absorption (MPA), MPA is the simultaneous absorption of multiple (two or more) photons of identical or different frequencies in order to excite a material from a lower energy state (usually the ground state) to a higher energy state (excited state). The excited state may be an excited electronic state or an ionized state. The energy difference between the higher and lower energy states of the material is equal to the sum of the energies of the two or more photons. MPA is a nonlinear process that is generally several orders of magnitude weaker than linear absorption. It differs from linear absorption in that the strength of MPA depends on the square or higher power of the light intensity, thus making it a nonlinear optical process. At ordinary light intensities, MPA is negligible. If the light intensity (energy density) is extremely high (above the critical threshold), such as in the region of focus of a laser beam source (particularly a pulsed laser beam source) including the laser beam defect line described herein, MPA becomes appreciable and leads to measurable effects in the material within the region where the energy density of the light source is sufficiently high. Within the focal region, the energy density⁷ may also be sufficiently high to result in ionization.

[0051] At the atomic level, the ionization of individual atoms has discrete energy requirements. Several elements commonly used in glass (e.g., Si, Na, K) have relatively low ionization energies (~5 eV). Without the phenomenon of MPA, a wavelength of about 248 nm would be required to create linear ionization at ~5 eV. With MPA, ionization or excitation between states separated in energy by -5 eV can be accomplished with wavelengths longer than 248 nm. For example, photons with a wavelength of 532 nm have an energy of ~2.33 eV, so two photons with wavelength 532 nm can induce a transition between states separated in energy by -4.66 eV in two-photon absorption (TP A), for example. Thus, atoms and bonds can be selectively excited or ionized in the regions of a material where the energy density of the laser beam is sufficiently high to induce nonlinear TPA of a laser wavelength having half the required excitation energy, for example.

[0052] MPA can result in a local reconfiguration and separation of the excited atoms or bonds from adjacent atoms or bonds. The resulting modification in the bonding or configuration can result in non-thermal ablation and removal of matter from the region of the material in which MPA occurs. This removal of mater creates a structural defect (e.g. a defect line, damage line, spot, or ‘"perforation”) that mechanically weakens the material and renders it more susceptible to cracking or fracturing upon application of mechanical or thermal stress. By controlling the placement of perforations, a contour or path along which cracking occurs can be precisely defined and precise micromachining of the material can be accomplished. The contour defined by a series of perforations may be regarded as a defect line and corresponds to a region of structural weakness in the material. In one embodiment, micromachining includes separation of an article from the material processed by the laser, where the part has a precisely defined shape or perimeter determined by a closed contour of perforations formed through MPA effects induced by the laser. As used herein, the term closed contour refers to a perforation path formed by the laser line, where the path intersects with itself at some location. An internal contour is a path formed where the resulting shape is entirely surrounded by an outer portion of material.

[0053] The preferred laser is an ultrashort pulsed laser (pulse durations on the order tens of picoseconds or shorter) that can be operated in pulse mode or burst mode. In pulse mode, a series of nominally identical single pulses is emited from the laser and directed to the workpiece. In pulse mode, the repetition rate of the laser is determined by the spacing in time between the pulses. In burst mode, bursts of pulses are emitted from the laser, where each burst includes two or more pulses (of equal or different amplitude). In burst mode, pulses within a burst are separated by a first time interval (which defines a pulse repetition rate for the burst) and the bursts are separated by a second time interval (which defines a burst repetition rate), where the second time interval is typically much longer than the first time interval. As used herein (whether in the context of pulse mode or burst mode), time interval refers to the time difference between corresponding parts of a pulse or burst (e.g. leading edge-to-leading edge, peak-to-peak, or trailing edge-to-trailing edge). Pulse and burst repetition rates are controlled by the design of the laser and can typically be adjusted, within limits, by adjusting operating conditions of the laser. Typical pulse and burst repetition rates are in the kHz to MHz range.

[0054] The laser pulse duration (in pulse mode or for pulses within a burst in burst mode) may be 10’¹⁰ s or less, or IO'¹¹ s or less, or 10"¹² s or less, or 10‘¹³ s or less. In the exemplary embodiments described herein, the laser pulse duration is greater than 10'¹⁵. [0055] The perforations may be spaced apart and precisely positioned by controlling the velocity of a substrate or stack relative to the laser through control of the motion of the laser and/or the substrate or stack. As an example, in a thin transparent substrate moving at 2.00 mm/sec exposed to a 100 kHz series of pulses (or bursts of pulses), the individual pulses would be spaced 2 microns apart to create a series of perforations separated by 2 microns. Uris defect line (perforation) spacing is sufficient to allow for mechanical or thermal separation along the contour defined by the series of perforations. Distance between adjacent defect lines along the direction of the defect lines can, for example, be in the range from 0.25 pm to 50 pm, or in the range from 0.50 pm to about 20 pm, or in the range from 0.50 pm to about 15 pm, or in the range from 0.50 pm to 10 pm, or in the range from 0.50 pm to 3.0 pm or in the range from 3.0 pm to 10 pm, or in the range from 5.0 pm to 10 pm.

[0056] Once a defect line with vertical defects is created, separation can occur via: 1) manual or mechanical stress on or around the defect line; the stress or pressure should create tension that pulls both sides of the defect line apart to break the areas that are still bonded together; 2) using a heat source, create a stress zone around the defect line to put the vertical defect One in tension and induce partial or total self-separation. In both cases, separation depends on several of the process parameters, such as laser scan speed, laser power, parameters of lenses, pulse width, repetition rate, etc.

[0057] Multi-layered glass assemblies, i.e. formed glass composite sheets, can be made by a multi-layer fusion draw system. As shown in FIG. 1, the multi-layered glass assembly includes at least one outer cladding layer on each surface of the core layer. The cladding layers may also be referred to as outer or outermost layers, and the core layer may also be referred to as an inner or interstitial layer. In one embodiment, the multi-layered glass assemblies have a core layer that is intermediate to high coefficient of thermal expansion (CTE) glass, while the cladding or outer layers are low CTE glasses. The multi-layered glass assemblies have a naturally pre-stressed central core, based upon the compositional difference between the core and the cladding layers. Such composite sheets are frequently difficult to cut and separate into usable parts, which are substantially free from damage. In addition, the creation of internal openings (e.g. slots or holes) within separated parts can be difficult.

[0058] The present disclosure is concerned w ith cutting of multi-layered glass assemblies from composite glass sheets, such as those with core and cladding regions of the type shown in FIG. 1 . Representative compositions of the core and cladding glasses are as follows: The cladding layer is a glass composition comprising from about 60 mol.% to about 66 mol.% S1O2; from about 7 mol.% to about 10 mol.% AI2O3; from about 14 mol.% to about 18 mol.% B2O3 ; and from about 9 mol.% to about 16 mol.% alkaline earth oxide, wherein the alkaline earth oxide comprises at least CaO and the CaO is present in the glass composition in a concentration from about 3 mol.% to about 12 mol.%: and wherein the glass composition is substantially free from alkali metals and compounds containing alkali metals. A specific cladding layer glass composition is shown in Table 1.

[8059] Representative core glass compositions comprise: about 60 mol% to about 75 mol% SiO₂, about 2 mol% to about 11 moi% AI2O.3, 0 mol% to about 11 mol% B₂O₃, 0 mol%to about 1 mol%Na₂O, about 1 mol% to about 18 mol% K₂O, 0 mol%to about 7 mol% MgO, 0 mol% to about 9 mol% CaO, about 1 mol% to about 8 mol% SrO, 0 mol% to about 4 mol% BaO, and, about 3 mol% to about 16 mol% R’O, wherein R’O comprises the combined mol% of MgO, CaO, SrO, and BaO in the composition. A specific core glass composition is shown in Table 2.

[0060] Laser cutting of multi-layered glass assemblies such as the one shown in FIG. 1 is accomplished using one or more of the methods described herein.

[0061] Each laser cutting method relies on the material transparency to the laser wavelength in the linear intensity regime, or low laser intensity, which allows maintenance of high surface quality and reduced subsurface damage created by the area of high intensity around the laser focus. An edge of a multi-layered glass assembly can have subsurface damage up to a depth less than or equal to about 75 microns, for example, by using the methods described herein. One of the key enablers of this process is the high aspect ratio of the defect created by the ultra-short pulsed laser, it allows creation of a defect line that extends from the top to the bottom surfaces of the material to be cut. In principle, the defect line can be created by a single pulse or a single burst of pulses and if desired, additional pulses or bursts can be used to form the defect line or to increase the extension of the affected area (e.g. depth and width). In preferred configurations, the defect line extends at least 250 pm. [0062] The method to cut and separate transparent materials is essentially based on creating a defect line in the material to be processed with an ultra-short pulsed laser, where the defect consists of a series of defect lines arranged to define the desired perimeter of a part to be separated from the material. Depending on the material properties (absorption, GTE, stress, composition, etc.) and laser parameters chosen for processing the material, the creation of a defect line alone may suffice to induce self-separation. In this case, no secondary separation processes, such as tension/bending forces, heating, or CO2 laser, are necessary.

[0063] In some cases, a defect line created along a contour defined by a series of perforations or defect lines is not enough to separate the part spontaneously and a secondary step may be necessary. If so desired, a second laser can be used to create thermal stress to separate the part, for example . In the case of formed glass composites, we found that separation can be achieved, after the creation of a defect line, by application of mechanical force or by using a CO2 laser to create thermal stress to effect separation of the part. Another option is to have the CO2 laser only start the separation and finish the separation manually. The optional CO2 laser separation is achieved with a defocused CW laser emitting at 10.6 microns with power adjusted by controlling its duty' cycle. Focus change (i.e,, extent of defocusing) is used to vary the induced thermal stress by varying the spot size. Defocused laser beams include those laser beams that produce a spot size larger than a minimum, diffraction-limited spot size on the order of the size of the laser wavelength. For example, defocused spot sizes of about 7 mm, 2 mm and 20 mm can be used tor CO2 lasers, for example, whose diffraction-limited spot size is much smaller given the emission wavelength of 10.6 microns.

[0064] There are several methods to create tire defect line. Hie optical method of forming the line focus can take multiple forms, using donut shaped laser beams and spherical lenses, axicon lenses, diffractive elements, or other methods to form the linear region of high intensity. The type of laser (picosecond, femtosecond, etc.) and wavelength (IR, green, UV, etc.) can also be varied, as long as sufficient optical intensities are reached to create breakdown of the substrate or workpiece material in the region of focus in the substrate material or fusion formed glass composite workpiece through nonlinear optical effects.

[0065] In the present application, an ultra-short pulsed laser is used to create a high aspect ratio vertical defect line in a consistent, controllable and repeatable manner. The details of the optical setup that enables the creation of this vertical defect line are described beknv, and in U.S. Patent No. 11,028,003, the entire contents of wfiich are incorporated by reference. The essence of this concept is to use an axicon lens element in an optical lens assembly to create a region of high aspect ratio, taper-free microchannels using ultra-short (picoseconds or femtosecond duration) Bessel beams. In other words, the axicon condenses the laser beam into a high intensity region of cylindrical shape and high aspect ratio (long length and small diameter) in the substrate material. Due to the high intensity created with the condensed laser beam, nonlinear interaction of the electromagnetic field of the laser and the substrate material occurs and the laser energy is transferred to the substrate to effect formation of defects that become constituents of the defect line. However, it is important to realize that in the areas of the material where the laser energy intensity is not high (e.g., glass volume of substrate surrounding the central convergence line), the material is transparent to the laser and there is no mechanism for transferring energy from the laser to the material. As a result, nothing happens to the glass or workpiece when the laser intensity is below the nonlinear threshold ,

[0066] Moreover, the laser cutting methods disclosed herein cut glasses, including thin glass, extremely accurately, extremely fast and without creating glass chips. The technology can perforate glass with extremely small holes (e.g. <1 micron) and short pitch spacing (e.g., 1 micron). Also, the glass can be perforated at extremely high speeds (e.g. 1-2 nieters/sec). In test cases, no chips have been observed on the edge of the glass. The laser process can perforate and separate small glass articles like a cell phone size (70 mm x 150 mm) shape out of a larger sheet of glass. This perforating and separating process of thin glass leaves behind an edge with an Ra surface roughness less than 400 nm and sub-surface micro-cracks at depths limited to 60 microns or less. This edge quality is close to the quality’ of a ground sheet of glass. Given this capability, hot glass can be laser cut at the fusion draw process that makes thin glass sheet.

[0067] Turning to FIGS. 2A and 2B, a method of laser cutting a multi-layered glass assembly includes focusing a laser beam 2 into a laser beam defect line 2b oriented along the beam propagation direction. The laser beam defect line 2b is preferably created using a

Bessel beam, with a field profile typically given by special functions that decay more slowly in the transverse direction (i.e. direction of propagation) than the Gaussian function. As shown in FIG. 3, laser 3 (not shown) emits a laser beam 2, which has a portion 2a incident to the optical assembly 6. The optical assembly 6 turns the incident laser beam into a laser beam defect line 2b on the output side over a defined expansion range along the beam direction (length 1 of the defect line). The planar substrate 1 is positioned in the beam path to at least partially overlap the laser beam defect line 2b of laser beam 2. The laser beam defect line is thus directed into the substrate. Reference la designates the surface of the planar substrate facing the optical assembly 6 or the laser, respectively, and reference lb designates the reverse (remote) surface of substrate 1. The substrate or workpiece thickness (in this embodiment measured perpendicularly to the planes la and lb, i.e., to the substrate plane) is labeled with d. The substrate or workpiece can also be referred to as a. glass article that is substantially transparent to the wavelength of the laser beam 2, for example.

[0068] As FIG. 2A depicts, substrate 1 (or the fusion formed glass composite workpiece) is aligned substantially perpendicular to the longitudinal beam axis and thus behind the same defect line 2b produced by the optical assembly 6 (the substrate is perpendicular to the plane of the drawing). Tire defect line being oriented or aligned along the beam direction, the substrate is positioned relative to the defect line 2b in such a way that the defect line 2b starts before the surface la of the substrate and stops before the surface lb of the substrate, i.e. defect line 2b terminates within the substrate and does not extend beyond surface lb. In the overlapping area of the laser beam defect line 2b with substrate 1 , i.e. in the substrate material covered by defect line 2b, the laser beam defect line 2b generates (assuming suitable laser intensity along the laser beam defect line 2b, which intensity is ensured by the focusing of laser beam 2 on a. section of length 1, i.e. a hue focus of length 1) a. section 2c (aligned along the longitudinal beam direction) along which an induced nonlinear absorption is generated in the substrate material, lire induced nonlinear absorption produces defect line formation in the substrate material along section 2c.

[0069] The defect line is a microscopic (e.g., >100 nm and <0.5 micron in diameter) elongated ‘''hole’’ (also referred to herein as perforations or damage tracks) in a substantially transparent material that is created using a one or more high energy pulses or one or more bursts of high energy pulses. The perforations represent regions of the substrate material modified by the laser. The laser-induced modifications disrupt the structure of the substrate material and constitute sites of mechanical weakness. Structural disruptions include compaction, melting, dislodging of material, rearrangements, and bond scission. The perforations extend into the interior of the substrate material and have a cross-sectional shape consistent with the cross-sectional shape of the laser (generally circular). The average diameter of the perforations may be in the range from 0. 1 pm to 50 pm, or in the range from 1 pm to 20 pm, or in the range from 2 pm to 10 pm, or in the range from 0.1 pm to 5 pm. In some embodiments, the perforation is a ‘‘through hole”, which is a hole or an open channel that extends from the top to the bottom of the substrate material.

[0070] In some embodiments, the perforation may not be a continuously open channel and may include sections of solid material dislodged from the substrate material by the laser. The dislodged material blocks or partially blocks the space defined by the perforation. One or more open channels (unblocked regions) may be dispersed between sections of dislodged material. The diameter of the open channels is < 1000 nm, or <500 nm, or <400 nm, or <300 nm or in the range from 10 nm to 750 nm, or in the range from 100 nm to 500 nm. The disrupted or modified area (e.g., compacted, melted, or otherwise changed) of the material surrounding the holes in the embodiments disclosed herein, preferably has diameter of <50 pm (e.g., <10 pm).

[0071] Individual perforations can be created at rates of several hundred kilohertz (several hundred thousand perforations per second), for example. With relative motion between the laser source and the material, the perforations can be placed adjacent to one another (spatial separation varying from sub-micron to several or even tens of microns as desired). This spatial separation (pitch) can be selected to facilitate separation of the material or workpiece. In some embodiments, the defect line is a “through hole”, which is a hole or an open channel that extends from the top to the bottom of the substantially transparent material. The defect line formation is not only local, but extends over the entire length of section 2c of the induced absorption. The length of section 2c (which corresponds to the length of the overlapping of laser beam defect line 2b with substrate 1) is labeled with reference L. The average diameter or extent of the section of the ind uced absorption 2c (or tlie sections in the material of substrate 1 undergoing the defect line formation) is labeled with reference D. This average extent D basically corresponds to the average diameter 8 of the laser beam defect line 2b, that is, an average spot diameter in a range of between about 0.1 micron and about 5 microns. Spot diameter D of a Bessel beam can be written as D = (2.4048 X)/(2;rB), where 1 is the laser beam wavelength and B is a function of the axicon angle.

[0072] As FIG. 2A shows, the substrate material (which is transparent to the wavelength x of laser beam 2) is heated due to the induced absorption along the defect line 2b arising from the nonlinear effects (e.g. two-photon absorption, multi-photon absorption) associated with the high intensity of the laser beam within defect line 2b. FIG. 2B illustrates that the heated substrate material will eventually expand so that a corresponding induced tension leads to micro-crack formation, with the tension being the highest at surface la.

[0073] To ensure high quality (regarding breaking strength, geometric precision, roughness and avoidance of re-machining requirements) of the surface of the separated part along which separation occurs, the individual defect lines positioned on the substrate surface along the line of separation should be generated using the optical assembly described below (hereinafter, the optical assembly is alternatively also referred to as laser optics). The roughness of the separated surface (or cut edge) is determined primarily by the spot size or tire spot diameter of the defect line. Roughness of a surface can be characterized, for example, by an Ra surface roughness parameter defined by the ASME B46. 1 standard. As described in ASME B46.1, Ra is the arithmetic average of the absolute values of the surface profile height deviations from the mean line, recorded within the evaluation length. In alternative terms, Ra is the average of a set of absolute height deviations of individual features (peaks and valleys) of the surface relative to the mean .

[0074] In order to achieve a spot size of, for example, 0.5 micron to 2 microns in case of a given wavelength A of laser 3 (interaction with the material of substrate 1 ), certain requirements must usually be imposed on the numerical aperture of laser optics 6. These requirements are met by laser optics 6 described below.

[0075] In order to achieve the required numerical aperture, the optics must, on the one hand, dispose of the required opening for a given focal length, according to the known Abbe formulae (N. A. = n sin (theta), n: refractive index of the glass or composite workpiece to be processed, theta: half the aperture angle; and theta ^::: arctan (DrZZf); Dr: aperture diameter, f: focal length). On the other hand, the laser beam must illuminate the optics up to the required aperture, which is typically achieved by means of beam widening using widening telescopes between the laser and focusing optics.

[0076] The defect or spot size should not vary too strongly for the puqrose of a uniform interaction along the defect line. This can, for example, be ensured (see the embodiment below) by illuminating the focusing optics only in a small, circular area so that the beam opening and thus the percentage of the numerical aperture only vary slightly. [0077] According to FIG. 3 (section perpendicular to the substrate plane at the level of the central beam in the laser beam bundle of laser radiation 2; here, too, laser beam 2 is perpendicularly incident to the substrate plane, i.e. incidence angle 0 is 0° so that the defect line 2 b or the section of the induced absorption 2c is parallel to the substrate normal), the laser radiation 2a emitted by laser 3 is first directed onto a circular aperture 8 which is completely opaque to the laser radiation used. Aperture 8 is oriented perpendicular to the longitudinal beam axis and is centered on the central beam of the depicted beam bundle 2a. The diameter of aperture 8 i s selected in such a way that the beam bundles near the center of beam bundle 2a or the central beam (here labeled with 2aZ) hit the aperture and are completely absorbed by it. Only the beams in the outer perimeter range of beam bundle 2a (marginal rays, here labeled with 2aR) are not absorbed due to the reduced aperture size compared to the beam diameter, but pass aperture 8 laterally and hit the marginal areas of the focusing optic elements of the optical assembly 6, which, in this embodiment, is designed as a spherically cut, bi-convex lens 7.

[0078] As illustrated in FIG. 3, the laser beam defect line 2b is not only a single focal point for the laser beam, but rather a series of focal points for different rays in the laser beam. The series of focal points form an elongated defect line of a defined length, shown in FIG. 3 as the length 1 of the laser beam defect line 2b.

[0079] Lens 7 is centered on the central beam and is designed as a non-corrected, biconvex focusing lens in the form of a common, spherically cut lens. The spherical aberration of such a lens may be advantageous. As an alternative, aspheres or multi-lens systems deviating from ideally corrected systems, which do not form an ideal focal point but a distinct, elongated defect line of a defined length, can also be used (i.e., lenses or systems which do not have a single focal point). The zones of the lens thus focus along a defect line 2b, subject to the di stance from the lens center. The diameter of aperture 8 across the beam direction is approximately 90% of the diameter of the beam bundle (defined by the distance required for the intensity of the beam to decrease to 1/e² of the peak intensity) and approximately 75% of the diameter of the lens 7 of the optical assembly 6. The defect line 2b of a non-abe n-ation-corrected spherical lens 7 generated by blocking out the beam bundles in the center is thus used. FIG. 3 show's the section in one plane through the central beam, and the complete three-dimensional bundle can be seen when the depicted beams are rotated around the defect line 2b. [0080] One potential disad vantage of this type of a defect line formed by lens 7 and the system shown in FIG. 3 is that the conditions (defect/spot size, laser intensity) may vary along the defect line (and thus along the desired depth in the material) and therefore the desired type of interaction (no melting, induced absorption, thermal-plastic deformation up to crack formation) may possibly occur only in selected portions of the defect line. This means in turn that possibly only a part of the incident laser light is absorbed by the substrate material in the desired way. In this way, the efficiency of the process (required average laser power for the desired separation speed) may be impaired, and the laser light may also be transmitted into undesired regions (parts or layers adherent to the substrate or the substrate holding fixture) and interact with them in an undesirable w^ray (e.g. heating, diffusion, absorption, unwanted modification).

[0081] FIG. 4 schematically illustrates a laser cutting process for a multi-layered glass assembly 100. Tire assembly 100 or mother sheet includes cladding or outer glass layers 110a, 110b (shown in gray), core or interstitial glass layer 120 (shown in gray), electrically conductive layers 130 (shown in red), liquid crystal alignment layers 140 (shown in green), liquid crystal interstitial layers 150 (shown in yellow), and edge seals 160 (shown in purple). Laser cuts 170 are represented in FIG. 4 by dashed lines (shown in black). FIG. 4 further illustrates how to cut cladding or outer glass layers to expose the electrically conductive layers with minimal damage or damage-free, where the electrical connection will be made to drive the liquid crystal molecules in and out of alignment. As used herein, the electrically conductive layer is preferably an indium -tin-oxide (ITO) layer or layer comprising ITO or one or other materials having substantially equivalent properties as that of an ITO layer.

[0082] Positioned below the multi-layered glass assembly are a plurality of multi-layered cells 200? after laser cutting has occurred. Here the plurality of multi-layered cells includes three cells 200?. The number of cells, however, should not be constmed as limiting as fewer or additional cells can be cut from the multi-layered assembly, depending on various factors. Such factors include, but are not limited to, application requirements, sheet size, and manufacturing capabilities ,

[0083] FIG. 5 schematically illustrates a multi-layered glass assembly 300 and methods of cutting the glass to expose the electrically conductive layers 330 (shown in green). The assembly 300 further includes cladding or outer glass layers 310a, 310b, a core or interstitial glass layer 320, liquid crystal interstitial layers 350 (shown in yellow), edge seals 160 (shown in blue). The assembly 300 may also include one or more spacers 372 such that a gap is formed between the electrically conductive layers 330 and the cladding or outer glass layers 310a, 310b. In preferred configurations, the gap is about 10 um .

[0084] The methods of cutting illustrated m FIG. 5 include mechanical scoring, laser ablation, and Bessel beam laser perforation. Both of the laser methods will score the glass, but each method includes a later secondary separation step to singulate/separate the glass.

The separation step is necessary for both methods because tensile stress (or force/pressure) will be required to separate the glass around a score line.

[0085] As particularly illustrated in FIG. 5, using lasers to cut the multi-layered glass assemblies is possible with different methods (ablation, Bessel beam, COz scribe and break, stealth dicing, etc.). Laser cutting has several advantages over mechanical methods but tends to have higher costs. Also, in general, laser cutting requires less force to separate cells after ablation or perforation. Unfortunately for some of these methods, it is very difficult to avoid damage to the electrically conductive layers. During laser processing, most of the laser energy will go through the glass layers and require a continuous defect for separation. This is particularly true when laser ablation is applied to remove material and separate the glass.

[0086] While laser ablation has been used to cut glass, it creates debris, melts material redeposits, resulting in heat affected zones (HAZ) where thermal stress can induce chipping and cracking. The longer the pulse width is, the larger the extent of the HAZ and the associated damage. Moreover, laser ablation tends to be a slow process, which produces varying edge quality depending on the pulse width and dynamics of laser-glass interaction, among other factors. Another issue is that in order to achieve glass ablation, the Gaussian beam has to be focused tightly to concentrate all of its energy into a small spot, which will inevitably ablate the electrically conductive layer and create a trench that will interrupt electrical conduction.

[0087] Together, FIGs. 6A, 6B, and 6C illustrate how glass layers 410 included in a multi-layered glass assembly 400 can be modified by a Bessel beam laser. FIG. 6A illustrates the optics associated with the Bessel beam laser, and particularly how its axicon lens element is positioned in an optical lens assembly. FIG. 6B shows two different views of the multi-layered glass assembly 400 with the top view' illustrating a top surface 408 of a glass layer 410 with a plurality of dots representing a defect line 412, including a plurality of spaced apart defects 414, which are substantially equidistant, and an arrow SI illustrating pitch or perforation spacing distance in the giass layer 410. The botom view of FIG. 6B is a microscopic view, taken with a scanning electron microscope (SEM), showing a cut edge 415 of a glass layer 410C after being laser cut. The bottom view of FIG. 6B thus illustrates how tlie pitch or perforation spacing distance SI corresponds to the spacing distance S2. FIG. 6C is an edge view of the cut glass layer 410C, showing its top surface 418 and bottom surface

420.

[0088] A s illustrated by the views shown in FIG. 6B, the plurality of defects 414 are substantially equally spaced vertical perforations that have gone through the thickness of the glass layer. By subsequently moving the laser or the giass a path of least resistance for separation. Typically, depending on the glass properties, the plurality of defects are separated by a distance ranging from about 5 pm to about 10 pm, which is known to be ideal for separation.

[0089] To evaluate the impact of the Bessel beam laser on the conductivity of the electrically conductive layer, the resistance of the electrically conductive layer between two points at a fixed distance around the laser ablated line is compared to tire same measurement of an area that has not been exposed to the Bessel beam laser. FIG. 7 illustrates how this measurement is performed using a multimeter. With a multimeter, resistance is measured on tin electrically conductive layer before application of the Bessel beam laser. In FIG. 7, this electrically conductive layer is referred to as "‘Bare ITO.” Then, for comparison purposes, resistance is measured of an electrically conductive layer after application of the Bessel beam laser. In FIG. 7 this electrically conductive layer is referred to as a “Through laser damaged ITO” with the laser damage line being represented by a vertical dashed line. Thus, FIG. 7 effectively characterizes damage to the functionality of the electrically conductive layer when a Bessel beam laser is used.

[0090] FIG. 8A illustrates laser focus height used in an experiment, and the damage on the electrically conductive layer caused by the Bessel beam laser and the change in electrical resistance as a function of the laser height relative to the glass surface, as represented by FIG. 8B and TABLE 3. Here, the laser damage width and impedance between a distance of 5 mm is characterized by measuring what will happen to a single electrically conductive layer when exposed to a Bessel beam laser. The higher the distance, the wider the damage caused by the Bessel beam laser. Hie impedance increases proportionally. When compared to an area of the electrically conductive layer that has not been exposed to the laser, it is clear that the laser line has an impact on its conductivity. The electric conductivity inversely drops with the extent of laser damage. The laser parameter used to perform this evaluation was adjusted to allow' the EXG (0.7 mm) separation. This parameter is used to evaluate the damage to the electrically conductive layer. Standard Bessel beam optics were used for this experiment with about 55 W of laser power at 1064 nm with an 8 pm pitch and a burst of 8 pulses at 100 kHz repetition rate and 10 psec pulse width. Comparing the pitch distance (separation of the laser spots) with the measured width of the laser damage, it becomes clear that the overlap of the spot damages to the electrically conductive layer tends to be much larger than the separation of the laser pitch. This means that there is physical discontinuity of tire electrically conductive layers due to the gap introduced by laser trenching.

[0091] The measurements shown in TABLE 3 illustrate what happens to the electrically conductive layer of a single glass sheet when exposed to the Bessel beam laser. In contrast, the methods disclosed herein related to laser cutting of multi-layered glass assemblies.

Accordingly, TABLE 4, FIGs. 9A-9B and FIGs.10A-10B illustrate an experiment in which two glass layers with electrically conductive layers being separated by a small gap (-90 pm). FIG. 9A shows the configuration used for this experiment, with the dotted line indicating where the laser went through the various surfaces. FIG. 9B is an image showing the separated edge of a top glass layer after separation. [0092] FIG. 10A is a top view, showing laser damage to the top glass surface in an image labeled SI. Here the top glass surface is clearly perforated.10 FIG. 10B is a top view showing an image, labeled S2, from the electrically conductive layer side after separation.

Tire increased impedance is a consequence of the laser ablation of the electrically conductive layer and, the material ejected from the S2 surface seems to be deposited on an image labeled S3, shown in FIG. 10C. Here, the impedance is still higher than the untouched electrically conductive layer (14 ohms) but beter than the S2 surface. FIG. 10D shows an image labeled S4 without any modification due to exposure to the Bessel beam laser, indicating that most of the laser energy has been reflected, absorbed or dissipated in SI, S2 and S3. The impedance increases by at least one order of magnitude on the S3 image. Ideally, the laser cutting methods disclosed herein minimize or maintain the original conductivity of the electrically conductive layer after cutting.

[0093] TABLE 5 and FIG. 11 illustrate aspects of another experiment in which a crack propagation control (CPC) Bessel beam laser was used. The laser focus height shown in FIG. 9A was also used in this experiment. As particularly shown in FIG. 1 1, a single glass layer was covered with an electrically conductive layer on the bottom after the glass layer was exposed to the CPC Bessel beam laser at different powers. Because of CPC was used, the defects or spots were effectively spaced apart by 25 pm, glass separation was attained as well as better conductivity on the electrically conductive layer (25 ohms) despite the width of the damaged spots. With increased laser power, slightly wider damage (—55 pm) and a moderate increase in impedance (—150 ohms) were apparent. The changes in impedance were observed to be slower becau se of the wider pitch allowed by the CPC Bessel beam laser.

TABLE 5: Impact on Electrically Conductive Layer after use of a CPC Bessel beam laser.

[0094] FIGs. 12A and 12B relate to another experiment in which a multi-layered glass assembly, having a top glass layer was cut on one side to expose the electrically conductive layer such that there was an overhang of the glass layer with respect to the electrically conductive layer. The oilier end of the glass layer was cut such that there was ‘‘flush” alignment. As shown particularly in FIG. 12B, the image labeled SI show's the surface of a top glass layer (after separation), the image labeled S2 shows the surface from the ITO side of the same glass layer. Tire image labeled “Edge” shows that full perforation was achieved, allowing for easy separation of the top glass layer. One interesting parameter of this experiment is that the impedance of S3 is generally equivalent to the impendence of a Bare electrically conductive layer that has not been exposed to a laser. Accordingly, the glass layer was effectively cut, and the original properties of the electrically conductive layer were generally unchanged.

[0095] Using the cutting method described with respect to FIGs. 12A and 12B, FIGs.

13A and 13B show in greater details the results of the experiment. In FIG. 13a, the dotted lines indicate position of the laser cut. This particular experiment used a 30 mm focal length lens and laser pitch of 25 um, 40 W of optical power at 100 kHz and burst of 7 pulses.

Moreover, the numerical aperture of the final focusing lens also impacted the size and separation of the damage spots caused by the CPC Bessel beam laser. In this case, a f = 30 mm lens was used. Use of this lens in combination with a wider pitch (25 pm) allowed the electrically conductive layer to maintain its original impedance of 14 ohms.

[0096] FIG. 14 compares standard Bessel beam laser cutting and its impact on the electrically conductive layer impedance to CPC Bessel beam laser cutting. In the latter case, the wider spacing between defects or spots not only prevents damage such as trenching to the electrically conductive layer but also keep the electrically conductivity of the electrically conductive layer intact.

[0097] It will be apparent to those skilled in tire art that various modifications and variations can be made without departing from the spirit or scope of the disclosure. The order of steps disclosed herein is meant to be illustrative and is not meant to limit the invention beyond the limitations explicitly set forth in the claims. Likewise, additional steps can be inserted between adjacent steps or executed in parallel or simultaneously, and still be within the scope and spirit of the invention as claimed. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the disclosure may occur to persons skilled in the art, the embodiments disclosed herein should be construed to include everything within the scope of the appended claims and their equivalents.

Claims

Claims What is claimed is:

1. A method of laser cutting a multi-layered glass assembly having at least one glass layer and at least one electrically conductive layer, comprising: focusing a laser beam into the multi-layered glass assembly such that an induced absorption is generated within the multi-layered glass assembly; translating the multi-layered glass assembly and the laser beam relative to each other; and exposing the at least one electrically conductive layer, wdierem the induced absorption produces at least one defect line on a surface of the multi-layered glass assembly such that the at least one electrically conductive layer is substantially damage-free after the at least one defect line is produced and a laser cut is initiated in the multi-layered glass assembly.

2. The method of claim 1 , further comprising cutting at least two glass layers such that an outermost edge of one glass layer is offset with respect to an outermost edge of the other glass layer,

3. The method of any one of claims 1-2, wherein the laser beam generated from a CPC Bessel beam laser.

4. The method of any one of claims 1 -3, wherein an impedance of the at least one electrically conductive layer after the at least one defect line is produced is substantially the same as the impedance of the at least one electrically conductive layer before the at least one defect line is produced.

5. The method of any one of claims 1 -4, wherein the at least one electrically conductive layer comprises indium-tin-oxide (ITO).

6. The method of any one of claims 1-4, further comprising controlling the direction of crack propagation with the laser beam

7. The method of any one of claims 1-5, wherein the at least one defect line comprises a plurality of defects spaced apart by a distance between 5 microns and 10 microns.

8. The method of any one of claims 1-5, further comprising creating a crack in a surface of the at least one glass layer that generates a separation path.

9. The method of any one of claims 1-7, further comprising exposing the at least one electrically conductive layer such that there is an overhang of at least one glass layer in the multi-layered glass assembly with respect to the at least one electrically conductive layer.

10. The method of any one of claims 1-7, wherein the at least one defect line extends at least 250 microns.

11. The method of any one of claims 1-10, wherein the multi-layered glass assembly comprises cladding and core layers with different coefficients of thermal expansion, with a total of three or more layers.

12. The method of any one of claims 1-11, further comprising separating the multilayered glass assembly along a contour.

13. The method of claim 12, wherein separating the multi-layered glass assembly along the contour includes directing the laser beam into the multi-layered glass assembly along or near the contour to facilitate separation of the multi-layered glass assembly along the contour.

14. The method of any one of claims 1 -13, wherein the laser beam has a wavelength and the multi-layered glass assembly is substantially transparent at the wavelength.

15. The method of claim 7, wherein the distance between each of the plurality of defects is substantially equidistant.

16. lire method of claim 7, wherein at least one of the plurality of defects has a damage width of about 60 um .

17. The method of claim 7, wherein at least one of the plurality of defects has a damage width of about 50 pm.

18. The method of claim 7, wherein at least one of the plurality of defects has a damage width of about 30 pm.

19. Tire method of claim 7, wherein at least one of the plurality of defects has a damage width of about 25 μm..

20. The method of any one of claims 1-13, wherein after the at least one defect line is produced the at least one electrically conductive layer has an impedance value between 10 ohms and 15 ohms.