Patent Publication Number: US-2022227081-A1

Title: Method of replicating optical elements and replicated optical elements

Description:
TECHNICAL FIELD 
     This disclosure relates to replicated optical elements. 
     BACKGROUND 
     Optical devices that include one or more optical light emitters and one or more optical sensors can be used in a wide range of applications including, for example, distance measurement, proximity sensing, gesture sensing, and imaging. Small optoelectronic modules such as imaging devices and light projectors employ optical assemblies that include lenses or other optical elements stacked along the device&#39;s optical axis to achieve desired optical performance. Replicated optical elements include transparent diffractive and/or refractive optical elements for influencing an optical beam. In some applications, such optoelectronic modules can be integrated into various consumer electronics, such as portable computing devices (e.g., smart phones, tablets, wearables, and laptop computers). 
     SUMMARY 
     The present disclosure describes techniques for controlling the flow of replication material (e.g., epoxy) during the formation of replicated optical elements. In general, flow barriers such as trenches and/or walls laterally surrounding an aperture in a coating on a transparent substrate help control the flow of replication material during the formation of a replicated optical element on the aperture. 
     For example, in one aspect, the present disclosure describes a method including providing a transparent substrate having a coating on its surface, wherein the coating includes an aperture therein. The coating further has at least one trench therein, wherein the at least one trench laterally surrounds the aperture. The method includes using a replication technique to form an optical element on the transparent substrate in the aperture, the optical element being composed of replication material. The at least one trench serves as a barrier to flow of the replication material. 
     This disclosure also describes an apparatus including a transparent substrate having a coating on its surface, wherein the coating includes an aperture therein. The coating further has at least one trench therein, wherein the at least one trench laterally surrounds the aperture. A replicated optical element is on the transparent substrate and is disposed within the aperture. The optical element has a yard portion extending laterally in a direction from the aperture toward the at least one trench. 
     In another aspect, the present disclosure describes a method including providing a transparent substrate having a coating on its surface, wherein the coating includes an aperture therein. At least one wall is disposed on the coating and laterally surrounds the aperture. The method includes using a replication technique to form an optical element on the transparent substrate in the aperture, the optical element being composed of replication material. The at least one wall serves as a barrier to flow of the replication material. 
     The disclosure also describes an apparatus including a transparent substrate having a coating on its surface, wherein the coating includes an aperture therein. The coating further has at least one wall thereon, wherein the at least one wall laterally surrounds the aperture. A replicated optical element is on the transparent substrate and is disposed within the aperture. The optical element has a yard portion extending laterally in a direction from the aperture toward the at least one wall. 
     Some implementations include one or more of the following features. For example, in some cases, the apparatus includes a light emitting or light sensing device having an optical axis aligned with the optical element. In some implementations, there are a plurality of trenches laterally surrounding the aperture. The optical element can be, for example, a microlens array. In some instances, the coating is composed of a chrome. 
     Other aspects, features, advantages will be apparent from the detailed description, the accompanying drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional view of a tool-substrate structure for replication. 
         FIG. 2  shows a replicated optical element having a yard portion. 
         FIG. 3  illustrates a cross-sectional view of a portion of the yard portion. 
         FIG. 4A  is a top view of a substrate including flow barriers. 
         FIG. 4B  is a cross-sectional view taken through the circle A of  FIG. 4A  showing the flow of replication material. 
         FIG. 5A  illustrates a cross-sectional view of another implementation of flow barriers. 
         FIG. 5B  is a cross-sectional view taken through the circle B of  FIG. 5A  showing the flow of replication material. 
         FIG. 6  shows a replicated optical element having a yard portion on a transparent substrate. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically shows a cross section of a replication tool  101 , and a transparent substrate  120  onto which optical elements are to formed by replication. The tool  101  includes a rigid or relatively hard back plate  102  composed of a first material, for example glass, and a replication portion  104  composed of a second, softer material, for example polydimethylsiloxane (PDMS). The relatively low stiffness of the replication portion  104  can allow the replication portion, under “normal” conditions (e.g., where no more pressure than the one caused by gravity forces of the tool lying on the substrate or vice-versa), to adapt to roughness, e.g., on a micrometer and/or sub-micrometer scale and, thus, may form an intimate connection to the substrate surface when they are brought into contact with one another. 
     The replication portion  104  forms a replication surface  108  including replication sections  106 , the surface of each of which is a (negative) copy of a surface shape an optical element to be manufactured by replication. The optical elements to be manufactured by replication may be, for example, lenses, diffusers, or other optical elements. In some instances, each optical element to be replicated is a microlens array (MLA). In some cases, the replication sections  106  can be, for example, convex and thus define a concave optical element surface, or can be convex and define a concave optical element surface. 
     The replication portion  104  has contact spacer portions  112  arranged peripherally. The contact spacer portions  112  are the structures of the replication tool  101  that protrude the furthest from the tool  101  along the z axis. The contact spacer portions  112  are essentially flat and, thus, are operable to rest against the substrate  120  during replication, with no material between the contact spacer portions  112  and the substrate  120 . The contact spacer portions  112  may, for example, form a ring laterally surrounding the periphery of the replication surface  108 , or may form discrete portions around the periphery. 
     The substrate  120  has a first side (e.g., substrate surface  126 ) and a second side and can be composed of any suitable material, for example glass. The substrate surface  126  may have a structure to which the replica is to be aligned. The structure may, for example, comprise a coating  122  structured in the x-y-plane, such as a screen with apertures, or a structured IR filter etc. The structure may in addition, or as an alternative, comprise further features like markings. 
     For replicating the replication surface  108  of the tool  101 , replication material  124  is applied to the substrate  120  or the tool  101  or both the tool  101  and the substrate  120 . Although a single portion of replication material  124  is illustrated in the figure, application of the replication material  124  may include applying multiple portions of replication material  124  (e.g., a respective portion for each of the replication sections  106 ). Each portion may, for example, be applied by dispensing (e.g., jetting) one or more droplets using a dispensing tool. The replication material  124  can be composed, for example, of epoxy. 
     After application of the replication material  124 , the substrate  120  and the tool  101  are aligned with respect to one another, for example, at an alignment station. Subsequent to the alignment, the substrate  120  and the tool  101  are brought together, with the contact spacer portions  112  resting against the substrate surface so as to define the height in the z dimension and also to lock the tool against x-y-movements. After the replication tool  101  and the substrate  120  have been moved towards each other with the replication material  124  between them, the substrate-tool-assembly can be removed from the alignment station and transferred to a hardening station, where the replication material  124  is hardened (e.g., cured). The replication tool  101  then can be removed. 
     Referring to  FIG. 2 , during replication, excess replication material or epoxy applied, for example, during jetting normally overflows the region of interest and forms a yard  130  when the tool and the substrate  120  are brought into contact. The yard  130  sometimes is annular or ring shaped and laterally surrounds the optical element  131 . The yard  130  results from more epoxy  124  being added during the replication process than each replicated structure (e.g., optical element) requires, causing an overflow. The additional epoxy ensures that the complete volume of replication material needed for a particular structure is available (as the tolerance of the epoxy volume is not zero), and the extra fluid pools to form the yard  130 . 
       FIG. 3  illustrates a cross-sectional view of a portion of the yard  130 , which sometimes includes a relatively thin membrane or overflow region  132 . The overflow region  132  may have a thickness on the order of less than 5 μm, with outer portions of the region  132  having a thickness of less than 1 μm. The epoxy used as the replication material  124  typically includes a photo-initiator, which allows the epoxy to be cured, for example, by the application of ultra-violet (UV) radiation. However, for thin sections of the yard (e.g., overflow region  132 ), there may be little or no photo-initiator present, such that the replication material  124  is not fully cured, and remains in a liquid state, even after application of the UV radiation. In the example of  FIG. 3 , the dashed-dotted line  136  indicates the minimum height of the replication material required for UV curing to be effective. The failure to achieve complete curing of the replication material  124  can be problematic, for example, because the epoxy may flow out to the edge of the module and may result in reliability issues. In  FIG. 3 , the arrow  138  indicates the direction of flow of uncured replication material. 
     To help prevent the formation of thin membrane or thin overflow regions  132  during the replication process, flow barriers can be provided on the substrate  120  so as to control the flow of the epoxy. A first example is illustrated in  FIGS. 4A and 4B . As shown in  FIG. 4A , a metal (e.g., a compound or alloy of chromium; chrome)  140  may be provided on the surface of the glass substrate  120 . Respective openings in the coating  140  (e.g., opening  142 ) define apertures onto which the optical elements are replicated. The apertures  142  can be formed, for example, by selectively etching the chrome coating  140  using standard etchants (e.g., ceric ammonium nitrate). During the replication process, some of the replication material (e.g., the epoxy) is dispensed or flows onto the surrounding coating  140  and forms the yard portion of the replicated element. As shown in  FIGS. 4A and 4B , one or more rectangular or annular trenches  144  laterally surround each respective aperture  142  so as to control the flow of the replication material  124  and, preferably, prevent formation of very thin overflow regions. The trenches  144  can be formed, for example, by selectively etching away the chrome coating  140  at the same time the apertures  142  are formed. The concave step(s) provided by the trench(s)  144  allow excess epoxy from the overflow replication material  124  to flow into, and accumulate in, the trench(es)  144  so as to reduce the likelihood of very thin (e.g., &lt;5 μm) regions of epoxy forming at the perimeter of the yard  130 . The presence of the trenches  144  in the coating  140  thus provides barriers to the flow of the replication material  124 . In some instances, a single trench  144  may be sufficient. In other cases, it may be beneficial to provide two or more trenches  144 , as shown in  FIG. 4B . 
     In some instances, instead of forming trenches  144  in the chrome coating  140 , one or more layers are added selectively over portions of the chrome coating  140  so as to form one or more respective walls  152  encircling the aperture  142  on which the optical element is replicated (see  FIGS. 5A and 5B ). The additional layer(s) for the walls  152  can include, for example, SiO 2 , chrome and/or gold, depending on the particular application. Other materials also can be used for the walls  152 . The presence of the walls  152  on the coating  140  thus provides barriers to the flow of the replication material  124 . If more than one wall  152  is present, the walls  152  can be separated by a narrow space  154 , which also can help control the flow of replication material  124  in the event, e.g., some of the replication material flows over one of the walls. 
     In some instances, the presence of the replication material flow barriers ( 144  and/or  152 ) can help improve the yield in the manufacturing process. The flow barriers also can serve as guidelines for visual inspection during the manufacture process, and in some cases, can help increase the accuracy of such inspections and may reduce manual inspection times. 
     The foregoing techniques can be performed, for example, at a wafer-level in which a glass or other transparent substrate has a metal (e.g., chrome) coating on its surface, where the coating has multiple apertures therein, each of which is surrounded by a respective one or more trenches (or walls) that serve as barriers to help control the follow of the replication material (e.g., epoxy) during the replication process. An optical element (e.g., a MLA) is replicated onto each of the apertures. The sub-assembly, including the transparent substrate having the replicated optical elements on its surface, then can be attached, for example, to another substrate (e.g., a printed circuit board) on which are mounted multiple light emitting devices (e.g., VCSELs, laser diodes, or LEDs). Each of the optical elements is aligned to an optical axis of a respective one of the light emitting devices. The stack of substrates then can be separated (e.g., by dicing) to form individual modules or packages each of which includes a light emitting device and an optical element. In this context, the substrate is “transparent” in the sense that it is substantially transparent to a wavelength of radiation (e.g., visible, infra-red (IR) or ultra-violet (UV)) emitted by the light emitting device. 
     In some implementations, the transparent substrate having the replicated optical elements on its surface is separated into individual units each of which includes a single one of the replicated optical elements (e.g., MLAs). The replicated optical elements then can be positioned (e.g., by pick-and-place equipment), for example, over a light emitter such as a VCSEL, an LED or laser diode as part of an optoelectronic package. 
     Providing barriers ( 144  and/or  152 ) as described below to control or restrict the flow of the replication material  124  can be advantageous for additional reasons as well. The replication material flow barriers can be useful in defining the outline or lateral shape of the replication material on the substrate  120 . Thus, in some instances, the outline of the replication material can be set such that regions of the substrate  120  remain uncovered by the replication material. For example, as shown in  FIG. 6 , even accounting for the yard portion  130  of the optical element  131 , regions  150  of the transparent substrate  120  will not be covered by the excess replication material (i.e., the yard  130 ). When the substrate  120  is singulated into individual optical units, the substrate can be diced along lines that do not cut through the replication material, including the yard  130 . This technique can be advantageous because it can help reduce the likelihood that the replication material (e.g., the epoxy) delaminates. Further, the regions  150  of the substrate  120  where there is no replication material present can be used to clamp the optical unit during its assembly into an optoelectronic module so as to hold the optical unit in place. Avoiding attaching, for example, a jig to regions of the substrate  120  where replication material is present can help reduce the occurrence of reliability problems. 
     In some instances, a sub-assembly, including the transparent substrate having the replicated optical elements on its surface, is attached, for example, to another substrate (e.g., a printed circuit board) on which are mounted multiple light (e.g., visible, IR or UV) sensors. In this context, the substrate is “transparent” in the sense that it is substantially transparent to a wavelength of radiation (e.g., visible, infra-red (IR) or ultra-violet (UV)) detectable by the light sensor. 
     Other implementations are within the scope of the claims.