Patent Publication Number: US-2020284953-A1

Title: Gap fill of imprinted structure with spin coated high refractive index material for optical components

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 16/120,733, filed Sep. 4, 2018, which claims benefit of U.S. Provisional Patent Application Ser. No. 62/692,247, filed on Jun. 29, 2018, which herein is incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments of the present disclosure generally relate to display devices for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide a method for forming an optical component for a display device. 
     Description of the Related Art 
     Virtual reality is generally considered to be a computer generated simulated environment in which a user has an apparent physical presence. A virtual reality experience can be generated in 3D and viewed with a head-mounted display (HMD), such as glasses or other wearable display devices that have near-eye display panels as lenses to display a virtual reality environment that replaces an actual environment. 
     Augmented reality enables an experience in which a user can still see through the display lenses of the glasses or other HMD device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as part of the environment. Augmented reality can include any type of input, such as audio and haptic inputs, as well as virtual images, graphics, and video that enhances or augments the environment that the user experiences. 
     Both virtual reality and augmented reality display devices utilize optical components, such as waveguides or flat lens/meta surfaces, including a patterned layer having high refractive index (RI), such as 1.7 or higher. The refractive index is a ratio of the speed of light in a vacuum to the speed of light in the medium. Conventional method for forming the patterned high RI layer includes pressing a stamp having the pattern onto a layer of nanoparticles of the high RI material to transfer the pattern to the layer of nanoparticles. The resulting patterned high RI layer has either non-uniform dispersion of the nanoparticles in the patterned high RI layer or brittle structure due to weak bonding between nanoparticles. 
     Accordingly, an improved method for forming optical components for virtual reality or augmented reality display devices is needed. 
     SUMMARY 
     Embodiments of the present disclosure generally relate to a method for forming an optical component, for example, for a virtual reality or augmented reality display device. In one embodiment, a method includes forming a first layer having a first refractive index on a substrate, pressing a stamp having a pattern onto the first layer, transferring the pattern to the first layer to form a patterned first layer, and forming a second layer having a second refractive index greater than the first refractive index on the patterned first layer by spin coating. 
     In another embodiment, a method includes forming a first layer having a first refractive index ranging from about 1.1 to about 1.5, pressing a stamp having a pattern onto the first layer, transferring the pattern to the first layer to form a patterned first layer, and forming a second layer having a second refractive index ranging from about 1.7 to about 2.4 on the patterned first layer by spin coating. 
     In another embodiment, a method includes forming a first layer having a first refractive index on a first surface of a substrate, pressing a first stamp having a first pattern onto the first layer, transferring the first pattern to the first layer to form a patterned first layer, and forming a second layer having a second refractive index ranging from about 1.7 to about 2.4 on the patterned first layer by spin coating. The second layer includes a metal oxide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments. 
         FIG. 1  is a flow diagram of a method for forming an optical component according to one embodiment described herein. 
         FIGS. 2A-2D  illustrate schematic cross-sectional views of the optical component during different stages of the method of  FIG. 1  according to one embodiment described herein. 
         FIGS. 3A-3D  illustrate schematic cross-sectional views of an optical component during different stages according to one embodiment described herein. 
         FIGS. 4A-4D  illustrate schematic cross-sectional views of an optical component according to embodiments described herein. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure generally relate to a method for forming an optical component, for example, for a virtual reality or augmented reality display device. In one embodiment, the method includes forming a first layer on a substrate, and the first layer has a first refractive index. The method further includes pressing a stamp having a pattern onto the first layer, and the pattern of the stamp is transferred to the first layer to form a patterned first layer. The method further includes forming a second layer on the patterned first layer by spin coating, and the second layer has a second refractive index greater than the first refractive index. The second layer having the high refractive index is formed by spin coating, leading to improved nanoparticle uniformity in the second layer. 
       FIG. 1  is a flow diagram of a method  100  for forming an optical component  200  according to one embodiment described herein.  FIGS. 2A-2D  illustrate schematic cross-sectional views of the optical component  200  during different stages of the method  100  of  FIG. 1  according to one embodiment described herein. The method  100  starts at block  102  by forming a first layer  204  having a first RI on a substrate  202 , as shown in  FIG. 2A . In one embodiment, the substrate  202  is fabricated from a visually transparent material, such as glass. The substrate  202  has a RI ranging from about 1.4 to about 2.0. The first layer  204  is fabricated from a transparent material, and the first RI ranges from about 1.1 to about 1.5. In one embodiment, the RI of the substrate  202  is the same as the first RI of the first layer  204 . In another embodiment, the RI of the substrate  202  is different from the first RI of the first layer  204 . The first layer  204  is fabricated from porous silicon dioxide, quartz, or any suitable material. In one embodiment, the first layer  204  is formed on the substrate  202  by spin coating. For example, a solution including a silicon precursor is spin-coated onto the substrate  202  and then heated in oxygen environment to form the first layer  204 . In some embodiments, there are no nanoparticles dispersed in the solution. The silicon precursor is dissolved in the solution. 
     Next, at block  104 , a stamp  206  having a pattern  208  is pressed onto the first layer  204 , as shown in  FIG. 2B . The stamp  206  is fabricated from any suitable material, such as silicon, quartz, glass, or a polymer. The polymer may be polyurethane, polybutadiene, polyisoprene, or poly(dimethylsiloxane) (PDMS). The pattern  208  formed on the stamp  206  may include a plurality of protrusions  210  and a plurality of gaps  212 . Adjacent protrusions  210  are separated by a gap  212 . The protrusions  210  may have any suitable shape. After the stamp  206  is pressed onto the first layer  204 , a curing process may be performed to cure the first layer  204 . The curing process may utilize UV light or thermal energy to cure the first layer  204 . 
     After the first layer  204  is cured, the stamp  206  is removed from the cured first layer  204 , and the pattern  208  of the stamp  206  is transferred to the cured first layer  204  to form a patterned first layer  214 , as shown at block  106  in  FIG. 1  and in  FIG. 2C . The pattern  208  of the patterned first layer  214  includes a plurality of protrusions  216  and a plurality of gaps  218 . Adjacent protrusions  216  are separated by a gap  218 . As shown in  FIG. 2C , the protrusion  216  has a rectangular shape. The protrusion  216  may have any other suitable shape. Examples of the protrusion  216  having different shapes are shown in  FIGS. 4A-4D . In one embodiment, the protrusions  216  are gratings. Gratings are a plurality of parallel elongated structures that splits and diffracts light into several beams traveling in different directions. Gratings may have different shapes, such as sine, square, triangle, or sawtooth gratings. Because the first layer  204 , or the patterned first layer  214 , does not contain any nanoparticles, there are no non-uniformity issues. Furthermore, the removal of the stamp  206  from the patterned first layer  214  does not damage the patterned first layer  214 , because the patterned first layer  214  is not formed by packing nanoparticles. 
     Next, at block  108 , a second layer  220  having a refractive index greater than that of the first layer  204  is formed on the patterned first layer  214  by spin coating, as shown in  FIG. 2D . The second layer  220  includes metal oxides, such as titanium oxide (TiO x ), tantalum oxide (TaO x ), zirconium oxide (ZrO x ), hafnium oxide (HfO x ), or niobium oxide (NbO x ). In one embodiment, the second layer  220  has a RI ranging from about 1.7 to about 2.4. In one embodiment, the second layer  220  includes nanoparticles of the metal oxides dispersed in a polymer matrix or a carrier liquid, and the nanoparticles are uniformly distributed throughout the second layer  220  due to the spin coating method. Furthermore, because the patterned first layer  214  has the pattern  208  formed thereon, the second layer  220  is also patterned as the second layer  220  is spin coated on the patterned first layer  214 . As shown in  FIG. 2D , the second layer  220  includes a plurality of protrusions  222 , and each protrusion  222  is formed in a corresponding gap  218  (as shown in  FIG. 2C ) of the patterned first layer  214 . The protrusions  216  of the patterned first layer  214  and the protrusions  222  of the second layer  220  are alternately positioned. Because the pattern of the second layer  220 , i.e., the protrusions  222 , are formed without using a stamp to press thereonto, the pattern of the second layer  220  is not damaged and the nanoparticles of the metal oxide material are uniformly distributed in the second layer  220 . 
     After the spin coating of the second layer  220 , a curing process may be performed to cure the second layer  220 . The curing process of the second layer  220  may be the same as the curing process of the patterned first layer  214 . The optical component  200  including layers having different RIs may be used in any suitable display devices. For example, in one embodiment, the optical component  200  is used as a waveguide or waveguide combiner in augmented reality display devices. Waveguides are structures that guide optical waves. Waveguide combiners are used in augmented reality display devices that combine real world images with virtual images. In another embodiment, the optical component  200  is used as a flat lens/meta surfaces in augmented and virtual reality display devices and 3D sensing devices, such as face ID and LIDAR. 
       FIGS. 2A-2D  illustrate the method  100  for forming the optical component  200  including layers having different RIs on one side of the substrate  202 . In some embodiments, both sides of the substrate  202  can be utilized to form layers having different RIs thereon.  FIGS. 3A-3D  illustrate schematic cross-sectional views of an optical component  300  during different stages according to one embodiment described herein. As shown in  FIG. 3A , the substrate  202  includes a first surface  302  and a second surface  304  opposite the first surface  302 . The patterned first layer  214  and the second layer  220  are formed on the first surface  302  of the substrate  202 , as described in  FIGS. 2A-2D . Next, a third layer  306  is formed on the second surface  304  of the substrate  202 , and the third layer  306  is patterned by the stamp  206 , as shown in  FIG. 3B . The third layer  306  may be fabricated from the same materials as the first layer  204  (as shown in  FIG. 2A ). The third layer  306  may be formed by the same process as the first layer  204 . The stamp  206  includes the pattern  208 . 
     Next, as shown in  FIG. 3C , the pattern  208  of the stamp  206  is transferred to the third layer  306  to form a patterned third layer  308 , and the stamp  206  is removed from the patterned third layer  308 . The patterned third layer  308  is cured by a curing process similar to the curing process performed on the patterned first layer  214  prior to removal of the stamp  206 . The patterned third layer  308  includes a plurality of protrusions  310  and a plurality of gaps  312 . Adjacent protrusions  310  are separated by a gap  312 . The patterned third layer  308  may be fabricated from the same material as the patterned first layer  214  and may have the same pattern as the patterned first layer  214 . In other words, the patterned third layer  308  may be identical to the patterned first layer  214 . In some embodiments, the patterned third layer  308  has a different pattern than the patterned first layer  214 . Next, as shown in  FIG. 3D , a fourth layer  316  is formed on the patterned third layer  308  by spin coating. The fourth layer  316  may be identical to the second layer  220  and may be fabricated by the same method as the second layer  220 . The fourth layer  316  includes a pattern, such as the plurality of protrusions  318 . The protrusions  310  of the patterned third layer  308  and the protrusions  318  of the fourth layer  316  are alternately positioned. The optical component  300  includes layers having different RIs formed on two surfaces of the substrate  202 . The optical component  300  may be used in any suitable display devices. For example, in one embodiment, the optical component  300  is used as a waveguide or waveguide combiner in augmented reality display devices. In another embodiment, the optical component  300  is used as a flat lens/meta surfaces in augmented and virtual reality display devices and 3D sensing devices, such as face ID and LIDAR. 
       FIGS. 4A-4D  illustrate schematic cross-sectional views of an optical component  400  according to embodiments described herein. As shown in  FIG. 4A , the optical component  400  includes the substrate  202 , the patterned first layer  214  disposed on the substrate  202 , and the second layer  220  disposed on the patterned first layer  214 . The patterned first layer  214  includes a plurality of protrusions  402 , and the second layer  220  includes a plurality of protrusions  403 . Each of the protrusions  402 ,  403  has a parallelogramical cross-sectional area, as shown in  FIG. 4A . The protrusions  402 ,  403  may be gratings. 
     As shown in  FIG. 4B , the optical component  400  includes the substrate  202 , the patterned first layer  214  disposed on the substrate  202 , and the second layer  220  disposed on the patterned first layer  214 . The patterned first layer  214  includes a plurality of protrusions  404 , and the second layer  220  includes a plurality of protrusions  405 . Each of the protrusions  404 ,  405  has a triangular cross-sectional area, as shown in  FIG. 4B . The protrusions  404 ,  405  may be gratings. 
     As shown in  FIG. 4C , the optical component  400  includes the substrate  202 , the patterned first layer  214  disposed on the first surface  302  of the substrate  202 , and the second layer  220  disposed on the patterned first layer  214 . The patterned first layer  214  includes the plurality of protrusions  402 , and the second layer  220  includes the plurality of protrusions  403 . The optical component  400  further includes the patterned third layer  308  disposed on the second surface  304  of the substrate  202  and the fourth layer  316  disposed on the patterned third layer  308 . The patterned third layer  308  includes a plurality of protrusions  406 , and the fourth layer  316  includes a plurality of protrusions  407 . The protrusions  406 ,  407  may be substantially the same as the protrusions  402 ,  403 , respectively. The protrusions  402 ,  403 ,  406 ,  407  may be gratings. 
     As shown in  FIG. 4D , the optical component  400  includes the substrate  202 , the patterned first layer  214  disposed on the first surface  302  of the substrate  202 , and the second layer  220  disposed on the patterned first layer  214 . The patterned first layer  214  includes the plurality of protrusions  404 , and the second layer  220  includes the plurality of protrusions  405 . The optical component  400  further includes the patterned third layer  308  disposed on the second surface  304  of the substrate  202  and the fourth layer  316  disposed on the patterned third layer  308 . The patterned third layer  308  includes a plurality of protrusions  408 , and the fourth layer  316  includes a plurality of protrusions  409 . The protrusions  408 ,  409  may be substantially the same as the protrusions  404 ,  405 , respectively. The protrusions  404 ,  405 ,  408 ,  409  may be gratings. The optical component  400  may be used in any suitable display devices. For example, in one embodiment, the optical component  400  is used as a waveguide or waveguide combiner in augmented reality display devices. In another embodiment, the optical component  400  is used as a flat lens/meta surfaces in augmented and virtual reality display devices and 3D sensing devices, such as face ID and LIDAR. 
     A method for forming an optical component including layers having different RIs is disclosed. A pattern is formed in the layer having a lower RI, and the layer having a higher RI is spin coated on the patterned layer with the lower RI. The spin coated layer having the higher RI has improved uniformity of nanoparticles of the high RI material. Furthermore, the layer having the higher RI is not damaged because imprinting of the layer having the higher RI using a stamp is avoided. The application of the optical component is not limited to augmented and virtual reality display devices and 3D sensing devices. The optical component can be used in any suitable applications. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.