Apparatus and methods of electrically conductive optical semiconductor coating

Abstract

To provide optics, and more specifically, electrically conductive coatings for broadband optics.SOLUTION: A method of coating an optical substrate with a transparent, electrically conductive coating includes depositing a semiconductor coating over a surface of an optical substrate. The semiconductor coating has broadband optical transmittance. Channels are formed in the semiconductor coating. The method includes coating over the semiconductor coating and filling the channels with a doped semiconductor. The doped semiconductor is removed from the semiconductor coating, leaving the doped semiconductor in the channels.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to optical components, and more particularly to conductive coatings for broadband optical components. [Background technology]

[0002] Electro-optical (EO) systems require windows to protect the sensors and electronics from the outside elements, and in addition to rain, dust, etc., windows often must also block electromagnetic interference (EMI) that can otherwise interfere with EO system performance.

[0003] EMI shielding can be achieved using windows that are both electrically conductive and optically transparent. There are three conventional types of shielding:

[0004] The first type of EMI shielding window uses a semiconductor material such as silicon or germanium that is doped with a Group V element such as phosphorus, arsine, or antimony to supply additional electrons to provide electrical conductivity. These windows are opaque to visible wavelengths and therefore useless for broadband EO systems.

[0005] The second type of shielding window uses a continuous, transparent conductive paint. These paints consist of wide bandgap semiconductors such as indium oxide (In2O3) and zinc oxide (ZnO), which have broadband optical transmittance. The semiconductors are doped to provide electrical conductivity. However, as doping is increased to increase electrical conductivity and EMI attenuation, the optical transmittance decreases. This effect begins at longer wavelengths where both plasma reflectance and free carrier absorption from electrons decrease transmittance. Conventional transparent conductive semiconductor coatings are only practical in the 0.4 to 2.0 micron range, from short wavelength visible to short wavelength infrared (SWIR).

[0006] A third type of shielded window is traditionally required for broadband applications from visible infrared to long wave infrared (LWIR). A grid of fine metal lines is applied to the surface of the window. Typical dimensions are 5 micron wide lines spaced 140 microns apart. These gridded windows allow light transmission over a wide wavelength range, but gridded windows limit light transmission through obscuration and scattering.

[0007] US Patent No. 9,276,034 presents a method for reducing optical scattering from a conductive grid. Grooves are etched into a window substrate and a conductive semiconductor is deposited into the grooves such that the window surface is planar. The semiconductor is transparent to visible and short wave infrared (SWIR) wavelengths, but reflective and absorptive to mid wave infrared (MWIR) and longer wavelengths. Using a semiconductor with a refractive index close to that of the substrate minimizes light scattering from the grid lines.

[0008] Conventional techniques have been deemed satisfactory for their intended purposes. However, there is a continuing need for improved conductive optical coatings for broadband optics. The present disclosure provides a solution to this problem. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 9,276,034 Summary of the Invention [Means for solving the problem]

[0010] A method of coating an optical substrate includes depositing a semiconductor coating on a surface of the optical substrate. The semiconductor coating has broadband optical transmittance. A groove is formed in the semiconductor coating. The method includes coating over the semiconductor coating and at least partially filling the groove with a conductive doped semiconductor. The doped semiconductor is removed from the semiconductor coating, leaving at least a portion of the doped semiconductor in the groove.

[0011] Forming the grooves may include applying a photoresist onto the semiconductor coating. The photoresist may be selectively exposed in a pattern and developed. The semiconductor coating may be etched in the pattern. The photoresist may be removed leaving the grooves in the pattern on the semiconductor coating. Forming the grooves may include etching the grooves using at least one of chemical etching, reactive ion etching, or ion beam milling.

[0012] Coating with a doped semiconductor on the semiconductor coating may include applying the doped semiconductor by a thin film coating. The pattern may be configured to provide electromagnetic interference (EMI) shielding to the optical substrate. The pattern may include a grid. Removing the doped semiconductor from the semiconductor coating may include polishing to form a flat surface on the semiconductor coating and the doped semiconductor in the grooves.

[0013] A protective coating can be applied over the semiconductor coating and the doped semiconductor in the trench. The method can include depositing a broadband anti-reflective coating over the protective coating. It is also contemplated that the method can include depositing a broadband anti-reflective coating, for example directly, over the semiconductor coating and the doped semiconductor in the trench.

[0014] The semiconductor coating may include at least one of In2O3 or ZnO. The doped semiconductor may include at least one of Sn, Mo, W, or Ti for In2O3, or Al or Ga for ZnO, for example. The undoped semiconductor coating may have broadband optical transmittance at least from the visible short wavelength to the long wavelength infrared (LWIR) spectrum. Depositing the semiconductor coating may include depositing the semiconductor coating while the semiconductor coating is undoped.

[0015] Depositing the semiconductor coating may include depositing the semiconductor coating generally on the surface of the optical substrate, and forming the grooves and leaving at least a portion of the doped semiconductor in the grooves may include forming the pattern such that the surface of the semiconductor coating is generally covered by the pattern.

[0016] The doped semiconductor, semiconductor coating, and optical substrate can be formed in the window without patterning or etching the optical substrate. The doped semiconductor and semiconductor coating can have closely matched refractive indices to reduce light scattering. The window can be produced by any embodiment of the process described above. The window can include a transparent substrate having a transparent semiconductor coating with a trench filled with a doped semiconductor.

[0017] These and other features of the disclosed systems and methods will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

[0018] Preferred embodiments thereof are described in detail herein below with reference to specific figures so that those skilled in the art to which the disclosure pertains will readily understand how to make and use the disclosed apparatus and methods without undue experimentation. [Brief description of the drawings]

[0019] [Figure 1]1 is a schematic cross-sectional elevation view of an exemplary embodiment of an optical component constructed in accordance with the present disclosure showing a semiconductor coating having broadband optical transmittance deposited on a surface of an optical substrate. [Diagram 2] 2 is a schematic cross-sectional elevation view of the optical component of FIG. 1 showing grooves defined by a pattern in a semiconductor coating. [Diagram 3] 1 is a flow diagram of an exemplary embodiment of a process according to the present disclosure showing a process for creating grooves in a semiconductor coating. [Figure 4] 2 is a schematic cross-sectional elevation view of the optical component of FIG. 1 showing a doped semiconductor coated over the semiconductor coating and within the grooves. [Diagram 5] 2 is a schematic cross-sectional elevation view of the optical component of FIG. 1 showing the doped semiconductor removed from the semiconductor coating but remaining in the grooves. [Figure 6] 2 is a schematic plan view of the optical substrate of FIG. 1 showing an exemplary grid pattern. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Reference is now made to the drawings in which like reference numerals identify similar structural features or aspects of the present disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of an optical component according to the present disclosure is shown in FIG. 1 and generally designated by the reference character 100. Other embodiments of optical components according to the present disclosure, or aspects thereof, are provided in FIGS. 2-6 as illustrated. The systems and methods described herein can be used to provide a conductive coating to an optical component, such as a window, where the coating has broadband optical transmittance.

[0021] The method of coating the optical substrate 102 with a transparent conductive coating includes depositing a semiconductor coating 104 on a surface of the optical substrate 102. The semiconductor coating 104 has a broadband optical transmittance. The semiconductor coating 104 may include at least one of indium oxide (In2O3) or zinc oxide (ZnO). Those skilled in the art will readily appreciate that any other suitable type of semiconductor material or alloys thereof may be used without departing from the scope of the present disclosure. The semiconductor coating 104 may have a broadband optical transmittance at least in the visible and infrared spectrum, such as, for example, long-wave infrared. Depositing the semiconductor coating 104 may include depositing the semiconductor coating in a state where the semiconductor coating is undoped. Depositing the semiconductor coating 104 may include depositing the semiconductor coating generally on a surface of the optical substrate 102, such as, for example, the top surface of the optical substrate 102 as positioned in FIG. 1.

[0022] As shown in Figure 2, the grooves 105 are formed in the semiconductor coating 104 in a pattern 108 as shown in Figure 6. With reference to Figure 3, forming the grooves 105 in the pattern 108 may include applying a photoresist over the semiconductor coating 104 as shown in box 110 of Figure 3. The photoresist may be selectively exposed in the pattern 108 and developed as shown in box 112. The semiconductor coating 104 may then be etched in the pattern 108 as shown in box 114. The photoresist may then be removed to leave the grooves 105 in the pattern 108 on the semiconductor coating 104 as shown in box 116. Forming the grooves 105 may include etching the grooves using at least one of chemical etching, reactive ion etching, or ion beam milling.

[0023] As shown in FIG. 4, the method includes coating on the semiconductor coating 102 and filling the grooves 105 with a doped semiconductor 106. Coating on the semiconductor coating 102 with the doped semiconductor 106 may include at least one of applying the doped semiconductor 106 by thin film coating or applying the doped semiconductor 106 by any other suitable process. The doped semiconductor may include at least one of Sn, Mo, W, Ti, Al, Ga, or any other suitable material for electrical conductivity. For example, if the semiconductor coating 104 includes undoped In2O3, the doped semiconductor 106 may include In2O3 doped with Sn, Mo, W, or Ti. In another example, if the semiconductor coating 104 includes undoped ZnO, the doped semiconductor 106 may include ZnO doped with Al or Ga.

[0024] Referring now to FIG. 5, the doped semiconductor 106 is removed from the semiconductor coating 102, leaving the doped semiconductor 106 in the grooves 105. Removing the doped semiconductor 106 from the semiconductor coating 104 includes polishing to form a flat surface on the semiconductor coating 104 and the doped semiconductor 106 in the grooves 105, as shown in FIG. 5. This forms the grid pattern 108 shown in FIG. 6 of the doped semiconductor 106 of the semiconductor coating 102. If the doped semiconductor is conductive when applied, it does not need to be activated. Polishing is one example of a technique for providing a final flat surface. Another example is to coat the doped semiconductor on a patterned photoresist and then lift off the doped semiconductor by removing, for example, by dissolving the photoresist.

[0025] 6, the pattern 108 of doped semiconductor 106 can be configured to provide electromagnetic interference (EMI) shielding to the optical substrate, for example, in any suitable grid pattern. For example, to EMI shield broadband optical components with a grid having optical transmittance in the visible and long wave infrared, a square grid having 5 micron wide lines with 140 micron spacing between the grid lines can be used. Forming the grooves 105 and leaving the doped semiconductor 106 in the grooves 105 can include applying the doped semiconductor 106 to the surface of the semiconductor coating 104 such that the surface of the semiconductor coating 104 is generally covered with the pattern shown in FIG. 6. The grid pattern 108 shown in FIG. 6 is schematic and not necessarily to scale.

[0026] 5, a protective coating 118 can be applied over the semiconductor coating 104 and the doped semiconductor 106 remaining in the grooves 105. The method can include depositing a broadband anti-reflective coating 120 over the protective coating 118. It is also contemplated that the broadband anti-reflective coating 120 can be applied directly over the semiconductor coating 104 and the doped semiconductor 106, such as by omitting the protective coating 118. Although shown as a single layer, the broadband anti-reflective coating can be comprised of multiple layers.

[0027] The doped semiconductor 106, the semiconductor coating 104, and the optical substrate 102 can be formed into an optical component 100, such as a window, with a conductive coating for EMI shielding, heating, etc., without patterning or etching the optical substrate 102 itself. This can be advantageous because it allows a single etching process to be used regardless of which material is used for the optical substrate 102. The doped semiconductor 106 and the semiconductor coating 104 have closely matched refractive indices to reduce scattering of visible and near-infrared light through the grid pattern. If the ratio of the refractive indices of the doped semiconductor and the semiconductor coating is between 0.82 and 1.22, the interface reflection will be less than 1% at normal incidence. For example, the refractive indices of doped In2O3 and undoped In2O3 at 632.8 nm are 2.00 and 1.77, respectively. A refractive index of 1.13 will result in a reflection of only 0.37%.

[0028] Those skilled in the art will readily appreciate that the order of layers of doped and undoped semiconductors, although shown and described above in the exemplary situation of first depositing an undoped semiconductor coating, etching trenches therein, and depositing a doped semiconductor in the trenches, can be reversed. In this example, the optical substrate 102 is covered with a doped semiconductor, e.g., having a low resistivity. The trenches are etched with a doped semiconductor coating, leaving a conductive grid pattern. The trenches are filled with a semiconductor having a broadband optical transmittance, and the surface can be finished as described above.

[0029] Those skilled in the art will readily understand that the doped and undoped semiconductors described herein are doped and undoped with respect to one another. In other words, the doped semiconductors described herein are doped to have enhanced electrical conductivity relative to the respective undoped semiconductors described herein. The undoped semiconductors described herein need not be free of all other dopants.

[0030] The methods and systems of the present disclosure, as described above and illustrated in the drawings, provide conductive coatings with superior properties, including broadband optical transmittance. Although the apparatus and methods of the present disclosure have been shown and described with respect to preferred embodiments, those skilled in the art will readily appreciate that changes and / or modifications may be made thereto without departing from the scope of the present disclosure. [Explanation of symbols]

[0031] 100 Optical Components 102 Optical board 104 Semiconductor Coating 105 Groove 106 Doped Semiconductors 108 Patterns 118 Protective Coating 120 Broadband Anti-Reflection Coating

Claims

1. 1. A method for coating an optical substrate, comprising the steps of: depositing a semiconductor coating on a surface of an optical substrate, the semiconductor coating having a broadband optical transmittance; forming a groove in the semiconductor coating; coating over the semiconductor coating to at least partially fill the grooves with a conductive doped semiconductor; removing at least a portion of the doped semiconductor from the semiconductor coating leaving at least a portion of the doped semiconductor in the groove; A method comprising:

2. The step of forming a groove comprises: applying a photoresist over said semiconductor coating; selectively exposing the photoresist to light and developing the photoresist in a pattern; Etching the semiconductor coating with the pattern; removing the photoresist to leave the grooves in the pattern of the semiconductor coating; The method of claim 1 , comprising:

3. The method of claim 2 , wherein the pattern comprises a grid.

4. The method of claim 1 further comprising applying a protective coating over said semiconductor coating and said doped semiconductor in said grooves.

5. The method of claim 4 further comprising the step of depositing a broadband anti-reflective coating over the protective coating.

6. The method of claim 1 further comprising the step of depositing a broadband anti-reflective coating over said semiconductor coating and said doped semiconductor in said grooves.

7. The method of claim 1 , wherein forming the groove comprises etching the groove using at least one of chemical etching, reactive ion etching, or ion beam milling.

8. The semiconductor coating is In ２ O ３ or ZnO.

9. The method of claim 1 , wherein the step of coating the doped semiconductor onto the semiconductor coating comprises at least one of applying the doped semiconductor by a thin film coating.

10. The method of claim 1 , wherein the doped semiconductor comprises at least one of Sn, Mo, W, Ti, Al, or Ga.

11. The method of claim 1 , wherein the semiconductor coating has broadband optical transmittance in at least the visible and infrared spectra.

12. The method of claim 1 , wherein the step of depositing the semiconductor coating comprises depositing the semiconductor coating in an undoped state.

13. 2. The method of claim 1, wherein removing the doped semiconductor from the semiconductor coating comprises polishing to form a flat surface in the semiconductor coating, leaving the doped semiconductor in the grooves.

14. The method of claim 1 , wherein the step of depositing a semiconductor coating comprises depositing the semiconductor coating entirely on a surface of the optical substrate.

15. 2. The method of claim 1, wherein forming grooves and leaving the doped semiconductor in the grooves comprises forming the pattern such that a surface of the semiconductor coating is generally covered with the pattern.

16. The method of claim 2 , wherein the pattern is configured to provide electromagnetic interference (EMI) shielding for the optical substrate.

17. The method of claim 1 , wherein the doped semiconductor, the semiconductor coating, and the optical substrate are formed in a window without patterning or etching the optical substrate.

18. The method of claim 1 , wherein the doped semiconductor and the semiconductor coating have closely matched refractive indices to reduce light scattering.

19. A window, A window comprising: a transparent substrate having a transparent semiconductor coating having grooves filled with a doped semiconductor.

20. 1. A method for coating an optical substrate, comprising the steps of: depositing a doped semiconductor coating on a surface of an optical substrate, the doped semiconductor coating having a broadband optical transmittance; forming a groove in the doped semiconductor coating; coating over the doped semiconductor coating and at least partially filling the grooves with an undoped semiconductor; removing at least a portion of the undoped semiconductor from the doped semiconductor coating leaving at least a portion of the undoped semiconductor in the groove; A method comprising:

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