High-precision and high-throughput measurement of optical loss ratio of optical devices

Abstract

Several embodiments described herein relate to an optical device metrology system including a light source for emitting light and a non-polarizing beam splitter for splitting the light into a first photodetector optical path and an optical path. A first photodetector is disposed in the first photodetector optical path and measures a total power of the light. An optical device substrate is disposed in the optical path and splits the light into a second photodetector optical path and a third photodetector optical path. A second photodetector is disposed in the second photodetector optical path from the optical device substrate. The second photodetector measures a reflected power of the light. A third photodetector is disposed in the third photodetector optical path. The third photodetector measures a transmitted power of the light. A controller receives a plurality of measurements from the first photodetector, the second photodetector, and the third photodetector to calculate a light loss rate in the optical device substrate.

Description

[Technical field]

[0001]

[0001] Embodiments of the present disclosure relate generally to optical devices. In particular, embodiments described herein relate to a measurement system and method for measuring the percentage light loss of at least one of an optical film, an optical device, or an optical device substrate. [Background technology]

[0002]

[0002] Optical devices, including waveguide combiners such as augmented reality waveguide combiners and planar optical devices such as metasurfaces, are used to assist in image overlay. Generated light is propagated through the optical device until the light exits the optical device and is overlaid onto the surrounding environment.

[0003]

[0003] The fabricated optical device tends to lose light by absorption or scattering when the light propagates through the optical device or the optical device substrate. The optical device is fabricated from the optical device substrate, and in some cases, the optical device is fabricated from an optical film, for example, an optical film disposed on the optical device substrate. It is beneficial to measure the light loss rate from the optical film and the optical device substrate before, during, and after the fabrication of the optical device.

[0004]

[0004] Therefore, there is a need in the art for a measurement system and method for measuring the optical loss factor of at least one of an optical film, an optical device, or an optical device substrate. Summary of the Invention

[0005] In one embodiment, an optical device metrology system is provided. The optical device metrology system includes a light source operable to emit light, a non-polarizing beam splitter disposed in a path of the light, a first photodetector, a second photodetector, a third photodetector, and a controller. The non-polarizing beam splitter is operable to split the light into a first photodetector light path and an optical light path. The first photodetector is disposed in the first photodetector light path and is operable to measure a total power of the light. The optical device substrate is disposed in the optical light path and is operable to split the light into a second photodetector light path and a third photodetector light path. The second photodetector is disposed in the second photodetector light path from the optical device substrate. The second photodetector is operable to measure a reflected power of the light. The third photodetector is disposed in the third photodetector light path. The third photodetector is operable to measure a transmitted power of the light. A controller is operable to receive a plurality of measurements from the first photodetector, the second photodetector, and the third photodetector to calculate an optical loss rate in the optical device substrate.

[0006] In another embodiment, a method of using an optical device metrology system is provided, the method including projecting light from a light source onto a non-polarizing beam splitter, splitting the light at the non-polarizing beam splitter into a first photodetector path and an optical path, projecting the light onto a first photodetector in the first photodetector path, measuring at the first photodetector the total power of the light in the first photodetector path, projecting the light onto an optical device substrate in the optical path, splitting at the optical device substrate into a second photodetector path and a third photodetector path, projecting the light onto a second photodetector in the second photodetector path, measuring at the second ... a second photodetector in the second photodetector path, measuring at the second photodetector the total power of the light in the first photodetector path, projecting the light onto a second photodetector in the second photodetector path, measuring at the second photodetector the power of the light in the first photodetector path, projecting the light onto a second photodetector in the second photodetector path, measuring at the second photodetector the power of the light in the first photodetector path, projecting the light onto a second photodetector in the second photodetector path, measuring at the second photodetector the total power of the light in the first photodetector path. measuring, in the controller, a reflected power of the light in the second photodetector optical path; projecting the light to a third photodetector in a third photodetector optical path; measuring, in the third photodetector, a transmitted power of the light in the third photodetector optical path; collecting, in the controller, a plurality of measurements from the first photodetector, the second photodetector, and the third photodetector, the plurality of measurements including total power, reflected power, and transmitted power; and calculating an optical loss rate in the optical device substrate using the plurality of measurements.

[0007]

[0007] In yet another embodiment, a controller for an optical device metrology system is provided. The controller stores instructions. When executed by a computer processor, the instructions cause the controller to calculate an optical loss rate of an optical device substrate using a plurality of measurements from a first photodetector, a second photodetector, and a third photodetector. The plurality of measurements are collected by projecting light from a light source toward a non-polarizing beam splitter, measuring a total power of the light at a first photodetector in a first photodetector optical path, measuring a reflected power of the light at a second photodetector in a second photodetector optical path, and measuring a transmitted power of the light at a third photodetector in a third photodetector optical path. The non-polarizing beam splitter splits the light into a first photodetector optical path and an optical path. The second photodetector optical path is formed by light reflected from an optical device substrate disposed in the optical path. The third photodetector optical path is formed by light transmitted through an optical device substrate disposed in the optical path. The plurality of measurements include a total power, a reflected power, and a transmitted power.

[0008]

[0008] In order that the features of the present disclosure described above may be understood in detail, a more particular description of the present disclosure briefly summarized above may be obtained by reference to a number of embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the attached drawings only show exemplary embodiments, and therefore should not be considered as limiting the scope of the present disclosure, and other equally effective embodiments may be acceptable. [Brief description of the drawings]

[0009] [Figure 1]

[0009] FIG. 1 is a perspective front view of an optical device substrate according to several embodiments described herein. [Diagram 2]

[0010] 1 is a schematic diagram of an optical device metrology system according to embodiments described herein. [Diagram 3]

[0011] FIG. 2 is a schematic diagram of a controller according to embodiments described herein. [Figure 4]

[0012] FIG. 2 is a flow diagram of a method for determining a light loss rate according to embodiments described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010]

[0013] For ease of understanding, the same reference numerals have been used, where possible, to designate identical elements common to the figures. It is believed that elements and features of one embodiment may be beneficially incorporated in other embodiments without additional recitation.

[0011]

[0014] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to optical devices. In particular, embodiments described herein relate to optical films, optical devices, and optical device metrology systems for measuring light lost in transparent optical device substrates.

[0012]

[0015] 1 is a perspective front view of an optical device substrate 101 according to embodiments described herein. In some embodiments, the optical device substrate 101 includes a plurality of optical devices 100 disposed on a surface 103 of the optical device substrate 101. The optical device 100 may be a waveguide combiner utilized for virtual reality, augmented reality, or mixed reality. In some embodiments, which may be combined with other embodiments described herein, the optical device 100 is a planar optical device, such as a metasurface.

[0013]

[0016] The optical device substrate 101 may be any optical device substrate used in the art, depending on the application of the optical device substrate 101. Furthermore, the optical device substrate 101 may vary in shape, thickness, and diameter. For example, the optical device substrate 101 may have a diameter of about 150 mm to about 300 mm. The optical device substrate 101 may have a circular, rectangular, or square shape. The optical device substrate 101 may have a thickness between about 300 μm to about 1 mm. Although only nine optical devices 100 are illustrated on the optical device substrate 101, any number of optical devices 100 may be disposed on the surface 103. The optical device metrology system 200 and method 400 described herein are utilized to measure the optical loss ratio of the optical films, optical device substrate 101, and optical devices 100 described herein.

[0014]

[0017] 2 is a schematic diagram of an optical device metrology system 200. The optical device metrology system 200 is operable to measure the amount of light lost (e.g., absorbed) by the optical device substrate 101, an optical film disposed on the optical device substrate 101, or the optical device 100. The optical device substrate 101, the optical device 100, or the optical device film of the optical device substrate 101 may be measured at one or more stages of manufacture.

[0015]

[0018] The optical device metrology system 200 includes a light source 202, a fiber coupler 204, a half-wave plate 206, a polarizing beam splitter 208, a non-polarizing beam splitter 210, a first photodetector 212, a second photodetector 214, and a third photodetector 216. The light source 202, the first photodetector 212, the second photodetector 214, and the third photodetector 216 are in communication with a controller 240.

[0016]

[0019] The optical device metrology system 200 is operable to support an optical device substrate 101. The optical device substrate 101 may include at least one optical device 100 disposed thereon. In some embodiments, the optical device 101 includes an optical film disposed thereon. In some embodiments, to support the optical device substrate 101 in the optical device metrology system 200, the optical device substrate 101 may be disposed on a substrate support 220 (e.g., an edge ring).

[0017]

[0020] The light source 202 is operable to emit light through a fiber coupler 204. In one embodiment, which may be combined with other embodiments described herein, the light source 202 is a light emitting diode (LED). In another embodiment, the light source is a laser, such as a red / green / blue (RGB) laser. The RGB laser may alternately or simultaneously emit a combination of blue light having a wavelength of about 473 nm, green light having a wavelength of about 520 nm, and red light having a wavelength of about 642 nm.

[0018]

[0021] The light emitted from the light source 202 is split at the non-polarizing beam splitter 210 into a first photodetector optical path 230A and an optical path 230B. The first photodetector optical path 230A is directed to a first photodetector 212. The first photodetector 212 measures the total power (P tot ) The optical light path 230B is directed towards the optical device substrate 101.

[0019]

[0022] The light following optical path 230B is split at the optical device substrate 101 into a second photodetector path 230C and a third photodetector path 230D. The second photodetector path 230C is directed to a second photodetector 214. The second photodetector 214 measures the reflected power (P refl The second photodetector 214 is operable to measure an angle of incidence θ inc In one embodiment, θ incHowever, the optical path length inside the optical device substrate 101 remains unchanged as different types of light are emitted from the light source 202. In one embodiment, the angle of incidence is about 6°±0.5°. In other embodiments, other angles may be used. The third photodetector optical path 230D is directed to a third photodetector 216. The third photodetector 216 measures the transmitted power (P trans ).

[0020]

[0023] A first photodetector 212 located in the first photodetector optical path 230A is used to measure the total power P tot and uses a second photodetector 214 located in the second photodetector optical path 230C to measure the reflected power P refl and using a third photodetector 216 in a third photodetector optical path 230D to measure the transmitted power P trans By measuring the total power P along the three separate optical paths, a measurement of the projected light power at the three detection points is obtained. tot , reflected power P refl , and the transmitted power P trans The optical loss factor can be measured in a completely optical manner. The optical device metrology system 200 obtains the three power measurements without contacting the optical device substrate 101 and does not require modal excitation of the optical device substrate 101, optical device 100, or optical film. The contact-free and modal excitation-free measurements improve the accuracy of the optical loss factor measurements and increase the overall manufacturing throughput of the optical device substrate 101, optical device 100, or optical film.

[0021]

[0024] FIG. 3 illustrates a controller 240 of the optical device metrology system 200. The optical device metrology system 200 communicates with the controller 240. The controller 240 facilitates control and automation of the method 400 for measuring the optical loss factor of the optical device substrate 101 described herein. The controller 240 may include a central processing unit (CPU) 350, a memory 360, and support circuits 370. The CPU 350 may be one of any form of computer processor used in industrial settings to control various processes and hardware (e.g., motors and other hardware) and monitor processes (e.g., changes in the optical loss factor in the optical device substrate 101 throughout the manufacturing process). The memory 360 is connected to the CPU and may be a readily available memory such as a random access memory (RAM). Software instructions and data may be coded and stored in the memory 360 to instruct the CPU 350. The support circuits 370 are also connected to the CPU to support the processor. The support circuits 370 may include cache, power supplies, clock circuits, input / output circuits, subsystems, etc. A program (or computer instructions) readable by the controller determines what tasks are performable on the optical device substrate 101. The program may be software readable by the controller 340 and may include, for example, code for monitoring changes in the optical loss factor in the optical device substrate 101 throughout the manufacturing process, or the wavelength of the light emitted by the light source 202.

[0022]

[0025] The controller 240 is configured to facilitate the operation of the optical device metrology system 200. In some embodiments, the controller 240 includes one or more inputs (e.g., three inputs) for the first photodetector 212, the second photodetector 214, and the third photodetector 216, as well as a common ground. The controller 240 is operable to select the wavelength of light emitted from the light source 202. In some embodiments, the controller 240 may simultaneously emit red light, blue light, or green light. In some embodiments, the controller 240 may simultaneously emit some combination of blue light, red light, or green light. In some embodiments, the controller 240 may alternate between red light, blue light, and green light.

[0023]

[0026] The controller 240 is operable to calculate an optical loss rate for the optical device substrate 101 using a plurality of measurements from the first photodetector 212, the second photodetector 214, and the third photodetector 216. The plurality of measurements may be calculated as a total power P tot , reflected power P refl , and the transmitted power P trans The three channels give data with both offset and fluctuations on the order of 100nV.

[0024]

[0027] The embodiments of the optical device metrology system 200 described herein provide the ability to remove electrical noise, such as DC offset, to increase the accuracy of the optical loss rate measurement. DC offset may be due to, among other things, light source power drift or photodetector reading fluctuations. Any DC offset in the optical device metrology system 200 may be measured by each of the first photodetector 212, the second photodetector 214, and the third photodetector 216. The controller 240 includes a common ground to remove the DC offset. The controller 240 having a common ground between the first photodetector 212, the second photodetector 214, and the third photodetector 216 allows the controller 240 to determine the level of DC offset in the optical device metrology system 200. The controller 240 ensures that the power measurements obtained from the first photodetector 212, the second photodetector 214, and the third photodetector 216 do not float, allowing for more accurate and precise measurements of the power obtained at each photodetector.

[0025]

[0028] 4 is a flow diagram of a method 400 for determining an optical loss rate (e.g., optical loss) using the optical device metrology system 200. The controller 240 is operable to facilitate the steps of the method 400. In step 401, light is projected from the light source 202 toward the non-polarizing beam splitter 210. In some embodiments, in optional step 402, the light passes through a fiber coupler 204 to emit the light. The fiber coupler 204 couples the light from the light source 202 to allow for flexible optical system setup.

[0026]

[0029] In optional step 403, the light is projected from the fiber coupler 204 onto a half wave plate 206, which aligns the polarization of the light emerging from the fiber coupler 204. In optional step 404, the light is projected from the half wave plate onto a polarizing beam splitter 208, which further fine tunes the alignment of the light emerging from the fiber coupler 204 and removes any misaligned light. In optional step 405, the light is projected from the polarizing beam splitter 208 onto a non-polarizing beam splitter 210.

[0027]

[0030] In step 406, the non-polarizing beam splitter 210 splits the light into a first photodetector optical path 230A and an optical path 230B. The first photodetector optical path 212 is disposed in the first photodetector optical path 230A. The first photodetector optical path 230A is formed from light reflected from the non-polarizing beam splitter 210. The optical device substrate 101 is disposed in the optical path 230B. The optical path 230B is formed from light that is transmitted through the non-polarizing beam splitter 210 and travels towards the optical device substrate 101.

[0028]

[0031] In step 407, the light reflected from the non-polarizing beam splitter 210 is projected towards the first photodetector 212 on the first photodetector optical path 230A. In step 408, the total power P tot is measured by the first photodetector 212. The non-polarizing beam splitter 210 has a transmission / reflection splitting ratio. tot ) is calculated using the splitting ratio of the non-polarizing beam splitter 210. The non-polarizing beam splitter 210 can split the light from about 20% reflection (80% transmission) to about 80% reflection (20% transmission). In one embodiment, the light projected toward the first photodetector 212 and the light traveling toward the optical device substrate 101 are directed at about 90 degrees to each other, although other angles are contemplated by the present disclosure.

[0029]

[0032] In step 409, the light transmitted through the non-polarizing beam splitter 210 is projected towards the optical device substrate 101 on optical light path 230B. In some embodiments, the optical device substrate 101 includes an optical film disposed on the optical device substrate 101. In some embodiments, the optical film is a patterned optical film. In some embodiments, the optical device substrate 101 includes one or more optical devices. In step 410, the optical device substrate 101 splits the light into the second photodetector light path 230C and the third photodetector light path 230D. As the light interacts with the optical device substrate 101, a portion is absorbed within the optical device substrate 101 (e.g., optical loss factor l) and a portion is reflected (e.g., reflected power P refl ), some of it is transmitted (e.g., transmitted power P trans The second photodetector 214 is disposed in the second photodetector optical path 230C. The third photodetector 216 is disposed in the third photodetector optical path 230D.

[0030]

[0033] In step 411, a portion of the light reflected from the optical device substrate 101 is projected towards a second photodetector 214 on a second photodetector optical path 230C. In step 412, the reflected power P refl is measured by the second photodetector 214. The second photodetector 114 is measured at an incident angle θ inc In one embodiment, θ inc However, the optical path length within the optical device substrate 101 remains unchanged when different types of light are emitted from the light sources 202. In one embodiment, the angle of incidence is about 6°±0.5°. In some embodiments, other angles may be used.

[0031]

[0034] In step 413, a portion of the light transmitted through the optical device substrate 101 is projected toward the third photodetector 216 on the third photodetector optical path 230D. In step 414, the transmitted power P trans is measured by the third photodetector 216.

[0032]

[0035] In step 415, the controller 240 collects a number of measurements from the first photodetector 212, the second photodetector 214, and the third photodetector 216. The measurements are used to derive a total power P tot , reflected power P refl , and the transmitted power P trans Includes all power P tot , reflected power P refl , and the transmitted power P trans are measured simultaneously by the first photodetector 212, the second photodetector 214, and the third photodetector 216, respectively, to reduce drift or fluctuations in the light source 202. In some embodiments, the optical losses of the blue, green, and red light can be measured separately.

[0033]

[0036] In step 416, the controller 240 uses the multiple measurements to calculate the light loss factor l in the optical device substrate 101. The light loss factor l (e.g., optical loss) may be measured using equation (1). l=1-P refl / P tot -P trans / P tot (1)

[0034]

[0037] In some embodiments, the light loss factor of the optical device substrate 101 is calculated before the optical device substrate 101 is processed. In other embodiments, the light loss factor of the optical device substrate 101 is calculated during processing of the optical device substrate 101. In still other embodiments, the light loss factor of the optical device substrate 101 is calculated after the optical device substrate 101 is processed. In still other embodiments, the light loss factor of the optical device substrate 101 is calculated before, during, and after processing, or some combination thereof.

[0035]

[0038] The method 400 can provide measurements from the first photodetector 212, the second photodetector 214, and the third photodetector 216 within a range of approximately 100 mV, with the three channels providing measurements on the order of 100 nV (e.g., 10 -6The fully optical method allows for the measurement of light loss rate with wavelengths ranging from ultraviolet to infrared at high throughput. The fully optical method means that the optical device substrate 101 being measured only interacts with the light projected onto it and not with any other physical apparatus. The design is compatible with multiple substrate chuck designs and allows for full automation of the measurement.

[0036]

[0039] In summary, an optical device metrology system and method for calculating the optical loss rate of an optical device substrate or optical device is provided herein. The optical device metrology system splits the emitted light into a first photodetector optical path and an optical optical path. The optical device substrate splits the light into a second photodetector optical path and a third photodetector optical path. The first photodetector is disposed in the first photodetector optical path, the second photodetector is disposed in the second photodetector optical path, and the third photodetector is disposed in the third photodetector optical path. By using the photodetectors, measurements of the power of the light projected at three detection points along the three separate optical paths are obtained. The total power P along the three separate optical paths is calculated as follows: tot , reflected power P refl , and the transmitted power P trans The optical loss factor can be measured in a completely optical manner. The optical device measurement system obtains the three power measurements without contacting the optical device substrate and does not require modal excitation of the optical device substrate, optical device, or optical film. The contact-free and modal excitation-free measurements improve the accuracy of the optical loss factor measurements and increase the overall throughput of the optical device substrate, optical device, or optical film manufacturing. The optical loss factor is calculated in a controller. The controller receives measurements from the first photodetector, the second photodetector, and the third photodetector. The optical loss factor can be calculated before, during, or after processing the optical device substrate or optical device, allowing for higher throughput. The common ground eliminates DC offsets in the optical device measurement system and allows the optical device measurement system to make corrections on the order of 100 nV (e.g., 10 of the optical loss factor measurements).-6 This allows the measurement of offsets and fluctuations (with a precision of 100 Hz to 100 Hz).

Claims

1. a light source operable to emit light; a non-polarizing beam splitter disposed in the path of the light, the non-polarizing beam splitter operable to split the light into a first photodetector path and an optical path; a first photodetector disposed in the first photodetector optical path and operable to measure a total power of the light; a second photodetector disposed in a second photodetector optical path from an optical device substrate, the optical device substrate disposed in the optical path and operable to split the light in the optical path into the second photodetector optical path and a third photodetector optical path, the second photodetector operable to measure a reflected power of the light; a third photodetector disposed in the third photodetector optical path and operable to measure a transmitted power of the light; and 11. An optical device metrology system comprising: a controller operable to receive a plurality of measurements from the first optical detector, the second optical detector, and the third optical detector to calculate an optical loss rate within the optical device substrate.

2. The optical device metrology system of claim 1 , wherein the second photodetector is positioned at an angle of incidence from the optical light path of about 5.5° to about 6.5°.

3. The optical device measurement system of claim 1 , wherein the controller includes a common ground for the multiple measurements.

4. Half-wave plate, and 10. The optical device metrology system of claim 1, further comprising a polarizing beam splitter, wherein the half wave plate and the polarizing beam splitter are operable to align the polarization of the light emitted from the light source.

5. The optical device metrology system of claim 1 , wherein a substrate support is operable to support the optical device substrate.

6. The optical device metrology system of claim 1 , wherein the optical device metrology system is non-modal excited.

7. projecting light from a light source onto a non-polarizing beam splitter; splitting the light at the non-polarizing beam splitter into a first photodetector path and an optical path; projecting the light onto a first photodetector in the first photodetector optical path; measuring, at the first photodetector, the total power of the light in the first photodetector optical path; projecting the light onto an optical device substrate within the optical light path; splitting the light into a second photodetector light path and a third photodetector light path at the optical device substrate; projecting the light onto a second photodetector in the second photodetector optical path; measuring, at the second photodetector, the reflected power of the light in the second photodetector optical path; projecting the light onto a third photodetector in the third photodetector optical path; measuring, at the third photodetector, a transmitted power of the light in the third photodetector optical path; collecting, in a controller, a plurality of measurements from the first optical detector, the second optical detector, and the third optical detector, the plurality of measurements including the total power, the reflected power, and the transmitted power; using the plurality of measurements to calculate an optical loss factor in the optical device substrate.

8. passing the light from the light source through a fiber coupler; projecting the light from the fiber coupler onto a half wave plate; projecting the light from the half wave plate onto a polarizing beam splitter; and The method of claim 7 , further comprising projecting the light from the polarizing beam splitter towards the non-polarizing beam splitter.

9. The method of claim 7 , wherein the method is an entirely optical method.

10. The method of claim 7 , wherein the light loss factor of the optical device substrate can be measured before processing of the optical device substrate, during the processing of the optical device substrate, after the processing of the optical device substrate, or a combination thereof.

11. The method of claim 7 , wherein the second photodetector is positioned at an angle of incidence from the optical light path of about 5.5° to about 6.5°.

12. The method of claim 7 , wherein a substrate support is operable to support the optical device substrate.

13. The method of claim 7 , wherein the controller includes a common ground for the multiple measurements.

14. 1. A controller for an optical device metrology system, comprising: calculating an optical loss factor of the optical device substrate using a plurality of measurements from the first optical detector, the second optical detector, and the third optical detector, the plurality of measurements comprising: projecting light from a light source towards a non-polarizing beam splitter, the non-polarizing beam splitter splitting the light into a first photodetector light path and an optical light path; measuring a total power of the light at the first photodetector in the first photodetector light path; measuring the reflected power of the light at the second photodetector in a second photodetector light path, the second photodetector light path being formed by light reflected from the optical device substrate disposed in the optical light path; and measuring a transmitted power of the light at the third photodetector in a third photodetector light path, the third photodetector light path being collected by measuring a transmitted power of the light formed by light transmitted through the optical device substrate disposed in the optical light path; The plurality of measurements include the total power, the reflected power, and the transmitted power.

15. The controller of claim 14 , wherein a substrate support is operable to support the optical device substrate.

16. The controller of claim 14 , wherein the controller further comprises a common ground for the multiple measurements.

17. The controller of claim 14 , wherein the controller is operable to select a wavelength of light emitted from the light source.

18. The controller of claim 17 , wherein the wavelengths of light include blue light, red light, green light, or a combination thereof.

19. The controller of claim 14 , wherein the second photodetector is positioned at an angle of incidence from the optical light path of about 5.5° to about 6.5°.

20. The controller of claim 14 , wherein the light loss rate of the optical device substrate can be measured before processing of the optical device substrate, during the processing of the optical device substrate, after the processing of the optical device substrate, or a combination thereof.

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