Optical device manufacturing method

Abstract

To manufacture an optical device in which the contact resistance between multilayer graphene and an electrode is reduced.SOLUTION: In a manufacturing method for an optical device, resist with a predetermined shape is formed on multilayer graphene, the multilayer graphene and the resist are processed into a tapered shape by anisotropic etching with oxygen, the resist covering a tilted end surface of the processed multilayer graphene is removed, and an electrode covering the titled end surface where the multilayer graphene is exposed is provided.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing an optical device. [Background technology]

[0002] Graphene is a two-dimensional material in which carbon atoms are arranged in a two-dimensional honeycomb pattern, and has a unique energy band structure. The conduction band and valence band of graphene can be modeled as a symmetrical cone whose apex meets at the Dirac point (K point or K' point in wave number space). Since the conduction band and valence band intersect at the Dirac point and there is no band gap, graphene has a certain degree of absorption for light in a wide wavelength range, and is also capable of absorbing terahertz light. Taking advantage of this property, graphene has been widely studied as a material for visible light and infrared light sensors and terahertz light sensors. Graphene's application to light-emitting devices that utilize the blackbody radiation is also being studied.

[0003] Graphene itself is a single-atom layer material, but the light absorption rate of single-layer graphene is only about 2.3%. Due to its low light absorption rate, it is difficult to effectively use single-layer graphene as an optical device unless it is combined with additional technologies. By using multi-layer graphene, the absorption rate can be improved compared to single-layer graphene. Unlike highly oriented pyrolytic graphite (HOPG), multi-layer graphene has multiple graphene layers stacked randomly and exhibits electronic properties similar to those of single-layer graphene.

[0004] A method is known in which an absorption layer in which multiple graphene layers randomly shifted in a planar view are stacked isotropically etched with oxygen plasma (see, for example, Patent Document 1). A method is known in which a silicon oxide film, a silicon nitride film, or the like is etched into a tapered shape by reactive ion etching (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-77779 A [Patent Document 2] Japanese Patent Application Publication No. 6-60323 Summary of the Invention [Problem to be solved by the invention]

[0006] It is difficult to obtain electrical contact with multi-layer graphene due to its multi-layer structure. This is because when electrodes are provided on the multi-layer graphene, the contact resistance between the electrodes and the graphene edges is large. The lower the layer of the multi-layer graphene, the more difficult it is to ensure physical contact between the electrodes and the graphene.

[0007] One aspect of the present invention aims to provide a method for manufacturing an optical device in which the contact resistance between multi-layer graphene and an electrode is reduced. [Means for solving the problem]

[0008] In one embodiment, a method for manufacturing an optical device includes the steps of: A resist having a predetermined shape is formed on the multi-layer graphene. The multilayer graphene is processed into a tapered shape together with the resist by anisotropic etching using oxygen; removing the resist covering the inclined end faces of the processed multilayer graphene; An electrode is provided to cover the exposed inclined end surface of the multilayer graphene. Effect of the Invention

[0009] It is possible to fabricate optical devices with reduced contact resistance between the multi-layer graphene and the electrodes. [Brief description of the drawings]

[0010] [Figure 1] 1A to 1C are diagrams illustrating basic manufacturing steps of an optical device according to an embodiment of the present invention. [Diagram 2]1 shows scanning electron microscope (SEM) images of an optical device produced by a method according to an embodiment, taken before and after resist removal. [Diagram 3] 1 shows SEM images before and after resist removal by the method of Comparative Example 1. [Figure 4] 1 is an optical microscope image of a sample for measuring the resistance of multi-layer graphene. [Diagram 5] FIG. 5 is a diagram showing the results of resistance measurement using the sample of FIG. [Figure 6] FIG. 13 is a schematic plan view of a multilayer graphene sample for resistance measurement produced by the method of Comparative Example 2. [Figure 7] FIG. 7 is a diagram showing the results of resistance measurement using the sample of FIG. 6. [Figure 8A] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 8B] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 8C] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 8D] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 8E] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 8F] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 8G] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 8H] 5A to 5C are detailed manufacturing process diagrams of the optical device according to the embodiment. [Figure 9A] 1A and 1B are a side view and a top view of multilayer graphene of Configuration Example 1. [Figure 9B] 1A and 1B are a side view and a top view of an optical device in which electrodes are provided on the multilayer graphene of Configuration Example 1. [Figure 10A] 1A and 1B are a side view and a top view of multilayer graphene of Configuration Example 2. [Figure 10B] 1A and 1B are a side view and a top view of an optical device in which electrodes are provided on multilayer graphene of an example configuration. [Figure 11A]1A and 1B are a side view and a top view of multilayer graphene of Configuration Example 3. [Figure 11B] 13A and 13B are a side view and a top view of an optical device in which electrodes are provided on the multilayer graphene of Configuration Example 3. [Figure 12] FIG. 11C is a schematic plan view of an optical sensor array in which the optical devices of FIG. 11B are arranged in an array. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In an embodiment, the multi-layer graphene is patterned in one process by anisotropic etching using oxygen to form tapered inclined end faces on the multi-layer graphene. By providing electrodes on the inclined end faces of the multi-layer graphene, the contact resistance between the electrodes and the multi-layer graphene can be reduced. In the following description, the same components are denoted by the same reference numerals, and duplicated description may be omitted.

[0012] FIG. 1 is a diagram showing a basic manufacturing process of an optical device according to an embodiment. In FIG. 1(A), a resist 16 having a predetermined shape is formed on a multi-layer graphene 15. In the multi-layer graphene 15, single-layer graphene is randomly stacked, and the lattice positions of the hexagonal rings of the graphene in each layer are not necessarily aligned in the in-plane direction. The resist 16 is formed into a predetermined shape by exposure and development according to the shape of the target element. In this example, the resist 16 is a negative photoresist.

[0013] In (B) of FIG. 1, the multi-layer graphene 15 together with the resist 16 is processed into a tapered shape by anisotropic etching using oxygen. Specifically, the multi-layer graphene 15 is processed together with the resist 16 by reactive ion etching (RIE) using oxygen. At this time, the multi-layer graphene 15 is not etched in small increments, but is patterned all at once by continuous RIE up to the bottom surface of the multi-layer graphene 15. Part of the resist 16 is also etched together with the multi-layer graphene 15 by this RIE.

[0014] During the RIE process, a portion of the resist 16 released by the collision of accelerated ions adheres to the processed surface of the multilayer graphene 15 being etched. The resist particles adhering to the end surface of the multilayer graphene 15 being processed are not removed by the ions accelerated from directly above, and remain on the end surface of the multilayer graphene 15. By covering the end surface of the multilayer graphene 15 with the resist 16, chemical reactions at the end surface of the multilayer resist 15 are suppressed, and anisotropic etching is performed. As a result, the processed surface is formed into a tapered slope that is inclined in a certain direction.

[0015] In FIG. 1C, resist 16 (see FIG. 1B) covering the end faces and upper surface of multilayer graphene 15 after processing is removed by RIE. The resist 16 remaining on the upper surface and the inclined end faces of multilayer graphene 15 may be continuously etched and removed in one RIE process, or may be etched and removed in multiple separate processes. This exposes inclined end faces 151 of multilayer graphene 15. The exposed end faces 151 of multilayer graphene 15 have a tapered inclined surface all around due to the anisotropic etching in the process of FIG. 1B.

[0016] 1D, electrodes 17 and 18 are provided on the inclined end surface 151 of the multi-layer graphene 15 from which the resist 16 has been removed. As described below, the contact resistance between the tapered end surface 151 and the electrodes 17 and 18 is significantly reduced. The connection between the tapered end surface 151 of the multi-layer graphene 15 and the electrodes 17 and 18 may be called an "edge contact."

[0017] Figure 2 shows SEM images of an optical device fabricated by the method of the embodiment before and after resist removal. (A) in Figure 2 is an SEM image before resist removal, which corresponds to the state shown in (B) in Figure 1. (B) in Figure 2 is an SEM image after resist removal, which corresponds to the state shown in (C) in Figure 1.

[0018] In FIG. 2A, oxygen gas is introduced and RIE is performed for 15 minutes at a radio frequency (RF) voltage of 400 V. At this time, the resist 16 is etched along with the multi-layer graphene 15. By processing the multi-layer graphene 15 together with the resist 16 in a single RIE, tapered multi-layer graphene whose surface is covered with resist is obtained, as shown in FIG. 2A. Both the end faces of the multi-layer graphene and the resist are inclined in a certain direction.

[0019] In FIG. 2B, the resist remaining on the multi-layer graphene is removed. The etching conditions at this time are to introduce oxygen gas, set the RF voltage at 400 V, and perform one RIE for a total of 6 minutes and 50 seconds. By removing the resist 16 in one RIE, multi-layer graphene 15 having smooth tapered end faces 151 all around is obtained, as shown in FIG. 2B.

[0020] In the case of isotropic etching, the etching proceeds in all directions, so the edge of the multilayer graphene directly below the resist is cut into an arc shape, causing undercuts. In contrast, by using anisotropic etching to process the edge of the multilayer graphene while protecting it with resist, a tapered shape as shown in Figure 2(B) can be obtained.

[0021] Fig. 3(A) is an SEM image before resist removal by the method of Comparative Example 1, and Fig. 3(B) is an SEM image after resist removal by the method of Comparative Example 1. In Comparative Example 1, anisotropic etching is performed, but unlike the above-mentioned embodiment, RIE is performed multiple times when processing multilayer graphene 15 together with resist 16. As in Fig. 2, oxygen gas is introduced, and RIE is performed multiple times for 2 to 4 minutes at an RF voltage of 400 V with a pause of 30 to 60 seconds. The total RIE time is 30 minutes.

[0022] In FIG. 3A, in the method of Comparative Example 1, the overall shape patterned with the resist is tapered, but the resist and graphene are rolled up outward at the end faces of the taper. This state at the end faces does not change even after the resist is removed. In FIG. 3B, oxygen gas is introduced and RIE is performed once for 6 minutes and 50 seconds at an RF voltage of 400 V to remove the remaining resist. Even after the resist is removed, the end of the multilayer graphene is rolled up and the end faces are very uneven, making it difficult to obtain a sufficient electrical connection between the multilayer graphene and the electrode.

[0023] From observation of FIG. 2 and FIG. 3, it can be seen that according to the method of the embodiment, the end faces of the multilayer graphene become smoothly tapered surfaces suitable for connection with electrodes.

[0024] <Electrical properties of multi-layer graphene> Next, the electrical properties of the multilayer graphene of the embodiment are confirmed. A plurality of multilayer graphene wiring samples with different wiring lengths are fabricated by the method of the embodiment described above, and the electrical resistance is measured by a four-terminal measurement method.

[0025] FIG. 4 is an optical microscope image of a sample used in measuring the resistance of multi-layer graphene. On a substrate, a plurality of types of multi-layer graphene wirings having the same line width but different wiring lengths are formed by the method of the embodiment. Electrodes are connected to both ends of the multi-layer graphene wiring in the longitudinal direction. The width between the electrodes is defined as the wiring length. In FIG. 4, the width between the electrodes, i.e., the wiring length of the multi-layer graphene, is changed to 2 μm, 3 μm, and 5 μm.

[0026] The linear multi-layer graphene patterning is performed in one go by RIE using oxygen gas at an RF voltage of 400V for 15 minutes. This results in a configuration in which the edges of the multi-layer graphene and resist are tapered. Then, to remove the resist remaining on the top surface of the inclined edges of the multi-layer graphene, an additional RIE is performed using oxygen gas at an RF voltage of 400V for 6 minutes and 50 seconds. The additional RIE for resist removal may be referred to as the "second RIE."

[0027] The time for the second RIE for removing the resist may be shorter than the time for the first RIE for patterning the multi-layer graphene and resist at once. After removing the resist covering the end faces and top face of the multi-layer graphene, an electrode is formed by electron beam evaporation. A thin film of titanium (Ti) with a thickness of 5 nm and a thin film of gold (Au) with a thickness of 50 nm are formed in this order to cover the exposed inclined end faces of the multi-layer graphene, and an electrode with the shape shown in Figure 4 is formed by the lift-off method.

[0028] Figure 5 shows the results of measuring the electrical resistance using the sample in Figure 4. The electrical resistance depends on the wiring length, and the longer the wiring length, the higher the resistance value. The contact resistance between the multilayer graphene and the electrode is calculated as half the y-intercept of the approximation line in Figure 5. The contact resistance calculated from the approximation line in Figure 5 is 5 Ωμm.

[0029] 6 is a schematic plan view of a multilayer graphene sample for resistance measurement produced by the method of Comparative Example 2. In Comparative Example 2, a multilayer graphene wiring without a taper is formed. The wiring length of the multilayer graphene is changed to 50 μm, 10 μm, 5 μm, and 2 μm, and four types of graphene wiring, G1 to G4, are formed.

[0030] The conditions for forming non-tapered multi-layer graphene wiring are as follows. First, oxygen gas is introduced, and RIE at 400V for 10 seconds is repeated 11 times (a total of 110 seconds of RIE) to process the multi-layer graphene together with the resist. Next, the resist is removed by non-directional plasma ashing. Oxygen gas is introduced into the plasma ashing device, and ashing is performed for 15 minutes with 400W RF power. This isotropic oxygen ashing forms non-tapered multi-layer graphene wiring.

[0031] Next, similar to the sample in Figure 4, a thin film of Ti with a thickness of 5 nm and a thin film of Au with a thickness of 50 nm are formed in that order by electron beam evaporation, and an electrode with the shape in Figure 6 is formed by the lift-off method.

[0032] FIG. 7 shows the results of resistance measurement using the sample in FIG. 6. The electrical resistance depends on the wiring length. The contact resistance between the multilayer graphene of Comparative Example 2 and the electrode is calculated as 1 / 2 of the y-intercept of the approximation line in FIG. 7. The contact resistance calculated from the approximation line in FIG. 7 is 530 Ωμm.

[0033] The contact resistance is more than 100 times larger than that of the multi-layer graphene with a tapered structure shown in Figure 4. It can be seen that the multi-layer graphene wiring formed by the method of Comparative Example 2, which does not have tapered end faces, has insufficient electrical contact between the end faces and the electrodes.

[0034] 8A to 8H show in more detail the manufacturing process of the optical device of the embodiment. In Fig. 8A, multi-layer graphene 15 is grown on a substrate 21. The substrate 21 is not particularly limited as long as it is an insulating substrate. In this example, a silicon substrate with a thermal oxide film is used, but a sapphire substrate, MgO substrate, etc. may also be used.

[0035] A catalyst 22 is formed on a substrate 21, and graphene is synthesized by a thermal CVD (Chemical Vapor Deposition) method. The catalyst 22 is, for example, an iron (Fe) catalyst with a thickness of 200 nm. Graphene is synthesized by thermal CVD using acetylene gas under conditions of 700°C and 20 minutes. During the synthesis, acetylene and argon (Ar) gases are mixed in a ratio of 1:9, and acetylene gas is introduced while maintaining a constant pressure (1 kPa) with Ar gas. The ratio of acetylene gas to the mixed gas is about 500 ppm of the total pressure.

[0036] The graphene synthesis temperature is not limited to 700° C., and can be appropriately selected within the temperature range of 500° C. to 1200° C. When the graphene is synthesized at a temperature of 900° C. or higher, methane gas may be introduced instead of acetylene gas.

[0037] The synthesis of graphene is not limited to thermal CVD, and may be performed using a hot filament CVD method, a remote plasma CVD method, or the like. As the raw material gas, a hydrocarbon gas such as methane or ethylene, or an alcohol gas such as ethanol or methanol may be used in addition to acetylene. As the dilution gas, helium (He) or hydrogen (H) may be used in addition to Ar.

[0038] The catalyst may be Fe, nickel (Nk), cobalt (Co), copper (Cu), or an alloy thereof. A thin film of the catalyst 22 is formed on the substrate 21 by sputtering or vapor deposition. To enhance the catalytic effect, a metal such as aluminum (Al), titanium (Ti), molybdenum (Mo), or tantalum (Ta), or an oxide or nitride thereof may be formed as the base metal of the thin film of the catalyst 22.

[0039] As described above, when synthesis is performed under conditions of 700° C. and 20 minutes using a 200 nm thick Fe catalyst 22, multi-layer graphene 15 with a thickness of about 30 nm (about 90 layers) is obtained. The thickness and total number of multi-layer graphene 15 are not limited to this example, and by changing the synthesis time and acetylene concentration, multi-layer graphene with a desired thickness and total number can be synthesized.

[0040] 8B, a support layer 26 such as a resin is formed on the synthesized multilayer graphene 15. The support layer 26 may be formed by applying a polymer such as polymethyl methacrylate (PMMA) by a spin coating method. The thickness of the support layer 26 may be any thickness as long as it can support the multilayer graphene 15. For example, the thickness of the support layer 26 may be 0.1 μm to 100 μm, and from the viewpoint of ease of handling, the thickness may be 1 μm to 100 μm.

[0041] In FIG. 8C, after the solvent component of the support layer 26 is volatilized, the catalyst 22 is removed using an iron chloride solution, and the multi-layer graphene 15 with the support layer 26 is separated from the substrate 21.

[0042] In Fig. 8D, a substrate 11 having an insulating film 12 formed on its surface is prepared. Multilayer graphene 15 supported on a support layer 26 is placed opposite the insulating film 12, and the multilayer graphene 15 is transferred onto the substrate 11. The substrate 11 and the insulating film 12 may be a silicon substrate and a thermal oxide film, respectively, or may be other combinations. After the transfer, the support layer 26 is dissolved and removed with an organic solvent.

[0043] 8E to 8H are the same as the steps (A) to (D) in FIG. 1, and therefore overlapping explanations may be omitted or simplified. In FIG. 8E, a photoresist is applied to the entire surface of the transferred multilayer graphene 15, and a resist 16 corresponding to the desired element shape is formed by exposure and development.

[0044] In FIG. 8F, the multi-layer graphene 15 is processed together with the resist 16 at once by RIE using oxygen gas. When processing the multi-layer graphene 15 having a thickness of about 30 nm, for example, patterning is performed at once under conditions of an RF voltage of 400 V and 15 minutes. By this RIE, the multi-layer graphene 15 is anisotropically etched together with the resist 16. When the multi-layer graphene 15 is processed down to the bottom surface and patterning is completed, the top surface and end surfaces of the multi-layer graphene 15 are covered with the resist 16.

[0045] In the case of RIE, positive ions accelerated in the reaction chamber are attracted to the negative potential (self-bias) generated on the substrate 11 side and collide straight toward the resist 16 and the multilayer graphene 15. Particles of the resist 16 released by the collision of the positive ions adhere to the surface of the multilayer graphene 15 being processed. Of these, the resist particles adhering to the end face of the multilayer graphene 15 are not easily repelled by the positive ions accelerated from directly above the substrate 21, and are deposited on the end face of the multilayer graphene 15. Since the reaction with oxygen gas does not proceed on the end face of the multilayer graphene 15 covered with the resist 16, the multilayer graphene 15 is etched mainly in the film thickness direction. This results in anisotropic etching.

[0046] By performing RIE on the multilayer graphene 15 together with the resist 16 without breaking it, a structure having a smoothly tapered surface is obtained as shown in FIG.

[0047] In FIG. 8G, the resist 16 covering the end faces and the upper surface of the multi-layer graphene 15 is removed. Oxygen gas is introduced into the same RIE apparatus, and RIE is performed under conditions of 400 V and 6 to 7 minutes, thereby removing the resist 16 covering the end faces and the upper surface of the multi-layer graphene 15. The RIE for removing the resist may be performed all at once or may be performed in several steps, as long as the inclined end faces 151 of the multi-layer graphene 15 are not deteriorated. The insulating film 12 does not react with oxygen ions, and the resist 16 remaining on the surface of the multi-layer graphene 15 is etched away.

[0048] In FIG. 8H, electrodes 17 and 18 are formed on the inclined end surface 151 of the multi-layer graphene 15 to fabricate the optical device 10. The electrodes 17 and 18 may be made of palladium (Pd), chromium (Cr), Ni, or the like, in addition to a laminate of Ti and Au. The materials of the electrodes 17 and 18 may be the same or different. The contact resistance between the electrodes 17 and 18 and the inclined end surface 151 of the multi-layer graphene 15 is reduced, and a low-resistance optical device 10 is obtained.

[0049] Some configuration examples of the optical device 10 using the multi-layer graphene 15 are shown below.

[0050] <Configuration example 1> Fig. 9A is a side view and a top view of multilayer graphene 15A of Configuration Example 1. Fig. 9B is a side view and a top view of optical device 10A in which electrodes are provided on multilayer graphene 15A of Configuration Example 1. Multilayer graphene 15A is patterned by anisotropic dry etching, and has end face 151 that is tapered over the entire circumference.

[0051] Multilayer graphene 15 is a randomly stacked single-layer graphene, and while it exhibits similar electronic properties to single-layer graphene, its absorption rate is much higher than that of single-layer graphene. Compared to single-layer graphene, a slight band gap appears in the band structure of multilayer graphene 15. However, the band gap in multilayer graphene is very small, and it absorbs light in a wide wavelength range, just like single-layer graphene. Multilayer graphene 15 can be effectively used as a light-receiving layer.

[0052] 9B, electrodes 17A and 18A are formed to cover two opposing end faces 151 of multilayer graphene 15A that has been processed into a rectangular shape. End face 151 is formed as a smoothly inclined tapered surface by anisotropic etching. Contact resistance is reduced at interface B between multilayer graphene 15A and electrode 17A, and at interface B between multilayer graphene 15A and electrode 18A.

[0053] When a bias voltage is applied between electrodes 17A and 18A, a gradient is generated in the energy band at the interface between electrode 17A and multilayer graphene 15 and at the interface between electrode 18A and multilayer graphene 15. In this state, when light is incident on multilayer graphene 15, the resistance value changes due to the generation of carriers caused by light absorption, and the photocurrent flowing between electrodes 17A and 18A changes. The change in photocurrent correlates with the amount of incident light. The amount of incident light can be measured by reading the change in photocurrent.

[0054] In the optical device 10A, the contact resistance between the multilayer graphene 10A and the electrodes 17A and 18A is reduced, so that the resistance change can be read with high sensitivity.

[0055] <Configuration example 2> Fig. 10A is a side view and a top view of multilayer graphene 15B of Configuration Example 2. Fig. 10B is a side view and a top view of optical device 10B in which electrodes are provided on multilayer graphene 15A of Configuration Example 2. Multilayer graphene 15B is patterned by anisotropic dry etching, and has end face 151 that is tapered over the entire periphery.

[0056] 10B, electrodes 17B and 18B are formed in diagonal regions of multilayer graphene 15B that has been processed into a substantially square shape, covering end face 151. End face 151 is formed as a smoothly inclined tapered surface by anisotropic etching, and contact resistance is reduced at the interface between multilayer graphene 15B and electrode 17B and at the interface between multilayer graphene 15B and electrode 18B.

[0057] The operating principle of the optical device 10B is the same as that of the optical device 10A of Configuration Example 1. Since the contact resistance between the multilayer graphene 10B and the electrodes 17B and 18B is reduced, the optical device 10B can sensitively read the resistance change.

[0058] <Configuration example 3> Fig. 11A is a side view and a top view of multilayer graphene 15C of Configuration Example 3. Fig. 11B is a side view and a top view of an optical device 10C in which electrodes are provided on multilayer graphene 15C of Configuration Example 3. Multilayer graphene 15C is patterned by anisotropic dry etching, and has end face 151 that is tapered over the entire periphery.

[0059] 11B, electrodes 17C and 18C are formed in mutually facing regions of multilayer graphene 15C processed into a circle, covering end face 151. Electrodes 17C and 18C are formed along part of the circumference of multilayer graphene 15. End face 151 of multilayer graphene 15 is formed as a smoothly inclined tapered surface by anisotropic etching. Contact resistance is reduced at the interface between multilayer graphene 15C and electrode 17C and at the interface between multilayer graphene 15C and electrode 18C.

[0060] The operating principle of the optical device 10C is the same as that of the optical device 10A of Configuration Example 1. Since the contact resistance between the multilayer graphene 10C and the electrodes 17C and 18C is reduced, the optical device 10C can sensitively read the resistance change.

[0061] Fig. 12 is a schematic plan view of an optical sensor array 40. The optical sensor array 40 is fabricated by arranging a plurality of optical devices 10 in an array on a substrate 41. The optical sensor array 40 is also an example of an optical device. Each optical device 10 constitutes each pixel 45 of the optical sensor array 40. In Fig. 12, the optical device 10 constituting the pixel 45 has the configuration shown in Fig. 11B, but any of the configurations of the optical devices 10A to 10C described above may be used.

[0062] By electrically connecting the optical sensor array 40 to a readout circuit and reading out the charges stored in each optical device 10 according to the amount of incident light, the distribution of light intensity on a two-dimensional plane can be obtained as an electrical signal. The electrical signal may be processed and applied to an imaging device that displays the distribution of light intensity as an image. Since the contact resistance between the multilayer graphene 15 and the electrode is reduced in each optical device 10 included in the optical sensor array 40, the change in resistance due to the incidence of light can be detected with high sensitivity.

[0063] Although the present invention has been described based on specific examples, the present invention is not limited to the above examples. In the case where a silicon substrate is used as the substrate 11, a gate electrode may be formed on the back surface of the substrate 11 to control the carrier density of the multi-layer graphene 15.

[0064] The edge contact between the multilayer graphene and the electrodes of the embodiment can also be applied to a light-emitting device using the multilayer graphene. Light emission by graphene is blackbody radiation emission caused by heating due to application of electric current. When the multilayer graphene 15 processed by the method of the embodiment is used as a light-emitting layer and electrodes for current flow are provided on both ends of the multilayer graphene 15, the contact resistance between the multilayer graphene 15 and the electrodes is reduced, and light emission can be efficiently obtained. [Explanation of symbols]

[0065] 10, 10A, 10B, 10C Optical Devices 11, 41 Board 12 Insulating film 15, 15A, 15B, 15C Multilayer graphene 151 End face 16 Resist 17, 17A, 17B, 17C, 18, 18A, 18B, 18C electrode 40 Optical sensor array (optical device)

Claims

1. A resist having a predetermined shape is formed on the multi-layer graphene. The multilayer graphene is patterned in a single process by anisotropic reactive ion etching using oxygen, so that the multilayer graphene is processed into a tapered shape together with the resist; removing the resist covering the inclined end faces of the processed multilayer graphene and having a part of the resist of the predetermined shape attached to the inclined end faces by the reactive ion etching; providing an electrode covering the exposed inclined end surface of the multilayer graphene; A method for manufacturing an optical device.

2. removing the resist attached to the inclined end face of the processed multilayer graphene by reactive ion etching in multiple steps; The method for manufacturing an optical device according to claim 1 .

3. The resist attached to the inclined end surface of the processed multilayer graphene is removed at once by a second anisotropic etching having a time shorter than that of the anisotropic etching. The method for manufacturing an optical device according to claim 1 .

4. arranging a plurality of the optical devices in a predetermined array on a substrate; The method for manufacturing an optical device according to claim 1 .

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