A high bandwidth graphene / silicon optical intensity modulator

Abstract

The application provides a high-bandwidth graphene / silicon light intensity modulator, and belongs to the field of silicon-based optoelectronic integrated chips.The modulator comprises a silicon optical waveguide substrate, a graphene-high-k gate dielectric-graphene capacitor structure, a bias end and a grounding end;the graphene-high-k gate dielectric-graphene capacitor structure is arranged on the silicon optical waveguide substrate;the graphene-high-k gate dielectric-graphene capacitor structure is composed of upper and lower graphene layers and high-k gate dielectric between the upper and lower graphene layers;the upper and lower graphene layers are respectively provided with the bias end and the grounding end at two ends thereof.The modulator utilizes inorganic molecular crystal antimony oxide / aluminum oxide as a composite high-k gate dielectric, can effectively maintain the material electrical quality such as silicon-based room temperature carrier mobility and residual carrier concentration of graphene, thereby reducing the resistance-capacitance parameters of the device, and provides a new solution for improving the high-frequency analog bandwidth of the graphene / silicon light intensity modulator.

Description

Technical Field

[0001] This invention relates to the field of silicon-based optoelectronic integrated chips, specifically to a high-bandwidth graphene / silicon light intensity modulator. Background Technology

[0002] Information perception and transmission are the cornerstones of information technology. Silicon photonics, a device technology that organically integrates optoelectronics and microelectronics, offers significant advantages in optical communication compared to traditional discrete optical modules, including higher bandwidth, lower power consumption, and higher integration. The silicon photonic intensity modulator, as a key functional device for tuning the intensity signal of the optical carrier, determines the bit rate, quality, and transmission distance of the transmitted optical signal. However, intensity modulators based on the carrier dispersion effect of silicon materials suffer from performance bottlenecks such as speed limitations, low modulation efficiency, and cumbersome fabrication. Graphene, a two-dimensional material with a single atomic layer thickness, possesses ultra-high mobility, a larger electro-optic coefficient than silicon, and compatibility with silicon photonics processes, promising new opportunities for realizing high-bandwidth silicon photonic intensity modulators.

[0003] The high-frequency bandwidth of graphene / silicon optical intensity modulators is determined by the device's resistance-capacitance (RC) parameters. In existing graphene / silicon optical intensity modulators, the material's electrical properties, such as silicon-based room-temperature carrier mobility and residual carrier concentration, significantly degrade during the heterogeneous integration of graphene and the gate dielectric. This leads to an increase in the device's RC parameters and a reduction in the overall high-frequency response bandwidth. Therefore, developing a gate dielectric integration technology that maintains the quality of graphene materials is crucial for obtaining high-bandwidth graphene / silicon optical intensity modulators. Summary of the Invention

[0004] The purpose of this invention is to provide a high-bandwidth graphene / silicon light intensity modulator that utilizes inorganic molecular crystals antimony oxide / alumina as a composite high-intensity modulator. k The gate dielectric maintains the electrical qualities of graphene, such as carrier mobility, thereby effectively reducing the device's resistance-capacitance (RC) parameters; this modulator has the advantages of high bandwidth and high modulation efficiency.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A graphene / silicon optical intensity modulator, comprising a silicon optical waveguide substrate, a graphene-high-strength silicon optical waveguide substrate, and a silicon optical waveguide substrate. k Gate dielectric-graphene capacitor structure, bias terminal and ground terminal;

[0007] Graphene-high-polymer material is disposed on the silicon optical waveguide substrate. k Gate dielectric-graphene capacitor structure; the graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, an upper layer and a lower layer of graphene, and a high-density interlayer between the upper and lower layers of graphene. kThe grid consists of a dielectric material; the upper and lower graphene layers are respectively provided with a bias terminal and a ground terminal at both ends;

[0008] The upper and lower graphene layers serve as active light-absorbing materials for absorbing the optical carrier in the waveguide; the bias terminal and ground terminal collect the light intensity modulation signal of the device.

[0009] In the graphene / silicon light intensity modulator described above, the silicon waveguide substrate is composed of a strip-shaped silicon waveguide structure with a width of 400-1000 nm and a height of 150-300 nm, and a silicon dioxide dielectric layer with a height of 10-40 nm on the upper layer of the waveguide.

[0010] In the graphene / silicon light intensity modulator described above, the graphene is a single-layer graphene.

[0011] The overlap region between the upper and lower graphene layers is 500-1000 nm wide.

[0012] In the graphene / silicon light intensity modulator described above, the high-k gate dielectric is antimony oxide with a thickness of 1-5 nm plus aluminum oxide with a thickness of 5-30 nm; preferably, it is antimony oxide with a thickness of 1-2 nm plus aluminum oxide with a thickness of 10-30 nm.

[0013] In the graphene / silicon light intensity modulator described above, the distance between the bias terminal and the ground terminal and the silicon waveguide is 0.5-1.5 μm; preferably 1-1.5 μm.

[0014] In the graphene / silicon light intensity modulator described above, the voltage applied to the bias terminal is 5-15 V.

[0015] In the graphene / silicon light intensity modulator described above, the bias terminal and the ground terminal are palladium with a thickness of 5-10 nm plus gold with a thickness of 50-100 nm; preferably, palladium with a thickness of 5-10 nm plus gold with a thickness of 50-60 nm.

[0016] The high-frequency analog bandwidth of the graphene / silicon light intensity modulator is 20-40 GHz.

[0017] The graphene / silicon light intensity modulator is used for light signal intensity modulation in the 1550 nm communication band.

[0018] The graphene / silicon light intensity modulator has a length of 50-100 μm.

[0019] Furthermore, the present invention also provides a method for fabricating the above-mentioned graphene / silicon light intensity modulator, comprising the following steps:

[0020] (1) Copper-based CVD graphene was transferred onto a silicon optical waveguide using a dry transfer method and then etched to obtain the lower layer of graphene.

[0021] (2) Palladium is deposited on the lower graphene layer described in (1), and then gold is deposited; finally, excess metal is removed;

[0022] (3) Antimony oxide is vapor-deposited on the lower graphene layer described in (1), and then aluminum oxide is deposited by atomic layer deposition.

[0023] (4) Prepare the upper layer of graphene using the same method as in step (1);

[0024] (5) Palladium and gold are vapor deposited using the same method as in step (2).

[0025] The method of this invention utilizes inorganic molecular crystals antimony oxide / alumina as a composite high-strength... k Antimony oxide, as an inorganic molecular crystal, has no dangling bonds on its surface, allowing it to form van der Waals interfaces with graphene. The weak interfacial interaction between graphene and antimony oxide makes it possible to maintain the quality of the graphene material. Simultaneously, the high hydrophilicity of antimony oxide effectively promotes the adsorption of precursors and the formation of alumina during subsequent atomic layer deposition. Combined with the precisely controllable thickness of atomic layer deposition, the antimony oxide / alumina composite gate dielectric can maintain the electrical quality of graphene while reducing the device's resistance-capacitance (RC) parameters and improving the device's high-frequency bandwidth. This device has a simple fabrication process and can achieve high-speed signal modulation, promising to promote the further development and application of graphene / silicon optical communication technology.

[0026] The present invention has the following advantages:

[0027] (1) The graphene / silicon light intensity modulator of the present invention utilizes inorganic molecular crystals antimony oxide / alumina as a composite high-intensity modulator. k The gate dielectric maintains the electrical qualities of graphene, such as carrier mobility, thereby effectively reducing the device's resistance-capacitance (RC) parameters and improving the device's high-frequency response bandwidth, which can reach up to 20-40 GHz.

[0028] (2) The static modulation extinction ratio of the graphene / silicon light intensity modulator of the present invention reaches 2-6 dB, and (0.8-3)×10 can be achieved with a graphene length of 50-100 μm. -2 Static modulation efficiency in dB / V / μm. Attached Figure Description

[0029] Figure 1 A two-dimensional equivalent circuit diagram of the graphene / silicon light intensity modulator provided by the present invention.

[0030] Figure 2 This is a top view of the graphene / silicon optical modulator of the present invention.

[0031] Figure 3This is an optical microscope image of the graphene / silicon light intensity modulator in Example 1.

[0032] Figure 4 The high-frequency response bandwidth curves of the graphene / silicon light intensity modulators in Example 1 and Comparative Example 1 are shown.

[0033] Figure 5 The static modulation characteristics of the graphene / silicon light intensity modulator in Example 2 are shown.

[0034] Figure 6 This study compares the electrical properties of graphene, such as mobility, before and after composite gate dielectric deposition.

[0035] Figure 7 High-speed data transmission characteristics for graphene / silicon light intensity modulators. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0037] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0038] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0039] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0040] The high-bandwidth graphene / silicon light intensity modulator provided by this invention has the following two-dimensional equivalent circuit diagram: Figure 1 As shown, the top view is as follows Figure 2 As shown in the figure; it can be seen from the figure that the high-bandwidth graphene / silicon optical intensity modulator of the present invention includes a silicon optical waveguide substrate, a graphene-high-bandwidth silicon optical waveguide substrate, and a silicon optical waveguide substrate. k The gate dielectric-graphene capacitor structure includes a bias terminal and a ground terminal; graphene-high-strength dielectric is disposed on the silicon optical waveguide substrate. k Gate dielectric-graphene capacitor structure; the graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, an upper layer and a lower layer of graphene, and a high-density interlayer between the upper and lower layers of graphene. k The grid consists of a dielectric material; the upper and lower graphene layers are respectively provided with a bias terminal and a ground terminal at both ends;

[0041] The upper and lower graphene layers serve as active light-absorbing materials for absorbing the optical carrier in the waveguide; the bias terminal and ground terminal collect the light intensity modulation signal of the device.

[0042] The graphene is a single-layer graphene.

[0043] This invention uses monolayer graphene grown by controlled chemical vapor deposition as the active region light-absorbing material. Since antimony oxide is an inorganic molecular crystal with no dangling bonds on its surface, it can form a van der Waals interface with graphene. Therefore, there is only a weak interfacial van der Waals interaction between graphene and antimony oxide. At the same time, the high hydrophilicity of the surface of antimony oxide can effectively promote the adsorption of precursors and the formation of alumina during subsequent atomic layer deposition. Therefore, the electrical properties of graphene, such as carrier mobility and residual carrier concentration, are not affected before and after the deposition of the antimony oxide / alumina composite gate dielectric.

[0044] To improve the static modulation efficiency of the device, this invention also imposes certain requirements on the gate dielectric thickness in the graphene / silicon optical intensity modulator. The specific design is as follows: the high-k gate dielectric uses antimony oxide with a thickness of 1-5 nm plus aluminum oxide of 5-30 nm. Under these conditions, the static modulation efficiency of the device can reach (0.8-3)×10⁻¹⁰ with a graphene length of 50-100 μm. -2 dB / V / μm.

[0045] By applying a DC voltage of 5-15 V to the bias terminal and applying a high-frequency optical signal to the device through a vector network analyzer, the high-frequency response bandwidth of the device can be obtained, which can reach up to 20-40 GHz.

[0046] The fabrication process of the graphene / silicon light intensity modulator of the present invention is roughly as follows: A single layer of graphene is grown on a copper wafer using chemical vapor deposition; this graphene is transferred to a silicon waveguide substrate using PMMA polymer transfer medium; unwanted graphene regions are removed by electron beam lithography and plasma etching to obtain the active region graphene pattern; a bias electrode pattern is fabricated again using electron beam lithography; palladium and gold are deposited using electron beam evaporation; finally, unwanted metal films are removed by peeling in acetone solution to obtain the desired electrode pattern; subsequently, antimony oxide and aluminum oxide films are grown using thermal evaporation and atomic layer deposition, respectively. Repeating the above-described fabrication process for the upper graphene layer and the ground electrode yields the graphene / silicon light intensity modulator.

[0047] In some embodiments, the graphene is monolayer graphene grown under controlled chemical vapor deposition.

[0048] In some embodiments, the metal materials used for the bias terminal and the ground terminal are palladium with a thickness of 5-10 nm plus gold with a thickness of 50-100 nm, preferably palladium with a thickness of 5-10 nm plus gold with a thickness of 50-60 nm. Too high an electrode thickness will increase the metal absorption loss of light, while too low an electrode thickness will result in poor electrode adhesion.

[0049] In some embodiments, the distance between the bias terminal and the ground terminal and the silicon optical waveguide ( WThe metal absorption loss of light is reduced by 0.5-1.5 μm (ng), preferably 1-1.5 μm.

[0050] In some embodiments, the width of the overlapping region of the upper and lower graphene layers ( W g) is 500-1000 nm;

[0051] In some embodiments, the high-k gate dielectric uses antimony oxide with a thickness of 1-5 nm and aluminum oxide with a thickness of 5-30 nm, preferably antimony oxide with a thickness of 1-2 nm and aluminum oxide with a thickness of 10-30 nm. Too thin a gate dielectric will increase the resistance-capacitance (RC) parameter of the device, while too thick a gate dielectric will reduce the static modulation efficiency of the device.

[0052] In some embodiments, the bias voltage applied to the bias terminal is 5-15 V.

[0053] In summary, this invention provides a high-bandwidth graphene / silicon optical intensity modulator. It utilizes inorganic molecular crystals antimony oxide / alumina as a composite high-k gate dielectric to maintain the electrical properties of graphene, such as carrier mobility. Furthermore, the thickness of the composite gate dielectric is carefully selected to reduce the device's resistance-capacitance (RC) parameters. This graphene / silicon optical intensity modulator offers advantages such as high analog bandwidth and high modulation efficiency, which can promote the further development of graphene in the field of silicon optical communication.

[0054] The present invention will be further illustrated by the following embodiments, but the invention is not limited thereto. Unless otherwise specified, the methods described are conventional methods. Unless otherwise specified, the raw materials and equipment described are available from publicly available commercial sources.

[0055] Example 1

[0056] An optical microscope image of the graphene / silicon light intensity modulator in this embodiment is shown below. Figure 3 As shown. The modulator includes a silicon optical waveguide substrate, graphene-high... k The gate dielectric-graphene capacitor structure includes a bias terminal and a ground terminal; graphene-high-strength dielectric is disposed on the silicon optical waveguide substrate. k Gate dielectric-graphene capacitor structure; the graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, an upper layer and a lower layer of graphene, and a high-density interlayer between the upper and lower layers of graphene. k The gate dielectric is composed of a bias terminal and a ground terminal, respectively, at both ends of the upper and lower graphene layers; in this embodiment, the overlap region width of the upper and lower graphene layers is... W g is 500 nm.

[0057] The waveguide in the silicon waveguide substrate is a strip of silicon with a width of 480 nm and a height of 220 nm, and the upper layer is a 10 nm thick silicon dioxide layer. On the silicon dioxide layer, a single layer of graphene grown by chemical vapor deposition is used as the light absorption material. The high-k gate dielectric is made of antimony oxide with a thickness of about 2 nm and aluminum oxide with a thickness of about 30 nm. The bias terminal and the ground terminal are made of palladium with a thickness of 5 nm and gold with a thickness of 50 nm. The distance between the bias terminal and the ground terminal and the silicon waveguide (i.e., the distance between the edge of the metal contact electrode and the edge of the silicon waveguide) is 1.0 μm, and the modulator length is 50 μm.

[0058] The fabrication method of this graphene / silicon light intensity modulator is as follows:

[0059] (1) Graphene transfer and patterning. Copper-based CVD graphene was transferred onto a silicon optical waveguide using a dry transfer method. After steps such as spin coating, exposure, and O2 plasma etching, the desired graphene pattern was obtained.

[0060] (2) Fabrication of the graphene contact electrode. Electron beam positive photoresist was uniformly applied and exposed to obtain a metal mask pattern. Then, 5 nm Pd / 50 nm Au was deposited using an electron beam evaporator. Finally, excess metal was removed by liftoff in acetone.

[0061] (3) Sb2O3 layer deposition. 2 nm Sb2O3 was deposited using a thermal evaporation machine.

[0062] (4) Al2O3 layer deposition. 30 nm Al2O3 was deposited on the Sb2O3 layer using an atomic layer deposition machine.

[0063] (5) Graphene transfer and patterning. The steps are similar to (1).

[0064] (6) Fabrication of graphene contact electrodes. The steps are similar to (2).

[0065] The modulator's bias terminal is supplied with a 10 V bias voltage. A high-frequency optical signal is applied to the device using a vector network analyzer, and the resulting electrical signal S21 curve is shown below. Figure 4 As shown. The modulator has a 3 dB bandwidth of 31 GHz.

[0066] Example 2

[0067] The difference from Example 1 is that, by applying a laser with an incident wavelength of 1550 nm (set at one end of the laser) to the device, an external bias voltage is applied to the bias terminal through an electrical source meter, and the light intensity signal is collected. The bias voltage varies from -10 V to 10 V, and the resulting change in light intensity with the bias voltage is as follows: Figure 5 As shown, the device achieves a static modulation efficiency of 1×10⁻⁶ at a bias voltage of 10 V. -2 dB / V / μm.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that aluminum oxide is directly deposited atomically on graphene as the gate dielectric. A bias voltage of 10 V is applied to the device's bias terminal. A high-frequency optical signal is applied to the device using a vector network analyzer, and the resulting electrical signal S21 curve is shown below. Figure 4 As shown, the device has a 3 dB bandwidth of 5 GHz.

[0070] Example 3

[0071] After micro-nano fabrication steps similar to those used in modulators, graphene-silicon-based field-effect transistors (FETs) can be fabricated. A bias voltage is applied to the bottom Si gate of the transistor using an electrical source meter, and the current signals across the source and drain terminals are collected. The bias voltage varies from -60 V to 60 V. The changes in source and drain currents with the gate voltage are shown below. Figure 6 As shown, taking the slope of the current-voltage curve near the Dirac point, the device achieves a room-temperature carrier mobility of 1×10⁻⁶. 4 cm 2 / Vs.

[0072] This invention uses monolayer graphene grown in a controlled manner via chemical vapor deposition as the light-absorbing material in the active region. Figure 6 This comparison examines the electrical properties of graphene, such as its mobility, before and after the deposition of the composite gate dielectric. Since antimony oxide, as an inorganic molecular crystal, lacks dangling bonds on its surface, it can form a van der Waals interface with graphene. Therefore, there is only a weak interfacial van der Waals interaction between graphene and antimony oxide. Simultaneously, the high hydrophilicity of antimony oxide effectively promotes the adsorption of precursors and the subsequent formation of alumina during atomic layer deposition. Thus, the electrical properties of graphene, such as carrier mobility and residual carrier concentration, are not affected before and after the deposition of the antimony oxide / alumina composite gate dielectric.

[0073] Example 4

[0074] The graphene / silicon light intensity modulator prepared in Example 1 was connected to the test link. A waveform generator was used to generate symbols. An oscilloscope was connected to the output of the receiving filter, and then the oscilloscope's scanning period was adjusted to synchronize the horizontal scanning period with the period of the received symbols. At this point, the symbols could be observed on the oscilloscope. Figure 7 The eye diagram shown. (By...) Figure 7 As can be seen, the graphene / silicon light intensity modulator of the present invention achieves a rate of 30 Gbit / s.

Claims

1. A graphene / silicon optical intensity modulator, comprising a silicon optical waveguide substrate, a graphene-silicon high-intensity modulator, and a silicon optical waveguide substrate. k Gate dielectric-graphene capacitor structure, bias terminal and ground terminal; Graphene-high-polymer material is disposed on the silicon optical waveguide substrate. k Gate dielectric-graphene capacitor structure; The graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, an upper layer and a lower layer of graphene, and a high-density interlayer between the upper and lower layers of graphene. k The gate dielectric consists of a graphene layer with a bias terminal at one end and a graphene layer with a ground terminal at one end. The upper and lower graphene layers serve as active light-absorbing materials for absorbing optical carrier waves in the waveguide; a voltage is applied to the bias terminal to adjust the optical intensity signal of the device. The high-k gate dielectric is composed of antimony oxide with a thickness of 1-5 nm and aluminum oxide with a thickness of 5-30 nm; The graphene-high k The gate dielectric-graphene capacitor structure is placed on the upper layer of the silicon optical waveguide structure; The overlapping area of ​​the upper and lower graphene layers is projected onto the silicon optical waveguide structure in a direction perpendicular to the substrate. The overlap region between the upper and lower graphene layers is 500-1000 nm wide.

2. The graphene / silicon light intensity modulator according to claim 1, characterized in that: The silicon waveguide substrate consists of a strip-shaped silicon waveguide structure with a width of 400-1000 nm and a height of 150-300 nm, and a silicon dioxide dielectric layer with a height of 10-40 nm on top of the waveguide.

3. The graphene / silicon light intensity modulator according to claim 1 or 2, characterized in that: The graphene is a single-layer graphene.

4. The graphene / silicon light intensity modulator according to claim 1 or 2, characterized in that: The distance between the bias terminal and the ground terminal and the silicon waveguide is 0.5-1.5 μm.

5. The graphene / silicon light intensity modulator according to claim 1 or 2, characterized in that: The voltage applied to the bias terminal is 5-15 V.

6. The graphene / silicon light intensity modulator according to claim 1 or 2, characterized in that: The bias terminal and ground terminal are composed of palladium with a thickness of 5-10 nm and gold with a thickness of 50-100 nm.

7. A method for preparing the graphene / silicon light intensity modulator according to any one of claims 1-6, comprising the following steps: (1) Copper-based CVD graphene was transferred onto a silicon optical waveguide using a dry transfer method and then etched to obtain the lower layer of graphene. (2) Palladium is deposited on the lower graphene layer described in (1), and then gold is deposited; finally, excess metal is removed; (3) Antimony oxide is vapor-deposited on the lower graphene layer described in (1), and then aluminum oxide is deposited by atomic layer deposition. (4) Prepare the upper layer of graphene using the same method as in step (1); (5) Palladium and gold are vapor deposited using the same method as in step (2).

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