High-bandwidth graphene / silicon light intensity modulator

Abstract

The invention 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, a graphene-high k gate medium-graphene capacitor structure is arranged on the silicon optical waveguide substrate; the graphene-high-k gate dielectric-graphene capacitor structure is composed of an upper layer of graphene, a lower layer of graphene and a high-k gate dielectric between the upper layer of graphene and the lower layer of graphene. And two ends of the upper and lower layers of graphene are respectively provided with a bias end and a grounding end. According to the modulator, inorganic molecular crystal antimony oxide / aluminum oxide is used as a composite high-k gate medium, the silicon-based room-temperature carrier mobility of graphene, the residual carrier concentration and other material electrical quality can be effectively kept, and therefore the resistance-capacitance parameter of a device is reduced, and the performance of the device is improved. And a new solution is provided for improving the high-frequency analog bandwidth of the graphene / silicon light intensity modulator.

Description

Technical Field

[0001] The invention relates to the field of silicon-based optoelectronic integrated chips, and in particular to a high-bandwidth graphene / silicon light intensity modulator. Background Art

[0002] The perception and transmission of information is the cornerstone of information technology. Silicon photonics is a device technology that organically integrates optoelectronics and microelectronics. Compared with traditional discrete optical modules, it has significant advantages in optical communications, such as higher bandwidth, lower energy consumption, and higher integration. As a key functional device for tuning the optical carrier intensity signal, the silicon photonic intensity modulator determines the code rate, quality, and transmission distance of the transmitted optical signal. However, the intensity modulator based on the carrier dispersion effect of silicon materials has performance bottlenecks such as limited speed, low modulation efficiency, and cumbersome preparation. Graphene, as a two-dimensional material with a single atomic layer thickness, has the characteristics of ultra-high mobility, a larger electro-optic coefficient than silicon, and compatibility with silicon photonic processes. It is expected to bring new opportunities for the realization of high-bandwidth silicon photonic intensity modulators.

[0003] The high-frequency bandwidth of graphene / silicon optical intensity modulators is determined by the resistance-capacitance (RC) parameters of the device. In existing graphene / silicon optical intensity modulators, due to the heterogeneous integration of graphene and gate dielectrics, the electrical quality of the silicon-based room temperature carrier mobility and residual carrier concentration will be significantly degraded, resulting in an increase in the device resistance-capacitance (RC) parameters, reducing the overall high-frequency response bandwidth of the device. Therefore, it is crucial to develop a gate dielectric integration technology that can maintain the quality of graphene materials and obtain a high-bandwidth graphene / silicon optical intensity modulator. Summary of the invention

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

[0005] To achieve the above object, the technical solution of the present invention is as follows: A graphene / silicon optical intensity modulator, comprising a silicon optical waveguide substrate, a graphene-high k A gate dielectric-graphene capacitor structure, a bias terminal and a ground terminal; The silicon optical waveguide substrate is provided with a graphene-high k Gate dielectric-graphene capacitor structure; the graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, the upper and lower layers, and a high kThe gate dielectric composition; the two ends of the upper and lower graphene layers are respectively provided with a bias terminal and a ground terminal; The upper and lower graphene layers are used as active region light absorbing materials to absorb the optical carrier in the waveguide; the bias end and the ground end collect the light intensity modulation signal of the device.

[0006] In the above-mentioned graphene / silicon optical intensity modulator, the silicon optical waveguide substrate is composed of a strip 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 waveguide upper layer.

[0007] In the above-mentioned graphene / silicon light intensity modulator, the graphene is a single-layer graphene; The width of the overlapping region of the upper and lower graphene layers is 500-1000 nm.

[0008] In the above-mentioned graphene / silicon light intensity modulator, 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, antimony oxide with a thickness of 1-2 nm plus aluminum oxide with a thickness of 10-30 nm.

[0009] In the above-mentioned graphene / silicon optical intensity modulator, the distance between the bias terminal and the ground terminal and the silicon optical waveguide is 0.5-1.5 μm, preferably 1-1.5 μm.

[0010] In the above-mentioned graphene / silicon light intensity modulator, the voltage applied to the bias end is 5-15 V.

[0011] In the above-mentioned graphene / silicon light intensity modulator, 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; The high-frequency analog bandwidth of the graphene / silicon optical intensity modulator is 20-40 GHz.

[0012] The graphene / silicon optical intensity modulator is used for optical signal intensity modulation in the 1550 nm communication band.

[0013] The length of the graphene / silicon light intensity modulator is 50-100 μm.

[0014] Furthermore, the present invention also provides a method for preparing the above-mentioned graphene / silicon light intensity modulator, comprising the following steps: (1) Using dry transfer to transfer copper-based CVD graphene to the silicon optical waveguide, and then etching it to obtain the lower layer of graphene; (2) Vapor-depositing palladium on the lower graphene layer described in (1), and then vapor-depositing gold; and finally removing excess metal; (3) evaporating antimony oxide on the lower graphene layer described in (1), and then depositing aluminum oxide by atomic layer deposition; (4) preparing an upper layer of graphene using the same method as step (1); (5) Evaporate palladium and gold using the same method as step (2).

[0015] The method of the present invention utilizes inorganic molecular crystal antimony oxide / aluminum oxide as a composite high k As a gate dielectric, antimony oxide, as an inorganic molecular crystal, has no dangling bonds on its surface and can form a van der Waals interface with graphene. The weak interface interaction between graphene and antimony oxide makes it possible to maintain the quality of graphene materials. At the same time, the high hydrophilicity of the surface of antimony oxide can effectively promote the adsorption of precursors and the subsequent formation of aluminum oxide during the subsequent atomic layer deposition process. In addition, the thickness of atomic layer deposition is precisely controllable. Therefore, the antimony oxide / aluminum oxide composite gate dielectric can maintain the electrical quality of graphene and reduce the device resistance-capacitance (RC) parameters, thereby improving the high-frequency bandwidth of the device. The device has a simple process and can achieve high-speed signal modulation, which is expected to promote the further development and application of graphene / silicon optical communication technology.

[0016] The present invention has the following advantages: (1) The graphene / silicon light intensity modulator of the present invention uses inorganic molecular crystal antimony oxide / aluminum oxide as a composite high k The gate dielectric maintains the electrical qualities of graphene such as carrier mobility, thereby effectively reducing the device resistance-capacitance (RC) parameters and improving the high-frequency response bandwidth of the device, with a bandwidth of up to 20-40 GHz; (2) The static modulation extinction ratio of the graphene / silicon optical intensity modulator of the present invention reaches 2-6 dB, and can achieve (0.8-3)×10 -2 Static modulation efficiency in dB / V / μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a two-dimensional equivalent circuit of a graphene / silicon light intensity modulator provided by the present invention.

[0018] Figure 2 This is a top view of the graphene / silicon light modulator of the present invention.

[0019] Figure 3 This is an optical microscope image of the graphene / silicon light intensity modulator in Example 1.

[0020] Figure 4 1 is the high frequency response bandwidth curve of the graphene / silicon light intensity modulator in Example 1 and Comparative Example 1.

[0021] Figure 5This is the static modulation characteristic of the graphene / silicon light intensity modulator in Example 2.

[0022] Figure 6 Comparison of electrical qualities such as mobility of graphene before and after composite gate dielectric deposition.

[0023] Figure 7 High-speed data transmission characteristics of graphene / silicon optical intensity modulators. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific embodiments. The given examples are only for illustrating the present invention, but not for limiting the scope of the present invention.

[0025] The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0026] The quantitative tests in the following examples were all repeated three times, and the results were averaged.

[0027] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0028] The high-bandwidth graphene / silicon light intensity modulator provided by the present invention has a two-dimensional equivalent circuit schematic diagram as shown in Figure 1 As shown, the top view is Figure 2 As shown in the figure, the high-bandwidth graphene / silicon optical intensity modulator of the present invention comprises a silicon optical waveguide substrate, a graphene-high k The gate dielectric-graphene capacitor structure, the bias terminal and the ground terminal; the graphene-high k Gate dielectric-graphene capacitor structure; the graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, the upper and lower layers, and a high k The gate dielectric composition; the two ends of the upper and lower graphene layers are respectively provided with a bias terminal and a ground terminal; The upper and lower graphene layers are used as active region light absorbing materials to absorb the optical carrier in the waveguide; the bias end and the ground end collect the light intensity modulation signal of the device.

[0029] The graphene is single-layer graphene.

[0030] The present invention adopts a single-layer graphene controlled by chemical vapor deposition as the light absorption material of the active region. Since antimony oxide, as an inorganic molecular crystal, has no dangling bonds on its surface, it can form a van der Waals interface with graphene, so 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 subsequent formation of aluminum oxide in the subsequent atomic layer deposition process, so the electrical qualities of graphene such as carrier mobility and residual carrier concentration before and after the deposition of the antimony oxide / aluminum oxide composite gate dielectric are not affected.

[0031] In order to achieve the purpose of improving the static modulation efficiency of the device, the present invention also has certain requirements on the thickness of the gate dielectric of the graphene / silicon light intensity modulator. The specific design is as follows: the material used for the high-k gate dielectric and the thickness of antimony oxide with a thickness of 1-5 nm plus aluminum oxide with a thickness of 5-30 nm. Under this condition, the static modulation efficiency of the device can reach (0.8-3)×10 at a graphene length of 50-100 μm. -2 dB / V / μm.

[0032] 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, and its bandwidth can reach up to 20-40 GHz.

[0033] The preparation process of the graphene / silicon light intensity modulator of the present invention is as follows: a single layer of graphene is grown on a metal copper wafer by chemical vapor deposition; it is transferred to a silicon optical waveguide substrate by PMMA polymer transfer medium, and unnecessary graphene areas are removed by electron beam exposure and plasma etching to obtain an active area graphene pattern; a bias terminal electrode pattern is made by electron beam exposure again, palladium and gold are deposited by electron beam evaporation, and finally unnecessary metal films are removed by stripping in an acetone solution to obtain a required electrode pattern; then antimony oxide and aluminum oxide films are grown by thermal evaporation and atomic layer deposition respectively. The graphene / silicon light intensity modulator is obtained by repeating the above-mentioned upper graphene and ground terminal electrode production process.

[0034] In some embodiments, the graphene is a single-layer graphene grown by chemical vapor deposition.

[0035] In some embodiments, the metal material used for the bias terminal and the ground terminal has a thickness of 5-10 nm palladium plus 50-100 nm gold, preferably 5-10 nm palladium plus 50-60 nm gold. Too high electrode thickness will increase the metal absorption loss of light, and too low electrode adhesion will be poor.

[0036] In some embodiments, the distances between the bias terminal and the ground terminal and the silicon optical waveguide are ( Wng) is 0.5-1.5 μm, preferably 1-1.5 μm, to reduce the metal absorption loss of light.

[0037] In some embodiments, the overlap width of the upper and lower graphene layers is W g) 500-1000 nm; In some embodiments, the material and thickness of the high-k gate dielectric are 1-5 nm antimony oxide plus 5-30 nm aluminum oxide, preferably 1-2 nm antimony oxide plus 10-30 nm aluminum oxide. Too thin a gate dielectric thickness will increase the device resistance-capacitance (RC) parameters, while too thick a gate dielectric thickness will reduce the static modulation efficiency of the device.

[0038] In some embodiments, the bias voltage applied to the bias terminal is 5-15V.

[0039] In summary, the present invention provides a high-bandwidth graphene / silicon optical intensity modulator, which uses inorganic molecular crystal antimony oxide / aluminum oxide as a composite high-k gate dielectric to maintain the electrical quality of graphene carrier mobility, and the thickness of the composite gate dielectric is selected to achieve the purpose of reducing the device resistance-capacitance (RC) parameters. The graphene / silicon optical intensity modulator of the present invention has the advantages of high analog bandwidth and high modulation efficiency, and can promote the further development of graphene in the field of silicon optical communication.

[0040] The present invention will be further described below by way of examples, but the present invention is not limited thereto. The methods are conventional methods unless otherwise specified. The raw materials and instruments can be obtained from public commercial sources unless otherwise specified.

[0041] Example 1 The optical microscope image of the graphene / silicon light intensity modulator of this embodiment is shown in FIG. Figure 3 The modulator includes a silicon optical waveguide substrate, a graphene- k The gate dielectric-graphene capacitor structure, the bias terminal and the ground terminal; the graphene-high k Gate dielectric-graphene capacitor structure; the graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, the upper and lower layers, and a high k The gate dielectric composition; the upper and lower graphene layers are provided with a bias terminal and a ground terminal at both ends; in this embodiment, the overlap area width of the upper and lower graphene layers is W g is 500 nm.

[0042] Among them, the waveguide in the silicon optical 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 is a single layer of graphene grown by chemical vapor deposition as a light absorption material; the material used for the high-k gate dielectric is about 2 nm thick antimony oxide plus about 30 nm thick aluminum oxide; the bias end and the ground end are made of 5 nm thick palladium plus 50 nm thick gold; the distance between the bias end and the ground end and the silicon optical waveguide (that is, 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.

[0043] The preparation method of the graphene / silicon light intensity modulator is as follows: (1) Graphene transfer and patterning. Copper-based CVD graphene is transferred to the silicon optical waveguide using dry transfer. After the steps of coating, exposure, O2 plasma etching, etc., the desired graphene pattern is obtained.

[0044] (2) Fabrication of electrodes in contact with graphene. Electron beam positive photoresist was uniformly applied and exposed to obtain a metal mask pattern. Then, 5 nm Pd / 50 nm Au was evaporated using an electron beam evaporator. Finally, excess metal was removed by liftoff in acetone.

[0045] (3) Sb2O3 layer deposition: 2 nm Sb2O3 was deposited using a thermal evaporator.

[0046] (4) Al2O3 layer deposition: 30 nm Al2O3 was deposited on the Sb2O3 layer using an atomic layer deposition machine.

[0047] (5) Graphene transfer and patterning. The steps are similar to (1).

[0048] (6) Fabrication of graphene contact electrode. The steps are similar to (2).

[0049] The bias voltage applied to the modulator bias terminal is 10 V. A high-frequency optical signal is applied to the device through a vector network analyzer, and the obtained electrical signal S21 curve is shown in Figure 4 The 3 dB bandwidth of the modulator reaches 31 GHz.

[0050] Example 2 The difference from Example 1 is that by applying a laser with an incident wavelength of 1550 nm to the device (set at one end of the laser), a bias voltage is applied to the bias end through an electrical source meter and the light intensity signal is collected. The bias voltage varies from -10 V to 10 V. The obtained light intensity varies with the bias voltage as shown in Figure 5 As shown in Figure 2, when the bias voltage is 10 V, the static modulation efficiency of the device reaches 1×10 -2 dB / V / μm.

[0051] Comparative Example 1 The difference from Example 1 is that aluminum oxide is directly deposited on the graphene as the gate dielectric. A bias voltage of 10 V is applied to the bias terminal of the device. A high-frequency optical signal is applied to the device through a vector network analyzer, and the obtained electrical signal S21 curve is as follows: Figure 4 As shown, the 3 dB bandwidth of the device is 5 GHz.

[0052] Example 3 After similar micro-nano processing steps as the modulator, the graphene-silicon-based field effect transistor device can be prepared. The bias voltage is applied to the Si gate terminal at the bottom of the transistor through the source meter and the current signal at the source and drain of the transistor is collected. The bias voltage varies from -60 V to 60 V. The change of the source-drain current with the gate voltage is shown in the figure below. Figure 6 As shown in the figure, taking the slope of the current-voltage curve near the Dirac point, the room temperature carrier mobility of the device reaches 1×10 4 cm 2 / Vs.

[0053] The present invention uses a single-layer graphene grown by chemical vapor deposition as the active region light absorption material. Figure 6 This is a comparison of the electrical qualities of graphene, such as mobility, before and after the composite gate dielectric deposition. Since antimony oxide, as an inorganic molecular crystal, has no dangling bonds on its surface, it can form a van der Waals interface with graphene, so 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 subsequent formation of aluminum oxide during the subsequent atomic layer deposition process, so the electrical qualities of graphene, such as carrier mobility and residual carrier concentration, before and after the deposition of the antimony oxide / aluminum oxide composite gate dielectric are not affected.

[0054] Example 4 The graphene / silicon optical intensity modulator prepared in Example 1 is connected to the test link, a waveform generator is used to generate code elements, an oscilloscope is connected to the output end of the receiving filter, and then the oscilloscope scanning cycle is adjusted to synchronize the horizontal scanning cycle of the oscilloscope with the cycle of the received code elements. At this time, the Figure 7 The eye diagram shown in Figure 1. Figure 7 It can be seen that the rate of the graphene / silicon optical intensity modulator of the present invention reaches 30 Gbit / s.

Claims

1. A graphene / silicon optical intensity modulator, comprising a silicon optical waveguide substrate, a graphene-high k A gate dielectric-graphene capacitor structure, a bias terminal and a ground terminal; The silicon optical waveguide substrate is provided with a graphene-high k Gate dielectric-graphene capacitor structure; the graphene-high k The gate dielectric-graphene capacitor structure consists of two layers of graphene, the upper and lower layers, and a high k The gate dielectric composition; the two ends of the upper and lower graphene layers are respectively provided with a bias terminal and a ground terminal; The upper and lower graphene layers are used as active region light absorbing materials to absorb the optical carrier in the waveguide; the bias end and the ground end collect the light intensity modulation signal of the device.

2. The graphene / silicon light intensity modulator according to claim 1, characterized in that: The silicon optical waveguide substrate consists of a strip 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 waveguide upper layer.

3. The graphene / silicon light intensity modulator according to claim 1 or 2, characterized in that: The graphene is a single-layer graphene; The width of the overlapping region of the upper and lower graphene layers is 500-1000 nm.

4. The graphene / silicon optical intensity modulator according to any one of claims 1 to 3, characterized in that: The high-k gate dielectric is antimony oxide with a thickness of 1-5 nm and aluminum oxide with a thickness of 5-30 nm.

5. The graphene / silicon optical intensity modulator according to any one of claims 1 to 4, characterized in that: The distances between the bias terminal and the ground terminal and the silicon optical waveguide are 0.5-1.5 μm.

6. The graphene / silicon optical intensity modulator according to any one of claims 1 to 5, characterized in that: The voltage applied to the bias terminal is 5-15 V.

7. The graphene / silicon optical intensity modulator according to any one of claims 1 to 6, characterized in that: The bias terminal and the ground terminal are palladium with a thickness of 5-10 nm and gold with a thickness of 50-100 nm.

8. The method for preparing the graphene / silicon light intensity modulator according to any one of claims 1 to 7, comprising the following steps: (1) Using dry transfer to transfer copper-based CVD graphene to the silicon optical waveguide, and then etching it to obtain the lower layer of graphene; (2) Vapor-depositing palladium on the lower graphene layer described in (1), and then vapor-depositing gold; and finally removing excess metal; (3) evaporating antimony oxide on the lower graphene layer described in (1), and then depositing aluminum oxide by atomic layer deposition; (4) preparing an upper layer of graphene using the same method as step (1); (5) Evaporate palladium and gold using the same method as step (2).

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