Waveguide structure integrated with moscap and phase modulator comprising the same

Abstract

The application particularly relates to a waveguide structure integrated with a MOSCAP and a phase modulator comprising the same. The waveguide structure is composed of a waveguide, a lower electrode layer, an insulator layer and a gate electrode, and a sandwich structure composed of the lower electrode layer, the insulator layer and the gate electrode from bottom to top is located above the waveguide; the waveguide is undoped monocrystalline silicon, and the lower electrode layer is conductive silicon material. The phase modulator prepared by using the waveguide structure maintains high controllability of the high-mobility lower electrode layer and the doping concentration and thickness, can avoid introduction of high carrier concentration in the non-effective modulation area and cause of additional optical loss relative to the existing lower electrode using the whole silicon waveguide, has low overall loss, low power consumption and good phase modulation effect.

Description

Technical Field

[0001] This invention relates to the field of silicon-based electronic integration, and more specifically to a waveguide structure integrating a MOSCAP and a phase modulator containing the same. Background Technology

[0002] Phase modulation is a crucial technology for silicon-based integrated circuits, playing an irreplaceable role in coherent optical communication, optical filters, and optical splitters. Currently, phase modulation in silicon-based devices is primarily based on thermo-optic or electro-optic modulation. Thermo-optic modulation alters the refractive index by changing the material temperature, resulting in significant power consumption. Electro-optic modulation, based on the plasma dispersion effect, often exhibits substantial optical loss and power consumption.

[0003] Electro-optic phase shifters based on metal oxide semiconductor capacitors (MOSCAPs) possess very high capacitance density due to their extremely thin insulating layer. This allows for significant carrier concentration changes at relatively low gate voltages, effectively altering the material's effective refractive index and modulating the optical signal phase. Furthermore, due to its capacitive structure, MOSCAPs only consume current and power during charging and discharging, exhibiting no power consumption in a static state, thus providing a significant performance advantage.

[0004] MOSCAP electro-optic phase shifters have low power consumption, but the plasma dispersion mechanism determines that they rely on the accumulation of non-equilibrium carriers in the capacitor to achieve the control effect, which will bring certain optical losses. These optical losses are unavoidable, but some optical losses can be avoided as much as possible through design. For example, integrating MOSCAP requires the introduction of metal electrodes, and the optical losses caused by the small distance between the metal electrodes and the optical field, as well as the insertion loss when no bias voltage is applied to MOSCAP.

[0005] Currently, in silicon photonics integrated MOSCAP phase shifters, the lower electrode is usually composed of an entire p-doped waveguide, which is relatively thick and not conducive to modulating carriers to form a higher local concentration. Modulation mainly depends on the gate. In addition, the doped waveguide does not improve the modulation effect, but adds extra losses. Summary of the Invention

[0006] Based on this, the objective of this invention is to provide a waveguide structure with integrated MOSCAP, which can avoid introducing high carrier concentration and additional optical loss in the non-effective modulation region, and has low overall loss and low power consumption.

[0007] The present invention achieves the above-mentioned technical objectives through the following technical solution: The present invention provides a waveguide structure for integrated MOSCAP, which consists of a waveguide, a lower electrode layer, an insulating layer and a gate. A sandwich structure consisting of the lower electrode layer, the insulating layer and the gate is located above the waveguide from bottom to top. The waveguide is undoped single crystal silicon and the lower electrode layer is made of conductive silicon material.

[0008] As a preferred embodiment, the waveguide includes, but is not limited to, rectangular waveguides, ridge waveguides, straight waveguides, curved waveguides, and micro-ring waveguides.

[0009] In a preferred embodiment, the conductive silicon material of the lower electrode layer includes, but is not limited to, amorphous silicon and polycrystalline silicon.

[0010] In a preferred embodiment, the doping concentration of the lower electrode layer is 10. 17 ~10 20 cm 3 The doping ions are B and / or P.

[0011] In a preferred embodiment, the insulating layer includes, but is not limited to, silicon dioxide and high-k dielectric.

[0012] As a preferred embodiment, the gate material includes, but is not limited to, metal materials, transparent conductive oxide materials, and polycrystalline silicon.

[0013] In a preferred embodiment, the thickness of the lower electrode layer is 5–20 nm, and / or the thickness of the insulating layer is 1–20 nm.

[0014] In a preferred embodiment, the lower electrode layer is deposited on the waveguide using various thin film deposition processes.

[0015] As a preferred embodiment, the deposition method of the insulating layer includes thermal oxidation and various thin film deposition processes.

[0016] In a preferred embodiment, the lower electrode layer is a conductive silicon material deposited on the waveguide and subjected to epitaxial annealing. The epitaxial annealing scheme includes, but is not limited to, furnace heating annealing and laser annealing.

[0017] The second objective of this invention is to provide a phase modulator based on MOSCAP, which includes at least a substrate, the aforementioned integrated MOSCAP waveguide structure, and contact electrodes. There are two contact electrodes, which are respectively connected to the lower electrode layer and the gate in the waveguide structure.

[0018] This MOSCAP-based phase modulator uses a single-crystal silicon waveguide structure. A lower electrode layer is fabricated on the single-crystal silicon waveguide structure as the lower electrode. When a bias voltage is applied to the lower electrode layer and the gate of the MOSCAP, charge accumulates on the lower electrode layer and the gate. This charge accumulation affects the effective refractive index of the material at the location through the plasma dispersion effect. Based on the overlap between the optical field and the carrier accumulation region, the optical phase is modulated. This application uses deposited conductive silicon as the lower electrode of the MOSCAP for electro-optic modulation. The doping concentration and thickness are highly controllable. Compared with existing methods that use the entire silicon waveguide as the lower electrode, this avoids introducing high carrier concentrations in non-effective modulation regions and causing additional optical losses. The overall loss is low, the power consumption is low, and the phase modulation effect is good. The photoelectric properties of the lower electrode layer are further improved by epitaxial annealing after deposition. Attached Figure Description

[0019] Figure 1 A schematic diagram of a waveguide structure integrating MOSCAP is provided for an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of a phase modulator based on MOSCAP provided for an embodiment of the present invention;

[0021] Figure 3 This is a flowchart illustrating the fabrication process of a specific phase modulator in one of the embodiments.

[0022] The attached diagram lists the components represented by each number as follows:

[0023] 1 Waveguide, 2 Lower electrode layer, 3 Insulator layer, 4 Gate electrode, 5 Contact electrode. Detailed Implementation

[0024] Currently, in silicon photonics integrated MOSCAP phase shifters, modulation efficiency and rate are typically prioritized over loss performance. However, in some applications requiring only static and small-scale phase compensation, the loss characteristics of the device are prioritized over modulation efficiency and rate. Furthermore, in existing silicon photonics integrated MOSCAP phase shifters, the lower electrode is usually composed of a single p-doped waveguide, resulting in significant thickness. This hinders the formation of higher localized carrier concentrations, making modulation primarily dependent on the gate. Additionally, the doped waveguide does not improve modulation performance but instead increases losses. This invention addresses these shortcomings by improving upon existing technologies to minimize losses while achieving phase modulation.

[0025] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the application. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be more thorough and complete.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0027] It is understood that spatial relation terms such as "below," "under," "below," "below," "above," "above," etc., can be used here to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as "below" or "below" of the other element or feature will be oriented "above" the other element or feature. Therefore, the exemplary terms "below" and "below" can include both upper and lower orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.

[0028] The waveguide structure with integrated MOSCAP provided in this embodiment, such as Figure 1 As shown, it consists of waveguide 1, lower electrode layer 2, insulator layer 3 and gate 4, wherein the sandwich structure consisting of lower electrode layer 2, insulator layer 3 and gate 4 from bottom to top is located above waveguide 1; waveguide 1 is undoped single crystal silicon, and lower electrode layer 2 is conductive silicon material.

[0029] This waveguide structure maintains high mobility by fabricating a lower electrode layer on the waveguide as the lower electrode, and the doping concentration and thickness of the lower electrode layer are more controllable. Compared with the existing method of using the entire silicon waveguide as the lower electrode, it can avoid introducing high carrier concentration in the non-effective modulation region and causing additional optical loss. The overall loss is low, the power consumption is low, and it has a better phase modulation effect.

[0030] Those skilled in the art will understand that the waveguide structure provided in this embodiment, compared with the prior art, has the following improvement: the waveguide 1 uses undoped large single crystal silicon, and then a conductive silicon material lower electrode layer 2 is fabricated on the waveguide 1. This maintains high mobility and the doping concentration and thickness of the lower electrode layer are more controllable. The structure of the waveguide 1 can take various forms, including but not limited to rectangular waveguides, ridge waveguides, straight waveguides, curved waveguides, and micro-ring waveguides.

[0031] The lower electrode layer 2 can typically be deposited on the waveguide 1 by deposition. Various thin film deposition processes can be used, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), and more specifically, low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD).

[0032] The conductive silicon material deposited in the lower electrode layer 2 includes, but is not limited to, amorphous silicon and polycrystalline silicon, preferably amorphous silicon. The doping concentration of the lower electrode layer 2 is 10. 17 ~10 20 cm 3 The doping ions are B and / or P, and the doping methods can be incorporation during the deposition process, thermal diffusion, or ion implantation.

[0033] After deposition, the lower electrode layer 2 is further improved by epitaxial annealing to enhance its photoelectric properties. The epitaxial scheme can use furnace heating annealing or laser annealing, with high-temperature solid-state epitaxy in a furnace heating chamber being preferred.

[0034] In this embodiment, the material of the insulating layer 3 can be either silicon dioxide or a high-k dielectric, such as hafnium dioxide (HfO2), zirconium dioxide, hafnium silicate, zirconium silicate, or nitrided hafnium silicate or zirconium silicate. The deposition method includes thermal oxidation and various thin film deposition processes.

[0035] The gate material can be a metal, such as Au, Cu, or Al, or a transparent conductive oxide (TCO), such as ITO, FTO, or ITiO, or a polycrystalline silicon material.

[0036] Furthermore, typically, the thickness of the lower electrode layer 2 is 5–20 nm, preferably 10 nm; the thickness of the insulating layer is 1–20 nm, preferably 5 nm.

[0037] This embodiment also provides a phase modulator based on MOSCAP, such as... Figure 2 As shown, it includes at least a substrate, the aforementioned waveguide structure, and contact electrodes 5. There are two contact electrodes 5, which are respectively connected to the lower electrode layer 2 and the gate 4 in the waveguide structure.

[0038] The following describes the structure of a specific phase modulator in more detail using its fabrication process:

[0039] See Figure 3 A ridge waveguide (lower layer height 150 nm, upper layer height 70 nm, upper layer width 470 nm) was fabricated on a 220 nm SOI substrate. The substrate was then placed in an LPCVD furnace tube for vapor deposition of 10 nm of amorphous silicon at a process temperature of 600 °C. BCl3 gas was introduced for boron ion doping at a concentration of 10%. 18 cm 3 A substrate with deposited amorphous silicon was placed in a furnace heating chamber for epitaxial annealing. The process parameters were as follows: the furnace temperature was gradually increased from 600℃ to 1150℃ at a heating rate of 100℃ / h. Subsequently, 5nm of hafnium dioxide and 10nm of ITiO were deposited by PVD. The lower electrode layer and gate were exposed at different locations by photolithography etching. Ni / Au electrodes were deposited by E-Beam deposition. Finally, Cu vias were deposited at the electrodes and brought out by electroplating.

[0040] When a bias voltage is applied to the lower electrode layer and gate of the MOSCAP, charge accumulates on these layers. This charge affects the effective refractive index of the material at that location through plasmon dispersion, modulating the optical phase based on the overlap between the optical field and the carrier accumulation region. This structure uses a thin epitaxial silicon layer as the lower electrode, which, compared to using an entire silicon waveguide as the lower electrode, avoids introducing high carrier concentrations in ineffective modulation regions and causing additional optical losses.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A waveguide structure integrating MOSCAP, characterized in that, A sandwich structure consisting of a waveguide, a lower electrode layer, an insulating layer, and a gate, arranged from bottom to top, is located above the waveguide. The waveguide is made of undoped single-crystal silicon, and the lower electrode layer is made of conductive silicon material.

2. The waveguide structure with integrated MOSCAP as described in claim 1, characterized in that, The waveguides include ridge waveguides and micro-ring waveguides.

3. The waveguide structure with integrated MOSCAP as described in claim 1, characterized in that, The conductive silicon material of the lower electrode layer includes, but is not limited to, amorphous silicon and polycrystalline silicon.

4. The waveguide structure with integrated MOSCAP according to claim 1, characterized in that, The doping concentration of the lower electrode layer is 10. 17 ~10 20 cm 3 The doping ions are B and / or P.

5. The waveguide structure with integrated MOSCAP according to claim 1, characterized in that, The insulating layer includes, but is not limited to, silicon dioxide and high-k dielectric.

6. The waveguide structure with integrated MOSCAP according to claim 1, characterized in that, Gate materials include, but are not limited to, metal materials, transparent conductive oxide materials, and polycrystalline silicon.

7. The waveguide structure with integrated MOSCAP according to claim 1, characterized in that, The thickness of the lower electrode layer is 5~20nm, and / or the thickness of the insulating layer is 1~20nm.

8. The waveguide structure of the integrated MOSCAP according to any one of claims 1 to 7, characterized in that, The lower electrode layer is deposited on the waveguide by a thin film deposition process; and / or the deposition method of the insulating layer includes thermal oxidation process and thin film deposition process.

9. The waveguide structure of the integrated MOSCAP according to any one of claims 1 to 7, characterized in that, The lower electrode layer is a conductive silicon material deposited on the waveguide and subjected to epitaxial annealing. The epitaxial annealing process includes, but is not limited to, furnace heating annealing and laser annealing.

10. A phase modulator based on MOSCAP, characterized in that, It includes at least a substrate, a waveguide structure of the integrated MOSCAP as described in any one of claims 1 to 9, and two contact electrodes, which are respectively connected to the lower electrode layer and the gate in the waveguide structure.

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