Micro-ring modulator and its preparation method

Abstract

The present invention provides a micro-ring modulator and a method for preparing the same, wherein the method comprises: providing a substrate layer; forming a coupled waveguide and a micro-ring resonant structure arranged in parallel on the substrate layer, wherein the micro-ring resonant structure comprises a first doping structure and a second doping structure stacked in sequence along the thickness direction of the substrate layer, wherein the first doping structure and the second doping structure have opposite doping types; and forming an electrode electrically connected to the micro-ring resonant structure.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a micro-ring modulator and a preparation method thereof. Background Art

[0002] Drawing on the development path of large-scale integrated circuits, research is being conducted at home and abroad to integrate active devices (such as modulators, detectors, etc.) and optical waveguide devices (such as splitters / combiners, etc.) onto a substrate to achieve photonic integrated chips with similar advantages to large-scale integrated circuits. Photonic integrated chips have the characteristics of low cost, small size, low power consumption, flexible expansion and high reliability. In the process of optical fiber communication, the intensity of light can be controlled by electro-optic modulators. Therefore, electro-optic modulators occupy an important position in optical fiber communication systems. At the same time, electro-optic modulators are also one of the important optoelectronic devices in photonic integrated chip solutions.

[0003] In recent years, silicon-based electro-optic modulators are an important research direction in electro-optic modulators, and they play a vital role in optical cross-connect (OXC) and optical differential multiplexing (OADM) in the field of optical communications. There are two main types of silicon-based electro-optic modulators: one is the electro-refractive index electro-optic modulator, which realizes the change from phase to intensity through an interferometer or resonant device, and finally realizes the modulation of optical signals; the other is the electro-absorption electro-optic modulator, which changes the imaginary part of the refractive index through an external electric field, thereby directly changing the intensity change of the light wave in the electro-optic modulator, and finally realizes the modulation of optical signals.

[0004] At present, a variety of silicon-based electro-optic modulators have been successfully designed and manufactured, and various technical indicators have been gradually improved. However, the comprehensive performance is still far behind the mature lithium niobate electro-optic modulator, and it cannot meet the future development requirements of optical interconnection and optical communication. Specifically, since the photoelectric effect of silicon material itself is very weak compared with other materials, the change of the external electric field makes the change of the refractive index of silicon material relatively small. In order to overcome this shortcoming, it is necessary to increase the size of the electro-optic modulator to achieve a better modulation effect. In order to achieve small-size integration, scientific researchers have studied many novel structures, among which the micro-ring modulator is a structure with a more obvious effect. In the related technology, it is necessary to reduce the size of the micro-ring modulator while further improving the modulation efficiency of the micro-ring modulator, thereby improving the integration of the photonic integrated chip and reducing the preparation cost. Summary of the invention

[0005] In view of this, an embodiment of the present invention is intended to provide a micro-ring modulator and a method for manufacturing the same.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] The method for preparing a micro-ring modulator provided by an embodiment of the present invention comprises:

[0008] providing a substrate layer;

[0009] forming a coupled waveguide and a micro-ring resonant structure arranged in parallel on the substrate layer, wherein the micro-ring resonant structure comprises a first doping structure and a second doping structure sequentially stacked in a thickness direction of the substrate layer, wherein the first doping structure and the second doping structure have opposite doping types; and

[0010] An electrode electrically connected to the micro-ring resonant structure is formed.

[0011] In the above scheme, the coupled waveguide and micro-ring resonant structure arranged in parallel on the substrate layer comprises:

[0012] forming a first material layer on the substrate layer;

[0013] removing part of the first material layer to form a coupling waveguide and a first doping structure material layer;

[0014] Performing a first doping on the first doping structure material layer to form the first doping structure;

[0015] forming a second material layer on the first doping structure;

[0016] removing a portion of the second material layer to form a second doped structure material layer;

[0017] The second doping structure material layer is subjected to a second doping process to form the second doping structure.

[0018] In the above solution, the removing part of the first material layer includes:

[0019] Performing a first etching on the first material layer to form the coupling waveguide and the first sub-material layer; the projection of the first sub-material layer on a preset plane is circular; the first etching stops on the top surface of the substrate layer; the preset plane is perpendicular to the thickness direction of the substrate layer;

[0020] The first sub-material layer is subjected to a second etching to form the first doped structure material layer having a groove; the projection of the portion of the first sub-material layer removed by the second etching on the preset plane is circular; the second etching stops in the first sub-material layer.

[0021] In the above solution, performing a first doping on the first doping structure material layer to form the first doping structure includes:

[0022] Performing a first sub-doping on a middle region at the bottom of the groove in the first doping structure material layer to obtain a first doping region;

[0023] The remaining area of ​​the first doping structure material layer is subjected to a second sub-doping of the same type as the first sub-doping to obtain a second doping region; wherein,

[0024] The first doping region and the second doping region together form the first doping structure.

[0025] In the above solution, the projection of the second doped structural material layer on the preset plane is a ring; the side edge of the second doped structural material layer is flush with the side edge of the first doped structural material layer;

[0026] The performing a second doping on the second doping structure material layer to form the second doping structure includes:

[0027] Performing a third sub-doping on the middle annular region of the second doping structure material layer to obtain a third doping region;

[0028] The remaining area of ​​the second doping structure material layer is subjected to a fourth sub-doping of the same type as the third sub-doping to obtain a fourth doping region; wherein,

[0029] The third doping region and the fourth doping region together form the second doping structure.

[0030] In the above solution, the first doping includes P-type doping, and the second doping includes N-type doping.

[0031] In the above scheme, the method further comprises:

[0032] A covering layer is formed to cover the coupling waveguide and the micro-ring resonant structure, wherein the refractive index of the covering layer is smaller than the refractive index of the coupling waveguide and the micro-ring resonant structure.

[0033] In the above solution, the electrode includes a first electrode and a second electrode; the electrode electrically connected to the microring resonant structure includes:

[0034] Performing a third etching on the cover layer to form a first electrode contact hole, wherein the third etching stops on the first doping structure; filling the first electrode contact hole with a conductive material to form the first electrode;

[0035] The cover layer is etched for the fourth time to form a second electrode contact hole, and the fourth etching stops on the second doping structure; and the second electrode contact hole is filled with a conductive material to form the second electrode.

[0036] An embodiment of the present invention further provides a micro-ring modulator, comprising:

[0037] substrate layer;

[0038] A coupled waveguide and a micro-ring resonant structure are arranged in parallel on the substrate layer, wherein the micro-ring resonant structure comprises a first doping structure and a second doping structure which are sequentially stacked along the thickness direction of the substrate layer, wherein the first doping structure and the second doping structure have opposite doping types; and

[0039] An electrode electrically connected to the microring resonant structure.

[0040] In the above solution, the first doping structure includes a first doping region and a second doping region having the same doping type as the first doping region and surrounding the first doping region;

[0041] The second doping structure includes a third doping region and a fourth doping region having the same doping type as the third doping region and surrounding the third doping region;

[0042] The first doping structure and the second doping structure are physically connected to the fourth doping region through the second doping region; and the first doping region has no physical contact with the third doping region.

[0043] The micro-ring modulator and its preparation method provided by the embodiment of the present invention, wherein the method comprises: providing a substrate layer; forming a coupled waveguide and a micro-ring resonant structure arranged in parallel on the substrate layer, wherein the micro-ring resonant structure comprises a first doping structure and a second doping structure arranged in sequence in a stacked manner along the thickness direction of the substrate layer, wherein the first doping structure and the second doping structure have opposite doping types; and forming an electrode electrically connected to the micro-ring resonant structure. In the embodiment of the present invention, a vertical (here, the direction referred to by vertical is parallel to the direction of the thickness of the substrate layer) PN junction electrical modulation structure is formed at the junction of the first doping structure and the second doping structure by stacking the first doping structure and the second doping structure in sequence in the thickness direction of the substrate layer, wherein the vertical PN junction electrical modulation structure can increase the overlapping area between the PN junction depletion region and the light wave mode field, improve the interaction between the light wave and the carrier, and thus improve the modulation efficiency; at the same time, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, thereby improving the integration of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide and the micro-ring resonant structure are directly formed on the substrate layer. Compared with a micro-ring modulator in which the coupling waveguide and the micro-ring resonant structure are formed in a planar waveguide layer, this avoids light loss caused by light leaking through the planar waveguide layer, further improves the modulation efficiency of the micro-ring modulator, and further reduces the size of the micro-ring modulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1A schematic diagram of the implementation process of a method for preparing a micro-ring modulator provided in an embodiment of the present invention;

[0045] Figure 2a-2m A cross-sectional schematic diagram of implementation steps of a method for preparing a micro-ring modulator provided by an embodiment of the present invention;

[0046] Figure 3 for Figure 2m Schematic diagram of the cross section along the AA direction;

[0047] Figure 4 for Figure 2m Schematic diagram of the cross section along the BB direction;

[0048] Figure 5 for Figure 2m Schematic diagram of the cross section along the CC direction. DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0050] In the description of the present invention, it is necessary to understand that the terms "length", "width", "depth", "up", "down", "outside", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0051] In the embodiments of the present invention, the term "substrate" refers to the material on which subsequent material layers are added. The substrate itself can be patterned. The material added on top of the substrate can be patterned or can remain unpatterned. In addition, the substrate can include a variety of semiconductor materials, such as silicon, germanium, gallium arsenide, indium phosphide, etc. Alternatively, the substrate can be made of non-conductive materials, such as glass, plastic, or sapphire wafers.

[0052] In an embodiment of the present invention, the term "layer" refers to a material portion including an area with a thickness. The layer may extend over the entirety of the lower or upper structure, or may have a range that is smaller than the range of the lower or upper structure. In addition, the layer may be a region of a homogeneous or inhomogeneous continuous structure having a thickness that is less than the thickness of the continuous structure. For example, the layer may be located between the top surface and the bottom surface of the continuous structure, or the layer may be between any horizontal faces at the top surface and the bottom surface of the continuous structure. The layer may extend horizontally, vertically and / or along an inclined surface. The layer may include multiple sublayers. For example, an interconnect layer may include one or more conductors and contact sublayers (where interconnects and / or via contacts are formed), and one or more dielectric sublayers.

[0053] In the embodiments of the present invention, the terms "first", "second", etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0054] It should be noted that the technical solutions described in the embodiments of the present invention can be arbitrarily combined without conflict.

[0055] In optical communication systems, electro-optic modulators are a key component. Currently, there are generally three types of commercial electro-optic modulators: electro-optic modulators based on lithium niobate, electro-optic modulators based on III-V materials, and silicon-based electro-optic modulators. However, the modulation efficiency of traditional lithium niobate modulators is low and the modulator size is large; the production cost of electro-optic modulators based on III-V materials is very high. Silicon-based modulators are compatible with the currently mature complementary metal oxide semiconductor (CMOS) process, so they can be processed and prepared on a large scale, reducing the production cost of electro-optic modulators.

[0056] Due to the centrosymmetric structure of silicon materials, there is no Pockels effect, and the Kerr effect and Franz-Keldish effect of silicon materials are also extremely weak; even if 10 5 The electric field of V / cm produces a refractive index change of less than 10 -5 , it is not realistic to use the Kerr effect and Franz-Keldish effect to achieve electro-optic modulation. Therefore, in silicon materials, the most effective electro-optic effect is the plasma dispersion effect. This effect can be expressed as: the refractive index of the material decreases with the increase of the carrier concentration in the material, and the absorption coefficient of the material to the light field increases with the increase of the carrier concentration. By using this effect, the carrier concentration in the silicon waveguide can be changed by applying an external voltage signal, and the transmission characteristics of light in the waveguide can be changed. Then, through certain optical structures, such as micro-ring resonators (Micro-Ring, MR), the purpose of electro-optic modulation can be achieved. Since the plasma dispersion effect is quite significant in electro-optic modulators, silicon-based electro-optic modulators are currently mainly realized through the plasma dispersion effect of free carriers in silicon materials.

[0057] In the related art, considering that the modulation efficiency of the plasma dispersion effect modulator is very low, in order to achieve the ideal modulation depth, the modulator needs to be designed to be very long, generally several millimeters in length, which leads to a large size of the modulator, making it difficult to further improve the integration, thereby increasing the preparation cost. The use of resonant structures such as micro-ring resonators, micro-disk resonators or photonic crystal resonators can greatly reduce the size of the modulator. Compared with traditional optical resonators, such as Fabry-Perot (FP) resonators and butterfly resonators, micro-ring resonators do not require cavity surfaces or gratings to provide feedback, so the manufacturing process is simple. The micro-ring resonator structure combined with a small cross-section, high refractive index waveguide can reduce the size of the modulator, reduce the loss of the curved waveguide, and increase the electro-optical modulation rate. Micro-ring-based modulators have the advantages of small size, high sensitivity, and easy integration, and have always attracted the attention of researchers in the industry.

[0058] In the related art, it is considered that the micro-ring modulator generally includes a P-type doping region and an N-type doping region arranged in parallel along the horizontal direction (parallel to the surface of the substrate layer), and the P-type doping region and the N-type doping region constitute a lateral PN junction. Since the lateral PN junction is easier to prepare, the micro-ring modulator generally adopts a lateral PN junction. However, the interaction between the lateral PN junction and the light field is small, which will lead to a low modulation efficiency of the micro-ring modulator, thereby affecting the size of the micro-ring modulator.

[0059] Based on this, the embodiment of the present invention aims to provide an ultra-small micro-ring modulator and a preparation method thereof. In the embodiment of the present invention, a first doping structure and a second doping structure are stacked in sequence along the thickness direction of the substrate layer, and a vertical PN junction electrical modulation structure is formed at the junction of the first doping structure and the second doping structure. The vertical PN junction electrical modulation structure can increase the overlapping area between the PN junction depletion region and the light wave mode field, improve the interaction between the light wave and the carrier, and thus improve the modulation efficiency; at the same time, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, thereby improving the integration of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide and the micro-ring resonant structure are directly formed on the substrate layer. Compared with the micro-ring modulator in which the coupling waveguide and the micro-ring resonant structure are formed in the planar waveguide layer, the light loss caused by the leakage of light through the planar waveguide layer is avoided, the modulation efficiency of the micro-ring modulator is further improved, and the size of the micro-ring modulator is further reduced.

[0060] An embodiment of the present invention provides a method for preparing a micro-ring modulator, wherein: Figure 1 FIG. 1 is a schematic diagram of the implementation process of the method for preparing a micro-ring modulator according to an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps:

[0061] Step 101, providing a substrate layer;

[0062] Step 102, forming a coupled waveguide and a micro-ring resonant structure arranged in parallel on the substrate layer, wherein the micro-ring resonant structure includes a first doping structure and a second doping structure stacked in sequence along the thickness direction of the substrate layer, and the first doping structure and the second doping structure have opposite doping types;

[0063] Step 103: forming an electrode electrically connected to the microring resonant structure.

[0064] Figure 2a-2m A schematic cross-sectional view of the steps of implementing a method for preparing a micro-ring modulator provided by an embodiment of the present invention. It should be understood that Figure 1 The operations shown in are not exclusive, and other operations may be performed before, after, or between any of the operations shown. Figure 1 , Figure 2a-2m The preparation method of the micro-ring modulator of this embodiment is described.

[0065] Execute step 101, such as Figure 2a As shown, a substrate layer 10 is provided. In practical applications, the material of the substrate layer 10 may include but is not limited to silicon dioxide.

[0066] Next, step 102 is performed to form a coupled waveguide 30 and a micro-ring resonant structure 40 arranged in parallel on the substrate layer 10, wherein the micro-ring resonant structure 40 includes a first doping structure 41 and a second doping structure 42 stacked in sequence along the thickness direction of the substrate layer 10, and the doping types of the first doping structure 41 and the second doping structure 42 are opposite.

[0067] Here, the micro-ring resonant structure 40 is used to modulate the light input from one end of the coupling waveguide 30 and coupled to the micro-ring resonant structure 40 under the action of the voltage transmitted by the electrode 50, and the modulated light is output from the other end of the coupling waveguide 30. Specifically, the doping type of the first doping structure 41 is opposite to that of the second doping structure 42, so that a vertical PN junction electrical modulation structure is formed at the physical junction of the first doping structure 41 and the second doping structure 42. According to the free carrier diffusion and drift effect in the PN junction, when a forward bias is applied to the PN junction in the micro-ring resonant structure 40, a current will be injected into the PN junction depletion region under the action of the external electric field, thereby causing a sharp increase in the free carrier concentration in the PN junction depletion region; when a reverse bias is applied to the PN junction in the micro-ring resonant structure 40, the free carriers distributed in the PN junction will be drawn away. At the same time, according to the plasma dispersion effect of silicon material, when the free carrier concentration in the silicon material changes, the refractive index of the silicon material will change. Therefore, the change of free carrier concentration in the PN junction will cause the refractive index of the waveguide material in the PN junction region to change. When an external voltage is applied to the micro-ring resonant structure 40, the free carrier concentration in the PN junction will change, thereby causing the refractive index of the silicon material to change, causing the wavelength of the optical signal transmitted in the optical waveguide to shift, thereby forming a modulation effect on the optical signal.

[0068] In practical applications, the first doping structure 41 may include a ridge waveguide microring, and the second doping structure 42 may include a polysilicon microring. The ridge waveguide microring and the polysilicon microring covering the ridge waveguide microring constitute a microring resonant cavity.

[0069] In practical applications, the distance between the coupling waveguide 30 and the microring resonant structure 40 is relatively close (usually several hundred nanometers), and the light input at one end of the coupling waveguide 30 can be coupled to the microring resonant structure 40 in the form of evanescent waves. That is to say, the optical wave mode field in the coupling waveguide 30 will be coupled with the waveguide in the microring resonant structure 40, and a part of the light will penetrate into the microring resonant cavity. When the light penetrating into the microring resonant cavity meets certain conditions, it can resonate in the microring resonant cavity and continuously strengthen due to the effect of positive feedback. At the same time, part of the light will also couple out of the microring and enter the coupling waveguide 30; if certain conditions are not met, the light in the microring resonant cavity will be continuously weakened. The other part of the light that is not coupled into the microring resonant cavity will be output from the other end of the coupling waveguide 30. In practical applications, when the wavelength of the transmitted light meets a specific relationship with the microring radius, the effective refractive index of the transmitted light in the microring, and other parameters, the light can resonate in the microring and continuously strengthen due to the effect of positive feedback.

[0070] In the embodiment of the present invention, the micro-ring resonant structure 40 is specially designed, that is, by stacking the first doping structure 41 and the second doping structure 42 in sequence along the thickness direction of the substrate layer 10, a vertical PN junction electrical modulation structure is formed at the physical junction of the first doping structure 41 and the second doping structure 42. It can be understood that in the micro-ring resonant structure 40 provided by the present invention, the vertical PN junction electrical modulation structure can increase the overlapping area between the PN junction depletion region and the light wave mode field, improve the interaction between the light wave and the carrier, and thus improve the modulation efficiency; at the same time, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, thereby improving the integration of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide 30 and the micro-ring resonant structure 40 are directly formed on the substrate layer 10. Compared with the micro-ring modulator in which the coupling waveguide 30 and the micro-ring resonant structure 40 are formed in the planar waveguide layer, the light loss caused by the leakage of light through the planar waveguide layer is avoided, the modulation efficiency of the micro-ring modulator is further improved, and the size of the micro-ring modulator is further reduced.

[0071] In one embodiment, if Figure 2b As shown, a first material layer 20 is formed on the substrate layer 10. In practical applications, the refractive index of the first material layer 20 is smaller than that of the substrate layer 10. Here, the first material layer 20 may include but is not limited to single crystal silicon.

[0072] Next, a portion of the first material layer 20 is removed to form a coupling waveguide 30 and a first doping structure material layer 412. Here, the coupling waveguide 30 is used to receive incident light and output outgoing light. In practical applications, the material of the coupling waveguide 30 may include single crystal silicon. The projection of the coupling waveguide 30 on the preset plane includes a long strip. Here, the preset plane is perpendicular to the thickness direction of the substrate layer 10.

[0073] It should be noted that, in each embodiment of the present invention, there is no limitation on the specific structure of the coupling waveguide 30. Specifically, the coupling waveguide 30 of the microring modulator in the embodiment of the present invention may include a strip waveguide or an L-shaped waveguide, or other waveguide structures with equivalent effects.

[0074] In practical applications, such as Figure 2c As shown, the first material layer 20 is subjected to a first etching to form the coupling waveguide 30 and the first sub-material layer 411; the projection of the first sub-material layer 411 on a preset plane is circular; the first etching stops at the top surface of the substrate layer 10; the preset plane is perpendicular to the thickness direction of the substrate layer 10.

[0075] In practical applications, such as Figure 2dAs shown, the first sub-material layer 411 is subjected to a second etching to form the first doped structure material layer 412 having a groove; the projection of the portion of the first sub-material layer 411 removed by the second etching on the preset plane is circular; the second etching stops in the first sub-material layer 411. Here, the projection of the side wall of the groove on the preset plane is annular, and the side wall of the groove and the bottom wall of the groove constitute the ridge waveguide microring.

[0076] In practical applications, the first etching and the second etching may include but are not limited to inductively coupled plasma (ICP) deep silicon etching.

[0077] In practical applications, such as Figure 2c As shown, the first etching stops at the top surface of the substrate layer 10. That is, the first material layer 20 around the coupling waveguide 30 and the first doping structure 41 is completely removed by the first etching, thereby avoiding light loss caused by light leaking through the first material layer 20 around the coupling waveguide 30 and the first doping structure 41, improving the interaction between light waves and carriers, and improving the modulation efficiency of the micro-ring modulator.

[0078] Next, the first doping structure material layer 412 is first doped to form the first doping structure 41 .

[0079] In practical applications, such as Figure 2e As shown, the first sub-doping is performed on the middle area of ​​the bottom of the groove in the first doping structure material layer 412 to obtain the first doping region 41A; the second sub-doping of the same type as the first sub-doping is performed on the remaining area of ​​the first doping structure material layer 412 to obtain the second doping region 41B; wherein the first doping region 41A and the second doping region 41B together form the first doping structure 41. Here, the middle area of ​​the bottom of the groove in the first doping structure material layer 412 includes the area at the center of the bottom of the groove and the surrounding area. In one embodiment, the middle area of ​​the bottom of the groove includes an area uniformly distributed along the geometric center line of the bottom of the groove. The remaining area of ​​the first doping structure material layer 412 includes other areas except the middle area of ​​the bottom of the groove, specifically, the remaining area includes the sidewalls of the groove and the bottom area of ​​the groove except the middle area.

[0080] Next, a second material layer 421 is formed on the first doping structure 41. In practical applications, the second material layer 421 includes polysilicon.

[0081] In one embodiment, the first material layer 20 and the second material layer 421 can be formed using one or more thin film deposition processes; specifically, the formation process of each layer structure includes but is not limited to a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process or a combination thereof.

[0082] In practical applications, before forming the second material layer 421 on the first doping structure 41, Figure 2f As shown, it also includes forming a covering material layer 111 on the coupling waveguide 30 and the first doping structure 41. Figure 2g As shown, part of the covering material layer 111 is removed to expose the top surfaces of the coupling waveguide 30 and the first doping structure 41. In practical applications, the method of removing part of the covering material layer 111 includes but is not limited to chemical mechanical polishing (CMP).

[0083] Next, if Figure 2h As shown, a second material layer 421 is formed on the first doping structure 41 .

[0084] Next, if Figure 2i As shown, a portion of the second material layer 421 is removed to form a second doping structure material layer 422 .

[0085] In practical applications, the projection of the second doped structural material layer 422 on the preset plane is annular; the side of the second doped structural material layer 422 is flush with the side of the first doped structural material layer 412. That is to say, along the stacking direction of the first doped structural material layer 412 and the second doped structural material layer 422, the outer side surfaces of the first doped structural material layer 412 and the second doped structural material layer 422 are located in the same plane, so that the exposed surface area of ​​the first doped structure 41 and the second doped structure 42 formed in the subsequent process can be reduced, thereby reducing the light scattering caused by the rough surface, reducing the light loss in the first doped structure 41 and the second doped structure 42, improving the interaction between light waves and carriers, and improving the modulation efficiency of the micro-ring modulator.

[0086] Next, the second doping structure material layer 422 is subjected to a second doping process to form the second doping structure 42 .

[0087] In practical applications, such as Figure 2jAs shown, the third sub-doping is performed on the middle annular area of ​​the second doping structure material layer 422 to obtain a third doping region 42A; the fourth sub-doping of the same type as the third sub-doping is performed on the remaining area of ​​the second doping structure material layer 422 to obtain a fourth doping region 42B; wherein the third doping region 42A and the fourth doping region 42B together form the second doping structure 42.

[0088] In practical applications, the first doping may include either P-type doping or N-type doping; correspondingly, the second doping may include either N-type doping or P-type doping.

[0089] In one embodiment, the first doping includes P-type doping, and the second doping includes N-type doping. That is, the first doping region 41A and the second doping region 41B include P-type doping, and the third doping region 42A and the fourth doping region 42B include N-type doping. Among them, the first doping region 41A is a P-type heavily doped region, and the second doping region 41B is a P-type lightly doped region; the third doping region 42A is an N-type heavily doped region, and the fourth doping region 42B is an N-type lightly doped region. Here, relative to the case where the second doping region 41B includes N-type doping and the fourth doping region 42B includes P-type doping, under the same voltage, the carriers in the P-type doping region are holes, so that more refractive index changes can be generated, and the loss is lower. Therefore, when the second doping region 41B close to the coupling waveguide 30 includes P-type doping, the modulation efficiency of the microring modulator is higher.

[0090] In practical applications, the second doping region 41B (P-type lightly doped region) is in physical contact with the fourth doping region 42B (N-type lightly doped region) to form a vertical PN junction, and the carrier type in the depletion region near the P-type lightly doped region in the vertical PN junction is electrons. When a reverse bias is applied to the electrode 50, the carriers distributed in the PN junction will be extracted. In the above embodiment, since the P-type lightly doped region, that is, the second doping region 41B is closer to the coupling waveguide 30, the interaction between the carriers and the light waves in the second doping region 41B is stronger. At the same time, since the mobility of electrons is much greater than the mobility of holes, when an external voltage is applied to the PN junction, the carriers near the P-type lightly doped region will be extracted faster, that is, the carrier concentration in the second doping region 41B changes faster. Therefore, when the concentration change rate of the carriers in the second doping region 41B close to the coupling waveguide 30 is faster, the modulation speed is faster. That is to say, when the second doping region 41B close to the coupling waveguide 30 is a P-type lightly doped region, the modulation speed of the micro-ring modulator is faster.

[0091] In practical applications, the first doping region 41A is a lightly doped region, and the second doping region 41B is a heavily doped region; the third doping region 42A is a lightly doped region, and the fourth doping region 42B is a heavily doped region. The first doping region 41A is in direct contact with the second doping region 41B, forming a first doping structure 41 including a ridge waveguide microring; the third doping region 42A is in direct contact with the fourth doping region 42B, forming a second doping structure 42 including a polysilicon microring. The ridge waveguide microring and the polysilicon microring covering the ridge waveguide microring form a microring resonant cavity. The microring resonant cavity can confine light waves within a very small range, greatly reducing the size of the electro-optic modulator.

[0092] In practical applications, the doping concentration of the first doping region 41A is higher than that of the second doping region 41B, and the doping concentration of the third doping region 42A is higher than that of the fourth doping region 42B, thereby reducing the contact resistance between the electrode and the doping region and further improving the efficiency of the microring modulator.

[0093] Next, step 103 is performed to form an electrode 50 electrically connected to the microring resonant structure 40. In practical applications, an external voltage is applied to the microring resonant structure 40 through the electrode 50. The electrode 50 includes a first electrode 51 and a second electrode 52. The first electrode 51 and the second electrode 52 are respectively positive and negative electrodes, and are connected to the microring resonant structure 40 to form a loop.

[0094] In practical applications, before forming the electrode 50, Figure 2k As shown, a cover layer 11 is formed to cover the coupling waveguide 30 and the micro-ring resonant structure 40, and the refractive index of the cover layer 11 is smaller than the refractive index of the coupling waveguide 30 and the micro-ring resonant structure 40. Here, the material of the cover layer 11 may include but is not limited to silicon dioxide.

[0095] In practical applications, such as Figure 2l As shown, the cover layer 11 is etched for the third time to form a first electrode contact hole 510, and the third etching stops on the first doping structure 41; the cover layer 11 is etched for the fourth time to form a second electrode contact hole 520, and the fourth etching stops on the second doping structure 42.

[0096] In practical applications, the third etching and the fourth etching may include but are not limited to dry etching.

[0097] Next, if Figure 2mAs shown, the first electrode contact hole 510 is filled with a conductive material to form the first electrode 51; the second electrode contact hole 520 is filled with a conductive material to form the second electrode 52. In practical applications, the top surface of the first electrode 51 and the top surface of the second electrode 52 may be higher than the top surface of the cover layer 11. Here, the conductive material may include, for example, gold, copper, aluminum, silver and / or other appropriate metal materials. In practical applications, Figure 4 As shown, the projection of the first electrode 51 on the preset plane is a circle; Figure 5 As shown, the projection of the second electrode 52 on the preset plane is annular. That is, the shape of the first electrode 51 may include a cylinder; the shape of the second electrode 52 may include a circular ring. It should be noted that the first electrode 51 and the second electrode 52 may also include other shapes.

[0098] It should be noted that although an exemplary method for forming a micro-ring modulator is described herein, it is understood that one or more steps may be omitted from the process of forming the micro-ring modulator.

[0099] Based on the above-mentioned method for preparing a micro-ring modulator, an embodiment of the present invention further provides a micro-ring modulator. Figure 3 for Figure 2m Schematic diagram of the cross section along the AA direction; Figure 4 for Figure 2m Schematic diagram of the cross section along the BB direction; Figure 5 for Figure 2m Schematic diagram of the cross section along the CC direction. Figure 2m , Figure 3 , Figure 4 and Figure 5 As shown, the micro-ring modulator includes: a substrate layer 10; a coupling waveguide 30 and a micro-ring resonant structure 40 arranged in parallel on the substrate layer 10, the micro-ring resonant structure 40 includes a first doping structure 41 and a second doping structure 42 stacked in sequence along the thickness direction of the substrate layer 10, the first doping structure 41 and the second doping structure 42 have opposite doping types; and an electrode 50 electrically connected to the micro-ring resonant structure 40.

[0100] It should be noted that Figure 2m , Figure 3 , Figure 4 and Figure 5 The micro-ring modulator shown is only an exemplary description of the micro-ring modulator provided by the embodiment of the present invention and should not be understood as a limitation on the micro-ring modulator.

[0101] In the above embodiment, the micro-ring resonant structure 40 is specially designed, that is, by stacking the first doping structure 41 and the second doping structure 42 in sequence along the thickness direction of the substrate layer 10, a vertical PN junction electrical modulation structure is formed at the physical junction of the first doping structure 41 and the second doping structure 42. It can be understood that in the micro-ring resonant structure 40 provided by the present invention, the vertical PN junction electrical modulation structure can increase the overlapping area between the PN junction depletion region and the light wave mode field, improve the interaction between the light wave and the carrier, and thus improve the modulation efficiency; at the same time, the vertical PN junction electrical modulation structure can reduce the size occupied by the modulation structure, thereby reducing the size of the micro-ring modulator, thereby improving the integration of the photonic integrated chip and reducing the preparation cost. In addition, the coupling waveguide and the micro-ring resonant structure are directly formed on the substrate layer, which avoids the light loss caused by the leakage of light through the slab waveguide layer compared to the micro-ring modulator in which the coupling waveguide and the micro-ring resonant structure are formed in the slab waveguide layer, further improves the modulation efficiency of the micro-ring modulator, and further reduces the size of the micro-ring modulator.

[0102] In one embodiment, the first doping structure 41 includes a first doping region 41A and a second doping region 41B having the same doping type as the first doping region 41A and surrounding the first doping region 41A; the second doping structure 42 includes a third doping region 42A and a fourth doping region 42B having the same doping type as the third doping region 42A and surrounding the third doping region 42A; wherein the first doping structure 41 and the second doping structure 42 are physically connected to the fourth doping region 42B through the second doping region 41B; and the first doping region 41A has no physical contact with the third doping region 42A.

[0103] In practical applications, the first doping structure 41 and the second doping structure 42 are physically connected to form a vertical PN junction through the second doping region 41B and the fourth doping region 42B; changes in carrier concentration in the vertical PN junction lead to changes in the refractive index of the waveguide material in the PN junction region.

[0104] In one embodiment, the top surface of the coupling waveguide 30 is flush with the top surface of the second doping region 41B. On the one hand, the top surface of the coupling waveguide 30 is flush with the top surface of the second doping region 41B, which can enhance the coupling effect and improve the interaction between the optical mode field and the carriers; on the other hand, the coupling waveguide 30 and the second doping region 41B can be completed in the same process, thereby simplifying the process.

[0105] In one embodiment, the projection of the coupling waveguide 30 on the preset plane is a long strip; the projection of the first doping region 41A on the preset plane is a circle, and the projections of the second doping region 41B, the third doping region 42A and the fourth doping region 42B on the preset plane are all ring-shaped. In other words, the micro-ring resonant structure 40 includes a ring-shaped modulation region, which changes the concentration of carriers by applying an external voltage, thereby changing the effective refractive index of the modulation region to achieve phase construction and phase destructiveness of light. The ring-shaped modulation region achieves a greater impact of a small refractive index change on the transmission effect through the resonance effect, thereby achieving lower power consumption and higher modulation rate.

[0106] In one embodiment, the diameter width of the physical contact between the second doping region 41B and the fourth doping region 42B ranges from 300 nanometers to 500 nanometers.

[0107] In practical applications, in order to improve the efficiency of the micro-ring modulator, the width of the PN junction should cover the range of the light wave mode field in the micro-ring as much as possible, but the width of the PN junction should not be too large, otherwise it will lead to a reduction in the bandwidth of the micro-ring modulator. Generally, the width of the PN junction is selected between 300 nanometers and 500 nanometers. In the above embodiment, a vertical PN junction is formed at the physical contact between the second doping region 41B and the fourth doping region 42B, and the width of the PN junction is the diameter width at the physical contact between the second doping region 41B and the fourth doping region 42B.

[0108] In practical applications, such as Figure 2m As shown, the micro-ring modulator includes a coupling waveguide 30 having a straight waveguide and a micro-ring resonant structure 40 having a ring waveguide coupled thereto, and the micro-ring modulator is a single-ring single-waveguide structure. In some embodiments, the micro-ring resonant structure 40 includes a racetrack-shaped waveguide, that is, the projection of the micro-ring resonant cavity on the preset plane includes a racetrack shape consisting of two identical straight lines and two identical semicircles. Of course, the embodiment provided by the present invention can also be expanded to a multi-ring single-waveguide structure, that is, the micro-ring modulator includes a coupling waveguide and a plurality of micro-ring resonant structures coupled thereto. In some embodiments, a coupling waveguide is arranged in parallel with a plurality of micro-ring resonant structures, and the plurality of micro-ring resonant structures are arranged along the direction in which the coupling waveguide extends. It should be noted that the "multiple ring waveguides" mentioned here refer to two or more ring waveguides. For both single rings and multi-rings, the resonance condition of the micro-ring modulator needs to be met, that is, when the signal wavelength and the circumference of the micro-ring resonant cavity meet certain conditions, the optical signal will be coupled into the micro-ring resonant cavity.

[0109] It should be noted that the solution provided in the embodiment of the present invention is applicable to silicon-based micro-ring modulators, and is also applicable to micro-ring modulators based on III-V group materials such as gallium arsenide (GaAs), indium phosphide (InP) and P-type doped gallium nitride (GaN).

[0110] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a microring modulator, characterized in that: include: providing a substrate layer; A coupled waveguide and a micro-ring resonant structure are formed on the substrate layer in parallel, wherein the micro-ring resonant structure comprises a first doping structure and a second doping structure which are sequentially stacked in a thickness direction of the substrate layer, wherein the first doping structure and the second doping structure have opposite doping types; as well as forming an electrode electrically connected to the microring resonant structure; The forming of the first doping structure includes: forming a first doping structure material layer on the substrate layer; performing a first sub-doping on a middle region at the bottom of the groove in the first doping structure material layer to obtain a first doping region; Performing second sub-doping of the same type as the first sub-doping on the remaining area of ​​the first doping structure material layer to obtain a second doping region; the first doping region and the second doping region together form the first doping structure; Forming the second doping structure includes: forming a second doping structure material layer on the first doping structure; the projection of the second doping structure material layer on a preset plane is a ring; the side edge of the second doping structure material layer is flush with the side edge of the first doping structure material layer; the preset plane is perpendicular to the thickness direction of the substrate layer; Performing a third sub-doping on the middle annular region of the second doping structure material layer to obtain a third doping region; The remaining area of ​​the second doping structure material layer is subjected to fourth sub-doping of the same type as the third sub-doping to obtain a fourth doping region; the third doping region and the fourth doping region together form the second doping structure.

2. The method for preparing a microring modulator according to claim 1, characterized in that: The coupled waveguide and micro-ring resonant structure formed in parallel on the substrate layer includes: forming a first material layer on the substrate layer; removing a portion of the first material layer to form a coupling waveguide and the first doped structure material layer; Performing a first doping on the first doping structure material layer to form the first doping structure; forming a second material layer on the first doping structure; removing a portion of the second material layer to form a second doped structure material layer; The second doping structure material layer is subjected to a second doping process to form the second doping structure.

3. The method for preparing a microring modulator according to claim 2, characterized in that: The removing part of the first material layer comprises: Performing a first etching on the first material layer to form the coupling waveguide and the first sub-material layer; the projection of the first sub-material layer on the preset plane is a circle; the first etching stops at the top surface of the substrate layer; The first sub-material layer is subjected to a second etching to form the first doped structure material layer having a groove; the projection of the portion of the first sub-material layer removed by the second etching on the preset plane is circular; the second etching stops in the first sub-material layer.

4. The method for preparing a microring modulator according to claim 2, characterized in that: The first doping includes P-type doping, and the second doping includes N-type doping.

5. The method for preparing a microring modulator according to claim 1, characterized in that: The method further comprises: A covering layer is formed to cover the coupling waveguide and the micro-ring resonant structure, wherein the refractive index of the covering layer is smaller than the refractive index of the coupling waveguide and the micro-ring resonant structure.

6. The method for preparing a microring modulator according to claim 5, characterized in that: The electrodes include a first electrode and a second electrode; The electrode electrically connected to the micro-ring resonant structure is formed, comprising: Performing a third etching on the cover layer to form a first electrode contact hole, wherein the third etching stops on the first doping structure; filling the first electrode contact hole with a conductive material to form the first electrode; The cover layer is etched for the fourth time to form a second electrode contact hole, and the fourth etching stops on the second doping structure; and the second electrode contact hole is filled with a conductive material to form the second electrode.

7. A micro-ring modulator, characterized in that: include: substrate layer; A coupled waveguide and a micro-ring resonant structure are arranged in parallel on the substrate layer, wherein the micro-ring resonant structure comprises a first doping structure and a second doping structure which are sequentially stacked along the thickness direction of the substrate layer, and the doping types of the first doping structure and the second doping structure are opposite; and, an electrode electrically connected to the micro-ring resonant structure; Wherein, the first doping structure includes a first doping region and a second doping region having the same doping type as the first doping region and surrounding the first doping region; The second doping structure includes a third doping region and a fourth doping region having the same doping type as the third doping region and surrounding the third doping region; wherein the first doping structure and the second doping structure are physically connected to the fourth doping region through the second doping region; and the first doping region has no physical contact with the third doping region.

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