Heterogeneous integrated electro-optic modulator based on write field stitching compensation and method of alignment thereof

Abstract

This invention discloses a heterogeneous integrated electro-optic modulator and its alignment method based on write field splicing compensation, relating to the field of silicon-based optoelectronics technology. The modulator comprises, from bottom to top, a silicon substrate with a thermal oxide layer, a bottom patterned waveguide layer, an intermediate transition dielectric layer, a top electro-optic thin film layer, and a top traveling-wave electrode structure. The bottom waveguide layer has a write field splicing region along the light propagation direction, within which a thermal compensation structure is configured, and a dedicated alignment mark is provided within a designated area. This mark is formed synchronously with the waveguide layer and the compensation structure within the same photolithographic write field. The top traveling-wave electrode structure is overlaid across layers based on this mark, forming a predetermined spatial matching relationship with the write field splicing region. This invention can solve the problems of optical scattering loss caused by long-distance bottom waveguide field-separated exposure splicing and the limited accuracy of cross-layer overlay after heterogeneous bonding, and achieves precise overlay positioning of the cross-layer traveling-wave electrode.

Description

Technical Field

[0001] This invention relates to the field of silicon-based optoelectronics technology, and in particular to a heterogeneous integrated electro-optic modulator based on write field splicing compensation and its alignment method. Background Technology

[0002] As optical communication networks evolve towards ultra-high capacity and long-distance transmission, the demand for high-performance electro-optic modulators with large bandwidth and low half-wave voltage is becoming increasingly urgent. In recent years, heterogeneous integration of thin-film electro-optic materials (such as lithium niobate, lithium tantalate, or barium titanate) with CMOS-compatible underlying semiconductor materials (such as silicon nitride) has become the mainstream architecture for overcoming the physical limitations of single materials. This heterogeneous integration platform, which combines patterned waveguides of the underlying material with top electro-optic thin films, can utilize the low-loss and high-density passive wiring capabilities of the underlying material while fully leveraging the excellent electro-optic effects of thin-film materials.

[0003] However, to achieve sufficiently low half-wave voltage and effective modulation over long distances, the interferometer arm length of these heterogeneous integrated electro-optic modulators often reaches the millimeter or even centimeter level. This geometric dimension far exceeds the effective writing field range of single-step or scanning ultraviolet lithography machines. Therefore, in the large-area fabrication process of the underlying optical waveguide, a writing field splicing process must be used to stitch multiple sub-field patterns into a complete long-distance waveguide structure.

[0004] Currently, existing heterogeneous integrated optoelectronic chips still face significant technical bottlenecks in handling field-write splicing issues. Firstly, direct splicing in the field-write process can introduce sub-micron-level alignment deviations, abrupt linewidth changes, or etching profile discontinuities at the splicing seams. This leads to increased waveguide sidewall roughness and abrupt changes in effective refractive index, resulting in waveguide mode mismatch and optical scattering loss. In long-distance transmission scenarios, this accumulated scattering loss causes a sharp increase in the overall insertion loss of the device, directly limiting the transmission distance of optical signals and system energy efficiency.

[0005] Secondly, in heterogeneous integration processes, electro-optic thin films (such as lithium niobate, lithium tantalate, or barium titanate) need to be transferred to the bottom waveguide using bonding or smart cut techniques to form an inverted ridge-shaped heterogeneous waveguide structure. The bonding stress and film deformation generated in this process can cause the traditional surface alignment marks to become distorted or even completely masked, making it difficult to control the cross-layer alignment accuracy between the upper film and subsequent structures and the bottom waveguide, thus failing to meet the accuracy requirements of subsequent overlay processes. Furthermore, cross-layer overlay deviations can further degrade electro-optic modulation performance. The core performance of long-distance modulators is highly dependent on the precise overlap of the high-frequency microwave field of the top traveling wave electrode and the optical wave field of the bottom layer. If the metal electrode structure accidentally overlaps with a splicing defect in the bottom optical waveguide, the irregular scattered light field caused by the splicing seam couples with the adjacent metal electrode, generating additional absorption and increasing the device's optical insertion loss. Simultaneously, unexpected abrupt changes in the optical waveguide structure below the electrode sensitive area can also cause local distortion and impedance mismatch in the microwave field, directly limiting the device's high-frequency modulation bandwidth and overall manufacturing yield.

[0006] The aforementioned problems are already evident in existing heterogeneous integration fields. For example, in a compact 100 GBaud thin-film lithium niobate (TFLN) modulator based on periodically capacitively loaded traveling-wave electrodes, the insertion loss of the device increases significantly due to write field splicing errors in the MZI arms, failing to meet the requirements for low-loss, high-speed modulation. Similarly, another study on high-performance TFLN modulators also points out that imperfect write field splicing and metal electrode alignment are among the main process defects limiting the improvement of extinction ratio. Furthermore, the currently proposed "seamless multi-mask photonics" method also indirectly confirms the limitations of traditional splicing techniques: conventional multi-mask splicing inevitably introduces additional scattering loss due to exposure misalignment, prompting researchers to develop novel transition structures to alleviate this problem. Summary of the Invention

[0007] The purpose of this invention is to provide a heterogeneous integrated electro-optic modulator based on write field splicing compensation and its alignment method, aiming to solve or improve at least one of the above-mentioned technical problems.

[0008] To achieve the above objectives, the present invention provides the following solution: A heterogeneous integrated electro-optic modulator based on write field splicing compensation includes: a silicon thermal oxide layer substrate, a bottom patterned waveguide layer, an intermediate transition dielectric layer, a top electro-optic thin film layer, and a top traveling wave electrode structure arranged sequentially from bottom to top. The bottom patterned waveguide layer is a silicon nitride waveguide layer, with at least one write field splicing area along the light propagation direction. A thermal compensation structure is provided at the write field splicing area. The bottom patterned waveguide layer also has a dedicated alignment mark within a designated area of ​​the write field splicing area. The dedicated alignment mark, the bottom patterned waveguide layer, and the thermal compensation structure are formed synchronously in the same photolithographic write field. The top traveling wave electrode structure is etched across layers based on the dedicated alignment mark, so that the top traveling wave electrode structure and the write field splicing area have a preset spatial matching relationship.

[0009] Optionally, the thermal insulation compensation structure may employ one or more of the following: a tapered transition structure that gradually widens along the direction of light propagation; a multi-segment widening structure; a piecewise linear transition structure; an approximate curved transition structure; and a locally equal-width widening platform structure.

[0010] Optionally, when the thermal compensation structure is a tapered transition structure that gradually widens along the direction of light propagation, the conventional waveguide width of the bottom patterned waveguide layer is 0.8μm to 3μm, the maximum width of the tapered transition structure is 2 to 5 times the conventional waveguide width, and the single-sided transition length is 20μm to 2000μm.

[0011] Optionally, the dedicated alignment mark is a combination of a cross and a square, with a size of 2μm to 100μm, and the distance between the center of the dedicated alignment mark and the center of the splicing seam of the writing field splicing area is 10μm to 500μm.

[0012] Optionally, the thickness of the bottom patterned waveguide layer is 200 nm to 1000 nm; the waveguide length covered by a single exposure area is 10 mm to 26 mm, and the total waveguide length after writing the field is 10 mm to 100 mm; the characteristic size of the lateral stitching error, edge discontinuity, or linewidth disturbance at the writing field stitching area is no greater than 200 nm.

[0013] Optionally, the intermediate transition medium layer is alumina, silicon dioxide, silicon oxynitride, or a polymer; when the intermediate transition medium layer is alumina, the thickness is 5 nm to 200 nm; when the intermediate transition medium layer is silicon dioxide or silicon oxynitride, the thickness is 30 nm to 1000 nm; when the intermediate transition medium layer is a polymer, the thickness is 100 nm to 1000 nm; the thickness of the top electro-optic thin film layer is 50 nm to 1000 nm; when the top electro-optic thin film layer is lithium niobate or lithium tantalate, the thickness is 300 nm to 700 nm; when the top electro-optic thin film layer is barium titanate, the thickness is 50 nm to 300 nm.

[0014] Optionally, the top traveling wave electrode is a conventional coplanar traveling wave electrode, and the strong electric field region formed between the signal electrode and the adjacent ground electrode of the conventional coplanar traveling wave electrode avoids the write field splicing region, or the write field splicing region is located in a weaker electric field region outside the boundary of the strong electric field region.

[0015] Optionally, the top-layer traveling wave electrode is a periodic capacitively loaded traveling wave electrode, which includes periodically arranged metal loading units and a metal-free gap region located between adjacent metal loading units; the metal-free gap region is correspondingly arranged with the write field splicing area in the vertical projection direction; the length of the metal-free gap region is 5μm to 100μm, and the projection deviation between the center of the metal-free gap region and the center of the splicing seam of the write field splicing area is no greater than 1μm.

[0016] This invention also provides an alignment method for heterogeneous integrated electro-optic modulators based on write field splicing compensation, comprising: Step 1: A bottom silicon nitride waveguide thin film is formed on the substrate, and a step-type or scanning ultraviolet lithography equipment is used for field exposure and etching to obtain a bottom patterned waveguide structure; wherein, a thermal compensation structure is set in the write field splicing area, and a special alignment mark located near the write field splicing area is simultaneously formed in the same lithographic write field. Step 2: An intermediate transition dielectric layer is formed on the bottom patterned waveguide structure and then planarized. Step 3: Bond or transfer the top electro-optic thin film layer onto the intermediate transition dielectric layer to form a heterogeneous integrated structure; Step 4: Using the dedicated alignment mark as a cross-layer overlay reference, expose and develop the top traveling wave electrode structure to ensure that the top traveling wave electrode structure and the write field splicing area meet the preset spatial matching relationship. Step 5: Complete the metal deposition and stripping process to form the top traveling wave electrode structure and obtain the heterogeneous integrated electro-optic modulator.

[0017] Optionally, the spatial matching relationship in step four includes: ensuring that the strong electric field region of the top traveling wave electrode avoids the write field splicing region; or, when the top traveling wave electrode is a periodic capacitively loaded traveling wave electrode, ensuring that the metal-free gap region of the periodic capacitively loaded traveling wave electrode corresponds to the write field splicing region in the vertical projection direction.

[0018] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: This invention discloses a heterogeneous integrated electro-optic modulator based on write field splicing compensation and its alignment method. The modulator includes, from bottom to top, a silicon-on-thermal oxide layer substrate, a bottom patterned waveguide layer, an intermediate transition dielectric layer, a top electro-optic thin film layer, and a top traveling-wave electrode structure. The bottom waveguide layer has a write field splicing region along the light propagation direction, within which an adiabatic compensation structure is configured, and a dedicated alignment mark is provided within a designated area. This mark is formed synchronously with the waveguide layer and the compensation structure within the same photolithographic write field. The top traveling-wave electrode structure is overlaid across layers based on this mark, forming a predetermined spatial matching relationship with the write field splicing region. This invention provides a heterogeneous integrated waveguide structure and process-coordinated alignment scheme to solve the problems of optical scattering loss caused by long-distance bottom waveguide field exposure splicing and the limited accuracy of cross-layer overlay after heterogeneous bonding, and to achieve precise overlay positioning of the cross-layer traveling-wave electrode, thereby improving the performance of long-distance heterogeneous integrated electro-optic modulators. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the heterogeneous integrated electro-optic modulator structure in this embodiment; Figure 2 This is a schematic diagram of the cross-sectional structure of the heterogeneous integrated ridge waveguide in this embodiment; Figure 3 This is a magnified top view of the SiN waveguide splicing area in this embodiment; Figure 4 This is a schematic diagram showing the vertical projection alignment relationship between the metal gap-free area of ​​the traveling wave electrode and the bottom insulation splice seam in this embodiment. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The purpose of this invention is to provide a heterogeneous integrated electro-optic modulator based on write field splicing compensation and its alignment method, aiming to solve or improve at least one of the above-mentioned technical problems.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] As a first aspect, the present invention provides a heterogeneous integrated electro-optic modulator based on write field splicing compensation, comprising: a silicon thermal oxide layer substrate, a bottom patterned waveguide layer, an intermediate transition dielectric layer, a top electro-optic thin film layer, and a top traveling wave electrode structure arranged sequentially from bottom to top.

[0025] The bottom patterned waveguide layer is a silicon nitride waveguide layer, with at least one write field splicing area along the light propagation direction. A thermal compensation structure is provided at the write field splicing area. The bottom patterned waveguide layer also has a dedicated alignment mark within a designated area of ​​the write field splicing area. The dedicated alignment mark, the bottom patterned waveguide layer, and the thermal compensation structure are formed synchronously in the same photolithographic write field. The top traveling wave electrode structure is etched across layers based on the dedicated alignment mark, so that the top traveling wave electrode structure and the write field splicing area have a preset spatial matching relationship.

[0026] As one specific implementation, the thermal compensation structure can be a tapered transition structure that gradually widens along the light propagation direction, a multi-segment widening structure, a piecewise linear transition structure, an approximate curved transition structure, a locally equal-width widening platform structure, or a combination thereof. As a preferred implementation, the thermal compensation structure is a tapered transition structure that gradually widens along the light propagation direction. The conventional waveguide width of the bottom patterned waveguide layer is 0.8 μm to 3 μm, the maximum width of the tapered transition structure is 2 to 5 times the conventional waveguide width, and the single-sided transition length is 20 μm to 2000 μm.

[0027] In one specific implementation, the dedicated alignment mark is a combination of a cross and a square, with a size of 2μm to 100μm, and the distance between the center of the dedicated alignment mark and the center of the splicing seam of the writing field splicing area is 10μm to 500μm.

[0028] In one specific implementation, the thickness of the bottom patterned waveguide layer is 200 nm to 1000 nm, more preferably 300 nm to 800 nm; the waveguide length covered by a single exposure area is 10 mm to 26 mm, and the total waveguide length after field writing is 10 mm to 100 mm, more preferably 20 mm to 80 mm; the characteristic size of the lateral stitching error, edge discontinuity, or linewidth disturbance at the field writing stitching area is no greater than 200 nm, more preferably no greater than 100 nm.

[0029] In one specific embodiment, the intermediate transition medium layer is alumina, silicon dioxide, silicon oxynitride, or a polymer; when the intermediate transition medium layer is alumina, the thickness is 5 nm to 200 nm; when the intermediate transition medium layer is silicon dioxide or silicon oxynitride, the thickness is 30 nm to 1000 nm; when the intermediate transition medium layer is a polymer, the thickness is 100 nm to 1000 nm; the thickness of the top electro-optic thin film layer is 50 nm to 1000 nm; when the top electro-optic thin film layer is lithium niobate or lithium tantalate, the thickness is 300 nm to 700 nm; when the top electro-optic thin film layer is barium titanate, the thickness is 50 nm to 300 nm, more preferably 80 nm to 200 nm.

[0030] In one specific implementation, the top traveling wave electrode is a conventional coplanar traveling wave electrode. The strong electric field region formed between the signal electrode and the adjacent ground electrode of the conventional coplanar traveling wave electrode avoids the write field splicing region, or the write field splicing region is located in a weaker electric field region outside the boundary of the strong electric field region.

[0031] In one specific implementation, the top-layer traveling wave electrode is a periodic capacitively loaded traveling wave electrode, which includes periodically arranged metal loading units and a metal-free gap region located between adjacent metal loading units; the metal-free gap region is correspondingly arranged with the write field splicing region in the vertical projection direction; the length of the metal-free gap region is 5μm to 100μm, and the projection deviation between the center of the metal-free gap region and the center of the splicing seam of the write field splicing region is no greater than 1μm.

[0032] As a second aspect, the present invention also provides an alignment method for heterogeneous integrated electro-optic modulators based on write field splicing compensation, comprising: Step 1: A bottom silicon nitride waveguide thin film is formed on the substrate, and a step-type or scanning ultraviolet lithography device is used for field exposure and etching to obtain a bottom patterned waveguide structure; wherein, a thermal compensation structure is set in the write field splicing area, and a special alignment mark located near the write field splicing area is formed synchronously in the same lithographic write field.

[0033] Step 2: An intermediate transition dielectric layer is formed on the bottom patterned waveguide structure and then planarized.

[0034] Step 3: Bond or transfer the top electro-optic thin film layer to the intermediate transition dielectric layer to form a heterogeneous integrated structure.

[0035] Step 4: Using the dedicated alignment mark as a cross-layer overlay reference, expose and develop the top traveling wave electrode structure to ensure that the top traveling wave electrode structure and the write field splicing area meet a preset spatial matching relationship; wherein, the spatial matching relationship includes: ensuring that the strong electric field area of ​​the top traveling wave electrode avoids the write field splicing area; or, when the top traveling wave electrode is a periodically capacitively loaded traveling wave electrode, ensuring that the metal-free gap area of ​​the periodically capacitively loaded traveling wave electrode corresponds to the write field splicing area in the vertical projection direction.

[0036] Step 5: Complete the metal deposition and stripping process to form the top traveling wave electrode structure and obtain the heterogeneous integrated electro-optic modulator.

[0037] Based on the above technical solution, the following is provided: Figures 1-4 The example shown.

[0038] Example 1: Heterogeneous integrated electro-optic modulator based on periodically capacitively loaded traveling wave electrodes.

[0039] This embodiment provides a heterogeneous integrated electro-optic modulator based on write field splicing compensation. The modulator includes a substrate, a bottom patterned waveguide layer disposed on the substrate, an intermediate transition dielectric layer disposed above the bottom patterned waveguide layer, a top electro-optic thin film layer disposed on the intermediate transition dielectric layer, and a top traveling wave electrode structure formed on the top electro-optic thin film layer.

[0040] In this embodiment, the substrate is a silicon-on-aluminum (SOA) substrate. The bottom patterned waveguide layer is preferably formed using silicon nitride. The bottom waveguide can constitute the input waveguide, beam splitter, two modulation arms, beam combiner, and output waveguide of a Mach-Zehnder modulator, wherein at least one modulation arm has a write field splicing region along the light propagation direction to achieve the fabrication of long-distance optical waveguides exceeding the length of a single exposure field.

[0041] In this embodiment, the thickness of the silicon nitride waveguide layer can be selected as 400 nm. The bottom waveguide is formed by field-separated exposure and etching using a step-type or scanning ultraviolet lithography device. When the length of the target modulation arm exceeds the length of a single exposure field, the bottom long waveguide is divided into multiple exposure fields for sequential exposure, and a write field splicing area is formed at the boundary of adjacent exposure fields. Figure 1 The document outlines the positional relationships of multiple splicing regions, and the actual number of splicing regions can be adjusted based on the device length and the exposure field division method. Preferably, the waveguide length covered by a single exposure field is 10 mm to 26 mm; in this embodiment, a single exposure field length of 26 mm can be selected. The total waveguide length after splicing can be 10 mm to 100 mm, more preferably 20 mm to 80 mm; in this embodiment, the total waveguide length of a single modulation arm can be designed to be 40 mm, forming two write field splicing regions in the waveguide propagation path.

[0042] Since the field-by-field exposure process inevitably introduces slight splicing errors, lateral misalignment, edge discontinuities, or linewidth perturbations may exist at the splicing area. To reduce the resulting mode mismatch and scattering loss, this embodiment sets an adiabatic compensation structure in the writing field splicing area of ​​the bottom waveguide. The adiabatic compensation structure is preferably a tapered transition structure that gradually widens along the light propagation direction and is located on both sides of the splicing seam. In this embodiment, the conventional transmission section waveguide width is 1.2 μm, the maximum width of the splicing compensation area is 3.0 μm, and the transition length on both sides of the splicing seam is 50 μm. Specifically, a gradually widening and a gradually contracting compensation waveguide are formed before and after the splicing seam, respectively, so that the optical mode is moderately expanded before reaching the splicing area and then returns to the conventional waveguide width after passing through the splicing area, thereby reducing the sensitivity of the optical field to abrupt changes at the splicing boundary.

[0043] To achieve high-precision cross-layer overlay after heterogeneous bonding, this embodiment synchronously sets dedicated alignment marks near the write field splicing area. These dedicated alignment marks, along with the underlying waveguide and thermal compensation structure, are simultaneously exposed and formed within the same photolithographic write field, thus establishing a one-to-one correspondence between the alignment marks and the splicing area in physical location. The dedicated alignment marks can adopt a combination of cross-shaped and square-shaped structures. Preferably, the alignment mark size is 2 μm to 100 μm; in this embodiment, a cross-shaped mark on the order of 20 μm and a matching square-shaped mark can be selected and placed in the vicinity of the splicing seam center within a range of tens to hundreds of micrometers for accurate identification during subsequent cross-layer overlay.

[0044] After completing the underlying patterned waveguide structure, an intermediate transition dielectric layer is formed on top of it. This intermediate transition dielectric layer is used to achieve interface planarization, mode modulation, and heterogeneous bonding transition. It can be made of silicon dioxide, alumina, silicon oxynitride, or a polymer dielectric, and is formed by deposition or spin coating. Depending on the material type, surface planarization can be achieved through chemical mechanical polishing, etch-back, or thermal curing to meet the bonding requirements of the subsequent top-layer electro-optic thin film. In this embodiment, silicon dioxide is preferably used as the intermediate transition dielectric layer, and its thickness can be selected as 100 nm. The specific material and thickness can be adjusted according to the required optical field coupling intensity, bonding process, and device operating wavelength.

[0045] Subsequently, a top electro-optic thin film layer is formed on the intermediate transition dielectric layer. This top electro-optic thin film layer can be made of lithium niobate, lithium tantalate, or barium titanate, and is formed on the intermediate transition dielectric layer through direct bonding or smart lift-off. In this embodiment, a lithium niobate thin film is preferably used as the top electro-optic thin film, and its thickness can be selected as 400 nm. After bonding is completed, the original support substrate can be removed as needed, and the top surface can be cleaned and planarized to obtain a device surface that meets the requirements of subsequent metal overlay processes.

[0046] After the top electro-optic thin film is formed, a top traveling wave electrode structure is fabricated on its surface. Specifically, photoresist can be spin-coated onto the surface of the top electro-optic thin film first, and then the electrode pattern can be exposed using a dedicated alignment mark formed by the bottom write field as a cross-layer overlay reference. Subsequently, the top electrode is formed through metal deposition and lift-off processes. The metal material can be gold, aluminum, copper, or a composite metal system thereof.

[0047] In this embodiment, the top traveling-wave electrode is preferably a periodic capacitively loaded traveling-wave electrode. The periodic capacitively loaded traveling-wave electrode includes metal loading units arranged periodically along the light propagation direction, forming a metal-free gap region between adjacent loading units. By using dedicated alignment marks on the bottom layer for cross-layer overlay etching, the metal-free gap region and the bottom layer writing field splicing area can be aligned in the vertical projection direction, further reducing optical insertion loss and improving local microwave impedance continuity.

[0048] Preferably, the length of the metal-free gap region is 5 μm to 100 μm; in this embodiment, a metal-free gap region length of 20 μm can be selected. The projection deviation between the center of the metal-free gap region and the center of the bottom layer splicing seam is preferably no greater than 1 μm; in this embodiment, this deviation can be controlled within 500 nm. Through the above spatial avoidance design, the bottom layer splicing defect area can be located in the region where the effect of the top layer electrode metal is weakened, thereby avoiding additional absorption of the diffused light field at the splicing defect by the solid metal and reducing microwave field distortion caused by local geometrical abrupt changes in the bottom layer.

[0049] After the device is completed, a synergistic relationship is formed between the bottom-layer write field splicing compensation structure, the dedicated alignment mark for the write field, and the top-layer periodic capacitively loaded traveling wave electrode. Specifically, the bottom-layer thermal insulation compensation structure reduces mode mismatch and scattering loss at the splicing points; the dedicated alignment mark establishes a high-precision positional reference required for cross-layer overlay; and the metal-free gap region of the top-layer electrode avoids splicing defects at the electrode level. Through this synergistic design, this embodiment can effectively reduce additional optical loss caused by splicing while ensuring the manufacturability of long-distance modulation structures and improving the high-frequency electro-optical synergistic performance of the device.

[0050] Example 2: Heterogeneous Integrated Electro-Optical Modulator Based on Conventional Coplanar Traveling Wave Electrodes The difference between this embodiment and Embodiment 1 is that the top electrode structure uses a conventional coplanar traveling wave electrode instead of a periodic capacitively loaded traveling wave electrode. The formation methods of the remaining bottom waveguide structure, write field splicing compensation structure, dedicated alignment mark, intermediate transition dielectric layer and top electro-optic thin film layer are the same as in Embodiment 1.

[0051] In this embodiment, the top-layer conventional coplanar traveling wave electrode is also overlaid across layers based on the bottom-layer dedicated alignment marks. Through layout planning, the strong electric field region corresponding to the bottom-layer waveguide modulation region between the signal electrode and the adjacent ground electrode is avoided from the bottom-layer write field splicing defect region, or the splicing defect region is located in a weaker electric field region outside the boundary of the strong electric field region, so as to reduce metal absorption and local microwave impedance disturbance. In this implementation, although the top-layer electrode does not have the metal-free gap region in the periodic capacitive loading structure, high-precision cross-layer overlay can still be achieved using the dedicated alignment marks formed by the bottom layer and the write field, thereby establishing a preset projection position relationship between the top-layer electrode structure and the bottom-layer splicing region.

[0052] In other embodiments, the bottom patterned waveguide layer can also employ silicon nitride waveguide structures of varying thicknesses and refractive index contrasts; the thermal compensation structure, in addition to the gradually widening tapered structure, can also employ a multi-segment widening structure, a segmented linear transition structure, an approximate curved transition structure, a locally equal-width widening platform structure, or a combination thereof. The dedicated alignment marks can also adopt different shapes and combinations depending on the device identification method. The intermediate transition dielectric layer can be selected from silicon dioxide, alumina, silicon oxynitride, polymer materials, or their composite layer structures, depending on the specific device platform. The top electro-optic thin film can also be replaced with a lithium tantalate thin film or a barium titanate thin film to meet the requirements of different wavebands, different modulation efficiencies, and different process compatibility.

[0053] In summary, this invention effectively improves the optical loss and electro-optic performance degradation problems caused by write field splicing and cross-layer overlay in long-distance heterogeneous integrated electro-optic modulators by setting an adiabatic compensation structure in the bottom waveguide write field splicing area, synchronously forming dedicated alignment marks within the same photolithographic write field, and achieving a predetermined spatial matching relationship between the top electrode structure and the bottom splicing area based on the alignment marks. Therefore, this invention can improve the optical transmission efficiency, cross-layer overlay stability, high-frequency modulation performance, and overall manufacturing yield of the device. Its specific beneficial effects are as follows: At the optical transmission level, this invention incorporates a thermal compensation structure in the writing field splicing region of the underlying waveguide. This structure, through gradual widening and gradual restoration of the waveguide before and after the splicing seam, allows the optical mode to be moderately expanded before entering the splicing region and restored to its normal transmission state after passing through the splicing region. This reduces the sensitivity of the optical field to abrupt changes at the splicing boundary, and minimizes mode mismatch and scattering loss caused by lateral misalignment, edge discontinuities, or linewidth perturbations.

[0054] At the layer-by-layer overlay level, this invention synchronously forms dedicated alignment marks, the underlying patterned waveguide, and the thermal compensation structure within the same photolithographic write field, thereby establishing a one-to-one correspondence between the alignment marks and the splicing area. Compared to traditional surface alignment methods, this approach can reduce the impact of heterogeneous bonding, thin film transfer, and interface stress deformation on overlay accuracy, providing a stable and reliable physical benchmark for precise alignment between the top electrode structure and the bottom splicing area.

[0055] At the electro-optic modulation level, this invention achieves a predetermined spatial matching relationship between the top-layer traveling-wave electrode structure and the bottom-layer splicing area through dedicated alignment marks. This ensures that the strong electric field region of the top-layer electrode avoids the bottom-layer splicing defect region, or that the splicing defect region is located in a region with a weaker electric field. This reduces the additional absorption of the stray light field by the metal and minimizes the impact of local geometric abrupt changes on the microwave field distribution and impedance continuity. Furthermore, in a preferred embodiment using periodically capacitively loaded traveling-wave electrodes, the metal-free gap region can be correspondingly positioned with the bottom-layer write field splicing region in the vertical projection direction. This further reduces light absorption and microwave impedance disturbances caused by the splicing region, making it more conducive to achieving low insertion loss and high bandwidth operation of long-distance heterogeneous integrated electro-optic modulators.

[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0057] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A heterogeneous integrated electro-optic modulator based on write field splicing compensation, characterized in that, include: The structure consists of a silicon thermal oxide layer substrate, a bottom patterned waveguide layer, an intermediate transition dielectric layer, a top electro-optic thin film layer, and a top traveling wave electrode structure arranged sequentially from bottom to top. The bottom patterned waveguide layer is a silicon nitride waveguide layer, with at least one write field splicing area along the light propagation direction. A thermal compensation structure is provided at the write field splicing area. The bottom patterned waveguide layer also has a dedicated alignment mark within a designated area of ​​the write field splicing area. The dedicated alignment mark, the bottom patterned waveguide layer, and the thermal compensation structure are formed synchronously in the same photolithographic write field. The top traveling wave electrode structure is etched across layers based on the dedicated alignment mark, so that the top traveling wave electrode structure and the write field splicing area have a preset spatial matching relationship.

2. The heterogeneous integrated electro-optic modulator based on write field splicing compensation according to claim 1, characterized in that, The thermal insulation compensation structure adopts one or more of the following: a tapered transition structure that gradually widens along the direction of light propagation, a multi-segment widening structure, a piecewise linear transition structure, an approximate curved transition structure, and a locally equal-width widening platform structure.

3. The heterogeneous integrated electro-optic modulator based on write field splicing compensation according to claim 2, characterized in that, When the thermal compensation structure is a tapered transition structure that gradually widens along the direction of light propagation, the conventional waveguide width of the bottom patterned waveguide layer is 0.8μm to 3μm, the maximum width of the tapered transition structure is 2 to 5 times the conventional waveguide width, and the single-sided transition length is 20μm to 2000μm.

4. The heterogeneous integrated electro-optic modulator based on write field splicing compensation according to claim 1, characterized in that, The dedicated alignment mark is a combination of a cross and a square, with a size of 2μm to 100μm. The distance between the center of the dedicated alignment mark and the center of the splicing seam of the writing field splicing area is 10μm to 500μm.

5. The heterogeneous integrated electro-optic modulator based on write field splicing compensation according to claim 1, characterized in that, The thickness of the bottom patterned waveguide layer is 200 nm to 1000 nm; the waveguide length covered by a single exposure area is 10 mm to 26 mm, and the total waveguide length after writing the field is 10 mm to 100 mm; the characteristic size of the lateral stitching error, edge discontinuity, or linewidth disturbance at the writing field stitching area is no greater than 200 nm.

6. The heterogeneous integrated electro-optic modulator based on write field splicing compensation according to claim 1, characterized in that, The intermediate transition medium layer is aluminum oxide, silicon dioxide, silicon oxynitride, or a polymer; when the intermediate transition medium layer is aluminum oxide, the thickness is 5 nm to 200 nm; when the intermediate transition medium layer is silicon dioxide or silicon oxynitride, the thickness is 30 nm to 1000 nm; when the intermediate transition medium layer is a polymer, the thickness is 100 nm to 1000 nm; the thickness of the top electro-optic thin film layer is 50 nm to 1000 nm; when the top electro-optic thin film layer is lithium niobate or lithium tantalate, the thickness is 300 nm to 700 nm; when the top electro-optic thin film layer is barium titanate, the thickness is 50 nm to 300 nm.

7. The heterogeneous integrated electro-optic modulator based on write field splicing compensation according to claim 1, characterized in that, The top traveling wave electrode is a conventional coplanar traveling wave electrode. The strong electric field region formed between the signal electrode and the adjacent ground electrode of the conventional coplanar traveling wave electrode avoids the write field splicing region, or the write field splicing region is located in a weaker electric field region outside the boundary of the strong electric field region.

8. The heterogeneous integrated electro-optic modulator based on write field splicing compensation according to claim 1, characterized in that, The top-layer traveling wave electrode is a periodic capacitively loaded traveling wave electrode, which includes periodically arranged metal loading units and a metal-free gap region located between adjacent metal loading units; the metal-free gap region is correspondingly arranged with the write field splicing area in the vertical projection direction; the length of the metal-free gap region is 5μm to 100μm, and the projection deviation between the center of the metal-free gap region and the center of the splicing seam of the write field splicing area is no greater than 1μm.

9. A method for aligning heterogeneous integrated electro-optic modulators based on write field splicing compensation, characterized in that, include: Step 1: A bottom silicon nitride waveguide thin film is formed on the substrate, and a step-type or scanning ultraviolet lithography equipment is used for field exposure and etching to obtain a bottom patterned waveguide structure; wherein, a thermal compensation structure is set in the write field splicing area, and a special alignment mark located near the write field splicing area is simultaneously formed in the same lithographic write field. Step 2: An intermediate transition dielectric layer is formed on the bottom patterned waveguide structure and then planarized. Step 3: Bond or transfer the top electro-optic thin film layer onto the intermediate transition dielectric layer to form a heterogeneous integrated structure; Step 4: Using the dedicated alignment mark as a cross-layer overlay reference, expose and develop the top traveling wave electrode structure to ensure that the top traveling wave electrode structure and the write field splicing area meet the preset spatial matching relationship. Step 5: Complete the metal deposition and stripping process to form the top traveling wave electrode structure and obtain the heterogeneous integrated electro-optic modulator.

10. The alignment method for heterogeneous integrated electro-optic modulators based on write field splicing compensation according to claim 9, characterized in that, The spatial matching relationship in step four includes: ensuring that the strong electric field region of the top traveling wave electrode avoids the write field splicing region; or, when the top traveling wave electrode is a periodic capacitively loaded traveling wave electrode, ensuring that the metal-free gap region of the periodic capacitively loaded traveling wave electrode corresponds to the write field splicing region in the vertical projection direction.

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