Electroabsorption modulator
Patent Information
- Application Number
- TW114110769
- Authority / Receiving Office
- TW · TW
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-03-21
- Publication Date
- 2026-10-01
- Estimated Expiration
- 2045-03-20
AI Technical Summary
Existing electroabsorption modulators (EAMs) face challenges with high capacitance values that limit modulation speed, power consumption, and signal quality, necessitating a balance between performance and cost-effectiveness.
The design incorporates a dielectric layer in the grooves outside the waveguide region with a thickness equal to the groove depth, reducing capacitance and enhancing bandwidth for high-speed modulation.
This approach reduces capacitance, increases bandwidth, and improves signal quality while maintaining process stability, avoiding issues like incomplete coverage and open circuits.
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Abstract
Description
[Technical Field]
[0001] This invention relates to an electroabsorption modulator. [Previous Technology]
[0002] Electroabsorption modulators (EAMs) play a crucial role in long-distance fiber optic communication and have the potential to integrate optoelectronic circuits. The capacitance value of the EAM is critical to its modulation performance, directly affecting modulation speed, power consumption, and signal quality. The RC time constant is determined by the capacitance (C) and drive resistor (R). Excessive capacitance increases the RC constant, reduces modulation speed, and limits its application in high-speed communication. Furthermore, excessive capacitance limits the frequency response range, leading to high-frequency signal attenuation and affecting signal integrity. To optimize performance, low-capacitance designs can be employed, such as increasing the active layer thickness, improving electrode arrangement, and using low-dielectric-constant materials. These methods can improve bandwidth, contributing to high-frequency modulation performance and improving signal quality. However, reducing capacitance may increase manufacturing difficulty and cost; therefore, a balance must be struck between performance and cost-effectiveness. Optimizing the capacitance value is a core issue in EAM design and is crucial for achieving efficient, high-speed optical communication. [Summary of the Invention]
[0003] In view of the above problems, the present invention provides an electro-absorption modulator that can reduce the capacitance value of the components to improve the modulation speed.
[0004] An embodiment of the present invention provides an electro-absorption modulator, comprising: a substrate; a waveguide region located on a first surface of the substrate, the waveguide region including: an optical waveguide and a pair of trenches located on both sides of the optical waveguide, the trenches having a first depth; at least one groove located outside the waveguide region and having a second depth, the second depth being greater than the first depth; and a first dielectric layer located in the groove, wherein the first dielectric layer includes a central portion, and the first thickness of the first dielectric layer in the central portion is approximately equal to the second depth.
[0005] In some embodiments, the second depth is at least greater than 3 micrometers.
[0006] In some embodiments, the refractive index of the first dielectric layer is 1.4 to 1.6.
[0007] In some embodiments, the material of the first dielectric layer includes silicon oxide (SiOx).
[0008] In some embodiments, a second dielectric layer is further included, located above the first dielectric layer and covering at least a portion of the first dielectric layer.
[0009] In some embodiments, the refractive index of the second dielectric layer is greater than that of the first dielectric layer.
[0010] In some embodiments, the refractive index of the second dielectric layer is 1.7 to 2.2.
[0011] In some embodiments, the material of the second dielectric layer includes silicon nitride (SiNx).
[0012] In some embodiments, the first dielectric layer further includes a peripheral portion surrounding the central portion, and the second thickness of the first dielectric layer in the peripheral portion is less than the first thickness.
[0013] In some embodiments, a recessed area is further included, formed on the first surface of the substrate and surrounding the groove.
[0014] In some embodiments, the recessed area has a third depth, which is less than the first depth of the trench.
[0015] In some embodiments, the third depth of the recessed region is greater than 0 nm to less than or equal to 100 nm.
[0016] In some embodiments, the electrode is located above the groove and extends into one of the pair of grooves and the optical waveguide.
[0017] In some embodiments, a third dielectric layer is further included, located above the groove and between the first dielectric layer and the electrode, and covering the first dielectric layer. The width of the third dielectric layer is greater than or equal to the width of the groove and partially overlaps with the electrode.
[0018] In some embodiments, the refractive index of the third dielectric layer is less than or equal to the refractive index of the first dielectric layer.
[0019] In some embodiments, a waterproof layer is further included, located above the substrate other than the optical waveguide.
[0020] In some embodiments, the waterproof layer is a stacked structure of silicon oxide (SiOx) and silicon nitride (SiNx).
[0021] An embodiment of the present invention provides an electro-absorption modulator, comprising: a substrate; a waveguide region located on a first surface of the substrate, the waveguide region including: an optical waveguide, wherein the substrate below the optical waveguide has a multilayer quantum well structure, the multilayer quantum well structure having a bottom; at least one groove located outside the waveguide region and having a depth exceeding the bottom of the multilayer quantum well structure; and a first dielectric layer located in the groove, wherein the first dielectric layer includes a central portion, the first thickness of the first dielectric layer in the central portion being approximately equal to the depth of the groove.
[0022] In some embodiments, a second dielectric layer is further included, located above the first dielectric layer and covering at least a portion of the first dielectric layer.
[0023] In some embodiments, the first dielectric layer further includes a peripheral portion surrounding the central portion, and the second thickness of the first dielectric layer in the peripheral portion is less than the first thickness.
[0024] Based on the above, the present invention provides an electro-absorption modulator, which has the technical feature that the dielectric layer in the groove located on the outside of the waveguide region has a thickness approximately the same as the depth of the groove, and the thicker the dielectric layer, the lower the capacitance value of the electro-absorption modulator. Therefore, the bandwidth can be increased to form a high-speed electro-absorption modulator.
[0025] In order to make the above features and advantages of the present invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are given in conjunction with the accompanying drawings.
Implementation Method
[0026] The invention is described more fully with reference to the drawings of this embodiment. However, the invention may be embodied in various different forms and should not be limited to the embodiments described herein. Sizes and distances in the drawings are drawn for visual clarity and are not the original sizes and distances. Identical or similar reference numerals denote identical or similar elements, which will not be described in detail in the following paragraphs.
[0027] As used herein, “contact” may refer to physical contact and / or electrical contact.
[0028] As used herein, “about,” “approximately,” “roughly,” or “substantially” includes the value mentioned and the average value within an acceptable range of deviations that can be determined by one of ordinary skill in the art, taking into account the measurement under discussion and the specific number of errors associated with the measurement (i.e., limitations of the measurement system). For example, “about” may mean within one or more standard deviations of the value, or within ±30%, ±20%, ±10%, ±5%. Furthermore, as used herein, “about,” “approximately,” “roughly,” or “substantially” may be chosen to select a more acceptable range of deviations or standard deviations depending on the optical, etched, or other properties, and a single standard deviation may not be applied to all properties.
[0029] The terminology used herein is for illustrative purposes only and is not intended to limit the scope of this disclosure. In this context, the singular form includes the plural form unless the context otherwise requires.
[0030] Figures 1 to 5 are schematic cross-sectional views of a method for forming an electro-absorbing modulator according to an embodiment of the present invention.
[0031] First, please refer to the electro-absorption modulator EAM shown in FIG1, which includes a substrate 100; a waveguide region 200 located on a first surface S1 of the substrate 100, the waveguide region 200 including an optical waveguide 210 and a pair of trenches 220 located on both sides of the optical waveguide 210, and the trenches 220 having a first depth D1; at least one groove 230 located on the outer side E of the waveguide region 200, and the groove 230 having a second depth D2, and the second depth D2 of the groove 230 being greater than the first depth D1 of the trenches 220 of the waveguide region 200. In this embodiment, the optical waveguide is described with a ridge waveguide structure. In another embodiment, the optical waveguide may also be a buried heterojunction waveguide.
[0032] In some embodiments, substrate 100 may include a semiconductor substrate, but is not limited thereto.
[0033] In some embodiments, the optical waveguide 210 may include a semiconductor material doped with P-type dopant or doped with N-type dopant, such as P-type InP semiconductor material, but is not limited thereto.
[0034] In addition, in some embodiments, the substrate 100 below the optical waveguide 210 includes a multi-quantum well (MQW) structure. This multi-quantum well structure MQW may include intrinsic semiconductors without P-type or N-type dopant, such as semiconductor materials such as AlInGaP and InGaAsP, but is not limited thereto.
[0035] Then, using various patterning processes such as photolithography, a pair of trenches 220 located on both sides of the optical waveguide 210 and at least one groove 230 located on the outer side E of the waveguide region 200 are formed in the first surface S1 of the substrate 100, wherein the second depth D2 of the groove 230 is greater than the first depth D1 of the trench 220 of the waveguide region 200.
[0036] In some embodiments, the second depth D2 of the groove 230 exceeds the bottom BMQW of the multilayer quantum well structure MQW. That is, as shown in FIG1, the bottom B230 of the groove 230 is deeper than the bottom BMQW of the multilayer quantum well structure MQW in the vertical direction Z from the first surface S1 of the substrate 100.
[0037] In some embodiments, the second depth D2 of the groove 230 is at least greater than 3 micrometers.
[0038] Furthermore, there is no particular limitation on the formation order of the groove 220 and the recess 230; they can be formed simultaneously, sequentially, or in various other orders.
[0039] In some embodiments, the groove 230 located on the outer side E of the waveguide region 200 includes at least one, for example, as shown in FIG1, the left and right outer sides E of the waveguide region 200 have grooves 230 respectively, but not limited thereto.
[0040] Next, referring to FIG2, a first dielectric layer 240 is formed on the first surface S1 of the substrate 100. This first dielectric layer 240 completely fills the trench 220 and the recess 230, and the first thickness T1 of the first dielectric layer 240 located in the center portion 242 of the recess 230 is approximately equal to the second depth D2 of the recess 230.
[0041] Next, as shown in FIG2, a second dielectric layer 250 is formed on the first dielectric layer 240 to cover the first dielectric layer 240.
[0042] The thickness of the first dielectric layer 240 is about 8 to 12 micrometers; in addition, the thickness of the second dielectric layer 250 is about 20 nm to 500 nm.
[0043] Furthermore, since the first dielectric layer 240 and the second dielectric layer 250 are conformally formed on the substrate 100 having the trench 220 and the recess 230, and considering the first thickness T1 deposited by the first dielectric layer 240, the distance of the second dielectric layer 250 on the peripheral portion 244 of the first dielectric layer 240 in the recess 230 from the bottom B230 of the recess 230 in the vertical direction Z will naturally be greater than the distance of the second dielectric layer 250 on the central portion 242 of the first dielectric layer 240 in the recess 230 from the bottom B230 of the recess 230 in the vertical direction Z. The peripheral portion 244 surrounds the central portion 242. That is, the second dielectric layer 250 on the peripheral portion 244 of the first dielectric layer 240 in the recess 230 will be higher than the second dielectric layer 250 on the central portion 242 of the first dielectric layer 240 in the recess 230, as shown in FIG2.
[0044] In some embodiments, the density of the second dielectric layer is higher than that of the first dielectric layer, in order to protect the first dielectric layer in subsequent processing. However, this is not a limitation.
[0045] In some embodiments, the refractive index of the first dielectric layer 240 is about 1.4 to 1.6.
[0046] In some embodiments, the first dielectric layer 240 may include a dielectric material such as silicon oxide (SiOx), but is not limited thereto.
[0047] In some embodiments, the refractive index of the second dielectric layer 250 is greater than that of the first dielectric layer 240. For example, the refractive index of the second dielectric layer 250 is about 1.7 to 2.2.
[0048] In some embodiments, the second dielectric layer 250 may include a dielectric material such as silicon nitride (SiNx), but is not limited thereto.
[0049] In some embodiments, the second dielectric layer 250 may not be formed on the first dielectric layer 240.
[0050] Then, referring to FIG2, a patterned first mask layer PR1 is formed on the electro-absorption modulator EAM, for example, a patterned photoresist layer is formed. This patterned first mask layer PR1 covers the waveguide region 200 and the second dielectric layer 250 and the first dielectric layer 240 above the groove 230.
[0051] Next, please refer to Figure 2 and Figure 3 at the same time.
[0052] First, a dry etching process is performed in the presence of the patterned first mask layer PR1 to disconnect the second dielectric layer 250 between the waveguide region 200 and the groove 230 from the first dielectric layer 240, as shown in FIG3.
[0053] As described above, since the second dielectric layer 250 located on the peripheral portion 244 of the first dielectric layer 240 in the groove 230 is higher than the second dielectric layer 250 located on the central portion 242 of the first dielectric layer 240 in the groove 230, the second dielectric layer 250 and part of the first dielectric layer 240 located on the peripheral portion 244 of the first dielectric layer 240 in the groove 230 can be removed by over-etching, so that the second dielectric layer 250 located above the first dielectric layer 240 covers at least a part of the first dielectric layer 240. More specifically, after the over-etching process, the second dielectric layer 250 is only located in the central portion 242 of the first dielectric layer 240 in the groove 230.
[0054] And since the above-mentioned over-etching has removed a portion of the surrounding portion 244 of the first dielectric layer 240 in the groove 230, the second thickness T2 of the surrounding portion 244 of the first dielectric layer 240 will be less than the first thickness T1 of the central portion 242 of the first dielectric layer 240, as shown in FIG3.
[0055] Furthermore, as shown in FIG2, the area between the waveguide region 200 and the groove 230 that is not covered by the first masking layer PR1 will undergo the above-mentioned dry etching and over-etching processes. Therefore, a recessed area 260 may be formed on the first surface S1 of the substrate 100 in the area between the waveguide region 200 and the groove 230. From the top view facing the first surface S1 of the substrate 100, this recessed area 260 will surround the groove 230. In addition, if the first dielectric layer 240 on the substrate 100 in this area is just removed by the dry etching and over-etching processes, the recessed area 260 may not be formed.
[0056] The recessed area 260 has a third depth D3, as shown in the enlarged view of the recessed area 260 in Figure 3. The third depth D3 of the recessed area 260 is less than the second depth D2 of the groove 230, and the third depth D3 of the recessed area 260 is less than the first depth D1 of the groove 220.
[0057] In some embodiments, the third depth D3 of the recessed region 260 is greater than 0 nm and less than or equal to 100 nm.
[0058] Next, referring to FIG4, a patterned second mask layer PR2 is formed on the electro-absorption modulator EAM, for example, a patterned photoresist layer is formed, and this patterned second mask layer PR2 exposes the waveguide region 200; then, the second dielectric layer 250 and the first dielectric layer 240 in the waveguide region 200 are removed by various etching processes, for example, the second dielectric layer 250 and the first dielectric layer 240 in the waveguide region 200 can be removed by wet etching or other processes, but not limited thereto.
[0059] Next, referring to FIG5, the electro-absorption modulator EAM can form a third dielectric layer 270 above the groove 230 to cover the first dielectric layer 240 and the second dielectric layer 250 in the groove 230, and the width W270 of this third dielectric layer 270 in the horizontal direction X is greater than or equal to the width W230 of the groove 230, as shown in FIG5.
[0060] In some embodiments, the refractive index of the third dielectric layer 270 is less than or equal to the refractive index of the first dielectric layer 240.
[0061] In some embodiments, the third dielectric layer 270 may be used to further reduce the capacitance value.
[0062] In some embodiments, the first dielectric layer 240 and the third dielectric layer 270 have the same material.
[0063] Please continue to refer to Figure 5. The electro-absorption modulator EAM also includes a waterproof layer 280. This waterproof layer 280 is located on the substrate 100 except for the optical waveguide 210. That is to say, this waterproof layer 280 does not cover the optical waveguide 210.
[0064] In some embodiments, the waterproof layer 280 may be, for example, a stacked structure of silicon oxide (SiOx) and silicon nitride (SiNx), but is not limited thereto.
[0065] Furthermore, referring to Figure 5, the electro-absorption modulator EAM further includes an electrode 290 located above the groove 230 and extending to one of a pair of trenches 220 of the waveguide region 200 and the optical waveguide 210.
[0066] Therefore, the third dielectric layer 270 is located between the first dielectric layer 240 and the electrode 290, and partially overlaps with the electrode 290.
[0067] Since the waterproof layer 280 is located above the substrate 100 except for the optical waveguide 210, the electrode 290 can make electrical contact with the optical waveguide 210 exposed from the waterproof layer 280.
[0068] In summary, because the electro-absorption modulator provided by the present invention has a dielectric layer in the groove located on the outer side of the waveguide region with a thickness approximately the same as the depth of the groove, and this thick dielectric layer can reduce the capacitance value of the electro-absorption modulator, power loss can be reduced and a fast-modulating electro-absorption modulator can be formed. Furthermore, because the thickness of the dielectric layer in the groove is approximately equal to the depth of the groove, problems such as incomplete coverage or open circuits caused by excessively thick dielectric layers when forming waterproof layers or electrodes can be avoided, and process stability can be increased.
[0069] Although the present invention has been disclosed above by way of embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims. [Simplified Explanation of the Diagram]
[0070] Figures 1 to 5 are schematic cross-sectional views of a method for forming an electro-absorbing modulator according to an embodiment of the present invention.
Claims
1. An electro-absorption modulator, comprising: a substrate; a waveguide region located on a first surface of the substrate, the waveguide region including: an optical waveguide and a pair of trenches located on both sides of the optical waveguide, the trenches having a first depth; at least one groove located outside the waveguide region and having a second depth greater than the first depth; and a first dielectric layer located in the groove, wherein the first dielectric layer includes a central portion, and a first thickness of the first dielectric layer in the central portion is approximately equal to the second depth.
2. The electro-absorption modulator as claimed in claim 1, wherein the second depth is at least greater than 3 micrometers.
3. The electro-absorption modulator as claimed in claim 1, wherein the refractive index of the first dielectric layer is 1.4 to 1.
6.
4. The electro-absorption modulator as claimed in claim 1, wherein the material of the first dielectric layer comprises silicon oxide (SiOx).
5. The electro-absorption modulator as claimed in claim 1, further comprising: a second dielectric layer located above the first dielectric layer and covering at least a portion of the first dielectric layer.
6. The electro-absorption modulator as claimed in claim 5, wherein the refractive index of the second dielectric layer is greater than the refractive index of the first dielectric layer.
7. The electro-absorption modulator as claimed in claim 6, wherein the refractive index of the second dielectric layer is 1.7 to 2.
2.
8. The electro-absorption modulator as claimed in claim 7, wherein the material of the second dielectric layer comprises silicon nitride (SiNx).
9. The electro-absorption modulator as claimed in claim 1, wherein the first dielectric layer further includes a peripheral portion surrounding the central portion, and the second thickness of the first dielectric layer in the peripheral portion is less than the first thickness.
10. The electro-absorption modulator as claimed in claim 1, further comprising: a recessed region formed on the first surface of the substrate and surrounding the recess.
11. The electro-absorption modulator as claimed in claim 10, wherein the recessed region has a third depth, the third depth being less than the first depth of the trench.
12. The electro-absorption modulator as claimed in claim 10, wherein the third depth of the recessed region is greater than 0 nm and less than or equal to 100 nm.
13. The electro-absorption modulator as claimed in claim 1, further comprising: an electrode located above the groove and extending to one of the pair of grooves and the optical waveguide.
14. The electro-absorption modulator as claimed in claim 13, further comprising: a third dielectric layer located above the groove and between the first dielectric layer and the electrode, and covering the first dielectric layer, the width of the third dielectric layer being greater than or equal to the width of the groove and partially overlapping the electrode.
15. The electro-absorption modulator as claimed in claim 14, wherein the refractive index of the third dielectric layer is less than or equal to the refractive index of the first dielectric layer.
16. The electro-absorption modulator as claimed in claim 1, further comprising: a waterproof layer located above the substrate other than the optical waveguide.
17. The electro-absorption modulator as claimed in claim 16, wherein the waterproof layer is a stacked structure of silicon oxide (SiOx) and silicon nitride (SiNx).
18. An electro-absorption modulator, comprising: a substrate; a waveguide region located on a first surface of the substrate, the waveguide region comprising: an optical waveguide, wherein, The substrate beneath the optical waveguide has a multilayer quantum well structure having a bottom; at least one groove located outside the waveguide region and having a depth exceeding the bottom of the multilayer quantum well structure; and a first dielectric layer located in the groove, wherein the first dielectric layer includes a central portion and a first thickness of the first dielectric layer in the central portion is approximately equal to the depth of the groove.
19. The electro-absorption modulator as claimed in claim 18, further comprising: a second dielectric layer located above the first dielectric layer and covering at least a portion of the first dielectric layer.
20. The electro-absorption modulator as claimed in claim 18, wherein the first dielectric layer further includes a peripheral portion surrounding the central portion, and the second thickness of the first dielectric layer in the peripheral portion is less than the first thickness.