Silicon-based micro-ring photoelectric detector
By introducing a Ge-on-Si double-layer microring structure and two-photon absorption effect into a silicon-based photodetector, the problem of poor detection performance of silicon-based photodetectors in the 2μm band is solved, realizing low-cost, highly integrated non-invasive blood glucose detection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI UNIV
- Filing Date
- 2022-11-24
- Publication Date
- 2026-07-31
AI Technical Summary
Existing silicon-based photodetectors struggle to effectively detect 2μm wavelength optical signals at low cost, especially in non-invasive blood glucose testing where they suffer from both low accuracy and high cost.
By combining the two-photon absorption effect with a silicon-based platform and a microring resonator structure, a germanium absorption layer is epitaxially grown on the upper surface of a silicon microring, and etching is performed in the coupling region to form a Ge-on-Si bilayer microring structure, thereby enhancing photon density and two-photon absorption effect.
A low-cost, highly integrated 2μm band photodetector has been developed, which improves the detector's responsivity and selectivity and is suitable for non-invasive blood glucose detection.
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Figure CN115939231B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of photodetectors, and more specifically, relates to a silicon-based microring photodetector that can be used for non-invasive blood glucose detection. Background Technology
[0002] A photodetector is a device that converts optical signals into electrical signals and plays a crucial role in modern optical communication technology. The signal detection principle of a photodetector is primarily based on the photoconductive effect, which utilizes the change in free carrier concentration in a semiconductor material under illumination of light within a certain wavelength range. This change causes a change in the semiconductor's conductivity. By detecting the change in the current flowing through the semiconductor before and after illumination, optical signals can be detected. Photodetectors are widely used in various signal receiving devices, sensors, and bio-information detection fields.
[0003] Patients need to test their blood glucose very frequently, especially those with severe diabetes, who need to self-test their blood glucose approximately 3-5 times a day. Traditional puncture blood glucose testing has high accuracy, but it inevitably causes pain and discomfort for patients. Non-invasive blood glucose testing provides a much better testing experience, but current non-invasive blood glucose meters face problems such as low accuracy, making them unsuitable as a reference for clinical diagnosis, and their prices are generally high, making the cost of non-invasive blood glucose testing a significant concern for many patients. The absorption spectrum of human blood glucose includes the 2μm band; therefore, designing a high-performance, low-cost detector that operates in the 2μm band is crucial for non-invasive blood glucose meters.
[0004] With the development of electronic information technology, especially the improvement of semiconductor manufacturing processes, the performance of commercial photodetectors is constantly improving, including parameters such as responsivity and operating bandwidth. Regarding manufacturing costs, due to the mature development of complementary metal-oxide-semiconductor (CMOS) technology, the manufacturing cost of integrated circuits can now be very low. However, ordinary optical waveguide technology is relatively difficult to achieve high integration at low cost. Researchers have thus extended the manufacturing process of integrated circuits to optical devices, leading to the development of silicon photonics technology, which involves fabricating optical devices on silicon substrates. The biggest advantage of silicon-based photodetectors is their compatibility with mature CMOS semiconductor processes, low manufacturing cost, and high product yield, which is conducive to large-scale production, especially enabling highly integrated optical information systems. Based on these advantages, silicon photonics has been promoted over the past decade as a platform providing revolutionary progress in fields such as data communication, medical technology, and sensing technology.
[0005] Since silicon is an indirect bandgap material with a bandgap width of 1.12 eV, the cutoff wavelength for the photoelectric effect in silicon is 1.1 μm. Light signals with wavelengths exceeding 1.1 μm are almost not absorbed in silicon, making it impossible to directly detect 2 μm light signals using silicon. Currently, solutions for 2 μm wavelength light detection mainly rely on group III-V materials with tunable bandgap, such as InGaAs / InP photodetectors. However, the fabrication process for group III-V material devices is complex and costly, hindering the promotion of commercial detection equipment based on such devices to ordinary individual users.
[0006] Normally, when a semiconductor material undergoes the photoelectric effect, it can only absorb one photon at a time, which is the energy required for a free electron to transition from its ground state to an excited state. However, under sufficiently high light intensity, the material molecules may absorb two photons, each with an energy that is half or more than half the energy difference between the ground and excited states of a free electron in the semiconductor material. Introducing the two-photon absorption effect into the detector can extend the operating wavelength of silicon-based photodetectors to the 2μm band.
[0007] Two-photon absorption requires sufficiently high light intensity, which essentially necessitates a sufficiently high photon density in the active region of the detector. Furthermore, two-photon absorption is a weak absorption effect; under the same input power, it is far weaker than intrinsic absorption. While increasing the power of the input light source can enhance the photon density in the active region of the detector and thus improve two-photon absorption, this is not an ideal solution. High-power light sources consume a lot of energy and require large laser control devices, which negatively impacts the safety, convenience, and wearability of non-invasive blood glucose monitoring devices. Increasing the area of the active region of the photodetector can also increase its responsivity, but this reduces the photodetector's wavelength selectivity, making the response signal more susceptible to interference. It also lowers the device's integration density, potentially reducing the photon density in the active region and causing the local light intensity to fall below the two-photon absorption threshold, resulting in reduced two-photon absorption.
[0008] For photodetectors based on the two-photon effect, special structures such as DBR mirrors, FP cavities, and microrings are often introduced to further improve their performance. The core structure of a microring includes a straight waveguide and a ring waveguide. Input light enters from the input end of the straight waveguide and couples to the ring waveguide via evanescent waves at the closest coupling region between the two waveguides. Light satisfying the resonance condition within the ring is coherently amplified, while light not satisfying the resonance condition gradually attenuates due to material losses and bending losses within the ring. Microring-based detectors benefit from the compactness, silicon-based platform compatibility, and ease of integration of the microring structure. Silicon waveguide-based microring resonators can confine the optical field within a very small waveguide. Furthermore, the standing wave effect of the microring generates enhanced resonance intensity within the ring, increasing the photon density. The key to fabricating a core photodetector for non-invasive blood glucose monitoring lies in improving the optical field in the active region of the microring-based photodetector to enhance the two-photon absorption effect and achieve 2μm band detection. Summary of the Invention
[0009] To address the current challenge of effectively detecting 2μm wavelength optical signals using silicon-based photodetectors, this invention utilizes two-photon absorption in nonlinear absorption to enable silicon-based detectors to perform 2μm wavelength optical detection.
[0010] The technical solution of the present invention:
[0011] A silicon-based photodetector includes a silicon waveguide layer 012, a ridged silicon bus waveguide 001 and a silicon microring 006 on the upper surface of the silicon waveguide layer 012, a coupling region 020 near the silicon bus waveguide 001 on the silicon microring 006, and a germanium absorption layer 004 on the upper surface of the silicon microring 006 except for the coupling region 020.
[0012] A middle electrode ring 005 is installed above the silicon microring 006. An inner electrode ring 007 is provided inside the silicon microring 006, and an outer electrode ring 003 is provided outside the silicon microring 006. The middle electrode ring 005 and the outer electrode ring 003 have a notch near the coupling region 020.
[0013] Silicon bus waveguide 001 and silicon microring 006 are obtained by etching. A germanium absorption layer 004 is epitaxially grown on the upper surface of silicon microring 006. A notch is formed by etching the germanium absorption layer 004 in coupling region 020.
[0014] The inner electrode ring 007, the middle electrode ring 005, and the outer electrode ring 003 are placed sequentially in their respective doped regions. A silicon dioxide filling layer 9 is injected onto the silicon waveguide layer 012 to cover the inner electrode ring 007, the middle electrode ring 005, and the outer electrode ring 003, leaving only the electrode plate 022 on the upper surface exposed.
[0015] The closest distance between silicon bus waveguide 001 and silicon microring 006 is 300nm. When a 2μm wavelength optical signal is re-input into silicon bus waveguide 001, the attenuation factor γ inside the ring is equal to the transmission coefficient t in the coupling region 020. The microring is in a critical coupling state, and the resonant light intensity inside the ring reaches its maximum.
[0016] The total length of the germanium absorption layer 004 is an odd multiple of the directional coupling length of light between the silicon microring 006 and the germanium absorption layer 004.
[0017] Below the silicon waveguide layer 012 are the buried oxide layer 013 and the silicon substrate 014.
[0018] Silicon-based photodetectors are used for non-invasive blood glucose detection.
[0019] The beneficial effects of this invention are:
[0020] This invention utilizes the two-photon absorption effect of semiconductor materials and employs a silicon-based platform and a microring resonant cavity structure to realize a low-cost, highly integrated 2μm band photodetector. The structure of the photodetector has been optimized by replacing the single-layer silicon microring with a Ge-on-Si double-layer microring and partially etching the germanium microring in the coupling region. The resulting microring detector retains compatibility with mature complementary metal-oxide-semiconductor (CMOS) technology while achieving excellent detection performance in numerical simulations. This provides a new approach for the design of future 2μm band and related infrared band photodetectors. Attached Figure Description
[0021] Figure 1 This is a top view of the silicon-based microring photodetector for non-invasive blood glucose detection in this invention.
[0022] Figure 2 for Figure 1 Cross-sectional view of the active region of the micro-ring (010);
[0023] Figure 3 for Figure 1 Cross-sectional view of the coupling region of the micro-ring (011);
[0024] Figure reference numerals: 001 Silicon bus waveguide; 003, 005, 007 Metal electrode pillars; 004 Germanium absorber layer; 006 Silicon microring; 009 Silicon dioxide protective layer; 010 Microring active region cross-section; 011 Microring coupling region cross-section; 012 Silicon waveguide layer; 013 Buried oxide layer; 014 Silicon substrate; 015 Height of germanium absorber layer; 016 Width of silicon microring; 017 Width of silicon bus waveguide; 018 Gap width of microring coupling region; Detailed Implementation
[0025] Example 1:
[0026] like Figure 2The silicon-based photodetector of the present invention comprises, from bottom to top, a silicon substrate 014, a buried oxide layer 013, a silicon waveguide layer 012, and a silicon dioxide filling layer 009.
[0027] The silicon waveguide layer 012 has a ridged silicon bus waveguide 001 and a silicon microring 006 on its upper surface. The section of the silicon microring 006 closest to the silicon bus waveguide 001 is the coupling region 020. Apart from the coupling region 020, the upper surface of the silicon microring 006 has a germanium absorption layer 004. The closest distance between the silicon bus waveguide 001 and the silicon microring 006 is 300 nm. When a 2 μm wavelength optical signal is re-input into the silicon bus waveguide 001, the attenuation factor γ within the ring is equal to the transmission coefficient t in the coupling region 020, and the microring is in a critical coupling state, with the resonant light intensity within the ring reaching its maximum. The total length of the germanium absorption layer 004 is an odd multiple of the directional coupling length between the silicon microring 006 and the germanium absorption layer 004.
[0028] A middle electrode ring 005 is installed above a silicon microring 006. An inner electrode ring 007 is disposed inside the silicon microring 006, and an outer electrode ring 003 is disposed outside the silicon microring 006. The middle electrode ring 005 and the outer electrode ring 003 have notches near the coupling region 020. The inner electrode ring 007 and the outer electrode ring 003 are located on the upper surfaces of the heavily doped regions 002 and 008, respectively.
[0029] The fabrication process is as follows: a silicon bus waveguide 001 and a silicon microring 006 are obtained by etching. A germanium absorption layer 004 is epitaxially grown on the upper surface of the silicon microring 006. A notch is formed by etching the germanium absorption layer 004 in the coupling region 020. The inner electrode ring 007, the middle electrode ring 005, and the outer electrode ring 003 are placed sequentially in their respective active regions. A silicon dioxide filling layer 009 is injected into the silicon waveguide layer 012 to cover the inner electrode ring 007, the middle electrode ring 005, and the outer electrode ring 003, leaving only the electrode plate 022 on the upper surface exposed.
[0030] Example 2:
[0031] See attached document Figure 1 , Figure 2 The main structure of the micro-ring photodetector provided by this invention includes:
[0032] The silicon substrate 014 includes a silicon dioxide buried oxide layer 013 and a silicon waveguide layer 012 on its upper surface. The thickness of the silicon buried oxide layer is 200 nm.
[0033] According to the process requirements provided by the wafer fab, the silicon waveguides involved in this invention are all ridge waveguides, and the photolithography method uses a 150nm deep etching, that is, the total height of the silicon waveguide layer 012 is 220nm, and the etched area is 150nm. The silicon waveguide layer includes a straight ridge waveguide 001, i.e., a bus waveguide; and a silicon microring 006;
[0034] To accommodate single-mode optical signals with a wavelength of 2μm, the silicon waveguide layer is etched to a fixed value;
[0035] Specifically, the width 017 of the bus waveguide 001 is 500 nm, and the width 016 of the silicon microring 006 is 540 nm. To reduce the loss caused by waveguide bending, the radius of the silicon microring 006 is designed to be 5 μm, that is, the distance from the center of the silicon microring waveguide to the center of the microring is 5 μm.
[0036] The closest distance between the bus waveguide 001 and the silicon microring is 300nm. When a 2μm wavelength optical signal is input at the input end of the microring detector and the gap 018 is 300nm, the attenuation factor inside the ring is equal to the transmission coefficient in the coupling region of the microring. The microring is in a critical coupling state, and the resonant light intensity inside the ring reaches its maximum at this time.
[0037] Preferably, an end-face coupler can be used to input the external laser to the input terminal 019 of the photodetector. The advantages of the end-face coupler are high coupling efficiency and polarization insensitivity.
[0038] Preferably, an external laser input can be a grating coupler, which is easy to align during testing;
[0039] A germanium absorption layer is epitaxially grown on the upper surface of the silicon microring to form a Ge-on-Si structure with the silicon microring. The two-photon absorption coefficient of germanium in the 2μm band is about 4000 times that of silicon, thereby further increasing the two-photon absorption effect in the ring.
[0040] Furthermore, a portion of the germanium absorption layer is etched away on both sides of the coupling region 011. For the Ge-on-Si waveguide structure, this ensures that when the light field is directionally coupled between the Ge and silicon layers, it is coupled back into the Si layer at the end of the Ge layer, rather than being scattered and lost at the edge of the Ge layer. A suitable length of the germanium absorption layer allows the light energy in the Ge-on-Si microring to be absorbed multiple times by the germanium layer, thereby further increasing the two-photon absorption effect within the ring and improving the detector's responsivity. According to FDTD numerical simulation results, for a 2 μm optical signal, the coupling length between the silicon and germanium microrings in the Ge-on-Si microring structure is approximately 0.68 μm. Therefore, the length of the germanium absorption layer etched away in the coupling region 011 can be designed to be 4.7 μm; refer to Appendix... Figure 2 The height 015 of the germanium absorption layer is 300 nm. When the height of the germanium absorption layer is scanned from 150 nm to 300 nm, the optical signal mode area of the Ge layer gradually increases. Considering the semiconductor manufacturing process, the height 015 of the germanium absorption layer is designed to be 300 nm. Numerical analysis results show that most of the optical field of the 2 μm wavelength optical signal base film in the Ge-on-Si waveguide is concentrated in the Ge absorption layer.
[0041] Reference Appendix Figure 2A contact electrode is fabricated on the upper surface of the silicon dioxide protective layer 009 and connected to the electrode post 003. The contact tip is an ohmic contact electrode, made of one of aluminum, chromium, gold, titanium, palladium, or silver, or a combination thereof. The electrode post 003 and the contact electrode 009 are prepared by resistance thermal evaporation, electron beam evaporation, or magnetron sputtering.
[0042] The working principle of the silicon-based microring photodetector of the present invention is as follows:
[0043] The 2μm optical signal output from the external laser source is input to the bus waveguide 001 through an end-face coupler or a grating coupler. In the coupling region where the bus waveguide 001 is close to the silicon microring 006, the optical signal is coupled to the silicon microring 006 through evanescent wave coupling. During the transmission of the optical signal in the silicon microring 006, it undergoes directional coupling with the germanium microring 004 and mainly generates two-photon absorption in the germanium microring 004, generating free electron-hole pairs. Under the external bias voltage applied through the electrodes, the free electron-hole pairs move directionally to form a photocurrent.
[0044] Example 3:
[0045] The optocoupler provided by this invention uses a micro-ring resonant cavity structure based on silicon-on-insulator technology as the core part of the detector, including:
[0046] The silicon substrate 014 serves as the base for the epitaxial layer, ensuring the stability and compactness of the device structure.
[0047] The buried oxide layer 013, composed of silicon dioxide, is placed on the silicon substrate 014 to reduce electron loss and device parasitic capacitance.
[0048] Above the buried oxide layer 013 is the top silicon layer, called the silicon waveguide layer 012. A silicon bus waveguide 001 and a ridge waveguide microring structure critically coupled to the bus waveguide - silicon microring 006 - are formed by photolithography. The structural parameters of silicon microring 006 are adjusted so that the resonant wavelength inside the ring covers the 2μm band, that is, the optical signal in the blood glucose absorption spectrum peak is resonated and enhanced, thereby improving the two-photon absorption effect of the photodetector under the same power optical signal input.
[0049] A silicon dioxide protective layer 009 is grown on top of the silicon waveguide layer 012 to reduce waveguide loss and separate the metal electrode from the waveguide.
[0050] The bottom of the silicon microring 006 is doped and a cathode electrode layer is deposited on the outer and inner sides of the ring. The metal wires of the cathode electrode layer extend from the bottom of the ridge waveguide type microring to the upper surface of the silicon dioxide protective layer and form an ohmic contact.
[0051] Furthermore, the silicon microring 006 adopts a Ge-on-Si double-layer ring structure. Because germanium has a high two-photon absorption coefficient, germanium is used as the active region absorption layer to further improve the two-photon absorption effect of the active region of the photodetector.
[0052] Furthermore, the microring structure based on the Ge-on-Si waveguide is partially etched, and part of the germanium in the upper germanium ring of the coupling region 020 is radially etched away to form a gap. This gap is used to form a directional coupling effect between the silicon microring and the germanium microring when light is coupled from the bus waveguide into the microring structure, so that the highest point of light intensity can be periodically completely located in the germanium microring to better trigger the two-photon absorption effect.
[0053] Furthermore, the etching length of the germanium microring in the coupling region was adjusted so that the total length of the germanium absorption layer was an odd multiple of the directional coupling length of light between the silicon microring and the germanium microring, in order to reduce the scattering loss of light resonating within the ring at the etching edge of the germanium microring, thereby increasing the photon density in the germanium absorption layer compared to the complete Ge-on-Si double ring.
[0054] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A silicon-based microring photodetector, comprising a silicon waveguide layer (012), characterized in that: The upper surface of the silicon waveguide layer (012) has a ridged silicon busbar waveguide (001) and a silicon microring (006). The section of the silicon microring (006) near the silicon busbar waveguide (001) is a coupling region (020). In addition to the coupling region (020), the upper surface of the silicon microring (006) has a germanium absorption layer (004). A middle electrode ring (005) is installed above the silicon microring (006). An inner electrode ring is provided inside the silicon microring (006). An electrode ring (007) is provided on the outside, and an outer electrode ring (003) is provided on the outside. The middle electrode ring (005) and the outer electrode ring (003) have a gap near the coupling region (020). A silicon bus waveguide (001) and a silicon micro ring (006) are obtained by etching. A germanium absorption layer (004) is epitaxially grown on the upper surface of the silicon micro ring (006). The germanium absorption layer (004) in the coupling region (020) is etched to form a gap.
2. The silicon-based microring photodetector according to claim 1, characterized in that: The closest distance between the silicon bus waveguide (001) and the silicon microring (006) is 300nm. When a 2μm wavelength optical signal is re-input into the silicon bus waveguide (001), the attenuation factor γ inside the ring is equal to the transmission coefficient t in the coupling region (020). The microring is in a critical coupling state, and the resonant light intensity inside the ring reaches its maximum.
3. The silicon-based microring photodetector according to claim 1, characterized in that: The total length of the germanium absorption layer (004) is an odd multiple of the directional coupling length of light between the silicon microring (006) and the germanium absorption layer (004).
4. The silicon-based microring photodetector according to any one of claims 1-3, characterized in that: Silicon-based photodetectors are used for non-invasive optical detection of blood glucose.