High-performance infrared focal plane detector based on super-structure lens effect

Abstract

The invention discloses a high-performance infrared focal plane detector based on a super-structure lens effect, and belongs to the technical field of photoelectric detection. The core of the invention lies in providing a novel detector architecture which carries out integrated collaborative design on metal microcavity resonance and a super-structure lens condensation effect at a pixel level. Multi-physical field collaborative optimization is carried out on a quantum well material, a metal microcavity structure and an array period, so that periodically arranged detector pixels simultaneously have dual functions of microcavity resonance frequency selection and microlens wavefront regulation and control. On one hand, incident infrared light is converged through a super-structure lens effect induced by an array period, and the energy density of a light field is enhanced; on the other hand, incident light coupled into the metal microcavity can excite a resonance mode in the microcavity, and the active area light field is further locally strengthened. According to the invention, additional optical elements are not needed, the process is completely compatible with the existing focal plane technology, and a brand new technical approach is provided for high-performance narrow-band infrared detection.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection technology, specifically relating to a high-performance infrared focal plane detector based on the metalens effect. Background Technology

[0002] Every object radiates infrared light into its environment. The intensity of this radiation is closely related to the object's temperature, material properties, and surface condition, which forms the basis of infrared detection. Infrared imaging detection is a non-contact sensing technology that captures the infrared light radiated by an object and converts it into a visual image. It has important applications in fields such as industrial inspection, medical diagnosis, and environmental monitoring.

[0003] Combining infrared detection with narrowband technology is key to achieving high-sensitivity and high-specificity target identification. Currently, the mainstream narrowband detection scheme involves adding a narrowband filter or beam splitter in front of a broadband-response detector (such as an HgCdTe detector). Quantum well infrared detectors (QWIPs), due to their inter-subband transition mechanism, inherently possess a narrow intrinsic response bandwidth, demonstrating advantages in narrowband gas detection and other fields. However, the quantum efficiency of inter-subband transitions in QWIPs is generally low, severely limiting their detection performance.

[0004] To improve the optical coupling and absorption efficiency of quantum well detectors, existing technologies mainly fall into two categories. One category integrates optical structures such as microlenses in front of or on the surface of the detector, increasing the incident light flux through geometric focusing. This type of approach is essentially an external optical element, which is difficult to integrate, has complex manufacturing processes, and offers only a single function, increasing light flux without achieving spectral selectivity. The other category utilizes the microcavity resonance effect to enhance light absorption, such as metal-insulator-metal (MIM) microcavity structures based on the plasmon effect. These structures form Fabry-Perot resonances through near-field coupling between upper and lower metal layers, significantly improving the responsivity at specific wavelengths. However, these structures suffer from severe metal ohmic losses, making it difficult to exceed the intrinsic material limit (typically below 20%), and their resonant bandwidth is relatively wide, limiting their narrowband filtering performance. In recent years, some studies have also used dielectric microcavities to achieve frequency selectivity. While this reduces metal absorption and achieves efficiencies of around 80%, it still lacks active focusing capability, and further efficiency improvements remain a bottleneck.

[0005] In summary, in existing technologies, the functions of focusing enhancement and resonant frequency selection are usually independent and implemented through different components or structures, making it difficult to integrate them at the pixel scale. How to significantly break through the theoretical upper limit of quantum efficiency while maintaining narrowband response characteristics, and achieve full compatibility with focal plane array technology, is a pressing technical challenge in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a high-performance infrared focal plane detector based on the metalens effect. The detector pixels are designed as microcavity structures. By utilizing the superposition of a specific periodic arrangement of the pixels and the active region resonance enhancement effect of the microcavity structure itself, the detector naturally possesses the focusing effect of a microlens and narrowband detection capabilities, thus significantly overcoming the quantum efficiency bottleneck of quantum well devices. Furthermore, due to its focal plane-scale pixel structure, compared to metasurface structures requiring additional custom fabrication processes, the detector provided by this invention not only achieves the ultra-high absorption quantum efficiency obtained through microlens focusing, but its device structure, compatible with focal plane fabrication processes, also facilitates the development of large-area focal plane array chips, making it of significant application value in high-sensitivity infrared imaging and other fields.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A high-performance infrared focal plane detector based on the metalens effect includes a periodically arranged array of metal microcavity pixels. Each metal microcavity pixel is a mesa-shaped metal microcavity structure, comprising, from bottom to top, a substrate, a lower electrode layer, a quantum well infrared light absorption layer, and an upper electrode layer; wherein,

[0009] The sidewalls and top surface of the mesa-shaped metal microcavity structure are sequentially covered with an insulating dielectric film and a continuous metal thin film. The metal thin film and the lower electrode layer together constitute a three-dimensional metal microcavity that encloses the quantum well infrared light absorption layer. The three-dimensional metal microcavity is used to excite a resonant mode at the target wavelength to achieve a narrowband spectral response.

[0010] The periodically arranged metal microcavity pixel array induces a metalens effect on a macroscopic scale, focusing the incident infrared light wavefront to the microcavity region of each pixel to achieve enhanced light concentration; Ohmic contact electrodes are respectively fabricated on the surfaces of the upper and lower electrode layers, and the Ohmic contact electrodes are interconnected with the readout circuit by opening windows in the insulating dielectric film.

[0011] The beneficial effects of this invention are as follows:

[0012] A theoretical breakthrough and performance leap in quantum efficiency have been achieved: the incident light field is actively focused through the metalens effect and further enhanced locally by microcavity resonance. The synergistic effect of the two effects enables the absorption quantum efficiency of the device at the target wavelength to exceed 100%, far exceeding the levels of existing quantum well detectors (usually 10%-20%) and ordinary microcavity devices (usually below 80%).

[0013] Excellent low-doping high quantum efficiency characteristics were achieved: This integrated design significantly reduces the dependence on the doping concentration of the quantum well material, enabling the device to maintain ultra-high quantum efficiency even under low-doping conditions. This helps to significantly reduce the device's dark current noise, improve detection sensitivity and detectivity, and reduce the inherent dependence of device performance on materials.

[0014] Intrinsic narrowband high-selectivity detection is achieved: the microcavity resonance mechanism endows the device with inherent narrowband spectral response characteristics, enabling high-selectivity detection of target wavelengths (such as gas characteristic absorption peaks) without the need for external filters, thus meeting the core requirement of high spectral purity for applications such as gas sensing and spectral analysis.

[0015] It combines high process compatibility with integration advantages: the technology is implemented entirely at the pixel scale, without the need to introduce additional filters, beam splitters or complex surface microlens structures. Its fabrication process is fully compatible with existing standard focal plane array processes, which facilitates the manufacturing of highly uniform, large-area focal plane array chips and has extremely high engineering application value. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the circular / square metal microcavity detector pixel structure and its microlens focusing effect according to an embodiment of the present invention. In this diagram, a is a schematic diagram of the circular metal microcavity detector pixel structure, and b is a schematic diagram of the periodic arrangement of circular pixels to form a microlens focusing effect.

[0017] Figure 2 This is a simulation diagram of the local electric field enhancement and Poynting vector distribution of a circular metal microcavity device at the peak wavelength.

[0018] Figure 3 It describes the quantum well material structure and its intrinsic response spectrum suitable for a 10.6 μm detection wavelength;

[0019] Figure 4 These are simulated quantum efficiency, reflectivity, and metal absorptivity spectra of a circular metal microcavity device.

[0020] Figure 5 These are simulated quantum efficiency curves of circular metal microcavity devices under different doping concentrations;

[0021] Figure 6 This is a schematic diagram of the focal plane chip integrating the detector pixels and its imaging principle;

[0022] Figure 7 It is a simulated local electric field and Poynting vector distribution of a square metal cavity device;

[0023] Figure 8 These are simulated quantum efficiency, reflectivity, and metal absorptivity spectra of a square metal cavity device. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] To address the challenges of achieving high quantum efficiency, narrowband response, and process compatibility simultaneously in existing infrared detectors, this invention proposes a high-performance infrared focal plane detector based on the metalens effect. The core of this invention lies in the multi-physics collaborative design of quantum well materials, metallic microcavity structures, and periodic pixel arrays. This allows the periodically arranged detector pixels to simultaneously possess the dual functions of microcavity resonant frequency selection and microlens wavefront modulation, thereby achieving high-performance narrowband infrared detection without the need for external optical components.

[0026] The basic structure of the detector is a periodically arranged array of metal microcavity pixels, such as... Figure 1 As shown in Figure a, a single detector pixel is a mesa-shaped metal microcavity structure. The material stack of this pixel, from bottom to top, includes: a substrate, a lower electrode layer, a quantum well infrared absorption layer, and a upper electrode layer. This material stack is formed into a three-dimensional cylindrical mesa through dry etching. Subsequently, an insulating dielectric film and a continuous metal thin film (i.e., the metal cladding layer shown in the figure) are sequentially covered on the sidewalls and top surface of the mesa. The insulating dielectric film provides electrical isolation, preventing direct contact between the metal thin film and the semiconductor material, which could lead to a short circuit. The outermost continuous metal thin film, together with the lower electrode metal layer at the bottom of the mesa, constitutes a three-dimensional metal microcavity enclosing the entire active region of the quantum well. This metal thin film layer primarily serves as the reflector wall of the optical microcavity and the phase modulation structure of the metalens, and is not used as an electrical electrode.

[0027] For electrical connections, ohmic contact electrodes are fabricated on the surfaces of the upper and lower electrode layers, respectively. Windows are created in the corresponding electrode regions of the insulating dielectric film to expose the ohmic contact electrode surfaces. Subsequently, indium pillars are deposited by vapor deposition and interconnected with the readout circuit chip using a flip-chip bonding process to form a closed electrical circuit (e.g., ...). Figure 1 (The electrical connection diagram in section a is shown).

[0028] This structure itself can support specific electromagnetic resonance modes, achieving a narrowband spectral response. The key lies in, for example... Figure 1 As shown in Figure b, when such pixels are arranged in the focal plane according to a specific period, the entire array can induce a metalens effect on a macroscopic scale. This allows incident light waves larger than the size of a single pixel to be effectively modulated and focused into the microcavity region of each pixel, thereby achieving spectral selectivity while significantly enhancing the local optical field energy density. Infrared light typically enters from the lower electrode layer side, passing sequentially through the substrate and the lower electrode layer before entering the microcavity region.

[0029] The implementation of this invention relies on precise multiphysics collaborative design. First, finite element simulation software (such as COMSOL Multiphysics) is used to establish... Figure 1 The three-dimensional model of the device shown in Figure a incorporates periodic boundary conditions to simulate array effects. Through parametric scanning, pixel structure parameters (including mesa shape, size, height, and surface grating geometry), array periodic parameters, and quantum well material parameters (thickness, composition, and doping concentration) are synergistically optimized to simultaneously achieve strong resonance and high focusing efficiency at the target wavelength. An example implementation using a circular mesa targeting a 10.6 μm probe wavelength (corresponding to the characteristic absorption peak of SF6 gas) is provided (see [link to documentation]). Figure 3 The material used is GaAs / Al x Ga 1-x As a quantum well structure, the intrinsic absorption peak is designed to be around 10.6 μm, and the absorption bandwidth is about 1.1 μm. Through simulation optimization, the diameter of the circular mesa is determined to be 7.1 μm, and four circular grating slots with a radius of 1.0 μm and a depth of 180 nm are distributed on the mesa. The pixel array period is 10.6 μm. Figure 2 The finite element simulation results show that the local electric field inside the device is significantly enhanced under this design, and the Poynting vector clearly shows the process of incident light being focused and guided into the microcavity, verifying the synergistic effect of focusing and resonance. Figure 4 The simulated spectra further demonstrate that, under this co-design, the device achieves an absorption quantum efficiency of over 100% at 10.6 μm, while the reflectivity is effectively suppressed and the response bandwidth is significantly compressed.

[0030] The detector is fabricated using conventional semiconductor processes compatible with existing focal plane arrays. First, a lower electrode layer, a quantum well light-absorbing layer, and a upper electrode layer are sequentially grown on a substrate using molecular beam epitaxy (MBE). Then, photolithography and dry etching are used to etch through the entire epitaxial layer, forming a mesa array with a surface grating structure. Next, ohmic contact electrodes are fabricated in the top and bottom regions of the mesa, and an insulating dielectric film and a metal thin film are sequentially deposited over the entire mesa and sidewalls using atomic layer deposition and magnetron sputtering, forming a metal microcavity covering the mesa. Afterward, windows corresponding to the ohmic contact electrodes are created on the insulating dielectric film using photolithography and etching to expose the electrode surface, and indium pillars are deposited for connection. Finally, flip-chip bonding is used to interconnect with the readout circuit chip, and substrate thinning is performed to form a structure resembling a... Figure 6 The complete focal plane detector assembly is shown.

[0031] To verify the universality of the invention, a square mesa structure was also designed as a variation. Its optimized parameters are: mesa side length 7.1 μm, surface grating period 3.8 μm, grating size 1.3 μm, depth 340 nm, array period also 10.6 μm, and the material structure remains unchanged. Figure 7 The simulated electric field and energy flow distribution inside the square metal cavity were shown, and obvious focusing and local enhancement effects were also observed. Figure 8Simulated spectra show that the square structure also achieves a high absorption quantum efficiency of approximately 110% and a narrow-band response, demonstrating the applicability of this invention to different mesa configurations. Compared to the circular structure, its response bandwidth is slightly wider, which stems from the difference in resonant modes and can be selected according to specific application requirements. Furthermore, Figure 5 The simulation results reveal an important advantage of the present invention: due to the additional light field enhancement provided by the microlens focusing effect, the device's dependence on the doping concentration of the quantum well active region is greatly reduced. Even at low doping concentrations, the device can still maintain a high quantum efficiency of nearly 120%, which lays the foundation for achieving device performance with low dark current and high detectivity.

[0032] 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 descriptions 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 high-performance infrared focal plane detector based on the metalens effect, characterized in that, It includes a periodically arranged array of metal microcavity pixels, each of which is a mesa-shaped metal microcavity structure, comprising, from bottom to top, a substrate, a lower electrode layer, a quantum well infrared absorption layer, and an upper electrode layer; wherein... The sidewalls and top surface of the mesa-shaped metal microcavity structure are sequentially covered with an insulating dielectric film and a continuous metal thin film. The metal thin film and the lower electrode layer together constitute a three-dimensional metal microcavity that encloses the quantum well infrared light absorption layer. The three-dimensional metal microcavity is used to excite a resonant mode at the target wavelength to achieve a narrowband enhanced spectral response. The periodically arranged metal microcavity pixel array induces a metalens effect on a macroscopic scale, focusing the incident infrared light wavefront to the microcavity region of each pixel to achieve enhanced light concentration; Ohmic contact electrodes are respectively fabricated on the surfaces of the upper and lower electrode layers, and the Ohmic contact electrodes are interconnected with the readout circuit by opening windows in the insulating dielectric film.

2. The high-performance infrared focal plane detector based on the metalens effect according to claim 1, characterized in that, The metal thin film serves only as an optical reflector wall constituting the three-dimensional metal microcavity and as a structure for controlling the wavefront phase to induce the metalens effect; it is not used as an electrical electrode.

3. A high-performance infrared focal plane detector based on the metalens effect according to claim 1, characterized in that, The insulating dielectric film is used to electrically isolate the metal thin film from the quantum well infrared light absorption layer, the upper electrode layer, and the lower electrode layer.

4. A high-performance infrared focal plane detector based on metalens effect according to claim 1, characterized in that, The mesa-type metal microcavity structure is a cylindrical mesa with multiple periodically arranged circular grooves on its top surface.

5. A high-performance infrared focal plane detector based on metalens effect according to claim 1, characterized in that, The table-shaped metal microcavity structure is a square columnar table with multiple square grooves arranged periodically on its top surface.

6. A high-performance infrared focal plane detector based on metalens effect according to claim 1, characterized in that, The arrangement period of the metal microcavity pixel array is associated with the target detection wavelength and is configured to match the focusing peak of the metalens effect with the resonant wavelength of the three-dimensional metal microcavity at the target wavelength.

7. A high-performance infrared focal plane detector based on metalens effect according to claim 1, characterized in that, The infrared light absorption layer of the quantum well is a GaAs / AlGaAs quantum well material structure.

8. A high-performance infrared focal plane detector based on metalens effect according to claim 1, characterized in that, The doping concentration of the quantum well infrared light absorption layer is lower than that of conventional quantum well infrared detectors.

9. A high-performance infrared focal plane detector based on metalens effect according to claim 1, characterized in that, The ohmic contact electrode is interconnected with the readout circuit via indium pillars deposited at the openings of the insulating dielectric film using a flip-chip bonding method.

10. A high-performance infrared focal plane detector based on the metalens effect according to claim 1, characterized in that, The quantum well infrared light absorption layer has a multi-layer periodic structure. The peak wavelength of its intrinsic absorption spectrum is designed to match the resonant wavelength of the three-dimensional metal microcavity and the focusing wavelength of the metalens effect, all located at the same target detection wavelength.

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