Metal-optical Tamm enhanced terahertz detector

Abstract

A metal-optical Tamm enhanced terahertz detector provided by the present invention is characterized in that a metal-optical Tamm resonant cavity comprises an upper Bragg reflector, a lower Bragg reflector, a substrate and a metal reflector, the upper Bragg reflector is formed by permutation and combination of double-period high-resistance silicon and an air medium, a single-period structure is that an air cavity is wrapped in the high-resistance silicon, and the lower Bragg reflector is formed by permutation and combination of the high-resistance silicon and the air cavity; the air cavity covers the terahertz detector, and the periphery of the air cavity is of a high-resistance silicon supporting structure and is used for combining to form an upper Bragg reflector; the lower Bragg reflector is of an air-high-resistance silicon-air sandwich structure, the upper portion and the lower portion of high-resistance silicon wrap an air cavity, and a high-resistance silicon supporting structure is arranged on the periphery of the air cavity and used for forming and fixing the lower Bragg reflector. According to the terahertz detector, the high quality factor and low loss characteristics of the resonant cavity are utilized, the resonant filtering function of terahertz signals is achieved, meanwhile, the interaction between the terahertz signals and the sensitive element of the detector is improved, and efficient detection of the terahertz signals is achieved.

Description

Technical Field

[0001] This invention relates to the field of terahertz signal detection, specifically to a metal-optical Tamm-enhanced terahertz detector. Background Technology

[0002] Terahertz waves refer to electromagnetic waves with frequencies between 0.1 and 10 THz, and they have wide applications in astronomical observation, high-speed wireless communication, radar imaging, and life sciences. As a cutting-edge technology, terahertz science and technology has made significant progress in the development of key components, representing a commanding height in the development of next-generation information and electronic technologies. Terahertz detectors, as key components for sensing terahertz waves, are crucial for conducting terahertz science and technology research and applications, and are of great significance in solving problems in terahertz security inspection, terahertz spectral testing and analysis, terahertz laser communication, and 6G mobile communication. Currently, terahertz detectors still have considerable room for improvement in terms of equivalent noise power, response rate, detection bandwidth, dynamic range, and functional integration. In particular, the low integration level of current terahertz detectors hinders their application. Therefore, integrating terahertz detectors with other devices can improve the practical application effect of current terahertz technology.

[0003] Terahertz optical cavities have been a focal point of terahertz research, driving the development of advanced terahertz devices such as sensors, narrowband filters, lasers, and sensitive detectors. For example, Fabry-Perot cavities have reportedly achieved strong optical-material coupling between electron gas and terahertz photons. Furthermore, asymmetric-coupled FP cavities have been used to construct tunable and sensitive terahertz detectors. For high quality factor applications, optical Tamm states, as specific surface waves that can be sustained at the interface between two mirrors, exhibit strong energy confinement capabilities. One class of Tamm states can be excited at the interface of a dielectric layer adjacent to a metal thin film, resulting in a highly efficient light absorption peak. Based on this structure, a terahertz Tamm cavity using silicon / air distributed Bragg mirrors has been proposed, with a quality factor (Q) of 230 determined by Fourier transform infrared spectroscopy. Furthermore, a record-breaking Q of 10¹⁷ has been achieved using a hybrid Tamm cavity. This hybrid structure innovatively utilizes the detector substrate as the adjacent dielectric layer to the gold mirror in the Tamm state structure and is directly characterized by a niobium nitride microbolometer detector. However, the ohmic losses introduced by metal-excited optical Tamm states are significant, and combined with dielectric losses, the quality factor of these cavities remains limited. Optical Tamm cavities using two dielectric Bragg mirrors, without requiring metal thin films to excite optical Tamm states, can minimize ohmic losses and further improve the Q value while considering dielectric losses. Furthermore, due to the long wavelength of terahertz electromagnetic waves, the dielectric layer thickness constituting the resonant cavity is on the order of hundreds of micrometers, making it very difficult to construct resonant cavities using traditional thin-film growth and stacking processes. Summary of the Invention

[0004] The purpose of this invention is to provide a metal-optical Tamm-enhanced terahertz detector.

[0005] The technical solution to achieve the objective of this invention is: a metal-optical Tamm-enhanced terahertz detector, which integrates a terahertz detector and a metal-optical Tamm resonant cavity. The metal-optical Tamm resonant cavity includes an upper Bragg mirror, a lower Bragg mirror, a substrate, and a metal mirror, wherein:

[0006] The upper Bragg reflector is composed of a combination of two-period high-resistivity silicon and air dielectric. Each periodic structure consists of a high-resistivity silicon core enclosing an air cavity, the area of ​​which covers the terahertz detector. The high-resistivity silicon support structure surrounds the core, which is used to assemble the upper Bragg reflector. The lower Bragg reflector is a sandwich structure of air-high-resistivity silicon-air, with high-resistivity silicon cores enclosing air cavities on the top and bottom. The high-resistivity silicon support structure surrounds the air cavities, which is used to form and fix the lower Bragg reflector.

[0007] The substrate is used to select the frequency of the resonant signal and to fix the terahertz detector, the upper Bragg mirror, and the lower Bragg mirror. The upper Bragg mirror is located on the upper surface of the substrate, the terahertz detector is located between the upper Bragg mirror and the substrate and is set on the upper surface of the substrate, and the lower Bragg mirror is fixed on the lower surface of the substrate. The upper and lower Bragg mirrors are used to filter terahertz signals in a specific frequency band and generate optical Tamm states to resonate with terahertz signals of a specific frequency. A metal mirror is fixed on the lower surface of the lower Bragg mirror to block the leakage of terahertz signals.

[0008] Furthermore, the terahertz detector is integrated at any point on the surface of the substrate.

[0009] Furthermore, the terahertz detector is a microthermometer, a field-effect transistor, a pyroelectric diode, a Schottky diode, graphene, or other two-dimensional material semiconductor detector.

[0010] Furthermore, the terahertz detector is fabricated on the upper surface of the substrate using micro-nano fabrication technology.

[0011] Furthermore, the terahertz detector is directly attached to the upper surface of the substrate.

[0012] Furthermore, the resonant frequency of the metal-optical Tamm resonant cavity is determined according to the formula... The value is determined, where N is the number of resonant cavity modes, representing the multiple of the optical path difference of the terahertz signal in the resonant cavity relative to the wavelength; c is the speed of light in vacuum; e is the thickness of the substrate; and n is the refractive index of the substrate.

[0013] Furthermore, the upper Bragg mirror is composed of a double-period arrangement of high-resistivity silicon and air dielectric. Each periodic structure consists of a high-resistivity silicon core enclosing an air cavity. The thickness h1 of the high-resistivity silicon core is calculated using the formula... Determined, where c is the speed of light in vacuum; f0 is the center frequency of the detection band; n1 is the refractive index of the corresponding high-resistivity silicon; and the air cavity thickness h2 is determined by the formula. Determine, where f0 is the center frequency of the detection band; n2 is the refractive index of air.

[0014] Furthermore, the lower Bragg reflector has a sandwich structure of air-high-resistivity silicon-air, with high-resistivity silicon surrounding the air cavity on the top and bottom. The air cavity is surrounded by a high-resistivity silicon support structure, which is used to form and fix the lower Bragg reflector. The thickness h1 of the high-resistivity silicon dielectric is calculated according to the formula... Determined, where c is the speed of light in vacuum; f0 is the center frequency of the detection band; n1 is the refractive index of the corresponding high-resistivity silicon; and the air cavity thickness h2 is determined by the formula. Determine, where f0 is the center frequency of the detection band; n2 is the refractive index of air.

[0015] Furthermore, the material of the metal reflector is gold.

[0016] A method for detecting terahertz signals involves a terahertz signal being directly incident from space onto the upper surface of an upper Bragg reflector and entering a resonant cavity. After passing through a substrate, the signal is reflected by a lower Bragg reflector and a metal reflector, generating resonance within the substrate. The resonance effect is used to localize the electric field on the upper surface of the substrate, i.e., the plane where the terahertz detector is located, thereby enhancing the coupling strength between the terahertz signal and the terahertz detector.

[0017] Compared with the prior art, the present invention has the following significant advantages: 1) It has an extremely high quality factor. Compared with traditional optical cavity integrated detectors, such as FP cavities, the quality factor of the metal-optical Tamm-enhanced terahertz detector will be improved by one to two orders of magnitude; 2) The manufacturing process is simple. The manufacturing of the terahertz detector is compatible with mature micro-nano manufacturing processes. The optical cavity can be fabricated using mature MEMS processes. Then, the metal-optical Tamm-enhanced terahertz detector can be assembled by simple bonding. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a metal-optical Tamm-enhanced terahertz detector.

[0019] Figure 2 This is a schematic diagram of the dimensions of a metal-optical Tamm-enhanced terahertz detector.

[0020] Figure 3 The image shows the reflection spectrum of the metal-optical Tamm-enhanced terahertz detector.

[0021] Figure 4 The electric field distribution diagram of the vertical cross section of the resonant cavity at the terahertz detector in resonance state.

[0022] Figure 5 This is a diagram showing the quality factor distribution of the resonant cavity in the resonant state.

[0023] In the figure, 1 is the terahertz detector, 2 is the upper Bragg mirror, 3 is the substrate, 4 is the lower Bragg mirror, 5 is the metal mirror, and 6 is the electric field intensity at the terahertz detector at the vertical section of the resonant cavity. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0025] like Figure 1-2As shown, a metal-optical Tamm-enhanced terahertz detector is integrated with a terahertz detector 1 and a metal-optical Tamm resonant cavity. The metal-optical Tamm resonant cavity includes an upper Bragg mirror 2, a substrate 3, a lower Bragg mirror 4, and a metal mirror 5. The terahertz detector 1 is located on the upper surface of the substrate 3, wherein:

[0026] Substrate 3 is used to select the frequency of the resonant signal and to fix the terahertz detector, upper Bragg reflector 2, and lower Bragg reflector 4. The upper Bragg reflector 2 is located on the upper surface of the substrate, the terahertz detector is located between the upper Bragg reflector 2 and the substrate 3 and is set on the upper surface of the substrate 3, and the lower Bragg reflector 4 is fixed on the lower surface of the substrate. The upper Bragg reflector 2 and the lower Bragg reflector 4 are used to filter the terahertz signal in a specific frequency band and generate an optical Tamm state to resonate with the terahertz signal at a specific frequency. The metal reflector 5 is fixed on the lower surface of the lower Bragg reflector 4 to block the leakage of the terahertz signal.

[0027] Furthermore, the terahertz detector 1 can be a microthermometer, a field-effect transistor, a pyroelectric diode, a Schottky diode, graphene, or other two-dimensional material semiconductor detector. The terahertz detector 1 can be integrated at any point on the upper surface of the substrate 3, fabricated on the upper surface of the substrate 3 using micro-nano fabrication technology, or the terahertz detector 1 can be directly attached to the upper surface of the substrate 3.

[0028] Furthermore, high-resistivity silicon is one of the most important materials for integrated circuits. It also exhibits low loss in the terahertz frequency band, with an absorption rate of only 0.05 cm⁻¹ at 0.4 THz. -1 In this implementation, high-resistivity silicon is selected as the substrate material. Deep silicon etching is a micro-nano fabrication process that uses deep silicon etching to obtain functional structures with feature sizes of tens of micrometers or even hundreds of micrometers. The upper and lower Bragg mirrors can be fabricated using deep silicon etching.

[0029] The input signal is coupled from free space into the resonant cavity via the upper Bragg mirror 2, and reflected by the lower Bragg mirror 4 and the metal mirror 5, resonating within the cavity. In the resonant state, the terahertz signal maintains its phase during reflection within the cavity, thus enhancing the intensity of the terahertz signal on the surface of substrate 3. The resonant frequency satisfies the formula... Where N is the number of resonant cavity modes, representing the multiple of the optical path difference of the terahertz signal relative to the wavelength in the resonant cavity; c is the velocity of light in vacuum; e is the thickness of the substrate; and n is the refractive index of the substrate. Combining the above two formulas, it can be seen that the resonant frequency of the resonant cavity is related to the substrate thickness e. In some embodiments, e is 510 μm.

[0030] Furthermore, the upper Bragg reflector 2 and the lower Bragg reflector 4 are respectively attached to the upper and lower surfaces of the substrate 3. The thicknesses of the high and low refractive index media in the Bragg reflectors are related to the refractive index of the medium material and the detection frequency. The upper Bragg reflector 2 has a periodic distribution of high and low refractive index media from top to bottom, while the lower Bragg reflector 4 has a periodic distribution of low and high refractive index media from top to bottom. The thickness h1 of the high refractive index medium is determined by the formula... Determined, where c is the speed of light in vacuum; f0 is the center frequency of the detection band; n1 is the refractive index of the corresponding high-refractive-index medium. The thickness h2 of the low-refractive-index medium is determined by the formula. Determine that c is the speed of light in vacuum; f0 is the center frequency of the detection band; and n2 is the refractive index of the corresponding low-refractive-index medium.

[0031] In this invention, the high-refractive-index medium is high-resistivity silicon, and the low-refractive-index medium is air. To ensure the efficiency and low loss of terahertz signal coupling into the resonant cavity, the number of periods of the Bragg reflector cannot be too high or too low; the upper Bragg reflector has 2 periods, and the lower Bragg reflector has 1.5 periods. Ultimately, the upper Bragg reflector 2 is composed of a combination of two periods of high-resistivity silicon and air. Each period consists of a high-resistivity silicon layer enclosing an air cavity, the air cavity area covering the terahertz detector 1, and surrounded by a high-resistivity silicon support structure, used to assemble and form the upper Bragg reflector 2. The lower Bragg reflector 4 is an air-high-resistivity silicon-air sandwich structure, with high-resistivity silicon enclosing the air cavity on the top and bottom, and the air cavity surrounded by a high-resistivity silicon support structure, used to form and fix the lower Bragg reflector 4.

[0032] In some embodiments, the specific meaning of the dimensional parameters is as follows: Figure 2 As shown, the target detection frequency is 0.65 THz, the high refractive index medium is high-resistivity silicon with a thickness of 33 μm, and the low refractive index medium is air with a thickness of 115 μm.

[0033] Furthermore, the metal reflector 5 is fixed to the lower surface of the lower Bragg reflector 4, and the metal reflector is made of gold.

[0034] Example

[0035] To verify the effectiveness of the present invention, a metal-optical Tamm-enhanced terahertz detector was fabricated and packaged according to the following process, and experimental tests and simulations were performed. The specific steps are as follows:

[0036] 1. Fabrication of terahertz detectors on silicon wafers;

[0037] 2. Silicon wafer thinning process, reducing the thickness of silicon wafers to 148μm;

[0038] 3. Using photolithography and deep silicon etching processes, a 115μm deep groove is etched in the center of the silicon wafer to form a single-cycle upper Bragg mirror, which is then stacked and bonded to form a two-cycle upper Bragg mirror.

[0039] 4. Stack and bond two single-cycle upper Bragg reflectors to form a two-cycle upper Bragg reflector;

[0040] 5. Silicon wafer thinning process, reducing the thickness of silicon wafers to 266μm;

[0041] 6. Using photolithography-deep silicon etching process, a 115μm deep groove is etched in the center of the silicon wafer;

[0042] 7. Using a back-overlay deep silicon etching process, a 115μm deep groove is also etched on the back of the groove to form a sandwich structure lower Bragg reflector;

[0043] 8. Fix the upper and lower Bragg mirrors to the upper and lower surfaces of the substrate, respectively, and fix the metal mirror to the lower surface of the lower Bragg mirror to form a metal-optical Tamm-enhanced terahertz detector;

[0044] 9. Fix the metal reflector 5 to the lower surface of the lower Bragg reflector 4 to block the leaked terahertz signal.

[0045] To verify the advantages of the metal-optical Tamm-enhanced terahertz detector, electromagnetic simulation software was used to calculate the reflection spectrum of the metal-optical Tamm-enhanced terahertz detector with the above parameters. The simulation frequency range was 0.4THz–1.3THz, and the lossy refractive index of high-resistivity silicon in this frequency band was considered to be 3.47+0.0008i. Figure 3 The reflectivity of the metal-optical Tamm resonator in this frequency band is given. Within the bandgap of the Bragg mirror (0.4–0.9 THz), the resonator generated seven resonant peaks, indicating the successful excitation of seven optical Tamm states. The reflectivity of the Tamm resonant peaks in the 0.5–0.9 THz range is less than 21%, with the lowest reflectivity at 0.5244 THz (0.5%) and the highest at 0.6056 THz (21%), demonstrating that terahertz signals can be efficiently coupled into the resonator to excite Tamm states.

[0046] To verify the enhancement effect of the resonant cavity on the integrated terahertz detector's response, the electric field distribution of the resonant cavity in the resonant state was further simulated. For example... Figure 4 As shown, when the frequency is 0.6056 THz, the resonant cavity is in a resonant state, and the electric field distribution |E| on the vertical cross section is as follows. 2 / |E0| 2This indicates that the electric field is well confined within the substrate. Simultaneously, the electric field exhibits a standing wave distribution within the substrate, with a maximum value of 49, appearing on the upper surface of the substrate, demonstrating that the electric field at the integrated terahertz detector is well focused and enhanced.

[0047] Figure 5 Showing Figure 4 The quality factor (Q value) of all optical Tamm resonant peaks is greater than 1000, except for the Tamm state at 0.5 THz, which has a Q value of only 553. The resonant peak at 0.687 THz has the largest Q value of 1618. Simulation experiments show that integrating the terahertz detector with the metal-Tamm resonator can significantly improve the responsivity and Q value of the terahertz detector.

[0048] The embodiments of the present invention are not limited to the described examples. Any changes, simplifications, substitutions, or combinations made without departing from the spirit and principle of the present invention should be included within the scope of protection of the present invention.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A metal-optical Tamm-enhanced terahertz detector, characterized in that, The device is integrated with a terahertz detector (1) and a metal-optical Tamm resonator, which includes an upper Bragg mirror (2), a lower Bragg mirror (4), a substrate (3), and a metal mirror (5), wherein: The upper Bragg reflector (2) is composed of a combination of high-resistivity silicon and air dielectric in a double-period arrangement. The single-period structure is an air cavity wrapped in high-resistivity silicon, the area of ​​which covers the terahertz detector (1), and the surrounding area is a high-resistivity silicon support structure, which is used to combine and form the upper Bragg reflector (2). The lower Bragg reflector (4) is a sandwich structure of air-high-resistivity silicon-air, with high-resistivity silicon wrapping the air cavity on the top and bottom, and the surrounding area of ​​the air cavity is a high-resistivity silicon support structure, which is used to form and fix the lower Bragg reflector (4). The substrate (3) is used to select the frequency of the resonant signal and to fix the terahertz detector, the upper Bragg reflector (2) and the lower Bragg reflector (4). The upper Bragg reflector (2) is located on the upper surface of the substrate. The terahertz detector is located between the upper Bragg reflector (2) and the substrate (3) and is set on the upper surface of the substrate (3). The lower Bragg reflector (4) is fixed on the lower surface of the substrate. The upper Bragg reflector (2) and the lower Bragg reflector (4) are used to filter the terahertz signal in a specific frequency band and generate an optical Tamm state to resonate the terahertz signal at a specific frequency. The metal reflector (5) is fixed on the lower surface of the lower Bragg reflector (4) to block the leaked terahertz signal.

2. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The terahertz detector (1) is integrated at any point on the upper surface of the substrate (3).

3. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The terahertz detector (1) is a microthermometer, field-effect transistor, pyroelectric diode, Schottky diode, graphene or other two-dimensional material semiconductor detector.

4. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The terahertz detector (1) is fabricated on the upper surface of the substrate (3) using micro-nano fabrication technology.

5. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The terahertz detector (1) is directly attached to the upper surface of the substrate (3).

6. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The resonant frequency of the metal-optical Tamm resonant cavity is based on the formula... The value is determined, where N is the number of resonant cavity modes, representing the multiple of the optical path difference of the terahertz signal in the resonant cavity relative to the wavelength; c is the speed of light in vacuum; e is the thickness of the substrate; and n is the refractive index of the substrate.

7. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The upper Bragg reflector (2) is composed of a double-period arrangement of high-resistivity silicon and air dielectric. The single-period structure is an air cavity wrapped in high-resistivity silicon. The thickness of the high-resistivity silicon, h1, is calculated according to the formula. Determined, where c is the speed of light in vacuum; f0 is the center frequency of the detection band; n1 is the refractive index of the corresponding high-resistivity silicon; and the air cavity thickness h2 is determined by the formula. Determine, where f0 is the center frequency of the detection band; n2 is the refractive index of air.

8. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The lower Bragg reflector (2) has a sandwich structure of air-high-resistivity silicon-air, with high-resistivity silicon surrounding the air cavity on the top and bottom. The air cavity is surrounded by a high-resistivity silicon support structure, which is used to form and fix the lower Bragg reflector. The thickness h1 of the high-resistivity silicon dielectric is calculated according to the formula. Determined, where c is the speed of light in vacuum; f0 is the center frequency of the detection band; n1 is the refractive index of the corresponding high-resistivity silicon; and the air cavity thickness h2 is determined by the formula. Determine, where f0 is the center frequency of the detection band; n2 is the refractive index of air.

9. The metal-optical Tamm-enhanced terahertz detector according to claim 1, characterized in that, The metal reflector (5) is made of gold.

10. A method for detecting terahertz signals, characterized in that, The terahertz signal is directly incident from space onto the upper surface of the upper Bragg reflector (2) and enters the resonant cavity. After passing through the substrate (3), it is reflected by the lower Bragg reflector (4) and the metal reflector (5), generating resonance in the substrate. The electric field is localized on the upper surface of the substrate (3), i.e. the plane where the terahertz detector (1) is located, by utilizing the resonance effect, thereby enhancing the coupling strength between the terahertz signal and the terahertz detector (1).

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