A terahertz detector based on nano-gap field-enhanced quantum tunneling effect

Abstract

This invention discloses a terahertz detector based on the field-enhanced quantum tunneling effect of a nano-gap, applicable to the fields of terahertz detection and micro / nanoelectronic devices. It addresses the problem of insufficient detection sensitivity caused by the extremely low coupling efficiency of traditional tunneling devices with free-space terahertz waves due to their extremely small size. The detector of this invention includes a dielectric substrate, a metal receiving antenna, a nano-gap enhancement region, and a signal monitoring circuit; its structure is a planar horizontal structure. This invention utilizes the metal receiving antenna to collect incident terahertz waves, thereby generating a high-intensity local electric field in the nano-gap enhancement region. This local electric field drives electrons in the metal to undergo nonlinear quantum tunneling or field emission within the nano-gap, achieving rectification and detection of the terahertz signal. Compared to traditional detectors, this invention requires no external light source pumping and possesses advantages such as room-temperature operation, large response bandwidth, high sensitivity, and ease of integration.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photodetectors and millimeter-wave / terahertz devices, and specifically relates to a terahertz detector. Background Technology

[0002] Terahertz (THz) and millimeter-wave (MMW) waves generally refer to electromagnetic waves with frequencies ranging from 0.1 THz to 10 THz. Due to the unique characteristics of terahertz waves compared to other electromagnetic wave bands, terahertz and millimeter-wave technologies have numerous applications in real life, including wireless communication, security detection, and materials analysis. Their research and applications encompass multiple disciplines such as biology, medicine, physics, astronomy, materials science, and electronic information. Research on terahertz and millimeter-wave technologies mainly includes three aspects: terahertz sources, functional devices, and detectors. Among these, terahertz and millimeter-wave detectors are of paramount importance in related research fields.

[0003] Current terahertz detectors are mainly divided into thermal detectors (such as thermionic radiometers) and photon / electron detectors. While thermal detectors have a wide bandwidth response, their response speed is slow and they typically require cryogenic cooling. Traditional electronic detectors (such as Schottky diodes) are limited by carrier transit time and parasitic parameters (RC constant), resulting in a sharp drop in sensitivity above 1 THz. Devices based on the quantum tunneling effect, due to the femtosecond timescale of tunneling, can theoretically support extremely high operating frequencies and have therefore attracted considerable attention. However, traditional tunneling devices (such as MIM diodes) suffer from extremely small size and very low coupling efficiency with free-space terahertz waves, leading to insufficient detection sensitivity.

[0004] In existing technologies, some studies have utilized metallic nanostructures to achieve localized enhancement of the optical field. For example, using nanoslit structures, even when the slit width is smaller than the metal's skin depth, photoinduced current can still charge the slit "capacitor," achieving a hundreds-fold increase in the electric field. If this field enhancement effect could be combined with an ultrafast tunneling mechanism, it holds promise for realizing a room-temperature, ultrafast, and highly sensitive terahertz detector. However, currently, there is a lack of practical devices that efficiently integrate sub-skin depth field enhancement with tunneling rectification mechanisms. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a terahertz detector based on the enhanced quantum tunneling effect of a nano-gap field. It utilizes a metal receiving antenna to collect incident high-frequency electromagnetic waves, and combines this with capacitor charging at sub-skin depth to compress the energy of the terahertz waves into the nano-gap, thereby generating a high-intensity local electric field at the nano-gap. This local electric field directly acts on the tunneling barrier within the gap, driving electrons to overcome the barrier and undergo Fowler-Nordheim quantum tunneling or field emission, converting the incident high-frequency terahertz signal into an electrical signal, achieving high-sensitivity detection at room temperature.

[0006] The technical solution adopted in this invention is as follows: a terahertz detector based on the enhanced quantum tunneling effect of a nano-gap field, comprising: a dielectric substrate, a metal receiving antenna, a nano-gap enhancement region, and a signal monitoring circuit; the metal antenna is disposed above the dielectric substrate and includes a first metal arm and a second metal arm; the nano-gap enhancement region is specifically a nano-slit structure formed between the first end face of the first metal arm and the first end face of the second metal arm, the width of the nano-slit structure being smaller than the skin depth of the metal receiving antenna material at the operating frequency; the second ends of the first metal arm and the second ends of the second metal arm are both connected to the signal monitoring circuit.

[0007] The beneficial effects of this invention are as follows: The basic working principle and process of the terahertz detector based on the enhanced quantum tunneling effect of the nano-gap field proposed in this invention are as follows: Energy focusing and signal conversion at the micro-nano scale are achieved using a macroscopic antenna structure. When a terahertz wave in free space is incident on a metal receiving antenna (such as a bowtie antenna) on a dielectric substrate, the antenna, acting as an energy harvester, generates a high-frequency induced current on the surface and concentrates the electromagnetic energy into the nano-gap region at the antenna feed center. Because the gap width is designed to be significantly smaller than the skin depth of the metal at the operating frequency, the induced current cannot penetrate and is forced to accumulate extremely at the metal tips on both sides of the gap. This subwavelength-scale charge accumulation forms a nanocapacitor charging effect. By combining the resonant characteristics of the antenna with micro / nano structure optimization, a high-intensity local electric field is generated in a nanometer gap with a width smaller than the skin depth of the metal. This local electric field directly acts on the tunneling barrier within the gap, driving electrons to overcome the barrier and undergo Fowler-Nordheim quantum tunneling or field emission. Since the tunneling current increases exponentially nonlinearly with the electric field strength, and with the antenna's geometry and impedance / gain design, the incident high-frequency terahertz signal is converted into an electrical signal, which is then detected with high sensitivity at room temperature via a signal monitoring circuit. This invention has the following advantages:

[0008] 1. This invention utilizes antenna coupling and subskin depth field enhancement effect to amplify weak incident signals thousands of times at the nanoscale, directly overcoming the tunneling barrier and improving detection sensitivity.

[0009] 2. This invention is based on the electron tunneling mechanism, with carrier transit time on the femtosecond level, which is not limited by lattice scattering, and the detection bandwidth can theoretically cover the entire terahertz frequency band.

[0010] 3. Compared with optical mixers or thermionic radiometers, this invention does not require external laser pumping or cryogenic cooling, has a simple structure, and extremely low power consumption.

[0011] 4. The present invention adopts a planar structure, which can be fabricated on a large-area substrate using standard micro-nano processes such as electron beam lithography, and is easy to integrate with on-chip circuits.

[0012] 5. Thanks to the ultrafast response characteristics of the antenna coupling structure of this application and the fact that the operating mode can be zero bias (without external voltage applied) or external bias (with bias voltage applied), this invention can not only perform incoherent detection (direct detection, envelope extraction) but also coherent detection (heterodyne mixing by introducing local oscillator signal to extract phase information); the detector proposed in this invention can be used for both direct terahertz detection and coherent terahertz mixing detection.

[0013] 6. This invention can utilize the asymmetry of the slit structure or antenna arm material to operate under zero bias voltage, achieving zero static power consumption detection; it can also apply a weak bias voltage to improve the responsivity. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a nano-air gap terahertz tunneling detector structure based on a bowtie antenna in Embodiment 1 of the present invention.

[0015] Among them, (a) is a symmetrical slit sidewall cross-section of the nano-air gap terahertz tunneling detector based on the bowtie antenna; (b) is a horizontal geometrically asymmetric slit sidewall cross-section of the nano-air gap terahertz tunneling detector based on the bowtie antenna; (c) is a vertically asymmetric slit sidewall cross-section of the nano-air gap terahertz tunneling detector based on the bowtie antenna; (d) is a left-right geometrically asymmetric and vertically asymmetric slit sidewall cross-section of the nano-air gap terahertz tunneling detector based on the bowtie antenna; (e) is a top view of the nano-air gap terahertz tunneling detector based on the bowtie antenna; and (f) is a three-dimensional structural schematic diagram of the nano-air gap terahertz tunneling detector based on the bowtie antenna.

[0016] Figure 2 This is a three-dimensional structural schematic diagram of a nano-dielectric gap terahertz tunneling detector based on a bowtie antenna in Embodiment 2 of the present invention.

[0017] Figure 3 This is a three-dimensional structural schematic diagram of a nano-gap terahertz tunneling detector based on a logarithmic spiral antenna in Embodiment 3 of the present invention.

[0018] Explanation of reference numerals in the attached figures: 11-Dielectric substrate, 12-First antenna arm of the metal receiving antenna, 13-Nano air slit structure, 14-Second antenna arm of the metal receiving antenna, 15-Lead of the external signal monitoring circuit, 16-Incident terahertz and millimeter-wave signals, 21-Dielectric substrate, 22-First antenna arm of the metal receiving antenna, 23-Nano dielectric slit structure, 24-Second antenna arm of the metal receiving antenna, 25-Lead of the external signal monitoring circuit, 26-Incident terahertz and millimeter-wave signals, 31-Dielectric substrate, 32-First antenna arm of the metal receiving antenna, 33-Nano air slit structure, 34-Second antenna arm of the metal receiving antenna, 35-Lead of the external signal monitoring circuit, 36-Incident terahertz and millimeter-wave signals. Detailed Implementation

[0019] To facilitate understanding of the technical content of this invention by those skilled in the art, the following description, in conjunction with the accompanying drawings, further illustrates the invention.

[0020] This invention proposes a nano-gap terahertz tunneling detector based on the subskin depth field enhancement effect, aiming to provide a novel terahertz detection scheme that requires no external light source, operates at room temperature, and possesses a large bandwidth and high sensitivity. The terahertz detector based on the nano-gap field enhancement quantum tunneling effect provided by this invention includes a dielectric substrate, a metal receiving antenna, a nano-gap enhancement region, and a signal monitoring circuit; the detector mainly adopts a planar horizontal structure. A metal receiving antenna is disposed above the dielectric substrate, and the antenna is composed of a first metal arm and a second metal arm arranged opposite each other; the nano-gap enhancement region is formed between the ends of the first and second metal arms; the spacing of the nano-gap enhancement region is smaller than the skin depth of the metal receiving antenna material at the operating frequency; the metal receiving antenna is connected to the signal monitoring circuit for outputting an electrical signal.

[0021] The following section provides a detailed description of nano-gap terahertz tunneling detectors based on the subskin depth field enhancement effect under different conditions.

[0022] Example 1

[0023] A nano-air gap terahertz tunneling detector based on a bowtie antenna, such as Figure 1 As shown, it includes: a dielectric substrate 11, a first antenna arm 12 of a metal receiving antenna, a nano-air slit structure 13, a second antenna arm 14 of a metal receiving antenna, and a signal monitoring circuit; the first antenna arm 12 and the second antenna arm 14 of the metal receiving antenna are connected to the signal monitoring circuit through a lead 15 of the external signal monitoring circuit.

[0024] In this embodiment, the dielectric substrate 11 is quartz; above the substrate are two bow-shaped antenna arms formed of metal of a certain thickness; the ends of the two antenna arms face each other to form a nano-slit structure with a certain horizontal distance, the slit is filled with air, the width of the slit is determined by the horizontal distance between the ends of the two antenna arms, and the height of the slit is determined by the thickness of the two antenna arms. The sidewalls at the ends of the two antenna arms constituting the nano-slit structure are designed to be symmetrical, horizontally geometrically asymmetrical, vertically asymmetrical, or both geometrically asymmetrical and vertically asymmetrical, respectively, as shown in the figures below. Figure 1 As shown in (a), (b), (c), and (d), when a symmetrical structure is used, the two antenna arms can be made of different metals; when an asymmetrical structure is used, the antenna arms can be made of the same or different metals. A signal monitoring circuit is connected to the other end of each antenna arm via leads. The top view and three-dimensional structural schematic of the detector are shown in Figure 1. Figure 1 As shown in (e) and (f).

[0025] In this embodiment, the sidewalls at the ends of the two antenna arms constituting the nano-slit structure are designed to be symmetrical, which should be understood as meaning that the sidewalls at the ends of the two antenna arms are completely identical. Figure 1 (a) Only the most common cases are shown. If both antenna sidewalls become conical or other shapes to form symmetry, they should also be included. Horizontal geometric asymmetry should be understood as the two antenna arm end sidewalls having the same height but different shapes in the horizontal direction. Figure 1 (b) Only the most common case is shown. Other cases where the end sidewalls of the two antenna arms have the same height but are asymmetrical in the horizontal direction should also be included. Vertical thickness asymmetry should be understood as the two antenna arms having the same horizontal geometry but different vertical heights of the end sidewalls. Figure 1 (c) Only the most common case is shown. Cases where the horizontal geometry of the two antenna arm ends is the same but the vertical height is asymmetrical should also be included. The corresponding left-right geometric asymmetry and vertical height asymmetry should be understood as the two antenna arm end sidewalls not only having different shapes in the horizontal direction but also different heights in the vertical direction. Figure 1 (d) only shows the most common cases; other cases with inconsistent shapes in the horizontal direction and asymmetry in height in the vertical direction should also be included.

[0026] Theoretically, if the materials and shapes of the left and right sides constituting the nanoslit structure are completely identical, their tunneling barriers will also be identical. In this case, the tunneling current from left to right is equal to the tunneling current from right to left, and the change in current cannot be detected in the external circuit (net current is 0). Therefore, this invention needs to design so that the barriers at the left and right ends are not completely identical. For cases where the end wall structures of the two antenna arms constituting the nanoslit structure are asymmetrical, the geometry will cause the left and right barriers to be inconsistent, resulting in electrical signals. Therefore, the same or different materials can be used. However, for cases where the geometry is completely identical, the barriers at the left and right ends must be made inconsistent by controlling the different materials.

[0027] The operation of this butterfly-tie antenna-based nano-air gap terahertz tunneling detector is as follows: When terahertz and millimeter-wave signals 16 incident in free space irradiate the device surface, the first antenna arm 12 and the second antenna arm 14, located on the dielectric substrate 11, act as broadband resonant antennas, collecting electromagnetic wave energy and generating a high-frequency induced current on the metal surface. The induced current converges towards the nano-air gap structure 13 at the center of the antenna. Since the width of the nano-air gap structure 13 is significantly smaller than the skin depth of the metal in the terahertz band, the induced current cannot penetrate the gap, resulting in extreme charge accumulation at the metal-air interface at the end of the antenna arm. This subwavelength-scale charge accumulation forms a nanocapacitor charging effect, generating a high-intensity local electric field at the nano-air gap. Under the action of this local electric field, the electron barrier at the end of the metal antenna arm is lowered. Electrons pass through the air gap via Fowler-Nordheim field emission or direct quantum tunneling mechanisms. Since the tunneling current has an exponential nonlinear relationship with the electric field strength, the incident terahertz signal can be detected by measuring the magnitude of the current through a signal monitoring circuit connected to both ends of the antenna.

[0028] Example 2

[0029] A nano-dielectric gap terahertz tunneling detector based on a bowtie antenna, such as Figure 2 As shown, it includes: a dielectric substrate 21, a first antenna arm 22 of a metal receiving antenna, a nano-dielectric slit structure 23, a second antenna arm 24 of a metal receiving antenna, and a signal monitoring circuit; the first antenna arm 22 and the second antenna arm 24 of the metal receiving antenna are connected to the signal monitoring circuit through a lead 25 of the external signal monitoring circuit.

[0030] In this embodiment, the dielectric substrate 21 is sapphire; above the substrate are two bow-shaped antenna arms formed by 100 nm gold layers; the ends of the two antenna arms are opposite each other to form a slit structure with a horizontal distance of 5 nm, and the interior of the slit is an insulating dielectric SiO2; at the other end of the two antenna arms, a signal monitoring circuit is connected to an external lead wire.

[0031] The materials of the nano-insulating dielectric layer include, but are not limited to, two-dimensional insulating materials such as alumina, silicon dioxide, and silicon nitride.

[0032] The operation of this butterfly-tie antenna-based nano-dielectric gap terahertz tunneling detector is as follows: When the terahertz and millimeter-wave signals 26 incident in free space irradiate the device surface, the first antenna arm 22 and the second antenna arm 24 located on the dielectric substrate 21 act as broadband resonant antennas, collecting electromagnetic wave energy and generating high-frequency induced current on the metal surface. The induced current converges towards the nano-dielectric gap structure 23 at the center of the antenna. Since the "gold-SiO2-gold" structure constitutes a classic metal-insulator-metal (MIM) structure, and its width (5 nm) and height (100 nm) are significantly smaller than the skin depth of the metal in the terahertz band, the electromagnetic energy is tightly bound in the dielectric layer. The presence of the insulating dielectric SiO2 further enhances the nanocapacitor charging effect. At the metal-SiO2 interface at the end of the antenna arm, the induced charge accumulates extremely, establishing a high-intensity local electric field inside the insulating dielectric that is far stronger than the incident field. Driven by the enhanced local electric field, the potential barrier of the SiO2 insulating layer tilts or narrows dramatically (Fowler-Nordheim tunneling effect), allowing electrons to gain sufficient energy to pass through the 5 nm SiO2 dielectric layer (or tunnel through defect states in the dielectric). Since the tunneling current has an exponential nonlinear relationship with the electric field strength, the incident terahertz signal can be detected by measuring the magnitude of this current through a signal monitoring circuit connected to both ends of the antenna.

[0033] Example 3

[0034] A nano-air gap terahertz tunneling detector based on a logarithmic spiral antenna, such as Figure 3 As shown, it includes: a dielectric substrate 31, a first antenna arm 32 of a metal receiving antenna, a nano-air slit structure 33, a second antenna arm 34 of a metal receiving antenna, and a signal monitoring circuit; the first antenna arm 32 and the second antenna arm 34 of the metal receiving antenna are connected to the signal monitoring circuit through a lead 35 of the external signal monitoring circuit.

[0035] In this embodiment, the dielectric substrate 31 is a porous alumina ceramic; above the substrate are two logarithmic spiral antenna arms formed by a 100 nm gold layer; the ends of the two antenna arms extend and face each other to form a slit structure with a horizontal distance of 50 nm, and the slit is filled with air; at the other end of the two antenna arms, a signal monitoring circuit is connected to an external lead wire.

[0036] The operation of this bowtie-antenna-based nano-air gap terahertz tunneling detector is as follows: When terahertz and millimeter-wave signals 36 incident in free space irradiate the device surface, the first antenna arm 32 and the second antenna arm 34, located on the dielectric substrate 31, act as broadband resonant antennas, capturing electromagnetic wave energy and generating a high-frequency induced current on the metal surface. The induced current converges towards the nano-air gap structure 33 at the center of the antenna. Since the width of the nano-air gap structure 33 is significantly smaller than the skin depth of the gold layer in the terahertz band, the induced current cannot penetrate the gap, resulting in extreme charge accumulation at the metal-air interface at the end of the antenna arm. This subwavelength-scale charge accumulation forms a nanocapacitor charging effect, generating a high-intensity local electric field at the nano-air gap. Under the action of this local electric field, the electron barrier at the end of the metal antenna arm is lowered. Electrons pass through the air gap via Fowler-Nordheim field emission or direct quantum tunneling mechanisms. Since the tunneling current exhibits an exponentially nonlinear relationship with the electric field strength, the incident terahertz signal can be detected by measuring the magnitude of this current through a signal monitoring circuit connected to both ends of the antenna. Furthermore, due to the self-similar structural characteristics of the logarithmic spiral antenna, this detector can maintain stable impedance matching and a high field enhancement factor over an extremely wide spectral range, achieving broadband detection.

[0037] In this invention, the dielectric substrate is not limited to one or more of semiconductors, metals, metalloids, insulators, glass substrates, ceramic materials, two-dimensional materials, and diamond; to reduce substrate loss, the substrate below the area where the metal receiving antenna is located can be removed to form a suspended thin film structure.

[0038] The metal receiving antenna structure in this invention includes, but is not limited to, a bow-shaped structure, a logarithmic spiral structure, and a dipole structure. The specific geometric structure design of the antenna in this invention is to meet the electromagnetic resonance conditions in the terahertz frequency band and achieve efficient energy coupling and focusing. Other antenna structures that meet the requirements are still within the protection scope of this invention.

[0039] In this invention, the horizontal spacing of the nano-gap enhancement region is less than 200 nm, preferably 1 nm to 100 nm; the nano-gap can also be a vacuum.

[0040] In this invention, the detector can operate under either an applied bias voltage or a zero bias voltage. When operating under an applied bias voltage, it is in the range where the field emission current increases exponentially, and the localized enhanced electric field generated by the terahertz signal under test in the nanometer gap can cause a huge change in the field emission current. When operating under a zero bias voltage, no external bias voltage is required, which simplifies the detection circuit.

[0041] The detector in this invention can be used for both direct terahertz detection and coherent terahertz mixing detection. When used for direct detection, only the terahertz signal to be measured needs to be incident, and a current signal is output. When used for coherent mixing detection, a local oscillator signal needs to be incident simultaneously with the terahertz signal to be measured, and an intermediate frequency or baseband signal is output.

[0042] Those skilled in the art will recognize that the embodiments described herein are for the purpose of helping to understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of the claims of the invention.

Claims

1. A terahertz detector based on the enhanced quantum tunneling effect using a nano-gap field, characterized in that, include: Dielectric substrate, metallic receiving antenna, nano-gap enhancement region, signal monitoring circuit; The metal antenna is disposed above the dielectric substrate and includes a first metal arm and a second metal arm; the nano gap enhancement region is specifically a nano slit structure formed between the first end face of the first metal arm and the first end face of the second metal arm, the width of the nano slit structure being smaller than the skin depth of the metal receiving antenna material at the operating frequency; the second end of the first metal arm and the second end of the second metal arm are both connected to the signal monitoring circuit.

2. The terahertz detector based on the enhanced quantum tunneling effect using a nano-gap field according to claim 1, characterized in that, The width of the nanoslit structure is less than 200 nm.

3. A terahertz detector based on nano-gap field-enhanced quantum tunneling effect according to claim 2, characterized in that, The width of the nanoslit structure is preferably between 1 nm and 100 nm.

4. A terahertz detector based on nano-gap field-enhanced quantum tunneling effect according to claim 3, characterized in that, The interior of the nanoslit structure is filled with air, vacuum, or a nano insulating dielectric layer.

5. A terahertz detector based on nano-gap field-enhanced quantum tunneling effect according to claim 4, characterized in that, The first end face of the first metal arm and the first end face of the second metal arm constituting the nano-slit structure are designed to be symmetrical, horizontally asymmetrical, vertically asymmetrical, or both geometrically asymmetrical and vertically asymmetrical.

6. A terahertz detector based on nano-gap field-enhanced quantum tunneling effect according to claim 5, characterized in that, When the nano-slit structure is filled with a nano-insulating dielectric layer, the first metal arm, the nano-slit structure, and the second metal arm together constitute a metal-insulator-metal tunneling diode structure.

7. A terahertz detector based on nano-gap field-enhanced quantum tunneling effect according to claim 6, characterized in that, The materials of the nano-insulating dielectric layer include, but are not limited to, aluminum oxide, silicon dioxide, or silicon nitride.

8. A terahertz detector based on the enhanced quantum tunneling effect using a nano-gap field according to any one of claims 1-7, characterized in that, Metal receiving antenna structures include, but are not limited to, bow-shaped structures, logarithmic spiral structures, and dipole structures.

9. A terahertz detector based on nano-gap field-enhanced quantum tunneling effect according to any one of claims 8, characterized in that, The dielectric substrate includes, but is not limited to, one or more of semiconductors, metals, metalloids, insulators, glass substrates, ceramic materials, two-dimensional materials, and diamond.

10. A terahertz detector based on the enhanced quantum tunneling effect using a nano-gap field according to any one of claims 9, characterized in that, The dielectric substrate beneath the area where the metal receiving antenna is located is removed to form a suspended thin-film structure.

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