Dynamically adjustable Van der Waals heterojunction pulse type event detector

Abstract

The invention discloses a dynamically adjustable Van der Waals heterojunction pulse type event detector, and belongs to the technical field of event detectors. The technical problem to be solved is that an existing sensor is limited in regulation and control capability on time response and pulse characteristics. According to the technical scheme, the sensor is characterized by comprising a substrate layer, an electrode structure and a two-dimensional material heterojunction layer which are sequentially arranged from bottom to top; the electrode structure comprises a source electrode, a drain electrode and a grid electrode, and the grid electrode is arranged between the source electrode and the drain electrode; and a two-dimensional material heterojunction layer is arranged on the source electrode and the drain electrode.

Description

Technical Field

[0001] This invention belongs to the field of event detector technology, specifically relating to a dynamically adjustable van der Waals heterojunction pulsed event detector. Background Technology

[0002] With the development of machine vision and neuromorphic computing, traditional frame-readout-based image sensing methods have gradually revealed problems such as large data redundancy, high response latency, and high power consumption in high-speed dynamic scenes. Especially in scenes with rapidly changing light intensity or high-speed target movement, continuous frame acquisition and back-end processing struggle to extract key information in a timely and effective manner.

[0003] Event-based detectors achieve asynchronous perception of dynamic information by outputting signals only when external stimuli change, offering advantages such as fast response speed, small data volume, and low power consumption. Existing event-based vision systems mostly rely on CMOS pixel-level circuits, generating pulse event outputs through comparison or differentiation circuits. However, their structures are complex, their integration is limited, and they mainly operate in the visible light band, which is not conducive to expansion into infrared applications.

[0004] To reduce system complexity, recent years have seen the emergence of in-sensor signal processing approaches that directly implement signal preprocessing and dynamic encoding at the sensor level. Related research indicates that pulse or event signals can be directly obtained from changes in light intensity through the transient response of the device itself or by combining it with simple electrical structures, thereby reducing the computational burden on the backend. However, existing solutions are mostly based on silicon-based device architectures, whose response bands are limited by materials, and whose ability to control time response and pulse characteristics is also limited.

[0005] Comparison document 1:

[0006] The journal or book title is *2D Materials*, the article title is "Gate-tunable MoS2–blackphosphorusheterojunction devices", volume number is 2D Mater. 2 (2015) 034009, and the publication date is 2015. Specifically, this refers to the academic paper "Gate-tunable MoS2–blackphosphorusheterojunction devices" published in 2015 in *2D Materials*, a prestigious journal under IOP Publishing focusing on two-dimensional materials research. This paper discloses that heterojunctions are the core building blocks of modern electronic and optoelectronic devices. The recent discovery of two-dimensional semiconductors has made it possible to construct heterojunctions with atomically clear interfaces through van der Waals interactions. MoS2–blackphosphorus (BP) heterojunction devices were fabricated. Due to the narrow bandgap and unpinned Fermi level of black phosphorus, this heterojunction can be tuned to either a pn junction or an nn junction via electrostatic gate voltage. Current rectification behavior was observed in both the pn and nn junctions. The current rectification effect of the MoS2-BP nn junction is attributed to the potential barrier formed at the interface between the wide-bandgap MoS2 and the narrow-bandgap BP. The gate voltage dependence of the forward current, reverse current, and current rectification characteristics of the heterojunction at different thickness scales was systematically studied, demonstrating that the electrical performance of the heterojunction can be tuned by designing the thickness of the MoS2 and BP sheets.

[0007] The aforementioned existing technologies, based on the research of two-dimensional material heterojunctions, mainly focus on steady-state photocurrent output, which makes it difficult to directly characterize the light intensity change process, and there is still a lack of pulsed output schemes for event-type detection. Summary of the Invention

[0008] The purpose of this invention is to provide a dynamically adjustable van der Waals heterojunction pulsed event detector to solve the technical problems that existing sensors are mostly based on silicon-based device systems, whose response bands are limited by materials, and whose ability to control time response and pulse characteristics is limited.

[0009] The purpose of this invention is to propose an event-type detector based on a van der Waals heterojunction. By utilizing the transient electrical response generated by the device under changes in external stimuli, pulse-type event output is achieved through structural and signal path design, and dynamic adjustment of pulse characteristics is supported to meet the needs of infrared event sensing and low-power machine vision applications.

[0010] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0011] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0012] The term "MoS2" used in this article refers to molybdenum disulfide.

[0013] The term "BP" used in this article refers to black phosphorus.

[0014] The term "Ti / Au" used in this article refers to titanium / gold.

[0015] The term "HBN" used in this article refers to boron nitride.

[0016] This invention provides a dynamically adjustable van der Waals heterojunction pulsed event detector, comprising a substrate layer, an electrode structure, and a two-dimensional material heterojunction layer arranged sequentially from bottom to top; The electrode structure includes a source and a drain, and a gate, with the gate disposed between the source and the drain; A two-dimensional material heterojunction layer is disposed above the source and drain electrodes.

[0017] Based on further solutions to the technical problems of the present invention, or simultaneous solutions to multiple technical problems, the preferred solutions provided by the present invention include: The first preferred option is a two-dimensional material heterojunction layer consisting of a molybdenum disulfide layer and a black phosphorus layer disposed on the source and drain electrodes, wherein the black phosphorus and molybdenum disulfide are stacked on each other to form a MoS2-BP heterojunction.

[0018] The second preferred option is that the source, drain, and gate thicknesses are equal.

[0019] The third preferred option is to place a molybdenum disulfide layer on the source or drain electrode, and a black phosphorus layer on the drain or source electrode accordingly; the end of the black phosphorus layer that contacts the molybdenum disulfide layer is located below the molybdenum disulfide layer.

[0020] The fourth preferred option is a substrate layer comprising a silicon material base layer and an insulating layer of silicon dioxide material disposed on the base layer.

[0021] The fifth preferred option is to place a metal electrode on the insulating layer.

[0022] The sixth preferred option is that both the source and drain electrodes adopt a Ti / Au double-layer metal structure; the gate electrode adopts Au metal.

[0023] The seventh preferred option is a Ti / Au dual-layer metal structure, in which the titanium layer is 10 nm thick, the gold layer is 90 nm thick, and the gate is 100 nm thick.

[0024] The eighth preferred option is to provide an isolation layer between the gate and the MoS2-BP heterojunction.

[0025] The ninth preferred option is to place one end of the black phosphorus layer on the source or drain electrode and the other end on the isolation layer; correspondingly, one end of the molybdenum disulfide layer is placed on the drain or source electrode and the other end on the black phosphorus layer.

[0026] Tenth preferred option: Boron nitride for the isolation layer.

[0027] Eleventh preferred option: Molybdenum disulfide layer thickness 40 nm; black phosphorus layer thickness 50 nm; isolation layer thickness 40 nm.

[0028] The present invention has at least the following beneficial effects: This invention features a two-dimensional material heterojunction layer above the source and drain electrodes, forming a van der Waals heterojunction event detector. It utilizes the transient electrical response generated by the device under changes in external stimuli to achieve pulse-type event output through structural and signal path design, and supports dynamic adjustment of pulse characteristics to meet the needs of infrared event sensing and low-power machine vision applications.

[0029] Black phosphorus and molybdenum disulfide are stacked to form a MoS2-BP heterojunction. Two-dimensional materials and their van der Waals heterojunctions exhibit significant advantages in novel photoelectric detection fields due to their high interface quality and tunable band structure. Black phosphorus possesses excellent infrared absorption capabilities, while molybdenum disulfide exhibits good electrical stability. By constructing a van der Waals heterojunction between the two, a highly sensitive infrared photoelectric response can be achieved.

[0030] Compared with prior art document 1, the present invention differs in the following ways: 1. Differences in the principles of pulse event generation: The scheme in Comparative Document 1 guides photogenerated carriers to migrate in different directions using a built-in electric field and collects them with the help of metal electrodes, outputting a photocurrent. This scheme mainly focuses on steady-state photocurrent output and does not directly mention the generation of pulse events.

[0031] The core innovation of this invention lies in using two opposite heterojunction structures to generate a pulse output by utilizing the time difference between the delayed response of one branch and the non-delayed response of the other. This pulse signal is used in event-type detectors, effectively generating pulse signals of varying light intensity through differential signaling, avoiding the response delay problem of traditional photodetectors, and adapting to machine vision applications with higher dynamic range.

[0032] 2. Ability to adjust photoelectric response and pulse modulation: In the design of prior art document 1, the intensity and polarity of the photocurrent are mainly adjusted by the gate voltage, but the photoelectric response does not emphasize the adjustable pulse characteristics.

[0033] This invention, through a parallel heterojunction structure, exhibits significant adjustability in response time, allowing for adjustment of pulse width and response speed via the introduction of capacitors. Furthermore, the gate voltage control mechanism enables fine-tuning of the output pulse intensity, providing more flexible control for event sensing and meeting the demands for low power consumption and high response speed.

[0034] 3. Differences in application scenarios: The structure in Comparative Document 1 mainly focuses on generating steady-state photocurrent through a built-in electric field, which is suitable for static photodetectors or scenarios that require stable photocurrent output.

[0035] This invention is designed for event-type detectors. Through a dynamic pulse generation mechanism, it can cope with changes in light intensity in high-speed dynamic scenes, making it suitable for high-frequency dynamic event perception applications such as machine vision and neuromorphic computing systems.

[0036] Compared with prior art document 1, the core innovation of this invention lies in the use of an opposite heterojunction structure and the generation of pulse events through the difference in their response delays. This design not only breaks through the limitations of the steady-state response of traditional van der Waals heterojunctions, but also provides dynamically adjustable pulse characteristics, significantly improving the application capability of the event detector in high-speed dynamic scenes, and is particularly suitable for machine vision applications with low power consumption and high response speed.

[0037] Compared with prior art document 2 (patent application document with publication number CN 115274911 A), the present invention has the following differences: Compared with the prior art document CN 115274911 A, which discloses a van der Waals heterojunction photodetector and its fabrication method, this invention has the following key differences: 1. Differences in heterojunction structure: The npn-type structure designed in Comparative Document 2 includes two layers of n-type molybdenum disulfide (MoS2) and one layer of p-type black phosphorus (BP). By forming a built-in electric field in the sandwich structure, photogenerated carriers are driven to different material layers, thereby generating photocurrent.

[0038] This invention employs two opposite types of van der Waals heterojunction structures: PN-type and NP-type heterojunctions. The two heterojunction branches are connected in parallel, with one branch exhibiting a fast photoelectric response and the other branch delaying the response by introducing a capacitor. This difference in response speed generates pulse events in response to changes in light intensity. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the detector structure provided by the present invention.

[0040] Figure 2 This is a schematic diagram of the independent energy bands of black phosphorus and molybdenum disulfide before they come into contact, according to the present invention.

[0041] Figure 3 This is a schematic diagram of the non-equilibrium state of black phosphorus and molybdenum disulfide in contact under light.

[0042] Figure 4 The transient response of the MoS2-BP heterojunction as a function of gate voltage and photocurrent response is shown in the figure provided by the present invention.

[0043] Figure 5 This is a schematic diagram of the event-driven spike generator circuit structure based on MoS2-BP heterojunction provided by the present invention.

[0044] Figure 6 The diagram shows the test circuit and results of the event-driven spike generator provided by this invention under 1550nm light pulse irradiation.

[0045] Figure 7 The diagram shows the output waveform of the pulse-type event provided by the present invention under the first gate voltage condition.

[0046] Figure 8 This is a schematic diagram of the output waveform of the pulse-type event provided by the present invention under the second gate voltage condition.

[0047] 1. Molybdenum disulfide layer; 2. Black phosphorus layer; 3. Source electrode; 4. Insulating layer; 5. Substrate layer; 6. Isolation layer; 7. Gate electrode; 8. Drain electrode. Detailed Implementation

[0048] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0049] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0050] See Figure 1 As shown, this embodiment provides a dynamically adjustable van der Waals heterojunction pulsed event detector, which includes a substrate layer, an electrode structure, and a two-dimensional material heterojunction layer.

[0051] The electrode structure includes a source 3, a drain 8, and a gate 7, with the gate 7 disposed between the source 3 and the drain 8; A two-dimensional material heterojunction layer is disposed above the source electrode 3 and the drain electrode 8.

[0052] The two-dimensional material heterojunction layer consists of a molybdenum disulfide layer 1 and a black phosphorus layer 2 disposed on the source electrode 3 and the drain electrode 8, wherein the black phosphorus and molybdenum disulfide are stacked on each other to form a MoS2-BP heterojunction.

[0053] The source 3, drain 8, and gate 7 have the same thickness.

[0054] A molybdenum disulfide layer 1 is disposed on the source electrode 3 or the drain electrode 8, and a black phosphorus layer 2 is disposed on the drain electrode 8 or the source electrode 3 accordingly; the end of the black phosphorus layer 2 that contacts the molybdenum disulfide layer 1 is located below the molybdenum disulfide layer 1.

[0055] The substrate layer includes a silicon substrate 5 and an insulating silicon dioxide layer 4 disposed on the substrate 5.

[0056] A metal electrode is disposed on the insulating layer 4.

[0057] Both the source 3 and drain 8 adopt a Ti / Au double-layer metal structure; the gate 7 adopts Au metal.

[0058] The structure consists of a Ti / Au dual-layer metal structure, with a titanium layer thickness of 10 nm and a gold layer thickness of 90 nm; the gate 7 has a thickness of 100 nm.

[0059] An isolation layer 6 is disposed between the gate 7 and the MoS2-BP heterojunction. The isolation layer 6 is made of HBN-boron nitride.

[0060] One end of the black phosphorus layer 2 is disposed on the source electrode 3 or the drain electrode 8, and the other end is located on the isolation layer 6; the corresponding molybdenum disulfide layer 1 is disposed on the drain electrode 8 or the source electrode 3, and the other end is located on the black phosphorus layer 2.

[0061] The thickness of molybdenum disulfide layer 1 is 40 nm; the thickness of black phosphorus layer 2 is 50 nm; and the thickness of isolation layer 6 is 40 nm.

[0062] The substrate layer includes a silicon (Si) material base layer 5 with a thickness of 500 μm, and an insulating layer 4 covered thereon with a silicon dioxide (SiO2) material with a thickness of 285 nm.

[0063] Metal electrodes are disposed on the insulating layer 4 of silicon dioxide; serving as the source 3 and drain 8 of the device, both the source 3 and drain 8 adopt a Ti / Au double-layer metal structure, wherein the titanium layer is 10 nm thick and the gold layer is 90 nm thick; Au metal is used as the gate 7, which is 100 nm thick, and is used to regulate the electrical characteristics of the device.

[0064] A 40 nm thick molybdenum disulfide layer 1 and a 50 nm thick black phosphorus layer 2 are disposed on the metal electrode, wherein the black phosphorus and molybdenum disulfide are stacked to form a van der Waals heterojunction. A 40 nm thick boron nitride (hBN) layer is disposed between the gate 7 and the van der Waals heterojunction to cover and isolate the van der Waals heterojunction structure.

[0065] See Figure 2 As shown in the figure, this diagram illustrates the band structure evolution of black phosphorus and molybdenum disulfide before and after forming a heterojunction.

[0066] Figure 2 This diagram illustrates the independent energy band structures of black phosphorus and molybdenum disulfide before their contact. Using the vacuum level as a unified reference, the conduction band bottom E of black phosphorus (BP) is shown. c Located at 4.3 eV below it, its Fermi level E v Located at 4.57 eV, it exhibits typical p-type characteristics, with a bandgap E g It is approximately 0.3 eV.

[0067] molybdenum disulfide (MoS2) conduction band bottom E c Located at 4.4 eV, Fermi level E v Located at 4.48 eV, exhibiting n-type characteristics, with a bandgap of E g Approximately 1.2 eV. The significant difference in their Fermi levels (ΔE) F (≈1.2 eV - 0.3 eV = 0.09 eV), providing the initial driving force for charge transfer and the formation of the built-in electric field after contact.

[0068] See Figure 3 As shown in the figure, this diagram illustrates the photoelectric conversion mechanism of black phosphorus and molybdenum disulfide before and after forming a heterojunction.

[0069] Figure 3 This represents a non-equilibrium state where black phosphorus and molybdenum disulfide (MoS2) are in contact under illumination. Upon contact, electrons spontaneously flow from the higher Fermi level of MoS2 to the BP side until the Fermi level of the system is unified. This process creates a built-in electric field at the interface pointing from MoS2 to BP, constructing a Type-II (interleaved) band arrangement. When excited by light (hν), photogenerated electron-hole pairs undergo efficient spatial separation driven by the built-in electric field: electrons converge and transfer to the conduction band of MoS2, while holes transfer to the valence band of black phosphorus. This physical process directly corresponds to the generation of measurable photocurrent in the external circuit, clearly revealing the core working principle of the device in converting optical signals into electrical pulses.

[0070] See Figure 4 As shown in the figure, this figure illustrates the photocurrent response characteristics of a photodetector based on a MoS2-BP heterojunction under different gate voltage modulations. The horizontal axis in the figure is v. g The gate voltage is adjustable from -60V to +60V; the vertical axis is I. d The corresponding photocurrent value is shown. Experimental results indicate that the device photocurrent exhibits a significant and continuous modulation characteristic with varying gate voltage. Within a specific gate voltage range, the photocurrent increases or decreases significantly with increasing voltage, and the overall response curve demonstrates good tunability. This characteristic confirms that the photoelectric response intensity and polarity of this heterojunction can be effectively controlled through gate voltage, providing an electrically tunable hardware basis for the signal amplitude, response speed, and sensitivity in optical pulse generation circuits. This is suitable for reconfigurable photoelectric sensing and neuromorphic computing systems.

[0071] See Figure 5 As shown in the figure, this diagram illustrates the circuit structure of an event-driven spike generator based on a MoS2-BP heterojunction. The circuit consists of two parallel heterojunction branches with opposite photoelectric characteristics: one is a PN-type MoS2-BP heterojunction, exhibiting fast photoelectric response and generating a forward photocurrent under zero bias; the other is an NP-type heterojunction, which introduces a response delay through a parallel capacitor, generating a reverse photocurrent under the same illumination conditions. Under steady-state illumination, the photocurrents of the two branches are equal in magnitude and opposite in direction, resulting in a net output current of zero. When the incident light intensity changes, the transient photocurrent becomes unbalanced due to the difference in response speed between the two branches, generating a positive spike signal when the light intensity increases and a negative spike signal when the light intensity decreases, thus achieving event-driven pulse output. This structure can be used in biomimetic vision sensors and light intensity change detection systems.

[0072] See Figure 6As shown in the figure, this diagram illustrates the test circuit and results of the dynamic response characteristics of the event-driven spike generator under 1550nm light pulse illumination. The figure reflects the voltage change waveform caused by the photocurrent by monitoring the voltage drop across the resistor connected in series with the photodetector. To adjust the system's response time, capacitors of different capacitance values ​​(0 nF, 150 nF, 330 nF, and 1 μF) are connected in parallel across the resistor, forming an adjustable low-pass filter network. Experimental results show that as the parallel capacitance value increases, the circuit's response speed to changes in light intensity decreases accordingly, and the rise and fall times of the output voltage waveform are prolonged, thereby achieving controllable adjustment of the output pulse timing characteristics. This structure verifies the adjustability and adaptability of the photoelectric spike generator in terms of pulse width and response speed, making it suitable for biomimetic vision and optical sensing systems with different timing requirements.

[0073] See Figure 7 , Figure 8 As shown, Figure 7 , Figure 8 This paper demonstrates a light pulse generation circuit based on a parallel differential structure under different gate voltage conditions, and its gate voltage modulation characteristics for the output pulse amplitude. The figure shows the positive and negative light pulses corresponding to light intensity changes generated after parallel differential processing of MoS2-BP heterojunction branches with complementary photoelectric response characteristics. The peak amplitude of the output pulse can be effectively adjusted by applying an adjustable bias voltage to the gate in the circuit. Figure 7 , Figure 8 Experimental results show that the amplitude of the pulse signal can be adjusted under different gate voltage conditions, thus achieving electrical modulation of the output pulse intensity. This modulation mechanism provides the system with additional signal reconfigurability and is suitable for applications requiring dynamic pulse intensity adjustment, such as neuromorphic visual sensing, adaptive optoelectronic signal processing, and spiking neural networks.

[0074] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A dynamically adjustable van der Waals heterojunction pulsed event detector, characterized in that, It includes, from bottom to top, a substrate layer, an electrode structure, and a two-dimensional material heterojunction layer; The electrode structure includes a source and a drain, and a gate, with the gate disposed between the source and the drain; A two-dimensional material heterojunction layer is disposed above the source and drain electrodes.

2. The dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 1, characterized in that, The two-dimensional material heterojunction layer consists of a molybdenum disulfide layer and a black phosphorus layer disposed on the source and drain electrodes, wherein the black phosphorus and molybdenum disulfide are stacked on each other to form a MoS2-BP heterojunction.

3. The dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 2, characterized in that, The source, drain, and gate have equal thicknesses.

4. The dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 3, characterized in that, A molybdenum disulfide layer is disposed on the source or drain electrode, and a black phosphorus layer is disposed on the drain or source electrode accordingly; the end of the black phosphorus layer that contacts the molybdenum disulfide layer is located below the molybdenum disulfide layer.

5. The dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 1, characterized in that, The substrate layer includes a silicon substrate layer and an insulating silicon dioxide layer disposed on the substrate layer.

6. A dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 5, characterized in that, A metal electrode is disposed on the insulating layer.

7. A dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 6, characterized in that, Both the source and drain electrodes adopt a Ti / Au double-layer metal structure; the gate electrode adopts Au metal.

8. A dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 7, characterized in that, The structure is a Ti / Au dual-layer metal structure, in which the titanium layer is 10 nm thick and the gold layer is 90 nm thick; the gate is 100 nm thick.

9. A dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 2, characterized in that, An isolation layer is provided between the gate and the MoS2-BP heterojunction.

10. A dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 9, characterized in that, One end of the black phosphorus layer is placed on the source or drain electrode, and the other end is placed on the isolation layer; the corresponding molybdenum disulfide layer is placed on the drain or source electrode, and the other end is placed on the black phosphorus layer.

11. A dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 9, characterized in that, The isolation layer is made of boron nitride.

12. A dynamically adjustable van der Waals heterojunction pulsed event detector according to claim 9, characterized in that, The molybdenum disulfide layer is 40 nm thick; the black phosphorus layer is 50 nm thick; and the isolation layer is 40 nm thick.

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