Ultrafast motion sensing floating gate transistor based on van der Waals heterojunction and its applications

Abstract

The present invention discloses an ultrafast motion sensing floating gate transistor based on van der Waals heterojunction and its application. The floating gate transistor of the present invention comprises a back gate substrate, a van der Waals heterojunction channel layer, and source and drain electrodes on both sides of the channel layer. The back gate substrate is heavily doped silicon with a surface covered with hafnium oxide / aluminum oxide / hafnium oxide (HfO2 / Al2O3 / HfO2) for non-volatile light storage, and the van der Waals heterojunction channel layer is composed of bismuth oxide selenium-palladium selenide nanosheets for sensing. The floating gate transistor of the present invention has both rapid response to a wide spectrum of ultraviolet-near infrared light and non-volatile storage capabilities of light, which can effectively improve the sensitive spectral response range and responsiveness of the photodetector, thereby realizing the in-device integration of dynamic target light signals in the spatial domain and time domain.

Description

Technical Field

[0001] The present invention relates to a method for realizing van der Waals heterojunction based ultrafast motion sensing floating-gate transistors (vdWsHeterojunction based Floating-Gate Phototransistors for Ultrafast MotionPerceptiopn), belonging to the technical field of high-performance sensing and sensing-storage-computing integration. Background Art

[0002] Neuromorphic sensors offer a promising approach to endow machines with the ability to sense, process, and respond to environmental stimuli. Based on the imitation of human sensory capabilities, the devices have revolutionary potential in areas such as intelligent robots, autonomous navigation, and intelligent monitoring. At the core of these applications is the need for wide-spectrum visual perception capabilities to ensure efficient operation under different lighting conditions. However, traditional wide-spectrum detectors are limited by materials and structures, and face challenges in latency, power consumption, volume, and functional integration in terms of devices and architectures. Due to the rich material system, two-dimensional materials have unique advantages. Not only can different functional layers and high-density heterogeneous integration be achieved, but the devices also exhibit high photon sensitivity and higher responsivity. However, high photoresponsivity often requires an extension of the photocarrier lifetime, which ultimately results in a response time extension of milliseconds, which largely hinders the applicability of neuromorphic sensors in real-time applications, which have high requirements for rapid and accurate response to environmental changes. On the other hand, in the system architecture, in-sensor computing, as a revolutionary intelligent sensing technology, can simultaneously detect and process visual information by distributing the underlying computing tasks to the perception terminal. Using van der Waals heterostructures of two-dimensional semiconductor materials, carriers stored on the interface can be precisely modulated by external electric fields or light stimulation, thereby generating dynamic response characteristics that contain both temporal and spatial information in the device, which is expected to be used for spatiotemporal visual information encoding and calculation for motion perception tasks. Therefore, an integrated innovation paradigm that combines high-performance wide-spectrum detectors, ultrafast optical information storage, and advanced computing is urgently needed, but this paradigm has not yet been realized. Summary of the invention

[0003] In order to realize the parallel sensing, memory and processing of ultrafast moving light information, the present invention proposes a floating gate transistor device based on a high-mobility bismuth oxide selenide / palladium selenide two-dimensional material heterojunction that is sensitive to ultraviolet-visible-near infrared wide-spectrum light information. By utilizing the carrier tunneling storage dynamics inside the heterojunction floating gate transistor, the sensing characteristics of wide-spectrum fast-moving targets are realized (the spectral sensing range is 380 nm to 1550 nm, the fastest response time to incident light is 3 μs, the response frequency is as high as 0.2 MHz, and the optical memory time is within 10 4The above optical pulse information storage capacity is 8 bits). The van der Waals heterojunction floating gate phototransistor of the present invention is used to form a wide-spectrum ultrafast motion light sensing device, which can achieve ultrafast non-volatile response and linear / nonlinear writing to ultraviolet-visible-near-infrared light pulses, thereby completing the memory and encoding of the target motion path characteristics, facilitating the subsequent visual information perception analysis and target recognition of ultrafast motion targets.

[0004] The technical solution provided by the present invention is as follows:

[0005] A heterojunction floating gate transistor, characterized in that it comprises a heavily doped silicon back gate substrate, a van der Waals heterojunction channel layer and source and drain electrodes on both sides of the channel layer, wherein the back gate substrate is a heavily doped silicon, a first hafnium oxide layer, an aluminum oxide layer and a second hafnium oxide layer (p++ Si / HfO2 / Al2O3 / HfO2) stacked in sequence from bottom to top, wherein the thickness of the first hafnium oxide layer as an insulating medium is in the range of 20-50 nm, the thickness of the aluminum oxide layer as a charge storage layer is in the range of 5-10 nm, and the thickness of the second hafnium oxide layer as a charge blocking layer is in the range of 5-10 nm, the van der Waals heterojunction channel layer is a bismuth oxide selenium nanosheet and a palladium selenide nanosheet stacked from bottom to top, the thickness of the bismuth oxide selenium nanosheet is in the range of 5-20 nm, and the thickness of the palladium selenide nanosheet is in the range of 5-20 nm, the source and drain electrodes are respectively composed of Ti / Au metal stacks, and the thickness of the source and drain electrodes does not exceed 100 nm.

[0006] A wide-spectrum ultrafast motion light sensing device, characterized in that the device includes an array composed of periodically arranged heterojunction floating-gate transistors, the array is used for ultrafast non-volatile response and linear / nonlinear writing to ultraviolet-visible-near-infrared light pulses, and the memory and encoding of the target motion path characteristics are completed by reading out the current.

[0007] A method for preparing a wide-spectrum ultrafast motion light sensing device comprises the following steps:

[0008] 1) Two-dimensional layered bismuth oxide selenide nanosheets and two-dimensional layered palladium selenide nanosheets were grown by chemical vapor deposition (CVD).

[0009] 2) Atomic layer deposition (ALD) is used to grow a first hafnium oxide layer / aluminum oxide layer / second hafnium oxide layer on heavily doped silicon as a back gate substrate;

[0010] 3) Transferring the two-dimensional layered bismuth oxide selenide nanosheets to the back-gate substrate;

[0011] 4) Position the transferred bismuth oxide selenide nanosheets and define the array area using electron beam lithography (EBL);

[0012] 5) Etch the excess area using inductively coupled plasma (ICP);

[0013] 6) Dry transfer of two-dimensional layered palladium selenide nanosheets onto bismuth oxide selenide nanosheets;

[0014] 7) Position the transferred PdSe nanosheets, define the array area using EBL, and etch the excess area using ICP again to form a van der Waals heterojunction channel layer array;

[0015] 8) Position the van der Waals heterojunction channel layer array and use EBL to define the source and drain electrode regions;

[0016] 9) Using electron beam evaporation, Ti / Au (10nm / 40 nm) metal stacks are deposited on both sides of each van der Waals heterojunction channel layer in the array, and then peeled off to obtain source and drain electrodes, thereby completing the preparation of the heterojunction floating gate transistor array.

[0017] The floating gate transistor based on bismuth oxygen selenium / palladium selenide heterojunction provided by the present invention has the ability of rapid response to ultraviolet-near infrared wide spectrum and non-volatile storage of light. In the electrical initialization programming, a positive gate voltage electric field is used to cause the electrons in the channel layer to tunnel through the thin charge blocking layer into the floating gate charge storage layer by Fermi-Norheim tunneling effect (FN), so that the channel conductance is reduced, corresponding to the low conductance state of the floating gate transistor. Then, when ultraviolet-near infrared wide spectrum light stimulation is applied to the channel layer of the heterojunction floating gate transistor, photogenerated electron-hole pairs are generated in the bismuth oxygen selenium / palladium selenide van der Waals heterojunction, and spontaneously move in a directional manner under the action of the internal electric field of the heterojunction, resulting in an increase in the conductance of the channel layer. At the same time, the electrons stored in the floating gate layer absorb the energy of the incident photons and pass through the interface charge blocking layer back to the channel layer, resulting in a further increase in the conductance of the heterojunction transistor, thereby achieving a rapid non-volatile response to wide spectrum light signals. Moreover, since the working process of this optical signal storage does not require the application of additional gate voltage assistance, it is more suitable for the development of low-power, ultra-compact high-speed motion sensing systems.

[0018] The advantages of the present invention are as follows:

[0019] 1) Using bismuth oxide selenide / palladium selenide van der Waals heterojunction as the channel, fully utilizing the characteristics of small electron effective mass and high mobility of two-dimensional bismuth oxide selenide nanosheets and small optical band gap of two-dimensional palladium selenide nanosheets, combined with the type II band arrangement of the van der Waals heterojunction, effectively improves the sensitive spectral response range and responsivity of the photodetector.

[0020] 2) Use heavily doped silicon / hafnium oxide / aluminum oxide / hafnium oxide as the back gate substrate. Relying on the gate voltage pulse and external light pulse stimulation, the carriers tunnel into the charge storage layer or return to the channel layer, generating non-volatile optical / electrical memory capabilities. The device exhibits linear / nonlinear optoelectronic hybrid programming characteristics, up to 8-bit storage capacity, high stability, and is easy to prepare large-scale device arrays.

[0021] 3) Using bismuth oxide selenide / palladium selenide van der Waals heterojunction and hafnium oxide / aluminum oxide / hafnium oxide back-gate substrate, the ultraviolet-near infrared wide spectrum absorption is achieved by relying on the light-sensitive characteristics of the heterojunction. The microsecond-level ultrafast non-volatile optical memory characteristics are generated by the heterojunction photovoltaic electric field induction and incident light-assisted electron tunneling, realizing the device integration of dynamic target optical signals in the spatial and temporal domains. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1-5 This is a schematic diagram of the preparation process of the ultrafast motion light information sensing device of the present invention;

[0023] Figure 6 This is a gate voltage scanning hysteresis curve characterization diagram of the bismuth oxide selenium / palladium selenide heterojunction floating gate transistor of the present invention, showing an obvious hysteresis loop, indicating the existence of a large memory window;

[0024] Figure 7 The actual long-term conductance retention characteristics of the bismuth oxide selenium / palladium selenide heterojunction floating gate transistor of the present invention are characterized. Under positive and negative gate voltage pulse programming, the floating gate transistor device exhibits long-term positive and negative conductance retention characteristics;

[0025] Figure 8 The present invention is based on the actual multi-conductance state storage characteristics of the bismuth oxide selenide / palladium selenide heterojunction floating gate transistor. The device can be programmed with electric pulses of different voltage amplitudes to achieve multiple clearly distinguished conductance states;

[0026] Fig. 9 The present invention is based on the actual multi-level photoconductivity state characteristics of the bismuth oxide selenium / palladium selenide heterojunction floating gate transistor under visible light pulse programming of different widths. The longer the time width of the incident light pulse, the more enhanced the non-volatility of the channel photoconductivity caused by the light-excited carrier tunneling.

[0027] Fig.10 The actual optical pulse multi-level nonlinear conductivity modulation (a) and linear conductivity modulation (b) of the bismuth oxide selenide / palladium selenide heterojunction floating gate transistor of the present invention are characterized by applying steady or gradually increasing intensity optical pulse programming, respectively. The photoconductivity programming capacity of the device is 8 bits;

[0028] Fig.11The present invention is based on the photoconductivity modulation characterization of multiple actual light pulses in different ultraviolet-near infrared bands of the bismuth oxide selenium / palladium selenide heterojunction floating gate transistor;

[0029] Fig.12 The actual ultrafast non-volatile light pulse response programming characteristics of the ultrafast motion light information sensing device of the present invention are characterized, and the light pulse frequency is 0.2 MHz. The inset is the high-time resolution photoconductive response characteristics of the device under microsecond ultrashort light pulse excitation;

[0030] Fig.13 To characterize the practical and stable multiple alternating optical pulse writing and electrical pulse erasing operation characteristics of the ultrafast motion optical information sensing device of the present invention;

[0031] Fig.14 It is a schematic diagram of the physical mechanism principle of the ultrafast conductance writing and erasing programming operation of the ultrafast motion light information sensing device of the present invention;

[0032] In the figure: 1—f-phase mica substrate; 2—two-dimensional bismuth oxide selenide nanosheets grown by CVD; 3—two-dimensional material transfer auxiliary polymer layer; 4—heavily doped silicon / hafnium oxide / aluminum oxide / hafnium oxide back gate structure substrate; 5—bismuth oxide selenide / palladium selenide van der Waals heterojunction channel layer; 6—source electrode; 7—drain electrode. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below by way of embodiments in conjunction with the accompanying drawings.

[0034] The floating gate transistor based on bismuth oxide selenium / palladium selenide heterojunction of the present invention comprises a heavily doped silicon back gate substrate, a van der Waals heterojunction channel layer and source and drain electrodes on both sides of the channel layer, wherein the back gate substrate is a heavily doped silicon, a first hafnium oxide layer, an aluminum oxide layer and a second hafnium oxide layer (p++ Si / HfO2 / Al2O3 / HfO2) stacked in sequence from bottom to top, wherein the thickness of the first hafnium oxide layer as an insulating medium is in the range of 20-50 nm, the thickness of the aluminum oxide layer as a charge storage layer is in the range of 5-10 nm, and the thickness of the second hafnium oxide layer as a charge blocking layer is in the range of 5-10 nm, the van der Waals heterojunction channel layer is a bismuth oxide selenium nanosheet and a palladium selenide nanosheet stacked from bottom to top, the thickness of the bismuth oxide selenium nanosheet is in the range of 5-20 nm, the thickness of the palladium selenide nanosheet is in the range of 5-20 nm, the source and drain electrodes are respectively composed of Ti / Au metal stacks, and the thickness of the source and drain electrodes does not exceed 100 nm. nm.

[0035] The hafnium oxide / aluminum oxide / hafnium oxide floating gate layer and the bismuth oxide selenium / palladium selenide nanosheet van der Waals heterojunction channel layer located on the heavily doped silicon substrate of the present invention are core components for realizing multi-level long-term memory of external ultrafast dynamic light information stimulation, and the source / drain (S / D) electrodes on both sides of the bismuth oxide selenium / palladium selenide heterojunction channel layer are used to collect the response current of the device reflecting the motion light stimulation.

[0036] The present invention adopts the above-mentioned heterojunction floating gate transistors arranged periodically to form an ultrafast motion light information sensing device, which can realize ultrafast non-volatile response and linear / nonlinear writing to ultraviolet-visible-near-infrared light pulses. Through the device readout current, the dynamic target light signal can be integrated in the device in the spatial domain and time domain, and the target motion path characteristics can be memorized and encoded, thereby extracting a series of effective expressions of motion state characteristics, further improving the subsequent visual information perception analysis and target recognition processing capabilities of ultrafast motion targets.

[0037] The preparation process of the ultrafast motion light information sensing device is as follows:

[0038] 1) Using bismuth oxide and bismuth selenide as precursors, two-dimensional bismuth oxide and selenide nanosheets were synthesized on f-phase mica substrates by chemical vapor deposition. Figure 1 As shown;

[0039] 2) On the surface of the mica substrate with the two-dimensional bismuth oxide selenide nanosheets grown, a layer of PMMA (polymethyl methacrylate) was spin-coated at a speed of 3000 rpm as an auxiliary polymer layer for the transfer of the two-dimensional material. Figure 2 As shown;

[0040] 3) soaking the mica substrate coated with the auxiliary polymer layer in a hydrofluoric acid solution to selectively etch the mica, then transferring the two-dimensional bismuth oxide selenium nanosheets to a heavily doped silicon / hafnium oxide / aluminum oxide / hafnium oxide floating gate structure substrate grown by ALD, and removing the auxiliary polymer layer by an acetone solution;

[0041] 4) Position the 2D bismuth oxide selenium nanosheets (thickness range 10 nm-20 nm), define the 3 × 3 array area by EBL, and etch the excess area by ICP, e.g. Figure 3 As shown;

[0042] 5) The 2D layered PdSe nanosheets (thickness ranged from 10 nm to 20 nm) were dry-transferred onto the BiOSe nanosheets and positioned, and the 3×3 array area was defined using EBL, and the excess area was etched again using ICP, e.g. Figure 4 As shown;

[0043] 6) Position the 3×3 heterojunction array and define the source and drain electrode regions using EBL; use electron beam evaporation to evaporate Ti / Au (10nm / 40 nm) metal electrode layers, followed by lift-off to form source and drain electrodes, such as Figure 5 shown.

[0044] The heterojunction floating-gate transistor and the ultrafast motion light information sensing device of the present invention were electrically tested by using a Lake-shore vacuum probe station and a semiconductor parameter analyzer 1500A. Multiple laser light sources in the ultraviolet-visible-near-infrared bands and random signal generators were used to apply light of different intensities and durations to the devices. An electrical signal generator was used to apply electric pulse stimulation of different intensities and durations to the devices.

[0045] Figure 6 The gate voltage scanning hysteresis curve of the heterojunction floating-gate transistor of the present invention was tested and showed an obvious hysteresis loop. When the gate voltage scanning amplitude was ±8 V, there was a large memory window of 3.5 V, which indicated that during the gate voltage scanning, part of the charge tunneled across the charge blocking layer under the action of the electric field and was subsequently stored in the floating gate layer.

[0046] To further verify the long-term conductance memory mechanism of ultrafast motion light information sensing devices, Figure 7 The actual non-volatile conductivity retention characteristics of the device of the present invention are characterized. Under the programming of positive and negative gate voltage pulses, the positive and negative conductivity retention times are both greater than 10 4 Second.

[0047] Figure 8 The actual multi-conductance state storage characteristics of the ultrafast motion light information sensing device of the present invention are characterized. The device can achieve 10 clearly distinguishable conductance states through electrical programming using electric pulses of different voltage amplitudes, which is very important for its application in multi-value analog computing and coding.

[0048] To further verify the non-volatile memory mechanism of light pulses in ultrafast motion optical information sensing devices, Fig. 9 The multi-level photoconductivity state characteristics of the device of the present invention are actually characterized under programming of visible light pulses of different widths. The longer the time width of the incident light pulse, the greater the number of carriers tunneling back to the channel layer due to light excitation, thus showing the non-volatile enhancement characteristics of photoconductivity.

[0049] Fig.10 The actual light pulse multi-level nonlinear conductivity modulation (a) and linear conductivity modulation (b) of the ultrafast motion optical information sensing device of the present invention are characterized by applying light pulses of stable or gradually increasing intensity respectively. The photoconductivity programming capacity of the device is 8 bits.

[0050] Fig.11The photoconductivity modulation of the ultrafast motion optical information sensing device of the present invention is characterized by actual multiple light pulses in different ultraviolet-near infrared bands. Photoconductivity enhancement is produced under the stimulation of multiple light pulses from 380 to 1550 nm, verifying the wide-spectrum optical memory capability of the device.

[0051] In order to further verify the ultrafast optical information storage mechanism of the ultrafast motion optical information sensing device, Fig.12 The figure shows the actual ultrafast non-volatile light pulse response programming characteristics of the device of the present invention, with a light pulse frequency of 0.2 MHz. The inset shows the high-time resolution photoconductive response characteristics of the device under microsecond ultrashort light pulse excitation, with the fastest light pulse programming response time of 3 μs, indicating that the device has fast dynamic light information response and memory characteristics.

[0052] Fig.13 The actual stable multiple alternating optical pulse writing and electrical pulse erasing operation characteristics of the ultrafast motion optical information sensing device of the present invention are characterized. 4 After the first photoelectric hybrid erase / write operation, the device performance did not show significant degradation, indicating the reliability of the device.

[0053] Fig.14 The schematic diagram of the physical mechanism principle of the ultrafast electrical / optical programming operation of the device of the present invention shows that in the electrical programming (a), a positive gate voltage is used to induce FN tunneling of electrons in the channel into the charge storage layer, resulting in a decrease in device conductivity, corresponding to the low-conductance state of the device (b). When ultraviolet-near-infrared light stimulates the device (c), the photogenerated electron-hole pairs in the van der Waals heterojunction move in a directional manner under the action of the internal electric field, increasing the conductivity of the channel layer. At the same time, the electrons in the floating gate layer are excited by the incident light to tunnel back into the channel layer, resulting in a further increase in conductivity, thereby achieving a fast non-volatile response to a wide-spectrum dynamic optical signal.

[0054] The embodiments described above are not intended to limit the present invention. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention is defined by the scope of the claims.

Claims

1. A heterojunction floating gate transistor, characterized in that: The invention comprises a back gate substrate, a van der Waals heterojunction channel layer and source and drain electrodes on both sides of the channel layer. The back gate substrate comprises heavily doped silicon, a first hafnium oxide layer, an aluminum oxide layer and a second hafnium oxide layer stacked in sequence from bottom to top. The van der Waals heterojunction channel layer is a bismuth oxide selenium nanosheet and a palladium selenide nanosheet stacked from bottom to top. The source and drain electrodes are respectively composed of Ti / Au metal stacks. The thickness of the first hafnium oxide layer is in the range of 20-50nm, the thickness of the aluminum oxide layer is in the range of 5-10nm, the thickness of the second hafnium oxide layer is in the range of 5-10nm, the thickness of the bismuth oxide selenium nanosheet is in the range of 5-20nm, and the thickness of the palladium selenide nanosheet is in the range of 5-20nm.

2. The heterojunction floating gate transistor according to claim 1, wherein: The thickness of the source and drain electrodes does not exceed 100 nm.

3. A wide spectrum ultrafast motion light sensing device, characterized in that: The device comprises an array composed of a periodic arrangement of heterojunction floating gate transistors as described in claim 1, the array is used for ultrafast non-volatile response and linear / non-linear writing to ultraviolet-visible-near-infrared light pulses, and completes the memory and encoding of the target motion path characteristics by reading out the current.

4. The method for preparing the wide spectrum ultrafast motion light sensing device according to claim 3, comprising the following steps: 1) Two-dimensional layered bismuth oxide selenide nanosheets and two-dimensional layered palladium selenide nanosheets were grown by chemical vapor deposition method; 2) Atomic layer deposition grows a first hafnium oxide layer / aluminum oxide layer / second hafnium oxide layer on heavily doped silicon as a back gate substrate; 3) Transferring the two-dimensional layered bismuth oxide selenide nanosheets to the back-gate substrate; 4) Positioning the transferred bismuth oxide selenide nanosheets and defining the array area using electron beam exposure; 5) Etch the excess area using inductively coupled plasma; 6) Dry transfer of two-dimensional layered palladium selenide nanosheets onto bismuth oxide selenide nanosheets; 7) Position the transferred PdSe nanosheets, define the array area using electron beam exposure, and etch the excess area using ICP again to form a van der Waals heterojunction channel layer array; 8) Position the van der Waals heterojunction channel layer array and define the source and drain electrode regions using electron beam exposure; 9) Using electron beam evaporation, Ti / Au metal stacks are evaporated on both sides of each van der Waals heterojunction channel layer in the array, and then peeled off to obtain source and drain electrodes, thereby completing the preparation of the heterojunction floating gate transistor array.

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