阅读说明：本技术 一种二维材料模拟电路及其制备方法和应用 (Two-dimensional material analog circuit and preparation method and application thereof ) 是由 叶镭 彭追日 童磊 李政 缪向水 于 2020-12-28 设计创作，主要内容包括：本发明属于二维半导体电路领域,具体涉及一种二维材料模拟电路及其制备方法和应用,包括：衬底,双极可调性二维材料,铁电衬底材料薄膜,以及顶部、底部金属电极；二维材料和铁电衬底材料薄膜层叠设置；二维材料的表面设置有顶部金属电极；铁电衬底材料薄膜的表面设置有底部金属电极；铁电衬底材料薄膜用于在不同极化状态下对二维材料中的沟道载流子类型和浓度进行调制；其中铁电衬底材料薄膜的极化通过在顶部和底部金属电极之间外接脉冲电场实现。本发明对铁电衬底材料极化之后撤掉电场,仅利用铁电衬底材料极化状态对二维材料沟道载流子调控,大幅降低功耗；同时通过设置铁电体不同极化状态调控二维材料沟道,具备可重构电路存储和计算能力。(The invention belongs to the field of two-dimensional semiconductor circuits, and particularly relates to a two-dimensional material analog circuit, a preparation method and application thereof, wherein the preparation method comprises the following steps: the device comprises a substrate, a bipolar tunable two-dimensional material, a ferroelectric substrate material film and top and bottom metal electrodes; two-dimensional material and ferroelectric substrate material film are stacked; a top metal electrode is arranged on the surface of the two-dimensional material; a bottom metal electrode is arranged on the surface of the ferroelectric substrate material film; the ferroelectric substrate material film is used for modulating the type and the concentration of channel carrier in the two-dimensional material under different polarization states; wherein the polarization of the thin film of ferroelectric substrate material is achieved by externally connecting a pulsed electric field between the top and bottom metal electrodes. The invention removes the electric field after polarizing the ferroelectric substrate material, and adjusts and controls the two-dimensional material channel current carrier only by using the polarization state of the ferroelectric substrate material, thereby greatly reducing the power consumption; meanwhile, the two-dimensional material channel is regulated and controlled by setting different polarization states of the ferroelectric, and the reconfigurable circuit has the storage and calculation capabilities.)

1. A two-dimensional material simulation circuit, comprising: a substrate, a bipolar tunable two-dimensional material, a ferroelectric substrate material film, a top metal electrode, and a bottom metal electrode;

the bipolar tunable two-dimensional material and the ferroelectric substrate material thin film are stacked; a top metal electrode is arranged on the surface of the bipolar adjustable two-dimensional material; a bottom metal electrode is arranged on the surface of the ferroelectric substrate material film;

the ferroelectric substrate material film is used for modulating the type and the concentration of channel carrier in the two-dimensional material under different polarization states; and the polarization of the ferroelectric substrate material film is realized by externally connecting a pulse electric field between the top metal electrode and the bottom metal electrode.

2. A two-dimensional material simulation circuit according to claim 1, wherein the top metal electrode is provided in plurality and the bottom metal electrode is provided in plurality according to the actual required circuit pattern, and the circuit pattern is realized by selecting different combinations of the top metal electrode and the bottom metal electrode and the direction and intensity of the pulse electric field connected between the different combinations.

3. A two-dimensional material modeling circuit as claimed in claim 1 or claim 2 wherein said bipolar tunable two-dimensional material is tungsten selenide.

4. A two-dimensional material simulation circuit according to claim 1 or 2, wherein the thin film of ferroelectric substrate material is a thin film of lithium niobate single crystal.

5. A method for fabricating a two-dimensional material simulation circuit according to any of claims 1 to 4, comprising:

obtaining a substrate, wherein the substrate is obtained by evaporating a bottom metal electrode on a silicon wafer and covering a layer of ferroelectric substrate material film on the bottom metal electrode;

covering a layer of bipolar adjustable two-dimensional material on the upper surface of the ferroelectric substrate material film;

and removing part of the two-dimensional material according to the actually required circuit pattern, and preparing a top metal electrode on the upper surface of the remained part of the two-dimensional material.

6. A method according to claim 3, wherein the covering of the upper surface of the thin film of ferroelectric substrate material with a layer of bipolar tunable two-dimensional material is implemented by:

and spin-coating PMMA on a silicon wafer attached with the bipolar adjustable two-dimensional material, and transferring the bipolar adjustable two-dimensional material to the upper surface of the ferroelectric substrate material film through wet transfer.

7. A method for manufacturing a two-dimensional material simulation circuit according to claim 3, wherein the removing of the two-dimensional material according to the actual required circuit pattern is implemented by:

spin-coating a photoresist on the upper surface of the two-dimensional material, and removing part of the photoresist by using photoetching or electron beam exposure according to an actually required circuit pattern, and reserving part of the photoresist in a required area;

and removing the exposed part of the two-dimensional material film by using oxygen plasma, and cleaning and removing the residual photoresist by using acetone.

8. The method for manufacturing a two-dimensional material analog circuit according to claim 3, wherein the top metal electrode is manufactured by:

spin-coating photoresist, etching electrode pattern by photoetching or electron beam exposure, and manufacturing a top metal electrode by electron beam evaporation and evaporation.

9. Use of a two-dimensional material simulation circuit according to any of claims 1 to 4, wherein the two-dimensional material simulation circuit having different functions is used to form an analog integrated circuit.

Technical Field

The invention belongs to the field of two-dimensional semiconductor circuits, and particularly relates to a two-dimensional material analog circuit and a preparation method and application thereof.

Background

The traditional analog circuit is mainly based on a silicon-based transistor device, and has better performances in threshold voltage, on-off ratio and gain, but with the further reduction of the size of the device, the short channel effect of the traditional silicon-based semiconductor device can greatly reduce the performance of the device, and the moore's law reaches the bottleneck. The search for new material systems and corresponding device structures to overcome the above-mentioned bottlenecks is the current research direction. In a novel material system, the two-dimensional material with the atomic layer thickness has multiple unique excellent properties, including compatibility with the existing semiconductor process, miniaturization, higher integration level, adjustability, low power consumption and the like, and is expected to replace the traditional silicon-based semiconductor material to continue the Moore's law.

Although the split gate structure defined by lithography configures a local potential capable of modulating the carrier type of the two-dimensional material, the large scale fabrication of the split gate structure requires a complicated circuit design and fabrication process. How to realize simple device structure and excellent device performance is worth further research.

Disclosure of Invention

The invention provides a two-dimensional material analog circuit and a preparation method and application thereof, which are used for solving the technical problems of complex circuit and complex process and limited application of the existing two-dimensional material p-n junction device and a circuit formed by the same due to the adoption of a separated gate structure.

The technical scheme for solving the technical problems is as follows: a two-dimensional material simulation circuit, comprising: a substrate, a bipolar tunable two-dimensional material, a ferroelectric substrate material film, a top metal electrode, and a bottom metal electrode;

the bipolar tunable two-dimensional material and the ferroelectric substrate material thin film are stacked; a top metal electrode is arranged on the surface of the bipolar adjustable two-dimensional material; a bottom metal electrode is arranged on the surface of the ferroelectric substrate material film;

the ferroelectric substrate material film is used for modulating the type and the concentration of channel carrier in the two-dimensional material under different polarization states; and the polarization of the ferroelectric substrate material film is realized by externally connecting a pulse electric field between the top metal electrode and the bottom metal electrode.

The invention has the beneficial effects that: compared with a split gate structure, the invention adopts the method that the ferroelectric substrate material is externally connected with the pulse electric field to be polarized, then the pulse electric field is removed, and the current carrier of the two-dimensional material channel is regulated and controlled only by utilizing the polarization state of the ferroelectric substrate material, thereby greatly reducing the power consumption; meanwhile, the device structure combines the ferroelectric and the two-dimensional semiconductor material, regulates and controls the channel of the two-dimensional material by setting different polarization states of the ferroelectric, has the storage and calculation capabilities of a reconfigurable circuit, is a good platform for realizing the multifunctional combination of the two-dimensional material, and can be used for expanding the application of the two-dimensional material in the field of integrated circuits.

On the basis of the technical scheme, the invention can be further improved as follows.

Furthermore, according to the actually required circuit pattern, a plurality of top metal electrodes are arranged, a plurality of bottom metal electrodes are arranged, and the circuit pattern is realized by selecting different combinations of the top metal electrodes and the bottom metal electrodes and the directions and the intensities of the pulse electric fields connected between the different combinations.

The invention has the further beneficial effects that: according to the actually required circuit pattern, a plurality of top metal electrodes and bottom metal electrodes are designed at different positions, and then the polarization of the ferroelectric substrate is subjected to patterning design by adjusting the direction of an external electric field in different areas of the ferroelectric substrate, so that the channel type of a two-dimensional material which is heterogeneously integrated with the ferroelectric substrate is modulated, and the channel type is cascaded to form an analog circuit with a specific function, and the expandability is high.

Further, the bipolar tunable two-dimensional material is tungsten selenide.

The invention has the further beneficial effects that: compared with other two-dimensional materials, the tungsten selenide has better bipolar adjustability and the switching ratio can reach 10⁴The magnitude of the current, the carrier mobility is high, the electrical property is good, the stability is high, and the surface of the material has no dangling bond and is beneficial to heterogeneous integration.

Further, the ferroelectric substrate material film is a lithium niobate single crystal film.

The invention has the further beneficial effects that: compared with other ferroelectric materials, the ferroelectric residual polarization intensity of the lithium niobate is higher (reaching 71 mu C cm)^-2) The method has the advantages of longer retention time of residual polarization, higher stability, better insulativity, mature industrial production technology and easy acquisition of large-area high-quality lithium niobate films.

The invention also provides a preparation method of the two-dimensional material analog circuit, which comprises the following steps:

obtaining a substrate, wherein the substrate is obtained by evaporating a bottom metal electrode on a silicon wafer and covering a layer of ferroelectric substrate material film on the bottom metal electrode;

covering a layer of bipolar adjustable two-dimensional material on the upper surface of the ferroelectric substrate material film;

and removing part of the two-dimensional material according to the actually required circuit pattern, and preparing a top metal electrode on the upper surface of the remained part of the two-dimensional material.

The invention has the beneficial effects that: the preparation method has the advantages of simple process, high repeatability, compatibility with the traditional silicon-based semiconductor CMOS process, realization of industrial mass production and potential of integrated preparation.

Further, the implementation manner of covering a layer of bipolar adjustable two-dimensional material on the upper surface of the ferroelectric substrate material film is as follows:

and spin-coating PMMA on a silicon wafer attached with the bipolar adjustable two-dimensional material, and transferring the bipolar adjustable two-dimensional material to the upper surface of the ferroelectric substrate material film through wet transfer.

Further, the implementation manner of removing part of the two-dimensional material according to the actually required circuit pattern is as follows:

spin-coating a photoresist on the upper surface of the two-dimensional material, and removing part of the photoresist by using photoetching or electron beam exposure according to an actually required circuit pattern, and reserving part of the photoresist in a required area;

and removing the exposed part of the two-dimensional material film by using oxygen plasma, and cleaning and removing the residual photoresist by using acetone.

Further, the implementation manner of preparing the top metal electrode is as follows:

spin-coating photoresist, etching electrode pattern by photoetching or electron beam exposure, and manufacturing a top metal electrode by electron beam evaporation and evaporation.

The invention also provides application of the two-dimensional material analog circuit, which adopts the two-dimensional material analog circuit with different functions to form an analog integrated circuit.

Drawings

Fig. 1 is a schematic structural diagram of a two-dimensional material simulation circuit according to an embodiment of the present invention;

FIG. 2 is a graph of a ferroelectric substrate modulated rectifying p-n diode structure and test results provided in accordance with an embodiment of the present invention;

FIG. 3 is a diagram showing the structure of a bridge rectifier circuit modulated by a ferroelectric substrate, an equivalent circuit and test results thereof according to an embodiment of the present invention;

FIG. 4 is a diagram of a ferroelectric substrate modulated neuromorphic synapse device structure in accordance with embodiments of the present invention;

FIG. 5 is a three-dimensional integrated circuit diagram of a two-dimensional material simulation circuit according to an embodiment of the present invention;

fig. 6 is a flowchart of a method for manufacturing a two-dimensional material simulation circuit according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Example one

A two-dimensional material modeling circuit, as shown in fig. 1, comprising: a substrate, a bipolar tunable two-dimensional material, a thin film of ferroelectric substrate material, a top metal electrode, and a bottom metal electrode.

The bipolar adjustable two-dimensional material and the ferroelectric substrate material thin film are stacked; a top metal electrode is arranged on the surface of the bipolar adjustable two-dimensional material; a bottom metal electrode is arranged on the surface of the ferroelectric substrate material film; the ferroelectric substrate material film is used for modulating the type and the concentration of channel carrier in the two-dimensional material under different polarization states; the polarization of the ferroelectric substrate material film is realized by externally connecting a pulse electric field between the top metal electrode and the bottom metal electrode.

According to the theory, the doping of the two-dimensional material is induced through the near-neighbor polarization effect of the ferroelectric material, the difficulty of a split gate structure can be overcome, the reconfigurable modulation of the carrier type of the channel of the two-dimensional material is realized without continuous gate voltage holding, the feasibility is provided for the next generation of analog circuits based on the two-dimensional material, and the method has important significance. The ferroelectric substrate material, particularly lithium niobate, is an industrially synthesized ferroelectric material which is relatively easy to obtain and has relatively stable polarization properties, and can be polarized by applying an external electric field, and a huge internal electric field can still be maintained after the electric field is removed. Bipolar two-dimensional materials (e.g. WSe)₂) The surface of the material has no dangling bonds, is beneficial to heterogeneous integration, can be adjusted in carrier type and concentration by using an electric field and has the value of 10⁴On-off ratio of order of magnitude. The ferroelectric material is combined with the two-dimensional material, and the channel conductivity type of the two-dimensional material is modulated by utilizing the spontaneous polarization and the residual polarization electric field of the ferroelectric material. This embodiment combines a ferroelectric substrate with a two-dimensional material, through an external powerAnd the field carries out patterning design on the circuit structure, so that a two-dimensional material analog circuit based on ferroelectric substrate regulation is realized.

Compared with a split gate structure, the scheme adopts the mode that the ferroelectric substrate material is externally connected with a pulse electric field to be polarized, then the pulse electric field is removed, and the current carriers of the two-dimensional material channel are regulated and controlled only by utilizing the polarization state of the ferroelectric substrate material, so that the power consumption can be greatly reduced; meanwhile, the device structure combines the ferroelectric and the two-dimensional semiconductor material, regulates and controls the channel of the two-dimensional material by setting different polarization states of the ferroelectric, has the storage and calculation capabilities of a reconfigurable circuit, is a good platform for realizing the multifunctional combination of the two-dimensional material, and can be used for expanding the application of the two-dimensional material in the field of integrated circuits.

Preferably, the top metal electrode is provided in plurality and the bottom metal electrode is provided in plurality according to an actually required circuit pattern, and the circuit pattern is realized by selecting different combinations of the top metal electrode and the bottom metal electrode and the directions and intensities of the pulse electric fields connected between the different combinations.

According to the actually required circuit pattern, a plurality of top metal electrodes and bottom metal electrodes are designed at different positions, and then the polarization of the ferroelectric substrate is subjected to patterning design by adjusting the direction of an external electric field in different areas of the ferroelectric substrate, so that the channel type of a two-dimensional material which is heterogeneously integrated with the ferroelectric substrate is modulated, and the channel type is cascaded to form an analog circuit with a specific function, and the expandability is high.

For example, the device structure is: the thin film solar cell comprises a substrate, a bottom metal electrode, lithium niobate, tungsten selenide and a top metal electrode (from bottom to top), wherein the substrate is a silicon substrate, the bottom metal electrode is Au, the lithium niobate is a single crystal thin film with the thickness of 300nm (the thickness of a lithium niobate ferroelectric thin film determines the size of a coercive field, the coercive field is large and the polarization state is difficult to adjust due to too thick film, the coercive field is small and easy to be influenced by an electric field in a channel and the polarization state is difficult to maintain due to too thin film), the thickness of the tungsten selenide is about 7-8 layers (6-7nm, and the tungsten selenide which is too thin or too thick is in a unipolar conductive state), and the top metal electrode is Cr (20nm)/Au (100nm) (only the electrode needs to be in good contact with a tungsten selenide channel material).

In the scheme of the embodiment, the polarization state of the lithium niobate is designed in a patterning manner, so that a reconfigurable circuit structure can be realized, and an analog differential amplification circuit, an operational amplifier, a neuromorphic synapse device, a three-dimensional integrated circuit and the like based on a two-dimensional material can be realized. The analog integrated circuit can be formed by adopting two-dimensional material analog circuits with different functions. The following examples are now given:

example 1:

the present example provides a ferroelectric substrate modulated rectifying p-n diode with a device structure and test results as shown in fig. 2.

Wherein, X₁And X₂Is a top Cr/Au metal electrode, D₁And D₂Representing the two polarization states of the lithium niobate region in which it is located. The upwardly polarized regions induce and accumulate electrons in the tungsten selenide channel and the downwardly polarized regions induce and accumulate holes in the tungsten selenide channel, forming a two-dimensional material tungsten selenide p-n junction therebetween. For the test results, the left graph shows that the p-n junctions are reversely connected and a sinusoidal voltage V is input₁₂(shown by the solid curve), output current I_D(dotted curve) only reverse current is output, and forward current is cut off; the right graph shows that the p-n junction is communicated in the forward direction and a sine voltage V is input₁₂(shown by the solid curve), output current I_D(the dashed curve) only outputs forward current, and the reverse current is cut off, so that the functional device has rectification capability and can be used as a rectifier diode.

Example 2:

the present example provides a bridge rectifier circuit modulated by a ferroelectric substrate, the device structure, equivalent circuit and test results thereof are shown in fig. 3.

The device structure is represented by a top view, X in the figure₁-X₄Is a top Cr/Au metal electrode, a bottom Au electrode is used for modulating the polarization state of lithium niobate (not shown in the figure), and X is enabled to be periodically modulated by polarization₁And X₂、X₃And X₂、X₄And X₃、X₄And X₂P-n junctions D are formed between the tungsten selenides below₁、D₂、D₃、D₄At X₁、X₃An input voltage V is applied across_iAt X₂、X₄Two ends generate output current I_o，R₁The load resistor is used to test the current. The test result is that a sinusoidal voltage signal (represented by a solid curve) is input, a full positive current signal (represented by a dashed curve) is output, and four diodes which are connected end to end in sequence form a bridge rectifier circuit, so that the amplitude of the input alternating voltage can be extracted. The feasibility of the device structure is further proved by the circuit realization formed by the connection of a plurality of diodes.

Example 3:

the present example provides a ferroelectric substrate modulated neuromorphic synapse device, the device structure being as shown in FIG. 4.

The device comprises three ferroelectric polarization areas, and the left ferroelectric domain and the right ferroelectric domain apply the same pulse voltage to generate a fixed polarization state, so that the tungsten selenide on the ferroelectric polarization areas has a fixed conductive state. The polarization direction and the intensity of the middle ferroelectric domain are modulated by applying a voltage pulse signal, so that the type of a conductive carrier of the tungsten selenide on the middle ferroelectric domain can be changed, potential barriers between the middle ferroelectric domain and the tungsten selenide on the left side and the right side are adjusted, and the conductance value of a conductive channel is adjustable. The applied voltage pulse signal simulates a spike pulse signal for stimulating synapses, and the action of the voltage pulse signal on a conducting channel and source-drain current of the conducting channel simulates the weight modulation effect of the nerve synapses, so that the function of a nerve morphology synapse device can be realized.

Example 4:

the present example provides a three-dimensional integration scheme for a two-dimensional material analog circuit, the device structure is shown in fig. 5.

By means of the capability of easy integration of two-dimensional materials, a plurality of layers of two-dimensional material analog circuits can be vertically stacked to realize three-dimensional integration application with higher device density. Each layer of the storage layer and the peripheral circuit layer is composed of an electrode circuit interconnection line, a two-dimensional channel material, a ferroelectric substrate and a silicon dioxide substrate with a bottom electrode from top to bottom. The storage layer adopts a cross bar array structure, a storage unit is realized by using two-dimensional materials of three ferroelectric domain regions, the same fixed polarization is applied to the left domain and the right domain, and the polarization direction and the polarization strength of the middle ferroelectric domain determine the ferroelectricThe conductance value of the two-dimensional channel material on the surface of the substrate. In the figure, W_i,jThe stored value is expressed by applying a pulse voltage to the intermediate ferroelectric domain to write the stored value, and passing V_DDAnd V_SSA particular memory cell is selected to read the stored value. Non-volatile storage of current data can be achieved by utilizing the retention capability of the ferroelectric substrate remnant polarization. The peripheral circuit layer uses a comparator, a power amplifier and the like to carry out analog calculation, and the required circuit structure is realized through a two-dimensional material regulated and controlled by a reconfigurable ferroelectric substrate, so that the preset circuit function can be realized more conveniently, efficiently and with low consumption. The vertically stacked three-dimensional structure can effectively increase the density of devices, reduce the interconnection distance and realize low-power-consumption near memory or memory calculation.

Example two

A method for fabricating a two-dimensional material analog circuit as described in embodiment one, comprising:

obtaining a substrate, wherein the substrate is obtained by evaporating a bottom metal electrode on a silicon wafer and covering a layer of ferroelectric substrate material film on the bottom metal electrode;

covering a layer of bipolar adjustable two-dimensional material on the upper surface of the ferroelectric substrate material film;

and removing part of the two-dimensional material according to the actually required circuit pattern, and preparing a top metal electrode on the upper surface of the remained part of the two-dimensional material.

The preparation method is based on a bottom-up method, and takes tungsten selenide as a two-dimensional material, lithium niobate as a ferroelectric material, Cr/Au as a top metal electrode and Au as a bottom metal electrode as an example, as shown in FIG. 6.

Substrate acquisition: evaporating a bottom metal electrode on a silicon substrate, and growing a lithium niobate single crystal film on the bottom metal electrode;

material transfer: spin-coating PMMA on a silicon wafer with few layers of tungsten selenide by using wet transfer, heating and curing, placing the silicon wafer in a NaOH solution for etching silicon, carefully cleaning the silicon wafer with deionized water after etching is finished, placing the substrate in the deionized water for fishing out the tungsten selenide, placing the substrate in an acetone solution for soaking to remove the PMMA, and drying the substrate with nitrogen, thereby transferring the bulk and few layers of tungsten selenide materials onto lithium niobate;

preparing a circuit: spin-coating a photoresist, using photoetching or electron beam Exposure (EBL) according to a required circuit pattern, reserving the required tungsten selenide, removing the unnecessary tungsten selenide by using oxygen plasma after exposure and development, cleaning the photoresist by using acetone, then spin-coating the photoresist, etching an electrode pattern by using the photoetching/EBL, and manufacturing a top metal electrode by using Electron Beam Evaporation (EBE) evaporation;

pattern polarization: and applying a pulse voltage between the top gate and the bottom gate, and patterning the polarization region according to the designed channel type.

Wherein the acquisition of the substrate can be customized by the relevant company; after PMMA is spin-coated, the heating and curing time is as long as possible, so that the PMMA is fully cured, and the conformal coverage of the PMMA on the tungsten selenide material is ensured; when the tungsten selenide is fished, the operation should be careful, the material is prevented from turning over in the solution, and the transferred tungsten selenide is ensured to have no folds as much as possible; the adopted photoetching technology is compatible with the traditional CMOS process, and the proper photoresist spin-coating parameters, photoetching parameters and electron beam evaporation metal are required to be selected. After the circuit is prepared, a suitable pulse voltage amplitude and duration is applied that is sufficient to modulate the lithium niobate polarization state.

The preparation method has the advantages of simple process, compatibility with a CMOS (complementary metal oxide semiconductor) process, high repeatability and the like.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.