Nonvolatile ferroelectric tunnel junction memristor and preparation method thereof

Abstract

The invention discloses a nonvolatile ferroelectric tunnel junction memristor and a preparation method thereof. The nonvolatile ferroelectric tunnel junction memristive device comprises at least one tunnel junction structure, the tunnel junction structure comprises a first semiconductor electrode, a ferroelectric layer and a second semiconductor electrode which are stacked in sequence, the first semiconductor electrode and the second semiconductor electrode are made of different materials, and the ferroelectric layer is made of different materials. And the ferroelectric layer, the first semiconductor electrode and the second semiconductor electrode form an asymmetric heterojunction. The nonvolatile ferroelectric tunnel junction memristive device based on the AlScN ferroelectric material, provided by the invention, has very important significance for realizing on-chip integration of a storage and calculation integrated embedded system, and the memristive device with low energy consumption and high response speed can be realized only by changing different semiconductor electrodes in theoretical design.

Description

Technical Field

[0001] The present invention particularly relates to a nonvolatile ferroelectric tunnel junction memristor device and a preparation method thereof, and belongs to the technical field of semiconductor electronic devices. Background Art

[0002] At present, most traditional non-volatile ferroelectric tunnel junction memristor devices are realized by using the classic ferroelectric oxide system. Ultra-thin ferroelectric oxide is used as an insulator, and the insulator is used as a barrier layer and electrodes are sandwiched on both sides to form a tunnel junction device. The tunnel junction barrier can be regulated by selecting metal electrodes with different work functions, or a semiconductor is used as an electrode on one side. Such ferroelectric oxide tunnel junction memristor devices can achieve storage effects by using different electrodes and changing the polarization state to regulate the tunnel junction barrier, so that the current of the memristor device changes significantly under different voltage states.

[0003] This non-volatile ferroelectric tunnel junction memristor device using ferroelectric oxide as the tunnel junction material has some disadvantages in terms of cost and performance, mainly including the following points, because there are a large number of oxygen vacancies in the crystal structure of ferroelectric oxide and almost all ferroelectric oxides are not compatible with mainstream semiconductor manufacturing processes: (1) High cost: Since the ferroelectric tunnel junction layer in this non-volatile ferroelectric tunnel junction memristor device uses ferroelectric oxides, and almost all ferroelectric oxides are difficult to be compatible with mainstream semiconductor manufacturing processes, it is necessary to develop new supporting manufacturing processes, resulting in high manufacturing costs.

[0004] (2) Device stability: There are a large number of oxygen vacancies in ferroelectric oxides. The large number of oxygen vacancies at the interface between the ferroelectric material and the electrode will cause interface effects, thereby affecting the performance of the memristor device. Therefore, the device stability is relatively poor. Summary of the invention

[0005] The main purpose of the present invention is to provide a nonvolatile ferroelectric tunnel junction memristor device and a preparation method thereof, thereby overcoming the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: A first aspect of an embodiment of the present invention provides a non-volatile ferroelectric tunnel junction memristor device, comprising: at least one tunnel junction structure, the tunnel junction structure comprising a first semiconductor electrode, a ferroelectric layer, and a second semiconductor electrode stacked in sequence, wherein the first semiconductor electrode and the second semiconductor electrode are made of different materials, and the ferroelectric layer forms an asymmetric heterojunction with the first semiconductor electrode and the second semiconductor electrode.

[0007] A second aspect of an embodiment of the present invention provides a method for preparing a nonvolatile ferroelectric tunnel junction memristor device, comprising: A first semiconductor electrode, a ferroelectric layer, and a second semiconductor electrode are stacked in sequence to form at least one tunnel junction structure having a semiconductor-ferroelectric-semiconductor structure, wherein the first semiconductor electrode and the second semiconductor electrode are made of different materials, and the ferroelectric layer forms an asymmetric heterojunction with the first semiconductor electrode and the second semiconductor electrode.

[0008] Compared with the prior art, the advantages of the present invention include: A nonvolatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided by the present invention is of great significance for realizing on-chip integration of storage and computing integrated embedded systems. In theoretical design, only different semiconductor electrodes need to be changed to realize a memristor device with low energy consumption and fast response speed.

[0009] The present invention provides a nonvolatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material, which is Si-based and can be directly integrated with existing products in a monolithic manner, thereby accelerating the speed of industrialization and achieving functional integration.

[0010] The preparation process of a non-volatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided by the present invention is compatible with the current nitride semiconductor process, so the non-volatile ferroelectric tunnel junction memristor device can be integrated into different nitride electronic systems, simplifying the difficulty of nitride on-chip integration. For manufacturers, the difficulty of integration is reduced, the complexity of the process is reduced, and the production cost of the manufacturer is reduced. For consumers, low-power memristor devices and even low-power storage and computing integrated embedded systems can reduce the use cost while improving the performance of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1a , Figure 1b They are the phase change model of AlScN material in the polarization switching process and the hysteresis loop of AlScN material; Figure 2 It is a schematic structural diagram of a bidirectional nonvolatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided in a typical implementation case of the present invention; Figure 3 It is an energy band diagram of a non-volatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided in a typical implementation case of the present invention; Figure 4 It is a schematic diagram of the structure of a preparation process of a bidirectional non-volatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided in a typical implementation case of the present invention. DETAILED DESCRIPTION

[0012] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0013] The present invention aims to provide a Si-based III-V ferroelectric nitride non-volatile ferroelectric tunnel junction memristor device and its preparation process based on the three principles of ferroelectric polarization, tunnel junction and interface regulation. Compared with the ferroelectric oxide used in the traditional non-volatile ferroelectric tunnel junction memristor device, the present invention adopts the III-V ferroelectric nitride-AlScN compatible with the mainstream semiconductor manufacturing process, which greatly reduces the preparation cost and also reduces the complexity and cost of the integration process. At the same time, there is no oxygen vacancy in AlScN, and the nitrogen vacancy formation energy is high, so it has high stability and durability; and the non-volatile ferroelectric tunnel junction memristor device provided by the embodiment of the present invention is Si-based, and the device can be directly integrated with existing products for monolithic integration, accelerating the speed of industrialization, thereby achieving functional integration. In addition, in the present invention, a new structure tunnel junction of semiconductor-ferroelectric-semiconductor is adopted. In the tunnel junction of this structure, due to the asymmetric heterojunction formed by the asymmetric semiconductor layer and the ferroelectric layer, nonlinear conductivity is realized, which broadens the application scenarios of the device. At the same time, due to the improvement of the freedom of electrode selection, the diversity of application scenarios of memristive devices is significantly enhanced.

[0014] A first aspect of an embodiment of the present invention provides a non-volatile ferroelectric tunnel junction memristor device, comprising: at least one tunnel junction structure, the tunnel junction structure comprising a first semiconductor electrode, a ferroelectric layer, and a second semiconductor electrode stacked in sequence, wherein the first semiconductor electrode and the second semiconductor electrode are made of different materials, and the ferroelectric layer forms an asymmetric heterojunction with the first semiconductor electrode and the second semiconductor electrode.

[0015] Furthermore, the material of the first semiconductor electrode includes n-type silicon.

[0016] Furthermore, the material of the second semiconductor electrode includes oxide semiconductor.

[0017] Furthermore, the oxide semiconductor includes indium tin oxide.

[0018] Furthermore, the first semiconductor electrode and the second semiconductor electrode have different thicknesses.

[0019] Furthermore, the material of the ferroelectric layer includes AlScN ferroelectric material.

[0020] Furthermore, the thickness of the ferroelectric layer is 0.1 nm-10 nm.

[0021] In a more specific implementation, the nonvolatile ferroelectric tunnel junction memristor device includes: a plurality of the tunnel junction structures, and the plurality of the tunnel junction structures are arranged at intervals from each other.

[0022] A second aspect of an embodiment of the present invention provides a method for preparing a nonvolatile ferroelectric tunnel junction memristor device, comprising: A first semiconductor electrode, a ferroelectric layer, and a second semiconductor electrode are stacked in sequence to form at least one tunnel junction structure having a semiconductor-ferroelectric-semiconductor structure, wherein the first semiconductor electrode and the second semiconductor electrode are made of different materials, and the ferroelectric layer forms an asymmetric heterojunction with the first semiconductor electrode and the second semiconductor electrode.

[0023] Furthermore, the material of the first semiconductor electrode includes n-type silicon.

[0024] Furthermore, the material of the second semiconductor electrode includes oxide semiconductor.

[0025] Furthermore, the oxide semiconductor includes indium tin oxide.

[0026] Furthermore, the first semiconductor electrode and the second semiconductor electrode have different thicknesses.

[0027] Furthermore, the material of the ferroelectric layer includes AlScN ferroelectric material.

[0028] Furthermore, the thickness of the ferroelectric layer is 0.1 nm-10 nm.

[0029] In a more specific embodiment, the method for preparing the nonvolatile ferroelectric tunnel junction memristor device includes: manufacturing a plurality of tunnel junction structures having a semiconductor-ferroelectric-semiconductor structure, wherein the plurality of tunnel junction structures are arranged at intervals from each other.

[0030] Furthermore, the preparation method specifically includes: manufacturing a first semiconductor layer, a ferroelectric layer, and a second semiconductor layer stacked in sequence, and performing a patterning process on the formed stacked structure, thereby forming a plurality of tunnel junction structures spaced apart from each other.

[0031] The technical solution, its implementation process and principle will be further explained below in conjunction with the accompanying drawings and specific implementation cases.

[0032] A bidirectional non-volatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided in an embodiment of the present invention is a technology that utilizes the ferroelectric properties of AlScN ferroelectric material to regulate the tunnel junction to store information. It expresses the two states of '0' and '1' stored in the computer as different polarization states of the ferroelectric tunnel junction. By regulating the ferroelectric polarization direction of the ferroelectric tunnel junction, the barrier height and barrier height of the ferroelectric tunnel junction are changed, thereby realizing the control of the resistance state of the ferroelectric tunnel junction. Combined with the property of the ferroelectric material having residual polarization strength, it can not only realize data reading when power is on, but also can still save data after the device is powered off, thereby reducing energy consumption and forming a non-volatile ferroelectric tunnel junction memristor device with a high switching ratio.

[0033] Moreover, the quasi-continuous reversal characteristics of the domains in the ferroelectric barrier can realize continuous adjustment of the resistance, forming a memristor device with good memristive characteristics. The present invention combines the advantages of the ferroelectric properties of AlScN ferroelectric materials and the ferroelectric tunnel junction technology, utilizes the residual polarization characteristics of the ferroelectric material to realize non-volatile storage, thereby reducing energy consumption, utilizes the polarization reversal characteristics of the ferroelectric material to regulate the barrier of the ferroelectric tunnel junction, thereby obtaining a high switching ratio, utilizes the small size of the ferroelectric tunnel junction and the characteristics of the two-terminal device being easy to integrate in three dimensions to realize high-density storage, thereby increasing the storage capacity, and utilizes the quasi-continuous reversal characteristics of the domains in the ferroelectric barrier to realize continuous adjustment of the resistance, which can not only meet the needs of high-density and low-energy storage, but also meet the needs of components of a low-energy storage-computing integrated computing architecture.

[0034] The characteristic of AlScN ferroelectric material is that it has spontaneous polarization, and the direction of its spontaneous polarization can be reversed with the reversal of the external field polarity. When the external electric field is removed, its polarization direction can be maintained. The phase transition of AlScN ferroelectric material during polarization switching is as follows: Figure 1a As shown, the polarization of AlScN ferroelectric material and the applied electric field are shown as Figure 1b The nonlinear relationship shown is called a hysteresis loop. Figure 1bWhere Ec is the coercive field, which is the minimum electric field that causes the ferroelectric polarization to flip, and Pr is the remnant polarization, that is, the polarization strength maintained in the AlScN ferroelectric material when the electric field is zero. At the maximum applied electric field, the ferroelectric polarization reaches saturation, and the ratio of its remnant polarization to the saturation polarization is called the rectangularity of the hysteresis loop. Usually, the ferroelectric properties of a material only exist within a specific temperature range. As the temperature increases, the ferroelectric material will transform into a paraelectric state, and this transition point is called the Curie temperature. From the perspective of phase transition, the transition from ferroelectric to paraelectric can be divided into two types: order-disorder transition: In this transition, the atoms or atomic groups in the ferroelectric phase are orderly distributed; when the temperature rises, this order will be destroyed, resulting in the disappearance of ferroelectricity. Displacement-type ferroelectric phase transition: This phase transition is related to the asymmetry of the crystal structure. In the paraelectric phase, the crystal symmetry of the material is high, and the centers of positive and negative charges coincide. When the material enters the ferroelectric phase, the crystal symmetry decreases, the centers of positive and negative charges separate, and an electric dipole is formed. These electric dipoles are oriented and arranged in a certain area to form electric domains, also called ferroelectric domains.

[0035] Example 1 A nonvolatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material, wherein the structure of the nonvolatile ferroelectric tunnel junction memristor device is a semiconductor-ferroelectric-semiconductor structure, and the nonvolatile ferroelectric tunnel junction memristor device includes at least one tunnel junction structure, and the structure of each tunnel junction structure is as follows: Figure 2 As shown, the tunnel junction structure includes an n-type Si electrode, an AlScN ferroelectric layer and an ITO (indium tin oxide) electrode stacked in sequence. This asymmetric semiconductor electrode structure forms different heterojunctions on both sides of the AlScN ferroelectric layer. When the ground electrode changes, the asymmetric semiconductor electrode and the AlScN ferroelectric layer cause the asymmetric ferroelectric barrier to change, thereby realizing a bidirectional storage function and doubling the storage density.

[0036] Specifically, the energy band diagram of a nonvolatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided by an embodiment of the present invention is as follows: Figure 3 As shown, the asymmetric heterojunction formed by the asymmetric semiconductor electrode and the AlScN ferroelectric layer realizes nonlinear conductivity, broadens the application scenarios of the device, and due to the improvement of the freedom of electrode selection, the diversity of application scenarios of memristive devices is significantly enhanced.

[0037] Of course, different semiconductor upper and lower electrodes can be selected according to the integration needs and application requirements. For example, when using oxide semiconductor ITO as the upper electrode, it can be used in optical systems due to its optical properties, and is expected to achieve key applications such as optical storage and computing integration and even green new display. It should be noted that the non-volatile ferroelectric tunnel junction memristor device can also be integrated with other devices on the same substrate.

[0038] Example 2 A method for preparing a non-volatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material. The preparation mainly uses electron beam evaporation coating equipment, MA6 double-sided alignment lithography machine, pulse laser deposition equipment (PLD) and other instruments. The main process steps are: substrate preparation, pulse laser deposition equipment to grow AlScN ferroelectric film, glue coating, photolithography, development, DC magnetron sputtering equipment sputtering, wet etching, NLD etching, the specific process flow is as follows: Figure 4 As shown, and the preparation method specifically includes: 1) Substrate preparation: The substrate used in the embodiment of the present invention is a Si substrate with an orientation of 100, a thickness of 0.5 mm, and a length and width of 10 mm×10 mm.

[0039] Since the metal film is grown on the substrate surface by electron beam evaporation, the roughness and smoothness of the substrate surface directly determine the uniformity and smoothness of the subsequent coating film. If the surface is not clean, it may cause the film to fall off during subsequent processes or cleaning.

[0040] In view of the above reasons, the steps for cleaning the substrate are usually as follows: first, take a glass beaker and a polytetrafluoroethylene basket of appropriate capacity, rinse them repeatedly with deionized water, and use a nitrogen gun to blow dry the excess water on the inner wall of the beaker and the basket; then take out the sample and put it in the basket, add acetone solution to the beaker, immerse the basket and the sample in the solution, and then put it into an ultrasonic cleaner for cleaning for 5 minutes, and repeat this operation twice; then replace the isopropanol solution to clean the substrate for 5 minutes, repeat twice, and the other operations are the same as the previous step; finally, rinse the substrate repeatedly with deionized water, blow it dry with nitrogen, and put it in the sample box.

[0041] 2) AlScN ferroelectric thin films were grown on Si substrates using a pulsed laser deposition system (PLD).

[0042] Specifically, a pulsed laser deposition system is used to grow a 5 nm thick AlScN ferroelectric film at a growth rate of 0.3 nm / min, a growth time of 16 min, an operating temperature of 400 °C, a laser frequency of 1 Hz, and a laser energy of 300 mJ.

[0043] 3) ITO electrodes were fabricated on AlScN ferroelectric films by magnetron sputtering.

[0044] Specifically, a DC magnetron sputtering system is used to deposit an ITO electrode, the thickness of which is 40 nm, which serves as the upper electrode of the device.

[0045] 4) Photolithography and development.

[0046] Spray positive photoresist AZ5214 on the ITO electrode and use the MA6 double-sided alignment lithography machine (in fact, any type of lithography machine can be used, depending on the size of the unit device) to make the required upper electrode size. The specific lithography parameters are as follows: Surface pretreatment: apply adhesive (HMDS); use AZ5214 for coating, forward rotation at 600 rpm for 5 s, and backward rotation at 3000 rpm for 30 s; Hard mode, 0.8 s; use 3038 for development, 45 s (start shaking after 10 s), fix with DI water for 1 min, and blow dry with nitrogen gun; use 5x and 20x objective lenses for microscopy.

[0047] 5) Wet etching.

[0048] Using photoresist as a mask, dilute hydrochloric acid is used to wet-etch ITO to remove excess ITO electrodes.

[0049] 6) NLD etching.

[0050] After the previous step, the preparation of the upper electrode of the ferroelectric tunnel junction memristor device has been completed. Next, etching downwards will be performed to prepare an independent non-volatile ferroelectric tunnel junction memristor device structural unit.

[0051] Using photoresist as a mask, only the NLD etcher is needed to etch away the 5 nm AlScN ferroelectric film in the gap between the upper electrode and ITO at one time, and the etching time is set to 30 s.

[0052] 7) Remove residual photoresist.

[0053] After etching, the sample is immersed in an acetone solution to completely strip the photoresist, thereby obtaining the required unit nonvolatile ferroelectric tunnel junction memristor device.

[0054] 8) Clean and prepare samples.

[0055] Finally, rinse with isopropanol and deionized water several times respectively, blow dry the sample with nitrogen gas to complete the preparation.

[0056] Different from the traditional non-volatile ferroelectric tunnel junction memristor device, the present invention uses ferroelectric oxide - AlScN material as the material of the ferroelectric tunnel layer, which can be obtained by being compatible with the mainstream semiconductor manufacturing process, greatly reducing the preparation cost, and also reducing the complexity and cost of the integration process. At the same time, there are no oxygen vacancies in the ferroelectric nitride - AlScN material, and the nitrogen vacancy formation energy is relatively high, so it has higher stability and durability.

[0057] The nonvolatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided in the embodiment of the present invention is Si-based, and the device is directly integrated with existing products in a monolithic manner, which speeds up the industrialization process and thus realizes functional integration.

[0058] The nonvolatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided in the embodiment of the present invention uses a novel structure of semiconductor-ferroelectric-semiconductor, and realizes nonlinear conductivity through an asymmetric heterojunction formed by an asymmetric semiconductor layer and a ferroelectric layer, thereby broadening the application scenarios of the device.

[0059] The non-volatile ferroelectric tunnel junction memristor device based on AlScN ferroelectric material provided in the embodiment of the present invention has a dual semiconductor electrode structure. In theory, different application requirements and integration needs can be met by selecting different semiconductor electrodes (at the same time, because it is a III-V group ferroelectric nitride, it is compatible with the current mainstream semiconductor process, so the difficulty of integration can be reduced). For example, when a transparent semiconductor material such as ITO is used as the upper electrode, it can be used in optical systems due to the optical properties of ITO, and is expected to realize key applications such as new light field control, optoelectronic hybrid storage and computing, and new displays.

[0060] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A nonvolatile ferroelectric tunnel junction memristor device, characterized in that: include: At least one tunnel junction structure, the tunnel junction structure comprising a first semiconductor electrode, a ferroelectric layer and a second semiconductor electrode stacked in sequence, wherein the first semiconductor electrode and the second semiconductor electrode are made of different materials, and the ferroelectric layer forms an asymmetric heterojunction with the first semiconductor electrode and the second semiconductor electrode.

2. The nonvolatile ferroelectric tunnel junction memristor device according to claim 1, characterized in that: The material of the first semiconductor electrode includes n-type silicon; And / or, the material of the second semiconductor electrode includes oxide semiconductor; Preferably, the oxide semiconductor includes indium tin oxide.

3. The nonvolatile ferroelectric tunnel junction memristor device according to claim 1, characterized in that: The first semiconductor electrode and the second semiconductor electrode have different thicknesses.

4. The nonvolatile ferroelectric tunnel junction memristor device according to claim 1, characterized in that: The material of the ferroelectric layer includes AlScN ferroelectric material; Preferably, the thickness of the ferroelectric layer is 0.1 nm-10 nm.

5. The nonvolatile ferroelectric tunnel junction memristor device according to claim 1, characterized in that: include: A plurality of the tunnel junction structures are arranged spaced apart from each other.

6. A method for preparing a nonvolatile ferroelectric tunnel junction memristor device, characterized in that: include: A first semiconductor electrode, a ferroelectric layer, and a second semiconductor electrode are stacked in sequence to form at least one tunnel junction structure having a semiconductor-ferroelectric-semiconductor structure, wherein the first semiconductor electrode and the second semiconductor electrode are made of different materials, and the ferroelectric layer forms an asymmetric heterojunction with the first semiconductor electrode and the second semiconductor electrode.

7. The method for preparing the nonvolatile ferroelectric tunnel junction memristor device according to claim 6, characterized in that: The material of the first semiconductor electrode includes n-type silicon; and / or the material of the second semiconductor electrode includes oxide semiconductor; Preferably, the oxide semiconductor includes indium tin oxide.

8. The method for preparing the nonvolatile ferroelectric tunnel junction memristor device according to claim 6, characterized in that: The first semiconductor electrode and the second semiconductor electrode have different thicknesses.

9. The method for preparing the nonvolatile ferroelectric tunnel junction memristor device according to claim 6, characterized in that: The material of the ferroelectric layer includes AlScN ferroelectric material; Preferably, the thickness of the ferroelectric layer is 0.1 nm-10 nm.

10. The method for preparing the nonvolatile ferroelectric tunnel junction memristor device according to claim 6, characterized in that: include: Manufacturing a plurality of tunnel junction structures having a semiconductor-ferroelectric-semiconductor structure, wherein the plurality of tunnel junction structures are arranged spaced apart from each other; Preferably, the preparation method specifically comprises: manufacturing a first semiconductor layer, a ferroelectric layer, and a second semiconductor layer which are stacked in sequence, and performing a patterning process on the formed stacked structure, thereby forming a plurality of tunnel junction structures which are spaced apart from each other.

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