A flexible hafnium oxide-based ferroelectric racetrack memory array and method of fabrication thereof

Abstract

The application discloses a flexible hafnium oxide-based ferroelectric memcapacitor integrated array and a preparation method thereof. The flexible hafnium oxide-based ferroelectric memcapacitor integrated array comprises, from top to bottom, a patterned top electrode, a patterned ferroelectric layer, a patterned bottom electrode and a flexible mica substrate. The ferroelectric layer is a hafnium oxide ferroelectric film doped with zirconium. The bottom electrode and the top electrode are both metal tungsten prepared by electron beam evaporation. The ferroelectric memcapacitor is integrated on the flexible mica substrate, so that the ferroelectric memcapacitor can withstand deformation such as bending and stretching and still has good ferroelectric performance and memcapacitor characteristics under different bending conditions, and is suitable for flexible electronic applications.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic materials, and in particular to a flexible hafnium oxide-based ferroelectric memristor integrated array and a preparation method thereof. Background Art

[0002] With the continuous advancement of the Internet of Things, artificial intelligence, and big data technologies, flexible wearable electronic devices, thanks to their lightness, flexibility, and ease of mass production, have been widely used in fields such as health monitoring and human-computer interaction, demonstrating broad market potential. At the same time, the rapid increase in data volume has placed greater demands on flexible information storage devices.

[0003] Memcapacitors operate on a similar principle to memristors, but their foundation is a capacitance mechanism. In the field of neuromorphic computing, non-volatile synaptic devices constructed using memcapacitors primarily use adjustable small-signal capacitance values ​​instead of conductance as synaptic weights, and perform computations based on charge rather than conductance. Memcapacitors exhibit multi-level variable capacitance controlled by an external electric field and retain their data state even after power failure. Compared to memristors, memcapacitor-based neuromorphic computing systems primarily rely on transient current and charge transfer, resulting in near-zero static power consumption. This enables selector-free access, reduces interconnect voltage losses, and effectively avoids crosstalk currents. Furthermore, their small-signal readout reduces read disturb and exhibits unique advantages in 3D stacked device structures. Therefore, memcapacitors hold great potential for promoting the development of neural networks that mimic brain functions with high parallel processing capabilities and low energy consumption, as well as for realizing low-power neuromorphic computing applications.

[0004] The ferroelectric memcapacitor arrays currently integrated are all on rigid substrates. For flexible wearable electronic devices that require flexibility and are developing rapidly, memcapacitor arrays integrated on flexible substrates have important research significance. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a flexible hafnium oxide-based ferroelectric memcapacitor integrated array with low energy consumption, high storage density and excellent bending resistance, and provides a preparation method of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array with simple process.

[0006] The technical solution of the present invention to solve the above technical problems is: a flexible hafnium oxide-based ferroelectric memristor integrated array, including a patterned top electrode, a patterned ferroelectric layer, a patterned bottom electrode, and a flexible mica substrate arranged in sequence from top to bottom; the ferroelectric layer adopts a zirconium-doped hafnium oxide ferroelectric film; the bottom electrode and the top electrode are both metal tungsten prepared by electron beam evaporation.

[0007] The flexible hafnium oxide-based ferroelectric memcapacitor integrated array is a cross array with a specification of 32×32. The overall size of the cross array is 1mm×1mm. The area of ​​the metal block electrode that conducts the test voltage is 0.09mm. 2 The width of the metal line in the middle is 6μm, and the size of the ferroelectric layer is 70μm×70μm.

[0008] The flexible hafnium oxide-based ferroelectric memcapacitor integrated array has consistent hysteresis loops and CV butterfly curves under different bending states.

[0009] The flexible hafnium oxide-based ferroelectric memcapacitor integrated array has a window value between a high capacitance state and a low capacitance state of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array in the range of 40 pF to 77 pF.

[0010] A method for preparing a flexible hafnium oxide-based ferroelectric memristor integrated array comprises the following steps:

[0011] Step 1: Pretreatment of the flexible substrate: Mechanical thinning of fluorophlogopite mica sheets was performed to obtain a flexible mica substrate that met the thickness and surface roughness standards. A three-stage ultrasonic cleaning process was performed, using acetone, ethanol, and deionized water in sequence. A titanium layer was deposited on the back of the flexible mica substrate by electron beam evaporation to achieve a partial light-shielding effect.

[0012] Step 2: preparing a patterned bottom electrode: a patterned metal tungsten is prepared as a bottom electrode on the upper surface of the flexible mica substrate by spin coating photoresist, pre-baking, alignment exposure, development, electron beam evaporation, and desmearing;

[0013] Step 3: preparing a patterned ferroelectric layer: growing a patterned hafnium zirconium oxide thin film as a ferroelectric layer on the upper surface of the bottom electrode by photoresist spin coating, pre-baking, alignment exposure, development, atomic layer deposition, and resist stripping;

[0014] Step 4: Prepare a patterned top electrode: prepare a patterned metal tungsten as a top electrode on the upper surface of the ferroelectric layer by spin coating photoresist, pre-baking, alignment exposure, development, electron beam evaporation, and stripping;

[0015] Step 5: Heat treatment: The obtained sample is placed in an annealing furnace filled with inert protective gas for annealing heat treatment. After the annealing furnace cools to room temperature, the sample is taken out to obtain a flexible hafnium oxide-based ferroelectric memristor integrated array.

[0016] The preparation method of the flexible hafnium oxide-based ferroelectric memristor integrated array, in the step 1, the thickness of the flexible mica substrate obtained by mechanical stripping is 50±5μm and the surface roughness is ≤0.4nm, the ultrasonic cleaning time of each stage is 10min; electron beam evaporation is used, and the cavity vacuum is 10 -4 Below Pa, the deposition rate is stable at 0.03nm / s.

[0017] In the preparation method of the above-mentioned flexible hafnium oxide-based ferroelectric memristor integrated array, in the step 2, the photolithography process adopts a double-layer glue process, first spin-coating LOR3A photoresist on the pretreated flexible mica substrate, then pre-spinning at 700 r / s for 10 seconds, then increasing to 5000 r / s and maintaining for 60 seconds, and pre-baking at 180°C for 60 seconds; then spin-coating S1805 photoresist, pre-spinning at 2200 r / s for 10 seconds, then increasing to 6500 r / s and maintaining for 60 seconds, and pre-baking at 110°C for 60 seconds.

[0018] The above-mentioned method for preparing the flexible hafnium oxide-based ferroelectric memristor integrated array comprises the following steps: in step 2, a contact photolithography machine is used for alignment exposure, and the flexible mica substrate after the coating is completed is exposed at a wavelength of 385nm and a power of 190W for 5 seconds, and then treated with ZX-238 developer for 50 seconds, followed by deionized water rinsing and nitrogen drying; the entire photolithography process, including coating, exposure and development, is carried out under a yellow light environment; the coating is removed by N-methylpyrrolidone at 100°C for 8 minutes, and the patterned bottom electrode is obtained by ethanol cleaning.

[0019] In the preparation method of the above-mentioned flexible hafnium oxide-based ferroelectric memristor integrated array, in step three, the hafnium source used in atomic layer deposition is tetrakis(dimethylamino)hafnium, namely Hf(N(CH3)2)4; the zirconium source is tetrakis(dimethylamino)zirconium, namely Zr(N(CH3)2)4; deionized water is used as the oxygen source; and 50 process cycles are performed at a deposition temperature of 100°C to obtain a uniform HZO film.

[0020] In the preparation method of the flexible hafnium oxide-based ferroelectric memristor integrated array, in step 5, the inert protective atmosphere is nitrogen, and the specific annealing process is: heating from room temperature to 550°C within 150 seconds, keeping the temperature for 200 seconds, and then cooling to room temperature before taking out.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention integrates a ferroelectric memcapacitor on a flexible mica substrate, so that the ferroelectric memcapacitor can withstand deformation such as bending and stretching and still has good ferroelectric performance and memcapacitive characteristics under different bending conditions, and is suitable for flexible electronic applications.

[0023] 2. The present invention uses the degree of ferroelectric polarization to regulate the capacitance of a memcapacitor to store information. By varying the applied voltage, the memcapacitor's capacitance state changes, with each capacitance state representing a stored signal. The size of the storage window increases with the degree of ferroelectric polarization. Different polarization degrees correspond to different capacitance states, enabling the memcapacitor to store information in multiple capacitance states.

[0024] 3. The present invention can improve the remnant polarization of hafnium zirconium oxide ferroelectric thin films by controlling the thickness of the ferroelectric layer, electrode thickness, and annealing process. The present invention is simple to manufacture and integrate, requiring no buffer or seed layer on the flexible mica substrate. It offers stable performance and excellent repeatability, and can be widely used in the development and application of novel memory devices and flexible electronic devices.

[0025] 4. This invention has achieved the integration of ferroelectric memristor arrays on flexible mica substrates for the first time, successfully verifying the feasibility of flexible substrates as high-density array integration bases. It has opened up new research directions and application potentials for the integration technology of new memory devices, and further expanded its application prospects in flexible electronics, wearable devices, transparent memory and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array of the present invention.

[0027] Figure 2 It is a schematic diagram of the surface structure of the flexible hafnium oxide-based ferroelectric memristor integrated array of the present invention.

[0028] Figure 3 This is a polarization-voltage curve of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array under different bending states.

[0029] Figure 4 This is the capacitance-voltage curve of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array under different bending states.

[0030] Figure 5 This is the capacitance-frequency curve of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array.

[0031] Figure 6 This is the capacitance-voltage curve of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] like Figure 1As shown, a flexible hafnium oxide-based ferroelectric memristor integrated array includes a patterned top electrode 1, a patterned ferroelectric layer 2, a patterned bottom electrode 3, and a flexible mica substrate 4 arranged in sequence from top to bottom; the ferroelectric layer 2 is made of a zirconium-doped hafnium oxide ferroelectric film; the bottom electrode 3 and the top electrode 1 are both made of metal tungsten prepared by electron beam evaporation.

[0034] The flexible hafnium oxide-based ferroelectric memristor integrated array is a cross array with a specification of 32×32. The overall size of the cross array is 1mm×1mm. The metal block electrode ( Figure 2 The area of ​​the electrodes numbered 1-32 is 0.09 mm 2 The metal line width in the middle is 6μm, and the size of the ferroelectric layer is 70μm × 70μm. The intersection of the crossbar array is the sandwich structure ferroelectric memristor.

[0035] The flexible mica substrate is 50 μm thick and has a smooth, uniform surface. Both the bottom and top electrodes are 20 nm thick, maintaining a symmetrical structure. The ferroelectric layer is 10 nm thick. The HZO film deposited by low-temperature ALD has a hafnium-to-zirconium ratio close to 1:1, resulting in a ferroelectric film with excellent density and performance.

[0036] The hysteresis loop and CV butterfly curve of the flexible hafnium oxide-based ferroelectric memristor integrated array remain consistent under different bending states.

[0037] The window value between the high capacitance state and the low capacitance state of the flexible hafnium oxide-based ferroelectric memristor integrated array is 40pF~77pF.

[0038] A method for preparing a flexible hafnium oxide-based ferroelectric memristor integrated array comprises the following steps:

[0039] Step 1: Pre-treatment of the flexible substrate: Fluorphlogopite mica sheets are mechanically thinned to obtain a smooth, crack-free flexible mica substrate approximately 50 microns thick. The thinning process aims to increase the substrate's flexibility. A three-stage ultrasonic cleaning process is employed: acetone, ethanol, and deionized water are used sequentially for ultrasonic treatment. A titanium layer is deposited on the back of the flexible mica substrate via electron beam evaporation to achieve partial light shielding.

[0040] The thickness of the flexible mica substrate obtained by mechanical stripping is 50±5μm and the surface roughness is ≤0.4nm. The ultrasonic cleaning time of each stage is 10min to remove the impurities remaining on the surface of the flexible mica substrate. Electron beam evaporation is used and the cavity vacuum is 10 -4 Below Pa, the deposition rate is stable at 0.03nm / s.

[0041] Step 2: Prepare a patterned bottom electrode: prepare a patterned metal tungsten as a bottom electrode on the upper surface of the flexible mica substrate by photoresist spin coating, pre-baking, alignment exposure, development, electron beam evaporation, and de-resin.

[0042] Since the flexible mica substrate is colorless and transparent, part of the light source will directly pass through during UV lithography, resulting in uneven exposure. Therefore, before UV lithography, a 10nm Ti layer is plated on the bottom of the flexible mica substrate by electron beam evaporation, and the cavity vacuum is kept at 10 -4 Below Pa, the deposition rate is stable at 0.03nm / s. Plating metal Ti on the bottom does not affect the performance of the prepared memory container and can also ensure uniform exposure.

[0043] The resulting flexible mica substrate was placed on a spin coater and a first layer of LOR3A photoresist was applied. The spin speed was set to 700 r / s for 10 seconds, then increased to 5000 r / s and held for 60 seconds. The flexible mica substrate was then placed on a heating plate at 180°C for 60 seconds before being pre-baked to cure. A second layer of S1805 photoresist was spin-coated at 2200 r / s for 10 seconds, then increased to 6500 r / s and held for 60 seconds. The flexible mica substrate was then placed on a heating plate at 110°C for 60 seconds before being pre-baked to cure.

[0044] Place the flexible mica substrate in a contact lithography machine and manipulate it to ensure a close fit between the flexible mica substrate and the designed photoresist. Set the machine power to approximately 190W, the light source wavelength to 385nm, and the exposure time to 5s. The exposed mica substrate is then developed in ZX-238 tetramethylammonium hydroxide, a positive photoresist developer, for 50s. Rinse in deionized water for 10s, and then use a nitrogen gun to blow dry the surface. It's important to note that the entire lithography process, including photoresist coating, exposure, and development, must be performed under yellow light.

[0045] The bottom electrode was prepared by electron beam evaporation on the flexible mica substrate after the above development, and the vacuum chamber was kept at 10 -4 Below Pa, the deposition rate is stable at 0.03nm / s. Prepare N-methylpyrrolidone, a degumming solution heated to 100°C, and soak the tungsten-plated flexible mica substrate in the degumming solution for 8 minutes. Then, rinse the sample in alcohol to remove any remaining degumming solution, and a patterned bottom electrode is obtained.

[0046] Step three, preparing a patterned ferroelectric layer: growing a patterned hafnium zirconium oxide thin film as a ferroelectric layer on the upper surface of the bottom electrode by photoresist spin coating, pre-baking, alignment exposure, development, atomic layer deposition, and resist stripping.

[0047] The sample obtained after step 2 was subjected to the same photoresist spin coating, pre-baking, alignment exposure, and development process as in step 2. A low-temperature hafnium zirconium oxide thin film was deposited on the resulting patterned bottom electrode using atomic layer deposition (ALD). To achieve excellent performance in the fabricated ferroelectric memristor, the hafnium:zirconium ratio in the low-temperature deposited hafnium zirconium oxide film must be controlled at 1:1, and the film thickness should be stabilized at approximately 10 nm. The hafnium source used in ALD was tetrakis(dimethylamino)hafnium, or Hf(N(CH3)2)4; the zirconium source was tetrakis(dimethylamino)zirconium, or Zr(N(CH3)2)4. Deionized water was used as the oxygen source, and the peak emission size and duration of the hafnium source were consistent with those of the zirconium source. Deionized water was used as the oxygen source, and the peak emission size and duration were twice that of the hafnium source. Fifty process cycles were performed at a deposition temperature of 100°C to obtain a uniform hafnium zirconium oxide thin film. The same stripping procedures as in step 2 were repeated to obtain a patterned hafnium zirconium oxide thin film.

[0048] Step 4, preparing a patterned top electrode: a patterned metal tungsten is prepared as a top electrode on the upper surface of the ferroelectric layer by spin coating photoresist, pre-baking, alignment exposure, development, electron beam evaporation, and desmearing.

[0049] Step 5: Heat treatment: The obtained sample is placed in an annealing furnace filled with inert protective gas for annealing heat treatment. After the annealing furnace cools to room temperature, the sample is taken out to obtain a flexible hafnium oxide-based ferroelectric memristor integrated array.

[0050] The inert protective atmosphere is nitrogen. The specific annealing process is: raise the temperature from room temperature to 550°C within 150s, keep it warm for 200s, then cool it to room temperature and take it out.

[0051] The flexible hafnium oxide-based ferroelectric memristor integrated array of the embodiment of the present invention was tested for electrical performance. Figure 3 As shown in the figure, a typical hysteresis loop is shown. Under the scanning voltage of ±3.2V, the residual polarization value (i.e. the polarization value when the voltage is 0) of the ferroelectric memcapacitor in the flat state, the bending radius of 8mm and the bending radius of 5mm is between 19.0 and 20.2 μC / cm 2 , showing excellent electrical properties, and the similar hysteresis loops at different bending radii also prove that the ferroelectric memcapacitor with mica as the substrate has excellent flexibility. The flexible hafnium oxide-based ferroelectric memcapacitor integrated array was tested for capacitance-voltage relationship, such as Figure 4 As shown in the figure, under the scanning voltage of ±3V, the ferroelectric memcapacitors in the flat state, the bending radius of 8mm and the bending radius of 5mm show similar and stable butterfly curves, indicating that there is a stable ferroelectric phase (such as orthorhombic phase) in the hafnium zirconium oxide film, rather than an amorphous or other non-ferroelectric phase. The flexible hafnium oxide-based ferroelectric memcapacitor integrated array was tested for capacitance-frequency relationship, as shown in the figure. Figure 5 As shown, Figure 5The blue line in the middle is the capacitance-frequency curve of the high capacitance state, and the orange line is the capacitance-frequency curve of the low capacitance state. Within the stable frequency test range (10~100kHz), as the test frequency increases, the window value between the high capacitance state and the low capacitance state gradually decreases. The window value between the high capacitance state and the low capacitance state is between 40pF and 77pF. The capacitance-voltage relationship of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array is tested. Figure 6 As shown in the figure, as the write voltage amplitude changes, the capacitance state of the memcappari also changes. Each capacitance state represents a type of stored information. It is possible to store information by regulating the capacitance state by changing the polarization degree, and this regulation is reversible.

Claims

1. A flexible hafnium oxide-based ferroelectric memristor integrated array, characterized by: The invention comprises a patterned top electrode, a patterned ferroelectric layer, a patterned bottom electrode, and a flexible mica substrate arranged in sequence from top to bottom; the ferroelectric layer is made of a zirconium-doped hafnium oxide ferroelectric film; the bottom electrode and the top electrode are both made of metal tungsten prepared by electron beam evaporation; The flexible hafnium oxide-based ferroelectric memristor integrated array is a 32×32 cross array with an overall size of 1mm×1mm. The area of ​​the metal block electrode conducting the test voltage is 0.09mm. 2 The width of the metal line in the middle is 6μm, and the size of the ferroelectric layer is 70μm×70μm.

2. The flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to claim 1, characterized in that: The hysteresis loop and CV butterfly curve of the flexible hafnium oxide-based ferroelectric memristor integrated array remain consistent under different bending states.

3. The flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to claim 1, characterized in that: The window value between the high capacitance state and the low capacitance state of the flexible hafnium oxide-based ferroelectric memristor integrated array is 40pF~77pF.

4. A method for preparing a flexible hafnium oxide-based ferroelectric memcapacitor integrated array, applied to the flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: Pretreatment of the flexible substrate: Mechanical thinning of fluorophlogopite mica sheets was performed to obtain a flexible mica substrate that met the thickness and surface roughness standards. A three-stage ultrasonic cleaning process was performed, using acetone, ethanol, and deionized water in sequence. A titanium layer was deposited on the back of the flexible mica substrate by electron beam evaporation to achieve a partial light-shielding effect. Step 2: preparing a patterned bottom electrode: a patterned metal tungsten is prepared as a bottom electrode on the upper surface of the flexible mica substrate by spin coating photoresist, pre-baking, alignment exposure, development, electron beam evaporation, and desmearing; Step 3: preparing a patterned ferroelectric layer: growing a patterned hafnium zirconium oxide thin film as a ferroelectric layer on the upper surface of the bottom electrode by photoresist spin coating, pre-baking, alignment exposure, development, atomic layer deposition, and resist stripping; Step 4: Prepare a patterned top electrode: prepare a patterned metal tungsten as a top electrode on the upper surface of the ferroelectric layer by spin coating photoresist, pre-baking, alignment exposure, development, electron beam evaporation, and stripping; Step 5: Heat treatment: The obtained sample is placed in an annealing furnace filled with inert protective gas for annealing heat treatment. After the annealing furnace cools to room temperature, the sample is taken out to obtain a flexible hafnium oxide-based ferroelectric memristor integrated array.

5. The method for preparing a flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to claim 4, characterized in that: In the step 1, the thickness of the flexible mica substrate obtained by mechanical stripping is 50±5 μm and the surface roughness is ≤0.4 nm. The time for each stage of ultrasonic cleaning is 10 min; electron beam evaporation is used, and the cavity vacuum is 10 -4 Below Pa, the deposition rate is stable at 0.03nm / s.

6. The method for preparing a flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to claim 4, characterized in that: In the step 2, the photolithography process adopts a double-layer glue process. First, LOR3A photoresist is spin-coated on the pretreated flexible mica substrate, and then pre-spinned at 700 r / s for 10 seconds, then increased to 5000 r / s and maintained for 60 seconds, and pre-baked at 180°C for 60 seconds; then S1805 photoresist is spin-coated, pre-spun at 2200 r / s for 10 seconds, then increased to 6500 r / s and maintained for 60 seconds, and pre-baked at 110°C for 60 seconds.

7. The method for preparing a flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to claim 4, characterized in that: In step 2, a contact photolithography machine is used for alignment exposure. The flexible mica substrate after the coating is completed is exposed to light at a wavelength of 385nm and a power of 190W for 5 seconds, and then treated with ZX-238 developer for 50 seconds. The substrate is then rinsed with deionized water and dried with nitrogen. The entire photolithography process, including coating, exposure, and development, is carried out under a yellow light environment. The substrate is subjected to a debonding treatment at 100°C with N-methylpyrrolidone for 8 minutes, and then washed with ethanol to obtain a patterned bottom electrode.

8. The method for preparing a flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to claim 4, characterized in that: In step 3, the hafnium source used in atomic layer deposition is tetrakis(dimethylamino)hafnium, i.e., Hf(N(CH3)2)4; the zirconium source is tetrakis(dimethylamino)zirconium, i.e., Zr(N(CH3)2)4; deionized water is used as the oxygen source; and 50 process cycles are performed at a deposition temperature of 100°C to obtain a uniform HZO film.

9. The method for preparing a flexible hafnium oxide-based ferroelectric memcapacitor integrated array according to claim 4, characterized in that: In step 5, the inert protective atmosphere is nitrogen, and the specific annealing process is: heating from room temperature to 550°C within 150s, keeping the temperature for 200s, and then cooling to room temperature before taking out.

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