Flexible hafnium oxide-based ferroelectric memory capacitor integrated array and preparation method thereof

Abstract

The invention discloses a flexible hafnium oxide-based ferroelectric memory capacitor integrated array and a preparation method thereof. The flexible hafnium oxide-based ferroelectric memory capacitor integrated array comprises a patterned top electrode, a patterned ferroelectric layer, a patterned bottom electrode and a flexible mica substrate which are sequentially arranged 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 through electron beam evaporation. The ferroelectric memcapacitor is integrated on the flexible mica substrate, so that the ferroelectric memcapacitor can bear deformation such as bending and stretching, still has good ferroelectric performance and memcapacitor characteristics under different bending conditions, and is suitable for flexible electronic application.

Description

Technical Field

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

[0002] With the continuous progress of Internet of Things, artificial intelligence and big data technologies, flexible wearable electronic devices, with their characteristics of being thin, light, flexible and easy for mass production, have been widely used in fields such as health monitoring and human-computer interaction, showing broad market potential. At the same time, the sharp increase in data volume has put forward higher requirements for flexible information storage devices.

[0003] The working principle of a memcapacitor is similar to that of a memristor, but its basis lies in the capacitance mechanism. In the field of neuromorphic computing research, non-volatile synaptic devices constructed using memcapacitors mainly use adjustable small-signal capacitance values to replace conductance as synaptic weights and perform calculations based on charge rather than conductance. Memcapacitors have the characteristics of multi-level variable capacitance regulated by an external electric field and can still maintain the data state after power-off. Compared with memristors, neuromorphic computing systems based on memcapacitors mainly rely on transient current and charge migration, which brings the advantage of almost zero static power consumption, enables selectorless access, reduces interconnection voltage loss, effectively avoids crosstalk current, and at the same time, due to its small-signal reading method, reduces reading interference and shows unique advantages in 3D stacked device structures. Therefore, memcapacitors have great potential in promoting the development of neural networks that simulate brain functions with high parallel processing capabilities and low energy consumption characteristics, and in realizing low-power neuromorphic computing applications.

[0004] Currently, the realized integration of ferroelectric memcapacitor arrays is 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 for the flexible hafnium oxide-based ferroelectric memcapacitor integrated array with a simple process.

[0006] The technical solution of the present invention to solve the above technical problems is: a flexible hafnium oxide-based ferroelectric memcapacitor 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 is a hafnium oxide ferroelectric thin film doped with zirconium; both the bottom electrode and the top electrode are tungsten metal prepared by electron beam evaporation.

[0007] The above flexible hafnium oxide-based ferroelectric memory device integrated array is a cross array with a specification of 32×32. The overall size of the cross array is 1 mm×1 mm, and the area of the metal block electrode for the on-state test voltage is 0.09 mm 2 , the width of the middle metal wire is 6 μm, and the size of the ferroelectric layer is 70 μm×70 μm.

[0008] For the above flexible hafnium oxide-based ferroelectric memory device integrated array, the ferroelectric hysteresis loop and C-V butterfly curve remain consistent under different bending states.

[0009] For the above flexible hafnium oxide-based ferroelectric memory device integrated array, the window value between the high capacitance state and the low capacitance state is between 40 pF and 77 pF.

[0010] A preparation method of a flexible hafnium oxide-based ferroelectric memory device integrated array includes the following steps:

[0011] Step 1, flexible substrate pretreatment: Select a fluorophlogopite sheet for mechanical thinning to obtain a flexible mica substrate with qualified thickness and surface roughness. Adopt a three-stage ultrasonic cleaning process: successively perform ultrasonic treatment with acetone, ethanol, and deionized water; deposit a titanium metal layer on the back of the flexible mica substrate by electron beam evaporation to achieve a partial light-shielding effect;

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

[0013] Step 3, prepare a patterned ferroelectric layer: Grow a patterned hafnium zirconium oxide thin film as the ferroelectric layer on the upper surface of the bottom electrode by means of 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 the top electrode on the upper surface of the ferroelectric layer by means of photoresist spin coating, pre-baking, alignment exposure, development, electron beam evaporation, and resist stripping;

[0015] Step 5, heat treatment: Place the obtained sample in an annealing furnace filled with inert protective gas for annealing heat treatment. Take out the sample after the annealing furnace cools down to room temperature to obtain the flexible hafnium oxide-based ferroelectric memory device integrated array.

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

[0017] For the preparation method of the above flexible hafnium oxide-based ferroelectric memristor integrated array, in Step 2, the lithography process adopts a bilayer resist process. First, LOR3A photoresist is spin-coated on the pretreated flexible mica substrate, then pre-spun at 700 r / s for 10 seconds and then raised to 5000 r / s and maintained for 60 seconds, and pre-baked at 180 °C for 60 seconds; subsequently, S1805 photoresist is spin-coated, pre-spun at 2200 r / s for 10 seconds and then raised to 6500 r / s and maintained for 60 seconds, and pre-baked at 110 °C for 60 seconds.

[0018] For the preparation method of the above flexible hafnium oxide-based ferroelectric memristor integrated array, in Step 2, contact lithography is used for alignment exposure. The flexible mica substrate after spin-coating is exposed at a wavelength of 385 nm and a power of 190 W for 5 seconds and then treated with ZX-238 developer for 50 seconds, and then rinsed with deionized water and dried with nitrogen; the entire lithography process, including spin-coating, exposure, and development, is carried out in an environment of yellow light; the photoresist is removed by N-methylpyrrolidone at 100 °C for 8 minutes, and the patterned bottom electrode is obtained by ethanol cleaning.

[0019] For the preparation method of the above flexible hafnium oxide-based ferroelectric memristor integrated array, in Step 3, the hafnium source used for atomic layer deposition is hafnium tetrakis(dimethylamino), i.e., Hf(N(CH3)2)4; the zirconium source is zirconium tetrakis(dimethylamino), i.e., Zr(N(CH3)2)4; deionized water is used as the oxygen source; a uniform HZO thin film is obtained after 50 process cycles at a deposition temperature of 100 °C.

[0020] For the preparation method of the above 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 s, holding for 200 s and then cooling to room temperature and then taking out.

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

[0022] 1. The present invention integrates ferroelectric memristors on a flexible mica substrate, enabling the ferroelectric memristors to withstand deformations such as bending and stretching and still have good ferroelectric properties and memristive characteristics under different bending conditions, which are suitable for flexible electronic applications.

[0023] 2. The present invention can use the ferroelectric polarization degree to regulate the capacitance of the memcapacitor for information storage. By changing the magnitude of the applied voltage, the capacitance state of the memcapacitor is changed, and each capacitance state represents a storage signal. The size of the storage window increases with the increase of the ferroelectric polarization degree, and different polarization degrees correspond to different capacitance states, enabling the memcapacitor to have multi-valued capacitance storage states.

[0024] 3. The present invention can improve the remanent polarization of hafnium zirconium oxide ferroelectric thin films by controlling the ferroelectric layer thickness, electrode thickness, and annealing process. The process of the present invention is simple, without adding any buffer layer and seed layer on the flexible mica substrate, easy to fabricate and integrate, with stable performance and good repeatability, and can be widely used in the development and application of new storage devices and flexible electronic devices.

[0025] 4. The present invention realizes the integration of ferroelectric memcapacitor arrays on flexible mica substrates for the first time, successfully verifies the feasibility of flexible substrates as high-density array integration substrates, opens up new research directions and application potentials for the integration technology of new storage devices, and further expands its application prospects in the fields of flexible electronics, wearable devices, and transparent memories. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0029] Figure 4 is a capacitance-voltage curve graph of the integrated array of flexible hafnium oxide-based ferroelectric memcapacitors in different bending states.

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

[0031] Figure 6 is a capacitance-voltage curve graph of the integrated array of flexible hafnium oxide-based ferroelectric memcapacitors. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The following further describes the present invention with reference to the drawings and embodiments.

[0033] As Figure 1As shown in the figure, 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 a hafnium oxide ferroelectric thin film doped with zirconium; both the bottom electrode 3 and the top electrode 1 are tungsten metal prepared by electron beam evaporation.

[0034] The flexible hafnium oxide-based ferroelectric memristor integrated array is a 32×32 cross array, the overall size of the cross array is 1mm×1mm, and the area of the metal block electrode ( Figure 2 the electrodes numbered 1 - 32 in 2 ) for conduction test voltage is 0.09mm

[0035] The size of the ferroelectric layer is 70μm×70μm. At the intersection points in the cross array are the ferroelectric memristors with a sandwich structure.

[0036] The ferroelectric hysteresis loops and C-V butterfly curves 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 between 40pF and 77pF.

[0038] A preparation method of a flexible hafnium oxide-based ferroelectric memristor integrated array includes the following steps:

[0039] Step 1, flexible substrate pretreatment: Select a fluorophlogopite sheet for mechanical thinning treatment to obtain a flexible mica substrate with a thickness of about 50 microns and a smooth and crack-free surface. The purpose of the thinning treatment is to increase the flexibility of the substrate. Adopt a three-stage ultrasonic cleaning process: perform ultrasonic treatment successively with acetone, ethanol, and deionized water; deposit a titanium metal layer on the back of the flexible mica substrate by electron beam evaporation to achieve a partial light-shielding effect.

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

[0041] Step 2, fabricate the patterned bottom electrode: On the upper surface of the flexible mica substrate, fabricate patterned tungsten metal as the bottom electrode through the processes of photoresist spin coating, pre-baking, alignment exposure, development, electron beam evaporation, and photoresist stripping.

[0042] Since the flexible mica substrate is colorless and transparent, during ultraviolet lithography, some light sources will directly transmit through, resulting in uneven exposure. Therefore, before ultraviolet lithography, deposit a 10-nm-thick Ti layer on the bottom of the flexible mica substrate by electron beam evaporation. The chamber vacuum is below 10 -4 Pa, and the deposition rate is stable at 0.03 nm / s. Depositing metal Ti on the bottom not only does not affect the performance of the fabricated memristor but also ensures uniform exposure.

[0043] Place the obtained flexible mica substrate on a spin coater, drop the first layer of photoresist LOR3A, and perform spin coating. Set the rotation speed to 700 r / s, and after 10 s, increase the rotation speed to 5000 r / s and maintain it for 60 s. Then place the flexible mica substrate on a heating table at 180 °C for 60 s for pre-baking and shaping. The spin coating speed of the second layer of photoresist S1805 is set to 2200 r / s. After 10 s, increase the rotation speed to 6500 r / s and maintain it for 60 s. Then place the flexible mica substrate on a heating table at 110 °C for 60 s for pre-baking and shaping.

[0044] Place the flexible mica substrate into a contact aligner, and manipulate the contact aligner to closely fit the flexible mica substrate and the lithography mask with the designed pattern. Set the power of the aligner to about 190 W, the light source wavelength to 385 nm, and the exposure time to 5 s. Then place the exposed mica substrate into the positive photoresist developer ZX-238 (tetramethylammonium hydroxide) for 50 s of development, then place it in deionized water for 10 s of cleaning, and then use a nitrogen gun to blow dry the surface moisture. It should be noted that the entire lithography process, including spin coating, exposure, and development, needs to be carried out in an environment of yellow light.

[0045] Use electron beam evaporation to fabricate the bottom electrode on the above-mentioned developed flexible mica substrate. The chamber vacuum is below 10 -4 Pa, and the deposition rate is stable at 0.03 nm / s. Prepare the photoresist stripper N-methylpyrrolidone heated to 100 °C, immerse the flexible mica substrate after tungsten plating in the photoresist stripper for 8 min, and then place the sample in alcohol to wash off the residual photoresist stripper to obtain the patterned bottom electrode.

[0046] Step 3, fabricate the patterned ferroelectric layer: On the upper surface of the bottom electrode, grow a patterned hafnium zirconium oxide thin film as the ferroelectric layer through the processes of photoresist spin coating, pre-baking, alignment exposure, development, atomic layer deposition, and photoresist stripping.

[0047] The sample obtained after step two is repeatedly subjected to the same processes of photoresist spin-coating, pre-baking, alignment exposure, and development as in step two. Hafnium zirconium oxide thin film is deposited at low temperature on the obtained patterned bottom electrode by atomic layer deposition (ALD). To achieve excellent performance of the fabricated ferroelectric memory device, the hafnium-to-zirconium ratio in the hafnium zirconium oxide thin film deposited at low temperature needs to be controlled at 1:1, and the thickness of the thin film is preferably stabilized at about 10 nm. The hafnium source used in atomic layer deposition is hafnium tetrakis(dimethylamino), i.e., Hf(N(CH3)2)4; the zirconium source is zirconium tetrakis(dimethylamino), i.e., Zr(N(CH3)2)4; deionized water is used as the oxygen source. The peak size and time of the hafnium source are the same as those of the zirconium source; deionized water is used as the oxygen source, and the peak size and time are twice that of the hafnium source. A uniform hafnium zirconium oxide thin film is obtained after 50 process cycles at a deposition temperature of 100 °C. Repeating the same photoresist stripping operation as in step two can obtain a patterned hafnium zirconium oxide thin film.

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

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

[0050] The inert protective atmosphere is nitrogen. The specific annealing process is as follows: It is heated from room temperature to 550 °C within 150 s, held for 200 s, and then cooled to room temperature before it can be taken out.

[0051] The flexible hafnium oxide-based ferroelectric memory device integrated array of the embodiment of the present invention is subjected to electrical property testing. As Figure 3 shown, it presents a typical ferroelectric hysteresis loop. Under a scanning voltage of ±3.2 V, the remanent polarization values (i.e., the polarization values when the voltage is 0) of the ferroelectric memory devices in the flat state, the state with a bending radius of 8 mm, and the state with a bending radius of 5 mm are in the range of 19.0 - 20.2 μC / cm 2 , showing excellent electrical properties. Also, the similar ferroelectric hysteresis loop diagrams at different bending radii prove that the ferroelectric memory device with mica as the substrate has excellent flexibility. The flexible hafnium oxide-based ferroelectric memory device integrated array is subjected to capacitance-voltage relationship testing. As Figure 4 shown, under a scanning voltage of ±3 V, the ferroelectric memory devices in the flat state, the state with a bending radius of 8 mm, and the state with a bending radius of 5 mm present similar and stable butterfly curves, indicating that there is a stable ferroelectric phase (such as the orthorhombic phase) in the hafnium zirconium oxide thin film, rather than an amorphous or other non-ferroelectric phase. The flexible hafnium oxide-based ferroelectric memory device integrated array is subjected to capacitance-frequency relationship testing. As Figure 5 shown, Figure 5The blue line is the capacitance-frequency curve in the high-capacitance state, and the orange line is the capacitance-frequency curve in the low-capacitance state. In the stable frequency test range (10~100 kHz), as the test frequency increases for the memcapacitor, the window value between the high-capacitance state and the low-capacitance state gradually decreases, and the window value between the high-capacitance state and the low-capacitance state is between 40 pF and 77 pF. The capacitance-voltage relationship of the flexible hafnium oxide-based ferroelectric memcapacitor integrated array was tested. As Figure 6 shown, as the amplitude of the writing voltage changes, the capacitance state of the memcapacitor also changes accordingly. Each capacitance state represents a kind of stored information, that is, information storage can be realized by changing the polarization degree to control the capacitance state, and this control is reversible.

Claims

1. A flexible hafnium oxide-based ferroelectric memristor integrated array, characterized in that: It includes a patterned top electrode, a patterned ferroelectric layer, a patterned bottom electrode, and a flexible mica substrate, which are arranged successively from top to bottom; the ferroelectric layer is a hafnium zirconium oxide doped ferroelectric thin film; both the bottom electrode and the top electrode are tungsten metal prepared by electron beam evaporation.

2. The flexible hafnium oxide-based ferroelectric memory integrated array according to claim 1, wherein: The flexible hafnium oxide-based ferroelectric memristor integrated array is a 32×32 crossbar array. The overall size of the crossbar array is 1 mm×1 mm, and the area of the metal block electrode for the on-state test voltage is 0.09 mm 2 , the width of the middle metal wire is 6 μm, and the size of the ferroelectric layer is 70 μm×70 μm.

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

4. The flexible hafnium oxide-based ferroelectric memory device integrated array according to claim 1, wherein: The window value between the high capacitance state and the low capacitance state of the flexible hafnium-based ferroelectric memory integrated array is between 40 pF and 77 pF.

5. A preparation method of a flexible hafnium oxide-based ferroelectric memory integrated array, applied to the flexible hafnium oxide-based ferroelectric memory integrated array described in any one of claims 1-4, characterized in that, It includes the following steps: Step 1, flexible substrate pretreatment: Select a fluorophlogopite sheet for mechanical thinning to obtain a flexible mica substrate with qualified thickness and surface roughness. Adopt a three-stage ultrasonic cleaning process: successively perform ultrasonic treatment with acetone, ethanol, and deionized water; deposit a titanium metal layer on the back of the flexible mica substrate by electron beam evaporation to achieve a partial light-shielding effect; Step 2, prepare the patterned bottom electrode: Prepare patterned tungsten metal as the bottom electrode on the upper surface of the flexible mica substrate by means of photoresist spin coating, pre-baking, alignment exposure, development, electron beam evaporation, and photoresist stripping; Step 3, prepare the patterned ferroelectric layer: Grow a patterned hafnium zirconium oxide thin film as the ferroelectric layer on the upper surface of the bottom electrode by means of photoresist spin coating, pre-baking, alignment exposure, development, atomic layer deposition, and photoresist stripping; Step 4, prepare the patterned top electrode: Prepare patterned tungsten metal as the top electrode on the upper surface of the ferroelectric layer by means of photoresist spin coating, pre-baking, alignment exposure, development, electron beam evaporation, and photoresist stripping; Step 5, heat treatment: Place the obtained sample in an annealing furnace filled with inert protective gas for annealing heat treatment. Take out the sample after the annealing furnace cools down to room temperature to obtain a flexible hafnium-based ferroelectric memory integrated array.

6. The preparation method of the flexible hafnium oxide-based ferroelectric memory device integrated array according to claim 5, wherein In the first step, the thickness of the flexible mica substrate obtained by mechanical exfoliation is 50 ± 5 μm and the surface roughness is ≤ 0.4 nm, and the time for each stage of ultrasonic cleaning is 10 min; electron beam evaporation is adopted, and the chamber vacuum is below 10 -4 Pa, and the deposition rate is stable at 0.03 nm / s.

7. The preparation method of the flexible hafnium oxide-based ferroelectric memory capacitor integrated array according to claim 5, wherein In the second step, the lithography process adopts a bilayer resist process. First, spin coat LOR3A photoresist on the pretreated flexible mica substrate, then pre-spin at 700 r / s for 10 seconds and then increase to 5000 r / s and maintain for 60 seconds, and pre-bake at 180 °C for 60 seconds; Subsequently, spin coat S1805 photoresist, pre-spin at 2200 r / s for 10 seconds and then increase to 6500 r / s and maintain for 60 seconds, and pre-bake at 110 °C for 60 seconds.

8. The preparation method of the flexible hafnium oxide-based ferroelectric memory device integrated array according to claim 5, characterized in that, In the second step, contact lithography is used for alignment exposure. The flexible mica substrate with spin-coated photoresist is exposed at a wavelength of 385 nm and a power of 190 W for 5 seconds and then treated with ZX-238 developer for 50 seconds, and then rinsed with deionized water and dried with nitrogen; The entire lithography process, including spin coating, exposure, and development, is carried out in an environment of yellow light; The photoresist is removed by N-methylpyrrolidone at 100 °C for 8 minutes, and the patterned bottom electrode is obtained by ethanol cleaning.

9. The preparation method of the flexible hafnium oxide-based ferroelectric memory device integrated array according to claim 5, characterized in that, In the third step, the hafnium source used for atomic layer deposition is hafnium tetrakis(dimethylamino), i.e., Hf(N(CH3)2)4; the zirconium source is zirconium tetrakis(dimethylamino), i.e., Zr(N(CH3)2)4; deionized water is used as the oxygen source; A uniform HZO thin film is obtained after 50 process cycles at a deposition temperature of 100 °C.

10. The preparation method of the flexible hafnium oxide-based ferroelectric memory device integrated array according to claim 5, wherein In the fifth step, the inert protective atmosphere is nitrogen, and the specific annealing process is as follows: heat from room temperature to 550°C within 150 s, keep the temperature for 200 s, and then cool to room temperature before taking out.

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