A floating gate memory device based on hollow structure nanoparticles and its preparation method

Abstract

The present invention discloses a floating gate memory device based on hollow structure nanoparticles and a preparation method thereof, which relates to the field of charge storage technology. The floating gate memory device comprises: a substrate; a tunnel oxide layer, which is arranged on the substrate; a storage medium layer, which is arranged on the tunnel oxide layer and contains CoO nanoparticles with a hollow structure; a control oxide layer, which is arranged on the storage medium layer; the preparation method comprises: forming a tunnel oxide layer on the substrate; continuing to form a storage medium layer, comprising: alternately depositing oxide and Co on the tunnel oxide layer by a pulsed laser deposition device, annealing in a protective gas atmosphere, and embedding Co nanoparticles in amorphous oxide; annealing in an oxygen atmosphere to form CoO nanoparticles with a hollow structure; and continuing to form a control oxide layer. The beneficial effect of the present invention is that hollow structured cobalt oxide nanoparticles are formed, which have more surface defects and interface states, can capture more injected charges, and enhance the charge storage capacity of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of charge storage, and in particular to a floating gate storage device based on hollow structure nanoparticles and a preparation method thereof. Background Art

[0002] In 1995, researchers from International Business Machines Corporation (IBM) published a paper at the International Electron Devices Conference on a non-volatile charge storage device based on a single transistor and a single nanoparticle. They pointed out that the device has better information retention characteristics and a higher state conversion speed than traditional electrically-erasable programmable read-only memory (EEPROM). Research on nanoparticle floating gate memory began from then on.

[0003] The materials of nanoparticle floating gate memory are mainly materials required by traditional complementary metal-oxide-semiconductor (CMOS) processes and metal materials (such as cobalt, etc.).

[0004] The main structure of the nanoparticle floating gate memory is similar to that of the charge trap memory, and the gate of the storage unit is composed of four parts, including the top control gate, the oxide control layer, the nanoparticle storage medium layer and the bottom oxide tunnel layer. The nanoparticle floating gate memory is a type of charge trap memory, so its basic working principle and operation mode are the same as those of the charge trap memory. The difference between its mirror storage flash memory and other charge trap memories is that the metal nanoparticles have a higher work function, which increases the number of charges that can be captured by the storage unit, thereby increasing the retention time of the storage unit. In addition, the discrete (similar to the scattered point form) storage of charges in the metal nanoparticles makes the retention time of this type of storage unit less dependent on the thickness of the tunnel oxide layer. At a smaller tunnel layer thickness, the device can have better performance. At this time, due to the reduction in the thickness of the tunnel layer, the probability of direct charge tunneling increases, which significantly reduces the programming and erasing voltages and improves the reading and erasing speeds.

[0005] Because nanoparticle floating gate memory has good retention characteristics, lower operating voltage and faster erase and write speed, this type of memory has great potential in embedded application scenarios.

[0006] However, as devices become increasingly miniaturized, the data storage density of nano-floating gate non-volatile memory is gradually approaching its limit. Therefore, in the absence of the ability to further increase data storage density, it is particularly important to explore a new method to increase the charge storage capacity of the device. Summary of the invention

[0007] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a floating gate memory device based on hollow structure nanoparticles and a preparation method thereof, by adopting pulsed laser deposition technology combined with a rapid annealing method, changing the morphology of the nanoparticles to form a hollow structure, regulating the surface defects and interface states of the nanoparticles, thereby enhancing its charge capture and storage capabilities.

[0008] The technical solution of the present invention is as follows:

[0009] A first aspect of the present invention provides a floating gate memory device based on hollow structure nanoparticles, comprising:

[0010] substrate;

[0011] A tunnel oxide layer, disposed on the substrate;

[0012] A storage medium layer is disposed on the tunnel oxide layer, wherein the storage medium layer contains CoO nanoparticles having a hollow structure;

[0013] The control oxide layer is arranged on the storage medium layer.

[0014] Optionally, the particle size of the CoO nanoparticles with a hollow structure is 9-11 nm.

[0015] Optionally, the storage medium layer further contains amorphous HfO2, and the CoO nanoparticles with a hollow structure are arranged in the amorphous HfO2.

[0016] Optionally, the CoO nanoparticles with a hollow structure are embedded in the amorphous HfO 2 to form the storage medium layer.

[0017] Optionally, the tunnel oxide layer and the control oxide layer both contain HfO2, and the substrate is an n-Si (100) substrate.

[0018] A second aspect of the present invention provides a method for preparing the floating gate memory device as described above, comprising the following steps:

[0019] forming a tunnel oxide layer on the substrate;

[0020] Continue to form a storage medium layer on the tunnel oxide layer;

[0021] Continue to form a control oxide layer on the storage medium layer;

[0022] The step of continuously forming a storage medium layer on the tunnel oxide layer specifically includes:

[0023] Placing the substrate with the tunnel oxide layer formed thereon in a pulsed laser deposition device, and alternately depositing HfO2 and Co on the tunnel oxide layer;

[0024] Placing the substrate having the tunnel oxide layer formed thereon in an inert gas atmosphere for a first annealing treatment, so as to form Co nanoparticles embedded in amorphous HfO2 on the tunnel oxide layer;

[0025] The substrate having the tunnel oxide layer formed thereon is placed in an oxygen atmosphere for a second annealing process to form the storage medium layer, wherein the Co nanoparticles are converted into CoO nanoparticles having a hollow structure.

[0026] Optionally, the step of forming a tunnel oxide layer on the substrate specifically includes:

[0027] The substrate is placed in a pulsed laser deposition device, and the pulsed laser deposition device is controlled to deposit HfO2 on the substrate with preset parameters; wherein the preset parameters include: the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 Torr~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300 seconds to 400 seconds, the pulse laser frequency is 5 Hz to 10 Hz, and the laser energy is 290 mJ to 310 mJ;

[0028] The substrate is taken out and placed in an inert gas atmosphere for a first annealing treatment with first preset parameters to form a tunnel oxide layer on the substrate; wherein the first preset parameters include: a heating temperature of 320°C to 360°C, a heating time of 32 seconds to 36 seconds, a holding time of 3 minutes to 7 minutes, and a rapid cooling time of 8 minutes to 11 minutes.

[0029] Optionally, the step of continuously forming a storage medium layer on the tunnel oxide layer specifically includes:

[0030] Connecting a high-purity metal Co target and a high-purity HfO2 target to form a combined target material, and placing the substrate formed with a tunnel oxide layer and the combined target material on a sample holder and a target holder of a pulsed laser deposition device, respectively;

[0031] The pulsed laser deposition device is controlled to alternately ablate the high-purity HfO2 target and the high-purity metal Co target in the combined target material by laser, and HfO2 and Co are alternately deposited on the tunnel oxide layer according to preset parameters; wherein the preset parameters include: the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 Torr~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300 seconds to 400 seconds, the pulse laser frequency is 5 Hz to 10 Hz, and the laser energy is 290 mJ to 310 mJ;

[0032] Placing the substrate having the tunnel oxide layer formed thereon in an inert gas atmosphere and performing a first annealing treatment with a first preset parameter to form Co nanoparticles embedded in amorphous HfO2 on the tunnel oxide layer;

[0033] The substrate formed with the tunnel oxide layer is placed in an oxygen atmosphere and subjected to a second annealing process with second preset parameters to form the storage medium layer, wherein the Co nanoparticles are converted into CoO nanoparticles with a hollow structure.

[0034] Optionally, the first preset parameters include: heating temperature of 320°C to 360°C, heating time of 32 seconds to 36 seconds, heat preservation time of 3 minutes to 7 minutes, and rapid cooling time of 8 minutes to 11 minutes;

[0035] The second preset parameters include: heating temperature of 380°C to 420°C, heating time of 38 seconds to 42 seconds, insulation time of 3 minutes to 7 minutes, and rapid cooling time of 9 minutes to 12 minutes.

[0036] Optionally, the step of continuing to form a control oxide layer on the storage medium layer specifically includes:

[0037] The substrate with the storage medium layer formed thereon is placed in a pulsed laser deposition device, and the pulsed laser deposition device is controlled to deposit HfO2 on the storage medium layer according to preset parameters; wherein the preset parameters include: the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 Torr~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300 seconds to 400 seconds, the pulse laser frequency is 5 Hz to 10 Hz, and the laser energy is 290 mJ to 310 mJ;

[0038] The substrate with the storage medium layer formed thereon is taken out and placed in an inert gas atmosphere for a first annealing treatment with first preset parameters to form a controlled oxide layer on the storage medium layer; wherein the first preset parameters include: a heating temperature of 320°C to 360°C, a heating time of 32 seconds to 36 seconds, a holding time of 3 minutes to 7 minutes, and a rapid cooling time of 8 minutes to 11 minutes.

[0039] Optionally, after the step of continuously forming a control oxide layer on the storage medium layer, the method further includes:

[0040] Further plating a layer of Ag array electrode on the control oxide layer, and plating a layer of Ag bottom electrode on the bottom of the substrate;

[0041] Among them, in the Ag array electrode, a single Ag electrode is square with a side length of 0.4mm~0.6mm, and the array interval is 0.4mm~0.6mm.

[0042] The present invention has at least one of the following beneficial effects:

[0043] 1. The present invention provides a floating gate memory device based on hollow structure nanoparticles. Compared with a floating gate memory device based on solid structure cobalt oxide nanoparticles with similar storage density and particle size, the floating gate memory device of the present invention has a more excellent charge storage performance.

[0044] 2. The present invention uses the Kirkendall effect to make cobalt nanoparticles form hollow-structured cobalt oxide nanoparticles, which have more surface defects and interface states, can capture more injected charges, and further enhance the charge storage capacity of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the structure of a floating gate memory device based on hollow structure CoO nanoparticles in an embodiment of the present invention and a floating gate memory device with solid structure CoO nanoparticles as a comparative sample, wherein a is a floating gate memory device based on hollow structure CoO nanoparticles in an embodiment, and b is a floating gate memory device with solid structure CoO nanoparticles as a comparative sample.

[0046] Figure numerals: 1. Ag array electrode; 2. Amorphous HfO2; 3. CoO nanoparticles with hollow structure; 4. Substrate; 5. Ag bottom electrode; 6. CoO nanoparticles with solid structure.

[0047] Figure 2TEM and corresponding SAED images, unit cell schematics, and Raman spectra of the CoO nanoparticles with a hollow structure in the embodiment of the present invention and the solid structure CoO nanoparticles as a comparative sample, wherein a~c correspond to the solid structure CoO nanoparticles of the comparative sample, and d~f are the CoO nanoparticles with a hollow structure in the corresponding embodiment.

[0048] Figure 3 3 are XPS graphs of CoO nanoparticles with a hollow structure in an embodiment of the present invention and CoO nanoparticles with a solid structure as a comparative sample, wherein a is a Co 2p XPS graph, b is a Hf 4f XPS graph, and c is an O 1s XPS graph.

[0049] Figure 4 It is a Raman spectrum diagram of CoO nanoparticles with hollow structure and solid structure in the embodiment of the present invention.

[0050] Figure 5 3 are capacitance-voltage (CV) test curves of a floating gate memory device based on hollow structure CoO nanoparticles in an embodiment of the present invention and a floating gate memory device based on solid structure CoO nanoparticles as a comparative sample, wherein a corresponds to the comparative sample and b corresponds to the floating gate memory device in the embodiment. DETAILED DESCRIPTION

[0051] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] An embodiment of the present invention provides a floating gate memory device, comprising a substrate, and a tunnel oxide layer, a storage medium layer, and a control oxide layer sequentially arranged on the substrate;

[0053] The storage medium layer contains CoO nanoparticles with a hollow structure.

[0054] The present invention forms hollow-structured CoO nanoparticles. On the one hand, the hollow-structured CoO nanoparticles have a larger specific surface area and structural complexity, which means that there are more surface atoms and interface areas, thereby increasing the possibility of forming an interface state; on the other hand, the transition area between the surface and the inner cavity of the hollow-structured nanoparticles may form a specific type of interface state; therefore, the floating gate memory device based on the hollow-structured nanoparticles of the present invention has better charge storage performance than the floating gate memory device based on the solid-structured cobalt oxide nanoparticles (with similar storage density and particle size).

[0055] In some embodiments, the particle size of the CoO nanoparticles having a hollow structure is 9-11 nm.

[0056] In some embodiments, the storage medium layer further contains amorphous HfO 2 , and the CoO nanoparticles having a hollow structure are embedded in the HfO 2 to form the storage medium layer.

[0057] The tetravalent coordinated oxygen vacancy defects in HfO2 are beneficial to improving the storage properties of charge trapping memory.

[0058] In some embodiments, the tunnel oxide layer and the control oxide layer both contain HfO2, and the substrate is an n-Si (100) substrate.

[0059] Another embodiment of the present invention provides a method for preparing a floating gate memory device, comprising the following steps:

[0060] forming a tunnel oxide layer on the substrate;

[0061] Continuing to form a storage medium layer on the tunnel oxide layer, comprising: alternately depositing HfO2 and Co on the substrate formed with the tunnel oxide layer by a pulsed laser deposition device, taking out the substrate formed with the tunnel oxide layer and placing it in a protective gas atmosphere for annealing treatment, so as to form Co nanoparticles embedded in amorphous HfO2 on the tunnel oxide layer; continuing to place the substrate formed with the tunnel oxide layer in an oxygen atmosphere for annealing treatment, so that the Co nanoparticles form CoO nanoparticles with a hollow structure, thereby forming a storage medium layer;

[0062] A control oxide layer is continuously formed on the storage medium layer.

[0063] The present invention forms hollow-structured CoO nanoparticles by changing the morphology of Co nanoparticles, and regulates the surface defects and interface states of the nanoparticles, thereby enhancing the charge capture and storage capabilities thereof.

[0064] In some embodiments, the step of forming a tunnel oxide layer on a substrate includes:

[0065] HfO2 is deposited on the substrate by a pulsed laser deposition device; wherein the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 ~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300-400 seconds, the pulse laser frequency is 5-10 Hz, and the laser energy is 290-310 mJ;

[0066] The substrate is taken out and placed in an inert gas atmosphere for rapid annealing to form a tunnel oxide layer on the substrate; wherein the heating temperature of the annealing treatment is 320-360° C., the heating time is 32-36 seconds, the holding time is 3-7 minutes, and the rapid cooling time is 8-11 minutes.

[0067] In some embodiments, the step of continuously forming a storage medium layer on the tunnel oxide layer specifically includes:

[0068] Connecting a high-purity metal Co target and a high-purity HfO2 target to form a combined target material, and placing the substrate formed with a tunnel oxide layer and the combined target material on a rotatable sample holder and a rotatable target holder of a pulsed laser deposition device, respectively;

[0069] The target holder is driven to rotate by a motor, and the combined target rotates with the target holder, so that the laser alternately ablates the high-purity metal Co target and the high-purity HfO2 target in the combined target, and HfO2 and Co are alternately deposited on the tunnel oxide layer; wherein the vacuum degree in the growth chamber of the pulsed laser deposition equipment is 8×10 -7 ~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300-400 seconds, the pulse laser frequency is 5-10 Hz, and the laser energy is 290-310 mJ;

[0070] The substrate having the tunnel oxide layer formed thereon is taken out and placed in an inert gas atmosphere for annealing treatment, so as to form Co nanoparticles embedded in amorphous HfO2 on the tunnel oxide layer;

[0071] The substrate with the tunnel oxide layer formed thereon is then placed in an oxygen atmosphere for annealing treatment, and the Co nanoparticles are transformed into CoO nanoparticles with a hollow structure, thereby forming a storage medium layer.

[0072] In some embodiments, in the step of annealing the substrate having the tunnel oxide layer formed thereon in an inert gas atmosphere, the heating temperature is 320-360° C., the heating time is 32-36 seconds, the holding time is 3-7 minutes, and the rapid cooling time is 8-11 minutes;

[0073] In the step of annealing the substrate with the tunnel oxide layer in an oxygen atmosphere, the heating temperature is 380-420° C., the heating time is 38-42 seconds, the holding time is 3-7 minutes, and the rapid cooling time is 9-12 minutes.

[0074] In some embodiments, the step of continuing to form a control oxide layer on the storage medium layer includes:

[0075] The substrate with the storage medium layer formed thereon is placed in a pulsed laser deposition device, and HfO2 is deposited on the storage medium layer by the pulsed laser deposition device; wherein the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 ~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300-400 seconds, the pulse laser frequency is 5-10 Hz, and the laser energy is 290-310 mJ;

[0076] The substrate with the storage medium layer is taken out and placed in an inert gas atmosphere for rapid annealing to form a controlled oxide layer on the storage medium layer; wherein the heating temperature of the annealing treatment is 320-360°C, the heating time is 32-36 seconds, the holding time is 3-7 minutes, and the rapid cooling time is 8-11 minutes.

[0077] In some embodiments, after the step of continuously forming a control oxide layer on the storage medium layer, the method further includes:

[0078] A layer of Ag array electrode is continuously plated on the top of the control oxide layer, and a layer of Ag bottom electrode is plated on the bottom of the substrate;

[0079] Among them, in the Ag array electrode, a single Ag electrode is square with a side length of 0.4-0.6 mm and an array interval of 0.4-0.6 mm.

[0080] In some embodiments, a method for preparing a floating gate memory device based on hollow structure nanoparticles is prepared by using pulsed laser deposition technology combined with a rapid annealing method, and specifically includes the following steps:

[0081] (1) In the preparation stage, the n-Si (100) substrate was cut into appropriate sizes, ultrasonically cleaned with anhydrous ethanol, and then immersed in a 5% HF solution for 3 minutes to remove the external native oxide layer. After that, the n-Si (100) substrate was repeatedly cleaned with deionized water and anhydrous ethanol;

[0082] (2) The Si substrate and the target material are placed on the sample holder and the target holder of the pulsed laser deposition system respectively. The target material is a composite target material in which a high-purity metal Co block target and a high-purity HfO2 round target are bonded together by copper glue. The purity of the high-purity metal Co block target is 99.99% and the size is 30×10 mm (length×width). The purity and diameter of the high-purity HfO2 round target are 99.99% and 50 mm respectively;

[0083] (3) The sample deposition chamber is evacuated to a high vacuum state, and a KrF excimer pulse laser is used to ablate the HfO2 target material to deposit an amorphous HfO2 film on the Si substrate as the tunnel oxide layer of the device. The high vacuum state refers to the vacuum in the growth chamber of 8×10 -7 ~5.0×10 -8 Torr, the wavelength of the laser light source is 248 nanometers. The time for laser ablation of the target material is 300-400 seconds, the pulse laser frequency is 10 Hz, and the laser energy is 290-310 mJ;

[0084] (4) Take out the sample and place it in a rapid annealing furnace filled with argon for rapid annealing, and wait for the sample to cool to room temperature. The heating temperature is 320~360℃, the heating time is 30~40 seconds, the holding time is 3~7 minutes, and the rapid cooling time is 8~11 minutes;

[0085] (5) The sample is placed back into the deposition chamber and evacuated, and the Co / HfO2 composite target is alternately ablated by laser, and the sample is continuously deposited on the HfO2 film to prepare a storage medium layer. The laser ablation time of the target is 300-400 seconds, the pulse laser frequency is 10 Hz, and the laser energy is 290-310 mJ;

[0086] (6) taking out the sample and placing it in a rapid annealing furnace filled with argon for rapid annealing, waiting for the sample to cool to room temperature, and obtaining metal Co nanoparticles embedded in amorphous HfO2. The heating temperature is 320-360°C, the heating time is 32-36 seconds, the holding time is 3-7 minutes, and the rapid cooling time is 8-11 minutes;

[0087] (7) Filling the rapid annealing furnace with oxygen, continuing the rapid annealing treatment on the sample, and waiting for the sample to cool to room temperature to obtain CoO nanoparticles with a hollow structure embedded in amorphous HfO2. The heating temperature is 380-420°C, the heating time is 38-42 seconds, the holding time is 3-7 minutes, and the rapid cooling time is 9-12 minutes;

[0088] (8) The sample is placed back into the deposition chamber and evacuated, and the HfO2 target is ablated by laser, and a layer of amorphous HfO2 thin film is deposited on the sample as the control oxide layer of the device. The laser ablation time of the target material is 300-400 seconds, the pulse laser frequency is 10 Hz, and the laser energy is 290-310 mJ;

[0089] (9) Take out the sample and place it in a rapid annealing furnace filled with argon for rapid annealing, and wait for the sample to cool to room temperature. The sample finally forms a sandwich structure of HfO2 (tunnel oxide layer) + hollow CoO / HfO2 (storage medium layer) + HfO2 (control oxide layer). The heating temperature is 320~360℃, the heating time is 32~36 seconds, the holding time is 3~7 minutes, and the rapid cooling time is 8~11 minutes;

[0090] (10) A layer of Ag array electrode is plated on the upper surface of the sample and a layer of Ag bottom electrode is plated on the bottom of the sample using a thermal evaporation coating apparatus and a mask. The mask has square array openings, the side length of a single square is 0.5 mm, and the interval between two holes is also 0.5 mm.

[0091] The applicant has found through research that the traps formed by the surface defects of nanoparticles and the nanoparticle / oxide interface have strong carrier capture capabilities. By changing the size, density and spatial distribution of nanocrystals, the charge capture position and density (storage capacity) can be effectively controlled. Therefore, the applicant tried to create a large number of defect states and deep traps on the surface of nanoparticles and at the nanoparticle / oxide interface to improve the charge storage performance. In order to make nanoparticles have more surface defects and traps to capture the injected charges, it is a potential strategy to make nanoparticles form hollow structures. Due to their geometric shape and unique structural features, hollow nanoparticles usually have a large specific surface area and structural complexity, such as multiple shells and porosity, which means that there are more surface atoms and interface areas, thereby increasing the possibility of forming interface states. In addition, the transition area between the surface and the inner cavity of hollow structured nanoparticles may form a specific type of interface state. For example, during the preparation process, a special boundary may be formed between the surface and the inner cavity, which may be the source of the defect state. Uncoordinated atoms may appear at the edges or corners of the internal cavity, and these positions are prone to forming suspended bonds or defects, thereby increasing the interface state of the nanoparticles. Therefore, under the premise that the storage density and storage unit size cannot be further improved, it is very important for the development and application of nano-floating gate non-volatile memory devices to change the morphology of nanoparticles to form a hollow structure and regulate the surface defects and interface states of the nanoparticles to enhance their charge capture and storage capabilities.

[0092] The present invention changes the morphology of nanoparticles to form a hollow structure, regulates the surface defects and interface states of the nanoparticles, and thus enhances the charge capture and storage capabilities of the nanoparticles.

[0093] The present invention is further described in detail below with specific examples, but the present invention is not limited to the following specific examples.

[0094] The experimental characterization methods described in the following examples are conventional methods unless otherwise specified; the reagents, materials and instruments and equipment described are all commercially available unless otherwise specified.

[0095] Embodiment 1:

[0096] like Figure 1 As shown in a, this embodiment provides a floating gate memory device based on hollow structure nanoparticles, which is prepared by pulsed laser deposition technology combined with a rapid annealing method and a thermal evaporation coating apparatus, and specifically includes the following steps:

[0097] (1) In the preparation stage, the n-Si (100) substrate was cut into 1.5 cm × 1.5 cm size, ultrasonically cleaned in anhydrous ethanol, and then immersed in 5% HF solution for 3 minutes to remove the external native oxide layer. After that, the n-Si (100) substrate was repeatedly cleaned with deionized water and anhydrous ethanol;

[0098] (2) The Si substrate and the target are placed on the sample holder and target holder of the pulsed laser deposition system respectively. The target is a composite target of two high-purity metal Co block targets (99.99%, length × width × height: 30 × 10 × 3 mm) and a high-purity HfO2 round target (99.99%, diameter 50 mm) bonded by copper glue;

[0099] (3) The sample deposition chamber was vacuumed to 5.0×10 -8 Torr, using 248nm krypton fluoride (KrF) excimer pulse laser to ablate high-purity HfO2 target for 300 seconds, with a pulse laser frequency of 10 Hz and a pulse laser energy of 300 mJ;

[0100] (4) The sample was taken out and placed in the heating zone of a rapid annealing furnace. In an argon atmosphere, it was rapidly heated to 350°C for 35 seconds, then kept warm for 3 minutes, and then rapidly cooled to room temperature (about 10 minutes) to obtain a HfO2 tunnel oxide layer.

[0101] (5) The sample was placed back into the deposition chamber and the vacuum was evacuated to 5.0×10 -8 Torr, the metal Co block target and HfO2 round target were alternately ablated by pulsed laser for 300 seconds, the pulsed laser frequency was 10 Hz, and the pulsed laser energy was 300 mJ;

[0102] (6) The sample was taken out and placed in the heating zone of a rapid annealing furnace. In an argon atmosphere, it was rapidly heated to 350 °C for 35 seconds, then kept warm for 5 minutes, and then rapidly cooled to room temperature (about 10 minutes) to obtain the initial metal Co nanoparticles embedded in the HfO2 film.

[0103] (7) The sample was allowed to remain in the heating zone of the rapid annealing furnace, and the argon atmosphere was replaced with an oxygen atmosphere, and the sample was rapidly heated to 400 °C for 40 seconds, then kept at this temperature for 5 minutes, and then rapidly cooled to room temperature (about 10 minutes) to obtain hollow-structured CoO nanoparticles embedded in the HfO2 film;

[0104] (8) The sample was placed back into the deposition chamber and the vacuum was evacuated to 5.0×10 -8 Torr, HfO2 target was ablated by pulsed laser for 300 seconds, the pulsed laser frequency was 10 Hz, and the pulsed laser energy was 300 mJ;

[0105] (9) The sample was taken out and placed in the heating zone of a rapid annealing furnace. In an argon atmosphere, it was rapidly heated to 350 °C for 35 seconds, then kept warm for 3 minutes, and then rapidly cooled to room temperature (about 10 minutes) to obtain a HfO2 controlled oxide layer.

[0106] (10) A layer of Ag array electrode was coated on the upper surface of the sample using a thermal evaporation coating apparatus and a mask, and a layer of a whole Ag bottom electrode was coated on the bottom of the sample. A single Ag electrode was square with a side length of 0.5 mm and an array spacing of 0.5 mm.

[0107] Comparative Example 1

[0108] like Figure 1 As shown in b, this comparative example provides a floating gate memory device based on solid structure CoO nanoparticles, and its structure is the same as that of Example 1, except that the hollow structure CoO nanoparticles are replaced with solid structure CoO nanoparticles.

[0109] The preparation method is as follows: when preparing the dielectric storage layer, the high-purity metal Co / HfO2 composite target is replaced with a high-purity CoO / HfO2 composite target. The sample is placed in a deposition chamber and evacuated to 5.0×10 -8 Torr, pulsed laser was used to alternately ablate CoO block target and HfO2 round target for 300 seconds, the pulsed laser frequency was 10 Hz, and the pulsed laser energy was 300 mJ. Then the sample was taken out and placed in the heating zone of the rapid annealing furnace, and rapidly heated to 350°C in an argon atmosphere for 35 seconds, then kept warm for 5 minutes, and then rapidly cooled to room temperature (about 10 minutes) to obtain solid CoO nanoparticles embedded in the HfO2 film.

[0110] Other methods for preparing HfO2 tunnel oxide layer and HfO2 control oxide layer and plating Ag electrode for solid CoO nanoparticle samples are exactly the same as those for hollow CoO nanoparticle samples.

[0111] Test and result analysis:

[0112] like Figure 2 Shown are TEM and corresponding SAED images of the CoO nanoparticles with a hollow structure in Example 1 of the present invention and the solid structure CoO nanoparticles of the sample in Comparative Example 1. Figure 2 The characterization revealed relatively uniform distribution, lattice spacing and crystal planes of hollow and solid CoO nanoparticles in the HfO2 matrix. Figure 2 As can be seen from d and f in the figure, the particle size of the CoO nanoparticles in Example 1 is about 10 nm and has a hollow structure.

[0113] Figure 3 3 is an XPS graph of the CoO nanoparticles with a hollow structure in Example 1 of the present invention and the CoO nanoparticles with a solid structure as a sample of Comparative Example 1. Figure 3 The elemental composition and valence state of the obtained hollow structure and solid structure CoO nanoparticles can be confirmed, indicating that Co and Hf in the storage medium layer exist in the form of CoO and HfO2, respectively.

[0114] Figure 4 It is the Raman spectrum of CoO nanoparticles with hollow structure in Example 1 of the present invention and solid structure in Comparative Example 1, which can confirm that both samples have typical cubic rock salt structures.

[0115] Figure 5 The graph is a capacitance-voltage (CV) test curve of the floating gate memory device based on the hollow structure CoO nanoparticles in Example 1 of the present invention and the floating gate memory device based on the solid structure CoO nanoparticles in Comparative Example 1. The research results show that under the same storage density and similar particle size, the charge storage performance of the hollow structure CoO nanoparticles is better than that of the solid structure CoO nanoparticles.

[0116] In summary, the present invention prepares a floating gate memory device based on hollow structure CoO nanoparticles. The nanoparticles are formed into a hollow structure through the Kirkendall effect, so that they have more surface defects and interface states, can capture more injected charges, and further enhance the charge storage capacity of the device.

[0117] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a floating gate memory device based on hollow structure nanoparticles, characterized in that: The following steps are involved: forming a tunnel oxide layer on the substrate; Continue to form a storage medium layer on the tunnel oxide layer; Continue to form a control oxide layer on the storage medium layer; The step of forming a tunnel oxide layer on the substrate specifically includes: The substrate is placed in a pulsed laser deposition device, and the pulsed laser deposition device is controlled to deposit HfO2 on the substrate with preset parameters; wherein the preset parameters include: the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 Torr~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300 seconds to 400 seconds, the pulse laser frequency is 5 Hz to 10 Hz, and the laser energy is 290 mJ to 310 mJ; The substrate is taken out and placed in an inert gas atmosphere for a first annealing treatment with first preset parameters to form a tunnel oxide layer on the substrate; wherein the first preset parameters include: a heating temperature of 320° C. to 360° C., a heating time of 32 seconds to 36 seconds, a heat preservation time of 3 minutes to 7 minutes, and a rapid cooling time of 8 minutes to 11 minutes; The step of continuously forming a storage medium layer on the tunnel oxide layer specifically includes: Connecting a high-purity metal Co target and a high-purity HfO2 target to form a combined target material, and placing the substrate formed with a tunnel oxide layer and the combined target material on a sample holder and a target holder of a pulsed laser deposition device, respectively; The pulsed laser deposition device is controlled to alternately ablate the high-purity HfO2 target and the high-purity metal Co target in the combined target material by laser, and HfO2 and Co are alternately deposited on the tunnel oxide layer according to preset parameters; wherein the preset parameters include: the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 Torr~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300 seconds to 400 seconds, the pulse laser frequency is 5 Hz to 10 Hz, and the laser energy is 290 mJ to 310 mJ; Placing the substrate having the tunnel oxide layer formed thereon in an inert gas atmosphere and performing a first annealing treatment with a first preset parameter to form Co nanoparticles embedded in amorphous HfO2 on the tunnel oxide layer; Placing the substrate having the tunnel oxide layer formed thereon in an oxygen atmosphere and performing a second annealing treatment with a second preset parameter to form the storage medium layer, wherein the Co nanoparticles are converted into CoO nanoparticles having a hollow structure; The first preset parameters include: heating temperature of 320°C to 360°C, heating time of 32 seconds to 36 seconds, heat preservation time of 3 minutes to 7 minutes, and rapid cooling time of 8 minutes to 11 minutes; The second preset parameters include: heating temperature of 380°C to 420°C, heating time of 38 seconds to 42 seconds, insulation time of 3 minutes to 7 minutes, and rapid cooling time of 9 minutes to 12 minutes.

2. The preparation method according to claim 1, characterized in that: The step of continuing to form a control oxide layer on the storage medium layer specifically includes: The substrate with the storage medium layer formed thereon is placed in a pulsed laser deposition device, and the pulsed laser deposition device is controlled to deposit HfO2 on the storage medium layer according to preset parameters; wherein the preset parameters include: the vacuum degree in the growth chamber of the pulsed laser deposition device is 8×10 -7 Torr~5.0×10 -8 The wavelength of the laser light source is 248 nanometers, the time of laser ablation of the target is 300 seconds to 400 seconds, the pulse laser frequency is 5 Hz to 10 Hz, and the laser energy is 290 mJ to 310 mJ; The substrate with the storage medium layer formed thereon is taken out and placed in an inert gas atmosphere for a first annealing treatment with first preset parameters to form a controlled oxide layer on the storage medium layer; wherein the first preset parameters include: a heating temperature of 320°C to 360°C, a heating time of 32 seconds to 36 seconds, a holding time of 3 minutes to 7 minutes, and a rapid cooling time of 8 minutes to 11 minutes.

3. The preparation method according to claim 1, characterized in that: After the step of continuously forming a control oxide layer on the storage medium layer, the method further comprises: Further plating a layer of Ag array electrode on the control oxide layer, and plating a layer of Ag bottom electrode on the bottom of the substrate; Among them, in the Ag array electrode, a single Ag electrode is square with a side length of 0.4mm~0.6mm, and the array interval is 0.4mm~0.6mm.

4. A floating gate memory device prepared by the preparation method according to any one of claims 1 to 3, characterized in that: include: substrate; A tunnel oxide layer, disposed on the substrate; A storage medium layer is disposed on the tunnel oxide layer, wherein the storage medium layer contains CoO nanoparticles having a hollow structure; The control oxide layer is arranged on the storage medium layer.

5. The floating gate memory device according to claim 4, characterized in that: The particle size of the CoO nanoparticles with a hollow structure is 9-11 nm.

6. The floating gate memory device according to claim 4, characterized in that: The storage medium layer further contains amorphous HfO2, and the CoO nanoparticles with a hollow structure are arranged in the amorphous HfO2.

7. The floating gate memory device according to claim 4, wherein: The tunnel oxide layer and the control oxide layer both contain amorphous HfO2, and the substrate is an n-Si (100) substrate.

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