A method for increasing the read current of a lithium niobate type ferroelectric domain wall memory using niobium electrode material

Abstract

The application belongs to the technical field of ferroelectric memory, and particularly relates to a method for increasing readout current of lithium niobate type ferroelectric domain wall memory by using niobium electrode material. In the application, the electrode electrically connected with the lithium niobate type ferroelectric material is a niobium metal electrode or a composite electrode containing niobium formed by growth at high temperature, so as to improve the contact state of the electrode / ferroelectric material interface, improve the injection and collection efficiency of the carrier to the ferroelectric domain wall conductive channel, thereby increasing the domain wall readout current, and improving the readout signal strength, storage window and switching ratio of the memory device, and improving the read-write speed and integration density of the memory. Experiments show that when the pure metal niobium electrode grown at 400 DEG C is used, the domain wall readout current of the lithium niobate single crystal is significantly higher than that of the comparative device using tungsten electrode and copper electrode. By increasing the readout current of the ferroelectric domain wall memory, the read-write operation speed and integration density of the ferroelectric memory can be greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of ferroelectric memory technology, specifically relating to a method and device for increasing the readout current of a ferroelectric domain wall memory. Background Technology

[0002] Ferroelectric memories (FORMs) are electronic devices that utilize the spontaneous polarization direction of ferroelectric materials to change with the direction of an applied positive or negative electric field, thereby enabling the storage and reading of data "0" and "1". They possess characteristics such as non-volatility, low power consumption, unlimited read / write cycles, and high radiation resistance, making them applicable to fields such as home appliances, automotive electronics, and aerospace. Traditional FORMs generally employ destructive readout techniques based on charge integration, requiring in-plane dimensions of storage cells larger than 200 nanometers. Commercially available storage capacities are typically 8 Mb, and three-dimensional stacking is difficult, limiting their high-density development. Current-based readout technology holds promise for overcoming these limitations in in-plane miniaturization, paving the way for high-density development. In particular, ferroelectric domain wall memories, developed in recent years, generate two parallel or antiparallel domains within the memory cell through positive and negative write electric fields, enabling non-volatile writing of logic information "0" and "1". Simultaneously, a conductive domain wall can be created or annihilated between the two domains, allowing for non-destructive readout of information via switching current. Examples include LiNbO3 domain wall memory, domain wall diodes / transistors / memristors, etc., which are currently a hot research area. Generally, the faster the read / write speed of a memory, the larger the required readout current. For example, a readout current greater than 1 microamp is required within 100 nanoseconds, and a readout current greater than 10 microamps is required within 1 nanosecond read / write time. However, in practical devices, the domain wall readout current strongly depends on the carrier injection / extraction conditions at the electrode-ferroelectric interface. Damage introduced by the interface Schottky barrier, dead layer, interface defects, and electrode processing significantly suppresses the domain wall current. The readout current of general memory devices is only in the nanoamp range, resulting in insufficient readout signal-to-noise ratio, small window size, low on / off ratio, and limited stability. Therefore, existing technologies still urgently need to find a new electrode material system or interface construction method to directly increase the readout current of ferroelectric domain walls without overly relying on complex embedded structures, intermediate layer engineering, or high-damage etching processes. This invention addresses the above problems by inventing a high-temperature grown niobium metal electrode or a niobium-containing composite electrode, which can significantly increase the domain wall readout current and storage window. Summary of the Invention

[0003] The purpose of this invention is to propose a method and device for increasing the read current of lithium niobate-type ferroelectric domain wall memory using niobium electrode material, which directly increases the read current of ferroelectric domain walls without excessively relying on complex embedded structures, intermediate layer engineering or high-damage etching processes.

[0004] The method for increasing the readout current of a lithium niobate-type ferroelectric domain wall memory provided by this invention uses niobium metal electrodes or niobium-containing composite electrodes grown at high temperatures as electrodes electrically connected to the lithium niobate-type ferroelectric material. This improves the contact state at the electrode / ferroelectric material interface, increases the injection and collection efficiency of charge carriers into the conductive channels of the ferroelectric domain walls, thereby increasing the domain wall readout current and improving the readout signal strength, storage window, and on / off ratio of the memory device, thus increasing the memory read / write speed and integration density.

[0005] Specifically, the present invention constructs a ferroelectric memory device comprising a ferroelectric material layer (102), a first electrode (1011), and a second electrode (1012); the ferroelectric material layer (102) is located between the first electrode (1011) and the second electrode (1012), and is constructed on a substrate (103), see [reference]. Figure 1 As shown; wherein the first electrode (1011) and / or the second electrode (1012) are niobium metal electrodes or niobium-containing composite electrodes grown under high temperature conditions; the electrodes are used in conjunction with the ferroelectric material layer to form conductive ferroelectric domain wall channels in the interior or adjacent area of ​​the ferroelectric material; the domain wall conductive channels are formed or erased by writing operations, and the switching current changes of the erasable and writable domain walls are detected by reading operations, thereby realizing non-destructive reading of non-volatile information.

[0006] Furthermore, the growth or annealing temperature of the niobium metal electrode or the niobium-containing composite electrode is 0℃~800℃, preferably 350℃~450℃.

[0007] Furthermore, the niobium-containing composite electrode includes a niobium conductive layer and a functional layer stacked thereon. The functional layer is one or more of an adhesion layer, a diffusion barrier layer, a protective layer, or a low-resistance contact layer. The material of the functional layer includes, but is not limited to, one or more of metals and inorganic non-metallic conductive materials.

[0008] Furthermore, the ferroelectric domain wall memory device includes out-of-plane or in-plane ferroelectric domain wall memory with a metal-ferroelectric material-metal structure, a cross-array ferroelectric memory, or other ferroelectric domain wall devices based on domain wall conductivity.

[0009] Furthermore, the lithium niobate ferroelectric material is a cover block or a thin film, and its materials include, but are not limited to, lithium niobate, lithium tantalate, lithium niobate salts and lithium tantalate salts doped with MgO, Mn2O5 or Fe2O3, blackened lithium niobate salts and blackened lithium tantalate salts. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the ferroelectric storage device structure according to an embodiment of the present invention.

[0011] Figure 2Scanning electron microscope (SEM) images of ferroelectric storage devices during the fabrication process.

[0012] Figure 3 Piezoelectric microscopy (PFM) images of ferroelectric storage devices in the off and on states.

[0013] Figure 4 This is a comparison of the current-voltage (IV) curves of lithium niobate ferroelectric devices using different electrode materials. Nb represents the example using a high-temperature grown pure niobium metal electrode, W and Cu represent comparative examples using pure tungsten and pure copper metal electrodes, respectively, and on and off represent the domain wall current being in the on and off states after polarization at + / -6V, respectively. To visually represent the current magnitude, the currents of the tungsten electrode device and the copper electrode device are magnified by a factor of 100 and 100, respectively.

[0014] Figure 5 This is a comparison of the open-state domain wall currents of lithium niobate devices with different electrode materials at a readout voltage of 2.5 V.

[0015] In the figure, the numbers 1011 represent the first electrode, 1012 the second electrode, 102 the ferroelectric material, and 103 the substrate. Detailed Implementation

[0016] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments, using X-cut LiNbO3 in-plane ferroelectric domain wall memory devices as examples, are used to illustrate the enhancing effect of high-temperature grown Nb-containing electrode layers on domain wall readout current, and should not be construed as limiting the type of ferroelectric material, electrode arrangement, or memory structure. Without departing from the technical concept of the present invention, those skilled in the art can apply the Nb-containing electrode layer to other ferroelectric devices based on domain wall conductivity readout.

[0017] In the description of the embodiments, the terms "first electrode" and "second electrode" are used to clearly illustrate the basic principles. These terms are for structural illustration only and do not represent any orientational limitation in the actual device. Furthermore, it should be noted that the two-electrode structure shown in the embodiments of this application is a basic model, possessing good scalability and universality, and can be applied to scenarios involving localized flipping of electric domains in regions of different shapes or with varying numbers of domains.

[0018] In the accompanying drawings, the thickness of layers and regions has been exaggerated for clarity, and the dimensional proportions between the parts shown do not reflect the actual dimensional proportions.

[0019] In the embodiments, the domain direction or polarization direction is given exemplarily to facilitate a detailed explanation of the principle. It should be understood that the domain direction or polarization direction is not limited to the directions shown in the embodiments of this application.

[0020] Example 1: High-Temperature Niobium Electrode Domain Wall Memory Based on X-cut LiNbO3 In-Plane Devices. A ferroelectric memory device includes an X-cut LiNbO3 ferroelectric substrate or a LiNbO3 single-crystal thin film (102), a first electrode (1011) and a second electrode (1012) disposed on its surface, wherein both the first electrode (1011) and the second electrode (1012) are made of niobium metal. The niobium electrode is formed by high-temperature deposition, preferably at 400°C; or by first depositing at room temperature and then annealing at high temperature.

[0021] During fabrication, the LiNbO3 surface is first cleaned to remove organic contaminants and surface particles; then, photolithography, electron beam lithography, or mask pattern transfer processes are used to define the electrode areas. The fabricated device is shown below. Figure 2 As shown; then, niobium electrode material is deposited under heated substrate conditions by magnetron sputtering.

[0022] When the device is operating, a write voltage higher than the local coercive voltage is applied between the two electrodes, causing local flipping of the ferroelectric domains in the region corresponding to the electrode gap. This flipped domains form ferroelectric domain wall conductive channels with the surrounding domains in the unflipped regions. At a lower readout voltage, the stored "1" information is read non-destructively by detecting the magnitude of the on-state current between the two electrodes. Under the erase voltage, the domain wall conductive channels disappear, thus achieving non-volatile storage of "0" information, and the readout current is in the off-state. The domain distribution of the ferroelectric storage device in the off-state and on-state are as follows: Figure 3 As shown.

[0023] A micro-nano probe stage was used to perform readout tests on the domain wall region: the domain wall positions were located and the domain wall conduction current was measured; the I-V curve and stable readout current were recorded; and tests were conducted under two states: "domain wall on state" and "domain wall off state". The test results show that, under the same readout voltage, the domain wall conduction current of the device in this embodiment is significantly increased.

[0024] like Figure 4 As shown, compared with the comparative devices using pure copper and pure tungsten as electrodes, the domain wall current of the pure niobium electrode device in this embodiment of the invention is significantly increased at the same read voltage: in the domain wall on state (on), the domain wall current (Nb) of the pure niobium electrode device is significantly increased. on Compared to the domain wall current (W) of devices using pure tungsten electrodes on The domain wall current (Nb) is increased by approximately 1 to 2 orders of magnitude using pure niobium electrode devices. on Compared to domain wall currents (Cu) using pure copper electrode devices on This represents an improvement of approximately 2 to 3 orders of magnitude.

[0025] like Figure 5 As shown, when the device is in the on state and the read voltage is 2.5 V, the open-state domain wall current of the device (Nb) in this embodiment is 20.6 μA, which is about 70 times and about 400 times higher than the open-state domain wall current of 0.28 μA of the comparative pure tungsten electrode device (W) and 5.1 nA of the comparative pure copper electrode device (Cu).

[0026] Comparative Example 1: A LiNbO3 domain wall memory device using tungsten electrodes (W). To verify the influence of electrode materials and interfaces on domain wall current, a comparative example device was constructed. Except for the use of tungsten as the in-plane electrode material, the conditions of the comparative example device were kept as consistent as possible with those of Example 1, including: the same type of X-cut LiNbO3 substrate; the same electrode pattern size and electrode spacing; and the same domain structure write / erase method and readout test procedure. The comparative results show that the on-state current at the tungsten / LiNbO3 contact domain wall is relatively small, with an on-state current of 0.28 μA at a read voltage of 2.5 V, which is significantly lower than the 20.6 μA of the pure niobium electrode device in Example 1.

[0027] Comparative Example 2: A LiNbO3 domain wall memory device using copper (Cu) electrodes. To verify the influence of electrode materials and interfaces on domain wall current, a comparative example device was constructed. Except for the use of copper as the in-plane electrode material, the comparative example device maintained as many conditions as possible the same as Example 1, including: the same type of X-cut LiNbO3 substrate; the same electrode pattern size and electrode spacing; and the same domain structure write / erase method and readout test procedure. The comparative results show that the on-state current at the copper / LiNbO3 contact domain wall is relatively small, with an on-state current of 5.1 nA at a read voltage of 2.5 V, significantly lower than the 20.6 μA of the pure niobium electrode device in Example 1.

[0028] In summary, this invention proposes a method to increase the readout current of lithium niobate-type ferroelectric domain wall devices by optimizing electrode materials. Using metallic niobium electrodes grown at approximately 400°C significantly improves the domain wall current readout current, storage window, and readout current on / off ratio, thereby meeting the application requirements of ferroelectric domain wall memories for high read / write speeds, high integration density, and high reliability.

Claims

1. A method for increasing the read current of a lithium niobate-type ferroelectric domain wall memory using niobium electrode material, characterized in that, The electrode electrically connected to the lithium niobate-type ferroelectric material is a niobium metal electrode or a niobium-containing composite electrode grown at high temperature. This improves the contact state at the electrode / ferroelectric material interface, enhances the injection and collection efficiency of charge carriers into the conductive channels of the ferroelectric domain walls, thereby increasing the domain wall readout current and improving the readout signal strength, storage window, and on / off ratio of the memory device, thus increasing the memory read / write speed and integration density.

2. The method according to claim 1, characterized in that, The growth or annealing temperature of the niobium metal electrode or the niobium-containing composite electrode is 0℃~800℃.

3. The method according to claim 2, characterized in that, The growth or annealing temperature of the niobium metal electrode or the niobium-containing composite electrode is 350℃~450℃.

4. The method according to claim 1, 2 or 3, characterized in that, The niobium-containing composite electrode includes a niobium conductive layer and a functional layer stacked thereon. The functional layer is one or more of an adhesion layer, a diffusion barrier layer, a protective layer, or a low-resistance contact layer. The material of the functional layer is one or more of a metal or an inorganic non-metallic conductive material.

5. The method according to claim 4, characterized in that, The ferroelectric domain wall memory is an out-of-plane or in-plane ferroelectric domain wall memory with a metal-ferroelectric material-metal structure, a cross-array ferroelectric memory, or other ferroelectric domain wall devices based on domain wall conductivity.

6. The method according to claim 5, characterized in that, The lithium niobate-type ferroelectric material is in bulk and thin film form, and its material is selected from lithium niobate, lithium tantalate, lithium niobate salts and lithium tantalate salts doped with MgO, Mn2O5 or Fe2O3, and blackened lithium niobate salts and lithium tantalate salts.

7. A lithium niobate ferroelectric domain wall memory using niobium electrode material, obtained by the method described in any one of claims 1-6.

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