A method for polarity switching of a memristive device made of a topological phase change material

Abstract

The present invention discloses a method for polar switching of a memristive device made of a topological phase change material. The memristive device includes a storage medium layer made of a pure-phase SrFeO<subgt;2.5< / subgt; or SrCoO<subgt;2.5< / subgt; material. The method for polar switching includes: grounding the bottom electrode layer of the memristive device, applying a 0-2V positive DC scanning voltage to the top electrode layer, and then applying a 0--2.5V negative DC scanning voltage to the top electrode layer; applying a 0-+6V positive DC scanning voltage to the top electrode layer, then applying a 0--2V negative DC scanning voltage to the top electrode layer, and then applying a 0-+2.5V positive DC scanning voltage to the top electrode; applying a 0--6V negative DC scanning voltage to the top electrode layer, then applying a 0-2V positive DC scanning voltage to the top electrode layer, and then applying a 0--2.5V negative DC scanning voltage to the top electrode layer. The present invention can effectively improve the application scenarios of the memristive device.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor information storage and artificial synaptic devices, and more specifically, relates to a method for polar switching of a topological phase change material memristor device. Background Art

[0002] "Topological phase transition" is an expression regarding the structural stability of materials. When a part of the constituent elements in a material is extracted, it still has a stable lattice framework, and its corresponding physical structure and chemical properties will change to a certain extent. Such materials are called topological phase change materials. A typical topological phase change material, SrFeO x (SFO), can mutually transform between the SrFeO3 perovskite (PV) phase and SrFeO 2.5 brownmillerite (BM) phase by gaining and losing oxygen. After an O 2p orbital in PV-SFO transfers an electron to the Fe 3d orbital, it is in an unoccupied state, the charge transfer energy is negative, there is no bandgap, and it shows a metallic conductive phase. The charge transfer energy between the O 2p orbital and the unoccupied Fe 3d orbital in BM-SFO is positive, forming a bandgap of about 2 eV, showing an insulating phase. By applying an external electric field, the SFO material can be transformed between the PV phase and the BM phase, and the resistance value of the material changes accordingly. Based on this property, it can be applied to the research in the field of memristors and has been a research hotspot in recent years. The memristor device based on the SFO material regulates the conductive channel of the SFO memristor through the migration of oxygen ions. During the SET (set) process, by applying a voltage, the oxygen ions migrate. The BM-SFO along the path receives the oxygen ions and transforms into PV-SFO to form a conductive filament channel connecting the upper and lower electrodes, and the device changes from a high resistance to a low resistance; during the RESET (reset) process, by applying a reverse voltage, the PV-SFO formed during the SET process loses oxygen ions and transforms into BM-SFO, thus disconnecting the conductive channel.

[0003] The operation direction of traditional bipolar memristor devices depends on the selection of the functional layer and the electrode layer. After the device structure is fixed, it is very difficult to switch and regulate its operation direction, which limits the operable range of the memristor. Figure 1 、 Figure 2 respectively show the logic units when the memristor constructs AND and OR logics. It can be seen that the switching of the logic needs to be achieved by changing the polarity of the input-terminal memristor. At this time, if the memristors M1 and M2 can freely switch their polarities, Figure 1 and Figure 2 the two logic units can be degenerate into one. Therefore, it is necessary to study a topological phase change material memristor device with switchable polarity to provide its usage scenarios after packaging. Summary of the Invention

[0004] Aiming at the defects of the prior art, the purpose of the present invention is to provide a method for polar switching of a topological phase change material memristor device. By applying a bias voltage to change the polarity of the memristor device, the application scenarios and potential of the memristor device can be effectively improved.

[0005] To achieve the above object, in a first aspect, the present invention provides a method for polar switching of a topological phase change material memristor device. The topological phase change material memristor device includes a substrate layer, a bottom electrode layer, a storage medium layer, and a top electrode layer arranged in sequence from bottom to top. The material of the storage medium layer is pure-phase SrFeO 2.5 or SrCoO 2.5 , and the polar switching method includes a first switching method of switching from positive setting and negative resetting to negative setting and positive resetting, and a second switching method of switching from negative setting and positive resetting to positive setting and negative resetting;

[0006] Among them, the first switching method includes the following steps:

[0007] (1) Ground the bottom electrode layer of the topological phase change material memristor device, and apply a negative DC sweep voltage of 0 to -9V to its top electrode layer to complete the electroforming operation;

[0008] (2) Apply a positive DC sweep voltage of 0 to 2V to the top electrode layer to complete the SET operation, and then apply a negative DC sweep voltage of 0 to -2.5V to the top electrode layer to complete the RESET operation, so that the topological phase change material memristor device is in a positive setting and negative reset state;

[0009] (3) Apply a positive DC sweep voltage of 0 to +6V to the top electrode layer, then apply a negative DC sweep voltage of 0 to -2V to the top electrode layer to complete the SET operation, and then apply a positive DC sweep voltage of 0 to +2.5V to the top electrode to complete the RESET operation, so that the topological phase change material memristor device is in a negative setting and positive reset state;

[0010] The second switching method includes the following steps:

[0011] (4) Apply a negative DC sweep voltage of 0 to -6V to the top electrode layer of the topological phase change material memristor device in step (3), then apply a positive DC sweep voltage of 0 to 2V to the top electrode layer to complete the SET operation, and then apply a negative DC sweep voltage of 0 to -2.5V to the top electrode layer to complete the RESET operation, so that the topological phase change material memristor device is in a positive setting and negative reset state.

[0012] The method for polar switching of the topological phase change material memristor device provided by the present invention uses pure-phase SrFeO 2.5 or SrCoO 2.5By applying a bias voltage to regulate the migration and aggregation behavior of oxygen ions in the storage medium layer, the polarity of the memristive device can be switched, effectively improving the usage scenarios of the device after packaging.

[0013] In one embodiment, the crystal orientation of the storage medium layer is <111> or <110> direction, and its thickness ranges from 30 to 50 nm.

[0014] In one embodiment, the bottom electrode layer is made of SrRuO3, whose crystal orientation is <111> or <110> direction, and its thickness ranges from 50 to 100 nm.

[0015] In one embodiment, the top electrode layer is made of pure phase Pt or Au, and its thickness ranges from 80 to 100 nm.

[0016] In one embodiment, the size of the top electrode layer is 60×60 to 100×100 μm. 2 .

[0017] In one embodiment, the substrate layer is made of pure phase SrTiO3, whose crystal orientation is <111> direction.

[0018] In a second aspect, the present invention provides a logic unit for realizing AND / OR functions, comprising two of the above-mentioned topological phase change material memristor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural diagram of a traditional AND gate logic unit;

[0020] Figure 2 It is a schematic diagram of the structure of the traditional OR gate logic unit;

[0021] Figure 3 1 is a schematic structural diagram of a topological phase change material memristor device provided by one embodiment of the present invention;

[0022] Figure 4 yes Figure 3 A flow chart of a polarity switching method for a topological phase change material memristor device is provided;

[0023] Figure 5 is a graph showing a current change curve of the storage medium layer under the bias voltage applied in step S20 in one embodiment of the present invention;

[0024] Figure 6 is a graph showing a change in current of the storage medium layer under the bias voltage applied in step S30 in one embodiment of the present invention;

[0025] Figure 7It is a current change curve graph of the storage medium layer under the bias voltage applied in step S40 in an embodiment of the present invention;

[0026] Figure 8 It is a schematic diagram of the principle of the polarity switching method of the topological phase change material memristor device provided in an embodiment of the present invention. Detailed implementation manners

[0027] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to 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.

[0028] Figure 3 It is a schematic structural diagram of a polarity-switchable topological phase change material memristor device provided in an embodiment of the present invention. As Figure 3 shown, the memristor device provided in this embodiment includes a substrate layer, a bottom electrode layer, a storage medium layer, and a top electrode layer that are sequentially arranged from bottom to top.

[0029] In this embodiment, the substrate layer mainly plays a supporting role. Its material can be pure-phase SrTiO3, and its crystal orientation can be in the <111> or <110> direction. The bottom electrode layer and the top electrode layer are two electrodes for inputting a bias voltage. Specifically, the material of the bottom electrode layer can be pure-phase SrRuO3, its crystal orientation is in the <111> or <110> direction, and its thickness range is 50-100 nm; the material of the top electrode layer can be pure-phase Pt or Au, its thickness range is 80-100 nm, and its size is 60×60-100×100 μm 2 .

[0030] The storage medium layer provided in this embodiment is made of a phase change material of pure-phase SrFeO 2.5 or SrCoO 2.5 . The present invention mainly regulates the bias voltage applied to the storage medium layer to control the migration and aggregation behavior of cations in pure-phase SrFeO 2.5 or SrCoO 2.5 to achieve the polarity transformation (operation direction transformation) of the topological phase change material memristor device, that is, the switching between two states of forward setting and negative resetting and negative setting and positive resetting.

[0031] Among them, as Figure 4 shown, the switching method of switching from forward setting and negative resetting to negative setting and positive resetting is specifically as follows:

[0032] S10, ground the bottom electrode layer of the topological phase change material memristor device, and apply a negative DC scanning voltage of 0 to -9V to its top electrode layer to complete the electroforming operation.

[0033] S20, asFigure 5 As shown, a positive DC scanning voltage of 0 to 2V is applied to the top electrode layer to complete the SET operation, and then a negative DC scanning voltage of 0 to -2.5V is applied to the top electrode to complete the RESET operation, so that the topological phase change material memristive device is in a positive SET and negative RESET state.

[0034] S30, as Figure 6 shown, a positive DC scanning voltage of 0 to +6V is applied to the top electrode layer, then a negative DC scanning voltage of 0 to -2V is applied to the top electrode layer to complete the SET operation, and then a positive DC scanning voltage of 0 to +2.5V is applied to the top electrode to complete the RESET operation, so that the topological phase change material memristive device is in a negative SET and positive RESET state.

[0035] The switching method from negative SET and positive RESET to positive SET and negative RESET is specifically as follows:

[0036] S40, as Figure 7 shown, a negative DC scanning voltage of 0 to -6V is applied to the top electrode of the topological phase change material memristive device in step 3, and the above-mentioned step S20 is repeated, that is, a positive DC scanning voltage of 0 to 2V is applied to the top electrode layer to complete the SET operation, and then a negative DC scanning voltage of 0 to -2.5V is applied to the top electrode layer to complete the RESET operation, and the topological phase change material memristive device can be in a positive SET and negative RESET state.

[0037] The polarity switching principle of the topological phase change material memristive device provided in this embodiment is:

[0038] As Figure 8 shown, Figure 8 in ① shows the initial state of the memristive device. After applying a negative bias voltage of 9V, oxygen in the air and on the surface will accumulate at the lower interface of the storage medium layer through the top electrode layer, and the memristive device completes electroforming, as Figure 8 shown in ②. At this time, when a positive bias voltage of 2V is continuously applied, some oxygen ions at the bottom of the storage medium layer will migrate upward to form a conductive filament, realizing the positive SET operation, as Figure 8 shown in ③. When a negative bias voltage of 2.5V is applied to the polarity of the memristive device, the oxygen ions return to the bottom of the storage medium layer, and the memristive device completes the negative RESET operation, as Figure 8 shown in ④, so that the memristive device at this time is in a positive SET and negative RESET state. Subsequently, when a positive bias voltage of 6V is continuously applied, a large number of oxygen ions migrate upward to the top of the storage medium layer, as Figure 8 shown in ⑤, and then when a negative bias voltage of 2V is continuously applied, some oxygen ions on the upper interface migrate downward to form a top-down conductive channel, and the memristive device realizes the negative SET operation, as Figure 8 shown in ⑥. At this time, when a positive bias voltage of 2.5V is applied again, this part of the oxygen ions returns to the upper interface, and the memristive device completes the positive RESET operation, as Figure 8As shown in ⑦, the memristive device is in the negative-set and positive-reset state at this time, thus completing the polarity switching from positive-set and negative-reset to negative-set and positive-reset.

[0039] When the memristive device is in the negative-set and positive-reset state, apply a 6V negative bias voltage. All the oxygen ions on the upper interface migrate back to the lower interface, and the device returns to the state just after electroforming, as Figure 8 shown in ⑧. Then repeat the above step 2 (the principle can be referred to the foregoing description), and the memristive device can be returned to the positive-set and negative-reset state.

[0040] The polarity switching method of the topological phase change material memristive device provided in this embodiment uses a pure-phase SrFeO 2.5 or SrCoO 2.5 for the storage medium layer. By applying a bias voltage to control the migration and aggregation behavior of oxygen ions in the storage medium layer, the polarity switching of the memristive device can be achieved, effectively improving the usage scenario of the device after packaging.

[0041] Based on the same inventive concept, the present invention also provides a logic unit for implementing AND or OR functions, including two topological phase change material memristive devices provided in the foregoing embodiments, that is, replacing the memristive devices M1 and M2 in the logic units of traditional AND gates or OR gates (as Figure 1 and Figure 2 shown) with the topological phase change material topological memristive devices provided by the present invention. The polarity of the memristive device in the replaced logic unit is switched by applying a bias voltage in the above embodiment, so that the AND function and the OR function can be achieved.

[0042] The present invention will be described in detail below with specific embodiments:

[0043] Embodiment 1 provides a topological phase change material memristive device, including:

[0044] The characteristic structure layer ① is a substrate layer, with a composition of pure-phase SrTiO3 and a crystal orientation of <111> direction.

[0045] The characteristic structure layer ② is a bottom electrode layer, with a composition of pure-phase SrRuO3, a crystal orientation of <111> direction, and a thickness of 50nm.

[0046] The characteristic structure layer ③ is a storage medium layer, with a composition of pure-phase SrFeO 2.5 , a crystal orientation of <111> direction, and a thickness range of 30nm.

[0047] The characteristic structure layer ④ is a top electrode layer, with a composition of pure-phase Au, a thickness range of 80 - 100nm, and a size of 60×60μm 2 .

[0048] Apply the following steps to switch the device polarity:

[0049] Step 1: Ground the bottom electrode and apply a negative DC sweep voltage of 0 to -9V to the top electrode to complete the electroforming operation.

[0050] Step 2: Apply a positive voltage of 2V to the top electrode to complete the SET operation.

[0051] Step 3: Apply a negative voltage of -2.5V to the top electrode to complete the RESET operation.

[0052] Step 4: Apply a positive voltage of +6V to the top electrode to complete the positive-to-negative polarity switching operation.

[0053] Step 5: Apply a negative voltage of -2V to the top electrode to complete the SET operation.

[0054] Step 6: Apply a positive voltage of +2.5V to the top electrode to complete the RESET operation.

[0055] Step 7: Apply a negative voltage of -5V to the top electrode to complete the negative-to-positive polarity switching operation.

[0056] Step 8: Apply a positive voltage of 2V to the top electrode to complete the SET operation (repeat Step 2).

[0057] Step 9: Apply a negative voltage of -2.5V to the top electrode to complete the RESET operation (repeat Step 3).

[0058] Example 2 provides a topological phase change material memristive device, including:

[0059] Characteristic structure layer ① is a substrate layer, with a composition of pure-phase SrTiO3 and a crystal orientation in the <110> direction.

[0060] Characteristic structure layer ② is a bottom electrode layer, with a composition of pure-phase SrRuO3, a crystal orientation in the <110> direction, and a thickness range of 60nm.

[0061] Characteristic structure layer ③ is a storage medium layer, with a composition of pure-phase SrCoO 2.5 , with a crystal orientation in the <110> direction and a thickness range of 40nm.

[0062] Characteristic structure layer ④ is a top electrode layer, with a composition of pure-phase Pt, a thickness range of 100nm, and a size of 80×80μm 2 .

[0063] Apply the following steps to switch the device polarity:

[0064] Step 1: Ground the bottom electrode and apply a negative DC sweep voltage of 0 to -9V to the top electrode to complete the electroforming operation.

[0065] Step 2: Ground the bottom electrode of the device and apply a +2V positive voltage to the top electrode to complete the SET operation.

[0066] Step 3: Apply a -2.5V negative voltage to the top electrode to complete the RESET operation.

[0067] Step 4: Apply a +6V positive voltage to the top electrode to complete the positive-to-negative polarity switching operation.

[0068] Step 5: Apply a -2V negative voltage to the top electrode to complete the SET operation.

[0069] Step 6: Apply a +2.5V positive voltage to the top electrode to complete the RESET operation.

[0070] Step 7: Apply a -5V negative voltage to the top electrode to complete the negative-to-positive polarity switching operation.

[0071] Step 8: Apply a +2V positive voltage to the top electrode to complete the SET operation (repeat Step 2).

[0072] Step 9: Apply a -2.5V negative voltage to the top electrode to complete the RESET operation (repeat Step 3).

[0073] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for polarity switching of a memristive device made of a topological phase change material, characterized in that, The topological phase change material memristive device includes a substrate layer, a bottom electrode layer, a storage medium layer, and a top electrode layer sequentially arranged from bottom to top. The material of the storage medium layer is a pure phase or , and the polarity switching method includes a first switching method of switching from positive setting and negative resetting to negative setting and positive resetting, and a second switching method of switching from negative setting and positive resetting to positive setting and negative resetting; Among them, the first switching method includes the following steps: (1) Ground the bottom electrode layer of the topological phase change material memristor device, and apply a negative DC scanning voltage of 0 to -9 V to its top electrode layer to complete the electroforming operation; (2) Apply a positive DC scanning voltage of 0 to 2 V to the top electrode layer to complete the SET operation, and then apply a negative DC scanning voltage of 0 to -2.5 V to the top electrode layer to complete the RESET operation, so that the topological phase change material memristor device is in a positive SET and negative RESET state; (3) Apply a positive DC scanning voltage of 0 to +6 V to the top electrode layer, then apply a negative DC scanning voltage of 0 to -2 V to the top electrode layer to complete the SET operation, and then apply a positive DC scanning voltage of 0 to +2.5 V to the top electrode to complete the RESET operation, so that the topological phase change material memristor device is in a negative SET and positive RESET; The second switching method includes the following steps: (4) Apply a negative DC scanning voltage of 0 to -6 V to the top electrode layer of the topological phase change material memristor device in step (3), then apply a positive DC scanning voltage of 0 to 2 V to the top electrode layer to complete the SET operation, and then apply a negative DC scanning voltage of 0 to -2.5 V to the top electrode layer to complete the RESET operation, so that the topological phase change material memristor device is in a positive SET and negative RESET state.

2. The polarity switching method of the topological phase change material memristor device according to claim 1, wherein The crystal orientation of the storage medium layer is in the <111> or <110> direction, and its thickness range is 30 to 50 nm.

3. The polarity switching method of the topological phase change material memristor device according to claim 1, characterized in that, The material of the bottom electrode layer is , whose crystal orientation is in the <111> or <110> direction, and whose thickness ranges from 50 to 100 nm.

4. The polarity switching method of the topological phase change material memristor device according to claim 1, characterized in that The material of the top electrode layer is pure-phase Pt or Au, and its thickness range is 80 to 100 nm.

5. The polarity switching method of the topological phase change material memristor device according to claim 1, characterized in that, The size of the top electrode layer is 60×60 to 100×100 .

6. The polarity switching method of the topological phase change material memristor device according to claim 1, characterized in that, The material of the substrate layer is a pure phase , and its crystal orientation is in the <111> direction.

7. A logic unit for implementing an AND-OR function, characterized in that, Execute the polarity switching method of the topological phase change material memristor device according to any one of claims 1 to 6.

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