CN108807668B - High-performance memristor based on metal oxide oxygen concentration gradient and preparation thereof - Google Patents
High-performance memristor based on metal oxide oxygen concentration gradient and preparation thereof Download PDFInfo
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Abstract
The invention discloses a high-performance memristor device based on metal oxide oxygen concentration gradient and a preparation method thereof, wherein a device unit of the memristor comprises an upper electrode, a functional layer and a lower electrode from top to bottom, the functional layer is made of metal oxide, and the oxygen content in the functional layer is in gradient change. According to the memristor, the internal composition of a key functional layer in the memristor, the preparation method of the functional layer and the like are improved, the metal oxide with the oxygen content changing in a gradient manner is used as the functional layer, the on-off of the conductive wire is localized in a high oxygen content area, the random on-off of a conductive channel is inhibited, and the stability, the consistency and the switching speed of a memristor device can be improved. The current limiting can be reduced, and simultaneously, the high/low impedance state can be improved, so that the power consumption is reduced. The functional layer based on the oxygen concentration gradient is easy to form a conical conductive channel, the conical top of the conductive channel with high oxygen content has the characteristic of easy on-off, and high-speed resistance change under low-voltage operation can be realized.
Description
Technical Field
The invention belongs to the technical field of microelectronic devices, and particularly relates to a high-performance memristor device based on metal oxide oxygen concentration gradient and a preparation method thereof.
Background
The memristor can be divided into continuously adjustable gradual resistance change and sudden resistance change according to different performance characteristics of the memristor. The former is proved to have great application prospect in the aspect of simulating the synapse of the neuron, and the latter can be applied to the aspect of data storage; due to the non-volatility, low power consumption and high switching characteristic of nanosecond level, the memory not only can be used as a next generation memory for replacing Flash, but also has great potential in the aspect of realizing calculation and storage fusion.
At the present stage, however, the memristor based on the conductive wire theory has the advantages of high speed, large resistance change window, low operating voltage and the like, has great commercial potential, and is a hot spot of domestic and foreign research. However, since the on-off of the conductive wire is difficult to control, and the on-off of a localized conductive path has great randomness, so that the distribution of on/off voltage and high and low resistance values is discrete, the power consumption of a crossbar structure which can be used for integration is increased due to misreading and leakage current caused by the problem of electrical crosstalk (cross), a complex peripheral circuit is usually required to be designed to improve the identification precision, the cost is increased, and the circuit area is increased;
in addition, according to the energy requirement of the memristor switching characteristic, namely the voltage pulse width × voltage amplitude, when the pulse width is reduced to 100ns or even 10ns, the voltage amplitude is greatly increased, the low power consumption of a chip is difficult to realize, and the integration of a high-speed chip circuit and the fusion of calculation and storage are not facilitated.
Disclosure of Invention
In view of the above defects or improvement requirements of the prior art, an object of the present invention is to provide a high performance memristor device based on a metal oxide oxygen concentration gradient and a preparation method thereof, wherein the internal composition of a key functional layer in the memristor and the preparation method thereof are improved, the metal oxide with the oxygen content changing in a gradient manner is used as the functional layer, the on-off of a conductive wire is localized in a high oxygen content region, the random on-off of a conductive channel is inhibited, and the stability, the consistency and the switching speed of the memristor device can be improved. The current limiting can be reduced, and simultaneously, the high/low impedance state can be improved, so that the power consumption is reduced. The functional layer based on the oxygen concentration gradient is easy to form a conical conductive channel, the conical top of the conductive channel with high oxygen content has the characteristic of easy on-off, and high-speed resistance change under low-voltage operation can be realized. The memristor provided by the invention has the advantages that the on-off of the conductive wire is localized, so that the resistance state is further improved, the stability is better, the voltage lower than 1V is shown under the high-speed tests of 100ns and 50ns, and the operating voltage lower than 3.3V is further realized under the pulse width of 10 ns.
In order to achieve the above object, according to one aspect of the present invention, there is provided a memristor based on a metal oxide oxygen concentration gradient, wherein a device unit of the memristor includes, from top to bottom, an upper electrode, a functional layer and a lower electrode, the functional layer is made of a metal oxide, the oxygen content in the functional layer varies in a gradient manner, and the oxygen content in the functional layer varies in an increasing or decreasing manner along a direction from the lower electrode to the upper electrode.
In a further preferred embodiment of the present invention, the metal oxide is an oxide of Ta, an oxide of Hf, an oxide of Al, or an oxide of Cu.
As a further preferred aspect of the present invention, the gradient change of the oxygen content in the functional layer is a continuous change.
As a further preferred aspect of the present invention, the upper electrode is an inert electrode, which is preferably Pt, Pd or Ir; the lower electrode is an active electrode, and the active electrode is preferably at least one of Ta, Hf, Al, Cu, Ti and Ag.
As a further preferred aspect of the present invention, the memristor includes a plurality of device units, and the plurality of device units correspond to the plurality of upper electrodes and share the same functional layer and the same lower electrode; the projection of any one upper electrode on the plane of the outer surface of the lower electrode is square;
preferably, the thickness of the lower electrode is 50nm-200nm, and the thickness of the functional layer is 10nm-100 nm; the thickness of any one of the upper electrodes is 50nm to 500 nm.
According to another aspect of the present invention, there is provided a method of making a metal oxide oxygen concentration gradient-based memristor, comprising the steps of:
(1) preparing a lower electrode on a substrate;
(2) preparing a functional layer:
sputtering the lower electrode by using a sputtering method to form a metal oxide, and gradually increasing or decreasing the content of oxygen in the environment atmosphere in which the sputtering is performed in the sputtering process to obtain the metal oxide with the oxygen content in gradient distribution so as to obtain a functional layer;
(3) and preparing an upper electrode on the functional layer, thereby finally obtaining the memristor based on the metal oxide oxygen concentration gradient.
As a further preferable aspect of the present invention, in the step (2), before the sputtering is started, the lower electrode further forms a photoresist layer corresponding to a photolithographic pattern on the surface of the lower electrode by a photolithographic process, so that the lower electrode is not completely covered by the functional layer during the sputtering, and a part of the lower electrode that is not covered by the functional layer is used for testing;
in addition, after the sputtering is finished, the photoresist layer is peeled off by adopting a method of acetone soaking and ultrasonic cleaning, then the photoresist layer is sequentially cleaned by absolute ethyl alcohol and deionized water, and the functional layer is obtained after the photoresist layer is dried by a nitrogen gun.
As a further preferable aspect of the present invention, in step (3), before the preparation of the upper electrode is started, the functional layer further forms a photoresist layer corresponding to a lithographic pattern on the surface of the functional layer by a lithographic process, so that the functional layer is not completely covered by the upper electrode in the process of preparing the upper electrode;
in addition, after the preparation of the upper electrode is finished, the photoresist layer is stripped by adopting a method of acetone soaking and ultrasonic cleaning, then the photoresist layer is sequentially cleaned by absolute ethyl alcohol and deionized water, and the memristor is obtained after the cleaning by a nitrogen gun;
preferably, the photoresist layer is used for forming an upper electrode which projects to be square on the plane of the substrate surface; the upper electrode is preferably plural.
In a further preferred embodiment of the present invention, in the step (2), the atmosphere in which the sputtering is performed is O2A mixed gas with Ar; preferably, the atmosphere of the sputtering environment maintains a fixed air pressure;
the oxygen content in the atmosphere in which the sputtering is carried out is preferably increased gradually during the sputtering process in the form of O2The flow ratio of the Ar to the Ar is 0/40,2/60,3/60,3/45 and 6/60 which are increased in sequence;
the oxygen content in the atmosphere in which the sputtering takes place is preferably reduced gradually during the sputtering process as O2The flow ratios 6/60, 3/45, 3/60, 2/60 and 0/40 of Ar are reduced in sequence.
As a further preferred mode of the present invention, in the step (1), the substrate is polished on a single surface and grown with SiO2A Si substrate of an insulating layer;
the step (1) is to prepare the lower electrode on the substrate by using a direct current magnetron sputtering method;
and (3) preparing the upper electrode by using a direct-current magnetron sputtering method.
Compared with the prior art, the technical scheme of the invention has the advantages that the metal oxide with the oxygen content changing in a gradient manner is used as the functional layer, for example, the oxygen content of the functional layer is gradually increased from the lower electrode to the upper electrode (the oxygen content of the functional layer can be gradually changed, namely continuously changed), the upper electrode can be used as the inert electrode, the lower electrode can be used as the oxygen storage pool (oxygen reservoir), the obtained memristor based on the metal oxide oxygen concentration gradient film, namely the oxygen concentration gradient type memristor, can inhibit the random on-off of a conductive channel, can effectively regulate and control a nano conductive path in a high oxygen content area, and can realize stable high-low impedance, low-voltage and high-speed operation. In the invention, the metal oxide preferably selects oxides of Ta, Hf, Al, Cu and the like compatible with a CMOS process as the gradient functional resistance change layer. The functional layer can be prepared by adopting a sputtering method, and in the sputtering preparation process of the functional layer, the oxygen content in the working gas is adjusted to obtain the oxygen gradient type metal oxide film, for example, the metal oxide functional layer containing the oxygen concentration gradient can be prepared by regulating and controlling the proportion of different argon and oxygen in the sputtering process; the invention can gradually increase the working gas O in the sputtering process of the functional layer2O in mixed gas with Ar2The content of (b) can be such that the content of oxygen in the functional layer gradually increases from the lower electrode to the upper electrode.
The functional layer in the memristor is metal oxide such as Ta oxide, Hf oxide, Al oxide or Cu oxide, and the oxygen content in the functional layer changes in a gradient manner from an upper electrode to a lower electrode, namely, x in Ta oxide TaOx, Hf oxide HfOx, Al oxide AlOx and Cu oxide CuOx changes in a gradient manner, for example, x in TaOx can change within 0-2.5, x in HfOx can change within 0-2, x in AlOx can change within 0-1.5 and x in CuOx can change within 0-2.
When the memristor functional layer with the oxygen content in the gradient distribution in the metal oxide is prepared, a sputtering process can be adopted, and the oxygen content in the environment atmosphere in which sputtering is carried out is gradually increased in the sputtering process, so that the metal oxide functional layer with the oxygen content in the gradient distribution is finally obtained. Taking the atmosphere in which the sputtering is carried out as O2For example, the mixed gas with Ar may be O during sputtering2The flow ratio of the Ar to the Ar is 0/40,2/60,3/60,3/45 and 6/60, the content of oxygen in the environment atmosphere in which sputtering is carried out is sequentially increased, and the functional layer with the oxygen content changing in a gradient manner can be obtained. Of course, the composition change of the environment atmosphere in which the sputtering is performed can be adjusted according to actual needs, so as to prepare the functional layer with the oxygen content changing in a sudden and gradient manner.
In the aspect of the performance of the memristor, the low resistance value of the gradient type memristor is improved to 10 under the low limiting current lower than 100uA4Omega or more, and further increase of high resistance is realized, thereby reducing leakage current, preventing electrical crosstalk between resistance change units, and suppressing discreteness of set voltage and reset voltage; meanwhile, the functional layer based on the oxygen content concentration gradient is easier to realize multi-level resistance change under the control of an electric field; under high-speed pulse tests of 100ns and 50ns, the memristor shows an operating voltage lower than 1V, and further achieves an operating voltage lower than 3.3V under a pulse width of 10 ns; the comprehensive performance of the memristor unit with the resistance change functional layer of oxygen gradient is obviously superior to that of the existing memristor device. The method can be applied to chip design of high-speed and low-power consumption operation, and has important guiding significance for high-density information storage, nerve morphology simulation and calculation.
Therefore, the metal oxide oxygen gradient-based thin film memristor can be applied to the next generation storage technology for replacing Flash; the memristor has the advantages of large capacity required by data storage, long required retention time and non-volatility, can realize stable binary resistance change, can be used for storing numerical values of '1' and '0' (namely logic true and logic false) respectively, and has higher speed compared with the traditional Flash. The memristor can be applied to the design of a low-voltage logic circuit, the logic calculation requires high calculation speed and low power consumption, the on-off of the conductive filament can be realized under the action of a low electric field due to the action of oxygen concentration gradient in the set process and the obvious Joule heat effect in the reset process, so that high-speed operation can be realized, the operating voltage is low, and the leakage current is reduced due to the improvement of the resistance state, so that the power consumption is reduced.
Drawings
FIG. 1 is a schematic diagram of a structure of a metal oxide oxygen concentration gradient memristor cell of the present disclosure.
In FIG. 2, (a) is an HRTEM image of the initial thin film, and (b) is an EDS line scan diagram of the corresponding O element.
FIG. 3 is a 100I/V DC characteristic curve scan of a memristor at 100uA current limit.
Fig. 4 is a high speed pulse test at 100 ns.
Fig. 5 is a high speed pulse test at 50 ns.
Fig. 6 is a high speed pulse test at 10 ns.
Fig. 7 is a multivalued modulation at different current limits.
Fig. 8 is a multivalued modulation at different reset voltage amplitudes for 80 ns.
FIG. 9 is a plot of 100I/V DC characteristic curves for a memristor of the uniform oxide thin film of comparative example 1.
The meaning of the reference symbols in fig. 1 is as follows: 1 is an upper electrode, 2 is a functional layer, 3 is a lower electrode, and 4 is SiO in a substrate2Layer 5 is a single crystal silicon layer in the substrate.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The high-performance memristor device based on the metal oxide oxygen concentration gradient can be a memristor unit with a three-layer pad structure, the structural schematic diagram of the high-performance memristor unit is shown in fig. 1, the high-performance memristor unit mainly comprises an upper electrode, a functional layer and a lower electrode from top to bottom, and the functional layer is arranged between the upper electrode and the lower electrode to form a sandwich structure.
In summary, the preparation method specifically includes preparing a lower electrode through sputtering, preparing a functional layer on the lower electrode through photoetching, sputtering and stripping, and preparing an upper electrode on the functional layer through photoetching, sputtering and stripping, so as to form a memristor device with a three-layer structure; wherein, when the functional layer is prepared by sputtering, Ar and O are required to be adjusted in the sputtering process2To achieve an oxygen concentration gradient functional layer. For example, the following steps may be included:
(1) preparing a lower electrode;
by the magnetron sputtering method, SiO is polished and grown on a single surface2A layer of metal lower electrode grows on the monocrystalline silicon substrate, the obtained lower electrode film can cover the whole substrate surface, and the total thickness can be 50nm-200 nm;
(2) preparing a functional layer;
firstly, preparing a photoetching pattern on the surface of the lower electrode by a photoetching process, and then preparing a metal oxide functional layer by a sputtering process; for example, a photoresist may be used to cover a portion of the edge of the lower electrode to expose the lower electrode for subsequent testing;
(2.1) lithography: preparing a photoetching pattern on the lower electrode through a photoetching process to expose a part of the stripped lower electrode, wherein the photoetching step comprises glue homogenizing, prebaking, postbaking and developing;
(2.2) sputtering: adjusting Ar and O in sputtering working gas2Sputtering a functional layer on the pattern obtained by photoetching according to the proportion (Ar can be replaced by other inert gases);
in the sputtering process, the content of oxygen in the working gas is gradually increased to realize that the content of oxygen in the functional layer is gradually increased from the lower electrode to the upper electrode, and the total thickness can be kept between 10nm and 100 nm;
(2.3) stripping: soaking the film sample prepared in the step (2.2) by using acetone, assisting in ultrasonic cleaning, sequentially cleaning by using absolute ethyl alcohol and deionized water, and finally drying by using a nitrogen gun;
(3) preparing an upper electrode;
(3.1) lithography: preparing a square photoetching pattern on the functional layer sample obtained in the step (2) through a photoetching process, wherein the photoetching step is the same as the step (2.1);
(3.2) sputtering: growing an upper electrode on the square photoetching pattern by a magnetron sputtering method, wherein the sputtering air pressure can be 0.5Pa, the direct-current power can be 35W, and the total thickness is 50nm-500 nm;
(3.3) peeling: soaking the film sample prepared in the step (3.2) by using acetone, assisting in ultrasonic cleaning, sequentially cleaning by using absolute ethyl alcohol and deionized water, and finally drying by using a nitrogen gun;
the memristor unit with the three-layer structure can be obtained through the process steps. In a memristor, the lower electrode may cover the entire substrate surface, the functional layer area is smaller than the lower electrode but may be equally connected together as an entire layer, and the upper electrode may be a single square structure.
The testing method of the prepared device unit can adopt the following specific steps:
(a) initializing the initial unit, grounding the lower electrode of the initial unit, applying negative voltage to the upper electrode, and forming a conductive path for connecting the upper electrode and the lower electrode for the subsequent resistance change process;
(b) applying a plurality of times of bidirectional direct current I/V voltage scanning on the unit initialized in the step (a) until the unit shows stable resistance change characteristics and the low resistance value of the unit is improved to a certain extent;
(c) testing the switching characteristics of the memristor under pulses, namely firstly, taking the low-resistance state obtained in the step (b) as a reference, and adjusting the pulse width and the amplitude of the pulses to obtain a high-resistance value of a resistance change window which is about 10 times that of the low-resistance state; then, on the basis of the high resistance value, the pulse width and the amplitude of the pulse are adjusted to enable the resistance of the device to return to the original low resistance value;
(d) under a direct current I-V scanning mode, adjusting different current limiting values to obtain different multi-valued resistance states;
(e) under a certain nanosecond pulse width, adjusting the reset voltage amplitude, adjusting different intermediate resistance states, and obtaining multiple values, so that the multiple-value storage characteristic can be realized;
the following are specific examples:
example 1
Taking a tantalum-based memristor as an example, the corresponding preparation method may include the following steps:
(1) preparing a lower electrode;
in the experiment, Ta is selected as a lower electrode, and SiO is polished and grown on a single surface by a magnetron sputtering method2A lower electrode is grown on the monocrystalline silicon substrate.
(1.1) substrate cleaning: firstly, cleaning for 10 minutes by using acetone in an ultrasonic environment, then cleaning for 10 minutes by using alcohol in the ultrasonic environment, and finally cleaning for 10 minutes by using deionized water in an ultrasonic manner, wherein the ultrasonic power is 60W;
(1.2) sputtering: sputtering 370s of Ta bottom electrode with the growth of 100nm in Ar gas atmosphere of 0.5Pa under the direct current sputtering power of 100W;
(2) preparing a functional layer;
the functional layer is made of TaOx material, and the TaOx material with oxygen concentration gradient is obtained by controlling the content of oxygen in sputtering working gas;
(2.1) lithography: preparing a photoetching pattern on the lower electrode through a photoetching process to expose a part of the stripped lower electrode, wherein the photoetching step comprises glue homogenizing, prebaking, postbaking and developing;
(2.2) sputtering: adjusting Ar and O in sputtering working gas2Sputtering a functional layer on the pattern obtained by photoetching;
gradually increasing the oxygen content in the sputtering working gas environment to realize the gradual increase of the oxygen content in the functional layer from the lower electrode to the upper electrode, wherein O is the oxygen content in the experiment2The ratio of the flow rate to Ar may be increased in the order of, for example, 0/40,2/60,3/60,3/45,6/60 (Ar and O)2Can be maintained at a constant total sputtering gas pressure and flow rate in sccm), sputtering with a TaOx target (x in the TaOx target can be 1.5), the total thickness being maintained at 15nm, i.e., 3nm for each working atmosphere sputteringDiffusion of the interface between the different components to form a gradual concentration gradient, as shown in fig. 2; as can be seen from (b) in fig. 2, the O element content shows an increasing change from the a position to the b position (wherein there is an unexpected decrease in the O element content near the b position, which is due to the test jitter, the oxygen content in the functional layer still actually changes incrementally);
the technological conditions of sputtering are as follows: the sputtering pressure is 0.5pa, and the power is 120W;
(2.3) stripping: soaking the film sample prepared in the step (2.2) by using acetone, assisting in ultrasonic cleaning, sequentially cleaning by using absolute ethyl alcohol and deionized water, and finally drying by using a nitrogen gun;
(3) preparing an upper electrode;
(3.1) lithography: preparing a square photoetching pattern on the functional layer sample obtained in the step (2) through a photoetching process, wherein the photoetching step is the same as the step (2.1);
(3.2) sputtering: the experiment uses a metal Pt target, and an upper electrode with the growth of 100nm is sputtered for 700s in Ar gas atmosphere of 0.5Pa under the sputtering power of 35W;
(3.3) peeling: soaking the film sample prepared in the step (3.2) by using acetone, assisting in ultrasonic cleaning, sequentially cleaning by using absolute ethyl alcohol and deionized water, and finally drying by using a nitrogen gun; and obtaining a final memristor sample.
The above embodiments may be tested using the following methods:
(a) initializing an initial unit, grounding a lower electrode of the initial unit, applying negative voltage of 0V-7V to an upper electrode, and setting the limiting current to be 10uA, wherein the purpose is to form a conductive path for connecting the upper electrode and the lower electrode so as to facilitate the subsequent resistance change process;
(b) and (c) applying multiple bidirectional direct current I/V voltage scanning to the unit initialized in the step (a), wherein the voltage scanning range is-2-2.2V, the limiting current is set to be 100uA, and the low resistance value of 10k omega is obtained. Until the unit shows stable resistance change characteristics;
(c) performing a switching characteristic test under a pulse on the memristor, firstly taking the low resistance state obtained in the step (b) as a reference, adjusting the pulse width to be 100ns, 50ns and 10ns respectively, then adjusting the corresponding reset voltage amplitude to be 0.96V, 0.98V and 3.2V respectively, so that the unit reset is about 100k omega, and adjusting the corresponding set voltage amplitude to be-0.64V, -0.67V and-2.3V respectively, so that the unit set is about 10k omega;
(d) adjusting the current limiting value to be 30uA-200uA, fixing the scanning voltage range to be-2V-2.2V, and measuring the multi-value resistance states under different current limiting conditions, as shown in FIG. 7;
(e) the pulse width is adjusted to 80ns, the set voltage is adjusted to-0.57V, the fixed low resistance is about 2k omega, the reset voltage amplitude is adjusted to be 0.7, 0.8, 0.85 and 0.94V respectively, and a plurality of resistance states of 5k omega, 10k omega, 20k omega and 50k omega are obtained respectively, as shown in FIG. 8.
The test result shows that the low resistance value of the memristor is improved to 10 under the current limiting of 100uA4Omega above, and shows good stability, the leakage current is further inhibited under the high resistance state, and the resistance state is improved; high-speed pulse tests show that stable low resistance and a certain window value can be obtained by accurately regulating and controlling the conductive filaments by accurately regulating the matching of voltage and amplitude, nanosecond-order pulse modulation realizes high-speed operation of a device, and amplitude smaller than 1V and amplitude smaller than 3.3V are obtained under pulse widths of 100ns and 50ns and 10ns respectively to realize low operating voltage; successfully verifies that the on-off of the localized conductive wire can be regulated and controlled in a region with high oxygen content through the gradient change of the oxygen content, so that a stable and high resistance state can be obtained under the condition of low current limiting, the leakage current is reduced, and the low-power-consumption memristive characteristic operation under the high-speed pulse operation is realized.
Comparative example 1
Taking a tantalum-based memristor as an example, the corresponding preparation method may include the following steps:
(1) preparing a lower electrode;
in the experiment, Ta is selected as a lower electrode, and SiO is polished and grown on a single surface by a magnetron sputtering method2A lower electrode is grown on the monocrystalline silicon substrate.
(1.1) substrate cleaning: firstly, cleaning for 10 minutes by using acetone in an ultrasonic environment, then cleaning for 10 minutes by using alcohol in the ultrasonic environment, and finally cleaning for 10 minutes by using deionized water in an ultrasonic manner, wherein the ultrasonic power is 60W;
(1.2) sputtering: sputtering 370s of Ta bottom electrode with the growth of 100nm in Ar gas atmosphere of 0.5Pa under the direct current sputtering power of 100W;
(2) preparing a functional layer;
the functional layer is made of TaOx material, and the TaOx material with oxygen concentration gradient is obtained by controlling the content of oxygen in sputtering working gas;
(2.1) lithography: preparing a photoetching pattern on the lower electrode through a photoetching process to expose a part of the stripped lower electrode, wherein the photoetching step comprises glue homogenizing, prebaking, postbaking and developing;
(2.2) sputtering: sputtering under pure Ar atmosphere, and sputtering a functional layer on the pattern obtained by photoetching;
the total sputtering pressure can be maintained to be constant in the sputtering process, a TaOx target is adopted for sputtering (x in the TaOx target can be 1.5), and the total thickness is kept at 15 nm;
the technological conditions of sputtering are as follows: the sputtering pressure is 0.5pa, and the power is 120W;
(2.3) stripping: soaking the film sample prepared in the step (2.2) by using acetone, assisting in ultrasonic cleaning, sequentially cleaning by using absolute ethyl alcohol and deionized water, and finally drying by using a nitrogen gun;
(3) preparing an upper electrode;
(3.1) lithography: preparing a square photoetching pattern on the functional layer sample obtained in the step (2) through a photoetching process, wherein the photoetching step is the same as the step (2.1);
(3.2) sputtering: the experiment uses a metal Pt target, and an upper electrode with the growth of 100nm is sputtered for 700s in Ar gas atmosphere of 0.5Pa under the sputtering power of 35W;
(3.3) peeling: soaking the film sample prepared in the step (3.2) by using acetone, assisting in ultrasonic cleaning, sequentially cleaning by using absolute ethyl alcohol and deionized water, and finally drying by using a nitrogen gun; and obtaining a final memristor sample.
The above comparative example 1 can be tested by the following method:
(a) initializing an initial unit, grounding a lower electrode of the initial unit, applying negative voltage of 0V-7V to an upper electrode, and setting the limiting current to be 10uA, wherein the purpose is to form a conductive path for connecting the upper electrode and the lower electrode so as to facilitate the subsequent resistance change process;
(b) applying a plurality of bidirectional direct current I/V voltage scanning to the unit initialized in the step (a), wherein the voltage scanning range is-2-2.2V, the limiting current is set to be 100uA, and the test result is shown in figure 9;
in the embodiment and the comparative example, Agilent B1500 is adopted to carry out I/V scanning and high-speed switching characteristic test under pulse under direct current on the memristor unit.
In addition to the tantalum-based memristor, according to actual needs, a hafnium-based, aluminum-based, and copper-based memristor may be prepared based on the preparation method of the present invention, for example, only the tantalum-based material (e.g., TaOx material used for the functional layer) appearing in the preparation method needs to be replaced by a corresponding hafnium-based material, aluminum-based material, or copper-based material, and the change manner of the atmosphere during the sputtering process of the functional layer may be kept unchanged (of course, since the metal materials of the lower electrode and the functional layer may be different, the Ta simple substance used for the lower electrode in embodiment 1 may be flexibly adjusted or may be kept unchanged).
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (12)
1. The application of the memristor based on the oxygen concentration gradient of the metal oxide in improving the stability, consistency or switching speed of a memristor device is characterized in that a device unit of the memristor comprises an upper electrode, a functional layer and a lower electrode from top to bottom, the functional layer is made of the metal oxide, the oxygen content in the functional layer is changed in a gradient manner, and the oxygen content in the functional layer is changed in an increasing or decreasing manner along the direction from the lower electrode to the upper electrode;
the metal oxide is an oxide of Ta, an oxide of Hf, an oxide of Al or an oxide of Cu.
2. The use according to claim 1, wherein the gradient of the oxygen content in the functional layer is a continuous variation.
3. The use according to claim 1, wherein the upper electrode is a noble electrode selected from the group consisting of Pt, Pd, and Ir; the lower electrode is an active electrode, and the active electrode is at least one of Ta, Hf, Al, Cu, Ti and Ag.
4. The application of claim 1, wherein the memristor comprises a plurality of device units, the plurality of device units correspond to a plurality of upper electrodes and share the same functional layer and the same lower electrode; any one of the upper electrodes is projected to be square on the plane of the outer surface of the lower electrode.
5. The use according to claim 4, wherein the lower electrode has a thickness of 50nm to 200nm and the functional layer has a thickness of 10nm to 100 nm; the thickness of any one of the upper electrodes is 50nm to 500 nm.
6. A method of making a metal oxide oxygen concentration gradient based memristor, comprising the steps of:
(1) preparing a lower electrode on a substrate;
(2) preparing a functional layer:
sputtering the lower electrode by using a sputtering method to form a metal oxide, and gradually increasing or decreasing the content of oxygen in the environment atmosphere in which the sputtering is performed in the sputtering process to obtain the metal oxide with the oxygen content in gradient distribution so as to obtain a functional layer; the metal oxide is Ta oxide, Hf oxide, Al oxide or Cu oxide;
(3) and preparing an upper electrode on the functional layer, so that the memristor based on the metal oxide oxygen concentration gradient is finally obtained, wherein the oxygen content in the functional layer is changed in an increasing or decreasing manner along the direction from the lower electrode to the upper electrode, and the stability, the consistency and the switching speed of the device can be improved.
7. The manufacturing method according to claim 6, wherein in the step (2), before the sputtering is started, the lower electrode is further formed with a photoresist layer corresponding to a photolithographic pattern on the surface of the lower electrode by a photolithographic process, so that the lower electrode is not completely covered by the functional layer during the sputtering, and the part of the lower electrode not covered by the functional layer is used for testing;
in addition, after the sputtering is finished, the photoresist layer is peeled off by adopting a method of acetone soaking and ultrasonic cleaning, then the photoresist layer is sequentially cleaned by absolute ethyl alcohol and deionized water, and the functional layer is obtained after the photoresist layer is dried by a nitrogen gun.
8. The method according to claim 6, wherein in the step (3), before the preparation of the upper electrode is started, the functional layer further forms a photoresist layer corresponding to a photolithographic pattern on the surface of the functional layer by a photolithographic process, so that the functional layer is not completely covered by the upper electrode in the preparation of the upper electrode;
in addition, after the preparation of the upper electrode is finished, the photoresist layer is stripped by adopting a method of acetone soaking and ultrasonic cleaning, then the upper electrode is sequentially cleaned by absolute ethyl alcohol and deionized water, and dried by a nitrogen gun to obtain the memristor.
9. The method according to claim 8, wherein the photoresist layer is used to form an upper electrode projected as a square on a plane on which the surface of the substrate is located; the upper electrode is provided with a plurality of electrodes.
10. The method according to claim 6, wherein in the step (2), the sputtering is performed in an atmosphere of O2A mixed gas with Ar; the atmosphere in which the sputtering is performed maintains a fixed gas pressure.
11. The method according to claim 6, wherein in the step (2), the oxygen content in the atmosphere in which sputtering is performed is gradually increased during sputtering as O2The flow ratio of the Ar to the Ar is 0/40,2/60,3/60,3/45 and 6/60 which are increased in sequence;
the oxygen content in the atmosphere in which the sputtering is carried out is gradually reduced during the sputtering process according to O2The flow ratios 6/60, 3/45, 3/60, 2/60 and 0/40 of Ar are reduced in sequence.
12. The method according to claim 6, wherein in the step (1), the substrate is polished on a single surface and grown with SiO2A Si substrate of an insulating layer;
the step (1) is to prepare the lower electrode on the substrate by using a direct current magnetron sputtering method;
and (3) preparing the upper electrode by using a direct-current magnetron sputtering method.
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| CN112701220B (en) * | 2020-10-23 | 2024-02-06 | 大连理工大学 | HfO with metal Hf buffer layer 2 Base memristor and manufacturing method thereof |
| CN112289930B (en) * | 2020-10-29 | 2022-08-05 | 华中科技大学 | CuxO memristor with volatility and non-volatility and regulation and control method thereof |
| CN112467027B (en) * | 2020-11-04 | 2023-05-30 | 华中科技大学 | Memristor based on interface doping and preparation method thereof |
| CN112909165A (en) * | 2021-01-22 | 2021-06-04 | 江苏集萃脑机融合智能技术研究所有限公司 | Preparation method of gradient metal oxide memristor |
| CN113054103B (en) * | 2021-03-16 | 2024-01-23 | 江苏集萃脑机融合智能技术研究所有限公司 | Method for quickly searching optimal alloy oxide memristive material |
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