Composite oxide memristor materials, memristors containing such materials, and their manufacture

Abstract

The present invention provides a thin-film material for memristors that linearizes the dependence between the quantity used to set the low-resistance (LRS) conductivity and the resulting conductivity value, and a memristor made of such a material. [Solution] R is one of Eu, Gd, Tb, or Nd, A is one of Ca, Sr, or Ba, B is one of Mn, Co, or Ni, x is greater than 0 and less than 1, a preferred example being Gd 1-x Ca x For MnO3(GCMO), x is 0.2 or greater to obtain a practical resistive switching ratio. The memristor can be manufactured by pulsed laser deposition using a sintered target of the aforementioned material. In one embodiment, the memristor includes a piece of memristor material 301 that constitutes at least one memristor connection between a first contact 310 and a second contact 303. The memristor material is of the type described above.

Description

[Technical Field]

[0001] The present invention relates to a memristor, that is, an electronic component whose current conduction characteristics depend on pre-given electrical conditions. In particular, the present invention relates to a memristor comprising a composite oxide as a memristor material, wherein the memristor material comprises gadolinium, calcium, and manganese. [Background technology]

[0002] A memristor is an electronic component whose current conduction characteristics depend on pre-given electrical conditions. As an example, Figure 1 shows a memristor 101, whose resistance is denoted by R. Instead of resistance, its reciprocal, i.e., conductance, can also be considered. The voltage across memristor 101 is U, and the current flowing through memristor 101 is I. Memristor 101 can exhibit a so-called high-resistance state HRS, or a so-called low-resistance state LRS, a somewhat idealized representation of which is shown in the voltage-to-current diagram in Figure 2. HRS appears as a horizontal line 201 along or very close to the x-axis, meaning that only a very small current flows through the memristor regardless of the voltage. The LRS state appears as a diagonal line 202, meaning that the current I flowing through memristor 101 is a linear function of voltage, following I = U / R.

[0003] The memristor 101 in Figures 1 and 2 exhibits bipolar switching between HRS and LRS. This means that the switching from HRS to LRS is performed with a different voltage U polarity than the switching from LRS to HRS. In Figure 2, the memristor is initially in HRS, and when the positive voltage across it reaches a first threshold point 203, the memristor switches to LRS according to arrow 204. When the operation at the negative end of the LRS region reaches a second threshold point 205, the memristor switches to HRS according to arrow 206.

[0004] A memristor becomes very interesting for many possible applications if the switching between HRS and LRS remains completely reversible even after many cycles, and more importantly, if a linear relationship can be observed between the voltage (or other quantity) used to perform the HRS→LRS transition and the thus obtained resistance R. The latter property means a kind of analog control of conductance, which opens up interesting applications in neuromorphic computing where the conductance of a memristor can be used to represent the weight or strength of synaptic connections between nodes in a neural network. Conventional memristors have proven difficult to achieve sufficient linearity. For use in ultra-miniature electronic circuits, memristors must be able to be manufactured in the form of thin films. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Therefore, the present invention aims to provide a thin film material for memristors that can linearize the dependence between the quantity used to set the LRS conductivity and the conductivity value thus obtained, and a memristor made of such a material. [Means for solving the problem]

[0006] The purpose of this is formula R (1-x) A x This is achieved by using a low-bandwidth perovskite called BO3 as the melistor material, where R is one of Eu, Gd, Tb, or Nd, A is one of Ca, Sr, or Ba, B is one of Mn, Co, or Ni, and x is greater than 0 and less than 1.

[0007] According to the first embodiment, a material for a memristor is provided, the material having the chemical formula R (1-x) A x It has BO3, where R is one of Eu, Gd, Tb, or Nd, A is one of Ca, Sr, or Ba, B is one of Mn, Co, or Ni, and x is greater than 0 and less than 1.

[0008] According to one embodiment of the first aspect, the material is of the chemical formula Gd (1-x) Ca x It contains MnO3, and x is greater than 0 and less than 1.

[0009] According to one embodiment of the first aspect, x is one of the ranges 0.31~0.99, 0.35~0.99, 0.4~0.98, 0.45~0.97, 0.5~0.96, 0.55~0.95, 0.6~0.95, 0.65~0.95, 0.7~0.95, 0.75~0.95, 0.8~0.95, and 0.85~0.95.

[0010] According to a second aspect, the use of materials of the types described above is provided for constructing a memristor.

[0011] According to a third aspect, a memristor is provided which includes a piece of memristor material constituting at least one memristor connection between a first contact and a second contact, wherein the memristor material is of the type described above.

[0012] According to one embodiment of the third aspect, the memristor material piece constitutes a film on the top of the substrate, and the thickness of the film in a direction perpendicular to the surface of the substrate is 1 nanometer to 500 nanometers.

[0013] According to one embodiment of the third aspect, the thickness of the film is 10 nanometers to 100 nanometers.

[0014] According to one embodiment of the third aspect, the first contact is mainly made of a first material, and the second contact is mainly made of a second material different from the first material.

[0015] According to one embodiment of the third aspect, the rectification characteristics of the junction between the first material and the memristor material are different from those of the junction between the second material and the memristor material.

[0016] According to an embodiment of the third aspect, the first material is one of aluminum and titanium.

[0017] According to an embodiment of the third aspect, the second material is one of gold, silver, copper, platinum, palladium, indium, and SrRuO3.

[0018] According to an embodiment of the third aspect, the substrate mainly consists of one of strontium titanate SrTiO3, silicon, lanthanum aluminate-strontium aluminum tantalite (LaAlO3) 0.3 (Sr2TaAlO6) 0.7 (LSAT), and lanthanum aluminate LaAlO3 (LAO).

[0019] According to an embodiment of the fourth aspect, a microelectronic circuit including at least one memristor of the above-described type is provided.

[0020] According to the fifth aspect, a method for manufacturing a memristor from a memristor material is provided. The method includes Gd (1-x) Ca x using MnO3 as a memristor material, where x is greater than 0 and less than 1.

[0021] According to an embodiment of the fifth aspect, the method includes depositing a thin film of the memristor material on top of a substrate.

[0022] According to an embodiment of the fifth aspect, the method includes using at least one of pulsed laser deposition, other physical vapor growth, sputtering, chemical vapor growth, and printing for the depositing step.

[0023] According to an embodiment of the fifth aspect, the method · mixing a first amount of gadolinium oxide, a second amount of calcium carbonate, and a third amount of manganese oxide to produce a dry mixture, and · pelletizing and firing the dry mixture. The steps include crushing, re-pelletizing, and sintering to form a solid target, The steps include using pulsed laser deposition for the deposition step, and using the solid target as the target to which the pulsed laser is focused in the pulsed laser deposition, Includes.

[0024] According to one embodiment of the fifth aspect, in the pulsed laser deposition, essentially 2 J / cm 2 The step involves using a 308-nanometer wavelength XeCl laser with an energy density and a frequency of 5 Hz.

[0025] According to one embodiment of the fifth aspect, in the pulsed laser deposition, the deposition temperature is 700°C and the oxygen partial pressure is essentially 23 Pa. [Brief explanation of the drawing]

[0026] The accompanying drawings are included to provide a further understanding of the present invention and constitute part of this specification, illustrating embodiments of the invention and helping to clarify the principles of the invention together with the description.

[0027] [Figure 1] This shows a memristor represented by a drawing symbol. [Figure 2] This shows the dependence of voltage and current in the high-resistance and low-resistance states of a memristor. [Figure 3] This shows a planar type memristor. [Figure 4] This shows a transversal type memristor. [Figure 5] This shows a multilayer film type memristor. [Figure 6] This shows a pulse train that can be used to characterize a memristor. [Figure 7] The idealized resistance of a memristor is shown as a function of the voltage used to set the memristor to a specific resistance state. [Figure 8]An example of the measured resistance of a memristor is shown as a function of the voltage used to set the memristor to a specific resistance state. [Figure 9] The measured resistance of a memristor made from the first material is shown. [Figure 10] The resistance measurements of a memristor made from the second material are shown. [Figure 11] The measured resistance of a memristor made from a third material is shown. [Figure 12] The measured resistance of a memristor made from the fourth material is shown. [Figure 13] The measured resistance of a memristor made from the fifth material is shown. [Figure 14] The resistance measurements of a memristor made from the sixth material are shown. [Figure 15] The measured resistance of a memristor made from the seventh material is shown. [Figure 16] The measured resistance of a memristor made from the eighth material is shown. [Figure 17] The measured resistance of a memristor made from the ninth material is shown. [Figure 18] The measured resistance of a memristor made from the tenth material is shown. [Figure 19] The measured resistance of a memristor made from the eleventh material is shown. [Figure 20] The measured resistance of a memristor made from the twelfth material is shown. [Figure 21] This shows the measured switching ratios of memristors made from different materials. [Figure 22] This shows the measured current flowing through a memristor with contacts made of different materials. [Figure 23] The manufacturing method is shown. [Figure 24] The detailed steps of the method shown in Figure 23 are illustrated. [Figure 25] This shows a pulse train that can be used to characterize the linear response of a memristor. [Figure 26] Another pulse train that can be used to characterize the linear response of a memristor is shown. [Figure 27] The measurement results for conversions with different write pulse lengths and amplitudes are shown. [Modes for carrying out the invention]

[0028] Figure 3 is a schematic cross-sectional view of what is known here as a planar memristor. The memristor consists of pieces of memristor material 301 that constitute a memristor connection between the first contact 302 and the second contact 303. The term "mristor material" is used here to clearly refer to the material that appears between the contacts, although the current understanding is that the memristor effect actually occurs not in the bulk of the memristor material itself, but in the junction or interface between the memristor material and the contacts. Conductive connections can be used to connect the first contact 302 and the second contact 303 to their respective nodes 304 and 305, expose the pieces of memristor material 301 to a desired voltage, and measure the resulting electrical properties of the pieces of memristor material 301.

[0029] Pieces of the memristor material 301 form a film on the substrate 306. In a planar memristor as shown in Figure 3, pieces of the memristor material 301 can be deposited directly on the surface of the substrate 306 in the form of a film, but this is not a requirement. For example, an intermediate layer of the desired material can be used between them if it is advantageous to obtain better compatibility between the crystal structures of the various materials involved.

[0030] Figure 4 is a schematic cross-sectional view of a memristor, which is a so-called transversal type, sometimes also called a capacitive type. In this case as well, pieces of memristor material 301 constitute the memristor connection between the first contact 302 and the second contact 303, and conductive connections couple them to the respective nodes 304 and 305. Pieces of memristor material 301 constitute a film on the top of the substrate 306, but not directly on the top of the substrate 306 because the second contact 303 forms a layer between them. Transversal type memristors like the one shown here have certain advantages compared to the planar type in Figure 3. For example, they may require a lower operating voltage. However, their manufacture requires more steps than the manufacture of a planar type memristor.

[0031] Figure 5 is a schematic cross-sectional view of a multilayer memristor. In this case, there may be two or more pieces of memristor material 301, each piece sandwiched between other layers. In the exemplary structure shown in Figure 5, the intermediate layers are the layers of the first contact 302 and the second contact 303, and as a result, each piece of memristor material 301 has the first contact layer on one side and the second contact layer on the other side in the lateral direction, i.e., perpendicular to the surface of the substrate 306.

[0032] In all of these and other exemplary embodiments in which pieces of memristor material form a film on the top of the substrate, the film thickness d in the direction perpendicular to the surface of the substrate may be, for example, between 1 and 500 nanometers, or in one preferred embodiment, between 10 and 100 nanometers. The film thickness d does not need to be constant throughout, but in many deposition methods that can be used to produce this type of thin film, a constant film thickness is a relatively common default feature of the method.

[0033] The first contact 302 and the second contact 303 may be made of the same material or of different materials. To say that a contact is made of a specific material is equivalent to saying that each contact is primarily composed of that material to the extent that the properties of that material govern the effect observed at the interface between the contact and a portion of the memristor material. In many embodiments where interesting properties have been observed, the first and second materials are different. In particular, it has been found that a memristor may exhibit interesting properties if the rectification characteristics of the junction between the first material and the memristor material differ from those of the junction between the second material and the memristor material.

[0034] An example of a material that can be used as the primary material is aluminum. Other examples of materials that can be used as the primary material also exist, including, but not limited to, titanium.

[0035] Examples of materials that can be used as a second material include gold and silver. Other examples of materials that can be used as a second material also exist, including, but are not limited to, copper, platinum, palladium, indium, and SrRuO3.

[0036] A typical characteristic of memristors is that their current conduction characteristics depend on the electrical conditions they have previously experienced. Particularly interesting in this description are memristors that can be "programmed" to have a specific resistance value by applying "write" pulses of a specific amplitude. Even more interesting are memristors that exhibit a linear or log-linear response to write pulses of different amplitudes. This concept will be explained in more detail below.

[0037] Figure 6 shows a series of voltage pulses, with the lower pulses shown in white being so-called read pulses and the higher pulses shown in black being so-called write pulses. Figure 7 shows the ideal behavior of the memristor's resistance when a pulse series like the one in Figure 6 is applied. The voltage axis in Figure 7 corresponds to the amplitude of the last write pulse received by the memristor. Each read pulse gives a point on the loop-shaped graph in Figure 7. Therefore, the resistance value of the memristor can be read both during the currently ongoing write pulse and during the subsequent read pulse. Ideally, these reads should give the same resistance value. In reality, the pulse series can consist of more write pulses with finer resolution, but the illustration in Figure 6 is a good conceptual diagram for characterizing memristors.

[0038] Assuming the memristor is initially in a high-resistance state HRS, the first read pulse gives point 701 in Figure 7. A number of write pulses with increasing amplitude may pass through without changing the resistance of the memristor, as there may be a first threshold write voltage required to cause a change in the current conduction characteristics. Here, we assume that the second write pulse 602 is just at the limit of the first threshold write voltage, and therefore the subsequent read pulse 603 still gives the HRS resistance value at point 702.

[0039] The region of linear or log-linear response begins at point 702, and each subsequent write pulse with increasing amplitude causes the memristor to take on a clearly corresponding, progressively decreasing resistance. Due to the coarse resolution of the schematic pulse train in Figure 6, not many such pulses are shown, but as explained earlier, the resolution achievable in actual measurements can be much better.

[0040] At a certain point, the second threshold write voltage is reached, and thereafter, even if the amplitude of the write pulse becomes larger, the memristor's resistance will not decrease further. Figure 6 shows the point where the write pulse labeled 604 reaches the second threshold write voltage, which corresponds to point 703 in Figure 7. The next write pulse 605 has an even larger amplitude, but as shown by point 704 in Figure 7, the resistance of the memristor does not change any further.

[0041] After the maximum amplitude positive write pulse 605, the amplitude of the write pulses in Figure 6 begins to decrease toward zero. In the graph of Figure 7, we assume that write pulses with increasingly lower amplitudes do not change the resistance of the memristor, so the read pulse 606 following a write section where no write pulses actually occur will give point 705 in the graph of Figure 7.

[0042] In the ideal case shown in Figure 7, the behavior of the memristor in response to a negative polarity write pulse is similar to that of a positive polarity write pulse, although factors such as the magnitude of the absolute value of the threshold voltage can differ significantly, for example, depending on the choice of contact material. In the idealized examples of Figures 6 and 7, the first few negative polarity write pulses still do not change the LRS resistance of the memristor until a write pulse 607 arrives that just satisfies the third threshold write voltage at point 706. Subsequently, a linear or log-linear response region continues until the amplitude of the write pulse 608 reaches the fourth threshold write voltage at point 707. Even if increasingly larger negative amplitude write pulses follow, the resistance of the memristor does not increase further and remains constant at the HRS level, as shown at point 708 in Figure 7. The remaining write pulses in the sequence shown in Figure 6 correspond to the gradually decreasing negative amplitude returning towards the first point 701 in the upper horizontal section of the loop-shaped graph in Figure 7.

[0043] Even if a pulse train like the one in Figure 6 is applied to an actual memristor and the resistance value is repeatedly read, it is rare to obtain an ideal graph like the one in Figure 7. However, if the memristor material has the chemical formula Gd (1-x)Ca x For memristors with MnO3 (where x is greater than 0 and less than 1), a sufficiently similar result was found. Figure 8 shows an example of such measured values. Repeated measurements were performed on this memristor, and pulse trains similar to the pulse train in Figure 6 were repeated many times. The thick graph 801 in Figure 8 shows the arithmetic mean of all loop graphs obtained from the measurements performed, and the thin graphs 802 and 803 show the limit values ​​that include the loop graphs of all measurements. The two vertical dashed lines 804 and 805 on the right side of Figure 8 define the first region of essentially linear or log-linear response, and the other two vertical dashed lines 806 and 807 define the second region of essentially linear or log-linear response.

[0044] Figures 9-20 further show the measurement results described above, the only difference being the compound Gd used as the memristor material. (1-x) Ca x These are the values ​​of the variable x in MnO3. The values ​​of x are 0.1 in Figure 9, 0.2 in Figure 10, 0.3 in Figure 11, 0.4 in Figure 12, 0.5 in Figure 13, 0.6 in Figure 14, 0.7 in Figure 15, 0.8 in Figure 16, 0.85 in Figure 17, 0.9 in Figure 18, 0.95 in Figure 19, and 1.0 in Figure 20. In each of Figures 9 to 20, the horizontal axis shows the voltage of the write pulse in volts, and the vertical axis shows the measured resistance of the memristor in ohms. It can be seen that the value of x has a significant effect on the characteristic operation of the memristor. Another feature seen in at least some of Figures 9 to 20 is the so-called cumulative effect of the write pulse, even after the write pulse of the maximum amplitude has already passed. When the value of x is greater than 0.3, the most favorable response of the memristor to the applied write pulse was found. When x falls within the ranges of 0.31~0.99, 0.35~0.99, 0.4~0.98, 0.45~0.97, 0.5~0.96, 0.55~0.95, 0.6~0.95, 0.65~0.95, 0.7~0.95, 0.75~0.95, 0.8~0.95, and 0.85~0.95, classes of embodiments exhibiting different levels of advantage were found.

[0045] Another feature, visible in at least some of Figures 9–20, is the so-called cumulative effect of write pulses, even after the write pulse with the largest amplitude has already passed. For example, in the lower right portion of the loop-shaped graph in Figure 19, as the voltage value begins to decrease from its maximum of approximately 11V, the graph does not continue directly horizontally to the left, but rather curves towards a slightly smaller resistance value between the decreasing amplitude values ​​of the most recent write pulse, from approximately 11V to approximately 2V. This cumulative effect of write pulses can be advantageous in some applications where the ability to track the occurrence of smaller amplitude pulses after larger amplitude pulses is valuable.

[0046] In addition to the linear or log-linear response of the memristor to the amplitude of the write pulse, another concern is the switching ratio, defined as the ratio Rmax / Rmin. Here, Rmax represents the HRS resistance and Rmin represents the LRS resistance of the memristor, which can be observed with the read pulse after the full loop of the write pulse has been applied. In the idealized case of Figure 7, the value Rmax would be the read value of the resistance at point 701, and the value Rmin would be the read value of the resistance at point 705. A larger switching ratio may make it easier to utilize memristors in practical applications such as neuromorphic computing, because the resolution required for quantities such as the connection strength between nodes in a neural network does not need to be so fine.

[0047] Figure 21 shows the switching ratios obtained by manufacturing memristors with the above-mentioned memristor material for x=0.1, x=0.2, x=0.3, x=0.4, x=0.5, x=0.6, x=0.7, x=0.8, x=0.85, x=0.9, x=0.95, and x=1 (black circles from left to right in Figure 21). These measurement results suggest that when the value of x is less than 0.2, it may be difficult to obtain a switching ratio sufficient for many practical applications known at the time of writing this specification, and as the value of x increases towards 0.9, values ​​of four orders of magnitude or more can be achieved, and increasingly larger switching ratios can be obtained.

[0048] The materials that can be used for the contacts are as briefly described in the main text. Figure 22 compares the measured currents flowing through memristors where both contacts are gold (dashed line), both contacts are aluminum (thick solid line), and one contact is aluminum and the other is gold (thin solid line). The large difference in the measured values ​​shown in Figure 22 is due to the fact that the rectification characteristics of the junction between aluminum and the memristor material are different from those of the junction between gold and the memristor material.

[0049] Figure 23 shows a method for manufacturing a memristor of the type of memristor material described above. Here, it is assumed that the memristor material is deposited on the top of the substrate in this method, but other methods for manufacturing memristors are not excluded. Step 2301 represents one or more preparation steps aimed at providing the memristor material in the form of a target or source that can be used in thin-film deposition techniques such as pulsed laser deposition, molecular beam epitaxy, or electron beam evaporation. Alternatively, other targets or sources may be manufactured in step 2301 if the memristor structure will include auxiliary layers such as contacts, insulators, and / or similar. Step 2302 represents one or more preparation steps aimed at providing a substrate on which the memristor material can be deposited on the top. Step 2303 represents manufacturing one or more thin films on the substrate such that at least one of the thin films constitutes the memristor material. Manufacturing contacts to the memristor material is shown as another step 2304 in Figure 23. For example, when pulsed laser deposition is used as a method for depositing memristor material, DC magnetron sputtering with a shadow mask can be used to deposit layers of a first contact material, and possibly a second contact material, which will constitute contacts to the memristor material.

[0050] Figure 24 shows an example of what the target preparation in step 2301 of Figure 23 looks like. In the exemplary embodiment of Figure 24, the first step 2401 represents the initial preparation of component materials such as gadolinium(III) oxide, calcium carbonate, and manganese(IV) oxide by, for example, drying them overnight in high-temperature (such as 200°C) air and mixing the dried component materials in mortar. The relative amounts of the component material containing gadolinium and the component material containing calcium ultimately result in the completed target material Gd (1-x) Ca x This will determine the value of x in MnO3. Step 2402 represents pelletizing the mixture of component materials, and step 2403 represents calcining the pelletized mixture, for example, by using a 7.5 to 60 hour pass with temperatures of 25°C → 750°C → 25°C in air. Step 2404 represents grinding the product from step 2403 in a mortar and re-pelletizing it. Step 2405 represents sintering, for example, by using a 13 to 24 hour pass with temperatures of 25°C → 1300°C → 25°C in air. Step 2406 represents grinding the product from step 2405 in a mortar and re-pelletizing it and re-sintering it into a solid target or source. Step 2407 represents performing Rietveld purification using X-ray diffraction to measure the product from step 2406. If the purity of the material is determined to be insufficient, return to step 2406. A solid target or source found to exhibit sufficient purity in step 2407 may be used as a target or source in the thin film deposition process according to step 2408. For example, the solid target can be used as a target to which a pulsed laser is focused in pulsed laser deposition. As an example, the wavelength is 308 nanometers and the energy density is essentially 2 J / cm². 2Therefore, a XeCl laser with a frequency of 5 Hz can be used in the pulsed laser deposition described above. Examples of process parameter values ​​in such pulsed laser deposition include a deposition temperature of 700°C and an oxygen partial pressure of 23 Pa. The values ​​of laser energy density, laser pulse frequency, deposition temperature, and oxygen partial pressure given here are merely examples, and many other combinations of values ​​other than these parameter values ​​can also be used.

[0051] Figures 25 and 26 show examples of pulse trains that can be used to characterize the linear response of the memristors of the types described above. In Figure 25, the linear response in the LRS → HRS transition can be examined. The pulse train begins with two so-called reset pulses 2501 and 2502, whose polarities are selected so that they reliably set the memristor to the low-resistance state LRS. The amplitudes of the reset pulses 2501 and 2502 may be around +7V, for example, assuming that the memristor is planar, the value x of the memristor material is 0.7 to 0.95, and one contact is made of gold and the other of aluminum. The length of each of the reset pulses 2501 and 2502 may be, for example, around 0.45ms, but significantly shorter or longer reset pulses are also possible. In other words, the useful length of the reset pulses may be 100ns to 2ms, or even shorter, such as 100ps. There may be a pause of about 5ms between the reset pulses 2501 and 2502.

[0052] The initial read pulse 2503 may be applied to confirm by measurement that the memristor is indeed at LRS. The amplification factor of the read pulse 2503 may be, for example, around +0.45V. In any case, it must be chosen to be sufficiently low to ensure that the read pulse does not cause a large change in the memristor's LRS. The time interval between the subsequent reset pulse 2502 and the read pulse 2503 may be, for example, around 0.5 seconds, or 0.1 to 1 second, and the duration of the read pulse 2503 may be, for example, around 0.5 seconds. What is described here as a single read pulse may actually be a series of read pulses, such as 20 read pulses, and the average read value of the LRS resistance is calculated from the read values ​​given by each pulse.

[0053] A write pulse 2504 may be applied to cause a transition from LRS to a high-resistance state. Assuming the structure and material-related factors of the memristor named above for the purpose of characterizing the linear response, the amplitude of the write pulse 2504 may be varied, for example, from -1V to -6.5V. The length of the write pulse 2504 may be varied, for example, from 50 to 250ms, or a significantly shorter write pulse of, for example, about 100ns may be applied. After the write pulse 2504, there may be a further pause, for example, 1 second, and a further read pulse 2505 may be applied to read the converted resistance of the memristor. Here again, what is described as a single read pulse may actually be a series of read pulses, such as 20 read pulses, and the average read value of the converted resistance is calculated from the read values ​​given by each pulse. Then, returning to the beginning of the pulse train, another pulse train, possibly a pulse train having some other amplitude and / or duration of the write pulse 2504, may be applied.

[0054] Figure 26 allows us to examine the linear response in the HRS→LRS transition. The pulse train restarts with two so-called reset pulses 2601 and 2602, whose polarity is now selected to set the memristor to the high-resistance state HRS. The amplitude of reset pulses 2601 and 2602 may be, for example, around -7.6V, assuming that the memristor is planar, the memristor material value x is 0.7 to 0.95, and one contact is made of gold and the other of aluminum. The length of reset pulses 2601 and 2602 may be, for example, around 1.4ms, or between 0.1ms and 2ms. There may be a pause of about 5ms between reset pulses 2601 and 2602.

[0055] An initial readout pulse 2603 may be applied to confirm by measurement that the memristor is indeed in HRS. The amplification factor and other characteristics of the readout pulse 2603 (or the sequence of first readout pulses) may be similar to those of the first readout pulse (or the sequence of first readout pulses) in Figure 25.

[0056] A write pulse 2604 may be applied to cause the memristor to transition from HRS to a low-resistance state. Assuming the structure and material-related factors of the memristor named above for the purpose of characterizing the linear response, the amplitude of the write pulse 2604 may be varied, for example, from +3.5V to +5.5V, and the length of the write pulse 2604 may be varied, for example, from 20ms to 120ms. After the write pulse 2604, there may be a further pause, for example, 0.5 seconds, to which a further read pulse 2605 may be applied to read the converted resistance value of the memristor. Here again, what is described as a single read pulse may actually be a series of read pulses, such as 20 read pulses, and the average read value of the converted resistance is calculated from the read values ​​given by each pulse. Then, returning to the beginning of the pulse train, another pulse train, possibly a pulse train having some other amplitude and / or duration of the write pulse 2604, may be applied.

[0057] Figure 27 shows the measured ratio (HRS-LRS) / LRS for different write pulse amplitudes and durations. Each graph in Figure 27 represents the amplitude of the write pulse according to the relevant legend, and the horizontal axis represents the width of each write pulse in milliseconds. These measurements indicate that both the amplitude and duration of the write pulse are important for the memristor to perform resistance conversion, and that linear or logarithmic operation can be achieved over a relatively wide range of converted resistances.

[0058] As technology advances, it will be obvious to those skilled in the art that the basic concept of the present invention can be implemented in various ways. For example, other thin-film deposition methods such as physical vapor deposition, sputtering, chemical vapor deposition, or printing can be used as an alternative to or in addition to pulsed laser deposition. Furthermore, even if most of the elements represented by R in the general chemical formula are gadolinium, other elements such as europium, terbium, or neodymium can be used. Similarly, even if most of the elements represented by A are calcium, other elements such as strontium or barium can be used. Likewise, even if most of the elements represented by B are manganese, other elements such as cobalt or nickel can be used. Thus, the present invention and its embodiments are not limited to the examples described above and can be modified within the scope of the claims.

Claims

1. The material has the chemical formula R （１－ｘ） A ｘ BO ３ A material for a memristor, characterized in that R is one of Eu, Gd, Tb, or Nd, A is one of Ca, Sr, or Ba, B is one of Mn, Co, or Ni, and x is greater than 0 and less than 1.

2. The chemical formula of the aforementioned material is Gd （１－ｘ） Ca ｘ MnO ３ The material according to claim 1, wherein x is greater than 0 and less than 1.

3. The material according to claim 1 or 2, wherein x is one of the ranges 0.31 to 0.99, 0.35 to 0.99, 0.4 to 0.98, 0.45 to 0.97, 0.5 to 0.96, 0.55 to 0.95, 0.6 to 0.95, 0.65 to 0.95, 0.7 to 0.95, 0.75 to 0.95, 0.8 to 0.95, and 0.85 to 0.

95.

4. Use of the material described in any one of claims 1 to 3 to construct a memristor.

5. A memristor comprising a piece of memristor material constituting at least one memristor connection between a first contact and a second contact, wherein the memristor material is the material described in any one of claims 1 to 3.

6. The memristor according to claim 5, wherein the memristor material piece constitutes a film on the top of the substrate, and the thickness of the film in a direction perpendicular to the surface of the substrate is 1 nanometer to 500 nanometers.

7. The memristor according to claim 6, wherein the thickness of the film is 10 nanometers to 100 nanometers.

8. The memristor according to any one of claims 5 to 7, wherein the first contact is mainly made of a first material, and the second contact is mainly made of a second material different from the first material.

9. The memristor according to claim 8, wherein the rectification characteristics of the joint between the first material and the memristor material are different from those of the rectification characteristics of the joint between the second material and the memristor material.

10. The memristor according to claim 9, wherein the first material is one of aluminum and titanium.

11. The second material mentioned above is gold, silver, copper, platinum, palladium, indium, SrRuO ３ A memristor according to claim 9 or 10, which is one of the above.

12. The substrate is mainly strontium titanate SrTiO ３ , silicon, lanthanum aluminate-strontium aluminum tantalite (LaAlO ３ ), ０．３ (Sr ２ TaAlO ６ ), ０．７ (LSAT), lanthanum aluminate LaAlO ３ (LAO), and the memristor according to any one of claims 6 to 11 consisting of one of them.

13. A microelectronic circuit comprising at least one memristor according to any one of claims 5 to 12.

14. A method for producing a memristor from a memristor material, wherein the method is based on the chemical formula R （１－ｘ） A ｘ BO ３ A method comprising the step of using a material having as the memristor material, wherein R is any of Eu, Gd, Tb, and Nd, A is any of Ca, Sr, and Ba, B is any of Mn, Co, and Ni, and x is greater than 0 and less than 1.

15. As the aforementioned memristor material, Gd （１－ｘ） Ca ｘ MnO ３ The method according to claim 14, comprising the step of using, where x is greater than 0 and less than 1.

16. The method according to claim 14 or 15, further comprising the step of depositing a thin film of the memristor material on the top of the substrate.

17. The method according to claim 16, comprising the step of using at least one of pulsed laser deposition, other physical vapor deposition, sputtering, chemical vapor deposition, and printing for the deposition step.

18. - A step of mixing a first amount of oxide R, a second amount of carbonate A, and a third amount of oxide B to produce a dry mixture, - The step of pelletizing the dry mixture and firing it, - Steps of crushing, re-pelletizing, and sintering to form a solid target, The method according to claim 17, comprising the steps of: using pulsed laser deposition for the deposition step, and using the solid target as a target to which the pulsed laser is focused in the pulsed laser deposition.

19. In the pulsed laser deposition described above, essentially 2 J / cm ２ The method according to claim 17 or 18, comprising the step of using a 308 nanometer wavelength XeCl laser having an energy density and a frequency of 5 Hz.

20. The method according to claim 19, wherein in the pulsed laser deposition, the deposition temperature is 700°C and the oxygen partial pressure is essentially 23 Pa.

21. The method according to any one of claims 14 to 20, comprising the step of generating a conductive contact on at least one surface of the memristor material.

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