A memristor and manufacturing method thereof

Abstract

The material used in memristors has the chemical formula R(1-x)AxBO3, where R is one of europium (Eu), thorium (Gd), treasury (Tb), and neodymium (Nd); A is one of calcium (Ca), strontium (Sr), and barium (Ba); B is one of manganese (Mn), cobalt (Co), and nickel (Ni); and x is greater than 0 but less than 1.

Description

[Technical Field]

[0001] This invention relates to memristors, i.e., electronic components whose conductivity depends on the electrical conditions they have previously experienced. In particular, this invention relates to a memristor comprising a composite oxide as a memristor material, said composite oxide comprising thionium, calcium, and manganese. [Previous Technology]

[0002] Memristors are electronic components whose conductivity depends on the electrical conditions they have previously experienced. For example, Figure 1 shows a memristor 101, whose resistance is labeled R. One can consider its inverse, conductance, instead of resistance. The voltage across memristor 101 is U, and the current through memristor 101 is I. Memristor 101 can exhibit a so-called high resistivity state (HRS) or a so-called low resistivity state (LRS), and the current-per-voltage plot in Figure 2 shows some idealized illustrations. HRS appears as a horizontal line 201 along or very close to the x-axis, meaning that only a small current flows through the memristor regardless of voltage. LRS appears as a diagonal line 202, meaning that the current I through memristor 101 is a linear function of voltage according to I=U / R.

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

[0004] If the switching between HRS and LRS is completely reversible even after a large number of cycles, and more importantly, if the memristor can follow a linear relationship between the voltage (or other quantity) used to make the HRS->LRS transition, and thus obtain the resistance R, the memristor will become very interesting for many possible applications. The latter characteristic would imply an analog control of conductance and would have interesting applications in neuromorphic computing, where the conductance of the memristor can be used to represent the weight or strength of synaptic connections between nodes in a neural network. For existing memristors, it has proven difficult to achieve sufficient linearity. For use in microelectronic circuits, it should be possible to fabricate memristors in thin-film form. [Summary of the Invention]

[0005] Therefore, the object of the present invention is to provide a thin film material for a memristor, and a memristor including the material, wherein the material can be used to establish a linear correlation between the amount of LRS conductivity and the obtained conductivity value.

[0006] This objective is achieved by using a low-bandwidth perovskite with the chemical formula R(1-x)AxBO3 as a memristor material, wherein R is one of europium (Eu), thorium (Gd), treasury (Tb), and neodymium (Nd); A is one of calcium (Ca), strontium (Sr), and barium (Ba); B is one of manganese (Mn), cobalt (Co), and nickel (Ni); and x is greater than 0 but less than 1.

[0007] According to the first state sample, a material for memristors is provided, the material having the chemical formula R(1-x)AxBO3, wherein R is one of europium, thorium, tungsten, neodymium; A is one of calcium, strontium, barium; B is one of manganese, cobalt, nickel; and x is greater than 0 but less than 1.

[0008] According to one embodiment of the first state sample, the material has the chemical formula Gd(1-x)CaxMnO3, where x is greater than 0 but less than 1.

[0009] According to one embodiment of the first state, x is in one of the following 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, 0.85-0.95.

[0010] According to the second state sample, a memristor is constructed using the materials of the above type.

[0011] According to the third state, a memristor is provided, which includes a memristor material that forms at least one memristive connection between the first and second contacts, wherein the memristor material is a material of the type described above.

[0012] According to one embodiment of the third state, the memristor material sheet forms a film on the top of the substrate, wherein the thickness of the film in a direction perpendicular to the surface of the substrate is between 1 nanometer and 500 nanometers.

[0013] According to one embodiment of the third state sample, the thickness of the film is between 10 and 100 nanometers.

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

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

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

[0017] According to one embodiment of the third state sample, the second material is one of gold, silver, copper, platinum, palladium, indium, and strontium ruthenium oxide (SrRuO3).

[0018] According to one embodiment of the third state sample, the substrate is mainly composed of one of the following: strontium titanate (SrTiO3), silicon, strontium tantalum lanthanum aluminate ((LaAlO3)0.3(Sr2TaAlO6)0.7(LSAT)), and lanthanum aluminate (LaAlO3(LAO)).

[0019] According to the fourth state, a microelectronic circuit including at least one memristor of the above type is provided.

[0020] According to the fifth state sample, a method for manufacturing a memristor material is provided. The method includes using a material having the chemical formula Gd(1-x)CaxMnO3 as the memristor material, wherein x is greater than 0 but less than 1.

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

[0022] According to one embodiment of the fifth state sample, the method includes using at least one of the following for the deposition: pulsed laser deposition, other physical vapor deposition, sputtering, chemical vapor deposition, and printing.

[0023] According to one embodiment of the fifth state sample, the method includes

[0023] - A dry mixture is produced by mixing a first amount of thiocyanate oxide, a second amount of calcium carbonate, and a third amount of manganese oxide.

[0023] - The dried mixture is granulated and calcined.

[0023] - Grinding, repelletizing, and sintering into solid targets, and

[0023] - The pulsed laser deposition method is used for this deposition, and the solid target is used as the target on which the pulsed laser is focused in the pulsed laser deposition method.

[0024] According to one embodiment of the fifth state sample, the method includes using a xenon monochloride (XeCl) laser with a wavelength of 308 nanometers, an energy density of substantially 2 J / cm2, and a frequency of 5 Hz in the pulsed laser deposition method.

[0025] According to one embodiment of the fifth state sample, the deposition temperature in the pulsed laser deposition method is 700°C and the oxygen partial pressure is substantially 23 Pa. [Simplified Explanation of the Diagram]

[0026] The accompanying drawings, which provide a further understanding of the invention and form part of this specification, illustrate embodiments of the invention and, together with the specification, help to explain the principles of the invention. In the drawings:

[0026] Figure 1 shows a memristor represented by a graphic symbol;

[0026] Figure 2 shows the relationship between voltage and current of the memristor in high resistance and low resistance states;

[0026] Figure 3 shows a planar memristor;

[0026] Figure 4 shows a lateral memristor;

[0026] Figure 5 shows a multilayer memristor;

[0026] Figure 6 shows a pulse train that can be used to characterize memristors;

[0026] Figure 7 shows the effect of the ideal resistance of the memristor and the voltage used to set the memristor to a specific resistance state;

[0026] Figure 8 shows an example of the measuring resistor of a memristor and the effect of the voltage used to set the memristor to a specific resistance state;

[0026] Figure 9 shows the measured resistance of a memristor made of the first material;

[0026] Figure 10 shows the measured resistance of a memristor made of a second material;

[0026] Figure 11 shows the measured resistance of a memristor made of a third material;

[0026] Figure 12 shows the measured resistance of a memristor made of a fourth material;

[0026] Figure 13 shows the measured resistance of a memristor made of a fifth material;

[0026] Figure 14 shows the measured resistance of a memristor made of a sixth material;

[0026] Figure 15 shows the measured resistance of a memristor made of a seventh material;

[0026] Figure 16 shows the measured resistance of a memristor made of the eighth material;

[0026] Figure 17 shows the measured resistance of a memristor made of the ninth material;

[0026] Figure 18 shows the measured resistance of a memristor made of the tenth material;

[0026] Figure 19 shows the measurement resistance of a memristor made of the eleventh material;

[0026] Figure 20 shows the measured resistance of a memristor made of the twelfth material;

[0026] Figure 21 shows the measured conversion ratio of memristors made of different materials;

[0026] Figure 22 shows the measured current through a memristor with contacts made of different materials;

[0026] Figure 23 illustrates the manufacturing method;

[0026] Figure 24 shows the detailed steps of the method in Figure 23;

[0026] Figure 25 shows a pulse train that can be used to characterize the linear response of a memristor;

[0026] Figure 26 shows another pulse train that can be used to characterize the linear response of a memristor;

[0026] Figure 27 shows the measurement results of different write pulse lengths and amplitude conversions.

Implementation Method

[0027] Figure 3 is a schematic cross-sectional view of the memristor, which is a so-called planar type. The memristor includes a piece of memristor material 301, which forms a memristive connection between the first junction 302 and the second junction 303. The term "memristor material" is used here to specifically refer to the material between the junctions, although, according to current understanding, memristor-type effects actually occur at the junction or interface between the memristor material and the junctions, rather than in the body of the memristor material itself. The first and second junctions 302 and 303 are electrically coupled to the corresponding nodes 304 and 305, which can be used to subject the memristor material 301 to the required voltage and to measure the electrical characteristics generated by the memristor material 301.

[0028] A sheet of memristor material 301 forms a film on top of the substrate 306. In the planar memristor shown in FIG3, the memristor material sheet 301 can be deposited directly on the surface of the substrate 306 in the form of a film, but this is not necessary; for example, if it is beneficial to achieve better compatibility between the crystal structures of the various materials involved, an intermediate layer of the desired material can be used between them.

[0029] Figure 4 is a schematic cross-sectional view of a memristor, which is a so-called lateral type, sometimes also called a capacitive type. Again in this example, the memristor material sheet 301 forms a memristor connection between the first contact 302 and the second contact 303, and conductively couples them to the corresponding nodes 304 and 305. The memristor material sheet 301 forms a film on top of the substrate 306 (not directly on top), because the second contact 303 forms a layer therebetween. Compared to the planar type of Figure 3, the lateral type memristor shown here has certain advantages: for example, it may require a lower operating voltage. However, its fabrication also requires more steps than that of a planar memristor.

[0030] Figure 5 is a schematic cross-sectional view of a multilayer memristor. In this example, there are two or more memristor materials 301, each of which can be sandwiched between other layers. In the exemplary structure of Figure 5, the intermediate layer is the layer of the first and second contacts 302 and 303, such that each memristor material 301 has a first contact layer on one side and a second contact layer on the other side in the lateral direction (i.e., the direction perpendicular to the surface of the substrate 306).

[0031] In all and other exemplary embodiments, a memristor material sheet forms a film on top of a substrate, the thickness d of which in a direction perpendicular to the substrate surface can be, for example, between 1 and 500 nanometers, or in a preferred embodiment between 10 and 100 nanometers. The film thickness d need not be constant over the entire area, but a constant film thickness is a relatively common default feature in many deposition methods that can be used to produce such thin films.

[0032] The first contact 302 and the second contact 303 may be made of the same material or of different materials. The fact that a contact is made of a specific material means that the corresponding contact is primarily composed of that material, and to some extent, the properties of that material determine the effect observed at the interface between the contact and the memristor material sheet. In some embodiments, interesting properties may be observed when the first material and the second material are different materials. In particular, the memristor may exhibit certain interesting properties if the rectification characteristics of the interface between the first material and the memristor material differ from those of the interface between the second material and the memristor material.

[0033] In one example of a material, aluminum can be used as the first material. In other examples, there are also materials that can be used as the first material, including but not limited to titanium.

[0034] In the examples of materials, gold and silver can be used as secondary materials. Other examples also include materials that can be used as secondary materials, including but not limited to copper, platinum, palladium, indium, and strontium ruthenium oxide (SrRuO3).

[0035] A typical characteristic of memristors is that their conductivity depends on the electrical conditions they have previously experienced. In this specification, particular attention is paid to memristors that can be "programmed" to have a specific resistance value by applying a "write" pulse of a specific amplitude. Even more interest is focused on memristors that exhibit a linear or logarithmically linear response to write pulses of varying amplitudes. This concept will be described in more detail below.

[0036] Figure 6 illustrates a voltage pulse train, where the low pulses marked in white are the so-called read pulses, and the high pulses marked in black are the so-called write pulses. Figure 7 illustrates the ideal behavior of the memristor's resistance when subjected to the pulse train shown in Figure 6. The voltage axis in Figure 7 corresponds to the amplitude of the last write pulse experienced by the memristor. Each read pulse gives a point on the loop diagram in Figure 7. Thus, the resistance of the memristor can be read during the ongoing write pulse and during the subsequent read pulse; ideally, these readings should give the same resistance value. In practice, the pulse train can include a very large number of write pulses with very fine resolution, but the illustration in Figure 6 provides a good conceptualization of the memristor's operation.

[0037] Assuming the memristor is initially in its high-resistance state HRS, the first read pulse will give point 701 in Figure 7. Some write pulses with increased amplitude may pass through but will not change the resistance of the memristor, because a first threshold write voltage may be required to cause any change in its conductivity. Here, it is assumed that the second write pulse 602 is exactly at the limit of the first threshold write voltage, so the subsequent read pulse 603 will still give the HRS resistance value at point 702.

[0038] The region of linear or log-linear response begins at point 702; therefore, each write pulse with increasing amplitude causes the memristor to assume a clearly corresponding, progressively lower resistance. While the coarse resolution of the pulse train in Figure 6 does not show many of these pulses, as previously mentioned, the actual resolution achievable in practical measurements is likely to be much better.

[0039] When the second threshold write voltage is reached at certain points, the memristor does not exhibit any further decrease in resistance, even if the amplitude of the write pulse is further increased. In Figure 6, the write pulse marked 604 is shown to reach the second threshold write voltage, corresponding to point 703 in Figure 7. The next write pulse 605 has an even larger amplitude, but the resistance of the memristor no longer changes, as shown at point 704 in Figure 7.

[0040] After the maximum amplitude positive write pulse 605, the amplitude of the write pulse in Figure 6 begins to decrease to 0. In the graph of Figure 7, it is assumed that the write pulse with gradually decreasing amplitude does not change the resistance of the memristor, such that the read pulse 606 following the write interval actually gives point 705 in the graph of Figure 7 in the absence of a write pulse.

[0041] In the ideal case shown in Figure 7, the memristor responds to a negative write pulse in a manner similar to that of a positive write pulse, although factors such as the choice of contact material can cause significant differences in factors such as the absolute magnitude of the threshold voltage. In the ideal examples of Figures 6 and 7, the first few negative write pulses do not change the LRS resistance of the memristor until write pulse 607 appears, whose amplitude just reaches the third threshold write voltage at point 706, followed by a region of linear or log-linear response until the amplitude of another write pulse 608 reaches the fourth threshold write voltage at point 707. As shown at point 708 in Figure 7, even if subsequent write pulses with increasingly larger negative amplitudes appear, the resistance of the memristor does not increase further but remains constant at the HRS level. The remaining write pulses in the sequence shown in Figure 6 have increasingly smaller negative amplitudes, correspondingly returning to the initial point 701 in the upper horizontal portion of the loop diagram formed in Figure 7.

[0042] Applying a pulse train similar to that in Figure 6 to a real memristor and repeatedly reading its resistance rarely yields the ideal graph shown in Figure 7. However, very similar results have been found when the memristor material has the following chemical formula: Gd(1-x)CaxMnO3, where x is greater than 0 but less than 1. Figure 8 illustrates an example of a practical measurement. The memristor in question is subjected to repeated rounds of measurement, in which a pulse train similar to that in Figure 6 is repeated many times. The thick line graph 801 in Figure 8 shows the arithmetic mean of all loop diagrams resulting from the measurement, while the thin line graphs 802 and 803 show the limits of the loop diagrams containing all the measured values. The two vertical dashed lines 804 and 805 on the right side of Figure 8 depict the first region of a substantially linear or log-linear response, and the other two vertical dashed lines 806 and 807 depict the second region of a substantially linear or log-linear response.

[0043] Figures 9 to 20 show further results of the measurements described above, differing only in the variable x value in the compound Gd(1-x)CaxMnO3 used as the memristor material. The x values ​​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 represents the voltage of the write pulse in volts, while the vertical axis represents the measured resistance of the memristor in ohms. It can be seen that the x value has a significant impact on the characteristics of the memristor. It was found that when x is greater than 0.3, the memristor has the most favorable response to the applied write pulse. Implementation categories with different advantage levels were found when x was in one of the following 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, 0.85-0.95.

[0044] Another feature that can be seen in at least some of the figures in Figures 9 to 20 is the so-called cumulative effect of write pulses, even after the write pulse with the maximum amplitude has passed. For example, in the lower right portion of the loop diagram in Figure 19, it can be seen that once the voltage value begins to drop from its maximum value of approximately 11V, these figures do not continue to shift directly to the left from the horizontal direction, but rather bend towards even smaller resistance values ​​between the recent write pulse's drop amplitude value of approximately 11V and approximately 2V. This cumulative effect of write pulses can be advantageous in some applications, as it has the value of the ability to track the occurrence of smaller amplitude pulses after larger amplitude pulses.

[0045] Besides the linear or logarithmically linear response of the memristor to the amplitude of the applied write pulse, another quantity of interest is the switching ratio, defined as the Rmax / Rmin ratio. Here, Rmax represents the HRS resistance of the memristor, and Rmin represents the LRS resistance of the memristor, which can be observed by reading the pulse after a complete write pulse cycle. In the ideal case of Figure 7, the Rmax value would be the resistance reading at point 701, and the Rmin value would be the resistance reading at point 705. A larger switching ratio makes it easier to use memristors in practical applications such as neuromorphic computing, because the required resolution (e.g., the connection strength between neural network nodes) does not need to be as fine.

[0046] Figure 21 illustrates the conversion ratios obtained by a memristor produced using the memristor material described above, where 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 dots from left to right in Figure 21). These measurements show that when x is less than 0.2, it may be difficult to obtain conversion ratios that satisfy many practical applications known at the time of writing of this specification, while as x increases toward 0.9, larger conversion ratios can be obtained, even reaching four orders of magnitude or potentially higher values.

[0047] Possible contact materials have been briefly discussed earlier in this specification. Figure 22 illustrates a comparison of measured current values ​​through memristors with two contacts made of gold (dashed lines), two contacts made of aluminum (thick solid lines), and one contact made of aluminum and one contact made of gold (thin solid lines). The rectification characteristics of the junction between aluminum and memristor materials differ from those between gold and memristor materials, which appears to cause significant differences in the measured values ​​shown in Figure 22.

[0048] Figure 23 illustrates a method for manufacturing a memristor using the memristor material of the type described above. It is assumed here that the memristor material is deposited on top of a substrate in this method, but other methods of manufacturing the memristor are not excluded. Step 2301 represents one or more preparation steps aimed at providing memristor material in the form of a target or source, which can be used in thin film deposition techniques such as pulsed laser deposition, molecular beam epitaxy, electron beam evaporation, etc. For example, if the memristor structure will include auxiliary layers such as contacts, insulators, and / or the like, other targets or sources may also be generated at step 2301. Step 2302 represents one or more preparation steps aimed at providing a substrate on which memristor material can be deposited. Step 2303 represents the generation of one or more thin films on top of the substrate, such that at least one of these thin films includes memristor material. A separate step 2304 in Figure 23 illustrates the contacts on which the memristor material is generated. For example, if pulsed laser deposition is used as the method for depositing memristor materials, DC magnetron sputtering with a shadow mask can be used to deposit layers of first and possibly second junction materials, which will form the junction with the memristor material.

[0049] Figure 24 illustrates an example of how the target material is prepared in step 2301 of Figure 23. In the example embodiment of Figure 24, the first step 2401 represents first preparing an appropriate amount of component materials (e.g., thorium oxide (III), calcium carbonate, and manganese oxide (IV)), for example, drying them overnight in hot (e.g., 200°C) air, ventilating them, and then mixing the dried component materials in a mortar. The relative amounts of the thorium oxide-containing component materials and the calcium-containing component materials will ultimately define the x value in the finished target material Gd(1-x)CaxMnO3. Step 2402 represents granulating the mixture of component materials, while step 2403 represents calcining the granular mixture, for example, by calcining it at an air temperature of 25°C -> 750°C -> 25°C for 7.5 hours to 60 hours. Step 2404 represents grinding the product of step 2403 in a mortar and regranulating it. Step 2405 involves sintering, for example, by varying the air temperature from 25°C to 1300°C and then back to 25°C for 13 to 24 hours. Step 2406 involves grinding the product from step 2405 in a mortar, regranulating it, and then re-sintering it into a solid target or source. Step 2407 involves using X-ray diffraction to measure the product from step 2406 to perform Rietveld refinement. If the material is found to be insufficiently pure, the process returns to step 2406. A solid target or source with sufficient purity found in step 2407 can be used as a target or source in a thin film deposition process according to step 2408, for example, as a target for pulsed laser focusing in pulsed laser deposition. For example, a xenon chloride (XeCl) laser with a wavelength of 308 nanometers, an energy density of approximately 2 J / cm², and a frequency of 5 Hz can be used in this pulsed laser deposition process. In this pulsed laser deposition method, an example of the process parameters is a deposition temperature of 700°C and an oxygen partial pressure of approximately 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 these parameters can be used.

[0050] Figures 25 and 26 illustrate an example of a pulse train that can be used to characterize the linear response of a memristor of the type 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, their polarities chosen so that they reliably set the memristor to the low-resistance state LRS. Assuming the memristor is planar, the x-value in the memristor material is between 0.7 and 0.95, and one of the contacts is made of gold and the other of aluminum, the amplitudes of the reset pulses 2501 and 2502 can be, for example, on the order of +7V. The length of each reset pulse 2501 and 2502 can be, for example, on the order of 0.45 ms, but obviously shorter or longer reset pulses are also possible: the available length of the reset pulse can be between 100 ns and 2 ms, or even shorter, such as 100 ps. There can be a pause of approximately 5 ms between the reset pulses 2501 and 2502.

[0051] A first read pulse 2503 may be applied to check that the memristor is indeed in LRS by measurement. The amplitude of the read pulse 2503 may be, for example, on the order of +0.45V; in any case, a sufficiently low read pulse should be chosen to ensure that the read pulse does not cause any noticeable change in the memristor LRS. The time interval between the subsequent reset pulse 2502 and the read pulse 2503 may be, for example, on the order of 0.5s, or between 0.1s and 1s, and the duration of the read pulse 2503 may be, for example, 0.5s. The description herein of a single read pulse can actually be a series of read pulses, for example, 20 read pulses, so the average read value of the LRS resistance is calculated based on the read values ​​given by each pulse.

[0052] A write pulse 2504 can be applied to transition the memristor from LRS to a higher resistance state. To characterize the linear response and assuming the aforementioned structural and material-related factors of the memristor, the amplitude of the write pulse 2504 can vary, for example, between -1V and -6.5V. The length of the write pulse 2504 can vary, for example, between 50 and 250ms, but significantly shorter write pulses, such as those on the order of approximately 100ns, can also be applied. A further pause, for example, of 1s, can be applied after the write pulse 2504, and an additional read pulse 2505 can be applied to read the transition resistance of the memristor. Again, described herein as a single read pulse, it can actually be a series of read pulses, for example, 20 read pulses, to calculate the average read value of the transition resistance from the read values ​​given by the individual pulses. Afterward, it is possible to return to the beginning of the pulse train, and another pulse train, possibly with some other amplitude and / or duration of the write pulse 2504, can be applied.

[0053] In Figure 26, the linear response in the HRS->LRS conversion can be examined. The pulse train again begins with two so-called reset pulses 2601 and 2602, this time choosing their polarities so that they reliably set the memristor to the high-resistance state HRS. Assuming the memristor is planar, the x-value in the memristor material is between 0.7 and 0.95, and one of the contacts is made of gold and the other of aluminum, the amplitudes of the reset pulses 2601 and 2602 can be, for example, on the order of -7.6V. The length of each reset pulse 2601 and 2602 can be, for example, on the order of 1.4ms, or between 0.1ms and 2ms. There may be a pause of approximately 5ms between the reset pulses 2601 and 2602.

[0054] A first read pulse 2603 may be applied to check that the memristor is indeed in HRS by measurement. The amplitude and other characteristics of the read pulse 2603 (or the first read pulse sequence) may be similar to the amplitude and other characteristics of the first read pulse (or the first read pulse sequence) in Figure 25.

[0055] A write pulse 2604 can be applied to transition the memristor from its HRS state to a lower resistance state. To characterize the linear response, and assuming the aforementioned structural and material-related factors of the memristor, the amplitude of the write pulse 2604 can be, for example, between +3.5V and +5.5V, and the length of the write pulse 2604 can vary, for example, between 20 and 120 ms. After the write pulse 2604, there can be a further pause of, for example, 0.5 s, and another read pulse 2605 can be applied to read the transformed resistance of the memristor. Again, described herein as a single read pulse, it can actually be a series of read pulses, for example, 20 read pulses, so that the average read value of the transformed resistance can be calculated based on the read values ​​given by the individual pulses. Thereafter, it is possible to return to the beginning of the pulse train, and another pulse train may be applied, possibly with some other amplitude and / or duration of the write pulse 2604.

[0056] Figure 27 shows the measurement results of the ratio (HRS-LRS) / LRS, where the amplitude and duration of the write pulse vary. Each individual graph in Figure 27 represents the write pulse amplitude according to the relevant legend, and the horizontal axis represents the width of the corresponding write pulse (in milliseconds). These measurements show that the amplitude and duration of the write pulse are significant in subjecting the memristor to resistance switching and can achieve linear or logarithmically linear behavior over a relatively large range of switching resistances.

[0057] It will be apparent to those skilled in the art that the basic concept of the present invention can be implemented in various ways as technology advances. As an example, other forms of thin film deposition methods, such as other physical vapor deposition methods, sputtering, chemical vapor deposition, or printing, can be used instead of pulsed laser deposition or in addition to pulsed laser deposition. Similarly, even though thiocyanate is mostly described as an element labeled R in the general chemical formula, other elements such as europium, tungsten, or neodymium can be used. Likewise, even though calcium is primarily described as an element labeled A, other elements such as strontium or barium can be used. Similarly, even though manganese is mostly described as an element labeled B, other elements such as cobalt or nickel can be used. Therefore, the present invention and its embodiments are not limited to the examples described above, but they can be varied within the scope of the claims.

Claims

1. A memristor comprising a sheet of memristor material forming at least one memristor connection between a first contact and a second contact, characterized in that: the memristor material has the chemical formula Gd(1-x)CaxMnO3, wherein, x is greater than 0 but less than 1. The first contact is mainly composed of a first material, and the second contact is mainly composed of a second material different from the first material. The rectification characteristics of the interface between the first material and the memristor material are different from the rectification characteristics of the interface between the second material and the memristor material. The first material is one of aluminum and titanium, and the second material is one of gold, silver, copper, platinum, palladium, indium, and strontium ruthenium oxide.

2. The memristor as described in claim 1, wherein, x is between 0.31 and 0.

99.

3. The memristor as described in claim 1, wherein, The memristor material of this piece forms a film on the top of the substrate, wherein the thickness of the film in the direction perpendicular to the surface of the substrate is between 1 nanometer and 500 nanometers.

4. The memristor as described in claim 3, wherein, The thickness of the film is between 10 and 100 nanometers.

5. The memristor as described in claim 3, wherein, The substrate is mainly composed of one of the following: strontium titanate, silicon, strontium tantalum aluminate, or lanthanum aluminate.

6. A microelectronic circuit comprising a memristor as described in any one of claims 1 to 5.

7. A method for manufacturing a memristor comprising a memristor material, characterized in that the method comprises: The memristor material uses a material having the chemical formula Gd(1-x)CaxMnO3, where x is greater than 0 but less than 1, and generates a first contact and a second contact with conductivity on at least one surface of the memristor material. The first contact is mainly composed of a first material, and the second contact is mainly composed of a second material different from the first material. The rectification characteristics of the junction between the first material and the memristor material are different from the rectification characteristics of the junction between the second material and the memristor material. The first material is one of aluminum and titanium, and the second material is one of gold, silver, copper, platinum, palladium, indium, and strontium ruthenate.

8. The method as described in claim 7, comprising depositing a thin film of the memristor material on top of a substrate.

9. The method as described in claim 8, comprising using at least one of the following for the deposition: pulsed laser deposition, other physical vapor deposition, sputtering, chemical vapor deposition, or printing.

10. The method as described in claim 9, comprising: A dry mixture is produced by mixing a first amount of oxide of R, a second amount of carbonate of A, and a third amount of oxide of B. The dried mixture was granulated and calcined. The target is ground, granulated, and sintered into a solid target, and then used for deposition using pulsed laser deposition, with the solid target serving as the target on which the pulsed laser is focused in the pulsed laser deposition process.

11. The method as claimed in claim 9, comprising using a xenon chloride laser with a wavelength of 308 nanometers, an energy density of substantially 2 J / cm2, and a frequency of 5 Hz in the pulsed laser deposition process.

12. The method as described in claim 11, wherein, The deposition temperature in this pulsed laser deposition method is 700°C, and the oxygen partial pressure is essentially 23 Pa.

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