TWI559305B - Resistive memory with multiple resistive states - Google Patents

Description

Resistive memory with multiple resistance states

The present invention relates to a non-volatile memory, and more particularly to a resistive memory having multiple resistance states.

Memory can be divided into volatile memory and non-volatile memory, and the resistive memory (RRAM) in non-volatile memory has a simple structure. Widely studied, low operating voltage, and ease of preparation.

The basic structure of the resistive memory is mainly metal/dielectric layer/metal, and the dielectric layer forms a current conduction path by applying a bias voltage, so that the resistive memory generates switching characteristics of different resistances, and has The high and low resistance states are used as "0" and "1" in the digital signal.

In order to increase the storage density of resistive memory and reduce the production cost, it is necessary to develop a memory with multiple resistance states. In general, when implementing multiple resistance states (RS) in resistive memory, one way is to control the thickness of the conduction path, that is, to generate different resistance values by adjusting the width of the conduction path to achieve multiple resistance states; One way is to achieve multiple power by regulating the number of conduction paths. configuration. However, the above-described manner of achieving multiple resistance states has the disadvantage of being difficult to control in operation.

Accordingly, it is an object of the present invention to provide a resistive memory having a multi-resistance state that can be easily achieved.

Therefore, the present invention has a resistive memory having multiple resistance states, comprising a first electrode, a second electrode, and an ion conducting unit.

The second electrode is spaced apart from the first electrode, and the second electrode has an oxidation potential smaller than the first electrode, and a plurality of metal cations can be generated after the positive voltage is applied to the first electrode.

The ion conducting unit is interposed between the first electrode and the second electrode, and includes a first ion conducting layer adjacent to the first electrode, and a first ion conducting layer and the second electrode a second ion conducting layer, the metal cations having a higher diffusion rate in the first ion conducting layer than in the second ion conducting layer.

The effect of the present invention is to utilize the characteristics that the diffusion rate of the metal cations in the first ion conducting layer is greater than the diffusion rate in the second ion conducting layer, when a positive voltage of a different magnitude is applied to the first electrode The resistive memory can be made to generate multiple resistance states.

2‧‧‧Resistive memory

21‧‧‧First electrode

22‧‧‧second electrode

23‧‧‧Ion Conduction Unit

231‧‧‧First ion conducting layer

232‧‧‧Second ion conducting layer

24‧‧‧Metal contact layer

25‧‧‧ metal cation

Other features and effects of the present invention will be apparent from the following description of the drawings, wherein: FIG. 1 is a schematic diagram illustrating the resistance of the present invention having multiple resistance states. A specific example 1 of the memory; FIG. 2 is a schematic view showing a specific example 2 of the resistive memory having multiple resistance states of the present invention; and FIG. 3 is a schematic view showing the resistive memory of the present invention having multiple resistance states A specific example 3 of the body; FIG. 4 is a relationship diagram of an energy scattering spectrometer, illustrating a composition ratio of a first ion conducting layer and a second ion conducting layer of the specific example 1 of the present invention; FIG. 5 is a current-voltage relationship FIG. 6 is a schematic diagram showing the four resistance states of the specific example 1 of the present invention; FIG. 7 is a schematic diagram illustrating the relationship between voltage switching and current of the specific example 1 and the specific example 2 to 3 of the present invention; A first intermediate resistance state of the specific examples 1 to 3 of the present invention; FIG. 8 is a schematic view showing a second intermediate resistance state of the specific examples 1 to 3 of the present invention; and FIG. 9 is a voltage diagram illustrating the present invention. The voltage values required for the specific examples 1 to 3 to switch to different resistance states are shown; FIG. 10 is a graph of resistance versus temperature, illustrating the resistance values of the different resistance states of the specific example 1 of the present invention at different temperatures; FIG. Is a resistance value versus switching cycle number relationship diagram, indicating The specific example 1 of the present invention has different resistance values in different resistance states for different switching cycles.

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same reference numerals.

Referring to FIG. 1, an embodiment of a resistive memory 2 having multiple resistance states of the present invention includes a first electrode 21, a second electrode 22, and an ion conducting unit 23.

The second electrode 22 is spaced apart from the first electrode 21, the ion conducting unit 23 is interposed between the first electrode 21 and the second electrode 22, and the oxidation potential of the second electrode 22 is smaller than the first electrode. 21, in other words, the activity of the first electrode 21 is greater than that of the second electrode 22. Therefore, after a positive voltage is applied to the first electrode 21, the first electrode 21 undergoes an oxidation reaction to generate a plurality of metals. cation.

The material suitable for the first electrode 21 of the present invention is a metal material selected from silver, copper, nickel or the like which is susceptible to oxidation reaction, and the second electrode 22 is a passive material selected from platinum or a doped germanium.

The ion conducting unit 23 includes a first ion conducting layer 231 adjacent to the first electrode 21, and a second ion conducting layer 232 between the first ion conducting layer 231 and the second electrode 22, and wherein The diffusion rate of the metal cations in the first ion conductive layer 231 is greater than the diffusion rate in the second ion conductive layer 232, and therefore, when the positive voltage is applied to the first electrode 21, the first electrode 21 The generated metal cations are sequentially diffused and conducted to the second electrode 22 via the first ion conductive layer 231 and the second ion conductive layer 232, thereby forming the first electrode 21 and the second electrode. 22 conductive path; and when the When a different negative voltage is applied to an electrode 21, the metal cation will move toward the negative voltage to be reduced. Therefore, the conductive path will be interrupted at different interfaces to generate different resistance states.

Specifically, the purpose of the first ion conducting layer 231 and the second ion conducting layer 232 is to cause a diffusion speed difference of the metal cations, so that the diffusion of the metal cations in the first ion conducting layer 231 can be performed. The rate may be greater than the diffusion rate in the second ion conducting layer 232, and the difference in the diffusion rates may be determined by the structural density or matching material of the first ion conducting layer 231 and the second ion conducting layer 232. Control, structure density is high (ie, film quality is good), metal cation diffusion rate is small; conversely, structure density is low (ie, film quality is poor), metal cation diffusion rate is larger. Therefore, the materials selected for the first ion conductive layer 231 and the second ion conductive layer 232 are not particularly limited and may be the same or different from each other. Preferably, the two layers of material may be selected from high dielectric materials such as yttria, yttria, or alumina.

When the first ion conducting layer 231 and the second ion conducting layer 232 are made of different materials, the materials may be selected to achieve different diffusion rates of the metal cations in the two conductive layers. purpose. When the first ion conducting layer 231 and the second ion conducting layer 232 are respectively made of the same material, the difference in material quality (ie, structural density) can be changed through the control of the process to achieve the metal cations. When the first ion conducting layer 231 and the second ion conducting layer 232 are diffused and transported, they can have different diffusion rate purposes. In other words, whether the materials used are the same or different, or the process is used to change the quality of the material. The purpose of the difference is to have the metal cations in the ion conducting unit 23 having different diffusion rates.

In detail, when the first ion conducting layer 231 and the second ion conducting layer 232 are made of the same material and the quality difference between the two is changed by the control of the process, respectively, by sputtering, sputtering, steaming Evaporation, plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition, or thermal vapor deposition, etc., as long as the second ion conducting layer The film quality of 232 is higher than that of the first ion conducting layer 231, so that the diffusion rate of the metal cations in the first ion conducting layer 231 is greater than the diffusion rate in the second ion conducting layer 232.

It should be noted that the difference in thickness between the first ion conductive layer 231 and the second ion conductive layer 232 is not particularly limited as long as the first ion conductive layer 231 and the second ion conductive layer 232 meet the aforementioned difference. However, when the thickness of one of them is too thin, the difference in resistance when forming a conductive path or an open circuit may be low, and therefore, preferably, the thickness of the first ion conductive layer 231 and the second ion conductive layer 232 The ratio is between 0.3 and 3.

The ion conducting unit of the resistive memory 2 embodiment of the present invention has a two-layer structure (the first ion conducting layer 231 and the second ion conducting layer 232), and therefore, the resistive memory 2 has its own Applying a voltage greater than a threshold voltage to form a conductive path, and generating a low resistance state (LRS), and applying a reverse voltage, causing the conductive path to form an open circuit, and generating a high resistance state (HRS), through the first ion conduction Layer 231 and the second ion pass The conductive layer 2 is configured to generate an additional first intermediate resistance state (MRS1) and a second intermediate resistance state (MRS2) when different voltages are applied, so that the resistive memory 2 can generate multiple (4 heavy) resistance state.

It is to be noted that the resistive memory 2 of the present invention is described by taking a two-layer structure as an example, but is not limited thereto, and it is also possible to further utilize a multilayer structure of two or more layers to achieve more heavy resistance states. the goal of.

In order to more clearly illustrate the resistive memory of the present invention having multiple resistance states, the following description will be made with three specific examples and experimental analysis thereof.

<Specific example 1>

Referring to FIG. 1, a cleaned n-type germanium wafer is prepared as the second electrode 22, and then a thickness of 15 nm is deposited on the second electrode 22 in a high temperature diffusion furnace. As the second ion conductive layer 232, cerium oxide (SiO ₂ ) is subsequently deposited on the second ion conductive layer 232 by a plasma enhanced chemical vapor deposition (PECVD) to deposit cerium oxide (SiO _{x )} having a thickness of 15 nm. x<2) as the first ion conductive layer 231, and finally, a silver (Ag) film having a thickness of 50 nm is formed by vapor deposition on the first ion conductive layer 231 by thermal evaporation as the first An electrode 21 is further formed on the first electrode 21 by thermal evaporation to form an aluminum (Al) film having a thickness of 300 nm as the metal contact layer 24. It should be noted that since the first electrode 21 is made of silver metal, when the positive voltage is applied to the first electrode 21, the generated metal cation is silver ions.

<Specific example 2>

Referring to FIG. 2, the implementation condition of a specific example 2 of the resistive memory having multiple resistance states of the present invention is substantially the same as that of the specific example 1, except that the thickness of the second ion conductive layer 232 is 8 nm. The thickness of the first ion conductive layer 231 is 22 nm.

<Specific example 3>

Referring to FIG. 3, the implementation condition of a specific example 3 of the resistive memory having multiple resistance states is substantially the same as that of the specific example 1, except that the thickness of the second ion conductive layer 232 is 22 nm. The thickness of the first ion conductive layer 231 is 8 nm.

<Data Analysis>

Referring to Fig. 4, an image analysis chart of the resistive memory 2 of the specific example 1 measured by an energy scatter spectrometer (EDS) is shown. From this analysis, it can be seen that the average ratio of oxygen (O) to cerium (Si) of cerium oxide (the first ion conducting layer 231) formed by plasma enhanced chemical vapor deposition (PECVD) is 1.68; The average ratio of oxygen (O) to cerium (Si) generated by cerium oxide (the second ion conducting layer 232) generated in a high temperature diffusion furnace was 1.96. It can be seen that when the first ion conducting layer 231 and the second ion conducting layer 232 are made of cerium oxide, different ratios of cerium oxide can be generated by different processes, when oxygen (O) and strontium ( The closer the ratio of Si) is to 2, the better the density is obtained. That is, in the specific examples 1 to 3, yttrium oxide formed in a high-temperature diffusion furnace is used as the second ion-conducting layer 232. The density is higher than the density of the first ion conducting layer 231 formed by the plasma enhanced chemical vapor deposition method. Therefore, the gold When the cation (silver ion) is conducted in the first ion-conducting layer 231 having a lower density, it has a faster diffusion rate than the conduction in the second ion-conducting layer 232 having a higher density.

Referring to FIGS. 5-8, before the resistive memory 2 of the specific examples 1 to 3 is operated, a sufficient positive voltage is applied to the first electrode 21 to cause the metal cation generated by the first electrode 21. 25 (silver ions) can be diffused and conducted by the first electrode 21 to the second electrode 22 via the ion conducting unit 23, generating a conductive path formed by the plurality of metal cations 25 to make the resistive memory 2 low. Resistance state (LRS) (see Fig. 6, taking this specific example 1 as an example), which is a forming process well known in the art. From the voltage applied by the forming process in FIG. 5 and the current graph thereof, since the thickness of the second ion conductive layer 232 of the specific example 3 is the thickest among the specific examples 1 to 3, A large voltage (about 15V) is required to complete the forming process.

Then, when the resistive memory 2 is in a low resistance state (LRS), the metal cations 25 can be reduced from the second electrode 22 to the first electrode 22 via the ion conducting unit 23 by applying a sufficiently large negative voltage. An electrode 21 interrupts the conductive path, so that the resistive memory 2 assumes a high resistance state (HRS) (see FIG. 6, which is exemplified by the specific example 1), which is a well-known weight in the art. Reset process. It should be noted that, according to the current and voltage graphs of FIG. 5, the resistive memory 2 of the present invention can be first applied with a suitable negative voltage (reset 1) during the reset process. The resistive memory 2 is caused to generate a first intermediate resistance state (MRS1) (see MRS1 of FIG. 6 and MRS1 of the specific example 1 to 3 of FIG. 7), and then continue to apply a larger The negative voltage (reset 2) returns to the high resistance state (HRS).

The reason for causing the first intermediate resistance state (MRS1) is that the first ion conductive layer 231 and the second ion conductive layer 232 are designed to pass the metal cations 25 to the first ion conductive layer 231. This is achieved by having a different diffusion rate from the second ion conducting layer 232. That is, when a suitable negative voltage is applied (reset 1), the diffusion rate of the metal cations 25 to the first ion conductive layer 231 is faster, and the diffusion rate of the second ion conductive layer 232 is slower. Therefore, the metal cations 25 located in the first ion conducting layer 231 move toward the first electrode 21 faster, so that the interface between the first ion conducting layer 231 and the second ion conducting layer 232 is not The first intermediate resistance state (MRS1) is formed by having the metal cations 25 (see MRS1 of FIG. 6 and MRS1 of the specific examples 1-3 of FIG. 7). When a larger negative voltage (reset 2) is continuously applied to the first intermediate resistance state (MRS1), most of the metal cations 25 are further moved toward the first electrode 21, so that the resistive memory Body 2 is a non-conducting high resistance state (HRS) (see Figure 6).

Finally, the resistive memory 2 can be returned from the high resistance state (HRS) back to the low resistance state (LRS) by applying a sufficiently large positive voltage, a well-known set process in the art. Similarly, it can be seen from the current and voltage graphs of FIG. 5 that the resistive memory 2 of the present invention can be applied by applying an appropriate positive voltage (set 1) during the set-up process. The memory 2 generates a second intermediate resistance state (MRS2) (see MRS2 of FIG. 6 and MRS2 of the specific example 1 to 3 of FIG. 8), and then continues to apply a larger positive voltage (set 2) to return. The low resistance state (LRS).

The reason for causing the second intermediate resistance state (MRS2) is also achieved by the design of the first ion conductive layer 231 and the second ion conductive layer 232. When a suitable positive voltage is applied (set 1), the metal cations 25 move faster through the first ion conducting layer 231 toward the second ion conducting layer 232, and the metal cations 25 are in the second The rate of movement in the ion conducting layer 232 is slower, so at the appropriate positive voltage, the interface between the second ion conducting layer 232 and the second electrode 22 does not have the metal cations (see MRS2 and Figure 6). The MRS 2) of the specific examples 1 to 3 of 8 forms the second intermediate resistance state (MRS2). When a larger positive voltage is continuously applied, the metal cations 25 are further moved toward the second electrode 22, causing the resistive memory to conduct a low resistance state (LRS) (see FIG. 6).

Referring to FIG. 9 in combination, as the specific examples 1-3 increase the thickness of the second ion conducting layer 232, whether it is a reset process or a set process, the required voltage is applied. It also increases. Mainly because the stoichiometric of the second ion conducting layer 232 is closer to SiO ₂ and has a denser state (see FIG. 4), so a higher voltage is required to drive.

Referring to FIG. 10, the specific example 1 is taken as an example, and a specific voltage of 25 V is used, and the specific example 1 is measured at different temperatures (25° C., 85° C., and 125° C.) for about 10 ⁴ s. The maintenance of this specific example 1 was tested. After the long-term test described above and the temperature is raised to 125 ° C, the difference between the two resistance states of the specific example 1 can be maintained at two orders of magnitude, and the respective resistance states can be effectively distinguished. The resistive memory 2 of the present invention has such good maintenance, mainly due to the use of a high-quality yttrium oxide layer by the ion-conducting unit 23, which has silver ions in the stacked yttrium oxide layer compared to other materials. The lower diffusion rate allows the silver ion regeneration of the first electrode 21 to be slowed down during the test to improve overall maintenance.

Referring to FIG. 11 in cooperation, the specific example 1 is taken as an example, and the specific example 1 is subjected to a cycling test, and the specific example 1 is applied to set 1, set 2, reset 1, and reset 2. The voltages are +3.5V, +6V, -4.5V, and -9V. The specific example 1 performs a continuous switching test (LRS→MRS1→HRS→MRS2→LRS) over five cycles, and can maintain a difference of two orders of magnitude between each of the resistance states.

In summary, the present invention has a resistive memory having multiple resistance states, and the first ion conductive layer 231 and the second ion conductive layer 232 having different structural qualities are formed through a process, thereby causing the first electrode 21 to be generated. The diffusion rate of the metal cation in the first ion conducting layer 231 is greater than the diffusion rate in the second ion conducting layer 232, so that the resistive memory 2 has a high resistance state (HRS) and a low resistance state. In addition to (LRS), the first intermediate resistance state (MRS1) and the second intermediate resistance can be generated by applying a suitable voltage to cause the resistive memory 2 to have different resistance values by applying a difference in the diffusion rate. The state (MRS2) makes the resistive memory 2 have multiple resistance states, so that the object of the present invention can be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, that is, the simple equivalent changes and modifications made by the patent application scope and patent specification content of the present invention, All remain within the scope of the invention patent.

2‧‧‧Resistive memory

21‧‧‧First electrode

22‧‧‧second electrode

23‧‧‧Ion Conduction Unit

231‧‧‧First ion conducting layer

232‧‧‧Second ion conducting layer

Claims (9)

A resistive memory having multiple resistance states, comprising: a first electrode; a second electrode disposed at an interval from the first electrode, wherein an oxidation potential of the second electrode is smaller than the first electrode, and is applied to the first electrode After a positive voltage, the first electrode can generate a plurality of metal cations; and an ion conducting unit sandwiched between the first electrode and the second electrode and including a first ion conducting adjacent to the first electrode a layer, and a second ion conducting layer between the first ion conducting layer and the second electrode, the metal cations having a higher diffusion rate in the first ion conducting layer than in the second ion conducting layer Diffusion rate. The resistive memory having multiple resistance states according to claim 1, wherein the constituent material of the ion conductive unit is selected from a solid electrolyte material. The resistive memory having multiple resistance states according to claim 1, wherein the constituent material of the ion conductive unit is selected from a high dielectric material. The resistive memory having a multiple electrical configuration according to any one of claims 1 to 3, wherein the first ion conducting layer is selected from the same material as the second ion conducting layer. The resistive memory having a multiple electrical configuration according to any one of claims 1 to 3, wherein the first ion conducting layer is selected from a material different from the material selected for the second ion conducting layer. The resistive memory having multiple resistance states according to claim 4, wherein the first ion conductive layer is composed of SiO _x , x < 2, and the second ion conductive layer is composed of SiO ₂ . The resistive memory having multiple resistance states according to claim 1, wherein a ratio of a thickness of the first ion conductive layer to a thickness of the second ion conductive layer is between 0.3 and 3. The resistive memory having multiple resistance states according to claim 1, wherein a ratio of a thickness of the first ion conductive layer to a thickness of the second ion conductive layer is equal to 1. The resistive memory having multiple resistance states according to claim 1, wherein the first electrode is selected from the group consisting of silver, copper, or nickel, and the second electrode is selected from platinum or a doped germanium.