PHASE CHANGE MATERIAL, PHASE CHANGE MEMORY CELL AND PREPARATION METHOD THEREFOR

Abstract

A phase change material, a phase change memory cell, and a preparation method thereof. The phase change material comprises elements tantalum, antimony and tellurium, the phase change material having a chemical formula of Ta.sub.xSb.sub.yTe.sub.z, wherein x, y, and z represent atomic ratios of the elements respectively; and 1≤x≤25, 0.5≤y:z≤3, and x+y+z=100. The phase change thin film material Ta.sub.xSb.sub.yTe.sub.z has a high phase change speed, outstanding thermal stability, strong data retention capability, a long cycle life, and a high yield. Ta.sub.5.7Sb.sub.37.7Te.sub.56.6 has ten-year data retention capability at 165° C.; and applying same in a device cell of a phase change memory achieves an operating speed of 6 ns and endurance of more than 1 million write-erase cycles. The crystal grains of the phase change material Ta.sub.xSb.sub.yTe.sub.z of the present disclosure are small, and after annealing treatment at 400° C. for 30 minutes, the grain size is still smaller than 30 nm.

Claims

1. A phase change material, comprising elements tantalum, antimony and tellurium, wherein the phase change material has a chemical formula of Ta.sub.xSb.sub.yTe.sub.z, wherein x, y, and z represent atomic ratios of the elements, respectively, wherein 1≤x≤25, 0.5≤y:z≤3, and x+y+z=100.

2. The phase change material according to claim 1, wherein the formula Ta.sub.xSb.sub.yTe.sub.z satisfies conditions 2≤x≤10, 25≤y≤45, and 40≤z≤70.

3. The phase change material according to claim 1, wherein the formula Ta.sub.xSb.sub.yTe.sub.z satisfies conditions 3.5≤x≤9, 30≤y≤40, and 50≤z≤60.

4. The phase change material according to claim 1, wherein the formula Ta.sub.xSb.sub.yTe.sub.z satisfies conditions 4≤x≤8, 36≤y≤39.6, and 54≤z≤59.4.

5. The phase change material according to claim 1, wherein the phase change material has an average grain size of less than 30 nm after annealing treatment at 400° C. for 30 minutes.

6. A phase change memory cell, comprising: a bottom electrode layer; a top electrode layer; and a phase change material layer between the bottom electrode layer and the top electrode layer, the phase change material layer comprising the phase change material of claim 1.

7. The phase change memory cell according to claim 6, wherein the phase change material has a thickness ranging from 20 nm to 150 nm.

8. A preparation method for a phase change memory cell, comprising the following steps: preparing a bottom electrode layer; preparing a phase change material layer on the bottom electrode layer, the phase change material layer comprising the phase change material of claim 1; and preparing a top electrode layer on the phase change material layer.

9. The preparation method for a phase change memory cell according to claim 8, wherein the phase change material layer is prepared by any one of magnetron sputtering, chemical vapor deposition, atomic layer deposition, and electron beam evaporation.

10. The preparation method for a phase change memory cell according to claim 8, wherein the phase change material is prepared by co-sputtering of monometallic targets or by sputtering of an alloy target.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a graph showing resistance-temperature relationships of Sb.sub.2Te.sub.3 and phase change materials Ta.sub.xSb.sub.yTe.sub.z with different components provided in the present disclosure.

[0025] FIG. 2 is a graph showing calculated results of data retention capabilities of phase change materials Ta.sub.xSb.sub.yTe.sub.z with different components provided in the present disclosure.

[0026] FIG. 3 is a graph showing resistance-voltage relationships of a phase change memory cell adopting phase change material Ta.sub.5.7Sb.sub.37.7Te.sub.56.6.

[0027] FIG. 4 is a graph showing fatigue performance of a phase change memory cell adopting phase change material Ta.sub.5.7Sb.sub.37.7Te.sub.56.6.

DETAILED DESCRIPTION

[0028] Embodiments of the present disclosure will be described below with specific examples, and other advantages and effects of the present disclosure may be easily understood by those skilled in the art from the disclosure in the specification. The present disclosure may also be carried out or applied in other different specific embodiments, and various modifications or changes may also be made to the details in the specification based on different ideas and applications without departing from the spirit of the present disclosure.

[0029] Please refer to FIGS. 1 to 4. It is to be noted that drawings provided in the embodiments only schematically illustrate the basic idea of the present disclosure, so the drawings only show components related to the present disclosure, and are not drawn according to the numbers, shapes and sizes of the components in actual implementation; the forms, numbers and proportions of the components in actual implementation may be varied as needed; and the layout of the components may be more complex.

Embodiment 1

[0030] This embodiment provides a phase change material. The phase change material includes elements tantalum (Ta), antimony (Sb) and tellurium (Te), and the phase change material has a chemical formula of Ta.sub.xSb.sub.yTe.sub.z, wherein x, y, and z represent atomic ratios of the elements, respectively; and 1≤x≤25, 0.5≤y:z≤3, and x+y+z=100.

[0031] Specifically, the contents of the three elements in Ta.sub.xSb.sub.yTe.sub.z can be adjusted to obtain storage materials with different crystallization temperatures, resistivity and crystallization activation energy. For example, the formula Ta.sub.xSb.sub.yTe.sub.z may further satisfy conditions 2≤x≤10, 25≤y≤45, and 40≤z≤70, or further satisfy conditions 3.5≤x≤9, 30≤y≤40, and 50≤z≤60, or further satisfy conditions 4≤x≤8, 36≤y≤39.6, and 54≤z≤59.4. In this embodiment, x, y, and z preferably satisfy conditions x=5.7, y=37.7, and z=56.6, i.e., the chemical formula of the phase change material is Ta.sub.5.7Sb.sub.37.7Te.sub.56. 6.

[0032] Specifically, the phase change material Ta.sub.xSb.sub.yTe.sub.z has at least two stable resistance states under the action of electrical pulse signals, is capable of reversible conversion between high and low resistance under the operation of electrical pulse signals, and its resistance value remains unchanged when there is no electrical pulse signal present.

[0033] Specifically, the phase change material Ta.sub.xSb.sub.yTe.sub.z have ten-year data retention capabilities at a temperature over 150° C., an operating speed of high than 6 ns, and a cycle life of more than 10.sup.6 cycles.

[0034] Specifically, the crystal grains of the phase change material Ta.sub.xSb.sub.yTe.sub.z are very small, and after annealing treatment at 400° C. for 30 minutes, its average grain size is still smaller than 30 nm, which is very important for the stability, low power consumption, and yield of a memory device.

[0035] Specifically, the phase change material Ta.sub.xSb.sub.yTe.sub.z may be in the form of a thin film. As an example, the phase change material Ta.sub.xSb.sub.yTe.sub.z has a film thickness ranging from 20 nm to 150 nm. For example, the thickness of the phase change material Ta.sub.xSb.sub.yTe.sub.z may be 30 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 150 nm, or the like. In this embodiment, the film thickness of the phase change material Ta.sub.xSb.sub.yTe.sub.z is preferably 60 nm.

[0036] FIG. 1 shows a graph of resistance-temperature relationships of Sb.sub.2Te.sub.3 and phase change materials Ta.sub.xSb.sub.yTe.sub.z with different components provided in the present disclosure. The chemical formulas of the phase change materials Ta.sub.xSb.sub.yTe.sub.z are Ta.sub.2.3Sb.sub.39.1Te.sub.58.6, Ta.sub.3.1Sb.sub.38.8Te.sub.58.1, and Ta.sub.5.7Sb.sub.37.7Te.sub.56.6, respectively (equivalent to Ta.sub.0.12Sb.sub.2Te.sub.3, Ta.sub.0.16Sb.sub.2Te.sub.3, and Ta.sub.0.30Sb.sub.2Te.sub.3, respectively). As can be seen from FIG. 1, the crystallization temperature of the phase change material Ta.sub.xSb.sub.yTe.sub.z can be adjusted between 150° C. and 250° C., which is a substantial increase compared to that of Sb.sub.2Te.sub.3 (about 70° C.). In addition, the crystallization temperature of the phase change material Ta.sub.xSb.sub.yTe.sub.z of the present disclosure is also obviously increased compared to that of the conventional Ge.sub.2Sb.sub.2Te.sub.5 (about 150° C.). Moreover, the high resistance of Ta.sub.xSb.sub.yTe.sub.z increases and then decreases with increase of the tantalum content, and its crystallization temperature increases with increase of the tantalum content. Therefore, the crystallization temperature of the phase change material Ta.sub.xSb.sub.yTe.sub.z may be controlled by adjusting the tantalum content.

[0037] Please refer to FIG. 2, which shows a graph of calculation results of data retention capabilities of the phase change materials Ta.sub.xSb.sub.yTe.sub.z with different components provided in the present disclosure. The chemical formulas of the phase change materials Ta.sub.xSb.sub.yTe.sub.z are Ta.sub.2.3Sb.sub.39.1Te.sub.58.6, Ta.sub.3.1Sb.sub.38.8Te.sub.58.1, and Ta.sub.5.7Sb.sub.37.7Te.sub.56.6, respectively (equivalent to Ta.sub.0.12Sb.sub.2Te.sub.3, Ta.sub.0.16Sb.sub.2Te.sub.3, and Ta.sub.0.30Sb.sub.2Te.sub.3, respectively). As can be seen from FIG. 2, the 10-year data retention temperature of the phase change material Ta.sub.xSb.sub.yTe.sub.z increases with the increase of its tantalum content. Furthermore, it can be seen that the 10-year data retention capability of the phase change material Ta.sub.xSb.sub.yTe.sub.z is improved compared to that of Ge.sub.2Sb.sub.2Te.sub.5 when the tantalum content exceeds 3.1%. Therefore, the thermal stability and data retention capability of the phase change material Ta.sub.xSb.sub.yTe.sub.z may be optimized by adjusting the tantalum content.

[0038] The phase change thin film material Ta.sub.xSb.sub.yTe.sub.z of the present disclosure has characteristics such as high phase change speed, outstanding thermal stability, strong data retention capability, long cycle life, and high yield, mainly for the following reasons: (1) the element tantalum is a common material for semiconductors and is compatible with COMS processes; (2) the atomic weight of the element tantalum (Ta) (180.947 g/mol) is much larger than that of the elements germanium (Ge) (72.59 g/mol), titanium (Ti) (47.90 g/mol), scandium (Sc) (44.95 g/mol) and the like, which means that Ta atoms diffuse more slowly in the phase change material and can function to inhibit grain growth and improve thermal stability, and increase the crystallization temperature and improve the ten-year data retention capability of the phase change material, which is especially important for engineering; (3) the thermal conductivity coefficient of Ta (57.5 J/m-sec-deg) is lower than that of Ge (60.2 J/m-sec-deg), and the overall thermal conductivity of the film is reduced due to the small grain size and increased grain boundaries, so PCM devices using Ta-doped Sb-Te-based phase change materials are expected to have relatively low operational power consumption; (4) the atomic radius of Ta (146 pm) is close to that of Sb (140 pm), and there exists a stable compound TaTe.sub.2 composed of Ta and Te, resulting in a possibility that Sb atoms are replaced after Sb-Te are doped with Ta atoms, thus forming a stable structure which promotes the crystallization of the Sb-Te-based phase change material, so high-speed phase change is expected to be achieved; and (5) the element Ta is chemically stable and does not react with oxygen and water in the air, and can reduce the damage of oxidation to device performance in the process, which is conducive to the improvement of the device yield.

Embodiment 2

[0039] This embodiment provides a phase change memory cell. The phase change memory cell includes a bottom electrode, a top electrode, and a phase change material layer between the bottom electrode layer and the top electrode layer. The phase change material layer includes the phase change material Ta.sub.xSb.sub.yTe.sub.z of Embodiment 1. That is, the phase change material includes elements tantalum (Ta), antimony (Sb) and tellurium (Te), and the phase change material has a chemical formula of Ta.sub.xSb.sub.yTe.sub.z, wherein x, y, and z represent atomic ratios of the elements, respectively; and 0.5≤y:z≤3, and x+y+z=100.

[0040] As an example, the phase change material layer has a thickness ranging from 20 nm to 150 nm.

[0041] As an example, on the top electrode layer, a leading-out electrode is formed, through which the top electrode layer and the bottom electrode layer may be integrated with a control switch, drive circuit, and peripheral circuit of the device cell.

[0042] Refer to FIG. 3, which shows a graph of resistance-voltage relationship for a phase change memory cell adopting a phase change material Ta.sub.5.7Sb.sub.37.7Te.sub.56.6. As seen in FIG. 3, the phase change memory cell can achieve a reversible phase change under the action of electrical pulses. In this embodiment, durations of voltage pulses for testing are 100, 80, 50, 20, 10, and 6 nanoseconds. It is to be noted that the memory cell device made of the phase change material Ta.sub.xSb.sub.yTe.sub.z can achieve “erase/write ” operations under an electrical pulse of as short as 6 nanoseconds, and “erase” and “write” operating voltages of the cell device are 4V and 2.3V, respectively.

[0043] Please refer to FIG. 4, which shows a graph of fatigue performance of the phase change memory cell using the phase change material Ta.sub.5.7Sb.sub.37.7Te.sub.56.6. As seen in FIG. 4, the device can endure repeated erase-write operations of 2.0×10.sup.6 times, and have stable resistance values at high and low resistance states, which ensures the reliability required of the device in application.

[0044] As can be seen from the above description, in the phase change memory cell of the present disclosure, the phase change material Ta.sub.xSb.sub.yTe.sub.z has at least two stable resistance states under the action of electrical pulses, is capable of reversible conversion between high and low resistance under the operation of electrical pulse signals, and its resistance value remains unchanged when there is no electrical pulse signal present. Ta.sub.5.7Sb.sub.37.7Te.sub.56.6 has ten-year data retention capability at 165° C., and the memory cell in the phase change memory using Ta.sub.5.7Sb.sub.37.7Te.sub.56.6 has an operating speed of 6 ns and endurance of more than 1 million write-erase cycles. In addition, the very small grain size of the phase change material Ta.sub.xSb.sub.yTe.sub.z results in more grain boundaries in the phase change material, which reduces the overall thermal conductivity of the phase change film, so a PCM device using the phase change material Ta.sub.xSb.sub.yTe, has relatively low operational power consumption.

Embodiment 3

[0045] This embodiment provides a preparation method of a phase change memory cell, including the following steps: [0046] S1: preparing a bottom electrode layer; [0047] S2: preparing a phase change material layer on the bottom electrode layer, the phase change material layer including the phase change material of Embodiment 1, i.e., the phase change material including elements tantalum (Ta), antimony (Sb) and tellurium (Te), and the phase change material having a chemical formula of Ta.sub.xSb.sub.yTe.sub.z, wherein x, y, and z represent atomic ratios of the elements, respectively; and 1≤x≤25, 0.5≤y:z≤3, and x+y+z=100; and [0048] S3: preparing a top electrode layer on the phase change material layer.

[0049] As an example, the bottom electrode layer may be prepared by sputtering, evaporation, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), etc. The material of the bottom electrode layer includes: one of monometallic materials Tungsten (W), platinum (Pt), gold (Au), titanium (Ti), aluminum (Al), silver (Ag), copper (Cu), and nickel (Ni), or an alloy formed by two or more of the above-mentioned monometallic materials, or a nitride or oxide of the monometallic materials. In this embodiment, the material of the bottom electrode layer is preferably W.

[0050] As an example, the phase change material layer may be prepared by a process such as magnetron sputtering, chemical vapor deposition, atomic layer deposition or electron beam evaporation.

[0051] As an example, the phase change material is prepared by co-sputtering of a Ta monometallic target and an Sb.sub.2Te.sub.3 alloy target according to the chemical formula Ta.sub.xSb.sub.yTe.sub.z of the phase change material.

[0052] As an example, an radio frequency power supply is used in sputtering of the Ta monometallic target, and a direct current power supply is used in sputtering of the Sb.sub.2Te.sub.3 alloy target; the sputtering power of the Ta monometallic target ranges from 20 W to 40 W, and the sputtering power of the Sb.sub.2Te.sub.3 alloy target ranges from 10 W to 30 W; and the sputtering time ranges from 10 to 30 minutes. In this embodiment, optionally the power of the Ta monometallic target is 20 W, the power of the Sb.sub.2Te.sub.3 alloy target is 20 W, and the sputtering time is 20 minutes.

[0053] As an example, during the preparation of the phase change material by co-sputtering of the Ta monometallic target and the Sb.sub.2Te.sub.3 alloy target, the base pressure is less than 3.0×10.sup.−4 Pa, the sputtering gas contains argon, and the sputtering temperature includes room temperature.

[0054] As an example, by adjusting process conditions, the contents of the three elements in the phase change material Ta.sub.xSb.sub.yTe, can be adjusted to obtain storage materials with different crystallization temperatures, resistivity and crystallization activation energy. For example, Ta.sub.xSb.sub.yTe.sub.z may further satisfy 2≤x≤10, 25≤y≤45, and 40≤z≤70, or further satisfy 3.5≤x≤9, 30≤y≤40, and 50≤z≤60, or further satisfy 4≤x≤8, 36≤y≤39.6, and 54≤z≤59.4. In this embodiment, the phase change material is preferably Ta.sub.5.7Sb.sub.37.7Te.sub.56.6, which has the advantages of higher thermal stability, stronger data retention capability, and faster crystallization.

[0055] As an example, the phase change material may also be prepared by three-target co-sputtering of a Ta monometallic target, an Sb monometallic target, and a Te monometallic target.

[0056] As an example, the phase change material may also be prepared by single-target sputtering of an alloy containing the elements tantalum, antimony and tellurium. The ratio of the three elements tantalum, antimony and tellurium in the alloy target is pre-configured. The alloy target may be prepared by physically mixing and sintering raw materials of the elements, or by chemical synthesis. The process of single-target sputtering can make the sputtering process easier to control compared to multi-target sputtering.

[0057] As an example, the top electrode layer may be prepared by sputtering, evaporation, chemical vapor deposition, plasma enhanced chemical vapor deposition, etc. The material of the top electrode layer includes: one of monometallic materials W, Pt, Au, Ti, Al, Ag, Cu, Ni, and Ta, or an alloy material formed by two or more of the above-mentioned monometallic materials, or a nitride or oxide of the monometallic materials. In this embodiment, the material of the top electrode layer is preferably TiN.

[0058] As an example, the preparation method further includes a step of forming a leading-out electrode on the top electrode layer, the material of the leading-out electrode including any one of W, Pt, Au, Ti, Al, Ag, Cu, Ta and Ni, or an alloy material formed by two or more of W, Pt, Au, Ti, Al, Ag, Cu, Ta and Ni. In this embodiment, the material of the leading-out electrode is preferably Al.

[0059] The preparation method for a phase change memory cell of the present disclosure is compatible with CMOS processes, and allows flexible adjustment of the contents of the elements in the phase change material Ta.sub.xSb.sub.yTe.sub.z, to obtain storage materials with different crystallization temperatures, resistivity, and crystallization activation energy.

[0060] In summary, the phase change thin film material Ta.sub.xSb.sub.yTe.sub.z of the present disclosure has the characteristics of high phase change speed, outstanding thermal stability, strong data retention capability, long cycle life, and high yield, and storage materials with different crystallization temperatures, resistivity and crystallization activation energy can be obtained by adjusting the contents of the three elements. Thus, the phase change material Ta.sub.xSb.sub.yTe.sub.z is highly adjustable, which is conducive to the optimization of various properties of the phase change material. Ta.sub.5.7Sb.sub.37.7Te.sub.56.6 has ten-year data retention capability at 165° C., and applying the same in a device cell of a phase change memory achieves an operating speed of 6 ns and endurance of more than 1 million write-erase cycles. Moreover, the crystal grains of the phase change material Ta.sub.xSb.sub.yTe.sub.z of the present disclosure are very small, and after annealing treatment at 400° C. for 30 minutes, the grain size is still smaller than 30 nm, which is very important for the stability, low power consumption, and yield of a device. The preparation method of a phase change memory cell of the present disclosure is compatible with CMOS processes, to facilitates accurate control of the composition of the phase change material. Therefore, the present disclosure effectively overcomes various shortcomings of the prior art and has a high value for industrial use.

[0061] The above embodiments are merely illustrative of the principles of the present disclosure and effects thereof, and are not intended to limit the present disclosure. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present disclosure. Therefore, all equivalent modifications or changes made by those with general knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present disclosure are still covered by the claims of the present disclosure.