CN112133824A - Phase change material, phase change storage unit and preparation method thereof - Google Patents
Phase change material, phase change storage unit and preparation method thereof Download PDFInfo
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- H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
- H10N70/8828—Tellurides, e.g. GeSbTe
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- H10B—ELECTRONIC MEMORY DEVICES
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- H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/021—Formation of switching materials, e.g. deposition of layers
- H10N70/023—Formation of switching materials, e.g. deposition of layers by chemical vapor deposition, e.g. MOCVD, ALD
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- H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
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- H10N70/021—Formation of switching materials, e.g. deposition of layers
- H10N70/026—Formation of switching materials, e.g. deposition of layers by physical vapor deposition, e.g. sputtering
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- H10N70/20—Multistable switching devices, e.g. memristors
- H10N70/231—Multistable switching devices, e.g. memristors based on solid-state phase change, e.g. between amorphous and crystalline phases, Ovshinsky effect
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Abstract
The invention relates to a phase change material, a phase change memory unit and a preparation method thereof. The chemical formula of the phase-change material is TaaInbSbcTed. The unit comprises a lower electrode layer, an upper electrode layer and a phase change material layer positioned between the lower electrode layer and the upper electrode layer. The preparation method of the unit comprises the following steps: preparing a lower electrode layer; preparing a phase change material layer on the lower electrode layer; and preparing an upper electrode layer on the phase change material layer. The phase-change material has the characteristics of small crystal grains, high phase-change speed, outstanding thermal stability, strong data retention capacity, long cycle life, high yield and the like.
Description
Technical Field
The invention belongs to the field of microelectronics, and particularly relates to a phase change material, a phase change memory unit and a preparation method thereof.
Background
The Phase Change Memory (PCM) has the advantages of nonvolatility, good micro-shrinkage, three-dimensional integration, high read-write speed, low power consumption, long cycle life, compatibility with a CMOS (complementary metal oxide semiconductor) process, excellent radiation resistance and the like, becomes the most powerful competitor in a novel storage technology, and is expected to become the mainstream storage technology of the next-generation non-volatile memory.
The principle of phase change memories is based on the reversible switching of a phase change material between high and low resistance under operation of an electrical pulse signal to achieve the storage of a "0" and a "1". That is, the phase change material exhibits a high resistance value in an amorphous state and a low resistance value in a crystalline state. The phase change material is the core of the phase change memory. The performance of the phase change memory is determined by the performance of the phase change material. The most typical phase change material at present is Ge2Sb2Te5The material has the characteristics of long cycle life and good micro-shrinkage, but the material has the problems of low speed, large power consumption and poor amorphous state thermal stability. The search for phase change materials with faster phase change speed, lower power consumption and better thermal stability is still the key to the development of phase change memories. Sb2Te3The phase change material has the characteristic of high phase change speed, but the crystallization temperature of the material is low, the data retention and the thermal stability are poor, and the application requirement of a phase change memory cannot be met. In addition, in the phase change memory operation process, the elements Sb and Te can be migrated due to repeated high-temperature writing and erasing operations, so that the internal components of the material are segregated, and meanwhile, the power consumption of the device is increased due to larger crystal grains, and the service life of the device is influenced. Therefore, how to improve the amorphous thermal stability, reduce the grain size and prevent the element diffusion becomes an urgent problem to be solved.
Disclosure of Invention
The invention aims to solve the technical problems of providing a phase-change material, a phase-change storage unit and a preparation method thereof, and overcoming the defects of low crystallization temperature, poor thermal stability, slow phase-change speed, large grain size, poor fatigue performance and incapability of meeting the performance requirement of replacing a dynamic random access memory in the prior art.
The invention provides a phase change material, the chemical formula of which is TaaInbSbcTedWherein a is more than or equal to 1 and less than or equal to 15, and b is more than or equal to 0.5 and less than or equal to 1510，1/3≤c/d≤1，a+b+c+d＝100。
The a, b, c and d all refer to atomic percentages of elements.
The a is 2-15, the b is 2-10, the c/d is 1/2-1, and the following is further preferable: a is more than or equal to 3 and less than or equal to 15, b is more than or equal to 2 and less than or equal to 10, and c/d is more than or equal to 7/12 and less than or equal to 1.
The chemical formula of the material is Ta8.93In9.14Sb38Te43.93，Ta11.55In9.33Sb36.65Te42.47，Ta14.67In9.51Sb35.01Te40.81。
The invention also provides a preparation method of the phase change material, and the phase change material is prepared by adopting a magnetron sputtering method, a chemical vapor deposition method, an atomic layer deposition method or an electron beam evaporation method.
The magnetron sputtering method is to adopt elementary substance target co-sputtering preparation or alloy target sputtering preparation to prepare the phase-change material. For example, Ta elementary substance target, In-Sb is adopted2Te3The phase-change material is prepared by alloy target co-sputtering, or the phase-change material is prepared by four-target co-sputtering of a Ta simple substance target, an In simple substance target, an Sb simple substance target and a Te simple substance target, or the phase-change material is prepared by single-target sputtering of an alloy rake containing tantalum element, indium element, antimony element and tellurium element; wherein, the proportion of tantalum, indium, antimony and tellurium in the alloy target is prepared in advance; the alloy target can be obtained by physically mixing and sintering raw materials of each element, or can be obtained by chemical synthesis. Compared with multi-target sputtering, the process of single-target sputtering is easier to control.
The invention also provides a phase change memory unit, which comprises a lower electrode layer, an upper electrode layer and a phase change material layer positioned between the lower electrode layer and the upper electrode layer, wherein the phase change material layer is any one of the phase change materials.
The material of the lower electrode layer and the upper electrode layer is a single metal material or an alloy material formed by combining any two or more of the single metal materials, or a nitride or an oxide of the single metal material.
The thickness of the phase change material layer is 20nm-150 nm.
The single metal material is W, Pt, Au, Ti, Al, Ag, Cu, Ta and Ni.
The invention also provides a preparation method of the phase change memory unit, which comprises the following steps:
(1) preparing a lower electrode layer;
(2) preparing a phase change material layer on the lower electrode layer in the step (1), wherein the phase change material layer is the phase change material;
(3) and (3) preparing an upper electrode layer on the phase change material layer in the step (2).
The preparation method of the lower electrode layer and the upper electrode layer comprises a sputtering method, an evaporation method, a Chemical Vapor Deposition (CVD) method or a Plasma Enhanced Chemical Vapor Deposition (PECVD) method.
The production method further includes a step of forming an extraction electrode on the upper electrode layer.
The material of the extraction electrode comprises any one of W, Pt, Au, Ti, Al, Ag, Cu, Ta and Ni, or an alloy material formed by combining any two or more of the W, Pt, Au, Ti, Al, Ag, Cu, Ta and Ni.
The invention also provides an application of the phase change material.
The invention also provides an application of the variable memory unit.
According to the invention, the crystallization temperature of the phase-change material is raised in a double-element doping mode, the thermal stability of the amorphous phase is improved, and the fatigue performance of the device is improved. The invention selects In element for doping, can improve the crystallization temperature of the material, and is beneficial to the improvement of thermal stability and fatigue performance because the In element can enter crystal lattices to form a single-phase change material. The Ta element is selected for doping, so that the crystallization temperature and the thermal stability of the material can be further improved, and most of the Ta element is positioned at a crystal boundary, so that the grain size of the material can be obviously limited, the element is inhibited from migrating in a large range in the operation process, and the thermal stability and the fatigue performance are improved.
Ta of the inventionaInbSbcTedThe phase-change film material has the characteristics of high phase-change speed, outstanding thermal stability, strong data retention capacity, long cycle life, high yield and the like, and is mainly based on the following reasons: (1) ta element is a common material for semiconductors and is compatible with COMS process; (2) the atomic weight (180.947g/mol) of the Ta element is far greater than elements such as Ge (72.59g/mol), Ti (47.90g/mol), Sc (44.95g/mol) and the like, which means that the Ta atom has a relatively slow diffusion speed in the phase-change material, can play a role in inhibiting the growth of crystal grains and improving the thermal stability, and improves the crystallization temperature and ten-year data retention of the phase-change material, which is particularly important for engineering; (3) the thermal conductivity coefficient (57.5J/m-sec-deg) of Ta is lower than that (60.2J/m-sec-deg) of Ge, and meanwhile, the overall thermal conductivity of the film is reduced due to small grain size and increased grain boundaries, so that a PCM device adopting Ta doped with Sb-Te based phase change material is expected to obtain lower operation power consumption; (4) the chemical property of the Ta element is stable, the Ta element does not react with oxygen and water in the air, the damage of oxidation to the performance of the device can be reduced in the process, and the yield of the device is improved. (5) The In and Te exist stable compounds, so that the possibility of replacing Sb atoms exists after the In atoms are doped with Sb-Te, a stable structure is formed, the function of promoting the crystallization of the Sb-Te based phase change material is realized, and the high-speed phase change is hopeful to be realized.
Advantageous effects
Ta of the inventionaInbSbcTedThe phase-change film material has the characteristics of small grain size, high phase-change speed, outstanding thermal stability, strong data retention capacity, long cycle life, high yield and the like, and the storage materials with different crystallization temperatures, resistivities and crystallization activation energies can be obtained by adjusting the contents of the four elements. Thus the TaaInbSbcTedThe phase-change material has strong adjustability and is beneficial to optimizing various performances of the phase-change material. Meanwhile, Ta of the present inventionaInbSbcTedThe crystal grains of the phase-change material are very small, and the size of the crystal grains is still less than 30 nanometers after annealing treatment at 400 ℃ for 30 minutes, which is very important for the stability, low power consumption and yield of devices. The preparation method of the phase change memory unit is compatible with the CMOS process, and is convenient for accurately controlling the components of the phase change material.
Drawings
FIG. 1 shows Ta of different compositions in example 1 of the present inventionaInbSbcTedResistance versus temperature graph for phase change materials.
FIG. 2 shows the use of Ta in example 1 of the present inventionaInbSbcTedTen year data capacity calculation results plot for phase change materials.
FIG. 3 shows the use of Ta in an embodiment of the present invention8.93In9.14Sb38Te43.93A resistance-voltage relationship diagram for a phase change memory cell of a phase change material.
FIG. 4 shows the use of Ta in an embodiment of the present invention8.93In9.14Sb38Te43.93Fatigue performance map of a phase change memory cell of a phase change material.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
This example provides a phase change material with a chemical formula of TaaInbSbcTedWherein a, b, c and d are atomic percentages of elements, a is more than or equal to 1 and less than or equal to 15, b is more than or equal to 0.5 and less than or equal to 10, c/d is more than or equal to 1/3 and less than or equal to 1, and a + b + c + d is 100. Specifically, TaaInbSbcTedIn the method, the contents of the four elements can be adjusted to obtain the storage materials with different crystallization temperatures, resistivities and crystallization activation energies. For example, TaaInbSbcTedIn the formula, a is more than or equal to 2 and less than or equal to 15, b is more than or equal to 2 and less than or equal to 10, c is more than or equal to 1/2 and less than or equal to 1, or a is more than or equal to 3 and less than or equal to 15, b is more than or equal to 2 and less than or equal to 10, and c/d is more than or equal to 7/12 and less than or equal to. In this embodiment, the chemical formula of the phase change material is Ta8.93In9.14Sb38Te43.93，Ta11.55In9.33Sb36.65Te42.47，Ta14.67In9.51Sb35.01Te40.81。
Ta in this example8.93In9.14Sb38Te43.93The phase-change material has at least two stable resistance states under the action of electric pulse, can realize reversible conversion of high and low resistance values under the operation of electric pulse signals, and the resistance value is kept unchanged under the operation without the electric pulse signals.
Ta in this example8.93In9.14Sb38Te43.93The ten-year data of the phase change material keeps the temperature at 153 ℃, the operation speed is 6ns, and the cycle life exceeds 106。
Ta in this example8.93In9.14Sb38Te43.93The crystal grain of the phase-change material is less than 10nm, and the average crystal grain size is still less than 30nm after annealing treatment at 400 ℃ for 30 minutes, which is very important for the stability, low power consumption and yield of the memory device.
Ta in this example8.93In9.14Sb38Te43.93The phase change material may be present in the form of a thin film. For example, Ta8.93In9.14Sb38Te43.93The thickness of the phase change material may be 30nm, 50nm, 60nm, 80nm, 100nm, 120nm, 140nm, 150nm, and so on. Ta in this example8.93In9.14Sb38Te43.93The film thickness of the phase change material was 60 nm.
FIG. 1 shows Ta of various compositions provided for in the inventionaInbSbcTedResistance versus temperature graph for phase change materials. Wherein, TaaInbSbcTedThe chemical formula of the phase-change material is respectively as follows: ta8.93In9.14Sb38Te43.93，Ta11.55In9.33Sb36.65Te42.47，Ta14.67In9.51Sb35.01Te40.81. As can be seen from FIG. 1, TaaInbSbcTedThe crystallization temperature of the phase-change material can be adjusted between 190 ℃ and 270 ℃, compared with the crystallization temperature of the phase-change materialSb2Te3It is greatly improved. In addition, compared with the conventional Ge2Sb2Te5(about 150 ℃ C.), Ta of the present inventionaInbSbcTedThe crystallization temperature of the phase-change material is also obviously improved. And TaaInbSbcTedThe high resistance of (a) increases and then decreases as the tantalum and indium content increases, and the crystallization temperature increases as the tantalum content increases. Ta can thus be controlled by adjusting the tantalum and indium contentsaInbSbcTedThe crystallization temperature of the phase change material.
FIG. 2 shows Ta of various compositions provided for in accordance with the present inventionaInbSbcTedAnd calculating the data retention capacity of the phase change material. Wherein, TaaInbSbcTedThe chemical formula of the phase-change material is respectively as follows: ta8.93In9.14Sb38Te43.93，Ta11.55In9.33Sb36.65Te42.47，Ta14.67In9.51Sb35.01Te40.81. As can be seen from FIG. 2, TaaInbSbcTedThe 10-year data retention temperature of the phase change material increases with increasing tantalum and indium content. Meanwhile, it can be seen that, when the content of Ta exceeds 8% and the content of In exceeds 9%, TaaInbSbcTed10-year data retention of phase change materials versus Ge2Sb2Te5Has certain improvement. Thus, TaaInbSbcTedThe thermal stability and data retention of the phase change material can be optimized by adjusting the tantalum content.
Example 2
This embodiment provides a phase change memory cell comprising a bottom electrode layer (W, thickness 600nm), a top electrode layer (TiN, thickness 10nm), and a phase change material layer between the bottom and top electrode layers, the phase change material layer comprising Ta as in embodiment 18.93In9.14Sb38Te43.93A phase change material. The thickness of the phase change material layer was 100 nm.
An extraction electrode (Al, the thickness is 300nm) is also formed on the upper electrode layer, and the upper electrode layer, the lower electrode layer, a control switch of the device unit, a driving circuit and a peripheral circuit can be integrated through the extraction electrode.
FIG. 3 shows the use of Ta8.93In9.14Sb38Te43.93A resistance-voltage relationship diagram for a phase change memory cell of a phase change material. As can be seen in FIG. 3, the phase change memory cell can achieve a reversible phase change under the application of an electrical pulse. In this example, the voltage pulses used for the test were 100 nanoseconds, 80 nanoseconds, 50 nanoseconds, 10 nanoseconds, and 6 nanoseconds. Notably, Ta8.93In9.14Sb38Te43.93Memory cell devices made of phase change materials can achieve "erase and write" operations with electrical pulses as short as 6 nanoseconds.
FIG. 4 shows the use of Ta8.93In9.14Sb38Te43.93Fatigue performance map of a phase change memory cell of a phase change material. As can be seen from FIG. 4, the device has repeated erase/write times of 1.0 × 106The high-resistance state and the low-resistance state have stable resistance values, and the reliability required by the application of the device is ensured.
As can be seen from the above, in the phase change memory cell of the present invention, Ta8.93In9.14Sb38Te43.93The phase-change material has at least two stable resistance states under the action of electric pulse, can realize reversible conversion of high and low resistance values under the operation of electric pulse signals, and the resistance value is kept unchanged under the operation without the electric pulse signals. Wherein, Ta8.93In9.14Sb38Te43.93Has a ten-year data retention of 153 ℃ and adopts Ta8.93In9.14Sb38Te43.93The phase change memory has an operation speed of 6ns and an erasing frequency of more than 100 ten thousand times. In addition, due to Ta8.93In9.14Sb38Te43.93The crystal grains of the phase-change material are very small, so that the crystal boundary in the phase-change material is increased, the integral heat conductivity of the phase-change film is reduced, and Ta is adoptedaInbSbcTedPCM device of phase change material with lower operation power consumption。
Example 3
The embodiment provides a method for preparing a phase change memory unit, which comprises the following steps:
s1: preparing a lower electrode layer;
s2: preparing a phase change material layer on the lower electrode layer, wherein the phase change material layer comprises the phase change material described in embodiment 1, and the chemical formula of the phase change material is Ta8.93In9.14Sb38Te43.93；
S3: and preparing an upper electrode layer on the phase change material layer.
In this embodiment, the material of the bottom electrode layer is W, and the preparation method of the bottom electrode layer is an atomic layer deposition technique.
According to the chemical formula Ta of the phase-change material8.93In9.14Sb38Te43.93Adopting Ta simple substance target, In-Sb2Te3And co-sputtering the alloy target to prepare the phase-change material. The sputtering of Ta single-substance target adopts a radio frequency power supply, In-Sb2Te3The sputtering of the alloy target adopts a radio frequency power supply, the sputtering power range of the Ta simple substance target is 10W-15W, and Sb2Te3The sputtering power of the alloy target ranges from 10W to 30W, and the sputtering time ranges from 10 minutes to 30 minutes. In this example, Ta single target power was selected to be 10W, In-Sb2Te3The power of the alloy target was 30W, and the sputtering time was 20 minutes.
Adopting Ta simple substance target, In-Sb2Te3In the process of preparing the phase-change material by alloy target co-sputtering, the background vacuum degree is less than 3.0 multiplied by 10-4Pa, the sputtering gas comprises argon, and the sputtering temperature comprises room temperature.
In this embodiment, the upper electrode layer is made of TiN, and the preparation method of the upper electrode layer is magnetron sputtering.
The production method further includes a step of forming an extraction electrode on the upper electrode layer. In this embodiment, the material of the extraction electrode is Al, and the preparation method is magnetron sputtering or electron beam evaporation.
The preparation method of the phase change memory unit is compatible with the COMS process, and the phase change memory unit can be flexibly adjustedTaaInbSbcTedThe components of each element in the phase-change material, so that the storage materials with different crystallization temperatures, resistivities and crystallization activation energies are obtained.
In conclusion, Ta of the present inventionaInbSbcTedThe phase-change film material has the characteristics of high phase-change speed, outstanding thermal stability, strong data retention capacity, long cycle life, high yield and the like, and can obtain storage materials with different crystallization temperatures, resistivities and crystallization activation energies by adjusting the contents of the four elements. Thus the TaaInbSbcTedThe phase-change material has strong adjustability and is beneficial to optimizing various performances of the phase-change material. Wherein, Ta8.93In9.14Sb38Te43.93The phase change memory has ten-year data retention of 153 ℃, and the application of the phase change memory in a device unit has the operation speed of 6ns and the erasing times of more than 100 ten thousand times. Meanwhile, Ta of the present inventionaInbSbcTedThe crystal grains of the phase-change material are very small, and the size of the crystal grains is still less than 30 nanometers after annealing treatment at 400 ℃ for 30 minutes, which is very important for the stability, low power consumption and yield of devices. The preparation method of the phase change memory unit is compatible with the CMOS process, and is convenient for accurately controlling the components of the phase change material. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. A phase change material, characterized in that the chemical formula of the material is TaaInbSbcTedWherein a is more than or equal to 1 and less than or equal to15，0.5≤b≤10，1/3≤c/d≤1，a+b+c+d＝100。
2. The material of claim 1, wherein a is 2 to 15, b is 2 to 10, and c/d is 1/2 to 1.
3. The material of claim 1, wherein the material has the chemical formula Ta8.93In9.14Sb38Te43.93，Ta11.55In9.33Sb36.65Te42.47，Ta14.67In9.51Sb35.01Te40.81。
4. The method for preparing the phase-change material according to claim 1, wherein the material is prepared by a magnetron sputtering method, a chemical vapor deposition method, an atomic layer deposition method or an electron beam evaporation method.
5. A phase change memory cell comprising a lower electrode layer, an upper electrode layer and a phase change material layer located between the lower electrode layer and the upper electrode layer, wherein the phase change material layer is the phase change material according to any one of claims 1 to 4.
6. The cell according to claim 5, wherein the material of the lower electrode layer and the upper electrode layer is a single metal material or an alloy material combined by any two or more of the single metal materials, or a nitride or an oxide of the single metal material; the thickness of the phase change material layer is 20nm-150 nm.
7. A method of making a phase change memory cell, comprising:
(1) preparing a lower electrode layer;
(2) preparing a phase change material layer on the lower electrode layer in the step (1), wherein the phase change material layer is the phase change material according to any one of claims 1 to 4;
(3) and (3) preparing an upper electrode layer on the phase change material layer in the step (2).
8. The method of claim 7, wherein the lower electrode layer and the upper electrode layer are prepared by a method including sputtering, evaporation, CVD or PECVD.
9. Use of a phase change material according to claim 1.
10. Use of a variable memory cell according to claim 5.
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