CN112687359B - Screening and matching method for insulating heat-insulating material and nanocrystalline metal material in nano current channel layer - Google Patents
Screening and matching method for insulating heat-insulating material and nanocrystalline metal material in nano current channel layer Download PDFInfo
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Abstract
The invention discloses a screening and matching method of an insulating heat-insulating material and a nanocrystalline metal material in a nano current channel layer, which comprises the following steps: determining an insulating and heat-insulating material according to a material selection principle; establishing a crystal model according to the insulating heat-insulating material, heating the crystal model to melt the crystal model, cooling the crystal model to a preset first temperature, and operating for a preset first time to obtain an amorphous model; calculating the formation energy, the mean square displacement and the radial distribution function of the selected nano current channel material atoms in the model according to the amorphous model; materials suitable for growing aggregates in insulating and adiabatic materials are screened based on formation energy, mean square displacement and radial distribution function. The nano current channel layer prepared by the material screened by the method is an insulating heat-insulating layer containing metal nano grains penetrating through the thickness of the layer, and current only flows between the electrode layer and the phase change layer through nano current channels formed by the metal nano grains; the power consumption of the phase change memory can be remarkably reduced.
Description
Technical Field
The invention belongs to the technical field of phase change storage, and particularly relates to a screening and matching method of an insulating heat-insulating material and a nanocrystalline metal material in a nano current channel layer.
Background
With the advent of the information age, memories have taken an increasing importance in life, and research on memories has been advanced toward high speed, low power consumption and high stability. Among them, a phase change memory (PCRAM) fabricated using the phase change properties of materials has great potential in the semiconductor market.
The basic principle of the phase change memory is that: the phase change material can be reversibly converted between crystalline state and amorphous state, and the data storage of '1' and '0' is realized by utilizing the huge resistance difference between different states of the material. The commonly used phase change material is a chalcogenide, the switching of the chalcogenide between crystalline and amorphous states can be easily controlled by controlling the amplitude and pulse width of the applied pulse current, and binary data stored in the phase change memory can be read out by measuring the resistance. The phase change memory has the advantages of high read-write speed, high memory density, compatibility with the traditional CMOS process and the like.
In all the current novel memory technologies, the positioning of the phase change memory is to replace the DRAM, and although the speed of the phase change memory is up to the order of the speed of the DRAM, the power consumption of the phase change memory needs to be further reduced, and particularly in the case of further improving the integration level such as 3D memory, the reduction of the power consumption of the phase change memory cell is also beneficial to reducing the thermal crosstalk among cells.
Because the phase change memory realizes the change of the internal temperature of the device by utilizing the thermal effect of current, thereby realizing the reversible transformation of the phase change material between crystalline state and amorphous state, the write current of the PCRAM unit is proportional to the quantity of the material participating in phase change, and the smaller the unit size is, the smaller the write power consumption of the unit is. In addition, under the condition that the size of the device unit is unchanged, the heat generating efficiency (the current density of the phase change area is improved, the heating efficiency of the phase change material is improved, the melting temperature of the phase change material is reduced, and the like) and the heat dissipation condition of the write current are strictly controlled, so that the power consumption of the device is reduced.
At present, methods for reducing the power consumption of the phase-change memory unit are mainly divided into two types, one type adopts a novel low-power-consumption phase-change material with high heating efficiency and low melting temperature, and the other type changes the structure of the device. The most direct method for changing the structure of the device is to reduce the amount of phase change material and increase the current density by reducing the size of the device, such as a limited phase change memory cell structure, but the method requires higher process, and has high process cost and high difficulty. Other methods for changing the structure of the device, such as edge contact type, asymmetric structure, annular electrode structure, adding two-dimensional material thermal resistance layer, etc., are realized by reducing the amount of materials participating in phase change or reducing the heat dissipation of the device as much as possible on the premise of not improving the process, but the methods all need to greatly change the structure and the process of the device, and have the problems of higher process cost and higher difficulty.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a screening and matching method of an insulating material and a nano-grain metal material in a nano-current channel layer, which aims at predicting the feasibility of forming metal nano-grains penetrating through the layer thickness in a selected insulating and insulating material by calculating the crystallization and grain growth characteristics of the metal material in the insulating and insulating material.
The invention provides a screening and matching method of an insulating material and a nanocrystalline metal material in a nano current channel layer, which comprises the following steps:
(1) Determining an insulating and heat-insulating material according to a material selection principle;
(2) Establishing a crystal model according to the insulating heat-insulating material, heating the crystal model to a preset first temperature, operating for a preset first time, melting the crystal model, cooling the crystal model to a preset second temperature, and operating for a preset second time to obtain an amorphous model; wherein the preset first temperature is higher than the melting temperature of the insulating heat-insulating material; the preset first time can be 1 ps-100 ps, the preset second temperature can be 300K, and the preset second time can be 1 ps-200 ps
(3) Calculating the formation energy of the selected nano current channel material atoms in the amorphous according to the amorphous model;
(4) Calculating the mean square displacement of the selected nano current channel material atoms in the amorphous according to the amorphous model;
(5) Calculating a radial distribution function of selected nano current channel material element atoms in the amorphous according to the amorphous model;
(6) And screening a nano current channel material suitable for growing and aggregating into grains in the insulating and heat-insulating material according to the formation energy, the mean square displacement and the radial distribution function of atoms in the amorphous model.
Wherein, the material selection principle is as follows: the insulating heat-insulating material needs to have larger resistivity and lower heat conductivity, the large resistivity ensures that current cannot be conducted in the whole layer, and the current can only enter the phase-change layer through the nano current channel, and the low heat resistance can enable the part of the layer except the nano current channel to have a heat preservation effect on heat generation in the phase-change layer, so that heat dissipation in the erasing process is reduced, and the RESET power consumption of the device is further reduced.
Further, the step (3) specifically includes:
doping atoms of a certain nano current channel material selected by a plan into an amorphous structure, and calculating the structural energy after carrying out structural optimization on the atoms;
according to formula E f ＝E nx@ insulating material -E Insulating material -nE x Calculating formation energy;
wherein E is nx@ insulating material Represents the total energy, E, of the system of n atoms in the insulating material Insulating material Represents the energy of the insulating material, nE x Representing the total atomic potential of the n incorporated atoms.
Further, the step (4) specifically includes:
atoms of a certain nano current channel material selected by a plan are randomly doped in an amorphous structure, the structure of the nano current channel material is optimized, and after the molecular dynamics of a preset third time is operated at a preset third temperature, the mean square displacement of the nano current channel material is counted. Wherein the preset third temperature is lower than the melting point of the amorphous material; the preset third time may be 1ps to 200ps.
Further, the step (5) specifically includes:
atoms of a certain nano current channel material with a certain proportion are randomly doped in an amorphous model of the insulating heat-insulating material, the structure of the material is optimized, and after the molecular dynamics of a preset fourth time is operated at a preset fourth temperature, the radial distribution function among the doped atoms is counted. The preset fourth time may be 1ps to 500ps.
Further, in amorphous SiO 2 The ratio of the number of the doped atoms is 1 to 40 percent of the atoms of the nano current channel material.
Still further, the specific principle of screening materials suitable for growing and aggregating into grains in the insulating and adiabatic material according to the formation energy, the mean square displacement and the radial distribution function in the step (6) includes:
(a) When the formation energy is positive, it means that selected elemental atoms can grow and agglomerate into grains in selected insulating and adiabatic materials; and the larger the positive formation energy value, the more easily the grains are aggregated and the nano-current channel is formed.
(b) The larger the value of the mean square displacement in the same time, the more intense the atoms move in the selected insulating material, the easier it is to achieve migration.
(c) The greater the peak of the radial distribution function, the greater the degree of aggregation of atoms in the selected insulating material, the more likely it is for nucleation and formation of large grains.
In the embodiment of the invention, the insulating and heat-insulating material and the nanocrystalline metal material obtained based on the screening and matching method can be used for preparing a nano current channel layer, and the phase change memory based on the nano current channel layer comprises: the phase change material layer is adjacent to the phase change material layer, the phase change material layer is adjacent to the nano current channel layer, and the second electrode layer is adjacent to the nano current channel layer; the nano current channel layer is an insulating heat-insulating layer single layer containing metal nano grains penetrating through the whole layer; the nano current channel layer is an insulating layer containing metal nano crystal grains penetrating through the thickness of the layer, and current flows between the electrode layer and the phase change layer only through nano current channels formed by the metal nano crystal grains. The nano current channel formed by the metal nano crystal grains reduces the contact area between the phase change layer and the electrode layer, and improves the local current density, thereby improving the heat production efficiency; meanwhile, the insulating heat-insulating material part of the nano current channel layer can prevent heat from being dissipated from the phase-change layer to the electrode layer, and the heat resistance effect is achieved. Therefore, the addition of the nano current channel layer can remarkably reduce the power consumption of the phase change memory.
The nano current channel layer is a thin film structure formed by an insulating heat-insulating material and metal nano crystal grains embedded in the insulating heat-insulating material, and the metal nano crystal grains penetrate through the layer to form a nano current channel.
Wherein, the material of the metal nano crystal grain is at least one of Fe, pt, W, cu, zn, al, ni, ti, au, ag simple substance metal materials, or alloy materials formed by any two or more simple substance metal materials Fe, pt, W, cu, zn, al, ni, ti, au, ag, or compounds with good conductivity generated by simple substance metal materials Fe, pt, W, cu, zn, al, ni, ti, au, ag.
Further, the metal nanocrystalline grains of the nanochannel layer have a higher electrical conductivity than the insulating thermal insulation material.
Further, the insulating and heat insulating material has a low heat conductivity, and is any one of silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, zinc oxide, tungsten oxide, titanium oxide, boron nitride, and silicon carbide.
Further, the thickness of the nano current channel layer is 1nm to 30nm.
Further, the size of the metal nano-crystal grain in the insulating layer is 1 nm-30 nm, and the size of the metal nano-crystal grain in the direction vertical to the film is not smaller than the thickness of the nano-current channel layer.
Still further, the phase change layer material layer includes a chalcogenide compound including any one of S, se and Te or an alloy compound with other non-chalcogenide materials including one or more of Ge, sb, ga, bi, in, sn, pb, ag, N and O.
Wherein the phase change material layer comprises GeTe, geSb, ge 2 Sb 2 Te 5 、Ge 1 Sb 2 Te 4 ，Sb 2 Te 3 AgInSbTe, and superlattice or heterostructure phase change materials containing sulfur-based compounds, including (GeTe)/(Sb) 2 Te 3 )，(GeTe)/(Bi 2 Te 3 )，(Sb 2 Te 3 )/(TiTe 2 ) GeTe/Sb, (Ge-Sb-Te)/(Sb-Te) or (Ge-Sb-Te)/C.
The phase change material layer comprises a compound formed by doping and modifying a sulfur compound, wherein the doping element comprises at least one of C, N, O, cu, cr, sc and Ti.
The phase change material layer comprises single-element phase change materials Sb or Te.
Further, the thickness of the phase change material layer is 20nm to 200nm.
Still further, the material of the first electrode and the material of the second electrode include elemental metal Au, ta, pt, al, W, ti, cu, ir and metal alloys and metal compounds thereof, such as TiW, tiN.
Wherein the thickness of the material of the first electrode and the material of the second electrode is 20 nm-200 nm.
Compared with the method for manufacturing the phase change memory unit as small as possible by adopting a more advanced process, the method can break through the process limit, further reduce the effective contact area of the electrode and the phase change material under a looser process, greatly improve the current density of the contact area and improve the heat production efficiency; meanwhile, the insulating and heat-insulating material with low heat conductivity in the nano current channel layer can effectively reduce heat loss and improve heat utilization efficiency; with the reduction of the effective contact area, the volume of the phase change area is correspondingly reduced, and the total energy required by phase change is lower, so that the writing power consumption of the phase change memory can be reduced under the conditions of not reducing the cell size and not improving the process.
In addition, compared with other methods for changing the structure of the device (such as side contact type, asymmetric structure, annular electrode structure, increase of two-dimensional material thermal resistance, etc.), the invention does not need to change the structure of the device too much, only needs to add one nano current channel layer, and the preparation method of the nano current channel layer is very simple, is compatible with the preparation method of the phase change layer, and has the advantage of simple process while greatly reducing the power consumption of the device.
Drawings
FIG. 1 is a flow chart showing the implementation of a method for screening and matching an insulating material and a nanocrystalline metal material in a nanochannel layer according to the present invention;
FIG. 2 is a cross-sectional view of an exemplary structure of a phase change memory having a nano-current channel layer according to embodiment 1 of the present invention;
FIGS. 3 (a) - (i) are respectively process flows for preparing a device structure containing nano-current channels in example 3 of the present invention;
FIG. 4 (a) shows a nano-current channel layer containing Ag crystal grains (the insulating portion is made of SiO) 2 ) A TEM image of (a);
FIG. 4 (b) is a graph showing the V-R relationship between a phase change memory device having a nano-current channel layer containing Ag crystal grains and a phase change device having the same structure without the layer, wherein the pulse width of the applied voltage RESET pulse is 50ns, which is performed in example 4 of the present invention;
FIG. 5 (a) shows a nano-current channel layer containing Au grains (the material of the insulating portion is SiO) according to example 5 of the present invention 2 ) A TEM image of (a);
FIG. 5 (b) is a graph showing the V-R relationship between a phase-change memory device having an Au nano-current path layer and a phase-change device having the same structure without the Au nano-current path layer, wherein the pulse width of the applied voltage RESET pulse is 50ns;
FIG. 6 is a chart of several atoms in SiO according to example 6 of the present invention 2 Running a mean square displacement MSD of 4ps under the condition of middle 1200K;
FIG. 7 shows several atoms in SiO according to example 6 of the present invention 2 The radial distribution function after 10ps is operated under the condition of 1200K.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention uses VASP, materials Studio, LAMMPS and other first property principles and molecular dynamics calculation software to calculate crystallization and grain growth characteristics of metal Materials in insulating and heat-insulating Materials, and predicts the feasibility of forming metal nano grains penetrating through the layer thickness in selected insulating and heat-insulating Materials. Adding selected metal atoms into the selected model of the heat insulating material to form a model of the nano current channel layer material, calculating the formation energy, the mean square displacement and the radial distribution function of the metal atoms in the heat insulating material, and judging whether the metal atoms are easy to migrate, aggregate and grow in the selected heat insulating material according to the calculation result to form grains. In general, the larger the positive formation energy value, the larger the mean square displacement value and the higher the first peak to peak value of the radial distribution function in the same time, the more easily the metal atoms form large grains in the selected insulating material.
Fig. 1 shows a flow of implementation of a method for screening and matching an insulating thermal insulation material and a nanocrystalline metal material in a nanochannel layer according to an embodiment of the present invention, and for convenience of explanation, only a portion related to the embodiment of the present invention is shown, which is described in detail below:
the screening and matching method for the insulating heat-insulating material and the nanocrystalline metal material in the nano current channel layer provided by the embodiment of the invention comprises the following steps:
(1) Determining an insulating and heat-insulating material according to a material selection principle; wherein, the material selection principle is as follows: the insulating heat-insulating material needs to have larger resistivity and lower heat conductivity, the large resistivity ensures that current cannot be conducted in the whole layer, and the current can only enter the phase-change layer through the nano current channel, and the low heat resistance can enable the part of the layer except the nano current channel to have a heat preservation effect on heat generation in the phase-change layer, so that heat dissipation in the erasing process is reduced, and power consumption is further reduced. As an embodiment of the present invention, siO may be used 2 As an insulating material in the nano-current channel layer.
(2) Establishing a crystal model according to the insulating heat-insulating material, heating the crystal model to a preset first temperature for a preset first time, melting the crystal model, cooling the crystal model to a preset second temperature for a preset second time, and obtaining an amorphous model;
(3) Calculating the formation energy of the selected element atoms in the amorphous structure according to the amorphous model; specifically, atoms of a certain nano current channel material selected by a plan are doped into an amorphous structure, and structural energy of the amorphous structure is calculated after structural optimization is carried out on the amorphous structure; according to formula E f ＝E nx@ insulating material -E Insulating material -nE x Calculating formation energy; wherein E is nx@ insulating material Represents the total energy, E, of the system of n atoms in the insulating material Insulating material Represents the energy of the insulating material, nE x Representing the total atomic potential of the n incorporated atoms.
(4) Calculating the mean square displacement of the selected element atoms in the amorphous structure according to the amorphous model; specifically, atoms of a certain nano current channel material selected by a plan are randomly doped in an amorphous structure, the structure of the nano current channel material is optimized, the molecular dynamics of a preset third time is operated at a preset third temperature, and the mean square displacement of the nano current channel material is counted.
(5) Calculating a radial distribution function of the selected element atoms in the amorphous structure according to the amorphous model; specifically, atoms of a certain nano current channel material with a certain proportion are randomly doped in an amorphous structure, the structure of the nano current channel material is optimized, the molecular dynamics of a preset fourth time is operated at a preset fourth temperature, and the radial distribution function among doped atoms is counted. As one embodiment of the invention, the method can be used for preparing amorphous SiO 2 The atoms of the nano-current channel material with the atomic number ratio of 12% are doped.
(6) Materials suitable for growing aggregates in insulating and insulating materials are selected based on the energy of formation, mean square displacement and radial distribution function of atoms in the amorphous model. Specific principles include (a) when the formation energy is positive, indicating that selected elemental atoms can grow and agglomerate into grains in selected insulating and adiabatic materials; and the larger the positive formation energy value, the more easily the grains are aggregated and the nano-current channel is formed. (b) The larger the value of the mean square displacement in the same time, the more intense the atoms move in the selected insulating material, the easier it is to achieve migration. (c) The greater the peak of the radial distribution function, the greater the degree of aggregation of atoms in the selected insulating material, the more likely it is for nucleation and formation of large grains.
The screening and matching method provided by the embodiment of the invention does not need to simulate a large number of atoms for a long time, and can reduce the workload required by simulation. For the nano current channel layer, the invention can accurately and rapidly screen out the matching material suitable for the nano current channel layer, and provides theoretical guidance for material selection for the preparation of the nano current channel layer. For the memory, the invention can screen out the element of the nano metal grain which can be relatively stable, and can reduce the erasing power consumption of the memory while maintaining the stability of the memory.
The screening and matching method provided by the embodiment of the invention can be adopted to obtain the metal material suitable for growing the aggregated nano-crystal grains in the insulating and heat-insulating material; the nano current channel layer prepared by adopting the insulating heat-insulating material and the nano grain metal material is mainly applied to a phase change memory, and the phase change memory based on the nano current channel provided by the invention is characterized in that a layer of nano current channel layer is inserted between an electrode and the phase change layer, wherein the nano current channel layer grows and gathers in the insulating heat-insulating material with low electric conductivity and low heat conductivity by metal or metal compound with high electric conductivity to form nano grains, and the nano grains grow to penetrate through the insulating layer under a certain technological condition to form a conductive nano current channel. The nano current channel layer is used for limiting the current path, so that current enters the phase-change layer from the high-conductivity nano crystal grains when flowing through the layer, the current is limited in the nano current channel, the nano conductive channel greatly reduces the contact area between the phase-change layer and the electrode layer, the current density of a local contact part is greatly improved, and the heat production efficiency of the current in the phase-change layer is improved. Meanwhile, the part outside the high-conductivity nano crystal grains in the nano current channel layer is an insulating heat-insulating material with low conductivity and low heat conductivity, and the low heat conductivity prevents heat in the phase-change layer from being dissipated to the electrode layer, so that the effect of thermal resistance is achieved, the electric heating utilization efficiency of the phase-change layer is improved, and the writing power consumption of the device is further reduced.
As one embodiment of the present invention, a structure of a phase change memory using a nano current channel sequentially includes:
a first electrode layer adjacent to the phase change material;
a phase change material layer;
the nano current channel layer is adjacent to the phase change material and is an insulating layer single layer containing metal nano grains penetrating through the whole layer;
and a second electrode adjacent to the nano-current channel layer.
The nano current channel layer is a thin film structure formed by an insulating heat-insulating material and metal nano crystal grains embedded in the insulating heat-insulating material, and the metal nano crystal grains penetrate through the layer to form a nano current channel.
The material of the metal nano-grain comprises a metal simple substance, a metal compound and a metal alloy.
Preferably, the metal nanocrystalline material is at least one of Fe, pt, W, cu, zn, al, ni, ti, au, ag single-substance metal materials, or an alloy material formed by any two or more of the single-substance metal materials Fe, pt, W, cu, zn, al, ni, ti, au, ag, or a compound with good conductivity generated by the single-substance metal materials Fe, pt, W, cu, zn, al, ni, ti, au, ag.
The insulating and heat-insulating material is at least one of silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, zinc oxide, tungsten oxide, titanium oxide, boron nitride and silicon carbide. Insulating and adiabatic materials are required to have low thermal and electrical conductivities.
Wherein the thickness of the nano current channel layer is 1 nm-30 nm. The size of the metal nano-grain in the insulating layer is 1 nm-30 nm, and the size of the metal nano-grain in the direction vertical to the film is not smaller than the thickness of the nano-current channel layer.
The phase change layer material comprises a chalcogenide compound and a single element phase change material.
Preferably, the chalcogenide compound comprises an alloy compound of one of S, se, te with other non-chalcogenide materials, wherein the non-chalcogenide materials comprise one or more of Ge, sb, ga, bi, in, sn, pb, ag, N, O.
Preferably, the thio compound comprises GeTe, geSb, ge 2 Sb 2 Te 5 、Ge 1 Sb 2 Te 4 ，Sb 2 Te 3 、AgInSbTe。
More preferably, the sulfur-based compound includes a compound formed by doping and modifying the alloy compound, wherein the doping element includes at least one of C, N, O, cu, cr, sc, and Ti.
The phase change material also comprises superlattice phase change material or heterostructure phase change material containing sulfur compound, including (GeTe)/(Sb) 2 Te 3 )，(GeTe)/(Bi 2 Te 3 )，(Sb 2 Te 3 )/(TiTe 2 )、GeTe/Sb、(Ge-Sb-Te)/(Sb-Te)、(Ge-Sb-Te)/C。
The phase change layer material also includes a single element phase change material such as Sb or Te.
According to still another aspect of the invention, the invention further provides a method for screening, matching and preparing the nano current channel layer material. The method is characterized in that through VASP, materials Studio, lamMPS and other software, the mean square displacement of metal atoms in the insulating and heat-insulating material is calculated through a first sexual principle and molecular dynamics, energy is formed, and a radial distribution function and the like are used for screening metal simple substances and metal alloys matched with the insulating and heat-insulating material.
According to still another aspect of the present invention, the present invention provides a method for preparing a nano current channel layer and a phase change memory including the nano current channel layer, which can be implemented by any one of a magnetron sputtering method, a chemical vapor deposition method, a plasma enhanced chemical vapor deposition method, a physical vapor deposition method, a laser pulse deposition method, an evaporation method, an electrochemical student growth method, an ion implantation method, a molecular beam epitaxy method, an atomic vapor deposition method, and an atomic layer deposition method. The method can increase local current density under the condition of not reducing the size of the device, so that the material can complete phase change, and the purpose of reducing the power consumption required by the device is achieved.
In order to further illustrate the screening and matching method of the insulating material and the nanocrystalline metal material in the nano current channel layer, the phase change memory based on the nano current channel and the preparation method thereof provided by the embodiment of the invention, the following details are given by combining the specific embodiments:
example 1:
an exemplary structure cross-sectional view of a phase change memory having a nano-current channel layer according to embodiment 1 of the present invention is shown in fig. 2. The bottom electrode 10 is formed of SiO 2 On the substrate, the material of the bottom electrode 10 is selected from the group consisting of W, pt, au, al, cu, ti, ta, and other metallic materials and conductive materials of alloys thereof. The nano-current channel 20 is formed on the bottom electrode 10, and the nano-current channel 20 is composed of an insulating material 22 and conductive nano-grains 21 embedded in the middle of the insulating material layer, wherein the thickness of the nano-current channel layer 20 is 1 nm-30 nm. The size of the conductive nano-particles in the insulating layer is 1nm to 30nm, and the size of the conductive nano-particles 21 in the direction perpendicular to the thin film is not smaller than the thickness of the nano-current channel layer 20. The conductive nano-crystal grains 21 have a smaller resistivity than the insulating heat insulating material 22, and the phase change material layer 30 is formed on the nano-current path 20, and the phase change material 30 includes a chalcogenide compound. Preferably, the sulfur-containing compound comprises an alloy compound of one of S, se, te with other non-sulfur-containing materials, wherein the non-sulfur-containing materials comprise one or more of Ge, sb, ga, bi, in, sn, pb, ag, N, O; preferably, the thio compound comprises GeTe, geSb, ge 2 Sb 2 Te 5 、Ge 1 Sb 2 Te 4 ，Sb 2 Te 3 AgInSbTe; more preferably, the sulfur-based compound includes a compound formed by doping and modifying the alloy compound, wherein the doping element includes at least one of C, N, O, cu, cr, sc, and Ti. The phase change material also comprises superlattice phase change material or heterostructure phase change material containing sulfur compound, including (GeTe)/(Sb) 2 Te 3 )，(GeTe)/(Bi 2 Te 3 )，(Sb 2 Te 3 )/(TiTe 2 ) GeTe/Sb, (Ge-Sb-Te)/(Sb-Te), (Ge-Sb-Te)/C. The phase change layer material also comprises single element phase change materialMaterials such as Sb, te. The upper electrode 40 is formed on the phase change material layer 30, and the material of the upper electrode 40 is selected from the group consisting of conductive materials of W, pt, au, al, cu, ti, ta, and other metallic materials and alloys thereof.
Embodiment 1 shows the simplest three-layer phase change memory cell structure, and is not limited to the three-layer structure, but may be a T-type structure or a limiting structure; the phase change memory cell structure of the additional gate tube can also be adopted.
Example 2:
according to embodiment 2 of the present invention, a phase change memory structure having a nano current channel layer and a conventional phase change memory structure writing process perform finite element simulation.
The simulation employed the simplest three-layer phase change memory cell structure of example 1. The material parameters used for simulation are listed in table 1 (thermal and electrical parameters of specific various materials used for finite element analysis), the upper and lower electrode materials of the two unit structures are Pt, and the insulating layer material is SiO 2 The phase-change layer material is Ge 2 Sb 2 Te 5 The thicknesses of the upper electrode, the lower electrode, the insulating layer and the phase change layer are all 100nm, the diameter of the unit device is 100nm, in the structure with the nano current channel layer, the thickness of the nano current channel layer is set to be 5nm, and the insulating part of the layer adopts SiO 2 The material used Ag as the nano-current channel was 6nm in diameter. RESET current pulses with amplitudes of 60uA and pulse widths of 50ns were applied to the two structural models, respectively.
TABLE 1
The maximum temperature and current density of the phase change layer after application of the same RESET current pulse in two different structures are compared. The results show that the highest temperature reached by the phase-change layer in the cell containing the nano-current channel layer is 963K and the current density is 5×10 at maximum 9 A/m 2 And the current density is at a maximum near the nanocurrent channel. In a normal cell structure, the highest temperature reached in the phase change layer is 845K. Electric currentDensity of at most 9 x 10 8 A/m 2 And the current density is at Ge 2 Sb 2 Te 5 The middle distribution is more uniform. From the analysis, the highest temperature that the device unit containing the nano current channel layer structure can reach under the same current pulse effect is higher than that of the common small hole structure, which indicates that the nano current channel layer structure can complete the RESET of the phase change memory under lower power consumption, and the device unit has the advantage of low power consumption.
Example 3:
according to embodiment 3 of the present invention, the process flow for preparing the T-type phase change memory cell containing the nano-current channel layer is as follows:
(1) Selecting SiO 2 Si (100) substrate, siO 2 The Si (100) substrate is ultrasonically cleaned with 40W power for 15 minutes in acetone solution, and is washed by deionized water;
(2) And (3) carrying out ultrasonic treatment on the treated substrate in an ethanol solution with power of 40w for 15 minutes, flushing the treated substrate with deionized water, and drying the surface and the back of the treated substrate by high-purity N2 gas to obtain the substrate to be sputtered.
(3) As shown in fig. 3 (a), a bottom electrode 10 was grown on a substrate 00 by using a magnetron sputtering method, the bottom electrode 10 was made of Pt material, high purity argon gas was introduced as a sputtering gas during the preparation, the sputtering gas pressure was 0.5Pa, the power supply was 35W, and the thickness of the bottom electrode 10 was generally 50nm to 300nm.
(4) As shown in fig. 3 (b), an insulating layer 60 is deposited on the bottom electrode 10 layer by physical vapor deposition (PECVD), the insulating layer 60 being SiO 2 The thickness was 100 nm.
(5) As shown in fig. 3 (c), a layer of photoresist 61 is uniformly spread on the insulating layer 60 using a photoresist leveler.
(6) As shown in fig. 3 (d), a photoresist mask 61 with circular holes of 250nm diameter is formed on the insulating layer 60 using an electron beam exposure system (EBL).
(7) As shown in fig. 3 (e), the insulating layer 60 is etched using a plasma etching technique (ICP), since a portion covered with the photoresist 61 is protected from etching, and a portion not covered with the photoresist 61 is exposed to the outside to be etched until the bottom electrode 10 is exposed.
(8) As shown in fig. 3 (f), the nano-current channel layer 20 is prepared using magnetron sputtering, ion implantation, annealing, and the like. Wherein metal nano-grains 21 grow and aggregate in the nano-current channel layer 20 to form a conductive channel. In this embodiment, the insulating material in the nano current channel layer is SiO 2 Ag is selected as the metal conductive material.
(9) The photoresist 61 is removed by the desmutting solution, and the final effect as shown in fig. 3 (g) is finally obtained.
(10) And (5) overlaying a square hole structure with the thickness of 100 mu m multiplied by 100 mu m on the small hole by using an ultraviolet lithography system. The square hole is centered with a circular small hole etched by ICP (not shown).
(11) As shown in fig. 3 (h), a phase change material layer 30 is deposited in the square hole by magnetron sputtering, and the phase change material of the phase change material layer 30 includes a chalcogenide compound. The chalcogenide comprising S, se, te phase change layer material 30 comprises a chalcogenide. Preferably, the chalcogenide compound comprises an alloy compound of one of S, se, te with other non-chalcogenide materials, wherein the non-chalcogenide materials comprise one or more of Ge, sb, ga, bi, in, sn, pb, ag, N, O; preferably, the thio compound comprises GeTe, geSb, ge 2 Sb 2 Te 5 、Ge 1 Sb 2 Te 4 ，Sb 2 Te 3 AgInSbTe; more preferably, the sulfur-based compound includes a compound formed by doping and modifying the alloy compound, wherein the doping element includes at least one of C, N, O, cu, cr, sc, and Ti. The phase change material also comprises superlattice phase change material or heterostructure phase change material containing sulfur compound, including (GeTe)/(Sb) 2 Te 3 )，(GeTe)/(Bi 2 Te 3 )，(Sb 2 Te 3 )/(TiTe 2 ) GeTe/Sb, (Ge-Sb-Te)/(Sb-Te), (Ge-Sb-Te)/C. The phase change layer material also includes single element phase change materials such as Sb, te. One of which forms an alloy compound with other non-chalcogenide materials, wherein the non-chalcogenide materials include Ge, sb, ga, bi, in, sn, pb; the phase change material used in this example was Ge 2 Sb 2 Te 5 As an example. The preparation method comprises introducing high purityArgon was used as a sputtering gas, the sputtering gas pressure was 0.5pa, the power supply power was 35W, the distance between the target and the substrate was 180mm, and the thickness of the phase change material layer 30 was 100nm.
(12) The upper electrode layer 40, which is also a Pt metal electrode material, is deposited by magnetron sputtering. After completion, the photoresist of the ultraviolet lithography is removed by a stripping process, and the final effect is shown in the structure of fig. 3 (i).
Example 4:
microscopic test is carried out on the film containing the Ag nano current channel layer to obtain SiO 2 Ag high resolution image, nano-current channel layer thickness of 5nm, siO visible in image 4 (a) 2 The clusters are formed, the diameter of the clusters is 10nm, and the clusters can penetrate SiO 2 The layer, by compositional analysis, showed that the clusters formed were Ag. This indicates that Ag grains can be formed on SiO 2 The nano current channel layer is conducted by the aggregation growth in the middle layer, and current can be conducted from the lower electrode layer to the phase change layer through Ag nano grains.
FIG. 4 (b) is a V-R relationship curve of the device containing the Ag nano-current channel layer in example 4 of the present invention and the RESET device of the control group. Except for the above 5nm Ag nano-current channel layer, both devices were identical in material and structure of the other layers. Wherein the phase change layer materials are Ge 2 Sb 2 Te 5 The thickness was 100nm. The diameter of the device unit is 250nm, and the material of the insulating layer is SiO 2 The thickness is 100nm, the upper and lower electrode materials are TiN, and the thickness is 100nm.
The RESET test method of the device is as follows: the RESET pulse with the pulse width of 50ns, the rising edge and the falling edge of 10ns and the voltage of which is gradually increased is respectively applied to the two by the B1500A semiconductor tester. The results showed that Ag-SiO was contained 2 The RESET voltage of the device of the nano current channel layer is 0.6V, and the required power consumption is 3.3×10 -5 J, while the RESET voltage of the conventional device structure is 1.6V, the required power consumption is 2.1 x 10 -4 J, comparing the two materials can obtain the current channel layer containing Ag nano grains, and the power consumption required in the phase change process of the device can be effectively reduced.
Example 5:
changing the metal material in the nano current channel layer, and performing microscopic test on the current channel layer film containing Au nano grains to obtain SiO 2 Au high resolution transmission electron microscope image, the thickness of the nanocurrent channel layer is 3nm, siO can be seen clearly in image 5 (a) 2 The clusters are formed, the diameter of the clusters is 3nm and can penetrate SiO 2 The layer, as can be seen by compositional analysis, forms clusters of Au. This indicates that Au-containing is capable of forming a reaction on SiO 2 The nano current channel layer is conducted by the aggregation growth in the nano-layer, and current can be conducted from the lower electrode layer to the phase change layer through the Au nano grains.
FIG. 5 (b) is a V-R relationship curve of the device containing the Au nano-current path layer described above in example 5 of the present invention and the RESET device of the conventional structure of the control group. Except for the 5nm thick Au nanocurrent channel layer described above, both devices were identical in material and structure of the other layers. Wherein the phase change layer materials are Ge 2 Sb 2 Te 5 The thickness was 100nm. The diameter of the device unit is 250nm, and the material of the insulating layer is SiO 2 The thickness is 100nm, and the upper and lower electrode materials are TiN. The thickness was 100nm.
The RESET test method of the device is as follows: the RESET pulse with the pulse width of 50ns, the rising edge and the falling edge of 10ns and the voltage of which is gradually increased is respectively applied to the two by the B1500A semiconductor tester. The results showed that Au-SiO was contained 2 The RESET voltage of the device of the nano current channel layer is 0.5V, and the required power consumption is 1.25×10 -4 J, while the RESET voltage of the conventional device structure is 1.6V, the required power consumption is 2.1 x 10 -4 And J, comparing the two materials to obtain the current channel layer containing Au nano grains, so that the power consumption required in the phase change process of the device can be effectively reduced.
Example 6:
according to embodiment 6 of the present invention, as shown in fig. 6 and 7, the insulating and insulating material in the nanocurrent channels and the nanocurrent channel material are selected and matched to ensure that the selected metallic conductive material can easily grow and aggregate into grains in the insulating and insulating material. The selection and matching methods of the two materials are as follows:
(1) First, select the insulationThe insulating material needs to have larger resistivity and lower heat conductivity, the large resistivity ensures that current cannot be conducted on the whole layer, the current can only enter the phase-change layer through the nano current channel, the low thermal resistance can enable the part of the layer except the nano current channel to have a heat preservation effect on heat generation in the phase-change layer, heat dissipation in the erasing process is reduced, and power consumption is further reduced. The choice of material may also be determined based on experimental conditions. In this embodiment, siO is selected 2 As an insulating material in the nano-current channel layer.
(2) Build up of crystalline SiO 2 Model, use of VASP software for crystal SiO 2 Heating the model to 5000K to melt the model, and cooling to 300K to operate for 2ps to obtain amorphous SiO 2 And (5) a model.
(3) Formation energy calculation: in amorphous SiO 2 The atoms of a certain nano current channel material selected by a plan are doped, the structure of the nano current channel material is optimized, the structural energy of the nano current channel material is calculated, and the nano current channel material is obtained through a formula E f ＝E nx@ insulating material -E Insulating material -nE x Calculating formation energy, wherein E nx@ insulating material Represents n atoms in the insulating material (SiO 2 ) Total energy of system E Insulating material Represents an insulating material (SiO) 2 ) Energy of nE x Representing the total atomic potential of the n incorporated atoms. In general, the formation of atoms capable of positively representing selected elements may be performed in selected insulating and adiabatic materials (SiO in this embodiment 2 ) The larger the positive formation energy value, the easier it is to aggregate into grains and form nano-current channels.
(4) Mean square displacement MSD calculation: in amorphous SiO 2 Randomly doping atoms of a certain nano current channel material selected by a plan, carrying out structural optimization on the atoms, running 4ps molecular dynamics calculation at 1200K, and counting the mean square displacement MSD. The mean square displacement size indicates that the selected element atoms are in the selected insulating material (SiO in this embodiment 2 ) Difficulty in migration. The larger the mean square displacement value at the same time, the more atoms are moved in the selected insulating materialThe more intense, i.e. the easier it is to effect migration.
(5) Calculation of radial distribution function: in amorphous SiO 2 The atoms of a certain nano current channel material with a certain proportion (the ratio of the atomic numbers is 12% in the embodiment) are randomly doped, the structure of the nano current channel material is optimized, the molecular dynamics calculation of 10ps is operated under 1200K, and the radial distribution function among doped atoms is counted. The magnitude of the peak of the radial distribution function reflects its degree of aggregation, with a larger peak indicating a higher degree of aggregation of atoms in the selected insulating material, easier nucleation and formation of large grains.
(6) Comprehensively consider atoms in SiO 2 Is suitable for SiO screening by the formation energy and the mean square displacement and the radial distribution function 2 And growing the aggregated material.
Table 2 shows the atomic SiO of several nano-current channel materials calculated 2 The formation energy in (a) is shown in FIG. 6 as SiO at 1200K for these material atoms 2 Is a mean square displacement MSD.
| Ag | Au | Al | W | Ti |
| 0.198eV | 2.536eV | -4.548eV | -5.731eV | -5.670eV |
TABLE 2
According to the formation energy contrast, the formation energy of Ag and Au is positive, and the Ag and the Au are easier to aggregate and grow compared with Al, ti and W, and the mean square displacement of the Ag and the Au is higher than that of the Al, W and Ti, which indicates that the Ag and the Au are easier to be on SiO compared with the Al, W and Ti 2 In the radial distribution function of FIG. 7, the peak values corresponding to Au and Ag are higher, and the aggregation degree is more obvious, so that Ag and Au are easier to be formed on SiO than other materials 2 Metal nano-grains are formed, and then a nano-current channel is formed.
Example 7: process for preparing nano current channel layer 1
The preparation method of the nano current channel layer is characterized in that a sputtering method can be adopted, and the specific sputtering mode is any one of the following four modes: (1) Co-sputtering a metal target and an insulating material target. (2) The metal target and the insulating material target are sputtered alternately. (3) And directly placing the metal sheet on an insulating material target material to perform doping sputtering. (4) And directly placing the insulating and heat-insulating material sheet on a metal target material for doping sputtering.
This example uses SiO containing Ag crystal grains 2 The nano current channel layer is exemplified by sputtering the nano current channel layer by using a magnetron sputtering method, and the specific preparation method comprises the following steps:
(a) SiO is put into the sputtering cavity 2 Target and Ag target, vacuum degree is pumped to 10 -4 Pa；
(b) Using high-purity Ar gas as sputtering gas, setting Ar gas flow to be stable to 10sccm, and regulating sputtering gas pressure to 0.5pa, wherein the distance between a target and a substrate is 120mm;
(c) Setting the power of an alternating-current sputtering power supply to be 200W, and connecting SiO 2 Target, sputtering for 100s, growing 2nmSiO 2 Turning off the AC power supply, setting the power of the DC sputtering power supply to be 30W, connecting an Ag target, sputtering for 10s, growing 1nmAg, turning off the DC power supply, and turning on the AC power supply again to sputter 100sSiO 2 Growing 2nmSiO 2 Then the power supply is turned off;
(d) The base obtained by sputteringThe tablets were placed in a vacuum annealing furnace, which was warmed to 400℃at a rate of 15℃per minute, and incubated at 400℃for 30min. Making metal Ag on SiO 2 Is grown and agglomerated to form penetrating SiO 2 Nano-metal grains of layer thickness as shown in fig. 4 (a).
The annealing temperature and holding time in step (d) can be determined according to SiO 2 The thickness ratio of the layer and the Ag layer is optimized, for example, the larger the thickness ratio is, the higher the annealing temperature is required and the longer the heat preservation time is, and the optimization aim is to lead the metal Ag to be in SiO 2 Is grown and agglomerated to form penetrating SiO 2 Nano metal crystal grains with the layer thickness.
Example 8: process for preparing nano current channel layer 2
The preparation method of the nano current channel layer is characterized in that a sputtering method can be adopted, and the specific sputtering mode is any one of the following four modes: (1) Co-sputtering a metal target and an insulating material target. (2) The metal target and the insulating material target are sputtered alternately. (3) And directly placing the metal sheet on an insulating material target material to perform doping sputtering. (4) And directly placing the insulating and heat-insulating material sheet on a metal target material for doping sputtering.
The embodiment uses SiO containing Au grains 2 The nano-current channel layer is exemplified by sputtering the nano-current channel layer 30 using a magnetron sputtering method, and the specific preparation method comprises the following steps:
(a) In SiO 2 Placing 8 Au sheets with the size of 1cm and 0.5cm at the etching ring on the surface of the target material, and vacuumizing to 10 -4 Pa；
(b) Using high-purity Ar gas as sputtering gas, setting Ar gas flow to be stable to 10sccm, and regulating sputtering gas pressure to 0.5Pa, wherein the distance between a target and a substrate is 120mm;
(c) Setting the power of an alternating-current sputtering power supply to be 200W, and sputtering for 200s;
(d) The sputtered substrate is placed in a vacuum annealing furnace, the temperature of the annealing furnace is raised to 400 ℃ at the speed of 15 ℃/min, and the temperature is kept at 400 ℃ for 30min. Making metal Au on SiO 2 Grown and agglomerated in the layer to form a penetrating SiO 2 Nano-metal grains of layer thickness as shown in fig. 5 (a).
Step (a)(d) The annealing temperature and the heat-preserving time in the process can be optimized according to the number of Au sheets (or the area of the Au sheets covered by the etching ring), for example, the smaller the number of the Au sheets (the smaller the area of the Au sheets covered by the etching ring), the higher the required annealing temperature and the longer the heat-preserving time, and the optimization aims to ensure that the metal Au is in SiO 2 Grown and agglomerated in the layer to form a penetrating SiO 2 Nano metal crystal grains with the layer thickness.
The co-sputtering method in this embodiment may also replace the subsequent annealing process by increasing the temperature of the substrate during sputtering. The increase of the substrate temperature is beneficial to increasing the migration kinetic energy of metal atoms, promoting the aggregation of the metal atoms and the growth of crystal grains, and the aim is to form nano metal crystal grains penetrating through the thickness of the nano current channel layer.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (6)
1. The method for screening and matching the insulating material and the nanocrystalline metal material in the nano current channel layer is characterized by comprising the following steps:
(1) Determining an insulating and heat-insulating material according to a material selection principle;
(2) Establishing a crystal model according to the insulating heat-insulating material, heating the crystal model to a preset first temperature and operating for a preset first time, cooling to a preset second temperature after melting the crystal model, and operating for a preset second time to obtain an amorphous model;
(3) Calculating the formation energy of the selected nano current channel material atoms in the amorphous according to the amorphous model;
(4) Calculating the mean square displacement of the selected nano current channel material atoms in the amorphous according to the amorphous model;
(5) Calculating a radial distribution function of atoms of the selected nano current channel material in the amorphous according to the amorphous model;
(6) Screening a material suitable for growth aggregation in an insulating and adiabatic material according to the formation energy, the mean square displacement and the radial distribution function of atoms in the amorphous model;
The material selection principle is as follows: the insulating heat-insulating material needs to have larger resistivity and lower heat conductivity, the large resistivity ensures that current cannot be conducted in the whole layer, and the current can only enter the phase-change layer through the nano current channel, and the low heat resistance can enable the part of the layer except the nano current channel to have a heat preservation effect on heat generation in the phase-change layer, so that heat dissipation in the erasing process is reduced, and the power consumption of the device is further reduced;
the step (3) specifically comprises:
doping atoms of a certain nano current channel material selected by a plan into an amorphous structure, and calculating the structural energy after carrying out structural optimization on the atoms;
according to formula E f =E nx@ insulating material -E Insulating material -nE x Calculating formation energy;
wherein E is nx@ insulating material Represents the total energy, E, of the system of n atoms in the insulating material Insulating material Represents the energy of the insulating material, nE x Representing the total atomic potential of the n incorporated atoms.
2. The method of screening and matching of claim 1, wherein step (4) specifically comprises:
atoms of a certain nano current channel material selected by a plan are randomly doped in an amorphous structure, the structure of the nano current channel material is optimized, and after the molecular dynamics of a preset third time is operated at a preset third temperature, the mean square displacement of the nano current channel material is counted.
3. The screening and matching method of claim 1, wherein step (5) specifically comprises:
atoms of a certain nano current channel material with a certain proportion are randomly doped in an amorphous structure, the structure of the nano current channel material is optimized, and after the molecular dynamics of a preset fourth time is operated at a preset fourth temperature, the radial distribution function among the doped atoms is counted.
4. The screening and matching method according to claim 3, wherein atoms of the nano current channel material having an atomic number ratio of 1% -40% are incorporated into the insulating material amorphous pattern.
5. The screening and matching method according to any one of claims 1 to 4, wherein the specific principle of screening materials suitable for growth and aggregation into grains in an insulating and adiabatic material according to the formation energy, the mean square displacement and the radial distribution function in step (6) comprises:
(a) When the formation energy is positive, it means that selected elemental atoms can grow and agglomerate into grains in selected insulating and adiabatic materials; and the larger the positive formation energy value is, the easier the large-size crystal grains are aggregated and the nano current channel is formed;
(b) The larger the value of the mean square displacement in the same time, the more violent the atoms move in the selected insulating and heat-insulating material, the easier the migration is realized;
(c) The greater the peak of the radial distribution function, the greater the degree of aggregation of atoms in the selected insulating material, the more likely it is for nucleation and formation of large grains.
6. The phase change memory is characterized by comprising a nano current channel layer arranged between a phase change layer and an electrode layer, wherein the nano current channel layer is an insulating and heat-insulating layer containing metal nano grains penetrating through the thickness of the layer, and current flows between the electrode layer and the phase change layer only through nano current channels formed by the metal nano grains; the material of the metal nano-grain and the insulating layer is obtained by the screening and matching method of any one of claims 1 to 5.
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