A phase change film, a film preparation method and a phase change memory

Abstract

The application provides a phase change film, a film preparation method and a phase change memory. x (Sb2Te3) 1‑x wherein x is the percentage of TiTe2, and 0

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microelectronic devices, and more particularly, to a phase change film, a film preparation method and a phase change memory. BACKGROUND

[0002] Human activities cannot be separated from information transmission and storage. The invention of memory makes the storage density of information higher and higher. The traditional DRAM has the characteristics of fast erasing and writing, long service life, and volatility. The FLASH has the characteristics of low cost, non-volatility, and slow erasing and writing. Users hope that the memory has the advantages of high speed, long life of DRAM and low cost, non-volatility of FLASH. Phase change memory is considered to be one of the next generation of non-volatile storage devices that can replace DRAM and FLASH, and has the characteristics of fast storage speed, high reliability, and long service life.

[0003] Phase change memory is a non-volatile memory based on phase change material (one or more chalcogenide compounds), which mainly uses the Joule heat of current to realize the transformation between the crystalline state and the amorphous state of the material to store information. In the phase change memory, the phase change material is the key part. The resistance of the material is high in the amorphous state, and the resistance is low in the crystalline state. We use the difference between the high and low resistance to realize the information storage of "0" and "1". A large amplitude and short duration electric pulse is applied to the crystalline material. Because of the large amplitude and high energy, the material can quickly reach the melting temperature and lose the crystalline structure, but because of the short duration and a rapid cooling process, the atoms have not had time to rearrange, so the material realizes the transformation from the crystalline state to the amorphous state. A medium amplitude and long duration electric pulse is applied to the amorphous material. The energy of the pulse can make the material reach the crystallization temperature and be lower than the melting temperature. Within the duration of the pulse, the atoms can rearrange and crystallize, realizing the transformation from the amorphous state to the crystalline state.

[0004] Sb2Te3 is a phase change material that grows dominant crystallization. Compared with Ge2Sb2Te5 that nucleates dominant crystallization, Sb2Te3 has faster SET speed, lower melting point, and smaller RESET power consumption. However, the crystallization temperature of Sb2Te3 is very low, about 100℃, and the amorphous stability is poor. Researchers optimize Sb2Te3 phase change memory through doping. At present, the research on Sb2Te3 phase change memory unit is mainly based on doping single element atoms. Studies have shown that doping single element atoms can effectively improve the amorphous stability of Sb2Te3, but generally at the cost of sacrificing the SET speed. In addition, the atoms doped in the crystallization process mostly replace the positions of Sb or Te atoms, destroying the original lattice structure of Sb2Te3. Therefore, the development of new doped Sb2Te3 materials with high amorphous stability and SET speed and their memories has important significance for improving the performance of phase change memory. SUMMARY

[0005] In view of the defects of the prior art, the present application aims to provide a phase change film, a film preparation method and a phase change memory, and aims to solve the problems that conventional single-element doping improves the amorphous stability of Sb2Te3 phase change material but reduces the SET speed, and conventional single-element doping destroys the lattice structure of Sb2Te3.

[0006] To achieve the above-mentioned purpose, in a first aspect, the present application provides a phase change film, the chemical formula of the phase change film is: (TiTe2) x (Sb2Te3) 1-x , 0 < x < 0.6.

[0007] In an optional example, when the phase change film is first crystallized, TiTe2 and Sb2Te3 are respectively crystallized;

[0008] After the phase change film is first crystallized, TiTe2 always remains in a crystalline state, the TiTe2 crystal nucleus is dispersedly distributed, the TiTe2 crystal structure is stable and does not react with Sb2Te3;

[0009] After the phase change film is first crystallized, Sb2Te3 can be repeatedly amorphized or crystallized, the mismatch degree between the Sb2Te3 crystal structure and the TiTe2 crystal structure is low, Sb2Te3 grows outward as a template of the TiTe2 crystal structure when Sb2Te3 is crystallized, and the time required for Sb2Te3 to complete crystallization is relatively shortened.

[0010] In an optional example, the greater the doping ratio x of TiTe2, the shorter the time required for Sb2Te3 to complete crystallization, the smaller the grain size of crystallized Sb2Te3, and the higher the amorphous stability of the phase change film in an amorphous state.

[0011] In a second aspect, the present application provides a preparation method of a phase change film, comprising the following steps:

[0012] Determining a substrate to be sputtered;

[0013] Determining Sb2Te3 target material and TiTe2 target material, and placing the two kinds of target materials above the substrate to be sputtered;

[0014] Sputtering the two kinds of target materials, and controlling the doping ratio x of TiTe2 by controlling the sputtering power of the two kinds of target materials, to deposit the chemical formula (TiTe2) x (Sb2Te3) 1-xTiTe2 as the doping material of the phase-change film, and Sb2Te3 as the phase-change material of the phase-change film, the TiTe2 and the Sb2Te3 are crystallized respectively when the phase-change film is crystallized for the first time; the TiTe2 always keeps a crystal state after the phase-change film is crystallized for the first time, the TiTe2 crystal nucleus is in a dispersed distribution, the TiTe2 crystal structure is stable and does not react with the Sb2Te3; the Sb2Te3 can be repeatedly amorphized or crystallized after the phase-change film is crystallized for the first time, the Sb2Te3 crystal structure has a low mismatch degree with the TiTe2 crystal structure, the Sb2Te3 grows outward with the TiTe2 crystal structure as a template when the Sb2Te3 is crystallized, and the time for the Sb2Te3 to complete crystallization is relatively shortened.

[0015] In an optional example, the doping ratio x of the doping material TiTe2 is controlled, the greater the x is, the smaller the time for the Sb2Te3 to complete crystallization when the phase-change film is crystallized, the smaller the Sb2Te3 crystal grain size after crystallization, and the higher the amorphous stability of the phase-change film in an amorphous state.

[0016] In a third aspect, the present application provides a phase-change memory, comprising: an upper electrode, a phase-change layer, an insulating and heat-insulating layer, and a lower electrode.

[0017] The upper electrode is arranged on the upper surface of the phase-change layer.

[0018] The lower electrode is arranged on the lower surface of the phase-change layer.

[0019] The insulating and heat-insulating layer is arranged around the phase-change layer and plays a role of isolation between phase-change memory cells.

[0020] The phase-change layer comprises a phase-change material and a doping material, the phase-change material is Sb2Te3, the doping material is TiTe2, and the doping ratio of the doping material is x, 0

[0021] In an optional example, when the phase-change memory is SET for the first time, the TiTe2 and the Sb2Te3 are crystallized respectively, and then the TiTe2 always keeps a crystal state, the TiTe2 crystal nucleus is in a dispersed distribution, and the TiTe2 crystal structure is stable and does not react with the Sb2Te3.

[0022] Subsequently, when the phase-change memory is RESET, the Sb2Te3 changes from a crystal state to an amorphous state; when the phase-change memory is SET, the Sb2Te3 changes from an amorphous state to a crystal state, the Sb2Te3 crystal structure has a low mismatch degree with the TiTe2 crystal structure, the Sb2Te3 grows outward with the TiTe2 crystal structure as a template when the Sb2Te3 is crystallized, the time for the Sb2Te3 to complete crystallization is relatively shortened, and the SET speed of the phase-change memory is relatively improved.

[0023] In an optional example, the greater the doping ratio x of TiTe2, the faster the SET speed of the phase change memory, the lower the RESET power consumption, and the smaller the resistance drift coefficient.

[0024] Compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects in general:

[0025] The present application provides a kind of phase change film, film preparation method and phase change memory, by the way of doping stable binary compound TiTe2 to improve the amorphous stability of Sb2Te3 phase change material, compared with Sb2Te3 phase change film, the amorphous stability of the phase change film of the present application is obviously improved, effectively solve the current situation of Sb2Te3 amorphous stability deficiency.Compared with Sb2Te3 phase change film, the ten-year data retention temperature of the phase change film of the present application is obviously improved, effectively improve the data retention capacity of Sb2Te3.Compared with Sb2Te3 phase change film, the grain size of the phase change film of the present application is obviously reduced, the time required for grain growth is shortened.

[0026] The present application provides a kind of phase change film, film preparation method and phase change memory, compared with Sb2Te3 phase change memory, the SET speed of the phase change memory of the present application can be further improved.Compared with Sb2Te3 phase change memory, the RESET power consumption of the phase change memory of the present application is obviously reduced.Compared with Sb2Te3 phase change memory, the resistance drift coefficient of the phase change memory of the present application is obviously reduced.

[0027] The present application provides a kind of phase change film, film preparation method and phase change memory, compared with the prior art of single element doping Sb2Te3, the amorphous stability of the present application is improved without sacrificing the SET speed of Sb2Te3 phase change memory, and even can further improve its SET speed.Compared with the prior art of single element doping Sb2Te3, the present application selects stable binary compound TiTe2 to be doped, TiTe2 and Sb2Te3 crystallize respectively after doping, and the original crystal structure of Sb2Te3 will not be damaged. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 XRD result graph of phase change film;

[0029] Figure 2 HRTEM result measured in embodiment 4 of the present application. Figure 2 Sb2Te3, (TiTe2)0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 High resolution image of phase change film;

[0030] Figure 3 The SAED results measured in Example 4 of the present invention. Wherein, Figure 3 (a) (b) (c) in the above (a) (b) (c) are Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 Selected area electron diffraction pattern of phase change film;

[0031] Figure 4 The Sb2Te3, (TiTe2) measured in Example 5 of the present invention. 0.1 (Sb2Te3) 0.9 , (TiTe2) 0.15 (Sb2Te3) 0.85 , (TiTe2) 0.25 (Sb2Te3) 0.75 and (TiTe2) 0.4 (Sb2Te3) 0.6 R-T curve of phase change film;

[0032] Figure 5 The Sb2Te3, (TiTe2) measured in Example 6 of the present invention. 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 Arrhenius extrapolation curve of phase change film;

[0033] Figure 6 The exemplary structure cross-sectional view of phase change memory cell used in Example 7 of the present invention.

[0034] Figure 7 The Sb2Te3, (TiTe2) measured in Example 9 of the present invention. 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 I-V characteristic curve of phase change memory;

[0035] Figure 8 The SET speed results measured in Example 10 of the present invention. Wherein, Figure 8 (a) (b) (c) in the above (a) (b) (c) are Sb2Te3, (TiTe2) 0.1(Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 V-R relationship diagram of the phase change memory SET process;

[0036] Figure 9 Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 V-R relationship diagram of the phase change memory RESET process;

[0037] Figure 10 Resistance drift results measured for the present embodiment 12. Among them, Figure 10 Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 Resistance value change curve of the phase change memory over time. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0039] To achieve the above object, the present application provides a phase change film, a film preparation method and a phase change memory, which improve the amorphous stability of Sb2Te3 by doping the binary compound TiTe2. In the phase change film of the present application, TiTe2 and Sb2Te3 crystallize respectively and do not destroy the original lattice structure of Sb2Te3. Moreover, the grain size of the present application is significantly reduced, which shortens the time required for grain growth, thereby improving the SET speed of the phase change memory. Inside the phase change material, TiTe2 becomes a dispersed crystal nucleus. With TiTe2 as a template, Sb2Te3 can be epitaxially grown, thereby improving the crystallization speed. The more TiTe2 crystal nuclei, the smaller the Sb2Te3 growth space is compressed, and the shorter the time required to complete crystallization. Experimental results prove that the Sb2Te3 phase change storage unit doped with the stable binary compound TiTe2 can improve the amorphous stability of Sb2Te3 without sacrificing the SET speed; at the same time, compared with the pure Sb2Te3 phase change memory, the RESET power consumption of the present application is significantly reduced and the resistance drift can be effectively inhibited. With the increase of the TiTe2 doping ratio, the RESET power consumption is further reduced, and the resistance drift coefficient is further reduced.

[0040] The phase change film provided by the application is crystallized with TiTe2 and Sb2Te3 respectively, and the chemical composition conforms to the general formula (TiTe2) x (Sb2Te3) 1-x x is the component ratio of TiTe2, and 0 < x < 0.6.

[0041] The reasons for selecting TiTe2 as the doping material are as follows: first, TiTe2 and Sb2Te3 are both cubic structures, and the lattice constant of TiTe2 is The lattice constant of Sb2Te3 is The difference between the lattice constants is small, and the lattice mismatch degree of the two is about 11%, which is relatively small. Second, the melting point of TiTe2 is relatively high, about 1500K, and the melting point of Sb2Te3 is about 900K. TiTe2 has strong stability, and still maintains a crystal state in the amorphization process of Sb2Te3, and provides a crystal nucleus seed with stable structure in the crystallization process. Third, TiTe2 has low thermal conductivity, which can effectively prevent heat loss. Fourth, TiTe2 has small resistivity and good electrical conductivity, which will not affect the current transport of the device.

[0042] Compared with the pure Sb2Te3 phase change film, the amorphous stability of the phase change film provided by the application is obviously improved, the data retention temperature is obviously increased, and the data retention capacity is obviously improved. With the increase of the doping ratio of TiTe2, the data retention capacity is further improved.

[0043] Compared with the pure Sb2Te3 phase change memory, the RESET power consumption of the phase change memory provided by the application is obviously reduced. With the increase of the doping ratio of TiTe2, the RESET power consumption is further reduced.

[0044] Compared with the pure Sb2Te3 phase change memory, the resistance drift coefficient of the phase change memory provided by the application is obviously reduced. With the increase of the doping ratio of TiTe2, the resistance drift coefficient is further reduced.

[0045] Further, the phase change memory unit structure comprises a substrate, a lower electrode, a phase change material layer and an upper electrode which are sequentially arranged above the substrate from bottom to top, and the phase change material is filled with insulating and heat-insulating material to realize electrical and thermal isolation in the horizontal direction.

[0046] Further, the insulating and heat-insulating material has low thermal conductivity, and the insulating and heat-insulating material is any one of silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, zinc oxide, tungsten oxide, titanium oxide, boron nitride and silicon carbide.

[0047] Further, the thickness of the phase change material layer is 2nm-300nm.

[0048] Further, the material of the upper electrode and the lower electrode comprises metal elements Au, Ta, Pt, Al, W, Ti, Cu, Ir and metal alloys and metal compounds thereof, such as TiW and TiN.

[0049] Further, the thickness of the material of the upper electrode and the lower electrode is 2nm-500nm.

[0050] The application provides a TiTe2-doped Sb2Te3 phase-change thin film and a phase-change memory, which effectively improves the amorphous stability of Sb2Te3 and further improves the SET speed of the memory device. In addition, the memory device provided by the application has the advantages of low power consumption and small resistance drift coefficient.

[0051] In order to further illustrate the TiTe2-doped Sb2Te3 phase-change thin film and the phase-change memory provided by the application, the following specific embodiments are described in detail as follows:

[0052] Embodiment 1

[0053] Preparation of (TiTe2) x (Sb2Te3) 1-x and Sb2Te3 phase-change thin films, and the specific process flow is as follows:

[0054] (1) Select SiO2 / Si(100) substrate, and clean the surface, dust particles and organic impurities by ultrasonicating the SiO2 / Si(100) substrate in an acetone solution at a power of 40W for 15 minutes, and then washing with deionized water;

[0055] (2) Ultrasonicate the treated substrate in an ethanol solution at a power of 40W for 15 minutes, wash with deionized water, and dry the surface and back surface with high-purity nitrogen to obtain a to-be-sputtered substrate;

[0056] (3) Apply a double-target co-sputtering method, and place Sb2Te3 target material and TiTe2 target material on the target position of a sputtering instrument, wherein the Sb2Te3 is sputtered by a radio frequency sputtering method, and the TiTe2 is sputtered by a direct current sputtering method;

[0057] (4) Fix the to-be-sputtered substrate on a sample tray, seal the sputtering instrument cavity, and close the external air valve;

[0058] (5) Turn on the vacuum gauge and the mechanical pump to perform vacuum pumping, and when the vacuum in the cavity reaches 5Pa or below, start the molecular pump, open the plug valve, and perform vacuum pumping to 1×10 -4 Pa or below;

[0059] (6) The AC power sputtering power of the Sb2Te3 target material is set to 26 W, and the DC power sputtering power of the TiTe2 target material is set to 10 W, 15 W, 20 W, and 25 W in sequence, and the sputtering time is 500 s;

[0060] (7) High-purity argon is used as the sputtering gas, the argon flow rate is set to 80 sccm, the sputtering gas pressure is 5 x 10 -1 Pa.

[0061] Meanwhile, the Sb2Te3 phase change film of the control group is prepared by the same method, the AC power sputtering power of the Sb2Te3 target material is set to 30 W, the DC power sputtering power of the TiTe2 target material is set to 0 W, and the sputtering time is 500 s.

[0062] Example 2:

[0063] The (TiTe2) x (Sb2Te3) 1-x phase change film prepared in Example 1 is subjected to EDS testing, the AC power sputtering power of the Sb2Te3 target material is 26 W, and according to the atomic percentage of Ti in the EDS test results, the percentage of TiTe2 in the phase change film with the DC power sputtering power of the TiTe2 target material being 10 W, 15 W, 20 W, and 25 W in sequence is 10%, 15%, 25%, and 40% in sequence. The (TiTe2) x (Sb2Te3) 1-x phase change film prepared in Example 2 is subjected to AFM testing, and the results show that the thickness of the prepared film is about 100 nm.

[0064] Example 3:

[0065] A 200-nm pure Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 , and (TiTe2) 0.4 (Sb2Te3) 0.6 phase change film is prepared and annealed at 250°C for 10 min, and then subjected to XRD testing. The XRD test results are as follows: Figure 1The results are shown in FIG. 4. As can be seen from the figure, the peak values of the diffraction peaks of TiTe2 and Sb2Te3 films at 28°, 39° and 49° are basically coincident, indicating that the two have the possibility of epitaxial growth. Studies have shown that the mismatch rate of TiTe2 and Sb2Te3 is about 11%, which can be epitaxially grown. As can be seen from the XRD results of the Sb2Te3 film doped with TiTe2, TiTe2 and Sb2Te3 crystallize respectively, which shows that doping TiTe2 will not destroy the original structure of Sb2Te3. Comparing the XRD results of the Sb2Te3 phase change film doped with TiTe2 and the pure Sb2Te3 phase change film, it can be seen that the half-height width of the diffraction peak of the film after doping increases significantly, which indicates that the grain size of the film after doping decreases significantly.

[0066] Example 4:

[0067] Preparation of 15 nm pure Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 phase change films on a copper mesh and annealed at 280°C for 10 min, and then TEM testing was performed. The HRTEM test results are shown in FIG. 5. Figure 2 Figure 2 (a) (b) (c) in FIG. 5 are high-resolution images of Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 phase change films, respectively. It is measured that the grain diameter of pure Sb2Te3 is about 41.23 nm. When TiTe2 is doped by 10%, the grain size is about 10 nm, which is reduced by about 75% compared with the Sb2Te3 film. When TiTe2 is doped by 40%, the grain size is reduced to less than 10 nm, and even to 5 nm, which is reduced by about 87.5% compared with the Sb2Te3 film. It can be seen that the Sb2Te3 phase change film doped with TiTe2 significantly reduces the grain size after crystallization compared with the pure Sb2Te3 phase change film, achieving the effect of refining the grain size. The higher the TiTe2 doping ratio, the smaller the grain size. This result is consistent with the above XRD results. Figure 3 Figure 3 (a) (b) (c) in FIG. 6 are selected area electron diffraction patterns of Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 phase change films, respectively. Analysis shows that the crystal face indices of Sb2Te3 and TiTe2 are obtained and are consistent with the standard card.​​Figure 1 The XRD results of the Sb2Te3 and TiTe2 crystallize separately, which further proves that the Sb2Te3 and TiTe2 crystallize separately. The decrease in grain size makes the selected area electron diffraction rings become diffuse.

[0068] Example 5:

[0069] Preparation of 200nm Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 、(TiTe2) 0.15 (Sb2Te3) 0.85 、(TiTe2) 0.25 (Sb2Te3) 0.75 and (TiTe2) 0.4 (Sb2Te3) 0.6 The crystallization temperature of the phase change film was tested by heating the temperature to 250°C at a rate of 10°C / min, and the RT curves of the phase change film with different doping concentrations were drawn, such as Figure 4 As shown in the figure, the crystallization temperature of Sb2Te3 is 103.8℃, (TiTe2) 0.1 (Sb2Te3) 0.9 The crystallization temperature is 124.7℃, (TiTe2) 0.15 (Sb2Te3) 0.85 The crystallization temperature is 135.1℃, (TiTe2) 0.15 (Sb2Te3) 0.85 The crystallization temperature is 150.9℃, (TiTe2) 0.4 (Sb2Te3) 0.6 The crystallization temperature is 178.0°C. The results show that doping with TiTe2 can effectively increase the crystallization temperature of Sb2Te3, improve its amorphous stability, and compensate for its lack of amorphous stability. Furthermore, as the TiTe2 doping concentration increases, the crystallization temperature also increases, and the amorphous stability becomes increasingly better.

[0070] Example 6:

[0071] Preparation of 200nm Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 The data retention capability of the phase change film was tested, and the results were as follows Figure 5 As shown in the figure, pure Sb2Te3 film can maintain data for ten years at 28℃, and the crystallization activation energy is 1.5eV. (TiTe2) 0.1 (Sb2Te3) 0.9The thin film can keep data for ten years at 62℃, and the crystallization activation energy is 2.5eV. (TiTe2) 0.4 (Sb2Te3) 0.6 The thin film can keep data for ten years at 113℃, and the crystallization activation energy is 2.8eV. The doping of TiTe2 can obviously improve the ten-year data retention temperature of Sb2Te3, and the greater the doping concentration of TiTe2, the higher the ten-year data retention temperature. The improvement of the ten-year data retention temperature indicates that the doping of TiTe2 can effectively improve the amorphous stability of the Sb2Te3 thin film, which is consistent with the above R-T test results. And the greater the doping ratio of TiTe2, the better the amorphous stability. At the same time, this further indicates that the doping of TiTe2 can effectively improve the data retention capability of the Sb2Te3 phase change memory unit.

[0072] It should be noted that the data retention time test can be divided into long-term test and accelerated test according to the test duration. Due to the test duration, the present application selects the accelerated test, and the corresponding ten-year data is obtained through the accelerated test. The accelerated test is to accelerate the failure of components or materials by increasing the stress without changing the failure mechanism, so as to obtain the data retention time and other data under the accelerated condition in a short time, and then calculate the reliability characteristic quantity under the normal stress condition.

[0073] Embodiment 7:

[0074] As shown in Figure 6 , the present application provides a TiTe2 doped Sb2Te3 phase change memory, which comprises a substrate 1, a lower electrode 2, an insulating and heat-insulating material 3, a phase change layer 4, and an upper electrode 5 arranged in turn above the substrate from bottom to top.

[0075] Specifically, the substrate 1 can adopt a silicon single wafer substrate or other semiconductor material substrate.

[0076] Specifically, the lower electrode 2 is a conductive material, which requires low resistivity and stable properties, and can adopt materials such as TiW, TiN, HfN, Ag, Al, Cu, W, Ta, Pt, etc. The upper electrode 5 can adopt the same material as the lower electrode 2.

[0077] Specifically, the insulating and heat-insulating material 3 requires high resistivity, low thermal conductivity, and stable properties, and can adopt materials such as SiO2, ZrO2, Y2O3, TiO2, etc.

[0078] Specifically, the phase change layer 4 is a phase change material, which requires reversible phase change properties, and the material adopted by the present application is (TiTe2) x (Sb2Te3) 1-x , wherein x is the percentage of TiTe2, and 0 < x < 0.6.

[0079] Embodiment 8:

[0080] According to the phase change memory cell structure of embodiment 7, (TiTe2) 0.1 (Sb2Te3) 0.9 , (TiTe2) 0.4 (Sb2Te3) 0.6 and Sb2Te3 phase change memory, the specific process flow is as follows:

[0081] (1) Select SiO2 / Si (100) substrate, and clean the surface, dust particles and organic impurities by ultrasonicating the SiO2 / Si (100) substrate in an acetone solution for 15 minutes at a power of 40 W, and then rinsing with deionized water.

[0082] (2) Ultrasonicate the treated substrate in an ethanol solution for 15 minutes at a power of 40 W, rinse with deionized water, and dry the surface and back surface with high-purity nitrogen to obtain a substrate to be sputtered.

[0083] (3) Grow a lower electrode on the substrate by using a magnetron sputtering method, the lower electrode uses Pt material, and high-purity argon gas is introduced as a sputtering gas during preparation, the sputtering gas pressure is 0.5 Pa, and the power supply power is 35 W, and the thickness of the lower electrode is usually 10 nm to 300 nm.

[0084] (4) Deposit an insulating layer on the lower electrode by using a physical vapor deposition (PECVD) method, the insulating layer is SiO2, and the thickness is 100 nm.

[0085] (5) Uniformly lay a layer of photoresist on the insulating layer by using a uniform coating machine.

[0086] (6) Form a photoresist mask with a circular small hole with a diameter of 250 nm on the insulating layer by using an electron beam exposure system (EBL).

[0087] (7) Etch the insulating layer by using an ionized plasma etching (ICP) technology, the part covered by the photoresist is protected and will not be etched, and the part without the photoresist covering is exposed and will be etched away until the lower electrode is exposed.

[0088] (8) Remove the photoresist by using a photoresist removing solution.

[0089] (9) Etch a square hole structure with a size of 100 μm x 100 μm on the small hole by using an ultraviolet photoetching system. The square hole is aligned with the center of the circular small hole etched by the ICP.

[0090] (10) Deposit a phase change material layer (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3)0.6 . vacuum to 1 x 10 -4 Pa, the AC power sputtering power of the Sb2Te3 target material is set to 26 W, the DC power sputtering power of the TiTe2 target material is set to 10 W and 25 W in turn, the sputtering time is 500 s, and the phase change material layer thickness is 100 nm. High-purity argon is used as the sputtering gas, the argon flow rate is set to 80 sccm, and the sputtering pressure is 5 x 10 -1 Pa. At the same time, the Sb2Te3 phase change material layer of the control group is deposited by the same method, the AC power sputtering power of the Sb2Te3 target material is set to 30 W, the DC power sputtering power of the TiTe2 target material is set to 0 W, the sputtering time is 500 s, and the phase change material layer thickness is 100 nm.

[0091] (11) The upper electrode is deposited by magnetron sputtering, and the upper electrode is also a Pt metal electrode material.

[0092] (12) The photoresist of the ultraviolet lithography is removed by a stripping process.

[0093] Example 9:

[0094] The phase change memory prepared in Example 7 is subjected to DC I-V testing, and the test results are shown in FIG. 8. Figure 7 As shown in the figure, the threshold current of Sb2Te3 is 8 μA. 0.1 (TiTe2) 0.9 The threshold current is 28 μA, which is 2.5 times that of pure Sb2Te3. 0.4 (TiTe2) 0.6 The threshold current of the phase change memory cell is 39 μA, which is 3.875 times that of pure Sb2Te3. The threshold current required during the transition of the phase change memory cell from amorphous state to crystalline state is related to the amorphous stability of the phase change memory cell. The greater the threshold current, the better the amorphous stability of the phase change memory cell. Therefore, doping TiTe2 can increase the threshold current of the Sb2Te3 phase change memory cell, thereby enhancing its amorphous stability. Moreover, as the doping concentration increases, the threshold current further increases, and the amorphous stability of the phase change memory cell is further improved. This is consistent with the R-T test results and the ten-year data retention time test results.

[0095] Example 10:

[0096] The phase change memory prepared in Example 7 is subjected to SET speed testing, and the test results are shown in FIG. 9. Figure 8 Figure 8 In FIG. 9, (a), (b), and (c) are Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 ​and (TiTe2) 0.4 (Sb2Te3) 0.6 V-R relationship diagram of phase change memory SET process. Wherein, the minimum SET pulse signal width value that can make the phase change memory complete the SET process is its SET speed. From Figure 8 It can be seen that the SET speed of Sb2Te3 is 50 ns, (TiTe2) 0.1 (Sb2Te3) 0.9 The SET speed of (TiTe2) is 50 ns, (TiTe2) 0.4 (Sb2Te3) 0.6 The SET speed of (TiTe2) is 30 ns. It is concluded that doping TiTe2 not only does not reduce the SET speed of Sb2Te3 phase change memory unit, but also further improves its SET speed. This shows that the Sb2Te3 phase change memory unit doped with TiTe2 can improve the amorphous stability and SET speed at the same time.

[0097] The mechanism analysis of the SET speed improvement of the Sb2Te3 phase change memory unit doped with TiTe2 can be started from two aspects. On the one hand, through film characterization, it can be concluded that doping TiTe2 refines the grain size. The reduction of grain size can shorten the time required for grain growth, thereby improving the SET speed. The increase of the proportion of TiTe2 doping, the grain size is further reduced, and the SET speed is further improved. On the other hand, since the melting point of TiTe2 is very high, about 1 500 K, and the melting point of Sb2Te3 is about 900 K. Therefore, when the Sb2Te3 doped with TiTe2 completely crystallizes and changes into amorphous state, TiTe2 still remains in crystalline state. At this time, TiTe2 becomes a dispersed crystal nucleus in the phase change material. With TiTe2 as a template, Sb2Te3 can be epitaxially grown, thereby improving the crystallization speed. The more TiTe2 crystal nuclei, the smaller the Sb2Te3 growth space is compressed, and the shorter the time required to complete the crystallization.

[0098] Example 11:

[0099] The RESET power consumption test of the phase change memory prepared in Example 7 was carried out, and the test results are shown in Figure 9 The RESET pulse width is set to 50 ns, the rising edge and the falling edge are both 8 ns, the amplitude is increased by 100 mV every 1 ms, and the resistance value is read once. The results show that the RESET voltage of Sb2Te3 is 1.27 V, and the required power consumption is 45 pJ. (TiTe2) 0.1 (Sb2Te3) 0.9 The RESET voltage of (TiTe2) is 0.47 V, and the required power consumption is 2 pJ. Compared with pure Sb2Te3, the RESET power consumption is reduced by 95.5%. (TiTe2) 0.4(Sb2Te3) 0.6 The RESET voltage is 0.37V, and the required power consumption is 0.55pJ, which is reduced by 98.7% compared with the pure Sb2Te3 phase change memory unit. It can be concluded from the comparison that the doping of TiTe2 effectively reduces the power consumption required in the Sb2Te3 phase change process, and the higher the doping concentration, the lower the power consumption.

[0100] It can be concluded from the thin film characterization that the doping of TiTe2 refines the grain size, which can reduce the phase change area, improve the heat utilization efficiency, and achieve the effect of reducing power consumption. Studies have shown that the grain size and thermal conductivity of common Ge2Sb2Te5, Sb2Te3 and their doped systems are approximately linearly related, and the smaller the grain size of Ge2Sb2Te5, Sb2Te3 and their doped systems, the smaller the thermal conductivity. Therefore, the grain size of the Sb2Te3 phase change memory unit doped with TiTe2 is reduced, and the thermal conductivity is also reduced. With the increase of the TiTe2 doping ratio, the thermal conductivity is further reduced. Studies have shown that thermal conductivity is the key to reducing power consumption. Thermal conductivity controls heat transfer and heat loss. Using the same heat source, the heat loss is reduced, the temperature of the working area is increased, the heat required to reach the same melting temperature is reduced, and the RESET power consumption is also reduced. The TiTe2 material selected in the present application has relatively low thermal conductivity itself, and doping TiTe2 in Sb2Te3 can effectively reduce the heat loss of the phase change layer, thereby reducing the RESET power consumption.

[0101] Example 12:

[0102] The resistance drift test of the phase change memory prepared in Example 7 is shown in Figure 10 . Figure 10 (a) (b) (c) are Sb2Te3, (TiTe2) 0.1 (Sb2Te3) 0.9 and (TiTe2) 0.4 (Sb2Te3) 0.6 The resistance value of the phase change memory changes with time. First, a SET pulse with a pulse width of 200ns, a rising edge of 100ns and a falling edge of 100ns is applied to the phase change memory unit to convert it into a crystalline state. Then a RESET pulse with a pulse width of 50ns, a rising edge of 8ns and a falling edge of 8ns is applied to convert it into an amorphous state. After the cycle operation, a small voltage of 100mV is applied to the crystalline and amorphous phase change memory units respectively, and the resistance value is continuously read. The resistance value is read every 6ms, a total of 50000 times, and the cumulative time is 3000s. It is calculated that the resistance drift coefficient of the Sb2Te3 phase change memory unit in the amorphous state is 0.003, and the (TiTe2) 0.1 (Sb2Te3) 0.90.0006, (TiTe2) 0.4 0.0006, (TiTe2) 0.6 0.0006, (TiTe2) 0.1 0.0006, (TiTe2) 0.9 0.0006, (TiTe2) 0.4 0.0006, (TiTe2) 0.6 0.00004.

[0103] As can be seen from the above, the resistance drift coefficient of the Sb2Te3 phase change memory doped with TiTe2 is significantly lower than that of the Sb2Te3 phase change memory. The greater the TiTe2 doping ratio, the smaller the resistance drift coefficient. The mechanism is analyzed as follows: structural relaxation is the main source of resistance drift. The grain size of the Sb2Te3 phase change layer doped with TiTe2 is reduced, so the volume ratio of the grain boundary is increased, and the greater the doping ratio, the greater the volume ratio of the grain boundary. The existence of the grain boundary limits the movement of the atoms of the phase change material, thereby inhibiting the structural relaxation near the grain boundary. When the phase change material is in an amorphous state, the local structure of TiTe2 which remains in a crystalline state can be regarded as a pinning point inside the material, which inhibits the structural relaxation of the amorphous Sb2Te3 near it. The higher the TiTe2 doping ratio, the more obvious this inhibitory effect. Therefore, doping TiTe2 can effectively inhibit the resistance drift of the Sb2Te3 phase change memory, and the greater the TiTe2 doping ratio, the smaller the resistance drift coefficient.

[0104] The present application starts from the actual preparation, compares the performance of the traditional Sb2Te3 and the Sb2Te3 phase change film and phase change memory doped with TiTe2, and demonstrates that doping TiTe2 can improve the amorphous stability of Sb2Te3 without sacrificing the SET speed of Sb2Te3, and even can further improve the SET speed. The present patent also demonstrates that doping TiTe2 can also effectively reduce the RESET power consumption of the Sb2Te3 phase change memory unit and can inhibit the resistance drift.

[0105] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A phase change film, characterized in that: The chemical formula of the phase change film is: (TiTe2) x (Sb2Te3) 1-x , 0 <x<0.6; The greater the TiTe2 doping ratio x, the shorter the time required for Sb2Te3 to complete crystallization, the smaller the Sb2Te3 grain size after crystallization, and the higher the amorphous stability of the phase change film in the amorphous state.

2. The phase change film according to claim 1, characterized in that When the phase change film is first crystallized, TiTe2 and Sb2Te3 are crystallized separately; After the phase change film is crystallized for the first time, TiTe2 always remains in a crystalline state, TiTe2 crystal nuclei are dispersed, the TiTe2 crystal structure is stable, and no chemical reaction occurs with Sb2Te3; After the phase change film is crystallized for the first time, Sb2Te3 can be repeatedly amorphized or crystallized. The mismatch between the crystal structure of Sb2Te3 and the crystal structure of TiTe2 is low. When Sb2Te3 is crystallized, it grows epitaxially using the TiTe2 crystal structure as a template, and the time for Sb2Te3 to complete crystallization is relatively shortened.

3. A method for preparing a phase change film according to claim 1 or 2, characterized in that: The steps include: determining a substrate to be sputtered; Determine the Sb2Te3 target and the TiTe2 target, and place the two targets on the substrate to be sputtered; Sputter the above two target materials, and control the doping ratio x of TiTe2 by controlling the sputtering power of the two target materials, so as to deposit a phase change thin film with the chemical general formula (TiTe2) x (Sb2Te3) 1-x on the substrate, where 0 < x < 0.6; wherein, TiTe2 is used as the doping material of the phase change thin film, and Sb2Te3 is used as the phase change material of the phase change thin film. When the phase change thin film is first crystallized, TiTe2 and Sb2Te3 are crystallized respectively; after the phase change thin film is first crystallized, TiTe2 always remains in the crystalline state, the TiTe2 crystal nuclei are diffusely distributed, the TiTe2 crystal structure is stable, and no chemical reaction occurs with Sb2Te3; after the phase change thin film is first crystallized, Sb2Te3 can be repeatedly amorphousized or crystallized, the mismatch degree between the Sb2Te3 crystal structure and the TiTe2 crystal structure is low, and when Sb2Te3 is crystallized, it grows epitaxially with the TiTe2 crystal structure as a template, and the time for Sb2Te3 to complete crystallization is relatively shortened.

4. The preparation method according to claim 3, characterized in that The doping ratio x of the doping material TiTe2 is controlled. The larger the x, the shorter the time required for Sb2Te3 to complete crystallization when the phase change film is crystallized, the smaller the Sb2Te3 grain size after crystallization, and the higher the amorphous stability of the phase change film in the amorphous state.

5. A phase change memory, characterized in that: include: An upper electrode, a phase change layer, an insulating layer and a lower electrode; The upper electrode is placed on the upper surface of the phase change layer; The lower electrode is placed on the lower surface of the phase change layer; The insulating and heat-insulating layer is placed around the phase change layer to isolate the phase change memory cells. The phase change layer comprises the phase change film according to claim 1 or 2, the phase change layer comprises a phase change material and a doping material, the phase change material is Sb2Te3, the doping material is TiTe2, and the doping ratio of the doping material is x, 0 <x<0.6。 6. The phase-change memory according to claim 5, wherein when the phase-change memory is first SET, TiTe2 and Sb2Te3 are crystallized separately, and then TiTe2 always remains crystalline, TiTe2 crystal nuclei are dispersed, and the TiTe2 crystal structure is stable and does not chemically react with Sb2Te3; Subsequently, when the phase change memory is RESET, Sb2Te3 changes from a crystalline state to an amorphous state; when the phase change memory is SET, Sb2Te3 changes from an amorphous state to a crystalline state. The mismatch between the crystal structure of Sb2Te3 and the crystal structure of TiTe2 is low. When Sb2Te3 crystallizes, it uses the TiTe2 crystal structure as a template to grow epitaxially. The time it takes for Sb2Te3 to complete crystallization is relatively shortened, which relatively improves the SET speed of the phase change memory.

7. The phase change memory according to claim 5, wherein: The greater the TiTe2 doping ratio x, the faster the SET speed of the phase change memory, the lower the RESET power consumption, and the smaller the resistance drift coefficient.

Images