Phase change material, phase change memory unit and preparation method thereof

Abstract

The invention relates to a phase change material which comprises an indium element and a sulfur element, the chemical formula of the phase change material is InxSy, x and y are atomic components of the elements, and 0 lt is met; x / (x + y) lt; 1, 0lt; y / (x + y) lt; 1; the invention also provides a phase change memory unit comprising the phase change material and a preparation method of the phase change memory unit. According to the InxSy phase change material, the resistance difference value before and after phase change is large, and very high adjustability is achieved; and when being applied to a phase change memory unit, the phase change memory unit has better data retention and higher operation speed.

Description

Technical Field

[0001] The present invention belongs to the field of microelectronic technology, and in particular relates to a phase change material, a phase change memory unit and a preparation method thereof. Background Art

[0002] Phase change memory (PCM) is a type of non-volatile semiconductor memory that has developed rapidly in recent years. Compared with traditional memory, it has the advantages of strong miniaturization, fast read and write speed, high data retention, low power consumption, long cycle life and excellent radiation resistance. Therefore, phase change memory has become a strong competitor in various new storage technologies, and is very likely to replace Flash+DRAM technology and become the mainstream storage technology of the next generation of non-volatile memory, so it has broad market prospects. At the same time, it can generate new applications in some fields that ordinary memory cannot reach, such as space, aerospace technology and military fields.

[0003] The application of phase change memory is based on the reversible conversion between high and low resistance of the phase change material under the operation of electric pulse signal to realize the writing and erasing of "0" and "1". The core of phase change memory is the phase change storage medium material. The traditional phase change material is mainly Ge2Sb2Te5. Due to its good comprehensive performance, it has been widely used in phase change optical disks and phase change memory. However, there are still some problems with this material: 1) The crystallization temperature is low, the thermal stability is poor, the data retention cannot be guaranteed, and it faces the risk of data loss. For example, in the field of automotive electronics, the service temperature requirement for storage devices is higher than 120℃, while the working temperature of Ge2Sb2Te5 that can provide 10 years of reliable data storage is only about 85℃; 2) The phase change speed is low. Studies have shown that the electric pulse for stable RESET operation of Ge2Sb2Te5-based phase change memory is at least in the order of hundreds of nanoseconds, while the electric pulse for stable SET operation also requires 20ns, which cannot meet the speed requirements of dynamic random access memory; 3) The density change is too large. After crystallization, the density change rate reaches 6%, which is not conducive to the reliability of the device.

[0004] Therefore, how to seek a phase change film material with high speed, high data retention, and low density change rate so that it has a wide temperature range has become an important technical problem that needs to be solved urgently by technical personnel in this field. Summary of the invention

[0005] The purpose of the present invention is to provide a phase change material, a phase change memory unit and a preparation method thereof, which are used to solve the problem that phase change materials such as Ge2Sb2Te5 in the prior art cannot guarantee data retention due to their low crystallization temperature and poor thermal stability, and are faced with the problem of data loss, and the density change rate of the phase change material before and after crystallization is too high, resulting in low device reliability and low phase change speed, which cannot meet the speed requirements of dynamic random access memory.

[0006] The present invention provides a phase change material, which includes indium and sulfur, and has a chemical formula of In x S y , x, y are the atomic components of the element, and satisfy 0 <x / (x+y)<1,0<y / (x+y)<1。

[0007] Preferably, the In x S y In the formula, 1≤x≤3, 1≤y≤4.

[0008] More preferably, the In x S y , x=2, y=3.

[0009] The present invention provides a method for preparing the phase change material, which comprises any one of magnetron sputtering, chemical vapor deposition, atomic layer deposition or electron beam evaporation.

[0010] Preferably, according to the chemical formula of the phase change material In x S y Adopt In x S y Alloy target sputtering to prepare phase change material, the In x S y The alloy target sputtering parameters are set as follows: the background vacuum is less than 3.0×10 -4 Pa, the sputtering gas includes argon, the sputtering pressure is 0.40-0.45Pa, the sputtering temperature is 1-80°C, the sputtering time is 10-30min, a radio frequency power supply is used, and the radio frequency sputtering power is 10-30W.

[0011] The present invention further provides a phase change memory unit, wherein the phase change memory unit comprises a phase change material layer, and the phase change material layer comprises the above-mentioned phase change material.

[0012] Preferably, the thickness of the phase change material layer is 20-200 nm.

[0013] More preferably, the thickness of the phase change material layer is 20 nm.

[0014] Preferably, the phase change memory unit comprises a lower electrode layer, an adhesive layer and a lead-out electrode layer which are arranged in sequence, and the phase change material layer is located between the lower electrode layer and the adhesive layer.

[0015] Preferably, the material of the lower electrode layer, the bonding layer and the lead-out electrode layer includes at least one of a single metal material, a nitride of a single metal material, and an oxide of a single metal material; wherein the single metal material includes W, Pt, Au, Ti, Al, Ag, Cu or Ni.

[0016] The present invention also provides a method for preparing the above phase change memory unit, comprising the following steps:

[0017] (1) forming a lower electrode layer;

[0018] (2) forming a phase change material layer on the lower electrode layer;

[0019] (3) forming an adhesive layer on the phase change material layer;

[0020] (4) Forming an extraction electrode layer on the adhesive layer.

[0021] Preferably, the method for forming the lower electrode layer, the bonding layer and the lead-out electrode layer includes any one of sputtering, evaporation, chemical vapor deposition, plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, metal compound vapor deposition, molecular beam epitaxy, atomic vapor deposition or atomic layer deposition; the method for forming the phase change material layer includes any one of magnetron sputtering, chemical vapor deposition, atomic layer deposition or electron beam evaporation.

[0022] Beneficial Effects

[0023] (1) In the present invention x S y Phase change materials have a large difference in resistance before and after phase change and have very strong adjustability, so they can provide specific performance according to actual needs.

[0024] (2) In the present invention x S y Phase change materials have good data retention and also have a faster operating speed when applied to phase change memory cells.

[0025] (3) In the present invention x S y Phase change materials, compared with traditional Ge2Sb2Te5, have a higher on-off ratio and comparable power consumption.

[0026] (4) The preparation method of the phase change material provided by the present invention is simple in process and convenient for precise control of material composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 1 is a resistance-voltage relationship diagram of a phase change memory unit using In2S3 phase change material in Example 2 of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0029] Embodiment 1

[0030] The present invention provides a phase change material, which includes indium element and sulfur element, and the chemical formula is In x S y , where x and y are the atomic components of the elements, and satisfy 0 < x / (x + y) < 1, 0 < y / (x + y) < 1; any one of magnetron sputtering method, chemical vapor deposition method, atomic layer deposition method or electron beam evaporation method can be used to prepare the phase change material layer.

[0031] By using the magnetron sputtering method to prepare the phase change material of the present invention, the contents of the two elements in the In x S y phase change material can be adjusted to obtain storage materials with different crystallization temperatures, resistivity and crystallization activation energies.

[0032] In this embodiment, the phase change material is In2S3, which is prepared by sputtering an In x S y alloy target; the base vacuum is less than 3.0×10 -4 Pa, the sputtering gas is argon, the sputtering pressure is 0.40 - 0.45 Pa, the sputtering temperature is 1 - 80 °C, the single sputtering time is 20 min, a radio frequency power supply is used, and the radio frequency sputtering power is 20 W.

[0033] Embodiment 2

[0034] The present invention provides a phase change memory cell, which includes a lower electrode layer, a phase change material layer, an adhesive layer and a lead-out electrode layer arranged in sequence. The materials of the lower electrode layer, the adhesive layer and the lead-out electrode layer include at least one of single metal materials, nitrides of single metal materials or oxides of single metal materials; wherein the single metal materials include W, Pt, Au, Ti, Al, Ag, Cu or Ni, and the phase change material layer includes the phase change material described in Embodiment 1.

[0035] The preparation method of the phase change memory cell in the present invention is as follows:

[0036] (1) Form a lower electrode layer;

[0037] (2) Form a phase change material layer on the lower electrode layer;

[0038] (3) Form an adhesive layer on the phase change material layer;

[0039] (4) Forming an extraction electrode layer on the adhesive layer.

[0040] The method for forming the lower electrode layer, the bonding layer and the lead-out electrode layer in the present invention includes any one of sputtering, evaporation, chemical vapor deposition, plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, metal compound vapor deposition, molecular beam epitaxy, atomic vapor deposition or atomic layer deposition; the method for forming the phase change material layer includes any one of magnetron sputtering, chemical vapor deposition, atomic layer deposition or electron beam evaporation, wherein when the magnetron sputtering method is used, the phase change material layer of different thicknesses can be obtained by adjusting the sputtering time.

[0041] In this embodiment, the material of the lower electrode layer of the phase change memory unit is TiN, the material of the phase change material layer is In2S3, the material of the adhesive layer is TiN, and the material of the lead-out electrode layer is Al.

[0042] In this embodiment, the preparation methods of the lower electrode layer, the bonding layer and the lead-out electrode layer of the phase change memory unit are all sputtering; the preparation method of the phase change material layer is magnetron sputtering, and the specific process is referred to Example 1. The thickness of the phase change material layer is 20nm.

[0043] Figure 1 The resistance-voltage relationship diagram of the phase change memory cell using In2S3 phase change material in this embodiment. In order to obtain the SET-RESET window (RV curve) of the phase change memory cell, the pulse time is first fixed to 300ns, and the phase change memory cell is scanned every 0.1V step in the [1V, 6V] interval; then the pulse time is changed (100ns, 50ns and 30ns) and scanned with the same voltage. The shortest pulse time for the complete SET-RESET window obtained by the above steps is the fastest operating speed of the phase change memory cell. The shortest pulse time of the In2S3 component is 50ns. It can be seen that under the action of an electric pulse, the phase change memory cell realizes a reversible phase change. Under an electric pulse of 50ns, the phase change memory cell realizes "erase" (high resistance to low resistance) and "write" (low resistance to high resistance) operations at 3V and 3.7V respectively.

[0044] The bonding layer in the phase change memory unit of the present invention is used to increase the bonding degree between the upper electrode layer and the phase change material layer, and the bonding layer material is required to have stable chemical properties and not react with the phase change material in a higher temperature range; the lead-out electrode layer is used to protect the phase change material layer and serve as the upper electrode layer when the device is electrically tested. It should be noted that if the material of the lead-out electrode layer itself has a high bonding strength with the phase change material and does not react with the phase change material during the heating process, the bonding layer can be omitted, or the bonding layer and the lead-out electrode layer can be made of the same material.

Claims

1. A phase change material, characterized in that: The phase change material includes indium and sulfur, and the chemical formula is In x S y , x, y are the atomic components of the element, and satisfy 0 <x / (x+y)<1,0<y / (x+y)<1。 2. The phase change material according to claim 1, characterized in that: In x S y In the formula, 1≤x≤3, 1≤y≤4.

3. A method for preparing the phase change material as claimed in claim 1, comprising any one of magnetron sputtering, chemical vapor deposition, atomic layer deposition or electron beam evaporation.

4. The method for preparing a phase change material according to claim 3, characterized in that: According to the chemical formula of the phase change material In x S y Adopt In x S y Alloy target sputtering to prepare phase change material, the In x S y The alloy target sputtering parameters are set as follows: the background vacuum is less than 3.0×10 -4 Pa, the sputtering gas includes argon, the sputtering pressure is 0.40-0.45Pa, the sputtering temperature is 1-80°C, the sputtering time is 10-30min, a radio frequency power supply is used, and the radio frequency sputtering power is 10-30W.

5. A phase change memory cell, characterized in that: The phase-change memory cell comprises a phase-change material layer, and the phase-change material layer comprises the phase-change material of claim 1 .

6. The phase change memory cell according to claim 5, characterized in that The thickness of the phase change material layer is 20-200 nm.

7. The phase change memory cell according to claim 5, characterized in that: The phase change memory unit comprises a lower electrode layer, an adhesive layer and an extraction electrode layer which are arranged in sequence, and the phase change material layer is located between the lower electrode layer and the adhesive layer.

8. The phase change memory cell according to claim 7, characterized in that: The materials of the lower electrode layer, the bonding layer and the lead-out electrode layer include at least one of a single metal material, a nitride of a single metal material, and an oxide of a single metal material; wherein the single metal material includes W, Pt, Au, Ti, Al, Ag, Cu or Ni.

9. A method for preparing a phase change memory cell according to any one of claims 5 to 8, comprising the following steps: (1) forming a lower electrode layer; (2) forming a phase change material layer on the lower electrode layer; (3) forming an adhesive layer on the phase change material layer; (4) Forming an extraction electrode layer on the adhesive layer.

10. The method for preparing a phase change memory unit according to claim 9, characterized in that: The method for forming the lower electrode layer, the bonding layer and the lead-out electrode layer includes any one of sputtering, evaporation, chemical vapor deposition, plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, metal compound vapor deposition, molecular beam epitaxy, atomic vapor deposition or atomic layer deposition; the method for forming the phase change material layer includes any one of magnetron sputtering, chemical vapor deposition, atomic layer deposition or electron beam evaporation.

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