Phase change memory device having a composite thin film structure and method of manufacturing the same

Abstract

The present application provides a phase change memory device with a composite thin film structure, which comprises a substrate, a reflecting layer on the substrate, a first protective layer on the reflecting layer, a dielectric layer on the first protective layer, a second protective layer on the dielectric layer, a semi-transparent semi-reflecting layer on the second protective layer, and optionally a third protective layer on the semi-transparent semi-reflecting layer. The present application also provides a method for preparing the phase change memory device with a composite thin film structure. The phase change memory device can realize ternary and binary information storage, and has high information storage density and storage life.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication. Specifically, this invention relates to phase change memory devices with composite thin film structures and their fabrication methods. Background Technology

[0002] Industrial production, internet technology, and people's daily lives generate massive amounts of data, recording all aspects of production and life, and forming an indispensable part of modern society. With the advancement of science and technology, the amount of information generated in people's production and daily lives is growing exponentially. Therefore, establishing a high-capacity, secure, and reliable information storage method is of great significance for the long-term and efficient preservation of data. Currently available information storage methods include books, magnetic tapes, floppy disks, hard drives, optical discs, USB flash drives, and memory cards, etc., which to some extent meet people's needs.

[0003] Information storage density and lifespan are important indicators for evaluating information storage methods. Hard drives have high information storage density but short lifespans, while optical discs have lower information storage density but longer lifespans. DVDs are primarily composed of germanium-antimony-tellurium alloy, a non-volatile phase-change material with both crystalline and amorphous states. The difference between these two states represents "0" and "1" in binary code, enabling the storage of binary information. The non-volatility of germanium-antimony-tellurium alloy gives optical discs a long lifespan. However, limited by the binary storage method and laser beam size, DVDs have relatively low information storage density. Currently, third-generation Blu-ray disc technology uses a 405-nanometer blue-violet laser for read / write operations, and the laser beam size is nearing its limit, making further improvements difficult. Therefore, it is necessary to address the storage mechanism by changing the binary storage method to fundamentally increase the information storage density of optical discs, thereby compensating for their lower density.

[0004] The literature, including Kim W, Chattopadhyay A, Siemon A, et al. Multistate memristive tantalum oxide devices for ternary arithmetic[J]. Scientific Reports, 2016, 6(1): 1-9 and Jung Y, Lee SH, Jennings AT, et al. Core-shell heterostructured phase change nanowire multistate memory[J]. Nano Letters, 2008, 8(7): 2056-2062, reports implementation schemes for ternary memory devices, but the fabrication process of these devices is relatively complicated, which is not conducive to the promotion of large-scale commercial applications. In addition, the devices of the above two schemes are difficult to fabricate on a large scale, so although their data storage density is high, the total amount of stored data is still low.

[0005] Therefore, designing a storage device with high storage density, large-area fabrication capability, and long storage life is of great practical significance. Summary of the Invention

[0006] Therefore, the present invention aims to provide a phase-change memory device with a composite thin-film structure, which can store both ternary and binary information, and has high information storage density and free selection of information storage type. Another object of the present invention is to provide a method for preparing the phase-change memory device with the composite thin-film structure of the present invention.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0008] In the context of this invention, the term "non-volatile" refers to the structural phase transition that occurs when the temperature rises to the material's phase transition temperature, transforming it from a low-temperature phase to a high-temperature phase. When the temperature drops below the phase transition temperature, the material's crystal structure remains in the high-temperature phase state.

[0009] In the context of this invention, the term "switching ratio" refers to the ratio of the reflectivity of a device before and after a change at a specific wavelength. A higher switching ratio indicates a greater difference in reflectivity before and after the change.

[0010] In a first aspect, the present invention provides a phase change memory device having a composite thin film structure, comprising:

[0011] Substrate,

[0012] The reflective layer located on the substrate,

[0013] The first protective layer is located above the reflective layer.

[0014] The dielectric layer located above the first protective layer,

[0015] A second protective layer located above the dielectric layer,

[0016] A semi-transparent, semi-reflective layer located above the second protective layer, and

[0017] Optionally, a third protective layer may be located above the translucent, semi-reflective layer.

[0018] The inventors of this application unexpectedly discovered that when a semi-transparent, semi-reflective layer is placed above the dielectric layer, the semi-transparent, semi-reflective layer and the reflective layer constitute a Fabry-Perot cavity. By changing the refractive index of the dielectric layer within the Fabry-Perot cavity, the wavelength corresponding to the minimum reflectance spectrum can be adjusted, thereby achieving a high on / off ratio. This allows the structure to utilize the high on / off ratio of the dielectric layer to store ternary information. Furthermore, when a semi-transparent, semi-reflective layer is placed above the dielectric layer, a memory with a composite thin-film structure can also utilize the high on / off ratio of the dielectric layer to store binary information.

[0019] In this invention, the phase change material in the dielectric layer undergoes a phase transition controlled by laser, enabling control over the reflection spectrum of the multilayer film structure. By utilizing the difference in reflectivity at specific wavelengths, information storage can be achieved. Furthermore, the phase change material in the dielectric layer can also undergo a phase transition by controlling its crystal structure through current or a hot plate.

[0020] In this invention, the first protective layer prevents atomic diffusion between the metal reflective layer and the dielectric layer, such as the germanium-antimony-tellurium layer, and can also help adjust the position of the Fabry-Perot resonance peak; the second protective layer prevents atomic diffusion between the metal reflective layer and the dielectric layer, such as the germanium-antimony-tellurium layer; and the third protective layer prevents the metal translucent semi-reflective layer from oxidizing in the air.

[0021] In this invention, a semi-transparent semi-reflective layer and a dielectric layer work together. The transparent semi-reflective layer and the reflective layer form a Fabry-Perot cavity. After the dielectric layer, such as germanium, antimony, or tellurium, undergoes a phase transition, its refractive index changes, altering the position of the Fabry-Perot resonance peak. This causes a change in the wavelength corresponding to the minimum reflectance spectrum, thereby achieving a high on / off ratio.

[0022] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the semi-transparent semi-reflective layer is composed of a multilayer thin film structure, and each layer of the multilayer thin film structure is independently formed of gold, silver, titanium, platinum, chromium or aluminum.

[0023] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the semi-transparent semi-reflective layer is composed of 1-5 thin film layers.

[0024] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the total thickness of the semi-transparent and semi-reflective layer is 5 nanometers to 15 nanometers.

[0025] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the dielectric layer is composed of a multilayer thin film structure and each of the multilayer thin film structures is independently formed of germanium antimony tellurium (GST) or vanadium dioxide.

[0026] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the dielectric layer is composed of 1-5 thin film layers.

[0027] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the total thickness of the dielectric layer is 15 nanometers to 100 nanometers; more preferably 80 nanometers to 100 nanometers.

[0028] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the reflective layer is composed of a multilayer thin film structure and each of the multilayer thin film structures is independently formed of gold, silver, titanium, platinum, chromium or aluminum.

[0029] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the reflective layer is composed of 1-5 thin film layers.

[0030] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the total thickness of the reflective layer is 20 nanometers to 200 nanometers.

[0031] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the first protective layer, the second protective layer and the third protective layer are each independently composed of a multilayer thin film structure and each thin film in the multilayer thin film structure is independently formed of aluminum oxide, silicon dioxide, hafnium dioxide, titanium dioxide, silicon nitride or zinc oxide.

[0032] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the thickness of the first protective layer is 5 nanometers to 200 nanometers.

[0033] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the thickness of the second protective layer is 5 nanometers to 95 nanometers.

[0034] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the thickness of the third protective layer is 5 nanometers to 95 nanometers.

[0035] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the substrate is selected from one or more of silicon, quartz, polyimide and polydimethylsiloxane.

[0036] Preferably, in the phase change memory device with a composite thin film structure according to the present invention, the thickness of the substrate is 200 micrometers to 1000 micrometers, more preferably 500 micrometers.

[0037] Secondly, the present invention provides a method for preparing a phase change memory device having a composite thin film structure, comprising the following steps:

[0038] (1) Form a reflective layer on the substrate;

[0039] (2) A first protective layer is formed on the reflective layer.

[0040] (3) A dielectric layer is formed on the first protective layer.

[0041] (4) A second protective layer is formed on the dielectric layer.

[0042] (5) A semi-transparent, semi-reflective layer is formed on the second protective layer, and

[0043] (6) Optionally, a third protective layer is formed on the semi-transparent semi-reflective layer.

[0044] In a specific embodiment of the present invention, the composite thin film structure with a semi-transparent and semi-reflective layer of the present invention can achieve a high on / off ratio in the near-infrared band of 1100 nm to 2000 nm.

[0045] In the composite thin film structure with a semi-transparent and semi-reflective layer of the present invention, the laser used for reading information is a near-infrared laser. The wavelength of the laser used for reading information is between 1200 nanometers and 1800 nanometers.

[0046] In a specific embodiment of the present invention, the composite thin film structure comprising a reflective layer, a dielectric layer, and a semi-transparent, semi-reflective layer is obtained using a bottom-up processing method. The bottom-up processing method includes physical vapor deposition methods such as electron beam evaporation deposition and magnetron sputtering deposition, chemical vapor deposition methods such as plasma-enhanced chemical vapor deposition and atomic layer deposition, and also thin film coating methods such as spin coating and spray coating. These processing methods are conventional methods for those skilled in the art; for details, please refer to: Gu Changzhi, Micro-Nano Fabrication and Its Application in Nanomaterials and Devices Research [M], Science Press, 2013.

[0047] The present invention has the following beneficial effects:

[0048] Traditional information storage methods struggle to balance high storage density and long storage lifespan. Therefore, developing a high-capacity information storage device with long storage life is of significant practical importance. This invention utilizes a semi-transparent, semi-reflective layer and a dielectric layer to fabricate a composite thin-film structure. The storage device incorporating this composite thin-film structure can control the phase transition of a specific region of the phase-change material using laser direct writing technology, thereby enabling data writing. By leveraging the changes in the optical parameters of the phase-change material in the dielectric layer before and after the phase transition, the multilayer film structure of this invention achieves a high on / off ratio in the near-infrared band. By changing the thickness of the dielectric layer, the wavelength corresponding to the high on / off ratio can be controlled. The dielectric layer of this invention is non-volatile, allowing for long-term data storage. The information storage device with this composite thin-film structure can store both ternary and binary information, offering high information storage density and flexible selection of information storage types.

[0049] Furthermore, the composite thin film structure of the present invention has a simple preparation process, short preparation time, low material cost, and can be prepared on a large scale, thus having application value. Attached Figure Description

[0050] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0051] Figure 1 A schematic diagram of a phase change memory device with a composite thin film structure according to a specific embodiment of the present invention is shown;

[0052] Figure 2 The image shows a reflectance image simulated using the finite-difference time-domain method for a phase change memory device with a composite thin film structure according to Embodiment 1 of the present invention.

[0053] Figure 3 The diagram shows an experimental test result of the reflectivity of a phase change memory device with a composite thin film structure according to Embodiment 1 of the present invention.

[0054] Figure 4 A schematic diagram illustrating the implementation of information storage in a phase-change memory device with a composite thin-film structure according to Embodiment 1 of the present invention is shown; wherein, GST represents germanium-antimony-tellurium material;

[0055] Figure 5 A schematic diagram of a phase change memory device with a composite thin film structure according to Comparative Example 1 is shown.

[0056] Figure 6 The experimental test results of the reflectivity of the phase change memory device with a composite thin film structure according to Comparative Example 1 are shown. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0058] In the following embodiments, the numerical simulation method is the finite-difference time-domain method, the instrument model of the laser direct writing device for inducing the phase transition of the phase transition material germanium-antimony-tellurium is DWL66+, and the instrument model for simulating and testing the reflectance spectrum is Vertex 80V.

[0059] Example 1

[0060] like Figure 1 As shown, the composite thin film structure with a semi-transparent and semi-reflective layer in this embodiment comprises seven layers, from bottom to top: a silicon substrate, a 100 nm platinum reflective layer, a 70 nm aluminum oxide layer, a 90 nm germanium-antimony-tellurium layer, a 10 nm aluminum oxide layer, a 10 nm gold layer, and another 10 nm aluminum oxide layer. The specific preparation method of this composite thin film structure includes the following steps:

[0061] A platinum thin film was deposited on the substrate surface using electron beam evaporation (EB / EL), with an electron gun acceleration power of 10 kW and a deposition rate of 3 nm / min. Then, an alumina thin film was deposited on the platinum film using atomic layer deposition (ALD) at a deposition temperature of 200°C. Next, a germanium-antimony-tellurium (CAST) thin film was deposited on the alumina film using magnetron sputtering at a deposition power of 50 W and a deposition rate of 6 nm / min. Following this, another alumina thin film was deposited on the germanium-antimony-tellurium (CAST) film using ALD at a deposition temperature of 90°C. Subsequently, a gold thin film was deposited on the alumina film surface using EB / EL, with an electron gun acceleration power of 10 kW and a deposition rate of 3 nm / min. Finally, an alumina thin film was deposited on the gold film using ALD at a deposition temperature of 90°C.

[0062] Figure 2 The results are obtained from the finite-difference time-domain numerical calculation of the composite thin film structure with a semi-transparent and semi-reflective layer in this embodiment.

[0063] like Figure 2 As shown in (a), when the germanium-antimony-tellurium alloy thin film is amorphous, the reflectivity of the composite thin film structure exhibits a minimum value at a specific near-infrared wavelength. As the thickness of the germanium-antimony-tellurium thin film changes (only the thickness is changed, and the rest of the preparation steps are the same as in Example 1), the wavelength corresponding to this minimum value changes accordingly, covering the near-infrared communication wavelengths of 1310 nm and 1550 nm.

[0064] like Figure 2As shown in (b), when the germanium-antimony-tellurium alloy thin film is crystalline, for germanium-antimony-tellurium thin films of the same thickness, the wavelength corresponding to the minimum reflectance of the composite thin film structure exhibits a red shift, and the minimum reflectance increases.

[0065] like Figure 2 As shown in (c), the inventors selected a 90-nanometer-thick germanium-antimony-tellurium alloy thin film. Due to the difference in reflectivity between the crystalline and amorphous germanium-antimony-tellurium alloy composite film structures, a high on / off ratio close to 10 appears near 1.6 micrometers (e.g., Figure 2 (d) is shown.

[0066] Figure 3 The results are the reflectance spectral test results of the composite thin film structure with a semi-transparent and semi-reflective layer in this embodiment.

[0067] The inventors induced a phase transition in the germanium-antimony-tellurium layer using a laser direct-writing device via laser heating. Reflectance spectroscopy experiments showed that at a laser power of 60mW, the minimum reflectance of the composite thin film structure red-shifted, indicating a partial phase transition in the germanium-antimony-tellurium material. At a laser power of 100mW, the minimum reflectance of the composite thin film structure red-shifted further, indicating a deeper phase transition. These two different phase transition degrees correspond to two different switching ratios, which can be used to achieve information storage functionality.

[0068] Figure 4 This diagram illustrates the principle of information storage using the composite thin film structure of this embodiment. When the composite thin film structure is heated by a laser and irradiated with a 1.6-micron readout laser, there are significant differences in reflectivity between the 100mW laser-heated area, the 60mW laser-heated area, and the unheated area (i.e., a high on / off ratio). The 100mW laser-heated area has the highest reflectivity, representing "2" in ternary mode; the 60mW laser-heated area has the second highest reflectivity, representing "1" in ternary mode; and the unheated area has the lowest reflectivity, representing "0" in ternary mode. This allows for the storage of ternary information. If only two germanium-antimony-tellurium material states are used, representing "0" and "1" respectively, binary information can be stored.

[0069] Comparative Example 1

[0070] like Figure 5 As shown, the memory device in this comparative example comprises a five-layer structure, from bottom to top: a silicon substrate, a 100 nm platinum reflective layer, a 70 nm alumina layer, a 90 nm germanium-antimony-tellurium layer, and a 10 nm alumina layer. This is compared to the seven-layer composite thin film structure containing a semi-transparent, semi-reflective layer described above. The preparation method for this five-layer composite thin film structure is the same as that in Example 1.

[0071] Figure 6 The experimental test results of the five-layer composite thin film structure in this comparative example are shown.

[0072] like Figure 6 As shown, due to the lack of a semi-transparent, semi-reflective layer, the five-layer composite thin film structure cannot form a Fabry-Perot cavity. Before and after the phase transition of the germanium-antimony-tellurium layer, the reflectivity difference of the five-layer composite thin film structure is not significant, making it impossible to achieve a high on / off ratio and thus ternary storage. Therefore, a semi-transparent, semi-reflective layer plays a crucial role in achieving a high on / off ratio and enabling information storage in this composite thin film structure.

Claims

1. A phase-change memory device having a composite thin-film structure, comprising: Substrate, The reflective layer located on the substrate, The first protective layer is located above the reflective layer. The dielectric layer located above the first protective layer, A second protective layer located above the dielectric layer, A semi-transparent, semi-reflective layer located above the second protective layer, and A third protective layer located above the semi-transparent, semi-reflective layer. The total thickness of the semi-transparent, semi-reflective layer is 5 nanometers to 15 nanometers. The total thickness of the dielectric layer is 80 nanometers to 100 nanometers. Furthermore, the phase-change memory device is configured to store ternary information using the dielectric layer with a high on / off ratio.

2. The phase change memory device with a composite thin film structure according to claim 1, wherein, The semi-transparent, semi-reflective layer is composed of a multilayer thin film structure, and each layer of the multilayer thin film structure is independently formed of gold, silver, titanium, platinum, chromium, or aluminum.

3. The phase change memory device with a composite thin film structure according to claim 1, wherein the semi-transparent semi-reflective layer is composed of 1-5 thin film layers.

4. The phase change memory device with a composite thin film structure according to claim 1, wherein, The dielectric layer is composed of a multilayer thin film structure, and each layer of the multilayer thin film structure is independently formed of germanium, antimony, tellurium, or vanadium dioxide.

5. The phase change memory device with a composite thin film structure according to claim 1, wherein, The dielectric layer consists of 1-5 thin film layers.

6. The phase change memory device with a composite thin film structure according to claim 1, wherein, The reflective layer is composed of a multilayer thin film structure, and each of the multilayer thin film structures is independently formed of gold, silver, titanium, platinum, chromium or aluminum.

7. The phase change memory device with a composite thin film structure according to claim 1, wherein, The reflective layer consists of a 1-5 layer thin film structure.

8. The phase change memory device with a composite thin film structure according to claim 1, wherein, The total thickness of the reflective layer is 20 nanometers to 200 nanometers.

9. The phase change memory device with a composite thin film structure according to claim 1, wherein, The first protective layer, the second protective layer, and the third protective layer are each independently composed of a multilayer thin film structure, and each thin film in the multilayer thin film structure is independently formed of aluminum oxide, silicon dioxide, hafnium dioxide, titanium dioxide, silicon nitride, or zinc oxide.

10. The phase change memory device with a composite thin film structure according to claim 1, wherein, The thickness of the first protective layer is 5 nanometers to 200 nanometers.

11. The phase change memory device with a composite thin film structure according to claim 1, wherein, The thickness of the second protective layer is 5 nanometers to 95 nanometers.

12. The phase change memory device with a composite thin film structure according to claim 1, wherein, The thickness of the third protective layer is 5 nanometers to 95 nanometers.

13. The phase change memory device with a composite thin film structure according to claim 1, wherein, The substrate is selected from one or more of silicon, quartz, polyimide and polydimethylsiloxane.

14. The phase change memory device with a composite thin film structure according to claim 1, wherein, The thickness of the substrate is 200 micrometers to 1000 micrometers.

15. The phase-change memory device with a composite thin-film structure according to claim 14, wherein, The substrate has a thickness of 500 micrometers.

16. A method for preparing a phase change memory device having a composite thin film structure as described in any one of claims 1-15, comprising the following steps: (1) Forming a reflective layer on the substrate; (2) A first protective layer is formed on the reflective layer. (3) A dielectric layer is formed on the first protective layer. (4) A second protective layer is formed on the dielectric layer. (5) A semi-transparent, semi-reflective layer is formed on the second protective layer, and (6) A third protective layer is formed on the semi-transparent and semi-reflective layer.

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