A lead-free inorganic double halide storage device based on perovskite

Abstract

A lead-free, inorganic storage device (100) based on double halide perovskite, wherein the device (100) comprises the following: a substrate (102) comprising indium tin oxide (ITO) coated on a flexible polyethylene terephthalate (PET) film (104); a cesium tin (IV) iodide perovskite film (106) formed on the ITO-coated PET substrate; and an aluminium electrode (108) formed on the Cs2SnI 6- perovskite film (106) to create a storage structure.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the field of memory devices. In particular, the present invention relates to the development of a lead-free inorganic memory device based on double halide perovskite. Furthermore, the invention focuses on the use of cesium tin(IV) iodide (Cs2SnI6) perovskite as a switching layer for flexible, environmentally friendly, and high-performance memory applications. BACKGROUND OF THE INVENTION

[0002] In the age of advanced technology, the demand for high-performance, energy-efficient, and cost-effective storage devices has increased exponentially. Non-volatile memory technologies, which store data without requiring a continuous power supply, are at the forefront of next-generation storage solutions. Among them, resistive switching (RS) memory devices have attracted considerable attention due to their exceptional switching characteristics, including fast switching speed, low operating voltage, simple structural design, superior mechanical properties, stable data storage, and low-cost manufacturing.

[0003] RS devices typically operate with a metal-insulator-metal (MIM) sandwich structure, with the insulator serving as the active switching layer. The basic principle is the transition between a high-resistance state (HRS) and a low-resistance state (LRS) upon application of an external electric field. This transition creates conductive pathways within the insulating matrix, enabling data storage and retrieval. The development of RS devices with fast switching speeds, high duty cycles, and low power consumption is critical for the realization of high-density non-volatile memory applications.

[0004] Over the past decade, various materials have been used as active layers in RS devices, including metal oxides, graphene, perovskite oxides, organic compounds, nanoparticles, and metal dichalcogenides. Recently, halide perovskites have gained traction due to their superior optoelectronic properties, tunable band gaps, and ease of fabrication. These materials offer a unique combination of high performance and low-cost manufacturing, making them highly suitable for RS applications.

[0005] Among halide perovskites, Cs2SnI6, a double halide perovskite, has attracted considerable interest due to its desirable properties, such as a tunable optical band gap in the range of 1.27 to 1.62 eV and excellent thermal stability at ambient conditions. These properties make Cs2SnI6 an ideal candidate for use in RS-based memory devices.

[0006] Against this background, the present invention focuses on the fabrication of a flexible memory device using Cs2SnI6 as a switching layer. The device is constructed with a structure consisting of an aluminum (Al) top electrode, a Cs2SnI6 film as the active layer, and an indium tin oxide-polyethylene terephthalate (ITO-PET) substrate as the bottom electrode. This novel device exhibits stable and reproducible bipolar resistive switching behavior with an impressive on / off ratio of approximately 10 3 and thus paves the way for its application in flexible and high-density non-volatile memory technologies.

[0007] The technical advances disclosed by the present invention overcome the limitations and disadvantages of existing and conventional systems and methods. SUMMARY OF THE INVENTION

[0008] The present invention relates to a lead-free, inorganic memory device based on double halide perovskite that uses cesium tin(IV) iodide (Cs2SnI6) as a switching material for resistive random access memory (RRAM). The perovskite material Cs2SnI6 is synthesized and confirmed to exhibit a pure cubic phase at room temperature, as evidenced by X-ray diffraction (XRD) analysis. Optical characterization shows broadband absorption around 580 nm in ultraviolet-visible (UV-Vis) spectra with an optical band gap of 1.68 eV and an intense photoluminescence (PL) emission peak at 540 nm. The memory device is fabricated with an aluminum (Al) electrode, a Cs2SnI6 perovskite film as the active layer, and an indium tin oxide-polyethylene terephthalate (ITO-PET) substrate, resulting in a flexible structure.The device exhibits bipolar resistive switching (RS) properties, which are due to ion movement within the Cs2SnI6 layer, enabling fast and efficient data storage and retrieval. This lead-free, environmentally friendly perovskite-based RRAM offers significant advantages in stability, functionality, and sustainability, making it a promising candidate for next-generation high-density memory and optoelectronic applications.

[0009] An object of the present invention is to develop environmentally friendly, lead-free inorganic memory devices based on double halide perovskite for high-density data storage applications.

[0010] Another aim of the present invention is the synthesis of cesium tin(IV) iodide perovskites (Cs2SnI6) with a pure cubic phase, which ensures superior structural stability and functionality.

[0011] Another object of the present invention is to fabricate a flexible Al / Cs2SnI6 / ITO-PET memory device using Cs2SnI6 perovskite films as a switching layer, which is suitable for non-volatile resistive random access memory (RRAM) applications.

[0012] Another object of the present invention is to achieve and demonstrate distinct bipolar resistive switching characteristics in the fabricated memory device that enable fast and reliable ON / OFF transitions.

[0013] Another object of the present invention is to ensure that the device has a high resistance ratio (~10 3 ), making it suitable for robust and efficient storage applications.

[0014] Another object of the present invention is to validate the mechanical flexibility, stability and reproducibility of the fabricated storage device under tensile bending conditions, thus ensuring the durability of portable and wearable electronics.

[0015] Another object of the present invention is to demonstrate precise control over switching parameters with low cycle-to-cycle (C / C) and device-to-device (D / D) variations, improving reliability for commercial applications.

[0016] Another object of the present invention is to optimize the SET and RESET voltages to ensure energy-efficient operation of the memory device.

[0017] Another object of the present invention is to provide a scalable, cost-effective and environmentally friendly solution for next-generation optoelectronic memory devices.

[0018] To provide a lead-free, inorganic memory device based on double halide perovskite, comprising: a substrate containing indium tin oxide (ITO) coated on a flexible polyethylene terephthalate (PET) film; a cesium tin (IV) iodide (Cs2SnI6) perovskite film formed on the ITO-coated PET substrate; and an aluminum electrode formed on the Cs2SnI6 perovskite film to create a memory structure.

[0019] To provide a system for forming a perovskite film from cesium tin(IV) iodide (Cs2SnI6). The system includes: a mixing chamber configured to dissolve 0.519 g of cesium iodide (CsI) and 0.626 g of tin(IV) iodide (SnI4) in 3 ml of acetonitrile to form a precursor solution; a stirrer cocentrically located within the mixing chamber to stir the precursor solution for 1–2 hours; a heating element connected to the mixing chamber to heat the precipitate to a controlled temperature; and a centrifuge connected to the mixing chamber to centrifuge the precipitate, which is further dried in sunlight, allowing it to cool naturally to obtain a dark black powder.

[0020] To further clarify the advantages and features of the present disclosure, a more detailed description of the invention will be given with reference to specific embodiments thereof illustrated in the accompanying drawings. It should be noted that these drawings represent only typical embodiments of the invention and are therefore not to be considered limiting its scope. The invention will be described and explained in additional detail and in greater detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE CHARACTERS

[0021] These and other features, aspects, and advantages of the present disclosure will be better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout. Fig.1 shows a block diagram of a lead-free inorganic double halide perovskite-based memory device according to an embodiment of the present disclosure; and Fig. 2 shows a block diagram of a system for forming a cesium tin(IV) iodide perovskite film (Cs2SnI6) according to an embodiment of the present disclosure.

[0022] Furthermore, those skilled in the art will recognize that elements in the drawings are shown for convenience and may not necessarily be drawn to scale. For example, the flowcharts illustrate the method by key steps to enhance understanding of aspects of the present disclosure.

[0023] Moreover, with respect to the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only the specific details relevant to understanding the embodiments of the present disclosure in order not to clutter the drawings with details that would be readily apparent to those skilled in the art who would benefit from the description herein. DETAILED DESCRIPTION:

[0024] To facilitate an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and described in specific language. It is to be understood, however, that this is not intended to limit the scope of the invention, as such changes and further modifications to the illustrated system and such further applications of the principles of the invention as illustrated therein are contemplated as would normally occur to one skilled in the art to which the invention pertains.

[0025] It will be understood by one skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be limiting thereof.

[0026] References in this specification to "one aspect," "another aspect," or similar language mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, occurrences of the phrase "in one embodiment," "in another embodiment," and similar language throughout this specification may or may not all refer to the same embodiment.

[0027] The terms "comprises," "comprising," or other variations thereof are intended to cover non-exclusive inclusion, such that a process or method comprising a list of steps not only includes those steps, but may also include other steps not expressly listed or inherent in such process or method. Likewise, one or more devices or subsystems or elements or structures or components preceded by "comprises..." does not preclude, without further limitation, the existence of other devices or other subsystems or other elements or other structures or other components or additional devices or additional subsystems or additional elements or additional structures or additional components.

[0028] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are for illustrative purposes only and should not be considered limiting.

[0029] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0030] Fig.1 shows a block diagram of a lead-free, inorganic memory device (100) based on double halide perovskite, the device (100) comprising: a substrate (102) including indium tin oxide (ITO) coated on a flexible polyethylene terephthalate (PET) film (104); a cesium tin (IV) iodide (Cs2SnI6) perovskite film (106) formed on the ITO-coated PET substrate; and an aluminum electrode (108) formed on the Cs2SnI6 perovskite film (106) to create a memory structure.

[0031] Fig.2 shows a block diagram of a system (200) for forming a cesium tin(IV) iodide (Cs2SnI6) perovskite film (106), the system (200) comprising: a mixing chamber (202) configured to dissolve 0.519 g of cesium iodide (CsI) and 0.626 g of tin(IV) iodide (SnI4) in 3 ml of acetonitrile to form a precursor solution; a stirrer (204) cocentrically positioned in the mixing chamber (202) to stir the precursor solution for 1-2 hours; a heating element (206) connected to the mixing chamber (202) to heat the precipitate to a controlled temperature; and a centrifuge (208) connected to the mixing chamber (202) for centrifuging the precipitate, wherein the precipitate is further dried in sunlight and thereby allowed to cool naturally to obtain a dark black powder.

[0032] In one embodiment, the precursor solution is preferably stirred at 300 rpm for 1 hour and 30 minutes.

[0033] In one embodiment, the controlled temperature is preferably 82°C.

[0034] The proposed invention focuses on a lead-free inorganic double halide perovskite memory device. The device is fabricated by synthesizing and characterizing cesium tin(IV) iodide (Cs2SnI6) perovskite using a system, which is then used as a switching layer in flexible resistive random access memory (RRAM) devices. Cs2SnI6 is synthesized by dissolving cesium iodide (CsI) and tin(IV) iodide (SnI4) in acetonitrile (ACN), followed by stirring, heating, centrifugation, and drying to obtain a pure, deep-black powder. X-ray diffraction (XRD) confirms the formation of a cubic-phase Cs2SnI6 structure with high phase purity, while field emission scanning electron microscopy (FESEM) reveals a nanocubic morphology. The optical band gap, determined by UV-Vis spectroscopy, is 1.68 eV, with an intense photoluminescence emission peak (PL) at 540 nm.The electrical characterization of the Al / Cs2SnI6 / ITO-PET memory device demonstrates bipolar resistive switching behavior with a high resistance ratio, stable operation over 100 cycles, and robust performance under mechanical bending conditions. The invention demonstrates the potential of Cs2SnI6 perovskite for use in next-generation non-volatile memory devices.

[0035] In one embodiment, X-ray diffraction (XRD) analysis confirms the cubic phase formation of Cs2SnI6 perovskite at room temperature with characteristic peaks indexed to the cubic phase (space group Fm3m, JCPDS No. 51-0466) and an average crystal size of 38.71 nm, free of impurities. Field emission scanning electron microscopy (FESEM) reveals a nanocubic structure, while energy dispersive X-ray analysis (EDX) shows the elemental composition of Cs, Sn, and I in stoichiometric ratios, further confirming the phase purity. Optical characterization shows significant absorption at 408 nm with a band gap of 1.68 eV, and photoluminescence exhibits intense emission at 540 nm. The electrical characterization of the Al / Cs2SnI6 / ITO-PET device demonstrates stable bipolar resistive switching with a SET voltage of 1.4 V and a RESET voltage of -1.16 V over 100 cycles with consistently high and low resistance states, supporting non-volatile memory applications. Statistical analysis shows Gaussian distributions for SET and RESET voltages with controlled parameters. The device maintains its mechanical flexibility, with stable electrical performance under tensile bending conditions, confirming robustness and reproducibility for flexible memory device applications.

[0036] A comparative analysis of resistive switching (RS) parameters, including SET voltage, RESET voltage, ON / OFF ratio, hold time, and flexibility, is shown in Table 1 below: Storage device structure Lead-free SAT Z Voltage (V) RESET ZEN Voltage (V) ON / OFF ratio Endurance cycles Retention (S) Flexural strength Al / CsPbBr3 / PEDOT:PSS / ITO / PET NO - 0.6 1.7 ~ 10 2 50 - Yes Ag / CsSnCl3 / ITO Yes 0.95 - 1.07 > 10 2 10 5 10.000 Yes Ag / PVOH ZnSnO 3 / Ag / PET Yes 1.5 - 1.5 ~ 100 500 1.29.600 Yes A1 / CsPbBr3 / ITO / PET NO 1.5 - 0.65 ~10 3 10 3 > 10.000 Yes Al / RbPbBr3 NO -2.4 2.5 10 3 1000 10.000 Yes / ITO / PET Al / FAPbBr3 / ITO Yes + 1.58 - 1.31 ~10 3 10 4 10.000 Yes Al / CsPb2Br5 / ITO-PET NO + 2.30 - 1.48 10 2 100 10 3 Yes Au / PMMA / CsSnI3 / ITO Yes 2 - 3 > 10 > 150 10000 NO Au / CH3NH3PbI3 / ITO / PET NO 0.7 - 0.5 ~ 10 400 10000 Yes Au / CH3NH3PbI 3 - x Cl x / FTO NO 1 - 1.5 < 10 > 100 > 10.000 NO At / PMMA / Cs3Cu2I5 / ITO Yes 0.6 - 0.44 >10 2 100 10000 NO Al / Cs2SnI6 / ITO Yes + 1.26 - 1.16 ~10 3 10 6 10000 Yes

[0037] Table 1 above highlights the superior performance of the flexible Al / Cs2SnI6 / ITO memory devices. Unlike previously reported devices, these memory devices exhibit formation-free operation, low threshold voltages, high mechanical flexibility, and extended retention times, making them a promising candidate for next-generation flexible electronic applications.

[0038] The drawings and the foregoing description provide examples of embodiments. Those skilled in the art will recognize that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be separated into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of the processes described herein may be changed and are not limited to the manner described herein. Furthermore, the actions of any flowchart need not be implemented in the order shown; nor do all actions necessarily need to be performed. Also, those actions that are not dependent on other actions may be performed in parallel with the other actions. The scope of the embodiments is in no way limited by these specific examples.Numerous variations, whether explicitly stated in the specification or not, such as differences in structure, dimensions, and use of materials, are possible. The scope of the embodiments is at least as broad as indicated in the following claims.

[0039] Advantages, other benefits, and solutions to problems have been described above with reference to specific embodiments. However, the advantages, benefits, solutions to problems, and any components that may cause an advantage or solution to occur or become more apparent are not to be construed as a critical, required, or essential feature or component of any or all of the claims. REFERENCES 100 A lead-free inorganic perovskite-based double halide memory device. 102 Substrat 104 Flexible film made of polyethylene terephthalate (PET) 106 Cesium tin(IV) iodide (Cs2SnI6) perovskite film 108 aluminum electrode 200 A system (200) for the preparation of a cesium tin(IV) iodide (Cs2SnI6) perovskite film 202 Mixing chamber 204 stirrers 206 Heating element 208 Centrifuge

Claims

[1] A lead-free, inorganic storage device (100) based on double halide perovskite, the device (100) comprising: a substrate (102) comprising indium tin oxide (ITO) coated onto a flexible polyethylene terephthalate (PET) film (104); a cesium tin (IV) iodide perovskite film (106) formed on the ITO-coated PET substrate; and an aluminum electrode (108) formed on the Cs2SnI 6 perovskite film (106) to create a memory structure. [2] A system (200) for forming a cesium tin (IV) iodide (Cs2SnI6) perovskite film (106) according to claim 1, wherein the system (200) comprises: a mixing chamber (202) configured to dissolve 0.519 g of cesium iodide (CsI) and 0.626 g of tin(IV) iodide (SnI4) in 3 ml of acetonitrile to form a precursor solution; a stirrer (204) positioned cocentrically within the mixing chamber (202) to stir the precursor solution for 1-2 hours; a heating element (206) connected to the mixing chamber (202) for heating the precipitate to a controlled temperature; and a centrifuge (208) connected to the mixing chamber (202) for centrifuging the precipitate, wherein the precipitate can be further dried in sunlight and thereby cooled naturally to obtain a dark black powder. [3] System according to claim 2, wherein the precursor solution is preferably stirred for 1 h 30 min at 300 rpm. [4] System according to claim 2, wherein the controlled temperature is preferably 82°C.

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