Although several studies report the use of Ag2S bulk blocks in energy devices, the fabrication of Ag2S thin-film-based stretchable electronics has never been realized due to the highly complicated synthetic procedures. The steps of the SET and RESET operations of the electrochemical metallization memory cell (ECM). Schematic image of the stretching test and typical optical microscope image of Ag2S thin film in the initial state (red square was analyzed for stretchability).
Schematic illustration of the switching mechanism for the operation of the Al/Ag2S/Ag RRAM. Ion, Ioff, and set/reset voltage distributions of Ag2S-based RRAM fabricated on a 4-inch wafer. Schematic illustration focused ion beam (FIB) cross-sectional view of the Ag2S-based stretchable RRAM.
Introduction
Solution-processed metal chalcogenide semiconductor
- Hydrazine chemistry based on dimensional reduction
- Alkahest solvent systems
First, the extended metal chalcogenide framework decomposes in the solution into individual metal chalcogenide anions. Next step includes deposition of the solution precursor on the substrate to form a solid precursor film. The simple approach to determine the solubility of various metal chalcogenide such as CuInSe2,.
All V2VI3 chalcogenide solutions indicated the thermal decomposition at 300 oC to 350 oC as shown in Figure 1.5a. Both Bi2S3 and Sb2Se3 thin films showed a uniform and high-quality crystalline realized by scanning electron microscope (SEM) in Figure 1.5d and e. 5. Demonstrated the utility of the alkahest solvent as a powerful tool for applications such as photovoltaic devices16, electrocatalysts17, flexible photodetectors18 and thermoelectric devices19.
Non-volatile memory…
- Introduction
- Magnetic Random Access Memory (MRAM)
- Ferroelectric Random Access Memory (FeRAM)
- Phase-change Random Access Memory (PRAM)
The STT-MRAM is a magnetic memory to take advantage of the fundamental platform built by MRAM's memory to enable scalable non-volatile memory solutions for advanced process nodes.20 MRAM stores data in accordance with the magnetization direction of each bit, and nano magnetic fields are introduced a bit of the existing MRAM. FeRAM is a non-volatile RAM that combines fast read and write access to the DRAM cells, consists of a capacitor and a transistor structure, as shown in Figure 1.7. The transistor will access the cell to sense the state of the ferroelectric capacitor dielectric.
The only drawback of FeRAM's read process is that it is destructive and needs the write-after-read architecture. PRAM, also known as chalcogenide RAM, can exist in two different phase states (crystalline and amorphous phase), a non-volatile type of RAM. 23,24 The basic structure of PRAM cells is shown in figure 1.8. Most phase change material includes one or more elements of a chalcogenide material in group 6 of the periodic table to create a memory device.
Resistive Random Access Memory (RRAM)
- The structure of RRAM
- Resistance switching modes
- Materials
- Switching mechanism
The formation of the memory cell filament occurs by subsequent deposition or reduction, a cation move (Cu+ or Ag+) and the subsequent deposition of inert or reducing metal electrodes (most commonly Ag or Cu).43 Therefore, RRAM is controlled by formation and annihilation. of resistive switching metal wires. The switching mechanism of RRAM cells is based on the growth of dielectric or semiconducting fibers inside conductive fibers (CF). Conductive filaments have a very small diameter on the order of nanometers for connecting the top and bottom electrodes of the memory.
VCM is based on a rearrangement of the oxygen ions and subsequent movement of the oxygen vacancy defects, which enables the formation of a conductive filament between the upper electrode and the lower electrode.47. The electrochemical metallization memory (ECM) SET and RESET operations step of the cell.. B) Anodic decomposition of metal material (M) after the reaction, where Mz- represents the metal cations in the solid electrolyte thin film. 38] Yang, L.; Kuegeler, C.; Szot, K.; Ruediger, A.; Waser, R., The influence of copper top electrodes on the resistive switching effect in TiO2 thin films studied by conducting atomic force microscopy.
Solution-processed stretchable Ag 2 S semiconductor thin films for wearable self-
Introduction
Resistive random access memory (RRAM) has been considered the next generation non-volatile memory device because it demonstrates a high operating speed, low power consumption, improved program/erase cycle reliability and scalability.[30 -33] In addition, resistance. The switching effect of RRAM cells mainly results from the reversible formation and annihilation of conductive channels in the active semiconductor layer of a metal-semiconductor-metal device structure.34-37 Metal oxide and chalcogenide compounds, such as TiOx, MoS2, WOx and Cu2S, are used as semiconductor layers in RRAM devices.38-41 However, due to their limited plasticity, only a few reports have realized the limited flexibility of resistive switching devices containing inorganic semiconductors.42-44 Therefore, most studies regarding Deformable resistance Memory devices have focused on organic-based and compound semiconductors,45-52, causing unresolved material-related issues of insufficient durability as well as low performance. Here, I present internally aligned, wafer-scale Ag2S thin films fabricated by a low-cost, scalable solution process. The fabricated thin film was determined to exhibit an internal mechanical tensile strain of 14.9%.
In addition, RRAM devices were fabricated with a wrinkled Ag2S thin film, which exhibited bipolar switching properties meeting the expected properties with a favorable Ion/Ioff ratio, operating endurance, and retention properties. In particular, the device showed 52% mechanical stretchability when the wrinkled Ag2S layer reached its fully stretched state without loss of electrical properties. Furthermore, I demonstrated the extremely high thermal and chemical durability of this inorganic RRAM device by performing uniform operations under thermal stresses at temperatures from -196 to 300 °C and the chemical stresses when exposed to various hydrophilic, hydrophobic and ionic environments, especially maintaining of the switching properties for 168 hours at 85 oC/85% relative humidity.
Finally, the integration of memory devices and motion sensors enables a self-sufficient and smart and wearable healthcare monitoring system for long-term data storage.
Results and Discussion
- Solution-processed fabrication of Ag 2 S thin films
- Mechanical properties of Ag 2 S thin films
- Fabrication of Ag 2 S-based RRAMs
- Environmental durability of Ag 2 S-based RRAMs
- Stretchable Ag 2 S-based RRAMs
- Self-powered Ag 2 S-based RRAMs for wearable healthcare monitoring system
The photograph of the thin film showed mirror-like specular reflection, which showed the highly uniform thin film surface (Figure 2.1b). Ag2S thin film on the stretchable substrate showed vertical wrinkles caused by relaxation of the residual stress during the transfer process. The stretchability of the thin Ag2S film on the stretchable substrate was estimated at a tensile stress of , since other parts of the film cannot be stretched with uniform strain after crack propagation.
The process introduced here led to the fabrication of Ag2S-based RRAM wafers (Figure 2.25). A solution-processed Ag2S thin film deposited on a 4-inch wafer showed uniform microstructures over the entire area, as shown in SEM images (Figure 2.26). In addition, to verify the practicality of the Ag2S thin film as a wafer-shaped active layer, I investigated the uniformity of operation by measuring the I−V characteristics of the RRAM cells at each point presented in Figure 2.27.
The intrinsic extensibility of the α-Ag2S thin films enabled the fabrication of highly stretchable Ag2S thin film wrinkled layers without any mechanical failure. The ultrathin shape of the RRAM (~3 μm total thickness; Fig. 2.33) enabled high deformability, including bending, stretching, and twisting. As shown in Figure 2.35, the peaks in the XRD patterns of the Ag2S thin films after the lithography and transfer processes are in good agreement with those of the pristine Ag2S thin films deposited on the glass substrate.
As shown in Figure 2.36, a flat Ag2S thin film was compressed and a wavy structure was formed on the surface by elastic recovery of the pre-strained substrate. A 40% relaxed Ag2S thin film shows the same feature shape compared to the surface profile shown in Figure 2.38. The flexibility of the Al/Ag2S/Ag RRAM device fabricated on a polyimide substrate was evaluated by measuring Ion and Ioff every 100 bending cycles at a bending radius of ~1.9 mm (Figure 2.39).
In addition, no cracks were observed in the SEM images of the transferred Ag2S, Ag, and Al thin film in the folded and stretched state (Figure 2.42). For energy conversion, different capacitors (10 nF and 1 nF) were placed in the circuit to control the open circuit output voltage (Voc) to the Ag2S memory device (Figure 2.47). In this frequency range, the RRAM maintained Ion and Ioff well after the stretch cycle (Figure 2.50).
Conclusion
Experimental section
- Materials
- Synthesis of purified Ag 2 S solution
- Deposition of Ag 2 S thin films
- Characterization of materials
- The Ag 2 S-based RRAM device fabrication
- Fabrication of the stretchable RRAM device
- Mechanical properties of Ag 2 S thin film & FEA simulation
- Fabrication of the wearable self-powered RRAM system
- Fabrication of the self-powered RRAM matrix
- The bending and stretching cycle test
- The chemical and thermal stability test
Then, Ti was deposited as an adhesion layer (∼5 nm) and ∼70 nm Al was deposited on titanium layer using a thermal evaporator. After Ag2S coating, ~70 nm Ag was deposited on Ag2S as top electrode of patterned metal mask thermal evaporator. Ti was deposited as an adhesion layer (10 nm) and ∼100 nm Al was deposited on Ti layer using a thermal evaporator.
Ti는 접착층(10 nm)으로 증착되었고 Al은 패턴화된 금속 마스크 열 증발기를 사용하여 Ti 층 위에 증착되었습니다. Ag2S 필름은 Al 전극 위에 코팅되었고, 200 nm Ag 전극은 패턴화된 금속 마스크가 있는 열 기화기에 의해 증착되었습니다. 짧지만 긴 실험실 생활이 앞으로의 삶에 큰 도움이 될 것이라고 믿습니다.
우선, 진심으로 존경하는 손재성 교수님께 깊은 감사의 말씀을 전하고 싶습니다. 변호 기간 동안 베풀어주신 소중한 조언과 아낌없는 칭찬과 격려의 말씀에 진심으로 감사드립니다. 좋은 교수님들의 큰 도움으로 연구를 마칠 수 있었던 것 같습니다.
NSE 연구실 구성원들에게도 감사의 말씀을 전하고 싶습니다. 진심으로 감사의 말씀을 전하고 싶습니다. 처음부터 교수님의 지도와 지도 덕분에 제가 이 훌륭한 연구를 성공적으로 마칠 수 있었다고 생각합니다.
제가 NSE에 왔을 때 잘 적응할 수 있도록 도와주시고 항상 무엇이든 도와주신 형 성헌님께 감사하다는 말씀 전하고 싶습니다.
