Abstract
We demonstrate in-plane field-free-switching spin-orbit torque (SOT) magnetic tunnel junction (MTJ) devices that are capable of low switching current density, fast speed, high reliability, ...and, most importantly, manufactured uniformly by the 200-mm-wafer platform. The performance of the devices is systematically studied, including their magnetic properties, switching behaviors, endurance and data retention. The successful integration of SOT devices within the 200-mm-wafer manufacturing platform provides a feasible way to industrialize SOT MRAMs. It is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.
Organic–inorganic halide perovskites have emerged as one of the most promising materials for photovoltaic applications. Because of the polycrystalline nature of perovskite thin films, it is crucial ...to investigate the impact of microstructures on device performance. In this study, we employ ramp-annealing to tailor the texture of perovskite thin films via controlling the nucleation of perovskite grains. Electrochemical impedance spectroscopy studies further suggest that the thin film texture impacts not only the charge collection at the contact but also the carrier transport in the bulk perovskite layer. The combination of the two effects leads to enhanced performance in devices constructed of preferentially oriented perovskite thin films.
The synthesis and characterization of a lead iodide layered perovskite, NH2C(I)NH22(CH3NH3)2Pb2I8, is described. The combination of an ideal bandgap of 1.61 eV and excellent compositional stability ...under ambient conditions make it a promising candidate for integration in solar cells. Planar solar cells utilizing NH2C(I)NH22(CH3NH3)2Pb2I8 exhibit two interesting phenomena in the photovoltaic performance: an exponential dependence of J sc on incident light intensity and abnormal J–V response. To investigate the photophysical properties of NH2C(I)NH22(CH3NH3)2Pb2I8 perovskite planar solar cells, intensity-modulated photocurrent spectroscopy (IMPS) and electrochemical impedance spectroscopy (EIS) were conducted. It is found that the planar structured solar cells of the layered perovskite suffer from bulk recombination which limits the charge collection and photocurrent. Use of a mesoporous TiO2 scaffold layer largely overcomes the recombination limitations of the layered perovskite and significantly improves the photovoltaic performance.
To deal with the increasing demand on energy and the concerns about fossil fuels, solar energy has become one of the most promising alternative energy. Photovoltaic technology has been developed to ...harnesses the solar energy. Different types of solar cells depending on the materials and structures of the devices have been developed, such as crystalline Si cells, dye sensitized solar cells, perovskite solar cells and organic photovoltaics. Solar cells with high efficiency, low cost, and excellent stability are desirable for the market. The first part of this study focuses on the organic-inorganic hybrid perovskite photovoltaics. Solar cells consisting of polycrystalline perovskite thin films have demonstrated a rapid increase of power conversion efficiency (PCE) in the past few years. To further boost the device performance, it is crucial to understand how the microstructures, such as the film texture, grains and grain boundaries, impact the electrical properties of the perovskite thin film. The ramp-annealing treatment is adapted to tailor the texture of perovskite films, where a strong correlation between the device performance and the thin film texture is revealed by X-ray diffraction (XRD) and J-V characteristics. Electrochemical impedance spectroscopy (EIS) further suggests that the enhanced texture structure not only suppresses recombination at the contact but also improves the carrier diffusion length, which ultimately contributes to better device performance. The other important feature of the polycrystalline thin film is grains and grain boundaries. To investigate the influence of these microstructures on device performance, photo-conducting atomic force microscopy (pc-AFM) and Kelvin probe force microscopy (KPFM) measurements, which provide the nano-scale resolution, are performed on perovskite thin films with columnar structures. Three discrete photocurrent levels are identified among perovskite grains, likely corresponding to the crystal orientation of each grain identified by electron backscattering diffraction (EBSD). Local J-V curves measured on these grains further suggest an anti-correlation behavior between short-circuit current (Jsc) and open-circuit voltage (Voc). These results suggest the orientation-dependent carrier mobility in perovskite thin films. In addition, the photoresponse of perovskite films displays a pronounced heterogeneity across grain boundaries, with low-angle boundaries exhibiting even better performance than the adjacent grain interiors. KPFM further reveals the downward band bending at grain boundaries which draws electrons and repels holes. Thus, the low-angle grain boundaries facilitate the electron transport and suppress recombination. The second part of this study focuses on the interface engineering of organic photovoltaics (OPVs). Organic photovoltaics have attracted a significant amount of attention as they offer potential benefits of low cost and mechanical flexibility. It is known that in OPV devices the energy level alignment at the interfaces between metal electrodes and the photoactive layer is critical in determining the charge collection efficiency. Here, zinc oxide (ZnO) buffer layer is introduced between the bulk heterojunction (BHJ) organic layer and the cathode material. By varying the processing condition of ZnO layer, the energy level alignment at the contact is tuned and thus the device performance. The interfacial energetics is further investigated by KPFM. Schottky barriers with varied widths are identified at ITO/ZnO interfaces. With electrons tunneling through the narrow Schottky barrier, the charge collection efficiency at the cathode is improved.
Abstract
We have successfully demonstrated a 1 Kb spin-orbit torque (SOT) magnetic random-access memory (MRAM) multiplexer (MUX) array with remarkable performance. The 1 Kb MUX array exhibits an ...in-die function yield of over 99.6%. Additionally, it provides a sufficient readout window, with a TMR/
R
P
_sigma% value of 21.4. Moreover, the SOT magnetic tunnel junctions (MTJs) in the array show write error rates as low as 10
−6
without any ballooning effects or back-hopping behaviors, ensuring the write stability and reliability. This array achieves write operations in 20 ns and 1.2 V for an industrial-level temperature range from −40 to 125 °C. Overall, the demonstrated array shows competitive specifications compared to the state-of-the-art works. Our work paves the way for the industrial-scale production of SOT-MRAM, moving this technology beyond R&D and towards widespread adoption.
The growth of epitaxial semiconductors and oxides has long since revolutionized the electronics and optics fields, and continues to be exploited to uncover new physics stemming from quantum ...interactions. While the recent emergence of halide perovskites offers exciting new opportunities for a range of thin‐film electronics, the principles of epitaxy have yet to be applied to this new class of materials and the full potential of these materials is still not yet known. In this work, single‐domain inorganic halide perovskite epitaxy is demonstrated. This is enabled by reactive vapor phase deposition onto single crystal metal halide substrates with congruent ionic interactions. For the archetypical halide perovskite, cesium tin bromide, two epitaxial phases, a cubic phase and tetragonal phase, are uncovered which emerge via stoichiometry control that are both stabilized with vastly differing lattice constants and accommodated via epitaxial rotation. This epitaxial growth is exploited to demonstrate multilayer 2D quantum wells of a halide‐perovskite system. This work ultimately unlocks new routes to push halide perovskites to their full potential.
Single‐domain halide perovskite heteroepitaxy is demonstrated and multiple epitaxial phases of archetypical halide perovskite are uncovered via stiochiometry control. The epitaxial growth is further exploited to demonstrate multilayer 2D quantum wells of a halide‐perovskite system and can ultimately enable their full potential in many emerging applications.
We have systematically investigated the reliability performance of spin-orbit torque (SOT) magnetic random access memory (MRAM) devices, including electromigration (EM), stress migration (SM), ...endurance and data retention. The results show that the SOT-MRAM devices pass the EM requirement over 10 years lifetime under the operation condition, and pass the SM requirement over 1000 hours baking at 175°C. Moreover, high endurance close to 10 14 cycles and robust data retention over 10 years storage time were demonstrated for the same SOT-MRAM devices. This full characterization fills the blank of SOT-MRAM reliability research and would contribute to the commercialization of the SOT-MRAM.
In article number 1701003, Richard R. Lunt and co‐workers demonstrate the controllable epitaxial growth of single‐crystal halide perovskites on low cost ionic crystal substrates investigated by in ...situ real‐time diffraction. Such growth is achieved by reactive vapor‐phase deposition enabling precise control for tuning epitaxial phases, demonstrating multilayer quantum wells, and providing a new route to uncover the full potential of halide perovskites.
This paper presents a 1 kb physical unclonable function (PUF) chip fabricated in a 180-nm CMOS process. The chip consists of in-plane magnetic anisotropy spin-orbit torque (IMA-SOT) PUF arrays and ...the necessary periphery circuits, which utilizes the manufacturing process deviation of common state of SOT devices to generate the randomness. Moreover, a dual-mode logic control design with a self-write back circuit is proposed to implement the transition between PUF and memory functions, which improves the flexibility and reliability of the PUF chip. The self-write back circuit is activated after reading the challenge-response pairs (CRPs), which can induce to the complementary states of SOT devices. The uniformity, uniqueness and reliability are experimentally measured by a comprehensive pretest procedure, and the inter- and intra-hamming distances are computed. Additionally, the SOT-PUF chips are subjected to repeated read testing at varying temperature and supply voltages to evaluate the stability under different operating conditions. This work provides a feasible approach for the preparation of highly integrated PUF chips based on SOT devices, offering a promising solution for secure hardware authentication applications.
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