Effects of controlling the film thickness of ferroelectric Hf 0.5 Zr 0.5 O 2 (HZO) thin film were investigated to figure out the important design strategies for the ...metal-ferroelectric-insulator-semiconductor (MFIS) capacitors. Even though the maximum remnant polarization (2P r ) was obtained to be <inline-formula> <tex-math notation="LaTeX">23.4~\mu \text{C} </tex-math></inline-formula>/cm 2 for the HZO capacitors with an HZO thickness of 20 nm, the ferroelectric memory window increased from 0.44 to 0.82 V with increasing the HZO thickness from 20 to 40 nm. The crystalline phases of the HZO thin films showed thickness-dependent variations with the relative dielectric permittivity.
Metal-ferroelectric-metal capacitors were fabricated to evaluate the ferroelectricity and switching dynamics of the undoped-HfO2 thin films prepared by atomic layer deposition. The film thickness was ...controlled to be 9 to 16 nm as an important control parameter. The value of remnant polarization (Pr) decreased with increasing the film thickness owing to the modulations in amounts of ferroelectric orthorhombic phase. The 11-nm-thick HfO2 thin film, which was strategically suggested as a critical film thickness, showed the Pr value of 8.47 μC/cm2. Based on the accurately calculated Pr by double-pulse switching measurement and Kolmogorov-Avrami-Ishibashi (KAI) model, the ferroelectric polarization switching time (ts) and the activation electric field (Ea) for polarization reversal were estimated with the variations in film thickness of the HfO2 thin films. The ts and Ea showed decreasing and increasing trends with increasing the film thickness, respectively. The values of Pr for the MFM capacitor were also found to be gradually modulated by controlling the ferroelectric partial polarization with pulse-width and pulse-number modulations, which corresponded to the emulations of assigning the synaptic weights for the synapse device applications.
Among the various metal oxides, SnO2 has been most widely exploited as a semiconductor gas sensor for its excellent functionalities. Models illustrating the sensing mechanism of SnO2 have been ...proposed and tested to explain experimentally derived “power laws”. The models, however, are often based on somewhat simplistic assumptions; for instance, the net charge transfer from an adsorbate to a sensor surface site is assumed to occur only by integer values independent of the crystallographic planes. In this work, we use layer-shaped SnO2 crystallites with one nanodimension (1ND-crystallites) as NO2 gas sensing elements under flat band conditions, and derive appropriate “power laws” by combining the dynamics of gas molecules on the sensor surface with a depletion theory of semiconductor. Our experimentally measured sensor response as a function of NO2 concentration when compared with the theoretically derived power law indicates that sensing occurs primarily through the chemisorption of single NO2 molecules at oxygen vacancy sites on the sensor surface.
Thermal management is essential for living organisms and electronic devices to survive and maintain their own functions. However, developing flexible cooling devices for flexible electronics or ...biological systems is challenging because conventional coolers are bulky and require rigid batteries. In nature, skins help to maintain a constant body temperature by dissipating heat through perspiration. Inspired by nature, an artificial perspiration membrane that automatically regulates evaporation depending on temperature using the programmed deformation of thermoresponsive hydrogels is presented. The thermoresponsive hydrogel is patterned into pinwheel shapes and supported by a polymeric rigid frame with stable adhesion using copolymerization. Both shape of the valve and mechanical constraint of the frame allow six times larger evaporation area in the open state compared to the closed state, and the transition occurs at a fast rate (≈1 s). A stretchable membrane is selectively coated to prevent unintended evaporation through the hydrogel while allowing swelling or shrinking of the hydrogel by securing path of water. Consequently, a 30% reduction in evaporation is observed at lower temperature, resulting in regulation of the skin temperature at the thermal model of human skins. This simple, small, and flexible cooler will be useful for maintaining temperature of flexible devices.
Perspiration, a cooling mechanism in nature, is mimicked in flexible membranes through programmed deformation of a thermoresponsive hydrogel microstructure. The pinwheel structure and mechanical constraint around its edge allow distinctive deformation for opening/closing operation. The artificial perspiration membrane can regulate the evaporation rate, which may help to solve thermal issues for artificial skin devices.
Highlights
A multiple-crosslinked poly(2-(methacryloyloxy)ethyl)dimethyl-(3-sulfopropyl)ammonium hydroxide-co-acrylamide multifunctional hydrogel was prepared via a one-pot synthesis method.
The ...proposed hydrogel exhibits water retention, antifreeze properties, self-healing, and transparency as well as improved strength, good adhesiveness, and a high gauge factor.
Flexible hydrogels are receiving significant attention for their application in wearable sensors. However, most hydrogel materials exhibit weak and one-time adhesion, low sensitivity, ice crystallization, water evaporation, and poor self-recovery, thereby limiting their application as sensors. These issues are only partly addressed in previous studies. Herein, a multiple-crosslinked poly(2-(methacryloyloxy)ethyl)dimethyl-(3-sulfopropyl)ammonium hydroxide-co-acrylamide) (P(SBMA-co-AAm)) multifunctional hydrogel is prepared via a one-pot synthesis method to overcome the aforementioned limitations. Specifically, ions, glycerol, and 2-(methacryloyloxy)ethyl)dimethyl-(3-sulfopropyl)ammonium hydroxide are incorporated to reduce the freezing point and improve the moisture retention ability. The proposed hydrogel is superior to existing hydrogels because it exhibits good stretchability (a strain of 2900%), self-healing properties, and transparency through effective energy dissipation in its dynamic crosslinked network. Further, 2-(methacryloyloxy)ethyl)dimethyl-(3-sulfopropyl)ammonium hydroxide as a zwitterion monomer results in an excellent gauge factor of 43.4 at strains of 1300–1600% by improving the ion transportability and achieving a strong adhesion of 20.9 kPa owing to the dipole–dipole moment. The proposed hydrogel is promising for next-generation biomedical applications, such as soft robots, and health monitoring.
Nonvolatile memory characteristics of the ferroelectric field-effect transistors (FeFETs) were investigated by introducing the metal-ferroelectric-metal-insulator-semiconductor (MFMIS) gate-stacks, ...employing Al-doped HfO 2 (Al:HfO 2 ) ferroelectric thin films. The obtained memory window (MW) of the MFMIS FETs increased from 1.0 to 2.8 V by increasing the areal ratios of the metal-insulator-semiconductor (MIS) to the metal-ferroelectric-metal (MFM) (S I /S F ) from 8 to 32. The device with an S I /S F ratio of 16 exhibited a 3-order-of-magnitude on/off memory margin even with a program pulse duration of 500 ns. The long-term data retention was also verified by improving the tolerance against the depolarization field by introducing the MFMIS gate-stacks, which can use fully saturated polarization. The temperature-dependent memory performance and operational reliabilities of the MFMIS-FETs were also investigated at high temperatures to exploit fully the thermal stability of the Al:HfO 2 . The obtained MWs were not markedly degraded for a retention time of 10 4 s from room temperature (RT) to 80 °C.
We present a simple, accurate open-circuit sensitivity model based on both analytically calculated lumped and empirically extracted lumped-parameters that enables a capacitive acoustic sensor to be ...efficiently characterized in the frequency domain at the wafer level. Our mixed model is mainly composed of two key strategies: the approximately linearized electric-field method (ALEM) and the open- and short-calibration method (OSCM). Analytical ALEM can separate the intrinsic capacitance from the capacitance of the acoustic sensor itself, while empirical OSCM, on the basis of one additional test sample excluding the membrane, can extract the capacitance value of the active part from the entire sensor chip. FEM simulation verified the validity of the model within an error range of 2% in the unit cell. Dynamic open-circuit sensitivity is modelled from lumped parameters based on the equivalent electrical circuit, leading to a modelled resonance frequency under a bias condition. Thus, eliminating a complex read-out integrated circuit (ROIC) integration process, this mixed model not only simplifies the characterization process, but also improves the accuracy of the sensitivity because it considers the fringing field effect between the diaphragm and each etching hole in the back plate.
Obesity has emerged as a prominent risk factor for the development of malignant tumors. However, the existing literature on the role of adipocytes in the tumor microenvironment (TME) to elucidate the ...correlation between obesity and cancer remains insufficient. Here, we aim to investigate the formation of cancer-associated adipocytes (CAAs) and their contribution to tumor growth using mouse models harboring dysfunctional adipocytes. Specifically, we employ adipocyte-specific BECN1 KO (BaKO) mice, which exhibit lipodystrophy due to dysfunctional adipocytes. Our results reveal the activation of YAP/TAZ signaling in both CAAs and BECN1-deficient adipocytes, inducing adipocyte dedifferentiation and formation of a malignant TME. The additional deletion of YAP/TAZ from BaKO mice significantly restores the lipodystrophy and inflammatory phenotypes, leading to tumor regression. Furthermore, mice fed a high-fat diet (HFD) exhibit decreased BECN1 and increased YAP/TAZ expression in their adipose tissues. Treatment with the YAP/TAZ inhibitor, verteporfin, suppresses tumor progression in BaKO and HFD-fed mice, highlighting its efficacy against mice with metabolic dysregulation. Overall, our findings provide insights into the key mediators of CAA and their significance in developing a TME, thereby suggesting a viable approach targeting adipocyte homeostasis to suppress cancer growth.
Metal–ferroelectric–metal (MFM) capacitors with Pt‐/Al‐doped HfO2 (Al:HfO2)/TiN structures are characterized to demonstrate the ferroelectricity of the Al:HfO2 thin films deposited by atomic layer ...deposition with H2O precursor at various annealing conditions. When the crystallization annealing temperature increases from 750 to 850 °C, the value of ferroelectric remnant polarization (2Pr) increases from 11.5 to 17.1 μC cm−2 for the postmetallization annealing (PMA) process, whereas it increases from 8.1 to 11.4 μC cm−2 for the postdeposition annealing (PDA) process. The variations in crystallinity of Al:HfO2 and interfacial properties between the electrodes are analyzed to explore the physical origins to initiate the differences in electrical properties of the MFM capacitors. Using the Al:HfO2 thin film prepared with PMA at 850 °C as a ferroelectric gate insulator, which exhibits a maximum value of 2Pr and polarization switching time as short as 1 μs, the ferroelectric field‐effect transistors (FeFETs) are fabricated with metal–ferroelectric–metal–insulator–semiconductor gate stack. The memory on/off ratios are secured to be 2.6 × 104 and 2.0 × 104 after a lapse of retention time of 105 s and after repeated program operations of 104 cycles, respectively.
Al‐doped HfO2 ferroelectric thin films prepared by atomic layer deposition with H2O oxygen source are verified to be feasible as ferroelectric gate insulators for nonvolatile memory field‐effect transistors (FETs) with metal–ferroelectric–metal–insulator–semiconductor (MFMIS) gate stack. The MFMIS–FET fabricated with optimum conditions exhibits robust retention and endurance performance due to good ferroelectric and interfacial properties of the MFMIS gate stack.
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