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The metallic glass with an amorphous structure can be a new approach for the electrode in flexible and stretchable electronics. In comparison with general crystalline metal, metallic glass has interesting mechanical and physical properties such as low Young's modulus (108GPa), hardness(5.91GPa), and high durability under mechanical stress. Also, we were able to enhance the mechanical property of metallic glass by adopting a multi-layer structure which is further investigated from our previous research. Using this metallic glass, we fabricated electronic skin that can mimic the pressure and temperature sensing ability of human skin. The pressure response of the sensor was studied with a wide range (from 100Pa to 5kPa), fast response (25ms), and good linearity in temperature response (0.22%/°C) with optimized NiTi/FeZr multi-layer structure. In this report, we present the feasibility of metallic glass as a stretchable electrode in soft electronics that also may find industrial applications in the health-care system, flexible sensors, and electronic skin for humanoid.

The various structures of ferroelectric tunnel junctions (FTJs) are widely studied. Among them, metal-ferroelectric-semiconductor (MFS) FTJs show great tunneling electroresistance (TER) ratio by forming a depletion region. However, the poor ferroelectricity of hafnia on semiconductor electrodes degrades the TER ratio. This study employed high-pressure annealing with forming gas to improve the ferroelectric properties of MFS FTJs. We achieved a high 2Pr value ( $47.54~\mu \text{c}$ /cm $^{2}$ ) and large TER ratio (22) in MFS FTJ for a 6 nm thick hafnia layer annealed at high pressure (200 atm) with forming gas. This work helps improve the quality of interface between a semiconductor and ferroelectric layer to increase the ferroelectricity of MFS stack devices.

Electrical and reliability characteristics of hafnia ferroelectric capacitor are influenced by a capping electrode layer which controls the type of stress and the amount of oxygen vacancy inside hafnia. Here, we present the impact of metal nitride and metal oxide electrode on the ferroelectricity of a Hf0.5Zr0.5O2 (HZO) capacitor. For comparison, we employed two different top electrodes (RuO2 and TiN) with hafnia ferroelectric layer, forming RuO2/HZO/TiN and TiN/HZO/TiN capacitors. The RuO2 top electrode provides additional oxygen to the HZO film, lowering the amount of oxygen vacancies in the film. From material analysis, we found that the top RuO2/HZO interface exhibits less oxygen vacancy in comparison to the top TiN/HZO interface. In addition, for RuO2/HZO/TiN, due to different thermal expansion coefficient between top and bottom electrodes, the HZO film experiences significant tensile stress, resulting in the high o-phase formation and remnant polarization ( $\sim 20~\mu \text{C}$ /cm2) as compared with that of TiN/HZO/TiN capacitor ( $\sim 13~\mu \text{C}$ /cm2). This article suggests an efficient solution to reduce the interfacial defects and oxygen vacancies as well as to enhance o-phase formation and ferroelectricity.

In this article, we report the fabrication of Zr-rich high- ${k}$ ferroelectric hafnium zirconium oxide (HZO) capacitor with TiN as the top and bottom electrodes demonstrating an equivalent oxide thickness (EOT) of 5.7 A and remanent polarization ( ${P}_{r}$ ) of $\sim 16~\mu \text{C}$ /cm2. High- ${k}$ value and low EOT was achieved by utilizing multiphase region of HZO as well as high pressure post metallization annealing (HPPMA). Despite the high- ${k}$ value of Zr-rich HZO films, the emergence of multiphase region at higher physical thickness when annealed using rapid thermal annealing (RTA) limits its EOT value. On the contrary, multiphase emerges at a smaller physical thickness in HPPMA due to the formation of more o-phase as revealed by grazing incidence X-ray diffractometer (GIXRD). The smaller physical thickness of HPPMA together with the demonstration of significantly higher dielectric constant (>50) by HZO in the vicinity of multiphase, was therefore, found to be very effective in reducing the EOT.

HfZrOx (HZO) materials exhibiting ferroelectricity in ultra-thin layers can be deposited in various ways. Specifically, in sputtered HZO layers, only weak ferroelectric switching with gradual transition and small remnant polarization ( $\text {P}_{\text {r}}$ ) is demonstrated using conventional rapid thermal annealing at high temperatures of at least 750 °C. Here we show that rapidly transited ferroelectric switching with a larger 2 Pr of $24~\mu $ C/cm2 is achieved by introducing a high pressure annealing (HPA) at even lower temperature of 550 °C. Our findings reveal that the HPA enhances the crystallinity of grains in the HZO, thereby enlarging the Pr and strengthening breakdown conditions. Through short pulse techniques, how interface and bulk region in the HZO are involved in the switching depending on the HPA is also investigated.

This article highlights the role of HfO2 seed/dielectric insertion layers on the ferroelectric properties of hafnium zirconium oxide (HZO)-based metal-ferroelectric-metal (MFM) capacitors. Maximum remanent polarization ( ${P}_{r}$ ) of $22.1~\mu \text{C}$ /cm2 was achieved when HfO2 seed layer of critical thickness (10 A) was inserted at the bottom of HZO films. However, as the bottom HfO2 seed layer thickness increases from 10 to 200 A, the ${P}_{r}$ was found to decrease. The same critical thickness of HfO2 seed layer when inserted at top of the HZO films was found to give a maximum ${P}_{r}$ of $19.6~\mu \text{C}$ /cm2. The obtained ${P}_{r}$ in both the cases (bottom and top HfO2 seed layer) was found to be better than the reference HZO device ( $17.7~\mu \text{C}$ /cm2). Moreover, increased coercive field $({E}_{c})$ was noticed due to the HfO2 seed layer insertion (1.11 MV/cm for bottom HfO2 and 1.09 MV/cm for top HfO2) when compared with the reference device (1.04 MV/cm). Short pulse switching measurements were carried out on the as-fabricated capacitors, and an enhanced ${E}_{c}$ and interfacial capacitance was observed in case of devices with HfO2 seed layer. The crystal structures, and interfacial layer effect was keenly observed and analyzed for the HZO films with and without the seed layer using grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS), respectively. The HfO2 seed layer was found to result in higher o-phase formation, and facilitates the diffusion/migration of oxygen atoms from seed layer to the substrate or vice versa in the HZO capacitors giving rise to enhanced ferroelectricity.

In this letter, we report excellent ferroelectricity with high remanent polarization (Pr) in Zr rich hafnium zirconium oxide (HZO) films using high pressure post metallization annealing (HPPMA). HZO films annealed using rapid thermal annealing (RTA) show highest ferroelectricity when the Hf:Zr ratio is 1:1 and exhibit antiferroelectric property for Zr rich films. However, under HPPMA, Zr rich films demonstrate enhanced ferroelectric property as compared to 1:1 HZO films and the best result was observed for 1:3 HZO films. The HZO (1:3) films by HPPMA show $\text{P}_{\text {r}}$ as high as $\sim ~29~\mu \text{C}$ /cm2, which is almost 50% higher than that achieved for the best condition of RTA ( $\text{P}_{\text {r}}~\sim ~19~\mu \text{C}$ /cm2). Besides, due to the presence of high Zr, the HZO (1:3) films by HPPMA exhibit considerably higher dielectric constant (k ~ 43) and low coercive field ( $\text{E}_{c}\sim 1.21$ MV/cm) as compared to that of HZO (1:1) films by RTA (k ~ 37, $\text{E}_{\text {c}}\sim ~1.35$ MV/cm). We believe the enhanced ferroelectricity in Zr rich HZO films can be due to more o/t-phase formation in ZrO2 under HPPMA as compared to that of RTA. On the other hand, more m-phase formation was observed in HfO2 under HPPMA, resulting in a significant drop of $\text{P}_{\text {r}}$ in case of Hf rich HZO. The demonstration of enhanced ferroelectric properties by Zr rich HZO films can be helpful for high functional semiconductor device applications.

Recently, hafnia-based ferroelectrics are currently being investigated as next-generation memory devices due to their excellent CMOS process compatibility and functionality. However, some of the ferroelectric devices commonly exhibit an imprint effect due to charged defects around the interfacial layer, which has negative impacts on the ferroelectric memory devices. However, it can be applied to various applications as long as the imprint field is carefully adjusted. In this work, we introduced a strategy to control the imprint field in bilayer capacitors by utilizing tantalum oxide (TaO) interfacial layers and various Zr contents in Hf0.83Zr0.17O2 (HZO) films. The TaO layer (1 nm) was inserted into the bilayer capacitors to alter the imprint field's (positive or negative) direction. Whereas to control the imprint fields, we adjusted the Zr doping content (17%–83%) in the ferroelectric HZO films (8 nm). As the Zr content increased, reduced imprint fields were observed in those bilayer capacitors. In addition, it was found that a high imprint field (+2.43 MV/cm) was observed in Hf-rich films (Hf0.83Zr0.17O2) due to the higher amount of oxygen vacancies. In addition, we examined those oxygen vacancies through x-ray photoelectron spectroscopy depth profile analysis by considering sub-oxide fractions in the tantalum, which further confirms the root cause of the imprint field variations in the bilayer capacitors. Our study will contribute to a deeper understanding of imprinted hafnia-based ferroelectrics and will provide an insight into devices that utilize the imprint effect.

Hafnia-based ferroelectric memory devices with excellent ferroelectricity, low power consumption, and fast operation speed have attracted considerable interest with the ever-growing desire for nonvolatile memory in flexible electronics. However, hafnia films are required to perform a high temperature (500 °C) annealing process for crystallization into the ferroelectric orthorhombic phase. It can hinder the integration of hafnia ferroelectric films on flexible substrates including plastic and polymer, which are not endurable at high temperatures above 300 °C. Here, we propose the extremely low-temperature (∼250 °C) process for crystallization of Hf

In the quest for highly scalable and three-dimensional (3D) stackable memory components, ferroelectric tunnel junction (FTJ) crossbar architectures are promising technologies for nonvolatile logic and neuromorphic computing. Most FTJs, however, require additional nonlinear devices to suppress sneak-path current, limiting large-scale arrays in practical applications. Moreover, the giant tunneling electroresistance (TER) remains challenging due to their inherent weak polarization. Here, we present that the employment of a diffusion barrier layer as well as a bottom metal electrode having a significantly low thermal expansion coefficient has been identified as an important way to enhance the strain, stabilize the ferroelectricity, and manage the leakage current in ultrathin hafnia film, achieving a high TER of 100, negligible resistance changes even up to 108 cycles, and a high switching speed of a few tens of nanoseconds. Also, we demonstrate that the usage of an imprinting effect in a ferroelectric capacitor induced by an ionized oxygen vacancy near the electrode results in highly asymmetric current-voltage characteristics with a rectifying ratio of 1000. Notably, the proposed FTJ exhibits a high density array size (>4k) with a securing read margin of 10%. These findings provide a guideline for the design of high-performance and selector-free FTJ devices for large-scale crossbar arrays in neuromorphic applications.

The passivation layers that should be formed on flexible electronics devices require high mechanical stability. Therefore, organic passivation has been used to enhance the electrical characteristics of various devices such as thin-film transistors (TFTs), organic light emitting diodes, and capacitors under mechanical stress. However, the conventional deposition of an organic film based on spin coating results in excessive thickness and the potential for chemical damage due to by-products such as organic solvents throughout the process. Here, we present the effects of a poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) organic passivation layer deposited by initiative chemical vapor deposition (iCVD) on the electrical and mechanical stabilities of oxide TFTs subjected to 30 000 repetitive tensile bending cycles. The highly ultrathin (50 nm) and excellent roughness (Rq = 0.33 nm) of the pV3D3 film assisted in preserving the mechanical stability of the device under external mechanical stress, and degradation of the electrical properties was suppressed compared with a device using SiO2 passivation. The mechanical properties of the type of passivation layer, including its Young’s modulus, affected the degradation of the electrical properties and reliability characteristics under repetitive bending. Finite-element structural simulations indicated a 15% reduction in equivalent stress applied to each layer of the device when pV3D3 (versus SiO2 passivation) was used. The iCVD-deposited pV3D3 film used in this study is a powerful candidate to act as the passivation layer of flexible electronics by strengthening the electrical stability of a device under external mechanical stress.

A self-organized n+/n homojunction is proposed to achieve ultrahigh performance of thin film transistors (TFTs) based on an amorphous (Zn,Ba)SnO3 (ZBTO) semiconductor with sufficiently limited scattering centers. A deposited Al layer can induce a highly O-deficient (n+) interface layer in the back channel of a-ZBTO without damaging the front channel layer via the formation of a metal-oxide interlayer between the metal and back channel. The n+ layer can significantly improve the field-effect mobility by providing a relatively high concentration of free electrons in the front n-channel ZBTO, where the scattering of carriers is already controlled. In comparison with a Ti layer, the Al metal layer is superior, as confirmed by first-principles density functional theory (DFT) calculations, due to the stronger metal-O bonds, which make it easier to form a metal oxide AlOx interlayer through the removal of oxygen from ZBTO. The field-effect mobility of a-ZBTO with an Al capping layer can reach 153.4 cm2/Vs, which is higher than that of the pristine device, i.e., 20.8 cm2/Vs. This result paves the way for the realization of a cost-effective method for implementing indium-free ZBTO devices in various applications, such as flat panel displays and large-area electronic circuits. A layer of aluminum improves the performance of electronic devices useful for high-resolution flat displays, according to researchers in South Korea. Thin-film transistors are ultrafast electrical switches comprising stacked layers of semiconductors, metals and oxide materials. Their tiny size and planar architecture make them useful for large-area electronics and displays. A key performance metric for these devices is mobility: a measure of how quickly a charged particle can move through the semiconductor. Ji-Min Park from Chungnam National University in Daejeon and colleagues have shown how adding a capping layer of a highly oxidizing metal such as aluminum can greatly enhance the mobility of zinc barium tin oxide thin-film transistors. This cost-effective and useful improvement was achieved without introducing significant defects into the semiconductor. The formation of the conductive region (n+ layer) in (Zn,Ba)SnO3 (ZBTO) semiconductor is proposed to achieve high performance of thin-film transistors (TFTs). The aluminum metal capping layer is adopted to enhance the field-effect mobility of ZBTO TFTs. The capped Al layer takes out oxygen in the back-channel region, where the AlOx interlayer is formed. As a result, the field-effect mobility of Al-capped ZBTO TFTs is remarkably increased from 20.8 to 153.4 cm2/Vs. Furthermore, the Al-capped ZBTO TFTs are stable even when exposed to air for 3 months.

Recently, hafnia ferroelectrics with two spontaneous polarization states have attracted marked attention for non-volatile, super-steep switching devices, and neuromorphic application due to their fast switching, scalability, and CMOS compatibility. However, field cycling-induced instabilities are a serious obstacle in the practical application of various low-power electronic devices that require a settled characteristic of polarization hysteresis. In this work, a large reduction in the field cycling-induced instabilities and significantly improved ferroelectric properties were observed in a Hf0.5Zr0.5O2 (HZO) thin film with a RuO2 oxide electrode. The oxide electrode can supply additional oxygen to the HZO film, consequently minimizing the oxygen vacancies at the interface which is the origin of low reliability. From the material and electrical analysis results, we verified that HZO with the RuO2 electrode has less non-ferroelectric dead layers and fewer oxygen vacancies at the interface, resulting in excellent switching properties and improved reliability. This result suggests a beneficial method to produce high-quality hafnia thin films free from interfacial defects and with stable field cycling electrical properties for actual applications.

Recently, dielectric/ferroelectric (DE/FE) bilayer systems have been extensively investigated for achieving high remanent polarization in Hf 0.5 Zr 0.5 O 2 (HZO) based MFM capacitors. Herein, we report significant enhancement in the ferroelectric property of HZO capacitors by incorporating Ta 2 O 5 as the dielectric seed layer. Thickness of the Ta 2 O 5 layer was incorporated at both top and bottom of the HZO films and the thickness of the seed layer was varied from 10 to 50 A. When the Ta 2 O 5 dielectric films were inserted at the top, the highest remanent polarization ~ $\mathbf{16.83}\ \mu\mathbf{C}/\mathbf{cm}^{\mathbf{2}}$ was observed in case of 20 A films as compared to that of ~ $\mathbf{13.21}\ \mu\mathbf{C}/\mathbf{cm}^{\mathbf{2}}$ of the reference HZO device. Similarly, for bottom Ta 2 O 5 dielectric films, the highest remanent polarization ~ $\mathbf{15.24}\ \mu\mathbf{C}/\mathbf{cm}^{\mathbf{2}}$ was observed in case of 20 A films. When we compared both the stacks, the best result was observed in case of top Ta 2 O 5 . The coercive field $(\mathbf{E}_{\mathbf{c}})$ was also found to be nearly same with the HZO based device despite the incorporation of the dielectric layer. The enhanced ferroelectricity of these devices can be used in memory devices, FeFETs, FTJ and sensors applications.

In recent years, hafnium zirconium oxide (HZO) has received significant attention of the research community due to the demontsrattion of ferroelectricity at sub 10 nm thickness and good CMOS-compatibility. However, ferroelectricity in HZO is dependent on various factors such as the HZO composition, materials used as top or bottom electrode, post metallization technique, annealing pressure and temperature etc. Herein, we have systematically investigated the effect of high pressure post metallization annealing (HPPMA) temperature on the ferroelectric properties of TiN/Hf 0.25 Zr 0.75 O 2 /TiN capacitors. Hf 0.25 Zr 0.75 O 2 , that show antiferroelectric behavior in rapid thermal annealing, demonstrate antiferroelectric to ferroelectric phase transition depending on the HPPMA temperature. Maximum remanent polarization (P r ) of ~29μC/cm2 is achieved for HPPMA temperature 550 °C whereas the maximum dielectric constant (k) of ~46 is achieved for HPPMA temperature 350 °C. The interfacial capacitance of the MFM capacitors increased with increasing the HPPMA annealing temperature. The results obtained in this study open up the possibility of achieving high-k ferroelectric capacitors using Zr rich HZO films that can be applicable to various electronic devices.

In this work, we demonstrate the development of a flexible self-powered pressure sensor with silk-based substrate. Silk is the thinnest and toughest fiber that can be obtained from nature. Based on these noble properties, its applications for health-care, human-machine interface, and humanoid robotics are highly desired. The synthesized film with silk and poly (vinylidene fluoride-co-trifluoro ethylene) shows piezoelectric coefficient of 6.24pm/V with transmittance up to 88% within visible light range(400~700nm). The obtained sensor shows remarkable linearity with sensitivity of 70Pa−1 in wide range (~500kPa) and high durability over 10,000 times repeated loading/unloading cycles.

Borage oil (BO) reverses a disrupted epidermal lipid barrier and hyperproliferation in essential fatty acid deficiency (EFAD). However, little is known about its effect on skin pH, which is maintained by epidermal lactate, free fatty acids (FFAs), and free amino acids (FAAs) which is generated by lactate dehydrogenase (LDH), secreted phospholipase A2 (sPLA2), or filaggrin degradation with peptidylarginine deiminase-3 (PADI3). We hypothesized that BO restores skin pH by regulating epidermal lactate, FFA metabolism, or FAA metabolism in EFAD. To test this hypothesis, EFAD was induced in guinea pigs by a hydrogenated coconut oil (HCO) diet for 8 weeks, followed by 2 weeks of a BO diet (group HCO + BO). As controls, groups HCO and BO were fed HCO or BO diets for 10 weeks. In group HCO + BO, skin pH, which was less acidic in group HCO, was restored; and epidermal lactate and total FFAs, including palmitate, stearate, linoleate, arachidate, behenate, and lignocerate, were higher than in group HCO. LDH and sPLA2 (mainly the PLA2G2F isoform) activities and protein expressions were similar between groups HCO + BO and BO. Epidermal acidic FAAs, as well as filaggrin and PADI3 protein and mRNA expressions were higher in group HCO + BO than in group HCO. Oleate, total FAAs including other FAAs, and LDH and sPLA2 mRNA expressions were not altered between groups HCO and HCO + BO. Basic FAAs were not altered among groups. Dietary BO restored acidic skin pH and increased epidermal levels of lactate, most FFAs, and acidic FAAs by up-regulating LDH, sPLA2, filaggrin, and PADI3 activities as well as protein or mRNA expressions in EFAD.

Magnetically manipulated biodegradable microrobots that encapsulate drugs from the outset are produced in a novel, simple way using UV-laser micro-machining. This method enables multiple microrobots to be produced rapidly, without the need for post-drug encapsulation or polymerization by light exposure, which may cause the drug compound to denature. The microrobot consists of poly (dl-lactic-co-glycolic acid) (PLGA), iron (Fe) particles and 5-fluorouracil (5-FU) as biodegradable, magnetic and drug material, respectively. The fabricated microrobots are precisely and remotely controlled in a fluidic environment by external magnetic fields. To prove the feasibility of targeted drug delivery, the drug release is profiled as a function of time, biodegrading in aqueous solution at 37 °C over 6 weeks. The Fe concentration has a significant effect on the biodegradation rate of the microrobots. The amount of drug encapsulated can be controlled by adjusting the concentration of the drug in the PLGA/Fe/5-FU mixture whilst fabricating the microrobots. Approximately 0.013 μg of 5-FU is released from a single PLGA/Fe/5-FU microrobot over a period of 6 weeks. In addition, we have conducted drug testing with human colorectal cancer (HCT116) cells to investigate the effect of drugs released from our microrobots on cancer cells. While no significant reduction in live cell ratio was observed with the controls, it decreased approximately 20% when cells were cultured with the PLGA/Fe/5-FU microrobot for 2 days. It presents that 5-FU was delivered from the microrobot to cancer cells and negatively affected them.

Defects in amorphous oxide thin-film transistor (TFT) influence major transistor parameters such as the threshold voltage, mobility, and subthreshold slope. Thus, understanding these defects is crucial in securing high-reliability and high-performance devices. However, only very limited electrical analysis methods such as multifrequency ${C}$ – ${V}$ and temperature-dependent ${I}$ – ${V}$ methods have been applied to accumulation mode devices and these do not provide direct pictures of the defects during carrier transport. In this investigation, we employed the discharging current analysis method to attain quantitative information involving the defect densities of amorphous hafnium–indium–zinc–oxide (a-HIZO) TFT. We were able to estimate the number of defect sites of a-HIZO TFT as being of the order of 1018/cm 3 , although this is dependent on the Hf content. We believe that this method can be widely used to estimate the defect density of oxide TFTs.

Atomic switches are well-known promising candidates for future application in non-volatile logic memory devices. The resistive switching characteristics of these devices depend on the formation of a conductive filament (CF) by active metal electrodes. However, the formation of a stable CF is still a challenge owing to filament overgrowth in the solid electrolyte. To achieve controlled CF growth, we have used a modified active electrode with different CuxSe1−x composition ratios (0.01 Se modified active electrode by the means of Ti buffer layer and the Ti O bond formation at the Ti/Al2O3 interface. In addition, depth profiles of the conductive filament based on Cu0.11Se0.89 with a Ti buffer layer were studied by performing current atomic force microscopy (I-AFM) to evaluate the enhancements in electrical performance and reliability resulting from the insertion of the Ti buffer layer.

The next-generation electronic society is dependent on the performance of nonvolatile memory devices, which has been continuously improving. In the last few years, many memory devices have been introduced. However, atomic switches are considered to be a simple and reliable basis for next-generation nonvolatile devices. In general, atomic switch-based resistive switching is controlled by electrochemical metallization. However, excess ion injection from the entire area of the active electrode into the switching layer causes device nonuniformity and degradation of reliability. Here, we propose the fabrication of a high-performance atomic switch based on Cux–Se1–x by inserting lanthanide (Ln) metal buffer layers such as neodymium (Nd), samarium (Sm), dysprosium (Dy), or lutetium (Lu) between the active metal layer and the electrolyte. Current-atomic force microscopy results confirm that Cu ions penetrate through the Ln-buffer layer and form thin conductive filaments inside the switching layer. Compared with t...

Wearable sensor systems with ultra-thinness, light weight, high flexibility, and stretchability that are conformally in contact with the skin have advanced tremendously in many respects, but they still face challenges in terms of scalability, processibility, and manufacturability. Here, we report a highly stretchable and wearable textile-based self-powered temperature sensor fabricated using commercial thermoelectric inks. Through various combinations of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), silver nanoparticles (AgNPs), and graphene inks, we obtained linear temperature-sensing capability. The optimized sensor generates a thermoelectric voltage output of 1.1 mV for a temperature difference of 100 K through a combination of PEDOT:PSS and AgNPs inks and it shows high durability up to 800 cycles of 20% strain. In addition, the knitted textile substrate exhibits temperature-sensing properties that are dependent upon the stretching directions. We believe that stretchable thermoelectric fabric has broader potential for application in human-machine interfaces, health-monitoring technologies, and humanoid robotics.

Electronic skin, which has pixels composed of various functional sensors and can be applied to robots and various medical devices by mimicking the human skin, requires flexible, multi-mode, high-sensitivity, and low-interference sensors. In this study, we used a flexible electrode material comprised of organic conductor-elastomer-metal nanoparticles, as the core material and the inkjet printing method as the core process. These were used to form a flexible sensor for electronic skin applications, which involved vertically laminated sensors that utilize different sensing principles, thus enabling the realization of a flexible bimodal sensor with negligible interference. The pressure sensor with low resistivity and a flexible electrode, which was implemented using the sophisticated synthesis method, performed well under low-voltage (0.5 mV) operation conditions, exhibited pressure sensitivity over a wide range (3 Pa to 5 kPa), and showed excellent reliability characteristics (100,000 cycles) that can withstand severe mechanical stress. The temperature sensor, which was formed by a long bent organic conductor-metal line, changes its resistance with temperature, has a resistance change sensitivity of 0.32% per degree of temperature change, and exhibits a hysteresis-free temperature sensing capability. In particular, this device has maintained its robustness even over 5000 bending cycles. The 25 pixels temperature-pressure bimodal sensor array demonstrates very fast response rates, high sensitivity, and negligible interference performance. The low-resistivity/high-flexibility conducting electrode, inkjet printing process, device architecture, and integration scheme proposed in this study are expected to be widely used for electronic skin, multi-mode sensors, and flexible devices.

Amorphous oxide semiconductor-based thin film transistors (TFTs) have been considered as excellent switching elements for driving active-matrix organic light-emitting diodes (AMOLED) owing to their high mobility and process compatibility. However, oxide semiconductors have inherent defects, causing fast transient charge trapping and device instability. For the next-generation displays such as flexible, wearable, or transparent displays, an active semiconductor layer with ultrahigh mobility and high reliability at low deposition temperature is required. Therefore, we introduced high density plasma microwave-assisted (MWA) sputtering method as a promising deposition tool for the formation of high density and high-performance oxide semiconductor films. In this paper, we present the effect of the MWA sputtering method on the defects and fast charge trapping in In-Sn-Zn-O (ITZO) TFTs using various AC device characterization methodologies including fast I-V, pulsed I-V, transient current, low frequency noise, and discharge current analysis. Using these methods, we were able to analyze the charge trapping mechanism and intrinsic electrical characteristics, and extract the subgap density of the states of oxide TFTs quantitatively. In comparison to conventional sputtered ITZO, high density plasma MWA-sputtered ITZO exhibits outstanding electrical performance, negligible charge trapping characteristics and low subgap density of states. High-density plasma MWA sputtering method has high deposition rate even at low working pressure and control the ion bombardment energy, resulting in forming low defect generation in ITZO and presenting high performance ITZO TFT. We expect the proposed high density plasma sputtering method to be applicable to a wide range of oxide semiconductor device applications.

We propose a HfZrO x (HZO)-based ferroelectric synapse device with multi-levels states of remnant polarization that is equivalent to multi-levels conductance states. By optimizing the pulse condition, we obtained 32 levels of remnant polarization states for both potentiation and depression. Furthermore, a ferroelectric field-effect transistor is simulated using the obtained multiple remnant polarization states. The simulation results show that linear and symmetric conductance states can be obtained by applying optimum potentiation and depression pulse conditions. A neural network was simulated using the proposed devices for pattern recognition. Using synapse parameters of the HZO-based ferroelectric device and a neural network simulator, we have confirmed that the pattern recognition accuracy of the MNIST data set is 84%. It shows that the HZO-based synapse device has potential for future high-density neuromorphic systems.

Amorphous InHfZnO (a-IHZO) thin-film devices have attracted considerable attention owing to their high mobility. However, the mobility of a-IHZO thin-film transistors has not been correctly determined, because it is affected by fast charging. In this letter, we investigated the effect of transient charging on the mobility. On the basis of the pulse IDS-VGS method, we present an approach to estimate a correction factor for the measured apparent mobility, which was extracted from pulse amplitude versus threshold voltage shift.

Paper-based electronic devices are attracting considerable attention, because the paper platform has unique attributes such as flexibility and eco-friendliness. Here we report on what is claimed to be the firstly fully integrated vertically-stacked nanocellulose-based tactile sensor, which is capable of simultaneously sensing temperature and pressure. The pressure and temperature sensors are operated using different principles and are stacked vertically, thereby minimizing the interference effect. For the pressure sensor, which utilizes the piezoresistance principle under pressure, the conducting electrode was inkjet printed on the TEMPO-oxidized-nanocellulose patterned with micro-sized pyramids, and the counter electrode was placed on the nanocellulose film. The pressure sensor has a high sensitivity over a wide range (500 Pa–3 kPa) and a high durability of 104 loading/unloading cycles. The temperature sensor combines various materials such as poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS), silver nanoparticles (AgNPs) and carbon nanotubes (CNTs) to form a thermocouple on the upper nanocellulose layer. The thermoelectric-based temperature sensors generate a thermoelectric voltage output of 1.7 mV for a temperature difference of 125 K. Our 5 × 5 tactile sensor arrays show a fast response, negligible interference, and durable sensing performance.

Hf0.5Zr0.5O2 (HfZrO) thin-film ferroelectric materials have recently drawn considerable attention due to their attractive properties such as large bandgap (>5 eV), extreme thin thickness ( ${\le} 10$ nm), and good Si-compatibility. However, high crystallization temperature (600 °C–1000 °C) and relatively low remanent polarization ( ${P}_{r}$ ) compared to conventional perovskite ferroelectric materials are not suitable for flexible energy related devices, and are insufficient to overcome the barriers of conventional ferroelectric memory. In this paper, we investigated the effect of high-pressure postmetallization annealing (HPPMA) on the ferroelectric properties of the HfZrO metal–ferroelectric–metal (MFM) devices. HfZrO MFM capacitors annealed at 450 °C/50 bar shows a ${P}_{r}$ value of over 20 $\mu \text{C}$ /cm2 which is very advanced ${P}_{r}$ value. Based on the short-pulse switching technique, we quantitatively and systematically examined the improved characteristics of HfZrO prepared by HPPMA in terms of coercive field ( ${E}_{c}$ ) and possibly involved interfacial capacitance ( ${C}_{i}$ ).

An amorphous InZnO/MoS

Transparent and conducting flexible electrodes have been successfully developed over the last few decades due to their potential applications in optoelectronics. However, recent developments in smart electronics, such as a direct human-machine interface, health-monitoring devices, motion-tracking sensors, and artificially electronic skin also require materials with multifunctional properties such as transparency, flexibility and good portability. In such devices, there remains room to develop transparent and flexible devices such as pressure sensors or temperature sensors. Herein, we demonstrate a fully transparent and flexible bimodal sensor using indium tin oxide (ITO), which is embedded in a plastic substrate. For the proposed pressure sensor, the embedded ITO is detached from its Mayan-pyramid-structured silicon mold by an environmentally friendly method which utilizes water-soluble sacrificial layers. The Mayan-pyramid-based pressure sensor is capable of six different pressure sensations with excellent sensitivity in the range of 100 Pa-10 kPa, high endurance of 105 cycles, and good pulse detection and tactile sensing data processing capabilities through machine learning (ML) algorithms for different surface textures. A 5 × 5-pixel pressure-temperature-based bimodal sensor array with a zigzag-shaped ITO temperature sensor on top of it is also demonstrated without a noticeable interface effect. This work demonstrates the potential to develop transparent bimodal sensors that can be employed for electronic skin (E-skin) applications.

In recent years, MoS2 has emerged as a prime material for photodetector as well as phototransistor applications. Usually, the higher density of state and relatively narrow bandgap of multi-layer MoS2 give it an edge over monolayer MoS2 for phototransistor applications. However, MoS2 demonstrates thickness-dependent energy bandgap properties, with multi-layer MoS2 having indirect bandgap characteristics and therefore possess inferior optical properties. Herein, we investigate the electrical as well as optical properties of single-layer and multi-layer MoS2-based phototransistors and demonstrate improved optical properties of multi-layer MoS2 phototransistor through the use of see-through metal electrode instead of the traditional global bottom gate or patterned local bottom gate structures. The see-through metal electrode utilized in this study shows transmittance of more than 70% under 532 nm visible light, thereby allowing the incident light to reach the entire active area below the source and drain electrodes. The effect of contact electrodes on the MoS2 phototransistors was investigated further by comparing the proposed electrode with conventional opaque electrodes and transparent IZO electrodes. A position-dependent photocurrent measurement was also carried out by locally illuminating the MoS2 channel at different positions in order to gain better insight into the behavior of the photocurrent mechanism of the multi-layer MoS2 phototransistor with the transparent metal. It was observed that more electrons are injected from the source when the beam is placed on the source side due to the reduced barrier height, giving rise to a significant enhancement of the photocurrent.

Thin films of ferroelectric materials are potential candidates to be implemented in the unfolding of a new paradigm in high-density memory devices. As the thickness of these films reaches the sub-10 nm level, the interface properties between the electrode and ferroelectric material undergo significant changes that play a crucial role in governing the ferroelectric behavior. The present state-of-the-art approach presents a detailed investigation of different high pressure annealing (HPA) conditions through simulation studies. The simulation studies were performed using Landau-Khalatnikov equations, with Landau's parameters calculated using the least regression method as described in the Method S1. The extracted coefficients were used to determine various relationships (free energy, ferroelectric potential and negative capacitance) with which to observe the impact of HPA on the negative capacitance (NC) effect on account of the majority ferroelectric phase. To verify the simulation results, pulse transient switching measurements were conducted using Pt/Ti/TiN/Hf

Flexible sensors have been developed over the decades due to their potential in various applications. However, recent developments in interactive user interface, healthcare device, tactile sensor, and artificial electronic skin require device with multifunctional properties such as various detection ability and good mobility. Research on such devices are still under developing. In this report, we demonstrate a flexible multimodal (pressure, temperature) sensor using embedded indium tin oxide (ITO). For the pressure sensor, the embedded ITO was adopted as a conductive layer with triple layer pyramid structure. We utilized water-soluble sacrificial layers for eco-friendly method. The triple layer pyramid-structured pressure sensor shows excellent sensitivity in dynamic range of 100 Pa to 10 kPa with high reliability of 105 cycles. For the temperature sensor, we used comb like structure with ITO. It shows negative temperature coefficient on resistance with good linearity. Due to the vertically stacked structure, we were able to ignore interface effect. This work present that the opportunity of transparent electrode towards flexible multimodal sensors that can beemployed for various flexible applications.

The Metallic glass which is having no crystal structure, can be adopted for enhance strength and a lower Young's modulus. Unlike crystalline metals, metallic glass can be used as an electrode in flexible, soft electronics. The external energy causes structural deformations in the metal with lattice structure, while a metallic glass disperses the energy. Therefore, the limitations of crystalline metals can be overcome by the metallic glass. However, void structure can be easily formed inside of the metal with Thornton’s model. To eliminate the porosity, we were able to control the sputtering condition of metal atoms and ions. Elastic modulus of 76.6GPa and a strength of 2.88GPa was achieved by optimized Fe 33 Zr 67 which has an amorphous structure. With this metallic glass, we fabricated a multi-functional sensor for electronic skin that can detect stimuli of pressure, temperature and light and also function as a heater. In this paper, we convinced the feasibility of the Fe 33 Zr 67 metallic glass in soft electronics for various industrial applications.

Investigation of the polarization switching mechanism in ferroelectric hafnium zirconium oxide (HZO) film is of great importance for developing high-quality ferroelectric memory devices. Recently, several works have been reported to describe the switching process of polycrystalline HZO film using the inhomogeneous field mechanism (IFM) model. However, no report has recorded the effect of high pressure annealing (HPA) on the polarization switching process. In this paper, we have carried out a careful investigation on the switching properties of HZO capacitors annealed at 600 °C with various high pressure conditions (1, 50, and 200 atm) using the IFM model. As pressure increases to 200 atm, the ferroelectric properties were enhanced in the HZO films, and, as a result, highest remanent polarization (Pr of 24.5 μC/cm2) was observed when compared with 1 and 50 atm. Similarly, as HPA increases, the HZO capacitors showed a decrement of the coercive field, which significantly improved the switching properties. The time consumed for reversing 80% polarization was 113.1, 105.7, and 66.5 ns for the sample annealed at 1, 50, and 200 atm, respectively. From the IFM model, the smallest active field (2.997 MV/cm) and a uniform distribution of the local electric field (0.304) were observed at 200 atm. Furthermore, the characteristic time constant ( τ 0 ) showed a decreasing trend (34.7, 18.1, and 11.7 ps) with increasing HPA. The improved switching properties and detailed findings recorded in this study may be helpful for developing the ferroelectric hafnia based non-volatile memory applications.

Hydrogen plays a crucial role in several oxide semiconductors, where the amount of hydrogen significantly influences the device performance. Thus, its manipulation in oxide semiconductors is important for device performance. In our investigation, we studied the effect of hydrogen on defects in In–Ga–Zn–O semiconductor thin-film transistors (TFTs), as it varies with Al2O3 atomic layer deposition temperature. We found that the total trap-density ( $N_{{\text {tot}}}$ ) extracted by the sub-threshold slope and the trap density ( $N_{t}$ ) measured by low-frequency noise (LFN) as well as the density-of-states analyzed by capacitance–voltage decreased with increasing amounts of hydrogen in the oxide semiconductor. Given that LFN data show that mobility fluctuation is the major origins of noise and the front channel of TFT is a major carrier transport region, our results indicate that hydrogen effectively passivates the defects in front channel of oxide semiconductor and contributes to achieving superior device performance.

Described herein is the role of hydrogen in aluminum oxide (Al2O3) gate dielectrics in amorphous indium–gallium–zinc oxide (a-InGaZnO or a-IGZO) thin-film transistors (TFTs). Compared to a-IGZO TFTs with a low-temperature (150°C) Al2O3 gate dielectric, a-IGZO devices with a high-temperature (250–300°C) Al2O3 gate dielectric exhibit poor transistor characteristics, such as low mobility, a high subthreshold slope, and huge hysteresis. Through DC and short-pulsed current–voltage (I–V) measurements, it was revealed that the degradation of the transistor performance stems from the charging and discharging phenomenon at the interface traps located in the interface between the a-IGZO semiconductor and the Al2O3 gate insulator. It was found that the low-temperature Al2O3 atomic layer deposition processed film contains a higher density of hydrogen atoms compared to high-deposition-temperature films. The study results show that a high concentration of hydrogen atoms can passivate the defect sites in the int...

We report on 4.5-nm-thick Hf0.5Zr0.5O2 (HZO) thin-film-based ferroelectric tunnel junctions (FTJs) with a tungsten (W) bottom electrode. The HZO on the W electrode exhibits stable ferroelectricity with a remanent polarization of 14 μC/cm2, an enhanced tunneling electroresistance of 16, and excellent synaptic properties. We found that a large tensile stress was induced on a HZO thin film, owing to a low thermal expansion coefficient of the W bottom electrode. The low thermal expansion coefficient results in the effective formation of an orthorhombic phase, even in an ultra-thin HZO film. This was verified by a comparative study of the electrical characteristics, grazing-angle incidence x-ray diffraction, and residual stress measurement of the HZO film on various bottom electrodes with different thermal expansion coefficients. In addition, this study demonstrates the suitable functions of the FTJ for electronic synapses, such as analog-like resistance transition under various pulse schemes. The fabricated stress-engineered FTJ exhibits an appropriate conductance ratio, linearly modulated long-term potentiation and depression characteristics, and excellent reliability. These characteristics render FTJs ideal electronic devices for neuromorphic computing systems.

Oxide semiconductor TFTs have attracted considerable attention in the recent past due to their excellent mobility, high optical transparency in the visible region, and most importantly their fabrication process at low-temperature. However, charge trapping formation in the gate dielectric and the interfaces in such oxide TFTs leads to serious issues such as their operational stability and reliability. Understanding the charge trapping mechanism is therefore of utmost importance to identify the root cause of the aforesaid problems. In this report, we present a detailed study on the charge trapping and dynamic charge transport of a-IGZO TFTs by examining microsecond fast IV (FIV), pulse IV (PIV), and transient IV measurements. The a-IGZO TFTs have designed and fabricated with various Ga compositions (0, 0.14 and 0.22). It was observed that the charge trapping in the a-IGZO TFT is reliant on the sweeping time and the carrier mobility measured using the FIV technique was found to be higher than that obtained from the conventional DC IV measurement. Mobility values ( μ m ) was also measured through the PIV technique and are found to be approximately 10%, 16%, and 21% lower than the intrinsic mobility values. Temperature-dependent study reveals that the intrinsic mobility values (18.45, 16.1 and 12.03 cm2 V−1 s−1) are higher than the pulse mobility values for various Ga compositions (0, 0.14 and 0.22) at higher temperature (175 °C) probably due to the formation of free carriers. Suitable optimization of process parameters of a-IGZO TFTs can therefore enhance the device stability and reliability characteristics leading to their potential utilization in flexible and stretchable electronic devices, sensors & detectors and biomedical devices.

Recently, negative capacitance (NC) effect in the dielectric/ferroelectric (DE/FE) bilayer system has received significant attention due to its potential in achieving sub- 60 mV/decade subthreshold swing in FETs as well as extremely large capacitance density in dynamic random-access memory (DRAM). However, such reports, to date, are primarily based on conventional perovskite FE materials which are not compatible with the present CMOS technology. Herein, we study the interfacial charge density ( σ i ) and negative capacitance (NC) effect in CMOS compatible Hf-Zr-Al-O (DE) /Hf0.5Zr0.5O2 (FE) bilayer system. The DE layer of various thicknesses (5–20 A) was deposited on the top of FE layer (100 A) and the DE layer thickness was found to play a crucial role in determining σ i . The NC effect in the aforesaid DE/FE system was suppressed due to the contribution of σ i . The σ i at the interface of the DE layer and FE layer was found to be in the range of −0.57 Cm−2 to −0.18 Cm−2 for the DE thickness range of 5–20 A.