Chun-Ho Lin

ALL-PRINTED PAPER MEMORY

We report the memory device on paper by means of an all-printing approach. Using a sequence of inkjet and screen-printing techniques, a simple metal–insulator–metal device structure is fabricated on paper as a resistive random access memory with a potential to reach gigabyte capacities on an A4 paper. The printed-paper-based memory devices (PPMDs) exhibit reproducible switching endurance, reliable retention, tunable memory window, and the capability to operate under extreme bending conditions. In addition, the PBMD can be labeled on electronics or living objects for multifunctional, wearable, on-skin, and biocompatible applications. The disposability and the high-security data storage of the paper-based memory are also demonstrated to show the ease of data handling, which are not achievable for regular silicon-based electronic devices. We envision that the PPMDs manufactured by this cost-effective and time-efficient all-printing approach would be a key electronic component to fully activate a paper-based circuit and can be directly implemented in medical biosensors, multifunctional devices, and self-powered systems.

Highly Deformable Origami Paper Photodetector Arrays

Flexible electronics will form the basis of many next-generation technologies, such as wearable devices, biomedical sensors, the Internet of things, and more. However, most flexible devices can bear strains of less than 300% as a result of stretching. In this work, we demonstrate a simple and low-cost paper-based photodetector array featuring superior deformability using printable ZnO nanowires, carbon electrodes, and origami-based techniques. With a folded Miura structure, the paper photodetector array can be oriented in four different directions via tessellated parallelograms to provide the device with excellent omnidirectional light harvesting capabilities. Additionally, we demonstrate that the device can be repeatedly stretched (up to 1000% strain), bent (bending angle ±30°), and twisted (up to 360°) without degrading performance as a result of the paper folding technique, which enables the ZnO nanowire layers to remain rigid even as the device is deformed. The origami-based strategy described herein suggests avenues for the development of next-generation deformable optoelectronic applications.

Photostriction of CH3NH3PbBr3 Perovskite Crystals

Organic-inorganic hybrid perovskite materials exhibit a variety of physical properties. Pronounced coupling between phonon, organic cations, and the inorganic framework suggest that these materials exhibit strong light-matter interactions. The photoinduced strain of CH3 NH3 PbBr3 is investigated using high-resolution and contactless in situ Raman spectroscopy. Under illumination, the material exhibits large blue shifts in its Raman spectra that indicate significant structural deformations (i.e., photostriction). From these shifts, the photostrictive coefficient of CH3 NH3 PbBr3 is calculated as 2.08 × 10-8 m2 W-1 at room temperature under visible light illumination. The significant photostriction of CH3 NH3 PbBr3 is attributed to a combination of the photovoltaic effect and translational symmetry loss of the molecular configuration via strong translation-rotation coupling. Unlike CH3 NH3 PbI3 , it is noted that the photostriction of CH3 NH3 PbBr3 is extremely stable, demonstrating no signs of optical decay for at least 30 d. These results suggest the potential of CH3 NH3 PbBr3 for applications in next-generation optical micro-electromechanical devices.

Surface effects of electrode-dependent switching behavior of resistive random-access memory

The surface effects of ZnO-based resistive random-access memory (ReRAM) were investigated using various electrodes. Pt electrodes were found to have better performance in terms of the devices switching functionality. A thermodynamic model of the oxygen chemisorption process was proposed to explain this electrode-dependent switching behavior. The temperature-dependent switching voltage demonstrates that the ReRAM devices fabricated with Pt electrodes have a lower activation energy for the chemisorption process, resulting in a better resistive switching performance. These findings provide an in-depth understanding of electrode-dependent switching behaviors and can serve as design guidelines for future ReRAM devices.

Surface-Controlled Metal Oxide Resistive Memory

To explore the surface effect on resistive random-access memory (ReRAM), the impact of surface roughness on the characteristics of ZnO ReRAM was studied. The thickness-independent resistance and the higher switching probability of ZnO ReRAM with rough surfaces indicate the importance of surface oxygen chemisorption on the switching process. Furthermore, the improvements in switching probability, switching voltage, and resistance distribution observed for ReRAM with rough surfaces can be attributed to the stable oxygen adatoms under various ambience conditions. The findings validate the surface-controlled stability and the uniformity of ReRAM and can serve as the guideline for developing practical device applications.

A flexible solar-blind 2D boron nitride nanopaper-based photodetector with high thermal resistance

Flexible electronics are expected to play a key role in connecting human lives with versatile smart electronic devices due to their adaptability to different shapes, surfaces, and even the human body. However, heat management issues found in most flexible devices due to the low thermal conductivity of conventional plastic or paper substrates become significant for large-scale integration or high-temperature applications. In this study, we employed high thermal conductivity nanopaper composed of two-dimensional (2D) hexagonal boron nitride nanosheets and one-dimensional nanofibrillated cellulose to form a flexible deep-ultraviolet photodetector demonstrating superior photodetectivity of up to 8.05 × 1010 cm Hz1/2/W, a short response time of 0.267 s, and excellent flexible durability featuring repeatable ON/OFF photoswitching over 200 bending cycles. Because the boron nitride paper has a high thermal conductivity of 146 W/mK, which is three orders of magnitude larger than plastic or paper substrates, the photodetectors can work at high temperatures of up to 200 °C. The boron nitride paper-based strategy described herein suggests a path for improving heat dissipation in flexible electronics and achieving high-performance deep-ultraviolet photodetectors, which can be applied in wearable applications.Flexible electronics: photodetectors based on h-BN nanosheets and nanofibrillated celluloseIncorporating hexagonal boron nitride (h-BN) in cellulose nanofibres improves thermal management in flexible electronics. A team led by Jr-Hau He at King Abdullah University of Science & Technology fabricated a high thermal conductivity paper combining two-dimensional h-BN nanosheets with one-dimensional nanofibrillated cellulose to form a flexible composite that can be used for optoelectronic applications. The resulting photodetector exhibited deep-ultraviolet response with detectivity up to 8.05 × 1010 cm Hz1/2/W, response time of 0.267 s, and bendability over 200 cycles. Owing to h-BN high thermal conductivity, the flexible photodetector offered superior heat dissipation, and could sustain temperatures as high as 200 °C without suffering from performance deterioration. The fabricated “paper” can be interfaced to conventional semiconductors and metal electrodes using standard deposition methods.