In Case You Missed It

Electrochemical Migration

“Effects of Concentration of Adipic Acid on the Electrochemical Migration of Tin for Printed Circuit Board Assembly”

Authors: Yi Sing Goh, et al.

Abstract: Continuous advancement in innovative electronic applications leads to closer interconnection spacing and higher electric field density, thus increasing the risk of electrochemical migration (ECM)-related failures. The ECM of tin (Sn) attracts great interest due to the wide use of Sn on the surface of the printed circuit board assembly. In this work, the authors investigated the effects of adipic acid (1 ppm–saturated concentration) on the ECM of Sn using the water drop test (WDT) at 5V. In situ observation and ex situ characterization of ECM products were carried out using optical and electrochemical techniques. Results show that the ECM failure probability is higher at intermediate adipic acid concentrations (10ppm, 100ppm and 1000ppm). The major ECM reactions include anodic corrosion and the formation of dendrites, precipitates and gas bubbles. ECM failure does not occur at higher adipic acid concentrations (≥5000ppm) although the anodic corrosion becomes more severe. The complexation of Sn with adipic acid to form Sn adipate complex is suggested as the main factor suppressing ECM failure at higher concentrations (≥5000ppm) by retarding ion transport. The electrochemical parameters (E_corr and I_corr) do not correlate with the ECM failure probability. They affect the anodic dissolution stage, but not the subsequent stages in the ECM mechanism. In this study, the ion transport stage plays a more significant role in determining the ECM failure probability. (Journal of Electronic Materials, March 2023, https://link.springer.com/article/10.1007/s11664-022-10155-2)

Energy-Efficient Electronics

“Epitaxial van der Waals Contacts for Low Schottky Barrier MoS2 Field Effect Transistors”

Authors: Huawei Liu, et al.

Abstract: Small contact resistance and low Schottky barrier height (SBH) are the keys to energy-efficient electronics and optoelectronics. Two-dimensional (2-D) semiconductors-based field effect transistors (FETs), holding great promise for next-generation information circuits, still suffer from poor contact quality at the metal – semiconductor junction interface, which severely hinders their further applications. Here, a novel contact strategy is proposed, where Bi₂Te₃ nanosheets with high conductivity were in-situ epitaxially grown on MoS₂ as van der Waals contacts, which can effectively avoid the damage to MoS₂ caused during the device manufacturing process, leading to a high-performance MoS₂ FET. Moreover, the small work function difference between Bi₂Te₃and MoS₂ [(Bi₂Te₃: 4.31 eV, MoS2: 4.37 eV, measured by Kelvin probe force microscopy (KPFM)], enables small band bending and Ohmic contact at the junction interface. Electrical characterizations indicate that the MoS₂ FET device with Bi2Te3 contacts possesses a high current on/off ratio (5 × 10⁷), large effective carrier mobility (90cm²/(V·s)), and low flat-band SBH (60meV), which is favorable as compared with MoS₂ FET with traditional Cr/Au electrodes contacts, and superior to the vast majority of the reported chemical vapor deposition (CVD) MoS₂-based FET device. The demonstration of epitaxial van der Waals Bi₂Te₃ contacts will facilitate the application of 2-D MoS₂ nanosheet in next-generation low-power consumption electronics and optoelectronics. (Nano Research, Dec. 5, 2022, https://doi.org/10.1007/s12274-022-5229-y)

MPTMs

“Magnetoactive Liquid-Solid Phase Transitional Matter”

Authors: Qingyuan Wang, et al.

Abstract: Magnetically actuated miniature machines can perform multimodal locomotion and programmable deformations. However, they are either solid magnetic elastomers with limited morphological adaptability or liquid material systems with low mechanical strength. Here, the authors report magnetoactive phase transitional matter (MPTM) composed of magnetic neodymium-iron-boron microparticles embedded in liquid metal. MPTMs can reversibly switch between solid and liquid phase by heating with alternating magnetic field or through ambient cooling. In this way, they uniquely combine high mechanical strength (strength, 21.2MPa; stiffness, 1.98GPa), high load capacity (able to bear 30kg), and fast locomotion speed (>1.5m/s) in the solid phase with excellent morphological adaptability (elongation, splitting, and merging) in the liquid phase. The authors demonstrate the unique capabilities of MPTMs by showing their dynamic shape reconfigurability by realizing smart soldering machines and universal screws for smart assembly and machines for foreign body removal and drug delivery in a model stomach. (Cell, Jan. 25, 2023, https://doi.org/10.1016/j.matt.2022.12.003)

Wearable Electronics

“Fully Screen-Printed PI/PEG Blends Enabled Patternable Electrodes for Scalable Manufacturing of Skin-Conformal, Stretchable, Wearable Electronics”

Authors: Sehyun Park, et al.

Abstract: Recent advances in soft materials and nano-microfabrication have enabled the development of flexible wearable electronics. At the same time, printing technologies have been demonstrated to be efficient and compatible with polymeric materials for manufacturing wearable electronics. However, wearable device manufacturing still counts on a costly, complex, multistep, and error-prone cleanroom process. Here, the authors present fully screen-printable, skin-conformal electrodes for low-cost and scalable manufacturing of wearable electronics. The screen printing of the polyimide (PI) layer enables facile, low-cost, scalable, high-throughput manufacturing. PI mixed with poly(ethylene glycol) exhibits a shear-thinning behavior, significantly improving the printability of PI. The premixed Ag/AgCl ink is then used for conductive layer printing. The serpentine pattern of the screen-printed electrode accommodates natural deformation under stretching (30%) and bending conditions (180°), which are verified by computational and experimental studies. Real-time wireless electrocardiogram monitoring is also successfully demonstrated using the printed electrodes with a flexible printed circuit. The algorithm developed in this study can calculate accurate heart rates, respiratory rates, and heart rate variability metrics for arrhythmia detection. (ACS Appl. Mater. Interfaces, Jan. 3, 2023, https://doi.org/10.1021/acsami.2c17653)