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1. Silk Fibroin-Sheathed Conducting Polymer Wires as Organic Connectors for Biosensors

   https://doi.org/10.3390/bios9030103  

   Jiang, Yanke; Xu, Meng; Yadavalli, Vamsi K (September 2019, Biosensors)

   Conductive polymers, owing to their tunable mechanical and electrochemical properties, are viable candidates to replace metallic components for the development of biosensors and bioelectronics. However, conducting fibers/wires fabricated from these intrinsically conductive and mechanically flexible polymers are typically produced without protective coatings for physiological environments. Providing sheathed conductive fibers/wires can open numerous opportunities for fully organic biodevices. In this work, we report on a facile method to fabricate core-sheath poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS-silk fibroin conductive wires. The conductive wires are formed through a wet-spinning process, and then coated with an optically transparent, photocrosslinkable silk fibroin sheath for insulation and protection in a facile and scalable process. The sheathed fibers were evaluated for their mechanical and electrical characteristics and overall stability. These wires can serve as flexible connectors to an organic electrode biosensor. The entire, fully organic, biodegradable, and free-standing flexible biosensor demonstrated a high sensitivity and rapid response for the detection of ascorbic acid as a model analyte. The entire system can be proteolytically biodegraded in a few weeks. Such organic systems can therefore provide promising solutions to address challenges in transient devices and environmental sustainability. 

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2. Biomechanical fracture mechanics of composite layered skin-like materials

   https://doi.org/10.1039/D1SM01187A  

   Maiorana, Christopher H.; Jotawar, Rajeshwari A.; German, Guy K. (March 2022, Soft Matter)

   Most protective biological tissues are structurally comprised of a stiff and thin outer layer on top of a soft underlying substrate. Examples include mammalian skin, fish scales, crustacean shells, and nut and seed shells. While these composite skin-like tissues are ubiquitous in nature, their mechanics of failure and what potential mechanical advantages their composite structures offer remains unclear. In this work, changes in the puncture mechanics of composite hyperelastic elastomers with differing non-dimensional layer thicknesses are explored. Puncture behavior of these membranes is measured for dull and sharp conical indenters. Membranes with a stiff outer layer of only 1% of the overall composite thickness exhibit a puncture energy comparable to membranes with a stiff outer layer approximately 20 times thicker. This puncture energy, scaled by its flexural capacity, achieves a local maximum when the top layer is approximately 1% of the total membrane, similar to the structure of numerous mammalian species. The mode of failure for these regimes is also investigated. In contrast with puncture directly beneath sharp tips caused by high stress concentrations, a new type of ‘coring’ type fracture emerges at large indentation depths, resulting from accumulated tensile strain energy along the sides of the divot as the membrane is deformed with a blunt indenter. These results could enhance the durability and robustness of stretchable materials used for products such as surgical gloves, packaging, and flexible electronics. 

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3. Atomistic mechanisms of water vapor–induced surface passivation

   https://doi.org/10.1126/sciadv.adh5565  

   Chen, Xiaobo; Shan, Weitao; Wu, Dongxiang; Patel, Shyam Bharatkumar; Cai, Na; Li, Chaoran; Ye, Shuonan; Liu, Zhao; Hwang, Sooyeon; Zakharov, Dmitri N; et al (November 2023, Science Advances)

   The microscopic mechanisms underpinning the spontaneous surface passivation of metals from ubiquitous water have remained largely elusive. Here, using in situ environmental electron microscopy to atomically monitor the reaction dynamics between aluminum surfaces and water vapor, we provide direct experimental evidence that the surface passivation results in a bilayer oxide film consisting of a crystalline-like Al(OH)₃top layer and an inner layer of amorphous Al₂O₃. The Al(OH)₃layer maintains a constant thickness of ~5.0 Å, while the inner Al₂O₃layer grows at the Al₂O₃/Al interface to a limiting thickness. On the basis of experimental data and atomistic modeling, we show the tunability of the dissociation pathways of H₂O molecules with the Al, Al₂O₃, and Al(OH)₃surface terminations. The fundamental insights may have practical significance for the design of materials and reactions for two seemingly disparate but fundamentally related disciplines of surface passivation and catalytic H₂production from water. 

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4. High‐Performance Zinc Tin Oxide TFTs with Active Layers Deposited by Atomic Layer Deposition

   https://doi.org/10.1002/aelm.202000195  

   Allemang, Christopher R.; Cho, Tae H.; Trejo, Orlando; Ravan, Shantam; Rodríguez, Robin E.; Dasgupta, Neil P.; Peterson, Rebecca L. (June 2020, Advanced Electronic Materials)

   Abstract New deposition techniques for amorphous oxide semiconductors compatible with silicon back end of line manufacturing are needed for 3D monolithic integration of thin‐film electronics. Here, three atomic layer deposition (ALD) processes are compared for the fabrication of amorphous zinc tin oxide (ZTO) channels in bottom‐gate, top‐contact n‐channel transistors. As‐deposited ZTO films, made by ALD at 150–200 °C, exhibit semiconducting, enhancement‐mode behavior with electron mobility as high as 13 cm²V⁻¹s⁻¹, due to a low density of oxygen‐related defects. ZTO deposited at 200 °C using a hybrid thermal‐plasma ALD process with an optimal tin composition of 21%, post‐annealed at 400 °C, shows excellent performance with a record high mobility of 22.1 cm²V^–1s^–1and a subthreshold slope of 0.29 V dec^–1. Increasing the deposition temperature and performing post‐deposition anneals at 300–500 °C lead to an increased density of the X‐ray amorphous ZTO film, improving its electrical properties. By optimizing the ZTO active layer thickness and using a high‐kgate insulator (ALD Al₂O₃), the transistor switching voltage is lowered, enabling electrical compatibility with silicon integrated circuits. This work opens the possibility of monolithic integration of ALD ZTO‐based thin‐film electronics with silicon integrated circuits or onto large‐area flexible substrates. 

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5. Probing Assessment Framework and Evaluation of Anti-probing Solutions

   Wang, Huanyu; Shi, Qihang; Forte, Domenic; Tehranipoor, Mark M. (January 2019, IEEE transactions on very large scale integration (VLSI) systems)

   Probing attacks against integrated circuits (IC) have become a serious concern, especially for security-critical applications. With the help of modern circuit editing tools, an attacker could remove layers of materials and expose wires carrying sensitive on-chip assets, such as cryptographic keys and proprietary firmware for probing. Most existing protection methods use active shield which provides tamper-evident covers at the top-most metal layers to the circuity below. However, they lack formal proofs of their effectiveness as some active shields have already been circumvented by hackers. In this paper, we investigate the problem of protection against front-side probing attacks and present a framework to assess a design’s vulnerabilities against probing attacks. Metrics are developed to evaluate the resilience of designs to bypass attack and reroute attack which are two common techniques used to compromise an anti-probing mechanism. Exemplary assets from an SoC layout are used to evaluate the proposed flow. Results show that long net and high layer wires are vulnerable to probing attack equipped with high aspect ratio FIB. Meanwhile, nets that occupy small area on the chip are probably compromised through rerouting shield wires. On the other hand, multi-layer internal orthogonal shield performs the best among common shield structures. 

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