Hardware-Intrinsic Physical Unclonable Functions by Harnessing Nonlinear Conductance Variation in Oxide Semiconductor-Based Diode.

With the advancement of the Internet of Things (IoT), numerous electronic devices are connected to each other and exchange a vast amount of data via the Internet. As the number of connected devices increases, security concerns have become more significant. As one of the potential solutions for security issues, hardware intrinsic physical unclonable functions (PUFs) are emerging semiconductor devices that exploit inherent randomness generated during the manufacturing process. The unclonable security key generated from PUF can address the inherent limitations of conventional electronic systems which depend solely on software. Although numerous PUFs based on the emerging memory devices requiring switching operations have been proposed, achieving hardware intrinsic PUF with low power consumption remains a key challenge. Here, we demonstrate that the process-induced nonlinear conductance variations of oxide semiconductor-based Schottky diodes provide a suitable source of entropy for the implementation of PUF without switching operation. Using a mild oxygen plasma treatment, the surface electron accumulation layer that forms naturally in oxide semiconductor film can be partially eliminated, resulting in a large variation of nonlinearity as an exotic entropy source. The mild plasma-treated Schottky diodes showed near ideal 50% average uniformity and uniqueness, as well as an ideal entropy value without the need for additional hardware area and power costs. These findings will pave the way for the development of hardware intrinsic PUFs to realize energy-efficient cryptographic hardware.

Graphene Oxide-Based Memristive Logic-in-Memory Circuit Enabling Normally-Off Computing.

Memristive logic-in-memory circuits can provide energy- and cost-efficient computing, which is essential for artificial intelligence-based applications in the coming Internet-of-things era. Although memristive logic-in-memory circuits have been previously reported, the logic architecture requiring additional components and the non-uniform switching of memristor have restricted demonstrations to simple gates. Using a nanoscale graphene oxide (GO) nanosheets-based memristor, we demonstrate the feasibility of a non-volatile logic-in-memory circuit that enables normally-off in-memory computing. The memristor based on GO film with an abundance of unusual functional groups exhibited unipolar resistive switching behavior with reliable endurance and retention characteristics, making it suitable for logic-in-memory circuit application. In a state of low resistance, temperature-dependent resistance and I-V characteristics indicated the presence of a metallic Ni filament. Using memristor-aided logic (MAGIC) architecture, we performed NOT and NOR gates experimentally. Additionally, other logic gates such as AND, NAND, and OR were successfully implemented by combining NOT and NOR universal logic gates in a crossbar array. These findings will pave the way for the development of next-generation computer systems beyond the von Neumann architecture, as well as carbon-based nanoelectronics in the future.

Artificial Multisensory Neuron with a Single Transistor for Multimodal Perception through Hybrid Visual and Thermal Sensing.

An artificial multisensory device applicable to in-sensor computing is demonstrated with a single-transistor neuron (1T-neuron) for multimodal perception. It simultaneously receives two sensing signals from visual and thermal stimuli. The 1T-neuron transforms these signals into electrical signals in the form of spiking and then fires them for a spiking neural network at the same time. This feature makes it feasible to realize input neurons for multimodal sensing. Visual and thermal sensing is achieved due to the inherent optical and thermal behaviors of the 1T-neuron. To demonstrate a neuromorphic multimodal sensing system with the artificial multisensory 1T-neuron, fingerprint recognition, widely used for biometric security, is implemented. Owing to the simultaneous sensing of heat as well as light, the proposed fingerprint recognition system composed of multisensory 1T-neurons not only identifies a genuine pattern but also judges whether or not it is forged.

A Vertical Single Transistor Neuron with Core-Shell Dual-Gate for Excitatory-Inhibitory Function and Tunable Firing Threshold Voltage.

A novel inhibitable and firing threshold voltage tunable vertical nanowire (NW) single transistor neuron device with core-shell dual-gate (CSDG) was realized and verified by TCAD simulation. The CSDG NW neuron is enclosed by an independently accessed shell gate and core gate to serve an excitatory-inhibitory transition and a firing threshold voltage adjustment, respectively. By utilizing the shell gate, the firing of specific neuron can be inhibited for winner-takes-all learning. It was confirmed that the independently accessed core gate can be used for adjustment of the firing threshold voltage to compensate random conductance variation before the learning and to fix inference error caused by unwanted synapse conductance change after the learning. This threshold voltage tuning can also be utilized for homeostatic function during the learning process. Furthermore, a myelination function which controls the transmission rate was obtained based on the inherent asymmetry between the source and drain in vertical NW structure. Finally, using the CSDG NW neuron device, a letter recognition test was conducted by SPICE simulation for a system-level validation. This multi-functional neuron device can contribute to construct a high-density monolithic SNN hardware combining with the previously developed vertical synapse MOSFET devices.

Self-Powered Artificial Mechanoreceptor Based on Triboelectrification for a Neuromorphic Tactile System.

A self-powered artificial mechanoreceptor module is demonstrated with a triboelectric nanogenerator (TENG) as a pressure sensor with sustainable energy harvesting and a biristor as a neuron. By mimicking a biological mechanoreceptor, it simultaneously detects the pressure and encodes spike signals to act as an input neuron of a spiking neural network (SNN). A self-powered neuromorphic tactile system composed of artificial mechanoreceptor modules with an energy harvester can greatly reduce the power consumption compared to the conventional tactile system based on von Neumann computing, as the artificial mechanoreceptor module itself does not demand an external energy source and information is transmitted with spikes in a SNN. In addition, the system can detect low pressures near 3 kPa due to the high output range of the TENG. It therefore can be advantageously applied to robotics, prosthetics, and medical and healthcare devices, which demand low energy consumption and low-pressure detection levels. For practical applications of the neuromorphic tactile system, classification of handwritten digits is demonstrated with a software-based simulation. Furthermore, a fully hardware-based breath-monitoring system is implemented using artificial mechanoreceptor modules capable of detecting wind pressure of exhalation in the case of pulmonary respiration and bending pressure in the case of abdominal breathing.

Functional Circuitry on Commercial Fabric via Textile-Compatible Nanoscale Film Coating Process for Fibertronics.

Fabric-based electronic textiles (e-textiles) are the fundamental components of wearable electronic systems, which can provide convenient hand-free access to computer and electronics applications. However, e-textile technologies presently face significant technical challenges. These challenges include difficulties of fabrication due to the delicate nature of the materials, and limited operating time, a consequence of the conventional normally on computing architecture, with volatile power-hungry electronic components, and modest battery storage. Here, we report a novel poly(ethylene glycol dimethacrylate) (pEGDMA)-textile memristive nonvolatile logic-in-memory circuit, enabling normally off computing, that can overcome those challenges. To form the metal electrode and resistive switching layer, strands of cotton yarn were coated with aluminum (Al) using a solution dip coating method, and the pEGDMA was conformally applied using an initiated chemical vapor deposition process. The intersection of two Al/pEGDMA coated yarns becomes a unit memristor in the lattice structure. The pEGDMA-Textile Memristor (ETM), a form of crossbar array, was interwoven using a grid of Al/pEGDMA coated yarns and untreated yarns. The former were employed in the active memristor and the latter suppressed cell-to-cell disturbance. We experimentally demonstrated for the first time that the basic Boolean functions, including a half adder as well as NOT, NOR, OR, AND, and NAND logic gates, are successfully implemented with the ETM crossbar array on a fabric substrate. This research may represent a breakthrough development for practical wearable and smart fibertronics.

Three-Dimensional Fin-Structured Semiconducting Carbon Nanotube Network Transistor.

Three-dimensional (3-D) fin-structured carbon nanotube field-effect transistors (CNT-FETs) with purified 99.9% semiconducting CNTs were demonstrated on a large scale 8 in. silicon wafer. The fabricated 3-D CNT-FETs take advantage of the 3-D geometry and exhibit enhanced electrostatic gate controllability and superior charge transport. A trigated structure surrounding the randomly networked single-walled CNT channel was formed on a fin-like 3-D silicon frame, and as a result, the effective packing density increased to almost 600 CNTs/µm. Additionally, highly sensitive controllability of the threshold voltage (VTH) was achieved using a thin back gate oxide in the same silicon frame to control power consumption and enhance performance. Our results are expected to broaden the design margin of CNT-based circuit architectures for versatile applications. The proposed 3-D CNT-FETs can potentially provide a desirable alternative to silicon based nanoelectronics and a blueprint for furthering the practical use of emerging low-dimensional materials other than CNTs.

Physically Transient Memory on a Rapidly Dissoluble Paper for Security Application.

We report the transient memory device by means of a water soluble SSG (solid sodium with glycerine) paper. This material has a hydroscopic property hence it can be soluble in water. In terms of physical security of memory devices, prompt abrogation of a memory device which stored a large number of data is crucial when it is stolen because all of things have identified information in the memory device. By utilizing the SSG paper as a substrate, we fabricated a disposable resistive random access memory (RRAM) which has good data retention of longer than 106 seconds and cycling endurance of 300 cycles. This memory device is dissolved within 10 seconds thus it can never be recovered or replicated. By employing direct printing but not lithography technology to aim low cost and disposable applications, the memory capacity tends to be limited less than kilo-bits. However, unlike high memory capacity demand for consumer electronics, the proposed device is targeting for security applications. With this regards, the sub-kilobit memory capacity should find the applications such as one-time usable personal identification, authentication code storage, cryptography key, and smart delivery tag. This aspect is attractive for security and protection system against unauthorized accessibility.

Foldable and Disposable Memory on Paper.

Foldable organic memory on cellulose nanofibril paper with bendable and rollable characteristics is demonstrated by employing initiated chemical vapor deposition (iCVD) for polymerization of the resistive switching layer and inkjet printing of the electrode, where iCVD based on all-dry and room temperature process is very suitable for paper electronics. This memory exhibits a low operation voltage of 1.5 V enabling battery operation compared to previous reports and wide memory window. The memory performance is maintained after folding tests, showing high endurance. Furthermore, the quick and complete disposable nature demonstrated here is attractive for security applications. This work provides an effective platform for green, foldable and disposable electronics based on low cost and versatile materials.

Vertically Integrated Nanowire-Based Unified Memory.

A vertically integrated nanowire-based device for multifunctional unified memory that combine dynamic random access memory (DRAM) and flash memory in a single transistor is demonstrated for the first time. The device utilizes a gate-all-around (GAA) structure that completely surrounds the nanowire; the structure is built on a bulk silicon wafer. A vertically integrated unified memory (VIUM) device composed of five-story channels was fabricated via the one-route all-dry etching process (ORADEP) with reliable reproducibility, stiction-free stability, and high uniformity. In each DRAM and flash memory operation, the five-story VIUM showed a remarkably enhanced sensing current drivability compared with one-story unified memory (UM) characteristics. In addition to each independent memory mode, the switching endurance of the VIUM was evaluated in the unified mode, which alternatively activates two memory modes, resulting in an even higher sensing memory window than that of the UM. In addition to our previous work on a logic transistor joining high performance with good scalability, this work describes a novel memory hierarchy design with high functionality for system-on-chip (SoC) architectures, demonstrating the practicality and versatility of the vertically integrated nanowire configuration for use in various applications.

Electrothermal Annealing (ETA) Method to Enhance the Electrical Performance of Amorphous-Oxide-Semiconductor (AOS) Thin-Film Transistors (TFTs).

An electro-thermal annealing (ETA) method, which uses an electrical pulse of less than 100 ns, was developed to improve the electrical performance of array-level amorphous-oxide-semiconductor (AOS) thin-film transistors (TFTs). The practicality of the ETA method was experimentally demonstrated with transparent amorphous In-Ga-Zn-O (a-IGZO) TFTs. The overall electrical performance metrics were boosted by the proposed method: up to 205% for the trans-conductance (gm), 158% for the linear current (Ilinear), and 206% for the subthreshold swing (SS). The performance enhancement were interpreted by X-ray photoelectron microscopy (XPS), showing a reduction of oxygen vacancies in a-IGZO after the ETA. Furthermore, by virtue of the extremely short operation time (80 ns) of ETA, which neither provokes a delay of the mandatory TFTs operation such as addressing operation for the display refresh nor demands extra physical treatment, the semipermanent use of displays can be realized.

Logic circuits composed of flexible carbon nanotube thin-film transistor and ultra-thin polymer gate dielectric.

Printing electronics has become increasingly prominent in the field of electronic engineering because this method is highly efficient at producing flexible, low-cost and large-scale thin-film transistors. However, TFTs are typically constructed with rigid insulating layers consisting of oxides and nitrides that are brittle and require high processing temperatures, which can cause a number of problems when used in printed flexible TFTs. In this study, we address these issues and demonstrate a method of producing inkjet-printed TFTs that include an ultra-thin polymeric dielectric layer produced by initiated chemical vapor deposition (iCVD) at room temperature and highly purified 99.9% semiconducting carbon nanotubes. Our integrated approach enables the production of flexible logic circuits consisting of CNT-TFTs on a polyethersulfone (PES) substrate that have a high mobility (up to 9.76 cm(2) V(-1) sec(-)1), a low operating voltage (less than 4 V), a high current on/off ratio (3 × 10(4)), and a total device yield of 90%. Thus, it should be emphasized that this study delineates a guideline for the feasibility of producing flexible CNT-TFT logic circuits with high performance based on a low-cost and simple fabrication process.

Triboelectric Nanogenerator Based on the Internal Motion of Powder with a Package Structure Design.

Harvesting the ambient mechanical energy that is abundant in the living environment is a green technology which can allow us to obtain an eco-friendly and sustainable form of energy. Here, we report a powder-based triboelectric nanogenerator (P-TENG) using polytetrafluoroethylene powder as a freestanding triboelectric layer. By employing powder, which has fluid-like characteristics, the device is able to harvest random vibrational energy from all directions and can be fabricated regardless of the size or shape of its container. Notably, this device shows excellent durability against mechanical friction and immunity against humidity. It is also capable of powering 240 green LEDs and charging a commercial energy-harvesting battery. The P-TENG is expected to be applicable as an energy harvester in self-powered systems for the upcoming Internet-of-Things era.

Coverage of Amputation Stumps Using a Latissimus Dorsi Flap With a Serratus Anterior Muscle Flap: A Comparative Study.

Amputation of the extremities is a definitive reconstructive option, and surgeons should aim to preserve maximum overall function. If the exposed bone cannot be adequately covered using local tissues, the stump can be reconstructed using a number of well-described free flap transfer techniques. Between January 2002 and December 2011, 31 patients with severe injuries to the lower extremities underwent above-the-knee, below-the-knee, and Chopart and Ray amputations. Bony stumps were covered using latissimus dorsi myocutaneous flaps alone (group 1), or together with serratus anterior muscle flaps (group 2). The groups were compared with respect to age, flap survival, skin flap size, immediate complications, wound sloughing, deep ulceration, need for bone amputation, limb visual analog scale score, time to prosthesis, and follow-up duration. The mean area of the latissimus dorsi skin flap was 255.9 cm, and immediate complications occurred in 8 (25.8%) patients. In the double-padding group, there were fewer cases of deep ulceration than in the single-flap group, and prostheses could be worn sooner. There were no statistically significant differences in other parameters. Successful reconstruction of amputation stumps requires an adequate, durable, weight-bearing, and well-contoured soft tissue cover. A latissimus dorsi musculocutaneous flap together with a serratus anterior muscle flap provides well-vascularized muscle tissue and a durable skin paddle, leading to less ulceration than conventional flap techniques.

Two-Step Incision for Periarterial Sympathectomy of the Hand.

BACKGROUND: Surgical scars on the palmar surface of the hand may lead to functional and also aesthetic and psychological consequences. The objective of this study was to introduce a new incision technique for periarterial sympathectomy of the hand and to compare the results of the new two-step incision technique with those of a Koman incision by using an objective questionnaire. METHODS: A total of 40 patients (17 men and 23 women) with intractable Raynaud's disease or syndrome underwent surgery in our hospital, conducted by a single surgeon, between January 2008 and January 2013. Patients who had undergone extended sympathectomy or vessel graft were excluded. Clinical evaluation of postoperative scars was performed in both groups one year after surgery using the patient and observer scar assessment scale (POSAS) and the Wake Forest University rating scale. RESULTS: The total patient score was 8.59 (range, 6-15) in the two-step incision group and 9.62 (range, 7-18) in the Koman incision group. A significant difference was found between the groups in the total PS score (P-value=0.034) but not in the total observer score. Our analysis found no significant difference in preoperative and postoperative Wake Forest University rating scale scores between the two-step and Koman incision groups. The time required for recovery prior to returning to work after surgery was shorter in the two-step incision group, with a mean of 29.48 days in the two-step incision group and 34.15 days in the Koman incision group (P=0.03). CONCLUSIONS: Compared to the Koman incision, the new two-step incision technique provides better aesthetic results, similar symptom improvement, and a reduction in the recovery time required before returning to work. Furthermore, this incision allows the surgeon to access a wide surgical field and a sufficient exposure of anatomical structures.

Vertically Integrated Multiple Nanowire Field Effect Transistor.

A vertically integrated multiple channel-based field-effect transistor (FET) with the highest number of nanowires reported ever is demonstrated on a bulk silicon substrate without use of wet etching. The driving current is increased by 5-fold due to the inherent vertically stacked five-level nanowires, thus showing good feasibility of three-dimensional integration-based high performance transistor. The developed fabrication process, which is simple and reproducible, is used to create multiple stiction-free and uniformly sized nanowires with the aid of the one-route all-dry etching process (ORADEP). Furthermore, the proposed FET is revamped to create nonvolatile memory with the adoption of a charge trapping layer for enhanced practicality. Thus, this research suggests an ultimate design for the end-of-the-roadmap devices to overcome the limits of scaling.

Floating Oscillator-Embedded Triboelectric Generator for Versatile Mechanical Energy Harvesting.

A versatile vibration energy harvesting platform based on a triboelectricity is proposed and analyzed. External mechanical vibration repeats an oscillating motion of a polymer-coated metal oscillator floating inside a surrounding tube. Continuous sidewall friction at the contact interface of the oscillator induces current between the inner oscillator electrode and the outer tube electrode to convert mechanical vibrations into electrical energy. The floating oscillator-embedded triboelectric generator (FO-TEG) is applicable for both impulse excitation and sinusoidal vibration which universally exist in usual environment. For the impulse excitation, the generated current sustains and slowly decays by the residual oscillation of the floating oscillator. For the sinusoidal vibration, the output energy can be maximized by resonance oscillation. The operating frequency range can be simply optimized with high degree of freedom to satisfy various application requirements. In addition, the excellent immunity against ambient humidity is experimentally demonstrated, which stems from the inherently packaged structure of FO-TEG. The prototype device provides a peak-to-peak open-circuit voltage of 157 V and instantaneous short-circuit current of 4.6 µA, within sub-10 Hz of operating frequency. To visually demonstrate the energy harvesting behavior of FO-TEG, lighting of an array of LEDs is demonstrated using artificial vibration and human running.

Surface Engineering of Triboelectric Nanogenerator with an Electrodeposited Gold Nanoflower Structure.

A triboelectric nanogenerator composed of gold nanoflowers is demonstrated. The proposed triboelectric nanogenerator creates electricity by contact-separation-based electrification between an anodic metal and a cathodic polymer. For the improvement of output power via the enlargement of the effective surface area in the anodic metal, gold nanoflowers that produce a hierarchical morphology at a micro-to-nano scale by electrodeposition are utilized. The hierarchical morphology is controlled by the applied voltage and deposition time. Even though the triboelectric coefficient of gold is inferior to those of other metals, gold is very attractive to make a flower-like structure by electrodeposition. Moreover, gold is stable against oxidation by oxygen in air. From a reliability and practicality point of view, the aforementioned stability against oxidation is preferred.

Predictive factors for successful limb salvage surgery in diabetic foot patients.

BACKGROUND: The goal of salvage surgery in the diabetic foot is maximal preservation of the limb, but it is also important to resect unviable tissue sufficiently to avoid reamputation. This study aims to provide information on determining the optimal amputation level that allows preservation of as much limb length as possible without the risk of further reamputation by analyzing several predictive factors. METHODS: Between April 2004 and July 2013, 154 patients underwent limb salvage surgery for distal diabetic foot gangrene. According to the final level of amputation, the patients were divided into two groups: Patients with primary success of the limb salvage, and patients that failed to heal after the primary limb salvage surgery. The factors predictive of success, including comorbidity, laboratory findings, and radiologic findings were evaluated by a retrospective chart review. RESULTS: The mean age of the study population was 63.9 years, with a male-to-female ratio of approximately 2:1. The mean follow-up duration was 30 months. Statistical analysis showed that underlying renal disease, limited activity before surgery, a low hemoglobin level, a high white blood cell count, a high C-reactive protein level, and damage to two or more vessels on preoperative computed tomography (CT) angiogram were significantly associated with the success or failure of limb salvage. The five-year survival rate was 81.6% for the limb salvage success group and 36.4% for the limb salvage failure group. CONCLUSION: This study evaluated the factors predictive of the success of limb salvage surgery and identified indicators for preserving as much as possible of the leg of a patient with diabetic foot. This should help surgeons to establish the appropriate amputation level for a case of diabetic foot and help prevent consecutive operations.