Review Articles
  • Smart gas sensor arrays powered by artificial intelligence

    Zhesi Chen, Zhuo Chen, Zhilong Song, Wenhao Ye, Zhiyong Fan

    J. Semicond.  2019, 40 (11): 111601

    doi: 10.1088/1674-4926/40/11/111601

    Abstract Full Text PDF Get Citation

    Mobile robots behaving as humans should possess multifunctional flexible sensing systems including vision, hearing, touch, smell, and taste. A gas sensor array (GSA), also known as electronic nose, is a possible solution for a robotic olfactory system that can detect and discriminate a wide variety of gas molecules. Artificial intelligence (AI) applied to an electronic nose involves a diverse set of machine learning algorithms which can generate a smell print by analyzing the signal pattern from the GSA. A combination of GSA and AI algorithms can empower intelligent robots with great capabilities in many areas such as environmental monitoring, gas leakage detection, food and beverage production and storage, and especially disease diagnosis through detection of different types and concentrations of target gases with the advantages of portability, low-power-consumption and ease-of-operation. It is exciting to envisage robots equipped with a "nose" acting as family doctor who will guard every family member's health and keep their home safe. In this review, we give a summary of the state-of the-art research progress in the fabrication techniques for GSAs and typical algorithms employed in artificial olfactory systems, exploring their potential applications in disease diagnosis, environmental monitoring, and explosive detection. We also discuss the key limitations of gas sensor units and their possible solutions. Finally, we present the outlook of GSAs over the horizon of smart homes and cities.

  • Recent advances in flexible photodetectors based on 1D nanostructures

    Senpo Yip, Lifan Shen, Johnny C Ho

    J. Semicond.  2019, 40 (11): 111602

    doi: 10.1088/1674-4926/40/11/111602

    Abstract Full Text PDF Get Citation

    Semiconductor nanowires have demonstrated excellent electronic and optoelectronic properties. When integrated into photodetectors, excellent device performance can be easily attained. Apart from the exceptional performance, these nanowires can also enable robust and mechanically flexible photodetectors for various advanced utilizations that the rigid counterparts cannot perform. These unique applications include personal healthcare, next-generation robotics and many others. In this review, we would first discuss the nanowire fabrication techniques as well as the assembly methods of constructing large-scale nanowire arrays. Then, the recent development of flexible photodetectors based on these different nanowire material systems is evaluated in detail. At the same time, we also introduce some recent advancement that allows individual photodetectors to integrate into a more complex system for advanced deployment. Finally, a short conclusion and outlook of challenges faced in the future of the community is presented.

  • Electrospun flexible sensor

    Qi Liu, Seeram Ramakrishna, Yun-Ze Long

    J. Semicond.  2019, 40 (11): 111603

    doi: 10.1088/1674-4926/40/11/111603

    Abstract Full Text PDF Get Citation

    Flexible sensors have received wide attention because of their ability to adapt to a variety of complex environments. Electrospinning technology has significant advantages in the preparation of flexible sensors. This paper summarizes the progress in the preparation of flexible sensors by electrospinning. Sensors that respond to light, stress, and gas are presented separately. Finally, some directions for electrospinning and flexible sensors are discussed.

  • Flexible and stretchable photodetectors and gas sensors for wearable healthcare based on solution-processable metal chalcogenides

    Qi Yan, Liang Gao, Jiang Tang, Huan Liu

    J. Semicond.  2019, 40 (11): 111604

    doi: 10.1088/1674-4926/40/11/111604

    Abstract Full Text PDF Get Citation

    Wearable smart sensors are considered to be the new generation of personal portable devices for health monitoring. By attaching to the skin surface, these sensors are closely related to body signals (such as heart rate, blood oxygen saturation, breath markers, etc.) and ambient signals (such as ultraviolet radiation, inflammable and explosive, toxic and harmful gases), thus providing new opportunities for human activity monitoring and personal telemedicine care. Here we focus on photodetectors and gas sensors built from metal chalcogenide, which have made great progress in recent years. Firstly, we present an overview of healthcare applications based on photodetectors and gas sensors, and discuss the requirement associated with these applications in detail. We then discuss advantages and properties of solution-processable metal chalcogenides, followed by some recent achievements in health monitoring with photodetectors and gas sensors based on metal chalcogenides. Last we present further research directions and challenges to develop an integrated wearable platform for monitoring human activity and personal healthcare.

  • Recent advances in lithographic fabrication of micro-/nanostructured polydimethylsiloxanes and their soft electronic applications

    Donghwi Cho, Junyong Park, Taehoon Kim, Seokwoo Jeon

    J. Semicond.  2019, 40 (11): 111605

    doi: 10.1088/1674-4926/40/11/111605

    Abstract Full Text PDF Get Citation

    The intensive development of micro-/nanotechnologies offers a new route to construct sophisticated architectures of emerging soft electronics. Among the many classes of stretchable materials, micro-/nanostructured poly(dimethylsiloxane) (PDMS) has emerged as a vital building block based on its merits of flexibility, stretchability, simple processing, and, more importantly, high degrees of freedom of incorporation with other functional materials, including metals and semiconductors. The artificially designed geometries play important roles in achieving the desired mechanical and electrical performances of devices and thus show great potential for applications in the fields of stretchable displays, sensors and actuators as well as in health-monitoring device platforms. Meanwhile, novel lithographic methods to produce stretchable platforms with superb reliability have recently attracted research interest. The aim of this review is to comprehensively summarize the progress regarding micro-/nanostructured PDMS and their promising soft electronic applications. This review is concluded with a brief outlook and further research directions.

  • Preparation and application of carbon nanotubes flexible sensors

    Shuo Li, Xiao Feng, Hao Liu, Kai Wang, Yun-Ze Long, S. Ramakrishna

    J. Semicond.  2019, 40 (11): 111606

    doi: 10.1088/1674-4926/40/11/111606

    Abstract Full Text PDF Get Citation

    Based on the good extensibility and conductivity, the flexible sensors (FSs) have a wide range of applications in the field of the electrochemical energy storage and variable stress sensors, which causes that the preparation of FSs also become a hot spot of research. Among the materials for preparing the FSs, the flexible carbon matrix composites (FCMCs) have become the widely used material since the good performance in the properties of electrochemistry and mechanics, which could be divided into three types: the carbon nanofibers (CNFs), the carbon nanospheres (CNSs) and the carbon nanotubes (CNTs). Compared with CNFs and CNSs, the CNTs wrapped by the polydimethylsiloxane (PDMS) have the advantages of the excellent extensibility and electrochemical stability. Therefore, the CNTs flexible sensor (CFS) could be well used in the field of the FSs. The purpose of this review is summarizing the preparation methods and application fields of CFS and proposing the research direction of CFS in the future. In this paper, two methods for fabricating the CFS have been designed by consulting the methods mentioned in the literature in recent years, and the advantages and disadvantages between the two methods have been explained. The application fields of CFS in recent years are enumerated, and the conclusion that the application fields of CFS are very wide is drawn. At the end of this paper, the review concludes with an overview of key remaining challenges in the application fields of the CFS.

  • Advances in flexible and wearable pH sensors for wound healing monitoring

    Mei Qin, Hao Guo, Zhang Dai, Xu Yan, Xin Ning

    J. Semicond.  2019, 40 (11): 111607

    doi: 10.1088/1674-4926/40/11/111607

    Abstract Full Text PDF Get Citation

    Wound healing has been recognized as a complex and dynamic regeneration process and attracted increasing interests on its management. For effective wound healing management, a continuous monitoring on the wound healing based on sensors is essential. Since pH has been found to play an important role on wound healing process, a variety of pH sensors systems for wound healing monitoring have been greatly developed in recent years. Among these pH sensors, flexible and wearable pH sensors which can be incorporated with wound dressing have gained much attention. In this review, the recent advances in the development of flexible and wearable pH sensors for wound healing monitoring have been comprehensive summarized from the range of optical and electrochemical bases.

  • Recent progress on gas sensors based on graphene-like 2D/2D nanocomposites

    Songyang Yuan, Shaolin Zhang

    J. Semicond.  2019, 40 (11): 111608

    doi: 10.1088/1674-4926/40/11/111608

    Abstract Full Text PDF Get Citation

    Two-dimensional (2D) nanomaterials have demonstrated great potential in the field of flexible gas sensing due to their inherent high specific surface areas, unique electronic properties and flexibility property. However, numerous challenges including sensitivity, selectivity, response time, recovery time, and stability have to be addressed before their practical application in gas detection field. Development of graphene-like 2D/2D nanocomposites as an efficient strategy to achieve high-performance 2D gas sensor has been reported recently. This review aims to discuss the latest advancements in the 2D/2D nanocomposites for gas sensors. We first elaborate the gas-sensing mechanisms and the collective benefits of 2D/2D hybridization as sensor materials. Then, we systematically present the current gas-sensing applications based on different categories of 2D/2D nanocomposites. Finally, we conclude the future prospect of 2D/2D nanocomposites in gas sensing applications.

  • III–V ternary nanowires on Si substrates: growth, characterization and device applications

    Giorgos Boras, Xuezhe Yu, Huiyun Liu

    J. Semicond.  2019, 40 (10): 101301

    doi: 10.1088/1674-4926/40/10/101301

    Abstract Full Text PDF Get Citation

    Over the past decades, the progress in the growth of materials which can be applied to cutting-edge technologies in the field of electronics, optoelectronics and energy harvesting has been remarkable. Among the various materials, group III–V semiconductors are of particular interest and have been widely investigated due to their excellent optical properties and high carrier mobility. However, the integration of III–V structures as light sources and numerous other optical components on Si, which is the foundation for most optoelectronic and electronic integrated circuits, has been hindered by the large lattice mismatch between these compounds. This mismatch results in substantial amounts of strain and degradation of the performance of the devices. Nanowires (NWs) are unique nanostructures that induce elastic strain relaxation, allowing for the monolithic integration of III–V semiconductors on the cheap and mature Si platform. A technique that ensures flexibility and freedom in the design of NW structures is the growth of ternary III–V NWs, which offer a tuneable frame of optical characteristics, merely by adjusting their nominal composition. In this review, we will focus on the recent progress in the growth of ternary III–V NWs on Si substrates. After analysing the growth mechanisms that are being employed and describing the effect of strain in the NW growth, we will thoroughly inspect the available literature and present the growth methods, characterization and optical measurements of each of the III–V ternary alloys that have been demonstrated. The different properties and special treatments required for each of these material platforms are also discussed. Moreover, we will present the results from the works on device fabrication, including lasers, solar cells, water splitting devices, photodetectors and FETs, where ternary III–V NWs were used as building blocks. Through the current paper, we exhibit the up-to-date state in this field of research and summarize the important accomplishments of the past few years.

  • Recent progress in epitaxial growth of III–V quantum-dot lasers on silicon substrate

    Shujie Pan, Victoria Cao, Mengya Liao, Ying Lu, Zizhuo Liu, Mingchu Tang, Siming Chen, Alwyn Seeds, Huiyun Liu

    J. Semicond.  2019, 40 (10): 101302

    doi: 10.1088/1674-4926/40/10/101302

    Abstract Full Text PDF Get Citation

    In the past few decades, numerous high-performance silicon (Si) photonic devices have been demonstrated. Si, as a photonic platform, has received renewed interest in recent years. Efficient Si-based III–V quantum-dot (QDs) lasers have long been a goal for semiconductor scientists because of the incomparable optical properties of III–V compounds. Although the material dissimilarity between III–V material and Si hindered the development of monolithic integrations for over 30 years, considerable breakthroughs happened in the 2000s. In this paper, we review recent progress in the epitaxial growth of various III–V QD lasers on both offcut Si substrate and on-axis Si (001) substrate. In addition, the fundamental challenges in monolithic growth will be explained together with the superior characteristics of QDs.

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