Xiaorong Luo
Professor
University of Electronic Science and Technology of China, China
Website: http://www.ese.uestc.edu.cn/info/5053/4663.htm

Speech Title: Novel High Breakdown Voltage GaN-Based Power Devices
Abstract: Compound semiconductor GaN has been an excellent material for the power devices over last few years. The high critical electric field (3.3 MV/cm) allows to fabricate transistors with high breakdown voltage (BV), and high mobility of the 2-dimensional electron gas (2DEG) reaches ultralow on-resistance (Ron). Therefore, GaN-based power devices have been promising candidates for the next-generation high efficiency and high-voltage power switches. The BV is one of the most important parameters for power devices. However, the electric field concentration effect and high leakage current limit its BV. In consequence, it is necessary to increase the BV. In this speech, three kinds of high voltage GaN-based power devices have been demonstrated. Firstly, an AlGaN/GaN MIS-HEMT with pulsed laser deposited (PLD) AlN interface protection layer (IPL) and trench termination (T2) structure is experimentally investigated. The T2 structure extends the depletion region and increases the average electric field strength, achieving an enhanced BV. The AlN IPL improves the interface quality and reduces the interface trap density, which is verified by frequency-dependent C-V measurement and conductance method. Secondly, we proposed a novel AlGaN/GaN HEMT with a high BV and low dynamic on-resistance, which features fluorine ion implantation in the thick SiNx passivation layer. Fluorine ion implantation in the thick passivation layer could keep the peak position of fluorine and vacancies distribution far away from the 2DEG channel, thus effectively suppress the current collapse. Fluorine ions in the passivation layer is also used to optimize the surface electric field distribution and thus increase the BV. Thirdly, an AlGaN/GaN schottky barrier diode (SBD) with double-heterojunction is experimentally investigated. The fabricated SBDs achieve a uniform and low turn-on voltage (Von), a high BV, a high on/off current ratio and a high Baliga's figure-of-merit.

Jianjun Yi
Professor
Director of Key Laboratory of synthetic resins, PetroChina, China

Speech Title: Effects of electron donors on hydrogen sensitivity of Ziegler-Natta catalysts
Abstract: Since the discovery of Ziegler-Natta catalyst in the 1950s, it has played a vital role in the development of polyolefin industry. With the increasing demand for high melt flow rate polypropylene products in the market, the hydrogen sensitivity of catalysts has gradually become one of the main hot spots in Ziegler-Natta catalyst research and development. However, there is still a lack of systematic research on the regulation and mechanism of hydrogen sensitivity on Ziegler-Natta catalyst system, which affects the improvement of hydrogen sensitivity of catalysts. The internal electron donor has an important influence on the hydrogen sensitivity of the catalyst, but the mode of action of the internal electron donor in the catalyst and the mechanism of action affecting the hydrogen sensitivity of the catalyst have not been clearly understood. Therefore, it is of great significance to study the influence of internal electron donor on the catalytic performance of the catalyst, especially the relationship between the structure of internal electron donor and the hydrogen sensitivity of the catalyst, as well as the mechanism of action of internal electron donor.
In this paper, we synthesized three internal electron donor compounds with similar structure, investigated the interactions of various components in catalysts by FT-IR, XPS, XRD. The interactions of catalysts components were also calculated by density functional theory method. The influence of structure of internal electron donor on the performance of the catalysts was also investigated. The results confirmed that that the hydrogen sensitivity is related to the ratio of the crystal forms β-magnesium chloride in the catalyst. The higher the ratio of β-magnesium chloride, the better the hydrogen sensitivity of the catalyst is, which is of great significance to the structural design of high hydrogen sensitivity catalysts.

Zhiyuan Liu
Professor
Chinese Academy of Sciences, China

Speech Title: Stretchable conductive materials by structural designs
Abstract: Stretchable electronics, which could be as soft and stretchable as human tissues, plays a vital role in the full integration of electronic components with human body. The key issue to realize stretchable electronics is how to make thin-film conductors accommodate strain and keep conductive under large mechanical deformation. Several methods were proposed to achieve the mesh/mesh-like structure of conductive materials to fabricate stretchable conductors. These methods were all based on the active material design which may limit the functionality of the conductor. Herein, we report an alternative strategy, surface strain regulation, to tune the strain transferring process from the polymeric substrate to the metal thin film, achieving a randomly-distributed locally-concentrated mode of the strain in the meat film. Thus, the metal film can possess a network structure and keep conductive under large mechanical strain. Also, multiple functions can be achieved. High stretchability of ~ 400%, anti-notch and self-healing ability, high interfacial adhesion of ~ 2.5 MPa of metal film and polymer, and hundreds of square centimeters fabrication are achieved. Taking advantages of these superior properties, the stretchable conductor is successfully utilized as the bio-interface electrode to monitor the on-skin and in-vivo bio-electrical signals. Three-month implantation to wirelessly detect intramuscular myoelectric signals in rats was achieved. Besides, based on the concept of surface strain regulation, the sensitivity of the stretchable strain gauge was also significantly enhanced both for our new fiber-shape sensors and for new 3D stretchable strain sensors, benefiting the subtle vibration detection and body gesture monitoring. Our strategy is independent of the metal film formation mechanism and the conductive material used, and opens up a new way to fabricate stretchable conductors with superior properties. It also provides a new design platform of stretchable conductive materials. Based on it, many other new methods and stretchable bio-interface sensors could be further developed.

Lan Wang
Associate Professor
RMIT University, Australia

Website: https://www.rmit.edu.au/contact/staff-contacts/academic-staff/w/wang-associate-professor-lan
Speech Title: Antisymmetric magnetoresistance in van der Waals Fe₃GeTe₂/graphite/Fe₃GeTe₂ tri-layer heterostructures
Abstract: Van der Waals (vdW) ferromagnetic materials are rapidly establishing themselves as effective building blocks for next generation spintronic devices. When layered with non-magnetic vdW materials, such as graphene and/or topological insulators, vdW heterostructures can be assembled (with no requirement for lattice matching) to provide otherwise unattainable device structures and functionalities. We report a hitherto rarely seen antisymmetric magnetoresistance (MR) effect in van der Waals heterostructured Fe₃GeTe₂/graphite/Fe₃GeTe₂ devices. Unlike conventional giant magnetoresistance (GMR) which is characterized by two resistance states, the MR in these vdW heterostructures features distinct high, intermediate and low resistance states. This unique characteristic is suggestive of underlying physical mechanisms that differ from those observed before. After theoretical calculations, the three resistance behavior was attributed to a spin momentum locking induced spin polarized current at the graphite/FGT interface. Our work reveals that ferromagnetic heterostructures assembled from vdW materials can exhibit substantially different properties to those exhibited by similar heterostructures grown in vacuum. Hence, it highlights the potential for new physics and new spintronic applications to be discovered using vdW heterostructures.

Jianyong Ouyang
Associate Professor
National University of Singapore, Singapore

Website: http://www.dmse.nus.edu.sg/staff/ouyang.php
Speech Title: Flexible Thermoelectric Polymers and Ionogels
Abstract: Thermoelectric materials can directly convert heat into electricity. There is abundant of low-grade heat on earth but most of them are dissipated to ambient environment as waste heat. The conventional thermoelectric materials are inorganic semiconductors and semi-metals. But those inorganic materials have problems of scarce elements, high cost, high toxicity and poor mechanical flexibility. Thus, thermoelectric polymers have been gaining more and more attention because they consists of common elements like C, O, S and H and have merits of low density, low cost, low thermal conductivity and high mechanical flexibility. In particular, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is very promising as the next-generation thermoelectric material because of its addition merit of solution processability. PEDOT:PSS can be dispersed in water and some polar organic solvents, and high-quality PEDOT:PSS films can be readily prepared by solution processing techniques like coating and printing. The main problem for thermoelectric polymers is their low power factor. It is important to develop novel methods to enhance the thermoelectric properties.
We develop a couple of methods to significantly enhance the power factor of PEDOT:PSS. At first, we improved the electrical conductivity and thus the power factor by secondary doping. Second, we developed the sequential treatments of PEDOT:PSS with acid and base. The sequential treatments can improve the power factor to 334 W/(m K2). We further enhance the power factor to be >700 W/(m K2) through the combination with ionic liquid. Finally, we will present our work in developing ionogels with ionic liquids for high-performance thermoelectric conversion.