3D bioprinter uses carbon nanotube enhanced cellulose

A group of researchers at Chalmers University of Technology have managed to print and dry three-dimensional objects made entirely by cellulose for the first time with the help of a 3D-bioprinter. They also added carbon nanotubes to create electrically conductive material. The effect is that cellulose and other raw material based on wood will be able to compete with fossil-based plastics and metals in the on-going additive manufacturing revolution, which started with the introduction of the 3D-printer. The tiny chair made of cellulose is a demonstrational object printed using the 3D bioprinter at Chalmers University of Technology. Photo: Peter Widing 3D printing is a form of additive manufacturing that is predicted to revolutionise the manufacturing industry. The precision of the technology makes it possible to manufacture a whole new range of objects and it presents several advantages compared to older production techniques. The freedom of design is great, the lead time is short, and no material goes to waste. Plastics and metals dominate additive manufacturing. However, a research group at Chalmers University of Technology have now managed to use cellulose from wood in a 3D printer. “Combing the use of cellulose to the fast technological development of 3D printing offers great environmental advantages,” says Paul Gatenholm, professor of Biopolymer Technology at Chalmers and the leader of the research group. “Cellulose is an unlimited renewable commodity that is completely biodegradable, and manufacture using raw material from wood, in essence, means to bind carbon dioxide that would otherwise end up in the atmosphere. The breakthrough was accomplished at Wallenberg Wood Science Center, a research center aimed at developing new materials from wood, at Chalmers University of Technology. The difficulty using cellulose in additive manufacturing is that cellulose does not melt when heated. Therefore, the 3D printers and processes designed for printing plastics and metals cannot be used for materials like cellulose. The Chalmers researchers solved this problem by mixing cellulose nanofibrils in a hydrogel consisting of 95-99 percent water. The gel could then in turn be dispensed with high fidelity into the researchers’ 3D bioprinter, which was earlier used to produce scaffolds for growing cells, where the end application is patient-specific implants. The circuit in the form of a tree is made up of cellulose, which has been made electronically conductive by means of carbon nanotubes, and printed using the 3D bioprinter at Chalmers University of Technology. Forest commodities provide new, environmentally friendly materials that can be used within the field of additive manufacturing. (Photo: Peter Widing) The next challenge was to dry the printed gel-like objects without them losing their three-dimensional shape. “The drying process is critical,” Paul Gatenholm explains. “We have developed a process in which we freeze the objects and remove the water by different means as to control the shape of the dry objects. It is also possible to let the structure collapse in one direction, creating thin films. Furthermore, the cellulose gel was mixed with carbon nanotubes to create electrically conductive ink after drying. Carbon nanotubes conduct electricity, and another project at Wallenberg Wood Science Center aims at developing carbon nanotubes using wood. Using the two gels together, one conductive and one non-conductive, and controlling the drying process, the researchers produced three-dimensional circuits, where the resolution increased significantly upon drying. The two gels together provide a basis for the possible development of a wide range of products made by cellulose with in-built electric currents. “Potential applications range from sensors integrated with packaging, to textiles that convert body heat to electricity, and wound dressings that can communicate with healthcare workers,” says Paul Gatenholm. “Our research group now moves on with the next challenge, to use all wood biopolymers, besides cellulose. The research findings are presented this week at the conference that takes place in Stockholm, Sweden, June 15-17. The research team members are Ida Henriksson, Cristina de la Pena, Karl Håkansson, Volodymyr Kuzmenko and Paul Gatenholm at Chalmers University of Technology.

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Emergence of 'Devil's staircase'

Researchers at the University of Tokyo have revealed a novel magnetic structure named the “Devil’s staircase” in cobalt oxides using soft X-rays ("Observation of a Devil’s Staircase in the Novel Spin-Valve System SrCo6O11"). This is an important result since the researchers succeeded in determining the detailed magnetic structure of a very small single crystal invisible to the human eye. The magnetic structure that gives rise to the Devil's Staircase. Magnetization (vertical axis) of cobalt oxide shows plateau like behaviors as a function of the externally-applied magnetic field (horizontal axis). The researchers succeeded in determining the magnetic structures which create such plateaus. Red and blue arrows indicate spin direction. (Image: Hiroki Wadati) Recent remarkable progress in resonant soft x-ray diffraction performed in synchrotron facilities has made it possible to determine spin ordering (magnetic structure) in small-volume samples including thin films and nanostructures, and thus is expected to lead not only to advances in materials science but also application to spintronics, a technology which is expected to form the basis of future electronic devices. Cobalt oxide is known as one material that is suitable for spintronics applications, but its magnetic structure was not fully understood. The research group of Associate Professor Hiroki Wada at the University of Tokyo Institute for Solid State Physics, together with the researchers at Kyoto University and in Germany, performed a resonant soft X-ray diffraction study of cobalt (Co) oxides in the synchrotron facility BESSY II in Germany. They observed all the spin orderings which are theoretically possible and determined how these orderings change with the application of magnetic fields. The plateau-like behavior of magnetic structure as a function of magnetic field is called the “Devil’s staircase,” and is the first such discovery in spin systems in 3D transition metal oxides including cobalt, iron, manganese. By further resonant soft X-ray diffraction studies, one can expect to find similar “Devil’s staircase” behavior in other materials. By increasing the spatial resolution of microscopic observation of the “Devil’s staircase” may lead to the development of novel types of spintronics materials.

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Successors to FinFET for 7nm and beyond to be presented

At this week’s VLSI 2015 Symposium in Kyoto (Japan), imec reported new results on nanowire FETs and quantum-well FinFETs towards post-FinFET multi-gate device solutions. As the major portion of the industry adopts FinFETs as the workhorse transistor for 16nm and 14nm, researchers worldwide are looking into the limits of FinFETs and potential device solutions for the 7nm node and beyond. Two approaches, namely Gate-All-Around Nanowire (GAA NW) FETs, which offer significantly better short-channel electrostatics, and quantum-well FinFETs (with SiGe, Ge, or III-V channels), which achieve high carrier mobility, are promising options. For the first time, imec demonstrated the integration of these novel device architectures with state-of-the-art technology modules like Replacement-Metal-Gate High-k (RMG-HK) and Self (Spacer)-Aligned Double-Patterned (SADP) dense fin structures. By building upon today’s advanced FinFET technologies, the work shows how post-FinFET devices can emerge, highlighting both new opportunities as well as complexities to overcome. Imec and its technology research partners demonstrated SiGe-channel devices with RMG-HK integration. Besides SiGe FinFET, a unique GAA SiGe nanowire channel formation during the gate replacement process has been demonstrated. The novel CMOS-compatible process converts fin channels to nanowires by sacrificial Si removal during the transistor gate formation. The process may even enable future heterogeneous co-integration of fins and nanowires, as well as Si and SiGe channels. The work also demonstrates that such devices and their unique processing can lead to a drastic 2x or more improvement in reliability (NBTI) with respect to Si FinFETs. Moreover, imec demonstrated Si GAA-NW FETs based on SOI with RMG-HK. The work compares junction-based and junction-less approaches and the role of gate work function for multi-Vt implementations. New insights into the improved reliability (PBTI) with junction-less nanowire devices have been gained. Extending the heterogeneous channel integration beyond Si and SiGe, imec demonstrated for the first time strained Ge QW FinFETs by a novel Si-fin replacement fin technique integrated with SADP process. Our results show that combining a disruptive approach like fin replacement with advanced modules like SADF-fin, RMG-HK, direct-contacts can enable superior QW FinFETs. The devices set the record for published strained Ge pMOS devices, outperforming by at least 40% in drive current at matched off-currents. Imec’s research into advanced logic scaling is performed in cooperation with imec’s key partners in its core CMOS programs including GLOBALFOUNDRIES, INTEL, Micron, Panasonic, Samsung, SK hynix, Sony and TSMC.

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