The research in professor Mario Lanza’s group is mainly dedicated to the development of micro and nanoelectronic devices using (mainly) advanced two dimensional (2D) materials. Currently, we are more than 20 members (including master, PhD and postdocs), and we have received generous funding above 8 Million CNY from the National Science Foundation, Ministry of Science and Technology, Ministry of Education, and Jiangsu government (among others). With these resources, we are currently working on:

Two-dimensional materials based memristors (70%)

Memristors are two-terminal metal/insulator/metal (MIM) nanocells that can change their resistivity depending on the electrical stimuli applied between the electrodes. This device has attracted enormous interest during the last decade due to their excellent performance as non-volatile electronic memory, and it is a very promising candidate to build electronic synapses for future artificial neural networks and neuromorphic (i.e. brain-like) computing systems. Our group was one of the first in the world that successfully introduced 2D materials in the structure of memristors, and so far we obtained some of the most outstanding performances. In our recent Nature Electronics paper, we synthesized multilayer hexagonal boron nitride (h-BN) via chemical vapor deposition, and used it to fabricate metal/h-BN/metal memristors that exhibit both volatile and non-volatile resistive switching, with very fast switching speed (~10 ns per transition), very stable relaxation process (low cycle-to-cycle variability), and ulta-low power consumption (0.1 fW in standby and 600 pW per transition). We also discovered a novel resistive switching mechanism in h-BN stack, which involves the migration of both intrinsic species (i.e. Boron ions) and extrinsic species (i.e. metallic ions) simultaneously. Overall, we demonstrate that metal/h-BN/metal memristors show outstanding performance as electronic synapses, and that they can effectively reproduce several plastic operations. Our collaborators in this field are: Jing Kong (MIT, USA), Phillip Wong (Stanford University, USA), Rainer Waser (Juelich Forschungszentrum, Germany), Luca Larcher (UNIMORE, Italy) and Xiaoming Xie (Chinese Academy of Sciences).

(Left) a,c, Cross-sectional TEM images of Au/Ti/5–7-layer h-BN/Cu and Au/15–18-layer h-BN/Au synapses, respectively. b,d, Zoom-in images of the areas highlighted with dashed squares in a and c, respectively. LD, lattice disorders; TF, thickness fluctuations. e, Top-view scanning electron microscopy (SEM) image of 5 µm × 5 µm Ag/h-BN/Au synapse. f, SEM image of a 150 nm × 200 nm Au/Ti/h-BN/Au cross-point synapse. Scale bars: 2 nm (a); 1 nm (b); 5 nm (c); 2 nm (d); 2 µm (e); 300 nm (f). (Right) a, Two sequences of 4 PVS (with 30 pulses each) collected in a 5 µm × 5 µm 5–7-layer h-BN synapse, showing progressive synapse potentiation with Vup = 0.8 V (blue) and Vup = 0.9 V (red). Vdown = 0.1 V and τup = τdown = 20 µs. b, Zoom-in of a, with the current in logarithmic scale. c, Sequence of PVS with Vup = 1.2 V, showing first an abrupt potentiation, and later an additional sudden current increase to the non-volatile RS regime. d, Two sequences of PVS showing synapse potentiation with Vup = 0.8 V (blue) and Vup = 0.9 V (red), using a pulse period τdown = 200 µs, longer than that used in a. All plots have been collected on the same device. Reprinted with permission from Y. Shi et al. Nature Electronics 1, 458–465, 2018. Copyright by Nature Publishing Group 2018.

Field effect transistors made of 2D materials (10%)

Despite the apparition of new breaking device configurations (like the aforementioned memristors), field effect transistors (FET) are still the core unit of most electronic circuits. In our group we are developing transistors using channels  made of graphene and molybdenum disulfide. As the interface of these materials with traditional dielectrics (like SiO2, HfO2 and Al2O3) is very problematic, we are using layered two dimensional dielectrics, like hexagonal boron nitride (h-BN). In this direction we like to concentrate in the study of the reliability of 2D dielectrics. In our Nano Energy article we fabricated MoS2 based phototransistors that exhibit ultra-low power consumption and high current on/off ratio, and the device was fabricated using 100% scalable processes. In this direction, our collaborators are:  Tibor Grasser (TU Wien, Austria) and Eilam Yalon (Technion – Israel Institute of Technology). Check out other more recent publications in Applied Physics Letters and Microelectronics Engineering.

(a) Schematic illustration of a matrix of field effect transistors with polycrystalline MoS2 channels. (b) Voltage dependent light/dark current ratio calculated for one of the devices shown in panel (a), using the backward curves. (c) Output characteristics measured under illumination for the device with a 20 µm wide MoS2 channel after annealing. Reproduced with permission from X. Jing et al. Nano Energy, 30, 494–502, 2016. Copyright by Elsevier 2016.

MEMS based on 2D materials (10%)

The first synthesis of graphene in 2004 opened up a new horizon in graphene and 2D materials research, as graphene properties could be for the first time experimentally characterized. After ten years of intensive research, graphene has shown unprecedented electronic, thermal, mechanical, magnetic and optical properties. Nevertheless, after more than 12 years working with 2D materials there is still a preoccupying lack of commercial applications. In our lab we also investigate the use of 2D materials in realistic electronic devices. For example, we have developed ultra-durable graphene-coated AFM tips using an industry-compatible fabrication method that allows production at low costs. Our invention, which is protected under an international patent, has already raised an investment of 550,000 €, as well as attracted the interest of the companies in the field. In this direction, our collaborators are: Andrea Ferrari (University of Cambridge, UK), Oliver Krause (NanoWorld, Germany) and Xiaoming Xie (Chinese Academy of Sciences). Visit our recent papers in Nanoscale and Advanced Materials.

Panels (a) and (c) show the SEM images of a standard AFM tip (OMCL-AC240) before (b) and after graphene coating (respectively). The presence of conformal graphene coating can be clearly observed. (b) Schematic of the graphene-coated AFM tip. Reproduced with permission from F. Hui et al. Surface & Coatings Technology, 320, 391–395, 2017. Copyright by Elsevier 2016.

Conductive atomic force microscopy (10%)

Professor Lanza is one of the world-leading experts in conductive atomic force microscopy (CAFM). With more than 14 years experience, Prof. Lanza has used CAFM systems from Park Instruments, Omicron, Bruker, NT-MDT, Seiko Instruments, Nanontec and Agilent, and has experience working in air, dry nitrogen, vacuum and ultra-high vacuum environments. Dr. Lanza contributed on the development of a logarithmic preamplifier that allows measuring currents from pico- to mili-amperes, a setup that later was adopted by many companies (e.g. Agilent, Park Systems). In 2016, Prof. Lanza edited the first book on CAFM for Wiley-VCH, which represented an important reference for all scientists in this field. Prof. Lanza has scanned samples from top companies (Infineon Technologies, Numonyx, Qimonda) and universites (Stanford, MIT).

Front cover of the book edited by Prof. Mario Lanza. Mario Lanza, “Conductive Atomic Force Microscopy: Applications in Nanomaterials”, Publisher: Wiley-VCH, ISBN: 978-3-527-34091-0, August 2017.

 

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