Prof. Mario Lanza
Institute of Functional Nano & Soft Materials, Soochow University,
The introduction of two dimensional (2D) materials in the structure of microelectronic devices is a promising strategy to further enhance and extend their capabilities. Several 2D metallic and semiconducting materials have been successfully introduced in the structure of electronic devices, but their interaction with traditional dielectrics is very poor. We foresee that insulating materials with a 2D (layered) structure will play a key role towards the development of future 2D electronic devices and technologies.
In this seminar I will present our recent progress on 2D (layered) insulators, with special emphasis on hexagonal boron nitride (h-BN). By combining device level and nanoscale experiments with theoretical modeling we observe that h-BN is much more reliable than HfO2 as dielectric when subjected to electrical fields, which may be very useful to enlarge the lifetime of logic electronic devices. The dielectric breakdown process of h-BN doesn't follow the well-known percolation model established for 3D dielectrics because the speed of defect formation is anisotropic, due to the different atomic interactions in-plane (covalent) and out-of-plane (van der Waals). More interestingly, h-BN shows the exciting capability of tuning its electrical resistance when subjected to specific electrical stresses, a phenomenon called resistive switching (RS) that can be used to fabricate cutting-edge NVMs, namely resistive random access memories (RRAM). I will present an entire family of h-BN based RRAM devices with forming-free bipolar and threshold operation, low switching voltages down to 0.4V, high current on/off ratios up to 106, long retention times above 10 hours and striking low variability. The switching mechanism, which is based on the simultaneous generation of B vacancies and penetration of metallic ions from adjacent electrodes, will be discussed. I will also show how to tune the properties of h-BN based RRAM devices by following three different approaches: i) h-BN thickness modification, ii) h-BN grain size modification and iii) graphene interfacial electrode insertion. I will make special emphasis on the use of scalable methods for the fabrication of the devices.
In the final part of the seminar I will briefly present our recent progress on other 2D materials based electronic devices, including field effect transistors and micro electromechanical systems (MEMS). More specifically, we have developed cost-effective graphene coated nanoprobes for atomic force microscopes that show extraordinary long lifetimes, which remarkably reduces the cost and enhances the reliability of the research. Our patented technology is receiving an investment of 3M$ during the next 5 years from the Beijing Institute of Collaborative Innovation with the aim of introducing this product in the market.