FocusThe research line focuses on current and emerging technologies, with activity in different fields: 1) non-volatile Flash memories, aiming at exploring scaled memory devices; 2) resistive- switching nanodevices where phenomena due to local phase and/or chemical transitions occur, aiming to provide physical insight to predict device reliability and to guide scaling behaviour; 3) organic semiconductor devices, aiming to explore solution-process carbon-based semiconductors as active materials in optoelectronic devices; 4) bio-devices, aiming to assess the electronic properties of bio molecules through the design of state of art instrumentation-on-chip. The research has a strong applicative nature and the activities are typically carried out in collaboration with leading industries and research institutes worldwide.
Fig. 1. Microelectrodes for electrical measurements in liquid of biological material, connected to the integrated circuit for signal processing
Copyright © Ing. Giorgio Uccellini 2009
Fig. 2. Numerical simulation of the thermal cross-talk between two neighboring PCM cells
A. Redaelli et al., J. Appl. Phys., 103, 111101, 2008
Most relevant research achievements
A numerical model for conduction and threshold switching in phase change memory (2007-2008)
The group has developed the first analytical model for conduction in the reset (amorphous) state of PCM devices and the first numerical model for electronic threshold switching, which enables phase transition and select/unselect operations in crossbar devices. These contributions are considered the standard explanation and model for PCM conduction and switching. The three papers introducing the experiments, theory and modeling of conduction and switching in PCM have received more than 200 citations by February 2012.
A numerical model for bipolar resistive switching memory (2011)
The group has developed the first numerical model for bipolar RRAM based on ion migration. The model accounts for the switching kinetics, the shape of switching characteristics in both polarities and the reliability characteristics. The model is currently being extended to (i) CBRAM devices, (ii) complicated structures e.g. antiparallel-connected switches and selector-memory pairs, and (iii) energy distribution of ion migration, to account for the observed scaling trends of set/reset voltage.
Single-electron effects in nanoscale memories (2007-2011)
The group investigated the limitations to the reliability of charge-based memories coming from threshold voltage fluctuations due to random telegraph noise , the ultimate programming accuracy stemming from the, the statistical electron injection toward the storage layer, the statistical distribution of the amplitude and time constants of the random telegraph noise in deca-nanometer MOSFETs. Application to charge-trap memories was also pursued, pointing out the limitations of the technology for mass storage applications.
Devices based on organic semiconductors
The research contributed to the analysis of transport and light-matter interaction phenomena in organic semiconductors. The dependence of the mobility on charge carrier density, on electric field and its correlation with polymer molecular weight have been addressed. The issue of contact resistances in organic transistors has been modelled and analysed. Organic photodetectors with efficiency up to 15% have been developed and tested for indirect X-ray detection to target biomedical applications. Efforts are now directed toward Ink-Jet printing technology for dispensing layers of functional materials in a precisely addressable way to fabricate imagers on plastic substrates.
Bio-molecule electrical characterisation
The properties of single layer supported biomembranes have been investigated using AFM with attoFarad resolution in capacitance images with nanometric spatial resolution. The electronic properties of transmembrane proteins have been studied (EU project BOND) aiming at using them as odorant detectors. A platform for tracking neuronal cell and electrical detection of neurotransmitter exocitosys (EU- EXCELL) has triggered the development of specific circuitry able to reach zeptoFarad resolution in impedance spectroscopy of bio-nano samples.