Electron Devices

Research focus

The Peer review has evaluated this group as Excellent

The research is focused on the design, experimental characterization and numerical modeling of innovative electronic devices, with particular emphasis on non-volatile memories and on devices based on organic semiconductors, and on the analysis of few basic physical properties of electronic devices at the nanoscale. The main research activities are described in detail in the following: Flash memory reliability The major issue in scaling the Flash memory technology is today that of reliability. Tunnel oxide reliability constraints limit its thickness to about 9 nm for the NOR technology, hindering any scaling of the channel length. Our research is devoted to the analysis of the mechanisms affecting the reliability of NOR Flash memories, to devise improved operating schemes and conditions for maximum reliability and allow the scaling of the technology to 45 and 32 nm nodes. In this frame, we have investigated the generation rate and statistics of the oxide defect in different technologies and developed new experimental methods for the characterization of their physical parameters (tunnelling times, spatial and energetic positions), contributing to substantial advancement in fundamental and applied understanding of the physics underlying the device reliability. Recently, a new reliability issue due to threshold voltage fluctuations due to charge trapping in the tunnel oxide, giving rise to giant random telegraph noise effects, has been investigated. Innovative technologies for post-Flash scenario As of today, it looks unlikely that the Flash technology for non-volatile storage will evolve beyond the 32 nm node, and new storage concepts must be conceived. The research activity is studying phase-change and discrete-trap memories for the post-floating-gate scenario. The phase-change memory (PCM) relies on the ability of some chalcogenide glasses to reversibly switch from the crystalline to the amorphous phase under the application of current pulses, heating the chalcogenide active region by Joule effect. Since the two phases have different resistivities, the cell state can be read electrically. We have conducted experimental and modelling activities to investigate the relevant issues of PCM characterization, programming, reliability and scaling. A self-consistent model has been developed, including electrical switching, phase change and data retention prediction. Most recently, we have focused on the analysis of the feasibility and reliability of multilevel PCM cells. The discrete-trap concept relies instead on storing charge in discrete sites rather than in a continuous floating-gate, thus eliminating the SILC reliability constraints and allowing further tunnel oxide scaling. The research activity was initially focused on nanocrystal memories, whose program, erase and reliability performance has been studied, identifying the trade-offs and constraints to the development of a successful non-volatile technology. More recently, we have studied nitride-based cells, where native traps in a nitride layer are used to store charge. Issues related to the localization of the stored charge and its impact on the device characteristics, as well as the conduction properties of high-K dielectric layers to be used to engineer the tunnel barrier, have been addressed. 333 Organic semiconductor devices The field of organic electronics, which exploits the semiconducting properties of a large class of organic compounds, is attracting considerable interest thanks to peculiar characteristics of organic semiconductors, such as ease of processability, mechanical flexibility, chemical tailoring of physical and electronic properties and electroluminescence in the visible range. The research is focused on three main topics: investigation of the carrier transport properties in amorphous layers through the realization and characterization of organic field effect transistors; investigation of the mechanism of conductance switching, a still debated issue in the scientific community, essential for the realization of organic memory cells and studies on the interaction of infrared light with small molecules and on the exciton dissociation efficiencies through the development and characterization of organic photodetectors. Access to the electronic properties of devices at the nanoscale through novel instrumentation Basic physical questions on the electrical behaviour of nanoscale devices deserve special instrumentation to be explored. We have developed instrumentation for noise analysis of nanodevices and applied it to the study of single spin resonant phenomena through the investigation of single charge trapping&detrapping in MOSFETs under strong magnetic fields and at sub-kelvin temperatures. The group is also investigating the electrical properties of biological materials with emphasis on the electrical response of mammal olfactory receptors upon interaction with specific odorants, aiming to explore high sensitive and selective bio-sensors. To address the single nanosome, the group had to develop a special AFM that could perform impedance spectroscopy measurements with attofarad resolution on nanometric areas. This instrument will also help in the fundamental questions arising on the dielectric properties of insulators at the nanoscale.

Departments

Dipartimento di Elettronica e Informazione (DEI)

Professors

Andrea Lacaita (full professor)
Marco Sampietro (full professor)
Alessandro Spinelli (full professor)
Daniele Ielmini (assistant professor)
Giorgio Ferrari (assistant professor)
Christian Monzio Compagnoni (assistant professor)
Dario Natali (assistant professor)