Atomically controlled interfaces for future nanoelectronics

Device miniaturization, speed of operation, and lower power demands are all responses to consumer needs. These driving forces are at the origin of the spectacular development of the microelectronic Si-based technology, characterized by an exponential scaling behaviour which has been persisting for over four decades [1]. During this extended period of time, this technology has almost exclusively relied on the extremely convenient physical properties of the SiSiO2 interface, the interface between crystalline silicon and its thermal oxide [2, 3]. In the present generation, gate-oxide layers are grown with thicknesses around 20 A and with interfaces which are nearly abrupt at the atomic scale. Furthermore, specific nitrogen concentration profiles are engineered across the thin film to control the diffusion of dopants [3]. Further scaling of the SiSiO2 system is now prevented because of fundamental limits associated to leakage currents and reliability concerns [l]. Overcoming these limitations will require the use of alternative gate-oxide materials, of higher dielectric constant (high-ic materials) than SiO2 [4]. The ability to control both the atomic structure and composition of these new oxide layers is emerging as one of the major challenges for the next generation of Si-based electronic devices. Controlling the atomic properties of thin dielectric films is currently becoming a relevant issue also for the development of oxide-based devices with other functional properties. Recent reports on surprising magnetic properties in oxides, including room-temperature ferromagnetism with giant magnetic moments, offer new perspectives for the development of magneto-optic and spin-electronic devices that could operate in ambient conditions [5-7]. The fundamental nature of the dielectric response in thin-film ferroelectric perovskite oxides is currently being addressed in view of identifying key materials for the development of novel random access memory technology [8]. Other relevant developments include the fabrication of field-effect transistors based on perovskite oxides as active elements [9] and atomically engineered hetero-oxide interfaces showing unusual charge states with surprisingly high carrier mobilities [10]. In all these developments, sophisticated oxide films play the central role.