DISPOSITIVI ELETTRONICI

The course aims to provide the basics of semiconductor physics, integrated circuit manufacturing technologies and modelling of the main electronic devices (diodes, bipolar transistors and MOS transistors).

With reference to the devices under study, at the end of the course, the student must be able to analyse the polarization, by providing an adequate circuit modelling, and must be able to discern which constructive characteristics will influence its performance. The student will also be able to analyse some simple device manufacturing steps in integrated technology.

The teaching is done through frontal lectures. Approximately one third of the lessons are devoted to numerical exercises in the classroom.

Electric field and potential. Current and current density. Thermal velocity of electrons. Drift current. Mobility coefficient. Ohm's law. Silicon as a semiconductor. Electrons and holes. Intrinsic concentration. Doped semiconductors. Types of doping and their effects. Mobility in doped semiconductors. Thermal equilibrium and the mass action law. Charge neutrality. Generation/recombination processes and injection of carriers. Low and high levels of injection. Recombination transient. Diffusion processes. Diffusion current. Einstein relationship. Continuity equation. Injected charge and profile of minority carriers. Potential in a non-uniform concentration material. Boltzmann equations. Fermi Potential.

Diodes

Pn junction. Space charge region. Abrupt junction analysis: electric field, potential, width of the depletion region. Analysis of the linear junction: electric field, potential, width of the depletion region. Nonequilibrium pn junction: potential barrier and carrier flows in direct and inverse polarization. Carriers at the edge of the depletion region. Long diode: profile of minority carriers, current density. Short diode: profile of minority carriers, current density, transit times. Current-voltage characteristic of the pn junction. Second order effects: low and high levels of injection. Temperature dependence. Capacitive effects: depletion capacitance, diffusion capacitance. Junction breakage and Zener diodes. Metal-semiconductor junctions: Schottky diodes and ohmic contacts. Static circuit models. Small-signal analysis. Low-frequency small-signal model. High-frequency small-signal model.

Bipolar transistors

Types of bipolar transistors: npn and pnp. The bipolar transistor in equilibrium. Operating regions. Analysis of the bipolar transistor in the forward active region. Current amplification in the common base configuration. Emitter efficiency. Base transport factor. Current amplification in the common emitter configuration. Current-to-voltage characteristic in the bipolar transistor: Forward and Reverse configuration. Ebers-Moll model. Simplification of the Ebers-Moll model: interdiction region, direct active region, inverse active region, saturation region. Second order effects: Early effect, bF dependence on the collector current. Characteristic curves in the common emitter configuration. Capacitive effects: base-emitter capacitance, base-collector capacitance. Temperature dependence. Low-frequency small-signal models. High-frequency small-signal models. Transition frequency. Parasitic effects: distributed resistances and substrate capacitance.

MOS transistors

The MOS capacitor. Flat band potential. Effect of the gate-substrate voltage on the MOS capacitor. Operating regions: accumulation, depletion, weak inversion, strong inversion. Surface potential and operating regions. Threshold voltage of the MOS capacitor. The MOS transistor: operating principle. Current-to-voltage characteristic in the MOS transistor: analysis of the conduction channel. Expression of the drain current. Operating regions: interdiction, triode and saturation. Body effect. Channel length modulation. Capacitive effects: gate-source capacitance, gate-drain capacitance, drain-bulk and source-bulk capacitances. Low-frequency small-signal models. High-frequency small-signal models.

Planar technology

Thermal oxidation. Thermal diffusion: Fick's law and diffusion profiles. Ionic implantation. Deposition of thin layers: chemical vapor deposition, physical vapor deposition. Annealing and gettering. Photolithography: masking, exposure and attack. Bipolar process. CMOS process.

1. G. Giustolisi, G. Palumbo, Introduzione ai Dispositivi Elettronici, Franco Angeli, 2005.
2. R. S. Muller, T. I. Kamins, Dispositivi elettronici nei circuiti integrati, Bollati Boringhieri, 1993.
3. S. Dimitrijev, Understanding semiconductor devices, Oxford University Press, 2000.