Risorse bibliografiche
Risorsa bibliografica obbligatoria
Risorsa bibliografica facoltativa
Scheda Riassuntiva
Anno Accademico 2019/2020
Scuola Scuola di Ingegneria Industriale e dell'Informazione
Insegnamento 095155 - ELECTRON DEVICES
Docente Monzio Compagnoni Christian
Cfu 10.00 Tipo insegnamento Monodisciplinare

Corso di Studi Codice Piano di Studio preventivamente approvato Da (compreso) A (escluso) Insegnamento

Obiettivi dell'insegnamento

The course aims to present an in-depth analysis of the most important semiconductor devices used in modern electronics, with emphasis on the MOS Transistor and the Bipolar Junction Transistor. A main goal is to allow students to clearly understand the working principles and the electrical behavior of the devices starting from the careful investigation of their basic physics and pointing out the role played by their most relevant design parameters. This, in turn, aims to make students develop the skills and critical-thinking needed not only to address the operation but also to optimize the performance of a semiconductor device. Thanks to that, students will be able to understand what are the driving forces behind the successful trends of microelectronic technologies and why these trends are the outcome of relentless changes in device structure/geometry/materials, representing another important goal of the course. In summary, the course aims to provide students with the background and competencies needed not only to master the operation of electron devices within circuit applications but also to directly work on state-of-the-art semiconductor devices and technologies.

Risultati di apprendimento attesi

Knowledge and understanding (Dublin Descriptor 1)

After this course, the student knows and understands:

- the basic physics, the working principles and the electrical characteristics of the most relevant electron devices used in modern electronics;

- the dependence of the electrical behavior of the investigated electron devices on their design parameters;

- the guidelines ruling the evolution of semiconductor devices and technologies.


Applying knowledge and understanding (Dublin Descriptor 2)

After this course, the student is able to:

- apply suitable analysis methodologies to investigate the operation of semiconductor devices;

- determine the impact of changes in the design parameters of the investigated electron devices on their electrical behavior;

- master the operation of the investigated electron devices in circuit applications;

- discuss problems related to semiconductor devices and technologies with clarity, using technical terms and with a solid physical and mathematical background.

Argomenti trattati

Review of basic properties of semiconductor materials

- Energy bands in a semiconductor material, dependence of the energy gap on temperature, density of states for the conduction and valence bands;

- Thermodynamic equilibrium: Fermi-Dirac and Maxwell-Boltzmann statistics, Fermi level, concentration of electrons and holes;

- Current transport by drift and diffusion of charge carriers, resistivity and sheet resistivity;

- Electrostatic potential in a semiconductor material: non-linear Poisson equation, Debye length;

- Non-equilibrium conditions: quasi-Fermi levels, continuity equation for electron and holes, dielectric relaxation time, Shockley-Read-Hall theory for carrier generation/recombination via defect-assisted processes.

p-n junction

- Basic structure and device electrostatics under thermodynamic equilibrium: band diagram, built-in potential, electric field profile;

- Forward and reverse bias: band diagram, quasi-Fermi levels, potential drops and current components along the junction, Shockley ideal-diode equation, wide-base and narrow-base diodes;

- Generation/recombination currents in the space-charge region of the junction, high level of injection and parasitic resistances, Gummel plot, temperature dependence of the current-voltage characteristics of the device;

- Small-signal model of the p-n junction.

Metal-semiconductor junction

- Basic structure and device electrostatics under equilibrium and non-equilibrium conditions;

- Current transport: Schottky's diffusion theory, Bethe's thermionic-emission theory, thermionic-emission-diffusion theory;

- Schottky effect;

- Tunneling ohmic contacts;

- Impact of interface states on device operation.

MOS capacitor

- The MOS system: basic structure, working principles, band diagram under thermodynamic equilibrium and in the presence of a gate bias, working regimes of the device;

- Analysis of device electrostatics: calculation of the substrate charge as a function of the surface potential from the solution of the Poisson equation, surface potential and substrate charge as a function of the gate bias, threshold voltage;

- Small-signal capacitance: dependence on the gate bias (C-V curve), low-frequency, high-frequency and deep-depletion regimes;

- MOS capacitor with ring: split C-V, impact of the ring bias on device electrostatics, on threshold voltage and on the C-V curve;

- Oxide charge and interface states: impact on device electrostatics and on the C-V curve;

- Polysilicon gate: technological benefits, electrostatic drawbacks and impact on the threshold voltage of an n-MOS and of a p-MOS.


- The long-channel MOSFET: basic structure of the device, working principles, gradual-channel approximation, electrostatic analysis and calculation of the depletion and inversion charge in the channel under subthreshold and strong-inversion conditions, general expression for the drain current;

- Current-voltage characteristics of the long-channel MOSFET above threshold: ohmic, parabolic and saturation regimes, pinch-off condition at the drain, band diagram and quasi-Fermi levels along the channel, small-signal model of the transistor, output resistance in the saturation regime and channel length modulation, carrier transit time in the channel, body-effect;

- Subthreshold conduction in the long-channel MOSFET: carrier diffusion from source to drain, subthreshold current, subthreshold slope, carrier generation in the channel, transcharacteristics of the transistor;

- Dependence of the electrical characteristics of the device on the oxide thickness, on substrate doping and on temperature, impact of oxide charge and interface states on the drain current, source/drain parasitic resistances and capacitances;

- Short-channel MOSFET: electrostatics, short-channel effect, DIBL, velocity saturation along the channel and its impact on the current-voltage characteristics of the device, early saturation of the drain current due to velocity saturation at the drain;

- MOSFET scaling: constant-field scaling and generalized scaling, scaling trade-offs and constraints, high-k dielectrics, metal gate, Tox-Wdmax space for the design of scaled MOSFETs, FinFETs and advanced MOSFET structures, relevant scaling issues in nanoscale devices, statistical variability, leakage currents. 

Bipolar junction transistor (BJT)

- Basic structure of the device, working principles, current gain, collector current of the prototype transistor;

- Electric field in the quasi-neutral base region: non-uniform doping, high injection, band-gap narrowing and engineering of the base material, expressions for the collector current;

- Base current: shallow emitter and deep emitter;

- Dependence of the current gain of the transistor on the collector current, Gummel plot, carrier recombination in the base/emitter depletion layer, parasitic resistances, Kirk effect, modulation of the base conductivity;

- Current-voltage characteristics of the BJT: saturation regime and forward-active regime, Early effect;

- Small-signal model of the BJT, frequency response, cut-off frequency and its dependence on the collector current, forward transit time;

- Evolution of device parameters, advanced device structures, polysilicon emitter, SiGe base. 


- Electrostatics

- Fundamentals of semiconductors

- Basic mathematics

Modalità di valutazione

The exam consists in an oral test. During the test, the student is asked questions related to all the topics debated in the course and has to prove not only his/her knowledge and understanding (see Dublin Descriptor 1) but also his/her abilities to apply the acquired knowledge and understanding (see Dublin Descriptor 2). The test may last up to, but not more than, one hour per student. The student is free to withdraw from the test at any moment; in that case, the test will be considered failed. At the end of the test the student is told whether he/she passed or not the exam. In the former case, the student receives a grade from 18 to 30 cum laude out of 30. In the latter, the student has to improve his preparation and repeat the test at another date. 

Risorsa bibliografica facoltativaY. Taur, T. H. Ning, Fundamentals of modern VLSI devices, Editore: Cambridge Univ. Press, Anno edizione: 2009, ISBN: 978-0-521-83294-6

2nd ed.

Forme didattiche
Tipo Forma Didattica Ore di attività svolte in aula
Ore di studio autonome
Laboratorio Informatico
Laboratorio Sperimentale
Laboratorio Di Progetto
Totale 100:00 150:00

Informazioni in lingua inglese a supporto dell'internazionalizzazione
Insegnamento erogato in lingua Inglese
Disponibilità di materiale didattico/slides in lingua inglese
Disponibilità di libri di testo/bibliografia in lingua inglese
Possibilità di sostenere l'esame in lingua inglese
schedaincarico v. 1.6.2 / 1.6.2
Area Servizi ICT