ELECTRONIC DEVICES

At the end of the course, the student will be able to understand and derive the electrical behavior of main silicon devices. He can also be able to use the derived models both for the component biasing and for the small signal analysis.  The student will be in the condition to understand the construction characteristics (process or design) of the silicon deices and how they affect the device performance, and can also analyze and understand the main manufacturing steps of the integrated technology devices.

1. Knowledge and understanding: the student will be able to understand the construction methods of and the operating principles of electronic devices (diodes, BJT, MOSFET).

2. Ability to apply knowledge and understanding: the student will be able both to derive the models of the semiconductor components, and to linearize them when the device is used inside a simple electronic circuit. The student will also be able to simulate, implement and test electronic circuits, firstly, modeled with open source simulation tools and, then, mounted on breadboard and characterized with laboratory instrumentations.

3. Making judgments: the student will be able to independently assess whether any devices meet the requirements for the applications on which they are working and make the necessary choices in order to adapt the device to the application itself.

4. Communication and learning skills: Upon completion of the course, the student is expected to acquire the ability to convey the knowledge acquired to their interlocutors in a clear and complete way and will also be able to rework the knowledge to extend it to situations not explicitly addressed, being also able to learn independently.

The teaching should be done through frontal lectures. Approximately half of the lessons are devoted to numerical exercises and laboratory activities in the classroom.

If the teaching is given in a mixed or remote mode, the necessary changes may be introduced with respect to what was previously stated, in order to respect the program envisaged and reported in the syllabus.

The teaching should be done through frontal lectures. Approximately half of the lessons are devoted to numerical exercises and laboratory activities in the classroom.

If the teaching is given in a mixed or remote mode, the necessary changes may be introduced with respect to what was previously stated, in order to respect the program envisaged and reported in the syllabus.

Phisics of semiconductors

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, β_F 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 (note)

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.

Experiments aimed at a better understanding of the functioning of the studied electronic device are foreseen for each single topic treated. Among the various experiences there are: introduction to the simulation tool and the electronic instrumentation that will be used; characterization of passive components and their use in simple circuits (voltage and current dividers, first order passive integrators and derivators); characteristic curve of the diode and its application as a rectifier, variable capacitor and temperature sensor; characteristic curves of bipolar and MOS transistors and their applications as controlled switches and amplifiers.

Main Textbook

1.       G. Giustolisi, G. Palumbo, Introduzione ai Dispositivi Elettronici, Franco Angeli, 2005.

Other Textbooks

1.   R. S. Muller, T. I. Kamins, Dispositivi elettronici nei circuiti integrati, Bollati Boringhieri, 1993.

2.   S. Dimitrijev, Understanding semiconductor devices, Oxford University Press, 2000.

Learning is verified through the final exam. This consists of a written test, lasting 2 hours, and an oral interview. The written test, preparatory to the oral exam, consists of 5 numerical exercises that cover the contents of the course. Each question is assigned a score from 0 to 6 which takes into account the correctness of the procedure, the clarity of presentation, the correctness of the calculations and what the student has managed to complete. Students who achieve a grade of less than 15 do not have adequate knowledge to pass the exam and are not admitted to the oral exam. The result of the written test is converted into a rating scale [RESERVE (from 15 to 18), SUFFICIENT (from 19 to 22), FAIR (from 23 to 26) and GOOD (from 27 to 30)] and published on the studium platform .unict.it. Students admitted with reserve will have a limitation on the final grade (max 25/30). The oral exam is mainly held on two topics on which the student must demonstrate adequate understanding, mastery of the topics discussed and clarity of presentation. The final grade will take into account the result of the written test and, with greater weight, the outcome of the oral interview.

Verification of learning can also be carried out electronically, should the conditions require it.

Prove Einstein's relationship

Obtain the continuity equation.

Given a pn junction, assuming the step approximation is valid, derive the trend of the electric field and potential.

Find the current-voltage relationship in a long-base diode.

Given a pnp-type BJT transistor, derive the expressions of the profiles of the minority carriers in the three regions.

Given an n-p-n type BJT transistor, derive the expression of the base transport factor.

Describe what is due to the Early effect in the BJT transistor.

Given a MOS capacitor with a p-type substrate, derive the expression of the threshold voltage.

Obtain the current-voltage relationship for an n-channel MOS transistor in the triode region.

Each question listed above will be preceded by a question concerning the characteristic curve and / or the structure of the device.