Session 0: Review of Solid State Devices From Atom to Transistor 1
Objective To Understand: how Diodes, and Transistors operate! p n p+ n p- n+ n+ p 2
21 Century Alchemy! Ohm s law resistivity Resistivity is characteristic of the material Art of VLSI design is: to put together materials with different resistivity's next to each other to perform a certain task. Conductor Al, Cu SiO 2 10 Ω 10 Ω Insulator 3
Periodic Table of Elements Bohr Atomic Model Abbreviated Periodic Table wave-particle duality de Broglie standing wave Energy Bands: 4
Bohr Atomic Model Single atom: 2 atoms: N atoms: 2N electrons forbidden energies allowed energies Pauli exclusion principle 5
Materials Conductor 10 Semi-conductor 10 Insulator Ω Conduction band Conduction band N electrons Valance band 2N states E G (Si) = 1eV E G (Ge) = 0.7eV Valance band E G (SiO 2 ) = 9eV 2N states empty seat / filled seat 6
Intrinsic Semiconductor +4 +4 +4 Covalent bands Valance electrons +4 Si +4 +4 +4 +4 +4 7
Intrinsic Semiconductor electron density +4 +4 +4 hole density Covalent bands hole free electron +4 Si +4 +4 Valance electrons +4 +4 +4 10 210 useless!! 8
n-type Semiconductor Donor: P, As, Sb +4 +4 +4 electron density hole density Covalent bands free electron for each dopant +4 P +5 +4 Si Valance electrons +4 +4 +4 10 210 9
p-type Semiconductor Acceptor: B, Ga, In Covalent bands +4 +4 +4 hole for each dopant electron density hole density +4 B +3 +4 Si Valance electrons +4 +4 +4 10 210 10
Energy Diagrams Potential Energy Kinetic Energy 11
Energy Diagrams 12
Energy Diagrams 13
Density of States Azadi stadium Boxing stadium In Stadium: Number of available seats could be a function of distance from the center so. : number of available states for the electrons could be function of Energy : Seats are not the same for fans so empty states for electrons! 14
Fermi Function Probability of Electron Distribution 1 1 is called the Fermi energy or the Fermi level. If we are 3kT away from the Fermi energy then we might use Boltzmann approximation: if 1 if 3 2 2 3 # of electrons at energy E 0 1 # of holes at energy E 0.5 1 15
Materials Conductor 10 Semi-conductor 10 Insulator Ω Conduction band Conduction band N electrons Valance band 2N states E G (Si) = 1eV E G (Ge) = 0.7eV Valance band E G (SiO 2 ) = 9eV 2N states empty seat / filled seat 16
Electron / Holes : Intrinsic intrinsic # of electrons at energy E 1 # of holes at energy E.. 1 1 17
Electron / Holes : n-type n-type # of electrons at energy E 1 # of holes at energy E.. 1 1 18
Electron / Holes : p-type p-type # of electrons at energy E 1 # of holes at energy E.. 1 1 19
Fermi Energy intrinsic n-type p-type 20
Fermi Energy p-type n-type p-type n-type 21
Flow of Charge Drift Electric field gravitational field Diffusion Charges move to be evenly distributed throughout space. Similar to perfume in room or heat in a solid 22
PN Junction p n 23
PN junctions p n 24
PN junctions p n Depletion region 25
PN junctions p n depletion region 26
PN junctions, Reverse Biased p n depletion region 27
PN junctions, Forward Biased p n depletion region 28
BJT Electrostatics pnp Emitter Base Collector p+ n p- Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions 29
BJT Electrostatics pnp Emitter Base Collector p+ n p- Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctions 30
BJT Electrostatics pnp Emitter Base Collector p+ n p- 31
JFET Junction FET Gate Source n p+ 2 Drain p+ Gate 32
JFET n p+ 2 p+ ~0 33
JFET n p+ 2 p+ 0 34
JFET n p+ 2 p+ ~0 35
JFET n p+ 2 p+ ~0 36
JFET n p+ 2 2 p+ 2 0 2 37
Qualitative Theory of the NMOSFET SiO2 A A n+ n+ 0 0 p The potential barrier to electron flow from the source into the channel region is lowered by applying V GS > V T 38
Qualitative Theory of the NMOSFET n+ n+ 0 p 0 n+ n+ 0 p n+ n+ p 39