Extra Practice Questions

Question 1

Which Classes of materials have band gaps?

Answer 1

Insulators & Semi-Conductors

Question 2

What is Fermi lvl (EF) and how does it relate to the Fermi Function?

Answer 2

The Fermi lvl is the value of energy when the Fermi Function f(EF) =0.5

Question 3

What is a legitimate reason to use Silicon technology for electronics (Assume microelectronic devices), and Why?

Answer 3

Silicon (Si) can easily be doped because it’s Easy to infuse Si with something that has more/less valence electrons to change it’s conductivity.

Question 4

True or False: A Wide Band Gap makes is easier for electrons to conduct

Answer 4

False: Wider band gap doesn’t make it easier to conduct e-

Question 5

How many electrons are in Valence Bands in Semi-Conductors & Insulators?

Answer 5

in Semi-Conductors & Insulators, the Valence Bands are Full.

Question 6

Which of the following is true of metals?

a) All the possible electron states are connected; there is no break in energies between states.

b) All the possible electron states are always occupied; there are no available unoccupied states.

c) There are empty states directly above occupied states without a break in energies.

d) There are empty states directly below occupied states without a break in energies.

Answer 6

a) Proven false by metal band diagram’s first case - Has a break

b) If every state was already occupied, metals couldn’t conduct

c) In case 1 of the metal band diagram’s the empty state is right above occupied states

d) Look at c)

Question 7

Describe the 2 cases that can produce metals/conductor properties (Metal Band Diagrams)

Answer 7

Case 1) The occupied state is at the very bottom, and is filled with electrons. The Empty state is right above the occupied state, and there is a gap between the empty state and the Conduction Band

Case 2) There are 2 Bands that overlap. The above band 1 is empty, and the band 2 beneath it contains electrons. The overlap allows the e- states in Band 1 to move into Band 2 with any amount of energy, so it can conduct into these states.

Question 8

How would you expect the drift velocity of electrons to change in a semiconductor when the applied voltage increases from –1V to 0V?

Answer 8

The magnitude of the Drift Velocity will Decrease, b/c using the formula of the Electric Field E =V/d we can compare initial & final magnitudes and see whether it increase or decreases. Magnitude of I -1 I is larger than I 0 I so the magnitude decreases thus Drift Velocity decreases magnitude aswell.

Question 9

Insulators do not allow current to flow easily, but neither does vacuum, so why do we bother to insert dielectrics between the parallel plates of our capacitors?

Answer 9

Presence of the Dielectric Increases amount of charges we can store on the plates.

Question 10

Capacitors can hold Both…

Answer 10

Capacitors can hold Both: Charge (In the plates) and Energy (In the dielectric)

Question 11

Which of the following is an incorrect statement about capacitors?

a) Switching to plates with higher dielectric constants increases capacitance.
b) Switching to dielectrics with lower dielectric constants increases capacitance.
c) Using a metal in place of a dielectric increases surface charge density.
d) Applying a stronger external voltage to a capacitor will increase its capacitance.
e) All Of The Above

Answer 11

a) Dielectric constant of dielectric matters only not the plates
b) C is proportional ∝ to ε (epsilon)
c) If put metal btwn plates, there nothing holding charges apart, since charges can flow through conductive metal
d) False
e) All Of The Above

Question 12

What does the Dielectric Constant Represent?

Answer 12

How well we are able to Polarize a material.

Question 13

Why might you expect the dielectric constants of polymeric materials with lots of cross-linkages to decrease at lower applied signal frequencies than those of polymeric materials with very few cross-linkages?

Answer 13

Changes in Orientation-based polarization since it is at the lowest frequency and is the first to fall off (Remember the εr vs f(Hz) graph). It is more difficult to polarize at a Higher Frequency for turning large objects.

Question 14

What are Electronic Energy bands?

Answer 14

Allowable energy states for electrons

Question 15

What is a Work Function

Answer 15

Energy needed to pull an electron off a metal

Question 16

What is the Matthiessen’s rule, and what type of material does it apply to?

Answer 16

Matthiessen’s rule: Ptotal = Po + ∝ ΔT + Pi + Pd only applies to metals. (Row total = Thermal conductive component of resistivity of an ideal metal + contribution of resistivity from impurities + contribution from deformation of martials)

Question 17

Parallel plate capacitors usually have _____ between their plates

Answer 17

Parallel plate capacitors usually have Insulators/Dielectrics between their plates

Question 18

What are Capacitors commonly used for? (Applications)

Answer 18

Surge Protection, AC-DC conversion, Energy storage, and Sensing

Question 19

Is this the symbol for the Permeability of a vacuum: εo

Answer 19

No: εo is the symbol for Permittivity, μ0 is the symbol for Permeability of a vacuum.

Question 20

Is an acceptor a substitution atom that contributes at least two surplus electrons?

Answer 20

No, Acceptor: Happens If we dope a S.C with something that has fewer valence e- and creates holes.

Question 21

Which of the following is ALWAYS true of the band structure for a conductor?
a) The conduction band and valence band never overlap
b) The conduction band is empty
c) There are open states available to electrons that are already at 𝐸𝑓

Answer 21

a) Represents a different type of conductor
b) Represents a different type of conductor
c) Will always have open states available for electrons that are already at Ef (directly adjacent)

Question 22

What happens if you apply a forward-bias to a PN junction?

Answer 22

Flows from Anode to the Cathode

Question 23

True or False: weaker doped regions account for more of the width of the depletion region?

Answer 23

True: Because weaker doped regions has fewer charge carriers, so the depletion region has to go further into that region to recover same amount of charges.

Question 24

The role served by Resist in the production of semiconductor devices is to:

Answer 24

Create a Mask - From the oxide layer on top of Si then create different doped regions

Question 25

What are the 5 steps of Fabrication?

Answer 25

1) Substrate Oxidization - Foundation (Easily Doped/Rigid & brittle)
2) Pattern - Creating a Stencil (sensitive coating resist)
3) Develop & Rinse - Resist ( +ve - resemble mask, -ve - opp to mask)
4) Deposition - Intrinsic & Extrinsic Regions (Depth depends on: Technique. Dopant, Substrate, Temp)
5) Metallization - Metal deposited to become electrical contacts (etch away to break shorts)

Question 26

Metallization is the process of:

Answer 26

Creating metallic contacts on a circuit

Question 27

What defines temperature?

Answer 27

Indicator of average atomic kinetic energy.

Not: A unit of Energy, a change in Energy, or vibrations within a solid

Question 28

True or False: Phonons are vibrations of an atomic lattice which are commonly modelled by a series of pullies.

Answer 28

False: Harmonic motion of atoms, and that motion we describe via Phonons

Question 29

What is a Diatomic Chain?

Answer 29

A chain the is infinite in one direction and is made up of alternating elements.

Question 30

Volumetric strain occurs when a material’s temperature changes. When is it equal to the cube of the linear strain?

Answer 30

When the material is Isotropic which means the material is expanding uniformly along all three axis.

Question 31

What does Anisotropic mean?

Answer 31

It is not Isotropic

Question 32

You have deposited and patterned a positive resist atop a piece of GaAs using a mask that allows light to pass through rectangular holes. What will the remaining resist layer look like after you have developed and rinsed the resist?

Answer 32

The resist layer will resemble the maskused for the patterning

Question 33

Why do we need to etch away part of a metallization layer to produce usable microelectronic devices?

Answer 33

So that we can get rid of Short Circuits, since it inherently creates device with them.

Question 34

Which of the following is true?

a) Resistivity of an intrinsic semiconductor is mostly due to the presence of holes.

b) Resistivity of an intrinsic semiconductor is equally dependent on holes and electrons.

c) Resistivity of a p-type semiconductor is mostly due to the presence of electrons.

d) Resistivity of an n-type semiconductor is mostly due to the presence of holes.

d) None of the above

Answer 34

d) None of the above

Solve by using formula of conductivity since it is inversely proportional to resistivity (1/p)

Question 35

The boundaries of the phonon dispersion curve depend most directly on…

Answer 35

Depend mostly on Atomic Spacing, since the boundaries of the curve are π/a and a = Atomic Spacing.

Question 36

What is the Formula of Thermal Conduction (k)?

Answer 36

Thermal Conduction = k = k(lattice) + k(electrons

Question 37

What is the dominant contribution to the thermal conduction of a ceramic?

Answer 37

Lattice Vibrations,

In a metal it would be electrons

Question 38

The interatomic spacing is the ________ of the intersections between a constant energy line and the vibrational energy curves

Answer 38

The interatomic spacing is the Midpoint of the intersections between a constant energy line and the vibrational energy curves.

Rememeber: E(r), r is the midpoint of E

Question 39

Why does tempering increase the TSR (Thermal Shock Resistance) of a material?

Answer 39

It increases the stress required for failure