Transistors and logic gates pt1

Question 1

Where do electron ‘holes’ come from

Answer 1

• Unfilled places in the outer shell
• Each shell holds up to 2n^2 electrons
• Notice how the atom is still balanced with holes

Question 2

How do free electrons appear and what is their behaviour

Answer 2

• As an electron absorbs more energy, it becomes excited; at some threshold, the electron is displaced and becomes free.
• A free electron can move between shells or between atoms (from an outer shell); roughly speaking they are “attracted” by holes.

Question 3

How do electrons and current flow in terms of potential

Answer 3

• Current (abs electrons or pos charge) moves from high to low potential
• Electrons thus move from low to high potential

Question 4

How does a capacitor/battery work

Answer 4

Question 5

Why is silicon a semi-conductor

Answer 5

It has intermediate conductivity which can be modified/”doped” to either be an insulator or conductor

Question 6

What is the difference between a P and N type semi-conductor

Answer 6

A P-type semi-conductor has extra holes, N-type has extra electrons.

Question 7

Properties of sandwitching P and N type semi conductors

Answer 7

• If we sandwich P-type and N-type layers together, electrons can only move in one way, i.e., from an N-type layer to a P-type layer, but not in the other direction.
• Extra electrons -> extra holes

Question 8

What was used before transistors

Answer 8

Vacuum tube
- Possibility to fail duing power on / off
- Large and bulky
- Bug / debug -> moth in tube

Question 9

What is a MOSFET

Answer 9

Type of transistor

Question 10

What is the basic design of a MOSFET

Answer 10

• FET transistors allow charge to flow through a conductive channel between source and drain terminals.
• The channel width, and hence conductivity, is controlled by the potential difference applied to gate terminal.
• In a MOSFET transistor, the channel is induced (vs. a JFET, where an explicit semi-conductor layer is used).

Question 11

What are the properties of an N-MOSFET

Answer 11

Question 12

What are the properties of a P-MOSFET

Answer 12

Question 13

What is the symbolic representation of an N-MOSFET

Answer 13

Question 14

What is the symbolic representation of a P-MOSFET

Answer 14

Question 15

What is a CMOS cell

Answer 15

A CMOS cell combines one N-MOSFET and one P-MOSFET; each transistor in a pair works in a complementary way:

Leads to low static power consumption

Question 16

What are the steps to manufacture transistors

Answer 16

Question 17

Why are components (transistors, processors etc.) packaged before being sold

Answer 17

Question 18

Moore’s law

Answer 18

Number of transistors in unit area doubles roughly every two years