Basics of Transistors

Links: video on physics of semiconductor doping and depletion region, flip-flop circuits, how to build SRAM

15 flashcards · Physics · by lakesare

1. What's the semiconductor?

   Material which conductance depends on the environment (current, temperature). Actually even insulators can conduct electricity if heated up (because that will allow their electrons to gain enough energy to leave their bands), but this temperature would be too high (glass will melt eg).

2. What's doping?

   Process of deliberately introducing other elements into a crystal.

3. How to create an N-type or P-type semiconductor?

   Usually silicon has 4 valence electrons: N-type: dope silicon with some element that has 5 valence electrons, so that 5th is free to move around P-type: dope silicon with some element that only has 3 electrons, so that hole is created (which is sort of a positive charge)

4. Why are N-type semiconductors called so?

   N-type is called so because it's the negative charge (non-bound electron) that moves. Not because of their charge! Both N-type and P-type semiconductors are neutral (because a doping material has corresponding amount of protons in its atom). Links: great youtube video

5. What types of semiconductors is transistor made of?

   Both N-type and P-type semiconductors.

6. Why are transistors used as a switch instead of eg mechanical switches?

   tiny solid-state (nothing moves), so they are incredibly fast

7. What's the fundamental difference between conductors and insulators?

   conductors: electrons can travel freely between atoms insulators: electrons don't have enough energy to travel between atoms Links: khan academy video

8. What's meant by ground?

   Actual ground may work. Basically a place that you could take from or give to infinitely many electrons.

9. What happens when we place N-type and P-type semiconductors together?

   A depletion region occurs! And prevents any current from floating through these semiconductors.

10. When N-type and P-type semiconductors are next to each other current doesn't flow. How do we make current flow?

    By applying a small voltage to base.

11. When is transistor considered to be in the 1 state, and when in 0?

    0: no current flows through it (default condition) 1: current flows through it (small voltage was applied to base)

12. What is a flip-flop circuit?

    A circuit that can store 1 bit of information. n transistors => n AND/ORs => flip-flop.

13. How does flip-flop circuit function?

    If write is enabled (1) - DATA IN turns into DATA OUT. If write is disabled (0) - nothing happens.

14. What's a valence electron?

    It's an electron on the outer shell of an atom, that can participate in formation of covalent bond with another atom.

15. When does a covalent bond form?

    When 2 atoms have some electrons on their outer shell (valence electrons), they can form a chemical bond.