Lecture Notes on Transistors

Introduction to Transistors

• Transistors revolutionized technology and civilization.
• Foundational component in smartphones (about 2 billion transistors in a processor).

Functions of Transistors

• Act like a switch (no moving parts).
• Amplify weak signals (basic function of a transistor).

Basic Structure of Transistors

• Made of semiconductors (e.g., silicon).
  • Silicon atoms bonded with four neighboring silicon atoms.
  • Each silicon atom has four electrons in its valence shell.
• Covalent bonds formed by sharing electrons among silicon atoms.

Electrical Conductivity of Silicon

• Pure silicon has low electrical conductivity.
• Electrons need energy to become free electrons to conduct electricity.

Doping Techniques

• Doping: Improves conductivity of semiconductors.
  • N-type Doping: Injecting phosphorus (5 valence electrons).
    • One free electron available for conduction.
  • P-type Doping: Injecting boron (3 valence electrons).
    • Creates holes; electrons can fill these holes.

Diodes and Their Function

• Formed by combining P-type and N-type silicon.
• Boundary of P-N junction creates electric field:
  • Electrons migrate to holes, creating positive/negative charge on either side.
• Forward Biasing:
  • Power source attracts electrons and allows current flow.
• Reverse Biasing:
  • Blocks electricity flow; no current.

Transistor Operation

• Consists of two diodes (P-N junctions) back to back.
• One diode reverse biased in any configuration, keeping transistor off.
• Applying sufficient voltage allows current to flow (forward biased).
• Small base current leads to a large collector current (current amplification).

Bipolar Junction Transistor (BJT)

• Transistor discussed is a bipolar junction transistor.
• Amplification can be enhanced by cascading multiple BJTs.
• Input signal leads to amplified output signal.

Transistor as a Switch

• Can act as a switch based on applied voltage.
• Fundamental property for digital electronics and memory.
• Example: Flip-flop, a basic dynamic memory element in computers.

Conclusion

• Encouragement to learn more about transistors via related videos.
• Support for educational content highlighted (patreon.com).

Note: Ensure to watch the related video on the transistor as a switch for deeper understanding.