Lecture on Magnetic Bubble Memory

Introduction

• Magnetic Bubble Memory
  • A type of computer memory using soft magnetic materials.
  • Magnetic domains (bubbles) are a few micrometers in diameter embedded in a matrix.
  • Operate similarly to magnetic disk memories used in computers.
  • Bubbles are moved electrically at high speeds.

Characteristics

• Magnetic Domains
  • Looks like wavy strips.
  • Can appear as bright or dark when polarized light is applied.
  • Strips arrange in two directions: pointing up and pointing down.

Behavior of Magnetic Domains

• Magnetic Field Application
  • Bubbles shrink when a magnetic field is applied perpendicularly.
  • At a particular magnetic field, domains concentrate into small circular areas, forming magnetic bubbles.
  • Bubbles are stable in a specific applied field region.

Material Examples

• Magnetic Bubble Memory Materials
  • Rare earth ortho ferrites
  • Hexagonal ferrites
  • Rare earth ferromagnetic garnets
  • Amorphous bubble materials

Structure

• Construction
  • Uses epitaxially grown thin films of materials like ortho ferrites and garnets.
  • The material has a wavy domain structure.

Magnetic Field and Bubble Formation

• Graph Explanation
  • As the applied magnetic field increases, strip domains form bubbles when reaching a saturation value.
  • The conversion from strips to bubbles involves reducing the strip diameter to a few micrometers.

Advantages

• Non-Volatile Memory
  • High density of bubbles.
  • Stores up to 10 million bits per cm².

Disadvantages

• Access Limitations
  • Not random access; information is read serially, limiting speed to a few hundred kilobytes per second.

Applications

• Usage in Technology
  • Used in chips like micro pushers and memory cards (SD cards, SIM cards).
  • Deployed in various electronic devices needing non-volatile memory.