Semiconductor Memories

Semiconductor Memories

Semiconductor Memory Overview

  • Semiconductor memory is integral to electronics using computer processing.
  • Memory cards are standard for temporary data storage in devices like cameras and mobile phones.

Types and Technologies

  • Diverse types and technologies exist to meet memory requirements.
  • Examples include ROM, RAM, EPROM, EEPROM, Flash, DRAM, SRAM, SDRAM, F-RAM, and MRAM.
  • Continuous development aims to enhance performance.

FRAM vs. MRAM

FRAM (Ferroelectric Random Access Memory)
  • Uses a ferroelectric capacitor architecture with ferroelectric materials.
  • Advantages over Flash:
    • Lower power usage.
    • Faster write performance.
    • Greater read/write endurance.
    • Data retention times exceed 10 years.
MRAM (Magnetoresistive Random Access Memory)
  • Offers unlimited performance and infinite read/write cycles.
  • FRAM reads are destructive, leading to wear-out over time.
  • Faster read/write cycle and access times: 35ns vs. 60ns (FRAM).
  • Provides data retention for 20 years.

SDRAM

  • DDR3, DDR4, and DDR5 represent different types of SDRAM.

ROM (Read-Only Memory)

  • Data is written once and not altered thereafter.
  • Non-volatile, permanent data storage.
  • Computers incorporate ROM containing start-up firmware (BIOS).
BIOS (Basic Input/Output System)
  • Boot firmware containing code for computer boot-up processes.
  • Includes loading the operating system (OS) into RAM.

Types of ROM

PROM (Programmable Read-Only Memory)
  • Used to update firmware like BIOS via installation software.
  • Modified only once by the user.
  • Blank PROM is programmed using a PROM programmer.
  • Small fuses inside the chip are burnt open during programming.
  • Not erasable.
Types of PROM:
  • UV-ROM (Ultraviolet-erasable ROM): Erasable and reprogrammable using ultraviolet light.
  • EPROM (Erasable Programmable ROM): Programmed using high voltages and ultraviolet light exposure for ~20 minutes.
  • EEPROM (Electrically-erasable Programmable ROM): Erased and reprogrammed multiple times, allowing single location erase/write.
Flash Memory
  • Updated version of EEPROM, enabling simultaneous changes to numerous memory locations.

Advantages of ROM

  • Non-volatile.
  • Cannot be accidentally changed.
  • Cheaper than RAM.
  • More reliable than RAM.
  • Static and do not require refreshing.
  • Contents are known and verifiable.

RAM (Random Access Memory)

  • Semiconductor memory for reading and writing data in any order.
  • Short-term memory for data the processor needs.
RAM in Computer Operations
  • Data is stored for tasks like playing games or streaming movies.
  • Processor accesses data quickly from RAM.
  • Replaced with new data upon task completion.
  • Insufficient RAM can slow down computer performance.

SDRAM Variants

  • SDRAM with DDR3, DDR4 and DDR5 are used in bulk.

SDRAM vs. DDR

  • SDRAM: Synchronous Dynamic Random Access Memory released in 1997.
  • DDR: Double Data Rate SDRAM released in 2000.
  • DDR transfers data at roughly twice the speed of SDRAM.
Speed Comparison
  • SDRAM speeds: 66 MHz, 100 MHz, 133 MHz.
  • DDR speeds: 200 MHz, 266 MHz, 333 MHz, 400 MHz.