Semiconductor Memory
Introduction
Semiconductor memory is a term for a device that stores digital data that is created using integrated circuit technology. It is also referred to as transistor memory, integrated-circuit memory, memory chips, large-scale integrated memory, and semiconductor storage.
Programs and data are stored in semiconductor memory, which serves as the primary memory component of microcomputer-based systems. The primary memory elements are semiconductor devices, which store code and data permanently. The microprocessor has direct access to the semiconductor memory. Additionally, the microprocessor's running time and the access time of the data stored in the main memory must coincide.
As a result, semiconductors are the recommended primary memory technology. Many technologies and memory types have arisen due to the explosive demand for semiconductor memories. In the electronics literature nowadays, one may find terms like ROM, RAM, EPROM, EEPROM, Flash memory, DRAM, SRAM, SDRAM, and the relatively new MRAM. Everyone has a unique set of benefits and applications.
Types of Semiconductor Memory
Based on how the memory functions, electronic semiconductor memory technology may be divided into two primary types or categories:
- Random Access Memory, or RAM
- Read-only memory, or ROM
The varieties of RAM and ROM that are available are diverse. These result from the multitude of accessible technology and the diversity of applications. This indicates several acronyms and abbreviations for different types of memories, such as Flash, MRAM, PROM.
1. Random Access Memory (RAM)
Random-access memory, or RAM as its name suggests, is a semiconductor memory technology used to read and write data in any sequence or as the processor needs. It is employed in applications like computer processor memory, where random access to variables and other storage is necessary. This kind of memory is used to store and read data repeatedly.
Because modern computing and processing technology demands vast amounts of memory to meet the memory-hungry applications utilized today, random access memory is employed extensively in computer applications. Numerous RAM varieties are widely used, including SDRAM with its DDR3, DDR4, and soon DDR5 versions.
DRAM
Random access memory comes in the form of dynamic RAM. Every bit of data in DRAM is stored on a capacitor, and each capacitor's charge level determines whether the bit is a logical 1 or 0. Nevertheless, the data must be updated regularly because these capacitors lose their charge over time. It becomes known as a dynamic RAM due to this dynamic refreshing.
DRAM is a semiconductor memory frequently utilized as the primary RAM in devices like workstations and personal computers. For usage in PCB assembly, semiconductor devices are often offered as integrated circuits (SIs) or, less frequently these days, as leaded components.
SRAM
Static Random Access Memory is what SRAM stands for. The name of this type of semiconductor memory comes from the fact that data does not need to be dynamically updated, in contrast to DRAM. These semiconductor devices have a substantially quicker cycle time since they do not require a break between accesses, allowing them to provide read and write timings generally 10 ns compared to 60 ns for DRAM.
SDRAM
Synchronous DRAM, or SDRAM. Compared to traditional DRAM, this type of semiconductor memory can operate at higher rates. It can open two sets of memory addresses simultaneously and is synchronized with the processor's clock. SDRAM reduces the latency caused by non-synchronous RAM, which must shut one address bank before opening the next, by randomly moving data from one set of addresses to the other.
There are several memory technology types included in the SDRAM family. The acronym DDR, or Double Data Rate, refers to them. The newest technology available now is DDR4. However, DDR5 will shortly overtake it and provide some notable performance gains.
MRAM
Also known as magnetic RAM, magneto-resistive RAM. Instead of storing data using electric charges, this non-volatile RAM system keeps data with magnetic heads. In contrast to DRAM and other technologies that depend on an uninterrupted supply of energy to preserve data integrity, MRAM maintains data integrity even during a power outage.
It only needs a little electricity for active operation, which is an additional benefit. Because production procedures have been established to permit its manufacture, this technology has the potential to become a significant participant in the electronics sector.
2. Read Only Memory (ROM)
One type of semiconductor memory technology is called read-only memory (ROM), in which data is written once and then left unchanged. Because of this, it is utilized when data must be kept safe, even during a power outage, as many memory technologies cause data loss under such circumstances.
For instance, ROM is where a computer's BIOS is kept. As the name suggests, writing data to ROM is difficult. Special hardware can be needed to write the data into the ROM initially, depending on the technology employed in the ROM.
PROM
PROM is an acronym that represents Programmable Read Only Memory. Since it is a semiconductor memory, information written to it only needs to be done once and is permanently stored there. These memory modules are purchased unprogrammed and require a specialized PROM programmer for programming. A PROM typically consists of several fusible linkages, some of which are "blown" to supply the necessary data pattern during programming.
The PROM uses a capacitor to store its data as a charge. Each cell has a charge storage capacitor that may be read twice if necessary. Nevertheless, it has been discovered that the data may be lost, and the charge may seep away after several years.
EPROM
Erasable Programmable Read-Only Memory, or EPROM for short. Semiconductor memory of this type allows for programming and erasure at a later date. Usually, silicon is exposed to UV radiation to do this. This is made possible by a circular window in the EPROM container that allows light to penetrate the silicon inside the chip. This window is often labeled when the PROM is in use, particularly if the data has to be kept safe for a long time.
EEPROM
Electrically Erasable Programmable Read Only Memory or EEPROM may be used to write and delete data by applying an electrical voltage. Usually, this is used on the chip's erase pin. Like other forms of PROM, EEPROM keeps its data in memory even during a power outage. EEPROM is slower than RAM, much like other forms of ROM. FGMOS, often called floating-gate MOSFETS, create EEPROM memory cells.
Flash Memory
One may think of flash memory as advancement in EEPROM technology. It may be used to write and delete data in blocks. It also allows for single-cell reading and writing of data. Programming voltages at levels compatible with electronic equipment are used to erase and reprogram portions of the chip. It is beneficial because it is also non-volatile.
Data is stored in flash memory using a variety of memory cells. FGMOS, often called floating-gate MOSFETS, are used to create the memory cells. These FG MOSFETs, often known as FGMOS for short, can store an electrical charge for up to 10 years without needing to be connected to a power source.
Disadvantages of Flash Memory
- It costs more per bit than hard discs.
- Not as quick as other types of memory
- A restricted quantity of write/erase cycles
PCM
Also referred to as P-RAM or simply Phase Change Memory, semiconductor memory is used in semiconductor devices. The phenomenon at the centre of it is the transition of chalcogenide glass from an amorphous (high resistance) to a polycrystalline (low resistance) state or phase. Since each cell's condition can be determined, this may be used to store data. Though it has yet to be widely released, this kind of memory is anticipated to rival flash memory.