NAND, eMMC, UFS, eMCP, uMCP, DDR, LPDDR and the difference between memory and memory
1. NAND Flash
The full name of NAND Flash is Flash Memory, which belongs to a non-volatile memory device (Non-volatile Memory Device). It is based on a floating gate transistor design, and charges are latched through the floating gate. Since the floating gate is electrically isolated, so Electrons reaching the gate are trapped even after the voltage is removed. This is the rationale for flash non-volatility. Data is stored in such devices and will not be lost even if the power is turned off.
According to different nanotechnology, NAND Flash has experienced the transition from SLC to MLC, and then to TLC, and is moving towards QLC. NAND Flash is widely used in eMMC/eMCP, U disk, SSD, automobile, Internet of Things and other fields due to its large capacity and fast writing speed.
SLC (English full name (Single-Level Cell - SLC) is a single-level storage
The characteristic of SLC technology is that the oxide film between the floating gate and the source is thinner. When writing data, the stored charge can be eliminated by applying a voltage to the charge of the floating gate and then passing through the source. , In this way, one information unit can be stored, that is, 1 bit/cell, the speed is fast, the life is the longest, the price is expensive (about 3 times the price of MLC), and the life of about 100,000 erasing and writing.
MLC (English full name Multi-Level Cell - MLC) is a multi-layer storage
Intel (Intel) first successfully developed MLC in September 1997. Its function is to store two units of information into a Floating Gate (the part where the charge is stored in the flash memory cell), and then use the charge of different potentials (Level), Accurate reading and writing through the voltage control stored in the memory.
That is, 2bit/cell, the speed is average, the lifespan is average, and the price is average, about 3000---10,000 times of erasing and writing. By using a large number of voltage levels, each cell stores two bits of data, and the data density is relatively large, and can store more than 4 values at a time. Therefore, the MLC architecture can have better storage density. TLC (English full name Trinary-Level Cell) is a three-tier storage
TLC is 3bit per cell. Each cell can store 1/2 more data than MLC. There are eight charging values in total, that is, 3bit/cell. There are also Flash manufacturers called 8LC. The access time is longer, so the transmission speed is slower.
The advantage of TLC is that the price is cheap, the production cost per megabyte is the lowest, and the price is cheap, but the life span is short, only about 1000 times of erasing and writing.
QLC (English full name Quadruple-Level Cell) four-layer storage unit
The full name is Quad-Level Cell, a four-layer storage unit, that is, 4bits/cell. QLC flash memory particles have higher storage density than TLC, and at the same time, the cost is lower than TLC. The advantage is that the capacity can be made larger and the cost is lower. .
It is not difficult to see that the performance of the four types of NAND flash memory is different. The cost per unit capacity of SLC is higher than that of other types of NAND flash memory, but its data retention time is longer and the reading speed is faster; QLC has larger capacity and lower cost, but due to its low reliability and longevity Shortcomings and other shortcomings still need to be further developed.
From the perspective of production cost, read and write speed and service life, the order of the four categories is: SLC>MLC>TLC>QLC;
The current mainstream solutions are MLC and TLC. SLC is mainly aimed at military and enterprise applications, with high-speed writing, low error rate, and long durability. MLC is mainly aimed at consumer-grade applications, its capacity is 2 times higher than SLC, low-cost, suitable for USB flash drives, mobile phones, digital cameras and other memory cards, and is also widely used in consumer-grade solid-state drives today.
NAND flash memory can be divided into two categories: 2D structure and 3D structure according to different spatial structures. Floating gate transistors are mainly used for 2D FLASH, while 3D flash mainly uses CT transistors and floating gate Is a semiconductor, CT is an insulator, the two are different in nature and principle. The difference is:
2D structure NAND Flash
The 2D structure of the memory cells is only arranged in the XY plane of the chip, so the only way to achieve higher density in the same wafer using 2D flash technology is to shrink the process node.
The downside is that errors in NAND flash are more frequent for smaller nodes; in addition, there is a limit to the smallest process node that can be used, and the storage density is not high.
3D structure NAND Flash
To increase storage density, manufacturers have developed 3D NAND or V-NAND (vertical NAND) technology, which stacks memory cells in the Z-plane on the same wafer.
In 3D NAND flash, the memory cells are connected as vertical strings rather than horizontal strings in 2D NAND, and building in this way helps achieve high bit density for the same chip area. The first 3D Flash products had 24 layers.
The processing process of Nand Flash
NAND Flash is processed from the original silicon material. The silicon material is processed into wafers, which are generally divided into 6 inches, 8 inches, and 12 inches. The wafer is produced based on this wafer. The number of wafers that can be cut out of a circle is determined by the size of the die, the size of the wafer, and the yield rate. Usually, hundreds of NAND FLASH chips can be made on one wafer.
The die before the chip is encapsulated becomes a Die, which is a small piece cut from a Wafer by a laser. Each Die is an independent functional chip, which is composed of countless transistor circuits, but can eventually be packaged as a unit Become a flash particle chip.
A wafer containing a NAND Flash wafer is first cut and then tested. After the test is passed, it is cut and packaged. After the package is completed, another test will be performed. Remove the intact, stable, and full-capacity die, and encapsulate it to form the daily Nand.
The rest on the wafer is either unstable, partially damaged and therefore insufficient capacity, or completely damaged. Taking into account the quality assurance, the original factory will declare this die dead, which is strictly defined as the disposal of all waste products.
Qualified Flash Die original packaging factory will package into eMMC, TSOP, BGA, LGA and other products as needed, but there are also defects in packaging, or the performance is not up to standard, these Flash particles will be filtered out again, and the product will be guaranteed through strict testing. quality.