Overview of NAND and NOR Flash Memory Products
With the increasing focus on integrated circuits, especially memory chips, in the domestic market, we have received a growing number of inquiries about NOR Flash, NAND Flash, SD NAND, eMMC, and Raw NAND.
To address these inquiries, we have written this article to:
Classify commonly used memory products.
Provide a brief description of their key characteristics.
Before diving into the details, we would like to recommend a highly user-friendly and stable Flash product: CS SD NAND, which offers the following features:
Driver-free operation – Plug-and-play functionality.
Surface-mountable – Suitable for automated manufacturing.
Compact size – 6×8mm, LGA-8 package.
Long endurance – High erase/write cycle lifespan.
Wide temperature tolerance – Resistant to extreme temperature fluctuations.
Optimal storage capacity – Ranges from 128MB to 4GB.
For more details, please refer to the following link: https://www.longsto.com/product/68-en.html
We categorize storage products into three main types: EEPROM, NOR Flash, NAND Flash.
Their structural frameworks are outlined as follows:
1. EEPROM
The storage capacity of EEPROM is very small, and it is commonly embedded in MCUs or used in household appliances such as remote controls and electric fans. It is primarily used for storing basic information. Since users generally do not pay much attention to this type of storage, we will not provide a detailed description here.
2. NOR Flash
NOR Flash is one of the most widely used types of memory chips, found in almost all mainstream electronic products. It is even integrated into smartphone camera modules and display driver boards. NOR Flash is primarily used for storing code and small data files.
Key Characteristics:
Interface: Predominantly SPI NOR
Typical Capacity: 1Mbit ~ 128Mbit
Packaging: Mostly SOP-8, with smaller form factors also available
Compact Size: Suitable for space-constrained applications
Due to its architectural design, NOR Flash has inherent limitations in capacity scalability and relatively slow read speeds. However, it offers a key advantage: ease of use. Engineers particularly appreciate the ability to access data directly via addresses, eliminating the need for a file system.
3. NAND Flash
NAND Flash is arguably the most popular type of storage chip today, as it is deeply integrated into the electronic products we use daily. When purchasing a smartphone, for example, you may consider whether to choose 64GB or 256GB of storage. Similarly, when buying a laptop, you might compare 256GB vs. 512GB SSDs—most of which are based on NAND Flash technology.
To better understand NAND Flash, we will categorize it based on the following aspects:
3.1 Internal Composition
NAND Flash can be categorized into SLC, MLC, TLC, and QLC based on the number of bits stored per memory cell. The fundamental difference lies in how much data each storage unit can hold:
SLC (Single-Level Cell): 1 bit per cell
MLC (Multi-Level Cell): 2 bits per cell
TLC (Triple-Level Cell): 3 bits per cell
QLC (Quad-Level Cell): 4 bits per cell
As the number of bits per cell increases, the storage density of the wafer doubles, improving cost efficiency. However, this also affects performance and endurance. Below are the key characteristics of these four types of NAND:
As we move from SLC to QLC, the erase/write cycles (endurance), performance, and quality generally decline. Currently, for mainstream consumer electronics with larger storage capacities, TLC and QLC are the most commonly used types, especially in devices such as smartphones and laptops (with SSD storage).
3.2 Manufacturing Process
There are currently two main types: 2D and 3D. The mainstream manufacturing process has now upgraded to 3D. The differences between 2D and 3D can be seen in the following illustration.
The 2D process can be understood as an old-style brick-and-mortar building, while the 3D process is akin to a skyscraper. The biggest advantage is the exponential increase in storage density. In recent years, the mainstream storage capacities in smartphones and laptops have been increasing, and this is directly related to the adoption of 3D NAND technology in the industry.
3.3 Usage Characteristics and Management Mechanisms
NAND Flash products have certain inherent characteristics, and to use them properly, corresponding management mechanisms are required. The main ones include:
1）Bit Flipping and Bit Shifting:
NAND Flash may experience bit flipping, where data such as 0101 might change to 1010 due to certain factors. This necessitates the use of Error Detection and Correction (EDC/ECC) mechanisms to ensure data integrity.
2）Bad Block Management:
NAND Flash may have bad blocks when shipped from the factory (this is normal, and the factory typically marks these blocks, which have a very low occurrence rate). Additionally, new bad blocks can develop during use. Therefore, both dynamic and static bad block management mechanisms are required to handle these issues.
3）Write Endurance Limits:
NAND Flash has a limited number of write/erase cycles for each block. To maximize the lifespan of the memory, an average read/write mechanism is implemented, ensuring that blocks are used evenly over time.
4）Erase-Then-Write Mechanism:
NAND Flash operates on an erase-then-write basis, meaning data must be erased before it can be written again. The high current used during block erasure may affect neighboring blocks. To mitigate this, garbage collection and charge balancing mechanisms are used to distribute the wear evenly and maintain performance.
These management mechanisms are crucial to ensuring NAND Flash's reliable and efficient operation over its lifespan.
The SD NAND produced by CS Semi integrates all these management algorithms internally. Below is a schematic illustration of how these algorithms are implemented:
3.4 Product Classification
Raw NAND essentially involves extracting the pad points from the NAND Flash wafer and packaging them into TSOP48/BGA chips. Since Raw NAND does not come with a controller, all management algorithms for NAND Flash must be handled by the CPU. This results in two main issues: 1. It requires dealing with write drivers. 2. It increases the CPU load.
For products with built-in controllers, we classify them into two types: chip-based and module-based products. Due to the different design purposes, the quality requirements for these two product types vary significantly. We have previously written an article specifically discussing these differences：https://www.longsto.com/news/145-en.html
Chip-based products include SD NAND, eMMC, and SPI NAND. The common feature among these is that they all come with internal management mechanisms for NAND Flash, which helps reduce the CPU load. However, SPI NAND is an exception, as it only includes part of the management algorithms, meaning that a write driver is still required.
Module-based products typically include TF/SD cards, SSDs, USB drives (U-disks), and similar devices. These products often provide more comprehensive solutions and are designed to be used in consumer electronics and other applications requiring high storage capacity and ease of use.
Here is a simple comparison of several commonly used products:
CS Semi SD NAND and several other products can be specifically compared, as referenced in the following article.
If you have any questions, please contact us
Email：line@longsto.com
