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In the beginning, NOR flash memory was invented

Until 1984, only SRAM or DRAM type memories existed. These were volatile memory types, which could not maintain their content without power, or they could, but only for a limited time. Dr. Fujio Masuoka sought to change this fact. After 1970 (the exact date is not known), he began research and development of transistor memory for Toshiba, which would be able to store bits (data) even without power. This was fulfilled by NOR-type memory introduced in 1984, but probably not as Masuoka had envisioned. Therefore, research and development continued and between 1987 and 1989, the first NAND-type memory was born. Although Masuoka couldn't have known at the time, his invention significantly influenced the future of computer technology.

A NAND memory chip is based on memory cells (cells), which must be able to maintain their value of 1 or 0 (one bit of user data) even without power. The memory cell is technologically based on a transistor with a floating gate, where the floating gate stores the value of the memory cell. However, to be able to do this without power, the floating gate is isolated by an oxide insulating layer. The oxide insulating layer, however, gradually loses its insulating properties with each charge and discharge (write and erase/reset) of the floating gate. After a certain number of charge and discharge cycles, the oxide insulating layer ceases to fulfill its function and the memory cell fails. However, the memory chip can handle this to a certain extent.

The original memory cells - SLC - Single Level Cell contained only 1 bit, i.e., a value of 1 or 0. However, to gain larger capacity, technologies were gradually developed that allow up to 4 bits (QLC - Quad Level Cell) to be placed in a single cell. Thus, one memory cell of a QLC chip can have up to 16 different states, but at the same time, it leads to a significant acceleration of the degradation of the oxide insulating layer, which logically shortens the lifespan of the entire NAND chip.

We'll try to shed light on the development from small capacities to today's capacities in the order of TB units and how memory chips manage the expected error rate in the following text.

From SLC to QLC, from hundreds of MB to TB units

Over the years, NAND flash memories evolved from SLC (Single-Level Cell) to QLC (Quad-Level Cell), significantly increasing the capacity of data storage media and reducing the cost per MB or GB. SLC memories store only one bit of data in each memory cell, whereas MLC (Multi-Level Cell), TLC (Triple-Level Cell), and QLC store two, three, and four bits of data in a single cell. Thanks to this evolution, NAND flash memory capacities increased from the original hundreds of megabytes to terabytes, making them key technology for modern storage devices such as SSDs, mobile phones, flash drives, memory cards, and other electronic devices.

SLC (Single-Level Cell) memories store one bit of data per memory cell. As each cell can take on only two states (0 or 1), SLC memories offer the highest performance, speed, and lifespan. However, because they store fewer data per cell, they have a lower capacity and a higher price per MB. SLC memories are often used in industrial and high-demand applications.

MLC (Multi-Level Cell) memories store two bits of data per memory cell, allowing four different states (00, 01, 10, and 11). This allows them to achieve higher capacities than SLC memories but at a slower speed and shorter lifespan. MLC memories were usually used in mainstream devices, such as standard SSD drives and flash drives, but are now being displaced by TLC and QLC memories.

TLC (Triple-Level Cell) memories store three bits of data per memory cell, enabling eight different states (000, 001, 010, 011, 100, 101, 110, and 111). TLC memories offer even higher capacities than MLC memories but at a slower speed and shorter lifespan. TLC memories have become the standard for consumer SSDs and flash drives.

QLC (Quad-Level Cell) memories store four bits of data per memory cell, allowing sixteen different states. QLC memories provide the highest capacities and the lowest costs per MB, but at the expense of slower speed and shorter lifespan than TLC, MLC, and SLC memories. QLC memories are used for the production of SSDs, flash drives, and SD cards with high capacity and lower performance requirements. QLCs are also inherently the least reliable due to the shorter lifespan of the memory cell.

3D NAND (V-NAND) improves characteristics and lifespan

The problem with the lower lifespan of TLC (Triple-Level Cell) and QLC (Quad-Level Cell) NAND chips compared to their SLC (Single-Level cell) and MLC (Multi-Level cell) predecessors is attempted to be solved by 3D NAND technology. 3D NAND is a more advanced technology that fundamentally changes the way memory cells are organized and stored. Its origin is credited to Samsung, which introduced 3D NAND in 2013. Today's SSDs, which reach TB unit capacities, would be hard to imagine without 3D NAND, especially for the average user who expects high capacity, good quality, and a reasonable price. 3D NAND is also used for the production of SLC and MLC media, but its greatest impact is on TLC and QLC.

3D NAND brings the following advantages:

  • Better quality of memory cells: The 3D structure allows the distance between individual memory cells to be increased, reducing electromagnetic interference between them and improving the overall quality and reliability of the memory cells.
  • Higher capacity: The vertical arrangement of memory cells allows for a higher storage density and thus a higher capacity in a smaller area.
  • Lower power consumption: Thanks to the smaller amount of energy required for operation and smaller operational losses (less energy leakage), 3D NAND memories are more energy-efficient than planar NAND.
  • Longer lifespan: A greater distance between memory cells improves their resistance to wear and degradation, extending the lifespan of the entire chip. This is probably the most crucial difference from the user's perspective, who expects a reliable data storage.

NAND Memory Chips Contain Manufacturing Errors, But Controllers Can Filter Them Out

NAND flash memories inherently have a certain level of error rate from the manufacturing process. This error rate is a result of the physical properties of memory cells and their manufacturing process. Even though manufacturers try to minimize errors during production, they cannot completely eliminate them. Aside from the errors inherent in the manufacturing process, the error rate is influenced by other factors, particularly how the memory medium is used.

The controller of the memory medium uses various internal functions to correct these errors, described below. One of the most important is ECC (Error Correction Code), which detects and corrects errors that may occur during data reading, writing, or storage. Additionally, there's Bad Block Management, which identifies faulty blocks and prevents them from being used for data storage. Other functions include Wear Leveling, TRIM, and Garbage Collection, which work together to optimize performance and extend the lifespan of NAND flash memories.

Thanks to these internal functions, NAND flash memories are capable of providing a relatively reliable and efficient data storage. The list of functions and their basic description is provided below in the article. Despite all these sophisticated error correction methods and 3D NAND improving QLC and older types of memory cells, manufacturers have yet to adopt newer memory chip production technologies that would allow the use of 5, 6 or more bits in a single memory cell. These technologies exist and are called Penta-Level Cell (PLC) and Hexa-Level Cell (HLC). NAND flash memories could then store five, or six bits of data per memory cell.

As of now (year 2023), however, manufacturers have refrained from using PLC and HLC, or these technologies remain in the research and development stage. Not only are PLC and HLC more prone to errors, their production is more complicated and puts more strain on the memory medium controller, but most importantly, there is no market demand for them. PLC, HLC, and potentially other similar technologies may bring us larger storage capacity in the future. The reasons for the delay in deploying PLC and HLC to the market could also be technical challenges and costs associated with the development and production of these memories. However, with further progress in research and development and potential increase in demand for higher capacities, we can expect these technologies to gradually become a common part of NAND flash memories.

Without advanced data management functions, the lifespan of today's data media would be low

NAND memory chip-based storage devices, or rather their controllers and firmware in collaboration with the operating system of a given device, manage data storage, deletion, corrections, and even wear of the memory chip through the use of these internal functions:

TRIM is a command that allows the operating system to inform the data storage about unused data blocks that can be deleted. This increases the efficiency of writing new data to the storage device, improving overall performance and lifespan. Not all NAND storage devices utilize the TRIM function.

Wear Leveling is a function that evenly distributes data writing and deletion across all the memory cells of a storage device. This ensures that no single cell is overloaded (used excessively), which could lead to its rapid wear and reduce the lifespan of the storage device. Wear Leveling is used in all current NAND storage devices.

Garbage Collection is a process through which a storage device automatically rearranges and deletes unused data. This is done during idle time (when no data is being written or read from the storage device), maintaining optimal performance for writing new data. The Garbage Collection function may or may not be implemented. Memory cards and flash drives may not need to be equipped with it; its presence and efficiency depend on the specific controller and firmware.

Over-Provisioning is a function that reserves a certain portion of the storage device's capacity for internal management and optimization. This improves performance and extends the lifespan of the storage device, as the system has more free blocks available for writing and deleting data. Not all devices are equipped with Over-Provisioning; its presence depends on the specific controller and firmware. However, SSDs typically include it.

Error Correction Code (ECC) is a method of error detection and correction that ensures data stored on NAND chips are error-free. ECC helps prevent data loss and ensures the reliability and lifespan of NAND chips.

Besides TRIM, Wear Leveling, Garbage Collection, Over-Provisioning, and ECC, NAND storage devices may contain and use other functions aimed at improving performance, reliability, and lifespan of the storage. Some of these functions include:

Bad Block Management: The management of faulty blocks includes the detection and mapping of faulty blocks in NAND flash memory and their replacement with spare blocks. This ensures greater reliability and lifespan of the memory.

Read Retry is a method that includes several attempts to read data from NAND flash memory in the event of a read error. This improves reliability and reduces the risk of data loss.

Write Cache is temporary storage that stores data before writing it to NAND flash memory. This improves the performance of the device and reduces the wear of NAND flash memory.

SLC cache is a technology that temporarily stores data in an SLC (Single-Level Cell) dedicated section of NAND memory. The purpose is to increase write speed. Once the cache is filled, the data is moved to the main storage - MLC, TLC, or QLC NAND memory.

Thermal Throttling is a process that reduces the performance of NAND flash memory if the temperature exceeds safe values. This protects data integrity and ensures the reliability of data storage.

DevSleep (Device Sleep) is a technology that allows the device to enter a deep sleep mode with low power consumption when not actively used. This reduces energy consumption, which is especially important for battery-powered mobile devices.

These functions can be implemented in NAND storage devices, such as SSDs, SD cards, and flash drives, to enhance their performance, reliability, and lifespan. However, their implementation depends on the specific controller, firmware, and data media manufacturer.

NAND Implementations: Standalone Chip, Monolith, COB

NAND flash memory chips can be implemented in various forms, such as a standalone chip, a monolithic chip (monolith), or Chip-On-Board (COB). Each of these options has its advantages and disadvantages, and the choice depends on the specific application requirements for the given device or media.

Standalone Chip is the basic form of NAND flash memory. The controller is placed separately. This implementation can be found in a wide range of devices, including SSDs, some USB flash drives, and memory cards.

Monolithic Chip (Monolith) is an integrated circuit that contains NAND flash memory and the controller in one piece of silicon substrate. This type of chip is often used in compact devices, such as mobile phones, flash drives, and microSD cards, where miniaturization and space-saving are important.

Chip-On-Board (COB) is a technology where the NAND flash memory chip is directly attached to the printed circuit board (PCB) and subsequently coated with a protective layer. COB allows reducing the size of the final device, improving thermal conductivity, and increasing resistance to vibration and shocks. However, from a data recovery perspective, it is a more complex solution.

Each of these options has its specific use depending on the requirements regarding performance, size, durability, and costs.

Data Recovery from NAND - SSDs, Mobile Phones, SD Cards, Flash Drives

Data recovery from SSDs, mobile phones, SD cards, flash drives, and other media is our main field. Each media has its own section on our website. If you need help with data recovery, select the type of media:

Cracked NAND Chip - Data Recovery is Often Impossible

If the NAND chip is physically damaged (typically cracked), data recovery becomes a very difficult task, often impossible. If there is no mechanical damage to the NAND chip itself, the solution might be similar to the case of a media controller failure. However, if the mechanical damage affects the NAND chip and the memory blocks are damaged, it can be stated that data recovery is impossible.

Should we venture beyond the current technologies for data recovery from memory cards, flash drives, SSDs, and mobile phones, and had an unlimited budget and access to advanced technologies, we could consider methods such as microscopic probing and laser decapsulation. Even so, their application for successful data recovery from a damaged memory chip is rather theoretical.

Therefore, it is important to protect NAND memory media from physical damage, which is true for all data media. Regular backup of important data is key. Do not hesitate to use modern methods, such as cloud storage.

FAQ - Frequently Asked Questions

What is NAND flash memory?

NAND flash is a type of memory storage used in a variety of electronic devices, such as SSDs, USB flash drives, memory cards, and mobile phones. NAND flash is popular due to its ability to quickly save and read data, even after the power supply is disconnected.

What are the main types of NAND flash memory?

NAND flash memory can occur in three main forms: standalone chip, monolithic chip (monolith), and Chip-On-Board (COB). The choice depends on the specific application requirements for the given device or medium.

What devices typically use NAND flash memory?

NAND flash memory is used in a wide range of electronic devices. You can find it in SSDs, USB flash drives, memory cards, mobile phones, and others.

Is data recovery from NAND - SSDs, mobile phones, memory cards, flash drives possible?

Yes, data recovery from NAND flash memory can be possible from various types of devices, including SSDs, mobile phones, memory cards, and others. The data recovery process can be complex and requires specialized tools and knowledge, but our company has extensive experience and has successfully recovered data from a large number of devices. If you need to recover data, contact us.

Is it possible to recover data from a damaged NAND chip?

If the NAND chip is physically damaged (typically cracked), data recovery becomes a very difficult task, often impossible. If the damage does not affect the memory blocks of the NAND chip, the data may still be recoverable.

What role does the controller play in NAND flash memory?

The controller in NAND flash memory is responsible for data management - it ensures their storage and reading from memory cells, manages errors, and controls a number of other advanced internal data management functions.

How can I prevent data loss from NAND flash memory?

Regular data backup is the best prevention of data loss. It is also recommended to protect devices from physical damage, such as shocks or extreme temperatures, that could damage the NAND flash memory.

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By Frantisek Fridrich
Frantisek Fridrich
Parent Category: Blog
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