Optimize NAND Flash Memory Verification: Part 1

Varun Agrawal, Mohit Bhardwaj

May 08, 2023 / 5 min read

Synopsys Verification IPs

Introduction to NAND Flash Memory

  • NAND non-volatile storage is the technology that enables solid-state drives (SSDs), mobile phone storage, embedded memory cards, USB devices, and much more
  • In Comparison to RAM (e.g., DRAM, SRAM), Non-Volatile Memory (NVM) retains the data it contains while being powered down
  • NVMs are appealing to industrial users, since they require a storage solution that can help to protect the data even if there is a power outage

Types of NAND Flash

The bit density on the NAND flash has evolved over time. Earlier NAND devices were Single Level Cell (SLC) flash. This suggests every flash cell stores one single bit. With Multi Level Cell (MLC), flash can store two or more bits per cell, therefore the bit density gets increased. Sounds great but with MLC there are downsides as well: with MLC NAND, allowing multiple electrical states can also lead to higher error rate and lower endurance. A few devices allow you to modify into a pseudo-SLC (PSLC) mode on parts of (or) all the storage.

This may reduce the dimensions of the storage whereas the endurance of the device gets increased. Since the worth of Flash depends on its die area, Flash would be more cost effective if more data are often stored within an equivalent area. There are four main sorts of NAND Flash: Single Level Cell (SLC), Multi-Level Cell (MLC), Triple Level Cell (TLC) and quad level cell (QLC).

NAND Memory Features Graph NAND Memory Features Graph

3D NAND Technology

Over the past decade, 3D NAND or Vertical NAND has been one of the biggest innovations in the flash market. Flash manufacturers have developed 3D NAND to solve the problems encountered when 2D NAND was downsized to achieve higher storage densities at lower cost. It also leads to higher speeds, better durability, and lower fuel specifications. Different from 2D NAND, manufacturers decided to stack the cells in a different dimension, resulting in 3D NAND, where the cells are stacked vertically. Stacking eliminates the electrical interference that occurs when cells are made smaller. The higher storage density allows for higher storage capacities without a huge price increase. 3D NAND also offers better endurance and lower power consumption.


3D NAND SSDs are sold by most major SSD vendors today. Samsung, for example, has used the technology to load 8 TB of flash memory into its latest NVMe NF1 SSD. Some of the leading 3D NAND flash manufacturers include Intel Corporation, Samsung Hynix, SK, and Western Multimedia Corporation- a partner of Toshiba. Overall, NAND is an extremely important storage technology because it offers fast erase and write times at a lower cost per bit. Various Industrial like data centers, telecom, automotive, PCs transitioning from HDDs to SSDs, This transition is helping NAND technology to evolve and meet the ever-increasing storage needs of consumers.

Key Features of NAND Flash Memory

Memory Verification Challenges vs Synopsys Verification Solutions:

There are various challenges in designing NAND Flash IP, though Synopsys verification solutions overcome all these challenges:

Verification Challenges

Synopsys Verification Solution

Growing Memory Size

The Synopsys configurable memory solution provides variety of density range verification- ONFI VIP like LUN, Targets, Blocks, Pages, and Number of data bytes per page

Higher Speeds Support

By offering highest speeds at 3600MTs faster NAND flash interfaces are made possible by the bidirectional source synchronous DQS and scalable I/O interface

Multiple Controller Designs

Synopsys VIP’s configurable parameter page provides the controller with all the device’s relevant capabilities for quicker design, qualification, and testing. Parameter page solves inconsistencies among devices by describing revision info, features, organization timing, and other vendor-specific data

Interface Switching

The memory solution offers the switching between asynchronous and source synchronous modes

Small Form Factor

A sophisticated die selection feature that reduces the number of chip enable (CE) pins, which in turn lowers the number of controller pins making PCB routing more efficient
  • Synopsys VIP enables CE_n pin reduction mechanism- a single CE_n pin from the host to be shared by multiple NAND Targets, thus enabling a significant reduction in CE_n pins required by the host

Vendor Support

Broad market support from top-level companies, including Micron, Samsung, CYPRESS, Winbond, Kioxia and respective vendor specific part support features

Debug Time

Native Integration with Verdi Protocol Analyzer, Trace Files, Debug ports, Detailed Error Message

Various Coverage Model

Built in Coverage model and Verification Plans

Configuration enables randomized testbench to achieve complete coverage of all configurations, all vendor components

Scope and Summary

All the main Flash manufacturers are aggressively performing on different methods to scale back the value per little bit of Flash while still creating products that are useful in various applications. Active research goes on to extend the number of vertical layers in 3D NAND Flash. While 15nm seems to be the littlest successful node for NAND Flash today, the shrinking of lithographic nodes for Flash remains being pursued. Combining MLC and TLC technologies with 3D NAND Flash is additionally actively being explored, and lots of manufacturers have already seen success. With the arrival of newer technologies, we may soon see memory cells which will store a byte of knowledge and vertical layers reaching 256 layers and even beyond.

In today’s marketplace, NAND Flash products can be bought with two kinds of interface: The Open NAND Flash Interface (ONFI) and the Toggle NAND Interface (TNAND, 3DNAND). Synopsys® Verification IP for NAND flash provides a comprehensive set of protocol, methodology, verification, and productivity features, enabling users to achieve accelerated verification closure. Also, Synopsys Verification Solution allows to randomize the user required configuration for flash memory with multiple options to cater the IP and SoC level requirements and supports wide variety of vendor defined parts from Samsung, Micron, Winbond, Toshiba and Kioxia.

Synopsys VIPs are natively integrated with the Synopsys Verdi® Protocol Analyzer debug solution as well as Synopsys Verdi® Performance Analyzer. Synopsys VIP can switch speed configurations dynamically at runtime and includes an extensive and customizable set of frame generation and error injection capabilities.

Running system-level payload on SoCs requires a faster hardware-based pre-silicon solution. Synopsys transactors, memory models, hybrid and virtual solutions based on Synopsys IP enable various verification and validation use-cases on the industry’s fastest verification hardware systems, Synopsys ZeBu® and Synopsys HAPS® .

In upcoming blogs on NAND Flash, we will be exploring application based verification challenges of memory and how different types of NAND Flash Memory are being utilized in various Industry Verticals. Stay Tuned @Verification Central !! For more information on Synopsys memory VIP, please visit http://synopsys.com/vip

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