Source: Semiconductor Industry Observation
In the past year, the soaring prices and promising prospects of Nor Flash have reignited confidence in encoded storage devices. Many manufacturers, including Gigadevice and Winbond, have made significant profits from this trend. While some may view this somewhat outdated product as lacking in technical content, Nor Flash faces various challenges in its development.
Recently, Cai Yimao from Peking University’s School of Micro-Nano Electronics discussed the various challenges facing Nor Flash in a presentation titled “Challenges, Reliability, and Characterization of NOR Flash Scaling.” Below are excerpts from his talk shared with our readers.
Evolution of Flash Memory
According to the principles of Nor Flash, it uses CHE for encoding and FN Tuning for erasing. The charge injection mechanism significantly impacts these two factors. Let’s examine the considerations and solutions for each:
First, let’s look at CEH. It is understood that the injection of CHE greatly enhances encoding speed and lg, while also expanding the influence on ionization rates (high lateral electric field) and affecting collection efficiency (high vertical electric field). However, as shown in the figure below, many factors influence CHE.
Therefore, TCAD simulation can be used to model the effects of CHE injection to improve product performance.
TCAD Simulation
The FN Tuning, located between the Floating Gate and Bulk, is also influenced by various factors.
FN Tunneling
At this point, using the MLC solution can perfectly address the related issues.
Comparison of SLC and MLC
For Nor Flash, we also need to consider reliability issues, such as Over-Erase, Nor Disturb, tunneling oxidation, and reliability. This requires some effective solutions. Additionally, during the miniaturization process, Nor Flash faces issues like Random Telegraph Signals Noise (RTN).
As mentioned above, Nor Flash must consider reliability, qualification, retention, and undergo retention characteristic failure analysis from design to production and delivery to customers. Only after passing these rigorous tests can Nor Flash meet user demands for operating temperatures (55 degrees), data retention time after power loss >10 years, and erase/write cycles >100,000 times.
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