研究目的
To present new experimental evidence of field-induced trap generation in the tunnel oxide of SuperFlash memory cells and study its effects on tunneling characteristics and reliability.
研究成果
The research demonstrates that high electric fields in non-uniform geometries, such as near floating gate tips, can induce trap generation in silicon dioxide without significant charge transport. This degradation is localized and does not critically impact the reliability of SuperFlash technology due to the non-uniform field distribution and design features that mitigate overerase issues. Future studies could explore broader applications and optimize cell geometries to minimize field-induced effects.
研究不足
The study is limited to specific SuperFlash memory cell technologies (ESF1 and ESF3) and may not generalize to other memory types. The negative voltage stress used is not typical for normal cell operation, potentially overestimating field effects. The experimental setup relies on indirect measurements of trap generation through Verase changes, and the electric field calculations are based on idealized geometric assumptions.
1：Experimental Design and Method Selection:
The study was conducted on two generations of SST SuperFlash cells (ESF1 and ESF3) to analyze the effect of negative voltage stress on tunnel oxide degradation. The methodology involved applying voltage stress and measuring voltage-to-erase (Verase) as a parameter for tunneling characteristics. Theoretical models for electric field distribution in non-uniform geometries were used.
2：Sample Selection and Data Sources:
Samples included ESF1 and ESF3 memory cells manufactured using 180 nm and 70 nm technology nodes, respectively. Mini-arrays of 64 cells were used for measurements.
3：List of Experimental Equipment and Materials:
SuperFlash memory cells (ESF1 and ESF3 models), voltage sources for stress application, measurement equipment for Verase and read current, UV irradiation source (254 nm) for electron generation experiments.
4：Experimental Procedures and Operational Workflow:
Negative WL (EG) voltage stress was applied to cells, followed by multiple Verase measurements. UV irradiation was used to introduce electrons in low-field conditions, and FG discharge was monitored. Steps included stress application, Verase measurement before and after stress, and UV exposure with bias variations.
5：Data Analysis Methods:
Data analysis involved comparing Verase values before and after stress, statistical analysis of distributions (e.g., using normalized probability scales), and correlation analysis between initial Verase and stress-induced changes. Theoretical calculations of electric field using concentric cylinder geometry models were performed.
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