Moore's Law drives semiconductor manufacturers of memory and logic chips to reduce product costs and improve performance by increasing transistor density. NAND flash memory is one of the electronic non-volatile computer memory storage mediums, in which the relationship between the bit line and the word lines resembles a NAND (NOT-AND) gate. In NAND Flash technology, the mainstream of the market now is 3D architecture rather than 2D flat architecture, which can increase the memory density linearly by increasing the number of 3D NAND chip stack layers. To better take advantage of the 3D NAND technology, understanding of its physical properties is necessary. As the NAND transform from planar to 3D, the process requires the use of polysilicon, the consequent reliability issues need to be studied. This thesis is going to focus on the random dopant fluctuation (RDF) and random telegraph noise (RTN) by doing numerical simulation on a 3D NAND cell with TCAD (Technology Computer Aided Design) and MATLAB. Chapter 1 introduces the fundamental knowledge of NAND, including: the reason and impact of the transformation of 3D NAND, the classification of NAND with their advantages and disadvantages, the way to improve its storage density, etc.. In the end of this chapter, the structure of the 3D NAND with vertical “macaroni” channel that we used for the simulation is presented. Chapter 2 concentrates on the reliability issue of 3D NAND, specifically, random dopant fluctuation and random telegraph noise. It explains the origin of RDF and RTN. Results gotten from others’ previous researches are concluded to provide a general idea of what may affect the magnitude of RDF and RTN. Chapter 3 explains in details how the simulation was carried on. The model created by TCAD is displayed and relevant parameters are listed. This chapter also shows the procedure of the simulation flow and the method to get a grain-random, trap-random NAND cell. II Chapter 4 shows the numerical values we got from the simulation. After being processed, they are put in figures, so we can observe the mean of VT, standard deviation of VT and RTN slope dependence visually from the variation tendency of the curves. Some interpretations are given to explain the data. Chapter 5 summarizes this work and concludes the results of the simulation. Proposal of the future work is mentioned at last.
La legge di Moore fa sì che i produttori di semiconduttori, di chip di memoria e di logica, possano ridurre i costi dei prodotti e incrementare le prestazioni aumentando la densità di transistor. La memoria NAND flash è uno dei supporti di archiviazione di tipo non-volatile per computer, in cui la relazione tra bit line e word line assomiglia a una porta NAND (NOT-AND). Nella tecnologia flash NAND attuale la tendenza dominante è l'architettura 3D piuttosto che l'architettura 2D, la quale è in grado di aumentare la densità di memoria linearmente, aumentando il numero di strati della pila di chip NAND 3D. Per utilizzare meglio la tecnologia NAND 3D è necessaria la comprensione delle sue proprietà fisiche. Poiché il processo della trasformazione NAND da planare a 3D richiede l'uso di polisilicio, devono essere studiati anche i suoi conseguenti problemi di affidabilità. Questa tesi si concentra sulla fluttuazione casuale del drogante (RDF) e sul rumore telegrafico casuale (RTN) attraverso una simulazione numerica su una cella NAND 3D con TCAD (Technology Computer Aided Design) e MATLAB. Il capitolo 1 introduce le nozioni fondamentali di NAND, in particolare: la ragione e l'impatto della trasformazione NAND 3D, la classificazione della NAND assieme ai suoi vantaggi e svantaggi, l’ottimizzazione della sua densità di transistor, ecc.. Questo capitolo si conclude con la presentazione della struttura NAND 3D con il canale verticale a "maccheroni" utilizzato per la simulazione. Il capitolo 2 si concentra sul problema dell'affidabilità di NAND 3D, in particolare sulla fluttuazione casuale del drogante e sul rumore telegrafico casuale, illustrando l'origine di RDF e RTN. Sono riportati i risultati di ricerche altrui, che forniscono un'idea generale di cosa può influenzare queste grandezze. Il capitolo 3 spiega in dettaglio come è stata eseguita la simulazione. Viene illustrato il modello creato da TCAD e vengono elencati i parametri rilevanti. In IV questo capitolo vengono inoltre illustrate le procedure della simulazione e i metodi per ottenere una cella NAND grain-random, trap-random. Il capitolo 4 mostra i valori numerici ottenuti dalla simulazione. Dopo l’elaborazione, sono stati riportati in grafici, dai quali possiamo osservare la media di VT, la deviazione standard di VT e la pendenza RTN, rilevabile dalla tendenza di variazione delle curve. Inoltre, sono state date alcune interpretazioni per spiegare i dati ottenuti. Il capitolo 5 riassume l’intero lavoro e completa la presentazione dei risultati della simulazione, concludendo con una proposta di possibile futura attività di ricerca.
Numerical simulation of RDF and RTN in 3D NAND
Chen, Ziyu
2020/2021
Abstract
Moore's Law drives semiconductor manufacturers of memory and logic chips to reduce product costs and improve performance by increasing transistor density. NAND flash memory is one of the electronic non-volatile computer memory storage mediums, in which the relationship between the bit line and the word lines resembles a NAND (NOT-AND) gate. In NAND Flash technology, the mainstream of the market now is 3D architecture rather than 2D flat architecture, which can increase the memory density linearly by increasing the number of 3D NAND chip stack layers. To better take advantage of the 3D NAND technology, understanding of its physical properties is necessary. As the NAND transform from planar to 3D, the process requires the use of polysilicon, the consequent reliability issues need to be studied. This thesis is going to focus on the random dopant fluctuation (RDF) and random telegraph noise (RTN) by doing numerical simulation on a 3D NAND cell with TCAD (Technology Computer Aided Design) and MATLAB. Chapter 1 introduces the fundamental knowledge of NAND, including: the reason and impact of the transformation of 3D NAND, the classification of NAND with their advantages and disadvantages, the way to improve its storage density, etc.. In the end of this chapter, the structure of the 3D NAND with vertical “macaroni” channel that we used for the simulation is presented. Chapter 2 concentrates on the reliability issue of 3D NAND, specifically, random dopant fluctuation and random telegraph noise. It explains the origin of RDF and RTN. Results gotten from others’ previous researches are concluded to provide a general idea of what may affect the magnitude of RDF and RTN. Chapter 3 explains in details how the simulation was carried on. The model created by TCAD is displayed and relevant parameters are listed. This chapter also shows the procedure of the simulation flow and the method to get a grain-random, trap-random NAND cell. II Chapter 4 shows the numerical values we got from the simulation. After being processed, they are put in figures, so we can observe the mean of VT, standard deviation of VT and RTN slope dependence visually from the variation tendency of the curves. Some interpretations are given to explain the data. Chapter 5 summarizes this work and concludes the results of the simulation. Proposal of the future work is mentioned at last.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/173105