A relevant topic that is getting an increasing concern is to find different strategies to enhance energy production from renewable sources, create appropriate storage systems to overcome the power demand in a smart way, and improve energy efficiency. Consequently, in the last decade, the interest was directed toward new solutions to achieve high-efficiency power converters. As the actual silicon-based power devices have reached their limit, the attention is directed to compound semiconductors such as Gallium Nitride (GaN) which is the optimal candidate for the next-generation power converters. This thesis work reports the analysis of the main mechanisms responsible for the degradation of performance in Gallium Nitride transistors and how they are eventually restored to fresh values. The attention is oriented to the innovative semi-vertical MOSFETs devoted to power applications and fabricated on the cheap Silicon substrates. Consequently, four typologies of device with different doping concentrations in the P region and alternative combinations of gate oxides are analyzed. Specifically, (i) wafer X10, Monolayer, with SiO2 oxide, (ii) wafer X07, Bilayer, similar to the previous but with a double oxide in SiO2 and Al2O3, (iii) wafer X03, Low doping, with a bilayer oxide and a relatively low doping concentration in P region, (iiii) wafer X04, High doping, with a higher doping concentration in P region respect to the previous sample. Accordingly, the first step includes DC characterizations to understand the fundamental electrical properties of the MOSFET and the ratings that it is expected to achieve. Then, appropriate measurement setups were implemented to stress the device in different operative regions to observe which characteristics are mainly affected by a specific external bias. The parameters that required a detailed analysis were the increase in the RDSON, the current leakage in the gate terminal with different oxide configurations, and the instability of the VTH value with the associated shift when several voltages at various temperatures are applied. Generally, the overall performance of devices from wafers X03 and X04 was improved but some critical issues are still affecting the technology in the gate region. Specifically, the VTH shift under different stress conditions was deeply investigated. On the other hand, the analysis on devices from wafers X07 and X10 confirmed the reliability of the combination of different oxides, showing how this latter allows sustaining higher voltages at the gate terminal. As consequence, it was possible to understand the trapping dynamics that rule the behavior of the devices by extrapolating the fingerprint of each event from the measured data. Moreover, appropriate physical models were defined with the perspective of further investigations.
La continua sfida nella ricerca di soluzioni per migliorare l’efficienza nella conversione dell’energia ha suscitato un crescente interesse verso semiconduttori innovativi come il Nitruro di Gallio, di cui però non si è ancora raggiunta una conoscenza compiuta. Di conseguenza, il lavoro proposto è incentrato sull’analisi dei principali meccanismi fisici responsabili del peggioramento delle prestazioni dei transistor realizzati in Nitruro di Gallio e come queste vengono eventualmente ripristinate ai valori iniziali. L’attenzione è rivolta all’innovativa architettura del MOSFET semi-verticale realizzato a partire dal substrato economico in Silicio e da impiegare nelle applicazioni di potenza. In particolare, si valutano le prestazioni in quattro tipologie di dispositivi con differenti concentrazioni di drogaggio nella regione P e con ossidi di materiali differenti in corrispondenza del terminale di gate: (i) wafer X10, Monolayer, con ossido realizzato in SiO2, (ii) wafer X07, Bilayer, simile al precedente ma con ossido in SiO2 e Al2O3, (iii) wafer X03, Low doping, con dispositivi a ossido bilayer e bassa concentrazione di dopante nella regione P, (iiii) wafer X04, High doping, simile al precedente ma con alta concentrazione di dopante nella regione P. Quindi, la prima fase è dedicata alla valutazione delle proprietà fondamentali del MOSFET attraverso caratterizzazioni DC per poi identificare le potenzialità di ciascuna tipologia di dispositivo. In seguito, opportuni setups di misura permettono di applicare condizioni operative stressanti per indagare in modo mirato le caratteristiche più sensibili a determinati bias esterni. I parametri per cui è presentata un’analisi dettagliata sono l’aumento di RDSON , le perdite parassite di corrente al terminale di gate in base alla tipologia di ossido impiegata e l’instabilità della tensione di soglia al variare della tensione di stress e della temperatura. In generale, si sono osservate prestazioni migliori nei wafer di fabbricazione più recente (X03 e X04) per quanto riguarda i leakage parassiti mentre alcune instabilità affliggono questa tecnologia in modo rilevante a livello della regione di gate. Di particolare interesse è lo spostamento della tensione di soglia che non risponde seguendo le aspettative e che ha richiesto un’analisi approfondita. Lo studio condotto sui wafer X07 e X10 ha confermato la superiorità delle prestazioni dei dispositivi che presentano combinazioni di ossidi a livello di gate, dimostrando come questi siano in grado di sopportare tensioni più elevate al terminale. Di conseguenza, è possibile comprendere in modo esaustivo i processi di trapping che regolano il comportamento del MOSFET a partire dalle dinamiche osservate durante le misure e, inoltre, vengono definite le basi per ulteriori indagini attraverso modellizzazioni con simulatore.
Analysis and Modelling of Semi-Vertical GaN devices
CAVALIERE, ALBERTO
2021/2022
Abstract
A relevant topic that is getting an increasing concern is to find different strategies to enhance energy production from renewable sources, create appropriate storage systems to overcome the power demand in a smart way, and improve energy efficiency. Consequently, in the last decade, the interest was directed toward new solutions to achieve high-efficiency power converters. As the actual silicon-based power devices have reached their limit, the attention is directed to compound semiconductors such as Gallium Nitride (GaN) which is the optimal candidate for the next-generation power converters. This thesis work reports the analysis of the main mechanisms responsible for the degradation of performance in Gallium Nitride transistors and how they are eventually restored to fresh values. The attention is oriented to the innovative semi-vertical MOSFETs devoted to power applications and fabricated on the cheap Silicon substrates. Consequently, four typologies of device with different doping concentrations in the P region and alternative combinations of gate oxides are analyzed. Specifically, (i) wafer X10, Monolayer, with SiO2 oxide, (ii) wafer X07, Bilayer, similar to the previous but with a double oxide in SiO2 and Al2O3, (iii) wafer X03, Low doping, with a bilayer oxide and a relatively low doping concentration in P region, (iiii) wafer X04, High doping, with a higher doping concentration in P region respect to the previous sample. Accordingly, the first step includes DC characterizations to understand the fundamental electrical properties of the MOSFET and the ratings that it is expected to achieve. Then, appropriate measurement setups were implemented to stress the device in different operative regions to observe which characteristics are mainly affected by a specific external bias. The parameters that required a detailed analysis were the increase in the RDSON, the current leakage in the gate terminal with different oxide configurations, and the instability of the VTH value with the associated shift when several voltages at various temperatures are applied. Generally, the overall performance of devices from wafers X03 and X04 was improved but some critical issues are still affecting the technology in the gate region. Specifically, the VTH shift under different stress conditions was deeply investigated. On the other hand, the analysis on devices from wafers X07 and X10 confirmed the reliability of the combination of different oxides, showing how this latter allows sustaining higher voltages at the gate terminal. As consequence, it was possible to understand the trapping dynamics that rule the behavior of the devices by extrapolating the fingerprint of each event from the measured data. Moreover, appropriate physical models were defined with the perspective of further investigations.File | Dimensione | Formato | |
---|---|---|---|
Cavaliere_Alberto.pdf
accesso riservato
Dimensione
19.11 MB
Formato
Adobe PDF
|
19.11 MB | Adobe PDF |
The text of this website © Università degli studi di Padova. Full Text are published under a non-exclusive license. Metadata are under a CC0 License
https://hdl.handle.net/20.500.12608/31494