Indium-tin oxide (ITO) is the outstanding one among the transparent conductive oxides (TCO’s) due to its combination of optical transparency and high electrical conductivity. Traditionally, ITO has been developed as a passive component for display technologies, antistatic coatings, photovoltaic applications, etc. Nonetheless, being also CMOS compatible, innovative research efforts focuses on applications where ITO is selected to create active components as thin film transistors (TFT’s). Similarly, Silicon photonics began to study ITO as an index tuneable plasmonic material with the possibility to produce devices for future integrated nanophotonics such as optical mode selector, fast optical modulators, heaters for thermo-optic switching and structures with large ultrafast nonlinearity. By virtue of these facts, ITO thin films were produced in the PoliFAB context with RF Sputtering deposition on crystalline Silicon (Si) and Silicon Dioxide/Silicon substrates looking for films with a suitable compromise between transparency and conductivity for photonic applications. Optimization was performed exploring the impact of the substrates and the effect of the controllable deposition parameters just as Argon flow, RF power, etc. All the samples were shaped looking for a thickness of 100 nanometres. Characterization of the produced ITO thin films began with measurement of thickness using Profilometer stylus and obtaining sheet resistance values through Four Point Probe equipment. Spectroscopic Ellipsometry data was collected and processed with a model elaborated in WVASE32 software whose outcomes allow the procurement of optical constants. Moreover, roughness was evaluated with Atomic Force Microscope (AFM) images. Additionally, the effect of annealing in air and Nitrogen was studied to identify the variation of the described properties. Films with a minimum sheet resistance of 150Ohm per square for as-deposited samples and 310Ohm per square for post-annealed samples were achieved. A minimum refractive index of 1.5 in the C-band was found among all the samples. The extinction coefficient for the best post-annealed samples was smaller than 0.08.
L’ossido di indio-stagno (più precisamente ossido di indio drogato con stagno, noto con l’acronimo ITO, dall’inglese Indium Tin Oxide) è un ossido conduttivo con buone proprietà di trasparenza. Tradizionalmente, l’ITO è stato sviluppato come componente fotovoltaico, in schermi al plasma, rivestimenti antistatici, ecc. Tuttavia, essendo anche compatibile con tecniche di fabbricazione CMOS, gli sforzi di ricerca si concentrano sulle applicazioni in cui l’ITO viene scelto per creare componenti attivi come transistor a film sottile al posto del silicio amorfo. Analogamente, la nanofotonica ha iniziato a studiare l’ITO come materiale d’indice di rifrazione tunabile con la possibilità di realizzare dispositivi per l'ottica integrata in silicio. Perciò, ITO a film sottile è stato realizzato nel PoliFAB mediante RF Sputtering su due substrati: silicio cristallino e biossido di silicio/silicio. Il nostro obiettivo era di ottenere i film più trasparenti e conduttivi possibile. L'ottimizzazione è stata raggiunta studiando l'impatto dei substrati e gli effetti dei parametri di deposizione controllabili come flusso di argon e potenza RF. Tutti i campioni sono stati sagomati cercando di ottenere uno spessore di 100 nanometri per cui sono state eseguite delle analisi profilometriche per ogni film. Vengono misurate anche le resistenze di strato attraverso il Four Point Probe Equipment. Le caratteristiche ottiche del film di ITO, ovvero gli indici di rifrazione n e coefficiente di estinzione k, sono stati raccolti da misure ellissometriche ed elaborati nel software WVASE32 e la rugosità viene valutata con le immagini dell'Atomic Force Microscope (AFM). Inoltre, l'effetto della ricottura (thermal annealing) in aria e azoto è studiato per conoscere la variazione delle proprietà descritte. Sono stati ottenuti film con una resistenza minima di 150 Ohm per square per i campioni senza ricottura e 310 Ohm per square per i pezzi post-temprati. Tra tutti i campioni è stato trovato un valore di n minimo pari a 1.5 nella banda C mentre il valore di k per i migliori campioni post-annealing è inferiori a 0.08.
Process development of indium tin oxide for photonics applications
MANDUJANO TOLENTINO, ANITA ANGELA
2017/2018
Abstract
Indium-tin oxide (ITO) is the outstanding one among the transparent conductive oxides (TCO’s) due to its combination of optical transparency and high electrical conductivity. Traditionally, ITO has been developed as a passive component for display technologies, antistatic coatings, photovoltaic applications, etc. Nonetheless, being also CMOS compatible, innovative research efforts focuses on applications where ITO is selected to create active components as thin film transistors (TFT’s). Similarly, Silicon photonics began to study ITO as an index tuneable plasmonic material with the possibility to produce devices for future integrated nanophotonics such as optical mode selector, fast optical modulators, heaters for thermo-optic switching and structures with large ultrafast nonlinearity. By virtue of these facts, ITO thin films were produced in the PoliFAB context with RF Sputtering deposition on crystalline Silicon (Si) and Silicon Dioxide/Silicon substrates looking for films with a suitable compromise between transparency and conductivity for photonic applications. Optimization was performed exploring the impact of the substrates and the effect of the controllable deposition parameters just as Argon flow, RF power, etc. All the samples were shaped looking for a thickness of 100 nanometres. Characterization of the produced ITO thin films began with measurement of thickness using Profilometer stylus and obtaining sheet resistance values through Four Point Probe equipment. Spectroscopic Ellipsometry data was collected and processed with a model elaborated in WVASE32 software whose outcomes allow the procurement of optical constants. Moreover, roughness was evaluated with Atomic Force Microscope (AFM) images. Additionally, the effect of annealing in air and Nitrogen was studied to identify the variation of the described properties. Films with a minimum sheet resistance of 150Ohm per square for as-deposited samples and 310Ohm per square for post-annealed samples were achieved. A minimum refractive index of 1.5 in the C-band was found among all the samples. The extinction coefficient for the best post-annealed samples was smaller than 0.08.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/141840