Development of p-type oxide semiconductors based on tin oxide and its alloys

201 Pages·2014·33.29 MB·English

by  Raquel Barros

Ana Raquel Xarouco de Barros

Mestre em Engenharia Microelectrónica e Nanotecnologias

Development of p-type oxide semiconductors
based on tin oxide and its alloys: application
to thin film transistors

Dissertação para obtenção do Grau de Doutor
em Nanotecnologias e Nanociências

Orientador: Doutora Elvira Maria Correia Fortunato, Professora
Catedrática, Faculdade de Ciências e Tecnologia da
Universidade Nova de Lisboa
Co-orientador: Doutor Rodrigo Ferrão de Paiva Martins, Professor
Catedrático, Faculdade de Ciências e Tecnologia da
Universidade Nova de Lisboa

Júri:
Presidente: Professor Doutor Nuno Manuel Robalo Correia
Arguentes: Professora Doutora Florinda Mendes da Costa
Professor Doutor Henrique Leonel Gomes
Vogais: Professor Doutor Albano Augusto Cavaleiro Rodrigues de
Carvalho
Professora Doutora Ana Maria Botelho Rego
Professor Doutor Pedro Miguel Cândido Barquinha

Novembro de 2014

Ana Raquel Xarouco de Barros
Master in Engineering Microelectronics and Nanotechnologies

Development of p-type oxide semiconductors
based on tin oxide and its alloys: application to
thin film transistors
Dissertação para obtenção do Grau de Doutor
em Nanotecnologias e Nanociências

Orientador: Doutora Elvira Maria Correia Fortunato, Professora
Catedrática, Faculdade de Ciências e Tecnologia da
Universidade Nova de Lisboa
Co-orientador:: Doutor Rodrigo Ferrão de Paiva Martins, Professor,
Catedrático Faculdade de Ciências e Tecnologia da
Universidade Nova de Lisboa

Júri:
Presidente: Professor Doutor Nuno Manuel Robalo Correia
Arguentes: Professora Doutora Florinda Mendes da Costa
Professor Doutor Henrique Leonel Gomes
Vogais: Professor Doutor Albano Augusto Cavaleiro

Rodrigues de Carvalho
Professora Doutora Ana Maria Botelho Rego
Professor Doutor Pedro Miguel Cândido Barquinha

Novembro de 2014
i
Development of p-type oxide semiconductors based on tin oxide and its alloys: application to thin film transistors

ii
Development of p-type oxide semiconductors based on tin oxide and its alloys:
application to thin film transistors

Copyright © Ana Raquel Xarouco de Barros, Faculdade de Ciências e Tecnologia,
Universidade Nova de Lisboa.

A Faculdade de Ciências e Tecnologia e a Universidade Nova de Lisboa têm o direito,
perpétuo e sem limites geográficos, de arquivar e publicar esta dissertação através de
exemplares impressos reproduzidos em papel ou de forma digital, ou por qualquer outro meio
conhecido ou que venha a ser inventado, e de a divulgar através de repositórios científicos e
de admitir a sua cópia e distribuição com objectivos educacionais ou de investigação, não
comerciais, desde que seja dado crédito ao autor e editor.

iii
Development of p-type oxide semiconductors based on tin oxide and its alloys: application to thin film transistors

iv
Acknowledgments

ACKNOWLEDGMENTS
It was a great privilege to be part of this creative and prestigious research group during these four
years, where an environment of great fellowship and friendship persists and in which this work
was only possible with the support of several people that I would like to sincerely thank.
First and foremost, I would like to thank Professor Elvira Fortunato, for allowing me to work in this
research group, for the form she guided my work and for all the support and suggestions, that
have contributed to my personal and professional development. I am grateful for her interest,
encouragement and friendship.
To Professor Rodrigo Martins, for the constant interest shown in my work and for the incentive
and help on understanding the results.
To Professor Pedro Barquinha, a special and grateful thank. Without his knowledge and ideas,
this work would not have taken the same direction. His unlimited support, motivation and
friendship were essential to my development as a researcher, a team member and as a person.
You are our “special one”.
To my friend and officemate, Dipl. Ing. Jonas Deuermeier, for the XPS measurements done at
Darmstad and for all the long talks about science, for the friendship and for being so patient to me
during the writing process. Thank you for teaching me that “stress” should not exist in our live.
For all the true moments of friendship, fun and support, I must thank to MSc Mafalda Costa, MSc
Paulo Duarte, MSc Sónia Pereira, MSc Alexandra Gonçalves, MSc Andreia Araújo and MSc
Nuno Neves. Their friendship was essential during this journey.
To Dr. Joana Vaz Pinto, for the major help with RBS characterization, the long talks about physics
and her friendship.
To past and present co!workers: MSc Bruno Veigas, MSc. Daniela Salgueiro, MSc. Ana Catarina
Santos, Professor Luís Pereira, Dr. Elangovan Elamurugu, Dr. Vítor Figueiredo, MSc. Diana
Gaspar, MSc. Tiago Mateus, MSc. António Vicente, MSc. Joana Neto, Dr. Pawel Wojcik, MSc.
Iwona Bernacka, Dr. Suman Nandy, Dr. Ana Pimentel, Dr. Daniela Nunes, Dr. Rita Braquinho,
MSc. Lídia Santos, Dr. Sergej Filonovich, MSc Ana Rovisco, MSc Jorge Martins and others that
probably I did not mention. Your help was essential! Thank you all!
To those who are responsible for administrative work at CENIMAT and were always helpful when
it was necessary to solve the most bureaucratic situations: Dr. Paulo Manteigas, Valéria Gomes,
Dr. Susana Mendes, and Dr. Patrícia Carrão. A special thank also to Antónia Conceição.
v
Development of p-type oxide semiconductors based on tin oxide and its alloys: application to thin film transistors
To the technicians who work or have worked in CENIMAT, CEMOP and DCM: Carlos Alcobia,
Manuel Quintela, Ricardo Ferreira and Salomão Lopes for the help solving the technical problems
related with production and characterization systems.
To all my friends, that always supported and motivated me, and understand my unavailability
during these years.
To the most important persons in my life: my parents and my sister that I love unconditionally. For
all their love and for always support and believe in me! I own them all that I am and today and no
words could ever be enough to thank them!
To Ricardo Guedes, that although was not present from the very beginning, his support,
companionship and love were essential in closing this chapter of my life!
Finally, to my grandfather, António, who will always be in my mind and heart for being my greatest
example of love, companionship, kindness and for teaching me to always smile, be positive and
never give up!

vi
Abstract

ABSTRACT
In spite of the recent p-type oxide TFTs developments based on SnO and Cu O, the results
x x
achieved so far refer to devices processed at high temperatures and are limited by a low hole
mobility and a low On-Off ratio and still there is no report on p-type oxide TFTs with performance
similar to n-type, especially when comparing their field-effect mobility values, which are at least
one order of magnitude higher on n-type oxide TFTs. Achieving high performance p-type oxide
TFTs will definitely promote a new era for electronics in rigid and flexible substrates, away from
silicon. None of the few reported p-channel oxide TFTs is suitable for practical applications, which
demand significant improvements in the device engineering to meet the real-world electronic
requirements, where low processing temperatures together with high mobility and high On-Off
ratio are required for TFT and CMOS applications.
The present thesis focuses on the study and optimization of p-type thin film transistors based on
oxide semiconductors deposited by r.f. magnetron sputtering without intentional substrate heating.
In this work several p-type oxide semiconductors were studied and optimized based on undoped
tin oxide, Cu-doped SnO and In-doped SnO .
x 2
The influence of the deposition parameters, such as the percentage of oxygen and the deposition
pressure and post deposition annealing treatments (up to 200 °C) parameters was investigated in
order to optimize the properties of the p-type thin films. The detailed study of the material was
accomplished through various techniques of characterization of their electrical and optical
properties, crystal structure, chemical composition, topology and morphology.
The obtained undoped SnO thin films showed p-type conduction for a narrow percentage of
x
oxygen, between 2.5% and 4%, after an annealing treatment at 150 °C and 200 °C. The thin films
have a mixture of both tetragonal β-Sn and α-SnO phases, mobilities between1.6 cm2/Vs and 2.6
cm2/Vs and a carrier concentration between 1016 and 1017 cm-3. TFTs produced with this material
were optimized presenting very good electrical performances, with On-Off ratio ~104, µ up to 3.5
FE
cm2/Vs and V between -0.41 V and 15 V. The influence of the dielectric was also studied and
th
leading to new results. Depending on the gate dielectric used, n-, p-type and ambipolar devices
were obtained for the same semiconductor deposition conditions.
Doping SnO with Cu also results in transparent p-type oxide semiconductors with mobilities
x
between 1.6 cm2/Vs and 2.6 cm2/Vs and a carrier concentration between 1016 and 1017 cm-3.
When applied as active layer, resulted in poor performance thin film transistors, with lower On-Off
ratio and the higher V , despite µ increased.
th FE
When doping the SnO films with In, p-type conduction was achieved without the need of the
2
annealing treatment. The obtained as deposited thin films are amorphous and show mobilities up
vii
Development of p-type oxide semiconductors based on tin oxide and its alloys: application to thin film transistors
to 27 cm2/Vs and very low resistivities ~10-3 Ω cm, obtaining in this way the a p-type oxide
transparent conductor with the lowest electrical resistivity so far reported in the literature.

viii