Printed and low-temperature-processed indium oxide thin-film transistors for flexible applications

Dissertation

Research output: ThesisDissertationCollection of Articles

Abstract

The convergence of printing and microelectronic technologies, often called printed electronics, is best embodied in printed thin-film transistor (TFT) semiconductor devices. TFTs, that are the key components in displays and flat panel X-ray sensors, are conventionally fabricated on rigid substrates from amorphous silicon (a-Si) using vacuum-processes and a high process temperature (> 250 °C). With the existing market pull for flexible and high-resolution organic light emitting diode (OLED) displays, novel semiconductor materials, such as organic and metal oxide (MO) semiconductors, are being developed to yield TFTs with flexibility and electrical performance beyond that of a-Si. Organic TFTs (OTFTs) can be printed and processed at low-temperature (<150 °C) on flexible substrates, whereas MO TFTs, that readily provide superior performance to both OTFTs and a-Si TFTs, are either vacuum-processed or require high-temperature processing (> 300 °C) when they are solution-processed. The thesis work focuses on the fabrication of MO semiconductors using printing processes and includes material, ink, and process development, as well as fabrication, characterization, and modelling of the printed MO TFT devices. We show in Publication [I] that thin, printed In2O3 layers can be used in enhancement-mode TFTs when the devices are stabilized using a post-contact annealing step at low-temperature. Moreover, we demonstrate, for the first time, that flexographyprinted In2O3 layers on flexible plastic substrate can be used in TFTs whose performance is beyond that of a-Si TFTs or printed OTFTs. In order to lower the annealing temperature of the MO materials, Publication [II] and Publication [III] introduce a low-temperature annealing method where low-wavelength far ultraviolet (FUV) exposure and thermal annealing are combined to reach the processing temperature (~150 °C) for an inkjet-printed In2O3 semiconductor that is compatible with low-cost plastic substrates. Finally, Publication [IV] demonstrates that high-gain depletion-load inverters can be fabricated via inkjet printing by exploiting the thicknessdependent electrical properties of the In2O3 semiconductors. In summary, this thesis demonstrates that MO semiconductors can be deposited using industrially-relevant printing processes and processed at low-temperature on flexible substrates. This could lead, in the future, to the use of printed MO TFTs in flexible applications, such as biosensors, flexible displays, large-area sensors, and integrated and radio-frequency circuits. The potential of these applications is also analysed in this thesis.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Kauppinen, Esko, Supervisor, External person
  • Alastalo, Ari, Advisor
Award date9 Jun 2017
Place of PublicationEspoo
Publisher
Print ISBNs978-952-60-7343-9, 978-951-38-8521-2
Electronic ISBNs978-952-60-7342-2, 978-951-38-8520-5
Publication statusPublished - 2017
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

printing
indium oxides
theses
transistors
metal oxide semiconductors
metal oxides
annealing
thin films
amorphous silicon
plastics
inverters
fabrication
sensors
inks
high gain
semiconductor devices
bioinstrumentation
microelectronics
temperature
radio frequencies

Keywords

  • printed electronics
  • metal oxide thin-film transistors
  • flexographic printing
  • inkjet printing
  • low-temperature annealing
  • depletion-load inverter

Cite this

@phdthesis{338786718a504c6583cf60f87524d251,
title = "Printed and low-temperature-processed indium oxide thin-film transistors for flexible applications: Dissertation",
abstract = "The convergence of printing and microelectronic technologies, often called printed electronics, is best embodied in printed thin-film transistor (TFT) semiconductor devices. TFTs, that are the key components in displays and flat panel X-ray sensors, are conventionally fabricated on rigid substrates from amorphous silicon (a-Si) using vacuum-processes and a high process temperature (> 250 °C). With the existing market pull for flexible and high-resolution organic light emitting diode (OLED) displays, novel semiconductor materials, such as organic and metal oxide (MO) semiconductors, are being developed to yield TFTs with flexibility and electrical performance beyond that of a-Si. Organic TFTs (OTFTs) can be printed and processed at low-temperature (<150 °C) on flexible substrates, whereas MO TFTs, that readily provide superior performance to both OTFTs and a-Si TFTs, are either vacuum-processed or require high-temperature processing (> 300 °C) when they are solution-processed. The thesis work focuses on the fabrication of MO semiconductors using printing processes and includes material, ink, and process development, as well as fabrication, characterization, and modelling of the printed MO TFT devices. We show in Publication [I] that thin, printed In2O3 layers can be used in enhancement-mode TFTs when the devices are stabilized using a post-contact annealing step at low-temperature. Moreover, we demonstrate, for the first time, that flexographyprinted In2O3 layers on flexible plastic substrate can be used in TFTs whose performance is beyond that of a-Si TFTs or printed OTFTs. In order to lower the annealing temperature of the MO materials, Publication [II] and Publication [III] introduce a low-temperature annealing method where low-wavelength far ultraviolet (FUV) exposure and thermal annealing are combined to reach the processing temperature (~150 °C) for an inkjet-printed In2O3 semiconductor that is compatible with low-cost plastic substrates. Finally, Publication [IV] demonstrates that high-gain depletion-load inverters can be fabricated via inkjet printing by exploiting the thicknessdependent electrical properties of the In2O3 semiconductors. In summary, this thesis demonstrates that MO semiconductors can be deposited using industrially-relevant printing processes and processed at low-temperature on flexible substrates. This could lead, in the future, to the use of printed MO TFTs in flexible applications, such as biosensors, flexible displays, large-area sensors, and integrated and radio-frequency circuits. The potential of these applications is also analysed in this thesis.",
keywords = "printed electronics, metal oxide thin-film transistors, flexographic printing, inkjet printing, low-temperature annealing, depletion-load inverter",
author = "Jaakko Lepp{\"a}niemi",
note = "135 + app. 35",
year = "2017",
language = "English",
isbn = "978-952-60-7343-9",
series = "VTT Science",
publisher = "Aalto University",
number = "148",
address = "Finland",
school = "Aalto University",

}

Printed and low-temperature-processed indium oxide thin-film transistors for flexible applications : Dissertation. / Leppäniemi, Jaakko.

Espoo : Aalto University, 2017. 162 p.

Research output: ThesisDissertationCollection of Articles

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AU - Leppäniemi, Jaakko

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N2 - The convergence of printing and microelectronic technologies, often called printed electronics, is best embodied in printed thin-film transistor (TFT) semiconductor devices. TFTs, that are the key components in displays and flat panel X-ray sensors, are conventionally fabricated on rigid substrates from amorphous silicon (a-Si) using vacuum-processes and a high process temperature (> 250 °C). With the existing market pull for flexible and high-resolution organic light emitting diode (OLED) displays, novel semiconductor materials, such as organic and metal oxide (MO) semiconductors, are being developed to yield TFTs with flexibility and electrical performance beyond that of a-Si. Organic TFTs (OTFTs) can be printed and processed at low-temperature (<150 °C) on flexible substrates, whereas MO TFTs, that readily provide superior performance to both OTFTs and a-Si TFTs, are either vacuum-processed or require high-temperature processing (> 300 °C) when they are solution-processed. The thesis work focuses on the fabrication of MO semiconductors using printing processes and includes material, ink, and process development, as well as fabrication, characterization, and modelling of the printed MO TFT devices. We show in Publication [I] that thin, printed In2O3 layers can be used in enhancement-mode TFTs when the devices are stabilized using a post-contact annealing step at low-temperature. Moreover, we demonstrate, for the first time, that flexographyprinted In2O3 layers on flexible plastic substrate can be used in TFTs whose performance is beyond that of a-Si TFTs or printed OTFTs. In order to lower the annealing temperature of the MO materials, Publication [II] and Publication [III] introduce a low-temperature annealing method where low-wavelength far ultraviolet (FUV) exposure and thermal annealing are combined to reach the processing temperature (~150 °C) for an inkjet-printed In2O3 semiconductor that is compatible with low-cost plastic substrates. Finally, Publication [IV] demonstrates that high-gain depletion-load inverters can be fabricated via inkjet printing by exploiting the thicknessdependent electrical properties of the In2O3 semiconductors. In summary, this thesis demonstrates that MO semiconductors can be deposited using industrially-relevant printing processes and processed at low-temperature on flexible substrates. This could lead, in the future, to the use of printed MO TFTs in flexible applications, such as biosensors, flexible displays, large-area sensors, and integrated and radio-frequency circuits. The potential of these applications is also analysed in this thesis.

AB - The convergence of printing and microelectronic technologies, often called printed electronics, is best embodied in printed thin-film transistor (TFT) semiconductor devices. TFTs, that are the key components in displays and flat panel X-ray sensors, are conventionally fabricated on rigid substrates from amorphous silicon (a-Si) using vacuum-processes and a high process temperature (> 250 °C). With the existing market pull for flexible and high-resolution organic light emitting diode (OLED) displays, novel semiconductor materials, such as organic and metal oxide (MO) semiconductors, are being developed to yield TFTs with flexibility and electrical performance beyond that of a-Si. Organic TFTs (OTFTs) can be printed and processed at low-temperature (<150 °C) on flexible substrates, whereas MO TFTs, that readily provide superior performance to both OTFTs and a-Si TFTs, are either vacuum-processed or require high-temperature processing (> 300 °C) when they are solution-processed. The thesis work focuses on the fabrication of MO semiconductors using printing processes and includes material, ink, and process development, as well as fabrication, characterization, and modelling of the printed MO TFT devices. We show in Publication [I] that thin, printed In2O3 layers can be used in enhancement-mode TFTs when the devices are stabilized using a post-contact annealing step at low-temperature. Moreover, we demonstrate, for the first time, that flexographyprinted In2O3 layers on flexible plastic substrate can be used in TFTs whose performance is beyond that of a-Si TFTs or printed OTFTs. In order to lower the annealing temperature of the MO materials, Publication [II] and Publication [III] introduce a low-temperature annealing method where low-wavelength far ultraviolet (FUV) exposure and thermal annealing are combined to reach the processing temperature (~150 °C) for an inkjet-printed In2O3 semiconductor that is compatible with low-cost plastic substrates. Finally, Publication [IV] demonstrates that high-gain depletion-load inverters can be fabricated via inkjet printing by exploiting the thicknessdependent electrical properties of the In2O3 semiconductors. In summary, this thesis demonstrates that MO semiconductors can be deposited using industrially-relevant printing processes and processed at low-temperature on flexible substrates. This could lead, in the future, to the use of printed MO TFTs in flexible applications, such as biosensors, flexible displays, large-area sensors, and integrated and radio-frequency circuits. The potential of these applications is also analysed in this thesis.

KW - printed electronics

KW - metal oxide thin-film transistors

KW - flexographic printing

KW - inkjet printing

KW - low-temperature annealing

KW - depletion-load inverter

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T3 - VTT Science

PB - Aalto University

CY - Espoo

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