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  4. A Fully Integrated Ferroelectric Thin-Film-Transistor - Influence of Device Scaling on Threshold Voltage Compensation in Displays
 
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2021
Journal Article
Title

A Fully Integrated Ferroelectric Thin-Film-Transistor - Influence of Device Scaling on Threshold Voltage Compensation in Displays

Abstract
Thin-film transistors (TFTs) based on amorphous indium-gallium-zinc-oxide (a-IGZO) have attracted vast attention for use in organic light-emitting diode (AMOLED) displays due to their high electron mobility and large current on off ratio. Although amorphous oxide semiconductors show considerably less threshold voltage (Vth) variation than poly-silicon, large-area processing and degradation effects can impede the characteristic parameters of a-IGZO TFTs, which manifests in an uneven brightness distribution across the display panel. Such Vth variations are usually reduced by additional compensation circuits consisting of TFTs and capacitors. Herein, a new approach to compensate such variabilities is demonstrated: the integration of a programmable ferroelectric (FE) film in the gate stack o f the TFT. This simplifies the complexity of the pixel cell and potentially minimizes the need for compensation circuits, which is crucial for transparent displays. To test this new approach, fully integrated FE-TFTs (i.e., with vias contacting a structured bottom gate electrode from the top) based on a-IGZO and FE hafnium-zirconium oxide (HZO) are developed. A single low-temperature post-fabrication treatment at 350 °C for 1 h in air is used to simultaneously crystallize the HZO film in the FE phase and to reduce the number of defects in the a-IGZO channel. The structural and electrical characterizations provide comprehensive guidance for the design of effective FE-TFT gate stacks and device geometries. An accurate control of the polarization state and linear switching between multiple intermediate states is shown by using programming pulses of various amplitudes and widths. Furthermore, a direct correlation between the channel length and the applied pulse width for programming is observed.
Author(s)
Lehninger, D.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Ellinger, M.
Fraunhofer-Institut für Integrierte Systeme und Bauelementetechnologie IISB  
Ali, T.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Li, S.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Mertens, K.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Lederer, M.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Olivio, R.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Kampfe, T.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Hanisch, N.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Biedermann, K.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Rudolph, M.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Brackmann, V.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Sanctis, C.
Electron Devices (LEB), Friedrich-Alexander University Erlangen-Nuremberg, Cauerstr. 6, Erlangen, 91058, Germany
Jank, M.
Fraunhofer-Institut für Integrierte Systeme und Bauelementetechnologie IISB  
Seidel, K.
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Journal
Advanced electronic materials  
Open Access
DOI
10.1002/aelm.202100082
Additional full text version
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Language
English
Fraunhofer-Institut für Integrierte Systeme und Bauelementetechnologie IISB  
Fraunhofer-Institut für Photonische Mikrosysteme IPMS  
Keyword(s)
  • analog switching

  • ferroelectrics

  • hafnium zirconium oxide

  • neuromorphic computing

  • thin-film transistor

  • threshold voltage variation

  • transparent display

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