A Fully Integrated Ferroelectric Thin‐Film‐Transistor – Influence of Device Scaling on Threshold Voltage Compensation in Displays. (9th May 2021)

• Record Type: Journal Article
• Authors: Lehninger, David; Ellinger, Martin; Ali, Tarek; Li, Songrui; Mertens, Konstantin; Lederer, Maximilian; Olivio, Ricardo; Kämpfe, Thomas; Hanisch, Norbert; Biedermann, Kati; Rudolph, Matthias; Brackmann, Varvara; Sanctis, Shawn; Jank, Michael P. M.; Seidel, Konrad
• Is Part Of: Advanced Electronic Materials. Volume 7:Number 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-09
• Subjects: analog switching -- ferroelectrics -- hafnium zirconium oxide -- thin‐film transistors -- threshold voltage variation -- transparent displays -- neuromorphic computing; Materials -- Electric properties -- Periodicals; Materials science -- Periodicals; Magnetic materials -- Periodicals; Electronic apparatus and appliances -- Periodicals; 537
• DOI: 10.1002/aelm.202100082
• Languages: English
• ISSNs: 2199-160X

Abstract

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 ( V th ) 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 V th 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 of 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. Abstract : Thin‐film transistors (TFTs) based on amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) have attracted vast attention for use in active‐matrix organic light‐emitting diode (AMOLED) displays. Usually, large‐area processing and degradation effects cause device‐to‐device threshold voltage fluctuations. Herein, a new approach to compensate such variations is demonstrated, namely the integration of a programmable ferroelectric film in the gate stack of the TFT.