Analysis of Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors with Bi-Layer Gate Dielectric Stacks Using Maxwell-Wagner Instability Model

Abstract

Aluminum oxide (Al2O3) and hafnium oxide (HfO2) have been grown, using atomic layer deposition (ALD), as single and bi-layer gate dielectric films. Electrical and structural characterization indicates that the material properties depend on layer thickness and growth order, when deposited as bi-layers. Charge trapping at the interface between the bi-layer stacks results from the Maxwell-Wagner (MW) instability, which states a difference of conductivities at the dielectric-dielectric interface with respect to the bulk dielectric films. Hence a build-up of this interface charge compensates for the condition that the current densities of individual dielectric films match that of the overall stack. This causes electrical instabilities in stack behavior. Bottom-gate amorphous indium-gallium-zinc-oxide thin-film transistors are fabricated with these gate oxides, single and bi-layer stacks, with low VTH and gate leakage current to understand this instability. By empirically adopting ideal MOSFET equations and single gate dielectric film behavior as a reference, this MW instability in bilayer gate dielectric stacks has been accounted for in amorphous indium-gallium-zinc-oxide thin-film transistor transfer characteristics with a good fit in both above threshold and subthreshold regimes.

Hole and electron trapping in HfO2/Al2O3 nanolaminated stacks for emerging non-volatile flash memories

“…There are attempts to combine the HfO 2 /Al 2 O 3 high-k stacks with different high-mobility channel materials (e.g. SiGe [11], GaAs [12,13], InP [14], In 2 Ga 2 ZnO 7 [15]) and more important with 2D materials, (e.g. black phosphorous [16] and MoS 2 [17]) which can open up new frontiers in a number of emerging applications such as: thin film transistors, non-volatile memory devices for flexible and transparent electronics, etc.…”

Challenges to Optimize Charge Trapping Non-Volatile Flash Memory Cells: A Case Study of HfO2/Al2O3 Nanolaminated Stacks

“…However, it appeared that the thickness of the layers and the number of interfaces should be carefully optimized as the performance of the cell could deteriorate by the electrostatic repulsion between the trapped charges [27]. The possibility to combine the HfO 2 /Al 2 O 3 dielectric stacks with high-mobility channel materials (e.g., SiGe [28], GaAs [29,30], InP [31], In 2 Ga 2 ZnO 7 [32]) as well as with 2D materials, (e.g., black phosphorous [33] and MoS 2 [24,34]) opens up new horizons for their implementation in emerging applications such as thin film transistors, non-volatile memory devices for flexible and transparent electronics, etc.…”