In the past two decades, the exploitation of new material and innovating engineering strategies have substantially increased the figure of merit of TE materials, zT (=S 2 T/ρκ, in which ρ, S, κ, and T are the electrical resistivity, Seebeck coefficient, total thermal conductivity, and temperature), the primary metric to measure the heat-to-electric power conversion efficiency. High zT values have been constantly reported in PbTe, [2,3] SnSe, [4-6] GeTe, [7-17] CoSb 3 , [18] Zn 4 Sb 3 , [19-21] Mg 3 Sb 2 , [22,23] and related materials in the mid-temperature range. Several important theories and concepts have also been proposed to elucidate the mechanisms leading to their extraordinary TE performance. [24-28] GeTe is a narrow bandgap semiconductor with a large hole carrier concentration of ≈10 21 cm-3 due to native Ge vacancies. It adopts a cubic structure (Fm3m, β-GeTe) at high temperatures, which undergoes a ferroelectric phase transition to a non-centrosymmetric Phase transition in thermoelectric (TE) material is a double-edged swordit is undesired for device operation in applications, but the fluctuations near an electronic instability are favorable. Here, Sb doping is used to elicit a spontaneous composition fluctuation showing uphill diffusion in GeTe that is otherwise suspended by diffusionless athermal cubic-torhombohedral phase transition at around 700 K. The interplay between these two phase transitions yields exquisite composition fluctuations and a coexistence of cubic and rhombohedral phases in favor of exceptional figures-of-merit zT. Specifically, alloying GeTe by Sb 2 Te 3 significantly suppresses the thermal conductivity while retaining eligible carrier concentration over a wide composition range, resulting in high zT values of >2.6. These results not only attest to the efficacy of using phase transition in manipulating the microstructures of GeTe-based materials but also open up a new thermodynamic route to develop higher performance TE materials in general.

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This study examines the transfer stability of amorphous InGaZnO thin film transistors, with and without a SiAlNO passivation layer. The passivation layer was magnetron sputtered at ambient temperature followed by an annealing at 320 • C in air, resulting in a stoichiometric (SiAl)(NO) layer. I-V characteristics were measured under positive bias stress (PBS) in O 2 or negative bias illuminated stress (NBIS) in vacuum. Both the PBS and NBIS stabilities of the passivated TFT were substantially improved by reducing the V th of PBS from 8.1 V to 0.1 V and the V th of NBIS from −22.6 V to −0.8 V.Thin film transistors (TFTs) based on amorphous InGaZn oxide (a-IGZO) have been studied extensively for potential application on next-generation flat-panel displays. 1 Although a-IGZO TFTs exhibit superior optical and electric properties, their long-term stability and reliability under bias and/or illumination stresses is a problem that has attracted considerable attention.Previous studies have demonstrated that exposing the active layer of bottom-gate a-IGZO TFTs to the environment causes dramatic shifts in the threshold voltage under either positive bias stresses (PBS) or negative bias illumination stresses (NBIS). 2-5 Oxygen and moisture was identified as a critical factor inducing the threshold voltage instability. 6,7 Accordingly, adopting a passivation layer to protect the active layer of the a-IGZO TFTs is essential. The passivation layers suggested were mostly deposited using the plasma-enhanced chemical vapor deposition (PECVD) process at temperatures between 150 and 350 • C. [8][9][10][11] However, the PECVD technique is challenging because of the tight processing parameters required and the damages created on the surface of the active layer by plasma bombardment. [12][13][14] Magnetron sputtering is a low-energy deposition technique which is the most popular process for depositing the a-IGZO layer and the metal electrodes for TFT fabrication. It is thus desirable to find suitable passivation materials that can also be deposited by using magnetron sputtering. This paper reports the use of a SiAlNO layer to passivate the a-IGZO channel of a bottom-gate TFT. The SiAlNO layer deposited using radio-frequency (RF) magnetron sputtering at room temperature was as thin as 25 nm. Excellent PBS and NBIS stabilities were observed for the passivated TFTs.A bottom-gate coplanar structure was used for preparing the TFTs. The gate layer was composed of Ti (50 nm), Al (200 nm) and Ti (50 nm) layers deposited on glass. PECVD was used to deposit a 300 nm-thick SiO x layer at 300 • C on the patterned gate electrode as the gate dielectric. The source and drain electrodes of the same Ti/Al/Ti structure were deposited and patterned. A 15 μm-wide and 9 μm-long a-IGZO layer was then deposited using RF magnetron sputtering at room temperature, using a compound target with a In, Ga and Zn atomic ratio of 1:1:1. Sputtering was carried out in an Ar + 6.7% O 2 atmosphere at 5 mtorr. After deposition, the TFTs were annealed at 320 • C in air for 1...

In article number 2005612, Pai‐Chun Wei, Hsin‐Jay Wu, and co‐workers leverage the interplay between the spinodal decomposition and athermal phase transition in GeTe‐based thermoelectric materials. The exquisite microstructure, featured by strong composition fluctuations and the coexistence of rhombohedral‐ and cubic‐GeTe, yield high zT values of >2.6. This work provides a new thermodynamic route to developing higher‐performance thermoelectric materials in general.