More Like this

1. Low‐Temperature‐Processed Printed Metal Oxide Transistors Based on Pure Aqueous Inks

   https://doi.org/10.1002/adfm.201606062  

   Scheideler, William J. ; Kumar, Rajan ; Zeumault, Andre R. ; Subramanian, Vivek ( March 2017 , Advanced Functional Materials)

   Additive patterning of transparent conducting metal oxides at low temperatures is a critical step in realizing low‐cost transparent electronics for display technology and photovoltaics. In this work, inkjet‐printed metal oxide transistors based on pure aqueous chemistries are presented. These inks readily convert to functional thin films at lower processing temperatures (T≤ 250 °C) relative to organic solvent‐based oxide inks, facilitating the fabrication of high‐performance transistors with both inkjet‐printed transparent electrodes of aluminum‐doped cadmium oxide (ACO) and semiconductor (InO_x). The intrinsic fluid properties of these water‐based solutions enable the printing of fine features with coffee‐ring free line profiles and smoother line edges than those formed from organic solvent‐based inks. The influence of low‐temperature annealing on the optical, electrical, and crystallographic properties of the ACO electrodes is investigated, as well as the role of aluminum doping in improving these properties. Finally, the all‐aqueous‐printed thin film transistors (TFTs) with inkjet‐patterned semiconductor (InO_x) and source/drain (ACO) layers are characterized, which show ideal low contact resistance (R_c< 160 Ω cm) and competitive transistor performance (µ_linup to 19 cm²V⁻¹s⁻¹, Subthreshold Slope (SS) ≤150 mV dec⁻¹) with only low‐temperature processing (T≤ 250 °C).

    

   more » « less
2. High‐Performance Zinc Tin Oxide TFTs with Active Layers Deposited by Atomic Layer Deposition

   https://doi.org/10.1002/aelm.202000195  

   Allemang, Christopher R. ; Cho, Tae H. ; Trejo, Orlando ; Ravan, Shantam ; Rodríguez, Robin E. ; Dasgupta, Neil P. ; Peterson, Rebecca L. ( June 2020 , Advanced Electronic Materials)

   New deposition techniques for amorphous oxide semiconductors compatible with silicon back end of line manufacturing are needed for 3D monolithic integration of thin‐film electronics. Here, three atomic layer deposition (ALD) processes are compared for the fabrication of amorphous zinc tin oxide (ZTO) channels in bottom‐gate, top‐contact n‐channel transistors. As‐deposited ZTO films, made by ALD at 150–200 °C, exhibit semiconducting, enhancement‐mode behavior with electron mobility as high as 13 cm²V⁻¹s⁻¹, due to a low density of oxygen‐related defects. ZTO deposited at 200 °C using a hybrid thermal‐plasma ALD process with an optimal tin composition of 21%, post‐annealed at 400 °C, shows excellent performance with a record high mobility of 22.1 cm²V^–1s^–1and a subthreshold slope of 0.29 V dec^–1. Increasing the deposition temperature and performing post‐deposition anneals at 300–500 °C lead to an increased density of the X‐ray amorphous ZTO film, improving its electrical properties. By optimizing the ZTO active layer thickness and using a high‐kgate insulator (ALD Al₂O₃), the transistor switching voltage is lowered, enabling electrical compatibility with silicon integrated circuits. This work opens the possibility of monolithic integration of ALD ZTO‐based thin‐film electronics with silicon integrated circuits or onto large‐area flexible substrates.

    

   more » « less
3. Trapped Carrier Scattering and Charge Transport in High‐Mobility Amorphous Metal Oxide Thin‐Film Transistors

   https://doi.org/10.1002/andp.201800341  

   Wang, Xiao ; Dodabalapur, Ananth ( November 2018 , Annalen der Physik)

   The multiple trap and release (MTR) model is extended to more completely and accurately describe charge transport in high‐mobility amorphous metal oxide thin‐film transistors (TFTs). In addition to trapping and release of charges, other scattering mechanisms that influence mobility are considered along with screening by free carriers. The mobility for each of the dominant scattering mechanisms is calculated using the Boltzmann transport equation (BTE) in the relaxation time approximation. It is found that trapped carriers very effectively scatter the charges that move in extended states. This type of scattering is unique to TFTs. Experimental data from high‐mobility amorphous metal oxide TFTs are compared with calculations with very good agreement. At high temperatures, scattering by longitudinal optical phonons and surface phonons becomes significant. This work represents the first successful combination of charge carrier scattering and the BTE with thermally activated MTR transport in a disordered semiconductor. Charge transport in amorphous metal oxide transistors is quantitatively described for the first time and the factors that influence the mobility at various temperatures and charge carrier densities are clearly described. This approach can be used for describing transport in several amorphous and polycrystalline semiconductors with significant disorder and trapping.

    

   more » « less
4. Realization of flexible AlGaN/GaN HEMT by laser liftoff

   https://doi.org/10.35848/1882-0786/ac7847  

   Alam, Md Didarul ; Hussain, Kamal ; Mollah, Shahab ; Simin, Grigory ; Khan, Asif ; Chandrashekhar, MVS ( June 2022 , Applied Physics Express)

   Abstract We demonstrate fully fabricated AlGaN/GaN high electron mobility transistors (HEMTs) transferred from sapphire to copper tape on flexible polyethylene terephthalate using 193 nm excimer laser liftoff (LLO). The heterojunction is structurally intact after LLO, leading to preserved electron mobility μ n ∼1630 cm 2 V −1 s −1 and carrier concentration n s ∼10 13 cm −2 . The maximum drain saturation current decreased by ∼18% after transfer, which is a lower reduction than other reported transfer methods. The drain current of this flexible HEMT increased monotonically under tensile stress applied using a convex-shaped plate, while the threshold voltage shifted more negative in quantitative agreement with the expected piezoelectric charge for an intact heterojunction. 

   more » « less
5. Self‐Sorting of 10‐µm‐Long Single‐Walled Carbon Nanotubes in Aqueous Solution

   https://doi.org/10.1002/adma.201901641  

   Wang, Peng ; Barnes, Benjamin ; Wu, Xiaojian ; Qu, Haoran ; Zhang, Chiyu ; Shi, Yang ; Headrick, Robert J. ; Pasquali, Matteo ; Wang, YuHuang ( June 2019 , Advanced Materials)

   Single‐walled carbon nanotubes (SWCNTs) are a class of 1D nanomaterials that exhibit extraordinary electrical and optical properties. However, many of their fundamental studies and practical applications are stymied by sample polydispersity. SWCNTs are synthesized in bulk with broad structural (chirality) and geometrical (length and diameter) distributions; problematically, all known post‐synthetic sorting methods rely on ultrasonication, which cuts SWCNTs into short segments (typically <1 µm). It is demonstrated that ultralong (>10 µm) SWCNTs can be efficiently separated from shorter ones through a solution‐phase “self‐sorting”. It is shown that thin‐film transistors fabricated from long semiconducting SWCNTs exhibit a carrier mobility as high as ≈90 cm²V⁻¹s⁻¹, which is ≈10 times higher than those which use shorter counterparts and well exceeds other known materials such as organic semiconducting polymers (<1 cm²V⁻¹s⁻¹), amorphous silicon (≈1 cm²V⁻¹s⁻¹), and nanocrystalline silicon (≈50 cm²V⁻¹s⁻¹). Mechanistic studies suggest that this self‐sorting is driven by the length‐dependent solution phase behavior of rigid rods. This length sorting technique shows a path to attain long‐sought ultralong, electronically pure carbon nanotube materials through scalable solution processing.

    

   more » « less