High Performance, Low Temperature Solution-Processed Barium and Strontium Doped Oxide Thin Film Transistors

Abstract

Amorphous mixed metal oxides are emerging as high performance semiconductors for thin film transistor (TFT) applications, with indium gallium zinc oxide, InGaZnO (IGZO), being one of the most widely studied and best performing systems. Here, we investigate alkaline earth (barium or strontium) doped InBa(Sr)ZnO as alternative, semiconducting channel layers and compare their performance of the electrical stress stability with IGZO. In films fabricated by solution-processing from metal alkoxide precursors and annealed to 450 °C we achieve high field-effect electron mobility up to 26 cm2 V–1 s–1. We show that it is possible to solution-process these materials at low process temperature (225–200 °C yielding mobilities up to 4.4 cm2 V–1 s–1) and demonstrate a facile “ink-on-demand” process for these materials which utilizes the alcoholysis reaction of alkyl metal precursors to negate the need for complex synthesis and purification protocols. Electrical bias stress measurements which can serve as a figure of merit for performance stability for a TFT device reveal Sr- and Ba-doped semiconductors to exhibit enhanced electrical stability and reduced threshold voltage shift compared to IGZO irrespective of the process temperature and preparation method. This enhancement in stability can be attributed to the higher Gibbs energy of oxidation of barium and strontium compared to gallium.

Flexography‐Printed In2O3 Semiconductor Layers for High‐Mobility Thin‐Film Transistors on Flexible Plastic Substrate

“…A large amount of work has concentrated on lowering the conversion temperature of the precursor solutions to semiconducting metal-oxide layers. Functional TFTs have been obtained at ≈200 °C or below (1) via the careful design of precursor chemistry utilizing metal alkoxides with controlled hydrolysis, [ 14,15 ] combustion process, [ 11,19 ] or the addition of oxidizing agents, [ 20 ] (2) via the use of additional energy in conversion such as various wavelengths of UV light, [ 8,15,21 ] or microwaves, [ 22 ] or (3) by employing conditions during annealing that promote effi cient precursor conversion such as ozone or vacuum. [ 6,7,20 ] After the fi rst report on inkjet-printed metal oxide layers from metal chloride precursors by Lee et al in 2007, [ 16 ] the deposition of metal-oxide semiconductor layers for TFTs has been successfully performed via several printing techniques.…”

“…The process leads into high-mobility In 2 O 3 TFTs on ALD-grown amorphous Al 2 O 3 with µ sat ≈ 8 cm 2 V −1 s −1 which show enhancement-mode operation with reproducible turn-on voltages at ≈0 V after a lowtemperature post-contact-annealing step. By combining the demonstrated process with available UV-based low-temperature annealing schemes, [ 8,15,21 ] roll-printed metal-oxide TFT devices and circuits on low-cost plastic substrates can be achieved in the future. [ 22 ] the solution was stirred at 75 °C for more than 12 h and fi ltered prior using with a 0.45 µm pore size glass fi bre fi lter.…”

“…Several precursor routes for solution-processed metal-oxide semiconductor layers based on metal alkoxides, [ 14,15 ] and on metal salts such as acetates, nitrates, and chlorides have been reported. [ 16,17 ] Precursors based on metal nitrates have been shown to convert into metal oxides generally at lower temperatures than acetateor chloride-based precursors.…”

High Electron Mobility Thin‐Film Transistors Based on Solution‐Processed Semiconducting Metal Oxide Heterojunctions and Quasi‐Superlattices

“…Because of the latter requirement it is not a trivial question whether high‐quality oxide heterointerfaces can be realized using simpler, cost‐efficient, and high‐throughput fabrication methods that are compatible with existing semiconductor fabrication processes (e.g., solution‐based) and even perhaps temperature‐sensitive substrate materials such as plastic. Thus, the development of ease to implement metal oxide hetero/multilayer structures could help overcoming important bottlenecks associated with the level of performance and manufacturing of incumbent TFT technologies, and enable the emergence of a host of large‐area, flexible optoelectronics 4, 26, 27, 28, 29, 30…”

UV‐Assisted Low Temperature Oxide Dielectric Films for TFT Applications

“…[1][2][3] To date, the research effort has focused on improving the semiconductor materials [4,5] , devising dielectric material formulations with optimized structures [6,7] , and on using low-temperature processing [8][9][10][11] in order to achieve compatibility with plastic substrates. Among the various methods investigated, ultraviolet (UV) photochemical activation of sol-gel precursors is particularly significant, as the technique can also be adapted to form the gate insulator.…”