Characteristics of Amorphous In‐Ga‐Zn‐O Thin Films with Various Compositions Under Microwave Annealing

Abstract

In this study, the effects of microwave annealing (MWA) on the electrical properties of amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) are evaluated. To measure the transfer and output characteristics of as-deposited, conventional thermal annealed (CTA), or microwave annealed TFTs, the devices are fabricated by varying the compositional ratios of IGZO films (In 2 O 3 :Ga 2 O 3 :ZnO ¼ 1:1:1, 1:1:2, and 2:1:2 at%). The reliability is evaluated by measuring the threshold voltage shift under the gate bias stress and by analyzing the charge trapping characteristics according to the operating temperature. In addition, the interface trap density of the a-IGZO channel/ gate insulator and the volume density of the shallow trap of the channel layer are extracted to evaluate the difference in trap density according to the channel composition and the variation in the trap density as a result of the annealing process. Lastly, the sub-gap density of states (DOS) of the TFTs is investigated to verify the compositional ratio and the annealing effect on the electrical characteristics and reliability of the devices. Based on these results, it is demonstrated that high-performance a-IGZO TFTs can be fabricated by using the low thermal budget MWA technique and by controlling the composition of the IGZO channel.

Enabling high performance n-type metal oxide semiconductors at low temperatures for thin film transistors

“…Microwave assisted annealing (MWA) technique has attracted significant attention due to the volumetric heating involved, that directly and uniformly delivers thermal energy to the MO film, while enabling low thermal budget and fast processing, primarily due to the short exposure duration 63,[104][105][106][107][108] . In principle, Microwaves compromise with rapid change in electric and magnetic field as well (Fig.…”

“…The temperature of the a-IGZO TFTs samples was measured by an infrared thermometer during the MW-PDA process and observed to be 399.6 ℃ on average. However CTA at 400℃ yielded poorer performance since MWA results in lowered defect densities (D it , N t ) and sub-gap density of state (DOS) 107 . Compared to conventional annealing techniques, the novel microwave annealing techniques facilitate low temperature activation of devices on flexible substrate and may be promising for roll to roll processing of flexible electronics 108 .…”

Systematic Study on the Amorphous, C-Axis-Aligned Crystalline, and Protocrystalline Phases in In–Ga–Zn Oxide Thin-Film Transistors

“…IGZO can be deposited by numerous techniques, including solution processing, − atomic layer deposition, − pulsed laser deposition, , physical vapor deposition (PVD), and mist-chemical vapor deposition . Postdeposition treatments include laser crystallization, rapid thermal annealing and conventional thermal annealing, and microwave annealing . Among these, PVD in the form of reactive sputtering from a ceramic IGZO target with thermal annealing as a post-treatment is the most common.…”

“…Substrate temperature T sub and the O 2 flow ratio in the O 2 + Ar sputtering gas mixture ( R O 2 ) are the most studied sputtering parameters for tuning of IGZO TFT performance. T sub is typically set in a range from 25 to 300 °C for IGZO sputtering. ,− R O 2 can be varied from 0 to 100% and affects the electronic defect density correlated with oxygen in IGZO films. IGZO TFT electrical properties, including bias stress, are largely influenced by the oxygen concentration and binding state in the films, − hence the optimization of R O 2 is essential for the development of IGZO TFTs with high bias stress stability.…”

“…19 Postdeposition treatments include laser crystallization, 20 rapid thermal annealing and conventional thermal annealing, 21 and microwave annealing. 22 Among these, PVD in the form of reactive sputtering from a ceramic IGZO target with thermal annealing as a posttreatment is the most common. Substrate temperature T sub and the O 2 flow ratio in the O 2 + Ar sputtering gas mixture (R O 2 ) are the most studied sputtering parameters for tuning of IGZO TFT performance.…”