Developing a low-temperature fabrication strategy of an amorphous InGaZnO (α-IGZO) channel layer is a prerequisite for high-performance oxide-based thin film transistor (TFT) flexible device applications. Herein, an ultraviolet-assisted oxygen ambient rapid thermal annealing method (UV-ORTA), which combines ultraviolet irradiation with rapid annealing treatment in an oxygen atmosphere, was proposed to realize the achievement of high-performance α-IGZO TFTs at low temperature. Experimental results have confirmed that UV-ORTA treatment has the ability to suppress defects and obtain high-quality films similar to high-temperature-annealing-treated samples. α-IGZO/HfAlO TFTs with high-performance and low-voltage operating have been achieved at a low temperature of 180 °C for 200 s, including a high μsat of 23.12 cm2 V-1 S-1, large Ion/off of 1.1 × 108, small subthreshold swing of 0.08 V/decade, and reliable stability under bias stress, respectively. As a demonstration of complex logic applications, a low-voltage resistor-loaded unipolar inverter based on an α-IGZO/HfAlO TFT has been built, demonstrating full swing characteristics and a high gain of 13.8. Low-frequency noise (LFN) characteristics of α-IGZO/HfAlO TFTs have been presented and concluded that the noise source tended to a carrier number fluctuation (ΔN) model from a carrier number and correlated mobility fluctuation (ΔN-Δμ) model. As a result, it can be inferred that the low-temperature UV-ORTA technique to improve α-IGZO thin film quality provides a facile and designable process for the integration of α-IGZO TFTs into a flexible electronic system.

Ultraviolet-Assisted Low-Thermal-Budget-Driven α-InGaZnO Thin Films for High-Performance Transistors and Logic Circuits.

Abstract This paper presents the post-annealing effects, caused by rapid thermal annealing (RTA), on amorphous indium gallium zinc oxide (a-IGZO) thin film transistor's (TFT) electrical characteristics, and its contact resistance ( R C ) with thermally grown SiO 2 gate dielectric on silicon wafer substrates. The electrical characteristics of two types of TFTs, one post-annealed and the other not, are compared, and a simple model of the source and drain contacts is applied to estimate the R C by a transmission line method (TLM). Consequently, it has been found that the post-annealing does improve the TFT performances; in other words, the saturation mobility ( μ sat ), the on/off current ratio ( I ON/OFF ), and the drain current ( I D ) all increase, and the R C and the threshold voltage ( V T ) both decrease. As-fabricated TFTs have the following electrical characteristics; a saturation mobility ( μ sat ) as large as 0.027 cm 2 /V s, I ON/OFF of 10 3 , sub-threshold swing (SS) of 0.49 V/decade, V T of 32.51 V, and R C of 969 MΩ, and the annealed TFTs have improved electrical characteristics as follows; a μ sat of 3.51 cm 2 /V s, I ON/OFF of 10 5 , SS of 0.57 V/decade, V T of 27.2 V, and R C of 847 kΩ.

The effect of annealing on amorphous indium gallium zinc oxide thin film transistors

Abstract Due to the unique outermost orbitals of Sn, hole carriers in tin monoxide (SnO) possess small effective mass and high mobility among oxide semiconductors, making it a promising p-channel material for thin film field-effect transistors (TFTs). However, the Sn vacancy induced field-effect mobility deterioration and threshold voltage ( V th ) shift in experiments greatly limit its application in complementary metal-oxide-semiconductor (CMOS) transistors. In this study, the internal mechanism of vacancy defect compensation by aluminum (Al) doping in SnO x film is studied combining experiments with the density functional theory (DFT). The doping is achieved by an argon (Ar) plasma treatment of Al 2 O 3 deposited onto the SnO x film, in which the Al 2 O 3 provides both the surface passivation and Al doping source. Experimental results show a wide V th modulation range (6.08 to −19.77 V) and notable mobility enhancement (11.56 cm 2 V −1 s −1 ) in the SnO x TFTs after the Al doping by Ar plasma. DFT results reveal that the most possible positions of Al in SnO and SnO 2 segments are the compensation to Sn vacancy and interstitial. The compensation will create an n-type doping effect and improve the hole carrier transport by reducing the hole effective mass ( m h *), which is responsible for the device performance variation, while the interstitial in the SnO 2 segment can hardly affect the valence transport of the film. The defect compensation is suitable for the electronic property modulation of SnO towards the high-performance CMOS application. 

Enhanced performance of p-type SnO x thin film transistors through defect compensation

Under varying growth and device processing conditions, ultrabroadband photoconduction (UBPC) reveals strongly evolving trends in the defect density of states (DoS) for amorphous oxide semiconductor thin‐film transistors (TFTs). Spanning the wide bandgap of amorphous InGaZnOx (a‐IGZO), UBPC identifies seven oxygen deep donor vacancy peaks that are independently confirmed by energetically matching to photoluminescence emission peaks. The subgap DoS from 15 different types of a‐IGZO TFTs all yield similar DoS, except only back‐channel etch TFTs can have a deep acceptor peak seen at 2.2 eV below the conduction band mobility edge. This deep acceptor is likely a zinc vacancy, evidenced by trap density which becomes 5‐6× larger when TFT wet‐etch methods are employed. Certain DoS peaks are strongly enhanced for TFTs with active channel processing damage caused from plasma exposure. While Ar implantation and He plasma processing damage are similar, Ar plasma yields more disorder showing a ≈2 × larger valence‐band Urbach energy, and two orders of magnitude increase in the deep oxygen vacancy trap density. Changing the growth conditions of a‐IGZO also impacts the DoS, with zinc‐rich TFTs showing much poorer electrical performance compared to 1:1:1 molar ratio a‐IGZO TFTs owing to the former having a ∼10 × larger oxygen vacancy trap density. Finally, hydrogen is found to behave as a donor in amorphous indium tin gallium zinc oxide TFTs.

/pdf/illuminating-trap-density-trends-in-amorphous-oxide-1k0t53qh.pdf

Illuminating Trap Density Trends in Amorphous Oxide Semiconductors with Ultrabroadband Photoconduction

Herein, indium-doped tin oxide (TIO) thin films were prepared using the solution process. The structural characteristics, surface morphologies, and chemical compositions of the prepared films were systematically investigated as a function of indium-doping contents. The films were integrated as a channel layer into thin-film transistors (TFTs). Results show that indium can be used as a carrier suppressor as well as a mobility enhancer for SnO2. The optimal devices exhibited satisfactory performance, achieving field-effect mobility of 8.94 cm2/V·s, positive threshold voltage of 0.25 V, small subthreshold swing of 0.4 V/decade, and on-to-off current ratio of 1.5 × 106. The results of this study suggest that TIO-TFTs are very promising for use in next-generation displays. 

Mobility enhancement of tin oxide thin-film transistor by indium-doping

In this study, an Ar/O2 plasma mixture treatment with different proportions of O2 was used to reduce the oxygen vacancy density in an amorphous indium gallium zinc oxide (a-IGZO) thin film. The objective was to enhance the field-effect carrier mobility in a thin-film transistor (TFT) with the IGZO film as the channel layer. Atomic force microscopy revealed that the roughness of the IGZO film after plasma treatment was higher than that of the untreated film; however, the surface roughness of the IGZO film decreased after the proportion of O2 was increased in the plasma. The Hall measurement results showed that the resistivity of the plasma-treated IGZO film increased with a decrease in the electron concentration in the film; in addition, the carrier mobility considerably increased. The IGZO TFT fabricated from this film exhibited a high field-effect carrier mobility of 36 cm2 V−1 s−1, a subthreshold swing (SS) of 1.25 V/decade, an I OFF current of 4.58 × 10−11 A, and an I ON/I OFF current ratio of 7.55 × 105. To further improve the device performance, the plasma-treated IGZO films were subjected to thermal annealing with the annealing temperature ranging from 100 °C to 300 °C. After the annealing process, the plasma-treated IGZO TFTs demonstrated a further improvement in the device performance with a field-effect carrier mobility of 38.8 cm2 V−1 s−1, SS of 0.7 V/decade, I OFF current of 1.04 × 10−11 A, and an I ON/I OFF current ratio of 9.93 × 106. In addition, a reliability test was performed to evaluate the stability of the IGZO TFT devices, which revealed that the threshold voltage maintained a high degree of stability during the long-term tests. Therefore, the plasma-treated IGZO TFTs with subsequent postgrowth annealing could be helpful for the fabrication of next-generation flat-panel displays.

https://iopscience.iop.org/article/10.1088/1361-6641/abe6da/pdf

Improvement of device characteristics of plasma-treated indium gallium zinc oxide thin-film transistors through thermal annealing

Effect of ion assistance on silicon nitride films deposited by reactive magnetron sputtering

Aluminum nitride (AlN) thin-film materials possess a wide energy gap; thus, they are suitable for use in various optoelectronic devices. In this study, AlN thin films were deposited using radio frequency magnetron sputtering with an Al sputtering target and N2 as the reactive gas. The N2 working gas flow rate was varied among 20, 30, and 40 sccm to optimize the AlN thin film growth. The optimal AlN thin film was produced with 40 sccm N2 flow at 500 W under 100% N2 gas and at 600 °C. The films were studied using X-ray diffraction and had (002) phase orientation. X-ray photoelectron spectroscopy was used to determine the atomic content of the optimal film to be Al, 32%; N, 52%; and O, 12% at 100 nm beneath the surface of the thin film. The film was also investigated through atomic force microscopy and had a root mean square roughness of 2.57 nm and a hardness of 76.21 GPa. Finally, in situ continual sputtering was used to produce a gallium nitride (GaN) layer on Si with the AlN thin film as a buffer layer. The AlN thin films investigated in this study have excellent material properties, and the proposed process could be a less expensive method of growing high-quality GaN thin films for various applications in GaN-based power transistors and Si integrated circuits.

/pdf/optimal-growth-conditions-for-forming-c-axis-002-aluminum-3au5i3tx.pdf

Optimal Growth Conditions for Forming c-Axis (002) Aluminum Nitride Thin Films as a Buffer Layer for Hexagonal Gallium Nitride Thin Films Produced with In Situ Continual Radio Frequency Sputtering

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Improvement of device characteristics of plasma-treated indium gallium zinc oxide thin-film transistors through thermal annealing

Effect of ion assistance on silicon nitride films deposited by reactive magnetron sputtering

Optimal Growth Conditions for Forming c-Axis (002) Aluminum Nitride Thin Films as a Buffer Layer for Hexagonal Gallium Nitride Thin Films Produced with In Situ Continual Radio Frequency Sputtering