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

Abstract

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.

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

“…Moreover, rapid annealing avoids the problem of the film surface being overoxidized, due to the short ramp-up and ramp-down times. Furthermore, the thermally activated atom diffusion caused by the rapid annealing process can reduce the surface roughness and repair the damage of the UV treatment on the film surface . In summary, UV-ORTA treatment enhances the film quality by suppressing structural defects and O-deficiency defects and enables the low-temperature preparation of high-performance α-IGZO TFTs based on HfAlO high- k gate dielectrics.…”

“…In addition, the trapped electrons at the interface will weaken the induction effect of the gate voltage on the electrons, resulting in a positive shift of the transfer curve. Some studies show that the negative shift of threshold voltage in the NBS test is caused by the release of electrons from the absorbed water molecules on the surface of the α-IGZO film . Moreover, the ionization of shallow-level donors and the release of trapped electrons from trap defects in the channel layer under negative gate voltage lead to an increase of electron concentration in the channel layer.…”

“…Flexible transparent substrate materials, such as polyimide (PI) and poly­(ether sulfone) (PES), are susceptible to thermal deformation at temperatures higher than 230 °C. − Therefore, low-temperature-processed TFTs becomes an essential technology for next-generation display technologies. By far, amorphous indium gallium oxide (α-IGZO) thin films have become a very competitive channel layer material for TFTs by virtue of their superior performance. − The prototype displays with an α-IGZO TFT as the driving circuit has shown satisfactory performance and has been applied in some commercial fields. − To realize flexible display applications, a lot of effort has been made to prepare high-performance α-IGZO TFTs at low temperature, and great progress has been made. ,− However, there exists still many problems in meeting flexible applications, including poor stability, threshold voltage shift, and degraded electrical performance. ,,,− …”

Electrical and Hysteresis Characteristics of Top-Gate InGaZnO Thin-Film Transistors with Oxygen Plasma Treatment Prior to TEOS Oxide Gate Dielectrics

“…Because oxygen vacancies are important for electron donation in the a-IGZO channel layer, the decreased OII peak intensity shown in the XPS analyses corresponded well with the reduced carrier concentration, which could be ascribed to a higher resistivity as a result of the increased O2 plasma time, as shown in Table 2. Therefore, as the O2 plasma time increased, the reduced carrier concentration in the IGZO channel layer may have resulted in an increase in the threshold voltage (Vth) of the IGZO TFT devices [13,17,24]. For the analysis of the SIMS depth profile results, we fabricated test samples with a 50 nm thick Mo/100 nm thick TEOS oxide/40 nm thick a-IGZO structure on silicon sub- For the analysis of the SIMS depth profile results, we fabricated test samples with a 50 nm thick Mo/100 nm thick TEOS oxide/40 nm thick a-IGZO structure on silicon substrates that were the same as the structure of the top-gate IGZO TFT devices.…”

“…The results indicated that O 2 and N 2 plasmas decreased oxygen vacancies, but Ar plasma treatment increased them. Liu et al recently reported [17] on IGZO thin films that were treated with an Ar/O 2 plasma combination with various oxygen content ratios, resulting in the bottom-gate IGZO TFTs have improved device operation characteristics. Wang et al reported [18] the O 2 plasma treatment on gate dielectrics (Al 2 O x ) for a-IGZO TFTs and demonstrated that O 2 plasma treatment can improve the gate dielectric performance.…”