Quantitative Analysis of the Effect of Hydrogen Diffusion from Silicon Oxide Etch-Stopper Layer into Amorphous In–Ga–Zn–O on Thin-Film Transistor

Abstract

To investigate the effect of hydrogen diffusion from the silicon oxide etch-stopper (SiO x ES) layer into the amorphous In-Ga-Zn-O (a-IGZO) on thin-film transistor (TFT) properties and stabilities, we fabricated a-IGZO TFTs with a SiO x ES layer deposited by plasma-enhanced chemical vapor deposition at various silane (SiH 4 ) partial pressures (P[SiH 4 ]). Then, quantitative analysis was performed to investigate the relationship between the hydrogen content of the a-IGZO and electrical properties and stability of the TFTs. We found that a low resistance region was formed at the backchannel of the TFT, when the SiO x ES layer was deposited at higher P[SiH 4 ], leading to a drastic negative threshold voltage (V th ) shift. In addition, it was also found that at the frontchannel, the increase in the carrier concentration of a-IGZO was proportional to the increase in the amount of hydrogen in a-IGZO. On the other hand, when P[SiH 4 ] was increased, the subthreshold swing, hysteresis, and gate-bias stability of the TFT improved. The results indicate that hydrogen diffused from the SiO x ES layer passivates the electron traps at the a-IGZO and/or gate insulator/a-IGZO interface, and almost all of the hydrogen also acts as shallow-donor in a-IGZO.Index Terms-Amorphous In-Ga-Zn-O (a-IGZO), etchstopper (ES), hydrogen diffusion, silane (SiH 4 ) partial pressure, silicon oxide (SiO x ), thin-film transistor (TFT).

Effect of hydrogen diffusion in an In–Ga–Zn–O thin film transistor with an aluminum oxide gate insulator on its electrical properties

“…Because H can be easily incorporated and/or diffused into the a-IGZO layer during the fabrication of TFT devices, an experimental design capable of revealing the role of H in a-IGZO TFT is not straightforward. Specically, SiO 2 and SiN x layers, which are widely used as gate insulators or passivation layers, are deposited through a plasma-enhanced chemical vapor deposition (PE-CVD) process, which can induce too much hydrogen in the lm, complicating the proper control of H. 11,16,17 To solve this problem, an Al 2 O 3 layer can be used due to its excellent diffusion barrier property against hydrogen. 12,18 In addition, Al 2 O 3 is usually deposited through the atomic layer deposition (ALD) method, and the H concentration in Al 2 O 3 can be controlled by the deposition temperature.…”

“…8,9 In addition, a benecial effect of hydrogen on the reliability of a-IGZO TFTs was reported. 10,11 However, the opposite effects of hydrogen, where it generates defect states and induces instability during photobias stress, were also reported.…”

High-Performance Top-Gate and Self-Aligned In–Ga–Zn-O Thin-Film Transistor Using Coatable Organic Insulators Fabricated at 150 °C

“…Since carrier trapping at the front-channel interface and/or carrier injection into the OGI are considered to be causes of the Vth shift under PBS testing for the TFT with the PSL [23,24], material selection for the PL would be a key factor for further improvement of the bias stress stabilities.…”

Development of flexible displays using back-channel-etched In-Sn-Zn-O thin-film transistors and air-stable inverted organic light-emitting diodes

“…Thus, formation of the solution‐processed organic passivation layer may assist recovery from the damage in the back channel region. Oxide TFT characteristics are significantly dependent on the plasma‐enhanced chemical vapor deposition conditions of the widely used SiO 2 passivation layer due to plasma exposure and hydrogen diffusion toward the back channel . Therefore, a solution‐phase process may enhance the quality of the back channel/passivation interface because it avoids plasma damage and hydrogen diffusion.…”