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).

A highly stable fluorine-passivated In-Ga-Zn-O (IGZO) thin-film transistor (TFT) was demonstrated under positive gate bias and temperature stress (PBTS). The defects in the IGZO TFT were passivated by fluorine, which was introduced into a SiO x etching stopper during the deposition of fluorinated silicon nitride for passivation and diffused during post-fabrication annealing. From the results of secondary ion mass spectrometry analysis, the reliability of the IGZO TFT under PBTS was observed to be markedly improved even at a stress temperature of 100 °C when fluorine diffusion was detected in the IGZO channel. The fluorine-passivated IGZO TFT has improved operation temperature and is advantageous for achieving high-performance and high-reliability oxide TFTs for next-generation displays.

No abstract

The effect of drain bias (V(DS)) on the negative gate bias and illumination stress (NBIS) stability of amorphous InGaZnO (a-IGZO) thin-film transistors was investigated using a double-sweeping gate voltage (V(GS)) mode. The variation in the transfer characteristics was explored using current-voltage and capacitance-voltage characteristics. In the initial stage (<1000 s) of NBIS with grounded V(DS) (V(GS) = -40 V and V(DS) = 0 V), the transfer characteristics shifted negatively with an insignificant change in the subthreshold swing (SS) because of hole trapping at an IGZO/gate insulator interface. On the other hand, on-current degradation was observed and was accelerated in the forward measurement as the NBIS duration increased. The results indicated that NBIS induced donor-like defects near the conduction band; however, the transfer curves in the reverse measurement shifted positively without on-current and SS degradations. It was found that the degradations were enhanced by applying a positive V(DS) bias (V(GS) = -40 V and V(DS) = 40 V); in contrast, they could be reduced by applying a small negative V(DS) of V(DS) > V(GS) (V(GS) = -40 V and V(DS) = -20 V). Furthermore, it was confirmed that the NBIS degradations could be suppressed by applying a large negative V(DS) bias of V(DS) < V(GS) (V(GS) = -40 V and V(DS) = -60 V) during NBIS.

The negative gate bias and illumination stress (NBIS) stability and photo-response of In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) with either silicon oxide (SiO X ) or fluorinated silicon nitride (SiN X :F) passivation were investigated. NBIS degradation can be suppressed when the fluorine (F) in SiNx:F diffused into an IGZO channel during long annealing period. Photo-response analysis revealed that F passivated effectively electron traps in the IGZO channel existing at an energy level close to the valence band maximum (near-VBM state). The fluorine-passivated IGZO TFT is thus advantageous for achieving highly reliable IGZO TFT for next-generation displays. An amorphous In-Ga-Zn-O (a-IGZO) semiconductor is widely accepted as a promising channel material for TFT applications owing to its outstanding electrical properties.3 However, it is recognized that degradation under negative gate bias and illumination stress (NBIS) is a unique but serious issue for oxide TFTs.4 When a negative gate voltage and illumination stresses are simultaneously applied to oxide TFTs, the enhancements of negative threshold voltage (V th ) shift and hysteresis were observed due to photo-excitation of electrons from high-density electron traps existing in an IGZO at an energy level close to the valence band maximum (near-VBM state). [5][6][7][8][9] The origin of the near-VBM state has been actively investigated from both experimental and theoretical standpoints. Kamiya et al. reported the oxygen vacancy with void in oxygen deficient IGZO film is an origin of the near-VBM state.10 In addition, weakly-bonded oxygen, interstitial oxygen, undercoodinated oxygen, and peroxide have been reported as origins of the near-VBM state in an IGZO film.11-14 Moreover, the -OH groups in the film have also been reported to relate the density of the near-VBM state. [15][16][17] Although the origin of the near-VBM state is still debatable, passivation or reduction of the near-VBM state originating from oxygen-related defects is essential to improve NBIS reliability. Wet-O 2 annealing has been reported to improve the NBIS reliability of the IGZO TFT. 17,18 It has also been reported that formation of OH-bonds in an IGZO is an important factor to passivate the near-VBM state.17 A theoretical study also indicated that a hydrogen atom preferentially binds to undercoordinated oxygen, resulting in a passivation of the near-VBM state.14 Although many researches have made numerous efforts to improve the NBIS reliability of oxide TFTs, NBIS degradation has as yet not been suppressed.We reported that reliability of the IGZO TFT under positive gate bias and temperature stress (PBTS) was drastically improved by a fluorine-passivated IGZO TFT. 19 It was found that fluorine (F) effectively passivated electron traps and weakly bonded oxygen in an IGZO channel and at a gate insulator (GI)/channel interface when F diffused into an IGZO channel. However, both the F passivation effect of the near-VBM state and its influence on the NBIS stability of the IGZO TFT have not bee...