A Light-induced Threshold Voltage Instability Based on a Negative-U Center in a-IGZO TFTs with Different Oxygen Flow Rates

Abstract

In this paper, we investigate visible light stress instability in radio frequency (RF) sputtered a-IGZO thin film transistors (TFTs). The oxygen flow rate differs during deposition to control the concentration of oxygen vacancies, which is confirmed via RT PL. A negative shift is observed in the threshold voltage (V TH ) under illumination with/without the gate bias, and the amount of shift in V TH is proportional to the concentration of oxygen vacancies. This can be explained to be consistent with the ionization oxygen vacancy model where the instability in V TH under illumination is caused by the increase in the channel conductivity by electrons that are photo-generated from oxygen vacancies, and it is maintained after the illumination is removed due to the negative-U center properties.

Influence of oxygen flow during sputtering process on the electrical properties of Ga-doped InZnSnO thin film transistor

“…While sputtering, the excess O 2 will form interstitial atoms. Therefore, the increase of SS would be caused by the increasing density of oxygen-interstitial defect between the gate insulator and Ga-IZTO film [30]. Meanwhile, the V TH shifted to positive side from 0.8 to 6.8 V. The increase of V TH can be explained by the changing of carrier concentration in the Ga-IZTO film [35].…”

“…Similar results were also seen in [26,28], with the increase of O 2 flow, the O stoichiometric proportion of the film will increase. The decrease of optical transmittance of Ga-IZTO thin films would be attributed to the increasing density of oxygen-interstitial in the films, which lead to stronger absorption and scattering of photons [28][29][30]. The insert picture of figure 1 Figure 3(a) exhibits the output characteristic of the Ga-IZTO TFTs deposited with only Ar.…”

Highly Repeatable and Recoverable Phototransistors Based on Multifunctional Channels of Photoactive CdS, Fast Charge Transporting ZnO, and Chemically Durable Al2O3 Layers

“…ZnO materials have also been studied as ultraviolet (UV) photodetectors, due to their wide band gap (∼3.2 eV at room temperature). Additionally, the photoresponse of ZnO semiconductors in the visible region was demonstrated; this phenomenon is associated with oxygen vacancy (V O ) related defects such as V O + and V O 2+ . − Accordingly, oxygen vacancies can be photoactivated during the photoionization process by visible light. This process donates one/two free electrons to the channels, resulting in a negative V th shift of the oxide TFT device.…”

“…Alternatively, ZnO-based oxide semiconductors are considered to be the most feasible semiconducting materials for transparent/flexible optoelectronic devices; this appeal is due to their unique high mobility, transparency in the visible region, and low-temperature processing capabilities. , It was recently reported that oxide semiconductors are more suitable for the sensing materials of photo-TFTs than conventional a -Si. The photoresponse of oxide-based photo-TFTs is largely attributed to the photoexcitation of subgap states, such as ionized oxygen vacancies, and the subsequent liberation of electrons. − However, the photoexcitation of ionized oxygen vacancies in oxide-based photo-TFTs is accompanied by lattice relaxation, which subsequently results in a persistent photocurrent, even after the light has been turned off. Unfortunately, this usually leads to long recovery times for oxide-based photo-TFTs, as compared to those of typical II–VI semiconductors. , …”

4‐3: Invited Paper: High Mobility Oxide Thin‐film Transistors for AMOLED Displays

“…However, in the presence of illumination, the Vth values do shift towards negative values. The ionization of oxygen vacant sites 11 (VO → VO 2+ + 2e -) or the formation of peroxides between neighboring oxygen ions 12 (O 2-+ O 2-→ O2 2-+ 2e -) are the most commonly accepted degradation mechanisms in oxide TFTs subjected to NBTIS.…”