Stability improvements of InGaZnO thin-film transistors on polyimide substrates with Al₂O₃ buffer layer

Abstract

We investigate the effects of atomic layer deposition (ALD)-grown Al2O3 buffer layer on the device characteristics of flexible amorphous InGaZnO thin-film transistors (TFTs) fabricated on ultrathin polyimide (PI) films. The TFT with a buffer layer exhibited a saturation mobility of 8.6 cm2 V−1 s−1 and a subthreshold swing of 0.16 V dec−1 after annealing at 150 °C. Under negative bias temperature stress at 40 °C, the turn-on voltage instabilities of TFTs with and without the buffer layer were estimated to be −1.0 and −13.2 V, respectively. This marked difference is mainly due to the adsorption of water molecules on the PI film resulting in a positively charged surface.

Alleviation of abnormal NBTI phenomenon in LTPS TFTs on polyimide substrate for flexible AMOLED

“…V th positive shift during NBTI is reported, and it is known to be related to hole detrapping from the gate oxide to the channel under a lower applied gate voltage, resulting in the repassivation or annihilation in trap states with hydrogen, which is called as NBTI recovery 18,19 . On the other hand, it is reported that moisture and/or hydrogen diffuse from the PI substrates to the channel and might be decreased with the insertion of a high density of barrier layer 5–7 . These NBTI recovery and moisture/hydrogen diffusion phenomena can be considered to explain the V th positive shift in NBTI stress of LTPS TFTs on PI substrate.…”

“…These NBTS instabilities are attributed to the adsorption of water molecules on the PI surface. After passivation of the PI film with ALD‐Al 2 O 3 layer, device instability is improved 5 . The simultaneous suppression of moisture and/or hydrogen diffusion from the underlying PI substrates to the channel is accomplished by the insertion of a SiN x /AlO x buffer layer, accompanied by the improvement of TFT performance and stability 6 .…”

Highly Robust Flexible Vertical-Channel Thin-Film Transistors Using Atomic-Layer-Deposited Oxide Channels and Zeocoat Spacers on Ultrathin Polyimide Substrates

“…First, the CPI solution was spin-coated onto a carrier glass and annealed at 80 and 290 °C for 30 min on a hot plate and in a furnace, respectively, for enhancing the film adhesion and removing the residual solvent. A 50 nm thick Al 2 O 3 buffer layer was deposited on the coated CPI film at 150 °C by ALD to effectively protect the adsorption of water vapors and transmission of hydrogen ions . A 150 nm thick indium–tin oxide (ITO) was deposited by dc sputtering and patterned as a source electrode by wet chemical etching (Figure a).…”

“…A 50 nm thick Al 2 O 3 buffer layer was deposited on the coated CPI film at 150 °C by ALD to effectively protect the adsorption of water vapors and transmission of hydrogen ions. 20 A 150 nm thick indium−tin oxide (ITO) was deposited by dc sputtering and patterned as a source electrode by wet chemical etching (Figure 1a). Then, Zeocoat solution was prepared by diluting with a mixed solvent of propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA) at a mixing ratio of 2:1.…”

Effect of Simultaneous Mechanical and Electrical Stress on the Electrical Performance of Flexible In-Ga-Zn-O Thin-Film Transistors

“…Indium-gallium-zinc oxide (IGZO) thin-film transistor (TFT) is being widely used for the backplane of large-area active-matrix organic-light-emitting diode displays, owing to its excellent properties including high field-effect mobility ( μ FE ), low-off current, high uniformity, and low process temperature [1,2,3,4,5,6,7,8,9,10,11]. Recently, there is increasing interest in the application of IGZO TFTs in demonstrating the active-matrix backplane for flexible displays [12,13,14,15,16]. Flexible displays have many advantages over conventional glass substrate-based displays including better durability, lighter weight, and thinner dimension.…”