Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 14, Issue 16, Pages 18646-18661Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.1c23889
Keywords
indium gallium zinc oxide; heterojunction; atomic layer deposition; thin-film transistor; high mobility; low operation voltage; high-kappa dielectric
Funding
- LG Display under the LGD-Hanyang University Incubation Program
- Samsung Research Funding & Incubation Center of Samsung Electronics [SRFC-TA1903]
- Samsung Electronics Co., Ltd [IO210701-08792-01, IO201210-08034-01]
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Amorphous indium-gallium-zinc oxide (a-IGZO) has become a standard channel ingredient of switching/driving transistors in active-matrix organic light- emitting diode (AMOLED) televisions. However, mobile AMOLED displays with a high pixel density and good form factor do not often employ a-IGZO transistors due to their modest mobility. This study investigates the use of all-oxide thin-film transistors (TFTs) with heterojunction stacks using atomic layer deposition (ALD) method as an alternative to a-IGZO transistors. The results show that the designed heterojunction stacks can achieve excellent electrical performance and stability, suggesting the feasibility of high-performance ALD-derived oxide TFTs for high-end mobile AMOLED displays.
Amorphous indium-gallium-zinc oxide (a-IGZO) has become a standard channel ingredient of switching/driving transistors in active-matrix organic light- emitting diode (AMOLED) televisions. However, mobile AMOLED displays with a high pixel density (>= 500 pixels per inch) and good form factor do not often employ a-IGZO transistors due to their modest mobility (10-20 cm(2)/(V s)). Hybrid low-temperature polycrystalline silicon and oxide transistor (LTPO) technology is being adapted in high-end mobile AMOLED devices due to its ultralow power consumption and excellent current drivability. The critical issues of LTPO (including a complicated structure and high fabrication costs) require a search for alternative all-oxide thin-film transistors (TFTs) with low-cost processability and simple device architecture. The atomic layer deposition (ALD) method is a promising route for high-performance all-oxide TFTs due to its unique features, such as in situ cation composition tailoring ability, precise nanoscale thickness controllability, and excellent step coverage. Here, we report an in-depth comparative investigation of TFTs with indium-gallium oxide (IGO)/gallium-zinc oxide (GZO) and indium-zinc oxide (IZO)/GZO heterojunction stacks using an ALD method. IGO and IZO layers with different compositions were tested as a confinement layer (CL), whereas the GZO layer was used as a barrier layer (BL). Optimal IGO/GZO and IZO/GZO channels were carefully designed on the basis of their energy band properties, where the formation of a quasi-two-dimensional electron gas (q2DEG) near the CL/BL interface is realized by rational design of the band gaps and work-functions of the IGO, IZO, and GZO thin films. To verify the effect of q2DEG formation, the device performances and stabilities of TFTs with CL/BL oxide heterojunction stacks were examined and compared to those of TFTs with a single CL layer. The optimized device with the In0.75Zn0.25O/Ga0.80Zn0.20O stack showed remarkable electrical performance: mu(FE) of 76.7 +/- 0.51 cm(2)/(V s), V-TH of -0.37 +/- 0.19 V, SS of 0.13 +/- 0.01 V/dec, and ION/ OFF of 2.5 x 1010 with low operation voltage range of = 2 V and excellent stabilities (Delta V-TH of +0.35, -0.67, and +0.08 V for PBTS, NBIS, and CCS, respectively). This study suggests the feasibility of using high-performance ALD-derived oxide TFTs (which can compete with the performance of LTPO transistors) for high-end mobile AMOLED displays.
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