Organic light-emitting transistors, three-terminal devices combining a thin-film transistor with a light-emitting diode, have generated increasing interest in organic electronics. However, increasing their efficiency while keeping the operating voltage low still remains a key challenge. Here, we demonstrate organic permeable base light-emitting transistors; these three-terminal vertical optoelectronic devices operate at driving voltages below 5.0 V; emit in the red, green and blue ranges; and reach, respectively, peak external quantum efficiencies of 19.6%, 24.6% and 11.8%, current efficiencies of 20.6 cd A–1, 90.1 cd A–1 and 27.1 cd A–1 and maximum luminance values of 9,833 cd m–2, 12,513 cd m–2 and 4,753 cd m–2. Our simulations demonstrate that the nano-pore permeable base electrode located at the centre of the device, which forms a distinctive optical microcavity and regulates charge carrier injection and transport, is the key to the good performance obtained. Our work paves the way towards efficient and low-voltage organic light-emitting transistors, useful for power-efficient active matrix displays and solid-state lighting. Vertical organic light-emitting transistors are realized by using a porous base electrode in the centre of the device, which improves efficiency and reduces operating voltage by regulating charge transport and forming an optical microcavity.

Efficient and low-voltage vertical organic permeable base light-emitting transistors.

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 cm2/(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: μFE of 76.7 ± 0.51 cm2/(V s), VTH of -0.37 ± 0.19 V, SS of 0.13 ± 0.01 V/dec, and ION/OFF of 2.5 × 1010 with low operation voltage range of ≥2 V and excellent stabilities (ΔVTH 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.

Comparative Study of Atomic Layer Deposited Indium-Based Oxide Transistors with a Fermi Energy Level-Engineered Heterojunction Structure Channel through a Cation Combinatorial Approach.

Reliability improvement of IGZO-TFT in hybrid process with LTPS

Due to the untiring efforts of scientists and researchers on oxide semiconductor materials, processes, and devices, the applications for oxide-based thin film transistors (TFTs) have been researched and promoted on a large scale. With the advantages of relatively high carrier mobility, low off-current, good process compatibility, optical transparency, low cost, and especially flexibility, oxide-based TFTs have already been adapted for not only displays (e.g., liquid crystal display (LCD), organic light emitting diode (OLED), micro-light-emitting diode (Micro-LED), virtual reality/augmented reality (VR/AR) and electronic paper displays (EPD)) but also large-area electronics, analog circuits, and digital circuits. Furthermore, as the requirement of TFT technology increases, low temperature poly-silicon and oxide (LTPO) TFTs, which combine p-type LTPS and n-type oxide TFT on the same substrate, have drawn further interest for realizing the hybrid complementary metal oxide semiconductor (CMOS) circuit. This invited review provides the current progress on applications of oxide-based TFTs. Typical device configurations of TFTs are first described. Then, the strategies to apply oxide-based TFTs for improving the display quality with different compensation technologies and obtaining higher performance integrated circuits are highlighted. Finally, an outlook for the future development of oxide-based TFTs is given.

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Strategies for Applications of Oxide-Based Thin Film Transistors

Due to tremendous efforts in materials chemistry and processing techniques of organic semiconductors (OSCs), organic thin-film transistors (OTFTs) with much higher mobilities than those of amorphous silicon (a-Si) TFTs have been reported. These progresses have motivated lots of engineering studies to build functional circuits and systems based on OTFTs. However, there is clearly a big gap between the exhibited performance of these circuits and systems and what can be expected based on the reported extraordinarily high mobility values of OSCs. From a different perspective, this review analyzes the performance specifications required for various circuit applications. Then, the choice of device structures and processes for circuit integration in a manufacturable way is discussed. On this basis, material design considerations for compatibility with manufacturing, device performance improvement and technology differentiation are revealed.

Seiichi Uchida

Papers

High refresh rate and low power consumption AMOLED panel using top-gate n-oxide and p-LTPS TFTs

24-4: Distinguished Paper: High Refresh Rate and Low Power Consumption AMOLED Panel Using Top-gate n-Oxide and p-LTPS TFTs

P‐31: Pixel Circuit with Backgate Feedback for Deep and Rich Black Expressions on Light‐Emitting Display