Abstract
In this study, InGaZnO (IGZO) thin film transistors (TFTs) with a dual active layer (DAL) structure are fabricated by inserting a homogeneous embedded conductive layer (HECL) in an amorphous IGZO (a-IGZO) channel with the aim of enhancing the electrical characteristics of conventional bottom-gate-structure TFTs. A highly conductive HECL (carrier concentration at 1.6 × 1013 cm-2, resistivity at 4.6 × 10-3 Ω∙cm, and Hall mobility at 14.6 cm2/Vs at room temperature) is fabricated using photochemical H-doping by irradiating UV light on an a-IGZO film. The electrical properties of the fabricated DAL TFTs are evaluated by varying the HECL length. The results reveal that carrier mobility increased proportionally with the HECL length. Further, a DAL TFT with a 60-μm-long HECL embedded in an 80-μm-long channel exhibits comprehensive and outstanding improvements in its electrical properties: a saturation mobility of 60.2 cm2/Vs, threshold voltage of 2.7 V, and subthreshold slope of 0.25 V/decade against the initial values of 19.9 cm2/Vs, 4.7 V, and 0.45 V/decade, respectively, for a TFT without HECL. This result confirms that the photochemically H-doped HECL significantly improves the electrical properties of DAL IGZO TFTs.
Highlights
There has been a growing need in the nextgeneration display industry for the development of new channel thin film transistors (TFTs) in order to implement active-matrix organic light-emitting diode (AMOLED) displays with a large area, rapid information transmission, high resolution, and high frame rates [1]
The dual active layer (DAL) were fabricated by forming an homogeneous embedded conductive layer (HECL) below the active layer; the placement of the HECL was selected by considering the actual channel path formed between the source and drain
When using a DAL structure design in which the DAL is formed by employing other highly conductive materials, the electronic band structure of these materials should be considered. This is because injected carriers from the source electrode can be blocked by the formation of a barrier and their movement toward the drain electrode can be hindered, which will lead to low mobility [14]. Under such a situation of barrier formation, the electrical properties are expected not to degrade, since the photochemically processed highly conductive HECL and the active layer are formed from the same material, namely, amorphous InGaZnO (a-IGZO), and they form a pseudo-homogeneous junction
Summary
There has been a growing need in the nextgeneration display industry for the development of new channel thin film transistors (TFTs) in order to implement active-matrix organic light-emitting diode (AMOLED) displays with a large area, rapid information transmission, high resolution, and high frame rates [1]. There is a great demand for TFTs with electron mobility higher than 30 cm2/Vs in order to realize the required display resolutions and pixel circuits [5] To fulfill these requirements, extensive research has been conducted in an attempt to enhance the electron mobility of a-IGZO via different methods, including oxygen vacancy control, [6,7] hydrogen annealing, [8,9] use of a Ca capping layer, [10] sputtering power control, [6] and by combining various oxide components [11,12]. Hydrogen annealing increases the number of oxygen vacancies by artificially creating a reducing atmosphere and makes it possible to realize high electrical conductivity; this method requires a lengthy thermal process carried out above 300°C and is very limited in its applicability as it may damage surrounding devices through rapid hydrogen diffusion. Sputtering power control and the combination of various oxide materials have reproducibility problems, since target, equipment, and process requirements have not been standardized
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