Studies on Thin-Film Transistor Devices Based on Rare Earth Materials


Student thesis: Doctoral Thesis

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Awarding Institution
Award date23 May 2017


Semiconductor devices, especially thin-film transistors (TFTs), have made great contributions to the modernization of society. Although massive studies on TFTs have been carried out in recent years, several obstacles still exist, including the leakage current issue during the device downscaling, and data storage capability and retentions of transistor memory, etc. Previous studies on employing rare-earth (RE) materials in electronic devices showed their high potentials to serve as candidates to overcome those challenges in TFTs. Motivated by solving those mentioned difficulties, in this thesis, three RE materials are functionalized and employed in typical TFTs. This thesis begins with an introduction to basics and recent advances in thin-film transistors (TFTs), TFT based flash memory and RE material, and relevant fabrication and characterization techniques are also introduced. The functionalization of RE materials in TFT devices in terms of replacing traditional silicon oxide with solution-processed ultra-thin RE oxide (REO) or RE-doped zirconia films, and improving the flexibility of device manipulation through a novel photo-reactive RE complex are then demonstrated, revealing the high feasibility of broadening the application of RE materials in TFTs.

We first present a general route to ultra-thin REO films on Si substrate and the functionalization of these REO films as gate dielectrics in organic TFTs (OTFTs) through a simple spin-coating and post-annealing method. All transistors based on solgel derived REO dielectrics present remarkable electrical properties and the performance of corresponding transistors can be further enhanced through a simple surface modification technique. Then, we demonstrate an approach to utilizing RE as dopants to improve the electrical properties of zirconia film and investigated the doping effect of yttrium in zirconia and expanded to erbium and ytterbium through a simple solution process, and functionalized these three dielectric films in oxide TFTs. Oxide transistors based on these RE-doped zirconia film can be operated at a low voltage and show high charge carrier mobility. Finally, we show the application of organic RE complex film as charge trapping element in an OTFT memory device. By making use of its photoluminescence property, the complex is also employed as a medium to the UV light, which can be considered as the fourth terminal in the memory device and provides an external control to manipulate the device. The memory window can be significantly enlarged by light-assisted programming and erasing procedures, during which the photo-induced excitons in the organic semiconductor layer are separated by voltage bias. The results obtained in this thesis show solid evidences that RE materials are promising candidates to overcome the challenges in transistor devices.