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Title: Solution-processed ZnO nanoparticles for optically addressed spatial light modulators and other applications
Author: Chang, Xin
ISNI:       0000 0004 9347 9160
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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Solution-processable materials are becoming increasingly attractive due to their use in low cost, high throughput and relatively easy fabrications. In addition, the possibility of high-resolution patterning makes solution-based materials particularly suitable for integrated applications. The material that was investigated in this work is zinc oxide nanoparticles (ZnO NPs) dispersion, motivated by the highest resolution on record of optically addressed spatial light modulators (OASLMs) using solution-based ZnO NP as photoactive material. ZnO is a popular type of semiconductor compound from II-VI group and ZnO NPs are the nanocrystalline form of ZnO, which exhibit many unique and superior properties such as direct and wide bandgap, large surface-to-volume ratio, antibacterial and eco-friendly nature. Therefore, the investigation of ZnO NPs in terms of their physical properties, post processing effect, patterning techniques, and applications are of great significance. In this work, thin films made from ZnO NP dispersion in ethanol was characterized in detail including their structural, electrical, dielectric and optical properties. The post-processing effect such as thermal annealing and oxygen plasma treatment was also investigated. Then ZnO NP-based OASLM was researched by simulation and device characterization regarding electrical and optical properties. More importantly, the optimization of ZnO NP-based OASLMs was conducted in terms of diffraction efficiency and response speed, which are two key factors limiting the development of ZnO NP-based OASLMs. The diffraction efficiency was improved by pinpointing the optimum parameters of the driving signal such as waveform, amplitude and frequency. And the response time was reduced by several methods such as thermal annealing, introducing an interfacial layer and replacing the photoconductive ZnO NP layer with ZnO NP-based photodiode structure. The sensing of oxygen partial pressure in air by ZnO NP thin film was also observed and studied. Moreover, device miniaturization was achieved by the mould-guided drying technique, indicating a promising future for integrated applications. This patterning technique was also used for another type of solution-based material: PEDOT:PSS. And PEDOT:PSS-based organic electrochemical transistors (OECTs) with nanoscale channel length and channel width were realized by including a lift-off process, which demonstrated a great high-frequency response.
Supervisor: Chu, Daping Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: ZnO nanoparticles ; Optically addressed spatial light modulator (OASLM) ; Oxygen sensor ; Organic electrochemical transistor ; Self-assembly