• Xiaochen Ma

Student thesis: Phd


Oxide semiconductor thin-film transistors (TFTs) have found applications in the driving circuitry of many devices due to their high performance and low cost. A low operating voltage is highly desirable for a variety of TFT applications such as displays, low-power electronics, battery-powered portable electronics, disposable electronics and sensors. A high gate capacitance is essential to achieve a low-voltage operation of TFTs. Generally, the two most common methods employed to achieve this are to decrease the dielectric thickness and to use a high dielectric constant (high-k) material as the dielectric. However, a thin gate dielectric normally leads to a relatively high gate leakage current and undesired issues, such as bias or temperature instability and high stress-induced leakage, which limit practical applications.Consequently, the aim of this research is to explore a simple alternative method to produce a dielectric with high capacitance, low processing temperature and low leakage current. Here, a novel solid-state oxide electrolyte deposited via room-temperature sputtering was developed for use as the gate dielectric in TFTs. The TFTs exhibit excellent properties, including a low operating voltage of 1 V, a low subthreshold swing around 80 mV /dec and a low leakage current below 1×10-10 A. The results demonstrate the promise of high-performance, fully-sputtered oxide semiconductor TFTs for low-voltage applications.The structure and composition of the electrolyte was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). It was found that the microstructure of the electrolyte held the key to the generation of high capacitance. Since the microstructure of the electrolyte is determined by sputtering conditions, the dependency of its physical and electrical properties on processing conditions were explored systematically. The results indicate that the properties of the sputtered electrolyte are tunable.In order to probe the operating mechanism of the electrolyte, the low frequency noise characteristics of the TFTs were measured. A typical 1/f2 noise was observed when the gate voltage exceeded 1 V. According to the analysis, the 1/f2 noise was caused by carrier generation and recombination, a consequence of the mobile ions inside the electrolyte.
Date of Award31 Dec 2016
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorAimin Song (Supervisor) & Leszek Majewski (Supervisor)


  • silicon dioxide
  • sputtering
  • transistor
  • oxide semiconductor
  • electrolyte

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