| Summary: | 碩士 === 國立交通大學 === 光電系統研究所 === 108 === In recent years, with the flourish of smart phones, Internet of Things (IoT) and other related applications, low-power consumption electronic devices are in urgent need. Tunneling FETs (TFETs) and Negative Capacitances (NCFETs) are been investigated to be different from traditional Si-based FETs to break through the thermophysical limitation of less than 60mV/decade subthershold (SS), allowing the transistors to turn on the devices with less biasing. Since the TFET has a shortage that Ion is hard to improve and a tradeoff effect with Ioff, the NC-FETs with negative capacitance effect have the potential to develop a low-power consumption transistor device.
The new ferroelectric materials retain the advantages, strong polarization performances, of traditional ferroelectric materials (SBT, PZT...) and overcome the problems that traditional ferroelectric materials cannot be shrunk. However, new challenges have been emerged due to the influence of miniaturization. The thinner the overall buffer is, the thinner the buffer layer and the ferroelectric layer are, resulting in a stronger ferroelectric material polarization, and a leakage current is increased at the interface. In this master thesis, we investigate ferroelectric HfZrO material which is the most mature HfO2-based ferroelectric application so far. First, we investigate the influences on ferroelectricity of different Zr dopant content. The high dopant content induces stronger ferroelectricity. However, when Zr dopant content too high, it will result in zirconium diffusion and further induce high leakage current. Therefore, the appropriate Zr dopant content not only can keep the strong ferroelectricity but also avoid high leakage current issue. Next, we try to scale the HfZrO thin films, finding that the thickness at 7nm can remain ferroelectricity due to the grain size effect. Last, in order to study relationship with the Zr diffusion and the interfacial layer, we fabricate different thickness of interlayer. Although thin interlayer is prone to Zr diffusion and lead higher leakage current, it exhibits good performance on gate controllability. When thicken the interlayer, the obvious depolarization will degrade the gate controllability on ferroelectric gate-stack and further induce increasing Ioff in MOSFET apparently. As a result, the investigation on Zr dopant content in HfZrO NC-FET, ferroelectric gate-stack scaling and the thickness of interlayer effect, we can sum up the optimization of HfZrO NC-FET. With the success of bipolar N-type and P-type NC-FET, the investigation will help the future integration of low-power CMOS circuit technology.
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