| Summary: | 博士 === 國立交通大學 === 電子工程系所 === 94 === In this dissertation, we report the layout designs and the process recipe for fabricating carbon nanotube field effect transistors (CNT-FETs) and bio-sensors, including the definitions of cell blocks, characters of device structures in detail. For the purpose of aligned growth of carbon nanotubes, two kinds of layouts for catalyst islands are also designed for catalytic chemical vapor deposition (CCVD) method.
To start with, we propose a conduction-type-tunable CNT-FETs with double-gated structure (DG CNT-FET). A specially designed narrow top-gate is created to modulate the energy band in the middle region of a single CNT. In the proposed DG device structure, the top-gate and bottom-gate biases exhibit independent modulation behaviors. Energy band diagram conducive to the physical mechanisms of the proposed DG CNT-FET device structure is proposed. Based on the proposed hypothesis, ambipolar CNT-FETs can indeed be converted to n- or p-type-like behaviors.
Next, we also demonstrate a novel plasma treatment method that allows us to convert metallic-type carbon nanotubes to semiconducting-type CNT-FETs. This is important as the production of single-walled carbon nanotubes (SWNTs), irrespective of synthesis methods, still yields a mixture of both types thus far, with the metallic type being prevalent. However, semiconducting-type SWNTs are needed for CNT-FETs as well as many sensors. Judging from our experimental results, we believe that the ion bombardment during plasma treatment attacks both metallic- and semiconducting-type nanotubes; however, the metallic-type carbon nanotubes are more vulnerable to the attack than the semiconducting-type, and are subsequently transformed into the latter type.
In order to apply CNTs to nanoelectronics, in this thesis we also demonstrate a precise growth of SWNTs on pre-assigned locations with only cobalt (Co) as catalyst. This is in contrast to the laborious and time-consuming physical manipulation of numerous nanotubes one at a time used in the conventional approach. Laterally-grown carbon nanotubes are accomplished in pre-assigned areas using an integrated-circuit (IC)-compatible process in this thesis. In order to synthesize SWNT to serve as the channel of a FET, the cobalt-mix-tetraethoxysilane (CMT) solution and catalytic chemical vapor deposition are used. Our results show that laterally-grown bundled-CNTs could be formed in CCVD with ethanol, by properly controlling the temperature of process, the process time, and the hydrogen reduction time. The use of pre-patterned catalyst islands, CCVD method and flexibility of silmutaneously manufacturing both n- and p-type CNT-FETs may open a new era for applications of CNT-based nanoelectronics.
Finally, we introduce a complementary carbon-nanotube(CNT)-gated CNT thin-film field effect transistor. By using two perpendicularly-crossed SWNT bundles as the gate and the channel interchangeably, a sub-50 nm complementary CNT-FET is demonstrated. It is found that the new CNT-FET shows acceptable FET characteristics by interchanging the roles of the gate and the channel. The unique dual-functionality of the device will open up a new possibility and flexibility in the design of future complementary CNT electronic circuits.
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