| Summary: | 碩士 === 國立臺灣大學 === 電機工程學研究所 === 87 === This thesis is to use E-beam lithography to fabricate Single Electron Tunneling (SET) transistor and study single electron tunneling phenomena of nanostructure under Coulomb Blockcade effect. The feature, electron transport in the SET devices one by one, is different from FET in which there are uncountable electrons transporting. Due to the characteristics of small size and low power consumption of a SET transistor, it may be a promising candidate to be a new potential device. In many cases, it could replace the FET, such as high-density memory.
We develop a program based on tunneling rate formula to simulate the operation of a SET transistor and observe the Coulomb Blockade and current modulation phenomena. We can adjust the characteristics of a SET transistor by applying different junction parameters, temperature and bias.
We use a modified SEM (Hitachi 4200) as E-beam lithography writer to fabricate our sample. With careful design, we can define ultra small size pattern on Si substrate. After exposure, development and skillful two-angle evaporation, two small size junctions can be perfectly formed at the same time to be a SET transistor.
In order to reduce thermal tunneling, we measure our sample in He3/He4 dilution refrigerator system. Dilution refrigerator can provide a low-temperature environment (below 50 mK) with varying magnetic field and temperature. Due to the ultra small signal of a SET device, we need to take care of environment noise. Thus good shielding is necessary in order to avoid unwanted tunneling event. We also use a home-made high input impedence pre-amplifier to measure our sample to promote our system accuracy.
We demonstrate simulation result and measured I-V curves of our sample. We can observe that the gate voltage modulates the current and the Coulomb blockade phenomena. Fitting the I-V curve by simulation results in order to acquire the simulation model parameters. Therefore, we can analyze the validness of the SET transistor model, understand how does our system perform and discuss other factors influencing the characteristics of a SET transistor. In conclusion, we have made aluminum single electron transistors, the charging energy was about 2.6 K. The samples were measured at 0.5 K, clear Coulomb blockade oscillations were observed and the results were compared with calculations.
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