Recently, many kinds of nanowire devices are studied because of not only their interesting one dimensional or quasi-one dimensional physical structures, but also chemical, electrical properties. Especially ZnO nanowire devices are a matter of concern in the several points of view such as field effect transistors (FETs) [1], Schottky Diodes [2], and gas sensors [3]. ZnO nanowire has a wide direct energy band gap (3.27eV) and normally n-type characteristic without any doping. However ZnO nanowire devices have the problem of the instability such as hysteresis and threshold voltage shifting [4]. From the point of practical devices, the noise property can be a good criterion for the qualitative or quantitative characterization of defects based on the Hooge's formula.
The e-beam lithography technique was used to make the ZnO FET structure. For the back gate structure, ZnO nanowires were dispersed well over the insulating layer on a heavily doped silicon substrate. After the development, Ti/Au electrodes were deposited succesively. At 350°C for 2min, rapid thermal annealing (RTA) was done to improve the contact resistance. To measure the I-V characteristics and the noise, HP 4140B and HP 3562A were used.
In the I-V measurement, the gate field effect was recorded with the hysteresis at the double scan mode. As the gate bias increased, the hysteresis became larger accordingly. 1/f noise characteristics were confirmed in the noise spectrum. However at the low current level below 1nA, only thermal noise could be found. At the higher current level, the higher noise level followed the exponent of the noise current dependence as 2.3. The parameter of 1/f noise was obtained using the origin program and mathematica programming.
The details of our experimental process and the noise mechanism will be discussed in the presentation
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