**4. Electrical properties of QC devices**

#### **4.1 I-V characteristics of Ni/Ni QC devices**

Fig. 9 shows the *I-V* characteristics for Ni/Ni QC devices fabricated using Ni/PEN films discussed above. The inset shows the experimental setup for the four-probe method. Since the Ni thickness is 17 nm, the cross-sectional area between two Ni thin films is 17×17 nm2. As seen from Fig. 9, the ohmic *I-V* characteristics have been obtained for both positive and negative bias at room temperature. Fig. 10 shows the aging properties for the voltage with constant currents of 0.1, 0.2, 0.3, 0.5, 0.7 and 1.0 A, respectively. The voltage is stable in any current and the standard deviation *V* of the voltage is 22-25 mV, which corresponds to the signal-to-noise (SN) ratio of 34-52 dB, where the SN ratio is defined by 20 log*V*/*V*. Here, it should be noted that the fabrication of nanojunctions using the film edges had been challenged by other researchers before (Nawate, et al., 2004). According to their attempts, Co and Ni thin films were evaporated onto glass substrates using vacuum evaporation and then they were cleaved and stuck to each other with their edges crossing. Although the current flowed across the junction, there remained a few problems: that the edge angle had to be inclined at a 15-25o and the film thickness had to be larger than 50 nm. Furthermore, the current was slightly changed as time passed although the current flowed. In contrast, such problems have not occurred in our experiments, and we have obtained stable ohmic characteristics, where there has been no change with time, for the 17 nm size junction. These experimental results indicate that our method using thin-film edges can be expected to work as a new nanostructure fabrication technology beyond conventional lithography.

Fig. 9. *I-V* characteristics for Ni/Ni QC devices with a junction area of 17×17 nm2. The inset shows the experimental setup for the four-probe method.

Fig. 9 shows the *I-V* characteristics for Ni/Ni QC devices fabricated using Ni/PEN films discussed above. The inset shows the experimental setup for the four-probe method. Since the Ni thickness is 17 nm, the cross-sectional area between two Ni thin films is 17×17 nm2. As seen from Fig. 9, the ohmic *I-V* characteristics have been obtained for both positive and negative bias at room temperature. Fig. 10 shows the aging properties for the voltage with constant currents of 0.1, 0.2, 0.3, 0.5, 0.7 and 1.0 A, respectively. The voltage is stable in any current and the standard deviation *V* of the voltage is 22-25 mV, which corresponds to the signal-to-noise (SN) ratio of 34-52 dB, where the SN ratio is defined by 20 log*V*/*V*. Here, it should be noted that the fabrication of nanojunctions using the film edges had been challenged by other researchers before (Nawate, et al., 2004). According to their attempts, Co and Ni thin films were evaporated onto glass substrates using vacuum evaporation and then they were cleaved and stuck to each other with their edges crossing. Although the current flowed across the junction, there remained a few problems: that the edge angle had to be inclined at a 15-25o and the film thickness had to be larger than 50 nm. Furthermore, the current was slightly changed as time passed although the current flowed. In contrast, such problems have not occurred in our experiments, and we have obtained stable ohmic characteristics, where there has been no change with time, for the 17 nm size junction. These experimental results indicate that our method using thin-film edges can be expected to work as a new nanostructure fabrication technology beyond

Fig. 9. *I-V* characteristics for Ni/Ni QC devices with a junction area of 17×17 nm2. The inset

shows the experimental setup for the four-probe method.

**4. Electrical properties of QC devices 4.1 I-V characteristics of Ni/Ni QC devices** 

conventional lithography.

Fig. 10. Aging properties for Ni/Ni QC devices with a junction area of 17×17 nm2.
