**8. Characterization of sol-gel-derived crystalline ZrO2 –Y2O3 thin films on Si(001) wafers**

Sol-gel-derived Y doped ZrO2 (ZrO2-Y2O3 ) thin films on Si(001) wafers fired in air between 350 and 700 °C provide electrical characteristics, such as lower leakage current, in MOS capacitors superior to those of sol-gel-derived ZrO2 thin films (Shimizu & Nishide, 2011). This is attributed to the reduced surface roughness of ZrO2-Y2O3 thin films. The crystallized ZrO2-Y2O3 surface fired at 700 °C clearly shows a crack-free state compared with ZrO2 thin films. Thus, crystallized ZrO2-Y2O3 thin films can reduce the leakage current, making them a promising material for gate insulators in aggressively scaled CMOS devices.

#### **8.1 Film thicknesses and refractive indexes of sol-gel-derived ZrO2-Y2O3**

The film thicknesses and refractive indexes were measured for sol-gel-derived ZrO2-Y2O3 films fired from 350 to 700 °C for 30 min (Figure 27). The film thickness tended to become thinner at temperatures higher than 450 oC (11 and 7 nm thick at 450 and 700 oC, respectively). If this ZrO2-Y2O3 thin film has excellent characteristics with high permittivity, this thickness is suitable for a gate insulator material. Though the refractive indices between 350 and 700 °C increased with increasing firing temperature, the present results were lower than that reported for monoclinic ZrO2 crystals (Niinisto et al., 2004).

Fig. 26. *C-V* curves for Al/ZrO2 /n-Si capacitors, showing a well-defined transition from depletion and inversion to accumulation as a function of the applied voltage. The firing

oxygen, inert gas, or forming gas must be used. Thus, there is some possibility for applying sol-gel-derived ZrO2 thin films as a semiconductor gate insulator material. To fabricate improved ZrO2 films, further experiments should be conducted to find an effective way of reducing impurities. Sol-gel-derived Y doped ZrO2(ZrO2-Y2O3 ) thin films

**8. Characterization of sol-gel-derived crystalline ZrO2 –Y2O3 thin films on** 

promising material for gate insulators in aggressively scaled CMOS devices.

**8.1 Film thicknesses and refractive indexes of sol-gel-derived ZrO2-Y2O3**

than that reported for monoclinic ZrO2 crystals (Niinisto et al., 2004).

Sol-gel-derived Y doped ZrO2 (ZrO2-Y2O3 ) thin films on Si(001) wafers fired in air between 350 and 700 °C provide electrical characteristics, such as lower leakage current, in MOS capacitors superior to those of sol-gel-derived ZrO2 thin films (Shimizu & Nishide, 2011). This is attributed to the reduced surface roughness of ZrO2-Y2O3 thin films. The crystallized ZrO2-Y2O3 surface fired at 700 °C clearly shows a crack-free state compared with ZrO2 thin films. Thus, crystallized ZrO2-Y2O3 thin films can reduce the leakage current, making them a

The film thicknesses and refractive indexes were measured for sol-gel-derived ZrO2-Y2O3 films fired from 350 to 700 °C for 30 min (Figure 27). The film thickness tended to become thinner at temperatures higher than 450 oC (11 and 7 nm thick at 450 and 700 oC, respectively). If this ZrO2-Y2O3 thin film has excellent characteristics with high permittivity, this thickness is suitable for a gate insulator material. Though the refractive indices between 350 and 700 °C increased with increasing firing temperature, the present results were lower

temperature of the ZrO2 film was 550 °C for 30 min (Shimizu et al., 2009).

on Si(001) wafers are also promising.

**Si(001) wafers** 

Fig. 27. Film thicknesses and refractive indices of sol-gel-derived ZrO2-Y2O3 films fired at 350, 450, 550 and 700 °C for 30 min (Shimizu & Nishide, 2011).
