Lulu Du

Low-frequency noise properties in Pt-indium gallium zinc oxide Schottky diodes

The low-frequency noise properties of Pt-indium gallium zinc oxide (IGZO) Schottky diodes at different forward biases are investigated. The IGZO layer and Pt contact were deposited by RF sputtering at room temperature. The diode showed an ideality factor of 1.2 and a barrier height of 0.94 eV. The current noise spectral density exhibited 1/f behavior at low frequencies. The analysis of the current dependency of the noise spectral density revealed that for the as-deposited diode, the noise followed Luos mobility and diffusivity fluctuation model in the thermionic-emission-limited region and Hooges empirical theory in the series-resistance-limited region. A low Hooges constant of 1.4 × 10−9 was found in the space-charge region. In the series-resistance-limited region, the Hooges constant was 2.2 × 10−5. After annealing, the diode showed degradation in the electrical performance. The interface-trap-induced noise dominated the noise spectrum. By using the random walk model, the interface-trap density was ...

Extremely Sensitive Dependence of SnOx Film Properties on Sputtering Power

An extremely sensitive dependence of the electronic properties of SnOx film on sputtering deposition power is discovered experimentally. The carrier transport sharply switches from n-type to p-type when the sputtering power increases by less than 2%. The best n-type carrier transport behavior is observed in thin-film transistors (TFTs) produced at a sputtering power just below a critical value (120 W). In contrast, at just above the critical sputtering power, the p-type behavior is found to be the best with the TFTs showing the highest on/off ratio of 1.79 × 104 and the best subthreshold swing among all the sputtering powers that we have tested. A further increase in the sputtering power by only a few percent results in a drastic drop in on/off ratio by more than one order of magnitude. Scanning electron micrographs, x-ray diffraction spectra, x-ray photoelectron spectroscopy, as well as TFT output and transfer characteristics are analyzed. Our studies suggest that the sputtering power critically affects the stoichiometry of the SnOx film.

Effects of substrate and anode metal annealing on InGaZnO Schottky diodes

By studying different annealing effects of substrate and anode metal, high-performance Schottky diodes based on InGaZnO (IGZO) film have been realized. It is observed that a suitable thermal annealing of the SiO2/Si substrate significantly improves the diode performance. On the contrary, annealing of the Pd anode increases surface roughness, leading to degradation in the diode performance. As such, by only annealing the substrate but not the anode, we are able to achieve an extremely high rectification ratio of 7.2 × 107, a large barrier height of 0.88 eV, and a near unity ideality factor of 1.09. The diodes exhibit the highest performance amongst IGZO-based Schottky diodes reported to date where IGZO layer is not annealed. The capacitance vs. voltage measurements indicate that the surface roughness is correlated with the trap state density at the Schottky interface.

Low Voltage Operation of IGZO Thin Film Transistors Enabled by Ultrathin Al2O3 Gate Dielectric

An ultrathin, 5 nm, Al2O3 film grown by atomic-layer deposition was used as a gate dielectric for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The Al2O3 layer showed a low surface roughness of 0.15 nm, a low leakage current, and a high breakdown voltage of 6 V. In particular, a very high gate capacitance of 720 nF/cm2 was achieved, making it possible for the a-IGZO TFTs to not only operate at a low voltage of 1 V but also exhibit desirable properties including a low threshold voltage of 0.3 V, a small subthreshold swing of 100 mV/decade, and a high on/off current ratio of 1.2 × 107. Furthermore, even under an ultralow operation voltage of 0.6 V, well-behaved transistor characteristics were still observed with an on/off ratio as high as 3 × 106. The electron transport through the Al2O3 layer has also been analyzed, indicating the Fowler–Nordheim tunneling mechanism.