| Abstract Scope |
High-k dielectrics have been widely employed in field-effect transistors (FETs) to realize low power consumption. Material deposition with solution-based approaches has been studied to achieve low fabrication cost and high throughput. Here, we present the effect of annealing temperature on the properties of solution-processed ZrO<SUB>2</SUB> dielectric. Material deposition on glass and flexible substrate are demonstrated. An ultralow subthreshold slope (74 mV/decade) is observed when employing a thin ZrO<SUB>2</SUB> dielectric in a zinc-tin oxide (ZTO) thin-film transistor (TFT). To study the property of the solution-processed ZrO<SUB>2</SUB> dielectric, a metal-insulator-metal structure was employed. The substrate was glass coated with 40 nm of Au<SUB>0.6</SUB>Pd<SUB>0.4</SUB> and the ZrO<SUB>2</SUB> precursors were deposited in a nitrogen environment followed by thermal annealing in the ambient air. The ZrO<SUB>2</SUB> precursor solution was synthesized with a sol-gel method by dissolving zirconium chloride [ZrCl<SUB>4</SUB>] and zirconium isopropoxide isopropanol complex {Zr[OCH(CH<SUB>3</SUB>)<SUB>2</SUB>]<SUB>4</SUB>•(CH<SUB>3</SUB>)<SUB>2</SUB>CHOH} powders (0.25 M each) in 2 methoxyethanol. Prepared precursor solution was spin-coated at 2000 rpm for 1 min and converted to ZrO<SUB>2</SUB> by thermal annealing in air for 1 hr. Three annealing temperatures, 500 °C, 400 °C and 300 °C, were studied. The deposition process was repeated once to form a dual-layer structure. 100 nm of Al was deposited as top metal electrodes. The resulted capacitance values for devices with annealing temperatures of 500 °C, 400 °C and 300 °C are 250, 225 and 150 nF/cm<SUP>2</SUP> at a measuring frequency of 1MHz. The tunneling current density depends on the annealing temperature and is less than 100 nA/cm<SUP>2</SUP> at 10 V for devices with annealing temperatures of 500 °C and 400 °C. XPS spectra of the films with different annealing temperatures are almost identical, for which the elements of zirconium and oxygen have an atomic molar ratio close to1:2 and no chloride element was detected. This indicates the precursors were fully converted to the oxide form and suggests that the ZrO<SUB>2</SUB> films can be processed at a temperature equal or less than 300 °C, which makes it possible for depositing ZrO<SUB>2</SUB> on flexible substrates, such as Kapton films. AFM images of the ZrO<SUB>2</SUB> surface shows all the films have a root-mean-square average roughness (Rq) less than 1 nm, which is very smooth for solution-processed dielectrics. A smooth dielectric surface is critical for a well behaved FET since the dielectric/semiconductor interface can affect the interfacial trap density and related FET behaviors, including stability and subthreshold slope. By employing the solution-processed ZrO<SUB>2</SUB> in a field effect transistor, the operation voltage and subthreshold slope can be significantly improved. We demonstrate a ZTO TFT with a 35 nm ZrO<SUB>2</SUB> dielectric having an operation voltage of 2 V and a subthreshold slope of 74 mV/decade. |