Guodong Cui

Effects of various oxygen partial pressures on Ti-doped ZnO thin film transistors fabricated on flexible plastic substrate

By applying a novel active layer of titanium zinc oxide (TiZO), we have successfully fabricated fully transparent thin-film transistors (TFTs) with a bottom gate structure fabricated on a flexible plastic substrate at low temperatures. The effects of various oxygen partial pressures during channel deposition were studied to improve the device performance. We found that the oxygen partial pressure during channel deposition has a significant impact on the performance of TiZO TFTs, and that the TFT developed under 10% oxygen partial pressure exhibits superior performance with a low threshold voltage (V th) of 2.37 V, a high saturation mobility (μsat) of 125.4 cm2 V−1 s−1, a steep subthreshold swing (SS) of 195 mV/decade and a high I on/I off ratio of 3.05 × 108. These results suggest that TiZO thin films are promising for high-performance fully transparent flexible TFTs and displays.

High-performance calcium-doped zinc oxide thin-film transistors fabricated on glass at low temperature

High-performance calcium-doped zinc oxide thin-film transistors (Ca-ZnO TFTs) have been successfully fabricated on transparent glass at low temperature by RF magnetron sputtering. To study the effects of calcium doping on zinc oxide thin-film transistors, the characteristics of Ca-ZnO TFTs and ZnO TFTs are compared and analyzed in detail from different perspectives, including electrical performance, surface morphology, and crystal structure of the material. The results suggest that the incorporation of calcium element can decrease the root-mean-square roughness of the material, suppress growth of a columnar structure, and improve device performance. The TFTs with Ca-ZnO active layer exhibit excellent electrical properties with the saturation mobility (μsat) of 147.1 cm2 V−1 s−1, threshold voltage (V t) of 2.91 V, subthreshold slope (SS) of 0.271 V/dec, and I on/I off ratio of 2.34 × 108. In addition, we also study the uniformity of the devices. The experimental results show that the Ca-ZnO TFTs possess good uniformity, which is important for large-area application.

Effects of channel structure consisting of ZnO/Al2O3 multilayers on thin-film transistors fabricated by atomic layer deposition

By applying a novel active layer comprising ZnO/Al2O3 multilayers, we have successfully fabricated fully transparent high-performance thin-film transistors (TFTs) with a bottom gate structure by atomic layer deposition (ALD) at low temperature. The effects of various ZnO/Al2O3 multilayers were studied to improve the morphological and electrical properties of the devices. We found that the ZnO/Al2O3 multilayers have a significant impact on the performance of the TFTs, and that the TFTs with the ZnO/15-cycle Al2O3/ZnO structure exhibit superior performance with a low threshold voltage (V TH) of 0.9 V, a high saturation mobility (μsat) of 145 cm2 V−1 s−1, a steep subthreshold swing (SS) of 162 mV/decade, and a high I on/I off ratio of 3.15 × 108. The enhanced electrical properties were explained by the improved crystalline nature of the channel layer and the passivation effect of the Al2O3 layer.

Characteristic research of zinc oxide based thin film transistor by ALD technology

Zinc oxide is a well-known wide band gap semiconductor material which can be applied to thin film transistors. Al-doped ZnO (AZO) has a better electrical conductivity than Zinc oxide at the same time with good photoelectric properties. In this paper, the method of atomic layer deposition (ALD) was used to prepare the ZnO and Al:ZnO (AZO) thin films as the active layers on silicon substrates at 100 °C. TEM and SEM were used to compare the characters of these films. While, transfer characteristic was an important basis for measuring the electrical characteristics of the devices with different active layers before and after annealing. The unannealed three-layers AZO-based thin film transistor (TFT) exhibits saturation mobility (µsat) of 5.97cm2V−1S−1, a lower subthreshold swing (SS) of 188mV/decade and a high Ion/Ioff ratio of 1.47 × 108.

Strain effect on electronic structure of La-doped monolayer graphene

As a basic block of carbon materials with different dimensions, graphene has shown great potential in novel device field. As a result, it becomes extremely important to break the zero-band-gap status of graphene sheet. In this work, the density functional theory (DFT) has been carried out to calculate the electronic structure of La-doped monolayer graphene under both X-direction uniaxial and Y-direction uniaxial strain. It turns out that both tensile uniaxial strain along the X-direction and compressive strain along the Y-direction help to broaden bandgap in La-doped graphene sheet. In addition, the La-doped graphene could get a biggest band gap while these two kinds of uniaxial strains are given to be 12% and −9%, respectively.