Low-Voltage In-Zn-O Double-Layer Thin Film Transistor Research

Oxide thin film transistor is attracting widespread research interests in the world because it has many advantages such as high mobility (>10cm2/Vs), room temperature fabricated, suitable for mass production, low cost, and wide range of applications, etc. Among the many types of oxide semiconductor which are used as the channel layer material, In-Ga-Zn-O (IGZO), with a very smooth surface structure, a very high mobility (>10 cm2/Vs), good substrate compatibility and non-toxic, is getting attention of many research groups. Since the weak capacitive coupling between the gate electrode and the active channel, traditional IGZO-TFTs require a large gate drive voltage (above 40 V), which greatly limits the range of applications. Moreover, with the development of flexible electronics, flexible thin-film transistors are getting more and more attention. Finally, the awareness of environmental protection makes it a trend to fabricate thin film transistors with non-toxic non-polluting natural biological materials.In this paper, we successfully fabricate low-voltage thin film transistors on the conventional conductive ITO glass and the new flexible paper substrates. We use natural egg white and beeswax film as gate dielectric, respectively. These thin film transistors are bottom-gate structure, and can be divided into four parts:glass and paper substrates, ITO and silver film bottom gate, egg white and beeswax gate dielectric, IZO channel and source/drain electrodes. The silver film is deposited by thermal evaporation process, the egg white and beeswax film is prepared by spin coating method, the IZO channel and the source/drain electrodes were grown by one-step magnetron sputtering. We use Keithley semiconductor parameter analyzer to test the performance of the device. Taking the low-voltage, beeswax film gate dielectric and paper substrate thin film transistors for instance, it’s an enhanced device, with gate dielectric capacitance per unit area of 5μF/cm2, low operating voltage of 2 V. The threshold voltage, field-effect mobility, ON/OFF ratio and subthreshold swing are 0.43 V,14.6cm2/Vs,7.6×106 and 86mV/decade, respectively. The leakage current is as low as 2.8 nA. After 30 days aging test and more than 3,000 bending test, its threshold voltage shift of only 0.1 V, and field-effect mobility is reduced by 15%, showing good aging and mechanical bending properties.These low-voltage natural biological material thin film transistors fabricated on flexible paper substrate has a very large application prospect in the next generation microelectronic device field, which ask for high performance, low power consumption, environment-friendly and flexible characteristics, especially in human body sensor applications.