5. ALD Al-doped ZnO Thin Film as Semiconductor and Piezoelectric Material: Transistors and Sensors

Based on the results of Rizk and Saadat (The IoT Physical Layer, pp. 23–46, Springer, Berlin, 2018, [1], The IoT Physical Layer, pp. 47–68, Springer, Berlin, 2018, [2]), this chapter covers the use of Al-doped ZnO films as active channel material for TFT devices. It shows the need to have semiconducting behavior of the ZnO films and how this is modulated by the synthesis method, Al doping and synthesis temperature. Then, this chapter covers the process flow and goes over the unique challenges of fabricating on flexible substrate versus Si substrate and the associated mitigation techniques. These challenges include adhesion, film reliability, heat dissipation, and its low-temperature processing on flexible substrates. This is followed by the characterization of the TFT and its demonstration as best in its class, when it comes to this material system and associated fabrication constraints.