Stability and encapsulation of metal-oxide based TFTs

In this paper we discuss the stability of metal-oxide based thin film transistors (TFT) with a special focus on the impact of the environment. Initially, the influence of adsorbates like water on the TFT characteristics (e.g. threshold voltage and hysteresis) is discussed. It is shown that the adsorption of water and oxygen affect device characteristics and govern the long-term stability. Importantly, the sensitivity of metal oxide based TFTs towards adsorbates depends on processing conditions and can be reduced by in-situ annealing of the semiconductor during the deposition process. Finally, strategies for encapsulation of the TFTs are discussed, highlighting a novel low-temperature approach using atomic layer deposition (ALD) based on ozone. Compared to the established water based ALD process the detrimental shift of the threshold voltage upon encapsulation can be avoided. Therefore, time and energy consuming post treatment can be avoided to recover the original TFT characteristics.