Transparent and Flexible Oxide Nano-Electronics

Oxide semiconductors are becoming a key material for future electronics because of their wide band gap, hence high transparency and low OFF current, compared with the ubiquitous silicon technologies. Besides oxides, for flexible electronics applications, organic semiconductors are gaining considerable interest due to their low-cost printing processes and mechanical flexibility. This talk will review the integration of oxides and fully printable organics for large area, including newly emerging application areas related to the Internet of Things. We will discuss the critical design considerations to show how device-circuit interactions should be handled and how compensation methods can be implemented for stable and reliable operation. In particular, the quest for low power becomes highly compelling in wearable devices. We will discuss thin-film transistor operation in the different regimes, and review device properties when operated in the deep subthreshold regime or in near-OFF state, addressing the pivotal requirement of low supply voltage and ultralow power leading to potentially battery-less operation.In order to minimize power consumption in oxide TFTs, the devices are operated in the deep subthreshold regime, i.e., near the OFF state, to reduce drain current that contribute to power consumption [1]. For organic TFTs, in particular, all-inkjet-printed devices, we will show that the operating voltage can also be lowered by reducing the semiconductor/dielectric interface trap density, and thus, power consumption can be further reduced [2]. The all-inkjet-printed devices exhibit a low operating voltage of 1 V, a nearly zero threshold voltage (Vth) of 0.01 V, a steep subthreshold slope of 0.069 V/decade, a high on/off ratio of 107, and negligible hysteresis. By investigating the polarity of the two dielectrics, we found that a Lewis-acid monopolar dielectric could exhibit lipophilicity and hydrophobicity at the same time, which ensures printability and avoids water molecule trapping, respectively. Therefore, the all-inkjet-printed organic TFTs with monopolar dielectric demonstrate much better electrically bias-stress stability than the devices with bipolar dielectric [3]. We will also address the noise that is associated with the operation of the subthreshold TFTs. In addition, we will discuss our recent work on low-power organic TFTs on fibers (i.e., cylinder-shape substrates) with various architectures. In particular, we will show a strain-compensated design for a stretchable fiber TFT, where the device can sustain up to 50% of stretching strain without degradation of performance. This strain-compensated stretchable fiber TFT is a promising device architecture for e-textiles and smart wearables [4].