Development of a robust fabrication process for single silicon nanowire-based omega gate transistors on polyamide substrate

Single silicon nanowire (SiNW) omega-gate field-effect transistors have been fabricated using a standard photolithography method on a Kapton flexible polyamide thin film attached to a sacrificial silicon substrate. SiNWs have been grown by the chemical vapor deposition method using a vapor–liquid–solid mechanism and gold as the catalyst. A key step for proper SiNW integration, Kapton surface flattening, was performed via an innovative method based on soap. Contrary to a previously reported integration process on flexible substrates, this flexible/rigid hybrid substrate is compatible with temperature as high as $400{}^{\circ }C$, allowing the formation of low-resistive nickel silicide at the source/drain contacts. As a consequence, our devices can exhibit excellent electrical properties such as $22{cm}^2{V}^{-1}{s}^{-1}$ hole mobility, 10⁵ $I_{\text{ON}}\text{-to-}{I}_{\text{OFF}}$ ratio and subthreshold slope of about $340mV{dec}^{-1}$. These parameters can compete with those of organic transistors or in some aspects even exceeding electrical parameters of similar single SiNW transistors fabricated onto flexible substrates. In addition, after separation from the rigid silicon substrate, devices on Kapton experience a significant improvement in their performance, such as two orders of magnitude for $I_{\text{ON}}/I_{\text{OFF}}$ ratio and halving the subthreshold slope. This flexible/rigid hybrid substrate, offering high chemical and thermal stability, as well as preserving good electrical features and even improving them, after detaching and transfering the polyamide layer to a plastic substrate, which opens up a new route for the integration of further nanostructures. (paper)