## 3 Results and Discussion
For example, in the BioTFT memory device, the holes transport at the interface between RNA-CTMA film and organic semiconductor film, and thus, defects or surface fluctuations could deteriorate the transport properties. In order to study the film morphology and microscopic structure of the RNA-CTMA film, atomic force micrographs (AFM) and X-ray diffraction patterns were investigated, respectively. Figure 5a exhibits the atomic force microscopy (AFM) image of the RNA-CTMA film depositing on the ITO substrates. The root mean square (rms) surface roughness \begin{table}
\begin{tabular}{c c c c} \hline \hline
**RNA** & **RNA–CTMA** & **DNA–CTMA** & **Assignments** \\ \hline
1226 & 1237 & 1240 & PO\({}_{2}\) antisymmetric \\
1127 & 1134 & 1089 & PO\({}_{2}\) symmetric \\
1066 & 1069 & 1062 & C–O sugar \\
1000 & 996 & 1010 & Sugar ring \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Wavenumber of RNA, RNA–CTMA, and DNA–CTMA film. Figure 4: **(a)** Thermogravimetric (TG) curves of CTMA and RNA–CTMA. **(b)** The DSC curve of the RNA and RNA–CTMA complex. of RNA-CTMA film (thickness of 1 \(\mu\)m) is \(\sim\)2.1 nm, which is quite smooth for such a thick film, and allows it to be a functional interface for charge transport in TFTs. Figure 5b shows the result of the X-ray diffraction patterns of RNA-CTMA complex. A sharp diffraction peak was observed in the small-angle region, corresponding to a spacing of about 39 A in the RNA-CTMA complex film. This sharp peak corresponds to the diameter of the packed RNA complex structure, indicating an ordered structure of the film, and may help reduce gate leakage during device operations. The BioTFT memory device was fabricated using the RNA-CTMA as the gate dielectric, and the measured transfer characteristics (I\({}_{\text{DS}}\)-V\({}_{\text{G}}\)) are shown in Figure 6. The dielectric DNA-CTMA polymer applied as control experiments, herein, have also been carried out. Typical memory windows were observed, and indicated that the RNA-CTMA complex film could work as the gate dielectric layer to prepare the memory device. The OFF currents were 3.5 \(\times\) 10\({}^{-10}\) A and 9.7 \(\times\) 10\({}^{-11}\) A for the devices with RNA-CTMA and DNA-CTMA complexes, respectively, indicating that the resistivity of both the biopolymer films could satisfy the operating requirement. The field effect mobility was calculated by fitting the plot of the square root of \(I_{\text{DS}}\) versus \(V_{\text{G}}\), using the following equation:  
\[I_{\text{DS}}=\frac{W}{2L}C\mu_{\text{sat}}(V_{\text{G}}-V_{\text{th}})^{2}. \tag{1}\]  
Here, \(I_{\text{DS}}\) is the saturation drain current, \(V_{\text{G}}\) is the gate voltage, \(V_{\text{th}}\) is the threshold voltage, \(C\) is the capacitance of gate dielectric per unit area, and \(W\) and \(L\) are the width and length of the channel of the device, respectively. The field-effect mobility of the RNA-CTMA-based device was calculated to be 0.108 cm\({}^{2}\)/V\(\cdot\)s. In addition, from the transfer characteristic, the device based on RNA-CTMA has a threshold voltage \(V_{\text{th}}\) of \(-\)34.5 V. The memory window is 52 V, which could be caused by the dipoles in the RNA-CTMA complex film [20]. The values are comparable with the values reported in recent years, indicating that the RNA-CTMA may be a potential candidate for the dielectric material for non-volatile memory device. Note that the ON current of the DNA-CTMA-based device was higher than that of the RNA-CTMA-based device. This result may be related to the morphological difference of the pentacene layer deposited on these different films. The AFM of the semiconducting pentacene film (thickness of 50 nm) was investigated as shown in Figure 7, comparing the films deposited on top of the RNA-CTMA and DNA-CTMA complex film, respectively. The pentacene film deposited on either complex film shows a highly crystalline structure. The average crystal grain size depositing on DNA-CTMA is  
Figure 5: (**a**) Topological graph of the RNA–CTMA complex film obtained by atomic force microscopy (AFM).