# Nonvolatile Organic Floating-Gate Memory Using N2200 as Charge-Trapping Layer
## 3 Results and Discussion
### Storage Characteristics  
Due to the hot charge carrier injection and FN tunneling mechanism, when a negative programming voltage is applied to FG-OFETM, the charge carriers enter the FG layer from the channel through the tunneling layer. On the other hand, when a positive erasing voltage is applied, the charge carriers captured by the FG layer are released into the channel. Both of the above-mentioned processes can lead to a shift in \(V_{\text{TH}}\), which enables the device to exhibit distinguishable physical states for representing the binary 0 and 1. As shown in Figure 3a, the simulated results show that the transfer characteristic of N2200 FG-OFETM has obvious negative and positive shifts under the P/E voltage of \(\pm\)45 V, 5 s, and the \(V_{\text{DS}}\) is constant at \(-\)5 V.  
Figure 3b shows the energy level of N2200 FG-OFETM without the application of voltage, where \(E_{0}\) is the vacuum energy level, and the LUMO and HOMO levels of pentacene are 3.1 eV and 5.1 eV, respectively. In Figure 3c, when a negative gate voltage (\(V_{\text{GS}}\)) is applied, holes are accumulated at the interface between the pentacene layer and PMMA layer; the energy band of PMMA is greatly bent, which causes holes to be injected into the N2200 FG layer from the channel. The holes captured by the FG layer generate an internal electric field in the opposite direction to the applied negative gate voltage, resulting in a negative shift in the transfer characteristic curve, which is a programming operation. Then, the positive erasing voltage is applied to the device; as shown in Figure 3d, the transfer characteristic curve is returned to the initial position. This is an erasing operation, which indicates that the holes captured by the N2200 FG layer during the programming operation are extracted back to the active layer due to the erasing operation. Figure 2: (**a**) Output characteristics and (**b**) transfer characteristics of N2200 FG-OFETM with tunneling layer of 8 nm. The storage characteristics of N2200 FG-OFETM are closely related to factors such as the thickness of the tunneling layer, the magnitude of the operating voltage, and the operation time of P/E voltages. Firstly, the impacts of different tunneling layer thicknesses on the memory window are investigated. There are five samples with tunneling layer thicknesses of 6 nm, 8 nm, 10 nm, 12 nm, and 14 nm. Figure 4a shows that the memory windows that vary with the thickness of the tunneling layer are 24.4 V, 16.1 V, 12.1 V, 7.9 V, and 4.7 V, respectively. It can be observed that the offset of the transfer characteristic curve is the largest when the thickness of the tunneling layer is 6 nm. The memory window decreases with the increase in tunneling layer thickness, because a thinner tunneling layer allows charge carriers to be more easily captured by the FG. However, the tunneling layer should have a suitable thickness. Thicker tunneling layers could make P/E operations difficult, while thinner layers could affect the retention time of storage devices. Therefore, in the subsequent simulation, N2200 FG-OFETM with a tunneling layer thickness of 8 nm is selected as the research object. Figure 4b,c show the various memory windows under different P/E operations. With the operating voltage changed from \(\pm\)40 V to \(\pm\)60 V (the operating time is uniformly 5 s), the corresponding memory windows are 12.4 V, 16.1 V, 25.9 V, 35.9 V, and 45.8 V, respectively. When \(V_{\text{P}}=-45\) V, the transfer characteristic curve returns to the initial position, indicating that all the holes captured by the FG layer are extracted back to the active layer after erasing. When \(V_{\text{P/E}}>\pm 45\) V, the transfer characteristic curves after erasing are on the right side of the initial position, which suggests that when the erasing voltage is increased, first, all holes in the FG layer are extracted back to the active layer, and then electrons are injected from the active layer to the FG layer and captured by the FG.