# Capacitor-Less Low-Power Neuron Circuit with Multi-Gate Feedback Field Effect Transistor
## 2 Fbfet  
### FBFET Simulation Results and Characteristics  
We configured the FBFET structure combined with PNPN body doping and two gates (Gate and Control Gate). Gate 1 adjusts the potential barrier height, and a control gate generates a potential well for electron accumulation. The device structure is designed by TCAD, and it is illustrated in Figure 1.  
Figure 2 shows the mechanism of FBFET and its operating principle as followed [14; 15; 16; 17; 18]. 1. Put in positive voltage to the control gate, and a potential well is created under the control gate to accumulate electrons. Figure 1: Simulation FBFET Structure with parameters. 2. Applying a positive bias to gate 1 lowers the potential barrier. Additionally, source electrons cross the potential barrier and accumulated in the potential well under the control gate. 3. The accumulated electrons lower the barrier height of the valence band on the drain, and then holes are accumulated in the p-body below the gate 1. 4. Likewise, the accumulated holes drop the potential barrier on the source, and the potential barriers become very low. Therefore, the current increases rapidly, and the FBFET turns on steeply. Consequently, the current is increased rapidly because of a positive feedback loop, and the FBFET is turned on. Figure 3 shows a difference in drain current according to various drain voltages. The drain current is constant after the FBFET is turned on, and it increases exponentially as Vd linearly increases. This is because the FEFET operates similarly to a forward-bias PN diode when the device is switched on by a positive feedback loop. When the gate voltage is equally applied, the drain v7 oltage is applied from 0.8 V to 1.4 V, and FBFET has the highest current ratio when the drain voltage is the highest. Additionally, after the FBFET is turned on, the drain current is saturated. This is because after the FBFET is turned on, the current is determined only by the pn diode voltages (drain voltage and source voltage) and is not affected by the gate voltage. We confirm the excellent steep switching characteristics of the FBFET, and the subthreshold swing (SS) is 6.27 mV/dec when the drain voltage is 1.4 V. The FBFET also has a different potential well depth depending on the control gate voltage. As the control gate voltage increases, the depth of the potential well increases, and the threshold voltage increases. Likewise, as the control gate voltage decreases, the threshold voltage decreases. Figure 4a shows the energy band diagram. Figure 4b shows that as the control gate voltage increases, the turn-on time increases. If the potential well is deep, more electrons must be accumulated to turn on the device, so the turn-on time is longer. Figure 5 is a graph of the accumulation of electrons in the floating body over transient time. When an applied voltage is less than the threshold to gate 1, the electrons gradually accumulate in the floating body. Additionally, when the number of electrons exceeds the threshold, the FBFET is turned on by a feedback loop between the electrons and the potential barrier. The graph shows that it turns on and off very quickly. Therefore, we suppressed short circuit current using the steep switching characteristics of FBFET and replaced the role of a membrane capacitor using the characteristics of accumulating charge in the floating body. Figure 6 shows the process measurement of the proposed FBFET structure. Figure 6a shows the detailed fabrication process of the proposed FBFET. Since the manufacturing method is compatible with CMOS, FBFET has the advantage of being integrated with the CMOS circuit [19]. An SEM image of the fabricated device after gate patterning is shown in Figure 6b. In addition, we calibrated  
Figure 2: Energy band diagram of the FBFET when it turned on. the simulation parameters based on the measurement results. (Figure 6c,d) [14]. These show the measurement result of the drain current that changes according to the various control gate voltages and the various drain voltages.