Study On Single Event Effects In CNTFET Devices And Memory Cell Circuits

As Moore’s Law gradually reaches its limit,one of the most promising solutions is to replace Metal-Oxide-Semiconductor Field-Effect Transistor(MOSFET)with Carbon Nanotube Field-Effect Transistor(CNTFET).Carbon nanotube(CNT)has extremely high carrier mobility,low capacitance,and high-frequency performance,which creates a new technology called CNTFET when used as the channel region for field-effect transistors.In the Very Large Scale Integration(VLSI)industry,CNTFET-based digital systems offer not only high speed,low power consumption,and low latency but also radiation resistance.In complex space environments,semiconductor devices experience structural and performance changes under the influence of high-energy particles or electromagnetic radiation.In particular,the Single-Event Effects of CNTFETs are difficult to measure in space environments,so this thesis investigates their single-event effects via computer simulation.The Sentaurus TCAD software is used to analyze and study the single-event effects of a novel GAA CNTFET device and its corresponding 6T SRAM cell circuit.First,twodimensional and three-dimensional models of the CNTFET device are established using Sentaurus TCAD software,and the transfer and output characteristics of the CNTFET are simulated.The results show that the CNTFET can be equivalently represented as a voltage-controlled switch and resistor model.Next,the CNTFET is bombarded with heavy ions at different incident positions,under different drain voltages,and with different Linear Energy Transfer(LET)values to obtain the time-dependent drain current curve.The simulations results show that when the heavy ions strike near the drain,and the LET value of the heavy ion is larger,the instantaneous pulse current at the drain is larger.As the drain voltage increases,the generated instantaneous pulse current increases slowly,indicating that the drain voltage has little sensitivity to single-event effects.When the LET value exceeds a certain threshold,the device in the off-state will experience a surge in drain current to reach the on-state current upon heavy ion irradiation,resulting in device failure.Subsequently,a 6T SRAM cell circuit is constructed with six CNTFETs,and its structure is analyzed in detail.The noise margin of the SRAM cell circuit is simulated to ensure its stability and reliability under various working conditions.Finally,a hybrid connection method of two-dimensional and three-dimensional structures is adopted to simulate the single-event effects of the SRAM cell circuit to obtain the LET threshold and sensitive positions in the cell circuit.Since the 6T SRAM cell circuit is a symmetric structure,it is only necessary to simulate the single-event effects of C1,C2,and C5 transistors.For C1 and C2 transistors,they form an inverter and one is always in the onstate while the other is in the off-state regardless of the situation.Bombarding the initially off-state transistor with heavy ions will cause the stored value in the cell circuit to flip when the LET value exceeds a certain threshold;otherwise,bombarding the initially onstate transistor will not cause the stored value to flip.As for the C5 tube,since it is an access transistor,if the value in the C5 transistor’s bitline is opposite to the initially stored value in the cell circuit,bombarding the C5 transistor with heavy ions could cause the stored value in the cell circuit to flip,as long as the LET is sufficiently large.Conversely,if the value in the C5 transistor’s bitline is the same as the initially stored value in the cell circuit,the stored value will not flip.