Time-dependent equivalent circuit modeling of ferromagnetic single electron transistors

In this paper, a physics-based time-dependent circuit model is proposed for ferromagnetic single electron transistors (FSETs). This model is based on a modified version of the single electronics orthodox theory and obtained by simultaneously solving the governing equations. The introduced model is valid for single or multi gate, symmetric or asymmetric, and magnetic or nonmagnetic island FSETs. The model describes accurately FSET characteristics for a wide range of temperatures and drain to source voltages and also includes the spin relaxation time effect. The proposed model is implemented in a commercial circuit simulator HSPICE for use in circuit simulation. Two series of SPICE simulations are then successfully carried out. In the first simulations, different DC characteristics of a nonmagnetic island FSET are produced and verified against the existing numerical and analytical results with good agreements. In the second simulations, the transient behavior of a nonmagnetic island FSET is analyzed by considering the effects of temperature and spin relaxation time. It is shown that there are two different time scales in the transient response; the shorter one originates from the discrete coulomb charging of the island and the longer one from the spin relaxation effect. As an application example of the model at the circuit level, a magnetic island FSET-based inverter is simulated. These results are verified against Monte Carlo simulation results with excellent agreement. Then, the transient behavior of the inverter is investigated using the model for the first time.