Device and circuit simulation of quantum electronic devices

Quantum electronic devices such as resonant tunneling diodes and transistors are now beginning to be used in ultrafast and compact circuit designs. These devices exhibit negative differential resistance (NDR) and/or negative transconductance in their I-V characteristics and have active dimensions of a few nanometers. Since the conventional drift-diffusion approximation is not valid for simulation of device behavior at this microscopic scale, quantum simulation models based on the Schriidinger equation are required to accurately predict the behavior of the device. However, these models are too slow for circuit simulation. This paper describes a modeling scheme that maintains the accuracy of the quantum simulation while achieving satisfactory speed for circuit simulation, and is applicable to a wide range of two and three terminal resonant tunneling devices and may also be extended to future scaled-down MOS and bipolar devices. A self-consistent solution of the Poisson and the Schriidinger equations for various bias points is used to build up tables of conductances, capacitances and other parameters. Table-lookup methods are then used during circuit simulation. Convergence techniques have been developed to overcome the problems caused by the NDR characteristics and the lookup-table model in simulation. While implementation details are presented for a resonant tunneling transistor (RTT), models for several other quantum electronic devices have also been implemented in NDR-SPICE.