External circuitry has become just as important to device simulation as the internal device physics. Hence, it is important to develop a means to couple the device and circuit information. Circuit information can be included in device simulation by adding the circuit matrix in the device matrix. Device simulation can be included in circuit simulation by including the device IV and conductance characteristics in the circuit matrix during newton iterations. A third method, limited to linear circuits, involves reducing the circuit components to a set a of boundary conditions for the device simulation.
All three have been used with DC, ac, and transient simulation of circuits which involve some complex physical phenomenon. Example have been demonstrated with the response of an LED in a fiber optic transmitter circuit, alpha particle upset in an SRAM cell, and poly- depletion in a ring oscillator. The boundary condition technique has been expanded to include harmonic balance simulation for analysis of large signal sinusoidal responses of circuit/devices. The harmonic balance simulation capability has been applied to an RF power amplifier to characterize the gain, efficiency, and linearity of the device and circuit.
Progress:
Recent progress has focused on the RF simulation of an LDMOS transistor from Motorola. During the summer quarter, the device was characterized and modeled using PISCES and harmonic balance simulation. The modeling consisted of tuning the device model to match experimental IV measurements while parasitics were tuned to match CV measurements. Upon developing a tuned modeled, more advance measurements for S-Parameters, large signal gain, and large signal efficiency were verified to match simulated data. With this tuned model, the effect of variations in the device structure and parasitics was examined.
The work during Fall 1997 focused on extracting physical parameters internal to the device to examine cause and effects of distortion. From single tone harmonic balance simulation results, Matlab routines were used to create contour plots of potential, electron concentration, hole concentration, and electric fields. In addition, current density vectors were also plotted.
Beyond internal effects, the external effect of the matching networks were examined by modeling a Maury Load-Pull system. The simulation showed that the matching networks employed in all the previous simulations were correct and were reasonable so as to provide good gain and efficiency.
Work during the Winter 1998 quarter will examine internal parameters in inter-modulation distortion. Current potentials, which can be used for generating flow lines, will be extracted; thus, providing more details into the physical responses. Finally, documentation on Harmonic Balance PISCES should be available by the end of the quarter.
Publication & Presentations:
Summer Internship:
Francis Rotella worked at Motorola in Tempe, AZ for the summer 1997 quarter. He transfered harmonic balance PISCES to Motorola and demonstrated its capabilities on a LDMOS power MOSFET.