Multi-Plot Rubberband Option is Implemented in UTMOST!

The recently developed multi-plot rubberband option is available for MOS and Bipolar technologies of UTMOST3. This new feature greatly enhances the existing capabilities of the single-plot rubberband option.

The multi-plot rubberband feature enables users to modify the SPICE model parameters and instantly see the simulated characteristics for different geometry's and curves. For example, in MOS technology the UTMOST user can modify the SPICE model parameter, "mobility" and instantly see the effects on IDS/VGS and IDS/VDS characteristics for long channel, short channel and narrow width devices (Figure 1).

Figure 1. Multi-Plot rubberband option for MOS technology.

In Bipolar technology, the forward and reverse characteristics (total of six curves) can be rubberbanned together (Figure 2). Some of the bipolar model parameters have an effect on both forward and reverse characteristics. Therefore analyzing these important parameters using the multi-rubberband option will be very beneficial to SPICE modeling engineers.

The existing local and global optimization techniques concentrate on minimizing the total error within the defined targets. Optimizers do not have the intelligence to find the trade-off points. This decision is made by the modeling engineer who is familiar with the limitations of the SPICE model equations. The multi-plot rubberband option enables experienced modeling engineers to find an optimum value which will provide a sufficient fit for different geometry's and/or characteristics. The multi-plot rubberband is also an excellent learning tool for users who are not very familiar with recently developed SPICE models such as BSIM3v3.

How to use the multi-plot rubberband feature

Follow these steps to activate the rubberband feature in MOS technology:

  • Load a log file which contains multiple geometry's. Select the ALL_DC routine.
  • Press the measure button to retrieve the IDS/VDS and IDS/VGS characteristics for several devices.
  • Press the Option button in the Graphics screen and select Rubberband from the pull-down menu.
  • Highlight a few parameters and move the sliding ruler right or left.

Simulation results will be updated instantly with changing parameter values. The speed of the simulation will depend on the speed and memory of the workstation.

Figure 2. Multi-Plot rubberband option for Bipolar technology.