Constant resistance and capacitance models for CMOS technologies

摘要

The use of constant resistance (R) and capacitance (C) models for MOSFETs in circuit and timing analysis tools can offer significant reductions in total execution time over standard circuit simulators such as SPICE, which use detailed, nonlinear MOSFET models. Two methods of determining the appropriate constant RC values for MOSFETs have been developed and applied to CMOS technologies ranging from 2mum down to 35nm. The first method uses a simple, RC propagation-delay model for inverters called the C&barbelow;onstant R&barbelow;C I&barbelow;nput-S&barbelow;ignal-T&barbelow;ransition-I&barbelow;nherent or CRISTI model. Constant RC values obtained from the CRISTI model give good approximations to inverter waveforms and delays obtained from SPICE. The second method uses a widely accepted "CV/ I" metric for characterizing transistors. This method is used to confirm the constant RC values obtained from the CRISTI model, and then it is used to project constant RC values for deep sub-micron CMOS technologies.;The CRISTI model was extended to more complex, multi-transistor (>2) logic gates. The model has been implemented into IRSIM, a previously existing timing analysis simulator. The new simulator is called C-IRSIM. Using constant RC values for a 0.18mum technology, C-IRSIM's estimates of propagation delay are within 10--15% of AIM-Spice values for static and dynamic digital CMOS circuits. C-IRSIM also offers ≈60% improvement over IRSIM. For a 1056-transistor 6-bit multiplier circuit, C-IRSIM demonstrates a 400x reduction in total execution time over AIM-Spice.;Constant RC values are also used in RIPE, the Rensselaer Interconnect Performance Estimator. RIPE allows one to investigate the effect of interconnect materials and strategies on microprocessor performance. RIPE is used to demonstrate the importance of having good RC values for MOSFETs by critically evaluating the very aggressive scaling trends proposed for CMOS technologies in the 1999 International Technology Roadmap for Semiconductors. Constant RC values are also used in the latest version of RIPE, RIPE 4.2, to perform an inductance optimization of on-chip wiring levels. This generally leads to a reduction of total wiring levels.;Finally, the methods of obtaining constant RC values are also applied to cryogenic (77K) CMOS and SOI CMOS.