Accurate assessment of circuits at cold temperatures is extremely difficult due to lack of models and tools that can simulate circuit behavior at cryogenic temperatures. A library of cryogenic temperature models was built, as well as a circuit simulator that can use those models and simulate complex circuits at temperatures as low as 4 K.
CoolSPICE is a new circuit simulator built specifically for cryogenic-temperature CMOS (complementary metal-oxide semiconductor) circuit modeling and simulation. It is based on the SPICE3f5 (Simulation Program with Integrated Circuit Emphasis) circuit simulation engine and incorporates device models for cryogenic temperature operation of NMOS and PMOS from a variety of technologies. The key technologies that have been implemented in the SPICE tool include IBM 130-nm, IBM 65-nm, and JAZZ 180-nm processes. The simulator can perform accurate simulations of circuits built using these technologies at temperatures as low as 4 K. This circuit simulator can read the netlist files from other circuit simulator tools such as Cadence, and run the circuit simulation at any temperature from 300 down to 4 K. The simulator also includes a schematic editor for designing new circuits and a plotter for evaluating the simulation results.
The full CoolSPICE package includes the cryogenic temperature models, two circuit simulation engines, the schematic editor, and the waveform plotter. The schematic editor is used to create a circuit using the active devices [MOSFETs (metal-oxide-semiconductor field-effect transistors)], passive devices (resistors, capacitors, etc.), and sources (current, voltage). The temperature can be set as part of the device models. When the circuit design is complete, a netlist is built. The netlist is then given to the SPICE engines and solved for the operating conditions (DC, AC, transient). The results of the simulation are then plotted using the CoolSPICE Plotter. (A student version for simulating standard parts at room temperature can be found online at http://coolcadelectronics.com/coolspice/.)
Fast, reliable, and robust analog and mixed-signal IC (integrated circuit) design for cryogenic environment applications can be achieved by using the new device models and the CoolSPICE software. This will allow a shorter R&D period, significantly reduce cost by allowing first-pass design, and also reduce time to market for new chips.
This work was done by Akin Akturk, Neil Goldsman, and Siddharth Potbhare of CoolCAD Electronics for Goddard Space Flight Center. GSC-16762-1