Circuit modeling and simulation

CoolSPICE: SPICE for niche applications

CoolSPICE is the proprietary SPICE suite of CoolCAD Electronics LLC. It is comprised of a SPICE engine, a schematics editor, a plotter application and a text editor. It is first developed for NASA to obtain SPICE models and to develop a SPICE simulation environment for cryogenic operation of CMOS electronics. For example, we have developed models for various size n- and p- channel MOSFETs fabricated using IBM 8RF, IBM10LP, Peregrine5FC technologies.


Besides cryogenic electronics, CoolSPICE also includes circuit elements for niche electronics applications. SPICE models for silicon carbide device models are currently being developed for use in power electronics simulations. The silicon carbide power library includes MOSFETs, JFETs, and diodes, along with simplified power switches and passives.


CoolSPICE also includes libraries for components for simulating photodetector circuits with elements such rectennas and avalanche photodiodes.


Click on the CoolSPICE page to download the student version!

Verilog-A modeling

Verilog-A is an analog hardware description / behavioral modeling language. Verilog-A runs in almost all commercial device simulators such as Cadence Spectre, Agilent ADS, Silvaco Smartspice, etc. Therefore it is very portable, and unlike BSIM type compact models Verilog-A codes are transparent enabling change of parameter lists as well as equations. Verliog-A programs running in SPICE engines take advantage of the built-in matrix solver of the SPICE simulator. Also devices described in Verilog-A can be simulated alongside standard SPICE elements. Lastly, Verilog-A language is relatively simple to understand and simulators allow users change the code or the equation set.


We develop Verilog-A models for various devices that cannot be found in standard SPICE libraries or devices operating in extreme environments that are not well modeled with standard device model sets. For example, cryogenic operation of CMOS devices are modeled with a modified BSIM equation set and coded into a Verilog-A for enabling simulation of cryogenic circuit operation in commercial SPICE simulators. (These Verilog-A libraries are similar to those coded in CoolSPICE using the C-programming language.) However we note that C-programming based codes have inherently faster running times than similar Verilog-A libraries. But Verilog-A libraries offer flexibility in terms of simulator choice and easy access to the device parameter set as well as device equations.

SPICE model extraction

CMOS SPICE Models / PDK SPICE Model Development: We develop SPICE models for n- and p- channel MOSFETs, resistors, diodes for several CMOS technologies.


For CMOS technologies, we design, lay out and have fabricated SPICE model extraction test chips. Using the test structures, we then extract SPICE models using measurements. We have applied this method to some CMOS technologies, and have developed SPICE models for an extreme temperature range and also for under radiation operation for this technologies. More specifically, our SPICE models predict n- and p-channel MOSFET operation for all width and length devices from 4K up to 300K for the technologies listed below:


  • IBM 8RF
  • IBM 10LP
  • Jazz CA18
  • Peregrine 5FC
  • AMI/ON C5


SPICE Models for Silicon Carbide Power Devices: We design and develop a comprehensive Silicon Carbide Power System CAD tool to address the need for improved methodologies for developing next generation high efficiency power electronics using Silicon Carbide power devices. To this end, we have developed SPICE models for SiC MOSFETs, JFETs and diodes. More specifically, we have developed SPICE models for CREE power MOSFETs valid from room temperature up to 200 C. We are also developing models for SiC diodes, and JFETs. These models are currently being incorporated into CoolSPICE-PS (CoolSPICE-Power System), and are coupled with a three-dimensional thermal simulator for resolving electrical as well as thermal characteristics for power modules.


SPICE Models for Niche Components: We develop SPICE models for niche devices such as MIM diodes, rectennas, and avalanche photodiodes. We can develop models for your various applications!

Thermal modeling and CoolSPICE-PS

We have experience in thermal simulation of power modules with realistic three- and two- dimensional structures. More specifically, we perform printed-circuit-board layout driven thermal analysis. We also have the capability to pursue this thermal analysis in conjunction with our SPICE (Simulation Program with Integrated Circuit Emphasis) engine CoolSPICE. CoolSPICE along with a thermal simulator is being developed to achieve self-consistent electrical-thermal simulations simultaneously at the power module and power device levels. This electrical-thermal simulator is called CoolSPICE-PS, named after CoolSPICE for power systems.


First we draw power module or circuit board in a three-dimensional CAD program. During the creation of the mesh, the geometry can be divided up into different "bodies", which can be associated with different generated heat. Additionally, each face of the surface can be associated with a different boundary condition: temperature is fixed; derivative of the temperature is fixed with various heat conductivities and thermal radiation coefficients. We then use the SPICE engine to determine the power consumed by the circuit components, and use the thermal engine to calculate the temperature of these components for given power consumption levels. We iterate electrical performance and heating figures until they both agree.


We specifically apply coupled thermal-electrical simulations to silicon carbide power devices and circuits. As silicon carbide components are generally aimed for high power applications, they are prone to heating that is experienced by all high power switches. For example, even for a highly efficient 5 kW system, with a few power switches only consuming 2% of total power, 100W of Joule heating will give rise to significant elevated temperatures at the switch level. This will in turn affect the electrical performance, since changes in temperature alter electrical performance characteristics, and it may even provide a positive feedback between temperature rise and power consumption, leading to excessive heating and reduced system efficiency.


CoolSPICE-PS is capable of incorporating temperature variations at the device level into circuit simulations, unlike the standard SPICE that forces the entire circuit operate at one ambient temperature. Even though there are efforts to incorporate some temperature variations into key circuit elements by using voltage and current controlled sources to provide feedback to electrical operation, these efforts often result in convergence problems in circuits with more than few parts, and also cannot resolve heat coupling between components.

TCAD simulations

We have many years of experience on semiconductor device modeling, and specifically on simulating field effect transistors such as siliocn carbide DMOSFETs and silicon MOSFETs, as well as sensors such avalanche photodiodes.


Our drift-diffusion based simulator solves for Poisson equation coupled with electron and hole current continuity equations to obtain two and one dimensional profiles of electron concentration, hole concentration and electrostatic potential, as well as terminal currents for given doping profiles and physical device layout.


Here we show calculated and measured current-voltage curves of a 0.6 μm long n-channel MOSFET. We also show doping profile for this MOSFET, calculated using an incomplete ionization model.

Mixed-mode simulations (SPICE/TCAD)

We perform self-consistent simulations of two-dimensional devices in conjunction with SPICE circuit elements. At the detailed device level, drift-diffusion equations that include electron and hole current continuity equations as well as Poisson equation are self-consistently solved for to calculate terminal currents and to obtain electron concentration, hole concentration and electrostatic potential profiles. At the circuit level, we solve for nodal equations to determine branch currents and voltages.


As an example, we show a boost converter circuit with the switching element modeled using TCAD, along with the simulated inductor current and output voltage. We also show an inverter circuit with NMOS and PMOS modeled using TCAD.

Monte-Carlo simulations

We develop full-band Monte Carlo simulators to investigate electron transport in one to three dimensional structures. The electron and phonon dispersion curves are first obtained by applying the tight-binding method or the empirical pseudopotential method to the two inequivalent atoms of the graphene unit cell, considering their nearest neighbors in real or Fourier space. The electron-phonon scattering rates for interactions that conserve momentum and energy are then determined using Fermi’s golden rule and the deformation potential approximation. Average electron velocities due to external fields applied in different directions are calculated using these electron-phonon scattering rates and a semiclassical electron and electric field interaction.

Related references

[SPICE]

A. Akturk, M. Holloway, S. Potbhare, D. Gundlach, B. Li, N. Goldsman, M. Peckerar, K. P. Cheung, "Compact and distributed modeling of cryogenic bulk mosfet operation ," IEEE Transactions on Electron Devices 57(6), 1334-1342 (2010).


A. Akturk, S. Potbhare, J. Booz, N. Goldsman, D. Gundlach, R. Nandwana, K. Mayaram, "CoolSPICE: SPICE for Extreme Temperature Range Integrated Circuit Design and Modeling," Proceedings of Int. Conf. on Simulation of Semiconductor Processes and Devices (SISPAD), (5-7 Sept. 2012).


[Verilog-A]

A. Akturk, M. Peckerar, K. Eng, J. Hamlet, S. Potbhare, E. Longoria, R. Young, T. Gurrieri, M. S. Carroll, N. Goldsman, "Compact modeling of 0.35μm SOI CMOS technology node for 4K dc operation using Verilog-A," Microelectronic Engineering 87(12), 2518-2524 (2010).


S. Potbhare, A. Akturk, N. Goldsman, M. Peckerar, J. M. McGarrity, A. Agarwal, "Modeling and design of high temperature silicon carbide DMOSFET based medium power DC-DC converter," Proceedings of Int. Conf. on High Temperature Electronics (HiTEC), (11-13 May 2010).


[Thermal]

A. Akturk, N. Goldsman, G. Metze, "Self-consistent modeling of heating and mosfet performance in three-dimensional integrated circuits," IEEE Transactions on Electron Devices 52(11), 2395-2403 (2005).


A. Akturk, N. Goldsman, L. Parker, G. Metze, "Mixed-mode temperature modeling of full-chip based on individual non-isothermal device operations," Solid-State Electronics49(7), 1127–1134 (2005).


Z. Dilli, A. Akturk, N. Goldsman, G. Metze, "Controlled on-chip heat transfer for directed heating and temperature reduction," Solid State Electronics 53(6), 590–598 (2009).