Method and system for computer-aided design of radiation-hardened integrated circuits
A method, system, and computer program product include electronic design automation (EDA) tools used with standard CMOS processes to design and produce radiation-hardened (rad-hard) integrated circuits (ICs) having a predictable level of radiation hardness while maintaining a desired level of performance and tracking circuit area. The tools include rad-hard design rule checking (DRC) decks, rad-hard SPICE models, and rad-hard cell libraries. A rad-hard parasitic components extraction process makes use of rad-hard DRC rules to locate occurrences of parasitic devices, calculate their effects on circuit performance, and return this information to layout and circuit simulation tools. Changes to the layout are suggested and implemented with varying degrees of automation. Some of these tools can be provided as components of a rad-hard process design kit (PDK). They can be used in conjunction with commercial EDA tools to facilitate the incorporation of rad-hard features into new or existing IC designs.
1. A computer-implemented method for designing a radiation-hardened integrated circuit comprising the steps of:
generating at least one device model for use in a circuit simulation, said device model having at least one parameter with a value that varies as a function of Total Ionizing Dose (TID);
entering a schematic of a circuit, said circuit comprising at least a portion of an integrated circuit, and a list of requirements comprising at least a radiation-hardness requirement, said radiation-hardness requirement comprising a requirement that the circuit meet a predetermined specification upon exposure to ionizing radiation at a specified first TID level;
performing a layout of the circuit;
assessing a rad-hard performance of the circuit, wherein said step of assessing comprises using a computing system to run a circuit simulation that uses said device model, said rad-hard performance characterized by a second TID level, upon exposure to which the circuit, if fabricated as laid out, will fail to meet the predetermined specification;
suggesting a change to the layout if the second TID level determined in assessing the rad-hard performance does not meet or exceed the first TID level specified in the radiation-hardness requirement; and
changing the layout in response to the suggested change, whereby a design for the circuit is produced that, if fabricated, will meet the radiation-hardness requirement.
2. The computer-implemented method of claim 1 , wherein said device model is a SPICE model.
3. The computer-implemented method of claim 1 , wherein the value of said at least one parameter is derived from electrical testing of a physical device after exposure to radiation at a known TID level.
4. The computer-implemented method of claim 1 , wherein said parameter is a threshold voltage.
5. The computer-implemented method of claim 4 , wherein the threshold voltage is the only parameter that varies as a function of TID.
6. The computer-implemented method of claim 1 , wherein the value of said parameter is specified by editing the device model manually.
7. The computer-implemented method of claim 1 , further comprising a step of adding said device model into a process design kit.
8. The computer-implemented method of claim 1 , wherein said device model represents an individual transistor.
9. The computer-implemented method of claim 1 , wherein said device model represents a functional block.
10. The computer-implemented method of claim 1 , wherein said device model includes an n-channel parasitic thick field transistor.
11. The computer-implemented method of claim 1 , wherein the step of assessing further comprises calculating a leakage current of an NMOS transistor as a function of total ionizing dose.
12. The computer-implemented method of claim 1 , wherein the step of assessing further comprises calculating a leakage current of an n-channel parasitic thick field transistor as a function of total ionizing dose.
13. The computer-implemented method of claim 1 , wherein the step of assessing further comprises locating an occurrence of a parasitic transistor that is induced by radiation and back-annotating a schematic of said parasitic transistor to the schematic of the circuit.
14. The computer-implemented method of claim 1 , wherein the step of suggesting a change to the layout is performed by the computing system.
15. The computer-implemented method of claim 1 , wherein the step of changing the layout is performed automatically by the computing system.
16. The computer-implemented method of claim 1 , wherein the predetermined specification is a value for a leakage current.