Apogee Semiconductor, Inc.

Mark Hamlyn

David A Grant

Gregory A Magel

Kyle Schulmeyer

Emily Ann Donnelly

Systems and methods for shutting down a functional circuit in response to a predetermined total ionizing dose of radiation employ at least two redundant sensing circuits operated in integrate and measure phases by one or more sequencer-type hardware or software controllers. NMOS TID sensors having leakage currents increasing monotonically with dose may be biased during integrate phases, with bias voltages or duty cycles adjusted to achieve a calibrated responsivity. TID measurements are compared to a corresponding reference, latched to generate overexpose signals, and tested for agreement. Disagreement triggers remeasurement to prevent erroneous shutdown until a minimum number of overexpose signals agree that TID exceeds the predetermined threshold. A disable circuit accepts the redundant overexpose signals and generates a signal to disable a functional circuit. Redundancy and remeasurement protect against unwarranted shutdowns due to radiation-induced single-event effects or other circuit transients or failures.

Total ionizing dose shutdown system and method

Devices with increased susceptibility to ionizing radiation feature multiple parasitic transistors having leakage currents that increase with total ionizing dose (TID) due to negative threshold shifts from radiation-induced charge buildup in the field oxide. Leakage currents of parasitic edge transistors associated with active region sidewalls under a gate are enhanced using branching gate patterns that increase the number of these sidewalls. Other variations combine parasitic edge transistors with parasitic field transistors formed under the field oxide between active regions, or between n-wells and active regions. Arrays of such devices connected in parallel further multiply leakage currents, while novel compact designs increase the density and hence the sensitivity to TID for a given circuit area. These NMOS-based radiation-intolerant devices can be integrated with more radiation-tolerant CMOS integrated circuits using commercial processes, to produce circuits having a level of radiation intolerance required for export, or to be used as dosimeters.

MOS devices for sensing total ionizing dose

Compact radiation-hardened NMOS transistors permitting close spacing for high circuit density can be fabricated using modern commercial foundry processes incorporating lightly-doped drain (LDD) and silicidation techniques. Radiation-induced leakage currents in parasitic field oxide transistors are reduced by spacing diffusions away from field oxide edges under the gate, forming gap regions from which n-type dopants and silicide formation are excluded using blocking patterns in the layout. P-type implants along these field oxide edges further increase radiation tolerance. Dimensions can be tailored to permit tradeoffs between radiation tolerance, breakdown voltage, and circuit density. Compact layouts for series-connected NMOS transistors are provided and applied to high-density rad-hard circuits. Methods for fabricating devices having these features are also provided, requiring minimal adaptation of standard processes. These designs and processes allow a mix of integrated circuits having differing levels of tolerance to total ionizing dose on the same semiconductor wafer.

Devices and methods for compact radiation-hardened integrated circuits

CMOS output stages, electrostatic discharge (ESD) protection circuits and input bus-keeper functions are provided that block dc and ac leakage paths within inactive powered-down integrated circuits used in redundant high-reliability system configurations employing cold-sparing to provide backup circuitry. These circuits and methods avoid both undesirable power consumption in a cold-spared backup unit and loading of connected active units when powered down, without compromising performance or functionality of the backup unit when in its active powered state. Inputs and outputs using an analog majority voting principle to implement in-circuit redundancy for on-chip fault tolerance are also provided, incorporating the low-leakage principles of the invention for low power dissipation when powered down. Such on-chip redundancy can harden an IC against various faults, such as single-event effects in high-radiation environments, while maintaining the other advantages in a cold-sparing system.

Circuits and methods for enabling redundancy in an electronic system employing cold-sparing

An integrated circuit for use in high-reliability electronic systems contains one or more digital majority voters with corresponding disagreement detectors connected to the same input signals producing a majority value output and an error signal that is active when not all input signals agree. Internal error signals from multiple majority voter/disagreement detectors as well as external error inputs may be combined using disjunctive error logic to produce an 'error detected' output indication. Cold-sparing and hot-plugging are supported by providing cold-sparable electrostatic discharge protection circuits and power-on reset circuitry controlling cold-sparable output stages. Internal modular redundancy provides immunity to single-event transients as well as enhanced reliability. Redundant electronic systems using the majority voter with error detection are also provided, as are fault notification systems that use the disjunctive error logic and external error input feedthrough capabilities of serially-connected integrated circuits to produce an error indication for a plurality of subsystems.

Majority voter with error detection

Systems and methods for fault-tolerant threshold circuits used in converting an analog input to a single-bit digital output employ N-modular redundancy of either inverting or non-inverting threshold circuits whose inputs are connected to a single input, and apply majority voting of their outputs to provide correction of transient or permanent faults in up to floor[(N&#x2212;1)/2] of the individual threshold circuits. Using summation to perform analog majority voting averages the N threshold circuit outputs and provides resilience to single-event transients, but may exhibit an output characteristic having intermediate voltage levels. A digital majority voter having N inputs connected to the outputs of N threshold circuits restores well-defined logic levels and clean hysteresis for Schmitt trigger threshold circuits. A single point of failure at the digital majority voter may be eliminated using an analog majority voter to sum the outputs of three or more redundant digital majority voters.

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Murphy, TX, United States of America

Mark Hamlyn