Radiation Hardening in Modern ASICs

Deep space is an unforgiving environment. Beyond the protective shield of Earth’s magnetosphere, electronic components are bombarded by high-energy cosmic rays, solar flares, and trapped radiation belts. For Application-Specific Integrated Circuits (ASICs) that control critical spacecraft systems, this radiation poses a severe threat, primarily through phenomena known as Single-Event Effects (SEEs).

The Threat: Single-Event Upsets (SEUs)

One of the most common issues engineers face is the Single-Event Upset (SEU). An SEU occurs when a high-energy particle strikes a sensitive node in a microcircuit, depositing enough charge to flip the state of a memory bit or flip-flop (e.g., changing a 0 to a 1). While usually non-destructive, an SEU can corrupt data, crash a flight computer, or cause uncommanded actions if not mitigated.

Mitigation Strategies

To combat these effects, space engineers employ “radiation hardening by design” (RHBD) techniques at the logic and architectural levels.

1. Triple Modular Redundancy (TMR)

The gold standard for mitigating SEUs in logic design is Triple Modular Redundancy. In TMR, a critical logic block or register is replicated three times. The outputs of these three identical blocks are fed into a majority voter circuit. If one block is hit by a particle and flips state, the other two blocks will still output the correct value. The voter circuit takes the majority consensus (2 out of 3), effectively masking the error.

2. Error Correction Codes (ECC)

For larger memory arrays where TMR is too expensive in terms of power and area, Error Correction Codes are used. By adding parity bits to stored data words, ECC can automatically detect and correct single-bit errors (and often detect double-bit errors) on the fly as data is read from memory.

3. Spatial Separation

When using TMR or other redundant logic, it’s crucial to physically separate the redundant nodes on the silicon die. A single high-energy heavy ion track can deposit a cloud of charge large enough to affect multiple adjacent transistors (Multiple-Bit Upset). By spatially separating the redundant circuits, we ensure a single particle strike cannot take out the majority vote.

The Future of Space Electronics

As we push further into the solar system and target missions to Mars and beyond, the radiation environment becomes even harsher. Simultaneously, the demand for high-performance computing in space—for autonomous navigation, terrain-relative sensing, and onboard data processing—requires smaller transistor nodes, which are inherently more susceptible to SEUs.

Balancing performance, power, area, and extreme reliability will continue to be the central challenge for the next generation of space pioneer engineers.