Radiation Hard IC Design

Circuits that should work under radiation such as satellite and nuclear plant electronics need to be radiation tolerant and there should not be any performance degradation. This is called the radiation-hard or radiation tolerant circuit design. Some circuits such as imaging systems in satellites should be open to radiation so that it can capture the image. Thus, both the detector and its electronics should be radiation tolerant, that is to say radiation should not damage the circuit or should not degrade the performance of the circuit.

Some effects of radiation are given below:

  • Neutron Effects: This effect is due to neutrons damaging the semiconductor lattice structure and interchange the location of atoms. In this way recombination centers are increased, hence minority carrier lifetime is decreased and reduce the gain of the transistor. BJT transistors are mainly effected by this phenomenon, since charge carrying actors in BJTs are minority carriers.
  • Total Ionizing Effects: This effect changes the threshold voltage of the transistors causing NMOS transistors to open easier and PMOS transistors to open more difficult. Accumulated charges can cause the transistors to stay open or close permanently, which makes them malfunctioning devices.
  • Single Event Effects: It effects mostly digital circuits. A highly energized particle can leave its trace while moving in semiconductor and may change the content of memories. In some cases, a single ion may change the content of many memory cells. This should be prevented in satellites and avionics.

  • These radiation effects can be prevented in two ways, changing the process or developing a new design methodology. Changing the process or developing a seperate process called radiation hard process is possible but is very costly. Since radiation hard circuits are not very common or usage is limited to some applications, a seperate process may not be affordable. Thus, developing new design metodologies that help integrated circuits can perform in radioactive environment is very crucial and a very important capability for some applications.

    For this purpose:

    • TUMSIS is developing radiadition hard/tolerant standard cell libraries for chosen process, hence makes this process eligible for radiation hard demanding applications.
    • TUMSIS designs radiation hard custom ASICs by using similar techniques used in radiation hard standard cell development. Previously developed standard cells can also be utilized in these ASICs.
    • TUMSIS is developing radhard CMOS image sensors for sattellite applications.
    • TUMSIS also looks for new techniques for radiation hard IC design, especially for satellite applications and avionics.