A study on total-ionizing-dose tolerant unit n-MOSFET for space electronics used in satellite

Abstract

Space applications such as space shuttle and satellites require radiation-tolerant application-specific integrated circuits. Outer space contains many radiation sources, including the Van Allen belt, solar flares, and cosmic rays. When complementary metal-oxide-semiconductor (CMOS) integrated circuits are operated in a radiation environment such as outer space, they are subjected to numerous types of anomalies. In severe cases, these radiation-induced anomalies can cause a system to lose all functionality. Among these radiation-induced anomalies, the total ionizing dose effect, which corresponds to long-term accumulated radiation damage, generally worsens the performance of CMOS integrated circuits by altering the characteristics of the n-type metal-oxide-semiconductors (n-MOSFETs) contained in the circuit. Therefore, space CMOS integrated circuits for long-term missions should have radiation-tolerant characteris-tics for n-MOSFETs in order to mitigate or eliminate the total ionizing dose effects. In the n-MOSFETs, the total ionizing dose effects arise from the trapping of radiation-induced holes at the silicon-silicon dioxide interface by the existing electric field. Furthermore, according to recent reports, n-MOSFETs fabricated by a deep sub-micron process using the gate oxide with a thickness of less than 10 nm are possible to have two kinds of leakage current paths by radiation-induced trapped fixed charges. The problems underneath the gate oxide tend to disappear, as radiation-induced holes are not trapped in thin oxides with thickness of less than 10nm; they are only trapped in thick oxides such as sidewall oxides and isolation field oxides. As a result, the radiation-induced leakage current paths are formed along the sidewall isolation oxide and underneath the isolation field oxide, causing greater system noise and power consumption. Several transistor layouts have been reported and evaluated for the purpose of eliminating these radiation-induced lea...