Thermopile detector radiation hard readout

Abstract

ABSTRACT The NASA Jupiter Europa Orbiter (JEO) conceptual payload contains a thermal instrument with six different spectral bands ranging from 8µm to 100 m. The thermal instrument is based on multiple linear arrays of thermopile detectors that are intrinsically radiation hard; however, the thermopile CMOS readout needs to be hardened to tolerate the radiation sources of the JEO mission. Black Forest Engineerin g is developing a thermopile readout to tolerate the JEO mission radiation sources. The thermal instrument and ROIC process/design techniques are described to meet the JEO mission requirements. Keywords: CMOS, NASA, Jupiter Europa Orbiter, thermopile, RHBD, ROIC, ASIC 1.0 INTRODUCTION The Europa Jupiter System Mission (EJSM) launch planned in year 2020 will provide a better understanding as to how gas giant planets and their satellites form and evolve. The Jupiter Europa Orbiter (JEO) is the NASA element of the EJSM. JEO will be built to withstand the intense radiation in Europa orbit, and will consist of an orbiter with different science instruments designed for extensive mapping of Europa. On the way to Europa, JEO will tour the Jovian system and make observations of Jupiter, its satellites and its environment. The JEO conceptual payload includes a thermal instrument (TI) based on thermopile detectors that are intrinsically radiation hard to at least 10 Mrad; however the thermopile readout IC needs to be hardened to tolerate the radiation sources of the JEO mission. Black Forest Engineering (BFE) on a NASA sponsored SBIR effort is developing a thermopile readout application specific integrated circuit (ASIC) using radiation hardened by design techniques (RHBD) to tolerate the JEO mission radiation sources. The readout ASIC when developed on Phase II of the SBIR effort and combined with JPL thermopiles will meet the thermal instrument requirements of the JEO. The thermal instrument designed and developed for the JEO mission will be subjected to four major radiation sources: (1) solar energetic particles (protons, electrons, and heavy ions ) during the interplanetary cruise; (2) galactic cosmic rays (protons and heavy ions) during the interplanetary cruise; (3) trapped charged particles (electrons, protons, and heavy ions) in the Jovian magnetosphere during Jovian Tour and the orbits at Europa; and (4) particles (neutrons and gammas) from the Multi-Mission Radioisotope Generator (MMRTG). Among the four radiation sources, the high energy trapped electrons and protons at Jupiter are the dominating contributors to the “life-limiting” effects. Both total ionizing dose (TID) and displacement damage dose (DDD) effects produce long-term permanent degradation in the thermal instrument performance characteristics. Thermopile signal readout is planned through 128 channel CMOS ICs on the focal plane very close to the detector arrays. Thus radiation hardness will depend on the hardness of both the thermopile arrays and the readout IC. Thermopiles have been tested for TID by JPL with excellent harness to 10 Mrad. The instruments on the JEO will be new designs in order to meet the radiation challenges for electronics and materials. Radiation hardened mixed-signal ASICs will be a key instrume nt technology. BFE is using RHBD techniques to create a new thermopile readout ASIC to meet the JEO radiation challenges. BFE is developing the readout ASIC using 180 nm CMOS. On-readout analog-to-digital conversion is used to improve instrument performance (especially dynamic range) and provide system noise immunity.