L. Adams

RADFET: A review of the use of metal-oxide-silicon devices as integrating dosimeters

Abstract Calibrated, radiation-sensitive metal-oxide-silicon field-effect transistors (RADFETs) have been launched into space and used in the laboratory to measure the doses from a variety of radiation sources. These experiments have demonstrated that the RADFET provides a convenient method for the continuous monitoring of total dose. The electrical output consists of a d.c. voltage which can be converted electronically to a value for accumulated dose. The voltage can be read remotely and displayed continuously. This review briefly outlines the physical mechanisms by which radiation dose is registered by RADFETs, describes the characteristics and performance of a practical RADFET and discusses applications. In addition to the name “RADFET”, these devices have been called “MOS Dosimeters”, “Mosimeters” and “Space Charge (SC) Transducers”.

Observation and prediction of SEU in Hitachi SRAMs in low altitude polar orbits

In-orbit SEU (single event upset) data from three microsatellites are separated into galactic cosmic ray (GCR), South Atlantic anomaly (SAA) and solar flare upsets. Heavy ion and proton testing of the same devices is reported, and predictions using LET (linear energy transfer)-dependent ion cross sections and a two-parameter fit to proton cross section data are compared with in-flight data. SEU trends in memory devices from a single manufacturer, from 16 kb to 4 Mb, are identified. The increasing density of the memories is found to be accompanied by an apparent decreasing sensitivity to the heavy ion environment in polar orbit. Although the LET threshold decreases, the decrease in asymptotic cross section has a greater effect. However, the sensitivity to proton-induced upsets is nearly similar in all memories, so the proton effects become dominant by an order of magnitude. This has important implications for future spacecraft with large onboard memories and high performance processors. >

The SEU Risk Assessment of Z80A, 8086 and 80C86 Microprocessors Intended for Use in a Low Altitude Polar Orbit

This paper presents the results of a test and analysis program carried out in support of an Earth Resources Satellite project in order to provide a quantitative SEU risk assessment for certain microprocessor based subsystems. The key features of the program were the low cost and comparative simplicity of the test techniques which, nevertheless, provided sufficient data for a quantitative risk assessment using the CREME suite of programs.

Cosmic Ray Simulation Experiments for the Study of Single Event Upsets and Latch-Up in CMOS Memories

Heavy ion induced single event upsets and latch-up in 4K CMOS RAMs and PROMs have been demonstrated using both the Harwell Variable Energy Cyclotron and a laboratory Californium-252 source. The latter provides a novel and convenient alternative which complements heavy ion accelerator techniques. A number of memories have been examined by both techniques, enabling appropriate cross sections to be measured.

The behaviour of measured SEU at low altitude during periods of high solar activity (spacecraft memories)

The UoSAT-2 spacecraft, launched in 1984 into a polar orbit at an altitude of 700 km, has a number of systems which have been observed to experience single-event upsets at significant rates. During the year 1989, several solar flare events occurred which elevated the upset rates at high latitudes. The October 19 event, in particular, resulted in very high high-latitude upset rates. The data are separated and analyzed, deriving upset rates for the various memory devices under quiet cosmic-ray, South Atlantic anomaly, and solar flare conditions. The results of the heavy ion and proton testing of UoSAT memories undertaken in order to compare predictions and observations are presented. >

Dose rate and annealing effects on total dose response of MOS and bipolar circuits

Different part types of major technology families were irradiated in order to study dose rate and post irradiation annealing effects. Results confirm that degradation of MOS technologies at low dose rates can be predicted from high dose rate and annealing measurements, while this is not possible for bipolar linear ICs. The ESA/SCC22900 test method is discussed.

Techniques for minimizing space proton damage in scientific charge coupled devices

The authors describe proton irradiation tests and theoretical prediction programmes, mounted as part of the European Space Agencys TRP project, to show the way in which damage in EEV scientific CCDs increases with time in space. The tests give hope that certain modifications of the chip, present in some of the samples tested, can alleviate the damage considerably. Radiation damage levels required with the passage of time in the XMM X-ray astronomy mission can now be stated. With fair confidence, one can now outline engineering measures to harden the system to minimize the space damage. >

A Comparison of Heavy Ion Sources Used in Cosmic Ray Simulation Studies of VLSI Circuits

A comparison has been made between the heavy ions from the ALICE cyclotron and Californium-252. The results of SEU cross-section measurements support the use of the CASE system (Californium-252 Assessment of Single-event Effects) to simulate cosmic ray effects in VLSI circuits.

An Experimental Study of the Effect of Absorbers on the Let of the Fission Particles Emitted by CF-252

The present work continues the developments of the 252Cf fission particle source for use in cosmic ray simulation. An experimental study has been made of the LET of 252Cf fission particles in thin aluminium foils, and of the variation of the mean LET with decreasing fission particle energy. Calculated LET values have been compared with the experimental results, and tabulation of LETs and ranges in aluminium and silicon included.

Generation and annealing behaviour of MeV proton and /sup 252/Cf irradiation induced deep levels in silicon diodes

The generation and annihilation of deep levels in diodes fabricated on nand p-type floating zone and Czochralski silicon substrates is discussed as a function of the substrate parameters and the irradiation and thermal annealing conditions. Both low fluence irradiations with MeV protons and with the fission products of a /sup 252/Cf source are investigated. The presence of deep levels with densities in the range of 4/spl times/10/sup 11/ to 2/spl times/10/sup 12/ cm/sup -3/, is correlated with increase of the diode leakage current. >