1 research outputs found
The effects of ionising radiation on implantable MOS electronic devices
Space exploration and the rapid growth of the satellite communications industry has
promoted substantial research into the effects of ionising radiation on modem electronic
technology. The enabling electronics and computer processing has seen a commensurate
growth in the use of radiation for diagnostic and therapeutic purposes in medicine.
Numerous studies exist in both these fields but an analysis combining the fields of study
to ascertain the effects of radiation on medically implantable electronics is lacking.
A review of significant ground level radiation sources is presented with particular
emphasis on the medical environment. Mechanisms of permanent and transient ionising
radiation damage to Metal Oxide Semiconductors are summarised. Three significant
sources of radiation are classified as having the ability to damage or alter the behavior
of implantable electronics; Secondary neutron cosmic radiation, alpha particle radiation
from the device packaging and therapeutic doses of high energy radiation.
With respect to cosmic radiation, the most sensitive circuit structure within a typical
microcomputer architecture is the Random Access Memory(RAM). A theoretical model
which predicts the susceptibility of a RAM cell to single event upsets from secondary
cosmic ray neutrons is presented. A previously unreported method for calculating the
collection efficiency term in the upset model has been derived along with an extension
of the model to enable estimation of multiple bit upset rates.
An Implantable Cardioverter Defibrillator is used as a case example to demonstrate
model applicability and test against clinical experience. The model correlates well with
clinical experience and is consistent with the expected geographical variations of the
secondary cosmic ray neutron flux. This is the first clinical data set obtained indicating
the effects of cosmic radiation on implantable devices. Importantly, it may be used to
predict the susceptibility of future implantable device designs to cosmic radiation.
The model is also used as a basis for developing radiation hardened circuit techniques
and system design. A review of methods to radiation harden electronics to single event
upsets is used to recommend methods applicable to the low power/small area
constraints of implantable systems