|dc.description.abstract||Investigations into single event effect (SEE)
induced charge collection in
Silicon Germanium (SiGe) heterojunction
bipolar transistors (HBT)
are made through three-dimensional (3-D) device simulation.
The transistor is constructed based on actual device.
The results indicate that collector-substrate (CS) junction plays an important role
due to the reverse biased CS junction.
Therefore by adding a dummy collector to the HBTs,
a recently published radiation hardening by design (RHBD) technique,
the total collector collected charge can be reduced due to
reduction of the diffusion charge collection at the intrinsic CS junction.
At present, the single event upset (SEU) sensitivity is primarily
characterized using the total amount of collector
charge collected during an ion strike.
This, however, may not be accurate,
as the contributions of different charge collection processes
are greatly influenced by external loading and the circuit topology.
The individual impact of
drift and diffusion charge collection
at the collector-base (CB)
and CS junctions
on SiGe HBT current mode logic (CML) circuit SEU
The CS junction diffusion charge
collection has negligible impact on circuit SEU,
despite its large charge
The CB drift charge collection is as important
as the CS drift charge collection,
even though its charge magnitude
is much less, because the
resulting current excitation
appears between collector and base nodes, and hence
Using selective ion track placement in 3-D simulations,
we further find that an ion track passing through the
physical CS junction is
much more effective in causing SEU than an
ion track not passing through the CS junction.
This is attributed to
potential funneling and consequent large induced
drift current magnitude, which is necessary
for SEU of CML circuit.
For emitter followers,
the conventional hardening
approach to minimize SEE
is using a higher emitter biasing current
as the emitter current determines output.
This, however, is shown to not work at all
with 3-D mixed mode simulations.
Instead, it is the CB junction charge collection
that dominates emitter output SEE,
because CB junction charge collection determines
the base voltage deviation,
and the emitter output follows the base deviation.
Therefore, the impedance and the electric field
across the CB junction are the most important
factors affecting emitter follower SEE.
From the simulation results,
the product of SEE induced base current and
the base biasing impedance
determines the amount of base voltage upset or deviation.
For base biasing impedance values found in practical circuits,
a smaller base biasing impedance should be used
to reduce emitter output voltage SEE,
as the emitter voltage upset tracks the base voltage upset.||en