Biomedical Engineering Reference
In-Depth Information
The objective during reconfiguration is to minimize the bioassay com-
pletion time while accommodating all microfluidic modules and optical
detectors in the fabricated microfluidic array. As resource constraints, the
defect-free parts of the microfluidic array and the number of fabricated
fault-free nonreconfigurable resources replace the original design specifi-
cations. In the placement phase, the locations of the defective cells are no
longer available. Note that the locations of nonreconfigurable resources such
as integrated optical detectors and reservoirs/dispensing ports are fixed in
the fabricated biochip. Using this enhanced synthesis tool, a set of bioassays
can be easily mapped to a biochip with a few defective cells; thus, we do not
need to discard the defective biochip.
2.3.2 Presynthesis Defect Tolerance
In this subsection, we discuss defect-tolerant design, whereby we attempt
to provide guarantees on correct bioassay operation even if the manufactur-
ing process introduces defects. Instead of dealing with defects after they are
detected, we attempt to achieve defect-tolerant mapping of bioassay protocols
to the microfluidic array under broad assumptions of defect occurrences.
The synthesis method described in Section 2.2 suffers from two main draw-
backs. First, it does not anticipate defect occurrences, and it does not consider
defect tolerance in the synthesis flow. Instead, it relies on the availability
of unused cells in the microfluidic array to avoid defective cells, which are
detected after manufacture. However, such a resynthesis procedure might
not be feasible, because of lack of availability of spare cells. Moreover, the
impact on assay completion time might be significant, and the upper limit
on assay completion time might be violated. In such scenarios, the fabricated
biochip must be discarded. A second drawback of defect-oblivious synthesis
is that after defects are identified, the complete synthesis process must be
repeated. Thus, this approach imposes an additional computation burden on
the design and implementation process.
We next present a new method to incorporate defect tolerance in the unified
s y nt he si s flow for m ic r olu id ic bio c h ip s. A novel l pa r t i a l r e co n ig u rat io n me t ho d
is also presented to enhance defect tolerance after the device is manufactured.
2.3.2.1 Defect Tolerance Index
The defect tolerance of a synthesized biochip can be evaluated in terms of
survivability, that is, the capability to perform bioassays on a microfluidic
array with defects. The defect tolerance index (DTI) is defined as the prob-
ability that defect tolerance can be achieved via successful partial reconfigu-
ration when the array contains defective cells [36]. Partial reconfiguration
refers to the relocation of only the modules that contain defective cells;
other modules are not affected. The relocated modules, therefore, “survive”
through the defects
(see Figure 2.4)
.
