Biomedical Engineering Reference
In-Depth Information
the times for the different diagnosis iterations, which are 57, 44, 32, 16, 8, 4,
and 2 s, respectively. On the other hand, the parallel scan-like test can simply
determine the defect site from testing readouts. No additional diagnosis
steps are needed, and the diagnosis time is the same as the testing time, that
is, 44 s, which corresponds to a 75% reduction compared to [36].
4.5 Functional Test
Since complicated fluidic operations are repeatedly executed with high pre-
cision in compact microfluidic arrays, a group of cells is repeatedly required
to perform a large number of operations. Traditional structural test methods,
which use test droplets to traverse the target array, do not provide a sufficient
level of confidence that these fluidic operations can be reliably performed on
the array [28]. For instance, some unit cells, that is, electrodes, may function
correctly during droplet transportation, but they might malfunction during
droplet dispensing from reservoirs. Similarly, unit cells that can be reliably
combined to operate as a mixer may malfunction when they are used for
droplet splitting. Moreover, a structural test does not cover nonreconfigu-
rable modules such as capacitive sensing circuits. A defect involving any of
the modules may result in catastrophic failure during the bioassay execution.
Therefore, before we use synthesis methods to map bioassay protocols to a
microfluidic array [15], it is important to carry out functional testing to verify
the integrity of the underlying microfluidic platform. To ensure that manu-
factured biochips are competitive in the emerging low-cost market for dis-
posable biochips and to avoid electrode degradation resulting from excessive
actuation, test methodologies should be inexpensive, quick, and effective.
In this subsection, we first present various defects that are typical for digital
microfluidic biochips. We relate these defects to logical fault models that can
be viewed not only in terms of traditional shorts and opens but also target a
biochip's functionality. Based on these fault models, we introduce the idea of
functional testing of digital microfluidic modules. We develop cost-effective
functional test methods that target fluidic operations such as droplet dis-
pensing, droplet transportation, mixing, and splitting. These methods also
test the functionality of nonreconfigurable modules such as capacitive sens-
ing circuits. The proposed methods allow functional testing using parallel
droplet pathways in both online and off-line scenarios. For each function, the
proposed approach identifies “qualified regions,” that is, groups of cells that
pass the test. Instead of placing fluidic modules in a fault-oblivious manner
on the microfluidic array, synthesis tools can map modules only to qualified
regions. In this way, the reliability of the synthesized biochip is significantly
increased. The application of these methods to pin-constrained biochips is
