Introduction - Digital Microfluidic Biochips - page 3

synthesis tool in [20] focuses only on compact designs, and it is prone to gen-
erate synthesis results with no feasible droplet-routing pathways. Moreover,
most designs resulting from [20] lead to a large number of control pins that
require expensive multilayer PCB technology. Furthermore, the test methods
in [20] do not address many realistic defects. As a result, the design tools pre-
sented in [20] are only of a conceptual nature, and they cannot be directly
used for chip design in practice. Finally, since testability is ignored during
chip design in [20], the test methods described in [20] are not always effective
for fabricated biochips.
This topic is focused on application-guided design automation tools that
address practical issues such as defects, routability, and fabrication cost. The
goal is to provide the means for the automated design and use of robust,
low-cost, and manufacturable digital microfluidic systems. A unified synthe-
sis tool that incorporates defect tolerance and droplet routing is developed.
Effective metrics are introduced and used to estimate the complexity of rout-
ing and system robustness of chip designs. Based on estimation results, the
unified synthesis tool uses a parallel recombinative simulated annealing
(PRSA) algorithm to search for robust and easily routable chip designs in the
candidate design space.
To reduce fabrication cost, pin-constrained design methods are presented to
reduce the number of control pins in microfluidic arrays. The first method is
based on droplet-trace-based array partitioning. It uses the concept of “droplet
trace,” which is extracted from the scheduling and droplet-routing results pro-
duced by the synthesis tool. An efficient pin-assignment method, referred to as
the “Connect-5 algorithm,” is combined with the array-partitioning technique
to address electrode arrays with a limited number of control pins. A second
pin-constrained design method targets a “cross-referencing” chip, which
allows the control of an N × M grid array with only N + M control pins. An
efficient droplet manipulation method is presented to achieve high through-
put on such cross-referencing chips. Finally, a broadcast-addressing-based
design method is described to reduce the number of control pins. This method
relies on the grouping of electrodes with compatible actuation sequences and
addresses these electrodes using a single control pin.
This topic also includes fault models for digital microluidics based on
observed defects in fabricated chips. A parallel scan-like method is presented
for efficient structural testing of digital microfluidic arrays. This method
relies on concurrent manipulation of multiple test droplets for target array
traversal. A comprehensive functional test method is described to verify the
correct operation of functional units. The proposed method provides func-
tional test techniques to address fundamental biochip operations such as
droplet dispensing, droplet transportation, mixing, splitting, and capacitive
sensing. For each operation, functional testing is carried out using parallel
droplet pathways, and it leads to qualified regions where synthesis tools can
map the corresponding microfluidic functional modules.