Biomedical Engineering Reference
In-Depth Information
5
Design-for-Testability for
Digital Mic
roluidic Biochips
Testing is essential for digital microfluidic biochips that are used for safety-
critical applications such as point-of-care health assessment, air-quality
monitoring, and food-safety testing. Recent research work has proposed a
number of test methods for digital microfluidic biochips [28,34,36]. However,
due to the fact that current design methods do not consider testability, the
effectiveness of these test techniques is limited.
To tackle the preceding testability problem, we introduce the concept of
design-for-testability (DFT) for biochips. The motivation of DFT for bio-
chips is analogous to that for integrated circuits (ICs). In the early days of
IC design, chip area and performance were the primary concerns for chip
designers, and testing was only an afterthought. However, as chip com-
plexity increased, test problems were greatly exacerbated and DFT became
essential. Compared to the IC industry, digital microfluidics technology is
still in its infancy. However, tremendous growth has been predicted for this
technology, and biochips for clinical diagnostics and cell sorting are now
appearing in the marketplace [24,67]. As these devices become more com-
plex, the need for DFT will be increasingly felt.
In this chapter, we provide a DFT solution to facilitate the testing of digital
microfluidic biochips. We describe a test-aware design method that incor-
porates test procedures into the fluidic manipulation steps in the target bio-
assay protocol. By applying pin-constrained design to the testability-aware
bioassay protocol, the method ensures that the resulting chip layout sup-
ports the effective execution of test-related droplet operations for the entire
chip. Therefore, the proposed DFT method allows design of pin-constrained
biochips with a high level of testability with negligible overhead in terms of
the number of control pins and assay completion time.
5.1 Testability of a Digital Microfluidic Biochip
Most recently proposed methods assume that the chip under test is a rectan-
gular array controlled using a direct-addressing scheme; that is, each elec-
trode on the array is connected to an independent control pin. This method
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