Introduction - Hardware/Software Co-Design and Optimization for Cyberphysical Integration in Digital Microfluidic Biochips - page 12

Fig. 1.9 Experimental setup for measuring the relationship between the volume of droplet and the
capacitance of the unit cell [ 30 ]

1.1.4 Fault Models

Catastrophic and parametric faults may occur in digital microfluidic systems, which
may affect the functionalities of the biochips [ 34 ]. Catastrophic faults may be
induced by the following physical defects:

• Dielectric breakdown: When a high actuation voltage is applied, a electrical

short between the droplet and the electrode may be created. As a result, no
charge can be accumulated at the interface between the droplet and the electrode.
As introduced in Sect. 1.1.1 , the electrowetting mechanism is depended on the
amount of energy stored in the capacitor formed by the electrode and the droplet.
Hence, when dielectric breakdown occurs, droplet will stick to the electrode.
Figure 1.10 shows a digital microfluidic biochip with dielectric breakdown
[ 34 , 35 ].

• Short between the adjacent electrodes: When an electrical short occurs between

two adjacent electrodes, the two electrodes effectively form one electrode with
longer length. As introduced in Sect. 1.1.1 , in order to move a droplet, the
droplet must contact electrodes that have different actuation voltages. If the
droplet that resides on the longer electrode is not large enough to overlap
the adjacent electrodes, the droplet cannot be moved [ 34 ].

• Degradation of the electrode: Degradation of electrodes is caused by their

repeated use. This degradation effect can become catastrophic during the opera-
tion of the system. Figure 1.11 shows the degradation of an electrode [ 34 ].