Building EWOD microfluidic array technology on top of foundry CMOS

This paper discusses the main issues associated with integrating electrode controlled droplet motion using electro wetting on dielectric (EWOD) with IC foundry technology. The motivation behind this approach is based upon the desire to increase the number of control electrodes, which requires the implementation of on-chip line-column microelectronics. Increasing the number of electrodes is attractive as it provides the opportunity to finely adjust droplet size, and also increases the number of droplets that can be individually moved simultaneously. The tradeoffs associated with minimising the drive voltage by appropriate choice of dielectric thickness, strength and permittivity, are discussed and examples presented of systems with the ability to move liquid droplets using voltages between 27 and 70V. A small electrode array has been designed using transistors with high voltage shields using a 100V CMOS process. This circuitry has been fabricated and can successfully apply 90V to the electrodes. The paper presents the considerations related to the chip design and the issues associated with EWOD post-processing and the microfluidic packaging requirements.