Leslie Haworth

Test structures for characterising the integration of EWOD and SAW technologies for microfluidics

This paper presents details of the design and fabrication of test structures specifically designed for the characterisation of two distinct digital microfluidic technologies: Electro-Wetting On Dielectric (EWOD) and Surface Acoustic Wave (SAW). A test chip has been fabricated that includes structures with a wide range of dimensions and provides the capability to characterise enhanced droplet manipulation as well as other integrated functions. In particular, we detail the use of EWOD to anchor droplets while SAW excitation is applied to perform mixing.

The integration of EWOD and SAW technologies for improved droplet manipulation and mixing

This paper details the first reported integration of two advanced digital microfluidic technologies where 100 µm silicon cubes are transported with ElectroWetting On Dielectric (EWOD) and the droplet then held with EWOD while the silicon cubes are mixed with another liquid using a Surface Acoustic Wave (SAW). Together these two technologies provide a comprehensive lab-on-a-chip combination with well developed functionalities. These include droplet generation, splitting and transportation offered by EWOD with transportation, mixing and biosensing being potentially available with SAW. The fabrication of both EWOD and SAW structures on LiNbO3 substrates used low temperature Ta/Ta2O5/CYTOP layer deposition and patterning technologies, which enabled efficient transportation and mixing functions to be demonstrated.

Wireless driven EWOD technology for a MEMS pond skater

A silicon swimming robot or pond skating device has been demonstrated. It floats on liquid surfaces using surface tension and is capable of movement using electrowetting on dielectric (EWOD) based propulsion. Its dimensions are 6 times 9 mm with a thickness of 380 mum. The driving mechanism involves the trapping of air bubbles within the liquid onto the hydrophobic surface of the device with the subsequent ejection using a recently reported Ta2O5 EWOD technology. The required driving voltage of ~15 V is low enough for RF power transmission, thus providing wire-free movement. A wired version has been measured to move 1.35 mm in 168 ms (a speed of 8 mm s-1). This low-voltage EWOD device, fabricated using a CMOS compatible process, is believed to be the worldpsilas smallest swimming MEMS device that has no mechanical moving parts. The paper also reports results of EWOD droplet operation driven by wireless power transmission and demonstrates that such a wireless design can be successfully mounted on a floating EWOD device.

Test Structures for Characterizing the Integration of EWOD and SAW Technologies for Microfluidics

This paper presents details of the design and fabrication of test structures specifically designed for the characterization of two distinct digital microfluidic technologies: electro-wetting on dielectric (EWOD) and surface acoustic wave (SAW). A test chip has been fabricated that includes structures with a wide range of dimensions and provides the capability to characterize enhanced droplet manipulation, as well as other integrated functions. The EWOD and SAW devices have been separately characterized first of all to determine whether integration of the technologies affects their individual performance, including device lifetime evaluation. Microfluidic functions have then been demonstrated, including combined EWOD/SAW functions. In particular, this paper details the use of EWOD to anchor droplets, while SAW excitation is applied to perform mixing. The relationship between test structure designs and the droplets anchoring performance has been studied.

Array Based Test Structure for Optical-Electrical Overlay Calibration

The novel overlay test structure reported in this paper was purposely designed to serve as an application-specific reference material. It features standard frame-in-frame optical overlay targets embedded in electrical test features and fabricated by the same process as the parts being manufactured. Optical overlay is commonly used in process control applications due to its utility for determining the relative positions of features patterned in photoresist. Electrical overlay, although it can only be measured on fully patterned test structures, is the metric of interest. Using this combined optical/electrical overlay test structure, we can derive the relationship between the routinely measured optical overlay and the electrical overlay for any specific combination of process and optical overlay tool.

The use of cavities for gettering in silicon microelectronic devices

This paper presents results from an ongoing three-year project in which the use of microcavities to getter transition metal impurities in silicon-based microelectronic devices has been investigated. The paper reports on the results of a fundamental study of bubble growth mechanisms and on a systematic study of possible detrimental effects of cavity gettering on 1.2 μm p-type metal–oxide-semiconductor field effect transistors.