This project details three derivatives of a fabrication process that gives the MEMS engineer increased freedom when designing planar microfluidic systems. This new family of processes was developed to laterally etch microfluidic channels in silicon and can be used to place an orifice (the “hole-in-the-wall”) in the center of the sidewall of a channel, Fig. 1.1. This creates improved valve seat geometry and has been used to create planar silicon microvalves that seal three orders of magnitude better than previous planar microvalves designs [1]. Planar valves are the current weak link in microfluidic systems and these new processes are the first of their kind to allow for the creation of functional, useful systems that take advantage of the simplicity inherent in planar design.
An overview is given for the three planar valve processes developed prior to this work for acknowledgement and comparison [2, 3, 4]. Each of these early versions creates a valve-seat geometry that does not address leakage above and below the gate. This causes a significant reduction in the sealing of the valve and is the most significant reason that usable planar valves have yet to be integrated with well-characterized planar mixers and assays to form microfluidic systems.
The ability for these new “hole-in-the-wall” processes to laterally etch silicon solves the problem of leakage over and under the gate of a microvalve [5]. Every new process derivative described here has attributes that make each more suitable for a specific set of applications but all stand to reduce the leakage through planar gate valves by producing an improved valve seat. Experimental verification and analysis are presented for two of the cases while the third is postulated. Design rules for each are given.