Heavily-Doped Bulk Silicon Sidewall Electrodes Embedded between Free-Hanging Microfluidic Channels by Modified Surface Channel Technology

Abstract

Surface Channel Technology is known as the fabrication platform to make free-hanging microchannels for various microfluidic sensors and actuators. In this technology, thin film metal electrodes, such as platinum or gold, are often used for electrical sensing and actuation purposes. As a result that they are located at the top surface of the microfluidic channels, only topside sensing and actuation is possible. Moreover, in microreactor applications, high temperature degradation of thin film metal layers limits their performance as robust microheaters. In this paper, we report on an innovative idea to make microfluidic devices with integrated silicon sidewall electrodes, and we demonstrate their use as microheaters. This is achieved by modifying the original Surface Channel Technology with optimized mask designs. The modified technology allows to embed heavily-doped bulk silicon electrodes in between the sidewalls of two adjacent free-hanging microfluidic channels. The bulk silicon electrodes have the same electrical properties as the extrinsic silicon substrate. Their cross-sectional geometry and overall dimensions can be designed by optimizing the mask design, hence the resulting resistance of each silicon electrode can be customized. Furthermore, each silicon electrode can be electrically insulated from the silicon substrate. They can be designed with large cross-sectional areas and allow for high power dissipation when used as microheater. A demonstrator device is presented which reached 119.4 ∘ C at a power of 206.9 m W , limited by thermal conduction through the surrounding air. Other potential applications are sensors using the silicon sidewall electrodes as resistive or capacitive readout.

μ-Coriolis Mass Flow Sensor With Differential Capacitive Readout

“…If the combs are further away from each other, the relation between capacitance and deflection is linear for a larger range of deflection. Another option is to develop a differential readout based on strain gauges on top of or embedded in the micro-channel [20], [22]. These would suffer less from non-linearity issues than the current capacitive readout structures.…”

Synthesis and Characterization of Boron Thin Films Using Chemical and Physical Vapor Depositions

“…The results described in this work demonstrate that PECVD boron films can be patterned with UV-lithography, dry plasma etching, wet etching (BHF) and the structured film can subsequently be used as a hard mask in an alkaline etch solution by means of which the underlying silicon substrate is selectively structured. These results hold promise for novel surface and bulk micromachining applications, and-upon proper embedding in fabrication processes-PECVD boron thin films may find their use as structural material, hard mask, sacrificial layer, functional film mask and/or boron source in (the realization of) applications such as cantilevers [72], hinges [73], pellicles [41], membranes [74], 3D micro electrode arrays [75], MEMS-based structures [76,77], crystalline silicon nanowires [78,79] or p/n junctions [80,81].…”

An Energy Efficient Thermally Regulated Optical Spectroscopy Cell for Lab-on-Chip Devices: Applied to Nitrate Detection

“…Here, we improve the energy efficiency of thermally regulated optical cells by incorporating on-chip insulation. Prior work by Zhao et al [ 30 ] and Dijkstra et al [ 31 ] showed that a suspended microfluidic channel surrounded by an air cavity can be used to efficiently couple thermal energy into a fluid. For example, the system presented by Zhao et al was able to heat a suspended microfluidic channel to 119.4 °C using only 206.9 mW [ 30 ].…”

“…Prior work by Zhao et al [ 30 ] and Dijkstra et al [ 31 ] showed that a suspended microfluidic channel surrounded by an air cavity can be used to efficiently couple thermal energy into a fluid. For example, the system presented by Zhao et al was able to heat a suspended microfluidic channel to 119.4 °C using only 206.9 mW [ 30 ]. Such suspended structures have been utilized as flow sensors by either measuring temperature deviation in the insulated channel [ 31 ] or vibrations caused by µ-Coriolis effects [ 32 ].…”