University of Twente Student Theses


Simplified trench-assisted surface channel technology for high-temperature microfluidics

Hoeven, S. (2022) Simplified trench-assisted surface channel technology for high-temperature microfluidics.

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Abstract:The Surface Channel Technology platform which is used for the fabrication of free-hanging microfluidic channels was advanced into newly technologies with integrated electrodes inside the bulk. This integration of electrodes leads to an improvement in design possibilities and functionalities. One promising solution for realizing this is called Trench-Assisted Surface Channel Technology. This technology enables the integration of highly-doped silicon sidewall heating elements parallel to the channel, whilst maintaining design freedom for microfluidic channel dimensions and for the placement of sensing elements. However, realizing actual devices with this technology is labour-intensive and requires hands-on skills. Due to the many micro-fabrication steps (>300), often complex optimization of problems was required. Together with problems in the release etch step, this called for the development of a new technology. Therefore, in this work, a simplified Trench-Assisted Surface Channel Technology is presented. This technology is developed to realize a simpler yet still effective method to create highly-doped silicon sidewall heating elements, with a large cross-sectional area and parallel to the channel. This new technology introduces a novel way of creating pyramid-shaped vias to the microfluidic channels. The vias are formed simultaneously with the release of the microfluidic channels from the bulk silicon, leaving only a small membrane behind. This membrane ensures full enclosure of the microfluidic channels during and after the final release step. Therefore, this approach enables the usage of wet etching in KOH solution, since the contamination of residual insoluble floccules inside the microfluidic channels is avoided this way. After all the micro-fabrication steps are completed, the membranes can be punctured manually creating the final access to the outside world. The main limitation of this simplified Trench-Assisted Surface Channel Technology showed to be a limitation for the electrode orientation, which can only be formed alongside the Si h110i directions on a Si {100} wafer. Any deviation from this angle will result in significant undercutting of the silicon heaters. However, by optimizing the mask windows and etch times, this undercutting of the heaters can be minimized. Another limitation is the formation of residual silicon on the outer walls of the trenches. Also, from the fabrication, it became clear that V-grooves on the surface of the wafer should be minimized, as this can make successive lithography steps problematic. This can be resolved by avoiding complex trench junctions and by using tapered T-junctions. Overall, this simplified Trench-Assisted Surface Channel Technology proved to be a simpler alternative to the existing Trench-Assisted Surface Channel Technology. This new technology can therefore be used to realize SCT-based devices, such as the Coriolis mass-flow sensors or Wobbe-index sensors. However, the performance of devices realized with this new technology has not yet been tested.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology, 58 process technology
Programme:Electrical Engineering MSc (60353)
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