Fabrication of 3-dimensional structure of metal oxide semiconductor field effect transistor embodied in the convex corner of the silicon micro-fluidic channel

As micro-fluidic systems and biochemical detection systems are scaled to smaller dimensions, the realization of small and portable biochemical detection systems has become increasingly important. In this paper, we propose a 3-dimensional structure of a metal oxide semiconductor field-effect transistor(3-D MOSFET) using tetramethyl ammonium hydroxide (TMAH) anisotropic etching, which is a suitable device for combining with a micro-fluidic system. After fabricating a trapezoidal micro-fluidic channel, the 3-D MOSFET embodied in the convex corner of the micro-fluidic channel was fabricated. The length of the gate is about 20 μm and the width is about 9 μm. The depth and top width of the trapezoidal micro-fluidic channel are about 8 μm and 60 μm, respectively. The measured drain saturation current of the 3-D MOSFET was about -22 μA at V_GS = -5 V and V_Ds = -5 V, and the device characteristics exhibit a typical MOSFET behavior. Moreover, a gold layer was used for the MOSFET's gate metal to detect charged biochemical samples using the affinity between gold and thiol.