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This paper presents a micromachined in-plane tunable optical filter using the thermo-optic effect of crystalline silicon. The device was fabricated by a silicon deep reactive ion etching process with a silicon-on-insulator wafer and thermal oxide removal to improve the sidewall smoothness. Optical fibers could be horizontally aligned on the fabricated TOF device by exploiting in-plane device structures, which enable TOFs to easily connect with other optical components. Tunability of the TOFs was experimentally achieved through thermal modulation of optical path length by heating the silicon etalon. As the input voltage increases, a notch in the reflectance spectrum shifts to a longer wavelength with an average tuning sensitivity of 0.9 nm K−1 and a best bandwidth of 1.1 nm. The proposed device can be utilized for spectroscopy or optical communication.

This paper presents a novel fabrication method of scalloping-free and footing-free vertical electrodes for micromachined capacitive inclinometers with a high sensing resolution. The proposed fabrication method is based on additional crystalline wet etching of a (1 1 0) silicon that is bonded to a silicon substrate with a patterned insulator layer. The sensing electrodes, which are aligned to the (1 1 1) plane, have very smooth sidewalls because the morphological defects formed by the silicon deep reactive ion etching (DRIE) process are drastically reduced in the crystalline wet etching. The fabricated capacitive inclinometer with smooth sensing electrodes was evaluated in terms of capacitance change and resolution. The capacitance of the fabricated inclinometer is changed from −0.246 to 0.258 pF for the inclination angle (−90° to 90°). The temporal deviation of the capacitance is as small as 0.2 fF, which leads to a high resolution of 0.1° or less for ±45°.

This study presents a fabrication method of a mass-producible silicon nanowire (SiNW) using a (1 1 0) silicon wafer. Microscale silicon lines, patterned in standard photolithography, are reduced to 300 nm in width in a two-step wet-etching process. The silicon lines are transformed into the SiNW by a thermal oxidation process. The formation of SiNW after thermal oxidation was verified using a numerical oxidation simulation considering the two-dimensional growth of the oxide. After thermal wet oxidation at 970 °C for 50 min, silicon lines of 300 nm in width were transformed into the SiNWs of an inverse triangular cross-section with an effective width of approximately 70 nm. At the same time, the fabricated SiNWs were electrically isolated from the substrate without using an expensive silicon-on-insulator wafer. The pH sensing test, which is usually performed as a preliminary experiment for the biosensor applications, was conducted with respect to various pH solutions. The experimental sensitivity to the pH level was 0.55 nS pH−1, when the voltage applied to the SiNW was 1 V. The SiNW has been completely fabricated by using only a conventional semiconductor process instead of a costly and time-consuming e-beam lithography process for the nanoscale patterning. The proposed fabrication method was successfully confirmed to have the potential of mass-producible and cost-effective SiNW devices for nano-biosensor applications.