We have developed new microelectromechanical logic gate devices using microelectromechanical systems (MEMS) technology based on gold electroplating on a silicon wafer. Each device comprises a single cantilever and two or more electrostatic drive electrodes with an ohmic contact-pad for electrical fan-out. The results are read out as a voltage through a pull-down or pull-up resistor. Although most electronic transistor logic gates are composed of four transistors or more, the device used in this work was made with a single cantilever that could be tailored as various types of logic gates such as NOT, NAND, exclusive NOR (XNOR), and exclusive OR (XOR). For this reason, the scheme of the developed device offers scalability by which to reduce its footprint even further. The microelectromechanical operation of the logic was demonstrated and confirmed experimentally. These devices have potential as stable logic-memory circuits that could be used in harsh environments, such as in high-altitude space applications.

A solid-state impedancemetric CO₂ sensor consisting of perovskite-type oxide (La_1-xSr_xMnO₃) as receptor material and a Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) disc as solid electrolyte transducer was investigated for the detection of various concentrations of CO₂ at 400 ºC. The responses of the lanthanum manganite/LATP-based sensor were divided into a resistance component and capacitance component. The sensitivities to CO₂ were largely affected by the type of receptor material used. The La_0.4Sr_0.6MnO₃/ LATP-based impedancemetric sensor element showed potential CO₂ sensing properties.

Micro-thermoelectric coolers (µ-TECs) using thermoelectric materials n-type Bismuth Telluride (Bi₂Te₃), p-type Antimony Telluride (Sb₂Te₃), and Platinum Bismuth Telluride (Pt/Bi₂Te₃) composite are designed, and the fabrication process of the prototype is developed. A silicon cooling stage is supported by surrounding thermoelectric legs of the n-type and p-type materials. The thermoelectric films are grown by using electrochemical deposition because of the ability to deposit thick films and the compatibility with microfabrication process. Two types of specific designs with different numbers of thermoelectric legs are considered, and their individual performance is calculated using material parameters of the electrodeposited thermoelectric materials. The calculation shows 0.46-0.52 of the maximum coefficient of performance (COP_max) and 18-26 K of maximum cooling temperature under small current supply. Fabrication process for the chip-scale cooling device is thus developed.

Anisotropic wet bulk micromachining is one of the main techniques used in microelectromechanical systems to fabricate microstructures that have applications in sensors and actuators. Potassium-hydroxide-based and tetramethylammonium-hydroxide-based solutions are the most commonly used wet anisotropic etchants. However, the etch rate attainable using these conventional etchants is limited and, hence, affects industrial productivity. Alkaline solutions with some additives show improved etching characteristics. The addition of NH₂OH to pure alkaline etchant solutions increases etch rate significantly. The etch depth attained per unit time is more in these modified solutions compared with pure alkaline solutions. This can be exploited to make microstructures with low fabrication time and high productivity. In this work, a simple etching mechanism is proposed to explain silicon wet anisotropic etching in NH₂OH-added alkaline solutions. The mechanism is based on a two-step etching process: (i) oxidation and (ii) removal of Si atoms by water molecules. The initial oxidation step has two possible pathways: chemical and electrochemical oxidation. In the presence of alkaline solutions, NH₂OH gives NH₂O^- ions and H₂O molecules. Thus, NH₂O^- ions, OH^- ions, and H₂O molecules are the reactive species in the modified etchant solution. The aim of this work is to elucidate the detailed reaction mechanism in NH₂OH-added alkaline solution and highlight the reason behind the enhanced etch rate.

This paper reports an area-selective supercritical fluid deposition (SCFD) of Cu with supercritical CO₂ and H₂ reductant. We demonstrated an area-selective Cu SCFD on TiN pre-patterned over a SiO₂ underlayer on Si substrate. Atomic force microscopy and Auger electron spectroscopy were employed to characterize the fabricated samples. Several SCFD experiments revealed deposition dependence on the surface material as well as the proximity effect, which made the selective SCFD possible on pre-patterned metal surfaces over insulating underlayers.