The fabrication and characterization of a novel co-planar humidity sensor based on organic semiconducting material, vanadyl phthalocyanine (VOPc), is presented in this paper. Here we examine the effect of different humidity conditions on the capacitive and resistive response of VOPc thin films in the Al/VOPc/Pt co-planar structure. The two asymmetric electrodes, aluminum (Al) and platinum (Pt), were deposited through the photolithography technique. Thin films of VOPc were spun-cast on the glass substrate with primarily deposited asymmetric metal electrodes, from a solution of 30 mg ml−1 in chloroform at 3000 rpm. The gap between the electrodes was 17 µm. A 100-fold increase was observed in the capacitance of the VOPc sensing material with an elevation of relative humidity level. The resistance of the sensor reduced from 2.9 GΩ to 2.1 MΩ with increasing level of humidity. The VOPc thin film has been analyzed by x-ray diffraction as well as atomic force microscopy in order to get structural and morphological information on the sample. Adequate sensing properties such as enough sensitivity, good selectivity, linearity and reasonable response and recovery times have been obtained. The humidity-dependent properties of the sensor make it a good match for its potential application in commercial hygrometers.

This paper presents simple and economical, yet reliable techniques to fabricate a micro-fluidic filter for MEMS lab-on-chip (LoC) applications. The microporous filter is a crucial component in a MEMS LoC system. Microsized components and contaminants in biological fluids are selectively filtered using copper and silicon membranes with precisely controlled microsized pores. Two techniques were explored in microporous membrane fabrication, namely copper electroplating and electrochemical etching (ECE) of silicon. In the first technique, a copper membrane with evenly distributed micropores was fabricated by electroplating the copper layer on the silicon nitride membrane, which was later removed to leave the freestanding microporous membrane structure. The second approach involves the thinning of bulk silicon down to a few micrometers thick using KOH and etching the resulting silicon membrane in 5% HF by ECE to create micropores. Upon testing with nanoparticles of various sizes, it was observed that electroplated copper membrane passes nanoparticles up to 200 nm wide, while porous silicon membrane passes nanoparticles up to 380 nm in size. Due to process compatibility, simplicity, and low-cost fabrication, electroplated copper and porous silicon membranes enable synchronized microfilter fabrication and integration into the MEMS LoC system.

Screen printing is a known method to produce disposable and low-cost sensors. Depending on the application such as food analysis, environmental health monitoring, disease detection and toxin detection, screen-printed electrodes can be fabricated in a variety of sizes and shapes. Modification of the electrode's material and geometrical dimension may be done to produce effective screen-printed three-electrodes system. Thus, the effects of varying the working electrode (WE) area in radius of 0.9 mm to 2 mm, gap spacing between electrodes ranging from 0.5 mm to 1.6 mm, and the width of the counter electrode in range of 0.7 to 1.3 mm on sensor's performance was investigated in this study through COMSOL simulation. It was found that the modification of the working electrode radius and the gap between the electrodes has the most significant effect on sensor's performance, while modifying the width of the counter electrode (CE) shows no significant effect. Sensors with 0.9 mm radius or 2.54 mm² WE area and 0.5 mm gap spacing has shown the optimum performance with 0.026 A/m² current density which is contributed by 0.044 pF capacitance value. As a conclusion, regardless of the width of counter electrodes, a smaller gap between electrodes and a smaller working area would lead to optimal performance of a screenprinted three-electrode sensor system.

A Dissolved Oxygen (DO) sensor has been designed and fabricated on an 8.5 x 22.5 mm Alumina substrate using thick film technology. The structure of the sensor device consisted of AgPd working/counter electrode, Ag/AgCl reference electrode, RuO2active layer, KCl electrolyte, and TiO2membrane. Formation of the Ag/AgCl reference electrode was done by chlorination of Ag layer using FeCl3, and the TiO2membrane was formed by screen printing of TiO2paste. Measurement was done to study the sensor’s performance based from the current-voltage characteristics between 1.1 – 1.6 V. The results showed that a stable diffusion current was obtained when the input voltage was 1.4 V, resulting in the best sensor performance with a sensitivity of 0.560 μA l/mg and a stable step response time of 4 min. The device showed highly potential to be used as candidate for online water quality monitoring system.

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