Using microelectromechanical systems technology, a high-performance extended-gate field-effect transistor (EGFET)-based pesticide microsensor for organophosphorus and carbamate (CM) detection is developed. To minimize the whole pesticide-sensing system, we also integrated a planar Ti/Ag/AgCl/KCl-gel microreference electrode into the same silicon chip. The total dimensions of the proposed pesticide-sensing system are only 0.92 × 0.95 × 0.1 cm3. This EGFET-based microsensor for organophosphorus and CMs demonstrates extremely high sensitivity (194 and 268.1 mV/dec, respectively) and sensing linearity (0.993 and 0.974, respectively) and extremely low response time (120 and 300 s, respectively). The microsensor detection limit for both pesticides is 0.001 ppm.
We have developed an extended gate field-effect-transistor (EGFET)-based carbon dioxide (CO2) sensing system with a packaged Ti/Ag/AgCl/KCl-gel microreference electrode using microelectro-mechanical systems (MEMS) technology. The total dimensions of the proposed CO2 sensing system are only 2.8×1.5×0.1 cm, which is approximately 30 times smaller than a conventional CO2 sensing system (including the commercial Ag/AgCl RE). All of the manufacturing processes adopted in this work are compatible with standard planar technology and are very suitable for mass production. The presented planar reference electrode shows a very small offset voltage (−3.0 mV) and a very small potential drift (2.5 mV in 30,000 s) that is approximately equal to that of the commercial Ag/AgCl RE (1.6 mV in 30,000 s). Additionally, the implemented EGFET-based CO2 microsensor with a coated CO2 solid electrolyte and gas permeable membranes on the gate sensing area demonstrates a very high sensitivity (44.4 mV/decade) and very high sensing linearity (98.37%), while sensing CO2 concentrations ranging from 0.25 to 50 mM. Furthermore, a very small hysteresis voltage (7.5 mV) was obtained during the sensing cycle of 2.5–5–25–50–25–5–2.5 mM; this result was achieved by improving the surface planarization and enlarging the sensing area of the EGFET to 1 mm2.
A low-hysteresis voltage and high-sensing linearity chloride ion-sensitive sensor based on an extended gate field-effect transistor (EGFET) for real-time water quality monitoring microsystem applications is presented. All of the EGFET-manufacturing processes adopted in this work are compatible with standard integrated circuits planar technology, and therefore, they are very suitable for the mass production. Two EGFET-based chloride ion-sensitive microsensors having same channel width/length ratio (1000 μm/10 μm ) but with different channel geometries (rectangular and annular types) are presented. At pCl 3 (log[Cl − ]=−3 ) test point, a very small hysteresis voltage of the rectangular- and annular-channels EGFET-based Cl − microsensors (5 and 7 mV, respectively) can be achieved. As the concentrations tested ranging from pCl 1 (log[Cl − ]=−1 ) to pCl 5 (log[Cl − ]=−5 ), a very high-sensing linearity (99.23% and 99.08%) of the two types of EGFET-based Cl − microsensors is achieved. However, the sensitivity of the rectangular-channel EGFET-based Cl − microsensor (45 mV/pCl ) is much higher than that of the annular-channel EGFET-based Cl − microsensor (37 mV/pCl ). The selectivity coefficient of the investigated EGFET-chloride ion sensor under four different interfering ions (OH − , F − , SO 2− 4 , and Br − ) are also measured and analyzed.
A novel silicon groove reflective grating structure (RGS) to reduce effectively the insertion loss of a high C-axis (002) thin-film zinc oxide (ZnO) surface acoustic wave (SAW) device is proposed. The insertion loss (S 21 parameter) of three types of SAW devices was investigated and compared; one type had no RGS design, and the other two types had either a conventional metal electrode RGS or a novel etched silicon groove RGS. The wave propagation modes, the harmonic response, and the displacement amplitude profile of the proposed SAW devices were simulated by finite element analysis software (ANSYS). The implemented basic SAW device consists of a sputter-deposited high-quality ZnO thin film on the surface of a Si/SiO 2 /Si 3 N 4 /Cr/Au substrate. The insertion loss of the proposed SAW device with silicon groove RGS can be reduced to −19.49 dB , which is much smaller than the insertion losses of the SAW devices with a metal electrode-type RGS (−33.15 dB ) and without an RGS (−47.9 dB ). The resonant frequencies of the SAW devices studied (47.37 to 48.05 MHz) are in close agreement with the simulated results (46.8 to 47.55 MHz).
Conventional flexural plate-wave (FPW) transducers have limited applications in biomedical sensing due to their disadvantages such as high insertion loss and low quality factor. To overcome these shortcomings, we propose a FPW transducer on a low phase velocity insulator membrane (5-μm-thick SiO 2 ) with a novel groove-type reflective grating structure design. Additionally, a cystamine self-assembly monolayer and a glutaraldehyde cross-linking layer are implemented on the backside of the FPW device to immobilize alpha-fetoprotein (AFP) antibody. A FPW-based AFP biosensor with low detection limit (5 ng/mL ) can be achieved and used to measure the extreme low concentration of AFP antigen in human serum for early detection of hepatocellular carcinoma. The proposed FPW-based AFP biosensor also demonstrates a very high quality factor (206), low insertion loss (−40.854 dB ), low operating frequency (6.388 MHz), and high sensing linearity (90.7%).
We describe the development of novel suspension bridge-type microthermoelectric generators (μ -TEGs) having 64,000 to 147,000 serial-connected thermocouples in a 1-centimeter-square chip area using surface micromachining techniques. Each microthermocouple is constructed by a pair of n/p bridge-type polysilicon thin-film thermolegs and a pair of cold- and hot-side Cr/Au metal planes. Under a controlled fixed temperature difference between the cold/hot sides, the open-circuit voltage and the output power of the proposed μ -TEGs are simulated by commercial software (ANSYS). The influences of thermocouple thermo-leg dimensions and number of thermocouples on the thermoelectric characteristics of presented μ -TEGs are investigated. The implemented suspension bridge-type thermopile has a 2.5-μm-height air-gap separation from substrate and its fabrication yield is higher than 75% in the laboratory environment. The measured maximum temperature difference between the cold/hot sides of the proposed μ -TEGs is about 1.29°C, a maximum open-circuit voltage of 4.64 V/cm 2 and output power of 0.65 μW/cm 2 can be obtained.
To identify the extreme low concentration of alpha-fetoprotein (AFP) antigen in human serum for early detection of hepatocellular carcinoma, we aim to develop a high-sensitivity and low-cost AFP biosensor using quartz crystal microbalance (QCM) and cystamine self-assembly monolayer (SAM) technologies. In this study, the surface topographies of concentrations (0.1 and 1.0 mg/mL) of AFP antibody with and without 1.25% glutaraldehyde cross-linking layer will be analyzed by an atomic force microscope system to investigate the effects of the glutaraldehyde layer on the sensing characteristics of the QCM-based AFP biosensor. According to our experimental results, the mass sensitivity was improved almost doubly (from 0.07 to 0.146 Hz mL mg−1) as the glutaraldehyde layer was added between the 20-mM cystamine SAM and the low-concentration (0.1 mg/mL) AFP antibody. Either with or without the glutaraldehyde layer, higher mass sensitivity (0.163 to 0.335 Hz mL mg−1) was obtained as the AFP antibody concentration increased to 1.0 mg/mL. However, a large AFP antibody requirement will increase fabrication cost and limit disposable application. We also demonstrated that high sensing linearities (95.67 to 99.6%) of the QCM-AFP biosensors can be achieved without being obviously affected by the glutaraldehyde layer and AFP antibody concentration.
This study presents a polyimide (PI) self-assembly technique for developing a 3-D surface-micromachined structure. The effects of geometric factors and curing temperatures of PI elastic joints on the lifting angles of such 3-D microstructures are investigated. Under the optimized curing condition (380°C), a maximum 74-deg lifting angle of 5.2×10−11 kg-weight polysilicon microplate is achieved utilizing a large thermal shrinkage force of a single PI joint. Before severe cross-linkage occurred (curing at 390 to 400°C), the lifting angle of the thermally actuated 3-D microstructure is nearly in direct proportion to the length/width-thickness ratio of the PI joint (with linearity of 95.5%) and the difference between curing and room temperatures (with linearity of 92.3 to 97%). The PI-based self-assembly process is very suitable for mass production due to its high yield of fabrication (80 to 91.6%) and high compatibility with the present IC and MEMS manufacturing processes.
Although solid-state microreference electrodes (µREs) have been developed for electrochemical and biomedical sensing applications for more than one decade, there are very few studies devoted to improving their performance through packaging. Using planar technology and a silicon cap sealing method, we implement a packaged Ti/Pd/Ag/AgCl/KCl-gel µRE with a total dimension of only 9 mm (L)×6 mm (W)×1 mm (H), a hundredfold less than the commercial Ag/AgCl reference electrode (RE). Compared with the unpackaged µRE, the presented chip-level packaged µRE demonstrates many improved characteristics, including a very stable cell potential (5-mV drift voltage in 30,000 s), an approximately zero offset voltage (−7 mV), a very low impedance (1.50 k) and phase shift (8.98 deg) at 1-kHz operation frequency, a very small double-layer capacitance (0.04 µF), and a very high reproducibility (±3.1-mV).
This study presents a rotary micromotor with low-friction and large-step displacement driven by a scratch drive actuator (SDA) with bounceback driving mechanism. The present SDA device has a shorter plate and wider bushing compared to those of the existing SDA, resulting in a new electrostatic scratch-and-bounceback driving mechanism with larger stepping size. The new scratch-and-bounceback actuating mechanism markedly reduces the friction and damping effect between the SDA plate and the nitride insulator surface and eliminates effectively the sudden reverse rotation of SDA-based micro rotary motor. This investigation incorporated three design features (corners-rounded supporting-beam, flanged cover, and corrugated/ribbed/dimpled inside ring) into the structure of a SDA-based rotary micromotor to further decrease the rotating abrasion between the rotor inside ring and the cover, the anchor, and the inside rail. The bouncing SDA-based micromotors developed in this work (with 398 µm diam) were fabricated using the MEMSCAP® Poly-MUMPs process and achieved many improvements, including low friction, large stepping size (196 nm), small damping effect, and no sudden reverse rotation phenomenon (from dc to 25 kHz).
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