Shaofeng Chen

Design and testing of a micromechanical resonant electrostatic field sensor

The design, fabrication and characterization testing of a high-performance micromechanical resonant electrostatic field sensor at low driving voltages is presented. Structures including sensing electrodes, shielding electrodes and suspension beam design are discussed. The electromechanical behavior around the resonant frequency is described by an equivalent electric circuit to predict the output characterization of the sensors. The device is fabricated by a surface micromachining process. With low driving voltages compared with other reported devices, the electrostatic field sensors (EFS) have a resolution of 200 V m−1, the best reported figure for a MEMS-based device used in ambient air at room temperature. A nonlinearity of 1.8% (end-point-straight-line) in a measurement range of 0–10 kV m−1 is achieved. We have also achieved an uncertainty of 4.62% for the measurement data.

Design and simulation of miniature vibrating electric field sensors

This paper presents the designs and optimizations of two kinds of novel miniature vibrating electric field sensors (EFS) based on microelectromechanical systems (MEMS) technology. The two kinds of new sensors have different structures and vibrating methods. The volume of the new sensors with operating principle of electron charge induction are much smaller than other types of charge-induced EFS such as field-mills. In miniaturizing, the signal is reduced enormously and a highly sensitive circuit is needed to detect the signal. Elaborately designed electrodes can increase the amplitude of the output current, making the detecting circuit simplified and improving the signal-to-noise ratio. Therefore, computer simulations for different structural parameters of the EFS and different vibrating methods have been carried out by the finite element method (FEM). It is proved that the new sensor structure can be implemented and the signal is measurable.

A micro amperometric immunosensor based on two electrochemical layers for immobilizing antibody

A micro amperometric immunosensor with a novel antibody immobilization scheme has been developed to detect human immunoglobulin G (HIgG). The microsensor was fabricated using standard silicon micromachining technique, with the sensitive area of only 2 mm2 . A double exposure of SU-8 photoresist process was developed to create both the sensor pool and reaction pool. Antibody was immobilized using two-layer electrochemical polymers. Firstly polypyrrole was electropolymerized on the electrode as the transition layer. Then antibody and poly o-phenylenediamine were electropolymerized. This is a fast and simple method to immobilize antibody and is the first time to be used in amperometric immunoassay. At working potential of -0.3V, the immunosensor displayed a good linear dose-response behavior for HIgG concentrations between 5 and 355ng/ml. The response time was about 5 minutes

A novel miniature interlacing vibrating electric field sensor

The miniature electric field sensor (EFS) presented in this paper consists of substrate, driving structure, shielding electrode and sensing electrode. Compared with its counterparts based on perpendicular and parallel vibrating structures driven by electric force with large driving voltage, the EFS, which employs a novel interlacing vibrating and sensing mode, increases the sensing signal remarkably. By employing piezoelectric ceramics driving structure, we realized a large displacement of the shielding electrode with a lower driving voltage of 2V, therefore reducing the crosstalk significantly. The experimental results show that the novel EFS has good dynamic stability, high S/N ratio and fine resolution of 100 V/m

A silicon-based bulk micro-machined microelectrode biosensor with SU-8 micro reaction pool

A new silicon-based amperometric microelectrode biosensor made with bulk micromachining technology is provided. We designed this new biosensor and fabricated it with anisotropic silicon wet etching technique. P-type silicon wafers, Au and SU-8 are used for making substrate, microelectrode and micro reaction pool respectively. To our knowledge, consecutive platinization and polymerization of pyrrole is firstly used consecutively for microelectrode surface modification. The sensor aims for low unit cost, small dimensions and compatibility with CMOS technology. SU-8 micro reaction pools are made to contain detection solution to reduce reagent volume and unit cost. Bulk micromachining, platinization and polymerization of pyrrole enhance sensitive coefficient, thus helping to miniaturize its dimensions and to reduce unit cost. Using p-type silicon wafers as substrates make compatibility with CMOS technology possible. Successful experimental results have been achieved for glucose detection. Compared to conventional amperometric biosensors and amperometric microelectrode biosensors made with surface micromachining technology, it has several advantages, such as smaller sensing surface area (1 mm /spl times/ 1 mm), lower detection limit (1/spl times/10/sup -4/ M), larger sensitive coefficient (39.640 nA mM/sup -1/ mm/sup -2/), broader linear range (1/spl times/10/sup -4/-1/spl times//sup -2/ M), better replicability (3.2% RSD for five respective detections) and stability (enzyme efficiency remains well above 95% after being stored for a month), easier to be made into arrays and to be integrated with processing circuitry, etc.

Thernally Driven Miniature Electric Field Sensor

A thermally driven miniature electric field sensor (MEFS) has been designed, fabricated and tested. It is mainly comprised of shielding electrodes, bent beam thermal driver, positive and negative sense electrodes and drive pads etc, the shielding electrodes are driven by a cascaded bent beam thermal driver to periodically cover or expose the positive and negative sense electrodes. The thermally driven MEFS has the advantage of small size, light weight, low driving voltage, easy to integrate with circuits, low drive-signal cross talk noise etc. When activated with a square wave of plusmn2 V amplitude at a frequency of 20 kHz, the electric field strength resolution of the thermally driven MEFS can reach 105.8 V/m when the electric field strength is over 20000 V/m, but its output sensitivity will decrease when the electric field strength goes down from 20000 V/m. We will improve the low electric field sensitivity in our future work

A Micro Amperometric Immunosensor Based on Protein A/Gold nanoparticles/Self-assembled Monolayer-Modified Gold Electrode

A novel amperometric immunosensor fabricated by microelectromechanical systems (MEMS) technology with a novel modified procedure for immobilization of antibody on gold electrode has been developed. Based on MEMS technology, immunosensor with a three-microelectrode system integrated with two SU-8 micro pools was fabricated. Employing self-assembled monolayers technique, the working electrode was modified by 1,6-hexanedithiol to assemble gold nanoparticles layer, subsequently, a layer of protein A was immobilized on nanogold layer to further capture antibody. Compared with the amperometric immunosensors using traditionally metal rod/slice electrode or screen-printed electrode, it has attractive advantages, such as miniaturization, compatibility with CMOS techniques and easy to be designed into micro array. Moreover, the studied immunosensor showed high specificity, good reproducibility and broad linear range for the detection of human immunoglobulin (HIgG), which makes it potentially attractive for clinical immunoassays

Fabrication of silicon-based bulk micro-machined amperometric microelectrode biosensor

A new silicon-based bulk micro-machined amperometric microelectrode biosensor, especially its fabrication, is provided. We designed the biosensor and fabricated it with anisotropic silicon wet etching. P-type silicon wafers are used as substrates, and Au and SU-8 are used for making electrodes and micro reaction pools, respectively. To our knowledge, consecutive platinization and polymerization of pyrrole is firstly used for surface modification. Successful experimental results have been achieved for glucose detection. It has several advantages, such as smaller sensitive surface area (1 mm/spl times/1 mm), lower detection limit (1/spl times/10/sup 4/ M), broader linear range (1/spl times/10/sup -4/ -1/spl times/10/sup -2/ M), larger sensitive coefficient (39.640 nA/spl middot/mm/sup -2//sub /spl middot//mM/sup -1/), better replicability (RSD 3.2% for five respective detections) and stability (sensitive coefficient remains well above 95% after being stored in a clean container at room temperature for a month), easier to be made into arrays and to be integrated with processing circuitry, etc.

Self-assembly of micro parts on normal glass substrate

Abstract Fluidic self-assembly is an approach by which micro parts less than one millimeter in size can be driven by the capillary force of a certain adhesive liquid and be fixed onto the desired sites on some substrates. Normal glass with the composition of Na2SiO3CaSiO34SiO2 has been widely used in fluidic microelectromechanical systems (MEMS) and bio-MEMS devices. We investigate the MEMS self-assembly experiment on normal glass substrate. The results of scanning electron microscopy (SEM) show that micro-parts of 400 μm × 400 μm squares can be precisely assembled in the expected area of the normal glass substrate.

RESEARCH ON BULK MICRO-MACHINED MICROELECTRODE BIOSENSOR

A new silicon-based amperometric microelectrode biosensor produced using bulk micromachining technology is presented here. Bulk micromachining, platinization and polymerization of pyrrole enhance sensitive coefficient, thus helping to miniaturize its dimensions and reduce unit cost. To our knowledge, platinization and polymerization of pyrrole is first used consecutively for microelectrode surface modification. Successful experimental results have been achieved for glucose detection. Compared to conventional amperometric biosensors and amperometric microelectrode biosensors made with surface micromachining technology, it has several advantages, such as smaller sensing surface area (1 mm × 1 mm), lower detection limit (1×10-4M), larger sensitive coefficient (39.640 nAmM-1mm-2), broader linear range (1 × 10-4-1 × 10-2M), better replicability (3.2% RSD for five respective detections) and stability (enzyme efficiency remains well above 95% after being stored for a month), easier to be made into arrays and to be integrated with processing circuitry, etc.