Xiaomei Yu

3-D microarrays biochip for DNA amplification in polydimethylsiloxane (PDMS) elastomer

Abstract In this paper, a rapid and low-cost fabrication technique for microarrays biochips is presented, and the fluorescence-based polymerase chain reactions (PCR) were performed in the chip for DNA amplification. The chip is consisted of 1064 column chambers. Each chamber has a volume of 25xa0nl, with the diameter of 460xa0μm and depth of 200xa0μm. The PCR chips were made of inexpensive silicone elastomer—polydimethylsiloxane (PDMS) and rapidly fabricated with micro-molding technique. The three-dimensional (3-D) PDMS replicas were molded directly from 3-D negative silicon master, which was fabricated by deep etching technique under the inductively coupled plasma (ICP) system. We demonstrated that the fluorescence-based PCR could be performed in the PDMS chip with nanoliter-volumes.

Design of High-Sensitivity Cantilever and Its Monolithic Integration With CMOS Circuits

Rectangular piezoresistive cantilevers with stress concentration holes opened were designed and fabricated in order to increase the response signals of piezoresistive cantilever first. Both the simulations and the measurements on the cantilever sensitivity show that this design can obviously result in an improvement on the displacement sensitivity of the piezoresistive cantilever. After a characterization study on the piezoresistive cantilever, a monolithic integration of the microcantilever array with a complementary metal-oxide-semiconductor (CMOS) readout circuitry based on the silicon-on-insulator (SOI) CMOS and the SOI micromachining technologies was designed. A cantilever array, a digital controlled multiplexer, and an instrumentation amplifier compose the integrated sensor system, and post-CMOS process was designed to fabricate the integrated system. The measurement results on the SOI CMOS circuitry of the integrated system prove a feasibility of the integration design

Design and characterization of high-sensitivity cantilevers

In order to increase the sensitivity of a cantilever-based biosensor, piezoresistive cantilevers with stress concentration holes were designed and fabricated. Firstly the stress distributions and the vertical displacements of the designed cantilevers were simulated through ANSYS analyzing system. Then the relative resistance changes of the piezoresistors as a function of the cantilever vertical displacements were measured. As expected, the stresses are highly concentrated for the designed cantilevers, and this design can obviously result in an improvement on the sensitivity of the surface-stress mode cantilevers

SOI-based capacitive micromechanical resonator with submicron gap-spacing

MEMS resonators are promising as micromechanical oscillators and filters in wireless communication systems. This paper reports on the fabrication and characterization of single crystal silicon (SCS) disk resonators with sub-micro capacitive gaps. Vertical capacitive gaps as small as 100nm have been demonstrated in this work. High frequency disk resonators have been implemented and tested.

Infrared enhanced absorption of TiN x nano films

In the design of infrared detectors, nano films are more and more frequently used to improve infrared absorption and mechanical sensitivity. In this paper, a Titanium nitride (TiNx) film was studied theoretically and experimentally as an infrared enhanced absorption layer. The TiNx films at two different thicknesses and in three different content ratios were deposited and infrared absorption experiments in the range of 8∼14µm were done. Experiment results show that the infrared absorbance is enhanced through depositing 5nm thick TiNx nano films on SiNx layer and the infrared absorbance of the films can be increased as the flow ratio of N2/Ar get increased.

Electric-field Assisted Immobilization and Hybridization of DNA Oligomers on Microcantilever Sensors

Gold-coated microcantilevers were used to develop sensitive micromechanical biosensor for detecting mismatch mutations in DNA hybrids. The selective 5-end immobilization of 25-mer single-stranded (ss) DNA probes to a gold-coated cantilever surface and the specific hybridization of ssDNA targets to the immobilized probe were performed by the direct electric field control. The controlled electric fields were used to regulate the transport of charged oligo-nucleotides. More than 70% of the immobilization and hybridization can be carried out in 2-3 seconds, and the detection rates are at least 102 times faster than in the passive control reactions performed without electric field

Monolithic integration of micromachined sensors and CMOS circuits based on SOI technologies

This note presents a novel way to monolithically integrate micro-cantilever sensors and signal conditioning circuits by combining SOI CMOS and SOI micromachining technologies. In order to improve the sensor performance and reduce the system volume, an integrated sensor system composed of a piezoresistive cantilever array, a temperature-compensation current reference, a digitally controlled multiplexer and an instrument amplifier is designed and finally fabricated. A post-SOI CMOS process is developed to realize the integrated sensor system which is based on a standard CMOS process with one more mask to define the cantilever structure at the end of the process. Measurements on the finished SOI CMOS devices and circuits show that the integration process has good compatibility both for the cantilever sensors and for the CMOS circuits, and the SOI CMOS integration process can decrease about 25% sequences compared with the bulk silicon CMOS process.

Study on Infrared Absorption Characteristics of Ti and TiNx Nanofilms

Infrared detector has a wide range of applications. To fabricate an IR detector with good sensitivity, an efficient IR absorber is needed. In this paper, we theoretically and experimentally investigated the absorption characteristics of Ti, multi-layer structured Ti-SiO2 and TiNx-SiNx nano films. The multi-layer structured TiNx-SiNx films with different nitrogen contents and Ti nano films with different thicknesses were deposited by ebeam sputtering. Their IR absorption characteristics were investigated by Fourier Transform Infrared Spectrometer. For single nano Ti film, 35% absorptivity was obtained at a wavelength of 1.67μm when the film thickness was 15.3nm. A better IR absorption characteristic was achieved for multi-layer structured Ti-SiO2 nano film. In this structure, an absorption peak of appears at a wavelength of 9.5μm. Compared with the absorption behavior of single SiNx film, an additional nano TiNx film obviously improved IR absorption at a wider band. And a maximum IR absorptivity of 27% was obtained at the wavelength of 14μm.

Study on infrared absorption of tungsten nanofilms

Thin metallic films have several potential applications in MEMS field, and one of them is used as infrared absorber. In this paper, we first build a model of metallic infrared absorption and then discuss the transmission characteristics of infrared through metal and dielectric film. For a thin film material, the maximum absorption will occur when its sheet resistance equals to the impedance of free space. In order to verify the absorption property, tungsten (W) nanofilms with different thicknesses have been deposited and their characteristics of infrared absorption were experimentally studied. The infrared absorbance of W nanofilms increased as the thickness of the films increased; more than 50% IR radiation could be absorbed by W nanofilms at the wavelength of 8-12 μm.

Micro-jet Pump for Micro-fluidic Systems

A novel micro-jet pump based on the principle of macroscopic jet pump are presented. The micro-jet pump can be used very easily for sampling in micro-fluidic systems under gas actuation. Vacuum suction mode provided by the pump can effectively decreases the formation of air bubbles and overcomes the interface tension between the liquid and solid wall in the micro-fluidic systems. Structurally the pump consists of a nozzle, a throat pipe and a pump chamber, which can be fabricated by means of silicon micro-machining technology. To obtain optimized parameters for the future designs, various pump configurations with different geometries were simulated through FLUENT, and the characteristics of the gas-actuated micro-jet pump was studied experimentally. The pump began to work at a threshold gas actuation pressure of 2 kPa, which can be realized easily by a medical syringe.