Jeongsik Sin

Reconfigurable micro-assembly system for photonics applications

The assembly of parts with dimensions several hundred microns or less is a challenging problem, and has received increasing attention for applications in areas such as telecommunication, automotive, and biotechnology. Current state of the art micro-assembly systems are often specialized devices and software. In this paper we present a reconflgurable assembly system designed to handle micro-parts in such a way that high precision actuation and sensing is used only in the subsystems where it is actually necessary. Aspects related to part gripping, fucturing, sensing, motion and bonding are discussed. Analysis and experiments are presented to show that this architecture can lead to a relatively low cost and flexible assembly solution.

On the precision alignment and hybrid assembly aspects in manufacturing of a microspectrometer

Microoptics is a fertile area for hybrid assembly of miniaturized components, due to the need to integrate different optical and actuation materials in a single precision bench. In this paper we discuss issues related to the assembly and alignment of a microspectrometer using 3D miniature non-silicon objects such as glass lenses, optical fibers, laser sources, and detectors onto silicon fixtures and microactuators. The resulting instrument, a fiber-coupled MOEMS spectrometer, requires high alignment precision, because it is based on interference fringes from a Michelson Interferometer bench. Our fiber-coupled Fourier-Transform microspectrometer has a nominal packaged size of 3 cm times 3 cm times 3 cm, and targets wavelengths in the visible and NIR spectra. We use modular microscale parts, including minimum energy compliant MEMS fasteners to configure a die-sized (1 cm times 1 cm times 0.5 cm) microoptical bench. We discuss the tolerance of this complex assembly, and present experimental results validating the automated assembly and alignment of the optical components on the microbench.

Assembled Fourier transform micro-spectrometer

Microassembly process plays a key role in building 3-dimensional heterogeneous microsystems. This paper presents a miniaturized Fourier transform spectrometer (FTS) implemented by combining silicon micromachining and microassembly techniques. The FTS is based on a Michelson interferometer where a scanning mirror mechanism creates an interferogram, and the recorded interferogram is converted to a spectrum by Fourier transform. The miniaturized Michelson interferometer is integrated on a microoptical bench, which is fabricated using Deep RIE (Reactive Ion Etching) process on a SOI (Silicon On Insulator) wafer. Key components of the FTS optical bench are a linear translation stage, mechanical assembly sockets, a beam splitter, and assembled mirrors. An electrothermal actuator with stroke amplification mechanisms provides the amplified scanning motion of a scanning mirror. The sockets are female mechanical flexure structures that allow a precise snap-fit assembly with micromachined silicon mirrors. The dimension of the FTS optical bench is 1cm2, and its embedded thermal actuator has a couple of V-beam structures whose beam length is 1mm. The mirrors are Deep RIE micromachined structures with reflection area 500x450μm2 and 750μm long flexure structures for pick & place assembly. The flexure structure allows large deflection so that a microgripper can pick up the mirror by inserting the gripper tip into the structure, and snap-fit assembles it into the mechanical socket of the bench. The linear translation stage generates up to 30μm scanning stroke at 22V input, which corresponds to a spectral resolution of 10nm at 775nm wavelength. While this microassembly method is designed to self-align the mirror in the socket, the mirror slightly tilts after assembly due to the slope of side wall of DRIE processed structures. The measured tilting angles of assembled mirrors range from -2.5° to 0.8° from several assembly trials. The tilting angle combined with beam divergence can cause the loss of power and resolution, spectrum shift and phase error. A He-Ne laser was used as a light source to create interferogram with the assembled microspectrometer. Formation of fringe patterns was successfully conducted with a prototype. Mirrors with a large tilting misalignment resulted in stripe pattern fringes, whereas an improved alignment generated circular pattern fringes. A detector was used to measure light power with respect to input voltage, and the displacement of a scanning mirror was measured and curve-fitted. The relationship between light power changes versus the displacement of a scanning mirror represents interferogram. Spectrum profiles showed a peak around 632nm with FWHM (Full Width Half Magnitude) 25nm approximately. While further research is on going to improve spectrum quality and microassembly technique for the integration of various components with heterogeneous materials and shapes, this approach is expected to facilitate the design and manufacturing of MOEMS from the constraints of micromachining processes.

An Infant Monitoring System Using CO/sub 2/ Sensors

In this paper, we proposed an infant monitoring system to reduce the potential risks for sudden infant death syndrome (SIDS). This system can be used for infants at home or in a hospital nursery room. The system consists of carbon dioxide (CO2 ) sensors and active radio frequency identification (RFID) technology. A commercial metal-oxide based CO2 sensor was chosen and characterized in sensitivity, selectivity and humidity dependence. A proof-of-concept system, to be used for two infants in the same room, was designed and assembled. The RFID transmission was accomplished with a wireless module at two different operating frequencies. The results are promising. A method for further practical applications in a large nursery room is also discussed in details in this paper.

Evaluation of commercial metal‐oxide based NO2 sensors

Purpose – Selection of a gas sensor requires consideration of environmental effects that can significantly affect performance and cause false alarms. Metal‐oxide sensors have high sensitivity due to the specific interactions of gas molecules with thin metal‐oxide films, however, the films can also be sensitive to variations in temperature and humidity and some oxidizing and deoxidizing gases. The purpose of this paper is to evaluate the environmental effect on metal‐oxide nitrogen dioxide (NO2) sensors quantitatively.Design/methodology/approach – Three commercial metal‐oxide NO2 sensors and one electrochemical sensor were tested simultaneously under controlled gas concentrations and various environmental conditions. For this test, a customized sensor testing setup was prepared including a gas mixer, heating module, gas chamber, electronics, and data acquisition units.Findings – Based on the test results for NO2 gas concentrations ranging from 0 to 10 ppm, the metal‐oxide sensors showed significant signal ...

BCB wafer bonding for microfluidics

In this paper we show that BCB wafer bonding, combined with deep-reactive-ion-etching (DRIE) for silicon, and HF etching for FOTURAN glass are viable methods to fabricate three-dimensional microfluidics. The BCB film is patterned by dry-etching technique with a photoresist mask and the target wafer is then bulk-micromachined together with the BCB mask. The two micromachined wafers are then bonded together under vacuum or nitrogen gas environment, at low temperature. Silicon-glass, silicon-silicon and glass-glass are all possible bonding pairs using thermocompressive bonding with BCB. It was found that hard-cured BCB bonding is more suitable for microfluidic channel fabrications than soft-cured BCB bonding, due to adhesive overflows in microfluidic channels and delamination during wet etching.

M3-Modular Multi-Scale Assembly System for MEMS Packaging

This paper presents recent results in prototyping of a multiscale (macro-micro) robotic assembly platform with modular and reconfigurable characteristics. The system components include precision robots, microstages, end-effectors and fixtures that accomplish assembly tasks in a shared workspace. The system components are systematically characterized in terms of accuracy and repeatability, and assembly plans are performed using kinematic identification, visual servoing, inverse kinematics, and dynamic vibration suppression. As an application packaging problem, various micro and meso scale parts are assembled into a MEMS device. The tolerance budget of assembly ranges from 4 microns to 300 microns, while the size of components in the assembly ranges from 126 microns to 30 mm. Various end-effectors and fixtures have been designed for use with off-the-shelf hardware (robots and microstages) and were tested for precision performance. The robots and the vision system are calibrated to accuracies of 10 microns or less. Inverse kinematics solutions for the robots have been developed in order to position parts in a global coordinate frame. Conclusions are drawn about implementation of calibration, fixturing and visual servoing in order to assemble within the specified tolerance budget

Electro-Thermal Analysis of In-Plane Micropump

This paper describes the modeling for a packaged in-plane micropump developed at the Automation and Robotics Research Institute, The University of Texas, Arlington, TX. Amongst the family of micro-electro-mechanical system (MEMS) devices, thermal actuators are important owing to their capability to deliver a large force and displacement. Due to fabrication and cost-savings advantages, these actuators are now commonly used in several applications, such as optical-communication switches, micro-assembly, and micro-positioners. The proposed micropump design is based on these actuators fabricated by a one-step deep reactive ion etching process and packaged for protection and appropriate thermal dissipation. In the current ongoing research, the thermal actuator forms an integral part of an in-plane micropump. The flow rate is controlled by the variations in actuator displacement and corresponding force generated. Flow rates of several micro-liters per minute can be obtained making this pump suitable for drug delivery applications. Actuation is caused by application of voltage and resulting joule heating effect of the MEMS chevron beams. This results in displacement of the beams (actuator) which is proportional to the difference in temperature. Some of the parameters governing the displacement include the applied voltage, resistivity of the device, substrate thickness, and air gap between the device and the substrate. In this paper, the proposed micro-pump was analyzed for its thermal performance, pumping force, and the corresponding flow rate. The analysis was performed at device, die, and package levels. Thermal analysis showed that there exists a linear relationship between the applied voltage and the resulting temperature. Maximum temperature was always noted at the center of the chevron beams. The analysis also showed that force generated by the thermal actuators mainly depends on the average temperature of the chevron beams. Maximum force of 3.73 mN was noted for the packaged micropump at 23 V. This corresponded to an average beam temperature of 453°C and a flow rate of 11.2 μl/min. Performance assessment of the pump showed that for every 5 kPa increase in backpressure, flow rate reduced approximately by 5%.

Polymer tube embedded in-plane micropump for low flow rate

This paper presents the design, analysis, and fabrication of a novel polymer tube embedded in-plane micropump. The key component of the proposed micropump is a Parylene polymer tube that is embedded into the silicon die. Advantages of embedding a Parylene polymer tube are biocompatibility and leakage free environments. The issue of leakage of fluid presented Sin, Lee and Stephanou (2004) is eliminated by inserting the polymer tube. The tube itself acts as a diaphragm, which transfers the force and motion of thermal actuators to fluid. The structural analysis and the fabrication of the Parylene tube shows that better deflection is achieved with higher aspect ratio tubes. Coupled-field multiphysics analysis of the electrothermal actuators is done to modify the actuator to avoid melting of the Parylene tube. 4 /spl mu/m thick Parylene is conformally deposited on the nickel coated DRIE processed silicon wafer, and peeled off and two Parylene layers are bonded together to form a tube. The maximum deflection achieved for the Parylene diaphragm is 5.4 /spl mu/m and the computed value of flow rate for the pump is 160 nl/min. This fabrication process can fabricate Parylene tubes with aspect ratios up to 1:3 by a novel technique of chemical release.

Design of polymer tube embedded in-plane micropump

This paper presents a design of micropump, which is an assembly of silicon micromachined actuator with a polymer tube diaphragm. The pump actuation principle is electrothermal expansion of a silicon V-beam structure, and its expansion is amplified through a lever structure to create greater diaphragm stroke as presented in J. Sin et al. (2004). Diffuser/nozzle structures are applied to direct the flow from an inlet to outlet port while the actuator provides pumping motion. Deep RIE (reactive ion etching) process is used to fabricate the pump structure on a SOI (silicon on insulator) wafer. Polymer tube is fabricated from Parylene conformal deposition process using a DRIE silicon mold and the tube structure is assembled with the silicon actuator module. FEM analysis is performed on the tube structure and the simulation results show that the stroke of the tube diaphragm becomes much smaller than original actuator stroke, mainly due to the constrained tube geometry in silicon structure. When the tube stroke is combined with the diffusion/nozzle flow mechanism, the resultant flow rate of the pump was about 160nl/min, which will be suitable for low flow rate and high precision applications. Further study is on going to build prototype of the pump