High-temperature and high-pressure connection between micro combustor and macro world for feeding of air/fuel gas is required in PowerMEMS development. A Kovar tubing-Glass-Si sealing process has been developed for an on-going PowerMEMS project to connect Kovar tubes with diameters of 2mm and 4mm, to top Si wafer of micro combustor fabricated by DRIE process. Due to the different CTEs (coefficients of thermal expansion) of the connected materials, thermal stress around the sealing area could probably influence the obturation and other properties of the sealed combustor. A numeric simulation on sealing of the structure was conducted on ANSYS software to investigate this kind of sealing process. The thermal stress and displacement from room temperature to combustion circumstance, and to sealing condition as high as 1220K were simulated. The size affection of glass bonder and the metal tubes was investigated. A process of high temperature sealing Kovar-glass-silicon was developed and a prototype of the packaged micro combustor was manufactured.
This paper reports on design, fabrication and characterisation of a MEMS-based micro combustor for micro power generation systems. The first micro combustor implemented was a static gas turbine engine. The micro combustor was composed of seven silicon wafers and fabricated using deep reactive ion etching (DRIE). The size of the prototype was 21mmx21mmx4.4 mm. The combustor was assembled, aligned, ignited and tested under a fixture jig. The temperature near the exit of the combustor reached 1550 K, when the mass flow rate and fuel/air equivalence ratio were 0.06 g/sec and 0.8, respectively.
As part of an effort to develop MEMS-based power generation system, an assembly solution for combustion test of a recent-developed micro combustion device micromachined from single crystal silicon were proposed. In order to supply hydrogen/air to inlets of micro combustor from room temperature to over 700°C at the pressure of 1~3bars, a stainless steel universal fixture was designed and fabricated for the combustion testing of prototype stacked by structured Si wafers of 21.5mmx21.5mm in square. By precisely welding and polishing process in fabrication of the fixture, a metal plate with 18nm roughness was prepared for tightly connecting micro combuster with fuel inlet of 2mm, air inlet 4mm in diameter on the top wafer, while the gap between tubings to be hermetically joined to top plate is about 0.3mm. Primary combustion experiments have been conducted after igniting the fuel/air mixture in the micro chamber. Stable hydrogen-air combustion has been observed to sustain inside the combustion chamber with exit temperature over 1200°C. During the combustion experiments, the silicon dies keep good mechanical integrity under assembly and no gas leakage is observed.
In micro fabricated gas turbine engine, a micro journal air bearing is used to offer high speed and low wear operations. Fabrication of such a journal bearing is a critical challenge since the clearance of the bearing is only several micrometers with aspect ratio of more than 20. This paper reports on the fabrication of ultra-high aspect ratio micro journal air bearing using ICP DRIE (inductively coupled plasma deep reactive ion etching) process. The process parameters that resulted in bowed and tpaered journal bearing were investigated to improve the profile of the etched journal bearing. Micro journal bearings with sidewall verticality of almost 90° were obtained.
Nano imprinting or Nano embossing process have been introduced to fabricate semiconductor, optical device and Micro Electro Mechanical Systems (MEMS) and the Nano Electro Mechanical Systems (NEMS) to reduce the fabrication cost. In our previous paper, micro hot embossing of Polycarbonate (PC) and Polyetheretherketone (PEEK) for optical switch with 8x8 mirrors was reported. The PC and PEEK sheets were embossed at elevated temperature with an embossing machine designed for the MEMS. In the application, the mirrors on the optical switch had some defects, such as slump, sticking and step at side of the mirror, due to embossing process and process conditions. These defects are attributed to the poor materials flow of plastics into the e Ni mold cavity of complicate shape with different aspect ratio. Therefore, the micro hot embossing is optimized in this paper with PTFE sheet to enhance the materials flow. In this paper, the PC and the PEEK sheets, thickness of 300um, are embossed at elevated temperature with the hot embossing machine with a Nickel mold. To control material flow of the PC or the PEEK sheets, Polytetrafluoroethylene (PTFE) sheet, the thickness of 100um, is placed on the PC or the PEEK sheets at elevated temperature. Mirror shape was transferred with better fidelity on the PC and PEEK sheet, and the thickness of cantilever became thinner than previous embossed structure without the PTFE. Especially, the mirror height and the thickness of cantilever on the PC have been improved at lower embossing temperature.
In this paper, the development of a 1X4 micro optical switch utilizing electrostatic actuation and vertical silicon mirrors was reported. This device was fabricated from silicon-on-insulator (SOI) wafer using a bulk micromachining process, which allowed the fabrication of vertical mirrors and U-grooves through deep reactive ion etching (DRIE) of silicon. A few process steps were required in the fabrication. Moreover, the device was patterned in a single lithographic step. A relatively high yield (up to 70%) was achieved during the microfabrication due to this compact process flow. More importantly, the footprint was less than 13mm2. To verify the design, the stress/strain distribution around the actuator was examined using FEM simulation. The relationship between driving voltage and mirror displacement derived from simulation agreed well with the measurement. Tapered lensed singlemode fiber were assembled into U-grooves and positioned passively by fiber stopper. The device was then packaged and pigtailed. Characterization on the mechanical and optical performance of this device show the promising characteristics of this 1×4 optical switch for use in optical networks.
In this paper, the development of a dual-function leak detector is presented. The system consists of a laser interference instrument, a portable helium leakage detector, a specially designed test chamber with a quartz-glass observation window, a pressure gauge. The developed measuring system offers new features for experimental investigation on the integrity of hermetic sealed structure. Both helium bombing mode and diaphragm deflection mode were investigated using the developed detector. Basically, the system can be used for helium leak bombing detection. By employing this system for leakage detection in a micro optical switch, it was shown that a leakage of less than 10-7 std cc/sec can be measured. The system can also be used to measure the surface deflection of a diaphragm. The measurement was accomplished by using laser interference technique to monitor the pressure variation within the small cavity of MEMS devices after pressurized gas was introduced. A leakage as low as 10-14 std cc/sec could be detected for a sample with several cubic millimeter cavity of 10-4 mbar.
A micro hot embossing process has been developed for low cost and mass-production fabrications of optical switching components. After illustrating the architecture design and mold fabrication of a proposed optical switch, this paper describes the optimizations of parameters for hot embossing process to manufacture components of the optical switch. Polycarbonate has been used as the process material. The height of embossed mirrors, the thickness of actuating cantilever and the deformation of switch platforms have been measured precisely. The influence of process parameters has been investigated, and the optimized process parameters have been recommended with the process temperature and loading force being around 180°C and 1500Kg, respectively. The design guideline of nickel mold for easier release after embossing has also been recommended. The experimental results have demonstrated technological feasibility of micro hot embossing for low cost and mass-production of micro optical devices.
This paper presents approaches to fabricate Au masks for LIGA process. The proposed fabrication process starts with deposition of a thick layer of Au film, then followed by electron cyclotron resonance (ECR) Ar+ etching and coating of a polymer material that is used as a membrane. Finally the ICP DRIE etching is applied from backside to figure out the membrane. The profiles of the Au microstructures on the mask have been improved thanks to the optimization of etching process and photoresist material. The fabricated masks have been used in the X-ray lithography and demonstrated a well acceptable performance. A nickel mold has been successfully realized by electroplating and used in a hot embossing process for forming optical components. Au masks made by using conventional Au-electroplating technique have also been demonstrated for a comparison.
In this paper, we report the development of a new 1X4 micro optical switching device which utilizes electrostatic actuation and vertical silicon mirrors. This device is fabricated using a bulk micromachining process, which allows the fabrication of vertical mirrors and U-grooves through deep reactive ion etching (DRIE) of silicon. A limited number of process steps are required in the fabrication. Moreover, the device is patterned in a single lithographic step. A relatively high yield (up to 70%) is achieved during the microfabrication due to this compact process flow. More importantly, a small footprint (<13mm2 in die size) is realized. A single mode fiber with a tapered end is placed into a U-groove and positioned passively by a fiber stopper, prior to adhesive bonding with a silicon substrate and a glass cover. Preliminary characterization on the mechanical and optical performance of this device has been carried out, which reveals the promising characteristics of this 1X4 optical switch for use in optical networks.