Bonding of a copper surface in a nonvacuum environment has been studied for the purpose of reducing manufacturing costs. Cu-Cu bonding in ambient air is demonstrated by using propylene carbonate (PPC) as a passivation layer. The decomposition of the PPC passivation layer during bonding would protect the copper surface from oxidation by providing a shielding gas atmosphere between the copper surface and the air. Further, the PPC passivation layer would also overcome the degradation of copper surface during storage in the atmosphere.
Metallic wafer bonding is becoming a key enabling technology in microelectromechanical systems packaging and heterogeneous integration. We realize the bonding of silicon (Si) wafers coated with aluminum (Al) film with thin tin (Sn) film as the intermediate layer. The bonding pressure is 0.25 MPa. The bonding is achieved at temperatures as low as 280°C after a short bonding time of 3 min. The average bonding strength is 9.9 MPa. The minimum variation of bonding layer thickness is about 0.2 μm within a large area. A fracture surface study and a cross-section analysis are conducted and the bond mechanism is investigated. It is found that the fracture mainly occurs at Al/Sn interface during the shear test. Two bonding conditions are compared and the results show that applying bonding pressure before heating is important to achieve a uniform bonding layer.
An optical-readout bimaterial microcantilever-type infrared detector improving both IR absorption and pixel
uniformity is proposed. A Focal Plane Array (FPA) of 128×128 pixels was fabricated using 4-inch silicon Micro-Electro
Mechanical System (MEMS) processes. The FPA design and process development are discussed and the Scanning Electron
Microscope (SEM) photos and imaging results of the FPA are presented. The Noise Equivalent Temperature Difference
(NETD) of the proposed device was measured to be 200mK by a gray level change method and the time constant
was calculated to be ~15 ms under a 10 mTorr pressure.
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.
Vacuum packaging is very important for some micro-electro-mechanical systems (MEMS) devices to perform their basic functions properly and to enhance their reliability by keeping these devices away from harmful external environment. In order to maintain high vacuum in a cavity of MEMS devices, residual gases and leaking gases must be eliminated by getter materials embedded. This paper will report the fabrication and characterization of advanced getter, or micro/nano getters for MEMS applications.
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.
KEYWORDS: Semiconducting wafers, Etching, Deep reactive ion etching, Plasma, Silicon, Photoresist materials, Photomasks, Ions, Surface roughness, Process control
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.
An approach to maintain vacuum in MEMS devices, by integrating MEMS fabrication process with getter material preparation, is presented in this paper. A coating process for thick film of getter material on silicon and glass wafers, which are common materials in fabrication of MEMS devices and package, has been investigated in detail. The getter material consists of a powder mixture of zirconium, vanadium and iron, which features high sorption capability to active gas such as H2, O2, N2, CO and H2O vapor. Several patterned NEG thick films to simulate different needs in MEMS application have been made. The sorption capacity of the coated getter material was examined. The coating of NEG thick film onto the inner surface of a MEMS pressure sensor and the activation of NEG during anodic bonding process were carried out.
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 micromachined tunable RF capacitor with interdigitated comb plate structure is investigated in this paper. Much effort to improve tuning ratio, such as minimizing parasitical capacitance, is presented. Analysis shows the bias voltage can be lowered through the optimization of the structure parameters. Also presented is the fabrication of this capacitor based on typical bulk silicon micromachining technology.
The electric field situation of three single-substrate AC- PDP cells has been investigated by computer simulation. The electric field distribution has been analyzed before firing and the period of extinguishing when charged particles deposited on the surface of the MgO layer. It is concluded that electric field on the region near barrier ribs is mainly dominated by electrode voltages existed, while the effect of charged particles could be overlooked.
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