Showing papers on "Anodic bonding published in 2001"

Ultrasonic micromixer for microfluidic systems

Abstract: This paper describes the design, fabrication and evaluation of an active micromixer for continuous flow. Mixing occurs directly from ultrasonic vibration. The intended use of the device is for integrated microchemical synthesis systems or for micro total analysis systems. The patterns of inlets, outlet and mixing chamber were formed in glass. The entire flow path was encapsulated by anodic bonding of a Si wafer to the glass. A diaphragm ( 6 mm ×6 mm ×0.15 mm ) was etched on the Si side to prevent ultrasonic radiation from escaping to the other parts of the device. The ultrasonic vibration originated from a bulk piezoelectric lead–zirconate–titanate (PZT) ceramic ( 5 mm ×4 mm ×0.15 mm ). The PZT was adhered on the diaphragm and was excited by a 60 kHz square wave at 50 V (peak-to-peak). Liquids were mixed in a chamber ( 6 mm ×6 mm ×0.06 mm ) with the Si oscillating diaphragm driven by the PZT. A solution of uranine and water was used to evaluate the effectiveness of mixing. The entire process was recorded using a fluorescent microscope equipped with a digital camera. The laminar flows of the uranine solution (5 ml/min) and water (5 ml/min) were mixed continuously and effectively when the PZT was excited. The temperature rise of our device was 15°C due to the ultrasonic irradiation.

Low temperature full wafer adhesive bonding

Abstract: We have systematically investigated the influence of different bonding parameters on void formation in a low-temperature adhesive bonding process. As a result of these studies we present guidelines ...

A novel MEMS pressure sensor fabricated on an optical fiber

Abstract: We describe the fabrication, and initial testing of a novel optically interrogated, microelectromechanical system (MEMS) pressure sensor in which the entire MEMS structure is fabricated directly on an optical fiber A new micromachining process for use on a flat fiber end face that includes photolithographic patterning, wet etching of a cavity, and anodic bonding of a silicon diaphragm is utilized. We have employed both 200- and 400-/spl mu/m-diameter multimode optical fibers. A pressure sensor fabricated on an optical fiber has been tested displaying an approximately linear response to static pressure (0-80 psi). This sensor is expected to find application in situations where small size is advantageous and where dense arrays may be useful.

Fuel cell assembly

Abstract: In a fuel cell assembly typically consisting of a plurality of cells each comprising an electrolyte layer (2), a pair of gas diffusion electrode layers (3, 4), and a pair of flow distribution plates (5), the electrolyte layer (2) comprises a frame (21) and electrolyte (22) retained in the frame; and the flow distribution plates and frames are made of materials having similar thermal expansion properties so that the generation of thermal stress between the frames of electrolyte layers and the corresponding flow distribution plates can be avoided, and the durability of the various components can be ensured. By joining each flow distribution plate with the corresponding frame by anodic bonding or using a bonding agent along a periphery thereof, the need for a sealing arrangement such as a gasket or a clamping arrangement can be eliminated, and this contributes to the compact design of the assembly.

A hermetic glass-silicon package formed using localized aluminum/silicon-glass bonding

Abstract: A hermetic package based on localized aluminum/silicon-to-glass bonding has been successfully demonstrated. Less than 0.2 MPa contact pressure with 46 mA current input for two parallel 3.5-/spl mu/m-wide polysilicon on-chip microheaters can raise the temperature of the bonding region to 700/spl deg/C bonding temperature and achieve a strong and reliable bond in 7.5 min. The formation of aluminum oxide with silicon precipitate composite layer is believed to be the source of the strong bond. Accelerated testing in an autoclave shows some packages survive more than 450 h under 3 atm, 100% RH and 128/spl deg/C. Premature failure has been attributed to some unbonded regions on the failed samples. The bonding yield and reliability have been improved by increasing bonding time and applied pressure.

Room-temperature wafer bonding of Si to LiNbO3, LiTaO3 and Gd3Ga5O12 by Ar-beam surface activation

Abstract: A room-temperature wafer bonding method using surface activation by Ar-beam sputter etching were applied to the bonding between dissimilar materials. LiNbO3, LiTaO3 and Gd3Ga5O12 wafers were successfully bonded to Si wafers without any heat treatment. This method is free from the various problems caused by the large thermal expansion mismatch between these materials during heat treatment in the conventional wafer bonding processes. The bond prepared by the Ar-beam treatment is so strong that fracture from inside the bulk materials is observed after the tensile test. The results of the bonding of Si wafers to both 128° Y-cut and Z-cut LiNbO3 wafers indicate that the influence of the crystal orientation on the bonding strength is negligible in this method. This method provides a very low damage bonding process for various material combinations regardless of any thermal expansion mismatch or crystal lattice mismatch.

Locally selective bonding of silicon and glass with laser

Abstract: A novel method for joining silicon and glass wafers with laser radiation is described. In order to characterize the locally selective bonding with laser (SBL) process, variations of laser parameters have been correlated with temperature measurements during bonding and the achieved bonding results. It was found that the temperature load outside the laser irradiated zone only lasted for seconds and remained below 300°C. The result of the investigations was a parameter field producing reproducible and strong silicon glass bonds. Basic knowledge for the thermal process of bonding and a understanding of the recognized bond defects was developed. Finally advantages and disadvantages of SBL with silicon and glass are discussed with respect to the anodic bonding technology putting emphasis on the low temperature and locally selective bonding capability of SBL.

Optically interrogated MEMS pressure sensors for propulsion applications

Abstract: Pressure sensors suitable for propulsion applications that uti- lize interrogation by fiber optics are described. To be suitable for many propulsion applications, sensors should have fast response, have a con- figuration that can be readily incorporated into sensor arrays, and be able to survive harsh environments. Microelectromechanical systems (MEMS) technology is utilized here for sensor fabrication. Optically inter- rogated MEMS devices are expected to eventually be more suitable than electrically interrogated MEMS devices for many propulsion applications involving harsh environments. Pressure-sensor elements are formed by etching shallow cavities in glass substrates followed by anodic bonding of silicon onto the glass over the cavity. The silicon is subsequently etched to form the pressure-sensitive diaphragm. Light emerging from a fiber is then used to interferometrically detect diaphragm deflection due to external pressure. Experimental results for static and dynamic pres- sure tests carried out in a shock tube demonstrate reasonable linearity, sensitivity, and time response. © 2001 Society of Photo-Optical Instrumentation

Microstructure examination of copper wafer bonding

Abstract: The microstructure morphologies and oxide distribution of copper bonded wafers were examined by means of transmission electron microscopy (TEM) and energy dispersion spectrometer (EDS). Cu wafers exhibit good bond properties when wafer contact occurs at 400°C/4000 mbar for 30 min, followed by an anneal at 400°C for 30 min in N2 ambient atmosphere. The distribution of different defects showed that the bonded layer became a homogeneous layer under these bonding conditions. The oxidation distribution in the bonded layer is uniform and sparse. Possible bonding mechanisms are discussed.

Low-temperature wafer-level transfer bonding

Abstract: In this paper, we present a new wafer-level transfer bonding technology. The technology can be used to transfer devices or films from one substrate wafer (sacrificial device wafer) to another substrate wafer (target wafer). The transfer bonding technology includes only low-temperature processes; thus, it is compatible with integrated circuits. The process flow consists of low-temperature adhesive bonding followed by sacrificially thinning of the device wafer. The transferred devices/films can be electrically interconnected to the target wafer (e.g., a CMOS wafer) if required. We present three example devices for which we have used the transfer bonding technology. The examples include two polycrystalline silicon structures and a test device for temperature coefficient of resistance measurements of thin-film materials. One of the main advantages of the new transfer bonding technology is that transducers and integrated circuits can be independently processed and optimized on different wafers before integrating the transducers on the integrated circuit wafer. Thus, the transducers can be made of, e.g., monocrystalline silicon or other high-temperature annealed, high-performance materials. Wafer-level transfer bonding can be a competitive alternative to flip-chip bonding, especially for thin-film devices with small feature sizes and when small electrical interconnections (<3/spl times/3 /spl mu/m/sup 2/) between the devices and the target wafer are required.

Buffer layer in flat panel display

Abstract: In devices such as flat panel displays, an aluminum oxide layer is provided between an aluminum layer and an ITO layer when such materials would otherwise be in contact to protect the ITO from optical and electrical defects sustained, for instance, during anodic bonding and other fabrication steps. This aluminum oxide barrier layer is preferably formed either by: (1) partially or completely anodizing an aluminum layer formed over the ITO layer, or (2) an in situ process forming aluminum oxide either over the ITO layer or over an aluminum layer formed on the ITO layer. After either of these processes, an aluminum layer is then formed over the aluminum oxide layer.

Wafer bonding of different III–V compound semiconductors by atomic hydrogen surface cleaning

Abstract: Large-area wafer bonding of different III–V compound semiconductors in an ultrahigh vacuum background is demonstrated. The bonding procedure, the microstructure, and the mechanical strength of the bonded GaAs/InP and GaAs/GaP interfaces were studied. The cleaning procedure and the bonding were separated in order to avoid undesired artifacts and thermal stress at the interface. First, thermally generated atomic hydrogen was employed to clean the surfaces. Then, the wafers were brought into contact below 150 °C. At contact, the interface formed spontaneously over the whole wafer area without application of a mechanical load. Transmission electron microscopy showed the formation of atomically direct interfaces and misfit dislocation networks. The fracture surface energy was measured as being comparable to that of respective bulk materials. Heat treatments of the bonded GaAs/InP samples led to relaxation of the interfaces but also to the formation of nanoscopic voids in the interface plane and volume dislocat...

Wafer-level membrane transfer bonding of polycrystalline silicon bolometers for use in infrared focal plane arrays

Abstract: In this paper we present a new, innovative technology for fabrication and integration of free-hanging transducers. The transducer structures are processed on the original substrate wafer (sacrificial device wafer) and then transferred to a new substrate wafer (target wafer). The technology consists only of low-temperature processes, thus it is compatible with integrated circuits. We have applied the new membrane transfer bonding technology to the fabrication of infrared bolometers for use in uncooled infrared focal plane arrays (IRFPAs). In the future this may allow bolometers to be integrated with high-temperature-annealed, high-performance thermistor materials on CMOS-based uncooled IRFPAs. Membrane transfer bonding is based on low-temperature adhesive bonding of the sacrificial device wafer to the target wafer. The device wafer is sacrificially removed by etching or by a combination of grinding and etching, while the transducer structures remain on the target wafer. The transducer structures are mechanically and electrically contacted to the target wafer and the adhesive bonding material is sacrificially removed. The free-hanging transducers remain on the target wafer. One of the unique advantages of this technology is the ability to fabricate and integrate free-hanging transducers with very small feature sizes. In principle, membrane transfer bonding can be applied to any type of free-hanging transducer including ferroelectric infrared detectors, movable micro-mirrors and RF MEMS devices.

Micromechanism fabrication using silicon fusion bonding

Abstract: Silicon fusion bonding is studied as an enabling technology for the fabrication of microrobotic mechanisms. The e!ects of both surface activation technique and annealing temperature on bond strength are considered using a crack-opening technique. As part of the study, the relationship between patterned silicon feature size and the resulting bond strength is explored. Based on the experimental results, recommendations for an optimal silicon fusion bonding process for micromechanism fabrication are presented. The experimental results indicate that bulk silicon bonding strength can be achieved independent of feature size at temperatures as low as 3003C, with positive implications for micromechanism fabrication. 2001 Elsevier Science Ltd. All rights reserved.

SOI/glass process for forming thin silicon micromachined structures

Abstract: Methods for making thin silicon layers suspended over recesses in glass wafers. One method includes providing a thin silicon-on-insulator (SOI) wafer, and a glass wafer. The SOI wafer can include a silicon oxide layer disposed between a first undoped or substantially undoped silicon layer and a second silicon layer. Recesses can be formed in the glass wafer surface and electrodes may be formed on the glass wafer surface. The first silicon layer of the SOI wafer is then bonded to the glass wafer surface having the recesses, and the second silicon layer is subsequently removed using the silicon oxide layer as an etch stop. Next, the silicon oxide layer is removed. The first silicon layer can then be etched to form the desired structure. In another illustrative embodiment, the first silicon layer has a patterned metal layer thereon. The SOI wafer is bonded to the glass wafer, with the patterned metal layer positioned adjacent the recesses in the glass wafer. Then, the second silicon layer is removed using the silicon oxide layer as an etch stop, and the silicon oxide layer is subsequently removed. The first silicon layer is then etched using the patterned metal layer as an etch stop. The patterned metal layer is then removed.

A method for the rapid thermal treatment of glass and glass-like materials using microwave radiation

Abstract: A method of thermally treating a glass or glass-like material, preferably a glass sheet, without the use of conventional tunnel-type furnaces, to effect rapid heating of glass and glass-like materials from any initial temperature to any required temperature so that the glass sheet can be processed by shaping, bending, tempering, annealing, coating and floating of the glass sheet without cracking of the glass sheet is described. In the inventive method a microwave radiation with appropriate uniformity, frequency and power density is chosen so as to accomplish glass heating from any initial temperature to any required (e.g., softened) temperature in a selected short time while ensuring that the temperature distribution on the external surfaces and in the interior of the glass sheet that arises from microwave exposure is uniform enough to prevent the exposed glass sheet's internal thermal stress from exceeding its modulus of rupture, thereby avoiding glass breakage.

Use of Selective Anodic Bonding to Create Micropump Chambers with Virtually No Dead Volume

Abstract: Membrane micropump chambers of 11 mm diam with virtually zero dead volume were realized using selective anodic bonding. The selective bonding was achieved with less than 1 nm thick metallic antibonding layers on the glass wafer. Experiments were carried out to come to a better understanding of the selective anodic bonding process. It was concluded that a conductive antibonding layer on the glass wafer prevents the formation of a bond, because in that case the electrostatic attraction between the Pyrex and silicon wafers will vanish upon contact. Chromium and Platinum were found to be suitable antibonding layers. Furthermore, it was found that during the anodic bonding process, the transport of oxygen ions from Pyrex toward the silicon-Pyrex interface results in the formation of SiO2, which forms the actual bond between both substrates. At positions of an intermediate antibonding layer the oxygen ions form oxygen gas. The Pyrex or silicon substrate may deform locally due to the buildup of oxygen gas pressure. This can be prevented by adding a gas outlet to the design. ©2001 The Electrochemical Society. All rights reserved.

High-energy x-ray reflectivity of buried interfaces created by wafer bonding

Abstract: The bonding interfaces separating two silicon wafers assembled for making a silicon-on-insulator system are studied using high-resolution high-energy x-ray reflectivity. The evolution of the bond structure upon annealing is investigated, in situ. These data directly exhibit water removal and oxide layer structural changes, throughout the temperature sequence.

Hermetic wafer bonding based on rapid thermal processing

Abstract: Hermetic wafer bonding based on rapid thermal processing (RTP) has been demonstrated for the first time. Microcavities encapsulated between glass and silicon substrate have been sealed with aluminum solder by using RTP at 990°C for 2 s. Reliability experiments of IPA leak and autoclave accelerated tests show that 100% of survival rate can be achieved. The best encapsulation results are accomplished when the aluminum bonding solder is 150 μm wide and 4.5 μm thick. Furthermore, it is found that the activation energy for Al-glass RTP bonding system is 3.5 eV and the lowest successful bonding temperature is 760°C with a processing time of 30 min. In the device-packaging demonstrations, a microheater and a surface micromachined heatuator have been successfully packaged by the RTP bonding method and are operational after the bonding process. This work demonstrates that RTP bonding can provide low thermal budget, insensitivity to rough surfaces, and excellent bonding characteristics. As such, it has promising potential for wafer-level MEMS fabrication and packaging.

Direct bonding of articles containing silicon

Abstract: Methods of bonding glass and silicon-containing articles are disclosed. Bonding is achieved without use of adhesives or high temperature fusion. A wide variety of glass and silicon-containing articles may be bonded by the methods of the invention.

Method and apparatus for producing bonded dielectric separation wafer

Abstract: The present invention provides a method for producing a bonded dielectric separation wafer in which an auto-alignment can be carried out with reference to the orientation flat of a supporting substrate wafer after the wafer bonding step, and also an apparatus to be used for bonding wafers When wafers are placed one upon another, the silicon wafers 10, 20 are irradiated with transmission light in order to capture the transmission images thereof The positions of the pattern of dielectric isolation grooves 13 in the silicon wafer 10 and the orientation flat 20 a of the silicon wafer 20 are determined from the images and the bonding position of the wafers 10, 20 is determined based on the determined positions Auto-alignment of the bonded dielectric separation wafer can thereby be carried out with reference to the orientation flat 20 a of the silicon wafer 20 after the wafer bonding step

Selective Wafer Bonding by Surface Roughness Control

Abstract: Selective wafer bonding is presented as a technique for fabrication of microelectromechanical systems (MEMS) devices with movable, contacting elements, e.g., micromachined valves. The selectivity of the wafer bonding is obtained by tailoring the wafer surface microroughness. The adhesion parameter is used as the design rule for the wafer bonding technique. The technique is demonstrated with bulk micromachined check valves and a pressure actuated normally closed valve, but can be used for fabricating MEMS devices using surface micromachining processes as well. For these valves the selective fusion bonding technique turned out to be a convenient way to bond different wafer layers and a promising fabrication step with a high, reliable product yield.

Glass-to-glass electrostatic bonding with intermediate amorphous silicon film for vacuum packaging of microelectronics and its application

Abstract: In this work, we have developed a new high vacuum packaging method using a glass-to-glass bonding with an intermediate amorphous silicon (a-Si) film for the application to microelectronic devices such as field emission display and plasma display panel. The glass-to-glass electrostatic bonding was established and optimized by introducing thin amorphous silicon interlayer. Also, we propose that the amount of oxygen ions is one of the important factors during the bonding process, as confirmed from the SIMS and XPS analyses for the reaction region of SiO bond in interface. Our method was very effective to reduce the bonding temperature and make the high vacuum package of microelectronic devices over 10 −4 Torr. Finally, to evaluate the vacuum sealing capability of devices packaged by the method, the leak characteristics of the vacuum was examined by a spinning rotor gauge during 6 months. The electron emission properties of the field emission display and plasma display panel were measured continuously for time variation.

Wafer bonding for integrated materials

Abstract: Wafer bonding and layer transfer technology has emerged as one of the fundamental technologies for the fabrication of integrated materials. In this paper, we will first discuss the basics and the generic nature of the wafer direct bonding process in terms of inter-molecular forces, surface mechanics and chemistry, interface reactions and bonding procedures. Based on the understanding of wafer bonding process, innovative low temperature wafer bonding technologies that operate at wafer level in ambient conditions have been developed to facilitate the integration of almost any materials that are similar or dissimilar. Room temperature chemical bonding and low temperature epitaxial or hetero-epitaxial-like bonding approaches are introduced. Finally, examples of integrated materials prepared by wafer bonding and layer transfer are presented.

Ejection head for aggressive liquids manufactured by anodic bonding

Abstract: A method for manufacturing an ejection head (10) or ejector suitable for ejecting in the form of droplets (16) a liquid (14) conveyed inside the ejection head (10), comprising a step of producing, from a silicon wafer, a nozzle plate (12) having at least one ejection nozzle (13); a step of producing, from another silicon wafer, a substrate (11) having at least one actuator (15) for activating the ejection of the droplets of liquid through the nozzle (13); and a step of joining the nozzle plate (12) and the substrate (11) together to form the ejection head, wherein this joining step comprises the production of a junction (25), made by means of the anodic bonding technology, between the substrate (11) and the nozzle plate (12), in such a way that, in the area of this junction (25), the ejection head (10) does not present structural discontinuities, and also possesses a resistance to chemical corrosion by the liquid (14) contained in the ejection head (10) at least equal to that of the silicon constituting both the substrate (11) and the nozzle plate (12). The method of the invention may be applied for manufacturing an ink jet printhead (110), having one or more nozzles (113a, 113b, etc.), which has the advantage, with respect to the known printheads, of also being suitable for working with special inks characterized by high level chemical aggressiveness. In general, the ejection head of the invention, thanks to its structure which is globally highly robust and also chemically inert in the area of the junction (25), can be used advantageously with various types of liquids, even with marked chemical aggressiveness, in different sectors of the art, for example for ejecting paints on various types of media, generally not paper, in the industrial marking sector, or for ejecting in a controlled way droplets of fuel, such as petrol, in an internal combustion engine.

Development of a microchannel catalytic reactor system

Abstract: The purpose of this article is to demonstrate the applicability of microreactors for use in catalytic reactions at elevated temperatures. Microchannels were fabricated on both sides of a silicon wafer by wet chemical etching after pattern transfer using a negative photoresist. The walls of the reactor channel were coated with a platinum layer, for use as a sample catalyst, by sputtering. A heating element was installed in the channel on the opposite surface of the reactor channel. The reactor channel was sealed gas-tight with a glass plate by using an anodic bonding technique. A small-scale palladium membrane was also prepared on the surface of a 50-Μm thick copper film. In the membrane preparation, a negative photoresist was spin-coated and solidified to serve as a protective film. A palladium layer was then electrodeposited on the other uncovered surface. After the protective film was removed, the resist was again spin-coated on the copper surface, and a pattern of microslits was transferred by photolithography. After development, the microslits were electrolitically etched away, resulting in the formation of a palladium membrane as an assemblage of thin layers formed in the microslits. The integration of the microreactor and the membrane is currently under way.

Glass frit wafer bonding process and packages formed thereby

Abstract: A method of glass frit bonding wafers to form a package, in which the width of the glass bond line between the wafers is minimized to reduce package size. The method entails the use of a glass frit material containing a particulate filler material that establishes the stand-off distance between wafers, instead of relying on discrete structural features on one of the wafers dedicated to this function. In addition, the amount of glass frit material used to form the glass bond line between wafers is reduced to such levels as to reduce the width of the glass bond line, allowing the overall size of the package to be minimized. To accommodate the variability associated with screening processes when low volume lines of paste are printed, the invention further entails the use of storage regions defined by walls adjacent the glass bond line to accommodate excess glass frit material without significantly increasing the width of the bond line. The storage regions also ensure adequate flow of glass frit material around electrical runners that cross the glass bond line, as well as into any isolation trenches surrounding the runners.