Low Temperature non-viscous adhesive bonding in MEMS (original) (raw)

Analysis of the surface effects on adhesion in MEMS structures

One of the main failure causes in microelectromechanical systems (MEMS) is stiction. Stiction is the adhesion of contacting surfaces due to surface forces. Adhesion force depends on the operating conditions and is influenced by the contact area. In this study, the adhesion force between MEMS materials and the AFM tips is analyzed using the spectroscopy in point mode of the AFM. The aim is to predict the stiction failure mode in MEMS. The investigated MEMS materials are silicon, polysilicon, platinum, aluminum, and gold. Three types of investigations were conducted. The first one aimed to determine the variation of the adhesion force with respect to the variation of the roughness. The roughness has a strong influence on the adhesion because the contact area between components increases if the roughness decreases. The second type of investigation aimed to determine the adhesion force in multiple points of each considered sample. The values obtained experimentally for the adhesion force were also validated using the JKR and DMT models. The third type of investigation was conducted with the purpose of determining the influence of the temperature on the adhesion force.

Wafer-level SLID bonding for MEMS encapsulation

Advances in Manufacturing, 2013

Hermetic packaging is often an essential requirement to enable proper functionality throughout the device's lifetime and ensure the optimal performance of a micro electronic mechanical system (MEMS) device. Solid-liquid interdiffusion (SLID) bonding is a novel and attractive way to encapsulate MEMS devices at a wafer level. SLID bonding utilizes a low-melting-point metal to reduce the bonding process temperature; and metallic seal rings take out less of the valuable surface area and have a lower gas permeability compared to polymer or glassbased sealing materials. In addition, ductile metals can adopt mechanical and thermo-mechanical stresses during their service lifetime, which improves their reliability. In this study, the principles of Au-Sn and Cu-Sn SLID bonding are presented, which are meant to be used for wafer-level hermetic sealing of MEMS resonators. Seal rings in 15.24 cm silicon wafers were bonded at a width of 60 lm, electroplated, and used with Au-Sn and Cu-Sn layer structures. The wafer bonding temperature varied between 300°C and 350°C, and the bonding force was 3.5 kN under the ambient pressure, that is, it was less than 0.1 Pa. A shear test was used to compare the mechanical properties of the interconnections between both material systems. In addition, important factors pertaining to bond ring design are discussed according to their effects on the failure mechanisms. The results show that the design of metal structures can significantly affect the reliability of bond rings.

Wafer Level Surface Activated Bonding Tool for MEMS Packaging

Journal of The Electrochemical Society, 2004

A wafer level surface activated bonding ͑SAB͒ tool has been developed for microelectromechanical systems ͑MEMS͒ packaging at low temperature. The tool accommodates 8 in. diam wafers. The principle features of the tool are the automatic parallel adjustment for 8 in. wafers to a margin of error within Ϯ1 m and the X, Y, and axis alignments with an accuracy of Ϯ0.5 m. We have approached a new integration technique for the integration of ionic crystals with transparent and nontransparent thin intermediate layers using this tool. Various sizes of patterned and bare silicon, Al silicate glass, and quartz wafers cleaned by a low energy argon ion source in a vacuum have been successfully bonded by this technique at low temperature. Radioisotope fine leak and vacuum seal tests of sealed silicon cavities show leak rates of 1.0 ϫ 10 Ϫ9 and 2.6 ϫ 10 Ϫ16 Pa/m 3 s, respectively, which are lower than the American military standard encapsulation requirements for MEMS devices in harsh environments. Void-free interfaces with bonding strengths comparable to bulk materials are found. Low adhesion between SAB-processed ionic crystals without adhesive layers is believed to be due to radiation-induced discontinuous polarization.

Low temperature silicon wafer bonding for MEMS applications

2002

Abstract This paper reports the investigation of low-temperature silicon wafer fusion bonding for MEMS applications. A bonding process utilizing annealing temperatures between 400 C and 1100 C was characterized. The silicon-silicon bonded interface was analyzed by Infrared Transmission (IT) and Transmission Electron Microscopy (TEM) and the bond strength was quantified by a four-point bending-delamination technique

Highly Compliant Bonding Material and Structure For Micro- And Opto-Electronic Applications

56th Electronic Components and Technology Conference 2006, 2006

Based on the developed analytical stress model, we demonstrate that the employment of highly compliant materials and structures as bonding layers in bi-material assemblies (joints) can lead to a significant stress relief. The model indicates that the interfacial shearing stress in an adhesively bonded or a soldered assembly is inversely proportional to the square root of the interfacial compliance, and that in "conventional" bi-material assemblies (characterized by moderately compliant bonding layers), the interfacial compliance is due to both the bonding layer and the bonded components. However, in assemblies with highly compliant bonds, it is the bonding material only that provides the high and favorable interfacial compliance. We suggest that an appropriate nano-wire array (NWA) fabricated on one or both bonded components be used as a suitable compliant bond. Based on the developed predictive model, we demonstrate that the application of the NWA as a compliant attachment can lead to a significant, about two orders of magnitude, increase in the interfacial compliance. This leads to a reduction in the interfacial shearing stress of about an order of magnitude (compared to the bonded joints using "conventional" adhesives or solders). We suggest that one of the modifications of the newly developed nano-particle material (NPM) be used in addition to, or instead of a NWA, to increase the compliance of the bonding layer. A suitable combination of both the NWA and NPM could be employed to provide a highly compliant and a highly reliable bonding material and structure. In this case the NPM is used as an embedding material for the NWA. Since the NPM has extraordinary mechanical and environmental properties, and, in combination with the appropriate NWA, can make an extremely highly compliant and a highly reliable bond, we expect that the NPM and NWA, used independently or in combination, will find a wide application in various bi-and multi-material assemblies employed in micro-and optoelectronics, and well beyond the "high-tech" area.

Wafer bonding - A powerful tool for MEMS

Wafer bonding techniques play a key role in the present day silicon bulk micromachining for MEMS based sensors and actuators. Various silicon wafer bonding techniques and their role on MEMS devices such as pressure sensors, accelerometers and micropump have been discussed. The results on the piezoresistive pressure sensors monolithically integrated with a MOSFET differential amplifier circuit have been presented to demonstrate the important role played by the Silicon Fusion Bonding technique for integration of sensors with electronics on a single chip.

On the analysis of spontaneous adhesion in MEMS

EuroSimE 2009 - 10th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, 2009

Spontaneous adhesion can seriously jeopardize the reliability of micro-electro-mechanical systems, both during the fabrication phase and in the operation conditions. For this reason, adhesion in MEMS has been the topic of abundant research works in the last decade. This paper aims at the formulation of a computational model in order to simulate the adhesion phenomena in various environmental conditions. The present approach is based on Finite Element (FE) simulations on a representative part of the surface. The micro-scale analyses include the contact behavior of the asperities and the mechanical deformation of the bulk material, which is comparatively modeled as elastic-plastic. The model validation has been based on a simple sphere-on-flat simulation. Some preliminary results are presented with reference to actual rough surfaces.

Microassembly Technologies for MEMS

1998

Microassembly promises to extend MEMS beyond the confines of silicon micromachining. This paper surveys research in both serial and parallel microassembly. The former extends conventional "pick and place" assembly into the micro-domain, where surface forces play a dominant role. Parallel assembly involves the simultaneous precise organization of an ensemble of micro components. This can be achieved by microstructure transfer between aligned wafers or arrays of binding sites that trap an initially random collection of parts. Binding sites can be micromachined cavities or electrostatic traps; short-range attractive forces and random agitation of the parts serve to fill the sites. Microassembly strategies should furnish reliable mechanical bonds and electrical interconnection between the micropart and the target substrate or subassembly.

Experimental evaluation and numerical modeling of adhesion phenomena in polysilicon MEMS

Meccanica, 2013

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Cost-Efficient Wafer-Level Capping for MEMS and Imaging Sensors by Adhesive Wafer Bonding

Micromachines, 2016

Device encapsulation and packaging often constitutes a substantial part of the fabrication cost of micro electro-mechanical systems (MEMS) transducers and imaging sensor devices. In this paper, we propose a simple and cost-effective wafer-level capping method that utilizes a limited number of highly standardized process steps as well as low-cost materials. The proposed capping process is based on low-temperature adhesive wafer bonding, which ensures full complementary metal-oxide-semiconductor (CMOS) compatibility. All necessary fabrication steps for the wafer bonding, such as cavity formation and deposition of the adhesive, are performed on the capping substrate. The polymer adhesive is deposited by spray-coating on the capping wafer containing the cavities. Thus, no lithographic patterning of the polymer adhesive is needed, and material waste is minimized. Furthermore, this process does not require any additional fabrication steps on the device wafer, which lowers the process complexity and fabrication costs. We demonstrate the proposed capping method by packaging two different MEMS devices. The two MEMS devices include a vibration sensor and an acceleration switch, which employ two different electrical interconnection schemes. The experimental results show wafer-level capping with excellent bond quality due to the re-flow behavior of the polymer adhesive. No impediment to the functionality of the MEMS devices was observed, which indicates that the encapsulation does not introduce significant tensile nor compressive stresses. Thus, we present a highly versatile, robust, and cost-efficient capping method for components such as MEMS and imaging sensors.