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Ceramics joining has been widely applied in MEMS sensors, microwave and imaging devices as well as other ceramic packaging applications to fabricate multifunctional ceramic components. In this study, a glass frit with gradient thermal expansion coefficient (TEC) has been applied as the bonding material to join the ceramic of Al2O3 and AlN. This glass frit consists of two types of glasses with different TEC. The Al2O3 and AlN ceramics have been successfully joined with this glass frit in muffle furnace at 850 °C for 1 h. The bonding strength of Al2O3/AlN ceramic joined via this glass frit exceeds 40 MPa without any cracks in the joining interface, which is much superior compared with that of conventional glass frit bonding. Our work demonstrates that the gradient-TEC glass frit bonding is an effective method to join different types of ceramics.

Glass frit bonding is a widely used technology to cap and seal micro-electromechanical systems on the wafer level using a low melting point glass. Screen printing is the main method to apply glass frit paste on wafers. Screen printing of glass frit paste is usually performed on less sensitive, less critical wafers, normally the capping wafer, because screen printing is a rough process involving the mechanical contact of the screen printing mesh and the wafer. However, for some applications in which contactless patterning of glass frit materials on the device wafers are preferred (e.g., 3D topographies, micro-lens and optics integration) jet dispensing could be a promising approach. Consequently, in this study, wafer-level jetting of glass frit materials on silicon wafers was proposed and investigated. The jetting parameters such as jetting distance, power and temperature were optimized for a glass frit paste. Additionally, the effect of jetted pitch size on the bond-line thickness was assessed. The wafers with jetted glass frit pastes were conclusively bonded in low vacuum and characterized. As a single-step (non-contact) additive approach, the jet printing of glass frit was revealed to be a straightforward, cost-effective and flexible approach with several implications for hermetic packaging.

Bonding with glass frit is important in many applications. Glass frit should wet and react chemically with the substrate. Its glass-wetting properties were improved by applying a lead oxide (PbO) layer fabricated through aerosol deposition (AD) which reacted with the glass frit. The 13 μm-thick PbO AD layer, which was mechanically anchored to the substrate, disappeared during bonding, since the PbO layer became diffused into the glass. The glass pellets on the PbO layer reacted with each other and were spread out at 455°C, which is lower than the equivalent temperature for glass frit on alumina (470°C) without an AD layer because of changes in the glass structure, as confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The coefficient of thermal expansion (CTE) hardly changed. These phenomena increased the bonding strength at the glass-substrate interface of each specimen from 133.61 kPa (without AD) to 180.21 kPa (with AD).

A novel packaging structure is designed and the packaging process is optimized for micro pressure sensors with glass frit bonding technology in this paper. The packaging structure with inner-outer reference walls, metal lead break, and thermal stress release break is designed. The height of the reference walls can precisely control the thickness of glass frit layer. The technological parameters of screen printing across metal lead steps are also explored in this article originally. By optimizing the presintering atmosphere, peak temperature and holding time, the covering issue of frit on the metal lead surface is solved. The micro holes in the glass frit are effectively removed by optimizing the bonding temperature. The results of experiments show that when the peak temperature of presintering is 400 °C and the presintering atmosphere is 30 minutes in vacuum and in air respectively, the coverage rate of glass frit on the metal leads reaches 85%, which meets the packaging requirements. When the bonding temperature is 500 °C, the micro holes in the interlayer of glass frit are completely removed and the bonding strength of the pressure sensor is 12.52 MPa.

Bonding of silicon strain gages on stainless-steel substrates is a critical issue in diaphragm-type pressure sensors because of the large mismatch in coefficients of thermal expansion between silicon and metal resulting in serious reliability problems. A new method to significantly improve the glass-frit bonding of silicon gages on metal diaphragms is reported based on an intermediate thin glass plate onto which silicon strain gages are fabricated. The glass interlayer enables very reliable bonds without post-bond misalignment, debonding, or cracking through the selection of glasses that very closely match silicon and the compressive surface strengthening of glasses. Furthermore, the proposed gage structure provides great improvement in the electrical performance, especially the thermal drifts of offset (zero) and span of Si strain-gage-based bridge transducers.

Laser-assisted glass frit bonding as a noncontact thermal bonding method has been widely applied in the organic light-emitting diodes (OLEDs) encapsulation field. However, blue light emitting from the OLEDs devices could cause many hazards. Therefore, it is of significance to develop a high reliable packaging technology with blue light-shielding performance for OLEDs. In this work, a BiVO 4 thin film capable of shielding blue radiation applied in glass frit laser encapsulation were developed. BiVO 4 thin films were deposited on glass by chemical solution deposition process. The effect of annealing temperature ranging from 573 to 873K on blue light-blocking performance has been investigated. The optimized BiVO 4 films exhibited the best blue light-shielding capability and could block 50.32 % short wavelength blue light (400 - 450 nm), while maintaining greater than 87 % average transmittance in the wavelength range of 500 - 800 nm. Finally, the laser-assisted glass frit bonding device combined with optimized BiVO 4 blue light-shielding film has been fabricated. Therefore, transparent BiVO 4 film with high blue light-shielding efficiency are desirable for practical encapsulation applications.

This paper presents the design, fabrication, and prototype testing of a high pressure sensor which can provide, for the first time, high withstand voltage (>2 kV) at the chip level, not a packaging structure improvement, without scarifying its performance and cost. This is achieved by a special design of silicon strain gauge, based on bonding silicon to alkali-free glass wafers. The pressure sensors composed of silicon strain gauges on-glass chip not only meet the high withstand voltage requirements, but also show excellent output properties such as linearity, hysteresis, sensitivity and accuracy. In addition, silicon gauges-on-a-glass chip is easy to use due to the presence of a glass substrate.

Hermetic sealing is important regarding functionality and reliability for MEMS components. Typically this sealing is done at the wafer level using wafer bonding, which simultaneously provides mechanical protective caps. Here, a universally usable MEMS Foundry technology for inertial sensors and the glass frit bonding to seal them are introduced. A test structure for inner cavity pressure measurement, utilizing the pressure dependence of heat transfer in gasses, which can be realized in this MEMS technology, is introduced and described for use in detailed investigations of factors, which influence the inner cavity pressure in the wafer pre-processing and wafer bonding step itself. These investigations ultimately allowed optimized wafer processing, improved process control, and reliability investigation. We show how, based on the inner cavity pressure measurements, the glass frit bond process can be set up, that side effects such as storing times of the glass frit can be understood, how fine tuning of the bond process can be done, and how both process stability and device reliability can be efficiently be proven.

We studied the feasibility of using Bi-based lead-free glass paste as bonding material on soda-lime glass substrates, without any activation preparation on the bonding surfaces. In order to fabricate Bi2O3-B2O3-ZnO-BaO-SrO system low-melting glass frit, quenching is performed using deionized water after melting using a muffle furnace. Glass paste consisting of glass frit mixed with organic solvent is deposited on the surface of the soda-lime glass substrate by screen printing, and the sealing of the glass substrate is finally achieved at the bonding temperature (500 °C). we discuss the properties of glass powder, the joint microstructure of irregular amorphous glass, the shear properties and the glass frit bonding mechanism based on the characterization results of DSC, XRD, FTIR, Raman, XPS, SEM and TEM. Furthermore, the investigation concentrated on mechanical properties and microstructural characterization of the joined area with two silica substrates. As the SrO content increased from 0 to 3 mol%, Tg increased from 396 °C to 418 °C with increasing SrO content. Accompanied by an increase in SrO content from 1 mol% to 2 mol%, the room-temperature shear strength of the glass specimens increased from 28.5 to 45 MPa. The growth of Bi24B2O39 crystallites precipitated at the interface was studied.

In this work, a systematic study on laser-assisted glass frit bonding process was carried out by response surface methodology (RSM). Laser power, sealing speed and spot diameter were considered as key bonding parameters. Combined with a central rotatable experimental design, RSM was employed to establish mathematical model to predict the relationship between the shear force after bonding and the bonding process parameters. The model was validated experimentally. Based on the model, the interaction effects of the process parameters on the shear force were analyzed and the optimum bonding parameters were achieved. The results indicate that the model can be used to illustrate the relationship between the shear force and the bonding parameters. The predicted results obtained under the optimized parameters by the models are consistent with the experimental results.

Laser-assisted glass frit bonding encapsulation (hereafter referred to as Laser bonding) is proposed for encapsulating air sensitive device that need a hermetic package with long-term stability. Laser bonding technology is a typical local non-contact heating technology, which allows temperature-sensitive devices to be used inside cell. With the excellent barrier performance, glass frit play an important role in encapsulation. Many factors such as the particles size, paste viscosity during process and unfairness of the surface morphology caused in screen printing process can cause the formation of defects in glass frit, weakening the barrier properties for blocking moisture and oxygen. We found that high saddle height difference comes out due to improper viscosity and improper printing process. In order to further verify the reliability of the glass laser encapsulation in the temperature output mode, the water vapor transmission rate (WVTR) of the encapsulated structure was tested using the active metal calcium electrical test method. Finally, we found that the lower saddle height difference is contributes to the smooth surface appearance. Furthermore the lower saddle height difference conducts to lower WVTR.

In this article, we report on the new design of a miniaturized silicon strain gauge and its application to hydrogen pressure sensor. The bulk-micromachined silicon gauges have the through holes and the closed structure, unlike the current competitive devices with open structure. This unique design concept reduces shifting or rotation of gauge position during glass frit bonding and enables the automation of alignment and bonding processes, which improves the sensor performance and yield and hence reduces sensor cost. The prototype pressure sensors tested under pressure ranging from 0 to 50bar at different temperature have a linear output with a typical sensitivity of about 0.72mV/V/bar(before calibration) and 16mV/V/bar(after calibration), and a calibrated offset drift of –6mV to 2mV.

The pressure sensor application gained recently substantial interest in many fields of basic and applied research and applications. In this paper, microelectromechanical system (MEMS)-based pressure sensor contains nanostructured electrode consisting of carbon nanotube (CNT) array. CNTs are directly grown on such electrode by plasma-enhanced chemical vapor deposition method using microwave plasma torch at atmospheric pressure. This growth method enables us to use a simple electrode structure without need of buffer layer and time-consuming lithography process. Combination of CNTs field emission and MEMS membrane mechanical properties make possible to enhance sensitivity of the sensor. Field emission properties of CNTs are measured by newly developed system enabling us precise measurement of expecting properties, such as dependence on diaphragm (upper electrode) distance, applied voltage, and stability of the sensor. Measured values are compared with a numerical modeling of the membrane system in Coventor Ware software by finite-element method. We also suggest encapsulating the sensor using glass frit bonding because such method is more suitable for high vacuum requirements of the field emission operation.

With the rapid development of modern microelectronics and optoelectronics technology, a novel potential sealing method,Laser-assisted glass frit bonding (hereafter referred to as Laser bonding), are proposed for encapsulating electronic, optical, and miniature micro-mechanical devices that require a hermetic seal with long-term stability. In this work, we fabricated two kinds of glass pastes which were bismuthate glass powder and phosphate vanadate glass powder mixed in the same organic component solvent, respectively. Then two pairs of blank glass substrate go through screen printing, pre-sintering and laser bonding with the glass pastes as two group sample. Next, we conducted a series of experiments to learn hermeticity of these two different kinds of sealing glass system. The tests were performed by dipping samples in a low-tension liquid-ethanol-colored with a dye. We have found that bismuthate glass frit cord showed strong steady erosion resistance and phosphate vanadate glass joining begin to breakdown in 12h. Hence, we analyzed the mechanism of encapsulation failure by Raman spectroscopy. We inferred that the V3+ and P5+ in the surface of glass dissolved in H 2 O while glass network cracked and defects came out. Over time, the depth of the erosion is more and more deep. In the end, encapsulation failed.

This study investigates the ceramic to ceramic bonding, using composite glass frit as the binding layer that is able to tolerate a high temperature environment for ruggedized microelectronic applications. Shear strength measurements were carried out at both room and high temperature (i.e. 250 °C) to evaluate room and high temperature performance of the joints. The glass joints in both the Al2O3/glass/Al2O3 and AlN/glass/AlN systems maintained their integrity even when shear-tested at 250 °C. The results of the mechanical and microstructural characterizations demonstrate that Bi-based two phase glass frit bonding is an effective ceramic bonding method for harsh-environment electronic packaging. Accepted version

This paper presents the microwave characterization of a wafer level packaging approach for RF MEMS devices, using glass frit as the bonding material. Coplanar waveguide transmission lines are packaged by silicon caps to carry out the RF characterization of the package structure. Prior to bonding of the cap on the transmission lines, cap wafers are bulk micromachined to form the cavities for housing the device to be packaged and pad windows to access the RF ports of the devices. Lateral feedthroughs are designed under the glass frit ring transitions in order to decrease the impedance loading effect of the silicon cap and the glass frit ring. The package is implemented using both high and low resistive silicon wafers in order to assess the microwave effects of cap wafer. A circuit model is used to extract the parameters of the feedthrough from the RF measurements. The loss of the feedthrough is measured to be 0.1 dB/transition at 10 GHz for high resistive silicon caps demonstrating the viability of glass frit in the packaging of RF MEMS devices.

This paper reports a sealing process for reliable hermetic wafer-scale packaging among three wafers forming sandwich structure by glass frit. The process could be applied to Si, quartz crystal, SiC wafers and so on. The device wafer is bonded to the capping wafer in the first step and to another capping wafer forming vacuum-cavities in the second step. Experimental results indicate that the average bonding strength of packaging structure reached as high as 0.85kg/mm2 fulfilling MIL-STD-833E standard. The average leakage rate fits the standard of GJB-548A.This paper also realizes glass frit hermetic bonding in the case of Au/Cr and Pt/Ti film feed-through deposited on the device wafer.Experimental results indicate that Pt/Ti film feed-through hold up to bonding temperature cycling and avoid dissolution and adherence reduction compared with Au/Cr film feed-through

Wafer-level glass frit bonding is an important technology for the hermetic encapsulation of microsystems. In this paper, the sintering characteristic of the glass frit material is investigated based on thermogravimetry/differential scanning calorimetry (TG/DSC) thermal analysis techniques. TG/DSC measurement results illustrate that the organic binder burnout temperature and glass transition temperature for the glass frit used in this paper are 300 °C and 331 °C, respectively. With the TG/DSC measured results, a wafer-level vacuum packaging approach for microsystems using glass frit bonding is developed through experimental analysis. The glass frit is presintered at 300 °C for 30 min to completely remove the organic binder and fired at 430 °C to seal the bonded wafers. The cross-sectional observation shows no void or gap is formed in the bonded layer. The average shear stress of the bonded devices is 6.2 kgf, which satisfies military standard-883E. Application of the glass frit bonding approach for a thermocouple vacuum gauge is demonstrated, which is employed to illustrate the feasibility of this process, and also to measure the vacuum degree in the packaged cavity. The measured results show that a vacuum of about 100-300 Pa can be sealed using this approach.

This paper reports a wide pressure measurement range CMOS-MEMS based integrated thermopile vacuum gauge with an XeF2 dry-etching process. By using XeF2 front-side dry-etching process, a small gap between the suspended heater and the substrate has been obtained, which can extend the upper pressure limit of the gauge. Meanwhile, a small size about 0.4 mm × 1.5 mm of the gauge structure has been obtained, and a good yield of 93% for elements in a wafer has been achieved. A cap mounted on the integrated thermopile vacuum gauge by wafer level glass frit bonding enhances the gas thermal conduction between the heater and the cap, which increases the sensitivity of the gauge and enlarges the sensing pressure range of the gauge. Moreover, a cap mounted on the gauge provides a chamber to protect the floating integrated thermopile vacuum gauge structure and a good yield of better than 90% for the packaged integrated thermopile vacuum gauge has been achieved. The constant power of 4.5 mW is applied to the device, and experimental results show the integrated thermopile vacuum gauge has a good response to the gas pressure from 5 × 10−3 Pa to 105 Pa.

A lead-free glass frit paste as a die-attach material for high-temperature microelectronic application is proposed in this study. The glass paste containing Bi-based powder with a moderate amount of solvent was used for joining Si dice on ceramic substrates without any metallization preparation for either of the bonding surfaces. The die was bonded to a ceramic substrate at 430°C for 10 min. The study focuses on the mechanical and microstructural characterization of the joints with Si dice on two different types of ceramic substrate. Shear strength measurements were carried out at both ambient and 250°C to evaluate room- and high-temperature performance. Furthermore, the effect of aging at 300°C for 500 h on the mechanical properties is presented. The results of the mechanical and microstructural characterization demonstrate that low-temperature glass frit bonding is an effective die-attach method for harsh-environment electronic packaging.

Room temperature and low temperature (120 degrees C) laser-assisted glass frit bonding of soda-lime glass substrates are accomplished in this work. The locally laser melted bonding showed hermeticity with helium leak rate of < 5 x 10(-8) atm cm(3) s(-1), maintaining its leak rate even after standard climatic cycle tests. Small size devices were bonded at room temperature while larger areas were sealed at the process temperature of 120 degrees C. The sealing parameters were optimized through response surface methodology that makes the process capable for further development regardless of device size.

Localized laser bonding using a glass frit intermediate layer is an ideal technology to hermetically package devices without heating the function components. The glass frit paste is mainly composed of functional fillers, low temperature vanadate glass powder and organic carrier. The viscosity of glass frit has an important influence on screen printing, pre-sintering and laser bonding quality. The content of thickener in organic carrier is a significant reason to affect the viscosity of the paste. In this paper, the effect of organic carrier viscosity in glass frit was investigated in detail. The research shows that the organic carrier viscosity has direct influence on the on screen printing, pre-sintering and laser bonding quality. Shear force test were used to evaluate the bonding quality. After a series of experiments and analysis, we found that adding 8% of ethylcellulose can get a better result of screen printing, pre-sintering and laser bonding.

A wafer-level vacuum package with silicon bumps and electrical feedthroughs on the cap wafer is developed for a microelectromechanical systems (MEMS) resonator device. A MEMS resonator wafer and a cap wafer are bonded together in a vacuum chamber using glass frit bonding. The cap wafer not only provides a vacuum chamber to protect the movable resonator structure and improve the resonant performance but also realizes the redistribution of the electrical feedthroughs by using the silicon bumps. The silicon bumps provide vertical interconnections between the cap wafer and the resonator wafer, which realizes the bonding pads “transferring” from the resonator wafer to the cap wafer. A gold-aluminum eutectic is used to ensure electrical contacts between the cap wafer and the device wafer. The device fabrication and glass frit hermetic bonding process as well as the packaged MEMS resonator characterization are presented in this paper. Experimental results show that the wafer-level vacuum-packaged MEMS resonator results in over 100× higher quality factor (Q) than the resonator vibrating in atmosphere pressure, which confirms the transmission performance improvement due to vacuum packaging. Vacuum inside the package is measured indirectly by measuring the Q of the MEMS resonator inside the package. The experimental results indicate that vacuum about 1 mbar can be sealed in this approach.

Glass frit bonding is a widely used encapsulation technology for micro-electro mechanical systems. In order to guarantee functionality and reliability of a bonding seal, qualified test methods are required for evaluating the quality and strength of the bonding interfaces which are considered key parameters. In the presented work adapting the micro-chevron-test for glass frit bonded samples and arising challenges are discussed. Motivated by the industrial application of glass frit bonding generally used for frame structures an application related guideline for the application of micro-chevron-testing is presented. In addition, high resolution acoustic inspection is used as a key technology for estimating the effective bond strength in combination with further experimental testing and is likewise used for sample pre-selection and defect localization. The presented content provides a sequential overview beginning with sample preparation of glass frit bonded micro chevron samples to mechanical testing and the result analysis as well as a statistical interpretation of a bonded silicon test wafer.

Adhesion caused by various forces can lead to either permanent or temporary stiction. This remains one of the most critical reliability issues for micro-electro-mechanical system (MEMS). In this paper, we present a study using a poly-SiGe micromirror array as a “stiction sensor” to investigate the stiction induced by outgassing during the glass frit bonding process. By comparing the width of the “pull-in windows”, the effect of the induced adhesion between the micromirror and its landing electrode can be identified and quantified.

This Letter presents the effect of high-temperature glass frit bonding conditions on the resistivity coefficient of gauge factor (RCGF), resistivity and gauge factor of polysilicon strain gauges. In previous works, the authors proposed the use of thin polysilicon strain gauges that were bonded onto metal structures with an inorganic glass frit adhesive. However, this glass frit bonding process was carried out at a high temperature, which could cause performance changes of the polysilicon strain gauges in terms of their RCGF, resistivity and gauge factor. To investigate the effect of the glass frit bonding process, the RCGF, resistivity and gauge factor of the polysilicon strain gauge before and after heat treatment by the conventional Al annealing condition and the glass frit bonding condition were compared and evaluated. In the results, large resistivity and gauge factor deviations in the polysilicon strain gauges that were not heat treated were observed. In spite of these large deviations, a linear relationship between the resistivity and the gauge factor was observed. After the polysilicon strain gauges were heat treated by the conventional Al annealing condition and the glass frit bonding condition, the deviations in the values of the resistivity and gauge factor became more uniform than those seen in the strain gauges that were not heat treated. The RCGFs of the polysilicon strain gauges heat treated with the Al annealing condition and the glass frit bonding condition coincided with that of the gauge that was not heat treated.

In this paper, we propose a thin polysilicon strain gauge for the measurement of strain in structural elements. Metal-foil strain gauges are commonly used for such measurements even though polysilicon strain gauges have better sensitivity. However, the proposed polysilicon strain gauge can be applied to structural elements because the strain gauge element is separated from the silicon wafer, due to the small size and low thickness of the proposed gauge. A microelectromechanical system fabrication process of the poly-silicon strain gauge and an inorganic bonding process with a metal substrate have been established. An inorganic bonder-glass frit-was used since the commonly used organic bonders exhibit plastic behavior. Subsequently, the performance of polysilicon strain gauges glass-frit-bonded onto metal cantilever beams was evaluated. The results demonstrate that the resistance increases linearly with tensile stress while it decreases with compressive stress. The gauge factor, which represents the sensitivity of the strain gauges, was 34.0. The resistance decreases linearly with temperature with a temperature coefficient of resistance (TCR) of -328 ppm/°C. The TCR is influenced by two factors-differences in the thermal expansion of the metal cantilever beam and silicon strain gauge and the thermionic emission of the carriers. In this study, the resistance change due to thermionic emission was more effective than that by thermal expansion. The nonlinearity and hysteresis values were 0.21% FS and 0.17 % FS, respectively; this is lower than those of conventional metal-foil strain gauges. Hence, our proposed strain gauge is useful for the measurement of the strain of structural elements.

In this paper, we propose a sensor design by using a polysilicon strain gauge bonded to a metal diaphragm. The fabrication process of the thin polysilicon strain gauges having thicknesses of was established using conventional MEMS technologies; further, the technique of glass frit bonding of the polysilicon strain gauge to the stainless steel diaphragm was established. Performance of the polysilicon strain gauge bonded to the metal cantilever beam was evaluated. The gauge factor, temperature coefficient of resistance (TCR), nonlinearity, and hysteresis of the polysilicon strain gauge were measured. The results demonstrate that the resistance increases linearly with tensile stress, while it decreases with compressive stress. The value of the gauge factor, which represents the sensitivity of strain gauges, is 34.0; this value is about 7.15 times higher than the gauge factor of a metal-foil strain gauge. The resistance of the polysilicon strain gauge decreases linearly with an increase in the temperature, and TCR is . Further, nonlinearity and hysteresis are 0.21 % FS and 0.17 % FS, respectively.

Glass frit bonding is an important technology for the hermetical encapsulation of microsensors. During the manufacturing process or in application the bonding layer is repeatedly exposed to temperature changes. Therefore a meaningful stability assessment must include temperature dependent fracture toughness parameters. This work shows that the influence of temperature changes on the fracture toughness depends on whether the bonding layer is subjected to externally pure tensile or combined tensile and shear loading. The reasons for this effect are discussed by use of finite element simulations. Two different kinds of cracks are compared with regard to the residual stresses that result from the wafer bonding process. These residual stresses have a high influence on the loading conditions at a crack tip, when the crack is kinking into the glass frit material. However the influence of residual stresses on an interfacial crack that propagates parallel to the plane of the bonding layer is almost negligible.