阳极键合强度及其评价方法

阳极键合作为一种在微机电系统(MEMS)中运用的关键技术,具有工艺简单、键合强度高、密封性好等优点。经过几十年的发展,该技术在键合机理和提高与评价键合强度等诸多方面都得到了很大的发展,并应用于越来越多的领域。对阳极键合技术的机理、键合基片材料的发展以及键合强度的评价方法等方面进行了综述和评价,并对阳极键合技术在MEMS中的发展趋势作出展望。     

Water glass bonding

The author developed a low-temperature (80°C), low-external loads (electric field, magnetic field, load, etc.) bonding technology using water glass which is used in making molds (silica sand). The adhesive area ratio attained by this bonding technology was more than 95% and the bonding strength was about 290 kgf/cm². As this water glass bonding technology is applicable at comparatively low-temperatures, the residual stress of the bond is so small as to be able to bond eight 4-inch wafers together in the 3rd dimensional direction. In addition, as the thickness of a bonding layer is as small as several nanometers, the precision bonding of a tolerance of ±3 μm was also possible through alignment, and we could successfully fixed a cap with having a bonding seal of 0.32 mm wide in the vacuum. The leak rate was less than the detection limit of the He leak detector (1×10⁻¹⁰ Pa m³/s), showing excellent air-tightness. Using this bonding technology, the author made a self-package type IR microsensor on an experimental basis, and carried out an accelerated environmental test. As a result, its MTTF (mean time to failure) was estimated to be 6 years.     

玻璃浆料键合气密性研究

研究玻璃浆料真空封装MEMS器件工艺,由于玻璃浆料键合工艺条件控制较为复杂,键合不当易失败漏气.利用光学显微镜、超声显微镜、激光显微镜、电镜等多种显微镜对各阶段玻璃浆料的形貌进行观察,对由印刷方式、预处理条件和键合工艺对键合气密性的影响进行了分析.提出了影响玻璃浆料键合气密性的几个原因,对玻璃浆料键合工艺条件控制有非常重要的指导意义.     

Low-temperature anodic bonding of silicon to silicon wafers by means of intermediate glass layers

Silicon wafers have been anodically bonded to sputtered lithium borosilicate glass layers (Itb 1060) at temperatures as low as 150–180 °C and to sputtered Corning 7740 glass layers at 400 °C. Dependent on the thickness of the glass layer and the sputtering rate, the sputtered glass layers incorporate compressive stresses which cause the wafer to bow. As a result of this bowing, no anodic bond can be established especially along the edges of the silicon wafer. Successful anodic bonding not only requires plane surfaces, but also is determined very much by the alkali concentration in the glass layer. The concentration of alkali ions as measured by EDX and SNMS depends on both the sputtering rate and the oxygen fraction in the argon process gas. In Itb 1060 layers produced at a sputtering rate of 0.2 nm/s, and in Corning 7740 layers produced at sputtering rates of 0.03 and 0.5 nm/s, respectively, the concentration of alkali ions in the glass layers was sufficiently high, at oxygen partial pressures below 10^-4 Pa, to achieve anodic bonding. High-frequency ultrasonic microanalysis allowed the bonding area to be examined non-destructively. Tensile strengths between 4 and 14 MPa were measured in subsequent destructive tensile tests of single-bonded specimens.     

A continuous-membrane micro deformable mirror based on anodic bonding of SOI to glass wafer

As one of the most important components in adaptive optics, the deformable mirror (DM) is required to have a flat surface for better performance. For micromachined DMs, single-crystal-silicon (SCS) membrane is an ideal material for high quality reflective mirror surface owing to its good flatness and small residual stress. In this research, a process was established to realize SCS mirror membrane by DRIE of SOI wafer and anodic bonding of SOI wafer to Pyrex 7740 glass. Using this process, the proof-of-concept for a micromachined DM composed of SCS mirror surface has been successfully demonstrated. The prototype DM shows a stroke of 4.23 μm at 120 V. The P–V and rms of the reflective mirror surface are 492 and 82 nm, respectively. The performance of the prototype DM can somewhat satisfy the need of AO in visible spectrum. Better surface quality is anticipated by employing SOI wafers with strictly controlled residual stress.     

A simple approach to fabricate multi-layer glass microfluidic chips based on laser processing and thermocompression bonding

Microfluidics and Nanofluidics - We study the influence of variations of cross-section on the drying dynamics by pervaporation in microfluidic channels surrounded by water-permeable...     

Manufacture of microfluidic glass chips by deep plasma etching, femtosecond laser ablation, and anodic bonding

Two dry subtractive techniques for the fabrication of microchannels in borosilicate glass were investigated, plasma etching and laser ablation. Inductively coupled plasma reactive ion etching was carried out in a fluorine plasma (C₄F₈/O₂) using an electroplated Ni mask. Depth up to 100 μm with a profile angle of 83°–88° and a smooth bottom of the etched structure (Ra below 3 nm) were achieved at an etch rate of 0.9 μm/min. An ultrashort pulse Ti:sapphire laser operating at the wavelength of 800 nm and 5 kHz repetition rate was used for micromachining. Channels of 100 μm width and 140 μm height with a profile angle of 80–85° were obtained in 3 min using an average power of 160 mW and a pulse duration of 120 fs. A novel process for glass–glass anodic bonding using a conductive interlayer of Si/Al/Si has been developed to seal microfluidic components with good optical transparency using a relatively low temperature (350°C).     

Mechanical and electrical bonding between silicon wafer and glass wafer with etched channels containing metal tracks

In this paper a novel process to bond and, at the same time, to electrically connect a silicon wafer to a glass wafer is presented. It consists of a low temperature anodic bonding process between silicon and glass by using a glass wafer with etched channels in order to contain metal tracks. The glass-to-silicon anodic bonding process at low temperatures (not exceeding 300°C) assures a strong mechanical link (Berthold et al. in Transducers 1999, June:7–10, 1999). The electrical contacts between the metal pads on the backside of a silicon wafer and the metal pads on the glass wafer are achieved by sintering and diffusion of metals due to a kind of thermo compression bonding. This bonding method permits a high vertical control due to a well-controlled etching of the cavity depth and to the thickness precision of both metallization (pads on silicon wafers and metal tracks on glass wafer). This IC-processing compatible approach opens up the way to a new electrical connection concept keeping, at the same time, a strong mechanical bond between glass and silicon wafers for an easier fabrication of a more complex micro-system.     

Characteristics of ACPDP test panels with aluminum fence electrode formed via anodic bonding with soda‐lime glass

Abstract— In an attempt to reduce materials and processing costs of ACPDPs, aluminum fence electrodes were prepared on soda‐lime glass substrates by chemically etching aluminum foil bonded directly onto the substrate via an anodic‐bonding process. Several different fence‐electrode patterns were designed and coated either with a glass dielectric layer or with an anodic aluminum oxide layer. Firing voltages, operation margin, luminance, and luminous efficiency of such test panels were evaluated. The results indicated that the performance of test panels with aluminum fence electrodes is comparable with conventional test panels with ITO/Ag electrodes, demonstrating the possibility of a dramatic reduction in the costs of ACPDPs.     

芯片焊接中焊点自动定位技术的研究

为实现自动焊接,在已定位芯片的基础上,对自动定位芯片和框架上的焊点进行了研究,提出了一个高效精确的方法.在系统运行初始,人工引导测定保存每对焊点相对于芯片中心的坐标,使得在自动焊接过程中,定位了芯片中心,就得到了每对焊点坐标.芯片在手工粘贴时存在旋转和偏移误差,还需修正每对焊点坐标.该方法实现了高速精确的焊点自动定位.     

阳极键合在MEMS封装中的研究进展

在微电子机械系统(Micro Electro Mechanical Systems,MEMS)领域,阳极键合是应用最为广泛的一项技术,有着广阔的发展前景。表面预处理和键合工艺是阳极键合中最为重要的两个因素。介绍了近年来在表面预处理和键合工艺方面的研究进展,分析总结了该技术的研制情况,指明了现阶段表面预处理和阳极键合存在的问题以及未来的研究方向。     

PMMA to Polystyrene bonding for polymer based microfluidic systems

A thermal bonding technique for Poly (methylmethacrylate) (PMMA) to Polystyrene (PS) is presented in this paper. The PMMA to PS bonding was achieved using a thermocompression method, and the bonding strength was carefully characterized. The bonding temperature ranged from 110 to 125 °C with a varying compression force, from 700 to 1,000 N (0.36–0.51 MPa). After the bonding process, two kinds of adhesion quantification methods were used to measure the bonding strength: the double cantilever beam method and the tensile stress method. The results show that the bonding strength increases with a rising bonding temperature and bonding force. The results also indicate that the bonding strength is independent of bonding time. A deep-UV surface treatment method was also provided in this paper to lower the bonding temperature and compression force. Finally, a PMMA to PS bonded microfluidic device was fabricated successfully.     

A glass box approach to adaptive hypermedia

Utilising adaptive interface techniques in the design of systems introduces certain risks. An adaptive interface is not static, but will actively adapt to the perceived needs of the user. Unless carefully designed, these changes may lead to an unpredictable, obscure and uncontrollable interface. Therefore the design of adaptive interfaces must ensure that users can inspect the adaptivity mechanisms, and control their results. One way to do this is to rely on the user's understanding of the application and the domain, and relate the adaptivity mechanisms to domain-specific concepts. We present an example of an adaptive hypertext help system POP, which is being built according to these principles, and discuss the design considerations and empirical findings that lead to this design.     

Artificial neural networks to optimize the extrusion of an aluminium alloy

Extrusion of aluminium alloys is a complex process which depends on the characteristics of the material and on the process parameters (initial billet temperature, extrusion ratio, friction at the interfaces, die geometry etc.). The temperature profile at the die exit, largely influences microstructure, mechanical properties, and surface quality of an extruded product, consequently it is the most important parameter for controlling the process. In turn the temperature profile depends on other process variables whose right choice is fundamental to avoid surface damage of the extruded product. In the present work, two neural networks were implemented to optimize the aluminium extrusion process determining the temperature profile of an Al 6060 alloy (UNI 9006/1) at the exit of induction heater (ANN1) and at the exit of the die (ANN2). The three-layer neural networks with Levemberg Marquardt algorithm were trained with the experimental data from the industrial process. The temperature profiles, predicted by the neural network, closely agree with experimental values.     

Characterization of aluminium nitride and aluminium oxide thin films sputter-deposited on organic substrates

In microsystems technology, passivation layers are generally required to protect micro devices and functional elements against environmental impact, particularly against corrosion, thus increasing reliability and lifetime to acceptable values. In this work, the use of sputter-deposited aluminium oxide and aluminium nitride thin films on flexible polyimide foils was investigated, aiming at the protection of flow sensitive elements. Due to a high defect density located at the interface between the passivation layer and the organic substrate, the adhesion of pure aluminium oxide thin films was found to be poor when applying a combination of mechanical stress (e.g. bombardment with water droplets) and thermal cycling as an accelerated ageing procedure. A bi-layer consisting of aluminium nitride and aluminium oxide, however, shows a defect-free interface to the organic substrate resulting in an enhanced adhesion. In addition, no structural failure can be detected after applying the aging procedure, making this bi-layer approach well suited for the targeted application.     

Enhancement of bonding strength of packaging based on BCB bonding for RF devices

This paper presents a Si cap zero-level packaging technique based on a double-layer BCB sealing ring. The BCB ring is defined before the housing cavity etching to achieve high BCB bonding strength. It is found that the non-uniformity of the BCB ring defined on a Si cap with housing cavity prevents the package having high bonding strength. Three different packages have been prepared for shear test; a Si cap without cavity, a recessed Si cap with a conventional BCB ring and a recessed Si cap with pre-defined BCB ring. The three samples for each type of package are measured. The average measured bonding strengths of the test samples are 71, 16 and 42?MPa, respectively, and hence the proposed BCB sealing ring process provides 60?% of bonding strength of Si cap package without cavity for Si cap package with cavity. In addition, the insertion loss change of the packaged CPW is less than 0.1?dB up to 67?GHz while the return loss better than 15?dB at the measured frequency range.     

Ultraviolet bonding of perfluoropolyethers to carbon surfaces investigated using quantum chemical methods

For improving the tribological performance of hard disk drives, nanometer-thick perfluoropolyether (PFPE) lubricant films are generally treated with ultraviolet (UV) irradiation to bond them to the carbon overcoats of the disks. By modeling UV irradiation as an electron emission and attachment process, we investigate the UV bonding of nonfunctional PFPE Z and functional PFPE Zdol to hydrogenated and nitrogenated carbon surfaces with quantum chemical methods. Our calculation results show that, upon electron attachment, Z dissociates at its main chain to two fragments terminated by CF₂CF₂ and CF₂O groups, whereas Zdol dissociates to a hydrogen fluoride and a fragment. The perfluoromethoxy oxygen in one of the Z fragments and the carbon radical and the hydrogen-truncated end group in the Zdol fragment interact strongly with sp² and oxidized sites on carbon surfaces. Imine moieties on the CNx surface also contribute considerably to the UV bonding of Zdol.     

Study of PMMA thermal bonding

The bond strength dependence on bonding temperature and bonding pressure in traditional thermal bonding and surface modification bonding of PMMA is investigated. The results show that the bond strength of the latter bonding method is larger than the former. The effects of post-annealing and aging on bond strength are also demonstrated. Then the bonding parameters of temperature and pressure are optimized, and typical bond strength of 1 MPa is obtained at bonding temperature of 95°C, bonding pressure at 2 MPa, bonding time for 3 min and 50°C post-annealing for 2 h. The successful bonded microfluidic device was obtained through this optimized thermal bonding method.     

常温静电封接技术的研究与实验尝试

根据静电封接的机理，配制了一种低温玻璃作为封接材料，初步完成了常温下的静电封接实验。