新型锯齿流道压电微泵加工制作及试验

以硅作为基底材料,采用深反应离子刻蚀（DRIE）技术加工出含有新型锯齿流道和传统锥形管的微泵,整个微泵结构为聚二甲基硅氧烷（PDMS）-玻璃-硅-PDMS式.采用阳极键合方法对硅和玻璃之间进行封装.PDMS和玻璃、PDMS和硅之间的封装采用紫外线照射方法,使PDMS表面改性,从而达到不可逆密封.分别对两种微泵在不同电压、频率以及波形驱动下的最大流量（MFR）和最大压力头（MPH）进行测试与比较,发现在固定频率下,两个微泵的最大流量和最大压力头均随驱动电压升高而升高,并且正弦波驱动下的效果要好于其他两种驱动波形;在固定电压下,最大流量随着频率升高在60Hz和200Hz两个频率点同时达到最大,最大压力头则在60～600Hz内一直处于最大值不变;锯齿流道微泵的最大流量和最大压力头明显高于传统锥形微泵.由于流道侧面环形面积的存在增加了流通面积,新形锯齿形流道微泵的效率明显高于传统锥形管微泵.     

用于微电子机械系统封装的体硅键合技术和薄膜密封技术

对静电键合、体硅直接键合和界面层辅助键合等三种体硅键合技术，整片操作、局部操作和选择保护等三种密封技术，以及这些技术用于微电子机械系统的密封作了评述，强调在器件研究开始时应考虑封装问题，具体技术则应在保证器件功能和尽量减少芯片复杂性两者之间权衡决定。     

Studies of semitransparent optoelectronic position sensors

Semitransparent optoelectronic position sensors (ALMY sensors) have been developed for high-precision multipoint position and angle measurements of collimated laser beams over a large measurement range. The sensors provide a position resolution in the order of a micrometer over sensitive areas of several square centimeters. They consist of a thin film of amorphous silicon deposited on a glass substrate between two transparent layers of crossed strip electrodes. A transmittance of 80%-90% has been achieved for 780-nm laser light produced by diode lasers. We report about recent optimizations of the sensor performance and tests of the long-term stability under laser illumination and of the radiation tolerance at high neutron doses. As expected, the radiation hardness of the amorphous silicon sensors exceeds the one of crystalline silicon devices. The custom-designed readout electronics allow for operation at sufficiently low laser intensities in order to prevent significant degradation of the performance of the amorphous silicon sensors under illumination with laser light.     

Improving the stability of amorphous silicon ultraviolet sensors

In this paper we present an improved structure of an amorphous silicon/amorphous silicon carbide ultraviolet sensor, previously presented in literature, whose overall performances have been enhanced by growing a very thin layer of chromium silicide film on the top of the sensor. The sensor is a n-type amorphous silicon/intrinsic amorphous silicon/p-type amorphous silicon carbide stacked structure deposited on a glass substrate. The substrate is covered with a chromium film that acts as back metal contact. The top metal contact is a grid shaped chromium/aluminum/chromium metal stack that allows the incident radiation to reach the active p-type layer.The responses of two sets of sensors fabricated with and without the alloy film under ultraviolet radiation have been studied. The role of the very thin chromium silicide layer is to increase the conductivity of the top surface without attenuating the UV radiation absorbed in the device active layer. The increased top-surface conductivity ensures a better collection of the photogenerated carriers and hides the resistivity variation of the underlying p-doped layer under ultraviolet light caused by dopant activation, leading to a stable and linear behavior. Comparing the photocurrent values obtained on sensors with different area and distance between the grid electrodes, we found that the presence of the chromium silicide film extends the charge collection length by a factor of 10, allowing a better device photoresponse.     

Ultra-Low-Powered Aqueous Shear Stress Sensors Based on Bulk EG-CNTs Integrated in Microfluidic Systems

Novel aqueous shear stress sensors based on bulk carbon nanotubes (CNTs) were developed by utilizing microelectricalmechanical system (MEMS) compatible fabrication technology. The sensors were fabricated on glass substrates by batch assembling electronics-grade CNTs (EG-CNTs) as sensing elements between microelectrode pairs using dielectrophoretic technique. Then, the CNT sensors were permanently integrated in glass–polydimethylsiloxane (PDMS) microfluidic channels by using standard glass–PDMS bonding process. Upon exposure to deionized (DI) water flow in the microchannel, the characteristics of the CNT sensors were investigated at room temperature under constant current (CC) mode. The specific electrical responses of the CNT sensors at different currents have been measured. It was found that the electrical resistance of the CNT sensors increased noticeably in response to the introduction of fluid shear stress when low activation current (≪1 mA) was used, and unexpectedly decreased when the current exceeded 5 mA. We have shown that the sensor could be activated using input currents as low as 100 $mu$A to measure the flow shear stress. The experimental results showed that the output resistance change could be plotted as a linear function of the shear stress to the one-third power. This result proved that the EG-CNT sensors can be operated as conventional thermal flow sensors but only require ultra-low activation power ($sim 1$ $mu$W), which is $sim 1000$ times lower than the conventional MEMS thermal flow sensors.      

A glass/silicon technology for low-power robust gas sensors

Semiconductor gas sensors are devices based on metallic oxides that operate at high temperatures for achieving good sensitivities to the gases of interest. Silicon micromachined structures are often used as platforms for obtaining both high temperatures and low-power consumption at the same time. In this paper, a microstructure based on the combination of micromachined silicon substrates and glass wafers is presented. The device incorporates an array of four different thin-film gas sensors that, depending on the design, can operate at the same or at different temperatures. The designs have been optimized by the finite element method (FEM) and the geometrical parameters of the structure have been selected in order to reduce the power consumption. The full process fabrication is presented. It is based on the combination of bulk micromachining, glass structuring, anodic bonding, and sensitive material deposition. Electrical, thermal, and mechanical tests have been done to demonstrate that the devices show high robustness and can reach high temperatures with low-power consumption.     

Preparation, morphology, and gas-sensing behavior of Cr/sub 2-x/Ti/sub x/O/sub 3+z/ thin films on standard silicon wafers

The effect of humidity on chromium titanium oxide (Cr/sub 2-x/Ti/sub x/O/sub 3+z/, CTO), on both baseline resistance and sensitivity, is small compared to SnO/sub 2/. This has been the key to development of thick-film sensors based on CTO, for detection of carbon monoxide and ammonia in synthetic air. Thin-film structures on silicon substrates offer the possibility to use fabricating, bonding and housing equipment and, hence, a low cost gas sensor production is possible. CTO thin-film sensors on silicon substrates use conventional photolithography, sputtering and evaporation techniques. A Ta/Pt resistance layer (25/200-nm thick) for heating the device to its operating temperature and interdigital electrodes are evaporated and structured on a silicon substrate which is covered by a 1-/spl mu/m SiO/sub 2/ insulating layer. The polycrystalline p-type CTO is deposited onto the electrodes by oxidizing reactive sputtering or evaporation of Cr/Ti-sandwich structures. The resulting sensors were characterized by means of energy dispersive X-ray analysis, secondary electron microscopy, and X-ray diffraction pattern. Also, gas responses toward NO/sub 2/, NH/sub 3/, CO and CH/sub 4/, and different humidity, were investigated.     

不可逆封合微流控芯片中高活性蛋白质阵列的制备

保持生物分子的高活性是在不可逆封合微流控芯片中构筑微阵列芯片的关键问题.首先,利用MEMS技术和表面修饰方法制作了一种聚二甲基硅氧烷(PDMS)/玻璃芯片.应用光刻技术制作了PDMS盖片上的通道,同时用光刻剥离技术制作了玻璃基片上的金膜图案.进而,使用双官能团修饰剂3-氨丙基三甲氧基硅氧烷(APTMS)在玻璃基体和金膜图案上进行选择性表面修饰以吸附形成蛋白质阵列,并在其上覆盖一层水溶性聚乙烯醇(PVA)来保护蛋白质,既可避免其在加热处理过程中的高温伤害,又能防止在PDMS盖片与玻璃基片进行不可逆封合过程中的氧等离子体轰击造成的活性伤害.然后,通入水溶液冲洗除去PVA膜.使用荧光显微镜和原子力显微镜(AFM)考察蛋白质阵列质量,并结合免疫反应实验和细胞捕获固定实验评估蛋白质阵列的活性.结果表明,使用该方法可在不可逆封合的微流控芯片制作中构筑具有直径为200μm的高分辨率蛋白质阵列图案,蛋白质保持高的免疫活性,且可用于固定Hela细胞.     

Splashing-Assisted Femtosecond Laser-Activated Metal Deposition for Mold- and Mask-Free Fabrication of Robust Microstructured Electrodes for Flexible Pressure Sensors (Small 24/2023)

Flexible pressure sensors play an indispensable role in flexible electronics. Microstructures on flexible electrodes have been proven to be effective in improving the sensitivity of pressure sensors. However, it remains a challenge to develop such microstructured flexible electrodes in a convenient way. Inspired by splashed particles from laser processing, herein, a method for customizing microstructured flexible electrodes by femtosecond laser-activated metal deposition is proposed. It takes advantage of the catalyzing particles scattered during femtosecond laser ablation and is particularly suitable for moldless, maskless, and low-cost fabrication of microstructured metal layers on polydimethylsiloxane (PDMS). Robust bonding at the PDMS/Cu interface is evidenced by the scotch tape test and the duration test over 10 000 bending cycles. Benefiting from the firm interface, the developed flexible capacitive pressure sensor with microstructured electrodes presents several conspicuous features, including a sensitivity (0.22 kPa⁻¹) 73 times higher than the one using flat Cu electrodes, ultralow detection limit (<1 Pa), rapid response/recovery time (4.2/5.3 ms), and excellent stability. Moreover, the proposed method, inheriting the merits of laser direct writing, is capable of fabricating a pressure sensor array in a maskless manner for spatial pressure mapping.     

Solventless adhesive bonding using reactive polymer coatings

A novel solventless adhesive bonding (SAB) process is reported, which is applicable to a wide range of materials including, but not limited to, poly(dimethylsiloxane) (PDMS). The bonding is achieved through reactions between two complementary polymer coatings, poly(4-aminomethyl-p-xylylene-co-p-xylylene) and poly(4-formyl-p-xylylene-co-p-xylylene), which are prepared by chemical vapor deposition (CVD) polymerization of the corresponding [2.2]paracyclophanes and can be deposited on complementary microfluidic units to be bonded. These CVD-based polymer films form well-adherent coatings on a range of different substrate materials including polymers, glass, silicon, metals, or paper and can be stored for extended periods prior to bonding without losing their bonding capability. Tensile stress data are measured on PDMS with various substrates and compared favorably to current methods such as oxygen plasma and UV/ozone. Sum frequency generation (SFG) has been used to probe the presence of amine and aldehyde groups on the surface after CVD polymerization and their conversion during bonding. In addition to bonding, unreacted functional groups present on the luminal surface of microfluidic channels provide free chemical groups for further surface modification. Fluorescently labeled molecules including rhodamine-conjugated streptavidin and atto-655 NHS ester were used to verify the presence of active functional groups on the luminal surfaces after bonding.     

Piezoresistive pressure sensing by porous silicon membrane

In this paper, the piezoresistive pressure-sensing property of porous silicon has been reported. The pressure sensitivity of a porous silicon membrane of 63% porosity and 20-/spl mu/m thickness has been observed to be about three times more than that of a conventional bulk silicon membrane of the same dimensions. The increased sensitivity is attributed to the improvement in piezoresistance due to quantum confinement in the porous silicon nanostructure. The piezoresistive coefficient of porous silicon is estimated for the first time and is observed to be about 50% larger than that of monocrystalline silicon for a 63% porosity porous silicon membrane. The response time has also been studied and observed to be significantly shorter. Power dissipation of the porous silicon pressure sensor is also much less compared to that of commercial bulk silicon piezoresistive pressure sensors.     

Silicon-to-indium tin oxide coated glass bonding for packaging of field emission arrays fabricated on silicon wafer

A silicon-to-In₂O₃:Sn coated glass bonding has been developed for the package of field emission arrays fabricated on the silicon wafer, utilizing a conventional silicon-to- silicon anodic bonding using the glass layer. A 1.8 m Pyrex #7740 glass layer was deposited on the In₂O₃:Sn coated glass by an electron beam evaporation. It was confirmed that the composition of the glass layer was nearly the same as that of the bulk Pyrex #7740 glass plate. In this work, bonding the silicon and In₂O₃:Sn coated glass was achieved at a temperature of 190 °C with an applied voltage of 60 V_dc. A secondary ion mass spectroscopy analysis was used to confirm the modeled bonding kinetics of the silicon-to-In₂O₃:Sn coated glass.     

锯齿型微流道微泵流动特性分析及性能测试

通过对新型锯齿型和传统扩张／收缩型两种微流道内部流场数值分析结果进行比较,得出微流道内流动状态随雷诺数的变化情况以及漩涡产生原因：锯齿型微流道由于侧面齿形角的存在．流动过程中较传统扩张／收缩型微流道易产生漩涡,正是由于漩涡的产生使流道压力损失降低．因而新型锯齿型微流道微泵性能优于传统扩张／收缩微流道微泵．最后采用先进的硅深反应刻蚀技术（DRIE）在硅片上加工制作出两种微流道及泵腔结构,并采用硅-玻璃阳极键合以及玻璃-聚二甲基硅氧烷（PDMS）紫外线键合的方法封装出三明治结构式微泵．通过对两种微泵分别在对称和电压偏置正弦波驱动下进行性能测试．得出电压正向偏置时微泵性能仅次于对称波形驱动下微泵性能,而电压负向偏置时最差．在对称波形驱动下,新型锯齿型微流道微泵最大流量（MFR）和最大压力头（MPH）值分别为扩张／收缩微流道微泵的1．4倍和1．9倍．因此采用新型锯齿型微流道结构将使微泵性能大大提高．     

Microelectromechanical system pressure sensor integrated onto optical fiber by anodic bonding

Optical microelectromechanical system pressure sensors based on the principle of Fabry-Perot interferometry have been developed and fabricated using the technique of silicon-to-silicon anodic bonding. The pressure sensor is then integrated onto an optical fiber by a novel technique of anodic bonding without use of any adhesives. In this anodic bonding technique we use ultrathin silicon of thickness 10 microm to bond the optical fiber to the sensor head. The ultrathin silicon plays the role of a stress-reducing layer, which helps the bonding of an optical fiber to silicon having conventional wafer thickness. The pressure-sensing membrane is formed by 8 microm thick ultrathin silicon acting as a membrane, thus eliminating the need for bulk silicon etching. The pressure sensor integrated onto an optical fiber is tested for static response, and experimental results indicate degradation in the fringe visibility of the Fabry-Perot interferometer. This effect was mainly due to divergent light rays from the fiber degrading the fringe visibility. This effect is demonstrated in brief by an analytical model.     

Fabrication and testing of bulk micromachined silicon carbide piezoresistive pressure sensors for high temperature applications

This paper explores the development of high-temperature pressure sensors based on polycrystalline and single-crystalline 3C-SiC piezoresistors and fabricated by bulk micromachining the underlying 100-mm diameter (100) silicon substrate. In one embodiment, phosphorus-doped APCVD polycrystalline 3C-SiC (poly-SiC) was used for the piezoresistors and sensor diaphragm, with LPCVD silicon nitride employed to electrically isolate the piezoresistor from the diaphragm. These piezoresistors fabricated from poly-SiC films deposited at different temperatures and doping levels were characterized, showing -2.1 as the best gauge factor and exhibited a sensitivities up to 20.9-mV/V*psi at room temperature. In a second embodiment, epitaxially-grown unintentionally nitrogen-doped single-crystalline 3C-SiC piezoresistors were fabricated on silicon diaphragms, with thermally grown silicon dioxide employed for the piezoresistor electrical isolation from the diaphragm. The associated 3C-SiC/SiO/sub 2//Si substrate was fabricated by bonding a (100) silicon wafer carrying the 3C-SiC onto a silicon wafer with thermal oxide covering its surface. The 3C-SiC handle wafer was then etched away in KOH. The diaphragm was fabricated by time etching the silicon substrate. The sensors were tested at temperatures up to 400/spl deg/C and exhibited a sensitivity of 177.6-mV/V*psi at room temperature and 63.1-mV/V*psi at 400/spl deg/C. The estimated longitudinal gauge factor of 3C-SiC piezoresistors along the [100] direction was estimated at about -18 at room temperature and -7 at 400/spl deg/C.     

An electrochemical pumping system for on-chip gradient generation

Within the context of microfluidic systems, it has been difficult to devise pumping systems that can deliver adequate flow rates at high pressure for applications such as HPLC. An on-chip electrochemical pumping system based on electrolysis that offers certain advantages over designs that utilize electroosmotic driven flow has been fabricated and tested. The pump was fabricated on both silicon and glass substrates using photolithography. The electrolysis electrodes were formed from either platinum or gold, and SU8, an epoxy-based photoresist, was used to form the pump chambers. A glass cover plate and a poly(dimethylsiloxane) (PDMS) gasket were used to seal the chambers. Filling of the chambers was accomplished by using a syringe to inject liquid via filling ports, which were later sealed using a glass cover plate. The current supplied to the electrodes controlled the rate of gas formation and, thus, the resulting fluid flow rate. At low backpressures, flow rates >1 microL/min have been demonstrated using <1 mW of power. Pumping at backpressures as high as 200 psi have been demonstrated, with 20 nL/min having been observed using <4 mW. By integrating two electrochemical pumps with a polymer electrospray nozzle, we have confirmed the successful generation of a solvent gradient via a mass spectrometer.     

一种硅基谐振型压力传感器技术研究

文章利用硅／硅键合、减薄抛光和IC工艺技术,开展硅基谐振型压力传感器技术研究,解决了三维体加工与IC工艺兼容的关键技术问题,成功地研制出一种硅基谐振型压力传感器样品,在常压下测试其Q值达到400,进一步参数测试还在进行中。     

基于柔性掩膜的高可靠性玻璃喷砂微加工工艺

喷砂是一种高效率的表面加工技术,将其应用于微加工领域可以实现对玻璃、硅和陶瓷等脆性材料的选择性刻蚀.本文着重探讨了掩膜性质及刻蚀条件对喷砂微加工刻蚀效率及刻蚀形貌的影响.实验中对柔性聚二甲基硅氧烷(PDMS)掩膜微结构的制备方法进行了改良,即借助精密切削工艺实现PDMS/SU-8微结构边界精确互补成形,制备了可以满足选择性刻蚀要求的掩膜结构.同时改变实验条件,研究了掩膜开口尺寸、压缩空气压强以及砂材粒径对喷砂速率及刻蚀形貌的影响.结果表明:适当增大压缩空气气压有助于待刻蚀材料从塑性到脆性的转变,刻蚀速率有明显提高.而将砂材粒径从30μm减小至20μm,可以改善成形形貌.初步研究结果表明,文中提出的玻璃喷砂微加工方法能够满足深度为500μm的玻璃通孔阵列的刻蚀要求.     

Review of cold spraying and its use for metallic glass coatings

Cold spraying (CS), a solid-state spraying technology, is expected to become an appropriate supplementary for traditional spraying methods owing to its plenty of merits such as high deposition efficiency, low temperature and little influence on the particles/substrate. The most reported researches are bulk alloys fabricated by CS. However, the systematic introduction and cold-sprayed metallic glass coatings have not been summarised. Therefore, in this paper, the international research status of CS including equipment structure, spraying process and parameters, advantages and disadvantages, deposit features and bonding mechanism were introduced. By using this technology, the successful researches about Fe-, Al-, Ni-, Cu- and Zr- based amorphous alloy coatings are reported. To overcome the limitations, further development and solutions were proposed.     

Calcium-assisted glass-to-glass bonding for fabrication of glass microfluidic devices

Glass is a desired material for many microfluidics applications. It is chemically resistant and has desirable characteristics for capillary electrophoresis. The process to make a glass chip, however, is lengthy and inconvenient, with the most difficult step often being the bonding of two planar glass substrates. Here we describe a new glass bonding technique, which requires only washing of the glass surfaces with a calcium solution and 1-2 h of bonding at 115 degrees C. We found calcium uniquely allows for this simple and efficient low-temperature bonding to occur, and none of the other cations we tried (e.g., Na (+), Mg (2+), Mn (3+)) resulted in satisfactory bonding. We determined this bond is able to withstand high applied field strengths of at least up to 4 kV x cm (-1). When intense pressure was applied to a fluid inlet, a circular portion of the coverslip beneath the well exploded outward but very little of the glass-glass interface debonded. In combination with the directed hydrofluoric acid etching of a glass substrate using a poly(dimethylsiloxane) (PDMS) etch guide, we were able to make glass chips with better than 90% yield within 6 h. This technique is compatible with inexpensive unpolished glass and is limited in resolution by the PDMS etch guide used and the intrinsic properties of isotropic etching.