An improved bulk acoustic waves chip based on a PDMS bonding layer for high-efficient particle enrichment

In this work, we developed a feasible way to package bulk acoustic waves chip with sandwich structure by inserting a polydimethylsiloxane (PDMS) layer as the adhesive between cover glass and silicon substrate. After spin-coating and curing process, a PDMS layer was formed on one side of the cover glass and then bonded to the silicon substrate with microchannels by oxygen plasma treating. Both simulation and experiment showed that the chip was not leaking and the acoustic waves produced by the piezoelectric transducer could be propagated through the PDMS layer. Finally, a standing wave field was formed in the microchannels. Compared with traditional chip bonded by anodic bonding, simulation results showed that this packaging method did decrease the acoustic pressure in the channel, but the reduction was acceptable. After optimizing the experimental parameters, we successfully aggregated 15-μm silica spheres under a very low input power (21 dBm) at a flow velocity of 1 ml/h, and the enrichment efficiency of silica spheres was greater than 97%.     

Carbon nanotube based miniaturized electron gun and column assembly

We report on the application of silicon micromachining for the fabrication of miniaturized electron gun (MEG) assembly using vertically aligned carbon nanotubes. The proposed MEG consists of two main parts of electron gun and the accelerating column. While the electron gun consists of carbon nanotubes grown on a silicon substrate acting as an electron emission source, the accelerating column is made of micromachined silicon wafers with 5 μm thick membranes operating as objective lenses. These two wafers are placed together and sealed using a three-dimensional packaging technique. The simulation and experimental results show the evolution of a narrow electron beam by applying a proper voltage to the anodes and objective lens. The diverging and focusing of the beam can be controlled by applying the proper voltage on electrostatic lenses. This structure could be suitable for low energy SEM devices and surface physics applications.     

Process development of a novel wafer level packaging with TSV applied in high-frequency range transmission

The process development of a novel wafer level packaging with TSV applied in high-frequency range transmission is presented. A specially designed TSV structure (a core TSV and six shielding TSVs) is adopted to connect the components on different sides of the high-resistivity silicon wafer. And the microstrip line in the microwave monolithic integrated circuit is used to transmit high-frequency signal in packaging structure together with the low permittivity intermediate dielectric polymer, benzocyclobutene. The TSV fabrication process and the multi-layer interconnection is illustrated in details. The electrical measurement result of the microstrip lines connected by TSVs reveals the resistances within 0.719 Ω, a return loss better than 23.8 dB and an insertion loss better than 2.60 dB from 14 to 40 GHz.     

基于低温共烧陶瓷的微机械差分电容式加速度计的研究

低温共烧陶瓷（LTCC）技术是实现电子设备小型化、高密度集成化的主流封装/组装集成技术,可适用于耐高温、耐受恶劣环境下的特性要求。报道了以LTCC为结构材料设计、制作的一种MEMS差分电容式加速度计。该器件的敏感质量、4根悬臂梁结构都内嵌于LTCC多层基板,质量块和上下盖板之间通过印刷电极组成差分电容对;高精度电容检测芯片表贴于LTCC基板表面,将差分电容信号转化为电压信号。论文讨论了微机械LTCC加速度计的设计与制备、检测电路和性能测试。LTCC的高密度多层布线减小了互连线的长度和相关耦合寄生电容;基于集成芯片的检测电路解决了分立式检测电路的引起噪声大、电路复杂等问题。测试结果表明：该加速度计结构灵敏度较高,小载荷情况下表现出良好的线性关系,灵敏度约为30.3 mV/gn。     

中国微米纳米-基于低温共烧陶瓷的微机械差分电容式加速度计的研究

低温共烧陶瓷（LTCC）技术是实现电子设备小型化、高密度集成化的主流封装/组装集成技术,可适用于耐高温、耐受恶劣环境下的特性要求。本文报道了以LTCC为结构材料设计、制作的一种MEMS差分电容式加速度计。该器件的敏感质量、四根悬臂梁结构都内嵌于LTCC多层基板,质量块和上下盖板之间通过印刷电极组成差分电容对;高精度电容检测芯片表贴于LTCC基板表面,将差分电容信号转化为电压信号。论文讨论了微机械LTCC加速度计的设计与制备、检测电路和性能测试。LTCC的高密度多层布线减小了互连线的长度和相关耦合寄生电容;基于集成芯片的检测电路解决了分立式检测电路的引起噪声大、电路复杂等问题。测试结果表明：该加速度计结构灵敏度较高,小载荷情况下表现出良好的线性关系,灵敏度约为30.3mV/g。     

The implementation and performance evaluation of a silicon-based LED packaging module with lens configuration

This study develops a transfer molding with flexible master for a silicon-based light emitting diode packaging with an aspherical lens and a microlens array using microelectromechanical systems technology. By transferring the pattern from wafer to wafer, the precise alignment of the lens configuration and the reflector of the silicon substrate can be achieved; batch processing can be used to reduce the costs. The size of the packaging element can be further reduced to allow more applications. For evaluating the packaging performance, the transfer of the pattern of various lens profiles is accomplished successfully using silicone gel and electroplating nickel as the lens molds, and experiments to determine the mechanical reliability are conducted. The experimental results show that the lens profiles of the silicone gel and nickel masters are exactly transferred onto the surfaces of epoxy and silicone gel encapsulations, respectively, without any damage to the material surface. The brightness of the packaging elements with a single aspherical lens profile and high fill factor microlens array are increased by 26 and 16 %, respectively, as compared with optical encapsulation with a smooth curved surface. The light uniformity is greatly improved for a 100 % fill factor microlens array. The proposed packaging solution satisfies the requirements of pattern transfer in a wafer level and improves lighting performance.     

Design and simulations of a new biaxial silicon resonant micro-accelerometer

This paper presents a new biaxial silicon resonant micro-accelerometer. The device basically consists of a single proof mass, four pairs of decoupled beams, four lever mechanisms and two pairs of resonators, which provides 2-D in-plane acceleration measurement with the decoupled two pairs of resonators. Structure optimization is implemented by taking advantage of the finite element analyses. From the simulation results we can see that the effective frequencies of two acceleration sensitive modes are 1010.18 and 1010.13 Hz respectively, and the undesired modes and effective modes are isolated apparently. Additionally, high linear relationship between the input acceleration and the resonant frequency shifts of resonators are demonstrated by the input–output characteristic simulation. Moreover, simulation results reveal the scale factor for the x-axis is 180.03 Hz/g, and the scale factor for y-axis is 180.75 Hz/g, while the cross-axis sensitivity for x-axis is 0.046 Hz/g, and the cross-axis sensitivity for y-axis is 0.027 Hz/g. The high sensitivity and low cross-axis sensitivity are thus adequately confirmed. By the way, the simulation of temperature dependent characteristics demonstrate that the differential scheme can effectively suppress the influence of temperature variation, and the thermal analysis shows that the device can bear the thermal stress induced by temperature change. All these simulations above can verify the feasibility of the structure design.     

Polymer microstructure generated by laser stereo-lithography and its transfer to silicon substrate using reactive ion etching

Micro-fabrication combining stereo-lithography with reactive ion etching is proposed. Three-dimensional polymer structures smaller than 1 mm are fabricated on silicon wafer by He-Cd (325.0 nm) laser stereo-lithography. Using the polymer structure having a high-aspect ratio as resist for deep reactive ion etching, the microstructure is transferred to the silicon substrate with an etching ratio of 0.5. The proposed technique has been demonstrated by the fabrication of lens-like structures.     

Fabrication of silicon-on-insulator MEM resonators with deep sub-micron transduction gaps

The paper proposes and validates a low-cost technological process for the realization of mono-crystalline micro-electro-mechanical (MEM) resonators with deep sub-micron transduction gaps, on silicon-on-insulator (SOI) substrates. The MEM resonators are designed to work as bulk lateral resonators (BLR) in which the resonance of a suspended mass is excited and detected by lateral electrodes. For MEM BLRs, nano-scaled gaps (<200 nm) are essential to reduce the motional resistance in the order of few kΩ as well as to avoid the use of large DC applied voltages. Only standard optical lithography with 1 μm resolution and IC-compatible processing steps are employed to obtain 100–200 nm wide gaps with very high aspect-ratios of more than [40:1], allowing the fabrication of high Q resonators for MHz to GHz operating frequency range.     

Monolithic integration of Pb(Zr,Ti)O3 thin film based resonators using a complete dry microfabrication process

Monolithic fabrication of lead zirconate titanate [Pb(Zr,Ti)O₃ or PZT] based thin film resonant devices such as microcantilevers, Lamb wave and bulk acoustic wave resonators are demonstrated. High-performance PZT thin films with a thickness of 2.6 μm are prepared on a silicon on insulator wafer by a sputtering deposition process. A highly selective reactive ion etching process is employed for micro-patterning of PZT, platinum electrodes, and SiO₂ insulation layer. Self-actuation of the PZT microcantilevers is demonstrated and the frequency response is characterized using a laser Doppler vibrometer. The frequency response of the Lamb wave resonator is evaluated by measuring its transmission characteristic using a network analyzer. For a Lamb wave resonator with a length of 240 μm and an interdigital period of 80 μm, the 1st order and 2nd resonance frequencies are 15.3 and 41.8 MHz, respectively.     

A simple thermo-compression bonding setup for wire bonding interconnection in pressure sensor silicon chip packaging

In the process of piezo-resistive pressure sensor packaging, a simple thermo-compression bonding setup has been fabricated to achieve the wire bonding interconnection of a silicon chip with printed circuit board. An annealed gold wire is joined onto a pad surface with a needle-like chisel under a force of 0.5–1.5 N/point. The temperature of the substrate was maintained in the range of 150–200°C and the temperature of the chisel was fixed at around 150°C during wire bonding operation. The tensile strength of the wire bonding was measured with a bonding tester by the destructive-pulling experiment and was found to be at the average of 132 mN/mm². The microstructure of the bonding point was examined by scanning electron microscopy. The interface of the thermo-compression boning was shown to possess an acceptable level of reliability for a micro-electromechanical system (MEMS)-based device. The results showed that this setup can be easily operated for fabrication and is suitable for fabricating not only low-cost pressure sensors, but also other MEMS devices.

     

Approaches for designing semilump filter utilizing LTCC with hybrid dielectrics

In this article, a semilump filter was implemented by using low‐temperature C‐fired ceramic (LTCC) technology with hybrid dielectrics to miniaturize the size and to attain the promising electrical properties. In the multilayer architecture, the striplines (inductors) were realized on the low‐K dielectric (K = 7.8) and capacitors were realized on the high‐K (K = 27) dielectric. Capacitor implemented by high‐permittivity dielectrics is shown to be very efficient in decreasing dimensions of semilump filter with low‐permittivity dielectric. Inductor implemented by low‐permittivity dielectric is shown to be enhanced the Q‐factor of the resonators. The design of the novel semilump filter has been developed and the prototypes fabricated by using the LTCC technology with hybrid dielectrics. The results of prototype measurement agree very well with the simulation results. The investigation proves the capability of the LTCC technology with hybrid dielectrics that is able to effectively miniaturize the filter and still attain the promising electrical performance of filters. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Laser transmission bonding of silicon to silicon with metallic interlayers for wafer-level packaging

For packaging of silicon components with low thermal load and high spatial selectivity laser transmission bonding (LTB) of silicon–silicon compounds with intermediate layers using a cw-thulium fiber laser (wavelength 1,940 nm) is investigated. The intermediate layer combination titanium and gold is examined with respect to the bond characteristics and the achievable mechanical properties of the bonded specimens. The tensile strength is measured by using tensile test. Similar specimens bonded with corresponding standard bond process using the same bond geometry are also analyzed in order to compare the measurements.     

A wafer-level package of wideband microwave transmission system based on BCB/metal structure embedded in Si substrate

In this paper, a wafer-level package for a microwave transmission system has been implemented and tested. Three monolithic microwave integrated circuits packaged in one microwave system are first proposed. The packaged system consists of an up-converter, a drive amplifier and a power amplifier. All the modules are embedded in the cavities pre-etched in a low-resistivity silicon substrate. Benzocyclobutene layers are coated on the components and silicon substrate, serving as interlayer dielectrics. Gold bumps are used as electric interconnections between different layers. Gold micro-strip lines are employed as transmission lines. The electrical properties of the packaging structure are investigated. The design procedure is proposed and the simulation regarding transmission line has been done. The thermal property of the packaged system is simulated and detailed discussion is presented. The measured transmission characteristics of the packaged system shows that the modules can work at very wide band, at the range of 6–18 GHz (X/Ku band) and its gain agrees well with the theoretical results.     

Submicron-scale surface acoustic wave resonators fabricated by high aspect ratio X-ray lithography and aluminum lift-off

A submicron-scale surface acoustic wave (SAW) resonator fabricated by high-aspect-ratio X-ray lithography (XRL) and metal lift-off that operates at microwave frequencies is presented. We demonstrate that XRL is especially well suited for SAW device templating, as long submicron-scale interdigitated transducer structures can be batch patterned with excellent structure quality. 0.4–2.0 μm thick PMMA layers were structured by X-ray lithography shadow projection using silicon nitride-based X-ray masks. Structures with a critical lateral feature size of down to 200–700 nm were processed. The polymer structures served as templates in a subsequent aluminum lift-off process. The metal electrodes were successfully tested as SAW resonators for high frequency applications, e.g. around 1.3 GHz, using calibrated 1-port RF wafer probing measurements. Compared with standard fabrication techniques, the high structure quality of submicron-scale polymer templates made of unusually thick PMMA layers offers additional possibilities to fabricate thicker metal transducers.     

Micro-mixer device with deep channels in silicon using modified RIE process: fabrication,packaging and characterization

In the present work, silicon based micromixer microfluidic devices have been fabricated in silicon substrates of 2-inch diameter. These devices are of 2-input and 1-output port configuration bearing channel depth in the range 80–280 µm. Conventional reactive ion etching (RIE) process used in integrated circuit fabrication was modified to get reasonably high silicon etch rate (~1.2 µm/min). It was anticipated that devices with channel depth in excess of 150 µm would become weak and susceptible to breakage. For such devices, a bonded pair of silicon having a 0.5 µm SiO₂ at the bonded interface was used as the starting substrate. The processed silicon wafer bearing channels was anodically bonded to a Corning^® 7740 glass plate of identical size for fluid confinement. Through-holes for input/output ports were made either in Si substrate or in glass plate before carrying out anodic bonding. Micro-channels were characterized using stylus and optical profiler. Surface roughness of the channel was observed to increase with increasing channel depth. The devices were packaged in a polycarbonate housing and pressure drop versus flow rate measurements were carried out. Reynolds number and friction factor were calculated for devices with 82 µm deep channels. It was observed that up to 25 sccm of gas and 10 ml/min of liquid, the flow was laminar in nature. It is envisaged that using bonded silicon wafer pair and combination of RIE and wet etching, it is possible to get an etch stop at the SiO₂ layer of the bonded silicon interface with much smaller value of surface roughness rendering smooth channel surface.     

Inline and canonical stripline filters with ridge coupling sections for LTCC applications

Inline and canonical filters employing stripline resonators coupled by evanescent‐mode ridge waveguide sections are presented. The proposed configurations are suitable choices for broadband chip filters integrated in printed circuit boards, especially for those with constraints on size and loss. Low temperature co‐fired ceramic (LTCC) technology can be used to manufacture such filters. To validate the idea, prototypes of Chebyshev and elliptic function filters are designed following a systematic procedure. Stepped impedance stripline resonators are used in the Chebyshev filter to improve the spurious response. A novel canonical structure is presented for achieving high selectivity elliptic function filter responses. Rigorous mode matching method is applied to analyze and optimize all the filters, whose results are validated by commercial software. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Micro porous polymer foil for application in evaporation cooling

A novel bionic cooling system for photo voltaic (PV)-cells based on a micro porous evaporation polymer foils is developed and the cooling mechanism is demonstrated. The foil consists of a two layer permanent resist on a silicon substrate with an evaporation pore diameter of 35 μm. Evaporation rates of the porous cooling area exceed those of bulk water by about three orders of magnitude. A homogeneous cooling effect on the PV front side of 4.2 K at an environment temperature of 55 °C and 45 % RH is proved. The developed fabrication is transferable to large scale mass production.     

Bulk disc resonators radial and wineglass mode resonance characterization for mass sensing applications

This paper reports the design and fabrication of bulk mode micromechanical disc resonators operating in radial and wine-glass modes of excitation. The reported structures are fabricated utilizing a single crystal SOI wafer through micromachining processes. Both resonators are fabricated on a device layer with a thickness of 20 µm and a gap size of 1.75 µm between the resonant beam and surrounding electrodes. Four anchors support the resonant disc using a T-shaped connection stem. The designed structures resonate at 2.87 and 3.99 MHz, in wine glass and radial modes respectively, and are electrostatically actuated by a DC voltage of 110 V between the disc and electrodes. The designed resonators show high quality factors while operating in air, 1,1876.2 for wine-glass and 7380 for radial. In addition, the resonators are used for distributed and point mass measurements of a sputtered gold metal layer. The wine glass resonator shows a frequency down shift of 1 kHz for a 44 ngr gold point mass, and a frequency shift of 22 kHz for a distributed mass of 83 µgr. Same test is performed on radial mode resonator and a resonance frequency shift of 1.24 and 25.54 kHz was observed for point and distributed mass, respectively in air and at room temperature.     

Development and characterization of a microthermoelectric generator with plated copper/constantan thermocouples

This work reports the development and the characterization of a microthermoelectric generator (μTEG) based on planar technology using electrochemically deposited constantan and copper thermocouples on a micro machined silicon substrate with a SiO₂/Si₃N₄/SiO₂ thermally insulating membrane to create a thermal gradient. The μTEG has been designed and optimized by finite element simulation in order to exploit the different thermal conductivity of silicon and membrane in order to obtain the maximum temperature difference on the planar surface between the hot and cold junctions of the thermocouples. The temperature difference was dependent on the nitrogen (N₂) flow velocity applied to the upper part of the device. The fabricated thermoelectric generator presented maximum output voltage and power of 118 mV/cm² and of 1.1 μW/cm², respectively, for a device with 180 thermocouples, 3 kΩ of internal resistance, and under a N₂ flow velocity of 6 m/s. The maximum efficiency (performance) was 2 × 10^?3 μW/cm² K².