Fabrication of a MEMS capacitive accelerometer with symmetrical double-sided serpentine beam-mass structure

This paper presents a symmetrical double-sided serpentine beam-mass structure design with a convenient and precise process of manufacturing MEMS accelerometers. The symmetrical double-sided serpentine beam-mass structure is fabricated from a single double-device-layer SOI wafer, which has identical buried oxides and device layers on both sides of a thick handle layer. The fabrication process produced proof mass with though wafer thickness (860 μm) to enable formation of a larger proof mass. Two layers of single crystal silicon serpentine beams with highly controllable dimension suspend the proof mass from both sides. A sandwich differential capacitive accelerometer based on symmetrical double-sided serpentine beams-mass structure is fabricated by three layer silicon/silicon wafer direct bonding. The resonance frequency of the accelerometer is measured in open loop system by a network analyzer. The quality factor and the resonant frequency are 14 and 724 Hz, respectively. The differential capacitance sensitivity of the fabricated accelerometer is 15 pF/g. The sensitivity of the device with close loop interface circuit is 2 V/g, and the nonlinearity is 0.6 % over the range of 0–1 g. The measured input referred noise floor of accelerometer with interface circuit is 2 μg/√Hz (0–250 Hz).     

A MEMS sandwich differential capacitive silicon-on-insulator accelerometer

A differential capacitive accelerometer with simple process is designed, simulated, and fabricated. To achieve a precision structure dimension with fewer processing steps, the silicon device layer transfer technology is being used to built a sandwich accelerometer based on a silicon-on-insulator (SOI) wafer, which was assembled by glass-si-glass multilayer anodic bonding. Deep reactive ion etching is being used to define symmetric beams and large mass block of equal thickness together in SOI device layer (up to 100 μm) in a single step to avoid alignment error in double side process. An actual accelerometer which is designed for 50 g measure range is fabricated with six lithography steps. Measurement results show 0.1166 V/g sensitivity and 0.022 % nonlinearity error in ±1 g gravity static response test. The accelerometer also provides a power spectrum less than 10.49 μVrms/Hz^1/2 (89.97 μg/Hz^1/2) in a non-isolated laboratory environment with a capacitive interface circuit.     

A new analytical model of single-stage microleverage mechanism in resonant accelerometer

Microleverage mechanism which is widely applied in microelectromechanical systems (MEMS) transfers and amplifies force or displacement from input to output. In this work, one-stage microleverage mechanism is integrated into a biaxial micro resonant accelerometer to improve sensitivity. Force amplification factor of the microleverage is analyzed and deduced by integral method. The results from theoretical model match well with the ones from finite element method (FEM) simulation, which proves that the proposed model is relatively accurate and the width of lever beam is a quite important parameter in design. The resonant accelerometer is successfully fabricated by MEMS technology. Preliminary experiments are conducted and demonstrate differential sensitivity of 71 Hz/g for the accelerometer with resonant frequency of 267.726 kHz.     

Design and simulation of a high-performance Z-axis SOI-MEMS accelerometer

This paper presents a new micromachined z-axis accelerometer as well as a new method to sense the out-of-plane displacement capacitively via comb finger arrays. The new design built the z-accelerometer using eight folded beam suspension to minimize the off axis sensitivities in both the x- and y- directions. The proposed method implements the sensing electrode as a comb finger arrays surrounding the sensor. This method enables the realization of the sensor by bulk micromachining process, increases the sense capacitance and reduces the off-axis sensitivity. This process allows building the micromachined accelerometer with large inertial mass. This work introduces the design and simulation for this accelerometer. The introduced method results in a high sense capacitance as well as high sensitivity. The simulated sense capacitance is 19.6627 pF. The sensor sensitivity is 2.037 μm/g with a very small total noise equivalent acceleration of 3.096 μg/ $ \sqrt {Hz} $ .     

三梁-质量块敏感结构高性能压阻式碰撞加速度计

研究了一种主要应用于碰撞测试领域的硅微机械高性能压阻式加速度计,量程范围为2 000 gn.为满足技术性能要求,加速度计采用一种三梁-质量块结合梳齿阻尼器的新颖结构,从而可以同时具有高灵敏度及高动态特性(包括高谐振频率及精确阻尼控制).这种加速度计采用n型(100)普通硅片制作,主要工艺过程包括双面ICP深刻蚀和压阻集成工艺.振动台测试结果表明,加速度计的灵敏度为0.11 mV/gn/5 V,谐振频率为31 kHz,灵敏度±5%变化下平坦带宽大于5 kHz.采用落杆测试法测试了加速度计的冲击响应及0～2 000 gn满量程范围内的非线性度.封装后的加速度计承受15 000 gn的冲击测试后没有受到损坏.     

Using bulk micromachined structures to enhance pool boiling heat transfer

This paper presents the important results of enhancing the boiling heat transfer of the pressurized water reactors (PWRs) by using LIGA or LIGA-like techniques to add microstructures on the surface of heater elements. The heater elements were made of 10 mm × 80 mm silicon strips with different in-line square micro-pin-fin configurations of 200 μm fin width, 35 μm fin height, and different inter-fin spacing values of 200, 400, 600, 800, 1000 μm and infinity. The experiments were conducted in de-ionized water at the atmospheric pressure. The input power, heater temperature, steam generation rate and video images of boiling phenomena were continuously recorded. Their relationships was studied and used to evaluate the total boiling heat transfer performance. The optimized microstructures can then be mass-fabricated on PWR tubes by using LIGA or LIGA-like technology. The experimental results suggest that by adding micro-sized in-line pin-fin arrays on heater surface and modifying heater surface morphology, the boiling process can be greatly enhanced through the improvements of vapor nucleation and vapor evolution processes at heater surface, which yields a low wall superheat and achieves a higher boiling heat transfer efficiency. The video images showed that the bubble nucleation sites are located immediately on top of each micro-pin fins. At current experimental setup, the 200 μm-spacing heater has the highest steam generation efficiency.     

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。     

Microthermal sensors for determining fluid composition and flow rate in fluidic systems

To analyze fluid mixtures a simple and low cost measurement method is realized using a microthermal sensor that introduces a short heat pulse into the fluid under test whilst the resulting temperature increase reflects thermal parameters of the fluid. For methanol in water this principle showed an almost linear dependence of the temperature increase on the methanol content for the volume concentration range 0–20 %. The sensitivity was determined to S = 0.19 K/(% (V/V)) for a heat pulse of 0.5 s duration and a heater power of 30 mW. The accuracy achieved in stopped-flow single pulse measurements is ~0.5 % (V/V). By integrating additional temperature sensors in front and behind the microheater the flow rate of the liquid can also be determined using thermal anemometry. The low cost sensor construction and simple signal analysis make this principle promising for use in low cost mobile applications like DMFC power supplies for laptops.     

Synergistic use of the two-temperature and split-window methods for land-surface temperature retrieval

A strategy is presented with the aim of achieving an operational accuracy of 2.0 K in land-surface temperature (LST) from METEOSAT Second Generation (MSG)/Spinning Enhanced Visible and Infrared Imager (SEVIRI) data. The proposed method is based on a synergistic usage of the split-window (SW) and the two-temperature method (TTM) and consists in combining the use of a priori land-surface emissivity (LSE) estimates from emissivity maps with LST estimates obtained from SW method with the endeavour of defining narrower and more reliable ranges of admissible solutions before applying TTM. The method was tested for different surface types, according to SEVIRI spatial resolution, and atmospheric conditions occurring within the MSG disc. Performance of the method was best in the case of relatively dry atmospheres (water-vapour content less than 3 g cm^?2), an important feature since in this case SW algorithms provide the worst results because of their sensitivity to uncertainties in surface emissivity. The hybrid method was also applied using real MSG/SEVIRI data and then validated with the Moderate resolution Imaging Spectroradiometer (MODIS)/Terra LST/LSE Monthly Global 0.05° geographic climate modeling grid (CMG) product (MOD11C3) generated by the day/night algorithm. The LST and LSE retrievals from the hybrid-method agree well (bias and root mean square error (RMSE) of??0.2 K and 1.4 K for LST, and around 0.003–0.02 and 0.009–0.02 for LSE) with the MOD11C3 product. These figures are also in conformity with the MOD11C3 performance at a semi-desert where LST (LSE) values is 1–1.7 K (0.017) higher (less) than the ground-based measurements.     

FBAR-on-diaphragm type electro-acoustic resonant micro-accelerometer: a theoretical study

We presented a theoretical study of the performance of a novel FBAR-on-diaphragm sensor-head structure for the FBAR-based electro-acoustic resonant micro-accelerometer. This structure overcomes disadvantages in the FBAR-beam structure for its limited cantilever beam thickness, and deficiencies in the embedded-FBAR structure for its complex micro-fabrication process. Its elastic diaphragm is made of silicon dioxide (SiO₂)/silicon nitride (Si₃N₄) bilayer film, which is not only more susceptible to the IC compatible integration process for the Si-based microstructure and the FBAR, but also improves sensitivity and temperature stability of the BAW accelerometer. FBAR-on-diaphragm type BAW accelerometer integrates the acceleration sensing structure, i.e., the SiO₂/Si₃N₄ bilayer diaphragm and the Si proof-mass, with the AlN FBAR electro-acoustic transducer. Preliminary performance analysis on FBAR-on-diaphragm type BAW accelerometer suggests that the FBAR-on-diaphragm structure is feasible. We obtained modal frequencies of the FBAR-on-diaphragm structure and stress distribution of the diaphragm under 0–100 g acceleration loads through the finite element modal analysis and static simulation, Applying the calculated maximum stress to the piezoelectric film in FBAR for qualitative analysis, and combining the dependency of elastic coefficient on stress in the Wurtzite AlN film calculated with the first-principle method, we roughly predicted the maximum elastic coefficient variation in the Wurtzite AlN film under different acceleration load. With the help of the RF simulation software ADS, we changed the longitudinal wave velocity corresponding to the elastic constants with variant acceleration loads. By comparing the resulted resonant frequencies of the sensor head without and with different acceleration loads, we qualitatively characterized its frequency shift and sensitivity. In our study, we gave further analysis of the simulation results. It reveals that the first-order modal frequency of the SiO₂/Si₃N₄ circular diaphragm is quite far away from the higher ones, which means less cross modal coupling. It also reveals that under the acceleration load, its resonant frequency with a quite linear acceleration–frequency shift characteristic will up-shift with the sensitivity of several KHz/g.     

高灵敏度谐振式微加速度传感器的设计与制作

为提高加速度传感器灵敏度,提出一种新的加速度敏感机制,并基于此原理设计了一种新的微机械谐振式加速度传感器结构.分析了加速度传感器的数学模型及影响灵敏度的关键参数,并以此为依据对传感器结构参数进行优化设计.采用扩散硅层作为谐振子,提高器件性能的同时简化了制作工艺,利用KOH溶液湿法腐蚀硅在各晶向上的各向异性,实现了支撑梁...     

MEMS面内大量程加速度传感器设计与分析

针对目前导弹引信等武器系统领域对大量程加速度传感器的迫切需求,设计了一种测量平面内加速度的大量程压阻式加速度传感器.该传感器结构双端固支梁-质量块结构,可有效消除敏感轴轴间的交叉干扰,提高了测量精度.仿真分析表明传感器在敏感轴轴向灵敏度为1.41 μV/gn,可实现对150 000 gn的加速度载荷的测量.     

不等基频硅微谐振式加速度计

分析了硅微谐振式加速度计的两个谐振器在谐振频率相交点附近区域产生耦合的原因,设计了一种新型的不等基频硅微谐振式加速度计,并对其进行了有限元仿真.该加速度计由质量块、放大惯性力的杠杆机构以及一对尺寸不同的谐振器组成.采用DDSOG工艺加工.利用ANSYS有限元软件进行仿真,结果表明加速度计上谐振器的谐振基频为124 67...     

A miniature in-plane piezoresistive MEMS accelerometer for detection of slider off-track motion in hard disk drives

A miniature in-plane pizoresistive MEMS accelerometer was designed, fabricated and characterized for detection of slider off-track motion in hard disk drives. The structure of the accelerometer consists of a central supporting beam and two stress-magnifying sensing beams. Under geometric constraints imposed by the trailing side of a pico slider, the accelerometer design was optimized to achieve approximately pure axial deformation in the sensing beams and a maximum sensitivity with a specified natural frequency of 300 kHz. Fabricated on a silicon-on-insulator (SOI) wafer, the accelerometer with a half Wheatstone bridge was wirebonded to external pads and interfaced with an amplifier circuit on a printed circuit board (PCB). The noise level, sensitivity, nonlinearity were characterized with vibration testing on a shaker. The miniature accelerometer (1 × 0.3 × 0.3 mm³) with a weight of only 0.2 mg offers a much higher resonant frequency with a comparable sensitivity compared with those in previous work.     

Low power highly sensitive platform for gas sensing application

This paper reports a low power miniaturized MEMS based integrated gas sensor with 36.84 % sensitivity (ΔR/R₀) for as low as 4 ppm (NH₃) gas concentration. Micro-heater based gas sensor device presented here consumes very low power (360 °C at 98 mW/mm²) with platinum (Pt) micro-heater. Low powered micro-heater is an essential component of the metal oxide based gas sensors which are portable and battery operated. These micro-heaters usually cover less than 5 % of the gas sensor chip area but they need to be thermally isolated from substrate, to reduce thermal losses. This paper elaborates on design aspects of micro fabricated low power gas sensor which includes ‘membrane design’ below the microheater; the ‘cavity-to-active area ratio’; effect of silicon thickness below the silicon dioxide membrane; etc. using FEM simulations and experimentation. The key issues pertaining to process modules like fragile wafer handling after bulk micro-machining; lift-off of platinum and sensing films for the realization of heater, inter-digitated-electrodes (IDE) and sensing film are dealt with in detail. Low power platinum microheater achieving 700 °C at 267 mW/mm² are fabricated. Temperature calculations are based on experimentally calculated thermal coefficient of resistance (TCR) and IR imaging. Temperature uniformity and localized heating is verified with infrared imaging. Reliability tests of the heater device show their ruggedness and repeatability. Stable heater temperature with standard deviation (σ) of 0.015 obtained during continuous powering for an hour. Cyclic ON–OFF test on the device indicate the ruggedness of the micro-heater. High sensitivity of the device for was observed for ammonia (NH₃), resulting in 40 % response for ~4 ppm gas concentration at 230 °C operating temperature.     

Dual‐band circularly polarized dielectric resonator antenna for wireless applications

This letter investigates an integrated antenna configuration for WLAN/WiMAX applications. The proposed composite antenna configuration is simply the grouping of ring dielectric resonator along with reformed square‐shaped slot antenna. Three significant characteristics of proposed article are: (1) aperture act as magnetic dipole and excite HE_11δ mode in ring dielectric resonator antenna; (2) reforming of square aperture generates orthogonal modes in ring DRA and creates CP in lower frequency band; (3) annular‐shaped Microstrip line along with reformed square aperture creates CP wave in upper frequency band. With the purpose of certifying the simulated outcomes, prototype of proposed structure is fabricated and tested. Good settlement is to be got between experimental and software generated outcome. Experimental outcomes show that the proposed radiating structure is operating over 2 frequency bands that is, 2.88‐3.72 and 5.4‐5.95 GHz. Measured 3‐dB axial ratio bandwidth in lower and upper frequency band is approximately 9.52% (3.0‐3.4 GHz) and 5.85% (5.64‐5.98 GHz), respectively. These outcomes indicate that the proposed composite antenna structure is appropriate for WLAN and WiMAX applications.     

The effect of physical training on objective and subjective measures of productivity and efficiency in industry

The aims of this study were to investigate the associations between an activity logbook and the RT3 accelerometer and to assess whether the RT3 can discriminate activity levels in healthy adults. Ten participants completed two trials wearing an RT3 accelerometer over a 4–6 h period and completed a detailed activity log. Results showed a poor correlation between the RT3 in moderate activities (r = 0.22) in comparison to low (r = 0.52) and hard (r = 0.70) from the logbook. A significant difference was found in average RT3 vector magnitude (VM) counts/min in each activity level (p < 0.0001). Discriminant analysis demonstrated that an RT3VM counts/min value of approximately 500 was found to have high sensitivity (88%), and specificity (88%) for discriminating between low and moderate activity levels from the logbook. This study found that accelerometry has the potential to discriminate activity levels in free living. This study is the first to investigate whether tri-axial accelerometry can discriminate different levels of free-living activity recorded in an activity logbook. The RT3 accelerometer can discriminate between low and moderate physical activities and offers a methodology that may be applicable to future research in occupational settings.     

A low power micro fluxgate sensor with improved magnetic core

The influence of an improved magnetic core on the micro fluxgate sensor about sensitivity and power consumption is investigated and discussed in this paper. We have fabricated the micro solenoid fluxgate sensors based on the MEMS technologies, with the electroplating permalloy cores, which are easy to process and used in common; and the amorphous soft magnetic ribbon cores, which have better soft magnetic performances but be hard to be integrated, respectively. Four magnetic core structures are designed, including rectangular structure, unequal width rectangular structure, multi rectangular ring structure and spiral structure. Spiral structure can improve the performances of the fluxgate sensor significantly, both sensitivity and power consumption. The micro fluxgate sensors with the amorphous soft magnetic ribbon cores are promoted in all aspects than those with the electroplating permalloy cores, including ultra low power consumption of 2.4 mW with unequal width rectangular structure, and high sensitivity of 118 V/T with rectangular structure in wide linear range of 0–800 μT.     

Intercalibration of NOAA and Meteosat window channel brightness temperatures

This study presents an intercalibration of Meteosat‐5 11 µm channel and NOAA‐14 10.8 µm and 12.0 µm channels, and their comparison for sea and land pixels. The intercalibration empirical relation is derived for clear‐sky sea measurements, with similar zenith viewing angles. The root mean square difference between NOAA‐14 and Meteosat‐5 intercalibrated brightness temperatures is about 1.4 K (4.7 K) for all clear‐sky sea (land) pixels. The discrepancies over land are analysed in terms of viewing angle, surface type, terrain elevation and exposure to sunlight. The satellite viewing geometry is responsible for two major impacts, namely: the obstruction by neighbouring clouds towards one of the satellites; and differences in surface solar illumination viewed by each sensor. It is also shown that the higher discrepancies between intercalibrated temperatures occur for the most heterogeneous surfaces (e.g. Open Shrublands). The effect of terrain variability is not linear and depends strongly on the surface type.