Fabrication of a guide block for measuring a device with fine pitch area-arrayed solder bumps

This paper describes the design and fabrication of a guide block and micro probes, which were used for a vertical probe card to test a chip with area-arrayed solder bumps. The size of the fabricated guide block was 10 mm × 6 mm. The guide block consisted of 172 holes to insert micro probes, 2 guide holes for exact alignment, and 4 holes for bolting between the guide block and the housing of a PCB. Pitch and size of the inserting holes were 80 μm, and 90 μm × 30 μm, respectively. A silicon on insulator wafer was used as the substrate of the guide block to reduce micro probes insertion error. The micro probes were made of nickel–cobalt (Ni–Co) alloy using an electroplating method. The length and thickness of the micro probes were 910 and 20 μm, respectively. A vertical probe card assembled with the fabricated guide block and micro probes showed good x–y alignment and planarity errors within ±4 and ±3 μm, respectively. In addition, average leakage current and contact resistance were approximately 0.35 nA and 0.378 ohm, respectively. The proposed guide block and micro probes can be applied to a vertical probe card to test a chip with area-arrayed solder bumps.     

MEMS design and fabrication of an electrostatic vibration-to-electricity energy converter

This paper presents a micro electrostatic vibration-to-electricity energy converter based on the micro-electromechanical system. For the 3.3 V supply voltage and 1 cm² chip area constraints, optimal design parameters were found from theoretical calculation and Simulink simulation. In the current design, the output power is 200 μW/cm² for the optimal load of 8 MΩ. The device was fabricated in a silicon-on-insulator wafer. Mechanical and electrical measurements were conducted. Residual particles caused shortage of the variable capacitor and the output power could not be measured. Fabrication processes are being refined to remove the back silicon substrate to eliminate residual particles and parasitic capacitance.     

Laser micro-structuring of magnetron-sputtered SnOx thin films as anode material for lithium ion batteries

SnO_x electrode thin films for lithium ion batteries were deposited by reactive and non-reactive rf magnetron sputtering of a SnO₂ target in an argon–oxygen atmosphere. Amorphous and nano-crystalline SnO_x films could be synthesized, with regard to the O₂:Ar volume ratio in the sputter gas which was adjusted to 0, 3.5 or 10%. Laser micro-structuring using a KrF excimer laser operating at a wavelength of λ = 248 nm was applied to create free-standing microstructures. Thus, the active surface of the anode material was significantly increased. Furthermore, it was expected that the large volume changes during electrochemical cycling of SnO_x could be better compensated by a microstructured surface. The laser parameters were optimized in a way which leads to structures without any defects and little debris. Depending on the laser fluence and pulse number, free-standing conical structures could be formed with a horizontal spacing of <0.5 μm up to 2 μm. The structured and unstructured thin films were cycled in a battery tester against metallic lithium. The structured SnO_x thin films exhibited significantly better battery performance with respect to cycling stability.     

Fabrication of micro sensors on a flexible substrate

Flexible micro temperature and humidity sensors on parylene thin films were designed and fabricated using a micro-electro-mechanical-systems (MEMS) process. Based on the principles of the thermistor and the ability of a polymer to absorb moisture, the sensing device comprised gold wire and polyimide film. The flexible micro sensors were patterned between two pieces of parylene thin film that had been etched using O₂ plasma to open the contact pads. The sacrificial Cr spacer layer was removed from the Cr etchant to release the flexible temperature and humidity sensors from the silicon substrate. Au was used to form the sensing electrode of the sensors while Ti formed the adhesion layer between the parylene and Au. The thickness of the device was 7 ± 1 μm, so the sensors attached easily to highly curved surfaces. The sensitivities of the temperature and humidity sensor were 4.81 × 10⁻³ °C⁻¹ and 0.03 pF/%RH, respectively. This work demonstrates the feasibility and compatibility of thin film sensor applications based on flexible parylene. The sensor can be applied to fuel cells or components that must be compressed.     

煤矿救灾机器人动力电源研究

针对机器人电源系统的需求,分析并比较了磷酸铁锂电池、超级电容以及磷酸铁锂电池并联超级电容的混合电源的性能,认为磷酸铁锂电池较适合作为煤矿救灾机器人的动力电源;研究了磷酸铁锂电池的小电流放电特性,建立了相应的放电模型,并据此对24V,40A.h的电池进行理论计算,得出结论:放电电流在30A以下时,电池自身消耗的能量可以控制在12%以下,降低输出电流可以降低电池自身的能量消耗,增加输出的能量。     

Micromachined PZT cantilever based on SOI structure for low frequency vibration energy harvesting

A PZT piezoelectric cantilever with a micromachined Si proof mass is designed and fabricated for a low frequency vibration energy harvesting application. The SiO₂ layer in the SOI wafer promotes accurate control of the silicon thickness that is used as a supporting layer in the cantilever beam structure. The entire effective volume of the fabricated device is about 0.7690 mm³. When excited at 0.75g (g = 9.81 m/s²) acceleration amplitude at its resonant frequency of 183.8 Hz, the AC output measured across a resistive load of 16 kΩ connecting to the device in parallel has an amplitude of 101 mV. The average power and power density determined by the same measurement conditions are, respectively, 0.32 μW and 416 μW/cm³.     

Flexible piezoelectric micromachined ultrasonic transducer (pMUT) for application in brain stimulation

We propose a new flexible piezoelectric micromachined ultrasonic transducer (pMUT) array integrated on flexible polydimethylsiloxane (PDMS) that can be used in studying brain stimulation by ultrasound. To achieve the technical demands of a high sound pressure level and flexibility, a diaphragm-type piezoelectric ultrasound transducer array was manufactured with 55 μm-thick bulk lead zirconate titanate (PZT) that was thinned after bonding with a silicon wafer. The ultrasound transducer array was then strongly bonded onto a PDMS substrate using an oxygen-plasma treatment followed by precise dicing with a fixed pitch to achieve flexibility. The radius of curvature was smaller than 5 mm, which is sufficient for attachment to the surface of a mouse brain. After a thinning process for the PZT layer, we observed that the PZT layer still maintained a high ferroelectric property. The measured remnant polarization (P_r) and coercive field (E_c) were 28.26 μC/cm² and 79 kV/cm, respectively. The resonant frequencies of fabricated pMUT elements with different membrane sizes of 700, 800, 900, 1200 μm in diameter were measured to be 694.4, 565.4, 430.8, and 289.3 kHz, respectively. By measuring the ultrasound output pressure, a pMUT showed a sound intensity (I_sppa) of 44 mW/cm² at 80 V, which is high enough for low-intensity ultrasound brain stimulation.

     

基于改进神经网络算法的医疗锂电池PHM系统设计

针对医疗电子设备锂电池不确定性发生故障耽误病人救治的问题,提出了一套医疗电子设备锂电池故障预测与健康管理系统(Prognostics and Health Management-PHM);搭建了一套医疗电子设备锂电池数据测试与退化状态模拟的实验平台;为了反映医疗电子设备锂电池健康状态,将锂电池四个健康因子作为医疗电子设备锂电池退化状态的特征进行提取,并通过非线性自回归(Nonlinear Autogressive with Exogenous Inputs-NARX)神经网络,对四个健康因子的数据进行训练,训练后用于容量估计,得出等间隔放电时间序列能够较好地表征锂电池健康状态;为了提高基本粒子滤波算法(Particle Filter-PF)的精度从而更精确地预测锂电池剩余寿命(Remaing Useful Life-RUL),通过人工免疫粒子滤波算法(Artificial Immune Particle FilterAIPF)与经验模型对锂电池进行剩余寿命预测,并将PF预测的结果与AIPF预测的结果进行对比,发现AIPF预测更加准确,说明AIPF有效抑制了PF重采样过程中粒子退化问题,验证了医疗电子设备锂电池故障预测与健康管理系统的可行性与可实施性。     

超低功耗的锂电池管理系统设计

为了满足某微功耗仪表的应用,提高安全性能,提出了一种超低功耗锂电池管理系统的设计方案。该方案采用双向高端微电流检测电路,结合开路电压和电荷积分算法实现电量检测。采用纽扣电池代替DC/DC降压电路最大程度降低功耗。系统实现了基本保护、剩余电量检测、故障记录等功能。该锂电池管理系统在仪表上进行验证,结果表明具有良好的稳定性和可靠性,平均工作电流仅145μA。     

A contact lens with integrated micro solar cells

We report the design, construction, characterization and in vivo testing of contact lenses incorporating solar cells. A fabrication process is outlined yielding free-standing 500 × 500 × 10 μm³ single crystal silicon solar cells which are subsequently integrated into a contact lens. Collections of micrometer-scale solar cells are interconnected on the contact lens in order to maintain flexibility, cover the proper area, and take advantage of crystalline materials. The solar cells show maximum efficiency at wavelength 725 nm with conversion efficiency of 1.24% at 310 mV. The contact lenses were tested on live rabbits and no adverse effects were detected. Contact lenses equipped with solar cells can harvest usable power from the environment and pave the way for the deployment of stand-alone contact lens systems that can be used for health-status monitoring.     

Micro robot system with moving micro-car driven by electrostatic comb-drive actuators

This paper describes a silicon micro robot system (MRS) that is capable of driving micro-cars in different directions based on a ratchet mechanism and electrostatic comb-drive actuators. Lateral movement of the ratchet racks makes the micro-car move in the perpendicular direction with different velocities. Based on MEMS technology, the MRS described in this article was fabricated from a silicon on insulator wafer by using only one photo mask. In our experiments, various driving frequencies ranging from 1 to 20 Hz were used to accelerate the micro-car up to 200 μm/s. It was observed that the velocity of the micro-car was proportional to the driving frequency used in the experiments. This relation was also confirmed with our theoretical calculation. When combined with microscopes, this MRS can be applied in bio-medical analysis for transportation and classification of small samples.     

Effect of localized KrF excimer laser treatment on fracture behaviors of freestanding <110> and <100> single crystal silicon beams

Microscale silicon structures oriented along <100> and <110> orientations were laser treated with different conditions with the cross section shape and tensile strength investigated after the treatment. Finite element simulation was performed to examine the temperature distribution at different conditions during laser treatment. Using a low energy (1.2 J/cm²) and high tilt angle (65°) led to a more preserved cross section with a slight strength improvement. The strength improvement was limited due to other surfaces that were not affected by laser treatment. An improvement of 30 % in tensile strength was achieved with a higher energy (4 J/cm²) lower tilt angle (45°) treatment that was consistent for different sample orientations. The cross section of the samples treated at such condition was significantly changed however. The effect of sample orientation on fracture behaviour was studied and unstable crack propagation was observed for <100> oriented samples that was more significant after laser treatment.     

Diagnostic techniques for the dynamics of a thin liquid film under forced flow and evaporating conditions

Motivated by quantification of micro-hydrodynamics of a thin liquid film which is present in industrial processes, such as spray cooling, heating (e.g., boiling with the macrolayer and the microlayer), coating, cleaning, and lubrication, we use micro-conductive probes and confocal optical sensors to measure the thickness and dynamic characteristics of a liquid film on a silicon wafer surface with or without heating. The simultaneous measurement on the same liquid film shows that the two techniques are in a good agreement with respect to accuracy, but the optical sensors have a much higher acquisition rate up to 30 kHz which is more suitable for rapid process. The optical sensors are therefore used to measure the instantaneous film thickness in an isothermal flow over a silicon wafer, obtaining the film thickness profile and the interfacial wave. The dynamic thickness of an evaporating film on a horizontal silicon wafer surface is also recorded by the optical sensor for the first time. The results indicate that the critical thickness initiating film instability on the silicon wafer is around 84 μm at heat flux of ~56 kW/m². In general, the tests performed show that the confocal optical sensor is capable of measuring liquid film dynamics at various conditions, while the micro-conductive probe can be used to calibrate the optical sensor by simultaneous measurement of a film under quasi-steady state. The micro-experimental methods provide the solid platform for further investigation of the liquid film dynamics affected by physicochemical properties of the liquid and surfaces as well as thermal-hydraulic conditions.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Analysis of interface states of metal–insulator–semiconductor photodiode with n-type silicon by conductance technique

A metal–insulator–semiconductor photodiode (MIS-PD) as active layer with n-type silicon as interdigitated Schottky electrodes has been fabricated. The current–voltage characteristics, density of interface states and photovoltaic properties of the MIS-PD diode have been investigated. The diode has a metal–insulator–semiconductor configuration with ideality factor higher than unity. The electronic parameters (ideality factor, series resistance and barrier height) of the diode were found to be 1.94, 2.23 × 10⁴ Ω and 0.74, respectively. At voltages between 0.13 and 0.50 V, the charge transport mechanism of the diode is controlled by space charge-limited current mechanism. The interface state density of the diode was found to vary from 5.54 × 10¹² to 5.67 × 10¹² eV⁻¹ cm⁻² with bias voltage. The Au/SiO₂/n-Si/Al device shows a photovoltaic behavior with a maximum open circuit voltage V_oc of 97.7 mV and short-circuit current I_sc of 17.4 μA under lower illumination intensities. The obtained electronic parameters confirm that the Au/SiO₂/n-Si/Al diode is a MIS type photodiode.     

锂电池健康状态快速测量及系统实现

为实现大规模退役锂电池的梯次利用，需要快速测量锂电池的健康状态。基于EIS的低频阻抗测量不仅耗时长，而且针对电池等效电路的还需要做复杂的参数估计，因此，建立了锂电池扩散过程健康因子与低频阻抗的关系，结合扩散过程健康因子和锂电池直流内阻以快速评估锂电池健康状态。其次，设计和构建快速测量系统以测量低频阻抗和直流内阻。实验结果表明，可通过测量扩散过程健康因子和直流内阻判断锂电池健康状态，测量过程仅需花费三分钟的时间，而且准确性较高，快速测量系统可应用于各个实际的工业现场，实现了集快速性、准确性、经济性于一体的目标。     

Characterization of RF sputtered thin film potassium sodium niobate (KNN) with silicon and nickel electrodes

A low cost recipe for thin film deposition of Potassium Sodium Niobate, (Na,K)NbO₃ (KNN) is pursued. The use of expensive noble metals as electrodes was avoided and instead highly doped silicon was used for both the structural layer and the bottom electrode. Nickel was used for the top electrode. In order to evaluate the outcome, the films were studied in terms of stoichiometry, crystal structure and leakage current density. RF sputtering of thin films of KNN at room temperature was successfully done. Proper crystal structure (Perovskite structure) was achieved after post deposition annealing. Though the leakage current density exhibited high dependency on the polarity of the applied voltage, a leakage current density of 1 × 10⁻⁶ A/cm² at 100 kV/cm was measured. A stoichiometry study revealed that the relative ratio of the volatile elements (Na and K) in the samples was within the acceptable range, however, a total loss of about 25–33 % was observed.

     

Capillary-based water removal cathode for an air-breathing micro direct methanol fuel cell

This paper presents a capillary-based water removal cathode for an air-breathing micro direct methanol fuel cell (μDMFC). The mechanism of water removal from the cathode is studied and an array of capillaries with hydrophilic surface is designed on the ribs of the cathode structure. Microfabrication techniques, including double-side lithography and ICP, were used to fabricate the anode and cathode plates of the μDMFC on the same silicon wafer simultaneously. The surface of capillary structure was treated by low temperature oxygen plasma to improve the hydrophilicity. One μDMFC with capillary-based water removal cathode and another regular one without were both assembled and characterized. Measured results show that the μDMFC with water removal cathode achieves a power density of 2.35 mW/cm², 12 % larger than that of the regular one with the value of 2.10 mW/cm². And the maximum current density of the novel μDMFC is 30 mA/cm², 20 % larger than that of the regular one, 25 mA/cm². It is also clearly observed during the μDMFC operation that the water is drawn out from the capillary-based water removal cathode expectantly.     

Direct bonding with on-wafer metal interconnections

A low temperature direct bonding process with encapsulated metal interconnections was proposed. The process can be realized between silicon wafers or silicon and glass wafers. To establish well-insulated electric connection, sputtered aluminum film was patterned between a bottom thermal SiO₂ and a top PE-SiO₂; the consequential uneven wafer surface was planarized through a chemical mechanical polishing (CMP) step. Benefit from this smooth surface finish, direct bonding is achieved at room temperature, and a general yielding rate of more than 95% is obtained. Test results confirmed the reliability of the bonding. The main advantages of this new technology are its electric connectivity, low thermal stress and hermeticity. This process can be utilized for the packaging of micro electro mechanical system (MEMS) devices or the production of SOI wafers with pre-fabricated electrodes and wires.     

基于多级多路径控制的无线传感器电源管理方法

无线传感器通常长期在野外工作,其电源能耗一直是受业界关注的技术问题.针对采用低压锂电池供电的无线传感器,提出采用多级多路径控制的电源管理方法,实现超低压降、电源超低功耗和大电流输出.采用本电源管理方法的无线传感器不仅能充分利用电池电能量,还能兼容多种供电电源(如锂电池、锂亚电池、干电池、铅酸电池等)的应用场景.