Micromachined catalytic combustible hydrogen gas sensor

An integrated catalytic combustion H₂ sensor has been fabricated by using MEMS technology. Both the sensing elements and the reference elements could be integrated into the suspended micro heaters connected in a suitable circuit such as a Wheatstone configuration with low power consumption. Two sensitive elements and two reference sensors were integrated together onto a single chip. The size of chip was 5.76 mm² and the catalytic combustion sensor showed high response to H₂ at operating voltage of 1 V. The response and recovery times to 1000 ppm H₂ were 0.36 s and 1.29 s, respectively.     

Stable SOI micromachined electrostatic AC voltage reference

We have designed and manufactured a micromachined moving plate capacitor to be used as an AC voltage reference in electrical metrology. The reference is based on the characteristic AC current–voltage curve of the component having a maximum, the value of which ideally depends only on the geometry of the component and material properties of single crystalline silicon. The electrode surface stability is essential in this application and hence a new fabrication process has been developed to metallize both surfaces of an electrostatically actuated micromachined structure. The stability of the AC reference voltage at a frequency of 100 kHz and an RMS voltage value 6.4 V was measured to be ±60 ppm over 14 h.     

An adaptive sliding mode controller design to cope with unmatched uncertainties and disturbance in a MEMS voltage reference source

Tunable micro-electro-mechanical systems (MEMS) capacitors as the fundamental parts are embedded in MEMS AC voltage reference sources (VRS). Being concerned with the accuracy of the output voltage in the reference sources, it gets important to address uncertainties in the physical parameters of the MEMS capacitor. The uncertainties have the great inevitable potentiality of bringing about output voltage perturbation. The output deterioration is more remarkable when the uncertainties are accompanied by disturbance and noise. Manufacturers have been making great attempts to make the MEMS adjustable capacitor with desired rigorous physical characteristics. They have also tried to mitigate physical parameter veracity. However, ambiguity in the values of the parameters inescapably occurs in fabrication procedures since the micro-machining process might itself suffer from uncertainties. Employing a proportional integral (PI) adaptive sliding mode controller (ASMC), both terms of matched and unmatched uncertainties as well as the disturbance, are addressed in this work for the MEMS AC VRS so that a strict voltage is stabilized while the system is simultaneously subjected into uncertainties and exogenous disturbance. Cross-talk, some inertial forces, and electrostatic coercions may appear as matched and unmatched disturbances. Alteration in stiffness and damping coefficients might also take place as matched uncertainties due to variations in the fabrication process or even working environment. The simulation results in the paper are persuasive and the controller design has shown a satisfactory tracking performance.     

Influences of perforation ratio in characteristics of capacitive micromachined ultrasonic transducers in air

Capacitive micromachined ultrasonic transducers (CMUTs) with a perforated membrane have been fabricated and characterized in air. Two types of CMUT device have been fabricated having perforation ratio (area ratio of holes = AR) of 10% and 20%, and analyzed about electrical and mechanical characteristics. The perforation ratio (AR) of membrane substantially influences on the electrostatic force and mechanical restoring force of the device since it leads to the area variation of electrode and membrane, it subsequently influences on the sensitivity and frequency response of the CMUT device. The electrostatic force and mechanical restoring force were improved by decreasing the AR and increasing the DC bias voltage. The open-circuit sensitivity of a CMUT having AR 10% membrane, 8.45 μV/Pa, is larger than that of AR 20%, 4.07 μV/Pa at DC 15 V. Furthermore, the resonance behaviors were observed in the range of 60-80 kHz, and the resonance frequency could be changed by varying the applied DC voltage and AR.     

PC sound card-based simple instrument for the potentiometric sensors

Development of a simple and low-cost instrument using a PC sound card for the potentiometric sensors has been reported in this work. It consists of a scanning-DC type data acquisition system which will allow us to acquire an AC signal data corresponding to the scanning-DC signal. Therefore in physical or chemical device characterization it can be used to acquire any DC dependent parameter such as the dielectric constant, capacitance, photocurrent of semiconductor heterostructure, electrochemical parameters, etc. Speaker port of the sound card has been used here to deliver an AC (0 –1 V) that is converted to a corresponding DC voltage externally by a hardware composed of a half-wave precision rectifier (HWPR), a low-pass filter and a level-shifter. The DC voltage can be scanned from +2 to −2 V in any desired steps. The PC sound card Microphone input has been used to collect the AC signal corresponding to the DC voltage steps. For outputting the DC an AC voltage having a frequency of 4000 Hz is sent to the PC sound card Speaker port. The sampling rate for the output voltage is fixed at 8000 sample/s. For collecting the data the configurable sampling rate (>Nyquist rate) depending on the frequency of the input signal has been used. As a test case it has been applied to obtain the AC photocurrent response of a Si₃N₄/SiO₂/Si heterostructure. The experimental results show a good promise for the novel very simple instrument to be used in the potentiometric sensing as well as an important tool for the characterization of physical and chemical devices.     

RF MEMS电容式开关结构层释放技术

研究了RF MEMS开关的制造工艺流程和聚酰亚胺牺牲层的去除工艺。在开关的设计和加工中采用在信号线两侧的地线上生长一层绝缘介质层,直流偏置线生成在绝缘介质层之上,与桥的锚点相连接,实现了交直流隔离。讨论了干法刻蚀和湿法刻蚀牺牲层技术。干法刻蚀容易造成绝缘介质层的刻蚀和损伤。采用湿法刻蚀结合临界点干燥技术,可以获得理想的微梁结构。通过测试,开关样品的下拉电压为34 V～40 V,下拉距离为(1.7±0.2)μm,满足设计要求。     

Design, fabrication and characterization of a high fill-factor micromirror array for wavelength selective switch applications

This paper presents the design, fabrication and characterization of a high fill-factor micromirror array in application of wavelength selective switch (WSS). The micromirror array consists of 52 independent micromirrors. Each micromirror is composed of a cantilever-type micromirror plate (800 μm × 120 μm) with a bumper and an eight-terraced bottom electrode with a limiting plane. A cantilever beam is designed to obtain the rotation angle of micromirror plate and achieve a high fill-factor for the micromirror array. Meanwhile, the bumper and limiting plane are used to prevent the damage possibly caused by the pull-in effect or some vibration instance. An eight-terraced electrode is utilized for reducing the driving voltage. The micromirror array with a high fill-factor in excess of 97% has been successfully achieved using the bulk micromachining technologies. The measured static and dynamic characteristics show that the micromirror can achieve a maximal rotation angle of 0.87° with a Direct Current (DC) driving voltage of 156 V. The turn-on responding time is 0.57 ms, and the turn-off responding time is 4.36 ms. Furthermore micromirror plate can be easily released from the pull-in state without damaged due to the novel bumper design. The switching function between the two output ports of a WSS optical system has also been demonstrated.     

GaAs-based tuning fork microresonators: A first step towards a GaAs-based coriolis 3-axis Micro-Vibrating Rate Gyro (GaAs 3-axis μCVG)

This paper presents the design of a piezoelectric MEMS Coriolis Vibrating Gyroscope (CVG) based on a single gallium arsenide vibrating structure allowing the measurement of rotation rate along 3 orthogonal sensitive axes. Based on a theoretical and FEM study, we demonstrate that the achieved sensitivities reached for each axis is about 1.6 × 10⁻¹⁶ C/(°/s). We then demonstrate the feasibility of the realization of simple MEMS structures from C-doped Gallium Arsenide (GaAs) using standard micromachining processes. Finally, we show the fabrication and characterization of GaAs-based tuning fork microresonators as a first step towards a complete 3-axis GaAs MEMS CVG. These resonators show a resonance frequency of 42 350 Hz, a quality factor of 122 000 and a frequency temperature coefficient of 24 ppm/°K, validating the high potential of GaAs as a structural material for 3-axis MEMS CVGs.     

Design, damping estimation and experimental characterization of decoupled 3-DoF robust MEMS gyroscope

This paper reports the design implementation of three degree-of-freedom (3-DoF) non-resonant MEMS gyroscope having 2-DoF drive-mode oscillator. The proposed architecture utilizes structurally decoupled active-passive mass configuration to achieve dynamic amplification of oscillation in 2-DoF drive-mode. This results in higher sensitivity and eliminates the need of mode matching for resonance. A low cost standard Metal-Multi User MEMS Processes (MetalMUMPs) is used to fabricate 20 μm thick nickel based gyroscope with an overall reduced size of 2.2 mm × 2.6 mm. The experimental characterization demonstrated that the frequency response of the 2-DoF drive-mode oscillator has two resonant peaks at 754 Hz and 2.170 kHz with a flat operational region of 1.4 kHz between the peaks. The sense-mode resonant frequency lies at 1.868 kHz within this flat operational region where gain is less sensitive to structural parameters and environmental variations. This results in improved robustness to fabrication imperfections and environmental variations and long term stability without utilizing tuning and feedback control. Gyroscope dynamics and system level simulations using behavioral modeling are carried out to predict the performance of the device. Experimental results show close agreement with the behavioral simulation results due to incorporation of improved damping models in behavioral model developed in CoventorWare.     

Varifocal liquid lenses with integrated actuator, high focusing power and low operating voltage fabricated on 200 mm wafers

We developed an innovative type of varifocal liquid lens actuated by electrostatic parallel plates. The 3 mm diameter lens is made of a polymer membrane that encapsulates a high permittivity liquid in a cavity on top of a glass wafer. Annular electrodes situated below the membrane and on the glass wafer form the electrostatic parallel plates actuator. By applying a voltage between the electrodes, the electrostatic actuation generated reduces the gap and pushes the liquid towards the center of the lens changing the curvature of the membrane.Compared to previous liquid lenses, very compact devices (≤6 mm × 6 mm × 0.7 mm) working at a reduced supply voltage (<25 V) are demonstrated. Wave front measurements indicate an optical power change of 8 m⁻¹ at 22 V_RMS that can be further improved. The lenses were fabricated on 200 mm wafers using standard microelectronics processes that make our solution a promising small outline, low voltage and low cost candidate for auto-focus devices in camera phones.     

The properties of lattice-shifted microcavity in photonic crystal slab and its applications for electro-optical sensor

In this paper, a micro electro-optic sensor structure and its sensing technique based on lattice-shifted resonant microcavity (H0-nanocavity) in a triangular lattice photonic crystals (PhCs) slab are presented. The H0-nanocavity is formed by only laterally shifting two adjacent holes outwards slightly in the opposite direction, which can realize a nanocavity with high quality factor (Q) value to meet the requirements of practical application. The electro-optic sensor is realized in hole-array based photonic crystal slab with triangular lattice air holes infiltrated with a nonlinear optical (NLO) polymer (n_poly = 1.6) in Silicon-on-Insulator (SOI) operating in the wavelength range from 1400 nm to 1600 nm. The simulation results of PhC electro-sensitive structure show that the optical properties of PhCs can be used to design sensing devices characterized by a high degree of compactness and good resolution. The properties of the sensor are analyzed and calculated using the plane-wave expansion (PWE) method and simulated using the finite-difference time-domain (FDTD) method. The simulation results display that the resonant wavelength of the mode localized in the microcavity shifts its spectral drop position following a linear behavior when a driving voltage ranging between 0.0 V and 3.2 V is applied, and the sensitivity of 31.90 nm/V is observed.     

MEMS可编程光栅动态驱动电路的研制

MEMS可编程光栅的工作性能很大程度依赖于驱动电路的性能。本文根据MEMS可编程光栅的工作特点及结构参数,提取出光栅的等效电容值,并采用集成高压运放研制出一种新型的MEMS可编程光栅的动态驱动电路。为了避免自激振荡的发生,电路中采用了频率补偿和并联反馈电容的方法,有效提高了电路的稳定性。实际电路经过测试,其动态性能与PSPICE10仿真的结果非常吻合。该动态驱动电路具有高的电压输出范围(0~180V),较高的频率响应(10kHz),大范围容性负载能力(1~1000pF),完全能够满足MEMS可编程光栅动态复杂控制的需要。     

Simultaneous determination of N-acetylcysteine and acetaminophen by voltammetric method using N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide modified multiwall carbon nanotubes paste electrode

A new dopamine-derivative, i.e. N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide (N-DHPB), was synthesized and its application was investigated for the simultaneous determination of N-acetylcysteine (NAC) and acetaminophen (AC) using modified multiwall carbon nanotubes paste electrode. This modified electrode exhibited a potent and persistent electron mediating behavior followed by well separated oxidation peaks of NAC and AC. The peaks current of differential pulse voltammograms of NAC and AC increased linearly with their concentration in the ranges of 0.5-200 μmol L⁻¹ NAC and 15.0-270 μmol L⁻¹ AC. The detection limits for NAC and AC were 0.2 μmol L⁻¹ and 10.0 μmol L⁻¹, respectively. The relative standard deviation for seven successive assays of 1.0 and 30.0 μmol L⁻¹ NAC and AC were 1.7% and 2.2%, respectively. The proposed sensor was successfully applied for the determination of NAC in human urine, tablet, and serum samples.     

Microparticle transfer onto pixel electrodes of 45 μm pitch on HV-CMOS chips—Simulation and experiment

Spatially selective deposition of electrically charged microparticles onto integrated circuits that generate electrical fields in programmable patterns using electrodes on their surface was previously limited to a pixel pitch of 100 μm. Now, we demonstrate spatially selective deposition onto pixels of 45 μm pitch in experiments on a test chip allowing arbitrary patterns, but being of limited size and of fixed characteristics, complemented by COMSOL simulations. Experiments on a prototype high voltage CMOS chip demonstrate the feasibility of miniaturisation in the first place, imply simulations of interest that cannot be tested experimentally and, conversely, complement the simplified simulation models by reality checks. Using COMSOL for the optimisation of the setup parameters, particles of decreasing average diameter in a number of aerosol and electrical field geometries are simulated with particular attention to minimising contamination (deposition of particles on undesirable locations). Combining these results, the average particle diameter is decreased from 10 μm to less than 3 μm and the deposition voltage is reduced from 100 V to 30 V, when using pixels with a pitch of 45 μm. Optimising these parameters allows for more than quadrupling the spot density compared to the previous chip, on which combinatorial particle deposition with minimal contamination is achieved. Peptide arrays, having been previously shown to be a major application for this method, benefit in particular, as the increase in density from 10,000 pixels/cm² to approximately 50,000 pixels/cm² promises a significant decrease in cost-per-peptide and amount of test specimens required.     

Pull-in-based μg-resolution accelerometer: Characterization and noise analysis

The pull-in time (t_pi) of electrostatically actuated parallel-plate microstructures enables the realization of a high-sensitivity accelerometer that uses time measurement as the transduction mechanism. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. Parallel-plate MEMS structures have been designed and fabricated using a SOI micromachining process (SOIMUMPS) for the implementation of the accelerometer. This paper presents the experimental characterization of the microdevices, validating the concept and the analytical models used. The accelerometer has a measured sensitivity of 0.25 μs/μg and a bandwidth that is directly related to the pull-in time, BW = 1/2t_pi ≈ 50 Hz. These specifications place this sensor between the state of the art accelerometers found both in the literature and commercially. More importantly, the resolution of the measurement method used is very high, making the mechanical-thermal noise the only factor limiting the resolution. The in-depth noise analysis to the system supports these conclusions. The total measured noise floor of 400 μg (100 μs) is mainly due to the contribution of the environmental noise, due to lack of isolation of the experimental setup from the building vibrations (estimated mechanical thermal noise of 2.8 μg/√Hz). The low requirements of the electronic readout circuit makes this an interesting approach for high-resolution accelerometers.     

Broadband radio frequency MEMS series contact switch with low insertion loss

A new radio frequency (RF) micro-electro-mechanical-system (MEMS) single cantilever series contact switch is designed as a low-insertion-loss and low-power electronic component that is intended to provide integrated control of the opening and closing signals of other MEMS devices operating over a wide frequency range (DC–60 GHz). The MEMS switching element consists of an A-type top electrode that is fixed onto coplanar waveguide lines through anchor points to reduce the insertion loss in the on-state of the device. The air gap between the top electrode and the actuation electrode of the designed MEMS switch is optimized to improve the isolation characteristics of the switch. In addition, the switching voltage required is approximately 24 V. The simulation results presented here show that the insertion loss of the switch in the on-state is less than 0.71 dB, while the minimum isolation is 20.69 dB in the off-state at 60 GHz. The proposed RF MEMS switch will be useful for communication devices and test instruments used in broadband applications.

     

Novel voltage programming n-channel TFT pixel circuit for low power and high performance AMOLED displays

This paper proposes a novel pixel circuit for high resolution, high frame rate, and low power AMOLED displays that is implemented with one driving n-channel TFT, six switching n-channel poly-Si TFTs, and a storage capacitor. The proposed pixel circuit adopts the voltage programming scheme for threshold voltage compensation. Because the whole line time is in use only for charging the data voltage, this pixel circuit is applicable to high resolution and frame rate displays. In addition, it compensates voltage variation of OLEDs and voltage drop of supply lines at lower power consumption. On the average, the non-uniformity of a proposed circuit is reduced to 2.5%, compared to 7.1% of the previous one at a 240 Hz full-HD display. On the other hand, the compensation voltage error, which is caused by feed-through and charge injection noises from falling control signals of switching TFTs, is much less in the proposed scheme than in the previous 5T2C structure. The average error of the proposed circuit is reduced to 0.18 V, compared to 0.75 V of the previous one. The initialization power consumption of the 7T1C circuit is reduced to 98 mW, compared to 530 mW of the 5T2C circuit and the average dynamic power saving ratio of data drivers is estimated in the 7T1C pixel as 98.7% over the 5T2C one for 24 test images.     

Noble metal dispersed multiwalled carbon nanotubes immobilized ss-DNA for selective detection of dopamine

A hybrid nanocomposite consisting of Pt nanoparticles decorated functionalized multiwalled carbon nanotubes (f-MWNT) immobilized with single strand-DNA (ss-DNA) has been devised for the selective detection of dopamine (DA). AFM and TEM analyses show that wrapping of ss-DNA over Pt/f-MWNT reduces the aggregation of the nanotubes arising from van der Waals interaction. In addition to serving as a noncovalent dispersion agent, ss-DNA facilitated electron transfer towards dopamine, as analyzed by cyclic voltammetric studies (CV) and amperometry. The sequence dependency of ss-DNA for DA detection has been analyzed using AC and GT ss-DNA. The hybrid nanocomposite biosensor consisting of AC/ss-DNA exhibits linearity of detection upto ∼315 μM, with a detection limit 0.8 μM towards dopamine. The best sensing performance with linearity of ∼800 μM and detection limit ∼0.45 μM has been obtained with GT/ss-DNA immobilized Pt/f-MWNT sensor. Further, the nafion coated ss-DNA wrapped Pt/f-MWNT immobilized biosensor exhibits good stability, fast response time (<3 s) and selective detection of DA in the presence of ascorbic acid and uric acid.     

Biased scan of plasma display panel for data voltage reduction

This paper proposes a method of reducing the data voltage V_d of plasma display panels (PDPs). The proposed biased-scan method uses two separate ground systems: one for the sustain pulse generator (FGND) and the other for the data address and control systems (CHGND). A dc voltage bias, which is applied between CHGND and FGND during the address period, reduces V_d while preventing the undesired glow discharge induced by a scan pulse only. CHGND is connected to FGND for the first sustain pulse of each subfield, which reduces the time lag of address discharge, but it is separated from FGND for the other sustain pulses to increase the margin of the sustain voltage. The proposed method was tested on a 15% Xe 50-in. Full HD (1920 × 1080) single-scan PDP which had a sustain discharge gap of 110 μm. V_d could be reduced by 20 V (30%), and the power consumption of the V_d voltage source decreased by ∼25 W (50%) from that of the conventional method.     

基于MEMS的压电微能量采集器的电路研究与测试

微能量采集技术是利用某种效应把周围环境中的某种形式的能量转换成电能,为嵌入式系统和无线传感网络中的MEMS器件供能。本文探讨了一种基于MEMS技术的压电型微能量采集器。微能量采集器工作于低频环境,当给其振动激励信号时,它能够把机械能转换为电能。但是能量采集器直接输出的是交流电压,一般不能直接为器件供能。所以,利用AC-DC电路把交流转换为直流,实现为MEMS器件供能。文中给出了微能量采集器的测试电路,同时给出了测试结果,论证了在低频环境下这种微能量采集器的可行性。