A micromachined wide-bandwidth magnetic field sensor based on all-PMMA electron tunneling transducer

All-PMMA-based tunneling magnetic sensors were fabricated by hot embossing replication with silicon templates. The silicon templates had smooth surfaces, positive profiles, and pyramid-like pits with a high aspect ratio. With this fast (20 min), simple (one-step), and repeatable method, the all-PMMA tunneling sensor platform yielded sharp tunneling tips with 75 /spl mu/m in baseline and 50 /spl mu/m in depth. The sensors were assembled and fixed with measurement circuits, after their electrodes were patterned with modified photolithography and Co film was deposited with e-beam evaporation. A natural frequency response of 1.3 kHz was observed, and a tunneling barrier height of 0.713 eV was tested. Due to the quadratic relation between magnetic force and the field, the sensor field response (7.0/spl times/10/sup 6/ V/T/sup 2/) was also quadratic. The noise voltage at 1 kHz is 0.2 mV, corresponding to a magnet field of 0.46/spl times/10/sup -6/ T. The bandwidth of this sensor is 18 kHz. This new type of sensor platform is promising for the next generation of microsensing applications.     

Design optimization and implementation of a microgravity capacitive HARPSS accelerometer

This paper reports on the design optimization and implementation of a lateral capacitive accelerometer with high sensitivity and micro-g resolution, fabricated through the high-aspect ratio polysilicon and single-crystal silicon process on regular silicon wafers. A new implementation of vertical corrugation in silicon electrodes is developed to reduce the mechanical noise equivalent acceleration of the sensor. The predicted effect of corrugation on thermomechanical noise and also on static sensitivity is verified using ANSYS steady-state thermal simulation and FEMLAB linear stationary electrostatics analysis, respectively. The number of corrugated electrodes and the sense gap spacing is optimized to minimize the system (sensor + circuit) noise floor, while satisfying process and electronics limits. The open-loop differential sensitivity of a 60-/spl mu/m-thick prototype accelerometer is measured to be 0.25 V/g equivalent to 4.5 pF/g over a 1-g range. The estimated total noise equivalent acceleration of the system (sensor + circuit) is 0.95 /spl mu/g//spl radic/Hz in atmosphere.     

Interface for MEMS-based rotational accelerometer for HDD applications with 2.5 rad/s/sup 2/ resolution and digital output

A 0.6 /spl mu/m BiCMOS interface for microelectromechanical systems (MEMS) based rotational accelerometers is presented. It is housed in an inexpensive standard SO-24 plastic package with a capacitive rotational accelerometer sensor produced using MEMS technology. This sensitive interface chip includes the analog-to-digital conversion, filtering, and interface functions. The analog-to-digital conversion is realized through a single-bit electromechanical /spl Sigma/-/spl Delta/ loop able to detect capacitive unbalancing as low as 50 aF (50/spl times/10/sup -18/ F). The produced bitstream is then processed by a digital chain and made available through a standard 3.3 V (5 V tolerant) three-wire serial bus. The signal bandwidth is about 800 Hz, the sensitivity is 2.5 rad/s/sup 2/, with a full-scale sinewave of 200 rad/s/sup 2/ and a signal-to-noise ratio peak of 38 dB over 30-800 Hz. Through the serial bus, it is also possible to program device characteristics including gain, offset, filter performance, and phase delay. The complete sensor is used in a feed-forward compensation scheme to cancel external disturbances acting on computer hard-disk drives so as to steadily keep the read-write heads on track: this allows greater track densities and better speed performance.     

Nonconducting polymers on Prussian Blue modified electrodes: improvement of selectivity and stability of the advanced H/sub 2/O/sub 2/ transducer

An approach to improve the analytical performance of a Prussian Blue (PB)-based hydrogen peroxide transducer is described. In support of this objective, both the stabilizing and anti-interferent properties of nonconducting films were used. Electropolymerization on the top surface of PB modified electrodes is possible due to the high oxidizing ability of Berlin Green, and the growth of nonconductive polymers may be independently monitored by investigating the redox activity of the inorganic polycrystal. The best performance characteristics, which are advantageous over existing H/sub 2/O/sub 2/ sensors, were obtained for PB electrodes covered with electropolymerized o-phenylenediamine (1,2-diaminobenzene). The reported transducer remained at the 100% response state for more than 20 h under continuous flow of 0.1-mM hydrogen peroxide (flow rate 1 mlmin/sup -1/), which improves the stability level among the selective H/sub 2/O/sub 2/ sensors by one order of magnitude. The selectivity factor of the PB-poly (1,2-diaminobenzene) based transducer relative to ascorbate is nominally 600. PB-poly(1,2-diaminobenzene) modified electrode allows the detection hydrogen peroxide in the flow-injection mode down to 10/sup -7/ M with sensitivity of 0.3 AM/sup -1/cm/sup -2/, which is two times lower compared to the uncovered PB-based transducer.     

Generation-recombination noise in pseudomorphic Modulation-doped Al/sub 0.2/Ga/sub 0.8/As/In/sub 0.1/Ga/sub 0.9/As/GaAs micro-Hall devices

The noise spectrum in micro-Hall devices based on pseudomorphic Al/sub 0.2/Ga/sub 0.8/As/In/sub 0.1/Ga/sub 0.9/As/GaAs modulation-doped heterostructures was measured between 4 Hz and 65 kHz, allowing components due to thermal, 1/f, and generation-recombination to be characterized. Applying deep level noise spectroscopy (DLNS) in the temperature range of 77-300 K to analyze the generation-recombination part of the spectrum, two electron traps contributing to noise density were identified. An emission activation energy of 474 meV was measured for the dominant trap, corresponding to the well-known DX center originating from the AlGaAs barrier. The other deep level, with an emission activation energy of 242 meV, is probably related to defects in the InGaAs layer. The structures under investigation resulted in high-performance micro-Hall devices: a supply-current-related sensitivity up to 725 V/spl middot/A/sup -1//spl middot/T/sup -1/ at 77 K independent of bias current, a signal-to-noise sensitivity of 155 dB/spl middot/T/sup -1/ and a detection limit of 340 pT/spl middot/mm/spl middot/Hz/sup -1/2/ at 77 K were measured.     

Thickness-dependent leakage current of (polyvinylidene fluoride/lead titanate) pyroelectric detectors

The novel pyroelectric IR detectors have been fabricated using the Polyvinylidene Fluoride (PVDF)/Lead Titanate (PT) pyroelectric bilayer thin films, which were deposited onto Pt(111)/SiO/sub 2//Si(100) substrates by a sol-gel process. The ceramic/polymer structure was constructed of the randomly oriented polycrystalline PT film (/spl sim/1 /spl mu/m) heated at 700/spl deg/C for 1 h and the /spl beta/-phase PVDF film crystallized at 65/spl deg/C for 2 h. The effects of PVDF thin film thickness (100 /spl sim/ 580 nm) on the pyroelectric response of IR detectors were studied. The results show that the depositions of PVDF thin films onto the PT films will cause the leakage current (J) of the detectors decrease from 6.37/spl times/10/sup -7/ A/cm/sup 2/ to 3.86/spl times/10/sup -7/ A/cm/sup 2/. The specific detectivity (D*) measured at 100 Hz decreased from 2.72/spl times/10/sup 7/ cm/spl middot/Hz/sup 1/2//W for detector without PVDF to 1.71/spl times/10/sup 7/ cm/spl middot/Hz/sup 1/2//W for detector with PVDF thickness of 580 nm. By optimizing the ratio of the specific detectivity (D*) to leakage current, D*/J, the detector with PVDF thickness of 295 nm exhibits the best performance.     

Optical frequency standards based on the /sup 199/Hg/sup +/ ion

We report on work directed toward the systematic evaluation of an optical frequency standard based on the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of a single, laser-cooled, trapped /sup 199/Hg/sup +/ ion, whose resonance frequency is 1.06/spl times/10/sup 15/ Hz. For the purpose of the evaluation, a second /sup 199/Hg/sup +/ standard has been constructed. In the cooling-laser system built for the second standard, an injection-locking scheme has been applied to a CW Ti-sapphire laser. We also report optical frequency measurements of the clock transition performed over the past 21 months with the first standard. During this term, the variation of the clock transition frequency is found to be less than /spl plusmn/1/spl times/10/sup -14/.     

Microbolometers on a flexible substrate for infrared detection

Uncooled semiconducting YBaCuO infrared microbolometers have been fabricated on a flexible polyimide substrate formed by spin-coating a silicon wafer with a release layer. The wafer was used as a carrier for the flexible substrate during fabrication. The finished microbolometers on the flexible substrate showed a temperature coefficient of resistance (TCR) TCR =(1/R)(dR/dT) of -3.03% K/sup -1/, at room temperature, which is comparable to the TCR values observed for semiconducting YBaCuO microbolometers fabricated directly on Si. In order to provide protection and better mechanical integrity, some of the devices were encapsulated. The microbolometers attained a responsivity and detectivity as high as 3.5/spl times/10/sup 3/ V/W and 1/spl times/10/sup 7/ cm/spl middot/Hz/sup 1/2//W, respectively, at 2.88 /spl mu/A of current bias. The responsivity and detectivity of the encapsulated microbolometers, on the other hand, were 1.6/spl times/10/sup 3/ V/W and 4.9/spl times/10/sup 6/ cm/spl middot/Hz/sup 1/2//W, respectively at 1 /spl mu/A of current bias. Spin-coated liquid polyimide solved two major problems previously encountered with the solid polyimide sheets when used as a flexible substrate. First, flatness of the flexible substrate was maintained with no air bubbles. Second, the thermal expansion of the flexible substrate during the fabrication process due to thermal cycling was minimal. All measurements reported in this paper, were taken prior to releasing the flexible substrate from the Si wafer containing the finished microbolometers.     

Application of some recently synthesized 9, 10-anthraquinone derivatives as new class of ionophores responsive to lead (II) ion

Lead-selective solvent polymeric membrane electrodes, based on some recently synthesized 9, 10-anthraquinone derivatives, are described. The electrode exhibits a good Nernstian response for Pb (II) ions over a wide concentration range of 1.0/spl times/10/sup -6/-1.0/spl times/10/sup -2/ M with a slope of 28.9 mV decade/sup -1/. The potential-pH profile of membrane based on 1-hydroxy-2-({2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}methyl)anthra-9, 10-quinone (A/sub 3/) demonstrated a lack of H/sup +/ interference within a wide pH range (1.5-6.8). The detection limit is 6.7/spl times/10/sup -7/ M. The developed sensor has a very short response time (2.0 s), and it can be used as a working electrode in a flow injection system. The lifetime of the proposed sensor is 120 days (without any considerable divergence in potentials) with good reproducibility (SD=/spl plusmn/0.1 mV). The proposed sensor revealed good selectivity for Pb (II) over a wide variety of other metal ions. It can be used as an indicator electrode in the potentiometric titration of lead ions, with EDTA, oxalate, chromate, and hydroxide ions, and in direct determination of lead in a wastewater sample.     

Direct resistance comparisons from the QHR to100 M/spl Omega/ using a cryogenic current comparator

Measurements of room-temperature 100 M/spl Omega/ standard resistors and cryogenic thin-film resistors based directly on a quantized Hall resistance standard have been made with a cryogenic current comparator (CCC) bridge. This 15 496:2 ratio CCC attains a current sensitivity of 10.7 fA/Hz/sup 1/2/ in measurements of cryogenic thin-film resistors, without extensive shielding or filtering. A resistive primary winding helps the CCC maintain stability in the presence of external noise. The resistive-winding technique may be useful for the absolute measurement of small currents delivered by single-electron tunneling devices.     

基于地球重力法的低频加速度计校准

ISO 16063-16描述的地球重力法只能用于低频加速度计灵敏度幅值静态校准, 无法用于灵敏度幅值与相位的动态校准。采用机器视觉方法测量激励加速度相位,并得到对应时刻的加速度计输出信号相位,该方法可同时实现基于地球重力法的灵敏度幅值与相位动态校准。该方法测量时由转台为被校加速度计提供峰值恒定为1g的正弦激励加速度,有效避免了低频时微小激励加速度引起的加速度计输出低信噪比信号对校准精度的影响。实验结果表明,地球重力法可实现从静态(DC)至10Hz范围内的灵敏度幅值与相位高精度校准。     

Design and fabrication of a microimpedance biosensor for bacterial detection

A biosensor for bacterial detection was developed based on microelectromechanical systems, heterobifunctional crosslinkers and immobilized antibodies. The sensor detected the change in impedance caused by the presence of bacteria immobilized on interdigitated gold electrodes and was fabricated from (100) silicon with a 2-/spl mu/m layer of thermal oxide as an insulating layer. The sensor active area is 9.6 mm/sup 2/ and consists of two interdigital gold electrode arrays measuring 0.8 /spl times/ 6 mm. Escherichia coli specific antibodies were immobilized to the oxide between the electrodes to create a biological sensing surface. The impedance across the interdigital electrodes was measured after immersing the biosensor in solution. Bacteria cells present in the sample solution attached to the antibodies and became tethered to the electrode array, thereby causing a change in measured impedance. The biosensor was able to discriminate between different cellular concentrations from 10/sup 5/ to 10/sup 7/ CFU/mL in pure culture. The sample testing process, including data acquisition, required 5 min. The design, fabrication, and testing of the biosensor is discussed along with the implications of these findings toward further biosensor development.     

Amorphous silicon two-color microbolometer for uncooled IR detection

This paper describes the modeling and design of two-color microbolometers for uncooled infrared (IR) detection. The goal is to develop a high resolution IR detector array that can measure the actual temperature and color of an object based on two spectral wavelength regions. The microbolometer consists of high temperature amorphous silicon (a-Si:H) thin film layer held above the substrate by Si/sub 3/N/sub 4/ bridge. A thin NiCr absorber with sheet resistance of 377 /spl Omega//sqr is used to enhance the optical absorption in the medium and long IR wavelength windows. A tunable micromachined Al-mirror was suspended underneath the detector. The mirror is switched between two positions by the application of an electrostatic voltage. The switching of the mirror between the two positions enables the creation of two wavelength response windows, 3-5 and 8-12 /spl mu/m. A comparison of the two response wavelength windows enables the determination of the actual temperature of a viewed scene obtained by an IR camera. The microbolometer is designed with a low thermal mass of 1.65/spl times/10/sup -9/ J/K and a low thermal conductance of 2.94/spl times/10/sup -7/ W/K to maximize the responsivity R/sub v/ to a value as high as 5.91/spl times/10/sup 4/ W/K and detectivity D/sup */ to a value as high as 2.34/spl times/10/sup 9/ cm Hz/sup 1/2//W at 30 Hz. The corresponding thermal time constant is equal to 5.62 ms. Hence, these detectors could be used for 30-Hz frame rate applications. The extrapolated noise equivalent temperature difference is 2.34 mK for the 8-12 /spl mu/m window and 23 mK for the 3-5 /spl mu/m window. The calculated absorption coefficients in the medium and long IR wavelength windows before color mixing are 66.7% and 83.7%. However, when the color signals are summed at the output channel, the average achieved absorption was 75%.     

硅微谐振式加速度计的温度效应及补偿

零偏和标度因数稳定性是衡量加速度计性能的两个重要参数.为了降低硅微谐振式加速度计的温度敏感性,对其温度影响机理进行了深入研究.通过温度实验发现,硅微谐振式加速度计的零偏和标度因数与设计理论参数有较大区别,且都具有较大的温度灵敏度,分别为0.72 g/℃和1.5℃-1.对弹性模量和谐振器应力与谐振器频率的关系进行了理论计算和FEA仿真验证,其中弹性模量引起的谐振频率-温度灵敏度为-0.7 Hz/℃,谐振器应力引起的谐振频率-温度灵敏度为180 Hz/℃.阐述了加工过程中键合应力产生的原因以及键合应力与谐振器残余应力的关系,发现谐振器应力是造成加速度计输出随温度漂移的主要因素.提出了一种隔离残余应力的隔离梁的设计方案,可使零偏温度灵敏度降至-35 Hz/℃,为温度补偿指明了方向.     

Nanoscale memory elements based on solid-state electrolytes

We report on the fabrication and characterization of nanoscale memory elements based on solid electrolytes. When combined with silver, chalcogenide glasses such as Se-rich Ge-Se are good solid electrolytes, exhibiting high Ag ion mobility and availability. By placing an anode that has oxidizable Ag and an inert cathode (e.g., Ni) in contact with a thin layer of such a material, a device is formed that has an intrinsically high resistance, but which can be switched to a low-resistance state at small voltage via reduction of the silver ions. An opposite bias will return the device to a high-resistance state, and this reversible switching effect is the basis of programmable metallization cell technology. In this paper, electron beam lithography was used to make sub-100-nm openings in polymethylmethacrylate layers used as the dielectric between the device electrodes. The solid electrolyte film was formed in these via-holes so that their small diameter defined the active switching area between the electrodes. The Ag-Ge-Se electrolyte was created by the photodiffusion, with or without thermal assistance, of an Ag layer into the Ge-Se base glass. Combined thermal and photodiffusion leads to a nanophase separated material with a dispersed Ag ion-rich material with an average crystallite size of 7.5 nm in a glassy insulating Ge-rich continuous phase. The nanoscale devices write at an applied bias as low as 0.2 V, erase by -0.5 V, and fall from over 10/sup 7/ /spl Omega/ to a low-resistance state (e.g., 10/sup 4/ /spl Omega/ for a 10-/spl mu/A programming current) in less than 100 ns. Cycling appears excellent with projected endurance well beyond 10/sup 11/ cycles.     

A microfabricated biosensor for detecting foodborne bioterrorism agents

A biosensor for the detection of pathogenic bacteria was developed for biosecurity applications. The sensor was fabricated using photolithography and incorporates heterobifunctional crosslinkers and immobilized antibodies. The sensor detected the change in impedance caused by the presence of bacteria immobilized on interdigitated gold electrodes and was fabricated from (100) silicon with a 2-/spl mu/m layer of thermal oxide as an insulating layer. The sensor has a large active area of 9.6 mm/sup 2/ and consists of two interdigital gold electrode arrays each measuring 0.8 /spl times/ 6 mm. Pathogenic Escherichia coli and Salmonella infantis were tested in serially diluted pure culture. Analyte specific antibodies were immobilized to the oxide between the electrodes to create a biological sensing surface. After immersing the biosensor in solution, the impedance across the interdigital electrodes was measured. Bacteria cells present in the sample solution attached to the antibodies and became tethered to the electrode array thereby causing a change in measured impedance. The biosensor was able to discriminate between different cellular concentrations from 10/sup 4/ - 10/sup 7/ CFU/mL (colony-forming units per milliliter) in solution. The sample testing process, including data acquisition, required 5 min. The design, fabrication, and testing of the biosensor is discussed along with the implications of these findings toward further biosensor development.     

A resonant accelerometer with two-stage microleverage mechanisms fabricated by SOI-MEMS technology

We present the design, fabrication, and testing of a push-pull differential resonant accelerometer with double-ended-tuning-fork (DETF) as the inertial force sensor. The accelerometer is fabricated with the silicon-on-insulator microelectromechanical systems (MEMS) technology that bridges surface micromachining and bulk micromachining by integrating the 50-/spl mu/m-thick high-aspect ratio MEMS structure with the standard circuit foundry process. Two DETF resonators serve as the force sensor measuring the acceleration through a frequency shift caused by the inertial force acting as axial loading. Two-stage microleverage mechanisms with an amplification factor of 80 are designed for force amplification to increase the overall sensitivity to 160 Hz/g, which is confirmed by the experimental value of 158 Hz/g. Trans-resistance amplifiers are designed and integrated on the same chip for output signal amplification and processing. The 50-/spl mu/m thickness of the high-aspect ratio MEMS structure has no effect on the amplification factor of the mechanism but contributes to a greater capacitance force; therefore, the resonator can be actuated by a much lower ac voltage comparing to the 2-/spl mu/m-thick DETF resonators. The testing results agree with the designed sensitivity for static acceleration.     

A sensitive differential capacitance to voltage converter forsensor applications

There is a need for capacitance to voltage converters (CVC's) for differential capacitive sensors like pressure sensors and accelerometers which can measure both statically and dynamically. A suitable CVC is described in this paper. The CVC proposed is based on a symmetrical structure containing two half ac bridges, is intrinsically immune to parasitic capacitances and resistances, is capable of detecting capacitance changes from dc up to at least 10 kHz, is able to handle both single and differential capacitances, and can easily be realized with discrete components. Its sensitivity is very high: detectable capacitance changes of the order of 2 ppm of the nominal value (24 aF with respect to a nominal capacitance of 12 pF) result in a measured output voltage of 1.5 mV. However, due to drift the absolute accuracy and resolution of the CVC is limited to 3.5 ppm. A differential accelerometer for biomedical purposes was connected to the CVC and showed a sensitivity of 4 V/g. The measured rms output voltage noise in the frequency range of 2-50 Hz is 750 μV, resulting in a signal to noise ratio of 75 dB at an acceleration of 1 g in the frequency range of 2-50 Hz     

Cucurbiturils: molecular nanocapsules for time-resolved fluorescence-based assays

A new fluorescent host-guest system based on the inclusion of the fluorophore 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) into the cavity of the molecular container compound cucurbit[7]uril (CB7) has been designed which possesses an exceedingly long-lived emission (690 ns in aerated water). The large binding constant of (4/spl plusmn/1)/spl times/10/sup 5/ M/sup -1/ along with the resistance of the CB7/spl middot/DBO complex toward external fluorescence quenchers allow the use of CB7 as an enhancer in time-resolved fluorescence-based assays, e.g., to screen enzyme activity or inhibition by using DBO-labeled peptides as substrates. The response of CB7/spl middot/DBO to different environmental conditions and possible quenchers are described.     

基于电磁激励的SOI-MEMS谐振式加速度计的闭环检测系统(英文)

介绍了一种基于电磁激励方式,采用基于绝缘体上硅的微电子机械系统(SOI-MEMS)加工方法制作谐振式加速度计及其闭环控制电路系统.传感器芯片制作采用的是SOI材料(10μm+2μm+290μm),利用MEMS加工工艺制作.当外界z轴方向加速度作用于加速度计时,加速度计的两根"H"型谐振梁因受到弯曲应力而产生谐振频率的漂移,通过检测谐振梁频率的变化标定加速度的大小.电磁激励检测方式有利于加速度计的最终闭环控制.闭环电路控制系统主要由增益放大部分、自动增益控制(AGC)电路缓冲系统和移相器组成.测试结果显示,当有1g重力加速度作用于加速度计,闭环电路可稳定输出检测正弦频率信号58.958 kHz,与开环扫频结果一致.加速度计的"H"型谐振梁空气中检测Q值约为400,灵敏度可达584 Hz/g.