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.     

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.     

一种微腔型PCR集成芯片的设计及其热分析

设计了一种新型的硅微聚合酶链式反应(PCR)芯片.该芯片采用掺杂半导体作为加热电阻来提高加热效率,改善反应腔内的温度均匀性.集成在芯片底部的Pt温度传感器与微加热器组成温度控制单元,为PCR反应过程提供所需的三种特定温度.此外,为了便于温度校准,设计了敞开式的反应腔,其容积约1.78 μL.采用集总参数法计算了芯片在加...     

Study on the effect of heating plate thickness on the micro induction heater for thermal bubbles generation

This paper designed a micro planar induction heater for thermal bubbles generation. The micro heater which consists of a micro planar coil, a copper heating plate and a glass slide was fabricated with MEMS fabrication process. The relations between the heating performance and the thickness of heating plate were studied in the simulation with the software of COMSOL. The experimental system has been built and the experimental tests for thermal bubble generation have been also carried out with the prototype. The process of thermal bubbles generation was recorded by the video camera. The frequency of AC current applied in the experiment is 100 kHz and the heating time of 1 s. The experimental results indicated that the micro heater has the best heating performance with the heating plate thickness of 12–16 μm, and the minimum power for thermal bubbles generation was only 0.427 W. This micro heater can be applied to a variety of thermal bubble devices, such as micro actuator, micro ejector and micro pump.     

一种飞行器燃料温控系统设计与优化

高空长航时飞行器由于长时间处于低温使用环境中,飞行器的燃料及其供给系统需进行温度控制功能设计,以保障飞行器长时间正常运行,以免造成飞行器损坏;飞行器燃料所处的低温环境受到内外部多种热源影响,且与飞行器的飞行任务剖面密切相关,温度环境复杂且难以有效计算仿真;针对飞行器在复杂低温环境中对燃料进行温度控制功能的需求,以及飞行器对温控系统高可靠性要求、资源条件限制苛刻等限制条件,开展了温控系统设计和优化,并完成了硬件设计和系统仿真;由于地面试验和真实环境差异较大,单一地面试验很难模拟真实热环境,对系统优化设计造成困难,针对性开展热环境分析,系统方案设计、地面试验和飞行试验联合验证,优化系统方案,实现了一种高效可靠,且易于工程应用的燃料贮箱温控功能,取得了良好的工程应用效果,同时该优化设计方法具有一定的扩展性。     

Modeling and Experimental Identification of Silicon Microheater Dynamics: A Systems Approach

Microfabricated silicon cantilevers with integrated heating elements are powerful tools for manipulation and interrogation at the nanoscale. They can be used for highly localized heating of surfaces and also serve as electrothermal probes such as topography and position sensors. A thorough understanding of the dynamics of these heating elements is essential for an effective design and operation of such devices. In this paper, we present a tractable feedback model that captures the dynamics of these microheaters. The operator model separates the thermal and the electrical response of the microheater into two operators, with a linear dynamic operator mapping the applied electrical power to the heater temperature and a second nonlinear but memoryless operator mapping the heater temperature to the electrical resistance. We present experimental results that show the identification of a write heater used in probe-based thermomechanical data storage and the accurate synthesis of arbitrary temperature profiles. In the application of microheaters as electrothermal probes, the signals being measured are believed to perturb the thermal system. Therefore, an extension of our model is presented to analyze the response to this perturbation. The extended model is used to identify and forecast the performance of electrothermal sensors, such as the read heater in probe-based data storage. Also presented are results on thermal position sensors, in which microheaters are employed as nanoscale position sensors for a MEMS-based microscanner. $hfill$[2007-0250]      

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.     

On-Chip Vacuum Generated by a Micromachined Knudsen Pump

This paper describes the design, fabrication, and testing of a single-chip micromachined implementation of a Knudsen pump, which uses the principle of thermal transpiration, and has no moving parts. A six-mask microfabrication process was used to fabricate the pump using a glass substrate and silicon wafer. The Knudsen pump and two integrated pressure sensors occupy an area of 1.5 mm$times$2 mm. Measurements show that while operating in standard laboratory conditions this device can evacuate a cavity to 0.46 atm using 80 mW input power. The pumpdown time of an on-chip chamber and pressure sensor cavity with a total volume of 80 000 cubic micrometers is only 2 s, with a peak pump speed of$1times 10^-6 cc/min$. High thermal isolation is obtained between the polysilicon heater and the rest of the device.hfillhbox[1073]     

Microelectromechanical systems vibration powered electromagnetic generator for wireless sensor applications

This paper presents a silicon microgenerator, fabricated using standard silicon micromachining techniques, which converts external ambient vibrations into electrical energy. Power is generated by an electromagnetic transduction mechanism with static magnets positioned on either side of a moving coil, which is located on a silicon structure designed to resonate laterally in the plane of the chip. The volume of this device is approximately 100 mm³. ANSYS finite element analysis (FEA) has been used to determine the optimum geometry for the microgenerator. Electromagnetic FEA simulations using Ansoft’s Maxwell 3D software have been performed to determine the voltage generated from a single beam generator design. The predicted voltage levels of 0.7–4.15 V can be generated for a two-pole arrangement by tuning the damping factor to achieve maximum displacement for a given input excitation. Experimental results from the microgenerator demonstrate a maximum power output of 104 nW for 0.4g (g=9.81 m s^?1) input acceleration at 1.615 kHz. Other frequencies can be achieved by employing different geometries or materials.     

Microelectromechanical systems vibration powered electromagnetic generator for wireless sensor applications

This paper presents a silicon microgenerator, fabricated using standard silicon micromachining techniques, which converts external ambient vibrations into electrical energy. Power is generated by an electromagnetic transduction mechanism with static magnets positioned on either side of a moving coil, which is located on a silicon structure designed to resonate laterally in the plane of the chip. The volume of this device is approximately 100 mm³. ANSYS finite element analysis (FEA) has been used to determine the optimum geometry for the microgenerator. Electromagnetic FEA simulations using Ansoft’s Maxwell 3D software have been performed to determine the voltage generated from a single beam generator design. The predicted voltage levels of 0.7–4.15 V can be generated for a two-pole arrangement by tuning the damping factor to achieve maximum displacement for a given input excitation. Experimental results from the microgenerator demonstrate a maximum power output of 104 nW for 0.4g (g=9.81 m s⁻¹) input acceleration at 1.615 kHz. Other frequencies can be achieved by employing different geometries or materials.

     

Fabrication and operation of polyimide bimorph actuators for aciliary motion system

In order to extract macroscopic mechanical work out of microelectromechanical systems, we have proposed the concept of distributed micromotion systems (DMMS). The key idea of DMMS is to coordinate simple motions of many microactuators in order to perform a task. Design, fabrication, and operation of a type of DMMS, called a ciliary motion system, are presented. A bimorph thermal actuator using two types of polyimides with different thermal expansion coefficients and a metallic microheater in between them was fabricated. The cantilever-shaped actuator curled up from the substrate owing to the residual stress in polyimides which built up during the cooling process after they were cured at 350°C. It flattened and moved downward by flowing current in the heater. The dimensions of the cantilever were 500 μm in length, 100 μm in width, and 6 μm in thickness. The tip of the cantilever moved 150 μm in the direction vertical to the substrate and 80 μm in the horizontal direction; these were the maximum displacements obtained with 33 mW dissipated in the heater. The cut-off frequency was 10 Hz. On a 1-cm-square substrate, 512 cantilevers were fabricated to form an array. Two sets of cantilevers were placed opposing to each other. We operated them in coordination to mimic the motion and function of cilia and carried a small piece of a silicon wafer (2.4 mg) at 27-500 μm/s with 4-mW input power to each actuator     

A Nondestructive Dynamic Characterization of a Microheater Through Digital Holographic Microscopy

This paper describes the possibility of employing a digital holographic microscope (DHM) to carry out a noncontact and nondestructive characterization of a microheater integrated on a silicon nitride membrane and subjected to a high thermal load. Microheaters can be affected by the presence of the residual stress due to the technological processes appearing in the form of undesired bowing of the membrane. Moreover, when the temperature of the microheater increases, a further warpage of the structure can be induced. A DHM allows for evaluation, with high accuracy, the deformations due to the residual stress and how these deformations are affected by the thermal loads due to the microheater operating mode. In particular, this dynamic analysis is made possible by measuring the unwanted longitudinal displacement induced by the thermal expansion of both the device and its mechanical support. Taking into account this displacement, it is possible to have a continuous monitoring of profile deformation induced by the working condition of the microheater.     

A MEMS-based thermal infrared emitter for an integrated NDIR spectrometer

A novel micromachined thermal infrared emitter using a heavily boron doped silicon slab as radiating element is presented. The fabrication process has been designed to allow the integration of such infrared emitters with an array of thermopile infrared detectors, with the aim of achieving an integrated non-dispersive infrared microspectrometer. A first set of infrared emitters with a common size for the doped silicon radiating slab (1,100?×?300?×?8?μm³) has been successfully fabricated and characterized. The working temperature of the Joule-heated radiating slabs has been controlled by means of DC and pulsed electrical signals, achieving temperatures well beyond 700°C. The thermal time constant measured in pulsed operation, around 50?ms, is adequate to enable the direct electrical modulation of the emitted radiation up to a frequency of 5?Hz while maintaining the full modulation depth. The temperature distribution in the radiating elements has been analyzed using two different thermal imaging methods.     

A CMOS low noise amplifier based on common source technique for ISM band application

In this paper a 2.45 GHz narrowband low noise amplifier (LNA) for wireless communication system is enunciated. The proposed CMOS Low Noise amplifier has been verified through cadence spectre RF simulation in standard UMC 90 nm CMOS process. The proposed LNA is designed by cascoding of two transistors; that is the common source transistor drives a common gate transistor. To achieve better power gain along with low noise figure, cascoding of two transistor and source degeneration technique is used and for low power consumption, the MOS transistors are biased in subthreshold region. At 2.45 GHz frequency, it exhibits power gain 31.53 dB. The S11, S22 and S12 of the circuit is ?9.14, ?9.22 and ?38.03 dB respectively. The 1 dB compression point of the circuit is ?16.89 dBm and IIP3 is ?5.70 dBm. The noise figure is 2.34 dB, input/output match of ?9.14 dB/?9.22 dB and power consumption 8.5 mW at 1.2 V.     

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.     

Sensitivity improvement using optimized heater design for dual axis thermal accelerometers

This paper investigates the sensitivity improvement of an air filled cavity based thermal accelerometer. The accelerometer does not contain any solid proof mass and it is realizable in CMOS technology. The sensitivity has been improved by a new square ring shaped heater structure. The sensitivity of accelerometer performance is compared with other different heater shapes. It is found that, heater design having higher heat dissipation in the suspended beam gives higher sensitivity. The simulation is carried out using commercial FEM simulator COMSOL Multiphysics. For the peak heater temperature of 609 K, the proposed square ring shaped heater provides a sensitivity of 0.335 K/g. Under same conditions, sensitivity of an accelerometer with a meander shaped heater structure is only 0.098 K/g and diamond shaped structure is 0.229 K/g.     

The design and fabrication of polymerase chain reaction platform

Thermalcycler was extensively used machine for amplify DNA sample. One of the major problems in the working time was that it spent most of time for cooling and heating. In order to improve the efficient, the study presented a novel method for amplify DNA sample. For this concept, the DNA sample in the silicon chamber which was pushed by a tappet through the three temperature regions around a center and then the DNA segments could be amplified rapidly after 30 cycles. The polymerase chain reaction (PCR) platform was composed of the thin-film heaters, Cu plates, DC powers, and temperature controllers. The photolithography and bulk etching technologies were utilized to construct the thin-film heater and DNA reaction chambers. Finally, 1 μl 100 bp DNA segment of Escherichia coli K12 was amplified successfully within 36 min on this PCR platform.     

Forced convection boiling in a microchannel heat sink

Micromachining technology was utilized to fabricate a transparent microchannel heat-sink system by bonding glass to a silicon wafer. The micro heat sink consisted of a microchannel array, a heater, and a temperature sensor array. This integrated microsystem allowed simultaneous qualitative visualizations of the flow pattern within the microchannels and quantitative measurements of temperature distributions, flow rates, and input power levels. Boiling curves of temperature as a function of the input power were established. No boiling plateau was observed in the boiling curves, consistent with our previously reported data but different from results reported for macrochannel heat sinks. Three stable boiling modes, depending on the input power level, have been distinguished from the flow patterns. Local nucleation boiling was observed in microchannels with a hydraulic diameter as small as 26 μm at the lower input power range. At the higher input power range, a stable annular flow was the dominant boiling mode. Bubbly flow, commonly observed in macrochannels, could not be developed in the present microchannels. Consequently, no boiling plateau was detected in the boiling curves     

聚酰亚胺隔热悬挂结构设计与制作

加热器在原子钟、气体传感器、生物传感器等器件中有着广泛的应用,降低加热功耗对于这些器件的实用化具有重要意义。设计并制作了一种集成了加热器和温度传感器的聚酰亚胺隔热悬挂结构,用于承载待加热的芯片,并利用集成制作在聚酰亚胺膜上的2组Pt线圈分别对芯片进行加热和温度检测。实验证明:聚酰亚胺隔热悬挂结构由热传导引起的功耗仅为没悬挂结构时的0.95%,大大降低了由热传导引起的功耗,即便在没有真空封装的情况下,在芯片工作在100℃时,功耗也可降低到36.7%;同时该结构也具有良好的机械性能,承载体积为14 mm×7 mm×1 mm的硅基芯片时,安全系数可达到56.58,具有很好的应用前景。     

A novel approach for estimating heat transfer coefficients of ethylene glycol–water mixtures

Ethylene glycol–water mixtures (EGWM) are vital for cooling engines in automotive industry. Scarce information is available in the literature for estimating the heat transfer coefficients (HTC) of EGWM using knowledge-based estimation techniques such as adaptive neuro-fuzzy inference systems (ANFIS) and artificial neural networks (ANN) which offer nonlinear input–output mapping. In this paper, the supervised learning methods of ANFIS and ANN are exploited for estimating the experimentally determined HTC. This original research fulfills the preceding modeling efforts on thermal properties of EGWM and HTC applications in the literature. An experimental test setup is designed to compute HTC of mixture over a small circular aluminum heater surface, 9.5 mm in diameter, placed at the bottom 40-mm-wide wall of a rectangular channel 3 mm × 40 mm in cross section. Measurement data are utilized as the train and test data sets of the estimation process. Prediction results have shown that ANFIS provide more accurate and reliable approximations compared to ANN. ANFIS present correlation factor of 98.81 %, whereas ANN estimate 87.83 % accuracy for test samples.