Fabrication of ultrathin p++ silicon microstructuresusing ion implantation and boron etch-stop

This paper discusses the fabrication of submicron p⁺⁺ silicon microstructures for a number of MEMS applications using boron ion implantation, rapid thermal annealing, and boron etch-stop. To form these thin structures, the silicon is implanted with boron at an energy of 40 keV and doses of 5×10¹⁵ cm^-2 and 7×10¹⁵ cm^-2, which produce a peak concentration of more than 10²⁰ cm^-3, sufficient for achieving an effective etch-stop in ethylene diamine pyrocathecol. The thickness of the p⁺⁺ layer varies from 0.2 to 0.3 μm depending on the annealing time and temperature. SUPREM simulation has been used to determine optimum implantation and annealing conditions. A number of microstructures, including thin silicon diaphragms as large as 2 mm on a side and 0.2 μm thick, hot wire anemometers with a temperature coefficient of resistance of ~1600 ppm/°C, and piezoresistive sound detectors, have been fabricated with high reproducibility, uniformity, and yield     

Process-dependent thin-film thermal conductivities for thermal CMOSMEMS

The thermal conductivities κ of the dielectric and conducting thin films of three commercial CMOS processes were determined in the temperature range from 120 to 400 K. The measurements were performed using micromachined heatable test structures containing the layers to be characterized. The κ values of thermally grown silicon oxides are reduced from bulk fused silica by roughly 20%. The κ of phosphosilicate and borophosphosilicate glasses are 0.94±0.08 W m^-1 K^-1 and 1.18±0.06 W m^-1 K^-1, respectively, at 300 K. A plasma-enhanced chemical-vapor-deposition silicon-nitride layer has a thermal conductivity of 2.23±0.12 W m^-1 K^-1 at 300 K. This value is between published data for atmospheric-pressure CVD and low-pressure CVD nitrides. For the metal layers, we found thermal conductivities between 167 W m^-1 K^-1 and 206 W m ^-1 K^-1, respectively, at 300 K, to be compared with 238 W m^-1 K^-1 of bulk aluminum. The temperature-dependent product κρ of κ with the electrical resistivity ρ agrees better than 8.2% between 180-400 K with that of pure bulk aluminum. The κ values of the polysilicon layers are between 22.4 W m^-1 K^-1 and 37.3 W m^-1 K^-1 at 300 K. They are reduced from similarly doped bulk silicon by factors of between 2.0-1.3. The observed discrepancies between thin film and bulk data demonstrate the importance of determining the process-dependent thermal conductivities of CMOS thin films     

Bulk-Micromachined Test Structure for Fast and Reliable Determination of the Lateral Thermal Conductivity of Thin Films

A novel bulk-micromachined test structure is presented for the fast and reliable determination of the lateral thermal conductivity of thin films. The device is composed of a heater resistor and thermocouples that are fabricated in polysilicon (poly-Si), and the associated processing and DC measurement procedures are straightforward. The validity of the method is supported by numerical simulations and verified by experimental determination of the lateral thermal conductivity of aluminum (Al), aluminum nitride (AlN), p-doped poly-Si, and silicon nitride (SiN) thin films. For Al, an average value of 217 W m^-1 K^-1 was found for 1-mum thick layers. For the other layers, a number of thicknesses were studied, and the increase of thermal conductivity with thickness was effectively detected: for AlN, values from 7 to 11.5 W m^-1 K^-1 were found, and for p-doped poly-Si, values went from 21 to 46 W m^-1 K^-1 for thicknesses from 0.15 to 1 mum. For SiN, a value of 1.8 was extracted for layers thicker than 0.5 mum.     

MgO sacrificial layer for micromachining uncooled Y-Ba-Cu-O IRmicrobolometers on Si3N4 bridges

This paper describes a new micromachining technique for fabrication of semiconducting yttrium barium copper oxide (YBCO) microbolometers using magnesium oxide (MgO) as the sacrificial layer. This type of bolometer can be operated at room temperature, providing a low-cost alternative for more expensive cryogenically cooled thermal detectors used for infrared (IR) imaging. The new micromachining techniques described here would enable the fabrication of YBCO IR focal plane array (FPA) with CMOS signal processing circuitry. Devices were fabricated by growing YBCO films on 4000-Å-thick suspended Si₃N₄ membranes measuring 40×40 μm² in area and extended over micromachined air gaps, which provide the low thermal conductivity that is required for high responsivity. The gap was created by etching an MgO sacrificial layer. This is the first example of using MgO in this type of application. The MgO sacrificial layer technique is fully CMOS compatible and presents no major fabrication challenges. Thermal conductivities achieved in vacuum with the Si₃N₄ suspended structures were on the order of 10^-7 W/K, yielding an effective thermal isolation for bolometer operation. Optical characterization has shown responsivity up to 60 kV/W and detectivity over 10⁸ cm.Hz^1/2/W to black-body IR radiation, indicating that this technology is a suitable candidate for low-cost thermal imaging     

Embedding of complete binary trees into meshes with row-columnrouting

This paper considers the problem of embedding complete binary trees into meshes using the row-column routing and obtained the following results: a complete binary tree with 2^p-1 nodes can be embedded (1) with link congestion one into a ⁹/₈√(2^p)×⁹/ ₈√(2^p) mesh when p is even and a √( ⁹/₈2^p)×√(⁹/ ₈2^p) mesh when p is odd, and (2) with link congestion two into a √(2^p)×√(2^p) mesh when p is even, and a √(2^p-1)×√(2^p-1) mesh when p is odd     

A hermetic glass-silicon micropackage with high-density on-chipfeedthroughs for sensors and actuators

This paper describes the development of a hermetic micropackage with high-density on-chip feedthroughs for sensor and actuator applications. The packaging technique uses low-temperature (320°C) electrostatic bonding of a custom-made glass capsule (Corning 7740, 2×2×8 mm³) to fine grain polysilicon in order to form a hermetically sealed cavity. High-density on-chip multiple polysilicon feedthroughs (200 per millimeter) are used for connecting external sensors and actuators to the electronic circuitry inside the package. A high degree of planarity over feedthrough areas is obtained by using grid-shaped polysilicon feedthrough lines that are covered with phosphosilicate glass (PSG), which is subsequently reflown at 1100°C in steam for 2 h. Saline and DI water soak tests at elevated temperatures (85 and 95°C) were performed to determine the reliability of the package. Preliminary results have shown a mean time to failure (MTTF) of 284 days and 118 days at 85 and 95°C, respectively, in DI water. An Arrhenius diffusion model for moisture penetration yields an expected lifetime of 116 years at body temperature (37°C) for these packages. In vivo tests in guinea pigs and rats for periods ranging from one to two months have shown no sign of infection, inflammation, or tissue abnormality around the implanted package     

A high-Tc superconductor bolometer on a silicon nitridemembrane

In this paper, we describe the design, fabrication, and performance of a high-T_c GdBa₂Cu₃O_7-δ superconductor bolometer positioned on a 2× 2-mm² 1-μm-thick silicon nitride membrane. The bolometer structure has an effective area of 0.64 mm² and was grown on a specially developed silicon-on-nitride (SON) layer. This layer was made by direct bonding of silicon nitride to silicon after chemical mechanical polishing. The operation temperature of the bolometer is 85 K. A thermal conductance G=3.3·10^-5 W/K with a time constant of 27 ms has been achieved. The electrical noise equivalent power (NEP) at 5 Hz is 3.7·10^-2 WHz^-1/2, which is very close to the theoretical phonon noise limit of 3.6·10^-12 WHz ^-1/2, meaning that the excess noise of the superconducting film is very low. This bolometer is comparable to other bolometers with respect to high electrical performance. Our investigations are now aimed at decreasing the NEP for 84-μm radiation by further reduction of G and adding an absorption layer to the detector. This bolometer is intended to be used as a detector in a Fabry-Perot (FP)-based satellite instrument designed for remote sensing of atmospheric hydroxyl     

Silicon membrane nanofilters from sacrificial oxide removal

Silicon micropore filter designs using a sacrificial oxide removal technique are described. These filters utilize surface and bulk micromachining for precise control of pore sizes in the tens of nanometers range. The semipermeable membrane of the sacrificial layer filters (SLFs) is typically composed of sandwiched p⁺ polysilicon/oxide/p⁺ silicon layers where the sacrificial oxide between the two silicon layers determines the pore size of the filter. The purpose of this paper is to address special design and fabrication considerations for control of pore size uniformity within 10%, adapting surface conditions for filtration fluxes of deionized water to fall in the range of 1 ml/cm²h, and maximization of the structural response of SLFs. Fluorescent beads are used to analyze the pore size uniformity of fabricated filters, with achievements of four-log reduction in fluorescent bead concentration     

Magnetic microactuation of polysilicon flexure structures

A microactuator technology that combines magnetic thin films with polysilicon flexural structures is described. Devices are constructed in a batch-fabrication process that combines electroplating with conventional lithography, materials, and equipment. A microactuator consisting of a 400×(47-40)×7 μm³ rectangular plate of NiFe attached to a 400×(0.9-1.4)×2.25 μm³ polysilicon cantilever beam has been displaced over 1.2 mm, rotated over 180°, and actuated with over 0.185 nNm of torque. The microactuator is capable of motion both in and out of the wafer plane and has been operated in a conductive fluid environment. Theoretical expressions for the displacement and torque are developed and compared to experimental results     

Fabrication of metallic heat exchangers using sacrificial polymermandrils

This paper demonstrates the use of poly(dimethylsiloxane) (PDMS), polyurethane (PU), epoxy, and poly(methyl methacrylate) (PMMA) as mandrils to fabricate metallic heat exchangers having 300-700 μm internal channels. The mandrils were prepared using two soft lithographic techniques-replica molding and microembossing. To fabricate the heat exchangers, the polymeric mandrils were coated with a thin layer of metal by thermal evaporation or sputtering; this layer acted as the cathode for electrodeposition of a shell of nickel or copper that was 100 μm thick. The polymers were removed by burning them out at 400°C in air, or by dissolving them with a tetrahydrofuran solution of tetrabutylammonium fluoride. Studies of heat dissipation showed that the nickel heat exchangers with features that range in size from 150-750 μm have thermal resistances ranging from 0.07 to 0.12°^-2 C W^-1 cm at flow rates of water of ~20 L h^-1 and pressures of 8.6-83×10³ N m^-2     

Elimination of post-release adhesion in microstructures usingconformal fluorocarbon coatings

The adhesion of polysilicon microstructures to their substrates is eliminated using a relatively conformal hydrophobic fluorocarbon (FC) coating grown in a field-free zone of a plasma reactor. Experiments show that the FC film deposition on top of the microstructure and on the underside was approximately 2:1. The FC coating is able to cover the entire underside of a 200×200 μm² plate, with a 20% deposition nonuniformity. The coating exhibits a contact angle of 110° and is able to prevent adhesion of cantilever beams and doubly supported beams to their substrates even after direct immersion in DI water. The durability of the coating was tested using an accelerated aging method, predicting a lifetime of greater than ten years at 150°C. Periodic wear tests indicate that the coating remains hydrophobic even after 10⁷ contact cycles     

Thermal characterization of surface-micromachined silicon nitridemembranes for thermal infrared detectors

The aim of this work is to provide a thorough thermal characterization of membrane structures intended for thermal infrared detector arrays. The fabrication has been conducted at temperatures below 400°C to allow future post processing onto existing CMOS readout circuitry. Our choices of membrane material and processing technique were plasma enhanced chemical vapor deposited silicon nitride (SiN) and surface micromachining, respectively. The characterization gave for the thermal conductance (G) and thermal mass between the membrane and its surroundings 1.8·10^-7 W/K and 1.7·10^-9 J/K, respectively, which are close to the best reported values elsewhere. From these results the thermal conductivity and specific heat of SiN were extracted as 4.5±0.7 W/m.K and 1500±230 J/kg.K. The contribution to G from different heat transfer mechanisms are estimated. A model describing the pressure dependence of G was developed and verified experimentally in the pressure interval [5·10^-3, 1000] mbar. Finally, the influence of the thermal properties of the membrane on infrared detector performance is discussed     

基于SPOT5遥感影像丰宁县植被地上生物量估测研究

利用SPOT5遥感影像数据和同期获得的野外调查样地数据,基于按植被类型分类估测的方法,研究了河北省丰宁满族自治县植被地上生物量的遥感估测技术。研究结果显示,SPOT5影像的4个波段反射率和中红外植被指数(VI3)结合建立的多元回归模型,可用于森林生物量的遥感估测,估测的R2值达0.540,说明中红外波段信息提高森林生物量的估测精度有一定作用;通过分析样地生物量与多种植被指数的相关性发现,基于比值植被指数(RVI)的指数回归模型是灌丛生物量估测的最佳模型,估测的R2值达0.711,基于归一化植被指数(NDVI)的简单线性回归模型为估测草地生物量的最佳模型,R2值达0.790。利用2008年的全覆盖SPOT5影像,获得了丰宁县2008年植被地上生物量分布图,除农田植被外,全县地上生物总量为3.706×107 t,单位面积生物量平均为51.223t/hm2,其中,森林植被总生物量为3.578×107 t,灌丛植被总生物量为1.048×106 t,草地植被总生物量为2.277×105 t。     

Fabrication of semiconducting YBaCuO surface-micromachinedbolometer arrays

Thermal infrared detectors require thermal isolation to permit the infrared-sensitive material to integrate the incident photon energy and thereby obtain high responsivity and detectivity. This paper describes the fabrication of semiconducting YBaCuO microbolometer arrays into thermal isolation structures by employing Si surface-micromachining techniques. An isotropic HF:HNO₃ etch was used to remove the underlying Si substrate from the front-side of the wafer and suspend SiO ₂ membranes into 1×10 pixel-array structures. The infrared-sensitive material, YBaCuO, was subsequently deposited onto the thermal isolation structures and patterned to form the detector arrays. The high-temperature coefficient of resistance and low noise of semiconducting YBaCuO at room temperature is attractive for uncooled infrared detection. The fabrication process was conducted entirely at room temperature. In this manner, infrared detectors are fabricated in a process that is compatible with CMOS technology to allow for the integration with on-chip signal processing circuitry. The end result is low-cost infrared-detector arrays for night vision in a variety of applications including transportation and security. Preliminary results show a temperature coefficient of resistance above 3%, voltage responsivity close to 10⁴ V/W, and detectivity over 10⁷ cm·Hz^1/2/W at a bias current of 0.79 μA     

Nanoscale Calorimetry Using a Suspended Bridge Configuration

Abstract A new setup for small-scale differential scanning calorimetry (DSC) studies based on a suspended bridge configuration is presented. The new setup has three major advantages over previously reported DSC setups: 1) superior temperature uniformity in the bridge cross section; 2) less heat loss to the surroundings by at least two orders of magnitude; and 3) a faster transient response by three orders of magnitude. This paper includes a thermal analysis to support these improvements. A major contribution of the new thermal analysis over previous reports is the inclusion of the thermal mass of the substrate in calculations, which makes thermal design more detailed, dramatically affecting accuracy and sensitivity in measurements. Furthermore, the new thermal analysis more accurately accounts for heat loss to the substrate and the surroundings in efforts to resolve suspected inconsistencies in previously reported data. Experimental validation of the new setup is presented by measuring the specific heat of thin layers of Si0₂ and CoFe. The specific heat of Si0₂ was found to be 2.2 times 10⁶ Jm ^-3 K^-1 which is nearly 10% different from the literature values of bulk specimens. For CoFe, the specific heat value of 3.16 x 10⁶ Jm ^-3 K^-1 is obtained using differential Cu/Si0₂ and Cu/Si0₂/CoFe structures compared to the value of 3.5 times 10⁶ Jm ^-3 K^-1 obtained using single CoFe suspended structure.     

Independent tuning of linear and nonlinear stiffness coefficients[actuators]

Using a combination of electrostatic actuators, we present a method to independently tune the linear and nonlinear stiffness coefficients of a uniaxial micromechanical device. To demonstrate the method's capability, we investigated the tuning of an oscillator with linear and cubic restoring forces. We successfully tuned the cubic stiffness from 0.31×10¹¹ to -5.1×10¹¹ N/m³ without affecting the resonant frequency or the linear stiffness. Numerical results are presented which characterize the actuators and indicate important design parameters. Finally, issues such as actuator design, quadratic stiffness, and stability are discussed     

Design of Ecological Compensation Scheme for River Basin based on Remote Sensing Data

A key problem is clarifying the relationship between compensation standard and the supply of additional ecosystem services in the study of ecological compensation.Focusing on the Gansu section of the Weihe River Basin,the specific target of ecological compensation is going to increase the soil conservation capacity.We will compensate people who have marginal farmland when the slope is more than 25°.Based on social and economic survey data and remote sensing data,we used minimum\| data approaches to simulate ecological compensation standards,then used InVEST model to simulate the results,analyze the potential of increased ecosystem service,and choose the best forest species after turn marginal farmland into forests.In the end,analyze additional ecosystem services in different compensation standards.The solution is that each county /district can select the best forest when turn marginal farmland of the slope is more than 25°,which can maximum add soil conservation quantity.Weiyuan County and Longxi County can plant evergreen coniferous forest,that newly add soil conservation quantity are 144×10⁴ t and 63.04×10⁴ t per hectare each year,the amount of compensation is 506.67×10⁴ CNY and 686.7×10⁴ CNY each year.The added soil conservation quantity is 1 152.00 t and 504.32 t in eight years.      

平衡态分子动力学 Green-Kubo 方法计算氮化硼 单层结构热导率的模型尺寸效应研究

分子动力学模拟可以直接表征体系原子的行为,因此成为研究氮化硼相关材料微观导热机理的重要工具,但目前尚没有关于氮化硼材料模型尺寸对其热传导相关性质影响规律的研究。该文采用平衡态分子动力学并结合 Green-Kubo 方法,研究了纯净氮化硼单层结构热导率、声子色散关系以及态密度随模拟尺寸的变化规律,并解释了其内部机理。实验发现,氮化硼单层材料热导率随着模拟尺寸的增大而减小,并在单层面积约 4.1 nm×4.1 nm 时收敛于(349±22)W/(m?K),此收敛值远小于平衡态分子动力学计算中石墨烯热导率的收敛尺寸(10 nm×10 nm),这说明氮化硼单层中声子之间的散射大于石墨烯。此外,不同于热导率,氮化硼单层结构的声子色散曲线、态密度几乎不受模拟尺寸的影响。该研究结果可为采用平衡态分子动力学研究氮化硼相关材料的微观导热机理提供重要参考。     

A micromachined system for the separation of molecules using thermal field-flow fractionation method

All silicon-glass micromachined thermal field-flow fractionation (TFFF) microsystem has been developed and presented for the first time. The device consists of seven layers of double side, deep, selectively etched silicon and glass substrates, bonded anodically. The built-in fluidic heater and cooler allows producing the high thermal gradient. In the 30 μm deep, 2 mm wide and 50 mm long separation channel, the temperature gradient 1.5×10⁶ K/m has been obtained for relatively low heating agent temperature (343 K). The TFFF microsystem has been equipped with two integrated, three-electrodes conductivity detectors. Some basic separation properties have been evaluated for low concentrated KCl test samples in water. It has been found that retention time of 0.6 μl sample of 0.01 M KCl in water, for 293/321 K (cooling/heating agents) compared to 0.9×10⁶ K/m, is almost two times longer than it has been obtained in the device during the absence of the temperature gradient.     

The development of a low-stress polysilicon process compatible withstandard device processing

When surface micromachined devices are combined with on-chip circuitry, any high-temperature processing must be avoided to minimize the effect on active device characteristics. High-temperature stress annealing cannot be applied to these structures. This work studies the effects of deposition parameters and subsequent processing on the mechanical properties of the polysilicon film in the development of a low-strain polysilicon process, without resorting to high-temperature annealing. The films are deposited as a semi-amorphous film and then annealed, in situ at 600°C for 1 h, to ensure the desired mechanical characteristics for both doped and undoped samples. This low temperature anneal changes the strain levels in undoped films from -250 to +1100 με. The best results have been obtained for an 850°C anneal for 30 min which is used to activate the dopant (both phosphorus and boron). No further stress annealing was used, and 850°C does not present problems in terms of thermal budget for the electrical devices. It is shown that these mechanical characteristics are achieved by forming the grain boundaries during subsequent low temperature annealing, and not during deposition. TEM (transmission electron microscopy) studies have been used to investigate the link between the structure and mechanical strain. This has shown that it is the formation of the grain boundary rather than the grain size which has a significant effect on strain levels, contrary to reports in the literature. Using the above-mentioned deposition process, a series of experiments have been performed to establish the flexibility in subsequent processing available to the designer. Therefore, by careful consideration of the processing, a low-temperature polysilicon process, which can be used to fabricate thin micromachined structures, has been developed