Search

In this paper, we derive an overall piezoresistance tensor for polycrystalline aggregates having an orthotropic texture in terms of the crystallite orientation distribution function (CODF) and the cubic single-crystal piezoresistance tensor. We found that the deviatoric part of the overall piezoresistance tensor is a function of the preferential crystallographic orientation of cubic single crystals and that the number of independent tensor components is three. Experimental results show that the variation of the texture strength plays the main role in representing the piezoresistance anisotropy for polycrystalline aggregates.

Motivated by the chaotic waterwheel subject to the Lorenz equations, which was invented by Malkus and Howard about 40 years ago, we have developed a chaotic gas turbine by mechanically simulating the Rayleigh-Benard convection of fluids heated from below and cooled from above. The rotational motion of the turbine erratically reverses its direction similarly to the random reversal of large-scale circulation in turbulent thermal convection at high Rayleigh numbers. The nondimensionalized expression for the equations of motion of our gas turbine is represented as a starlike network of many Lorenz subsystems sharing the dimensionless angular velocity of the turbine rotor as the central node, referred to as augmented Lorenz equations. We report the observed motion of the turbine and discuss its dynamical properties.

This paper proposed the derivation method of upper and lower bounds for variable piezoresistive coefficients of polycrystalline silicon (polysilicon) films having preferred orientation. Two sets of fundamental piezoresistive coefficients of the polysilicon film were derived from the coefficients of single-crystalline silicon using two approximation models based on assumptions that the stress is uniform and the resistivity change is uniform at any point of the film. The upper and lower bounds for the effective piezoresistive coefficients were mathematically defined using the piezoresistive coefficients obtained from the two approximation models. In order to confirm the validity of this definition, the upper and lower bounds, which are applicable to any polysilicon film, were calculated, and were compared with the measurement results previously reported by some groups. The upper and lower bounds were consistent with the measurement results, which supports the validity of this derivation.

This paper presents a wet etching simulation method for sacrifice layer of MEMS (micro electro mechanical system) that considers physical phenomenon including flow, diffusion and chemical reaction. In this method, a partial differential equation with implicit parameterization of etching properties was studied that was solvable by any commercial CFD code. Two parameters for flow and reaction were determined by fitting the numerical result to experimental one obtained using a test device. For automatic calibration of parameters, an error function was proposed considering the position of etching front, averaged etching rate and shape of etching front. The distribution of the error (response surface) was predicted by second order Lagrange interpolation. The iteration algorithm for this automatic calibration contributed to reduce the computational cost. Once the parameters were determined, the etching simulation of real MEMS device could be practically carried out.

In this work, the isotropic piezoresistance in the (0001) plane of p-type 4H-SiC was discovered by means of the hole energy shift calculation and the coordinate transformation. These results were also confirmed by the measurement of the piezoresistance using a bending beam method. The fundamental longitudinal and transverse piezoresistive coefficients π11 and π12 were found to be 6.43 × 10−11 Pa−1 and −5.12 × 10−11 Pa−1, respectively. The isotropy of the piezoresistance in the basal plane of p-type 4H-SiC is attributed to the isotropic hole energy shift under uniaxial strain. This interesting phenomenon in p-type 4H-SiC is promising for the design and fabrication of mechanical sensors and strain-engineered electronics since high sensitivity and consistent performance can be achieved regardless of the crystallographic orientation.

In this study, mechanical and thermal properties of the co-sputtered tungsten silicide (WSi) thin film were evaluated to consider the possibility of its use in MEMS applications. WSi film was prepared by co-sputtering and basic micromachining processes, and its mechanical and thermal properties such as Young’s modulus, temperature coefficient of resistance (TCR), strain gauge factor, coefficient of thermal expansion (CTE) and thermal stress were studied. The measurement method was simple and efficient since only one test pattern was used for all measurements. At room temperature, the TCR, gauge factor, CTE and thermal stress were measured to be −670 ppm/°C, 2.8, 32 ppm/°C and 1.76 GPa, respectively. The dependence of these coefficients on temperature was also evaluated experimentally.

We have simulated the electronic states and piezoresistance coefficients in single-crystal silicon (Si) nanosheets on the basis of first-principles calculations of model structures. The carrier conductivities of the hydrogen-terminated Si nanosheet models with (001) surface orientation have been calculated using band carrier densities and their corresponding effective mass tensors derived from the two-dimensional (2D) band diagram by our original approach for a small amount of carrier occupation. The [110] uniaxial tensile stress causes band deformation, leading to the redistribution of carriers, and a drastic change of conductivity can be observed for nanosheet models. The p-type longitudinal and transverse piezoresistance coefficients about the [110] tensile stress swell up as the nanosheet becomes thinner, and we have obtained high piezoresistance coefficients of 343 × 10−11 Pa−1 of πl[110] and − 141 × 10−11 Pa−1 of πt [110] for about 1 nm thickness. It is expected that p-type ultra-thin Si(001) nanosheet will be a suitable candidate for nanoscale piezoresistors due to its giant piezoresistivity. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

This technical note is a review of the contract research at Ritsumeikan University for the “Highly Integrated, Complex MEMS Production Technology Development” Project (“Fine MEMS” Project) sponsored by New Energy and Industrial Technology Development Organization (NEDO). Our research focuses on characterization of physical properties of nanoscale microelectronic materials and carbon nanotube (CNT) to elucidate new effects for potential applications in advanced micro/nano electromechanical devices, and consists of two main parts. The first part deals with experimental evaluation of mechanical, thermal, and electrical properties of tungsten silicide (WSi) and CNT thin films. We have clarified that the WSi film will be promising as a structural material for high-performance capacitive micro accelerometer. In the second part, piezoresistive effect of single crystal silicon nanostructures has been theoretically and experimentally investigated. The p-type ultra-thin silicon nanowire (SiNW), in particular oriented SiNW, will be a good piezoresistor with a giant longitudinal piezoresistance coefficient. We have carried out the research in cooperation with Hitachi, Ltd. and National Institute of Advanced Industrial Science and Technology (AIST), and these cooperative relationships have greatly contributed to the advancement of the research and development. Achievements in the contract research are very promising and significant for mechanical sensing applications.

We have developed a method for constructing energy-saving sensor networks that are robust against external attacks to the sensor nodes. In our sensor network model, hierarchical sensor systems belonging to different classes that are ranked according to the hardware specifications for wireless communication and electric power source are used to form sensor networks with heterogeneous topological structure. Random attacks to the network cause the deficiencies mainly of terminal sensor nodes of the lowest class, which allows saving energy for establishing communication routes in the network.

MEMS structures and machines fabricated by photolithography and/or etching have often repeated unit microstructure. We need to design not only the global parameters but also microscopic and local parameters. In pursuit of this, a dynamic analysis of global/local problem is essential, and especially fast computational method and convenient modeling technique are both required for the MEMS design. Hence, this paper presents the application of model order reduction (MOR) for fast dynamic analysis combined with the finite element mesh superposition (FEMS) technique for practical and convenient modeling of the above-mentioned microstructures. Through two examples, the accuracy is carefully investigated for both global and local responses associated with the base vectors in MOR algorithm. The first example is analyzed by a kind of homogenization technique and MOR. The number of DOFs was finally reduced by a factor of approximately 1/6 (47,362/296,268). In addition, MOR enabled us to reduce the coefficient matrix size to only 300. The second example is analyzed by both FEMS and MOR, and it was found that MOR is also applicable to an unusual matrices generated by FEMS.

In this study, we have simulated the piezoresistance effect in bulk silicon and silicon nanowires (SiNWs) based on the first-principle calculations of model structures. The band structure changes according to stress was observed o the SiNWs model. The piezoresistance coefficients with respect to cross-sectional area of 50 nm SiNW together with SEM image of the model were presented.

A micro-electro-mechanical-system internal combustion engine (MEMS IC engine) is fabricated to demonstrate the energy conversion from heat to mechanical power. The dimensions and surface-to-volume ratio of combustion chamber are 5 mm × 3 mm × 1 mm (0.015 cc) and 3.07 mm −1 , respectively. The reciprocation motion of a piston can be sustained by the force balance between combustion pressure and the repulsion force of an elastic spring. A premixture gas composed of hydrogen and oxygen is used for fuel under stoichiometric combustion (equivalent ratio is 1). The combustion is confirmed by pressure measurement and the direct observation of flame propagation. A high-speed CMOS camera is adopted for the flame observation. A maximum combustion pressure of 142.6 kPa, a displacement of 9.5 mm 3 , and a mechanical power of 29.1 mW were obtained for the MEMS IC engine. This experimental evidence provides a positive outlook for the materialization of the MEMS heat engine concept.

This paper presents a miniaturized three-axis piezoresistive accelerometer using bulk micromachining technology. The accelerometer consists of a highly symmetric single-crystalline silicon crossbeam structure with 12 conventional two-terminal p-type piezoresistors diffused on the surface of the beams. The die size of the acceleration chip is 3 mm × 3 mm. In addition, it is significantly smaller than those of previously presented approaches. It measures three components of acceleration up to ± 10 g on three orthogonal axes simultaneously. The average measured sensitivities of the fabricated sensor for accelerations Ax, Ay, Az on the X, Y, Z axes are about 1.14, 1.15, 0.98 mV (V g)−1 respectively. The measurement results show a cross-axis sensitivity of

A thermoelectric power generation system is developed with a flexible structure. Its micro fabrication has the advantage of miniaturization and integration. Thermoelectric materials are fabricated by using micro fabrication technology. The developed structure is composed of a polyimide sheet as a substrate, thermoelectric materials deposited on the substrate, a heat absorber sheet and a heat sink sheet. The flexibility of this structure depends on the wavy form of the substrate and slits in the substrate, and the heat absorber and heat sink sheets. Because of the characteristic evaluation, open-circuit voltage of 16 µV K−1 per thermocouple was obtained. In addition, the thermopile generator does not break till a bending radius of curvature of 9 mm is reached. A prospect for practical application of the thermoelectric power generator for a curved surface was confirmed.

This paper presents a miniaturized six-degree-of-freedom (6-DOF) piezoresistive accelerometer. The accelerometer is capable of measuring three components of linear acceleration and three components of angular acceleration on three orthogonal axes at the frequency bandwidth of 300 Hz. The obtained experimental results showed good agreement with the finite element simulation. The sensor is ideal for use in biomechanical research applications requiring detection of multiple components of acceleration such as the study of human gesture recognition systems.

This paper describes elevated temperatures tensile strength and inelastic constitutive relationship of electroplated nickel (Ni) thin films used in high-density micro connectors. The compact tensile tester operated in Scanning Probe Microscope (SPM) evaluated mechanical properties of electroplated Ni specimens, with nominal dimensions of 15 μm in thickness, 50 μm in width and 600 μm in length, at elevated temperatures. All specimens have line patterns on their specimen gauge section to measure axial elongation under tensile loading with an SPM cantilever. Strain rates faster than 5 %/sec were employed to obtain the time-independent Young's modulus and yield stress of the Ni specimens. Averaged Young's modulus was closed to that of a bulk of Ni, however ultimate tensile strength showed a larger value. Yield stress and breaking elongation were also quite different from previous reported values of the bulk. Inelastic constitutive equations were proposed as a function of temperature in order to reveal inelastic deformation behavior of the Ni micro connector at elevated temperatures in finite element analyses.

本研究は, UV厚膜レジストによるフォトリソグラフィと電鋳の組み合わせによりマイクロコネクタを作製し, その特性評価を行った。作製したマイクロコネクタは100ピンで, 厚さ50μm, 最小幅15μm, 最大アスペクト比3.3であり, 端子間のピッチは80μmである。特性評価として接触力, 接触抵抗, ヤング率, 許容電流値の測定を行った。ソケット端子の変位量が5μmのときの接触力は3.3mNであった。四探針法により測定した端子間の接触抵抗は50mΩ以下であった。SPM法などにより端子を構成するNi構造体のヤング率を測定したところ180GPaであった。また, 環境試験を実施した結果, 設計したマイクロコネクタはAuめっきを施すことで安定した電気的接触が得られる見通しを得た。

Piezoresistance in n-type 6H SiC was analyzed on the basis of electron transfer and mobility shift mechanisms for hexagonal many-valley semiconductors. Three important gauge factors or coefficients for piezoresistive sensor application, i.e., the longitudinal, transverse and shear, were calculated by using band parameters. The calculation was compared with experimental results taken from the literature. It was shown that incorporation of the electron transfer and the mobility shift mechanisms gives reasonable interpretation for the piezoresistance in n-type 6H SiC within the temperature range from 300 K to 773 K, and impurity concentration n = 2 × 1019 to 3.3 × 1019 cm−3. These conditions correspond to typical operation ranges of state-of-the-art MEMS-based piezoresistive sensors.

Air-bridge structure of p-type single crystal silicon nano-wire (NW) was fabricated by using 50 nm thick device layer and sacrificial layer etching of 130 nm thick buried oxide (BOX) in separation by implanted oxygen (SIMOX) substrate. The piezoresistance of the nano-wire bridge (NWB) was measured in order to verify its ability for sensing element of the nano-mechanical sensors. Longitudinal piezoresistance coefficient π 1[110] and apparent transverse piezoresistance coefficient π t[110] were found to be 38.7 x 10 -11 and 0 Pa -1 , respectively, at surface concentration of N s = 9 × 10 19 cm -3 . The value of π 1[110] was in close agreement with that of NW without releasing from the substrate, and 54.8% larger than that of p + diffused piezoresistor obtained by Tufte and Stelzer four decades ago (25 × 10 -11 Pa -1 and at N s = 9 × 10 19 cm -3 ). The value of apparent π t[110] was much smaller than that of the NW without releasing from the substrate. An advantage ofthe vanished apparent π t[110] for design of the piezoresistive mechanical sensors will be discussed. Obtained results are useful for design consideration of nano-metric piezoresistive elements used in the nano-mechanical sensors.

A reciprocating engine was designed for a micro power generator. It is expected to be used for a portable micro power generator with high energy density. The proposed reciprocating engine has the spring system, which is composed of opposite-pistons supported by an elastic spring. Combination of resonance of the spring system by the combustion pressure and an induction coil generates electricity due to generated voltage. Working cycle analysis, structural analysis, vibration analysis, and generated voltage calculations were carried out. Adopting H2 gas as a fuel and Si as a structural material, the theoretical output was found to be 41 mW under the conditions that compression ratio is 5, the maximum combustion temperature is 850 K and resonance frequency of the spring system is 582 Hz.

A p-type single crystal silicon nanowire bridge and a four-terminal nanowire element were fabricated by electron-beam direct writing. The piezoresistance was investigated in order to demonstrate the usefulness of these sensing elements as mechanical sensors. The longitudinal piezoresistance coefficient πl[110] was found to be 38.7×10−11 Pa−1 at a surface impurity concentration of Ns=9×1019 cm−3 for the nanowire bridge. The shear piezoresistance coefficient π44 was found to be 77.4×10−11 Pa−1 at Ns=9×1019 cm−3 for the four-terminal nanowire element. These values are 54.8% larger than the values obtained from p+ diffused piezoresistors, which are used in conventional mechanical sensors.

Typical p-type silicon mechanical sensors are designed to operate under temperature range from /spl sim/173 K to /spl sim/373 K and subjected to stress less than /spl sim/100 MPa. The operation range is mainly restricted by the electrical and mechanical properties of silicon. The authors derived an approximate piezoresistance equation valid for typical operation range of the p-type silicon mechanical sensors, from valence band model of Bir and Pikus taking into account the spin-orbit interaction. The piezoresistance in p-type silicon was analyzed based on hole transfer and conduction mass shift due to stress. These mechanisms were introduced by Suzuki et al. [1984] to interpret piezoresistance in p-type silicon, based on the valence band equation in the vicinity of k=0. Under the typical operation range for p-type silicon mechanical sensors, holes are located where the value of k is relatively large, i.e., off k=0 and degenerate band split due to stress is incomplete. The hole behavior in the valence band was compatible with the typical operation range for p-type silicon mechanical sensors.

This paper presents the design concept, theoretical investigation, and fabrication of a six-degree of freedom (6-DOF) turbulent flow micro sensor utilizing the piezoresistive effect in silicon. Unlike other flow sensors, which typically measure just one component of wall shear stress, the proposed sensor can independently detect six components of force and moment on a test particle in a turbulent flow. By combining conventional and four-terminal piezoresistors in Si (111), and arranging them suitably on the sensing area, the total number of piezoresistors used in this sensing chip is only eighteen, much fewer than the forty eight piezoresistors of the prior art piezoresistive 6-DOF force sensor.

A fork-type micro connector with high aspect ratio and high packaging density was fabricated using UV thick photoresist and Ni electroforming. A negative photoresist (THB-130N) was used as a mold of Ni electroforming. The tips of socket terminal of the micro connector were formed as movable portions using Cu sacrificial layer etching. In order to make firm contact of the micro connector, two-step guidance was adopted. The size of the terminal of fabricated micro connector was 50 mm- thickness and 15 mm-width (minimum). The maximum aspect ratio of the fabricated micro connector is 3.3 and the terminal pitch is 80 mm. Figure 1 shows SEM photograph of the socket terminal which was formed by the Ni electroforming. A contact resistance of a 50 mW,a contact force of 2.08mN,Young痴 modulus of 80 GPa and a permissible current of 400 mA (single pair of the plug and socket terminals) were obtained practicl use for the micro connector.

This paper describes the first study on a polycrystalline Si (poly-Si) nano wire from the viewpoint of MEMS mechanical sensor application. In order to confirm an ability of the poly-Si nano wire piezoresistor as a sensing element of a mechanical sensor, current-voltage (I-V) characteristics and the piezoresistive effect were investigated. The poly-Si nano wire piezoresistor, whose thickness is 32nm and width is 53nm, was fabricated by the combination of the electron beam (EB) direct writing and RIE. A remarkable phenomenon was observed. The longitudinal piezoresistive coefficient πl of the nano wire piezoresistor increased with a decrease in the cross section area, while the transverse piezoresistive coefficient πl was approximately zero and invariant despite variation of the cross section area. The maximum value of the longitudinal piezoresistive coefficient πl of the nano wire piezoresistor was 22×10-5(1/MPa) at impurity concentration N=5×1019 (cm-3).

A high sensitive miniature piezoresistive force sensor utilizing combination of three-axis stress components has been developed. This work aims to develop a force sensor which acts as a sensing unit assembled in a new miniature high pressure sensor. By using a force transmission rod, forces are applied to piezoresistors on a Si diaphragm of the sensor. Resistance changes of the piezoresistors depend on combination of stress components generated by the applying forces. FEM stress analysis was carried out, in order to investigate dependence of stress components on dimensions and Young's modulus of the rod, and diaphragm thickness. A sensor structure to obtain large resistance changes of the piezoresistors was found by utilizing valid combination of three-axis stress components according to the analysis. As an experimental result, an output voltage more than 140mV/5V at 150N was obtained.

To investigate the effect of non-metallic inclusions on fatigue properties of quenched and tempered 0.46% carbon steel (HV≅650) in super-long life fatigue range (107≤N≤5.0×108), tension–compression fatigue tests were carried out. The fatigue strength was discussed based on the area parameter model. The results obtained are: 1. Fatigue fracture origins were mostly at a non-metallic inclusion. 2. However, the location of the inclusion at fracture origin were not uniformly distributed over the specimen section due to the non-uniform distribution of residual stress induced by heat treatment. 3. The fatigue limit by the cycle N=5.0×108 can be predicted by the area parameter model, i.e. with three parameters, the Vickers hardness, HV, of the matrix, the square root of the projected area of inclusions, area , and residual stress. 4. The expected value of inclusion size area max of 0.46% carbon steel in a definite number of specimens can be estimated using the statistics of extreme values. The lower bound of the scatter of fatigue strength was predicted with the combination of the area parameter model and the value of area max .

To investigate the effect of non-metallic inclusions on the fatigue properties of quenched and tempered 0.46% carbon steel (HV≅650) in the super-long life fatigue range (N≤5.0×108), tension-compression fatigue tests were carried out. The fatigue strength was discussed based on the √area parameter model.The results obtained are:(1) Fatigue fracture origins were mostly at a non-metallic inclusion.(2) However, the locations of the inclusion at fracture origin were not uniformly distributed over the specimen section due to the nonuniform distribution of residual stress induced by heat treatment.(3) The fatigue limit defined by the cycle N=5.0×108 can be predicted by the √area parameter model, i.e. with three parameters, the Vickers hardness, HV, of the matrix, the square root of the projected area of inclusions, √area, and residual stress.(4) The expected value of inclusion size √areamax of 0.46% carbon steel in a definite number of specimens can be estimated using the statics of extreme values. The lower bound of the scatter of fatigue strength was predicted with the combination of the √area parameter model and the value of √areamax.

This paper examines the material strength of thin film PDMS widely used for biomedical MEMS and μTAS. This study focuses on the material strength of PBA membrane. Stress-strain diagram of PDMS is examined through the tensile test. Breaking strength is also estimated with an aim to relate with the fracture of balloon membrane of PBA. As the result of PDMS tensile test, non-linear stress-strain relation could be observed. We defined stress as T and l'/l as λ(here, l is distance between two diamond-shaped gauge marks, l' is l+Δl). Logarithmic relationship between T and λ plays important role for analysis of mechanical behavior of polymer such as PDMS by the neo-Hookean constitutive equation.

In this paper, the design, microfabrication, and direct measurement of the static pressure distribution for the aerodynamics of a single-crystal-silicon microscale supersonic nozzle are described. The microscale supersonic nozzle has a convergent–divergent section and a throat area of 100μm × 300μm. The microscale supersonic nozzle was fabricated by silicon bulk micromachining technology. The degree of the rarefaction of nozzle flow was determined by the Knudsen number (Kn). The operation envelope that determines whether the continuum or rarefied flow assumption is appropriate can be expressed as a function of Kn and related parameters. The effect of nonadiabatic operation on microscale nozzle flow was investigated on the basis of wall heat transfer. These physical correlations were taken into account for the classical Shapiro's equations to analyze the microscale nozzle flow aerodynamics (Shapiro, 1953, The Dynamics and Thermodynamics of Compressible Fluid Flow, Ronald, New York, Chap. 7,8; Greitzer et al., 2006, Internal Flow, Cambridge University, Cambridge, UK, Chap. 2,10). Furthermore, the solutions of Shapiro's equations were compared with the experimental results by the authors and other research institutions in order to demonstrate the validity of the proposed aerodynamics design concept for microscale continuum flow.