Uncooled multimirror broad-band infrared microbolometers

A new generation of microbolometers were designed, fabricated and tested for the NASA CERES (Clouds and the Earth's Radiant Energy System) instrument to measure the radiation flux at the Earth's surface and the radiant energy now within the atmosphere. These detectors are designed to measure the earth radiances in three spectral channels consisting of a short wave channel of 0.3 to 5 /spl mu/m, a wide-band channel of 0.3 to 100 /spl mu/m and a window channel from 8 to 12 /spl mu/m each housing a 1.5 mm x 1.5 mm microbolometers or alternatively 400 /spl mu/m x 400 mm microbolometers in a 1 /spl times/ 4 array of detectors in each of the three wavelength bands, thus yielding a total of 12 channels. The microbolometers were fabricated by radio frequency (RF) magnetron sputtering at ambient temperature, using polyimide sacrificial layers and standard micromachining techniques. A semiconducting YBaCuO thermometer was employed. A double micromirror structure with multiple resonance cavities was designed to achieve a relatively uniform absorption from 0.3 to 100 /spl mu/m wavelength. Surface micromachining techniques in conjunction with a polyimide sacrificial layer were utilized to create a gap underneath the detector and the Si/sub 3/N/sub 4/ bridge layer. The temperature coefficient of resistance was measured to be -2.8%/K. The voltage responsivities were over 10/sup 3/ V/W, detectivities above 10/sup 8/ cm Hz/sup 1/2//W, noise equivalent power less than 4 /spl times/ 10/sup -10/W/Hz/sup 1/2/ and thermal time constant less than 15 ms.     

Pulsed-laser annealing, a low-thermal-budget technique for eliminating stress gradient in poly-SiGe MEMS structures

In this paper, we demonstrate eliminating the stress gradient in polycrystalline silicon germanium films at temperatures compatible with standard CMOS (Al interconnects) backend processing. First, we study the effect of varying the germanium concentration from 40% to 90%, layer thickness, deposition pressure from 650 to 800 mtorr and deposition temperature from 400 to 450/spl deg/C, on the mechanical properties of SiGe films. Then the effect of excimer laser annealing (248 nm, 38 ns, 780 mJ/cm/sup 2/) on stress gradient is analyzed. It is demonstrated that stress gradient can be eliminated completely by depositing Si/sub x/Ge/sub 1-x/(10%相似文献   

Zirconium tungstate (ZrW/sub 2/O/sub 8/)-based micromachined negative thermal-expansion thin films

Negative expansion materials are relatively rare but promise to be particularly useful in designing thermally sensitive mechanical devices. Although negative thermal expansion (NTE) in bulk materials such as ZrW/sub 2/O/sub 8/ has been extensively studied, this paper reports the first deposition of a NTE material thin film. ZrW/sub x/O/sub y/ films were deposited by electron beam evaporation and reactive cosputtering. The films were processed and patterned for various microstructures. The coefficients of thermal expansion of the deposited thin films were determined by measuring the change in curvature with temperature. It was found that evaporated films but not sputtered films, which were denser than the evaporated films, exhibited NTE. It was also found that NTE behavior occurred across a variety of stoichiometries. Since crystalline ZrW/sub 2/O/sub 8/ and thin film ZrW/sub x/O/sub y/ both have low densities and show negative expansion, it is speculated that similar physical mechanisms, as discussed in the text, are at work. Further, since the deposition conditions of a thin film can often be changed to control density, it is speculated that a wider variety of thin films than bulk crystals might be made to have NTE.     

Single crystal silicon nano-wire piezoresistors for mechanical sensors

A p-type silicon (Si) nano-wire piezoresistor, whose minimum cross-sectional area is 53 nm/spl times/53 nm, was fabricated by combination of thermal diffusion, EB (electron beam) direct writing and RIE (reactive ion etching). The maximum value of longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor was found to be 48/spl times/10/sup -5/ (1/MPa) at surface impurity concentration of 5/spl times/10/sup 19/ (cm/sup -3/) and it has enough sensitivity for mechanical sensor applications. The longitudinal piezoresistance coefficient /spl pi//sub l[011]/ of the Si nano-wire piezoresistor increased up to 60% with a decrease in the cross sectional area, while transverse piezoresistance coefficient /spl pi//sub t[011]/ decreased with a increase in the aspect ratio of the cross section. These phenomena were briefly investigated based on a hole energy consideration and FEM (finite element method) stress analysis.     

A min-max approach to fuzzy clustering, estimation, and identification

This study, for any unknown physical process y=f(x/sub 1/,...,x/sub n/), is concerned with the: 1) fuzzy partition of n-dimensional input space X=X/sub 1//spl times//spl middot//spl middot//spl middot//spl times/X/sub n/ into K different clusters, 2) estimating the process behavior y/spl circ/=f(x/spl circ/) for a given input x/spl circ/=(x/spl circ//sub 1/,/spl middot//spl middot//spl middot/,x/spl circ//sub n/)/spl isin/X, and 3) fuzzy approximation of the process, with uncertain input-output identification data {(x(k)/spl plusmn//spl delta/x/sub k/),(y(k)/spl plusmn/v/sub k/)}/sub k=1,.../, using a Sugeno type fuzzy inference system. A unified min-max approach (that attempts to minimize the worst-case effect of data uncertainties and modeling errors on estimation performance), is suggested to provide robustness against data uncertainties and modeling errors. The proposed method of min-max fuzzy parameters estimation does not make any assumption and does not require a priori knowledge of upper bounds, statistics, and distribution of data uncertainties and modeling errors. To show the feasibility of the approach, simulation studies and a real-world application of physical fitness classification based on the fuzzy interpretation of physiological parameters, have been provided.     

Remarks on the L/sup p/-input converging-state property

Let X /spl sub/ /spl Ropf//sup N/ and consider a system x/spl dot/ = f(x,u), f : X /spl times/ /spl Ropf//sup M/ /spl rarr/ /spl Ropf//sup N/, with the property that the associated autonomous system x/spl dot/ = f (x,0) has an asymptotically stable compactum C with region of attraction A. Assume that x is a solution of the former, defined on [0,/spl infin/), corresponding to an input function u. Assume further that, for each compact K /spl sub/ X, there exists k > 0 such that |f(z,v) - f(z,0)| /spl les/ k|v| for all (z,v) /spl isin/ /spl times/ /spl Ropf//sup M/. A simple proof is given of the following L/sup p/-input converging-state property: if u /spl isin/ L/sup p/ for some p /spl isin/ [1,/spl infin/) and x has an /spl omega/-limit point in A, then x approaches C.     

L/sup p/ approximation of Sigma-Pi neural networks

A feedforward Sigma-Pi neural network with a single hidden layer of m neurons is given by /sup m//spl Sigma//sub j=1/c/sub j/g(n/spl Pi//sub k=1/x/sub k/-/spl theta//sub k//sup j///spl lambda//sub k//sup j/) where c/sub j/, /spl theta//sub k//sup j/, /spl lambda//sub k//spl isin/R. We investigate the approximation of arbitrary functions f: R/sup n//spl rarr/R by a Sigma-Pi neural network in the L/sup p/ norm. An L/sup p/ locally integrable function g(t) can approximate any given function, if and only if g(t) can not be written in the form /spl Sigma//sub j=1//sup n//spl Sigma//sub k=0//sup m//spl alpha//sub jk/(ln|t|)/sup j-1/t/sub k/.     

Fabrication and measured performance of a first-generation microthermoelectric cooler

The measured performance of a column-type microthermoelectric cooler, fabricated using vapor-deposited thermoelectric films and patterned using photolithography processes, is reported. The columns, made of p-type Sb/sub 2/Te/sub 3/ and n-type Bi/sub 2/Te/sub 3/ with an average thickness of 4.5 /spl mu/m, are connected using Cr/Au/Ti/Pt layers at the hot junctions, and Cr/Au layers at the cold junctions. The measured Seebeck coefficient and electrical resistivity of the thermoelectric films, which were deposited with a substrate temperature of 130/spl deg/C, are -74 /spl mu/V/K and 3.6/spl times/10/sup -5/ /spl Omega/-m (n-type, power factor of 0.15 mW/K/sup 2/-m), and 97 /spl mu/V/K and 3.1/spl times/10/sup -5/ /spl Omega/-m (p-type, power factor of 0.30 mW/K/sup 2/-m). The cooling performance of devices with 60 thermoelectric pairs and a column width of 40 /spl mu/m is evaluated under a minimal cooling load (thermobuoyant surface convection and surface radiation). The average cooling achieved is about 1 K. Fabrication challenges include the reduction of the column width, implementation of higher substrate temperatures for optimum thermoelectric properties, and improvements of the top connector patterning and deposition.     

The critical role of environment in fatigue damage accumulation in deep-reactive ion-etched single-crystal silicon structural films

The importance of service environment to the fatigue resistance of n/sup +/-type, 10 /spl mu/m thick, deep-reactive ion-etched (DRIE) silicon structural films used in microelectromechanical systems (MEMS) was characterized by testing of electrostatically actuated resonators (natural frequency, f/sub 0/, /spl sim/40 kHz) in controlled atmospheres. Stress-life (S-N) fatigue tests conducted in 30/spl deg/C, 50% relative humidity (R.H.) air demonstrated the fatigue susceptibility of silicon films. Further characterization of the films in medium vacuum and 25% R.H. air at various stress amplitudes revealed that the rates of fatigue damage accumulation (measured via resonant frequency changes) are strongly sensitive to both stress amplitude and, more importantly, humidity. Scanning electron microscopy of high-cycle fatigue fracture surfaces (cycles to failure, N/sub f/>1/spl times/10/sup 9/) revealed clear failure origins that were not observed in short-life (N/sub f/<1/spl times/10/sup 4/) specimens. Reaction-layer and microcracking mechanisms for fatigue of silicon films are discussed in light of this empirical evidence for the critical role of service environment during damage accumulation under cyclic loading conditions.     

Microfabrication of palladium-silver alloy membranes for hydrogen separation

In this paper, a process for the microfabrication of a wafer-scale palladium-silver alloy membrane (Pd-Ag) is presented. Pd-Ag alloy films containing 23 wt% Ag were prepared by co-sputtering from pure Pd and Ag targets. The films were deposited on the unetched side of a <110>-oriented silicon wafer in which deep grooves were etched in a concentrated KOH solution, leaving silicon membranes with a thickness of ca. 50 /spl mu/m. After alloy deposition, the silicon membranes were removed by etching, leaving Pd-Ag membranes. Anodic bonding of thick glass plates (containing powder blasted flow channels) to both sides of the silicon substrate was used to package the membranes and create a robust module. The hydrogen permeability of the Pd-Ag membranes was determined to be typically 0.5 mol H/sub 2//m/sup 2//spl middot/s with a minimal selectivity of 550 for H/sub 2/ with respect to He. The mechanical strength of the membrane was found to be adequate, pressures of up to 4 bars at room temperature did not break the membrane. The results indicate that the membranes are suitable for application in hydrogen purification or in dehydrogenation reactors. The presented fabrication method allows the development of a module for industrial applications that consists of a stack of a large number of glass/membrane plates.     

Design, fabrication, and measurement of high-sensitivity piezoelectric microelectromechanical systems accelerometers

Microelectromechanical systems (MEMS) accelerometers based on piezoelectric lead zirconate titanate (PZT) thick films with trampoline or annular diaphragm structures were designed, fabricated by bulk micromachining, and tested. The designs provide good sensitivity along one axis, with low transverse sensitivity and good temperature stability. The thick PZT films (1.5-7 /spl mu/m) were deposited from an acetylacetonate modified sol-gel solution, using multiple spin coating, pyrolysis, and crystallization steps. The resulting films show good dielectric and piezoelectric properties, with P/sub r/ values >20 /spl mu/C/cm/sup 2/, /spl epsiv//sub r/>800, tan/spl delta/<3%, and |e/sub 31,f/| values >6.5 C/m/sup 2/. The proof mass fabrication, as well as the accelerometer beam definition step, was accomplished via deep reactive ion etching (DRIE) of the Si substrate. Measured sensitivities range from 0.77 to 7.6 pC/g for resonant frequencies ranging from 35.3 to 3.7 kHz. These accelerometers are being incorporated into packages including application specific integration circuit (ASIC) electronics and an RF telemetry system to facilitate wireless monitoring of industrial equipment.     

H/sub /spl infin// design with first-order controllers

The problem of determining all first order controllers (C(s)=(x/sub 1/s+x/sub 2//s+x/sub 3/)) which stabilize a given single-input-single-output (SISO) linear time-invariant (LTI) plant of arbitrary order has been recently solved. In this note, these results are extended to determine the subset of controllers which also satisfy various robustness and performance specifications which can be formulated as specific H/sub /spl infin// norm constraints. The problem is solved by converting the H/sub /spl infin// problem into the simultaneous stabilization of the closed-loop characteristic polynomial and a family of related complex polynomials. The stability boundary of each of these polynomials can be computed explicitly for fixed x/sub 3/ by solving linear equations. The union of the resulting stability regions yields the set of all x/sub 1/ and x/sub 2/ which simultaneously satisfy the H/sub /spl infin// condition and closed-loop stability for a fixed x/sub 3/. The entire three-dimensional set meeting specifications is obtained by sweeping x/sub 3/ over the stabilizing range.     

Micromachined jets for liquid impingement cooling of VLSI chips

Two-phase microjet impingement cooling is a potential solution for removing heat from high-power VLSI chips. Arrays of microjets promise to achieve more uniform chip temperatures and very high heat transfer coefficients. This paper presents the design and fabrication of single-jets and multijet arrays with circular orifice diameters ranging from 40 to 76 /spl mu/m, as well as integrated heater and temperature sensor test devices. The performance of the microjet heat sinks is studied using the integrated heater device as well as an industry standard 1 cm/sup 2/ thermal test chip. For single-phase, the silicon temperature distribution data are consistent with a model accounting for silicon conduction and fluid advection using convection coefficients in the range from 0.072 to 4.4 W/cm/sup 2/K. For two-phase, the experimental results show a heat removal of up to 90 W on a 1 cm/sup 2/ heated area using a four-jet array with 76 /spl mu/m diameter orifices at a flowrate of 8 ml/min with a temperature rise of 100/spl deg/C. The data indicate convection coefficients are not significantly different from coefficients for pool boiling, which motivates future work on optimizing flowrates and flow regimes. These microjet heat sinks are intended for eventual integration into a closed-loop electroosmotically pumped cooling system.     

Computation of the frequency response of multilinear affine systems

Deals with the problem of computing the frequency response of an uncertain transfer function whose numerator and denominator polynomials are multiples of independent uncertain polynomials of the form P(s, q) = l/sub o/ (q) + l/sub 1/ (q) s + /spl middot//spl middot//spl middot/ + l/sub n/, (q) s/sup n/ whose coefficients depend linearly on q = [q/sub 1/, q/sub 2/, ..., q/sub q/]/sup T/ and the uncertainty box is Q = {q: q/sub i/ /spl epsiv/ [q/sub i/, q/sub i/], i = 1, 2,..., q}. Using the geometric structure of the value set of P(s, q), a powerful edge elimination procedure is proposed for computing the Bode, Nyquist, and Nichols envelopes of these uncertain systems. A numerical example is included to illustrate the benefit of the method presented.     

An electrostatic, on/off microvalve designed for gas fuel delivery for the MIT microengine

The MIT micro-gas turbine engine requires an integrated fuel-metering device in order to implement on-board engine control. Graded fuel control can be achieved with an array of on/off valves. Each valve in the array must withstand an annealing temperature of 1100/spl deg/C during fabrication and open against 1 MPa of supply pressure at 400/spl deg/C operating temperature. This paper presents the design, fabrication and testing of an electrostatic, on/off silicon prototype valve. Tested with nitrogen at room temperature, the valve opened against a differential pressure of 0.9 MPa with 136 V and delivered a mass flow rate of 45 sccm (3.38 g/h). At 0.1y MPa upstream pressure, the helium leak-rate was measured to be 6/spl times/10/sup -3/ sccm. The valve showed no sign of failure after being continuously actuated for more than 10/sup 5/ cycles. The prototype valve will serve as the base-line design for the engine fuel valve array.     

MEMS-based solid propellant microthruster design, simulation, fabrication, and testing

A new design concept of solid propellant microthruster is proposed for micropropulsion applications. Modeling and simulation have been performed before the fabrication of the microthrusters using MEMS technologies. At sea level, the predicted thrust magnitudes range from 0.76 mN to 4.38 mN and the estimated total impulses range from 1.16/spl times/10/sup -4/ N/spl middot/s to 4.37/spl times/10/sup -4/ N/spl middot/s using HTPB/AP/AL as the propellant. In space, the predicted thrust magnitudes range from 9.11 mN to 26.92 mN and the estimated total impulses range from 1.25/spl times/10/sup -3/ N/spl middot/s to 1.70/spl times/10/sup -3/ N/spl middot/s. Single microthruster, microthruster layers and arrays have been successfully fabricated. Preliminary testing for microcombustion is conducted to verify the feasibility of the novel design. Continuous combustion has been achieved after igniting the solid propellant and successful production of thrust has been verified by the microthruster displacement.     

Magnetic induction machines integrated into bulk-micromachined silicon

This paper presents the design, fabrication, and characterization of laminated, magnetic induction machines intended for high-speed, high-temperature, high-power-density, silicon-based microengine power generation systems. Innovative fabrication techniques were used to embed electroplated materials (Cu, Ni/sub 80/Fe/sub 20/, Co/sub 65/Fe/sub 18/Ni/sub 17/) within bulk-micromachined and fusion-bonded silicon to form the machine structures. The induction machines were characterized in motoring mode using tethered rotors, and exhibited a maximum measured torque of 2.5 /spl mu/N/spl middot/m.     

Piezoelectric Al/sub 0.3/Ga/sub 0.7/As longitudinal mode bar resonators

This paper reports the modeling, fabrication, and experimental characterization of piezoelectric longitudinal mode bar resonators based on thin film single crystal Al/sub 0.3/Ga/sub 0.7/ As. Fabricated resonators with lengths ranging from 1000 /spl mu/m to 100 /spl mu/m have been characterized for operation in their first five odd longitudinal modes. Resonance frequencies range from 2.5 to 75 MHz, with quality factors up to 25 390 at 21.8 MHz in vacuum. Power handling capacity as high as -2.6 dBm is demonstrated at 18.8 MHz. Motional resistance and temperature stability of the resonators are also evaluated.     

The wonham filter with random parameters: rate of convergence and error bounds

Let /spl alpha/(t) be a finite-state continuous-time Markov chain with generator Q=(q/sup ij/)/spl isin/R/sup m/spl times/m/ and state space M={z/sup i/,...,z/sup m/}, where z/sup 1/ for i/sub /spl middot//spl middot//spl middot//spl middot//m are distinct real numbers. When the state-space and the generator are known a priori, the best estimator of /spl alpha/(t) (in terms of mean square error) under noisy observation is the classical Wonham filter. This note addresses the estimation issue when values of the state-space or values of the generator are unknown a priori. In each case, we propose a (suboptimal) filter and prove its convergence to the desired Wonham filter under simple conditions. Moreover, we obtain the rate of convergence using both the mean square and the higher moment error bounds.