Thin-Film PZT Lateral Actuators With Extended Stroke

Many microelectromechanical system applications require large in-plane actuation forces, with stroke lengths ranging from submicrometer to tens of micrometers in distance. Piezoelectric thin films are capable of generating very large actuation forces, but their motion is not easily directed into lateral displacement in microscale devices. A new piezoelectric thin-film actuator that uses a combination of piezoelectric unimorph beams to generate lateral displacement has been developed. The piezoelectric actuators were fabricated using chemical-solution-derived lead zirconate titanate thin films. These actuators have demonstrated forces greater than 7 mN at displacements of nearly 1 $muhbox{m}$, with maximum stroke lengths at 20 V greater than 5 $muhbox{m}$ in a 500- $muhbox{m}$-long by 100-$mu hbox{m}$-wide actuator. Force and displacement capabilities can be manipulated through simple changes to the actuator design, while actuator nonlinearity can produce dramatic gains in work capacity and stroke length for longer actuators.$hfill$[2007-0298]      

Seal Formation in Silicon Planar Patch-Clamp Microstructures

This paper presents a microfabricated planar patch-clamp electrode design and looks at the impact of several physical characteristics on seal formation. The device consists of a patch aperture, 1.5–2.5 $muhbox{m}$ in diameter and 7–12 $muhbox{m}$ in depth, with a reverse-side deep-etched 80- $muhbox{m}$ well. The patch aperture was coated with either thermal oxide or plasma-enhanced chemical vapor deposited (PECVD) $ hbox{SiO}_{2}$. Some of the thermal oxide devices were converted into protruding nozzle structures, and some were boron-doped. Seal formation was tested with cultured N2a neuroblastoma cells. The PECVD oxide devices produced an average seal resistance of 34 $hbox{M}Omega (n = 24)$ , and the thermal oxide devices produced an average seal resistance of 96 $hbox{M}Omega (n = 59)$. Seal resistance was found to positively correlate with patch aperture depth. Whole-cell recordings were obtained from 14% of cells tested with the thermal oxide devices, including a single recording where a gigaohm seal was obtained.$hfill$ [2007-0159]      

Radioisotope Thin-Film Fueled Microfabricated Reciprocating Electromechanical Power Generator

A radioisotope power generator with a potential lifetime of decades is demonstrated by employing a 100.3-year half-lifetime $^{63}hbox{Ni}$ radioisotope thin-film source to electrostatically actuate and cause reciprocation in a microfabricated piezoelectric unimorph cantilever. The radioisotope direct-charged electrostatic actuation of the piezoelectric unimorph cantilever results in the conversion of radiation energy into mechanical energy stored in the strained unimorph cantilever. The gradual accumulation of the actuation charges leads to the pull-in of the unimorph cantilever into the radioisotope thin-film, and the resulting discharge leads to vibrations in the unimorph cantilever. During the vibrations, the stored mechanical energy is converted into electrical energy by the piezoelectric thin-film. The generator was realized by using both microfabricated lead zirconate titanate oxide–silicon (PZT–Si) and aluminum nitride–silicon (AlN–Si) unimorph cantilevers. The radioisotope direct-charged electrostatic actuation of the AlN–Si unimorph cantilevers by a 2.9-mCi $^{63}hbox{Ni}$ thin-film radiating 0.3 $muhbox{W}$ led to charge–discharge–vibrate cycles that resulted in the generation of 0.25% duty cycle 12.95- $muhbox{W}$ power pulses (across an optimal load impedance of 521 $hbox{k}Omega$) at an overall energy conversion efficiency of 3.97%. These electrical power pulses can potentially be useful for periodically sampling sensor microsystems. $hfill$[2008-0009]      

Fracture Toughness, Fracture Strength, and Stress Corrosion Cracking of Silicon Dioxide Thin Films

The fracture toughness, fracture strength, and stress corrosion cracking behavior of thin-film amorphous silicon dioxide $(hbox{SiO}_{2})$ deposited on silicon wafers via plasma-enhanced chemical vapor deposition have been measured using specimens with length scales comparable to micromachined devices. Clamped–clamped microtensile specimens were fabricated using standard micromachining techniques. These devices exploit residual tensile stresses in the film to create stress intensity factors at precrack tips and stress concentrations at notches, in order to measure fracture toughness and fracture strength, respectively. The fracture toughness of thin-film $hbox{SiO}_{2}$ was $0.77 pm 0.15 hbox{MPa}cdot hbox{m}^{1/2}$, and the fracture strength was $0.81 pm 0.06 hbox{GPa}$. Stress corrosion cracking (slow crack growth) was also measured in the $hbox{SiO}_{2}$ devices with sharp precracks subjected to residual tensile stresses. These data are used to predict lifetimes for a $hbox{SiO}_{2}$-based microdevice. $hfill$[2007-0304]      

Cryogenic Etching of Silicon: An Alternative Method for Fabrication of Vertical Microcantilever Master Molds

This paper examines the use of deep reactive ion etching of silicon with fluorine high-density plasmas at cryogenic temperatures to produce silicon master molds for vertical microcantilever arrays used for controlling substrate stiffness for culturing living cells. The resultant profiles achieved depend on the rate of deposition and etching of an $hbox{SiO}_{x}hbox{F}_{y}$ polymer, which serves as a passivation layer on the sidewalls of the etched structures in relation to areas that have not been passivated with the polymer. We look at how optimal tuning of two parameters, the $ hbox{O}_{2}$ flow rate and the capacitively coupled plasma power, determine the etch profile. All other pertinent parameters are kept constant. We examine the etch profiles produced using electron-beam resist as the main etch mask, with holes having diameters of 750 nm, 1 $muhbox{m}$ , and 2 $muhbox{m}$. $hfill$[2008-0317]      

Tungsten-Based SOI Microhotplates for Smart Gas Sensors

This paper is concerned with the design, fabrication, and characterization of novel high-temperature silicon on insulator (SOI) microhotplates employing tungsten resistive heaters. Tungsten has a high operating temperature and good mechanical strength and is used as an interconnect in high temperature SOI-CMOS processes. These devices have been fabricated using a commercial SOI-CMOS process followed by a deep reactive ion etching (DRIE) back-etch step, offering low cost and circuit integration. In this paper, we report on the design of microhotplates with different diameters (560 and 300 $muhbox{m}$) together with 3-D electrothermal simulation in ANSYS, electrothermal characterization, and analytical analysis. Results show that these devices can operate at high temperatures (600 $^{circ}hbox{C}$ ) well beyond the typical junction temperatures of high temperature SOI ICs (225 $^{circ}hbox{C}$), have ultralow dc power consumption (12 mW at 600 $^{circ}hbox{C}$), fast transient time (as low as 2-ms rise time to 600 $^{circ}hbox{C}$), good thermal stability, and, more importantly, a high reproducibility both within a wafer and from wafer to wafer. We also report initial tests on the long-term stability of the tungsten heaters. We believe that this type of SOI microhotplate could be exploited commercially in fully integrated microcalorimetric or resistive gas sensors. $hfill$[2007-0275]      

Controlled Thermophoresis as an Actuation Mechanism for Noncantilevered MEMS Devices

A microelectromechanical system actuator based on thermophoretic, or Knudson, forces is proposed using analytical calculations. It can potentially execute scanning or spinning motions of a body that is not mechanically attached to the reference substrate. For a silicon device of 100-$muhbox{m}$ diameter, it is calculated that it can be levitated at a distance of about 0.5 $muhbox{m}$ from a substrate and that it can execute scanning motion and use quasi-springs by laterally acting thermal forces. In this way, an engine with spinning motion of a floating body having a diameter of 200 $muhbox{m}$ with up to 5 kHz can be achieved.$hfill$[2008-0013]      

A Low-Voltage Large-Displacement Large-Force Inchworm Actuator

Inchworm microactuators are popular in micropositioning applications for their long ranges. However, until now, they could not be considered for applications such as in vivo biomedical applications because of their high input voltages. This paper reports on the modeling, design, fabrication, and testing of a new family of pull-in-based electrostatic inchworm microactuators which provides a solution to this problem. Actuators with only 7-V operating voltage are achieved with a $pm 18hbox{-}muhbox{m}$ total range and a $pm 30hbox{-}muhbox{N}$ output force. Larger operating voltage (16 V) actuators show even better results in force ($pm 110 mu hbox{N}$) and range $(pm 35 muhbox{m})$. The actuator has an in-plane angular deflection conversion which provides a force-displacement tradeoff and allows us to set step sizes varying from few nanometers to few micrometers with a minor change in design. In this paper, we designed 1- and 4-$muhbox{m}$ step-size devices. The actuator step size may change during the operation because of the slipping of the shuttle and the beam bending; however, our model successfully explains the reasons. One of our actuator prototypes has survived more than 25 million cycles without performance deterioration. The device is fabricated using the silicon-on-insulator-based multiuser MEMS process.$hfill$[2007-0146]      

MEMS Vertical Probe Cards With Ultra Densely Arrayed Metal Probes for Wafer-Level IC Testing

We have developed a MEMS probe-card technology for wafer-level testing ICs with 1-D line-arrayed or 2-D area-arrayed dense pads layouts. With a novel metal MEMS fabrication technique, an area-arrayed tip matrix is realized with an ultradense tip pitch of $90 muhbox{m} times 196 mu hbox{m}$ for testing 2-D pad layout, and a 50-$muhbox{m}$ minimum pitch is also achieved in line-arrayed probe cards for testing line-on-center or line-on-perimeter wafers. By using the anisotropic etching properties of single-crystalline silicon, novel oblique concave cavities are formed as electroplating moulds for the area-arrayed microprobes. With the micromachined cavity moulds, the probes are firstly electroplated in a silicon wafer and further flip-chip packaged onto a low-temperature cofired ceramic board for signal feeding to an automatic testing equipment. The microprobes can be efficiently released using a silicon-loss technique with a lateral underneath etching. The measured material properties of the electroplated nickel and the Sn–Ag solder bump are promising for IC testing applications. Mechanical tests have verified that the microprobes can withstand a 65-mN probing force, while the tip displacement is 25 $muhbox{m}$, and can reliably work for more than 100 000 touchdowns. The electric test shows that the probe array can provide a low contact resistance of below 1 $Omega$, while the current leakage is only 150 pA at 3.3 V for adjacent probes.$hfill$[2008-0273]      

Serially Connected Weight-Balanced Digital Actuators for Wide-Range High-Precision Low-Voltage-Displacement Control

This paper presents the design, fabrication, and characterization of a new serial digital actuator, achieving an improvement in range-to-precision and range-to-voltage performance. We propose a weight-balanced design for the serial actuators with serpentine springs with a serial arrangement of unit digital actuators. We have measured the displacement range, precision, and drive voltage of unit and serial actuation at 1 Hz. The serial digital actuators produce a full-range displacement of $28.44 pm 0.02 muhbox{m}$ , accumulating unit displacements of $2.8 pm 0.5 muhbox{m}$ at an operating voltage of 4.47 $pm$ 0.07 V. In addition, the serial digital actuators that have a displacement precision of 37.94 $pm$ 6.26 nm do not accumulate the displacement errors of the unit actuators, i.e., 36.0 $pm$ 17.7 nm. We experimentally verify that the serial digital actuators achieve a range-to-squared-voltage ratio of 1.423 $muhbox{m/V}^{2}$ and a range-to-precision ratio of 749.6.$hfill$ [2009-0020]      

On the NP-Hardness of Checking Matrix Polytope Stability and Continuous-Time Switching Stability

Motivated by questions in robust control and switched linear dynamical systems, we consider the problem checking whether all convex combinations of $k$ matrices in $R^{n times n}$ are stable. In particular, we are interested whether there exist algorithms which can solve this problem in time polynomial in $n$ and $k$. We show that if $k= lceil n^{d} rceil $ for any fixed real $d>0$, then the problem is NP-hard, meaning that no polynomial-time algorithm in $n$ exists provided that $P ne NP$, a widely believed conjecture in computer science. On the other hand, when $k$ is a constant independent of $n$ , then it is known that the problem may be solved in polynomial time in $n$. Using these results and the method of measurable switching rules, we prove our main statement: verifying the absolute asymptotic stability of a continuous-time switched linear system with more than $n^{d}$ matrices $A_{i} in R^{n times n}$ satisfying $0 succeq A_{i} + A_{i}^{T}$ is NP-hard.      

Evanescent-Wave Spectroscopy Using an SU-8 Waveguide for Rapid Quantitative Detection of Biomolecules

A 30-mm-long multimode waveguide, 40 $muhbox{m}$ wide and 40 $muhbox{m}$ high, is fabricated on a silicon wafer using polymer SU-8 as the core and liquid buffer as the cladding. Antibodies are successfully immobilized on the SU-8 surface designated for binding target antigens dispersed in the buffer solution. Evanescent-wave spectroscopy is performed by exciting the fluorescently labeled antigens, bound to the waveguide surface within its evanescence field, and measuring the emission light intensity. This evanescent-wave biosensor detects specific molecular interaction. The optical output as a function of the antigen concentration can be described by Langmuir equation. Antigen concentration as low as 1.5 $muhbox{g}/hbox{mL}$ is detected; concentrations higher than 100 $muhbox{g}/hbox{mL}$ lead to sensor saturation. $hfill$[2008-0058]      

Analytical Model of Valveless Micropumps

The flow driven by a valveless micropump with a single cylindrical pump chamber and two diffuser/nozzle elements is studied theoretically using a 1-D model. The pump cavity is driven at an angular frequency $omega$ so that its volume oscillates with an amplitude $V_{rm m}$. The presence of diffuser/nozzle elements with pressure-drop coefficients $zeta_{+}$, $zeta_{-}( ≫ zeta_{+})$ and throat cross-sectional area $A_{1}$ creates a rectified mean flow. In the absence of frictional forces the maximum mean volume flux (with zero pressure head) is $Q_{0}$ where $Q_{0}/V_{rm m}omega = (zeta_{-} -break zeta_{+})pi/16(zeta_{-}+zeta_{+})$, while the maximum pressure that can be overcome is $Delta P_{max}$ where $ Delta P_{max}A_{1}^{2}/V_{rm m}^{2} omega^{2} !=! (zeta_{-} -break zeta_{+})/16$. These analytical results agree with numerical calculations for the coupled system of equations and compare well with the experimental results of Stemme and Stemme.$hfill$ [2008-0244]      

$ {cal L}_{2}$ Gain of Periodic Linear Switched Systems: Fast Switching Behavior

We investigate the $ {cal L}_{2}$ gain of periodic linear switched systems under fast switching. For systems that possess a suitable notion of a time-average system, we characterize the relationship between the ${cal L}_{2}$ gain of the switched system and the ${cal L}_{2}$ gain of its induced time-average system when the switching rate is sufficiently fast. We show that the switched system ${cal L}_{2}$ gain is in general different from the average system ${cal L}_{2}$ gain if the input or output coefficient matrix switches. If only the state coefficient matrix switches, the input-output energy gain for a fixed ${cal L}_{2}$ input signal is bounded by the ${cal L}_{2}$ gain of the average system as the switching rate grows large. Additionally, for a fixed ${cal L}_{2}$ input, the maximum pointwise in time difference between the switched and average system outputs approaches zero as the switching rate grows.      

Modeling, Design, Fabrication, and Demonstration of a Digital Micromirror With Interdigitated Cantilevers

We present the modeling, design, fabrication, and measurement results of a novel digital micromirror based on a new actuator called interdigitated cantilevers. In contrast to conventional micromirrors that rotate through the twisting actuation of a hinge, this micromirror has a symmetric bidirectional rotation through a bending actuation of interdigitated cantilevers hidden under a mirror plate. For the static and dynamic characteristics of the proposed micromirror, analytical models were developed first on the basis of the Euler–Bernoulli beam equation, as well as both distributed- and lumped-parameter models. The results of the developed analytical models are in good agreement with those of a finite-element-method (FEM) simulation, having just a 10% deviation. On the basis of these analytical models, we successfully designed, fabricated, and evaluated a micromirror with a mirror size of $16 muhbox{m} times 16 muhbox{m}$. The fabricated micromirror has a mechanical rotation angle of $pm 10^{circ}$, a pull-in voltage of 54 V, a resonant frequency of 350 kHz, and a switching response time of 17 $muhbox{s}$. The measurement results compare favorably with those of analytical models and FEM simulations, with deviations of less than 15% and 10%, respectively. $hfill$[2009-0139]      

A Laterally Movable Gate Field Effect Transistor

A laterally movable gate field effect transistor (LMGFET) device that directly couples lateral mechanical gate motion to drain current of a FET is presented in this paper. Lateral motion of the FET gate results in a change in channel width, keeping the channel length and the gap between the gate and the oxide layer constant. This results in a change in channel current that, in principle, is linearly proportional to mechanical motion. The operating principle of an LMGFET, along with details of the fabrication process for a depletion-type LMGFET device, is described. Fabricated LMGFET shows an average drain current sensitivity to gate motion of $-5.8 muhbox{A}/muhbox{m}$ at $V_{rm DS} = 20 hbox{V}$ and $V_{rm GS} = 0 hbox{V}$ for 60-$muhbox{m}$ gate motion. A model for the fabricated LMGFET is developed based on electrical measurements. The device shows promise both as a sensor and as an actuator in MEMS and other related applications.$hfill$ [2008-0147]      

Fiber-Optic Laser Doppler Vibrometer to Dynamically Measure MEMS Actuator With In-Plane Motion

An on-axis laser Doppler vibrometer (LDV), where the direction of the incident beam is the same as the direction of the movement of the actuator, intrinsically offers an accurate dynamic measurement, although it cannot be currently applied to MEMS actuators with in-plane motion due to its limited access to the sidewall. The only currently available method is an off-axis LDV, which still shows serious measurement errors, depending on the target surface pattern of the device. In this paper, an on-axis fiber-optic LDV (FLDV) with a 45 $^{circ}$-angled optical fiber is proposed as a means of measuring the in-plane motion of a MEMS actuator. The device demonstrated displacements in the range between 6.5 $muhbox{m}$ at 2 Hz and 11.0 $muhbox{m}$ at 280 Hz, corresponding to the minimum and maximum velocities of 81.6 $muhbox{m/s}$ and 19.3 mm/s, respectively. The measurement capability of the proposed FLDV is then confirmed to cover the movement of most MEMS actuators such that it can greatly enhance the flexibility of dynamic measurements in MEMS actuators. $ hfill$[2008-0297]      

On Compensating Long Actuator Delays in Nonlinear Control

We are interested in finite-escape open-loop unstable plants that are globally stabilizable in the absence of actuator delay but require controller redesign in the presence of delay. The simplest such plant is $ {mathdot Z} (t)= Z(t)^{2} + U(t-D)$, where $D$ is actuator delay of arbitrary length. For this system we present a control law that compensates the delay and achieves feedback linearization (of the entire ODE+delay infinite-dimensional cascade). However, even though exponential stability is achieved, the result is not global because the plant can have a finite escape with an initial condition $Z(0)geq 1/D$ before the feedback control “reaches” it at $t=D$ . We prove a stability result whose region of attraction is essentially $Z(0)≪ 1/D$ and for which we derive an asymptotic stability bound in terms of the system norm $Z(t)^{2} + int _{t-D}^{t} U(theta )^{2} dtheta $.      

Large-Deflection Spiral-Shaped Micromirror Actuator

We present a new two-axis spiral-shaped micromirror manipulator developed for free-space optical switching. The actuator is an electrostatic actuator, which is composed of two different parts that are fabricated using conventional surface-micromachining processes and are then assembled. Instead of conventional monolithic self-assembling design approaches, these two parts are fabricated on two different chips and assembled using a spatial–mechanical approach. The design utilizes the increased flexibility of the spiral-shaped electrode and the zipping-effect technique in order to increase the maximum rotation angle. The footprint of the assembled device is $600 muhbox{m} times 600 muhbox{m}$, and the height of the micropyramid is 200 $muhbox{m}$. The switch is simulated using an energy method and a coupled electromechanical model. Its performance is measured statically using a reflection measurement approach. A continuous rotational actuation of 17$^{ circ}$ has been achieved with an actuation voltage of 235 V.$ hfill$[2008-0319]      

Post-CMOS-Compatible Aluminum Nitride Resonant MEMS Accelerometers

This paper describes the development of aluminum nitride (AlN) resonant accelerometers that can be integrated directly over foundry CMOS circuitry. Acceleration is measured by a change in resonant frequency of AlN double-ended tuning-fork (DETF) resonators. The DETF resonators and an attached proof mass are composed of a 1- $muhbox{m}$ -thick piezoelectric AlN layer. Utilizing piezoelectric coupling for the resonator drive and sense, DETFs at 890 kHz have been realized with quality factors $(Q)$ of 5090 and a maximum power handling of 1 $muhbox{W}$. The linear drive of the piezoelectric coupling reduces upconversion of $1/f$ amplifier noise into $1/f^{3}$ phase noise close to the oscillator carrier. This results in lower oscillator phase noise, $-$96 dBc/Hz at 100-Hz offset from the carrier, and improved sensor resolution when the DETF resonators are oscillated by the readout electronics. Attached to a 110-ng proof mass, the accelerometer microsystem has a measured sensitivity of 3.4 Hz/G and a resolution of 0.9 $hbox{mG}/surdhbox{Hz}$ from 10 to 200 Hz, where the accelerometer bandwidth is limited by the measurement setup. Theoretical calculations predict an upper limit on the accelerometer bandwidth of 1.4 kHz.$hfill$ [2008-0190]