Optical micro-paddle beam deflection measurement for electrostatic mechanical testing of nano-scale thin film application to MEMS

The authors describe their design for a paddle-like cantilever beam sample to relieve non-uniform stress distribution in beam-bending tests of the mechanical properties of thin film applications to MEMS. We added the sample to a custom-designed system equipped with an electrostatic panel and optical interferometer. The system overcomes problems associated with using nano-indentation for testing, and reduces errors tied to the amount of contact force required to bend the beam. Accurate paddle cantilever beam deflection was obtained using a four-step phase-shifting process with a Michelson interferometer. Film strain was determined using a simple force equilibrium equation. Residual stresses were measured at −41.3 MPa for 150 nm silver film, −3.2 MPa for 150 nm gold film, and −16.8 MPa for 150 nm copper film. We observed residual stresses for copper films at different thicknesses. The results indicate high tensile stress forms during the early deposition stage for thin copper film due to grain coalescence, and a decrease in stress with an increase in film thickness. In copper films with thicknesses greater than 153 nm, lattice relaxation associated with the surface mobility of metallic atoms changed residual stress from tension to compression.     

Characterization of a novel segmented micro mirror

The static and dynamic characteristics of a designed novel segmented micromirror are discussed. At first, the equivalent elastic coefficients of supporting structure are deduced based on energy theory for mirrors under different actuating states. Then the static deflection as a function of driving voltage, resonant frequency and transient response are analyzed with respect to the piston movement along Z-axis. The results show that the deflection can reach 2 μm when 115 V voltage is applied, the resonant frequency is 58.805 kHz and the rise time is only 2.86 × 10⁻⁶ s, which hold promise of application. The validity of the theory analysis in this paper is also proved through the comparison with the simulation results obtained with ANSYS.     

Design and development of a novel paddle test structure for the mechanical behavior measurement of thin films application for MEMS

A new technique was developed for studying the mechanical behavior of thin films on substrate applications for micro-electro-mechanical system (MEMS). The test structure was designed on novel “paddle” cantilever beam coated thin film specimens with dimensions of a few hundred to 50 nm. This beam has a triangle shape that provides a uniform plane strain distribution. Standard clean room processing was used to prepare the paddle sample. The experiment can be operated using the electrostatic force to deflect the “paddle” cantilever beam and measure the mechanical response of the sample with surface deposited thin film. A capacitance measurement is used to observe the deflection of the cantilever plate on the other side of the sample with respect to the electrostatic force on the one side. The measured strain was then converted through this capacitance measurement to conduct mechanical behavior studies on the coated thin film. Both system performance experiments and calculations were studied to verify the design concepts. The residual thin film stress measurements were performed and compared with the calculated results from three different forces exerted on the “paddle” cantilever beam, including the force due to the film, compliance force, and electrostatic force.     

Vibration perception and excitatory direction for haptic devices

Vibration feedback is one of the most popular ways to communicate between human and haptic interfaces nowadays. In order to deliver a wider variety of information accurately and efficiently, significant design factors of the vibration need to be investigated and applied to haptic devices. In this study, the excitatory direction was examined as a design factor of the vibration in terms of sensitivity and emotion. We conducted two experiments. In the first experiment, the sensitivities of three excitatory directions—X (lateral), Y (fore-and-aft) and Z (vertical) axes were estimated by the absolute thresholds of the vibration perception with two frequency levels (150 and 280 Hz). Based on ten participants’ estimated absolute thresholds, we conclude that the vibration with X axis is less sensitive than Z axis at the frequency of 150 Hz, while the vibration with Y axis is less sensitive than Z axis at the frequency of 280 Hz. In the second experiment, the agreeability of 29 emotional expressions to the vibrations was measured by a 7-point scale with a total of 12 conditions (2 frequencies × 2 amplitudes (i.e., 50 × 10⁻³ and 500 × 10⁻³ g) × 3 excitatory directions). Based on 20 participants’ responses, it is concluded that at the frequency of 150 Hz and the amplitude of 50 × 10⁻³ g, the vibration is perceived as ‘light’, and as even ‘lighter’ if the vibration is with Y axis rather than with Z axis. Likewise, at the frequency of 150 Hz and the amplitude of 500 × 10⁻³ g, the vibration is perceived as ‘repulsive’, and as even ‘more repulsive’ if the vibration is with Y or Z axis rather than with X axis. Therefore, three excitatory directions can be selectively utilized to design the distinguishable vibration by its sensitivity and emotion.     

Effect of dispersed phase viscosity on maximum droplet generation frequency in microchannel emulsification using asymmetric straight-through channels

Uniformly sized droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a Sauter mean diameter of d _3,2 = 26–35 μm and a distribution span of 0.21–0.25 have been produced at high throughputs using a 24 × 24 mm silicon microchannel plate consisting of 23,348 asymmetric channels fabricated by photolithography and deep reactive ion etching. Each channel consisted of a 10-μm diameter straight-through micro-hole with a length of 70 μm and a 50 × 10 μm micro-slot with a depth of 30 μm at the outlet of each channel. The maximum dispersed phase flux for monodisperse emulsion generation increased with decreasing dispersed phase viscosity and ranged from over 120 L m⁻² h⁻¹ for soybean oil to 2,700 L m⁻² h⁻¹ for n-tetradecane. The droplet generation frequency showed significant channel to channel variations and increased with decreasing viscosity of the dispersed phase. For n-tetradecane, the maximum mean droplet generation frequency was 250 Hz per single active channel, corresponding to the overall throughput in the device of 3.2 million droplets per second. The proportion of active channels at high throughputs approached 100% for soybean oil and MCT oil, and 50% for n-tetradecane. The agreement between the experimental and CFD (Computational Fluid Dynamics) results was excellent for soybean oil and the poorest for n-tetradecane.     

Development of enzyme immobilized monolith micro-reactors integrated with microfluidic electrochemical cell for the evaluation of enzyme kinetics

This paper describes a simple and efficient method for producing an on-chip enzyme immobilized monolith micro-reactor that integrates a microfluidic electrochemical cell for rapid characterization of enzymatic kinetics. The monolith was generated using a sol–gel method, followed by PEI functionalization and enzyme immobilization via electrostatic attraction between electronegative enzymes and electropositive PEI polymers. Using the proposed immobilization strategy, a glucose oxidase (GOD) immobilized monolith micro-reactor has been produced with the controllable porosity that gives better enzyme kinetics compared to previously reported devices. This can be attributed to a favourable enzyme-substrate affinity in which more than 98% of the immobilized enzyme remains in an active conformation. The kinetic studies conducted have identified that a similar value of the k _cat is obtained for immobilized GOD (13.4 s⁻¹) and GOD free in solution (14 s⁻¹) whilst the immobilized Michaelis constant K _m(app) (7.2 mM) is ~4 times lower than GOD in solution (25 mM). In addition, the immobilized GOD exhibits increased stability, retaining at least 95% of the initial activity when stored of 30 days at 4°C, compared to only 60% for GOD in solution. Furthermore, the same enzyme immobilization strategy has been used for choline oxidase immobilization and similar kinetics to choline oxidase in solution were observed, once again indicating better maintenance of the enzyme conformation provided by the proposed method.     

Rapid quantification of bio-particles based on image visualisation in a dielectrophoretic microfluidic chip

We studied an imaging-based technique for the rapid quantification of bio-particles in a dielectrophoretic (DEP) microfluidic chip. Label-free particles could be successively sorted and trapped in a continuous flow manner under the applied alternating current (AC) conditions. Both 2 and 3 μm polystyrene beads at a concentration of 1.0 × 10⁷ particles ml⁻¹ could be rapidly quantified within 5 min in our DEP system. Capturing efficiencies higher than 95% could be 2 μm polystyrene beads with a linear flow speed, applied voltage and frequency of 0.89 mm s⁻¹, 20 V_p-p and 5 MHz. Yeast cells (Candida glabrata and Candida albicans) could also be captured even at a lower concentration of 2.5 × 10⁵ cells ml⁻¹. Images of aggregative particles taken from the designed trapping area were further processed based on the intensity of relative greyscale followed by correction of the particle numbers. The imaging-based quantification method showed higher agreement than that of the conventional counting chamber method and proved the stability and feasibility of our AC DEP system.     

Design and fabrication of a resonant scanning micromirror suspended by V shaped beams with vertical electrostatic comb drives

A scanning micromirror suspended by a pair of V-shaped beams with vertical electrostatic comb drives was designed, modeled, fabricated and characterized. The dynamic analyses were carried out by both theory calculation and FEM simulation to obtain frequency response, stiffness characteristics, oscillation modes and their resonance frequencies. The device was fabricated using the silicon-on-insulator process by only two photolithography masks. Some problems during the process such as the micromirror distortion and the side sticking of the comb fingers were effectively solved by thermal annealing and alcohol-replacement methods, respectively. Based on the fabricated device, the typical scanning patterns for 1-D and 2-D operation were obtained. The experimental results reveal that the micromirror can work in resonant mode with the resonant frequency of 2.38 kHz. The maximum deflection angles can reach ±4.8°, corresponding to a total optical scanning range of 19.2° at a driving voltage of 21 V.     

Integrated micro Pirani gauge based hermetical package monitoring for uncooled VO x bolometer FPAs

This paper presents the design and fabrication of a micro Pirani gauge using VO _x as the sensitive material for monitoring the pressure inside a hermetical package for micro bolometer focal plane arrays (FPAs). The designed Pirani gauge working in heat dissipating mode was intentionally fabricated using standard MEMS processing which is highly compatible with the FPAs fabrication. The functional layer of the micro Pirani gauge is a VO _x thin film designed as a 100 × 200 μm pixel, suspended 2 μm above the substrate. By modeling of rarefied gas heat conduction using the Extended Fourier’s law, finite element analysis is used to investigate the sensitivity of the pressure gauge. Also the thermal interactions between the micro Pirani gauge and bolometer FPAs are verified. From the fabricated prototype, the measured device TCR is about −0.8% K⁻¹ and the sensitivity about 1.84 × 10⁻³ W K⁻¹ mbar⁻¹.     

On the tunability of a MEMS based variable capacitor with a novel structure

In this work a novel MEMS based variable capacitor has been presented. To increase the tunability and decrease the applied voltage, the conventional fixed-fixed beam used in CPW lines has been changed to a fixed-simple supported beam. The proposed structure is a simple cantilever micro-beam in the first step of deflection and is changed to a fixed-simple supported micro-beam in the second step of motion. In the capacitive micro-structures increasing the applied voltage decreases the equivalent stiffness of the structure and leads the system to an unstable condition by undergoing to a saddle node bifurcation. In the proposed structure to avoid pull-in instability and increase the capacitance tuning range, mechanical stiffness of the structure is increased by changing boundary conditions by locating a pedestal in the end of the cantilever beam. The governing nonlinear equation for static deflection of the micro-beam, based on Euler–Bernoulli micro-beam theory has been presented. The results show that the proposed structure increases the capacitance tuning range and decreases the applied voltage. The results also show that the position of the pedestal affects the tunability and the threshold voltage of the structure.     

Shape optimization and dynamic characterization of multiple-electrostatically deformable microbridges

The nonlinear nature of electrostatic fields in micromachined structures, such as, cantilevers, bridges or plates, makes it difficult to achieve desired deflection shapes. An analytical approach to predict the static deflection and dynamic behavior of a microbridge subjected to electrostatic fields of multiple electrostatic actuators is presented in this paper. The boundary support conditions of the micromachined structures are nonhomogeneous in nature and are modeled with artificial translational and rotational springs. The static and dynamic behaviors of the microbridge are investigated by the Rayleigh–Ritz method using boundary characteristic orthogonal polynomials. The deflection of the microbridge and the natural frequencies under certain applied voltages are also presented. Least-squares fitting method is used to optimize the applied voltage of actuators in order to generate the desired static deflection. The proposed method is simple and can be easily extended to complicated configurations which are suitable for adaptive optics applications.     

Fabrication of microfluidic devices for packaging CMOS MEMS impedance sensors

This work presents a polydimethylsiloxane (PDMS) microfluidic device for packaging CMOS MEMS impedance sensors. The wrinkle electrodes are fabricated on PDMS substrates to ensure a connection between the pads of the sensor and the impedance instrument. The PDMS device can tolerate an injection speed of 27.12 ml/h supplied by a pump. The corresponding pressure is 643.35 Pa. The bonding strength of the device is 32.44 g/mm². In order to demonstrate the feasibility of the device, the short circuit test and impedance measurements for air, de-ionized water, phosphate buffered saline (PBS) at four concentrations (1, 2 × 10⁻⁴, 1 × 10⁻⁴, and 6.7 × 10⁻⁵ M) were performed. The experimental results show that the developed device integrated with a sensor can differentiate various samples.     

Dynamic response of a torsional micromirror to electrostatic force and mechanical shock

In this paper dynamic characteristics of a capacitive torsional micromirror under electrostatic forces and mechanical shocks have been investigated. A 2DOF model considering the torsion and bending stiffness of the micromirror structure has been presented. A set of nonlinear equations have been derived and solved by Runge–Kutta method. The Static pull-in voltage has been calculated by frequency analyzing method, and the dynamic pull-in voltage of the micromirror imposed to a step DC voltage has been derived for different damping ratios. It has been shown that by increasing the damping ratio the dynamic pull-in voltage converges to static one. The effects of linear and torsional shock forces on the mechanical behavior of the electrostatically deflected and undeflected micromirror have been studied. The results have shown that the combined effect of a shock load and an electrostatic actuation makes the instability threshold much lower than the threshold predicted, considering the effect of shock force or electrostatic actuation alone. It has been shown that the torsional shock force has negligible influence on dynamic response of the micromirror in comparison with the linear one. The results have been calculated for linear shocks with different durations, amplitudes, and input times.     

Digitally-controlled array of solid-state microcoolers for use in surgery

This paper presents an approach for generating a well-defined cooling pattern over an area of tissue. An array of solid-state microcoolers is used, which could be included in a probe that provides local cooling. This medical instrument can be used for removal of scar tissue in the eye or for the rapid stopping of bleeding due to micro-cuts, which makes it a useful tool to medical doctors and could make surgery more secure to the patient. The array of microcoolers is composed of 64 independent thermo-electric elements, each controlled using an integrated circuit designed in CMOS. The independent control allows the flexible programming of the surface temperature profile. This type of control is very suitable in case abrupt temperature steps should be avoided. Cooling by lateral heat flow was selected in order to minimize the influence of heat by dissipation from the electronic circuits. Moreover, a thermo-electric component with lateral heat allows fabrication of the cooling elements using planar thin-film technology, lithography and wet etching on top of the silicon wafer. This approach is potentially CMOS compatible, which would allow for the fabrication of the thermo-electric elements on top of a pre-fabricated CMOS wafer as a post-process step. Each pixel is composed of thin-films of n-type bismuth telluride, Bi₂Te₃ and p-type antimony telluride, Sb₂Te₃, which are electrically interconnected as thermocouple. These materials have excellent thermoelectric characteristics, such as thermoelectric figures-of-merit, ZT, at room temperatures of 0.84 and 0.5, respectively, which is equivalent to power-factors, PF, of 3.62 × 10⁻³ W K⁻¹ m⁻² and 2.81 × 10⁻³ W K⁻¹ m⁻², respectively. The theoretical study presented here demonstrates a cooling capability of 15°C at room temperature (300 K ≈ 27°C). This cooling performance is sufficient to maintain a local tissue temperature at 25°C, which makes it suitable for the intended application. A first prototype was successfully fabricated to demonstrate the concept.     

Dynamic simulation of a contact-enhanced MEMS inertial switch in Simulink?

A novel contact-enhanced design of MEMS (micro-electro-mechanical system) inertial switch was proposed and modeled in Simulink^?. The contact effect is improved by an easily realized modification on the traditional design, i.e. introducing a movable contact point between the movable electrode (proof mass) and the stationary electrode, therefore forming a dual mass-spring system. The focus of this paper is limited to a vertically driven unidirectional one for the purposes of demonstration, but this design concept and Simulink^? model is universal for various kinds of inertial micro-switches. The dynamic simulation confirmed the contact-enhancing mechanism, showing that the switch-on time can be prolonged for the dynamic shock acceleration and the bouncing effect can be reduced for the quasi-static acceleration. The threshold acceleration of the inertial switch is determined by the proof mass-spring system’s natural frequency. Since the inertial switches were fabricated by the multilayer electroplating technology, the proof mass thickness were assigned two values, 100 and 50 μm, in order to get threshold levels of 56 and 133 g respectively for the dynamic acceleration of half-sine wave with 1 ms duration. Other factors that influence the dynamic response, such as the squeeze film damping and the contact point-spring system’s natural frequency were also discussed. The fabricated devices were characterized by the drop hammer experiment, and the results were in agreement with the simulation predictions. The switch-on time was prolonged to over 50 μs from the traditional design’s 10 μs, and could reach as long as 120 μs. Finally, alternative device configurations of the contact-enhancing mechanism were presented, including a laterally driven bidirectional inertial switch and a multidirectional one.     

A voltage source model on thermoelectric power sensor based on MEMS technology

In order to achieve monolithic integration of thermoelectric power sensor and its amplification system and improve the measurement accuracy of microwave power, a voltage source model is researched in this paper. And the thermoelectric power sensor is designed and fabricated using MEMS technology and GaAs MMIC process. It is measured in the X-band (8–12 GHz) with the input power in 100 mW range. When the input microwave power is at 10, 50 and 100 mW, respectively, the frequency dependent coefficient k₁ is −0.073, −0.39 and −0.82 mV/GHz, respectively. The sensitivity coefficient k₂ is 0.311, 0.303, 0.293, 0.284 and 0.279 mV/mW at 8, 9, 10, 11 and 12 GHz, respectively, and has an excellent linearity. Based on the voltage source model, the feedback coefficient of its amplification system is set to 0.0078 × P_in to compensate the loss power caused by frequency dependent characteristic. In addition to miniaturization and low cost, an advantage using this model is significantly improved measurement accuracy.     

Design of CWDM multiplexers based on series coupled ring resonators: analysis, potential and prospects on MEMS fabrication technologies

New designs for a 1 × 4 and a 1 × 8 CWDM multiplexers based on cascaded groups of series coupled ring resonators (Little et al. in J Lightwave Technol 15:998–1005, 1997; IEEE Photon Technol Lett 10:2263–2265, 2004; Hryniewicz et al. in IEEE Photon Technol Lett 12:320–322, 2000) are presented. Compared to other integrated optical alternatives such as MMI phasars (Paiam and MacDonald in Appl Opt 36: 5097–5108, 1997), cascaded Mach–Zehnder interferometers (Wang and He in J Lightwave Technol 23:1284–1290, 2005) and cascaded AWG (Dragone in IEEE Photon Technol Lett 3:812–815, 1991; Uetsuka in IEEE J Sel Top Quant Electron 10:393–402, 2004), the proposed circuits offer superior performance in their very sharp roll-off factor that exceeds 0.75, their reduced crosstalk level that lies below −60 dB and their negligible insertion loss for the 1 × 4 design. For the 1 × 8 design, the worst case insertion loss is 4 dB. However, the performances obtained exhibit passband ripples in the order of 5 dB, and besides, they are not very tolerant to fabrication errors. Being designed for SOI technology, the proposed circuits are compact as the circuit areas are 130 × 130 and 90 × 150 μm² for the 1 × 4 and 1 × 8 designs, respectively. They also have a high potential for MEMS tunability.     

Simulation of lazer light propagation and thermal processes in red blood cells exposed to infrared laser tweezers (λ = 1064 nm)

Continuous-wave laser micro-beams are generally used as diagnostic tools in laser scanning microscopes or, in the case of near-infrared micro-beams, as optical traps for cell manipulation and force characterization. Because single beam traps are created with objectives of high numerical aperture, typical trapping intensities and photon flux densities are in the order of 10⁶ W/cm² and 10³ cm⁻² s⁻¹, respectively. These extremely high fields may induce two-photon absorption processes and anomalous biological effects. We studied effects occurring in red blood cells (RBCs) radiated by near-infrared laser tweezers λ = 1064 nm). The main idea of our study was to investigate the thermal reaction of RBCs irradiated by laser micro-beam. It is supported by the fact that many experiments have been carried out on RBCs using laser near infrared tweezers. Usually they are relatively long lasting and the thermal aspects of such experiments are not examined. In the present work it has been identified that the laser affects a RBC with a density of absorbed energy at approximately 10⁷ J/cm³, which causes a temperature rise in the cell of about 10–15°C.     

Parameter identification of damping models in multibody dynamic simulation of mechanical systems

To reduce vibration and noise, a damping mechanism is often required in mechanical systems. Many types of dampers are currently used. In this paper, several typical damping models, i.e., structural damping, frictional damping, and viscoelastic damping, are illustrated, and their parameters are identified for multibody dynamic simulation. Linear damping, widely adopted for structural damping, is applied to beam deflection. Quadratic damping including air resistance is applied to plate deflection. To model stick phenomenon in mechanical dampers, a STV (stick-transition velocity) model was first introduced. To identify parameters, an optimization process is applied to the damping parameters. A new MSTV (modified stick-transition velocity) model is proposed for a friction damper. A modified Kelvin–Voight model is suggested for a rubber bushing model used in vehicle dynamics, and its parameters are identified. A modified Bouc–Wen model is also proposed; it includes the hysteretic behavior of an elastomer, and optimized results with parameter identification are compared to test results.     

Electrical properties and crystallization behavior of Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>100−<Emphasis Type="Italic">x</Emphasis></Subscript> thin films

The structural transformation and transformation kinetics of Sb _x Se_100−x films (60 ≤ x ≤ 70) were studied to investigate the feasibility of applying Sb _x Se_100−x alloys in phase-change nonvolatile memories. The temperature-dependent van der Pauw measurements, Hall measurements, X-ray diffraction and a static tester were used to investigate the electrical properties and crystallization behavior of the Sb _x Se_100−x films. The sheet resistance difference between amorphous and crystalline state was higher than 10⁴ Ω per square According to Hall measurement, Sb _x Se_100−x films have p-type conduction and the Hall mobility and carrier concentration increases with the increase in Sb content. The crystalline structure of the metastable phase of Sb _x Se_100−x alloys, which plays a major roll in fast crystallization, is similar to that of Sb₂Te (rhombohedral structure). The transition temperature, sheet resistance and activation energy for transformation decrease as the amount of Sb increases in the Sb _x Se_100−x film. Applying the Kissinger method, the activation energies for crystallization were in the range from 1.90 ± 0.15 to 4.16 ± 0.28 eV. The desired crystallization speed can be obtained by a systematic change of the composition owing to the variation of the activation barrier with stoichiometry.