On the integration of flexible circuit boards with hot embossed thermoplastic structures for actuator purposes

In this work, the integration of flexible printed circuit boards (FPCB) on thermoplastic structures has been studied for the first time. The process was developed with the objective to provide thermal paraffin-based microactuators with local heaters. Essentially, such actuators consist of rigid cavities sealed with flexible membranes deflecting on the melting of enclosed paraffin. Following this concept, 100 μm deep and 2.5 mm wide, circular cavities were fabricated by means of hot embossing of polycarbonate (PC) and joined thermally and by gluing to FPCB or blank polyimide (PI). The bond strength was measured by cavity bursting. The adhesion between PC and PI with thermal bonding was too low to allow any mechanical post processing, whereas gluing facilitated satisfactory joining. Here, the bond strength, measured with cavity bursting was found to depend heavily on the curing conditions. For instance, the use of an intensive UV-exposure could increase the adhesion with a 100% compared to curing with an ordinary UV-lamp. Investigation of channel cross-sections revealed an overall glue thickness of 2–15 μm and that only a minor amount of glue migrated into the channels.Two embossing tools of different resilience were investigated for the embossing of the microstructures. A polydimetylsiloxane (PDMS) mould replicated from SU-8-patterned silicon was compared to a more conventional nickel mould replicated from dry-etched silicon. The embossed samples were inspected in polarised light and it was found that PDMS embossed samples contained no interference fringes. This indicated that ridges, otherwise occurring just outside the cavities, were eliminated in these samples. Electron spectroscopy for chemical analysis (ESCA) revealed a slight difference in silicon contents between surfaces resulting from the two moulds. The nickel embossed surfaces were essentially free from silicon, whereas the PDMS embossed surfaces typically contained a significant concentration of silicon.A couple of actuators with FPCB joined to PDMS embossed PC cavities were fabricated using the developed process. These devices facilitated heating far beyond the melting point of paraffin but failed through paraffin leakage at the bond interface after a small number of activation cycles.     

Performance of nonplanar silicon diaphragms under large deflections

The successful realization of many high-performance microactuators, including many microvalves and micropumps, depends critically on the development of diaphragms which are capable of large displacements and free from fatigue. Thin nonplanar silicon diaphragms are promising candidates for such applications since they can be batch fabricated using techniques and materials that are compatible with the other portions of these devices. This paper reports the detailed simulation, fabrication, and characterization of such diaphragms, which are corrugated-bossed structures that unfold, accordion-like, to produce high boss deflections. Boron-doped diaphragms 1 mm on a side, 3 μm in thickness, and containing five 10-μm-deep corrugations produce boss deflections of more than 30 μm at 760 mmHg, in close agreement with simulations. The maximum deflection measured at diaphragm fracture is 38 μm under a 1050 mmHg differential pressure. The effects on load-deflection performance due to changes in diaphragm internal stress (residual stress), corrugation profile, and diaphragm thickness are also explored     

Electrothermally activated paraffin microactuators

A new family of electrothermally activated microactuators that can provide both large displacements and forces, are simple to fabricate, and are easily integrated with a large variety of microelectronic and microfluidic components are presented. The actuators use the high volumetric expansion of a sealed, surface micromachined patch of paraffin heated near its melting point to deform a sealing diaphragm. Two types of actuators have been fabricated using a simple three mask fabrication process. The first device structure consists of a 9 μm thick circularly patterned paraffin layer ranging in diameter from 400 to 800 μm all covered with a 4-μm-thick metallized p-xylylene sealing diaphragm. All fabricated devices produced a 2.7-μm-peak center deflection, consistent with a simple first order theory. The second actuator structure uses a constrained volume reservoir that magnifies the diaphragm deflection producing consistently 3.2 μm center diaphragm deflection with a 3-μm-thick paraffin actuation layer. Microactuators were constructed on both glass and silicon substrates. The actuators fabricated on glass substrates used between 50-200 mW of electrical power with response times ranging between 30-50 ms. The response time for silicon devices was much faster (3-5 ms) at the expense of a larger electrical power (500-2000 mW)     

A microgripper using piezoelectric actuation for micro-object manipulation

Design, fabrication and tests of a monolithic compliant-flexure-based microgripper were performed. The geometry design and the material stresses were considered through the finite element analysis. The simulation model was used to study in detail profiles of von Mises stresses and deformation. The maximum stress in the microgripper is much smaller than the critical stress values for fatigue. The microgripper prototype was manufactured using micro-wire electrode discharge machining. A displacement amplification of 3.0 and a maximum stroke of 170 μm were achieved. The use of piezoelectric actuation allowed fine positioning. Micromanipulation tests were conducted to confirm potential applications of the microgripper with piezoelectric actuation in handling micro-objects. The simulation and experimental results have proven the good performance of the microgripper.     

Design of MEMS PZT circular diaphragm actuators to generate large deflections

This paper presents a design of lead zirconate titanate (PZT) circular diaphragm actuators to generate large deflections. The actuators utilize a unimorph structure consisting of an active PZT and a passive thermally grown SiO/sub 2/ layer. The diaphragm structures were formed by deep reactive ion etching (DRIE). Two different designs, where the PZT layer in the diaphragm actuators was driven by either interdigitated (IDT) electrodes or parallel plate electrodes, were investigated. Both finite element analysis and experimental results proved that the IDT configuration is favorable to generate deflections larger than the diaphragm thickness. The IDT configuration creates an expansion in the PZT layer in the radial direction and a contraction in the tangential direction under forward bias, which enables large deflections. At applied voltages of 100 V, an actuator 800 /spl mu/m in diameter could generate center deflections of around /spl sim/7.0 /spl mu/m, significantly greater than the diaphragm thickness of 2.8 /spl mu/m. The deflection profiles for the diaphragm actuators became flatter when an inactive region in the annular IDT configuration was introduced. There was also a proportional reduction of the maximum deflection.     

Electroactive polymer based microfluidic pump

A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1 J/cm³ have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80 μm thick and 2.2 mm × 2.2 mm in lateral dimensions, showed an actuation deflection of 80 μm for an applied electric field of 90 MV/m. The microfluidic pump could pump methanol at a flow rate of 25 μl/min at 63 Hz with a backpressure of 350 Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively.     

A Micromachined Refreshable Braille Cell

A new concept for the realization of a refreshable Braille cell is presented. An electrothermally controlled microactuator that exploits the hydraulic pressure due to the volumetric expansion of melted paraffin wax is described. The paraffin wax is contained within a bulk micromachined silicon container. The container is sealed using an elastic diaphragm of silicone rubber. The container is heated using gold microheaters located on an underlying glass substrate. All the layers used to make up the containers are bonded together using an overglaze paste. The complete 3$,times,$2 dot Braille cell has air gaps between containers, to prevent unwanted actuation by means of heat leakage from adjacent containers. The prototype Braille cell measures 7$,times,$8.5$,times,$2 mm$^3$and its raised dots are held in equilibrium by pulsed actuation voltages. To maintain a dot height at 50% of its maximum, a duty factor of more than 0.8 was found, with an average power of 0.30 W ($ PRF = 0.027$Hz). The total actuation time for a dot on an up/down cycle was$sim50$s. The dot height increases with an increasing duty factor with a fixed PRF, and increases with decreasing PRF with a fixed duty factor. A stable maximum dot height was achieved by reducing the cooling time.hfillhbox[1381]     

Development of a novel micromirror based on surface micromaching technology

A novel 3 × 3 micromirror array is designed and successfully fabricated with multi-layer silicon surface micromaching technology. It is composed of bottom electrode, support part and mirror plate, in which a T type beam structure is used to support the mirror plate. It can provide mirror with the vertical movement and the rotation about two horizontal axes, thus enabling phase modulation and amplitude modulation for the incident light. The test results show that the maximum deflection length along the vertical direction of the mirror plate is 2 μm, while the rotation angle about X- and Y-axis are ±2.3° and ±1.45°, respectively.     

Design and fabrication of a new MEMS capacitive microphone using a perforated aluminum diaphragm

In this paper, a novel single-chip MEMS capacitive microphone is presented. The novelties of the method relies on the moveable aluminum (Al) diaphragm positioned over the backplate electrode, where the diaphragm includes a plurality of holes to allow the air in the gap between the electrode and the diaphragm to escape and thus reducing acoustical damping in the microphone. Spin-on-glass (SOG) was used as a sacrificial and isolating layer. Backplate is monocrystalline silicon wafer, that it is more stiff. This work will focus on design, simulation, fabrication and characterization of the microphone. The structure has a diaphragm thickness of 3 μm, a diaphragm size of 0.5 mm × 0.5 mm, and an air gap of 1.0 μm. The results show that the pull-in voltage is 105 V, the initial stress of evaporated aluminum diaphragm is around 1500 MPa and the zero bias capacitance of microphone is 2.12 pF. Comparing with the previous works, this microphone has several advantages: the holes have been made on diaphragm, therefore no need of KOH etching to make back chamber, in this way the chip size of each microphone is reduced. The fabrication process uses minimal number of layers and masks to reduce the fabrication cost.     

Two-terminal ultrahigh frequency carrier type thin-film magnetic sensor using impedance matching lines

This article reports on output and band characteristics of the two-terminal ultrahigh frequency (UHF) carrier type magnetic field sensor, which is based on impedance change due to magnetic field dependent permeability, and a magnetic field is detected as an amplitude modulation of a UHF carrier voltage. Two types of transmission line configurations (type-A and type-B) are proposed to make a two-terminal sensor rather than the four terminals of the conventional sensor operating on this principle, because the two-terminal sensor is more advantageous in terms of designing and fabricating of the sensor element and the transmission lines than the four-terminal sensor. In the type-A, a half-wave impedance matching line is added between the element and the carrier power supplying points. Also, in the type-B, a carrier power is supplied on the quarter-wave matching line located between the element and the load. The type-A sensor exhibits a lower output and a much narrower 3 dB-bandwidth of a few tens of MHz than the four-terminal sensor. In contrast, a higher output than that in the four-terminal sensor and a 3 dB-bandwidth of ～100 MHz are confirmed in the type-B sensor by experiments and calculations.     

Synthesis and performance evaluation of thin film PPy-PVDF multilayer electroactive polymer actuators

Bending-type microactuators less than 1 mm in length and comprising of two polypyrrole (PPy) layers separated by polyvinylidene fluoride (PVDF) membrane have previously been fabricated and was shown to operate both in air and aqueous media. The main limiting factor to increase the bending angle and to further miniaturise these actuators was the thickness of the commercially-available PVDF membrane used (～110 μm). In this study, we have synthesised a porous PVDF thin film with a thickness of 32 μm using a spin coating technique, and electrochemically deposited PPy layers on both sides of this thin film to make ultra thin film polymer actuators. The electromechanical and electrochemical properties are investigated and compared with those of the thicker actuator system using the commercially-available PVDF and under identical conditions. The thin film shows very promising performance compared to its thicker counterpart.     

Displacement amplification of piezoelectric microactuators with a micromachined leverage unit

One of the so-called Aero-MEMS applications is the drag reduction on airfoils by using an array of dedicated microactuators. When applying active wave cancellation principles in thin transitional boundary layers, these actuators need to exhibit relatively large stroke at relatively high operational frequencies. For this purpose, a novel micromachined mechanical amplification unit for increasing the stroke of piezoelectric microactuators up to high frequencies is presented in this paper. The mechanical lever is provided by a silicon membrane, sliced in a cake-like fashion. The fabrication and assembly process as well as results of dynamic simulations and experimental measurements are reported. For frequencies from quasi-static up to 15 kHz and for varying spacer positions, an amplification ratio of 5–13 is obtained when comparing displacements at the piezoelement and at the lever tip. Results from finite element simulations were found to be in good agreement with experiments. Finally, the application of these microactuators on airfoils for manipulating the transition point between laminar and turbulent flow conditions is discussed.     

Fiber optics sensor for sub-nanometric displacement and wide bandwidth systems

In this paper, we report fiber optics sensor with sub-nanometric resolution and wide bandwidth. It relies on an increase of the reception fibers number and on low-noise electronics. Moreover, a reference channel has been implemented using a semi-reflective plate to eliminate the source fluctuations and the fiber sensor was isolated to limit external influence of temperature and pressure. Thus we achieve both a sub-nanometric resolution on a 400 ms integration time and a long-term drift as low as 40 nm h^?1. The setup has been also adapted to high speed applications by increasing the bandwidth up to 38 kHz. It can display a 28 nm peak-to-peak limit of resolution on an aluminized piezoactuator. It has been successfully used to test the resonance frequency of a vibrating plate actuated by two high-frequency prototypes of piezoactuators. These improvements lead to low cost fibers optic sensors interesting for non-contact displacement measurements with high sensitivity.     

Critical pressure for capillary valves in a Lab-on-a-Disk: CFD and flow visualization

Capillary valves are used as pressure barriers to control flow sequencing in microfluidic devices. Influence of valves height on liquid flow pattern and critical pressure are studied through flow visualization and CFD predictions (Gambit® 2.2.30 and FLUENT® 6.2.16). Both hydrophilic and hydrophobic walls are studied. Results show that the surface tension plays a major role in the liquid progress through the microchannel/valve and also in the valve filling process. Critical pressure varies linearly with the valve hydraulic diameter in the range 0.91 < D_h < 3.5 [mm] according to: P = 14.14 · D_h + 47.42 [Pa].     

Packaging effect investigation of WL-CSP with a central opening: A case study on pressure sensors

This study reports the packaging effects of wafer-level chip scale packaging (WL-CSP) with a central opening on piezoresistive pressure sensors. A regular pressure sensor with calculated sensitivity of 3.1 × 10^?2 mVV^?1 kPa^?1 and a sensitive pressure sensor with calculated sensitivity of 32.0 × 10^?2 mVV^?1 kPa^?1 are investigated. A finite element (FE) model validated by experimental measurements is used to explore the sensing characteristics of the pressure sensors. The results show that the output variation of the packaged pressure sensor is dominated by the CTE mismatch not the piezoresistive coefficient change as temperature varies. WL-CSP with small polyimide (PI) thickness and large PI opening produces small packaging induced stress, making it ideal for precision sensing for both regular and sensitive pressure sensors.     

Mechanical design and characterization of a resonant magnetic field microsensor with linear response and high resolution

A resonant magnetic field microsensor based on Microelectromechanical Systems (MEMS) technology including a piezoresistive detection system has been designed, fabricated, and characterized. The mechanical design for the microsensor includes a symmetrical resonant structure integrated into a seesaw rectangular loop (700 μm × 450 μm) of 5 μm thick silicon beams. An analytical model for estimating the first resonant frequency and deflections of the resonant structure by means of Rayleigh and Macaulay's methods is developed. The microsensor exploits the Lorentz force and presents a linear response in the weak magnetic field range (40–2000 μT). It has a resonant frequency of 22.99 kHz, a sensitivity of 1.94 V T^?1, a quality factor of 96.6 at atmospheric pressure, and a resolution close to 43 nT for a frequency difference of 1 Hz. In addition, the microsensor has a compact structure, requires simple signal processing, has low power consumption (16 mW), as well as an uncomplicated fabrication process. This microsensor could be useful in applications such as the automotive sector, the telecommunications industry, in consumer electronic products, and in some medical applications.     

Design of membrane actuator based on ferromagnetic shape memory alloy composite for synthetic jet applications

The active flow control (AFC) technology has been studied and shown that it can help aircraft improve aerodynamic performance and jet noise reduction. AFC can be achieved by a synthetic jet actuator injecting high momentum air into the airflow at the appropriate locations on aircraft wings. To produce strong synthetic jet flow at high frequency, a new membrane actuator based on ferromagnetic shape memory alloy (FSMA) composite and hybrid mechanism was designed and constructed. The hybrid mechanism is the stress-induced martensitic phase transformation caused by large force due to large magnetic field gradient, thus enhancing the displacement, as the stiffness of shape memory alloy reduces due to the martensitic transformation. This sequential event can take place within milliseconds. The high momentum airflow will be produced by the oscillation of the circular FSMA composite diaphragm close to its resonance frequency driven by electromagnets. Due to large force and martensitic transformation on the FSMA composite diaphragm, the membrane actuator that we designed can produce 190 m/s synthetic jets at 220 Hz.     

Optimal design analysis of electrothermally driven microactuators

This paper explores a comparative study between different designs of electrothermal microactuators with emphasis on optimal design and performance key factors. For this purpose, two typical designs for electrothermal microactuators with the same material properties are studied: one with different beam lengths (design A), other one with different beam sections and a flexure part (design B). Analytical model and finite element model (FEM) have been developed and validated by comparison of simulation results with experimental results in literature. Optimal geometrical dimensions to achieve maximum deflection have been obtained using genetic algorithm (GA). As the key factors, temperature distribution, power consumption and deflection of these microactuators have been compared in the range of microactuator functionality. Design B is more sensitive to geometrical dimension variation. Using optimal geometrical dimensions, an increase of almost 40 and 55% has been achieved for design A and B tip deflections, respectively. The modified design A with a gold layer results to an increase of 70% for tip deflection comparing to its optimal design.     

An intelligent strategy for checking the annual inspection status of motorcycles based on license plate recognition

License plate recognition techniques have been successfully applied to the management of stolen cars, management of parking lots and traffic flow control. This study proposes a license plate based strategy for checking the annual inspection status of motorcycles from images taken along the roadside and at designated inspection stations. Both a UMPC (Ultra Mobile Personal Computer) with a web camera and a desktop PC are used as hardware platforms. The license plate locations in images are identified by means of integrated horizontal and vertical projections that are scanned using a search window. Moreover, a character recovery method is exploited to enhance the success rate. Character recognition is achieved using both a back propagation artificial neural network and feature matching. The identified license plate can then be compared with entries in a database to check the inspection status of the motorcycle. Experiments yield a recognition rate of 95.7% and 93.9% based on roadside and inspection station test images, respectively. It takes less than 1 s on a UMPC (Celeron 900 MHz with 256 MB memory) and about 293 ms on a PC (Intel Pentium 4 3.0 GHz with 1 GB memory) to correctly recognize a license plate. Challenges associated with recognizing license plates from roadside and designated inspection stations images are also discussed.     

Investigation of Ni-based thermal bimaterial structure for sensor and actuator application

Thermal bimaterial structures made of Ni and Ni-diamond nanocomposite for sensor and actuator application are proposed, fabricated, and tested. Two deflection types of thermal bimaterial structures, including upward and downward bending types, can be easily fabricated by controlling electroplating sequence of Ni and Ni-diamond nanocomposite. According to thermal performance measurement, the tip deflection of upward and downward types can reach about 82.5 μm and ?22.5 μm for a temperature change of 200 °C, respectively. In the condition, the thermomechanical sensitivity and output force are 412.5 nm/K and 97.0 μN for upward type thermal bimaterial structure; and ?112.5 nm/K and ?26.5 μN for downward type one. Due to the low electroplating process temperature (～50 °C) for both Ni-based layers, diminutive pre-deformation of as-fabricated structure and strong interlaminar bonding strength are verified by SEM and vibrational test. The resonant frequency of the structure remains unchanged after 10⁹ cycles.