Search

Lead zirconate titanate (PZT) has wide applications in microelectromechanical systems (MEMS) due to its large piezoelectric coefficients. However, there exist serious issues during PZT wet etching even with multiple etching steps, such as residues on etching fronts and large undercut. In this paper, a one-step residue-free wet etching process of ceramic PZT is developed with fluoroboric acid. In this work, the design of experiments (DOE) method is employed to minimize undercut and residues without sacrificing etching rate. The acid concentration, temperature, and agitation are the process parameters considered in the DOE. Through DOE analysis of the experimental data, an optimal recipe is identified as the volume ratio of HBF(4):H(2)O=1:10 at 23 °C. This new PZT etching recipe leads to a high etching rate (1.54 μm/min) with no observable residues and a small undercut (0.78:1) as well as a high selectivity over the photoresist (900:1). This etching recipe can be used for making various piezoelectric transducers.

Polarized skylight provides navigation compass for many polarization sensitive birds and insects. In this paper, a method based on polar coordinate transformation (PCTA) is proposed to use all the polarization information of the polarization angle image. First, a polar coordinate system is set up on the image of angle of polarization (AOP), and then the single pixel ring corresponding to each pole diameter is extracted. After that, the corresponding point of the same pixel value is found from the two consecutive single pixel rings, and the relative rotation angle of the solar meridian is calculated according to the trigonometric relationship. Finally, simulation and outdoor experiments are performed. The algorithm is preliminarily tested and the accuracy of the simulation is in −0.004°∼+0.045°. The outdoor static experiment is carried out on a roof of a building on campus. The experiment shows that the outdoor static experimental precision is within 0.63°. In order to be applied to the estimation of the actual carrier rotation angle, the dynamic application research experiment is carried out. The center region is chosen as the true value of AOP. The error is about −0.7°∼+0.5°. It proves that the proposed algorithm is effective and accurate.

Vertical comb drives are critical for electrostatic optical switches and variable optical attenuators (VOAs), but fabricating vertical comb drives requires the formation of two levels of comb fingers and thus suffers from the difficulty of dealing with the comb-finger alignment. This paper presents a vertical comb drive design and its micro-fabrication method that can realize self-aligned two-level comb fingers. The self-aligned vertical comb fingers are enabled by a novel vertically-elevated flat-end (VEFE) bimorph structure. Both the stator and rotor fingers of the vertical comb drive are formed by the same photomask and the same silicon etching step, which automatically ensures accurate alignment of the stator and rotor fingers. The vertical separation between the stator and rotor is created by the VEFE structure. A 1mm-aperture MEMS mirror with the proposed VEFE comb drive has been fabricated using SOI wafers with buried cavities. The mirror rotates 0.94° at 8 Vdc. The resonant frequency is 1.428 kHz. The MEMS mirror has been assembled into a VOA module. Measurements show that the VOA achieved a dynamic range of 55 dB and an insertion loss of less than 0.4 dB and met the telecommunications standards on shock, vibration and long-term stability.

It is well known that the heat transfer at microscale is quite different from that at macroscale, but the dynamic thermal behavior of micro-actuators with movable microstructures still lacks comprehensive investigation. This work presents a thorough study on thermal behaviors of an electrothermally actuated scanning micromirror, which has a 1 mm × 1 mm central mirror plate supported on four sides by four pairs of electrothermal bimorph actuators. The heat transfer from the thermal actuator to the ambience, including the substrate and the environmental air, are investigated experimentally with several different driving powers and various frequencies under natural convection, forced convection, and in vacuum. The results indicate that the heat conduction dominates the heat transfer process of electrothermal bimorph actuators, while the convection has little impact on the overall heat transfer even under strong forced convection. Furthermore, an equivalent circuit model of the electrothermal micromirror is developed and experimentally verified, from which the effective heat transfer coefficient of the electrothermal bimorphs is extracted to be in the range from 1900 to 2282 W/(m 2 K), which is one to two orders of magnitude larger than that at macroscale.

Wavelength-selective switches (WSSs) are the core devices for reconfigurable optical add-drop multiplexers (ROADMs) that are essential in all-optical networks. WSSs based on microelectromechanical (MEMS) mirror arrays exhibit high potential due to their high switching speed and large port counts, but there still exist challenges to achieve large optical scanning angle at low voltage. This paper presents a 1×20 MEMS mirror array (MMA) design that can scan over 10° in both axes at less than 5 V. The MMA is based on an unique electrothermal bimorph actuator design that can perform 2D scanning and its fill factor reaches 96 %. The 1×20 MMA design has been successfully fabricated using a combined bulk- and surface- micromachining process. The size of each mirror plate is 240 μm by 500 μm. The measured maximum optical scan angles in the x-axis and y-axis are 29.3° and 11.8°, respectively, at 3 V. The measured response time is about 3.7 ms. The thermal crosstalks between adjacent electrothermal actuators are about 10 %. Long-term stability tests show that the angular drifts of the individual mirrors are about 0.002°/h.

Resonant rotational scanning micromirrors with electrostatic comb-drive actuators are widely used in generating structured lights for 3D sensing, but their resonant scanning stability is affected considerably by the working temperature, which in turn compromises the sensing accuracy. The resonant scanning instability is mainly exhibited as the temperature drifts of the quality factor (Q) and the resonance frequency. In this paper, we focus on the Q variation due to the temperature dependence of air damping. The temperature dependence of the air damping in a comb-drive micromirror is investigated using both simplified analytical damping models and computational fluidic dynamic (CFD) models. The modeling results show that the temperature dependence of the viscous damping of the comb drive is opposite to that of the drag damping of the mirror plate, providing a means of minimizing the temperature dependence of Q by adjusting the structural parameters of the comb drive and the mirror plate. It has also been found from the modeling that the lengths of the comb-drive fingers and the mirror plate play the most significant role while the cavity height under the mirror plate has little effect if it is more than 10 % of the mirror plate length. Meanwhile, four micromirrors with different comb-finger or mirror-plate lengths are designed and fabricated. The testing results from these four fabricated mirrors have confirmed that the temperature coefficient of the Q value of an angular scanning comb-drive micromirror can be altered and ultimately compensated by changing the mirror-plate and/or comb-finger lengths.

MEMS speakers are attracting more and more interests due to their potential applications in portable and wearable electronics. However, insufficient sound pressure level (SPL) associated with the reduced size is a main challenge for most existing MEMS speakers. This paper presents the design, fabrication and characterization of a high-SPL piezoelectric MEMS speaker based on high-piezoelectric constant ceramic PZT. The ceramic PZT, bonded on an SOI substrate, was thinned down to only 5 μm successfully. The microfabricated piezoelectric MEMS speakers exhibited significantly enhanced SPLs. At a distance of 10 mm, a maximum SPL of 119 dB was achieved in open air by such a single MEMS speaker with a footprint of 6.7 mm × 6.7 mm under a low driving voltage of only 10 Vpp. The SPLs at frequencies as low as 400 Hz still reached over 90 dB. These SPLs are comparable to those of conventional loud speakers or micro-speaker arrays with significantly larger sizes.

Polarization navigation techniques become more and more significant for a wide range of researches and applications. However, most of the polarization navigation sensors can only output the navigation angle information of a carrier based on the angle of polarization (AoP) from the skylight in the daytime; they cannot provide the displacement information in day and night. In this paper, a polarized contrast-enhanced (PCE) optical flow method is proposed to improve the accuracy of displacement estimation and reduce the influence of the ambient brightness. We acquire the degree of linear polarization (DoLP) images during the motion of the carrier in low illumination environment, and the hypothesis of the DoLP continuity is used for the theoretical foundation of this PCE optical flow method under the conditions of parallel light source and small displacements. The displacement calibration on the experimental platform is obtained by using a laser interferometer and spectrometer, and the contrast of the polarimetric image and the calculated polarized optical flow value are used as the validation criteria. Under 0.7198Lx illumination intensity, the cumulative error of the displacement obtained by the PCE method is less than 8 mm and the accuracy of the displacement estimation is almost 2 times higher than that of the traditional Lucas-Kanade(LK) optical flow method. Our experimental results have also shown that under 10°, 10−1, or even 10-2 levels of the standard illumination, the displacement values from the PCE optical flow method are in good agreement with the theoretical values.

An electromagnetically actuated micromirror with precise tilt angle control for application as a bi-stable optical switch is reported. A tilt angle control of ±2.3° is achieved by utilizing the 4 μm buried oxide (BOX) layer thickness of an SOI wafer together with a carefully controlled pulsed low frequency deep silicon backside etch to construct precise mechanical stoppers, while maximizing the torsion beam out-of-plane stiffness for angle fixing. The device is packaged with a KOH etched textured silicon encapsulation, which prevents reflection from the back cavity to promote high contrast, and also increases vibration resistance. By incorporating the magnetization response of the permalloy material, a compact analytical model for the quasi-static/dynamic analysis of the device was constructed, which corresponds well with the measured tilt angle versus applied magnetic field, frequency response, and switching time. A pulsed voltage driving circuit was also applied to increase the electromagnet response speed. Latchability can be easily established by employing an electro-permanent magnet or electrostatic clamping between the stoppers. The mirror reflectivity was measured to be 87.2% (0.6 dB) at a wavelength of 632.8 nm, and the static and dynamic deformation of the mirror was also measured and reported. The device is suitable for optical telecommunication in harsh environments that do not permit any electrical sparks.

Mechanical property data for brain tissue are needed to understand the biomechanics of neurological disorders and response of the brain to different mechanical and surgical forces. Most studies have characterized mechanical behavior of brain tissues over large regions or classified tissue properties for either gray or white matter regions only. In this study, spatially heterogeneous viscoelastic properties of ex vivo rat brain tissue slices were measured in different anatomical regions including the cerebral cortex, caudate/putamen, and hippocampus using an optical coherence tomography (OCT) indentation system. Cell viability was also tested to observe neuronal degeneration and morphological changes in tissue slices and provide a proper timeline for mechanical tests. Shear modulus was estimated by fitting normalized deformation data (D/t(i)), which was defined as the ratio of deformation depth (D) to initial thickness of the tissue slice (t(i)), to a viscoelastic finite element model. The estimated shear modulus decayed nonlinearly over 10 min in each anatomical region, and the range of instantaneous to equilibrium shear modulus was 3.8 to 0.54 kPa in the cerebral cortex, 1.4 to 0.27 kPa in the hippocampus and 1.0 to 0.17 kPa in the caudate/putamen. Although these regions are all gray matter structures, their measured mechanical properties were significantly different. Accurate measurement of inter-regional variations in mechanical properties will contribute to improved understanding organ-level structural parameters and regional differential susceptibility to deformation injury within CNS tissues.

This paper reports a Silicon Optical Bench (SiOB) integrated with two vertically-oriented tip-tilt micromirrors that can perform active beam steering. The curling of W/SiO2 bimorphs is utilized to bend microstructures out of plane. The vertical orientation is realized by using a combination of curling W/SiO2 bimorphs and stoppers. W is employed as one of the bimorph materials to increase the bimorph stiffness, attributed to its much higher Young’s modulus than other materials. At the same time, the stress of the W layer is tuned to maximize the bending angle range of the W/SiO2 bimorphs. The fabrication process of making this new SiOB platform has been developed. Particularly, two electrothermal bimorph-based MEMS mirrors are successfully fabricated and stand upright on an SiOB. The two upright micromirrors are parallel to each other and can perform 2-axis forward-view optical scanning. The mirror plate is made of a 20 μm-thick silicon layer coated with aluminum and its diameter is 0.72 mm. The mirror can rotate ±8° at 4.5 V. This MEMS scanner has potential applications in miniature LiDAR for Micro Air Vehicles (MAVs).

This paper presents the design, fabrication and characterization of a tip–tilt–piston (TTP) piezoelectric micromirror. A unique double S-shaped unimorph piezoelectric (dSUP) actuator design is employed. The dSUP actuator design can generate large vertical displacement. With four such actuators symmetrically located on the four sides of the mirror plate, both tip and tilt as well as piston motion can be realized. Lead zirconate titanate (PZT) is used due to its high piezoelectric coefficient and it is fabricated with a sol–gel method. The Zr/Ti ratio of the PZT material is 53/47. The dSUP actuators consist of Pt/Ti/PZT/Pt/Ti/SiO2 multilayers. The thickness of the PZT layer is 0.7 μm. The 1.1 mm × 1.1 mm mirror plate is backed by a 50 μm-thick single-crystal silicon layer to ensure the flatness. Backside deep silicon etching and front-side isotropic silicon undercut are used to release the device. Experiments show that the resonant frequency of the tip–tilt scan modes is 3.5 kHz. 27 μm vertical displacement was observed under 5 V DC driving of one pair of opposite actuator and the scan angle can achieve 9.65° under sine wave resonant driving at 2 V amplitude on one pair of opposite actuator.

A curved concentric electrothermal actuator has been designed and developed to actuate circular micromirrors with improved area efficiency, while at the same time achieving large scan range at low voltage. This actuator consists of three curved concentric Aluminum/Tungsten bimorphs for fast thermal response and high responsivity, and two rigid frames connected in between for scan range amplification. A tip–tilt–piston micromirror with a circular mirror plate based on this actuator design has been proposed and fabricated. The mirror is capable of scanning ±11° at 0.6 V, and generating a 227 μm piston displacement at only 0.8 V. The measured lateral shift and tilt angle of the mirror plate are less than 7 μm and 0.7°, respectively, through the entire piston displacement. A piston-only micromirror has also been demonstrated, and it has even smaller lateral shift of less than 3 μm and tilt of less than 0.4° through the piston scan range. This mirror generates large vertical displacement of about 200 μm at only 0.9 V.

We report a circular micromirror with a 1 mm aperture that has an optical scan range of 60° at 0.68 V applied voltage and 11 mW power input. The mirror is actuated by a semicircular aluminum (Al)–tungsten (W) electrothermal multimorph that bends and twists upon controlled Joule heating. W acts as an active layer of the multimorph and a resistive heater. The curved actuator design not only maximizes the efficiency of chip area usage, but also achieves high resonant frequency due to torsional stiffness encountered during beam deformation. The first three resonant modes of the micromirror are at 104 Hz, 400 Hz and 416 Hz, respectively. Two-dimensional (2D) optical scanning is demonstrated by using the second resonant mode. The low power consumption may be attributed to the use of a single actuator beam. Mirror-center shift produced by actuator bending and twisting partially compensate each other and this results in 1.6 times lower center-shift compared to previously reported straight multimorph based designs. Device fabrication involves surface and bulk micromachining on an SOI wafer.

This paper presents the design, fabrication and characterization of a piezoelectrically actuated high-fill-factor tip-tilt-piston (TTP) micromirror with small tilt and lateral shift during scanning. The piezoelectric material is a sol–gel lead zirconate titanate (PZT) thin film with a Zr/Ti ratio of 53/47. The small initial tilt and lateral-shift-free (LSF) of the mirror plate is achieved by a folded, three-segment piezoelectric unimorph actuator design. The piezoelectric unimorph actuation beams consist of Pt/Ti/PZT/Pt/Ti/SiO 2 multilayers, which are released via undercutting the substrate silicon. The fabricated piezoelectric micromirror can be actuated about two rotational axes in the mirror plane and for translational vertical scan (piston actuation). The resonant frequencies of the piston and rotation modes are 316 Hz and 582 Hz, respectively. At their respective resonant frequencies, the maximum piston magnitude at resonant driving is 32 μm, and the two-dimensional rotating scan ranges are about 5°, both measured at a 2V pp sinusoidal driving voltage.

Monolithic integration of DC–DC converters with on-chip inductors has emerged as a viable means to reduce size and increase transient performance for portable electronics. MEMS techniques have been used to integrate power inductors on chip, but those MEMS inductors have low power handling capability due to high DC resistance, high core loss or small saturation current. This paper reports a unique silicon-molding technique that is capable of embedding thick electroplated metal layers (both Cu and permalloy) into the silicon substrate, in which through-wafer silicon trenches are used as the electroplating molds. These silicon trenches are coated with SU-8 to enhance electrical isolation and relax the thermal stress. The thickness of the embedded metals is up to that of the silicon substrate which ranges from 200 μm to 500 μm, leading to small DC resistance. Two thick magnetic plates are fabricated on the both sides of the silicon substrate, which are connected by through-wafer magnetic vias to achieve high inductance. A pot-core inductor with a low-frequency inductance of 134 nH, a DC resistance of 9.1 mΩ and over 1 A saturation current has been demonstrated.

The orange (Citrus sinensis) is one of the most important agricultural crops in Florida. Heavy reliance on agricultural chemicals and low fertilizer use efficiencies in citrus production have raised environmental and economic concerns. In this study, a nitrogen sensor was developed to predict nitrogen concentrations in orange leaves. Four design criteria were chosen to maximize the sensing efficiency and reliability. They were: (1) coverage of the spectral N sensing range, (2) no moving parts, (3) single leaf detection, and (4) diffuse reflectance measurement. Based on chlorophyll and protein spectral absorption bands, the sensor's wavelength ranges were chosen to be 620-950nm and 1400-2500nm. A reflectance housing was designed to block environmental noise and to ensure single leaf measurement. A halogen light source, two detector arrays, two linear variable filters, and data acquisition cards with 16-bit analog-to-digital converters were used to collect data. The designed N sensor had a spectral resolution less than 30nm. Test results showed that the nitrogen sensor had good linearity (r>0.99) and stability. With averaged signal-to-noise ratio (SNR) of 299, the system was able to predict N content with a root mean square difference (RMSD) of l.69gkg^-^1 for the validation data set. Using the N sensor, unknown leaf samples could be classified into low, medium and high N levels with 70% accuracy.

This paper reports a novel electrothermal actuator design that can generate large vertical displacements with almost no lateral shift. The lateral-shift-free (LSF) piston motion is achieved by using a unique three-bimorph actuation mechanism. Both micromirrors and microlens holders based on this new actuator design have been fabricated using a combined surface- and bulk-micromachining process. A 0.62 mm vertical displacement is measured at only 5.3 V for a fabricated 0.8 mm by 0.8 mm micromirror, and both the lateral shift (10 μm) and tilting angle (0.7°) are very small in that full vertical displacement range. The measured resonant frequency of the vertical motion mode is about 0.5 KHz. The thermal response time is about 25 ms.

This paper reports the design, fabrication and operation of a two-dimensional (2D) micromirror that can generate large bi-directional scans at low actuation voltages. This single-crystal silicon (SCS) micromirror device has been fabricated by using a unique DRIE CMOS-MEMS process that can simultaneously provide thin-film and SCS microstructures. A fabricated micromirror has negligible initial tilt angle, and can perform large bi-directional 2D optical scans (over ±30°) at less than 12 V dc. 2D dynamic scanning using this mirror has been demonstrated by obtaining a 14° × 50° angular raster scan pattern. This device can also perform vertical displacements up to 0.5 mm at about 15 V dc.

This paper reports a novel large vertical displacement (LVD) microactuator that can generate large piston motion and bi-directional scanning at low driving voltage. A LVD micromirror device has been fabricated by using a unique deep reactive ion etch (DRIE) post-CMOS micromachining process that simultaneously provides thin-film and single-crystal silicon microstructures. The bimorph actuation structure is composed of aluminum and silicon dioxide with an embedded polysilicon thermal resistor. With a size of only 0.7 mm × 0.32 mm, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at 6 V dc. This device can also be used to perform bi-directional rotational scanning through the use of two bimorph actuators. The micromirror rotates over ±15 ◦ at less than 6 V dc, and over ±43 ◦ (i.e., >170 ◦ optical scan angle) at its resonant frequency of 2.6 kHz.

This paper reports a single-crystalline silicon (SCS) micromirror used for laser beam scanning in an endoscopic optical coherence tomography (OCT) system. The micromirror is fabricated by using a deep reactive-ion-etch (DRIE) post-CMOS micromachining process. Thin bimorph actuation structures and movable bulk silicon structures are simultaneously achieved. The micromirror is 1 mm by 1 mm in size, coated with aluminum, and thermally actuated by an integrated polysilicon heater. The radius of curvature of the mirror surface is 50 cm. The mirror has a resonance frequency of 165 Hz and rotates 178 when a 15 mA d.c. current is applied. A discontinuity in the dynamic response curve is observed. By using a white-light profilometer, we found that the discontinuity is caused by localized buckling of the bimorph actuation mesh. Cross-sectional images of 500 � 1000 pixels covering an area of 2.9 mm by 2.8 mm are acquired at 5 frames/s by using an OCT system based on this micromirror. # 2003 Elsevier Science B.V. All rights reserved.

A new method for out-of-plane (vertical) electrostatic actuation and capacitive displacement-sensing that utilizes sidewall capacitance change of multiconductor comb fingers is analyzed and experimentally verified. Combining the inherited in-plane (lateral) actuation and sensing capacities of comb fingers, three-dimensional actuation/sensing can be realized. A maskless post-CMOS micromachining process is employed and the fabrication is compatible with standard CMOS processes. Applications include an three-axis microstage, a z -axis accelerometer and a lateral-axis gyroscope that use the proposed vertical comb-finger actuation/sensing method. The measured maximum vertical displacement of the microstage is 3.5 μm with a resonant frequency of 6.17 kHz. Measured sensitivity of the z -axis accelerometer is 0.5 mV/g with less than −40 dB cross-axis sensitivity, noise floor 6 mg/√Hz, and linear range from −27 to 27 g. The lateral-axis gyroscope design uses integrated comb drives for out-of-plane actuation, and is motivated by the desire to integrate three-axis gyroscopes on a single chip. The packaged gyroscope operates at atmospheric pressure with a sensitivity of 0.12 mV/ o /s and the resonant frequency of the drive mode is thermomechanically tuned between 4.2–5.1 kHz. Resonant frequency matching between the drive and sense modes is realized by integrating a polysilicon heater inside the spring beams.