Bo Woon Soon

Feasibility study of a 3D vibration-driven electromagnetic MEMS energy harvester with multiple vibration modes

A novel electromagnetic energy harvester (EH) with multiple vibration modes has been developed and characterized using three-dimensional (3D) excitation at different frequencies. The device consists of a movable circular-mass patterned with three sets of double-layer aluminum (Al) coils, a circular-ring system incorporating a magnet and a supporting beam. The 3D dynamic behavior and performance analysis of the device shows that the first vibration mode of 1285 Hz is an out-of-plane motion, while the second and third modes of 1470 and 1550 Hz, respectively, are in-plane at angles of 60 ◦ (240 ◦ ) and 150 ◦ (330 ◦ ) to the horizontal (x-) axis. For an excitation acceleration of 1 g, the maximum power density achieved are 0.444, 0.242 and 0.125 μ Wc m −3 at vibration modes of I, II and III, respectively. The experimental results are in good agreement with the simulation and indicate a good potential in the development of a 3D EH device. (Some figures may appear in colour only in the online journal)

Quality Factor Dependence on the Inactive Regions in AlN Contour-Mode Resonators

This paper investigates the dependence of the quality factor (Q) of AlN contour mode resonators (CMRs) on the characteristics of the inactive regions located between the main resonator body (active region) and the stress-free surfaces placed beside the anchors. This paper shows that it is possible to reduce the energy leakage through the anchors by optimally sizing the width of such regions. To validate this concept, we built 16 different configurations of 225-MHz AlN CMRs, differing just by the size of the resonator inactive regions.

Experimental Investigation of a Cavity-Mode Resonator Using a Micromachined Two-Dimensional Silicon Phononic Crystal in a Square Lattice

A 2-D silicon phononic crystal (PnC) slab of a square array of cylindrical air holes in a 10-μm-thick freestanding silicon plate with line defects is characterized as a cavity-mode PnC resonator. A piezoelectric aluminum nitride (AlN) film is employed as the interdigital transducers to transmit and detect acoustic waves, thus making the whole microfabrication process CMOS compatible. Both the band structure of the PnC and the transmission spectrum of the proposed PnC resonator are analyzed and optimized using finite-element method. The measured quality factor (Q factor) of the microfabricated PnC resonator is over 1000 at its resonant frequency of 152.46 MHz. The proposed PnC resonator shows promising acoustic resonance characteristics for radio-frequency communications and sensing applications.

Methods for improving electromechanical coupling coefficient in two dimensional electric field excited AlN Lamb wave resonators

An AlN piezoelectric Lamb-wave resonator, which is excited by two dimensional electric field, is reported in this paper. Rhombus-shape electrodes are arranged on AlN thin film in a checkered formation. When out-of-phase alternating currents are applied to adjacent checkers, two dimensional acoustic Lamb waves are excited in the piezoelectric layer along orthogonal directions, achieving high electromechanical coupling coefficient, which is comparable to film bulk acoustic resonators. The electromechanical coupling coefficient of the 285.3 MHz resonator presented in this paper is 5.33%, which is the highest among AlN based Lamb-wave resonators reported in literature. Moreover, the spurious signal within a wide frequency range is significantly suppressed to be 90% lower than that of the resonance mode. By varying the electrode dimension and inter-electrode distance, resonators having different resonant frequencies can be fabricated on a single wafer, making single-chip broadband filters, duplexers, and multi...

Fabrication and Characterization of a Vacuum Encapsulated Curved Beam Switch for Harsh Environment Application

A vacuum-encapsulated silicon switch with a curved electrode is characterized for operation in harsh environments. An ultraclean vacuum encapsulation process (episeal) seals the switch after release, providing a pristine operating environment for switching operations. In these devices, the curved beam of the actuator enhances the overdrive voltage tolerance to be more than 100 V. The ON/OFF cycle tests were carried out up to 105 cycles at room temperature, and at least 104 cycles under an elevated temperature of 300°C. Throughout the 300°C tests, an average contact resistance of ~ 28 kΩ is measured, demonstrating the stability of the contact. Finally, high speed pulse I-V monitoring unit was used to observe 13-μs switching speed.

Micromechanical Resonators Based on Silicon Two-Dimensional Phononic Crystals of Square Lattice

Phononic crystal (PnC) resonators of Bloch-mode resonance made by replacing periodically arranged two or three rows of air holes with one row of air holes on a two-dimensional (2-D) silicon slab with air holes of square lattice have been investigated. Piezoelectric aluminum nitride (AlN) film is employed as the interdigital transducers to transmit and detect acoustic waves, thus making the whole microfabrication process CMOS compatible. We also fabricate a PnC structure which has a stopband of 140 MHz <; f <; 195 MHz which agrees well with the simulation results. From our experimental results, we found that the two kinds of microfabricated PnC resonators have different optimization conditions in terms of resonant frequency and Q factor, as well as insertion loss, despite their similar design approach. As compared to PnC resonators of hexagonal lattice, the proposed Bloch-mode PnC resonators of square lattice demonstrated higher resonant frequency, higher Q factor, and a smaller device area. The promising acoustic characteristics may be further optimized for applications such as microfluidics, biomedical devices, and radio-frequency communications in the gigahertz range.

A bi-stable nanoelectromechanical non-volatile memory based on van der Waals force

By using complementary-metal-oxide-semiconductor processes, a silicon based bi-stable nanoelectromechanical non-volatile memory is fabricated and characterized. The main feature of this device is an 80 nm wide and 3 μm high silicon nanofin (SiNF) of a high aspect ratio (1:35). The switching mechanism is realized by electrostatic actuation between two lateral electrodes, i.e., terminals. Bi-stable hysteresis behavior is demonstrated when the SiNF maintains its contact to one of the two terminals by leveraging on van der Waals force even after voltage bias is turned off. The compelling results indicate that this design is promising for realization of high density non-volatile memory application due to its nano-scale footprint and zero on-hold power consumption.

Application of statistical element selection to 3D integrated AlN MEMS filters for performance correction and yield enhancement

By 3D integration of an array of 12 nominally identical AlN MEMS sub-filters with a CMOS switching matrix and application of statistical element selection to the same system, we have built a self-healing filter offering 495 unique filter responses and a tuning range of 500 kHz for both center frequency and bandwidth. The demonstrated system enables correction of intrinsic, fabrication-induced variation in filter performance that would otherwise constitute a severe yield limitation to the manufacture of standalone filters.

All metal nanoelectromechanical switch working at 300 °C for rugged electronics applications.

An all metal based electrostatic nanoelectromechanical switch has been fabricated using a one mask process. High temperature cycling behavior is demonstrated in a vacuum chamber at 300 °C for more than 28 hours. The compelling results indicate that the design is promising for the realization of rugged electronics with three-dimensional integration.

Study of hybrid driven micromirrors for 3-D variable optical attenuator applications

Aluminium-coated micromirrors driven by electrothermal and electromagnetic actuations have been demonstrated for 3-D variable optical attenuation applications. Three types of attenuation schemes based on electrothermal, electromagnetic and hybrid, i.e. combination of electrothermal and electromagnetic, actuations have been developed. In addition, two different designs have been fabricated and characterized to investigate the effects of the variations made to both the actuators on the optical attenuation performances of the micromirror. Our unique design of using both ET and EM actuators simultaneously to achieve attenuation is the first demonstration of such hybrid driven CMOS compatible MEMS VOA device.