Jongcheol Park

Micro-fabricated lead zirconate titanate bent cantilever energy harvester with multi-dimensional operation

At present, a cantilever with an inertial mass at its free end is the most widely used form for a vibration-based energy harvester, due to its simple structure and fabrication. However, the one-dimensional operation limits device installation. We first report a multi-dimensional piezoelectric cantilever-type energy harvester that oscillates not only in the vertical direction but also in the radial direction. While the conventional cantilever-type energy harvester maintains almost its maximum output power when it is installed within 20° of the operating direction, the proposed device presents the significantly improved result that the output power is independent of the installation angle.

High performance piezoelectric MEMS energy harvester based on D33 mode of PZT thin film on buffer-layer with PBTIO3 inter-layer

In this paper, a MEMS energy harvester was investigated to scavenge power from ambient vibration source. It was designed to convert low level vibration to electrical power via the piezoelectric effect. The proposed energy harvester was fabricated by patterning Pt electrodes into inter-digital geometry on top of the sol-gel-spin coated Pb(Zr,Ti)O<inf>3</inf> thin film for d33 mode on silicon cantilever with proof mass. In order to obtain well grown PZT thin film, PbTiO3 seed-layer was newly applied as an inter-layer between PZT and ZrO<inf>2</inf> layer. The fabricated energy harvester generated 1.1uW of electrical power to 2.2MΩ of load with 4.4V<inf>peak-to-peak</inf> from a vibration of 0.39g acceleration at it resonant frequency of 528Hz. The corresponding power density was 2.8mW·cm^−3·g⁻¹.

A power amplifier module with fully embedded passive components in a LTCC substrate for K-PCS band mobile phone

Use Accurate circuit models for embedded RF passive components in LTCC(Low Temperature Co-fired Ceramics) provide a way to efficiently design high performance RFmodules. In this study, in order to increase the accuracy of circuit models, the library of components was developed and the parasitic components were extracted. And with the circuit model, the PAM(Power Amplifier Module) was developed using LTCC process. The module was fabricated with fully embedded passive components within a compact 6x6x1.2 mm3 size, and it exhibited power performance sufficient forK-PCS bandmobile phone.

Piezoelectrically operated MEMS corner cube retroreflector for optical communications

A bulk-micromachined corner cube retroreflector (CCR) was designed and fabricated for free-space optical communications with ultra-low voltage operation and negligible power consumption. The proposed CCR was comprised of a bulk-micromachined vertical mirror which has two mutually orthogonal reflective surfaces and a horizontal mirror with piezoelectric actuator. The fabricated vertical and horizontal mirrors have sizes of 300 ?m ? 300 ?m and 150 ?m???150 ?m, respectively. The vertical mirror was fabricated using a double silicon-on-insulator wafer and the anisotropic wet etching of a (1?1?0) silicon wafer. The horizontal mirror was comprised of two supporting and one actuating lead zirconate titanate (PZT) cantilevers. The supporting cantilevers were utilized for the accurate angular alignment of the mirror by balancing and isolating the residual stresses occurring in the PZT cantilevers. The bottom-actuated mirror exhibited an angular displacement of 1.37? at an applied voltage of 5 V. The fabricated CCR exhibited a good angular misalignment of less than 0.35? and switching characteristics with an off-to-on-state transition of 163 ?s and on-to-off-state transition of 276 ?s at a rectangular input voltage and switching frequency of 10 V and 1 kHz, respectively. The fabricated CCR also exhibited a cutoff frequency of 2.5 kHz and could be digitally modulated up to about 5 kb s?1.

FR-4 Embedded Wideband Micro-Balun with Coupled LC Resonators

In this paper, a compact wideband balun has been newly designed and fabricated by using magnetically coupled LC resonators. The proposed balun was comprised of two pairs of magnetic coupled LC resonators which share one resonator with each other. The balun was specially designed in order to obtain precise phase difference, identical magnitude, and DC isolation characteristics between two balanced ports with impedance transformation. It was fabricated by embedding high Q spiral inductors and BTO MIM capacitors into a multi-layered FR-4 packaging substrate. The fabricated balun showed excellent phase and magnitude imbalanced characteristics. The measured results were an maximum insertion loss of 1.4 dB, a minimum return loss of 10 dB, a phase imbalance of 5 degree, and magnitude imbalance of 0.7 dB at wide frequency bandwidth of 1 GHz ranged from 1.6 GHz to 2.6 GHz, respectively. The measured results were well agreed with the simulated ones.

A bulk-micromachined corner cube retroreflector with piezoelectric micro-cantilevers

A piezoelectrically actuated corner cube retroreflector (CCR) has been investigated for free space optical communications. The proposed CCR consisted of two mutually orthogonal bulk-micromachined mirror assembled with piezoelectrically actuated horizontal mirror. The vertical mirrors were fabricated by using anisotropic wet-etching of double silicon-on-insulator (SOI) wafer and horizontal mirror was supported by two stress-compensating and one actuating lead zirconate titanate (PZT) micro-cantilevers. The fabricated CCRs exhibited angular displacement of 1.87° at 5 volts and switching times of 276 µ s. It also exhibited a good cut-off frequency of 2.5 kHz which can be digitally modulated up to about 5 kb/s.

A curled PZT cantilever based MEMS harvester

A curled PZT cantilever based MEMS energy harvester using inter-digitally shaped electrodes was newly developed to generate high output voltage at a low resonance frequency from ambient vibrations. The curled piezoelectric cantilever was utilized to scavenge both vertical and longitudinal vibrations. It was comprised of polyimide, electrodes, PZT, and low stress silicon nitride layers and formed by using the intrinsic stress-induced bending deformation of a multi-layered cantilever. The inter-digitally shaped electrodes were employed for the d33 piezoelectric mode operation and high output voltage. The polyimide was utilized as an elastic layer to decrease the resonance frequency of the harvester to below 200 Hz. The fabricated MEMS energy harvester generated the output voltage of 0.5 V and 1.08 V at its resonance frequency of 114.7 Hz under vertically and longitudinally induced small vibrations with acceleration of 2.3 m/s2.

Development and characterization of piezoelectrically actuated corner cube retroreflectors for applications in free-space optical sensor network

In this paper, we report the development of an optical sensor network (OSN) based on piezoelectrically actuated corner cube retroreflectors (PA-CCRs). PA-CCRs were fabricated by microelectromechanical systems processes and assembled by aligning horizontally actuated mirrors and vertical side walls in a holder, which allows mass production. Fabricated PA-CCRs showed a tilting angle by more than 1.5 deg at 5 V bias voltage. A 3 dB cutoff frequency was measured to be in the range of 3.5 kHz. To show the feasilbility, an OSN was established based on fabricated PA-CCRs for on-off keying passive transmission links. The results demonstrated data transmission at a rate up to 5 kb/s.

A Hair-cell Structure based Piezoelectric Energy Harvester Operating under Three Dimensional Arbitrary Vibrations

A hair-cell structure based piezoelectric energy harvester was newly developed to effectively scavenge three-dimensional vibrations. The cantilever of the proposed energy harvester, called a hair-cell structure, is deliberately elongated and curled so that it oscillates with decent displacement under not only vertically induced vibrations, but also under longitudinally and horizontally induced vibrations. The proposed energy harvester is comprised of an elongated and curled piezoelectric cantilever and a proof mass with high aspect ratio at the free end of the cantilever. The fabricated device generated the peak output voltage of 15 mV under vertically induced vibrations with an acceleration of 50 m/s2 at its resonance frequency of 116 Hz. Furthermore, it also generated the peak output voltage of 33 mV and 10 mV under longitudinally and horizontally induced vibrations, respectively.

Silicon bulkmicromachined piezoelectrically actuated corner cube retroflector

In this paper, a bulk-micromachined corner cube retroflector (CCR) with ultra-low voltage operation and negligible power consumption has been newly designed and fabricated for free space optical communication applications. The proposed CCR was comprised of bulk-micromachined vertical mirror which has two mutually orthogonal reflective surfaces and one piezoelectrically actuating horizontal mirror. The fabricated CCR has 300µm × 300µm of reflective surfaces. The vertical mirror with two orthogonal reflective surfaces can be obtained by using double SOI-wafer and anisotropic wet etching of (110) silicon wafer. The horizontal bottom mirror was comprised of two supporting and one actuating PZT cantilevers with meander shaped hinges. The supporting cantilevers and the meander hinges were used for accurate angular alignment of mirror by balancing and isolating the residual stresses occurred in the released PZT cantilevers after fabrication. The bottom actuated mirror exhibited a angular displacement of 1.87° at 5 volts applied with on-off switching in 276µs. The fabricated CCR can be digitally modulated up to 1kb/s.