Hyo-Jin Nam

Bio: Hyo-Jin Nam is an academic researcher from LG Electronics. The author has contributed to research in topics: Cantilever & Piezoelectric sensor. The author has an hindex of 17, co-authored 46 publications receiving 1028 citations.

Design, fabrication and RF performances of two different types of piezoelectrically actuated Ohmic MEMS switches

Abstract: In this paper, we have proposed, fabricated and characterized piezoelectrically actuated RF MEMS (radio-frequency micro-electro-mechanical system) switches. They have been designed to operate at a low operation voltage for advanced mobile/wireless handset applications. The proposed switches are largely composed of piezoelectric cantilever actuators with an Au contact electrode and CPW (coplanar wave) transmission lines suspended over the substrate. Two different types of RF MEMS switches have been suggested to find the better geometry. One has the structure of one single piezoelectric cantilever and a contact electrode attached to its edge with three hinges (type-A), and the other contains four piezoelectric cantilevers that are symmetrically combined through each hinge to support a centered contact electrode (type-B). The two different fabricated (type-A and type-B) RF MEMS switches have insertion losses of −0.22 and −0.23 dB at an operation voltage of 2.5 V and a frequency of 2 GHz, respectively. Although the difference in insertion loss is trivial, there exist different dependences of insertion loss on applied voltage between them. The insertion losses of type-A switches are changed with varying operation voltage because the touching area between the contact electrode and the signal transmission lines is variable. Meanwhile, the type-B switches show nearly constant insertion losses regardless of operation voltage. The type-A and type-B switches have isolation values of −40.8 and −42.5 dB at a frequency of 2 GHz, respectively.

Ultrahigh-density phase-change data storage without the use of heating

Abstract: Non-volatile memories based on scanning probes offer very high data densities, but existing approaches require the probe to be heated, which increases the energy expenditure and complexity of fabrication. Here, we demonstrate the writing, reading and erasure of an ultrahigh-density array of nanoscopic indentations without heating either the scanning probe tip or the substrate. An atomic force microscope tip causes microphase transitions of the polystyrene-block-poly(n-pentyl methacrylate) of a block copolymer to occur at room temperature by application of pressure alone. We demonstrate a data storage density of 1 Tb in(-2), which is limited only by the size of the tip. This demonstration of a pressure-based phase-change memory at room temperature may expedite the development of next-generation ultrahigh-density data storage media.

Contact materials and reliability for high power RF-MEMS switches

Abstract: This paper presents test and characterization of various thin film contact materials for reliable high power RF- MEMS switches. We selected Au, Pt, Ir, and AuPt alloys for contact materials and fundamentally studied on contact phenomena and reliability of similar or dissimilar contacts using a contact measurement apparatus at high current condition. We also investigated the electrical contact behavior of the MEMS switches. From these studies, Au-to-Pt, Pt-to-Pt and Au-to-Ir contact showed reliable characteristics for the high power RF-MEMS switches.

PZT actuated micromirror for fine-tracking mechanism of high-density optical data storage

Abstract: A micromirror actuated by piezoelectric cantilevered unimorphs is proposed as a fine-tracking device for high-density optical data storage. Bending motions of the metal/PZT/metal unimorphs translate an integrated micromirror along the out-of-plane vertical direction. The micromirror alters the optical path of the incident laser beam and linearly steers the reflected laser beam by its out-of-plane parallel actuation. Numerical analysis shows that the actuated micromirror can satisfy the tracking speed imposed by the requirement on the access time for the high-density optical data storage up to few tens Gbit/in.2 owing to the light mass of the micromirror. In this paper, preliminary characteristics of the micromachined PZT actuated micromirror (PAM) are reported. Only a 3600 A-thick PZT film deposited by sol–gel process shows both good electrical and mechanical characteristics for the fine-tracking actuator. The micromirror can be easily actuated up to several micrometers under low voltage operation condition well below 10 V.

Nanoscale investigation of domain retention in preferentially oriented PbZr0.53Ti0.47O3 thin films on Pt and on LaNiO3

Abstract: We report results on domain retention in preferentially oriented PbZr0.53Ti0.47O3 (PZT) thin films on Pt and on LaNiO3 (LNO) electrodes. Domain images are obtained by detecting an electrostatic force exerted on the biased conductive probe. We demonstrate that polarization loss of PZT domains on LNO electrodes occurs less under no external field rather than that of PZT on Pt. The time dependence of the remnant polarization is found to follow a stretched exponential decay.

Modeling MEMS and NEMS

Abstract: INTRODUCTION MEMS and NEMS A Capsule History of MEMS and NEMS Dimensional Analysis and Scaling Exercises A REFRESHER ON CONTINUUM MECHANICS Introduction The Continuum Hypothesis Heat Conduction Elasticity Linear Thermoelasticity Fluid Dynamics Electromagnetism Numerical Methods for Continuum Mechanics SMALL IS DIFFERENT The Backyard Scaling Systems Exercises THERMALLY DRIVEN SYSTEMS Introduction Thermally Driven Devices From PDE to ODE: Lumped Models Joule Heating of a Cylinder Analysis of Thermal Data Storage Exercises MODELING ELASTIC STRUCTURES Introduction Examples of Elastic Structures in MEMS/NEMS The Mass on a Spring Membranes Beams Plates The Capacitive Pressure Sensor Exercises MODELING COUPLED THERMAL-ELASTIC SYSTEMS Introduction Devices and Phenomena in Thermal-Elastic Systems Modeling Thermopneumatic Systems The Thermoelastic Rod Revisited Modeling Thermoelastic V-Beam Actuators Modeling Thermal Bimorph Actuators Modeling Bimetallic Thermal Actuators Exercises MODELING ELECTROSTATIC-ELASTIC SYSTEMS Introduction Devices Using Electrostatic Actuation The Mass-Spring Model Modeling General Electrostatic-Elastic Systems Electrostatic-Elastic Systems - Membrane Theory Electrostatic-Elastic Systems - Beam and Plate Theory Analysis of Capacitive Control Schemes Exercises MODELING MAGNETICALLY ACTUATED SYSTEMS Introduction Magnetically Driven Devices Mass-Spring Models A Simple Membrane Micropump Model A Small-Aspect Ratio Model Exercises MICROFLUIDICS Introduction Microfluidic Devices More Fluidic Scaling Modeling Squeeze Film Damping Exercises BEYOND CONTINUUM THEORY Introduction Limits of Contiuum Mechanics Devices and Systems Beyond Continuum Theory Exercises REFERENCES APPENDICES Mathematical Results Physical Constants INDEX Each chapter also contains Related Reading and Notes sections.

Cantilever-like micromechanical sensors

Abstract: The field of cantilever-based sensing emerged in the mid-1990s and is today a well-known technology for label-free sensing which holds promise as a technique for cheap, portable, sensitive and highly parallel analysis systems. The research in sensor realization as well as sensor applications has increased significantly over the past 10 years. In this review we will present the basic modes of operation in cantilever-like micromechanical sensors and discuss optical and electrical means for signal transduction. The fundamental processes for realizing miniaturized cantilevers are described with focus on silicon- and polymer-based technologies. Examples of recent sensor applications are given covering such diverse fields as drug discovery, food diagnostics, material characterizations and explosives detection.

MEMS Laser Scanners: A Review

Abstract: Laser scanners have been an integral part of MEMS research for more than three decades. During the last decade, miniaturized projection displays and various medical-imaging applications became the main driver for progress in MEMS laser scanners. Portable and truly miniaturized projectors became possible with the availability of red, green, and blue diode lasers during the past few years. Inherent traits of the laser scanning technology, such as the very large color gamut, scalability to higher resolutions within the same footprint, and capability of producing an always-in-focus image render it a very viable competitor in mobile projection. Here, we review the requirements on MEMS laser scanners for the demanding display applications, performance levels of the best scanners in the published literature, and the advantages and disadvantages of electrostatic, electromagnetic, piezoelectric, and mechanically coupled actuation principles. Resonant high-frequency scanners, low-frequency linear scanners, and 2-D scanners are included in this review.

Stepping piezoelectric actuators with large working stroke for nano-positioning systems: A review

Abstract: Precision positioning systems with large working stroke (millimeter or more) and micro/nano-scale positioning resolution are widely required in both scientific research and industries. For this kind of applications, piezoelectric materials based actuators show unique advantages and have been widely employed. To overcome the demerit of the limited working stroke for single piezoelectric element, various stepping motion principles have been proposed in the past years, and accordingly, stepping piezoelectric actuators with various structures have been designed and evaluated. This review is aimed to summarize the recent developments and achievements in stepping piezoelectric actuators with large working stroke. Especially, the emphasis is on three main types of stepping piezoelectric actuators, i.e., inchworm type, friction-inertia type, and parasitic type. The motion principles of these three types of piezoelectric actuators and the corresponding developments of various actuators are discussed respectively, followed by pointing out the existing problems in these three types of piezoelectric actuators and proposing some potential research directions in this topic. It is expected that this review is helpful for relevant researchers to understand stepping motion principles as well as piezoelectric actuators, and to successfully select and design stepping piezoelectric actuators for specific applications.