Seong-Moon Cho

Origin of forward leakage current in GaN-based light-emitting devices

The authors fabricated GaN-based light-emitting diodes (LEDs) on two different GaN templates with the same LED structure. One on thin GaN template (∼2μm) with high dislocation density [low (109cm−2)] grown by metal-organic vapor-phase epitaxy (sample A) and the other on thick GaN template (∼20μm) with comparatively low dislocation density [high (108cm−2)] by hydride vapor-phase epitaxy (sample B). In order to understand the mechanism of leakage current in LEDs, the correlation between current-voltage characteristics and etch pit density of LEDs was studied.

Microcantilevers integrated with heaters and piezoelectric detectors for nano data-storage application

A thermomechanical writing system and a piezoelectric readback system have been demonstrated using silicon cantilevers integrated with heaters and piezoelectric sensors for a low-power scanning-probe-microscopy data-storage system. A thin polymethylmethacrylate film has been used as a media to record data bits of 50 nm in diameter and 25 nm in depth using the silicon cantilever. The sensitivity of 0.22 fC/nm was also obtained using the fabricated cantilever. Finally, to obtain readback signals using the piezoelectric cantilever, a patterned oxide wafer with 30 nm depth was scanned to show the distinctive charge signals.

PZT actuated micromirror for nano-tracking of laser beam for high-density optical data storage

A micromirror actuated by piezoelectric cantilevers is proposed as a fine-tracking device for high-density optical data storage. Metal/PZT/metal thin film actuators translate an integrated micromirror along the out-of-plane vertical direction. The parallel motion of the micromirror steers linearly the optical path of the reflected laser beam. 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/sup 2/. In this paper, preliminary characteristics of the micromachined PZT actuated micromirror (PAM) are reported. The design and the fabrication process of the PZT actuated micromirror are described. Only a 3600 /spl Aring/-thick PZT film deposited by sol-gel process shows both good electrical and mechanical characteristics for the actuators. The micromirror can be easily actuated up to several micrometers under low voltage operation condition.

Finger tissue model and blood perfused skin tissue phantom

Measurements of optical properties of fingernail and underlying tissues using OCT are presented. Review and measurements of Raman spectra of tissue and phantom compounds were done. Updating of modeling algorithm for scattering coefficient calculation on the basis of integrating sphere measurements accounting for particle size-distribution was also done. The adequate fingernail and underlying tissue optical model at 830 nm was evaluation. Tissue phantoms potentially suitable for calibration of Raman instrumentation for glucose sensing were designed and tested on the basis of epoxy resin, TiO2-nanoparticles and micron-sized silica particles with the capillary net-work.

Fabrication and characteristics of piezoelectric PZT cantilever for high speed atomic force microscopy

Abstract A PZT actuator integrated onto cantilever structure was fabricated for high speed atomic force microscopy (AFM). Five different electrodes were used to investigate the effect of top electrodes on the adhesion and the electrical properties in the PZT capacitors. The PZT capacitors with RuO2 top electrodes exhibited the best characteristics of five electrodes. The tip deflection and the resonant frequency of the PZT actuator were 11 μim at 10 V and 79 kHz, respectively. The PZT actuator provided much better AFM image quality and imaging speed than those done by using the conventional bulk PZT tube scanner. The creep distortion in the AFM image was greatly improved by using the high speed PZT film actuator.

A self-actuating PZT cantilever integrated with piezoresistor sensor for AFM with high speed parallel operation

In this research, we studied the parasitic parameters inducing the electrical coupling between a sensor and PZT actuator using a simple equivalent circuit model of the cantilever with a piezoresistor sensor and PZT actuator. A fully integrated self-actuating PZT cantilever with a piezoresistor has been newly designed, fabricated, and characterized for high speed AFM. The fabricated PZT cantilevers provide 0.55 /spl mu/m/V of high tip displacement and about 5 times lower crosstalk than the previous cantilever structure. The measured resonant frequency was 73 kHz, which is 100 times higher than a conventional piezotube scanner. The piezotube scanner shows creep phenomena at approximately 180 /spl mu/m/sec of scan speed, but the fabricated self-actuating PZT cantilever has a good scanned image at 1 mm/sec.

Low voltage PZT actuated tilting micromirror with hinge structure

In this paper, a bulk micromachined PZT micromirror with low voltage operation, large tilting angle, and two-axes degree of freedom is discussed for optical applications. The micromirror is connected to PZT cantilevers by hinge structure to minimize mechanical constraint. The maximum tilting angle of the fabricated micromirror is 3.5/spl deg/ at low voltage of 40 V.

Calibration of non linear properties of Pb(Zr, Ti)O3 cantilever using integrated piezoresistive sensor for high speed atomic force microscopy

A piezoresistive sensor was integrated in a self-actuating Pb(Zr, Ti)O3 (PZT) cantilever to calibrate hysteresis and creep phenomena of a PZT actuator for high speed atomic force microscopy. The fabricated PZT cantilevers provided high tip displacement of 0.37 µm/V and high resonant frequency of 85 kHz. The hysteresis of the PZT cantilever was well calibrated using the integrated piezoresistive sensor. The creep phenomenon of the PZT cantilever is solved by the piezoresistive sensor. The self-actuating PZT cantilever showed a good image at a high scan speed of 1 mm/s.

The high-quality spectral fingerprint of glucose captured by Raman spectroscopy in non-invasive glucose measurement

Optical spectroscopy has the inherent advantage of directly measuring glucose levels by means of the unique nature of a spectral fingerprint for the target analyte, glucose, which is determined in the form of a calibration spectrum (a product of multivariate analysis method). The literature is replete with claims of successful in-vivo glucose measurements in terms of Clark error grid analysis. However, all of them fail to demonstrate an in vivo glucose-specific calibration spectrum. In this study we use Raman spectroscopy to capture a high quality spectral fingerprint of the glucose molecule noninvasively and demonstrate calculated correlation coefficients between a pure glucose spectrum and calibration spectra at over 0.8.

Integration of a split word line ferroelectric memory using a novel etching technology

Abstract A ferroelectric random access memory (FeRAM) was fabricated using a novel processing technology to investigate the characteristics of the FeRAM with a new cell structure. The new cell includes two split word lines (SWLs) which play roles not only as word lines but also as plate lines. This structure can enhance operation speed and prevent the decrease of remnant polarization of non-selected cell capacitors in write/read operation since SWLs can be driven independently. The cell capacitors were composed of Pt electrodes and the sol-gel derived Pb(Zr,Ti)O3 films. An efficient procedure to realize the new cell structure is proposed by introducing a new etching method, which includes the one-step patterning of a metal-ferroelectric-metal (MFM) and a metal-ferroelectric (MF) using a metal mask (Ti or Ru) and an etch stopping layer (TiO2 or RuO2). The degradation of the ferroelectric capacitors due to etching process and interlayer dielectric (ILD) deposition process was almost recovered by annealing...