Kyongmi Lee

DETECTION MECHANISM OF SPONTANEOUS POLARIZATION IN FERROELECTRIC THIN FILMS USING ELECTROSTATIC FORCE MICROSCOPY

Mechanism on the detection of spontaneous polarization in a Pb(Zr0.5Ti0.5)O3 (PZT) film using contact mode of electrostatic force microscopy (EFM) is investigated. Theoretical calculations are performed on deflections induced by electrostatic force (uωe) between the tip and the sample and electromechanical vibrations (uωp) of the ferroelectric materials, respectively. From the calculation, uωe and uωp are 3.73×10-9 and 1.77×10-13 m. Enhanced mode of EFM shows the complete cancellation of the EFM image induced by the electrostatic force between the tip and the film through controlling dc voltage. Hence, electrostatic force effect is a main contributor on the detection mechanism of spontaneous polarization using EFM in contact mode.

Head design scheme for perpendicular recording with single layered media

For ultra high areal recording density, we suggest the perpendicular recording scheme with ring head and single layered media for easy implementation. To improve the perpendicular head field and its gradient, conventional ring head is modified by cutting the top pole edge. Head field was calculated with nonlinear finite element method. The write process was simulated with micromagnetics using the calculated head field of two heads (original and modified) at each magnetic grain of recording disk, instead of using Karlqvist head field. Both simulated and measured MFM images show that the transition of modified head is clearer than original one. Also, TAA and SNR of modified head are higher than results of original head. With simple modification, currently used ring head can be easily applied to high density perpendicular recording HDD system.

Formation and observation of ferroelectric domains in PbZr1-xTixO3(PZT) thin films using atomic force microscopy

Very small-sized ferroelectric domains were induced and observed using a modified atomic force microscopy (AFM). Bias voltage between a conductive AFM tip and a sol-gel processed PZT film caused the switching of small ferroelectric domains. ELectrostatic forces between the polarized area and the tip provide the imaging of the polarized small domains. Applying voltage with the opposite sign can depolarize the polarized area and the formation of a series of data dots was demonstrated. In addition, the retention phenomena of micron size domains in PZT films were investigated. The polarized images disappeared within a few days even without an application of voltage - often called the retention loss or failure. An empirical relationship between relaxation time, bit size and poling time is established and verified. Two operative processes for the retention loss are either the stray charge accumulation on the polarized surfaces or the stress relaxation of the piezoelectric films. An effective way of improving the retention characteristics is suggested. The experimental results obtained in this study provide substantial insight into the mechanism for the retention failure of the polarized domains as well as the polarization behavior in PZT films with a nanometer scale.

Reliability Improvement of Passivated Power Line in Memory Devices

In the present study, several different types of amorphous passivation layers such as PECVD-SiN and PECVD-TEOS were tested to learn how effectively they protect underlying Al interconnection lines. According to the experimental results, a thick monolithic passivation layer composing of PECVD-SiN was found to be highly susceptible to stress-related migration because it did not have sufficient elasticity. Moreover, since silicon nitride also has a high dielectric-breakdown strength, it exhibits an increased impedance to electric current due to parasitic resistance that exists in the path between the two passivated metal lines. On the other hand, passivation thickening through the use of PECVD-TEOS as an initial layer was estimated to be a more effective way to improve device reliability because of its better step coverage and smaller dielectric constant. The FEM simulation explains why the thick multilayer compromising an alternating sequence of mechanically dissimilar layers is an effective way to suppress stress-induced passivation damage during thermal cycling without having a significant effect on the IC pattern.

The effect of hybrid media to achieve both good thermal stability and excellent read/write performance

In this paper, hybrid media to achieve both good thermal stability and excellent read/write performance were analyzed. Hybrid media consist of 1/sup st/ recording layer having low noise properties and 2 /sup nd/ recording layer having high anisotropy energy.

Enhancement of signal to noise ratio by underlayer control in CoCr-based perpendicular magnetic recording media

In this paper, enhancement of signal to noise ratio by underlayer control in CoCr-based perpendicular magnetic recording media was discussed. Underlayer control for SNR, thermal stability, magnetic hysteresis, structure of the media also investigated.

An application of polarized domains in ferroelectric thin films using scanning probe microscope

The feasibility of utilizing PZT films as future data storage media has been investigated using a modified AFM. Applying voltages between a conductive AFM tip and the PZT films causes the switching of ferroelectric domains. The domains are observed using an EFM imaging technique. The experimental results and calculations revealed that the electrostatic force generated between the polarized area and the tip is a main contributor for the imaging of the polarized domains. The written features on ferroelectric films were less than 100 nm in diameter, implying the possibility of realizing data storage devices with ultrahigh areal density. The disappearance of the polarized images without any applied voltage spontaneous reversal polarization was observed, which is a drawback in this application of PZT thin films.