Dong-Ki Min

Scanning resistive probe microscopy: Imaging ferroelectric domains

We report a resistive probe that detects electric field by field-induced resistance changes in a small resistive region at the apex of the tip and demonstrate a method of imaging ferroelectric domains at high speed, which is named scanning resistive probe microscopy (SRPM). We designed and fabricated the probe by self-aligning process that readily implemented the resistive region at the tip apex. In order to measure the field sensitivity, we contacted the probe with a thermally oxidized silicon sample and detected a 0.3% resistance change per volt applied to the sample. We obtained domain images of freshly cleaved triglycine sulfate (TGS) single crystal by contact mode SRPM. The operating voltage of the probe was 4 V and the scan rate and size were 2 Hz and 40×40 μm2, respectively. We controlled the polarization of Pb(Zr0.4Ti0.6)O3 (PZT) by applying voltage between the resistive tip and the bottom electrode of PZT, and acquired the domain images with the same tip at 2 Hz scan rate. By controlling and dete...

Correlation between grain size and domain size distributions in ferroelectric media for probe storage applications

The relationship between grain size and domain size distributions has been studied by piezoelectric force microscopy in ferroelectric films with average grain size of 150nm. As the ratio of domain size to grain size increases, the domain size deviation decreases in a 1∕xn-type function, where n is 1.105. Extrapolation of the model shows that in order to obtain 10% domain size deviation in 1Tbit∕in.2 media, a grain size smaller than 14nm is required. The obtained results imply that either nanograin or single crystalline/epitaxial films provide reliable domain distributions for probe storage applications.

Tip traveling and grain boundary effects in domain formation using piezoelectric force microscopy for probe storage applications

Tip traveling and grain boundary effects have been investigated by varying the voltage pulse width on Pb(Zr0.25Ti0.75)O3 films using piezoelectric force microscopy. Depending on pulse width, the authors distinguish three regions of domain formation. It was found that grain boundaries act as electric shield, which prevents domain growth across grains. Domain growth across grains was mainly due to the tip traveling effect. Calculations based on the authors’ model matched well with experimental data.

High-resolution field effect sensing of ferroelectric charges.

Nanoscale manipulation of surface charges and their imaging are essential for understanding local electronic behaviors of polar materials and advanced electronic devices. Electrostatic force microscopy and Kelvin probe force microscopy have been extensively used to probe and image local surface charges responsible for electrodynamics and transport phenomena. However, they rely on the weak electric force modulation of cantilever that limits both spatial and temporal resolutions. Here we present a field effect transistor embedded probe that can directly image surface charges on a length scale of 25 nm and a time scale of less than 125 μs. On the basis of the calculation of net surface charges in a 25 nm diameter ferroelectric domain, we could estimate the charge density resolution to be as low as 0.08 μC/cm(2), which is equivalent to 1/20 electron per nanometer square at room temperature.

Offset compensation of capacitive sensors for electrostatic microactuators

An offset problem caused by the static parasitic capacitors is analyzed and then some techniques to reduce their effect on the capacitive position sensor are represented. Using a charge balancing technique, the offset problem is compensated. By adjusting the magnitudes of the modulating signals, the charge imbalance between electrodes caused by the parasitic capacitors is eliminated without sensor gain variation. Simulation results are given to validate the proposed compensation technique.

Design and Analysis of the Position Detection Algorithm for a Probe Storage

A new two-axis positional error detection algorithm for probe storage is proposed. Using only probes, this algorithm can detect two-axis positions simultaneously and continuously for off-track control and synchronization. Two decomposition signals are multiplied to the probe readback signal while vibrating the scanner in low frequency of the specific value to extract two position error signals from it. In addition, the same algorithm using only one decomposition signal is proposed. Because this algorithm provides very precise positional errors continuously, off-track and synchronization errors can be controlled to zero continuously, and the sensitivities to disturbances can be reduced

A Time-of-Flight 3-D Image Sensor With Concentric-Photogates Demodulation Pixels

In this paper, we develop pixels with concentric-photogates for applications in time-of-flight 3-D image sensors with single-tap architecture. The pixel uses a buried-channel device and features a reduced effective electron transit length, for the rapid transfer of a signal electron. A reduction in the interpixel irregularity of signal levels and a consequent increase in the demodulation signal amplitude are observed in the single-tap operation mode as opposed to the multitap operation mode. Specifically, we are able to achieve a demodulation contrast higher than 50% from 20 MHz modulation of an 850 nm light-emitting diode illumination. Finally, we construct a sensor composed of 198 × 108 concentric photogate pixels, each with a pitch of 28 μm, and use it to generate a 3-D image conveying gross distance information and detailed object features with a distance error of less than 1% over a range of 1 to 7 m.

Construction of probe-based data storage with ultra-high areal density

Our probe-based data storage (PDS) system consists of four parts: signal processing module, multi-probe array, xy-planar actuator, and recording media. The signal-processing module has 2 layers attached to each other. The first layer has 3 D wiring, and it is assembled to the second layer (ASIC module) for the signal processing circuit. The multi-probe array is designed to increase recording and reading speed of the data bits. Each probe has cantilever and tip that are characterized by a tip height of 15 /spl mu/m, a tip radius of 15 nm, a natural frequency of 18.75 kHz and a DC sensitivity of 16.7 nm/V. Poly-silicon probe was fabricated by molding technique to produce high aspect ratio tips. The electrostatic planar actuator serves as a scanner that positions the probe to the right place by moving the media in xy-plane. The moving distance was /spl plusmn/40 /spl mu/m at 10/spl plusmn/10 V, DC gain was 3.04 /spl mu/m/V at 4 V, and the resonance frequency was 143 Hz. The: recording media stores the recorded information in the form of electric polarization in ferroelectric materials. Ferroelectric Pb(Zr,Ti)O/sub 3/ thin film is a candidate material for the media, and it can yield a memory density as high as 400 Gb/in/sup 2/ by recording bits as small as 35 nm in diameter. The bits are fully rewritable and retain the information for a generation at the temperature range below than 50 /spl deg/C.

Characterization of Sensitivity and Resolution of Silicon Resistive Probe

The resistive probe, which can detect the variation in probe resistance while scanning over positive/negative biased bits, has been considered as the one of the most suitable candidate for used as a high-speed, ultralarge-storage systems. Ultralarge-storage density has been demonstrated by the electrical recording technique in which surface charge is read in ferroelectric materials, which is named as scanning resistive probe microscopy (SRPM). Because of the difficulty of fabricating, the SRPM device little has been previously done on relating probe properties with process parameters. As it is important in probe design to analyze the properties of sensitivity and resolution for different process and device parameters, the parameters of the fabricated microscope are embedded in the simulation performed in this study. To obtain the optimum resistive probe design, we analyze the effect of different process parameters on the properties. In the first part of the paper, the device structure fabricated to identify the electrostatic charge effects between the tip and the poly silicon domain (surface) is presented. In the second part, we explain the process conditions of the resistive probe. In the third part, we present the sensitivity and resolution for different process conditions. The probe is placed in contact with a poly silicon domain (surface) to measure the field sensitivity, and a 0.3% resistance change per voltage applied to the surface is detected with a spatial resolution of less than 1000 nm. The sensitivity and resolution for different implantation doses, wet oxidation time, and resistances in the high-doped n-type region are also presented. We found that there is a correlation between sensitivity and resolution for different implantation doses and annealing times. Although the sensitivity decreases as resistance increases, the change is less than 10% even at a resistance of 200 Ω. Therefore, the resistance of the cantilever can be neglected in our study of probe sensitivity.

New positional error detection algorithm for a probe-based data storage

New 2-axis positional error detection algorithm for probe-based data storage is proposed. This algorithm can detect two-axis positions simultaneously and continuously for off-track control and synchronization purposes by vibrating the scanner in low frequency of the specific value. Then two decomposition signals are multiplied to the probe readback signal to extract two position error signals from it. Since this algorithm provides very precise positional errors continuously, off-track error and synchronization error can be controlled to zero continuously and the sensitivities to disturbances can be reduced.