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We have formed nanometer-wide lines & spaces by graphoepitaxy of sphere type polystyrene-poly dimethyl siloxane (PS-PDMS), with a molecular weight (MW) of 14.6 kg/mol., along electron-beam (EB)-drawn resist guide lines. We have 3-dimensionally ordered the sphere type PS-PDMS by controlling a thickness of the PS-PDMS along improved guide lines to form the line and space pattern. We obtained the thickness dependence on the pattern change such as nano-dot arrays and nano-line & space patterns. When the thickness increased to about +4 nm from the upper thickness for formation of the dot arrays, the line & space patterns have been formed with about 7 nm in line width and 14 nm in pitch.

Recent technologies of tip-enhanced Raman spectroscopy (TERS) and scanning near-field optical microscopy (SNOM) with Raman spectroscopy are reviewed. In TERS technology, it has been developed based on surface-enhanced Raman spectroscopy (SERS). The some TERS are reviewed as follows: 1. Bottom illumination mode TERS has been described, and it has demonstrated fine spatial resolution and gigantic enhancement of Raman scattering signal using single wall carbon nano tube (SWNT). 2. Side- and modified top-illumination mode TERS have been described, and they have demonstrated enhancement of Raman scattering signal and resolution of subwavelength. 3. There are, however, some technical issues such as metal contamination, stress measurement of Si device, etc. This means that it is difficult to apply to an evaluation of semiconductor devices, etc. In SNOM technologies, illumination-collection mode SNOM has been described with regard of aperture type SNOM probe and aperture-less pyramidal SNOM probe. 4. Using the aperture type SNOM probe, it is difficult to obtain fine spatial resolution because the aperture makes only near-field optical probe incompletely. 5. M. Yoshikawa et al. demonstrated spatial resolution of about 200 nm in peak-frequency shift image with Raman Si peak of VLSI standard sample using illumination-collection mode with the aperture type SNOM probe. 6. S. Hosaka et al. have proposed the aperture-less pyramidal probe in illuminationcollection mode SNOM to improve near-field optical probe and to protect from the metal contamination to the device surface. The SNOM and Raman spectroscopy was combined with UV laser. The prototyped microscopy demonstrated following possibilities. a. By calculating near-field light propagations in the aperture-less pyramidal probe by FDTD method, strong near-field light propagation from top of the aperture-less

In this paper, electrical characteristics of an HfO2-based resistive switching memory device are investigated before and after γ-ray radiation with various total ionizing doses (TIDs). The device can still function properly even if irradiated with a TID of 20 Mrad(Si). The small changes of resistance states and set/reset voltages induced by γ-ray radiation can hardly influence the proper function of the device. The γ-ray radiation does not significantly degrade both retention and endurance characteristics even after a high-TID exposure. The radiation effects on the resistive switching memory device show little dependence on the cell area. The results suggest that the HfO2-based resistive switching memory device has good γ-ray radiation-resistant capability.

In this paper, we proposed a phase-change memory (PCM) structure which has a ring confined chalcogenide (RCC) for reducing reset operation current. The temperature distributions of normal bottom contact (NBC), confined chalcogenide (CC) and proposed RCC PCMs were simulated by 3 dimensional finite element method. It was very clear that a much higher temperature can be obtained for RCC than NBC cell at a certain programming current. The programming characteristics also exhibited that the operation current of RCC cell can be as low as about 45% of NBC cell while that of CC cell was about 82% of CC cell.

We propose an approach to study the dependence of crystallization on temperature of GeTe-based phase change resistor (PCR) for staircase-shaped voltage pulses. We tune the resistance between the amorphous and crystalline states via varying the width of second subpulse. Then, the crystallized fractions are calculated as a function of the second subpulse widths. Furthermore, the temperature distributions under variable second subpulses are analyzed. At last, the pulse-dependent-recrystallization-temperatures are estimated using experimental and simulation results. We demonstrate that the crystallization of the GeTe-PCR is faster than that of Ge 2 Sb 2 Te 5 -PCR due to the high pulse-dependent-recrystallization-temperature and low activation energy.

Ge 1 Sb 4 Te 7 (GST147) was adopted as the storage media for multiple resistance levels. It was exhibited that the resistivity of GST147 gradually dropped by about 3–4 orders of magnitude due to crystallization with the annealing temperature, which is critical to realize multiple resistance levels. The ultra-multiple 27 resistance levels in TiSi 3 /GST147 lateral phase-change memory device were demonstrated simply by controlling the maximum sweeping currents for programming the device resistance. Furthermore, the reproducibility of the six resistance levels was demonstrated and these levels were distinguishable from each other. This study indicates that GST147 is a media suitable for stable ultra-multiple level storage, enabling low-cost ultrahigh-density nonvolatile memory.

Although there is a huge progress in complementary-metal-oxide-semiconductor (CMOS) technology, construction of an artificial neural network using CMOS technology to realize the functionality comparable with that of human cerebral cortex containing 1010–1011 neurons is still of great challenge. Recently, phase change memristor neuron has been proposed to realize a human-brain level neural network operating at a high speed while consuming a small amount of power and having a high integration density. Although memristor neuron can be scaled down to nanometer, integration of 1010–1011 neurons still faces many problems in circuit complexity, chip area, power consumption, etc. In this work, we propose a CMOS compatible HfO2 memristor neuron that can be well integrated with silicon circuits. A hybrid Convolutional Neural Network (CNN) based on the HfO2 memristor neuron is proposed and constructed. In the hybrid CNN, one memristive neuron can behave as multiple physical neurons based on the Time Division Multiplexing Access (TDMA) technique. Handwritten digit recognition is demonstrated in the hybrid CNN with a memristive neuron acting as 784 physical neurons. This work paves the way towards substantially shrinking the amount of neurons required in hardware and realization of more complex or even human cerebral cortex level memristive neural networks.

Synaptic memristor has attracted much attention for its potential applications in artificial neural networks (ANNs). However useful applications in real life with such memristor-based networks have seldom been reported. In this paper, an ANN based on memristors is designed to learn a multi-variable regression model with a back-propagation algorithm. A weight unit circuit based on memristor, which can be programed as an excitatory synapse or inhibitory synapse, is introduced. The weight of the electronic synapse is determined by the conductance of the memristor, and the current of the synapse follows the charge-dependent relationship. The ANN has the ability to learn from labeled samples and make predictions after online training. As an example, the ANN was used to learn a regression model of the house prices of several Boston towns in the USA and the predicted results are found to be close to the target data. Published version

In this study, we intensively investigated oxygen doped Sb2Te3 (ST–O) for high-performance phase-change memory (PCM) based on X-ray diffraction analysis and electrical measurements. The crystal became more ordered with increasing annealing temperature and the lattice deformed with the interstitial sites occupied by doped O atoms. It also exhibited that mean crystal size decreased from 8 nm to 3 nm and thus crystal growth was significantly suppressed by fine oxides due to O-doping. The resistivity of crystalline O–ST could be around 3–4 orders of magnitude higher than that of crystalline ST, which enables great reduction in reset current. It was clear that the high resistivity was able to be tuned simply by doping O into the conventional ST phase-change material for improving the performance of PCM.

International audience; We have produced Sb\textendashTe alloy nanostructures from a thin Sb2Te3 layer deposited on a highly oriented pyrolytic graphite substrate using a simple rf-magnetron sputtering and annealing technique. The size, shape, and chemical composition of the structures were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectrometry (EDX), respectively. The shape of the nanostructures was found to depend on the annealing temperature; nanoparticles appear on the substrate by annealing at 200 \smwhtcircleC, while nanoneedles are formed at higher temperatures. Chemical composition analysis has revealed that all the structures were in the composition of Sb:Te = 1:3, Te rich compared to the target composition Sb2Te3, probably due to the higher movability of Te atoms on the substrate compared with Sb. We also tried to observe the production process of nanostructures in situ using SEM. Unfortunately, this was not possible because of evaporation in vacuum, suggesting that the formation of nanostructures is highly sensitive to the ambient pressure.

This paper is dedicated to develop an atomic force microscope (AFM) system cou-pled with a high resolution optical microscope (OM), which serves to observe AFM image from a desired micro-area. The system employs through-the-lens optical path for detecting atomic force based on optical lever. By switching the objective lenses from low to high magni cation, a micro-area for obtaining AFM image can be easily found. AFM images of magnetic nanodotarrays with 300 nm and 150 nm pitches are obtained from two local micro-areas using the system. The results demonstrate the proposed prototype has the su cient function to nd out a micro-area for obtaining AFM image.

We demonstrate the possibility of forming long-range-ordered self-assembled nanodot arrays with dots size of 5 nm and pitches of 10×7.5 nm2using guide line templates and low molecular weight (MW) (4,700–1,200 g/mol) poly (styrene)-poly (dimethylsiloxane) (PS-PDMS) for application in ultrahigh density patterned media. The self-assembled PDMS nanodots are controlled in a long range by varying the heights and gaps of the guide lines. Adopting the 14-nm-high resist guide lines with suitable gaps, the 5-nm-sized and 10×7.5 nm2-pitched self-assembled nanodots were ordered in maximum 7 dot arrays with long-range order. The experimental results demonstrate that the method is possible for achieving patterned media with magnetic recording densities of 8.6 Tbit/in.2using low MW PS-PDMS and slim guide lines.

In this study, we tried to develop the scanning near-field polarization microscope (SNPM) and challenge to observe magnetization of the magnetic nanodot in the arrays. The CoPt dot arrays with a size of 25 nm and a pitch of 150 nm were adopted. The nanodots change contrast after changing the direction of the external magnetic field. This implied that our prototyped SNPM system had the resolution of less than 25 nm. So, it is demonstrated that SNPM is an effective tool for the observation of magnetization of the magnetic nanodot on the nanometer scale.

We studied DNA damages in heavy ion irradiation for its radiotherapy using molecular dynamics (MD) method. We adopted semi-empirical hybrid quantum mechanics/molecular mechanics (QM/MM) method of Amber in order to investigate the cleavage of chemical bond by heavy ion in our simulation. We found the cleavage of chemical bond, although the simulated energy of heavy ion turned out to be slightly higher than the one determined by experiment.

One of the real challenges in realization of many of graphene’s anticipated applications is the development of a common chemical route for modifying graphene with varieties of functionalities. Here, we successfully demonstrate the organic modification of epitaxial graphene (EG) grown on the Si-face of SiC substrate through two-step chlorination–alkylation reactions. Pristine and chemically modified graphene are characterized by scanning tunneling microscope and spectroscopy, X-ray photoelectron spectroscopy, and Raman measurements. The first-step photochlorination is found to occur very selectively on the monolayer graphene region leaving the bi- and trilayer graphene regions clean. Consequently, the CH3-functionalized graphene is observed only in the monolayer graphene regions after the chlorinated EG was treated with CH3MgBr in air-free condition. Both Cl and CH3 are observed to be chemically bonded to the basal plane of the graphene. The CH3-functionalized graphene is thermally more stable than that of...

Graphical abstractDisplay Omitted We succeeded in ordering 6-nm-sized dot arrays with 10-nm-pitch between guide lines.The ordering was achieved by graphoepitaxy with self-assemble and the line template.3 to 7-ordered PDMS dot arrays were formed between 12-nm-wide EB-drawn guide lines.The block copolymer was PS-PDMS with a molecular weight of 7000-1700kg/mol.The 10×12-nm-pitched nanodot arrays corresponds to 5 Tbit/in2 magnetic storage. We studied the possibility to form long-range ordering of self-assembled nanodot arrays with a dot size of 6nm and a dot pitch of 12nm using guide-line templates for ultrahigh-density patterned media. This was realized by using self-assembled block copolymers of polystyrene-poly dimethyl siloxane (PS-PDMS) and the templates made of hydrogen silsesquioxane (HSQ) negative electron beam (EB) resist. We have demonstrated that the method could possibly achieve a minimum pitch of about 10nm using PS-PDMS of molecular weight 7000-1500g/mol and EB-drawn guide lines. These results evidence the promising potential of a technology for achieving 5 Tbit/in2 magnetic storage devices.

The influences of different concentrations of NaCl in tetramethyl ammonium hydroxide (TMAH) developer on the electron beam lithography resolution of hydrogen silsesquioxane (HSQ) resist were studied, using original development model based on the three-dimensional (3D) energy deposition distributions (EDDs) and the experimental developing behaviors. The development behaviors of HSQ resist developed in 2.3wt.% TMAH, 2.3wt.% TMAH with 2wt.% NaCl and 2.3wt.% TMAH with 4wt.% NaCl developer were measured, respectively, to provide the solubility rates at different exposure dosages for the simulation. On the basis of the solubility rates and 3D-EDDs, the optimal EDD regions were determined for achieving sharp nanodot patterns. The optimal resist profiles of the three different developers were compared, showing that the 2.3wt.% TMAH with 4wt.% NaCl developer is suitable to form 7-nm-sized, 15-nm-pitched nanodots with sufficient height. The simulations were demonstrated to be useful for estimating the pattern resolutions with different solubility rates of developers, especially for sub-10nm nanodot fabrication.

In this study, we investigated ultra-multilevel-storage (UMLS) in lateral phase change memory (PCM) on the basis of device structure, reliability and programming method. We found that the number of resistance levels was limited strictly by the number of PC layers in multilayer multilevel cell (ML-MLC). A number of distinct levels up to 16 were obtained using a simple single-layer multilevel cell (SL-MLC). And material engineering is expected to greatly improve the reliability of MLS. We believe that fast-freely-achievable (FFA)-MLC by stair-like-pulse programming is a very promising method for futures application.

In this study, we investigate the recrystallization process in phase-change memory by applying staircase pulses. The controlled recrystallization process is expected to be applied to freely achievable multilevel storage. Simulation results exhibit that the phase change material is heated above its melting point during the first subpulse of the staircase pulse and then annealing temperature can be controlled by varying amplitude of the second subpulse. This implies that the recrystallization region is controllable by applying staircase pulses. V-shaped resistance change vs. the amplitude of the second subpulse, which is caused by the growth and the shrinkage of recrystallized region, is obtained at each width of second subpulse.

To explore the chemical and electronic states of oxidized epitaxial graphene (EG) grown on the Si face of SiC(0001), we employ the Hummers oxidizing agents (H2SO4 + NaNO3 + KMnO4) under different reaction conditions that oxidize the graphene layer. The resulting material is characterized with scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). A mild “drop-cast” procedure at 60 °C is found to be equally effective at oxidizing EG as the conventional Hummers procedure. This aqueous-phase oxidation reaction appears to proceed in an autocatalytic manner as indicated by the concurrent observation of patches of oxidized and clean graphene areas in atomically resolved STM images on partially oxidized EG. STS further reveals substantial changes in electronic structure for oxidized EG including the opening of a local band gap of ∼0.4 eV. The oxidation is confined to the graphene layers as verified by XPS characterization of the...

The progress of information technology has increased the demand of the capacity of storage media. Bit patterned media (BPM) has been known as a promising method to achieve the magnetic-data-storage capability of more than 1 Tb/in.2. In this work, we demonstrated fabrication of magnetic nanodot array of CoPt with a pitch of 33 nm using a pattern-transfer method of block copolymer (BCP) self-assembly. Carbon hard mask (CHM) was adopted as a mask to pattern-transfer self-assembled nanodot array formed from poly (styrene)-b-poly (dimethyl siloxane) (PS-PDMS) with a molecular weight of 30,000-7,500 mol/g. According to our experiment results, CHM showed its high selectivity against CoPt in Ar ion milling. Therefore, this result boosted the potential of BCP self-assembly technique to fabricate magnetic nanodot array for the next generation of hard disk drive (HDD) due to the ease of large-area fabrication, and low cost.

We calculated thehydrogen silsesquioxane (HSQ) resistprofiles with different contrast developers (γ from 1.9 to 8.1) to reveal the effect of resist contrast on pattern resolution performance. Based on our home-made development modeling, the suitable energy deposition distribution (EDD) regions for various developers were determined by evaluating the quality of simulated patterns. High contrast TMAH 2.3 wt%/NaCl 4 wt% developer was demonstrated that it is suitable to form very fine dot arrays with a size of 7 nm. Low contrast developer has the limitation of forming fine pattern with sufficient height. The simulation results indicated that increasing developer contrast is benefit to improve pattern resolution.

We have developed a GUI(Graphical User Interface)-based Monte Carlo simulation tool for electron beam lithography. Simulation was executed by changing initial energy, thickness of resist, and target material. We focused on penetration range, backscattering coefficient and spatial distribution of lost energy. Comparison with other theory indicates that our simulation is reliable in the 10-50keV range of the energy of the electron. It seems that backscattering coefficient is strongly affected by the kind of atoms in the target, not initial energy.

Atomic force microscopy (AFM) is the useful tool for measuring the micro fabricated devices. Measuring sample surface with AFM, tip-induced distortions are serious problem for accurate measurement. In order to overcome this problem, many studies are reported to reconstruct surface image to original sample surface. We studied method of reconstruction technique of the AFM image by using estimated 3-D tip shape from the impulse response technique. To reconstruct the image of the sample surface, we used a morphological reconstruction process. We demonstrated how to obtain the 3-D tip from the using impulse response technique and then how to reconstruct the 3-D AFM image using estimated tip shape.

We investigated the possibility of ordering of 12 nm pitced self-assembled nanodots from block copolymer (BCP) improved by the guide pattern with low line edge roughness (LER) for patterned media. We found that LER of the line pattern (σ-value) was reduced by using high-resolution salty development for HSQ resist line pattern fabrication compared with conventional tetramethyl ammonium hydroxide (TMAH) developer. By adopting this development technique to guide pattern fabrication, we demonstrated 10 rows of ordered self-assembled BCP nanodot arrays with a size of 6 nm and a pitch of 12 nm (5 Tbit/in.2) between the guide patterns.

A possibility to fabricate nanodot arrays with a dot size of 2 using self-assembling with PS-PDMS of molecular weight 7000-1500 and EB-drawing for narrow guide lines. These results prove that the fusion method is required for achieving extremely small dot arrays as 5 Tbit/in2magnetic storage devices.Keywords: Nanodot, self-assembly, electron-beam drawing, graphoepitaxy, patterned media, magnetic recording.

In this study, we have fabricated 25-nm-pitched magnetic dot arrays using electron beam lithography (EBL), reactive ion etching (RIE) and ion-milling. We have used double mask method with calixarene resist and carbon film as a hard mask to transfer fine pattern to CoPt magnetic film. We transferred the calixarene resist dot arrays to carbon layer using O2gas in RIE as a first mask, then transferred the carbon dot arrays to CoPt magnetic layer as a second hard mask using ion-milling. We demonstrated that double mask method is very suitable to fabricate 25-nm-pitched magnetic dot arrays with a dot size of 18 nm and a height of 15 nm for patterned media with 1 Tb/in2.

A Phase change Memory (PCM) device with a separate heater structure was proposed in order to control the crystallization process of the device. Some experimental works have been done to investigate the possibility. A SET pulse with amplitude ranging from 0 V to 3 V and pulse width of 100 ns was applied to the separate-heater layer, TiSi3 for heating up the memory layer, Ge2Sb2Te5. From the experimental result, the resistance of the memory layer dropped gradually by more than two orders of magnitude. This will allow multilevel storage for the memory device.

We investigated the fabrication of self-assembled nanodot array using poly (styrene)-poly (dimethyl-siloxane) (PS-PDMS) block copolymer and its transfer technique as a promising method to fabricate magnetic nanodot arrays for ultrahigh density recording. A carbon (C) layer with a high etch-resistance was especially adopted for magnetic nanodot fabrication. We fabricated PDMS nanodot using PS-PDMS block copolymer with a molecular mass of 11,700-2,900 g/mol. The nanodots were first transferred into silicon (Si) layer and then into C layer on Si substrate by carbon tetrafluoride (CF4) and oxygen (O2) reactive ion etching (RIE), respectively. We succeeded in fabricating C nanodots with a diameter of 10 nm and an average pitch of 20 nm.

We demonstrated the fabrication of silicon nanowire (SiNW) sensors by focused ion beam (FIB) method and determined the effects of changes of nanowire parameters of width and wire-number on the SiNW electrical property. SiNW sensors were fabricated on a silicon-on-insulator (SOI) wafer with Au-Cr electrodes by the FIB method. We fabricated the SiNW sensor with a minimum width of 90 nm, length of 20 μm and height of 60 nm. The I-V characteristics in the state of ohmic contact were obtained, and the SiNW resistance was found to have 0.86 MΩ and a resistivity of 0.02 Ωcm. In addition, the electrical resistance dependence on width and wire-number was investigated. We found that wire conductance could be increased by increasing the wire-number and wire width.

In this work, we report two methods to fabricate the nanophase-change memory: (1) electron beam lithography (EBL) using the positive resist ZEP-520A followed by phase change material deposition and lift-off processes, (2) EBL using the negative resist hydrogen silsesquioxane (HSQ) followed by reactive ion etching (RIE) after phase change material deposition. For the former method, the optimized exposure dosage is around 40 μC/cm2 and the finest nanowire is about 80 nm in width. On the other hand, the latter method shows that the finest nanowire can be as small as about 15 nm in width after RIE process and the optimized exposure dosage is around 2.0 mC/cm2. In this case, collapse-preventing pattern becomes necessary for fabrication of such a fine nanowire.

Undoped and B-doped silicon-based nanowires (SiNWs) were synthesized by vapor-liquid-solid growth, and SiNW devices using Au electrodes were prototyped using focused ion beam (FIB) processing. Needle-shaped thin SiNWs were formed at a substrate temperature between 1170 and 1313 °C. The average and minimum diameters of the B-doped SiNWs were 72 nm and 52 nm, respectively. According to the current-voltage characteristics, SiNW devices have ohmic properties, and the estimated resistivity of the undoped and B-doped SiNWs are about 3.8 × 103Ωcm and 1.7 × 103Ωcm, respectively.

Our simulation reveals that the programming current of phase change memory (PCM) is expected to dramatically reduce to tens of μA with the help of a heating layer. TiSiN films by reactive RF magnetron co-sputtering are investigated for application to the heating layer of the ultra-low-current PCM. The resistivity of TiSiN films is well controlled from around to with increasing N2partial flow rate to 10%. The effect of annealing on the TiSiN films exhibits the relative stability of the resistivity of the films. This implies that these TiSiN films can be used as a universal heating layer for the intensively researched phase change materials.

We have carried out spectroscopic ellipsometry measurements for liquid- and solid-phase InSb around its melting point for wavelengths of 300 to 1700 nm. The real and imaginary parts of the complex refractive index for liquid and solid InSb appear to be completely different, with the imaginary part for the liquid being higher than that of the solid. This result agrees with the proposed mechanism for the super-resolution readout effect in optical disks using an InSb film. From a dielectric function analysis, we find that InSb characteristics clearly change from semiconducting in the solid to metallic in the liquid.

Phase change memory (PCM), which exploits the phase change behavior of chalcogenide materials, affords tremendous advan- tages over conventional solid-state memory due to its nonvolatility, high speed, and scalability. However, high power consumption of PCM poses a critical challenge and has been the most significant obstacle to its widespread commercialization. Here, we present a novel approach based on the self-assembly of a block copolymer (BCP) to form a thin nanostructured SiOx layer that locally blocks the contact between a heater electrode and a phase change material. The writing current is decreased 5-fold (corresponding to a power reduction by 1/20) as the occupying area fraction of SiOx nanostructures is increased from a fill factor of 9.1% to 63.6%. Simulation results theoretically explain the current reduction mechanism by localized switching of BCP-blocked phase change materials.

Silicon-based nanowires (Si-NWs) were fabricated by vapor liquid solid (VLS) growth, and Si-NW device was prototyped using focused ion beam (FIB) processing. The needle shaped thin Si-NWs were formed at a substrate temperature between 1120 and 1313°C. The average and minimum diameters of the NWs were confirmed 60 nm and 44 nm, respectively. As the double-layered structure was observed in the NWs by transmission electron microscope images, it is possible that those are silicon-based NWs with Si core and SiO2shell structure. From current-voltage characteristics, the Si-NW device has a semiconducting property, and the estimated resistivity of the Si-NW is about 3.1 x 104Ωcm.

CoPt magnetic dot arrays with a fine pitch of 30 nm have been fabricated using electron beam (EB) lithography and ion milling. The possibility to ion-mill CoPt film using EB drawn calixarene resist pattern as a mask has been studied. We formed 30 nm pitch resist dot arrays with a dot diameter of 20 nm using 30-keV-EB lithography with calixarene resist. The resist dot arrays were ion-milled for 4 min using 200-eV Ar ion milling to fabricate CoPt dot arrays on a Si substrate. We fabricated fine pitched CoPt magnetic dot arrays with a diameter of 22-35 nm and a pitch of 30-150 nm. Results show that the ion-milled CoPt dot diameter increased with the dot pitch while the resist dot had a similar diameter of 20 nm.

A novel phase change memory structure with a separate heater was proposed for a multilevel storage. Finite element analysis was conducted to investigate the possibility of multilevel storage. 100 ns SET pulses, with an increasing amplitude from 0.5 V to 3 V, were applied for heating the phase change layer, Ge2Se2T5 (GST). From the simulation result, it was exhibited that the temperature in the GST layer increased gradually when an increasing pulse is applied to the separate heater layer (N-TiSi3). This implies that crystallization is well controlled by changing the amplitude of the applied SET pulse. The gradual increase in the temperature leads to gradual resistance drop, depending strongly on the capping material. The gradual resistance drop will allow multilevel storage for the memory device.

We numerically modeled the process of exposure and development of the calixarene negative resist and ZEP520 positive resist in electron beam lithography (EBL) in order to understand the limitation of nanopatterning of these two resists and to improve the resolution of the patterning. From the calculation of energy deposition distribution (EDD) in resist at various beam diameters, it is obvious that the fine probe beam with a diameter of 2 nm and thin resist should be adopted for formation of very fine dots. The simulation of resist development profile indicates that a dot size of 2 nm with a pitch of 20 nm can even be obtained at a higher critical energy density by using calixarene resist, while it cannot form the small pattern by using the ZEP520 resist because of the capillary force.

In this work, a new-type piezo-resistive acceleration sensor with a slit in the beams is proposed to improve sensitivity by reducing the twisting of the beams. Experimental results demonstrated that the new-type acceleration sensor has about 3.5 times higher than that of the conventional acceleration sensor without the slit. Furthermore, resonant frequency of the new-type sensor increases to about 5 kHz by a factor of 25, compared with commercial acceleration sensor.

In this work, improvement of the observation contrast was investigated by using a carbon film as the hard mask for pattern transfer of block copolymer (BCP) nanodots. The PS-PDMS (Poly (styrene-b-dimethyl siloxane)) block copolymer was adopted here. The observation contrast was greatly improved after transferring block copolymer (BCP) nanodots pattern to the underlying Si substrate through the carbon hard mask compared that before nanodot pattern transfer. Pattern transfer was also demonstrated to be very effective using carbon hard mask.

Here, we report multi-level storage (MLS) in multi-layer (ML) and single-layer (SL) phase change memories (PCM). For the former ML-PCM device, the active medium with two layers of chalcogenide consists of a top 30 nm TiN/180 nm SbTeN/20 nm TiN/bottom 120 nm SbTeN stacked multi-layer. Three stable and distinct resistance states are demonstrated in both static and dynamic switching characteristics of the multi-layer devices. For the latter SL-PCM device, the active medium with only one layer of chalcogenide consists of a top 50 nm TiN/150 nm SbTeN. We demonstrate that the number of distinguishable resistance levels can readily reach 16 and even higher. These levels in this study result from the initial threshold switching and the subsequent current-controlled crystallization induced by Joule heating. Therefore, the latter memory allows the creation of many distinct levels, thus enabling the low-cost ultra-high-density non-volatile memory.