Zulfakri bin Mohamad

The Electrical Characteristics of Aluminium Doped Zinc Oxide Thin Film for Humidity Sensor Applications

The electrical characteristics of aluminum (Al) doped zinc oxide (ZnO) thin film for high sensitivity humidity sensors are presented. The effects of Al doping concentration at 0∼0.6 at % on the Al doped ZnO thin film properties were investigated using current-voltage measurement. The optical and structural properties were characterized using photoluminescence (PL), scanning emission microscope (SEM), and X-ray diffraction (XRD). Parameter 0.6 at % Aluminum doped show high sensitivity and suitable for humidity sensor. PL show an emissions band with two peaks centered at about 380 nm (ultra-violet (UV)) and 600 nm (green) in a room temperature. The length of the nanorods increases as the doping concentration increases. XRD results show the intensity of the (002) peak decreased with the increasing of doping concentration.

Extremely Small Proximity Effect in 30 keV Electron Beam Drawing with Thin Calixarene Resist for 20?20 nm2 Pitch Dot Arrays

We studied proximity effect in 30 keV electron beam (EB) drawing with calixarene resist for patterned media and quantum devices. Using about 15-nm-thick calixarene resist on Si substrate in conventional EB drawing system, the proximity effect has been studied by forming and observing 20-, 25-, 30-, and 40-nm-pitch resist dot arrays and measuring exposure dosage intensity distribution (EID) function. As a result, the proximity effect is negligible small due to comparing with some dot sizes in center, side and corner of 2 µm square with 25×25 nm2 pitch dot arrays. In addition, the proximity effect parameter η in EID function is less than 0.3. It is clear that the EB drawing and calixarene resist system is very suitable for forming ultrahigh packed dot arrays pattern. We demonstrated 20×20 nm2 pitch resist dot arrays (about 1.6 Tb/in.2) with a dot diameter of about 14 nm and the same size as everywhere in the pattern.

Possibility of Forming 18-nm-Pitch Ultrahigh Density Fine Dot Arrays for 2 Tbit/in.2 Patterned Media Using 30-keV Electron Beam Lithography

We studied the possibility of forming ultrahigh-density fine dot arrays using 30-keV electron beam (EB) drawing for 2 Tbit/in.2 patterned media. We investigated the effects of calixarene resist thickness and exposure dosage on the drawing of dot arrays with a minimum pitch. We found that the 13-nm-thick calixarene resist was very suitable for forming resist dot arrays with a pitch of 20 nm. Furthermore, the allowable region of proper exposure dosage became narrow as the pitch decreased. It is clarified that there exists a minimum pitch of 18 nm in drawing ultrahigh density fine dot arrays with a 13-nm-thick resist.

Electron Beam Lithography of 15×15 nm2 Pitched Nanodot Arrays with a Size of Less than 10 nm Using High Development Contrast Salty Developer

We investigated the effects of developer and hydrogen silsesquioxane (HSQ) resist thickness in the formation of dot arrays with a pitch of <18×18 nm2 by using 30-keV electron beam (EB) lithography for bit patterned media (BPM). Optimum resist thickness and developer were investigated for the formation of fine dot arrays. We found that a 12-nm-thick HSQ resist was suitable to form fine dot patterns and the addition of NaCl into tetramethylammonium hydroxide (TMAH) could improve the development contrast (γ-value) of HSQ (the highest is 9.7). By using the 12-nm-thick HSQ resist film and 2.3 wt % TMAH/4 wt % NaCl developer, we successfully fabricated very fine resist dot arrays with a dot size of <10 nm and a pitch of 15×15 nm2, which corresponds to a storage density of about 3 Tbit/in.2 in BPM.

Fabrication of CoPt nanodot array with a pitch of 33 nm using pattern-transfer technique of PS-PDMS self-assembly

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.

Fabrication of 30-nm-Pitched CoPt Magnetic Dot Arrays Using 30-keV-Electron Beam Lithography and Ion Milling for Patterned Media

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 with a Separate Heater Characterized by Constant Resistance for Multilevel Storage

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.

Coercive Force Enhanced by Nanometer-Sizing of Magnetic Column and Measured by X-Ray Magnetic Circular Dichroism (XMCD)

We have studied the possibility to form fine magnetic column arrays using 30-keV-electron beam (EB) drawing with thin calixarene resist and 200-eV-Ar ion milling, and nanometer-sizing effect of the magnetic column on the corecive force for patterned media. We achieved 20-nm-sized resist dot arrays on PtCo magnetic and thin metals layers on glass substrate. We formed fine magnetic column arrays with a diameter of 39 to 106 nm and a space of about 100 nm using the resist pattern by the 200-eV Ar ion-milling. Using the nano magnetic column arrays, the hysteresis were measured by X-ray magnetic circular dichroism (XMCD) with an energy of 11.57 keV, which corresponds to an energy edge of Pt-L3. It is clarified that a coercive force of the nanometer-sized magnetic column increased as the diameter decreased.

Observation of Magnetic Nanodot Arrays Using Near-Field Polarization Microscope

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.

Effect of a separate heater structure for crystallisation to enable multilevel storage phase-change memory

The effect of a separate-heater structure for crystallisation to enable multilevel storage for phase-change memory (PCM) device was investigated. This separate-heater is characterised by a constant resistant R h . Existing power from the heater layer (TiSi 3 ) can be well controlled, enabling crystallisation process for multilevel storage. Ge 2 Sb 2 Te 5 (GST) was used as the memory layer. A simulation using COMSOL 3.2 was done to study the temperature distribution in the GST layer by applying an SET pulse ranging from 0 V to 3 V directly to the heater layer. The temperature of the GST layer increased gradually with increasing pulse amplitude, making multilevel storage possible due to the gradual resistance drop. For experimental work, when an increasing pulse amplitude at 100 ns pulse width was applied to the separate heater layer, resistance in the memory layer dropped gradually for more than three orders of magnitude. This indicates that the existing power from the separate heater was well controlled for efficient crystallisation in the memory layer, GST, enabling multilevel storage. The reproducibility of the device was also investigated by applying a RESET pulse directly to the GST layer. A PCM device with a separate-heater structure is stable and has the ability to reproduce more than two cycles.