In this study, sputtered undoped and nitrogen doped Sb 2 Te 3 ͑ST and STN͒ films were systematically investigated by x-ray diffraction ͑XRD͒ and resistance measurements. Their application to lateral phase-change memory ͑PCM͒ is presented as well. The STN film sputtered at a flow rate ratio ͑N 2 /Ar͒ of 0.07 proved to have both high stability and low power consumption, implying its high performance in PCM applications. In the STN films ͑N 2 /ArϾ 0.15͒, the hexagonal Te phase first appeared at 160°C, and then the orthorhombic SbN phase appeared at 290°C. The phase separation made it very difficult for these films to switch reversibly between the crystalline and the amorphous phase.

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We studied the electrical properties of 20-and 50-nm-thick Ge 2 Sb 2 Te 5 and AgInSbTe films for nonvolatile lateral transistor memory devices. Both kinds of thin films were prepared as film samples and device samples which were then annealed at temperatures from 140 to 415 C. It is known that crystal size can be effectively reduced with film thickness on the basis of Xray diffraction analysis. The resistances of all film samples annealed at 140-415 C decreased by approximately 5-6 orders of magnitude. In the case of device samples, however, the source-drain resistances of Ge 2 Sb 2 Te 5 samples were first reduced and then reversely increased and it seemed that the resistances of AgInSbTe samples did not drop. The abnormal resistance increase above the crystallization temperature may be caused by phase change and thermal expansion, as we analyzed in this paper. Finally, the resistance changes of device samples with channel lengths in the range of 0.4-3 mm were discussed from the point of view of miniaturizing the phase change memory device.

The formation of very fine Si dots with a bit pitch and a track pitch of less than 25 nm using electron-beam ͑EB͒ lithography on ZEP520 and calixarene EB resists and CF 4 reactive ion etching has been demonstrated. The experimental results indicate that the calixarene resist is very suitable for forming an ultrahigh-packed bit array pattern of Si dots. This result promises to open the way toward 1 Tbit/ in. 2 storage using patterned media with a dot size of Ͻ15 nm. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2400102͔ Available magnetic recording density is rising at a rate of 60% per year. High-end magnetic storage media with a recording density of over 100 Gbit/ in. 2 have already been commercialized. In optical recording, the Blu-ray disk and the high-definition digital versatile disk ͑DVD͒ with a capacity of 25 Gbytes have also been developed. However, there are many technical issues to be solved for recording densities as high as 1 Tbit/ in. 2 . A breakthrough is required for future recording systems. Today, we have some technical proposals such as patterned media 1 and near field optical recording 2 which address the above issues.Electron-beam ͑EB͒ lithography is expected to allow the formation of very fine pit or dot arrays for patterned media and next generation DVDs. Many variations of EB drawing ͑exposure͒ have been developed to allow the fabrication of semiconductor devices and optical disks. 3-5 So far, pit patterns with a minimum bit pitch ͑BP͒ and track pitch ͑TP͒ of 40 and 80 nm, respectively, have been achieved on ZEP520. 6 Furthermore, the formation of very fine dot arrays using calixarene has been reported by 8 They demonstrated the formation of 15 nm diameter dot arrays with 100 and 60 nm pitches for quantum devices and magnetic recording media. These recording media were, however, very far from the areal density of 1 Tbit/ in. 2 , because the pitches were too large. In this letter, we describe the ultrahigh-packed nanofabrication of a 1 Tbit/ in. 2 storage medium using EB exposure and reactive ino etching ͑RIE͒.In order to achieve fine bit arrays with densities of over 1 Tbit/ in. 2 , we carried out ͑1͒ a very fine EB exposure with a fine probe and a high probe current; we also prepared ͑2͒ a thin resist layer to prevent the spread of incident electron scattering; finally, we designed ͑3͒ a highly packed pattern with a hexagonal or centered rectangular lattice structure such as cross stitch to prevent proximity effects. Item ͑2͒ refers to a thin resist layer which requires an increased acceleration voltage for precise EB drawing. We used a resist layer with thicknesses of 70 and 15 nm for ZEP520 and calixarene, respectively. The minimum thicknesses were determined so that the layer would suffer no deformation and would allow sufficient contrast in scanning electron microscopy ͑SEM͒ observation after exposure and development.Calixarene is so tough under electron irradiation that we were able to use layers as thin as 15 nm.Our EB drawing system consists of a high-resolution SEM ͑JSM650...