Nanoscale Ferromagnetic Cobalt‐Doped ZnO Structures Formed by Deep‐UV Direct‐Patterning

Abstract

COMMUNICATION (1 of 8)structures patterned by holographic dissolution technique. [1] Photopatterned metal oxide structures have shown excellent electrical, optical, and magnetic properties. [2][3][4][5][6] Compared to conventional lithography techniques, photopatterning technologies significantly simplify the process, avoiding in particular the etching step that is delicate on metal oxide and requires toxic chemicals and sophisticated setup. The feature line-width of photo patterned metal oxide structures is related to both photosensitivity of metal oxide precursor and the wavelength of light source. Submicroor nanoscale dimensions can be achieved with the use of high photosensitive metal oxide precursors and short wavelengths light sources such as deep-UV (DUV) (193 nm) and extreme UV (13.5 nm), making photopatterning a promising technology for fabricating micro or even nanoscale devices. [7][8][9][10] Moreover, photopatterning can be applied to obtain multielement metal oxide materials by mixing photosensitive precursor in conditions that control their dispersion at the atomic scale. [11] In recent years, wide bandgap diluted magnetic semiconductors (DMSs) such as transition metal (TM)-doped ZnO and TM-doped TiO 2 are catching intense interest due to their expected potential applications in spin transistors, spin light emitting diodes, spin filters, sensors, and memories. [12][13][14][15][16][17][18] By using photopatterning techniques, TM-doped metal oxide structures can be easily integrated in complex systems. In previous studies, Chen et al. have used photosensitive precursors and UV light to fabricate Co-doped ZnO and Co-doped TiO 2 patterns. [19,20] However, these DMS structures are in microscale dimensions (>100 µm), which cannot be integrated into small-dimension devices. In addition, the effect of photopatterning on the magnetic properties of the TM-doped metal oxides was not investigated. In the present work, we used DUV (193 nm) lithography and photosensitive zinc methacrylate (ZnMAA) precursor doped with cobalt (II) acetate to fabricate Co:ZnO films. At first, the effect of DUV-patterning as well as thermal annealing on the magnetic properties of Co:ZnO films derived from Co-doped ZnMAA precursor was investigated. Then, DUV nano patterning of the photosensitive solutions was demonstrated.In a previous study, zinc methacrylate was used to prepare ZnMAA resist with photosensitivity to DUV light of 193 nm. [21] Cobalt (II) acetate is mixed with zinc methacrylate (ZnMAA) to form a photopatternable Co-doped zinc oxide precursor. By using deep-UV (DUV) interference lithography, Co-doped ZnMAA precursor can be patterned as negative tone resist and transformed into ferromagnetic Co:ZnO films after thermal treatment. Moreover, Co:ZnO patterns as small as 300 nm line-width can be easily obtained. To have an in-depth understanding to the effect of DUVpatterning process as well as thermal annealing on Co:ZnO films derived from Co-doped ZnMAA precursor, optical, magnetic, and electrical characterizations are perf...

Direct Photopatterning of Solution–Processed Amorphous Indium Zinc Oxide and Zinc Tin Oxide Semiconductors—A Chimie Douce Molecular Precursor Approach to Thin Film Electronic Oxides

“…Additionally, no significant residual carbon contamination from incomplete precursor decomposition was detected within the film, which is known to deteriorate TFT performance severely. [11b] Only trace carbon signals were found on the surface arising from adsorbed environmental species like CO 2 . Furthermore, such treated IZO and ZTO films still exhibit a low surface roughness, i.e., R RMS ≈0.23 nm for IZO and R RMS ≈0.25 nm for ZTO after all processing steps, i.e., UV treatment, washing, and further annealing at 350 °C ( Figure ).…”

“…A higher thermal budget was needed in this case owing to a higher annealing temperature to ensure suitable decomposition of the bulky methacrylate ligand, which provides scope for improved design for metal oxide precursor for a facile photopatterning approach. [11b] Although photopatterning approaches using indium‐based precursors have been demonstrated so far, indium‐free alternative such as ZTO to generate photopatterned amorphous oxide TFTs has not yet been reported to the best of our knowledge. Such a direct photoactive precursor‐solvent system would be ideal to advance the progress in this direction to enable photopatterning of various functional metal oxides.…”

“…These admixtures which are added to the solution of the actual metal oxide precursor material help to initiate the initial UV‐energy transfer to the molecular precursors, facilitating a smooth decomposition of the otherwise not readily decomposable metal oxide precursor. Similar approaches using acrylate–based ZnO precursor have shown a useful strategy toward direct photopatterning . The overall thin film transistor (TFT) performance can be improved further by subsequent processing steps.…”

Solution‐Based Micro‐ and Nanoscale Metal Oxide Structures Formed by Direct Patterning for Electro‐Optical Applications

“…f) DUV‐induced crosslinking improves the uniformity of Co ions in ZnO lattice. d–f) Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…Moreover, by using SDP techniques, TM‐doped MO nanostructures can be easily obtained. Yeh et al demonstrated ferromagnetic Co‐doped ZnO nanostructures by using a Co‐doped ZnMAA precursor that can be crosslinked by DUV irradiation, as shown in Figure d . By using DUV‐interference patterning, periodic Co‐doped ZnO lines with a 300 nm line width can be fabricated (Figure e).…”