A Method of Forming a Polycrystalline Si with the Biomolecule Ferritin

Abstract

We studied the metal-induced crystallization of a-Si using a Ni-ferritin molecule of 7 nm diameter. The Ni-ferritin molecules were coated onto the SiN x /amorphous silicon ͑a-Si͒/buffer/glass and it was heated at 580°C for 20 h for crystallization after UV burning of the biomaterial. It was found that the grain size of poly-Si increases with decreasing the ferritin density. A grain size of ϳ220 m was achieved, and its surface roughness was 2.1 nm.Polycrystalline-Si ͑poly-Si͒ thin-film transistors ͑TFTs͒ on glass is of increasing interest for applications to high-resolution liquidcrystal displays, active-matrix organic light-emitting diodes ͑AMOLEDs͒, and system on glass ͑SOG͒ because of its high fieldeffect mobility. Common methods for crystallizing amorphous silicon ͑a-Si͒ are solid phase crystallization ͑SPC͒, excimer laser annealing ͑ELA͒, and metal-induced crystallization ͑MIC͒. 1 Of the various approaches available, Ni-mediated crystallization of amorphous silicon is one of promising techniques for large-scale manufacturing of high-performance poly-Si TFTs with low cost. This is based on the fact that NiSi 2 crystallites have the same lattice structure with Si with a very small mismatch of 0.4%. Then, the NiSi 2 crystallites which can be formed at 400°C are seeds for crystallization of a-Si. The a-Si is crystallized as a result of migration of the seeds throughout the a-Si network. 2 To improve the quality of the poly-Si, several approaches have been conducted on the crystallization of a-Si, including a capping layer on it. For example, to control the lateral growth of ELA poly-Si through lateral thermal gradients, three different patterned capping layers have been used: antireflective ͑SiO 2 ͒, heat-sink ͑SiN x ͒, and reflective ͑metal͒ capping layers. 3 We introduced a cap layer on the a-Si to reduce metal contamination and to have a clean and smooth surface. 4,5 Recently, Kirimura et al. demonstrated the biotechnology to obtain MIC poly-Si thin-films using ferritin with a Ni core ͑7 nm͒. 6 They achieved the grain size of ϳ3 m prepared by Ni-mediated crystallization with ferritin molecules.In this work, we studied the crystallization of a-Si using Niferritin molecules on silicon nitride ͑SiN x ͒ cap layers to reduce protein contamination and to obtain large-grain poly-Si thin-films. The Ni on the cap layer diffuses through the cap and forms the seeds in a-Si for crystallization. Disk-shaped grains of 220 m were achieved, which was confirmed by optical microscopy and by electron backscattered diffraction ͑EBSD͒.

Ferritin: A Versatile Building Block for Bionanotechnology

“…The density and domain size correlated well with the initial ferritin nanoparticle distribution and can be position-controlled by appropriate surface patterning. , By introducing a silicon nitride cap layer, nickel is filtered by diffusion, and protein contamination of the poly-Si is better avoided. Large crystal grains of up to 220 μm in diameter are obtained, as compared to 3 μm without cap layer, and the surface remains smoother . Electron backscattered diffraction and pseudo-Kikuchi pattern revealed a radial texture with predominant (111) and (101) orientation normal to the surface.…”

“…Large crystal grains of up to 220 μm in diameter are obtained, as compared to 3 μm without cap layer, and the surface remains smoother. 301 Electron backscattered diffraction and pseudoKikuchi pattern revealed a radial texture with predominant (111) and (101) orientation normal to the surface. Such lowtemperature crystallized thin films are of potential interest for thin film transistors or flat-panel displays.…”