Large Area Flexible Electronics Fabricated Using Self-Aligned Imprint Lithography

Abstract

This paper presents Self-Aligned Imprint Lithography (SAIL), a technology for producing submicron layer-to-layer alignments on large, dimensionally variable flexible plastic structures. The roll-to-roll compatible process is used to make 1 μm channel length transistors and active matrix arrays using a-Si and zinc-tin-oxide (ZTO) with electrical characteristics that nearly match those obtained using photolithography. The remaining issues for commercialization are discussed

A review of thin-film transistors/circuits fabrication with 3D self-aligned imprint lithography

“…For α-Si TFT a highly doped microcrystalline silicon (μc-Si) layer can be introduced between the top metal layer and the active layer for charge injection. An example of this kind of film stack was developed by Hewlett-Packard (HP) Laboratories: Cr(S-D)/μc-Si/α-Si/SiNx/Al(G)/substrate [43]. Etching selectivity of the top and bottom metal layers is important because it ensures that one metal layer is less affected while another metal is etched.…”

“…This change translates into 100 μm of overlay misalignment if a 10 cm wide web is used, which is larger than the pixel size of display, and makes the interlayer alignment with optical lithography very challenging. To address this problem a roll-to-roll based on 3D SAIL technology has been developed [43]. In the 3D SAIL process, all geometric information is coded in a monolithic, multi-level 3D polymer mask that is imprinted on a stack of device materials pre-deposited on a substrate.…”

“…A stack of multi-layered films was pre-deposited on a substrate and then a 3D polymer mask was generated by SAIL. Figures 4 and 5 are schematic illustrations of the thin-film stack and pattern transfer process for fabrication of a bottom-gated transistor [43]. After creation of a 3D polymer mask (figure 5(a)) etching (both wet and dry) was used to entirely etch through the film stack (figure 5(b)).…”

“…However, it is only suitable to produce single-layered structures, and it is challenging to build up subsequent layers aligned with existing structures. The problem of layer-to-layer alignment on flexible substrates can be solved using a 3D self-aligned imprint lithography (SAIL) by encoding all geometric information required for all patterning steps into a monolithic 3D mask that is imprinted on a thin film stack deposited on a flexible substrate [12][13][14]. Since the monolithic mask (normally made of polymers) itself also distorts with the substrate, alignment is preserved throughout subsequent processing.…”

Fabrication of three-dimensional imprint lithography templates by colloidal dispersions

“…Flexible substrates undergo non-uniform deformations during device fabrication so the usual photolithographic tools requiring precise layer-to-layer alignment are difficult and costly to implement. The problem of layer-to-layer alignment has been solved using a self-aligned imprint lithographic (SAIL) process [1][2][3] by encoding all the geometry information required for the entire patterning steps into a monolithic three-dimensional (3D) mask that is imprinted on the thin film stack deposited on a flexible substrate. Since this monolithic masking structure distorts with the substrate, alignments are preserved throughout subsequent processing (Fig.…”