Metal-assisted chemical etched Si nanowires for high-performance large area flexible electronics

Silicon (Si) nanowires (NWs) are considered important building blocks for high-performance flexible and large-area electronics (LAE). Attributes such as bendability, mobility, ability to achieve high on/off current ratio and suitability for device fabrication make Si-NWs suitable candidates for applications in electronics, optoelectronics, photonics, photovoltaics, sensing and wearable technologies [1-3]. Functionalized or non-functionalized Si-NWs based large area arrays over flexible substrates could be used both as sensing material as well as switching devices. Synthesis of single crystalline doped Si-NWs, controlled NW transfer process and the fabrication of NW field-effect transistors (FETs) are the key steps to realize these applications. Here we present the fabrication and characterisation of flexible NWs based FETs using a cost-effective Si-NWs synthesis and transfer process.

Metal-assisted chemical etching (MACE) is considered as one of the cost-effective techniques for the synthesis of single crystalline Si-NWs. This top-down approach uses bulk single crystalline wafer as a starting material for the synthesis of Si-NWs. First, the catalyst metals with nanosized circular patterns are prepared over Si wafer surface and then the wafer was immersed in an etching solution consisting of HF and H2O2. The advantage of this technique is the ability to synthesize Si-NWs at wafer scale, with good control over doping, NW size and NW-to-NW spacing. This approach is favourable for printing of Si-NWs over large areas and non-conventional surfaces. In the current work, Si NWs were synthesised using Nano Sphere Lithography (NSL) patterning followed by MACE process (Fig. 1(e, f)). Close-packed assembly of silica nanospheres (NSs), deposited by dip-coating method, act as a mask for Ag catalyst. The initial dimension of NSs determines the pitch of the nano-mesh (Fig. 1(c,d)). Reactive ion etching (RIE) is carried out subsequently to shrink the NSs to desired dimensions which eventually determines the diameter of resulting NW. Si NWs are synthesised in the diameter range of 26100 nm, lengths up to hundreds of microns, and printed over flexible substrates at defined locations. NW FETs were fabricated (Fig.1(g)) and their performance was studied through current-voltage (I-V) characteristics. This research sets a platform to realize high performance electronics over flexible large-area materials using inorganic nanostructures.