Towards Reconfigurable Electronics: Silicidation of Top-Down Fabricated Silicon Nanowires

Novel Mixed-Dimensional hBN-Passivated Silicon Nanowire Reconfigurable Field Effect Transistors: Fabrication and Characterization

This work demonstrates the novel concept of a mixed-dimensional reconfigurable field effect transistor (RFET) by combining a one-dimensional (1D) channel material such as a silicon (Si) nanowire with a two-dimensional (2D) material as a gate dielectric. An RFET is an innovative device that can be dynamically programmed to perform as either an n- or p-FET by applying appropriate gate potentials. In this work, an insulating 2D material, hexagonal boron nitride (hBN), is introduced as a gate dielectric and encapsulation layer around the nanowire in place of a thermally grown or atomic-layer-deposited oxide. hBN flake was mechanically exfoliated and transferred onto a silicon nanowire-based RFET device using the dry viscoelastic stamping transfer technique. The thickness of the hBN flakes was investigated by atomic force microscopy and transmission electron microscopy. The ambipolar transfer characteristics of the Si-hBN RFETs with different gating architectures showed a significant improvement in the device's electrical parameters due to the encapsulation and passivation of the nanowire with the hBN flake. Both n- and p-type characteristics measured through the top gate exhibited a reduction of hysteresis by 10-20 V and an increase in the on-off ratio (ION/IOFF) by 1 order of magnitude (up to 108) compared to the values measured for unpassivated nanowire. Specifically, the hBN encapsulation provided improved electrostatic top gate coupling, which is reflected in the enhanced subthreshold swing values of the devices. For a single nanowire, an improvement up to 0.97 and 0.5 V/dec in the n- and p-conduction, respectively, is observed. Due to their dynamic switching and polarity control, RFETs boast great potential in reducing the device count, lowering power consumption, and playing a crucial role in advanced electronic circuitry. The concept of mixed-dimensional RFET could further strengthen its functionality, opening up new pathways for future electronics.

Monolithic and Single-Crystalline Aluminum-Silicon Heterostructures

Overcoming the difficulty in the precise definition of the metal phase of metal-Si heterostructures is among the key prerequisites to enable reproducible next-generation nanoelectronic, optoelectronic, and quantum devices. Here, we report on the formation of monolithic Al-Si heterostructures obtained from both bottom-up and top-down fabricated Si nanostructures and Al contacts. This is enabled by a thermally induced Al-Si exchange reaction, which forms abrupt and void-free metal-semiconductor interfaces in contrast to their bulk counterparts. The selective and controllable transformation of Si NWs into Al provides a nanodevice fabrication platform with high-quality monolithic and single-crystalline Al contacts, revealing resistivities as low as ρ = (6.31 ± 1.17) × 10^-8 Ω m and breakdown current densities of J_max = (1 ± 0.13) × 10¹² Ω m^-2. Combining transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed the composition as well as the crystalline nature of the presented Al-Si-Al heterostructures, with no intermetallic phases formed during the exchange process in contrast to state-of-the-art metal silicides. The thereof formed single-element Al contacts explain the robustness and reproducibility of the junctions. Detailed and systematic electrical characterizations carried out on back- and top-gated heterostructure devices revealed symmetric effective Schottky barriers for electrons and holes. Most importantly, fulfilling compatibility with modern complementary metal-oxide semiconductor fabrication, the proposed thermally induced Al-Si exchange reaction may give rise to the development of next-generation reconfigurable electronics relying on reproducible nanojunctions.

Conductive Materials with Elaborate Micro/Nanostructures for Bioelectronics

Bioelectronics, an emerging field with the mutual penetration of biological systems and electronic sciences, allows the quantitative analysis of complicated biosignals together with the dynamic regulation of fateful biological functions. In this area, the development of conductive materials with elaborate micro/nanostructures has been of great significance to the improvement of high-performance bioelectronic devices. Thus, here, a comprehensive and up-to-date summary of relevant research studies on the fabrication and properties of conductive materials with micro/nanostructures and their promising applications and future opportunities in bioelectronic applications is presented. In addition, a critical analysis of the current opportunities and challenges regarding the future developments of conductive materials with elaborate micro/nanostructures for bioelectronic applications is also presented.

Controlled Silicidation of Silicon Nanowires Using Flash Lamp Annealing

Among other new device concepts, nickel silicide (NiSi_x)-based Schottky barrier nanowire transistors are projected to supplement down-scaling of the complementary metal-oxide semiconductor (CMOS) technology as its physical limits are reached. Control over the NiSi_x phase and its intrusions into the nanowire is essential for superior performance and down-scaling of these devices. Several works have shown control over the phase, but control over the intrusion lengths has remained a challenge. To overcome this, we report a novel millisecond-range flash lamp annealing (FLA)-based silicidation process. Nanowires are fabricated on silicon-on-insulator substrates using a top-down approach. Subsequently, Ni silicidation experiments are carried out using FLA. It is demonstrated that this silicidation process gives unprecedented control over the silicide intrusions. Scanning electron microscopy and high-resolution transmission electron microscopy are performed for structural characterization of the silicide. FLA temperatures are estimated with the help of simulations.

Monolithic Metal-Semiconductor-Metal Heterostructures Enabling Next-Generation Germanium Nanodevices

Low-dimensional Ge is perceived as a promising building block for emerging optoelectronic devices. Here, we present a wafer-scale platform technology enabling monolithic Al-Ge-Al nanostructures fabricated by a thermally induced Al-Ge exchange reaction. Transmission electron microscopy confirmed the purity and crystallinity of the formed Al segments with an abrupt interface to the remaining Ge segment. In good agreement with the theoretical value of bulk Al-Ge Schottky junctions, a barrier height of 200 ± 20 meV was determined. Photoluminescence and μ-Raman measurements proved the optical quality of the Ge channel embedded in the monolithic Al-Ge-Al heterostructure. Together with the wafer-scale accessibility, the proposed fabrication scheme may give rise to the development of key components of a broad spectrum of emerging Ge-based devices requiring monolithic metal-semiconductor-metal heterostructures with high-quality interfaces.