Integrating two-dimensional (2D) materials into semiconductor manufacturing lines is essential to exploit their material properties in a wide range of application areas. However, current approaches are not compatible with high-volume manufacturing on wafer level. Here, we report a generic methodology for large-area integration of 2D materials by adhesive wafer bonding. Our approach avoids manual handling and uses equipment, processes, and materials that are readily available in large-scale semiconductor manufacturing lines. We demonstrate the transfer of CVD graphene from copper foils (100-mm diameter) and molybdenum disulfide (MoS2) from SiO2/Si chips (centimeter-sized) to silicon wafers (100-mm diameter). Furthermore, we stack graphene with CVD hexagonal boron nitride and MoS2 layers to heterostructures, and fabricate encapsulated field-effect graphene devices, with high carrier mobilities of up to $$4520\;{\mathrm{cm}}^2{\mathrm{V}}^{ - 1}{\mathrm{s}}^{ - 1}$$
4520
cm
2
V
−
1
s
−
1
. Thus, our approach is suited for backend of the line integration of 2D materials on top of integrated circuits, with potential to accelerate progress in electronics, photonics, and sensing.
We report on the fabrication and characterization of field-effect transistors (FETs) based on chemical vapor deposited (CVD) graphene encapsulated between few layer CVD boron nitride (BN) sheets with complementary metal-oxide-semiconductor (CMOS) compatible nickel edge contacts. Noncontact terahertz time-domain spectroscopy (THz-TDS) of large-area BN/graphene/ BN (BN/G/BN) stacks reveals average sheet conductivity >1 mS/sq. and average mobility of 2500 cm 2 /V • s. Improved output conductance is observed in dc measurements under ambient conditions, indicating the potential for radio frequency (RF) applications. Moreover, we report a maximum voltage gain of 6 dB from a low-frequency signal amplifier circuit. RF characterization of the GFETs yields an f T × L g product of 2.64 GHz • µm and an f Max × L g product of 5.88 GHz • µm. This paper presents for the first time THz-TDS usage in combination with other characterization methods for device performance assessment on BN/G/BN stacks. The results serve as a step toward scalable, all CVD 2-D material-based FETs for CMOS compatible future nanoelectronic circuit architectures.
Two-dimensional
(2D) materials, such as graphene, are seen as potential candidates
for fabricating electronic devices and circuits on flexible substrates.
Inks or dispersions of 2D materials can be deposited on flexible substrates
by large-scale coating techniques, such as inkjet printing and spray
coating. One of the main issues in coating processes is nonuniform
deposition of inks, which may lead to large variations of properties
across the substrates. Here, we investigate the role of surface morphology
on the performance of graphene ink deposited on different paper substrates
with specific top coatings. Substrates with good wetting properties
result in reproducible thin films and electrical properties with low
sheet resistance. The correct choice of surface morphology enables
high-performance films without postdeposition annealing or treatment.
Scanning terahertz time-domain spectroscopy (THz-TDS) is introduced
to evaluate both the uniformity and the local conductivity of graphene
inks on paper. A paper-based strain gauge is demonstrated and a variable
resistor acts as an on–off switch for operating an LED. Customized
surfaces can thus help in unleashing the full potential of ink-based
2D materials.
We have performed far-field extinction measurements and near electric field measurements on gold bowtie antennas resonant at THz frequencies. These measurements show a very large shift between the resonant frequencies of the near-field and the far-field spectra. We use the established damped-driven harmonic oscillator model for resonators to model the far-field response of the antennas from the near-field spectrum and show that there is a large discrepancy between the predicted and measured far-field response. We were able to explain this discrepancy by improving the oscillator model with a Fano model. This large shift makes the prediction of the near-field response of resonant structures at THz frequencies very imprecise, provided that only information of the far-field response is available and establishes the necessity of measuring near fields for a correct and accurate characterization of these structures.
Integrated terahertz (THz) pulse generation and amplification in a THz quantum cascade laser (QCL) is demonstrated. Intracavity THz pulses are generated by exciting the facet of the QCL with an ultrafast Ti:Sapphire laser (∼100 fs) and detected using electro-optic sampling. Maximum THz field emission is found with an interband transition of 1.535 eV (809 nm) and by narrowing the excitation laser bandwidth to ∼3 THz. These resonance conditions correspond to the narrowband excitation of the quantum cascade miniband, indicating that the THz pulse is generated by the photoexcited carriers that are accelerated by the applied field. The generated pulse is subsequently amplified by the narrowband gain of the laser as it propagates through the QCL cavity.
Silicon is not an electro-optic material by itself but the required second-order optical nonlinearity can be induced by breaking the inversion symmetry of the crystal lattice. Recently, an attractive approach has been demonstrated based on a surface-activation in a CMOS-compatible HBr dry etching process. In this work, we further investigate and quantify the second-order nonlinearity induced by this process. Using THz near-field probing we demonstrate that this simple and versatile process can be applied to locally equip silicon nanophotonic chips with micro-scale areas of electro-optic activity. The realization of a first fully integrated Mach-Zehnder modulator device - based on this process - is applied to quantify the nonlinearity to an effective χ((2)) of 9 ± 1 pm/V. Analysis of the thermal stability of the induced nonlinearity reveals post-processing limitations and paths for further efficiency improvements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.