Graphene on Substrates

Wafer-Scale CVD Graphene on Substrates

Graphene — a single atomic layer of sp²-hybridized carbon atoms arranged in a honeycomb lattice — is the defining material of the 2D materials era. With a theoretical electron mobility exceeding 200,000 cm²/V·s, optical absorption of exactly 2.3% per layer across the entire visible spectrum, a Young's modulus of 1 TPa, and the highest intrinsic tensile strength (130 GPa) ever measured, graphene possesses a portfolio of properties unmatched by any single bulk material.

The transition from laboratory exfoliated flakes (μm-scale) to wafer-scale films suitable for device fabrication and industrial application has been driven by chemical vapor deposition (CVD) on catalytic metal substrates — primarily copper foil — followed by transfer to device-compatible substrates. Today, monolayer graphene with > 95% coverage can be routinely produced on 100mm and 150mm wafers, with sheet resistances of 200–600 Ω/sq and FET mobilities of 1,000–5,000 cm²/V·s, making graphene-on-substrate products accessible for prototyping, pilot production, and fundamental research.

At GINECHIP, we supply CVD-grown graphene transferred onto SiO₂/Si (90nm, 285nm, and 300nm thermal oxide), sapphire, quartz, PET, and PEN substrates. Available in monolayer, bilayer, and few-layer formats at wafer sizes up to 150mm. Every lot includes a comprehensive Certificate of Analysis with Raman mapping, AFM, optical transmission, sheet resistance, and SEM characterization data.

CVD Growth Process

Chemical vapor deposition (CVD) on copper foil is the most established method for producing large-area, high-quality monolayer graphene. The process exploits copper's low carbon solubility and catalytic surface activity to achieve self-limiting monolayer growth:

1. Substrate Preparation: High-purity copper foil (25μm or 50μm thickness, 99.999%) is electropolished or chemically cleaned to reduce surface roughness and remove native oxide, then loaded into a quartz-tube or cold-wall CVD reactor.
2. Annealing: The Cu foil is heated to 1,000–1,050°C under H₂/Ar flow (typically 5–50 sccm H₂ in 100–500 sccm Ar) at reduced pressure (0.5–5 Torr) to enlarge Cu grains (from ~50μm to > 200μm) and remove surface contaminants. Grain size of the Cu substrate directly impacts graphene domain size.
3. Growth: A carbon precursor — most commonly methane (CH₄) at 1–20 sccm — is introduced into the reactor. CH₄ decomposes on the Cu surface, and carbon atoms nucleate and grow into graphene domains that coalesce into a continuous polycrystalline film. Growth time is typically 10–60 minutes, with longer times favoring larger domains but also increased bilayer adlayer formation.
4. Cooling: The reactor is cooled under H₂/Ar flow. Rapid cooling (> 50°C/min) suppresses additional nucleation and adlayer formation, while controlled slow cooling can be used to tune bilayer coverage.

The resulting graphene-on-Cu can be used as-grown (for applications where the Cu substrate is incorporated into the device architecture) or transferred to a target substrate via a polymer-supported wet or dry transfer process.

Transfer Methods: Wet vs Dry

Transferring graphene from its growth substrate (Cu foil) to a device-compatible target substrate without introducing defects, contamination, or mechanical damage is the critical process step that determines final film quality. Two approaches are employed:

Wet Transfer (PMMA-Assisted)

A thin layer of poly(methyl methacrylate) (PMMA) is spin-coated onto the graphene/Cu surface to serve as a mechanical support layer. The underlying Cu is then etched away using an ammonium persulfate ((NH₄)₂S₂O₈) or iron chloride (FeCl₃) solution, leaving the PMMA/graphene membrane floating on the etchant. After rinsing in deionized water, the membrane is scooped onto the target substrate and dried. PMMA is subsequently dissolved in acetone, followed by thermal annealing (200–350°C in Ar/H₂) to remove residual polymer. This method is well-established and compatible with most substrate types.

Dry Transfer (Bubble / Electrochemical Delamination)

In electrochemical delamination (also called "bubble transfer"), the PMMA/graphene/Cu stack serves as the cathode in an aqueous electrolyte (e.g., NaOH or K₂S₂O₈). Hydrogen bubbles generated at the cathode electrochemically separate the PMMA/graphene film from the Cu substrate without etching the copper, enabling Cu reuse. The delaminated film is transferred to the target substrate, and PMMA is removed as in wet transfer. Dry transfer methods typically produce cleaner graphene surfaces with lower residue compared to wet etching approaches.

For all transfer methods, GINECHIP employs optimized PMMA formulations, multi-step annealing protocols, and cleanroom handling (Class 100) to minimize polymer residue, metal contamination, and mechanical damage. Post-transfer thermal annealing (300–350°C, Ar/H₂) is standard for all SiO₂/Si, sapphire, and quartz substrates.

Characterization & Quality Control

Comprehensive characterization is essential for graphene quality verification, as the atomic-scale nature of the material demands multi-technique validation to distinguish monolayer from few-layer regions, assess defect density, and quantify electronic quality.

Raman Spectroscopy

Raman spectroscopy is the primary, non-destructive fingerprinting technique for graphene. Under 532nm excitation, the key spectral features are: the G peak (~1,580 cm⁻¹, in-plane sp² C–C stretching), the 2D peak (~2,680 cm⁻¹, second-order zone-boundary phonon), and the D peak (~1,350 cm⁻¹, defect-activated). Monolayer graphene is identified by an I₂D/I_G intensity ratio > 2 and a 2D peak that fits a single Lorentzian with FWHM of 25–35 cm⁻¹. The D/G ratio quantifies defect density — ratios below 0.1 indicate high-quality CVD graphene.

Atomic Force Microscopy (AFM)

AFM provides topographic information critical for verifying monolayer thickness (~0.34 nm step height at graphene edges), quantifying surface roughness, and assessing transfer quality — wrinkles, folds, tears, and polymer residue particles are all readily identified. RMS roughness on SiO₂/Si substrates is typically < 0.3nm after optimized transfer, comparable to the bare substrate.

Electrical Characterization

Sheet resistance is measured via four-point probe mapping and/or transfer length method (TLM) structures. FET mobility is extracted from back-gated devices fabricated on SiO₂/Si substrates using standard photolithography or shadow-mask-defined contacts (Ti/Au or Cr/Au). Typical as-transferred monolayer graphene exhibits p-type doping (Dirac point at positive gate voltage, V_Dirac = +10 to +30 V) with hole mobilities of 1,000–5,000 cm²/V·s in ambient conditions.

Graphene vs ITO & Other Transparent Conductive Materials

Indium tin oxide (ITO) has been the dominant transparent conductor for decades, but its brittleness, reliance on the critical raw material indium, and high-temperature processing requirements have driven the search for alternatives. The table below compares graphene with ITO and silver nanowire networks across key performance metrics.

Applications & Market Segments

Technical Specifications

Metrology & Quality Assurance

Every graphene-on-substrate lot is characterized through a multi-technique protocol at ISO 9001:2015 certified facilities. A comprehensive Certificate of Analysis (CoA) including Raman spectra and mapping, AFM topography, UV-Vis transmission, sheet resistance maps, and SEM imaging is provided with each shipment.